New folate analogs of the 10-deaza-aminopterin series. Further evidence for markedly increased antitumor efficacy compared with methotrexate in ascitic and solid murine tumor models

A group of folate analogs of the 10-deaza-aminopterin series, which were designed on the basis of the results of an intensive biochemical and pharmacokinetic program, have been examined in therapy experiments utilizing a group of murine tumor models. These new analogs were found to be markedly superior to methotrexate against four of five ascites tumors (L1210 leukemia, Sarcoma 180, Ehrlich carcinoma and Tapper carcinosarcoma) and against four of five solid tumors (S180, Tapper carcinosarcoma, E0771 mammary adenocarcinoma, Lewis lung carcinoma, and T241 sarcoma). Analogs alkylated (methyl or ethyl) at the 10 position of 10-deaza-aminopterin were found to be the most effective of the group. These analogs achieved log10 reduction in tumor burden several-fold greater in magnitude than methotrexate against L1210 and S180 ascites tumors and there were also long-term survivors. 10-Deaza-aminopterin itself gave a result intermediate between those obtained with the 10-alkyl derivatives and methotrexate. Against the solid forms of the Tapper tumor some partial regressions were obtained with methotrexate and 10-deaza-aminopterin, but a far greater number, extending over a longer period were obtained with the 10-ethyl derivative of 10-deaza-aminopterin. Against the E0771 tumor, 10-deaza-aminopterin was 2-fold and the ethyl derivative of 10-deaza-aminopterin was greater than 5-fold more effective than methotrexate in retarding tumor growth. Evidence for partial regressions and marked effects against metastatic disease were also obtained in the case of the 10-alkyl derivative. Similar results were also obtained with the T241 sarcoma. For Lewis lung carcinoma the relative potency was about the same but overall antitumor effects were more modest.