Combination antitumor effect with central nervous system depressants on rat ascites hepatomas

Combined effect of twenty-one central nervous system depressants with several antitumor agents was studied in the in vitro and in vivo experimental systems, using rat ascites hepatoma call lines, AH13 and AH44, sensitive and insensitive to alkylating agents, respectively. Reserpine remarkably enhanced the cytotoxic effect of 1-(gamma-chloropropyl)-2-chloromethylpiperidine hydrobromide (CAP-2) both on AH13 and AH44 cells. In the in vivo combined experiments, reserpine also synergistically enhanced the life-prolonging effect of CAP-2 on AH13-bearing rats and, although CAP-2 was not potent on the prolongation of life span of AH44-bearing rats and reserpine was also ineffective at the doses examined, the life span of tumor-bearing rats receiving the combined administration was apparently prolonged compared with control groups. Thus, there was a parallelism between in vitro and in vivo experiments. These findings suggested that the antitumor-enhancing effect of reserpine might be due to the direct action on the tumor cells, and a possible mechanism that reserpine inhibited the DNA damage-repairing activity of the cells was contradictory. Other mechanisms are also discussed.