pyrazofurin and Sarcoma-180

The expression of plasminogen activator activity (PA) by L1210 leukemic ascitic cells, obtained from the peritoneum of BDF1 mice, increases in the terminal stages of the disease. Treatment of mice carrying advance leukemia (day 6 following inoculation with 10(6) cells i.p.) with 6-azauridine (AzUR) results in prolonged survival (2-3 days) and also in increased expression of PA activity by the ascitic cell population. Similar treatment with pyrazofurin (PF), another inhibitor of orotidylate decarboxylase and of de novo pyrimidine synthesis, fails to produce either of these effects. Neither AzUR or PF, given at the early stage of tumor growth (day 3), extend the life span nor do they cause increase of the PA activity. Thus, the elevation in PA activity following treatment with AzUR is associated with the asymptotic stage of the disease and this phenomenon correlates positively with the life-prolonging effects of this drug. An analysis of the PA activity elicited by intact cells, secretions, and cellular digests suggests that most of the activity originates on the surface of the cells. The results indicate that the described in vivo effect of AzUR, but not that of PF, on late-stage leukemia, is mediated by the changes in the fibrinolytic potential of the tumor or host cells rather than through the inhibition of the de novo pyrimidine synthesis.

Topics: Amides; Animals; Azauridine; Female; Fibrinolysis; Leukemia L1210; Mice; Mice, Inbred Strains; Orotidine-5'-Phosphate Decarboxylase; Plasminogen Activators; Pyrazoles; Pyrimidines; Ribonucleosides; Ribose; Sarcoma 180; Time Factors

Pyrazofurin, an inhibitor of orotidylate decarboxylase, imposes an absolute nutritional requirement for exogenous uridine to maintain normal growth of L5178Y, P388, L1210, W256 and S180 cells in vitro. The amount of uridine necessary for cell division when de novo uridine nucleotide synthesis is inhibited by pyrazofurin is: L5178Y, 30.5; P388, 39.7; L1210, 53.3: W256, 70.6; and S180, 886 fmol/cell. Cytidine, which can be deaminated to uridine, will substitute for uridine to maintain normal cell growth in the presence of growth-inhibitory concentrations of pyrazofurin (5 microM). The requirements for cytidine and uridine are identical. If cytidine deamination is prevented by tetrahydrouridine (100 microM), cytidine can no longer support growth in the presence of pyrazofurin. Cytidine and uridine, as expected, are additive in their effect to permit normal growth of pyrazofurin treated cells. Tetrahydrouridine does not alter this additive effect, indicating that when both nucleotides are added to pyrazofurin treated cells each nucleotide replenishes their respective nucleotide pools and cytidine deamination is unnecessary to allow cell growth. Incorporation of [14C]uridine into the acid insoluble cell fraction of L5178Y cells was 25 fmol/cell at 48 h and remained constant during the remaining growth of the pyrazofurin treated cell suspension. The [14C]uridine acid soluble pool of 4 fmol/cell also was maximum at 48 h but declined during the subsequent growth of the suspension culture to approx. 2 fmol/cell at 96 h. This decline in the acid soluble pool is correlated with a 42% decrease in modal cell volume during this phase of cell growth which would maintain a constant specific activity of uridine in this pool. This may explain the decline in the acid soluble pool while the acid insoluble pool remains constant during growth of suspension cultures of L51878Y cells. The block in pyrimidine synthesis de novo induced by pyrazofurin provides a useful and quick method for the evaluation of uridine and cytidine metabolism of tumor cell specimens.

Topics: Amides; Animals; Carcinoma 256, Walker; Cells, Cultured; Cytidine; Leukemia L1210; Leukemia L5178; Leukemia P388; Mice; Neoplasms, Experimental; Pyrazoles; Pyrimidines; Ribonucleosides; Ribose; Sarcoma 180; Uridine