Recombinant human tumor necrosis factor-α: evidence of an indirect mode of antitumor activity

The antitumor activity of recombinant human tumor necrosis factor (rTNF-α) was examined on murine tumors in mice and in cultured cells in vitro . Mice were implanted intradermally with Meth A fibrosarcoma (Meth A) on day 0. rTNF-α caused tumor necrosis and inhibited the tumor growth when given i.v. on day 7 or 10, but not when given on day 3. When rTNF-α was given i.v. in doses of 0.1–3.2 µg/mouse twice a week for 3 weeks beginning on day 7 or 11, the growth of solid Meth A, Colon 26 adenocarcinoma, Colon 38 carcinoma, Sarcoma-180, and M5076 reticulum cell sarcoma tumors implanted s.c. or intradermally was markedly inhibited, and the life of the mice bearing these tumors, except M5076 reticulum cell sarcoma, was prolonged. The growth of Meth A implanted i.m. was also markedly inhibited by rTNF-α given i.v. However, the life of mice bearing i.p. Colon 26 adenocarcinoma, MH134 hepatoma, Sarcoma-180, and Ehrlich carcinoma was not prolonged by rTNF-α given i.p. nine times (days 1–9) in doses up to 1.0 or 3.2 µg/mouse. Only in the case of mice bearing i.p. Meth A, the life was slightly prolonged by i.p. treatment with rTNF-α but not by i.v. treatment. In experiments against in vitro cultured cells, rTNF-α did not show any direct cytotoxicity against mouse tumor cells: Meth A, Colon 26 adenocarcinoma, Colon 38 carcinoma, and Sarcoma-180, but had a cytotoxic effect against L929 mouse fibroblast. The results suggest that rTNF-α is a unique antitumor drug with potent necrotizing activity against solid tumors in mice, and that this activity may derive from indirect mechanisms related to the growth of tumors and not to the direct cytotoxicity of the drug.