pyrazofurin and ritrosulfan

The purpose of this study was to test for a possible synergism in the antitumor action of the antimetabolite pyrazofurin (PF) and the alkylating agent lycurim (LY) [1,4-di(2'-mesyloxy-ethylamino)-1,4-dideoxy-m-erythritol dimethylsulfonate] on proliferating and resting rat hepatoma 3924A cells in tissue culture. Earlier studies showed that PF killed hepatoma cells only in the logarithmic phase of growth as determined by colony-forming ability. Now we report that LY killed hepatoma cells in both the exponential and plateau phases. Treatment of cultures in each phase for 1 or 2 hrs resulted in threshold exponential type dose-response curves, yielding Do values of 3 and 1 microM, respectively. LY is a cycle-specific drug, although fluctuations in cell age-dependent survival were also demonstrated. In synchronized cultures, cells were most sensitive to 0.1 microM LY in early G1 phase, but in higher concentration (5 microM), LY killed the cells during the entire cell cycle, especially in G1, early and mid S phases, and M phase. Lycurim and PF given together in their IC50 concentrations (0.016 and 0.085 microM, respectively) yielded synergistic cell kill in 7-day treatment of proliferating cultures. Two-hour treatment of exponentially growing cells with LY and PF at their IC50 concentrations (1 and 20 microM, respectively) also yielded synergistic killing action, but in plateau-phase cells only summation was observed. Synergistic activity of LY and PF in hepatoma 3924A cells was dependent on drug concentration and incubation time.

Topics: Amides; Animals; Cell Cycle; Cell Line; Cell Survival; Chemical Phenomena; Chemistry; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Drug Stability; Drug Synergism; Erythritol; Kinetics; Liver Neoplasms, Experimental; Pyrazoles; Rats; Ribonucleosides; Ribose

Hepatoma 8999 was sensitive to Lycurim [1,4-di-(methylsulfonyloxy-ethylamino)-1,4-dideoxy-ms-erythritol] with a mean lethal dose (LD50) of 8.1 X 10(-8) M for a 6-hour treatment in vitro. The drug dose lethal to 10% of the rats with Lycurim (10 mg/kg) injected ip 12 times into hepatoma 8999-bearing BUF rats at 10-day intervals provided a mean increase in life-span (ILS) of 156%. The more rapidly growing, less differentiated hepatoma 3924A was tenfold less sensitive to Lycurim in vitro, and three treatments in vivo (10 mg/kg given every 8 days) gave an ILS of only 18% in ACI/N rats. Because hepatoma 8999 had a high adenosine kinase activity, the effect of Pyrazofurin (PF; 3-beta-D-ribofuranosyl-4-hydroxypyrazole-5-carboxamide) was examined in vitro: The LD50 was 8.5 X 10(-8) M in a 6-hour exposure. In hepatoma 3924A, with a fifteenfold lower adenosine kinase, the LD50 was 22-fold higher. Three treatments with PF (4 mg/kg given every 2 days) in hepatoma 8999 caused an 18% ILS and no host toxicity, but in hepatoma 3924A no significant ILS was observed. Lycurim combined with PF (0.05 microM each) in hepatoma 8999 cells in vitro provided synergistic kill, but Lycurim and PF (0.3 and 1 microM, respectively) in hepatoma 3924A cells yielded summation. When 10 rats with hepatoma 8999 were treated 15 times with the optimal dose of Lycurim (7.5 mg/kg every 10 1/2 days), 1-year survivors numbered 7. Alternate doses of Lycurim (7.5 mg/kg) and PF (3 mg/kg) at 5-day intervals for 4 months to 10 rats gave an ILS of 152% with eight 1-year survivors and no host toxicity.

Topics: Adenosine Kinase; Amides; Animals; Antimetabolites, Antineoplastic; Cell Line; Cell Survival; Cells, Cultured; Drug Administration Schedule; Drug Evaluation, Preclinical; Drug Therapy, Combination; Erythritol; Lethal Dose 50; Liver Neoplasms, Experimental; Pyrazoles; Rats; Ribonucleosides; Ribose