The roles of various biochemical effects produced by 5-fluorouracil in early growth inhibition of Bacillus cereus

Chemotherapeutic Efficacy of 5-Fluorouracil with Concurrent Thymidine Infusion against Transplantable Colon Tumors in Rodents

The therapeutic efficacy of 5-fluorouracil (FU) given concomitantly with thymidine (TdR) versus that of FU alone at an equitoxic dose was evaluated when these agents were given by 72-h continuous i.v. infusion or as an i.v. push dose through the tail vein to Fischer rats bearing a transplantable colon carcinoma or to BALB/c or C57BL/6J mice bearing murine colon tumors no. 26 or 38, respectively. In the presence of TdR, the dose of FU maximally tolerated by normal rats and mice was reduced by approximately half. In tumor-bearing rats, infusion of FU alone (150 mg/kg X 72 h) was as effective as concurrent infusion of FU (100 mg/kg X 72 h) with TdR (5 g/kg X 72 h), as evaluated in terms of tumor-free survivors (7/22 and 6/20, respectively). In addition, both regimens were more effective than an i.v. push dose of FU (200 mg/kg) or FU (80 mg/kg) and TdR (2 g/kg), which resulted in 2/18 and 0/18 tumor-free survivors, respectively. No significant differences in tumor growth inhibition were seen using either murine colon tumor, whether FU or the FU with TdR combination was administered as an i.v. push dose or as an infusion. Quantitation of the levels of TdR and thymine (T) in rat plasma obtained during infusion of various doses of TdR showed dose-dependent levels of TdR and T, indicating conversion of TdR to T in vivo. These data showed that, under the conditions employed, TdR did not modify significantly the antitumor activity of FU against rodent colon tumors. The toxicity of FU, however, could be enhanced by the coadministration of TdR, probably due, in part, to a reduced degradation of FU resulting from competition by T.

Treatment of cultured human colon carcinoma cells with fluorinated pyrimidines

The shape of the initial part of the dose-dependent response curve of LoVo cells, an established human colon carcinoma cell line, exposed for 1 hr to graded concentrations of 5-FU depended on the medium supplement, i.e., fetal calf serum (FCS), in which the cells were treated and subsequently incubated for colony-formation. At concentrations of 50--100 micrograms/ml (equivalent to peak plasma levels following an in vivo bolus dose of 15 mg/kg) cell kill was completely prevented by FCS. The serum did not contain thymidine (TdR) but had significant amounts of uridine (UR). When 5-FU was delivered in dialyzed FCS, concentrations of 50--100 micrograms/ml achieved only a modest 15% cell kill after 1 hour treatment. Regardless of medium supplement, the killing effect of 5-FU did not increase beyond concentrations greater than 2,000 micrograms/ml. Increasing the exposure interval dramatically increased the killing of LoVo cells by 5-FU, although the effects of medium supplement on the degree of cell survival persisted for about 12 hours. Virtually all of the incorporated 5-FU was transformed into 5-FUR, and a very small proportion eventually was incorporated into nucleic acids, suggesting that the killing effect of 5-FU on LoVo cells is mediated mostly by ribosidation and not by conversion into the deoxyribonucleoside. This conclusion is supported by the failure of 5-FUdR to kill LoVo cells after a treatment interval of one hour, even at concentrations of 5000 micrograms/ml; yet after the same exposure interval, 5-FUR effectively killed cells at concentrations of 50--100 micrograms/ml. TdR afforded no protection from cell kill by 5-FU. In contrast, UR was capable of protecting LoVo cells from the lethal effects of both 5-FU and 5-FUR even at concentrations as low as 10 micrograms/ml. Ftorafur exposed to LoVo cells for 1 hour had a slight killing effect (about 20--25%) at concentrations ranging up to 2000 micrograms/ml. Although the lethal effect of ftorafur was slightly increased after longer periods of incubation, it failed to reach 90% even after intervals of 48 hours. The results on cellular sensitivity that we obtained for LoVo cells treated with various fluorinated pyrimidines differ substantially from those of other investigators who used different methods to assess cell killing on nonhuman and noncolonic cell systems. The predictive relevance of these data as compared to those obtained in other systems is justified by the suboptimal results with these agents in clinical practice.