Reduced cytocidal efficacy for adriamycin in cultured human carcinoma cells depleted of polyamines by difluoromethylornithine treatment.

We have studied the effect of pretreatment with difluoromethylornithine (DFMO), an ornithine decarboxylase inhibitor, on the cytocidal responses of four human adenocarcinoma cell lines to Adriamycin (ADR). The cell lines utilized included HuTu-80 (duodenum), HT-29 (colon), ME-180 (cervix), and A-427 (lung). A 48-h DFMO pretreatment reduced putrescine and spermidine content to less than 10 and less than 1% of control levels and decreased spermine to between 70 and 30% of controls. Plating efficiency assays were used to generate ADR dose-response survival curves for DFMO-treated and control cultures. The DFMO pretreatment significantly protected human adenocarcinoma cells from the lethal effects of ADR. Addition of exogenous putrescine to the DFMO-treated cultures 24 h before treatment with ADR restored their cytocidal response to ADR to near control levels. Putrescine had no effect on cell survival in cultures that were not pretreated with DFMO. These observations suggest that DFMO-induced protection from ADR may be a specific consequence of DFMO-induced inhibition of polyamine biosynthesis. Alternatively, since ADR efficacy varies directly with cellular growth rates and DFMO inhibits proliferation, the protection may have resulted from DFMO-induced growth inhibition. Comparison of ADR uptake in DFMO-pretreated and control cells showed that the protection did not result from decreased intracellular accumulation of ADR.