5-fluoro-2--deoxycytidine and 5-chloro-2--deoxycytidine

To extend our findings in previous radiation and biochemical studies with five rodent tumors, in which we used one and occasionally two or three irradiations. The extent of control of the EMT-6 mammary adenocarcinoma was determined using fractionated radiation (12 irradiations) over a 3-week period using the radiosensitizer 5-chloro-2'-deoxycytidine (CldC) and biomodulators of its metabolism: N-(Phosphonacetyl)-L-aspartate (PALA), tetrahydrouridine and 5-fluoro-2'-deoxycytidine (FdC).. Mammary adenocarcinoma EMT-6 tumors implanted 1 week prior to therapy in BALB/c mice were subjected to single daily doses of focused radiation, not exceeding a total of 60 Gy, on days 2-5 of each week. N-(Phosphonacetyl)-L-aspartate (PALA) was administered on the first day of therapy. Five-fluoro-2'-deoxycytidine and CldC were administered in the morning and afternoon, respectively, of the next 2 days, and CldC was administered on the fourth day. Tetrahydrouridine was always coadministered with FdC or CldC. Drug and radiation treatments overlapped for 3 weeks.. Fifty to 80% cures (usually 70%) were obtained with no apparent morbidity and the same moderate weight loss that occurs with radiation alone. Neither tumor regrowth delay nor cures were obtained with drugs or radiation alone. An apparent threefold dose increase effect was obtained with the end point: "days to reach 4 times initial tumor volume." Increasing the radiation dose threefold (without drugs) resulted in four out of five deaths; increasing the dose twofold (without drugs) resulted in extensive weight loss and hair loss in the entire ventral area and no cures. Increasing the dose of drugs or radiation 1.5-fold, in the complete protocol, did not result in increased morbidity. Comparative studies with Iododeoxyuridine demonstrate the heightened efficacy of CldC.. One cannot achieve the same results obtained with CldC and the modulators by merely increasing the dose of radiation. There is a significant window of safety in this approach. The evidence we have obtained with EMT-6, the fifth rodent tumor we have studied with CldC, as well as the demonstrated and proposed reasons for its superior efficacy over 5-Iododeoxyuridine (and 5-Bromodeoxyuridine), drugs in current use, indicate that CldC will allow more aggressive treatment of human tumors with radiation than is now feasible.

Topics: Adenocarcinoma; Animals; Aspartic Acid; Body Weight; Deoxycytidine; Idoxuridine; Mammary Neoplasms, Experimental; Mice; Mice, Inbred BALB C; Phosphonoacetic Acid; Radiation-Sensitizing Agents; Radiotherapy Dosage; Tetrahydrouridine

Bolus doses of 5-chlorodeoxycytidine (CldC) administered with modulators of pyrimidine metabolism, followed by X-irradiation, resulted in a 2-fold dose increase effect against RIF-1 tumors in C3H mice. Pool size studies of the fate of [14C]-CldC in BDF1 mice bearing Sarcoma-180 tumors, which demonstrated the rapid formation of 5-chlorodeoxycytidylate (CldCMP), and incorporation of CldC as such in RIF-1 tumor DNA, indicate that CldC is a substrate for deoxycytidine kinase, as our past Km studies have shown. Our data indicate that 5-chlorodeoxyuridine triphosphate (CldUTP) accumulates from both the cytidine deaminase-thymidine kinase pathway, as well as from the deoxycytidine kinase-dCMP deaminase pathway, in tumor tissue. As shown in a previous study, tetrahydrouridine (H4U), a potent inhibitor of cytidine deaminase, can effectively inhibit the enzyme in the normal tissues of BDF1 mice. When H4U was administered with the modulators N-(phosphonacetyl)-L-aspartic acid (PALA) and 5-fluorodeoxycytidine (FdC), the levels of CldC-derived RNA and DNA directed metabolites increased in tumor and decreased in normal tissues compared to when CldC was administered alone. These modulators inhibit the de novo pathway of thymidine biosynthesis, lowering thymidine triphosphate (TTP) levels, which compete with CldUTP for incorporation into DNA. 5-Benzylacyclouridine (BAU), an inhibitor of uridine phosphorylase, was also utilized. DNA incorporation studies using C3H mice bearing RIF-1 tumors showed that the extent of incorporation of 5-chlorodeoxyuridine (CldU) into DNA correlates with the levels of cytidine and dCMP deaminases; this is encouraging in view of their high activity in many human malignancies and the low activities in normal tissues, including those undergoing active replication. Up to 3.9% replacement of thymidine by CldU took place in RIF-1 tumors, whereas incorporation into bone marrow was below our limit of detection. CldC did not result in photosensitization under conditions in cell culture in which radiosensitization to X rays was obtained. Thus, the combination of CldC with modulators of its metabolism has potential as a modality of selective radiosensitization for ultimate clinical use in a wider range of tumors than those of the brain.

Topics: Animals; Aspartic Acid; Combined Modality Therapy; Cytidine Deaminase; Deoxycytidine; DNA, Neoplasm; Drug Therapy, Combination; Mice; Mice, Inbred C3H; Phosphonoacetic Acid; Radiation-Sensitizing Agents; Sarcoma, Experimental; Tetrahydrouridine; Uracil; Uridine Phosphorylase