Cell lines derived from the human ovarian tumor, TAOV, which is sensitive, and TAOV-Tr20, which is highly resistant to taxol, were clonally isolated. The latter was found to express P-glycoprotein (P-GP) by fluorescent staining with anti-P-glycoprotein monoclonal antibody and Western blotting. Transfection of MDR1 gene in TAOV cells resulted in moderate resistance to taxol and expressed P-GP, but the resistance was not as dominant as in TAOV-Tr20 cells. The influx of 3H-taxol into TAOV- Tr20 cells was 37-fold lower than that of TAOV, and 16-fold lower than that of the MDR1 gene transfected cell line. HPLC analysis of taxol metabolites in the taxol exposed cells as well as in culture media indicated the taxol was converted to one or two major metabolites in TAOV. Metabolism of taxol in the resistant cells was undetectable because of the low level of 3H-taxol uptake. Treatment of the resistant cells with verapamil, a calcium channel blocker, resulted in a significantly higher level of cell death and active taxol metabolism, indicating that the transport (influx and efflux) and metabolic conversion of taxol are under kinetic coordination. These results suggest that the resistance against taxol in TAOV-Tr20 cells depends on an efficient transport mechanism as well as drug metabolism, both of which appear to be regulated by a coordinative signal transduction.
