Sensitivity of drug-resistant human ovarian tumor cell lines to combined effects of tumor necrosis factor (TNF-alpha) and doxorubicin: failure of the combination to modulate the MDR phenotype.

We have examined four human ovarian tumor lines (A2780, AD10, OVC-8, and SKOV-3) selected for their sensitivity and/or resistance to the recombinant human tumor necrosis factor alpha (TNF-alpha) and the chemotherapeutic drug doxorubicin (DOXO). The tumor lines were either sensitive to both agents, resistant to one or the other, or resistant to both. Of the four lines examined only the DOXO-resistant line AD10 exhibited the multidrug-resistance (MDR) phenotype. Enhanced cytotoxicity was seen with the combination of TNF-alpha and DOXO in each line regardless of their sensitivity or resistance patterns and, thus, demonstrates that drug resistance due to the expression of the MDR phenotype or its absence can be overcome by TNF-alpha and DOXO. We then examined whether TNF-alpha or TNF-alpha and DOXO modulated the MDR phenotype in AD10 as a possible mechanism of overcoming drug resistance. TNF-alpha had no effect on either DOXO intake or efflux as measured by flow cytometry. Further, TNF-alpha treatment showed no effect on the level of MDR-1 mRNA. These results suggest that the enhanced cytotoxicity seen with the combination of TNF-alpha and DOXO is not the result of any modulation of drug influx or efflux levels by TNF-alpha. Overall, these findings suggest that combination treatment with TNF-alpha and DOXO can overcome resistance inflicted by different mechanisms.