BACKGROUND OF THE INVENTION 1. Field of the Invention Embodiments of the present invention relate in general to methods and compounds useful for the detection and diagnosis of certain tissue conditions associated with rapidly dividing cells. Embodiments of the present invention also relate to methods and compounds useful in the detection and diagnosis of certain tissue conditions associated with the aberrant proliferation of cells, such as tumors. More particularly, embodiments of the present invention include the use of compounds readily taken up by rapidly dividing cells and which localize within such rapidly dividing cells and which can be used to detect, diagnose and/or treat tissue conditions associated with the rapidly dividing cells. Even more particularly, embodiments of the present invention relate to the intravenous administration and localization of certain compounds within certain tissue without substantial degradation of the compounds prior to localization.

2. Description of Related Art The use of certain nucleosides to treat and/or diagnose tissue conditions such as tumors is known. See US Patent Nos. 5,077,034,5,094,835 and 5,308,605 hereby incorporated by reference in their entireties for all purposes. Nucleoside compounds are typically labeled with an effector group such as a diagnostic or therapeutic moiety and administered to a patient. The nucleoside compounds are incorporated into DNA during the synthetic phase of the cell cycle. The incorporated nucleoside is retained for the life of the cell or its progeny. The cells are then able to be detected, diagnosed or treated depending upon which type of effector group is chosen to be attached to the nucleoside.

In general, to facilitate targeting of tumors, an effector compound, i. e. a compound including an effector group such as a diagnostic or therapeutic moiety, is directly introduced

into the target tissue or into an arterial blood supply that immediately precedes the target tissue. In order to achieve sufficient uptake of the effector compound by the cells of the target tissue, (1) the target tissue should be approximately within an area that can be easily accessed, (2) once within the vicinity of the target tissue, the agent (a) freely diffuses throughout all the target tissue, (b) is innocuous outside of the cells of the target tissue, and (c) is selectively taken up either passively or actively and indefinitely retained by the cells of the target tissue, (3) once the effector compound has diffused out of the target area, it must either be converted quickly into an inactive, i. e., nontoxic, form and/or be excreted from the body, and (4) the biologic behavior of the effector compound is not altered by repeated injection, i. e., it lends itself to repeat/continuous injections.

The use of a specific prior art compound in vivo, i. e. radiolabeled IudR (iododeoxyuridine), presents a number of challenges. The first relates to the matter of achieving therapeutic ratios in cancer cells, especially in the face of efficient hepatic dehalogenation (with a typical half-life being approximately a few minutes or less). The second relates to the uptake of such radiopharmaceuticals by actively proliferating normal cell renewal systems (bone marrow, gut) and the consequent possible production of toxic side effects. A third challenge is one shared with other cycle-dependent drugs and relates to the matter of labeling the entire tumor population: like many cycle-dependent agents, IUdR can only label cells in S-phase.

One effort to meet the above challenges has been locoregional drug administration.

The underlying rationale is that this approach would ensure the availability of the radiolabeled IUdR molecules to dividing cancerous cells. Studies have been conducted with various animal tumor models and in patients where locoregional administration is feasible.

These studies have consistently supported the"locoregional administration of radiolabeled nucleotide/nucleoside"concept.

'25IUdR has been administered intraperitoneally into mice bearing an ascites ovarian cancer. The cells within the peritoneal cavity are exposed directly (locoregionally) and repeatedly (dose fractionation) to'25IUdR before the radiopharmaceutical enters the systemic circulation where it is degraded. The results demonstrate a 5 log reduction in tumor cell survival. These experiments have been repeated using'23IUdR ('23I is also an Auger electron emitter) and have observed comparable results.

'23IUdR/'25IUdR has also been injected intracerebrally into rats bearing an intraparenchymal gliosarcoma. In this instance, the cells within the solid brain tumor are exposed to IUdR before the radiopharmaceutical escapes into the systemic circulation and is degraded. It was found that (a) there is a 1 to 1 correlation between the localization of the radioactivity (as demonstrated by autoradiography) and the cancerous cells, (b) no DNA- incorporated radioactivity can be demonstrated by autoradiography in normal brain tissues (nor is it demonstrable in any cells within the bone marrow, colon, eyes, heart, kidney, large intestine, lungs, lymph nodes, muscle, skin, small intestine, spleen, or testes), (c) external gamma imaging ('z3I) visualizes intracerebral tumors as small as 0.5 mm in diameter; and (d) in addition to the head region in tumor-bearing animals, the radioactivity is visible only within the regions of the stomach and the bladder; and (e) the survival of treated animals is significantly prolonged by the injection or infusion of'25IUdR.

Locoregional administration was further examined in a study in which patients suspected of having primary gliomas were given a single intracerebral injection of'23IUdR.

Scintigraphic imaging shows that the distribution of radiolabeled IUdR is very similar to that observed in the tumor-bearing rat studies described above, i. e. radioactivity is apparent mainly in the tumor, stomach, and bladder.

Radiolabeled IUdR has been instilled intravesically into the bladder of rats bearing bladder tumors and showed that (a) scintigraphic detection of bladder tumors is achieved with high sensitivity and specificity (virtual absence of radioactivity within the bladders of nontumor-bearing rats while the only visible area of activity remaining in the tumor-bearing animals is over the bladder region), (b) favorable tumor to normal tissue ratios are obtained, (c) IUdR uptake is detected at a very early stage of tumor development (hyperplasia stage), and (d) autoradiography demonstrates the DNA incorporation of radiolabeled IUdR into tumor cells and its absence from normal urothelium and other normal dividing tissues.

The incorporation of'23IUdR infused intra-arterially in patients with liver metastases from colorectal cancer has also been evaluated. The data indicate that (a) radiolabeled IUdR is instantaneously taken up by the tumor cells (during the first pass), (b) all perfused metastases can by clearly visualized by scintigraphy, (c) a substantial proportion of the administered IUdR (1 %-11 %) is taken up and retained by the metastases, (d) all radioactivity within blood (i. e. post liver percolation) is in the form of free iodide and/or iodouracil (i. e.

blood is void of the radiopharmaceutical), and (e) no significant uptake is detected in the bone marrow or other normal dividing tissues. These results demonstrate that the administration of radiolabeled IUdR into the hepatic artery of patients with colon metastases will lead to the rapid and efficient incorporation of the radiopharmaceutical into tumor cells.

Since blood sampling indicated that the blood is devoid of the radiopharmaceutical, the results indicate that a single passage of IUdR by dividing tumor cells is sufficient for uptake to occur (-20, 000 IUdR molecules can be taken up per DNA-synthesizing cell per second).

The methods of the prior art administer radioactively-labeled nucleotides, such as '23IUdR, by locoregional injection/infusion, i. e., by modes other than intravenous administration primarily because of the identified problem of degradation of the compounds (prior to effective uptake by proliferating cells) by enzymes associated with the circulatory system. Nucleoside compounds introduced into the circulatory system are rapidly catabolized to inert or harmless compounds by post-aortic enzymes such as those found in the liver thereby reducing the amount of compound available for uptake by proliferating cells. Prior art methods of intra-arterial administration of a nucleoside are useful to treat, detect or diagnose proliferating cells where the cells are upstream of the liver. The nucleoside is effectively degraded by the liver and so is effectively unavailable for uptake into proliferating cells found downstream of the liver.

Numerous diseases are characterized by the proliferative growth of aberrant cells in tissues that normally are not proliferating. Certain medical conditions associated with aberrantly proliferating cells include numerous forms of cancer that are exemplified by tumors, such as those found within the lungs, heart, and aorta. Other medical conditions which exhibit proliferation of cells include atherosclerosis and restenosis, which are causes of coronary heart disease. Accordingly, a need exists for methods by which radionuclide or radio-detectable reagents can be used in diagnosis and treatment of aberrant proliferating cells. More importantly, a need exists to develop methods of targeting effector compounds to proliferating cells without substantial degradation of the effector compounds prior to reaching their intended target and incorporating into dividing cells.

SUMMARY OF THE INVENTION Embodiments of the present invention are based on the discovery that effector compounds, i. e. compounds including a diagnostic and/or therapeutic moiety, normally susceptible to degradation by enzymes associated with the circulatory system can be advantageously administered intravenously and can localize in proliferating cells in effective diagnostic or therapeutic amounts. Effector compounds within the scope of the invention include those that are susceptible to degradation by enzymes associated with the circulatory system and include nucleoside-based compounds and analogs thereof including an effector group, such as a radionuclide moiety.

According to the method of the present invention, an effector compound is administered intravenously to a mammal, including a human patient, and the effector compound contacts proliferating cells prior to contacting an enzyme associated with the circulatory system that degrades the administered effector compound. The proliferating cells are characterized in that they are perfused by the drug-laden blood prior to its passage through the systemic circulation, such as when the proliferating cells are perfused by pre-aortic blood as opposed to post-aortic blood. The administered effector compound is selectively taken up by the proliferating cells, as compared to nonproliferating cells, in an effective diagnostic or therapeutic amount. In the case of an effector compound including a diagnostic moiety or agent, the diagnostic moiety or agent is then detected and optionally measured. In the case of an effector compound including a therapeutic moiety or agent, the therapeutic moiety or agent treats the cell in a manner to reduce or eliminate further growth or proliferation.

According to another aspect of the present invention, a systemically administered effector compound is used to target DNA-synthesizing cells. The DNA-synthesizing cells are characterized in that they are perfused by pre-aortic blood as opposed to post-aortic blood.

The effector compound is selectively taken up by the DNA-synthesizing cells prior to degradation by enzymes associated with the circulatory system.

Embodiments of the present invention are advantageous in that they provide methods for diagnosing or treating proliferating cells perfused with pre-aortic blood which are more effective than existing methods. The methods of the present invention provide for advantageous uptake and selectivity while avoiding disadvantageous degradation of the administered diagnostic or therapeutic agent.

One object of the present invention, therefore, is to improve the efficiency of uptake of effector compounds and, therefore, diagnostic or therapeutic agents, into proliferating cells characterized in that they are perfused with pre-aortic blood. Another object of the present invention is to utilize an intravenous mode of administration to diagnose or treat conditions associated with cell proliferation using compounds normally degraded by enzymes associated with the circulatory system. Another object of the present invention is to provide a method of selectively introducing a diagnostic or therapeutic agent to proliferating cells as compared to surrounding non-proliferating cells.

Other objects, features and advantages of certain embodiments of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTIONS OF THE DRAWINGS In the course of the detailed description of certain preferred embodiments to follow, reference will be made to the attached drawings, in which, Fig. 1 is a graph of the biodistribution of radioactivity in mice bearing subcutaneous LS174T human tumors 24 hours post'25IUdR intravenous injection.

Fig. 2 is a graph of tumor/normal tissue ratios in mice bearing subcutaneous LS174T tumors 24 hours post'ZSIUdR intravenous injection.

Fig. 3 is a graph of the biodistribution of radioactivity in mice bearing 2-week-old lung metastases from LS174T human tumor cells 24 hours post 25IUdR intravenous injection.

Fig. 4 is a graph of tumor/normal tissue ratios in mice bearing 2-week-old lung metastases from LS174T human tumor cells 24 hours post'25IUdR intravenous injection.

Fig. 5 is a graph of the biodistribution of radioactivity in mice bearing 3-week-old lung metastases from LS174T human tumor cells 24 hours post'25IUdR intravenous injection.

Fig. 6 is a graph of tumor/normal tissue ratios in mice bearing 3-week-old lung metastases from LS174T human tumor cells 24 hours post'ZSIUdR intravenous injection.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS The principles of the present invention may be applied with particular advantage to obtain methods for selectively administering effector compounds that include diagnostic and/or therapeutic moieties to cells which are characterized in that they divide and/or proliferate at a rate greater than surrounding cells. According to the present invention, the effector compounds are taken up by the rapidly dividing cells during DNA-synthesis.

Common to all cells which rapidly divide, whether cancerous or not, is the process of DNA synthesis and the uptake of certain compounds, such as nucleosides, nucleotides and analogs thereof. It is to be understood that the present invention includes all cell types which rapidly divide and are capable of incorporating the effector compound into their DNA during DNA synthesis and cell division. Specifically included within the scope of the present invention are tumor cells, i. e. tumors within the lungs, heart and aorta surrounded by normal cells and also vascular smooth muscle cells, the proliferation of which leads to atherosclerosis and/or restenosis.

The compounds of the present invention are characterized in that they are relatively unstable in vivo due to rapid degradation by intracellular mechanisms occurring in post-aortic tissue, such as the liver. According to a preferred embodiment of the present invention, IUdR is a thymidine (TdR) analog in which the 5-methyl group of TdR is replaced by iodine. Since the 5-methyl group and the iodine atom have similar van der Waals'radii, the substituted compound behaves remarkably like TdR. Within the cell, both TdR and IUdR are phosphorylated by thymidine kinase to TdR-monophosphate (dTMP) and IUdR- monophosphate (IdUMP), respectively. The former is then further phosphorylated in a stepwise fashion and is incorporated into the DNA. IdUMP, on the other hand, may either follow the fate of dTMP or be dehalogenated by thymidylate synthetase (TS) to dUMP which is further converted to dTMP via the"de novo"TS-catalyzed reaction. It is important to note that (i) IUdR is taken up by DNA-synthesizing cells at very high rates (10,000-20,000 molecules per second), and (ii) most of the DNA-incorporated IUdR is retained for the cell or its progeny.

The methods of the present invention include contacting rapidly dividing cells with an effector compound in an amount effective to diagnose or treat the cells. The cells are characterized in that they are perfused with pre-aortic blood as distinguished from post-aortic

blood. The compounds are administered intravenously at a point upstream of the rapidly dividing cells. The compounds are selectively taken up by aberrantly proliferating cells as opposed to surrounding cells which are non-proliferating. The compounds then travel post- aorta and are degraded by enzymes such as those found in the liver.

Certain useful compounds according to the present invention include the small molecule compounds of formula I and their analogs Formula I wherein R, is absent or OH; R2 is absent or phosphate;, R3 is absent or phosphate; R4 is absent or phosphate, such that where R2, R3 and R4 is absent, then R, is OH; R5 is H, F, OH or phosphate; R6 is H, F, or OH; and R7 is an effector moiety. Effector moieties within the scope of the present invention include purines such as adenine or guanine or pyrimidines such as cytosine, uracil or thymine which have been modified according to methods well known in the art to include a particular diagnostic or therapeutic group.

Diagnostic or therapeutic groups within the scope of the present invention include radioactive atoms that emit alpha, beta, gamma or positron particles. As used herein, the term"radio-detectable agent"refers to an agent or molecule that is radiolabeled with a gamma-, positron-, Auger electron-, beta-, or alpha-emitting isotope. Alternatively, a"radio- detectable agent"can be an agent or molecule that is labeled with a non-radioactive atom that can be activated by neutron irradiation to emit an alpha particle or that can be activated by external beam photons to emit low-energy Auger electrons.

Certain radioactive atoms within the scope of the present invention are characterized in that they emit particles having an energy sufficient to image photographic film commonly used with external body gamma camera imaging and/or positron emission tomography. Each of external body gamma camera imaging and/or positron emission tomography are methods

well know to those of skill in the art. Certain radioactive atoms useful within the scope of the present invention as diagnostic agents include"C,'3N,'40,'S0,'8F, SBr,'6Br,"Br, $° Br, 122I, 123I, 124I, 126I and 131I. It is to be understood that one of skill in the art would be able to readily identify additional radioactive atoms useful as diagnostic agents based upon the present disclosure.

Therapeutic groups within the scope of the present invention include radioactive atoms commonly used in radiotherapy. Certain radioactive atoms are characterized in that they emit low energy electrons, i. e. those having an energy between about 1 eV and about 1000 eV. Certain other radioactive atoms are characterized in that they emit medium or high energy electrons, i. e. those having an energy between about 1000 eV and about 2,000,000 eV.

Certain radioactive atoms useful as therapeutic agents commonly decay by electron capture and/or internal conversion and, as a result, emit Auger, coster-kronig and/or super coster- kronig electrons. Certain other radioactive atoms are characterized in that they emit high energy alpha particles. Certain radioactive atoms useful within the scope of the present invention as therapeutic agents include 75Br, 76Br, 77Br, 80Br, 80mBr 123I, 125I, 131I, 211At, 212Bi, and 2"Bi.

Therapeutic groups useful within the scope of the present invention also include non- radioactive groups that when irradiated with neutron irradiation result in capture of a neutron and emission of an alpha particle suitable for therapy. Such therapeutic groups include those commonly used with neutron capture therapy such as'°B. Additional therapeutic groups useful within the scope of the present invention further include groups that can be activated by low-energy photons to release Auger electrons commonly known in the art as photon activation therapy. Such groups include"Br and 1211.

According to one aspect of the method of the present invention, the compound of Formula I or an analog thereof is prepared in a pharmaceutically acceptable vehicle and administered intravenously. The compound contacts rapidly dividing cells characterized in that they are perfused with pre-aortic blood as opposed to post-aortic blood."Pre-aortic blood"refers to blood within the circulatory system upstream of the aorta and downstream of the liver."Post-aortic blood"refers to blood within the circulatory system downstream of the aorta and upstream of the liver.

According to one particular aspect of the present invention, the compound of Formula I is administered intravenously at a location such that the compound travels via the circulatory system to the heart, then to the pulmonary artery, perfuse the lungs, travel back through the pulmonary vein to the heart, and finally to the rest of the body through the aorta.

According to this method of the present invention, the compound of Formula I contacts rapidly dividing cells, for example in the form of a tumor, which may be present in the heart and/or lungs prior to degradation by the liver. In this manner, the compound of Formula I is readily taken up by the rapidly dividing cells in a diagnostically or therapeutically useful amount.

One of ordinary skill in the art, however, will recognize that the compounds of Formula I can be administered at any location intravenously depending upon the location of the desired target site of rapidly dividing cells. Accordingly, the present invention includes methods of detecting, diagnosing, and treating aberrant proliferating cells that are associated with cancers and other disease conditions anywhere within the circulatory system where the proliferating cells are characterized by being perfused with pre-aortic blood. It is to be understood that one of ordinary skill in the art will readily identify targeted cells within the scope of the present invention as those which are dividing at a rate in excess of normal cell division which include tumors and which may be associated with certain disease conditions.

For example, coronary heart disease remains the leading cause of death in the United States and is responsible for more than 500,000 deaths annually. The underlying cause of coronary heart disease is coronary atherosclerosis. It is believed that when the intima, i. e. the inner most coating of a blood vessel, is injured, a sequence of reactions begins including platelet aggregation, macrophage accumulation, intimal smooth muscle proliferation, fibrous tissue proliferation and lipid accumulation, all of which result in the development of obstructive atheroma. Repeat intimal injury and cycling of this process lead to further progression of the atheroma and coronary artery occlusion. See Am Heart J 1992: 1106-9; J Heart Lung Transplant 1995; 14: S207-ll ; Am Heart J 1995 ; 129: 791-9 ; Int J Cardiol 1997 ; 62 Suppl 2: S125-34 ; and Ann Thorac Surg 1997; 63: 885-94 each of which are hereby incorporated by reference in their entireties for all purposes. In addition, atherosclerosis and restinosis are characterized by the proliferation of vascular smooth muscle cells. Thromb Haemost 1995; 74: 406-10 ; Micron 1995; 26: 51-68; Semin Thromb Hemost 1996 ; 22: 139-44 ; Int JMol Med

1998; 2: 81-9; Circulation 1998 ; 98: 82-9; Cardiol Rev 1999; 7: 219-31 ; In Vivo 1999; 13: 93-7 each of which are hereby incorporated by reference in their entireties for all purposes. The major factor limiting the long-term success of cardiac transplantation is the development of accelerated arteriosclerosis that occurs in the coronary arteries of the cardiac allograft.

Transplant arteriosclerosis is characterized by diffuse, uniform, concentric narrowing of the artery by a proliferative, fibrocellular intima. See IntJCardiol 1997 ; 62 Suppl 2: S125-34.

The major cause of late death in cardiac transplant recipients is cardiac allograft vasculopathy (i. e., cardiac transplant atherosclerosis), which occurs in 15-20% of transplant recipients, and may be caused by damage to endothelial cells that results in myointimal proliferation. See Am Heart J 1995 ; 129: 791-9.

According to one aspect of the present invention, the methods of the present invention comprise the direct intravenous administration of an effective amount of an antitumor therapeutic or diagnostic dose of radiolabeled nucleotide or nucleoside, such as that identified by formula I, and more specifically 5-iodo-2'-deoxyuridine ('25IUdR, 13'IUdR, or'23IUdR) or 5-astato-2'-deoxyuridine ("'AtUdR). The radiolabeled nucleotide/nucleoside is targeted to a diseased tissue in the patient whereby the diseased tissue contains an aberrant, DNA synthesizing cell population and is characterized by being perfused with pre-aortic blood.

Diseased tissue of this nature includes tumors and cells associated with the disease conditions described above, including but not limited to lung cancer, cancer metastases to the lung, coronary heart disease, atherosclerosis and restinosis.

Upon delivery of the radionuclide to the diseased tissue, the radionuclide may be detected and measured for diagnostic purposes. Alternatively, the radionuclide may serve as a therapeutic agent through incorporation of an effective amount of the radionuclide into the DNA of the aberrant, proliferating cells, such that growth of the cells is inhibited.

The following examples are set forth as representative of the present invention. These examples are not to be construed as limiting the scope of the invention as these and other equivalent embodiments will be apparent in view of the present disclosure, figures, tables, and accompanying claims.

EXAMPLE I Preparation of Compounds of Formula I Compounds within the scope of Formula I are either commercially available or can be readily prepared by those having ordinary skill in the art. Specifically, the preparation of 5-iodo-2'-deoxyuridine (IUdR) is detailed in US Patent No. 5,720,935 hereby incorporated by reference in its entirety. Briefly, IUdR (1.41 mmol, 500 mg) is dissolved in 1,4-dioxane (20 ml) while the flask is maintained at 50°C. After cooling to room temperature (RT), bis (tributyltin) (3.1 mmol, 1.6 ml) and tetrakis (triphenylphosphine) palladium (0) (0.04 mmol, 50 mg) are added and the mixture is heated at 105°C overnight under a stream of nitrogen. the solvent is removed by rotary evaporation and the dark mixture is subjected to flash chromatography (silica gel, chloroform/methanol, 80/20) and TLC (chloroform/methanol, 92/8). The desired product (Rf = 0.23) is obtained as a pale yellow oil (584.1 mg, 80%).

Na"'I (1-100 mCi) is added to a solution of Bu3SnUdR (100pg) in ethyl acetate (100 ul) along with 100 ul of a solution containing 30% hydrogen peroxide/acetic acid (1/3, v/v).

The mixture is vortexed for 15 seconds and 100 ul distilled water are added followed by 100 ut 0. 1 N Hcl. The solution is loaded onto a Sep-Pak C, g cartridge (previously washed with 6 ml methanol followed by 3 x 6 ml water) and the cartridge is eluted with 1 ml water to obtain 25IUdR. The sample is diluted (1 : 1) in 2 x saline and sterilized, e. g. by filtration, prior to administration to a mammal.

It is to be understood that one of skill in the art would be able to prepare other radiolabeled compounds of the present invention within the scope of formula I and their analogs based upon the disclosure presented herein.

EXAMPLE II Uptake of Intravenously Injected Radiolabeled IUdR by Subcutaneous Tumors Studies were conducted to determine the extent of uptake of compounds of Formula I by subcutaneous tumors perfused by post-aortic blood, i. e. where tumor cells are perfused by blood wherein a significant proportion of the compounds have already passed through the liver (i. e. a non-first-pass situation). Specifically, logarithmically growing LS174T human adenocarcinoma cells (2 X 10") were injected subcutaneously into Balb/c nude mice (n = 5).

On Day 8 (when the tumors were approximately 100 mm'), the mice were injected intravenously with 5pCi of'ZSIUdR/100 l saline and were killed 24 hours later. The percent injected dose per gram (% ID/g) of l25I in blood, tumor, and various tissues and organs was determined and tumor/normal tissue (T/NT) ratios were calculated. As shown in Fig. 1, the data indicate that <1% of the injected dose is present per gram of subcutaneous tumor. As shown in Fig. 2, the T/NT ratios of many tissues are <1. The results of Fig. 1 and Fig. 2 confirm that compounds of the present invention administered intravenously are not significantly taken up into tumors that are perfused by post-aortic blood. While not wishing to be bound by scientific theory, it is believed that the compounds are degraded by passage through the liver prior to contact with the tumor tissue.

EXAMPLE III Uptake of IUdR by Two-Week-Old Lung Tumors Following Intravenous Injection Studies were done to determine the extent of uptake of compounds of Formula I into tumor tissue perfused by pre-aortic blood, i. e. blood containing the compounds which has not yet traveled through the liver and has not yet been subjected to enzymatic degradation.

Specifically, logarithmically growing LS174T cells (3 x 106) were injected intravenously through the tail vein of Balb/c nude mice (n=5) to produce two week old lung metastases. On day 14, the mice were injected intravenously with 10 pCi 25IUdRI100, ul saline (5 nontumor- bearing mice were also injected with'25IUdR and served as controls). The animals were killed 24 hours later, the lungs inflated with 0.5 ml phosphate buffered formalin, the radioactivity associated with them and all other tissues was measured in a gamma counter, and the % ID/g and T/NT ratios were calculated. Additionally, the lungs were sectioned (5- am thick) and stained with H&E.

Histology demonstrated the presence of tumor foci within each lung section from tumor-bearing animals (results not shown). Despite the fact that most of the lungs were devoid of tumor, the biodistribution studies, the results of which are shown in Fig. 3, indicate that (i) in the tumor-bearing animals, 12.9 1.4% of the injected dose is present per gram of tumor-containing lungs; (ii) radioactivity is virtually absent from normal (i. e. no tumor) lungs (0.12 0.05% ID/g); and (iii) as expected, all normal tissues have minimal

radioactivity. Consequently, as the data presented in Fig. 4 indicates, extremely favorable T/NT ratios (38-937) are obtained in all tissues. It is important to note that the % ID/g obtained in the lungs of tumor-bearing mice underestimates the true % ID/g since most of the "tumor weight"reflects that of normal lung tissue and not the small masses of tumor cell metastases within. These experimental results demonstrate that IUdR is taken up very rapidly and very efficiently by dividing cancerous cells present within the lungs.

In addition, mice bearing 3-week-old LS174T lung tumor metastases (i. e. in these studies, the tumors are somewhat larger than the 2-week-old tumors) were injected intravenously with 10, uCi'25IUdR/100, ul saline. The animals were killed 24 hours later, and the radioactivity associated with the lungs and all other tissues was measured in a gamma counter, and the % ID/g and T/NT ratios were calculated. The biodistribution studies, the results of which are shown in Fig. 5, indicated that (i) the radioactive content of the lungs in tumor-bearing animals is much higher than that in the lungs of mice bearing 2-week-old tumors (48.8 14.7% ID/g compared 12.9 1.4% ID/g) ; and (ii) all normal tissues have minimal radioactivity (values very similar to those seen in mice bearing-2-week-old lung tumors). Consequently, as shown in Fig. 6, even more favorable T/NT ratios (range: 322-11, 037) are obtained in all tissues. Here again, it is important to recall that the % ID/g obtained in the lungs of tumor-bearing mice underestimates the true % ID/g since more of the"tumor weight"reflects that of normal lung tissue and not the small masses of tumor cell metastases within.

It is to be understood that the embodiments of the present invention which have been described are merely illustrative of some of the applications of the principles of the invention.

Numerous modifications may be made by those skilled in the art based upon the teachings presented herein without departing from the true spirit and scope of the invention.