tezacitabine and Colonic-Neoplasms

Tezacitabine is a nucleoside analogue characterized by a dual mechanism of action. Following intracellular phosphorylation, the tezacitabine diphosphate irreversibly inhibits ribonucleotide reductase, while the tezacitabine triphosphate can be incorporated into DNA during replication or repair, resulting in DNA chain termination. In the present study we have investigated the effect of the combination of tezacitabine and 5-fluorouracil (5-FU) or 5-fluoro-2'-deoxyuridine (FUdR) on HCT 116 human colon carcinoma cells and xenografts. We used response surface analysis (RSA) and clonogenic assay to evaluate combination effects of tezacitabine and 5-FU. Tezacitabine is antagonistic when combined with 5-FU in the RSA assay and does not effect the clonogenicity of HCT 116 cells when compared with cells treated with 5-FU alone. However, when combined sequentially with FUdR, tezacitabine leads to potentiation of cell killing in the clonogenic assay, additivity in the RSA assay, and increased apoptosis when compared to FUdR alone, suggesting that cytotoxicity of fluoropyrimidines such as FUdR that have more DNA-directed effects can be potentiated by tezacitabine. We also report that oral administration of the fluoropyrimidine capecitabine, an oral prodrug of 5-FU, in combination with tezacitabine shows statistically significant additivity in the HCT 116 xenograft model. This interaction may be explained by the finding that tezacitabine elevates activity of thymidine phosphorylase (TP), the enzyme required for activation of the capecitabine prodrug in tumors. Our results provide evidence that tezacitabine enhances the DNA-directed effects of fluoropyrimidines in human colon cancer cells and may modulate the antitumor activity of fluoropyrimidines.

Topics: Apoptosis; Cell Line, Tumor; Colonic Neoplasms; Deoxycytidine; DNA; DNA Damage; Floxuridine; Fluorouracil; Humans; Thymidine Phosphorylase; Thymidylate Synthase; Transplantation, Heterologous

(E)-2'-deoxy-2'-(fluoromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide-diphosphate reductase, has been shown to have anti-tumor activity against solid tumors and sensitize tumor cells to ionizing radiation. Pentoxifylline (PTX) can potentiate the cell killing induced by DNA-damaging agents through abrogation of DNA-damage-dependent G2 checkpoint. We investigated the cytotoxic, radiosensitizing and cell-cycle effects of FMdC and PTX in a human colon-cancer cell line WiDr. PTX at 0.25-1.0 mM enhanced the cytotoxicity of FMdC and lowered the IC50 of FMdC from 79 +/- 0.1 to 31.2 +/- 2.1 nM, as determined by MTT assay. Using clonogenic assay, pre-irradiation exposure of exponentially growing WiDr cells to 30 nM FMdC for 48 hr or post-irradiation to 0.5 to 1.0 mM PTX alone resulted in an increase in radiation-induced cytotoxicity. Moreover, there was a significant change of the radiosensitization if both drugs were combined as compared with the effect of either drug alone. Cell-cycle analysis showed that treatment with nanomolar FMdC resulted in S-phase accumulation and that such an S-phase arrest can be abrogated by PTX. Treatment with FMdC prior to radiation increased post-irradiation-induced G2 arrest, and such G2 accumulation was also abrogated by PTX. These results suggest that pharmacological abrogation of S and G2 checkpoints by PTX may provide an effective strategy for enhancing the cytotoxic and radiosensitizing effects of FMdC.

Topics: Antineoplastic Agents; Cell Cycle; Cell Survival; Cesium Radioisotopes; Colonic Neoplasms; Deoxycytidine; DNA Damage; Dose-Response Relationship, Drug; Dose-Response Relationship, Radiation; G2 Phase; Humans; Pentoxifylline; Radiation-Sensitizing Agents; S Phase; Tumor Cells, Cultured

Antitumor and radiosensitizing effects of (E)-2'-deoxy-2'-(fluromethylene) cytidine (FMdC), a novel inhibitor of ribonucleotide reductase, were evaluated on nude mice bearing s.c. xenografts and liver metastases of a human colon carcinoma. FMdC given once daily or twice weekly has a dose-dependent antitumor effect. The maximum tolerated dose in the mice was reached with 10 mg/kg applied daily over 12 days. Twice weekly administration of FMdC reduced its toxicity but lowered the antitumor effect. Treatment of preestablished liver micrometastases obtained via intrasplenic injection of tumor cells, with 5 or 10 mg/kg FMdC, significantly prolonged the survival of the mice as compared to controls (P < 0.025 and P < 0.001, respectively). Ten mg/kg resulted in longer survival than 5 mg/kg FMdC (P < 0.05). Radiotherapy alone of s.c. xenografts (10 fractions over 12 days) yielded the radiation dose required to produce local tumor control in 50% of the treated mice (TCD50) of 43.0 Gy. When combined with FMdC, TCD50 was reduced to 22.5 and 19.0 Gy at doses of 5 and 10 mg/kg given i.p. 1 h before each irradiation, respectively. The corresponding enhancement ratios were 1.91 and 2.43, respectively. FMdC produced moderate and reversible myelosuppression. When 5 mg/kg FMdC was combined with irradiation, there was no increased skin or hematological toxicity as compared to radiotherapy or FMdC alone. At the 10 mg/kg level, however, lower leukocyte counts were observed. These results show that FMdC appears to be a potent anticancer drug and radiosensitizer.

Topics: Animals; Antineoplastic Agents; Carcinoma; Colonic Neoplasms; Deoxycytidine; Humans; Injections, Intraperitoneal; Injections, Intravenous; Leukocyte Count; Liver Neoplasms; Mice; Mice, Nude; Neoplasm Metastasis; Neoplasm Transplantation; Radiation-Sensitizing Agents; Ribonucleotide Reductases; Survival Analysis; Transplantation, Heterologous