Involvement of the mitochondrion respiratory chain in the synergy achieved by treatment of human ovarian carcinoma cell lines with both tumor necrosis factor-alpha and cis-diamminedichloroplatinum.

BACKGROUND

Previous studies have demonstrated that treatment of human tumor cell lines with a combination of cis-diamminedichloroplatinum (CDDP) and tumor necrosis factor-alpha (TNF-alpha) results in additive/synergistic cytotoxic effects and reverses tumor cell resistance to TNF drugs. Free radical intermediates are induced by both TNF-alpha and CDDP; however, the role of free radicals in synergy is not known. This study investigated the effect of two inhibitors on synergy, phenoxan (Phe) and butylated hydroxyanisole (BHA), which inhibit Complex I and Complex I and II of the mitochondrion respiratory chain, respectively.

METHODS

Three human ovarian carcinoma cell lines of different sensitivity to TNF-alpha and/or CDDP were selected for the study and consisted of 222, a TNF/CDDP-sensitive line, 222TR (TNF-resistant), a TNF-resistant, CDDP-sensitive line, and AD10, a TNF-sensitive, CDDP-resistant line. Cytotoxicity was determined by the microculture tetrazolium dye assay.

RESULTS

Synergy in cytotoxicity was achieved in all three lines treated with a combination of TNF-alpha and CDDP. Cytotoxicity by either TNF-alpha or CDDP or by both TNF-alpha and CDDP was inhibited in the presence of either Phe or BHA. Pretreatment of tumor cells with either Phe or BHA for up to 4 hours, washed and followed by the addition of the cytotoxic agents (alone or combined), resulted in no inhibitory effect. Pretreatment of the cells with the cytotoxic agent for up to 2 hours, washed and then followed by the addition of Phe, resulted in significant inhibition of cytotoxicity. In contrast to Phe, the addition of BHA as late as 12 hours post pretreatment of the cells with the cytotoxic agent(s) still inhibited cytotoxicity. These results demonstrated that free radicals are involved in cytotoxicity mediated by a single agent, and in synergy with both agents. Further, the results demonstrated that Phe acts at an early stage of the cytotoxic pathway and that BHA acts at both an early and a late stage of the cytotoxic pathway.

CONCLUSIONS

These results demonstrated that both TNF-alpha and CDDP rapidly stimulate the induction of free radicals but a lag of several hours was necessary to initiate the irreversible program of cell death. Further, the studies demonstrated that synergy and reversal of drug resistance in ovarian tumor cells by TNF-alpha and CDDP, used in combination, share the same pathway of cytotoxicity as that mediated by TNF-alpha or CDDP used as a single agent.