CHARACTERIZATION OF AN ETOPOSIDE-RESISTANT HUMAN OVARIAN-CANCER CELL-LINE

Etoposide (VP-16) is one of the most important anticancer agents avail able and is used in many chemotherapeutic regimens. To characterize re sistance to this drug, we established a VP-16-resistant human ovarian cancer cell line, SKOV3/VP, by continuous stepwise exposure of SKOV3 c ells to VP-16. The degree of resistance to VP-16 of SKOV3/VP was about 25 times that of the parent cell line (SKOV3), and SKOV3/VP showed cr oss-resistance to teniposide, adriamycin, CPT-11, and vincristine. The accumulation of [H-3]-VP-16 observed in SKOV3/ VP cells was about hal f that seen in SKOV3 cells, and the accumulation of Adriamycin by this resistant cell line was also lower than that of its parent. Overexpre ssion of neither the multidrug resistance gene mdr-1, the multidrug-re sistance-associated protein (mrp) gene, nor P-glycoprotein was detecte d using reverse transcriptase-polymerase chain reaction analysis and f low cytometry with MRK-16, a monoclonal antibody against P-glycoprotei n. The topoisomerase II activity of nuclear extracts from SKOV3/VP cel ls was lower than that from the parental cells, as was the amount of D NA topoisomerase II, demonstrated by immunoblotting. These results sug gest that the mechanism responsible for the multidrug resistance of th is cell line may be attributable to changes on its DNA topoisomerase I I and to its reduced accumulation of the drugs as compared with the pa rental line SKOV3.