AND METHODS OF USE CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S.S.N. 61/943,421 filed

February 23, 2014 by Craig W. Hendrix, Justin Hanes, and Richard Cone for "Microbicidal Compositions and Methods of Use" and U.S.S.N. 62/108,354 filed January 27, 2015 by Katharina Maisel, Laura Ensign, Justin Hanes, and Richard Cone for "Hypotonic Hydrogel Formulations for Enhanced

Transport of Active Agents at Mucosal Surfaces".

FIELD OF THE INVENTION

This invention is generally in the field of formulations administered rectally or vaginally for enhanced drug delivery, in particular drug delivery at mucosal surfaces. STATEMENT REGARDING FEDERALLY SPONSORED

RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant Nos. 5R21AI079740, 5R21AI094519, and 5R33AI094519 awarded by the National Institutes of Health. The government has certain rights in the invention.

BACKGROUND OF THE INVENTION

UN AIDS estimates approximately 2.3 million new HIV infections in 2012, indicating an ongoing need for prevention of HIV infection. Men who have sex with men (MSM) are the group at highest risk of HIV acquisition through unprotected receptive anal intercourse (URAI) and are an important part of the epidemic in both developed and low and middle income countries. MSM remain the majority of the U.S. epidemic where most incident infections are among MSM (63% overall and 78% among men). These men also serve as a source of HIV infection for other risk groups. In Baltimore neighborhoods, 38% of MSM have HIV infection with seroincidence rates of 11% in young African American MSM. In a survey of U.S. MSM, 36% reported having RAI at last sex, and the percentage who reported not using condoms ranged from 38-65%. Women globally also engage in anal intercourse at 10-20% levels, substantial given their percent of the population, and report lower condom use than most MSM surveys. The combination of high RAI frequency, low condom use, and higher risk of HIV infection via RAI argues strongly for strategies to prevent HIV infection associated with URAL

Pre-exposure prophylaxis (PrEP) with the NRTI tenofovir (TFV)- based drug regimens has been tested in 6 randomized controlled trials (RCTs) and demonstrates a clear plasma concentration-HIV protection response among studies. In iPrEx, the only study targeting MSM, daily oral TFV disoproxil fumarate (TDF)/emtricitabine (FTC) provided 92% protection with evidence of only 2 doses per week (measurable plasma TFV) whereas heterosexual studies indicated similar protection only with 6-7 doses per week.

Reports of enema use before sex by MSM range widely: 51-96% in New York City, 67% in Baltimore, 18-53% in African- Americans, and 28% in Peru. Typically, enemas were taken within 2 hours before and 1 hour after sex (when enemas are used less often) for reasons of hygiene, partner desire, and belief in HIV protection. Several MSM studies indicate between 80% and 100% willingness to use rectal microbicide enemas, especially in the absence of condoms.

A number of formulations have been tested for this purpose, for example, in prior IP/CP U19 programs, MDP (Anton, PI) and CHARM (McGowan, PI). For example, RMP-02/MTN-006 studied rectal application of VF (vaginal formulation) TFV 1% gel (used in CAPRISA 004 and VOICE), a very hyperosmolar formulation compared to RF (rectal optimized formulation, developed in MDP) and RGVF (reduced glycerin vaginal formulation, developed in MTN). RMP-02/MTN-006 demonstrated that VF applied rectally was associated with gastrointestinal-related Grade 3 adverse events (only during 7-day exposure) and less than desired acceptability. Another MDP study and a CDC funded study also demonstrated mucosal tissue abnormalities with hyperosmolar enemas and gels, respectively.

The rectal columnar epithelium is fragile and extremely vulnerable to HIV-1 infection, in part due to the proximity of sub-epithelial stromal tissues that are densely populated with cells receptive to incident HIV-1 infection, such as dendritic cells (DCs), macrophages and T-cells that express both CD4 and both HIV-1 co-receptors CCR5 and CXCR4. Although the mechanisms of viral uptake and infection across rectal mucosa are not fully established, such physiological and anatomical differences may explain why HIV is more readily transmitted across rectal than across the cervicovaginal genital epithelium. In conjunction with this higher transmission risk of rectal versus vaginal exposure to HIV, there is a higher concentration of tenofovir achievable in colonic tissue than in vaginal tissue. The plasma concentration of tenofovir associated with 90% protection (EC90) in PK/PD models, 107 ng/mL, was not achieved by the most highly adherent heterosexual subpopulations. Achievement of concentrations above 107 ng/mL requires fastidious adherence and daily dosing. This is in contrast to the protective effect for MSM which is achieved with only 2 to 4 doses of oral TFV per week.

Given the (1) very high efficacy of TFV-based PrEP, (2) more efficient delivery of active drug to the colon with rectal compared to oral dosing, (3) the large negative impact of poor adherence on PrEP outcomes, (4) frequency of URAI in men and women, and (5) the common pre-existing behavior of enemas use before and after RAI by many MSM, there exists an unmet need for the development of a pharmacokinetically-enhanced TFV prodrug enema capable of protecting subjects from HIV acquisition.

It is therefore an object of the present invention to provide a formulation providing enhanced colorectal distribution of both MPP and water soluble drugs, improved tissue uptake by water-soluble drugs, and improved colorectal safety. It is another object of the present invention to provide enema formulations that will induce rapid fluid absorption by the colon to take advantage of the speed with which advective transport by the bulk flow of water will deliver drugs to the epithelium.

SUMMARY OF THE INVENTION

Advective transport of solutes is dominated by the bulk flow of a fluid, as in a solution passing through a filter. Since the colon absorbs water to dry the feces, fluid absorption by the colorectum can advectively transport drugs and mucus penetrating particles (MPP) to the epithelium with great rapidity, much faster than by diffusion, and can move solutes and MPP through the unstirred layer of mucus adhering to the colonic epithelium. This distributes them to the entire colorectal surface and minimizes systemic exposure to reduce toxic side effects. The formulation for drug delivery markedly improves the uniformity of distribution of drugs and MPP, over the epithelial surface. The formulations are particularly effective for delivery of microbicides for preventing rectal HIV transmission, as well as therapeutic drugs for the colon.

An absorption-inducing (hypotonic) enema delivers drugs advectively to the colon epithelium by the bulk flow of water (advection) and is nontoxic. This was demonstrated by advective delivery of a small hydrophilic drug in solution (tenofovir, a candidate microbicide for blocking HIV) as well as mucus-penetrating nanoparticles (MPP) designed for mucosal drug delivery. The absorption-inducing hypotonic enema formulations caused both free drug and MPP to be transported rapidly to the epithelial surface, unimpeded by the unstirred mucus barrier coating the epithelium. Advective transport delivered both free drug and MPP deep into the colorectal folds to reach virtually the entire colorectal epithelial surface. In contrast, secretion-inducing (hypertonic) enema formulations markedly reduced drug uptake, prevented MPP from reaching the epithelial surface, and caused both free drug and MPP to be expelled from the colon. Enemas induced rapid absorption even when sodium chloride was moderately hyperosmolal with respect to blood (~500 vs ~300 mOsm), presumably because sodium is actively pumped out of the colon.

The formulations are preferably stored at room temperature and administered rectally at least one hour before intercourse. These may be provided in single dosage containers, either as a solution/suspension or in dried form which is rehydrated at the time of use.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph of the concentration of tenofovir in mouse colorectal tissue at up to 4 h after intrarectal administration in various vehicles. 1% tenofovir was administered in ultrapure water (20 mOsm), simulated colon solution (a fluid-based enema vehicle mimicking the ionic composition of feces, SCS) (150 mOsm), isotonic tris-buffered saline (TBS, 450 mOsm), gel containing 5% glycerol (760 mOsm), and FLEET® enema (2200 mOsm). Studies were performed in at least n=3 mice. Data are calculated as means ± SEM. *P < 0.05 using Student's t-test.

Figure 2 is a graph of the quantified surface coverage of MPP in sodium based tris buffer with various osmolalities on flattened mouse colonic tissue. Data are calculated as means ± SEM. *P < 0.05 as compared to DI water (20 mOsm), Student's t-test.

Figure 3 is a graph of the quantified surface coverage of MPP in potassium phosphate buffer with various osmolalities on flattened mouse colonic tissue. Data are calculated as means ± SEM. *P < 0.05 as compared to DI water (20 mOsm), Student's t-test.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

As generally used herein "pharmaceutically acceptable" refers to those compounds, materials, compositions, and/or dosage forms which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of human beings and animals without excessive toxicity, irritation, allergic response, or other problems or complications

commensurate with a reasonable benefit/risk ratio. "Biocompatible" and "biologically compatible", as used herein, generally refer to materials that are, along with any metabolites or degradation products thereof, generally non-toxic to the recipient, and do not cause any significant adverse effects to the recipient. Generally speaking, biocompatible materials are materials which do not elicit a significant inflammatory, immune or toxic response when administered to an individual.

The terms "gel" and "hydrogel", as used interchangeably herein, refer to a swollen, water-containing network of finely-dispersed polymer chains that are water-insoluble, where the polymeric molecules are in the external or dispersion phase and water (or an aqueous solution) forms the internal or dispersed phase. The chains can be chemically crosslinked (chemical gels) or physically crosslinked (physical gels). Chemical gels possess polymer chains that are connected through covalent bonds, whereas physical gels have polymer chains linked by non-covalent bonds or cohesion forces, such as Van der Waals interactions, ionic interaction, hydrogen bonding, or hydrophobic interaction. The polymer chains are typically hydrophilic or contain hydrophilic polymer blocks. "Gel-forming polymers" is used to describe any biocompatible polymer, including homopolymers, copolymers, and combinations thereof, capable of forming a physical hydrogel in an aqueous medium when present at or above the critical gel concentration (CGC).

The "critical gel concentration", or "CGC", as used herein, refers to the minimum concentration of gel-forming polymer needed for gel formation, e.g. at which a solution-to-gel (sol-gel) transition occurs. The critical gel concentration can be dependent on a number of factors, including the specific polymer composition, molecular weight, temperature, and/or the presence of other polymers or excipients.

The term "thermosensitive gel-forming polymer" refers to a gel- forming polymer that exhibits one or more property changes with a change in the temperature. For example, some thermosensitive gel-forming polymers are water soluble below a certain temperature but become water insoluble as temperature is increased. The term "lower critical solution temperature (LCST)" refers to a temperature, below which a gel-forming polymer and solvent are completely miscible and form a single phase. For example, "the LCST of a polymer solution" means that the polymer is uniformly dispersed in a solution at that temperature (i.e., LCST) or lower, but aggregates and forms a second phase when the solution temperature is increased beyond the LCST.

"Hydrophilic," as used herein, refers to molecules which have a greater affinity for, and thus solubility in, water as compared to organic solvents. The hydrophilicity of a compound can be quantified by measuring its partition coefficient between water (or a buffered aqueous solution) and a water-immiscible organic solvent, such as octanol, ethyl acetate, methylene chloride, or methyl fert-butyl ether. If after equilibration a greater concentration of the compound is present in the water than in the organic solvent, then the compound is considered hydrophilic.

"Hydrophobic," as used herein, refers to molecules which have a greater affinity for, and thus solubility in, organic solvents as compared to water. The hydrophobicity of a compound can be quantified by measuring its partition coefficient between water (or a buffered aqueous solution) and a water-immiscible organic solvent, such as octanol, ethyl acetate, methylene chloride, or methyl tert-butyl ether. If after equilibration a greater concentration of the compound is present in the organic solvent than in the water, then the compound is considered hydrophobic.

As used herein, the term "treating" includes inhibiting, alleviating, preventing or eliminating one or more symptoms or side effects associated with the disease, condition, or disorder being treated.

The term "reduce", "inhibit", "alleviate" or "decrease" are used relative to a control. One of skill in the art would readily identify the appropriate control to use for each experiment. For example a decreased response in a subject or cell treated with a compound is compared to a response in subject or cell that is not treated with the compound. As used herein the term "effective amount" or "therapeutically effective amount" means a dosage sufficient to treat, inhibit, or alleviate one or more symptoms of a disease state being treated or to otherwise provide a desired pharmacologic and/or physiologic effect. The precise dosage will vary according to a variety of factors such as subject-dependent variables (e.g., age, immune system health, etc.), the disease or disorder, and the treatment being administered. The effect of the effective amount can be relative to a control. Such controls are known in the art and discussed herein, and can be, for example the condition of the subject prior to or in the absence of administration of the drug, or drug combination, or in the case of drug combinations, the effect of the combination can be compared to the effect of administration of only one of the drugs.

"Excipient" is used herein to include any other compound that can be included in the formulation that is not a therapeutically or biologically active compound. As such, an excipient should be pharmaceutically or biologically acceptable and non-toxic to the subject when administered by the intended route.

The term "osmolarity", as generally used herein, refers to the total number of dissolved components per liter. Osmolarity is similar to molarity but includes the total number of moles of dissolved species in solution. An osmolarity of 1 Osm/L means there is 1 mole of dissolved components per L of solution. Some solutes, such as ionic solutes that dissociate in solution, will contribute more than 1 mole of dissolved components per mole of solute in the solution. For example, NaCl dissociates into Na ⁺ and CI ^" in solution and thus provides 2 moles of dissolved components per 1 mole of dissolved NaCl in solution. Physiological osmolarity is typically in the range of about 280 to about 310 mOsm/L.

The term "tonicity", as generally used herein, refers to the osmotic pressure gradient resulting from the separation of two solutions by a semi- permeable membrane. In particular, tonicity is used to describe the osmotic pressure created across a cell membrane when a cell is exposed to an external solution. Solutes that readily cross the cellular membrane contribute minimally to the final osmotic pressure gradient. In contrast, those dissolved species that do not cross the cell membrane, "impermeable solutes", will contribute to osmotic pressure differences and thus tonicity. The term

"hypertonic", as generally used herein, refers to a solution with a higher concentration of impermeable solutes than is present on the inside of the cell. When a cell is immersed into a hypertonic solution, water will flow out of the cell, concentrating the impermeable solutes inside the cell until it becomes equal to the concentration of impermeable solutes outside the cell. The term "hypotonic", as generally used herein, refers to a solution with a lower concentration of impermeable solutes than is present inside of the cell. When a cell is immersed into a hypotonic solution, water will flow into the cell, diluting the concentration of impermeable solutes inside the cell until it becomes equal to the concentration of impermeable solutes outside the cell. The term "isotonic", as generally used herein, refers to a solution wherein the osmotic pressure gradient across the cell membrane is essentially balanced and no water flows into or out of the cell. The same meanings for tonicity apply for water flow through intestinal epithelia; hypertonic solutions cause water to flow into the lumen, whereas hypotonic solutions cause water to flow out of the lumen. Tonicity depends on the permeability properties of the cell or epithelium to different solutes, whereas osmolarity depends only on the total concentration of all solutes.

II. Compositions

There are many benefits for delivering drugs directly to the colorectum, including increasing mucosal drug concentrations while decreasing systemic side effects. Direct delivery of free drug and/or nanoparticle drug carriers to the colorectum has the potential to improve the delivery and efficacy of medications for a variety of diseases such as inflammatory bowel disease, colorectal cancers, gastrointestinal infections, and prevention of sexually transmitted infections. A. Hypotonic Carriers

The compositions include a hypotonic carrier. The hypotonic carrier will typically be a biocompatible carrier that preferably causes little to no signs of irritation when administered to human subjects. The carrier can be naturally occurring or non-naturally occurring including both synthetic and semi-synthetic carriers. Preferred carriers are sodium-based. Other solutions, including sugar-based (e.g. glucose, mannitol) solutions and various buffers (phosphate-buffers, tris-buffers, HEPES), may also be used.

When hypotonic solutions are applied to an epithelial surface, water flows out of the lumen, into cells and across the epithelium. This can cause swelling of the epithelial cells. In some cases, when the osmotic pressure difference is too large, the epithelial cells may burst, causing tissue irritation or disruption of the epithelial lining.

Advective transport of solutes is dominated by the bulk flow of a fluid, as in a solution passing through a filter. Since the colon absorbs water to dry the feces, fluid absorption by the colorectum can transport drugs advectively to the epithelium with great rapidity, much faster than by diffusion, and can move solutes through the unstirred layer of mucus adhering to the colonic epithelium. This distributes solutes to the entire colorectal surface, and if the formulation composition selectively improves tissue absorption rather than systemic absorption, minimizes systemic toxic side effects. The formulation for drug delivery markedly improves the uniformity of distribution of drugs over the epithelial surface. The formulations are particularly effective for delivery of microbicides for preventing rectal HIV transmission, as well as therapeutic drugs for the colon.

An absorption-inducing (hypotonic) enema delivers drugs

advectively to the colon epithelium by the bulk flow of water (advection) and is nontoxic. This was demonstrated by advective delivery of a small hydrophilic drug in solution (tenofovir, a candidate microbicide for blocking HIV). The absorption-inducing hypotonic enema formulations caused free drag to be transported rapidly to the epithelial surface, unimpeded by the unstirred mucus barrier coating the epithelium. Moreover, advective transport delivered free drag deep into the colorectal folds to reach virtually the entire colorectal epithelial surface. In contrast, secretion-inducing (hypertonic) enema formulations markedly reduced drug uptake, and caused free drug to be expelled from the colon. Enemas induced rapid absorption even when sodium chloride (NaCl) was moderately hyperosmolal with respect to blood (-500 vs -300 mOsm), presumably because sodium is actively pumped out of the lumen of the colon.

Hypotonic solution refers to a solution that contains less impermeable solutes compared to the cytoplasm of the cell. Examples of hypotonic solutions include, but are not limited to, Tris[hydroxylmethyl]- aminomethane hydrochloride (Tris-HCl, 10-100 mM, pH. 6-8), (4-(2- hydroxyethyl)-l-piperazineethanesulfonic acid (HEPES, 10-100 mM, pH 6- 8) and dilute solutions of PBS, such as a solution containing 0.2 grams KC1, 0.2 grams KH ₂ P0 ₄ , 8 grams NaCl, and 2.16 grams Na ₂ HP0 ₄ *7H ₂ 0 in 1000 ml H ₂ 0, and dilute solutions of normal saline (typically containingO.9% NaCl).

The hypotonic carrier can be water containing one or more tonicity modifying excipients. Sodium chloride is the excipient that is most frequently used to adjust tonicity of a solution. Other excipients used to adjust the tonicity of solutions include glucose, mannitol, glycerol, propylene glycol and sodium sulphate. Tonicity modifying excipients can include pharmaceutically acceptable salts such as sodium chloride, sodium sulfate, or potassium chloride. Other excipients used to adjust tonicity can include glucose, mannitol, glycerol, or propylene glycol.

The tonicity of a formulation varies for different cells and mucosal surfaces; it also depends on whether or not the cell or epithelium actively transports solutes and ions; e.g. it has been found that the isotonic point in the vagina for sodium-based solutions is about 300 mOsm/L, similar to the osmolarity of serum, but in the colorectum, it is significantly higher, about 450 mOsm/L (presumable because the colorectum actively transports sodium ions out of the lumen). In some embodiments the solution has a tonicity from 50 mOsm/L to 280 mOsm/L, from 100 mOsm/L to 280 mOsm/L, from 150 mOsm/L to 250 mOsm/L, from 200 mOsm/L to 250 mOsm/L, from 220 mOsm/L to 250 mOsm/L, from 220 mOsm/L to 260 mOsm/L, from 220 mOsm/L to 270 mOsm/L, or from 220 mOsm/L to 280 mOsm/L. Studies have demonstrated optimum results using a tonicity similar to fecal matter, approximately 150 mOsm/L.

The hypotonic carrier can include one or more pharmaceutically acceptable acids, one or more pharmaceutically acceptable bases, or salts thereof. Pharmaceutically acceptable acids include hydrobromic, hydrochloric, and sulphuric acids, and organic acids, such as lactic acid, methanesulphonic acids, tartaric acids, and malcic acids. Pharmaceutically acceptable bases include alkali metal (e.g. sodium or potassium) and alkali earth metal (e.g. calcium or magnesium) hydroxides and organic bases such as pharmaceutically acceptable amines. The hypotonic carrier can include pharmaceutically acceptable buffers such as citrate buffers or phosphate buffers.

B. Hydrogel-Forming Polymers

Gel-forming compositions that are capable of forming uniform gel coatings on epithelial surfaces but do not gel under storage conditions can be used with the hyptonic formulations. The gel-forming compositions contain one or more gel-forming polymers in a hypotonic carrier, optionally containing one or more additional excipients and/or one or more therapeutic, prophylactic, or diagnostic agents. Hypotonic carriers concentrate the gel- forming polymer at an epithelial surface, resulting in uniform gel formation on the surface. These are added to the formulation so that the final tonicity is hypotonic to enhance uptake.

Thermosensitive or thermoresponsive hydrogels are solutions that undergo sol-gel transitions when 1) at or above the critical gelling concentration (CGC) and 2) at or above the critical gelling temperature. Thermosensitive gelling agents (at or above their CGC) used for biomedical applications are liquid at room temperature, but form a gel at body temperature. The increase in temperature induces a rearrangement and alignment of the polymer chains, leading to gelation into a 3 -dimensional structure. This phenomenon is generally governed by the ratio of hydrophilic to hydrophobic moieties on the polymer chain. A common characteristic is the presence of a hydrophobic methyl, ethyl, or propyl group. Any thermosensitive polymer that fits these criteria can be administered hypotonically below the CGC to mucosal epithelial and form a uniform gel coating in vivo. Any polymer that has thermosensitive gelling properties, with a critical gelling temperature at or below 37C, can be used. Examples of thermosensitive gel formers that can be used include polyoxyethylene- polyoxypropylene-polyoxyethylene triblock copolymers such as, but not limited to, those designated by the CTFA names Poloxamer 407 (CAS 9003- 11-6, molecular weight 9,840-14,600 g/mol; available from BASF as

LUTROL® F127) and Poloxamer 188 (CAS 9003-11-6, molecular weight 7680-9510 g/mol; available from BASF as LUTROL® F68); TETRONICs tetra-functional block copolymers based on ethylene oxide and propylene oxide

The hydrogels can be formed from individual gel formers or as a combination of gel formers. For example, a poloxamer and another gel former (e.g., a TETRONIC® polymer) may be used in combination to attain the desired characteristics. In addition, various forms of the same gel former (e.g., Poloxamer 188 and Poloxamer 407) can be combined to attain the desired characteristics.

The polymer is provided in a concentration less than the

concentration that forms a gel in a test tube when heated to 37°C. The concentration must be sufficiently high, but below the CGC, such that water flow through the epithelium will concentrate the hydrogel to reach or exceed the CGC in vivo, so gelation will occur on the mucosal epithelial surface. The range of time that it takes for gelation to occur depends on the mucosal surface (the capacity and rate of water absorption), the tonicity of the solution administered (more hypotonic solutions will drive more rapid fluid absorption), and the concentration of polymer administered (if the polymer concentration is too low, not enough fluid absorption will occur to concentrate the polymer to its CGC). However, gelation generally occurs within 1 h in the vagina and colorectum.

C. Therapeutic agents, prophylactic agents, diagnostic agents, and/or nutraceutical agents

The hypotonic compositions can contain one or more agents to be delivered including therapeutic agents, prophylactic agents, diagnostic agents, and/or nutraceuticals. The formulations can contain a therapeutically effective amount of a therapeutic agent to treat, inhibit, or alleviate one or more symptoms of a disease state being treated or to prevent one or more symptoms of a disease or disorder. Direct delivery of free drug and/or nanoparticle drug carriers to the colorectum can improve the delivery and efficacy of medications for a variety of diseases such as inflammatory bowel disease, colorectal cancers, gastrointestinal infections, and prevention of sexually transmitted infections.

The dosage to be administered is based on the pharmacokinetics of the drug being delivered, taking into consideration that it is local delivery, not systemic, that is desired. The purpose of the formulation is to enhance penetration into the gastrointestinal epithelial cells, not the systemic blood stream.

"Bioactive agent" and "active agent" are used interchangeably include without limitation physiologically or pharmacologically active substances that act locally or systemically in the body. A biologically active agent is a substance used for the treatment (e.g., therapeutic agent), prevention (e.g., prophylactic agent), diagnosis (e.g., diagnostic agent), cure or mitigation of disease or illness, a substance which affects the structure or function of the body, or pro-drugs, which become biologically active or more active after they have been placed in a predetermined physiological environment. Examples can include, but are not limited to, small-molecule drugs including antibiotics, anti-inflammatories, anti-spasmodics, and anti- diarrheal drugs, peptides, proteins, antibodies, sugars, polysaccharides, nucleotides, oligonucleotides, aptamers, siRNA, nucleic acids, and combinations thereof. The agents can be a small molecule (e.g., molecular weight less than 2000, 1500, 1000, 750, or 500 atomic mass units (amu)) or a biomolecule, such as peptides, proteins, nucleic acids, polysaccharides, lipids, glycoproteins, lipoproteins, or combinations thereof. Exemplary classes of agents include, but are not limited to, synthetic and natural proteins (including enzymes, peptide-hormones, receptors, growth factors, antibodies, signaling molecules), and synthetic and natural nucleic acids (including RNA, DNA, anti-sense RNA, triplex DNA, inhibitory RNA (RNAi), and oligonucleotides), and biologically active portions thereof. The agents can include one or more of those described in Martindale: The Complete Drug Reference, ^! Ed. (Pharmaceutical Press, London, 2011).

Exemplary classes of small molecule therapeutic agents include, but are not limited to, analgesics, anti-inflammatory drugs, antipyretics, antidepressants, antiepileptics, antiopsychotic agents, neuroprotective agents, anti-proliferatives, such as anti-cancer agent, anti-infectious agents, such as antibacterial agents and antifungal agents, antihistamines, antimigraine drugs, antimuscarinics, anxiolytics, sedatives, hypnotics, antipsychotics, bronchodilators, anti-asthma drugs, cardiovascular drugs, corticosteroids, dopaminergics, electrolytes, gastro-intestinal drugs, muscle relaxants, nutritional agents, vitamins, parasympathomimetics, stimulants, anorectics and anti-narcoleptics. Nutraceuticals can also be incorporated. These may be vitamins, supplements such as calcium or biotin, or natural ingredients such as plant extracts or phytohormones.

Several drugs can be used to treat colorectal cancer. Often, two or more of these drugs are combined to try to make them more effective. The drugs most often used for colorectal cancer include 5-Fluorouracil (5-FU), which is often given with the vitamin-like drug leucovorin (also called folinic acid), which makes it work better, capecitabine (XELODA ) a prodrug to 5-FU, Irinotecan (Camptosar ^® ), and Oxaliplatin (Eloxatin ^® ). Common drug combinations used for adjuvant treatment include FOLFOX: 5-FU, leucovorin, and oxaliplatin; CapeOx: Capecitabine and oxaliplatin; 5- FU and leucovorin; and Capecitabine.

Irritable bowel syndrome ("IBS") is usually treated with drugs to reduce symptoms. Examples include anticholinergic and antispasmodic medications, antidepressants, anti-diarrheal medications, fiber supplements, and antibiotics. Two drugs currently approved for treatment of IBS include alosetron and lubiprostone.

As used herein, the term "microbicide" or "microbicidal

composition" means compounds that can be applied inside the rectum to protect against sexually transmitted infections (STIs) including HIV, especially when administered as microbicidal enema formulation suitable for rectal use. As used herein, the term "Nucleoside and Nucleotide Reverse Transcriptase Inhibitors" or "NRTIs" include those compounds that exhibit anti-HIV effects by inhibiting the activity of HIV reverse transcriptase. In a preferred embodiment, the antiviral is a NRTI in a mildly hypotonic solution. Examples include, but are not limited to, abacavir (ABC), didanosine (ddl), emtricitabine (FTC), lamivudine (3TC), stavudine (d4T), tenofovir (TFV), zidovudine (AZT) and zalcitabine (ddC), and their physiologically functional derivatives. Examples of other classes of antiviral compounds include NNRTIs, protease inhibitors, fusion or entry inhibitors, and integrase inhibitors. In the most preferred embodiment, the NRTI is tenofovir ((R)-9- (2-phosphonylmethoxypropyl)adenine; and phosphonic acid, [[(lR)-2-(6- amino-9H-purin-9-yl)-l-methylethoxy]methyl]. In another embodiment, the NRTI used in the microbicidal formulations is tenofovir disoproxil fumarate (2,4,6,8-Tetraoxa-5-phosphanonanedioic acid, 5-[[(lR)-2-(6-amino-9H- purin-9-yl)-l-methylethoxy]methyl]-, bis(l-methylethyl) ester, 5-oxide, (2E)-2-butenedioate (l:l)). Examples of NRTIs include, but are not limited to, for example, delavirdine, efavirenz, etravirine, rilpilvirine and nevirapine. Examples of protease inhibitors include, but are not limited to, for example, amprenavir, fosamprenavir, atazanavir, darunavir, indinavir, lopinavir, nelfinavir, ritonavir, saquinavir, and tipranavir. Examples of fusion or entry inhibitors include, but are not limited to, for example, enfuvirtide and maraviroc. Examples of integrase inhibitors include, but are not limited to raltegravir, elvitegravir, and dolutegravir.

Tautomeric forms, isomeric forms including diastereoisomers, and the pharmaceutically-acceptable salts thereof can also be used. The term "pharmaceutically acceptable salts" embraces salts commonly used to form alkali metal salts and to form addition salts of free acids or free bases.

Examples of acids which may be employed to form pharmaceutically acceptable acid addition salts include such inorganic acids as hydrochloric acid, sulphuric acid and phosphoric acid, and such organic acids as maleic acid, succinic acid and citric acid. Other pharmaceutically acceptable salts include salts with alkali metals or alkaline earth metals, such as sodium, potassium, calcium and magnesium, or with organic bases, such as dicyclohexylamine. Suitable pharmaceutically acceptable salts include, for example, acid addition salts which may, for example, be formed by mixing a solution of the compound with a solution of a pharmaceutically acceptable acid, such as hydrochloric acid, sulphuric acid, methanesulphonic acid, fumaric acid, maleic acid, succinic acid, acetic acid, benzoic acid, oxalic acid, citric acid, tartaric acid, carbonic acid or phosphoric acid. All of these salts may be prepared by conventional means by reacting, for example, the appropriate acid or base with the corresponding compounds. Salts formed from free carboxyl groups can also be derived from inorganic bases such as, for example, sodium, potassium, ammonium, calcium, or ferric hydroxides, and such organic bases as isopropylamine, trimethylamine, 2-ethylamino ethanol, histidine, and procaine, or other pharmaceutically acceptable salts. Hydrates of the compounds may be used. The term "hydrate" includes but is not limited to hemihydrate, monohydrate, dihydrate, and trihydrate.

Hydrates of the compounds may be prepared by contacting the compounds with water under suitable conditions to produce the hydrate of choice.

Exemplary diagnostic materials include paramagnetic molecules, fluorescent compounds, magnetic molecules, and radionuclides. Suitable diagnostic agents include, but are not limited to, x-ray imaging agents and contrast media. Radionuclides also can be used as imaging agents.

Examples of other suitable contrast agents include gases or gas emitting compounds, which are radioopaque. Nanoparticles can further include agents useful for determining the location of administered particles. Agents useful for this purpose include fluorescent tags, radionuclides and contrast agents.

D. Particles

Drug can be provided in solution, suspension or in nanoparticles. Nanoparticle drug carriers can be delivered directly to the colon to provide sustained local drug release and further minimize systemic exposure. Mucus- penetrating nanoparticles (MPP), as described in published US. Application Nos. 20080166414 and 20100215580, significantly improve distribution on the colorectal epithelium compared to conventional mucoadhesive nanoparticles (Ensign, et al. Adv. Drug Deliv. Rev. 64(6):557-579 (2012)). Solutions that induce fluid absorption by the vaginal epithelium (hypotonic solutions) rapidly transport water-soluble drugs, and MPP, to the epithelial surface by advection (Ensign, et al. Biomaterials 34(28):6922-9 (2013)). In contrast, MPP administered in isotonic vehicles remain in the vaginal lumen and only slowly diffuse through the mucosal barrier, and hypertonic vehicles cause rapid expulsion of MPP from the vaginal lumen. These studies demonstrate how MPP provide a simple and sensitive method for observing fluid movements both during fluid absorption, and secretion, by the epithelium, establishing MPP are useful for optimizing formulations for mucosal drug delivery. MPP provide enhanced mucosal delivery and distribution of drugs that are poorly water soluble. Core Polymer

Any number of biocompatible polymers can be used to prepare the nanoparticles. In one embodiment, the polymer(s) is biodegradable. In another embodiment, the particles are non-degradable. In other

embodiments, the particles are a mixture of degradable and non-degradable particles.

Exemplary polymers include, but are not limited to, cyclodextrin- containing polymers, in particular cationic cyclodextrin-containing polymers, such as those described in U.S. Patent No. 6,509,323; polymers prepared from lactones, such as poly(caprolactone) (PCL); polyhydroxy acids and copolymers thereof such as poly(lactic acid) (PLA), poly(L-lactic acid) (PLLA), poly(glycolic acid) (PGA), poly(lactic acid-co-glycolic acid) (PLGA), poly(L-lactic acid-co-glycolic acid) (PLLGA), poly(D,L-lactide) (PDLA), poly(D,L-lactide-co-caprolactone), poly(D,L-lactide-co- caprolactone-co-glycolide), poly(D,L-lactide-co-PEO-co-D,L-lactide), poly(D,L-lactide-co-PPO-co-D,L-lactide), and blends thereof, polyalkyl cyanoacralate, polyurethanes, polyamino acids such as poly-L-lysine (PLL), poly(valeric acid), and poly-L-glutamic acid; hydroxypropyl methacrylate (HPMA); polyanhydrides; polyesters; polyorthoesters; poly(ester amides); polyamides; poly(ester ethers); polycarbonates; polyalkylenes such as polyethylene and polypropylene; polyalkylene glycols such as poly(ethylene glycol) (PEG) and polyalkylene oxides (PEO), and block copolymers thereof such as polyoxyalkylene oxide ("PLURONICS®"); polyalkylene

terephthalates such as poly(ethylene terephthalate); ethylene vinyl acetate polymer (EVA); polyvinyl alcohols (PVA); polyvinyl ethers; polyvinyl esters such as poly( vinyl acetate); polyvinyl halides such as poly(vinyl chloride) (PVC), polyvinylpyrrolidone; polysiloxanes; polystyrene (PS; celluloses including derivatized celluloses such as alkyl celluloses, hydroxyalkyl celluloses, cellulose ethers, cellulose esters, nitro celluloses, hydroxypropylcellulose, and carboxymethylcellulose; polymers of acrylic acids, such as poly(methyl(meth)acrylate) (PMMA), poly(ethyl(meth)acrylate), poly(butyl(meth)acrylate), poly(isobutyl(meth)acrylate), poly(hexyl(meth)acrylate),

poly(isodecyl(meth)acrylate), poly(lauryl(meth)acrylate),

poly(phenyl(meth)acrylate), poly(methyl acrylate), poly(isopropyl acrylate), poly(isobutyl acrylate), poly(octadecyl acrylate) (jointly referred to herein as "polyacrylic acids"); polydioxanone and its copolymers;

polyhydroxyalkanoates; polypropylene fumarate; polyoxymethylene;

poloxamers; poly(butyric acid); trimethylene carbonate; and

polyphosphazenes,. Examples of preferred natural polymers include proteins such as albumin, collagen, gelatin and prolamines, for example, zein, and polysaccharides such as alginate. Copolymers of the above, such as random, block, or graft copolymers, or blends of the polymers listed above can also be used.

Functional groups on the polymer can be capped to alter the properties of the polymer and/or modify (e.g., decrease or increase) the reactivity of the functional group. For example, the carboxyl termini of carboxylic acid contain polymers, such as lactide- and glycolide-containing polymers, may optionally be capped, e.g., by esterification, and the hydroxyl termini may optionally be capped, e.g. by etherification or esterification.

Copolymers of PEG or derivatives thereof with any of the polymers described above may be used to make the polymeric particles. In certain embodiments, the PEG or derivatives may be located in the interior positions of the copolymer. Alternatively, the PEG or derivatives may locate near or at the terminal positions of the copolymer. For example, one or more of the polymers above can be terminated with a block of polyethylene glycol. In some embodiments, the core polymer is a blend of pegylated polymer and non-pegylated polymer, wherein the base polymer is the same (e.g., PLGA and PLGA-PEG) or different (e.g., PLGA-PEG and PLA). In certain embodiments, the microparticles or nanoparticles are formed under conditions that allow regions of PEG to phase separate or otherwise locate to the surface of the particles. The surface-localized PEG regions alone may perform the function of, or include, the surface-altering agent. In particular embodiments, the particles are prepared from one or more polymers terminated with blocks of polyethylene glycol as the surface-altering material.

The weight average molecular weight can vary for a given polymer but is generally from about 1000 Daltons to 1,000,000 Daltons, 1000 Daltons to 500,000 Dalton, 1000 Daltons to 250,000 Daltons, 1000 Daltons to 100,000 Daltons, 5,000 Daltons to 100,000 Daltons, 5,000 Daltons to 75,000 Daltons, 5,000 Daltons to 50,000 Daltons, or 5,000 Daltons to 25,000 Daltons.

Coated drug particles

In some embodiments, the particles are coated with a mucosal penetration enhancing coating. The mucosal penetration enhancing coating can be covalently or non-covalently associated with the agent. In some embodiments, it is non-covalently associated. In other embodiments, the active agent contains a reactive functional group or one is incorporated to which the mucosal penetration enhancing coating can be covalently bound.

The micro- and/or nanoparticles preferably are coated with or contain one or more surface altering agents or materials. "Surface-alternating agents", as used herein refers to an agent or material which modifies one or more properties of the particles for the surface, including, but not limited to, hydrophilicity (e.g., makes the particles more or less hydrophilic), surface charge (e.g., makes the surface neutral or near neutral or more negative or positive), and/or enhances transport in or through bodily fluids and or tissues, such as mucus. In some embodiments, the surface-alternating material provides a direct therapeutic effect, such as reducing inflammation.

Examples of the surface-altering agents include, but are not limited to, proteins, including anionic proteins (e.g., albumin), surfactants, sugars or sugar derivatives (e.g., cyclodextrin), therapeutics agents, and polymers. Preferred polymers include heparin, polyethylene glycol ("PEG") and poloxomers (polyethylene oxide block copolymers). The most preferred material is PEG or PLURONIC F127®, a polyethylene oxide block copolymer available from BASF.

Examples of surfactants include, but are not limited to, L-a- phosphatidylcholine (PC), 1 ,2-dipalmitoylphosphatidycholine (DPPC), oleic acid, sorbitan trioleate, sorbitan mono-oleate, sorbitan monolaurate, polyoxyethylene (20) sorbitan monolaurate, polyoxyethylene (20) sorbitan monooleate, natural lecithin, oleyl polyoxyethylene (2) ether, stearyl polyoxyethylene (2) ether, lauryl polyoxyethylene (4) ether, block copolymers of oxyethylene and oxypropylene, synthetic lecithin, diethylene glycol dioleate, tetrahydrofurfuryl oleate, ethyl oleate, isopropyl myristate, glyceryl monooleate, glyceryl monostearate, glyceryl monoricinoleate, cetyl alcohol, stearyl alcohol, polyethylene glycol 400, cetyl pyridinium chloride, benzalkonium chloride, olive oil, glyceryl monolaurate, corn oil, cotton seed oil, and sunflower seed oil, lecithin, oleic acid, and sorbitan trioleate.

In one embodiment, the particles are coated with or contain polyethylene glycol (PEG) or F127. Alternatively, the PEG or F127can be in the form of blocks covalently bound (e.g., in the interior or at one or both terminals) to the core polymer used to form the particles. In particular embodiments, the particles are formed from block copolymers containing PEG. In more particular embodiments, the particles are prepared from block copolymers containing PEG, wherein PEG is covalently bound to the terminal of the base polymer. Representative PEG molecular weights include 300 Da, 600 Da, 1 kDa, 2 kDa, 3 kDa, 4 kDa, 6 kDa, 8 kDa, 10 kDa, 15 kDa, 20 kDa, 30 kDa, 50 kDa, 100 kDa, 200 kDa, 500 kDa, and 1 MDa and all values within the range of 300 Daltons to 1 MDa. In preferred embodiments, the PEG has a molecular weight of about 5kD. PEG of any given molecular weight may vary in other characteristics such as length, density, and branching.

Surface density of poly(ethylene glycol) (PEG) on microparticles and/or nanoparticles is a key parameter in determining their successful applications in-vivo. (As used herein, general references to PEG on the surface of particles is extrapolatable to PLURONIC® F127. The controlled delivery of drugs to mucosal surfaces is challenging because of the presence of the protective mucus layer, and the mucus-penetrating particles show promise at improved drug distribution, retention and efficacy at mucosal surfaces. The dense coating of PEG on biodegradable nanoparticles can allow rapid penetration through mucus because of the greatly reduced adhesive interaction between mucus constituents and nanoparticles.

In a preferred embodiment, nuclear magnetic resonance (NMR) is used to assess the surface PEG density on PEG-containing polymeric nanoparticles described herein, both qualitatively and quantitatively (PEG peak typically observed ~3.65 ppm). When nanoparticles are dispersed within the NMR solvent D ₂ 0, only the surface PEG, not the PEG embedded within the core, can be directly detected by NMR. Therefore, NMR provides a means for directly measure the surface density of PEG.

In some embodiments, PEG surface density can be controlled by preparing the particles from a mixture of pegylated and non-pegylated particles. For example, the surface density of PEG on PLGA nanoparticles can be precisely controlled by preparing particles from a mixture of poly(lactic-co-glycolic acid) and poly(ethylene glycol) (PLGA-PEG).

QuantitativeΉ nuclear magnetic resonance (NMR) can be used to measure the surface PEG density on nanoparticles. Multiple particle tracking in human mucus and the study of mucin binding and tissue distribution in mouse vagina revealed that there exists a PEG density threshold, which is approximately, 10-16 PEG chains/lOOnm , for PLGA-PEG nanoparticles to be effective in penetrating mucus. This density threshold may vary depending on a variety of factors including the core polymer used to prepare the particles, particle size, and/or molecular weight of PEG.

The density of the coating can be varied based on a variety of factors including the surface altering material and the composition of the particle. In one embodiment, the density of the surface altering material, such as PEG, as measured by 1H NMR is at least, 0.1, 0.2, 0.5, 0.8, 1, 2, 5, 8, 10, 15, 20, 25, 40, 50, 60, 75, 80, 90, or 100 chains per nm . The range above is inclusive of all values from 0.1 to 100 units per nm ² . In particular embodiments, the density of the surface altering material, such as PEG, is from about 1 to

9 9 about 25 chains/nm , from about 1 to about 20 chains/nm , from about 5 to

9 9 about 20 chains/nm , from about 5 to about 18 chains/nm , from about 5 to

9 9

about 15 chains/nm , or from about 10 to about 15 chains/nm . In other particular embodiments, the density is from about 0.05 to about 0.5 PEG chains/nm ² .

The concentration of the surface altering material, such as PEG, can also be varied. In particular embodiments, the density of the surface-altering material (e.g., PEG) is such that the surface-altering material (e.g. PEG) adopted an extended brush configuration. In other embodiments, the mass of the surface-altering moiety is at least 1/10,000, 1/7500, 1/5000, 1/4000, 1/3400, 1/2500, 1/2000, 1/1500, 1/1000, 1/750, 1/500, 1/250, 1/200, 1/150, 1/100, 1/75, 1/50, 1/25, 1/20, 1/5, 1/2, or 9/10 of the mass of the particle. The range above is inclusive of all vales from 1/10,000 to 9/10.

The particles can contain an emulsifier, particularly a low molecular weight emulsifier. The emulsifier is incorporated into the particle during particle formation and therefore is a component of the finished particle. The emulsifier can be encapsulated within the particle, be dispersed in whole or in part within the polymer matrix (e.g., part of the emulsifier extends out from the polymer matrix), and/or is associated (e.g., covalently or non- covalently) with the surface of the particle.

"Low molecular weight", as used herein, generally refers to an emulsifier having a molecular weight less than 1500, 1400, 1300, 1200, 1100, 1000, 900, 800, 700, 600, 500, 400, or 300 amu. In some

embodiments, the molecular weight is less than 1300 amu. In some embodiments, the molecular weight is from about 300 amu to about 1200 amu.

The emulsifier can be positively charged, negatively charged, or neutral. Examples of negatively charged emulsifiers include, but are not limited to, cholic acid sodium salt (CHA, MW = 430) and dioctyl sulfosuccinate sodium (DSS, MW = 455). Examples of positively charged emulsifiers include, but are not limited to, hexadecyltrimethyl ammonium bromide (CTAB, MW = 364). Examples of neutral emulsifiers include, but are not limited to, sapon (MW = 1191), TWEEN 20 (MW = 1,225), TWEEN 80 (MW = 1310), and sugar ester D1216 (sucrose laurate, SE, MW = 524). In addition to having a low molecular weight, the emulsifier must be capable of suitably stabilizing the emulsion droplets during particle formation in order to prevent particle aggregation. In addition to suitably stabilizing the emulsion droplets to prevent aggregate formation, the stabilizer must be small enough to be completely shielded at the particle surface by the surface altering material corona (e.g., PEG) to provide a neutral or near neutral surface charge. The transport of charged particles may be hindered due to the interaction of the charged particles with oppositely charged species in vivo. For example, the ability of the particles to penetrate mucus rapidly is dependent, at least in part, on the surface charge of the particles. In order to facilitate their diffusion through mucus, the nanoparticles described herein typically possess a near neutral surface charge. In certain embodiments, the nanoparticle possess a ζ-potential of between about 10 mV and about -10 mV, preferably between about 5 mV and about -5 mV, preferably between about 3 mV and about -3 mV, more preferably between about 2 mV and about -2 mV.

While the particles described herein are referred to as nanoparticles, and thus typically have an average diameter in the range of 1 nm up to, but not including, about 1 micron, more preferably from about 5 nm to about 500 nm, most preferably from about 5 nm to about 100 nm, in certain

embodiments, the average diameter of the particles is from about 100 nm to about 150 nm. However, particles can be prepared that are sized in the micron-range. The conditions and/or materials used to prepare the particles can be varied to vary the size of the particles. E. Proposed Formulations

The most commonly used commercial enema formulations rely on their hypertonicity to cause a large and rapid influx of water to cleanse the rectal vault. However, hypertonic sexual lubricant gels cause significant loss of single columnar epithelium within minutes of applying a single dose. In contrast, when an "isoosmolar" (osmolarity similar to that of blood) lubricant was used, there was no loss of single columnar epithelium. Other studies have also reported mucosal damage due to hypertonic solutions. A large proportion of users simply use tap water (a strongly hypotonic formulation) due to easy availability, however, epithelial loss (toxicity) has also been reported after its use. To address the potential use of an enema formulation of a microbicidal agent, either alone or as a complement to another method, a study was designed to assess the safety, distal gastrointestinal distribution, retention, and acceptability of three different types of enema. Given the concern for potential increased HIV acquisition posed by the widely used, strongly hypertonic enemas, a mild (hypotonicr/isoosmolar) enema was compared to the commonly used FLEET® (hypertonic) and distilled water (hypotonic) enemas in a cross-over design allowing paired comparisons within each individual.

As used herein, the terms "mildly hypotonic" or "near isotonic," means an aqueous solution or carrier having an osmolarity greater than tap water (0 mOsm), and between about 20 mOsm to about 290 mOsm. In some embodiments, the hypotonic or mildly hypotonic formulation of the microbicidal compositions have osmolarity in the range of 200 mOsm to about 240 mOsm, preferably about 220 mOsm. The microbicidal compositions are preferably formulated using known buffers and salts, including, for example, normal saline, phosphate buffered saline (PBS), Tris- buffered saline (TBS), or HEPES buffered saline.

As demonstrated by the examples, an enema formulation that has an osmolality of approximately 150 mOsm gave the best results. The solution contained both sodium (25 mM) and potassium (75 mM), but it was found that fluid absorption only occurred if sodium was present in the solution. If sodium was removed, leaving potassium unchanged at 75 mM (SCS— Na+), no fluid absorption occurred and TFV-FITC remained in the lumen. In contrast, if potassium was removed leaving sodium unchanged at 25 mM (SCS -K+), fluid was rapidly absorbed by the colorectal epithelium, distributing TFV throughout all of the folds of the mouse colorectum.

III. Methods of Administration

The formulations described herein are prepared and administered as described in the examples. Typically, the formulations are prepared as pre- solublized drug which is in a single use, squeezable container with a flexible tip for ease of rectal insertion. The formulation can be administered as needed to produce an effective local drug concentration, or in the case of administration of a microbiocide, ould also be administered at the time of or immediately after intercourse, although this is not preferred.

The formulations may also be provided as a tablet which is added to a reusable or single use container, to which deionized water is also added to dissolve the tablet. The tablet contains salts, gel forming polymer as well as the microbiocide and any other additives.

For rectal administration, it may be preferred to use an applicator which distributes the composition substantially evenly throughout the rectum. For example, a suitable applicator is a tube 2.5 to 25 cm, preferably 5 to 10 cm, in length having holes distributed regularly along its length which is capable of distribution of the formulations within the colon.

The formulations can be administered directly to the mucosal surface for the treatment of a variety of diseases such as inflammatory bowel disease, colorectal cancers, gastrointestinal infections, and prevention of sexually transmitted infections. The terms "reduce", "suppress" and "inhibit," as well as words stemming therefrom, have their commonly understood meaning of lessening or decreasing. These words do not necessarily imply 100% or complete treatment, reduction, suppression, or inhibition. In some embodiments, the compositions are administered to the rectum of the subject at least 30 minutes to 3 hours before RAI. In other embodiments, the microbicidal compositions are administered to the rectum of the subject at least 30 minutes to 2 hours after RAI. The formulations may provide inhibition of HIV infection of the colon and rectum for up to 7 days post application with one or more doses. Patterns of use of enemas underline the importance of the rapid achievement of sustained drug levels in the relevant tissues. Modeling studies indicate oral TFV PrEP regimens require one week to achieve protective concentrations of the active drug form, TFV diphosphate (TFV-DP), in tissue. These concentrations can be achieved within 30 minutes after TFV 1% rectal gel dosing. Another marked advantage of topical strategies is the limited systemic absorption of drug, which minimizes adverse long- and short-term systemic side effects.

The present invention will be further understood by reference to the following non-limiting examples.

Example 1: Effect of osmolality of sodium based solutions on colorectal drug distribution

Materials and Methods

Animal Model

Rodents are commonly used as animal models for delivery to the gastrointestinal tract. However, their defecation rate is much more rapid than typical for humans, and their hard, desiccated pellets do not resemble human feces. To simulate the softer stool consistency and less frequent defecation rate of humans, female 6-8 week old CF-1 mice (Harlan) were starved for 24 h to make the feces softer, more human-like, and less abundant. Mice were housed in cages with wire bottoms to prevent coprophagia. 20 or 50 μΐ of the various test solutions were administered to mice intrarectally with a Wiretrol (Drummond, Inc.). Control experiments confirmed that the osmolality of vehicles administered after DI water cleansing enemas was unaltered when vehicle fluid was collected after expulsion, indicating that this cleansing enema did not affect fluid absorption. Mice were anesthetized with the drop- method via isofluorane for shorter times, or injected with 300 mg/kg avertin (2, 2, 2-Tribromoethanol), using a 20 mg/mL working solution in phosphate buffered saline (PBS), when more extended anesthesia times were required. All experimental procedures were approved by the Johns Hopkins Animal Care and Use Committee.

Enema formulations

lOx Tris-buffered saline (Mediatech; IX TBS is 20 raM Tris, 138 mM NaCl, pH 7.4) was diluted with ultrapure water to obtain sodium-based solutions of various osmolalities. Similarly, potassium phosphate buffer was prepared by dilution of 1 M Κ ₂ ΗΡ0 ₄ (Sigma) pH 5.5, with ultrapure water to obtain potassium-based solutions of various osmolality (e.g. 150 mOsm buffer was made by diluting 1M K ₂ HP04 approximately 12 fold). The simulated colon solution (SCS) was made by dissolving sodium bicarbonate, potassium chloride, dibasic potassium phosphate and monobasic potassium phosphate (Sigma) in ultrapure water at the following ion concentrations: 75 mM K, 25 mM Na, 35 mM CI, 30 mM P0 ₄ , and 25 mM C0 ₃ . Solution osmolality was measured with a vapor pressure osmometer (Wescor Vapro). FLEET® enema solution and FLEET® Naturals were purchased over the counter, and all enema solutions were sterile-filtered through a 0.2 μηι filter prior to in vivo use. A 5% w/v glycerol gel was obtained by mixing the universal placebo HEC gel (ReProtect, Inc.) with glycerol.

Toxicity of enema formulations in the mouse colorectum

Mice were anesthetized by avertin, and 50 μΐ of tap water, SCS, or FLEET® was administered. Mice were kept in supine position for 20-30 min prior to sacrificing them and excising the tissues. Tissues were fixed in formalin and taken to the Johns Hopkins Medical Institutions Reference Histology Laboratory for standard paraffin embedding, sectioning, and hematoxylin and eosin (H&E) staining. Images were obtained using a light microscope with a lOx/0.25 NA objective (Nikon E600). Free drug uptake into plasma after administration to the mouse colorectum

Mice were anesthetized using avertin, and 20 μΐ of the various solutions containing 1% w/v unlabeled TFV and 1 μΐ, of H ³ -TFV (1 mCi/ml, suspended in ethanol, Moravek Biochemicals) was administered

intrarectally. For the 0 min time point, retro-orbital blood collection was used to collect blood immediately after administration of each solution; for the 30 min time point blood was removed 30 min post administration. Whole blood was centrifuged in heparinized tubes to obtain plasma, and 200 μΐ of plasma was dissolved in 5 ml of SOLVABLE™ and bleached using hydrogen peroxide. 500 μΐ of plasma/SOLVABLE™ solution was added to 10 ml of Ultima Gold and H ³ content was analyzed using a scintillation counter. Concentrations were calculated using a calibration curve of free H -TFV. A serial dilution of H ³ -TFV was made to include the full range of sensitivity of the scintillation counter. Separate standard curves were made for lower and higher count samples. Concentrations of H ³ -TFV in plasma were estimated using the standard curves. H ³ -TFV was administered in a 1% unlabeled TFV solution to ensure no difference in uptake because of drug concentrations. Total drug concentration in plasma was calculated assuming that

radioactively labeled and unlabeled drugs were taken up at similar rates. Pharmacokinetic studies of free drug in the mouse colorectal tissue

Mice were anesthetized using avertin, and 20 μΐ of the various solutions containing 1% (w/v) unlabeled TFV and 1 μΐ H -TFV (1 μθ/ιηο^ε) was administered intrarectally to mice. Tissue was harvested at 5 min, 30 min, 1 h, 2 h, and 4 h time points and processed as described above. H ³ tissue content was measured using a scintillation counter and normalized based on individual tissue weights. Values were obtained from n = 5 mice, and the highest and lowest values were removed from each group to obtain n = 3 per time point for each solution used. Results

Studies in the mouse vagina showed that vehicles causing advective absorption (hypotonic) are advantageous for improving the distribution of water soluble hydrophilic drugs at mucosal surfaces. Studies were performed to demonstrate colorectal delivery of TFV in a hypotonic enema vehicle for HIV pre-exposure prophylaxis (PrEP). TFV was covalently labelled with FITC (TFV-FITC) and mixed at a 1 : 10 ratio with unlabeled TFV to visualize distribution. Sodium-based enema vehicles of varying osmolality were compared: deionized water and isotonic saline (300 mOsm), which induce absorption, an essentially isotonic TBS (450 mOsm), and a slightly hypertonic TBS (650 mOsm) that induces fluid secretion.

Table 1 shows that the hypertonic solutions resulted in systemic uptake of

V lik h h i f l i Figure 1 is a graph of the concentration of tenofovir in mouse colorectal tissue at up to 4 h after intrarectal administration in various vehicles. 1% tenofovir was administered in ultrapure water (20 mOsm), simulated colon solution (a fluid-based enema vehicle mimicking the ionic composition of feces, SCS) (150 mOsm), isotonic tris-buffered saline (TBS, 450 mOsm), gel containing 5% glycerol (760 mOsm), and FLEET® enema (2200 mOsm). The graph shows significantly higher levels of TFV with the 150 mOsm formulation.

Distribution in transverse colonic cryosections after rectal

administration of 1 % TFV-FITC in TBS vehicle (450 and 650 mOsm), DI water (20 mOsm), and isoosmolar saline (310 mOsm) showed that colorectal tissue coverage (and therefore access to target cells and tissues) was improved by using an absorption inducing enema. Bulk fluid flow transports the water-soluble, small molecule drug through the mucus barrier and into the epithelium, and also transports the drug deep into the folds of the (collapsed) colorectum.

To minimize risk of epithelial toxicity that could be caused by osmotic gradients much larger than typically occur in the colon, an enema formulation that has sodium and potassium concentrations similar to those found in feces was used. The osmolality of the simulated colon solution (SCS) was approximately 150 mOsm. Since the solution contained both sodium (25 mM) and potassium (75 mM), the effect of the individual contributions of these ions were assessed. It was found that fluid absorption only occurred if sodium was present in the solution. If sodium was removed, leaving potassium unchanged at 75 mM (SCS -Na+), no fluid absorption occurred and TFV-FITC remained in the lumen. In contrast, if potassium was removed leaving sodium unchanged at 25 mM (SCS -K+), fluid was rapidly absorbed by the colorectal epithelium, distributing TFV throughout all of the folds of the mouse colorectum. Example 2: Nanoparticle and free drug distribution on tissues

Materials and Methods

MPP 40 nm in diameter were diluted 1 : 10 in TBS and KP0 ₄ buffers of various osmolalities to make a range of sodium-based and potassium- based buffered solutions. To observe the colorectal distribution of TFV, fluorescein isothiocyanate (FITC) was covalently reacted to the free amine group. FITC-labeled TFV (FITC-TFV) was then dissolved 1:10 with unlabeled TFV in the various solutions at an overall concentration of 1% (w/v), the concentration of TFV in the microbicide formulation used in the CAPRISA 004 trial.

Mice were anesthetized using isofluorane during administration. For qualitative distribution, 20 μΐ of solution was administered intrarectally to mice. The mice were sacrificed after 5-10 min. 1-2 cm segments of tissue were flash-frozen in Optimal Cutting Temperature (OCT) compound.

Transverse sections of tissue 6 μπι thick were cut at various points along the length of the colorectum using a Leica CM-3050-S cryostat. Sections containing nanoparticles were fixed with formalin and stained using ProLong Gold antifade reagent with DAPI (Invitrogen). Sections containing free drug were not fixed to reduce quenching of the fluorophore and stained with ProLong Gold antifade reagent with DAPI. Fluorescent images were obtained using an inverted epifluorescence microscope (Zeiss Axio

Observer).

To quantify nanoparticle and drug distribution, 50 μΐ of solution was administered to the colorectum. Within 5-10 min, the colorectal tissue was removed, sliced open longitudinally, and flattened between two glass slides. Six images at regular intervals along the colon were obtained for each tissue as previously described for vaginal tissue (LE Blomatl). Control tissues (no drug or nanoparticles administered) were imaged to ensure the fluorescent signal from tissues containing nanoparticle or drug solutions were above tissue autofluroescence. Images were then threshholded and the percentage of surface coverage was quantified using ImageJ. The percent surface coverage for each animal was averaged over the six images, and then an overall average was calculated for n = 3 mice. With this method, some additional spreading occurs when fluid remains in the lumen, leading to a smaller difference in distribution between isotonic and hypotonic solutions in the quantified distribution that would be attributed with the qualitative distribution via cryo section.

Results

A hypotonic vehicle applied to the mouse vagina induces fluid absorption that rapidly transports MPP advectively through the unstirred mucus barrier to contact the entire epithelial surface (LE STM, Biomatl, KM MPP colon). When administered in an isotonic vehicle that does not cause bulk fluid flow, MPP diffused very slowly through the mucus barrier and remained more distant from the epithelium. In this way, MPP serve as a probe for the directionality, extent, and timing of fluid absorption at epithelial surfaces. One of the primary functions of the colon is water absorption accomplished by electrogenic 3Na/2K ATPase pumps in the basolateral membranes of apical cells, and high conductance sodium, potassium, and chloride channels in the apical membrane of colonic epithelial cells. Therefore the effects of altering enema sodium concentration on MPP distribution in the mouse colorectum was examined. It was evident that sodium-based enema vehicles below a certain osmolality (~400 mOsm, ~210 mM NaCl) induce fluid absorption that results in MPP becoming evenly coated on the epithelial surface.

Figure 2 shows the quantified distribution of 40nm PSPEG in transverse colonic cryosections after rectal administration of DI water and Tris buffer (TBS) with osmolalities of 20, 260, 350, 450 (1ST), and 860 mOsm, 5% glycerol in DI water with osmolality of 600 mOsm, as well as with commercially available enema formulation clinical isoosmolal saline (ISO), Fleet Naturals ® (FN) and regular Fleet ® (F) with osmolalities of 310, 250 and 2200 mOsm respectively. Cell nuclei in transverse crysections were stained with DAPI. The quantified surface coverage of MPP in sodium based Tris buffer with various osmolalities on flattened mouse colonic tissue demonstrated that sodium-based enema vehicles with osmolality >400 caused fluid secretion and bowel distension, preventing MPP from close approach to the epithelial surface, resulting in MPP remaining more centrally located in the lumen, and more rapidly expelled.

MPP surface coverage was then quantified as a function of absorption or secretion inducing formulations. The results show that MPP administered in the sodium-based enema vehicles with osmolalities below the isotonic osmolality of 400 mOsm provided greater than 80% coverage of the colorectal epithelium, whereas MPP administered in solutions with an osmolality of 530 mOsm and above did not enter the epithelial folds, reducing the surface coverage by MPP to as low as 30% when administered in a FLEET ® enema. Epithelial coverage decreased as osmolality increased beyond the isotonic (1ST) point.

Potassium, in contrast to sodium, is actively pumped into the lumen of the colorectum, creating a potassium gradient the opposite of sodium, and producing a high potassium/sodium ratio in feces. It was hypothesized that increasing the potassium concentration in an enema would slow fluid absorption by the epithelium. MPP administered in 150 mOsm potassium buffer that is markedly hypo-osmolal with respect to blood, would be expected on the basis of osmolality to induce fluid absorption, but instead this enema did not induce absorption.

A sodium-based enema with the same osmolality, 150 mOsm, induced rapid absorption that advectively transported MPP to coat epithelial surface uniformly throughout the colorectum similarly to MPP administered in DI water. In additional experiments, even lower potassium concentrations still reduced fluid absorption. The isotonic (no fluid flow) concentration for potassium phosphate was between 20 and 70 mOsm, and colorectal tissue coverage decreased as the osmolality of the potassium-based enema solution increased above this range. The sodium-based enema vehicles were significantly more effective for achieving maximal tissue distribution of MPP.

Example 3: Effect of osmolality of sodium based solutions on colorectal drug distribution

Materials and Methods

Studies were conducted on colorectal delivery of TFV in a hypotonic enema vehicle for HIV pre-exposure prophylaxis (PrEP). TFV was covalently labeled with FITC (TFV-FITC) and mixed at a 1:10 ratio with unlabeled TFV to visualize distribution. Sodium-based enema vehicles of varying osmolality were compared: deionized water and isotonic saline (300mOsm), which induce absorption, an essentially isotonic TBS (450 mOsm), and a slightly hypertonic TBS (650 mOsm) that induces fluid secretion.

Materials and Methods

Distribution in transverse colonic cryosections after rectal administration of 1% TFV-FITC in TBS vehicle (450 and 650 mOsm), DI water (20 mOsm), and isoosmolar saline (310 mOsm), was consistent with MPP distribution: colorectal tissue coverage (and therefore access to target cells and tissues) was improved by using an absorption inducing enema. Bulk fluid flow transports the water-soluble, small molecule drug through the mucus barrier and into the epithelium, and also transport the drug deep into the folds of the (collapsed) colorectum.

Advective transport via epithelial fluid absorption is well suited to provide enhanced drug delivery to the colonic and rectal epithelium. Unlike convective transport (here defined as mechanical stirring such as may occur during rectal intercourse), advective transport can transport soluble drugs or drugs contained in MPP through the adherent "unstirred" mucus layer overlying the colorectal epithelium, the layer that is highly resistant to convective stirring. Moreover, unlike convection or diffusion, advective transport can provide distribution deep into epithelial folds, where convective stirring motions may fail to reach (Achilles et al,) and where diffusion is far too slow.

The colon absorbs 1.4-1.8 L of water every day, driven by active ion transport. This robust physiological mechanism provides an opportunity to optimize fluid absorption to achieve effective drug concentrations in the tissue. Unlike MPP that will neither enter the epithelium nor get drawn through epithelial junctions, small molecule drugs can be drawn into and through the epithelial layer. Strongly hypotonic solutions such as DI water cause a loss of drug into systemic circulations. Isotonic solutions (no fluid flow) will result in slow drug absorption driven only by diffusion, resulting in long times before sufficient drug levels are reached in the tissue, or preventing effective tissue concentrations to be reached. Mildly hypotonic solutions, however, can provide robust fluid flow and result in increased local drug levels, while avoiding overly-rapid trans-epithelial advection and systemic absorption. Sodium drives fluid absorption in the colorectum, as long as levels are below 210 mM NaCl in the mouse, similar to the 220 mM NaCl found to cause fluid secretion in humans. Potassium, on the other hand, seems to induce fluid secretion even at very low levels. By varying the amounts of each of these two ions, optimal concentrations can be found that attain the highest tissue levels. Tissue levels may depend on the specific drug's interaction with mucus and the epithelium, and enema products could be fine-tuned by varying potassium and sodium concentrations. A substantial number of people use tap water enemas prior to RAI, but drug administration in this highly absorption-inducing enema vehicle results in loss of drug into the plasma. An enema with only mild advective absorption can provide improved colorectal drug distribution and tissue uptake without excessive loss of drug to systemic circulation. The SCS matches ion concentrations found in feces, making it an optimal starting point due to a low chance of causing toxicity while still inducing sufficient advective fluid absorption to create optimal local drug levels. The FLEET® enema, one of the most common products used for bowel cleansing, is exceptionally hypertonic and causes significant toxicity. Similar toxicity occurs in the mouse colorectum, where epithelial damage occurred within 30 min of application of a FLEET® enema. Moreover, a variety of rectally applied products have been tested on human colorectal biopsies, and those that caused hyper-osmolar epithelial toxicity also cause increased susceptibility to sexually transmitted infection. In contrast, no discernible epithelial toxicity was observed after administration of advectively absorptive, hypotonic enema solutions. In addition to increased epithelial toxicity, hypertonic enemas actually had slightly decreased acceptability among study participants and their partners, compared to tap water and mildly hypotonic saline when used prior to RAI. Developing a safe, hypotonic enema is thus key to improving drug delivery to the colorectum.

For certain applications, systemic delivery is desirable. Rectal delivery has long been used to administer medications, such as anti-arthritic, anti-emetic and anti-angiogenic agents, to the systemic circulation. Most of these medications have improved bioavailability when administered intrarectally, which avoids first-pass metabolism and degradation by stomach acid and digestive enzymes. The findings indicate that both advectively absorbing and advectively secreting vehicles result in detectable systemic drug concentrations only 30 min after intrarectal administration. However, the toxicity induced by advectively secreting (hypertonic) vehicles in the colorectum may limit the utility of hypertonic enemas, particularly if epithelial toxicity would be detrimental. On the contrary, extremely hypotonic vehicles can transport drug through the epithelium by both paracellular and transcellular fluid absorption and deliver drug to the blood that can increase drug plasma levels. Clinical data also suggests that hypotonic delivery is favorable for systemic delivery, and intestinal epithelial cells show increased transport of hydrophilic molecules when the molecules are applied in a 50% hypotonic solution. This further emphasizes the need for the optimization of an enema solution depending on the intent of the application, and indicates the potential for systemic as well as local drug delivery using hypotonic enemas.