Antitumor Effects of Kethoxal-Bis(Thiosemicarbazone) and 6-Mercaptopurine in Neonatally Thymeetomized Mice. ∗

Summary

The incidence of complete regression of Sarcoma 180 induced by treatment with kethoxal-bis(thiosemicarbazone) and 6-mercaptopurine was greatly reduced in neo-natally thymectomized but not in neonatally splenectomized animals. The inhibition of tumor growth observed at the end of treatment was not affected by neonatal surgery per se. In contrast, the delayel retardation of tumor growth seen in treated intact mice 2 to 4 weeks after implantation was significantly reduced in neonatally thymectomized animals. The survival of allogeneic skin grafts was only slightly prolonged in intact animals by treatment with the two drugs at doses capable of inducing therapeutic effects on Sarcoma 180. In neonatally thymectomized mice treated with the drugs, however, survival of the skin graft was substantially prolonged. These results indicate that, in intact animals implanted with Sarcoma 180, kethoxal-bis(thio-semicarbazone) and 6-mercaptopurine exert therapeutic effects by impairing the growth of the tumor selectively, thus permitting the immunological defenses of the host to bring about the complete regression of the chemo-therapeutically impaired tumors.