Mechanisms of the cytotoxic actions of tumor necrosis factor (TNF) in cultured cancer cells

Tumor necrosis factor's (TNF) cytotoxic mechanism of action was examined using cultured cancer cell lines. TNF demonstrated cytolytic and cytostatic effects on L929 fibrosarcoma and MCF-7 adenocarcinoma cells. TNF failed to show any specific effects on RNA, DNA or protein synthesis or ATP content in tumor cells in vitro. It did not cause DNA single strand breaks. Decreased cellular levels of reduced thiols did not predict sensitivity to the cytotoxic effects of TNF. Depletion of cellular glutathione failed to increase the sensitivity of TNF-sensitive or resistant cells. However, various non-specific and specific lysosomotropic agents lead to an inhibition of TNF's cytotoxic action. Differences in enzyme activity, primarily lysosomal, were noted between TNF-sensitive and resistant cells. These changes involved a general halving of lysosomal proteins and enzymes in the TNF-resistant cells. The antitumor activity of TNF does not involve specific inhibition of macromolecular synthesis but may involve alterations in lysosomes