The development of drug resistance is one of the most common causes of drug failure in the treatment of diseases involving replicating biological entities (i. e., cancer and infectious diseases). Drug resistance often results from a reduction in drug-binding affinity and can be quantified by the ratio of drug binding affinity (Kd) for variant and wild type target proteins. Administration of a drug introduces a selective pressure upon the replicating biological entity.

The result is the emergence of drug resistant strains.

Drug resistance is a major obstacle to the successful treatment of many cancers and infections, both bacterial and viral. For example, increased resistance of bacterial infections to antibiotic treatment has been extensively documented and has now become a generally recognized medical problem, particularly with nosocomial infections. See, for example, Jones et al., Diagn.

Microbiol. Infect. Dis. 31: 379 (1998) ; Munay, Adv. Intern. Med. 42: 339 (1997); and Nakae, Microbiologia 13: 273 (1997).

Drug resistance has complicated the treatment for HIV as new mutant strains of HIV have emerged that are resistant to multiple, structurally diverse, experimental and chemotherapeutic antiretrovirals, including HIV protease inhibitors (PIs), nucleoside and non-nucleoside HIV reverse transcriptase inhibitors (NRTIs and NNRTIs), and HIV fusion inhibitors (FIs).

More than 60 million people have been infected by HIV in the last two decades, and 20 million people have died from HIV/AIDS. While the development of highly active antiretrovirals to treat HIV/AIDS has led to

significant reductions in the mortality and morbidity of AIDS, the rapid emergence and spread of drug-resistant mutant strains of HIV is rendering current drugs ineffective, and is the major cause of treatment failure. Recent estimates are that nearly 50% of drug-experienced patients in North America harbor HIV that is resistant to one or more of the 16 FDA-approved antiretroviral agents used in multi-drug'coclctails' (Ref. dont have this ref).

Moreover, it has been estimated that drug-resistant HIV accounts for up to 12% of new infections (Little et al., N. Engl. J. Med., 347: 385 (2002)).

Accordingly, drug resistant HIV strains represent distinct infectious entities from a therapeutic viewpoint, and pose new challenges for drug design as well as drug treatment of existing infections. Substitutions have been documented in over 45 of the 99 amino acids of the HIV protease monomer in response to protease inhibitor treatment (Mellors, et al., Iiiterizational, 4ntivi7-al News, 3: 8 (1995) ; Eastman, et al., J. Virol., 72: 5154 (1998); Kozal, et al., Nat.

Med., 2: 753 (1996)). The particular sequence and pattern of mutations selected by PIs is believed to be somewhat drug-specific and often patient-specific, but high level resistance is typified by multiple mutations in the protease gene which give rise to cross-resistance to all of the PIs.

In view of the foregoing problems, there exists a need for inhibitors against drug resistant and mdrHIV strains. Further, there exists a need for inhibitors against drug resistant and multi-drug resistant HIV proteases (mdrPR). Further still, there exists a need for inhibitors of HIV that can prevent or slow the emergence of drug resistant and mdrHIV strains in infected individuals.

Inhibitors with the ability to inhibit mdrHIV strains, and to slow the emergence of drug resistant strains in wild type HIV infections, are defined as "resistance-repellent"inhibitors.

There also exists a need for robust methods that can be used to design "resistance-repellent"inhibitors.

More generally, there is a need for therapeutic regimens that minimize the likelihood that resistance will occur in a disease involving a replicating biological entity. In one approach, drugs may be designed which have similar activity against both the wild type and mutant forms of their target. Such drugs minimize the probability of a mutant population emerging by reducing the selective pressure introduced by the drug when used to treat wild type infections. Such drugs also can be used to treat mutant infections and can be used for salvage therapy.

There is also an urgent need to develop potent, broad-spectrum, and mechanistically-novel antimicrobials suitable for tackling the growing problem of antibiotic-resistant bacteria strains, and for treating and/or preventing outbreaks of infectious diseases, including diseases caused by bioterrorism agents like anthrax, plague, cholera, gastroenteritis, multidrug-resistant tuberculosis (MDR TB). The recent anthrax attack of 2001 underscored the reality of large-scale aerosol bioweapons attack by terrorist groups. It also revealed that there is an urgent and pressing need to discover and develop novel and potent antimicrobials that can be used therapeutically and prophylactically for biodefense against new bioattacks. The NIH and CDC have identified a number of High Priority pathogens based on their likelihood of causing widespread contagious disease and/or death to the general population. Research on methods of protection against potential agents of bioterrorism has been a priority for several years at the NIH. A recent analysis suggested the existence of ongoing offensive biological weapons programs in at least 13 countries (Inglesby, T. V. , et al., JAMA, 287 : 2236, (2002)).

The widespread use of antibiotics in human medical as well as in agricultural applications has promoted the emergence and spread of drug resistant bacteria that are no longer sensitive to existing drugs. The ease with which drug resistant microorganisms can be selected in a simple laboratory setting is a further concern when contemplating pharmaceutical-based

strategies for biodefense. There is an urgent need to discover and develop novel therapeutic agents to combat pathogens that are likely to be used in a bioterrorist scenario.

A list of selected agents rated by likelihood to cause the greatest harm in a bioterrorist attack has been compiled by the CDC and NIAID (Lane, H. C. , et al. , Nat Med., 7: 1271 (2001)). B. afztlzracis, the bacterium that causes anthrax, is one of the most serious of the group A pathogens. Dissemination of B. anthracis spores via the US Postal Service in 2001 established the feasibility of large-scale aerosol bioweapons attack. It has been estimated that between 130, 000 and 3 million deaths would follow the release of 100 kg of B. anthracis, a lethality matching that of a hydrogen bomb (Inglesby, T. V. , et al., JAMA, 287: 2236, (2002) ). Penicillin, doxycycline and ciprofloxacin are currently approved by the FDA for the treatment of inhalation anthrax infections. However, it was advised that antibiotic resistance to penicillin-and tetracycline-class antibiotics should be assumed following a terrorist attack (Inglesby, T. V. , et al., JAMA, 281 : 1735-45 (1999) ). Moreover, in vitro selection of a B. anthracis strain that is resistant to ofloxacin (a fluoroquinilone closely related to ciprofloxacin) has been reported (Choe, C. H. , et al., Antirraicrob. Agents. Chemother., 44: 1766 (2000) ). Following the anthrax attacks of 2001, the CDC advocated the use of a combination of 2-3 antibiotics.

As a post-exposure prophylaxis, 60 days of treatment with ciprofloxacin is currently recommended. Strict compliance to this drug regimen is complicated by moderate to severe gastrointestinal tract intolerance.

Another group A pathogen, Y. pestis, is the causative agent of plague. If 50 kg of Y. pestis were released as an aerosol over a city of 5 million, pneumonic plague would afflict an estimated 150,000 individuals and result in 36,000 deaths (Inglesby, T. V. , et al., JAMA, 283: 2281, (2000)). Streptomycin, tetracycline and doxycycline are the FDA-approved treatment for plague.

Wide spread use of these antibiotics in the US raises concerns about possible resistance. A US-licensed, formaldehyde-killed whole bacilli vaccine was discontinued by its manufacturers in 1999 and is no longer available.

C. jejuni and Y cholera are category B pathogens which can present a significant threat to the safety of food and water supplies. C. jejuni infections are one of the most commonly identified causes of acute bacterial gastroenteritis worldwide and area frequent cause of Traveler's diarrhea (Allos, B. M., Clin InfectDis, 32: 1201 (2001)). Currently, the CDC estimates that 2.4 million cases of Campylobacter infection occur in the United States each year, affecting almost 1% of the entire population. In the past few years, a rapidly increasing proportion of Campylobacter strains all over the world have been found to be fluoroquinolone-resistant. High rates of resistance make tetracycline, amoxicillin, ampicillin, metronidazole, and cephalasporins poor choices for the treatment of C. jejuni infections. All Campylobacter species are inherently resistant to vancomycin, rifampin, and trimethoprim. V cholera, a causative agent of cholera, is responsible for 120,000 deaths annually (Faruque, S. M. , et al., Microbiol Mol Biol Rev, 62: 1301 (1998)) and is characterized by a rapidly changing pattern of antibiotic resistance.

TB is one of the most common and devastating infectious diseases known to man. An estimated one third of the global population is infected with Mycobacteria tuberculosis. Eight million people develop an active infection and 2 million victims die yearly (Dye, C. , et al., JAMA, 282 : 677 (1999.)).

Currently, a combination of four drugs is recommended for TB treatment: isoniazid, rifampicin, pyrazinamide and ethambutole. The treatment course lasts 6 months. Such a multidrug combination together with the lengthy duration of treatment is prone to side-effects and adherence problems, which in turn can often lead to the development of drug resistance. The current drugs used to treat TB infections were introduced into clinical practice more than 30 years ago, in the absence of any knowledge of molecular mechanism. There is an urgent need to identify novel, effective, non-toxic and specific drugs that

can shorten the duration of treatment, reduce side-effects, combat latent infection and reduce the spread of MDR TB strains. In addition, it is important to recognize the need for mechanistically novel drugs, i. e. , antimicrobial agents that target biochemical pathways distinct from those of existing TB drugs, in order to be effective against MDR TB strains.

In summary, there is a clear need for the discovery of novel, non-toxic, broad spectrum antibiotics that can be used to (1) treat drug-resistant bacterial infections, and (2) protect civilians and military personnel in case of bioterrorist attacks. In one approach, drugs may be designed which have similar activity against both the wild type and variant forms of their target.

Such drugs should minimize the probability of the emergence of mutant populations by reducing the selective pressure introduced by the drug when used to treat wild type infections. Such drugs also can be used to treat mutant infections and can be used for salvage therapy. In another approach, drugs may be designed which have similar activity against various isotypes of a homologous target. Such drugs can be used to treat multiple species of pathogenic microorganisms since they will be active against the target of each species. In a third approach, drugs can be designed that combine the properties and the uses of both of the above approaches.

There also exists a need for robust methods that can be used to design such broad spectrum antibiotics.

Summary of the Invention In a first aspect the invention features a method for the structure-based design of a drug that can act as an inhibitor of at least two different biological entities, the method comprising the steps of : (a) providing at least one structure of a wild type target protein or an inhibitor-wild type target protein complex; (b) providing at least one structure of a variant target protein or an inhibitor- variant target protein complex; (c) comparing at least one structure from step (a) with at least one structure from step (b) to determine whether there exists a

common three-dimensionally conserved substructure comprising the atomic coordinates of the structurally conserved atoms of the inhibitors and structurally conserved atoms of the target proteins; and (d) if a conserved substructure exists, using the atomic coordinates of the conserved substructure to select a compound having atoms matching those of the structurally conserved atoms of the inhibitors, wherein the selection of the compound is performed using computer modeling.

The invention also features a method for the structure-based drug design of a broad spectrum compound, the method comprising the steps of : (a) providing at least one structure of a wild type target protein or an inhibitor-wild type target protein complex; (b) providing at least one structure of a variant target protein or an inhibitor-variant target protein complex; (c) comparing at least one structure from step (a) with at least one structure from step (b) to determine whether there exists a common three-dimensionally conserved substructure comprising the atomic coordinates of the structurally conserved atoms of the target proteins or a common three-dimensionally conserved substructure comprising the atomic coordinates of the structurally conserved atoms of the inhibitors and structurally conserved atoms of the target proteins; and (d) if a conserved substructure exists, using the atomic coordinates of the conserved substructure to select a compound having atoms matching those of the structurally conserved atoms of the inhibitors or to design a compound that binds to the target protein, wherein the selection of the compound is performed using computer modeling.

Desirably, the above method further comprises the steps of : (e) comparing at least one structure from step (a) with at least one structure from step (b) to determine whether there exists a three-dimensionally non-conserved substructure comprising the atomic coordinates of the structurally non- conserved atoms of the inhibitors and structurally non-conserved atoms of the target proteins; and (f) if a non-conserved substructure exists, using the atomic coordinates of the non-conserved substructure to reject a compound having

atoms matching those of the structurally non-conserved atoms of the inhibitors, wherein the rejection of the compound is performed in conjunction with computer modeling.

In any of the above methods, at least two, four, six, or eight structures from step b can be used in step c. The methods can be applied using several structures, including at least two, four, six, or eight variant forms of the target protein.

The inhibitors used in the inhibitor-wild type target protein complex and the inhibitor-variant target protein complex can be the same or different. The inhibitors can be selected from competitive or noncompetitive inhibitors.

Furthermore, the inhibitors can be selected from reversible, or irreversible inhibitors.

In any of the above methods, the variant target protein can be a homologous protein or a mutant protein.

In any of the above methods, the structures can be selected from crystal structures, NMR structures, computer models, any acceptable experimental, theoretical or computational method of deriving a three-dimensional representation of a structure, or a combination thereof.

Target proteins for use in the present invention include any therapeutically relevant protein. The target protein can be a viral, bacterial, protozoan, or fungal protein. In some instances, the target protein is one that is expressed in a neoplasm.

Preferably, the target protein can be an enzyme, a receptor, a structural protein, a component of a macromolecular complex, a component of a metabolic pathway, or an assembly of biological molecules. Desirably, the target protein is necessary for the survival of the replicating biological entity.

For example, the target protein can be an enzyme selected from the group consisting of reverse transcriptases, proteases, DNA and RNA polymerases, methylases, oxidases, esterases, acyl transferases, helicases, topoisomerases,

and kinases. The target protein can be a component of a metabolic pathway, such as the shilcimate pathway. Desirable target proteins include HIV protease or 3-dehydroquinate dehydratase, among others.

Where the target protein is HIV protease, suitable inhibitors for use in the methods of the invention include those selected from the group consisting of indinavir, nelfinavir, ritonavir, saquinavir, amprenavir, lopinavir, and UIC- 94003.

A broad spectrum protease inhibitor can be designed using the susbstructure of structurally conserved atoms described by the atomic coordinates in Table 8, which includes the structurally conserved atoms of the inhibitor and structurally conserved atoms of the protease. A broad spectrum protease inhibitor can also be designed using the structurally conserved atoms of the inhibitor alone. These are described by the atomic coordinates in Table 8.

A broad spectrum 3-dehydroquinate dehydratase inhibitor can be designed using the susbstructure of structurally conserved atoms described by the atomic coordinates in Table 12, which includes the structurally conserved atoms of the 3-dehydroquinate dehydratase. A broad spectrum 3- dehydroquinate dehydratase inhibitor can also be designed using the structurally conserved atoms of the inhibitor alone. These are described by the atomic coordinates in Table 12.

The invention also features compounds having a chemical structure selected using any of the methods above. Such compounds are broad spectrum inhibitors and have broad spectrum activity against replicating biological entities expressing a particular target protein. Thus, if the target protein is expressed by a microbe or a neoplasm, the compound will have broad spectrum activity against the microbe or neoplasm, respectively.

The invention features a compound having broad spectrum activity against HIV protease wherein the compound has a chemical structure selected using the methods above, including those methods utilizing the atomic coordinates of Table 8.

The invention features a compound having broad spectrum activity against 3-dehydroquinate dehydratase wherein the compound has a chemical structure selected using the methods above, including those methods utilizing the atomic coordinates of Table 12.

The compounds of the invention exclude bis-THF compounds (e. g., analogs of compounds 1 and 3) as described in J. Med. Chem. 39: 3278-3290 (1996) (compounds 49-52 and 58-60), Bioorg Med. Chem. Lett. 8 : 979-982 (1998), W099/65870, U. S. Patent No. 6,319, 946, W002/08657, W002/092595, W099/67417, EP00/9917, and WO00/76961 ; and also exclude fused ring THF structures as described in Bioorg Med. Chem. Lett. 8: 687-690 (1998) and U. S. Patent No. 5,990, 155.

For any of the broad spectrum inhibitors of the invention, broad spectrum activity can be measured by the ratio of the inhibitory concentrations of the broad spectrum inhibitor for the variant and wild type biological entities (IC50, aiat/IC50, wild type). Desirably, the ICso, variant/ICso, wild type ratio for a broad spectrum inhibitor is less than 100,80, 60,40, 30,20, 10,8, 6, or, most desirably, less than 3.

A broad spectrum inhibitor can be active against several different mutant biological entities. Desirably, the inhibitor will have broad spectrum activity against at least 1,2, 3,4, 5,6, 7,8, 9,10, 11, or 12 mutant biological entities.

A broad spectrum inhibitor can also be active against different organisms or neoplastic cell types expressing homologous target proteins that possess sufficient structural similarity. Desirably, the inhibitor will have broad

spectrum activity against at least 1,2, 3,4, 5,6, 7, 8, 9,10, 12,14, 16,18, or 20 different organisms or neoplastic cell types expressing homologous target proteins.

The invention also features a pharmaceutical composition that includes a broad spectrum inhibitor described herein in any pharmaceutically acceptable form, including isomers such as diastereomers and enantiomers, salts, solvates, and polymorphs thereof. The composition can include an inhibitor of the invention along with a pharmaceutically acceptable carrier or diluent.

The invention also features methods of treating disease in a patient in need thereof, which includes the administration of a pharmaceutical composition of the invention to the patient in an amount sufficient to treat the disease. The pharmaceutical composition includes any broad spectrum inhibitor described herein. Such broad spectrum inhibitors have broad spectrum activity against replicating biological entities expressing a particular target protein. Thus, if the target protein is expressed by a microbe or a neoplasm, the disease to be treated will be a microbial infection or neoplasm, respectively.

The invention features a method of treating an HIV infection in a patient in need thereof, the method including the step of administering to the patient a pharmaceutical composition including a broad spectrum protease inhibitor described herein in amounts effective to treat the HIV infection.

The invention features a method of treating a bacterial infection in a patient in need thereof, the method including the step of administering to the patient a pharmaceutical composition including a broad spectrum 3- dehydroquinate dehydratase inhibitor described herein in amounts effective to treat the bacterial infection. The bacterial infection to be treated using the above method can be caused by a bacterium selected from the group consisting of C. jejuni, V cholerae, Y. pestis, B. anthracis, P. putidas, and M. tuberculosis. Furthermore, this method can be used to treat infections by any microbe the utilizes 3-dehydroquinate dehydratase.

The invention also features the use of a pharmaceutical composition described herein in the manufacture of a medicament for the treatment of a disease. The pharmaceutical composition includes any broad spectrum inhibitor described herein. Such broad spectrum inhibitors and have broad spectrum activity against replicating biological entities expressing a particular target protein. Thus, if the target protein is HIV protease or 3-dehydroquinate dehydratase, the disease to be treated will be an HIV infection or bacterial infection, respectively.

The term"replicating biological entity"includes, for example, bacteria, fungi, yeasts, viruses, protozoa, prions and neoplasms Neoplasms include, for example, carcinomas of the bladder, breast, colon, kidney, liver, lung, head and neck, gall-bladder, ovary, pancreas, stomach, cervix, thyroid, prostate, or skin; a hematopoietic tumor of lymphoid lineage; a hematopoietic tumor of myeloid lineage; a tumor of mesenchymal origin; a tumor of the central or peripheral nervous system; melanoma; seminoma; teratocarcinoma ; osteosarcoma; thyroid follicular cancer; and Kapos's sarcoma. Hematopoietic tumors of lymphoid lineage can be leukemia, acute lymphocytic leukemia, acute lymphoblastic leukemia, B-cell lymphoma, T-cell-lymphoma, Hodgkin's lymphoma, non-Hodglcin's lymphoma, hairy cell lymphoma and Burkett's lymphoma.

By"wild type target protein"is meant a protein obtained from a replicating biological entity that has not been subjected to drug selection pressure, and could include polymorphisms or isoforms thereof. A replicating biological entity that expresses wild type target protein is referred to herein as a wild type biological entity.

By"variant target protein"is meant a mutant target protein or a homologous target protein. A replicating biological entity that expresses variant target protein is referred to herein as a variant biological entity.

By"mutant target protein"is meant a target protein that contains one or more amino acid substitutions with respect to the wild type target protein,

including proteins from the same organism that have evolved under drug selection pressure. In general, mutant target proteins will have one or more amino acid substitutions and should be readily identified as related to the cognate wild type protein using standard sequence comparison methods. A replicating biological entity that expresses mutant target protein is referred to herein as a mutant biological entity.

By"homologous target protein"is meant a variant target protein that is expressed in a different species or neoplastic cell type than the wild type target protein, but has the same, or similar, function.

By"structurally conserved target substructure", and by"structurally"or "three-dimensionally conserved substructure"as applied to target proteins, is meant the regions of the target protein structure which are not significantly affected by amino acid mutations or substitutions. Such regions can be defined using standard methods of comparative analysis of three-dimensional structures of proteins, such as superposition analysis, for example. In the case of HIV protease, these regions were identified using a pair wise superposition analysis of wild type and mutant protease structures complexed with inhibitors. The superposition of structures can be performed using the iterative procedure described herein. In the case of DHQase, these regions were identified using a pair wise superposition analysis of wild type and homologous DHQase structures from different bacterial species with and without inhibitors. It is apparent that the overall compositions of structurally conserved target substructures will likely differ for different, non-homologous target proteins, especially when the frequency of amino acid substitutions in high. However, a quantitative definition can be derived from the superposition analysis, which provides both the identities and the positions of the atoms that comprise these substructures. The regions that comprise structurally conserved target substructures contain atoms whose superimposed pairs have three-dimensional atomic coordinates that match to within a distance of 1 Å, 0.6 Å, 0.4 Å, or 0.2 Å.

By"broad spectrum inhibitor"is meant a compound having broad spectrum activity, i. e. , an inhibitor that is active against two different biological entities, e. g. , both a wild type biological entity and one or more variants of that biological entity. Thus, broad spectrum activity can be described by the inhibitor's action against a particular target protein (e. g. , broad spectrum activity against protease) or a particular target organism (e. g. , broad spectrum activity against HIV). Broad spectrum inhibitors will have medically insignificant interactions with non-conserved regions. Broad spectrum inhibitors can be useful for the treatment and/or prevention of infectious diseases caused by multiple infectious agents, as well as for decreasing the development of drug-resistance by these organisms.

As used herein, the term"treating"refers to administering a pharmaceutical composition for prophylactic and/or therapeutic purposes. To "prevent disease"refers to prophylactic treatment of a patient who is not yet ill, but who is susceptible to, or otherwise at risk of, a particular disease. To"treat disease"or use for"therapeutic treatment"refers to administering treatment to a patient already suffering from a disease to ameliorate the disease and improve the patient's condition. Thus, in the claims and embodiments, treating is the administration to a patient either for therapeutic or prophylactic purposes.

The term"microbial infection"refers to the invasion of the host patient by pathogenic microbes (e. g. , bacteria, fungi, yeasts, viruses, protozoa). This includes the excessive growth of microbes that are normally present in or on the body of a patient. More generally, a microbial infection can be any situation in which the presence of a microbial population (s) is damaging to a host patient. Thus, a patient is"suffering"from a microbial infection when excessive numbers of a microbial population are present in or on a patient's body, or when the presence of a microbial population (s) is damaging the cells or other tissue of a patient.

The term"microbes"includes, for example, bacteria, fungi, yeasts, viruses and protozoa.

The term"administration"or"administering"refers to a method of giving a dosage of a pharmaceutical composition to a patient, where the method is, e. g., topical, oral, intravenous, intraperitoneal, or intramuscular.

The preferred method of administration can vary depending on various factors, e. g., the components of the pharmaceutical composition, site of the potential or actual disease and severity of disease.

The term"patient"includes humans, cattle, pigs, sheep, horses, dogs, and cats, and also includes other vertebrate, most preferably, mammalian species.

Where"atomic coordinates"are provided, or otherwise referred to, these coordinates define a three dimensional structure. That such a structure may be defined by more than one different coordinate system, e. g. , by translation or rotation of the coordinates, does not change the relative positions of the atoms in the structure. Accordingly, any reference to atomic coordinates herein is intended to include any equivalent three dimensional structure defined by the coordinates.

By"computer modeling"is meant the use of a computer to visualize or compute a compound, a portion of a compound, a target protein, a portion of a target protein, a complex between a compound and a target protein, or a portion of a complex between a compound and a target protein.

Other features and advantages of the invention will be apparent from the following detailed description and from the claims.

Brief Description of the Drawings FIGURE 1 is a table depicting the structures of compounds 1-7, gt33, and qxa.

FIGURE 2 illustrates the amino acid alignment of type II DHQases.

Fully conserved residues are framed. Catalytically important amino acids are marked by stars. Arrows denote amino acids that make hydrogen bonds and ionic interactions in the structure of M. tuberculosis DHQase complexed with the inhibitor, 3-dehydroquinic acid oxime.

FIGURE 3 illustrates the key interactions of the substrate-based inhibitor, DHQO, with the active site residues for the Type II DHQase from M. tuberculosis.

Detailed Description We have discovered that the comparative analysis of the structures of complexes of inhibitors bound to wild type and variant forms of a target protein can be used to design compounds that are broad spectrum inhibitors.

The methods of the invention entail the design of compounds having a particular structure. The methods rely upon the use of structural information to arrive at these compounds. The structural data define a three dimensional array of the important contact atoms in an inhibitor that bind to the target protein in a fashion that results in broad spectrum activity against biological entities expressing variants of the target protein.

Inhibitor-Target Protein Structures Atomic structural coordinates can be selected from crystal structures, NMR structures, computer models, any acceptable experimental, theoretical or computational method of deriving a three-dimensional representation of a structure, or a combination thereof. Atomic coordinates for use in the methods of the invention can be obtained from publicly available sources, e. g. from the Protein Data Bank, or obtained using known experimental or computational methods.

Atomic structural coordinates for use in the methods of the invention include crystal structures of HIV protease/inhibitor complexes derived from

wild type and drug-resistant mutant proteases, and of DHQase and DHQase inhibitor complexes derived from two or more bacterial species, among others.

In examples 1-3, the methods of the invention are applied using the coordinates of wild type HIV protease complexed with amprenavir, wild type HIV protease complexed with UIC-94003, and V82F/I84V mutant HIV protease complexed with UIC-94003. In example 4, the methods of the invention are applied using the coordinates of wild type DHQase from M. tuberculosis and from Pseudomonasputidas. a complex between a compound and a target protein.

The coordinates of other representative structures of HIV protease and DHQase should be useful for performing the methods of the present invention.

Conserved Substructures Conserved substructures can be identified for target proteins, for target protein-inhibitor complexes, and/or for inhibitors, depending on the nature of the structures that are used in the comparative superposition analysis. In one approach, at least one structure of a wild type target protein is compared to at least one structure of a mutant or homologous target protein to determine whether a common three-dimensionally conserved substructure is present among the wild type protein and the mutant or homologous proteins, respectively. In another approach, at least one structure of an inhibitor-wild type target protein complex and at least one structure of an inhibitor-mutant target protein complex are compared to determine whether a common three- dimensionally conserved substructure is present among the mutant and wild type complexes. In a third approach, at least one structure of an inhibitor-wild type target protein complex and at least one structure of a mutant or homologous target protein without inhibitor are compared to determine whether a common three-dimensionally conserved substructure is present among the respective mutant or homologous protein and the wild type complexes. Variations of the approached described above can also be used. In each case, such a comparison can be made by means of (a) an overall

superposition of the atoms of the protein structures; and, where feasible, (b) a study of the distances from atoms of the inhibitors to atoms of the protein. This analysis requires three-dimensional atomic coordinates of the protein structures and of the bound inhibitor.

The superposition of the protein structures can be performed in a two step process: 1) the distance between all pairs of corresponding Ca atoms (Ca atom of residue number 1 in one protein to Ca atom of residue number 1 in the second protein; Ca atom of residue number 2 in one protein to Ca atom of residue number 2 in the second protein; and so on) of the polypeptide chains is minimized by means of a least-square algorithm; 2) the superposition is refined by minimizing, in an iterative process, the distances between corresponding Ca atoms that are closer than a given distance (0. 25 A for example), thus eliminating regions of the structures having large conformational differences to compute the superposition parameters. Furthermore, where a partial structure is provided (e. g. , from NMR data) the available coordinates are superimposed.

The conserved substructure identifies the relevant portion of the target protein that is the active site, or binding region, defined by that pant of the target protein interacting with inhibitor. Important interactions between the target protein and inhibitor are identified by mapping the contacts between the two.

Structurally conserved regions of the target protein not near the binding site are generally not relevant to the design of the broad spectrum inhibitor.

Accordingly, the selection of the meaningful substructure is identified using the above mentioned contacts.

Design of a Broad Spectrum Inhibitor The coordinates of the conserved inhibitor substructure are used to design an inhibitor having atoms matching those of the three-dimensionally structurally conserved atoms of the inhibitors. The result is an inhibitor for

which ICso, variant and IC50, wild type are similar, minimizing the selective pressure introduced by the drug.

The methods of the invention can employ computer-based methods for designing broad spectrum inhibitors. These computer-based methods fall into two broad classes: database methods and de novo design methods. In database methods the compound of interest is compared to all compounds present in a database of chemical structures and compounds whose structure is in some way similar to the compound of interest are identified. The structures in the database are based on either experimental data, generated by NMR or x-ray crystallography, or modeled three-dimensional structures based on two- dimensional (i. e. , sequence) data. In de novo design methods, models of compounds whose structure is in some way similar to the compound of interest are generated by a computer program using information derived from knows structures, e. g. , data generated by x-ray crystallography and/or theoretical rules.

Such design methods can build a compound having a desired structure in either an atom-by-atom manner or by assembling stored small molecular fragments.

The success of both database and de novo methods in identifying compounds having the desired activity depends on the identification of the functionally relevant portion of the compound of interest. The functionally relevant portion of the compound, the pharmacophore, is defined by the structurally conserved substructure. A pharmacophore then is an arrangement of structural features and functional groups important for obtaining an inhibitor having broad spectrum activity.

Not all identified compounds having the desired pharmacophore will act as broad spectrum inhibitors. The actual activity can be finally determined only by measuring the activity of the compound in relevant biological assays.

However, the methods of the invention are extremely valuable because they can be used to greatly reduce the number of compounds which must be tested to identify those likely to exhibit broad spectrum activity.

Programs suitable for generating predicted three-dimensional structures from two-dimensional data include: Concord (Tripos Associated, St. Louis, Mo. ), 3-D Builder (Chemical Design Ltd. , Oxford, U. K. ), Catalyst (Bio-CAD Corp. , Mountain View, Calif.), and Daylight (Abbott Laboratories, Abbott Park, Ill.).

Programs suitable for searching three-dimensional databases to identify molecules bearing a desired pharmacophore include: MACCS-3D and ISIS/3D (Molecular Design Ltd. , San Leandro, Calif. ), ChemDBS-3D (Chemical Design Ltd. , Oxford, U. K. ), and Sybyl/3DB Unity (Tripos Associates, St.

Louis, Mo.).

Programs suitable for pharmacophore selection and design include: DISCO (Abbott Laboratories, Abbott Park, Ill.), Catalyst (Bio-CAD Corp., Mountain View, Calif. ), and ChemDBS-3D (Chemical Design Ltd. , Oxford, U. K.).

Databases of chemical structures are available from Cambridge Crystallographic Data Centre (Cambridge, U. K. ) and Chemical Abstracts Service (Columbus, Ohio).

De novo design programs include Ludi (Biosym Technologies Inc. , San Diego, Calif. ) and Aladdin (Daylight Chemical Information Systems, Irvine Calif.).

One skilled in the art may use one of several methods to screen chemical entities for their ability to match the conserved substructure. This process may begin by visual inspection of, for example, the active site on the computer screen based on the atomic coordinates for the target protein. Docking may be accomplished using software such as Quanta and Sybyl, followed by energy minimization and molecular dynamics with standard molecular mechanics forcefields, such as CHARMM and AMBER.

Specialized computer programs may also assist in the process of selecting chemical entities. These include:

1. GRID (Goodford, P. J. ,"A Computational Procedure for Determining Energetically Favorable Binding Sites on Biologically Important Macromolecules,"J. Med. Chem, 28 : 849 (1985) ). GRID is available from Oxford University, Oxford, UK.

2. MCSS (Miranker, A. and M. Karplus, "Functionality Maps of Binding Sites: A Multiple Copy Simultaneous Search Method." Proteins : Structure, Function, and Genetics, 11: 29 (1991)). MCSS is available from Molecular Simulations, Burlington, Mass.

3. AUTODOCK (Goodsell, D. S. and A. J. Olsen,"Automated Docking of Substrates to Proteins by Simulated Annealing,"Proteins : Structure, Function, and Genetics, 8 : 195 (1990)). AUTODOCK is available from Scripps Research Institute, La Jolla, Calif.

4. DOCK (Kuntz, 1. D. et al. ,"A Geometric Approach to Macromolecule-LigandInteractions,"J. Mol. Biol., 161: 269 (1982)).

DOCK is available from University of California, San Francisco, Calif.

Once the conserved substructure for the inhibitor has been identified, the conserved atoms of the inhibitor can be selected for assembly into a single inhibitor. Assembly may be proceed by visual inspection of the relationship of the fragments to each other on the three-dimensional image displayed on a computer screen in relation to the structure coordinates of the target protein.

This may be followed by manual model building using software such as Quanta or Sybyl.

Useful programs to aid one of skill in the art in assembly of the individual chemical entities or fragments include: 1. CAVEAT (Bartlett, P. A. et al, "CAVEAT : A Program to Facilitate the Structure-Derived Design of Biologically Active Molecules". In

"Molecular Recognition in Chemical and Biological Problems,"Special Pub., Royal Chem. Soc., 78: 182 (1989) ). CAVEAT is available from the University of California, Berkeley, Calif.

2.3D Database systems such as MACCS-3D (MDL Information Systems, San Leandro, Calif.). This area is reviewed in Martin, Y. C., "3D Database Searching in Drug Design,"J. Med. Chez., 35: 2145 (1992)).

3. HOOK (available from Molecular Simulations, Burlington, Mass.).

Other molecular modeling techniques may also be employed in accordance with this invention. See, e. g. , Cohen, N. C. et al.,"Molecular Modeling Software and Methods for Medicinal Chemistry,"J. Med. Chem., 33: 883 (1990). See also, Navia, M. A. and M. A. Murcko, "The Use of Structural Information in Drug Design,"Current Opinions in Structural Biology, 2: 202 (1992).

Once a broad spectrum inhibitor has been optimally designed, as described above, substitutions may then be made in some of its atoms or side groups in order to improve or modify its binding properties. Generally, initial substitutions are conservative, i. e. , the replacement group will have approximately the same size, shape, hydrophobicity and charge as the original group. It should, of course, be understood that components known in the art to alter conformation should be avoided.

In general, inhibitors designed using the methods of the invention can be tested for broad spectrum activity using any of the to in vitro and/or in vivo methods described below, among others.

Broad Spectrum Inhibitors Broad spectrum inhibitors match the pharmacophore defined by the structurally conserved substructure. The pharmacophore is the arrangement of structural features and functional groups important for obtaining an inhibitor having broad spectrum activity. This pharmacophore is derived using structural data for known inhibitors complexed to a target protein.

Accordingly, broad spectrum inhibitors will often be structurally related to known compounds lacking broad spectrum activity, but useful in the design of broad spectrum inhibitors using the methods disclosed herein. These known inhibitors serve as lead compounds for both the design and synthesis of a broad spectrum inhibitor. Using the synthetic methods for making the lead compounds and standard synthetic methods as described by, for example, J.

March, Advanced Organic Chemistry: Reactions, Mechanisms and Structure," John Wiley & Sons, Inc. , 1992; T. W. Green and P. G. M. Wuts,"Protective Groups in Organic Synthesis" (2nd Ed. ), John Wiley & Sons, 1991; and P. J.

Kocienski, "Protecting Groups, "Georg Thieme Verlag, 1994, one can synthesize the broad spectrum inhibitors described herein.

Typically the lead compounds bear varied functional groups which are present in the pharmacophore, including hydrogen-bond donors, hydrogen- bond acceptors, ionic moieties, polar moieties, hydrophobic moieties, aromatic centers, and electron-donors and acceptors. These are linked by a structural scaffold which imparts the appropriate a three dimension arrangement of the functional groups.

Numerous modifications of the lead compound can be made using techniques known in the art. These include changing a functional group by replacing it with another moiety of the same group. For example, one hydrogen-bond donor may be substituted by another. A good hydrogen bond donor has an H atom bonded to a very electronegative atom (e. g., O-H or N-H).

Examples of hydrogen-bond donors include alcohols, carboxylic acids, oximes, and amides, among others. Similarly, one hydrogen-bond acceptor may be

substituted by another. A good hydrogen bond acceptor has an electronegative element with lone pairs (e. g., O, N, or F). Examples of hydrogen bond acceptors include water, halogen atoms, alcohols, amines, carbonyls, ethers, and amides, among others. It may also be desirable to alter the distance between functional groups in a lead compound. This is achieved by employing synthetic methods analogous to those used to prepare the lead compound, but replacing the scaffold with a structurally related scaffold that provides the desired distance (e. g. , a scaffold that incorporates more or fewer atoms linking the relevant functional groups). In some instances it may also be desirable to alter the stereochemistry in a lead compound. This can be accomplished by employing racemic starting materials, or by employing reaction conditions that result in racemization of the relevant chiral center, followed by separation of the enantiomeric or diastereomeric mixture.

Assays Inhibitors designed using the methods disclosed herein may be further assayed, using standard in vitro models or animal models, to evaluate therapeutic activity and toxicity. These assays are described in the literature and are familiar to those skilled in the art. These include but are not limited to assays for monitoring or measuring efficacy against HIV, bacteria, and neoplasms.

One skilled in the art will be familiar with methods of measuring the IC50's of a broad spectrum inhibitor described herein. The ICso value is determined by plotting percent activity versus inhibitor concentration in the assay and identifying the concentration at which 50% of the activity (e. g., growth, enzymatic activity, protein production, etc. ) remains. Inhibitors can be tested for antimicrobial activity against a panel of organisms according to standard procedures described by the National Committee for Clinical Laboratory Standards (NCCLS document M7-A3, Vol. 13, No. 25, 1993/NCCLS document M27-P, Vol. 12, No. 25,1992). Inhibitors can be

dissolved (0.1 llg/ml-500 pg/ml) in microbial growth media, diluted, and added to wells of a microtiter plate containing bacteria or fungal cells in a final volume of an appropriate media (Mueller-Hinton Broth ; Haemophilus Test Media; Mueller-Hinton Broth+5% Sheep Blood; or RPMI 1690). Typically, the plates are incubated overnight at an appropriate temperature (30 C to 37 C) and optical densities (measure of cell growth) are measured using a commercial plate reader.

ICs0's for broad spectrum protease inhibitors can be measured against wild type HIV and clinically isolated mutant HIV isolates, utilizing the PHA-PBMC exposed to HIV-1 (50 TCIDso dose/IXIO PBMC) as target cells and using the inhibition of p24 Gag protein production as an endpoint. The amounts of p24 antigen produced by the cells can be determined on day 7 in culture using a commercially available radioimmunoassay kit. Drug concentrations resulting in 50% inhibition (ICSO'S) of p24 antigen production can be determined by comparison with the p24 production level in drug-free control cell cultures.

Therapy The invention features a method of identifying a compound having broad spectrum activity. Broad spectrum inhibitors of the present invention may be administered by any appropriate route for treatment or prevention of a disease or condition associated with a bacterial infection, viral infection, or neoplastic disorder, among others. These may be administered to humans, domestic pets, livestock, or other animals with a pharmaceutically acceptable diluent, carrier, or excipient, in unit dosage form. Administration may be topical, parenteral, intravenous, intra-arterial, subcutaneous, intramuscular, intracranial, intraorbital, ophthalmic, intraventricular, intracapsular, intraspinal, intracisternal, intraperitoneal, intranasal, aerosol, by suppositories, or oral administration.

Therapeutic formulations may be in the form of liquid solutions or suspensions; for oral administration, formulations may be in the form of tablets or capsules; and for intranasal formulations, in the form of powders, nasal drops, or aerosols.

Methods well known in the art for making formulations are found, for example, in"Remington: The Science and Practice of Pharmacy" (20th ed. , ed.

A. R. Gennaro AR. , 2000, Lippincott Williams & Wilkins). Formulations for parenteral administration may, for example, contain excipients, sterile water, or saline, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, or hydrogenated napthalenes. Biocompatible, biodegradable lactide polymer, lactide/glycolide copolymer, or polyoxyethylene-polyoxypropylene copolymers may be used to control the release of the compounds.

Nanoparticulate formulations (e. g. , biodegradable nanoparticles, solid lipid nanoparticles, liposomes) may be used to control the biodistribution of the compounds. Other potentially useful parenteral delivery systems include ethylene-vinyl acetate copolymer particles, osmotic pumps, implantable infusion systems, and liposomes. Formulations for inhalation may contain excipients, for example, lactose, or may be aqueous solutions containing, for example, polyoxyethylene-9-lauryl ether, glycholate and deoxycholate, or may be oily solutions for administration in the form of nasal drops, or as a gel. The concentration of the broad spectrum inhibitor in the formulation will vary depending upon a number of factors, including the dosage of the drug to be administered, and the route of administration.

The broad spectrum inhibitor may be optionally administered as a pharmaceutically acceptable salt, such as a non-toxic acid addition salts or metal complexes that are commonly used in the pharmaceutical industry.

Examples of acid addition salts include organic acids such as acetic, lactic, pamoic, maleic, citric, malic, ascorbic, succinic, benzoic, palmitic, suberic, salicylic, tartaric, methanesulfonic, toluenesulfonic, or trifluoroacetic acids or the like; polymeric acids such as tannic acid, carboxymethyl cellulose, or the

like; and inorganic acid such as hydrochloric acid, hydrobromic acid, sulfuric acid phosphoric acid, or the like. Metal complexes include zinc, iron, and calcium, among others.

Administration of compounds in controlled release formulations is useful where the broad spectrum inhibitor has (i) a narrow therapeutic index (e. g. , the difference between the plasma concentration leading to harmful side effects or toxic reactions and the plasma concentration leading to a therapeutic effect is small; generally, the therapeutic index, TI, is defined as the ratio of median lethal dose (LDso) to median effective dose (ED50)) ; (ii) a narrow absorption window in the gastro-intestinal tract; or (iii) a short biological half- life, so that frequent dosing during a day is required in order to sustain the plasma level at a therapeutic level.

Many strategies can be pursued to obtain controlled release in which the rate of release outweighs the rate of metabolism of the broad spectrum inhibitor. For example, controlled release can be obtained by the appropriate selection of formulation parameters and ingredients, including, e. g. , appropriate controlled release compositions and coatings. Examples include single or multiple unit tablet or capsule compositions, oil solutions, suspensions, emulsions, microcapsules, microspheres, nanoparticles, patches, and liposomes.

Formulations for oral use include tablets containing the active ingredient (s) in a mixture with non-toxic pharmaceutically acceptable excipients. These excipients may be, for example, inert diluents or fillers (e. g., sucrose and sorbitol), lubricating agents, glidants, and antiadhesives (e. g., magnesium stearate, zinc stearate, stearic acid, silicas, hydrogenated vegetable oils, or talc).

Formulations for oral use may also be provided as chewable tablets, or as hard gelatin capsules wherein the active ingredient is mixed with an inert solid diluent, or as soft gelatin capsules wherein the active ingredient is mixed with water or an oil medium.

Pharmaceutical formulations of broad spectrum inhibitor described herein include isomers such as diastereomers and enantiomers, mixtures of isomers, including racemic mixtures, salts, solvates, and polymorphs thereof.

The formulations can be administered to human patients in therapeutically effective amounts. For example, when the broad spectrum inhibitor is an antimicrobial drug, an amount is administered which prevents, stabilizes, eliminates, or reduces a microbial infection. Typical dose ranges are from about 0. 01 u. g/kg to about 2 mg/kg of body weight per day. The exemplary dosage of drug to be administered is likely to depend on such variables as the type and extent of the disorder, the overall health status of the particular patient, the formulation of the compound excipients, and its route of administration. Standard clinical trials maybe used to optimize the dose and dosing frequency for any particular broad spectrum inhibitor.

The following examples are meant to illustrate, but in no way limit, the claimed invention.

Example 1 This example illustrates the method by which experimentally- determined crystal structures of the same inhibitor in complex with wild type and mutant species of HIV protease can be compared and analyzed for the existence of a three-dimensionally conserved substructure.

The structures of wild type HIV-1 protease and a mutant, V82F/I84V, HIV-1 protease, both in complexes with the inhibitor shown in Figure 1 were determined using conventional x-ray crystallography techniques. The structures were analyzed by means of (a) an overall superposition of the atoms of the protein structures; and, (b) a study of the distances from atoms of the inhibitors to atoms of the protein. This analysis requires three dimensional atomic coordinates of the protein structures and of the bound inhibitor.

The superposition of the protein structures was performed in a two step process: 1) the distance between all pairs of corresponding Ca atoms (Ca atom

of residue number 1 in one protein to Ca atom of residue number 1 in the second protein; Ca atom of residue number 2 in one protein to Ca atom of residue number 2 in the second protein; and so on) of the polypeptide chains is minimized by means of a least-square algorithm; 2) the superposition is refined by minimizing, in an iterative process, the distances between corresponding Ca atoms that are closer than a given distance (0.25 A in this example), thus eliminating regions of the structures having large conformational differences to compute the superposition parameters. The distances between equivalenced Ca atoms after the minimization procedure are shown in Table 4.

Table 4 Distances between equivalent Ca atoms Molecule 1: HIV-1 PR wt : 1 Molecule 2: HIV-1 PR V82F/I84V mutant: 1 Molecule 1 Molecule 2 distance [A] CA PRO 1 CA PRO 1 0.455 CA GLN 2 CA GLN 2 0.434 CA ILE 3 CA ILE 3 0.418 CA THR 4 CA THR 4 0.317 CA LEU 5 CA LEU 5 0.172 CA TRP 6 CA TRP 6 0.228 CA GLN 7 CA GLN 7 0.364 CA ARG 8 CA ARG 8 0.166 CA PRO 9 CA PRO 9 0.057 CA LEU 10 CA LEU 10 0.183 CA VAL 11 CA VAL 11 0.194 CA THR 12 CA THR 12 0.168 CA ILE 13 CA ILE 13 0.146 CA LYS 14 CA LYS 14 0. 229 CA ILE 15 CA ILE 15 0.266 CA GLY 16 CA GLY 16 0. 662 CA GLY 17 CA GLY 17 0.491 CA GLN 18 CA GLN 18 0. 267 CA LEU 19 CA LEU 19 0.112 CA LYS 20 CA LYS 20 0.128 CA GLU 21 CA GLU 21 0.190 CA ALA 22 CA ALA 22 0.169 CA LEU 23 CA LEU 23 0. 218 CA LEU 24 CA LEU 24 0.233 CA ASP 25 CA ASP 25 0.160 CA THR 26 CA THR 26 0. 200 CA GLY 27 CA GLY 27 0. 303 CA ALA 28 CA ALA 28 0.169 CA ASP 29 CA ASP 29 0.150 CA ASP 30 CA ASP 30 0.038 CA THR 31 CA THR 31 0.047 CA VAL 32 CA VAL 32 0.173 CA LEU 33 CA LEU 33 0.194 CA GLU 34 CA GLU 34 0.310 CA GLU 35 CA GLU 35 0.260 CA MET 36 CA MET 36 0.136 CA SER 37 CA SER 37 0.494 CA LEU 38 CA LEU 38 0.607 CA PRO 39 CA PRO 39 0.094 CA GLY 40 CA GLY 40 0.774 CA ARG 41 CA ARG 41 0.448 CA TRP 42 CA TRP 42 0.204 CA LYS 43 CA LYS 43 0.596 CA PRO 44 CA PRO 44 0. 625 CA LYS 45 CA LYS 45 0.541 CA MET 46 CA MET 46 0.643 CA ILE 47 CA ILE 47 0.361 CA GLY 48 CA GLY 48 0.240 CA GLY 49 CA GLY 49 0.182 CA ILE 50 CA ILE 50 0.110 CA GLY 51 CA GLY 51 0.243 CA GLY 52 CA GLY 52 0.200 CA PHE 53 CA PHE 53 0.119 CA ILE 54 CA ILE 54 0.255 CA LYS 55 CA LYS 55 0.295 CA VAL 56 CA VAL 56 0.108 CA ARG 57 CA ARG 57 0.129 CA GLN 58 CA GLN 58 0.074 CA TYR 59 CA TYR 59 0.372 CA ASP 60 CA ASP 60 0. 496 CA GLN 61 CA GLN 61 0.780 CA ILE 62 CA ILE 62 0.406 CA LEU 63 CA LEU 63 0.211 CA ILE 64 CA ILE 64 0.260 CA GLU 65 CA GLU 65 0. 193 CA ILE 66 CA ILE 66 0.181 CA CYS 67 CA CYS 67 0. 518 CA GLY 68 CA GLY 68 0.641 CA HIS 69 CA HIS 69 0.319 CA LYS 70 CA LYS 70 0.179 CA ALA 71 CA ALA 71 0.265 CA ILE 72 CA ILE 72 0.350 CA GLY 73 CA GLY 73 0.253 CA THR 74 CA THR 74 0.301 CA VAL 75 CA VAL 75 0.187 CA LEU 76 CA LEU 76 0.186 CA VAL 77 CA VAL 77 0.070 CA GLY 78 CA GLY 78 0. 306 CA PRO 79 CA PRO 79 0.047 CA THR 80 CA THR 80 0. 470 CA PRO 81 CA PRO 81 0.404 CA VAL 82 CA PHE 82 0.556 CA ASN 83 CA ASN 83 0.146 CA ILE 84 CA VAL 84 0.196 CA ILE 85 CA ILE 85 0.163 CA GLY 86 CA GLY 86 0.224 CA ARG 87 CA ARG 87 0.127 CA ASN 88 CA ASN 88 0.048 CA LEU 89 CA LEU 89 0.081 CA LEU 90 CA LEU 90 0.197 CA THR 91 CA THR 91 0.226 CA GLN 92 CA GLN 92 0. 176 CA ILE 93 CA ILE 93 0. 151 CA GLY 94 CA GLY 94 0.338 CA CYS 95 CA CYS 95 0.233 CA THR 96 CA THR 96 0.305 CA LEU 97 CA LEU 97 0.089 CA ASN 98 CA ASN 98 0.260 CA PHE 99 CA PHE 99 0.250 CA PRO 101 CA PRO 101 0.227 CA GLN 102 CA GLN 102 0. 108 CA ILE 103 CA ILE 103 0.206 CA THR 104 CA THR 104 0.169 CA LEU 105 CA LEU 105 0.125 CA TRP 106 CA TRP 106 0.363 CA GLN 107 CA GLN 107 0.296 CA ARG 108 CA ARG 108 0.400 CA PRO 109 CA PRO 109 0.173 CA LEU 110 CA LEU 110 0.182 CA VAL 111 CA VAL 111 0.085 CA THR 112 CA THR 112 0.123 CA ILE 113 CA ILE 113 0. 107 CA LYS 114 CA LYS 114 0.368 CA ILE 115 CA ILE 115 0.226 CA GLY 116 CA GLY 116 0. 638 CA GLY 117 CA GLY 117 0.516 CA GLN 118 CA GLN 118 0.414 CA LEU 119 CA LEU 119 0.102 CA LYS 120 CA LYS 120 0.191 CA GLU 121 CA GLU 121 0.206 CA ALA 122 CA ALA 122 0.197 CA LEU 123 CA LEU 123 0.231 CA LEU 124 CA LEU 124 0.145 CA ASP 125 CA ASP 125 0.235 CA THR 126 CA THR 126 0.311 CA GLY 127 CA GLY 127 0.200 CA ALA 128 CA ALA 128 0.102 CA ASP 129 CA ASP 129 0. 143 CA ASP 130 CA ASP 130 0.261 CA THR 131 CA THR 131 0.172 CA VAL 132 CA VAL 132 0.232 CA LEU 133 CA LEU 133 0.103 CA GLU 134 CA GLU 134 0. 175 CA GLU 135 CA GLU 135 0. 190 CA MET 136 CA MET 136 0.220 CA SER 137 CA SER 137 0.739 CA LEU 138 CA LEU 138 0.277 CA PRO 139 CA PRO 139 0.325 CA GLY 140 CA GLY 140 0.390 CA ARG 141 CA ARG 141 0.174 CA TRP 142 CA TRP 142 0.168 CA LYS 143 CA LYS 143 0.304 CA PRO 144 CA PRO 144 0.194 CA LYS 145 CA LYS 145 0.456 CA MET 146 CA MET 146 0.362 CA ILE 147 CA ILE 147 0.178 CA GLY 148 CA GLY 148 0.390 CA GLY'149 CA GLY 149 0.434 CA ILE 150 CA ILE 150 0.050 CA GLY 151 CA GLY 151 0.199 CA GLY 152 CA GLY 152 0. 152 CA PHE 153 CA PHE 153 0.455 CA ILE 154 CA ILE 154 0.198 CA LYS 155 CA LYS 155 0.470 CA VAL 156 CA VAL 156 0.590 CA ARG 157 CA ARG 157 0.607 CA GLN 158 CA GLN 158 0.465 CA TYR 159 CA TYR 159 0.301 CA ASP 160 CA ASP 160 0.294 CA GLN 161 CA GLN 161 0.308 CA ILE 162 CA ILE 162 0.274 CA LEU 163 CA LEU 163 0.235 CA ILE 164 CA ILE 164 0.367 CA GLU 165 CA GLU 165 0.410 CA ILE 166 CA ILE 166 0.201 CA CYS 167 CA CYS 167 0.409 CA GLY 168 CA GLY 168 0.406 CA HIS 169 CA HIS 169 0.410 CA LYS 170 CA LYS 170 0.282 CA ALA 171 CA ALA 171 0.273 CA ILE 172 CA ILE 172 0.317 CA GLY 173 CA GLY 173 0.563 CA THR 174 CA THR 174 0. 129 CA VAL 175 CA VAL 175 0.237 CA LEU 176 CA LEU 176 0.155 CA VAL 177 CA VAL 177 0. 240 CA GLY 178 CA GLY 178 0.386 CA PRO 179 CA PRO 179 0.340 CA THR 180 CA THR 180 0.335 CA PRO 181 CA PRO 181 0.446 CA VAL 182 CA PHE 182 0.343 CA ASN 183 CA ASN 183 0.205 CA ILE 184 CA VAL 184 0.262 CA ILE 185 CA ILE 185 0.096 CA GLY 186 CA GLY 186 0.118 CA ARG 187 CA ARG 187 0.202 CA ASN 188 CA ASN 188 0.073 CA LEU 189 CA LEU 189 0.108 CA LEU 190 CA LEU 190 0.127 CA THR 191 CA THR 191 0.177 CA GLN 192 CA GLN 192 0.175 CA ILE 193 CA ILE 193 0.241 CA GLY 194 CA GLY 194 0.118 CA CYS 195 CA CYS 195 0.375 CA THR 196 CA THR 196 0.437 CA LEU 197 CA LEU 197 0. 167 CA ASN 198 CA ASN 198 0. 178

Table 4 shows that the I84V, V82F mutations induce structural changes relative to the wild type structure in some parts of the enzyme, but that other regions are less affected. The regions of the protein structure which are not significantly affected by the amino acid mutations are defined as structurally

conserved regions. In the present example, the mutations result in localized structural changes in the baclçbone of HIV protease over a wide range, from 0. 038-0. 774 A.

The distances between the strongly interacting atoms of the inhibitor to atoms of the wild type and mutant protein, that is hydrogen-bond donors and acceptors, were computed and they are displayed in Table 5.

Table 5 Distances between atoms of the inhibitor and atoms of the protein HIV PR wt: 1 V82F/I84V : 1 02-Wat301 2. 92 2. 89 N1-027 3. 36 3. 46 06-N30 3. 30 3. 61 06-N29 3. 19 3. 55 07-N29 2. 84 2. 87 07-OD1 293. 423. 54 07-01 3. 31 3. 19 03-OD 25 (out) 2. 5 0 2. 94 03-OD 25 (in) 2. 65 2. 67 03-OD125 (out) 3. 27 3. 21 03-OD125 (in) 2. 80 2. 67 05-Wat301 2. 70 2. 79 08-N130 3. 16 2. 96

Table 5 shows that the atoms of the inhibitor interact with the same atoms of the two different proteins, in this case the wild type and V82F/I84V mutant HIV proteases. From Table 5, it can be seen that the atoms of the enzymes with which the inhibitor interacts belong to the structurally conserved regions. The effects of mutations on the protein-inhibitor interactions can be quantified in terms of the distances between interacting pairs of atoms from the inhibitor and from atoms of the three-dimensionally conserved substructure of the protein. These distances are similar in the wild type and in the mutant complexes; the average of their differences is only 0.07 A. The range of the differences is 0.02-0. 36 A.

Example 2 This example illustrates the method by which experimentally- determined crystal structures of two different inhibitors in complexes with wild type HIV protease can be compared and analyzed for the existence of a three- dimensionally conserved substructure. The structures of wild type HIV-1 protease in complexes with inhibitor 1 and with Amprenavir (inhibitor 2) were analyzed by means of (a) an overall superposition of the protein structures; and (b) a study of the distances from atoms of the inhibitors to atoms of the protein.

The superposition of the protein structures is performed in a two step process: 1) the distance between all pairs of corresponding Ca atoms (Ca atom of residue number 1 in one protein to Ca atom of residue number 1 in the second protein; Ca atom of residue number 2 in one protein to Ca atom of residue number 2 in the second protein; and so on) of the polypeptide chains is minimized by means of a least-square algorithm; 2) the superposition is refined by minimizing, in an iterative process, the distances between corresponding Ca atoms that are closer than a given distance (0.25 A in this example), thus eliminating regions of the structures having large conformational differences to compute the superposition parameters. The distances between equivalenced Ca atoms after the minimization procedure are shown in Table 6.

Table 6 Distances between equivalent Ca atoms Molecule 1: HIV-1 PR wt : 1 Molecule 2: HIV-1 PR wt: 2 Molecule 1 Molecule 2 distance CA PRO 1 CA PRO 1 0.200 CA GLN 2 CA GLN 2 0.320 CA ILE 3 CA ILE 3 0.147 CA THR 4 CA THR 4 0. 405 CA LEU 5 CA LEU 5 0. 225 CA TRP 6 CA TRP 6 0.296 CA GLN 7 CA GLN 7 0.317 CA ARG 8 CA ARG 8 0.154 CA PRO 9 CA PRO 9 0.143 CA LEU 10 CA LEU 10 0.259 CA VAL 11 CA VAL 11 0. 275 CA THR 12 CA THR 12 0.307 CA ILE 13 CA ILE 13 0.207 CA LYS 14 CA LYS 14 0.273 CA ILE 15 CA ILE 15 0.434 CA GLY 16 CA GLY 16 0.469 CA GLY 17 CA GLY 17 0.414 CA GLN 18 CA GLN 18 0.319 CA LEU 19 CA LEU 19 0. 161 CA LYS 20 CA LYS 20 0.155 CA GLU 21 CA GLU 21 0.196 CA ALA 22 CA ALA 22 0.338 CA LEU 23 CA LEU 23 0.246 CA LEU 24 CA LEU 24 0.292 CA ASP 25 CA ASP 25 0.142 CA THR 26 CA THR 26 0.109 CA GLY 27 CA GLY 27 0.176 CA ALA 28 CA ALA 28 0.193 CA ASP 29 CA ASP 29 0.087 CA ASP 30 CA ASP 30 0.118 CA THR 31 CA THR 31 0. 111 CA VAL 32 CA VAL 32 0. 087 CA LEU 33 CA LEU 33 0. 306 CA GLU 34 CA GLU 34 0. 333 CA GLU 35 CA GLU 35 0.399 CA MET 36 CA MET 36 0.296 CA SER 37 CA SER 37 0.454 CA LEU 38 CA LEU 38 0. 451 CA PRO 39 CA PRO 39 0.397 CA GLY 40 CA GLY 40 0.444 CA ARG 41 CA ARG 41 0.535 CA TRP 42 CA TRP 42 0.346 CA LYS 43 CA LYS 43 0.442 CA PRO 44 CA PRO 44 0.548 CA LYS 45 CA LYS 45 0.307 CA MET 46 CA MET 46 0.320 CA ILE 47 CA ILE 47 0.403 CA GLY 48 CA GLY 48 0.237 CA GLY 49 CA GLY 49 0.280 CA ILE 50 CA ILE 50 0.206 CA GLY 51 CA GLY 51 0. 368 CA GLY 52 CA GLY 52 0.315 CA PHE 53 CA PHE 53 0.378 CA ILE 54 CA ILE 54 0.180 CA LYS 55 CA LYS 55 0.149 CA VAL 56 CA VAL 56 0.302 CA ARG 57 CA ARG 57 0. 098 CA GLN 58 CA GLN 58 0.219 CA TYR 59 CA TYR 59 0.279 CA ASP 60 CA ASP 60 0.385 CA GLN 61 CA GLN 61 0.431 CA ILE 62 CA ILE 62 0.343 CA LEU 63 CA LEU 63 0.473 CA ILE 64 CA ILE 64 0.344 CA GLU 65 CA GLU 65 0.456 CA ILE 66 CA ILE 66 0.481 CA CYS 67 CA CYS 67 0.920 CA GLY 68 CA GLY 68 0.999 CA HIS 69 CA HIS 69 0.295 CA LYS 70 CA LYS 70 0. 406 CA ALA 71 CA ALA 71 0.446 CA ILE 72 CA ILE 72 0.374 CA GLY 73 CA GLY 73 0.259 CA THR 74 CA THR 74 0.276 CA VAL 75 CA VAL 75 0.165 CA LEU 76 CA LEU 76 0.220 CA VAL 77 CA VAL 77 0.202 CA GLY 78 CA GLY 78 0.231 CA PRO 79 CA PRO 79 0.131 CA THR 80 CA THR 80 0.374 CA PRO 81 CA PRO 81 0.472 CA VAL 82 CA VAL 82 0.554 CA ASN 83 CA ASN 83 0.149 CA ILE 84 CA ILE 84 0.261 CA ILE 85 CA ILE 85 0.223 CA GLY 86 CA GLY 86 0.130 CA ARG 87 CA ARG 87 0.165 CA ASN 88 CA ASN 88 0.103 CA LEU 89 CA LEU 89 0.072 CA LEU 90 CA LEU 90 0.076 CA THR 91 CA THR 91 0.114 CA GLN 92 CA GLN 92 0. 115 CA ILE 93 CA ILE 93 0.204 CA GLY 94 CA GLY 94 0.220 CA CYS 95 CA CYS 95 0.068 CA THR 96 CA THR 96 0.185 CA LEU 97 CA LEU 97 0.095 CA ASN 98 CA ASN 98 0.311 CA PHE 99 CA PHE 99 0.216 CA PRO 101 CA PRO 101 0. 455 CA GLN 102 CA GLN 102 0.121 CA ILE 103 CA ILE'103 0.120 CA THR 104 CA THR 104 0.109 CA LEU 105 CA LEU 105 0.128 CA TRP 106 CA TRP 106 0.205 CA GLN 107 CA GLN 107 0.229 CA ARG 108 CA ARG 108 0.211 CA PRO 109 CA PRO 109 0. 195 CA LEU 110 CA LEU 110 0.135 CA VAL 111 CA VAL 111 0. 086 CA THR 112 CA THR 112 0. 166 CA ILE 113 CA ILE 113 0.199 CA LYS 114 CA LYS 114 0.333 CA ILE 115 CA ILE 115 0.356 CA GLY 116 CA GLY 116 0.671 CA GLY 117 CA GLY 117 0.709 CA GLN 118 CA GLN 118 0.370 CA LEU 119 CA LEU 119 0.258 CA LYS 120 CA LYS 120 0.156 CA GLU 121 CA GLU 121 0.250 CA ALA 122 CA ALA 122 0. 276 CA LEU 123 CA LEU 123 0.103 CA LEU 124 CA LEU 124 0. 112 CA ASP 125 CA ASP 125 0.078 CA THR 126 CA THR 126 0.057 CA GLY 127 CA GLY 127 0.121 CA ALA 128 CA ALA 128 0.098 CA ASP 129 CA ASP 129 0.190 CA ASP 130 CA ASP 130 0. 302 CA THR 131 CA THR 131 0.073 CA VAL 132 CA VAL 132 0.178 CA LEU 133 CA LEU 133 0.147 CA GLU 134 CA GLU 134 0.239 CA GLU 135 CA GLU 135 0.101 CA MET 136 CA MET 136 0.235 CA SER 137 CA SER 137 0.391 CA LEU 138 CA LEU 138 0.364 CA PRO 139 CA PRO 139 0.532 CA GLY 140 CA GLY 140 0.213 CA ARG 141 CA ARG 141 0.448 CA TRP 142 CA TRP 142 0. 133 CA LYS 143 CA LYS 143 0.195 CA PRO 144 CA PRO 144 0.082 CA LYS 145 CA LYS 145 0.359 CA MET 146 CA MET 146 0.306 CA ILE 147 CA ILE 147 0.076 CA GLY 148 CA GLY 148 0.214 CA GLY 149 CA GLY 149 0.205 CA ILE 150 CA ILE 150 0. 163 CA GLY 151 CA GLY 151 0.287 CA GLY 152 CA GLY 152 0.318 CA PHE 153 CA PHE 153 0. 125 CA ILE 154 CA ILE 154 0.189 CA LYS 155 CA LYS 155 0.384 CA VAL 156 CA VAL 156 0.510 CA ARG 157 CA ARG 157 0.405 CA GLN 158 CA GLN 158 0. 139 CA TYR 159 CA TYR 159 0. 361 CA ASP 160 CA ASP 160 0.252 CA GLN 161 CA GLN 161 0.414 CA ILE 162 CA ILE 162 0.337 CA LEU 163 CA LEU 163 0.202 CA ILE 164 CA ILE 164 0.359 CA GLU 165 CA GLU 165 0.463 CA ILE 166 CA ILE 166 0.347 CA CYS 167 CA CYS 167 0.256 CA GLY 168 CA GLY 168 0. 471 CA HIS 169 CA HIS 169 0.658 CA LYS 170 CA LYS 170 0.489 CA ALA 171 CA ALA 171 0.445 CA ILE 172 CA ILE 172 0.396 CA GLY 173 CA GLY 173 0 : 523 CA THR 174 CA THR 174 0.130 CA VAL 175 CA VAL 175 0. 156 CA LEU 176 CA LEU 176 0.077 CA VAL 177 CA VAL 177 0.129 CA GLY 178 CA GLY 178 0.276 CA PRO 179 CA PRO 179 0.272 CA THR 180 CA THR 180 0.580 CA PRO 181 CA PRO 181 0.436 CA VAL 182 CA VAL 182 0.328 CA ASN 183 CA ASN 183 0.180 CA ILE 184 CA ILE 184 0.151 CA ILE 185 CA ILE 185 0. 104 CA GLY 186 CA GLY 186 0.059 CA ARG 187 CA ARG 187 0.058 CA ASN 188 CA ASN 188 0.183 CA LEU 189 CA LEU 189 0. 164 CA LEU 190 CA LEU 190 0.051 CA THR 191 CA THR 191 0.216 CA GLN 192 CA GLN 192 0.162 CA ILE 193 CA ILE 193 0.158 CA GLY 194 CA GLY 194 0.047 CA CYS 195 CA CYS 195 0.050 CA THR 196 CA THR 196 0.200 CA LEU 197 CA LEU 197 0.165 CA ASN 198 CA ASN 198 0. 074

The distances between the atoms of the inhibitors 1 and 2 to atoms of the protein, that is, hydrogen-bond donors and acceptors, were computed and are shown in Table 7.

Table 7 Distances between atoms of inhibitors and atoms of the proteins Wt : 1 complex Wt: 2 complex 02-Wat301 2. 92 3. 02 NI-027 3. 36 3. 58 06-N30 3. 30 3. 50 06-N29 3. 19 3. 51 07-N29 2. 84 07-OD1 29 3. 42 07-01 3. 31 03-OD 25 (out) A 2. 50 2. 80 03-OD 25 (in) A 2. 65 2. 66 03-OD 25 (out) B 3. 27 3. 07 03-OD 25 (in) B 2. 80 2. 68 O5-Wat301 2. 70 2. 77 08-N 30 3. 16 N3-N 30 3.17 N3-OD2 30 3. 15

Inhibitors 1 (Figure 1) and 2 (Amprenavir) have similar structural elements, in particular their core, i. e. groups at the PI-PI'positions. However, 2 has a THF group while 1 has a bis-THF group at the P2'position. The P2 groups are identical except for the substitution of an ether oxygen atom in 1 as compared to an amine nitrogen atom at the same position in 2. Table 7 shows that 1 forms more interactions with the atoms of the protein that were

previously identified as belonging to the structurally conserved substructure than does compound 2. For example, the 07 oxygen atom in compound 1, that forms an interaction with N29 nitrogen of the protease, has no counterpart in compound 2. Instead, the 06 oxygen atom of 2 forms longer (and presumably weaker) hydrogen bonds with both N30 (3. 50 A) and N29 (3.51 A). In contrast, the 06 oxygen of compound 1 forms a shorter (and presumably stronger) hydrogen bond with N29 (3. 19 A). Additionally, as can be seen in Table 7, where both compounds 1 and 2 form interactions with atoms in the structurally conserved substructure of HIV protease, the distances between interacting atoms are consistently shorter for compound 1, indicative of presumably stronger binding interactions.

Examples 1 and 2 were used to identify a three dimensionally-conserved substructure of HIV protease that is involved in the binding of HIV protease inhibitors and, in particular, to identify atoms of these substructural elements that are involved in forming interactions with atoms of HIV protease inhibitors.

This substructure is defined by the set of atomic coordinates (in orthogonal coordinates) provided in Table 8 and any equivalent set derived by applying arbitrary rotations and translations to the set of atomic coordinates in Table 8.

The values of the coordinates (X, Y, Z) of the atoms defining the substructure are affected by a standard error a. Therefore (X, Y, Z) values for each atom are those defined in the intervals (X-c, X+ cs) for coordinate X, (Y-, Y+) for coordinate Y, and (Z-cs, Z+ o) for coordinate Z.

Table 8 Three dimensionally-conserved substructure of HIV protease Atom X [A] YfA] Z [A] o [A] Description Substructure of the protein atoms Oxygen-7.9 13.6 27. 4 0.5 Oxygen atom of water molecule coordinated to main chain amide nitrogen atoms of amino acid Gly 49 and Glyl49 027-13. 8 17.7 30.4 0.5 Main Chain carbonyl oxygen atom of amino acid Gly 27 N29-13.4 18. 2 34.5 0.5 Main chain amide nitrogen atom of amino acid Asp 29 N30-11.9 18.6 36.7 0.5 Main chain amide nitrogen atom of amino acid Asp 30 OD1 25-11. 3 21.2 28.7 0.5 Carboxylate oxygen atom of aminoacid Asp 25 OD2 25-9. 4 20.4 29.3 0.5 Carboxylate oxygen atom of aminoacid Asp 25 OD1 125-12.7 20.3 26.4 0.5 Carboxylate oxygen atom of aminoacid Asp 125 OD2 125-12. 7 20.3 26.4 0.5 Carboxylate oxygen atom of aminoacid Asp 125 N129-8. 9 20.5 20.7 0.5 Main chain amide nitrogen atom of amino acid Asp 129 N130-10.1 19.5 18. 6 0.5 Main chain amide nitrogen atom of amino acid Asp 130 Substructure of the inhibitor atoms Hydrogen-8.8 17.5 25.7 0.5 Interacting with main chain Bond carbonyl oxygen atom of amino donor acid Gly 27 Atom Hydrogen-8. 5 15.3 25.1 0.5 Interacting with Oxygen atom of Bond water molecule coordinated to acceptor main chain amide nitrogen Atom atoms of amino acid Gly 49 and Gly 149 Hydrogen-10.4 19.1 27.4 0.5 Interacting with carboxylate Bond oxygen atoms of aminoacids donor-Asp 25 and Asp 125 acceptor Atom Hydrogen-8. 9 14.0 29. 8 0.5 Interacting with Oxygen atom of Bond water molecule coordinated to acceptor main chain amide nitrogen Atom atoms of amino acid Gly 49 and Glyl49 Hydrogen-8.6 17.3 20.7 0.5 Main chain amide nitrogen atom Bond of amino acid Asp 30 acceptor Atom Hydrogen-6.9 18.7 21.4 0.5 Interacting with main chain Bond amide nitrogen atom of amino acceptor acid Asp 29 Atom 08-10. 7 15. 8 35. 8 0. 5 Interacting with main chain amide nitrogen atom of amino acid Asp 130

Example 3 The following example demonstrates that a protease inhibitor that contains atoms that can make favorable interactions with the atoms of the substructure may exhibit broad spectrum activity.

Compounds land 3 contain a Bis-THF group at the P2 position that contains two atoms, in particular, hydrogen bond acceptor oxygen atoms, that can form hydrogen bonds with the two hydrogen atoms attached to the backbone amide nitrogen atoms on the protein at residues 29 and 30..

Compound 2 is similar to 1 except that 2 contains a THF group at P2 with only a single hydrogen bond acceptor oxygen atom. All three compounds differ in the P2'substituent. Compounds 1 and 3 both are unaffected by the two active site mutations, V82F and 184V, and Ki values for wild type and mutant enzymes are similar for both compounds. In contrast, compound 2, which contains only a single hydrogen bond acceptor atom in the P2 substitutent, is dramatically affected by the active site mutations, which demonstrate high level resistance to 2.

The antiviral activity of compounds 1 and 3 against HIV derived from patient isolates that contain multiple mutations are equivalent to their activity against wild type HIV strains. In contrast, compound 2 is much less effective against the same mutant viruses. None of the patients from whom virus was isolated had ever been exposed to any of the compounds tested herein.

Nonetheless, compound 2 exhibited cross resistance to these virus strains that is typically seen with all clinically useful HIV protease inhibitors-4 (Saquinavir), 5 (Ritonavir), 6 (Indinavir) and 7 (Nelfinavir). Compounds 2,4, 5,6, and 7 have very different chemical structures, but nonetheless behave as a

single class with respect to their antiviral behavior against wild type and multidrug resistant HIV strains. All compounds are dramatically less potent against the multidrug resistant strains of HIV.

In sharp contrast, compounds 1 and 3, which closely resemble each other as well as compound 2, exhibit broad spectrum activity in that they are equally effective against wild type and mutant HIV strains that exhibit high level multidrug resistance towards compounds 2,4, 5,6, and 7. The broad spectrum activity of compound 1 was completely unexpected and contrasts with the common and typical loss of antiviral potency experienced with compounds like 2,4, 5,6, 7, and indeed most other HIV protease inhibitors represented as similar or different structures that have been reported.

The development and application of the 3D motif method described above successfully revealed the presence of a unique, three dimensionally- conserved substructure of HIV protease that is useful in the design of broad spectrum inhibitors. Based on this method, compound 3 was predicted, on the basis of comparative molecular modeling using the coordinates of the complexes of compound 1 with wild type and V82F/I84V mutant HIV proteases, to be able to make the same key interaction as compound 1 and thereby to exhibit broad spectrum activity. Based on these data, it is feasible to design protease inhibitors that are predicted to have broad spectrum activity, and are predicted to be useful for the treatment of both wild type (first line therapy) and drug resistant (salvage therapy) HIV infections.

Example 4 This example illustrates the method by which experimentally- determined crystal structures of two different target proteins, DHQases, from two different bacterial species can be compared and analyzed for the existence of a three-dimensionally conserved substructure even in the absence of readily discernible or statistically significant sequence similarity. DHQases from different bacterial species typically exhibit less than 30% sequence identity

(Figure 2). A schematic map showing the key interactions of the substrate- based inhibitor, DHQO, with the active site residues for the Type II DHQase from M. tuberculosis is provided in Figure 3.

The structures of wild type DHQase from M. tuberculosis and a homologous DHQase from Pseudomonas putidas were determined using conventional x-ray crystallography techniques. The structures were analyzed by means of (a) an overall superposition of the atoms of the protein structures.

This analysis requires three dimensional atomic coordinates of the protein structures.

The superposition of the protein structures was performed in a two step process: 1) the distance between all pairs of corresponding Ca atoms (Ca atom of residue number 1 in one protein to Ca atom of residue number 1 in the second protein; Ca atom of residue number 2 in one protein to Ca atom of residue number 2 in the second protein; and so on) of the polypeptide chains is minimized by means of a least-square algorithm; 2) the superposition is refined by minimizing, in an iterative process, the distances between corresponding Ca atoms that are closer than a given distance (0. 4 A in this example), thus eliminating regions of the structures having large conformational differences to compute the superposition parameters. The distances between equivalenced Ca atoms after the minimization procedure are shown in Table 9.

Table 9 Distances between equivalent Ca atoms Molecule 1: DHQase P. putida wt: qxa Molecule 2: DHQase M. tuberculosis wt : gt33 Molecule 1 Molecule 2 distance [A] CA MET 2 CA GLU 2 1.078 CA ALA 3 CA LEU 3 1.504 CA THR 4 CA ILE 4 1.800 CA LEU 5 CA VAL 5 1.283 CA LEU 6 CA ASN 6 0.911 CA VAL 7 CA VAL 7 0.715 CA LEU 8 CA ILE 8 0.298 CA HIS 9 CA ASN 9 0. 211 CA GLY 10 CA GLY 10 0.591 CA PRO 11 CA PRO 11 0.599 CA ASN 12 CA ASN 12 0.487 CA LEU 13 CA LEU 13 0.428 CA ASN 14 CA GLY 14 0.229 CA LEU 15 CA ARG 15 0.685 CA LEU 16 CA LEU 16 0.541 CA GLY 17 CA GLY 17 1.693 CA THR 18 CA ARG 18 2.287 CA ARG 19 CA ARG 19 2.956 CA GLN 20 CA GLN 20 3.475 CA PRO 21 CA PRO 21 3.390 CA GLY 22 CA ALA 22 4.037 CA THR 23 CA VAL 23 3.770 CA TYR 24 CA TYR 24 2.521 CA GLY 25 CA GLY 25 1. 170 CA SER 26 CA GLY 26 1.642 CA THR 27 CA THR 27 1.454 CA THR 28 CA THR 28 1.532 CA LEU 29 CA HIS 29 1.471 CA GLY 30 CA ASP 30 1.632 CA GLN 31 CA GLU 31 1.966 CA ILE 32 CA LEU 32 1.586 CA ASN 33 CA VAL 33 1.875 CA GLN 34 CA ALA 34 2.230 CA ASP 35 CA LEU 35 2.343 CA LEU 36 CA ILE 36 1.927 CA GLU 37 CA GLU 37 2.284 CA ARG 38 CA ARG 38 2.980 CA ARG 39 CA GLU 39 2.917 CA ALA 40 CA ALA 40 2.719 CA ARG 41 CA ALA 41 3.367 CA GLU 42 CA GLU 42 3.534 CA ALA 43 CA LEU 43 3.281 CA GLY 44 CA GLY 44 3.161 CA HIS 45 CA LEU 45 2.899 CA HIS 46 CA LYS 46 1.844 CA LEU 47 CA ALA 47 1. 599 CA LEU 48 CA VAL 48 1.201 CA HIS 49 CA VAL 49 2.053 CA LEU 50 CA ARG 50 1.045 CA GLN 51 CA GLN 51 0.266 CA SER 52 CA SER 52 0.300 CA ASN 53 CA ASP 53 0.282 CA ALA 54 CA SER 54 0.348 CA GLU 55 CA GLU 55 0.326 CA TYR 56 CA ALA 56 0.238 CA GLU 57 CA GLN 57 0.380 CA LEU 58 CA LEU 58 0.455 CA ILE 59 CA LEU 59 0. 413 CA ASP 60 CA ASP 60 0.984 CA ARG 61 CA TRP 61 1.452 CA ILE 62 CA ILE 62 1. 338 CA HIS 63 CA HIS 63 1.310 CA ALA 64 CA GLN 64 2.327 CA ALA 65 CA ALA 65 2.526 CA ARG 66 CA ALA 66 3.063 CA ASP 67 CA ASP 67 3.449 CA GLU 68 CA CA GLY 69 CA ALA 68 2.318 CA VAL 70 CA ALA 69 1.691 CA ASP 71 CA GLU 70 0. 812 CA PHE 72 CA PRO 71 0.515 CA ILE 73 CA VAL 72 0.561 CA ILE 74 CA ILE 73 0.547 CA LEU 75 CA LEU 74 0.380 CA ASN 76 CA ASN 75 0.277 CA PRO 77 CA ALA 76 0.369 CA ALA 78 CA GLY 77 0.952 CA ALA 79 CA GLY 78 0.421 CA PHE 80 CA LEU 79 0.714 CA THR 81 CA THR 80 0.575 CA HIS 82 CA HIS 81 0. 142 CA THR 83 CA THR 82 0.222 CA SER 84 CA SER 83 0.741 CA VAL 85 CA VAL 84 0.719 CA ALA 86 CA ALA 85 0.415 CA LEU 87 CA LEU 86 0.667 CA ARG 88 CA ARG 87 0.660 CA ASP 89 CA ASP 88 0.426 CA ALA 90 CA ALA 89 0.697 CA LEU 91 CA CYS 90 1.233 CA LEU 92 CA ALA 91 1.319 CA ALA 93 CA GLU 92 2.852 CA VAL 94 CA LEU 93 4.165 CA SER 95 CA SER 94 3.605 CA ILE 96 CA ALA 95 3.840 CA PRO 97 CA PRO 96 2.414 CA PHE 98 CA LEU 97 0.314 CA ILE 99 CA ILE 98 0.251 CA GLU 100 CA GLU 99 0.095 CA VAL 101 CA VAL 100 0.131 CA HIS 102 CA HIS 101 0.318 CA ILE 103 CA ILE 102 0.117 CA SER 104 CA SER 103 0.229 CA ASN 105 CA ASN 104 0.203 CA VAL 106 CA VAL 105 0.193 CA HIS 107 CA HIS 106 0.499 CA LYS 108 CA ALA 107 0.498 CA ARG 109 CA ARG 108 0.292 CA GLU 110 CA GLU 109 0.333 CA PRO 111 CA GLU 110 0.377 CA PHE 112 CA PHE 111 0. 651 CA ARG 113 CA ARG 112 0.611 CA ARG 114 CA ARG 113 0. 469 CA HIS 115 CA HIS 114 0.467 CA SER 116 CA SER 115 0.293 CA TYR 117 CA TYR 116 0.483 CA PHE 118 CA LEU 117 0.468 CA SER 119 CA SER 118 0.367 CA ASP 120 CA PRO 119 0.676 CA VAL 121 CA ILE 120 0.445 CA ALA 122 CA ALA 121 0.334 CA VAL 123 CA THR 122 0.405 CA GLY 124 CA GLY 123 0.372 CA VAL 125 CA VAL 124 0.375 CA ILE 126 CA ILE 125 0.250 CA CYS 127 CA VAL 126 0. 328 CA GLY 128 CA GLY 127 0.332 CA LEU 129 CA LEU 128 0.473 CA GLY 130 CA GLY 129 0.272 CA ALA 131 CA ILE 130 0.551 CA THR 132 CA GLN 131 0.564 CA GLY 133 CA GLY 132 0.289 CA TYR 134 CA TYR 133 0.276 CA ARG 135 CA LEU 134 0.476 CA LEU 136 CA LEU 135 0.556 CA ALA 137 CA ALA 136 0.677 CA LEU 138 CA LEU 137 0.703 CA GLU 139 CA ARG 138 0.861 CA SER 140 CA TYR 139 0.876 CA ALA 141 CA LEU 140 1.330 CA LEU 142 CA ALA 141 1.529 CA GLU 143 CA GLU 142 1.492 CA, GLN 144 CA HIS 143 1.738 CA LEU 145 CA VAL 144 3. 487

Table 9 shows that the two structures are remarkably similar overall despite their low level sequence identity. However, the structures exhibit very large deviations in some regions, and are highly conserved in others. In particular, this analysis reveals that regions of the enzyme are minimally affected by the large number of amino acid sequence substitutions. The regions of the protein structure which are not significantly affected by the amino acid substitutions are defined as structurally conserved regions. In the present example, the substitutions result in localized structural changes in the backbone of DHQase over a wide range, from 0.095-4. 165 A.

The distances between the strongly interacting atoms of the inhibitor to atoms of the homologous DHQase proteins, that is P. putida wt: qxa and M. tuberculosis wt: gt33 complexes, were computed and they are displayed in Tables 10 and 11, respectively.

Table 10 Distances between atoms of the inhibitor and atoms of the protein DHQase P. putida wt: qxa distance [A] C6-PRO11 (O) 3.31 C6-ASN12 (CB) 3.10 N7-TYR24 (OH) 2.45 012-ASN76 (HD2) 2.96 013-HIS102 (CB) 3.38 012-SER104 (N) 3. 35 C6-ASN12 (CB) 3.10 Table 11 Distances between atoms of the inhibitor and atoms of the protein DHQase M. tuberculosis wt : gt33 distance [A] N14-PR011 (O) 3.35 015-PRO11 (O) 3.01 015-LEU 13 (CG) 3.36 015-ARG 19 (NH1) 3.26 015-ARG 19 (NH2) 3.32 07-ASN 75 (OD1) 2.50 013-ASN 75 (ND2) 2.98 N14-GLY 77 (CA) 3.01 09-HIS 81 (NE2) 2.82 07-HIS 101 (ND1) 3.25 011-ILE102 (N) 3.33 013-ILE 102 (N) 2.77 01 1-SER 103 (N) 2.96 011-SER 103 (OG) 2.68 09-ARG 112 (NH2) 3.09 O10-ARG 112 (NH2) 3.02

The methods of Examples 1-3 were applied to the DHQase data to identify a three dimensionally-conserved substructure of DHQase that is involved in the binding of DHQase inhibitors, in particular, to identify the relevant target substructure for developing broad spectrum inhibitors. This substructure is defined by the set of atomic coordinates (in orthogonal coordinates) provided in Table 12 and any equivalent set derived by applying arbitrary rotations and translations to the set of atomic coordinates in Table 12.

The values of the coordinates (X, Y, Z) of the atoms defining the substructure are affected by a standard error s. Therefore (X, Y, Z) values for each atom are those defined in the intervals (X-, X+ cs) for coordinate X, (Y-a, Y+ o) for coordinate Y, and (Z-cs, Z+ cs) for coordinate Z.

Table 12 Three dimensionally-conserved substructure of DHQase, M. tuberculosis Atom X [Å] Y [Å] Z [Å] # [Å] Description Substructure of the protein atoms OD1 ASN75 26.265 68.912 21.219 0.5 Side chain carbonyl oxygen atom of amino acid ASN 75 ND2 ASN 75 27.336 66.960 20.951 0.5 Side chain nitrogen atom of amino acid ASN 75 NE2 HIS 81 28.343 76.425 22.111 0.5 Side chain nitrogen atom of amino acid HIS 81 ND1 HIS 101 28. 079 70.604 23.662 0.5 Side chain nitrogen atom of amino acid HIS 101 N ILE 102 31.227 67.167 22. 168 0.5 Main chain amide nitrogen atom of amino acid ILE 102 N SER103 33.754 68.315 21.558 0.5 Main chain amide nitrogen atom of amino acid Ser 103 OG SER 103 33.946 71.059 20.735 0.5 Side chain hydroxyl oxygen atom of amino acid SER 103 Substructure of the inhibitor Hydrogen bond 29.600 68.554 20.298 0.5 Interacting with main acceptor atom chain nitrogen atom of ILE 102 and side chain nitrogen atom of ASN 75 Hydrogen bond 28.031 70.739 20.422 0.5 Interacting with side chain donor-acceptor oxygen atom of ASN75 atom and side chain nitrogen atom of HIS 101 Hydrogen bond 29.664 74. 658 20.493 0.5 Interacting side chain donor-acceptor nitrogen atom of HIS 81 atom Hydrogen bond 31.451 69.835 20.531 0.5 Interacting with main acceptor atom chain nitrogen atom and side chain oxygen atom of SER 103

Other Embodiments All publications and patent applications, and patents mentioned in this specification are herein incorporated by reference.

While the invention has been described in connection with specific embodiments, it will be understood that it is capable of further modifications.

Therefore, this application is intended to cover any variations, uses, or adaptations of the invention that follow, in general, the principles of the invention, including departures from the present disclosure that come within known or customary practice within the art.

Other embodiments are within the claims. What we claim is: