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Increased Immunosensitivity in Nitrogen Mustard-resistant Yoshida Sarcoma¹

Division of Cancer Chemotherapy, Cancer Institute, 1-37-1 Kami-Ikebukuro, Toshima-ku, Tokyo 170, and Tokyo Biochemical Research Institute, 3-41-8 Takada-Minami-cho, Toshima-ku, Tokyo 170, Japan

Yoshida sarcoma cells acquired resistance to nitrogen mustard on repeated in vitro contact with the agent. When rats were inoculated s.c. with these highly resistant Yoshida sarcoma cells (resistance index, 2500) and not treated, initial tumor growth was followed by regression and all of the animals survived. Inoculation was made into the right hind footpad, a site favorable for the experimental induction of lymph node and organ metastases. Among these animals, the size of the right foot enlarged, accompanying lymph node metastasis, but the tumors began to regress starting about 2 weeks after inoculation and disappeared completely after 1 month. With antiserum or peritoneal lymphoid cells obtained from rats immunized with either drug-sensitive or -resistant Yoshida sarcoma cells, it was found that the immunosensitivity of drug-resistant Yoshida sarcoma cells increased in comparison with the cells of the original sensitive line. It is suggested that increased immunosensitivity could account for the observation of greater chemotherapeutic response to 6-mercaptopurine for rats inoculated i.p. with resistant Yoshida sarcoma cells as compared with those inoculated with the original sensitive line.

¹ This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Japan.

Received 9/ 8/72. Accepted 1/29/73.