pyrazofurin and Carcinoma

The combination of pyrazofurin (PF) and 5-azacytidine (5-aza-CR) was evaluated in 12 patients with neoplastic diseases who had failed conventional therapies. They included 6 patients with acute myelocytic leukemia (AML) and 6 with various carcinomas. PF was given by i.v. bolus at doses ranging from 25 to 200 mg/m2 followed by 5-aza-CR given by continuous 24-hour infusion at doses ranging from 30 to 120 mg/m2/24 h during 40-ic diseases who had failed conventional therapies. They included 6 patients with acute myelocytic leukemia (AML) and 6 with various carcinomas. PF was given by i.v. bolus at doses ranging from 25 to 200 mg/m2 followed by 5-aza-CR given by continuous 24-hour infusion at doses ranging from 30 to 120 mg/m2/24 h during 40-ic diseases who had failed conventional therapies. They included 6 patients with acute myelocytic leukemia (AML) and 6 with various carcinomas. PF was given by i.v. bolus at doses ranging from 25 to 200 mg/m2 followed by 5-aza-CR given by continuous 24-hour infusion at doses ranging from 30 to 120 mg/m2/24 h during 40--120 h. Dose-limiting toxicity was mucocutaneous, which appeared in 11/17 courses. Skin rash was similar to that produced by PF alone, but was present after much lower doses of PF when followed by 5-aza-CR. Moderate and reversible thrombocytopenia and leukopenia occurred in 3/6 patients with carcinoma. No objective response was seen in patients with carcinoma, and no marrow remission occurred in patients with AML. 24-Hour urinary excretion of orotidine and oroticacid were measured during 11 courses in 8 patients, and were not much different than those obtained previously with PF alone. The occurrence of mucocutaneous toxicity precluded the use of higher doses of PF and 5-aza-CR, which might have been therapeutically more active.

Topics: Adenocarcinoma; Adult; Aged; Amides; Azacitidine; Carcinoma; Carcinoma, Small Cell; Drug Therapy, Combination; Female; Humans; Leukemia, Myeloid; Lung Neoplasms; Male; Middle Aged; Pyrazoles; Ribonucleosides; Ribose

Variants of the Lewis lung carcinoma were selected for resistance to N-(phosphonacetyl)-L-aspartic acid (PALA) by treatment of tumor-bearing mice with repetitive subcurative doses of PALA. The specific activity of the target enzyme, L-aspartic acid transcarbamylase (ATCase), was measured in the four variants developed. Three had markedly elevated ATCase activities; however, the fourth line, LL/PALA-C, had an ATCase activity identical to that of the parent, PALA-sensitive line (LL/O). One high-ATCase variant, LL/PALA-J, and LL/PALA-C were compared with LL/O in subsequent biochemical studies on the mechanism of resistance to PALA. Enzyme activities in the salvage pathways which phosphorylate pyrimidine nucleosides and deoxynucleosides were found to be similar in all three lines. ATCase in these lines exhibits closely comparable kinetics with its natural substrates as well as with PALA. The time courses of restitution of ATCase after a single therapeutic dose of PALA show that both resistant variants recover full activity more rapidly than the parent. Additionally, inhibition of ATCase 24 hr following graded doses of PALA is lower in the resistant lines. The uptake of [14C]PALA in vitro into cell lines derived from the three Lewis lung carcinomas apparently occurs by passive diffusion and at comparable rates in both sensitive and resistant cells. Analysis of the nucleotide content of tumors reveals comparable spectrums of purine and pyrimidine nucleotide levels in the LL/O and LL/PALA-C lines, whereas the LL/PALA-J line has augmented nucleotide pools. In all three lines, 24 hr after treatment with PALA (400 mg/kg), uridine and cytidine nucleotide levels were substantially diminished (70 to 80%) while adenosine 5'-triphosphate and guanosine 5'-triphosphate levels were elevated (50 to 100%). Estimations of precursor flux through the de novo pyrimidine pathway by measuring orotate and orotidine levels in tumors of mice treated with pyrazofurin (an inhibitor of orotidine-5'-monophosphate decarboxylase) and either 0.9% NaCl solution or PALA shows that PALA treatment eliminates orotate and orotidine accumulation in LL/O but reduces it by only 75 and 50% in LL/PALA-C and LL/PALA-J, respectively. Similarly, PALA treatment (20 microM) of tumor lines in culture provokes a dramatic decrease in the incorporation of NaH14CO3 into pyrimidine intermediates and nucleotides in the LL/O cell line only. Determinations of specific activities of the other enzymes in this pathway

Topics: Amides; Animals; Aspartate Carbamoyltransferase; Aspartic Acid; Carcinoma; Cell Line; Dose-Response Relationship, Drug; Drug Resistance; Lung Neoplasms; Mice; Neoplasms, Experimental; Orotic Acid; Phosphonoacetic Acid; Pyrazoles; Pyrimidines; Ribonucleosides; Ribose