COEXPRESSION OF MDR-ASSOCIATED MARKERS, INCLUDING P-170, MRP AND LRP AND CYTOSKELETAL PROTEINS, IN 3 RESISTANT VARIANTS OF THE HUMAN OVARIAN-CARCINOMA CELL-LINE, OAW42

Variants of the human ovarian carcinoma cell line, OAW42, exhibiting l ow-level intrinsic resistance (OAW42-SR) and drug-induced higher-level resistance (OAW42-A1 & OAW42-A), were studied along with a sensitive clonal population (OAW42-S) which was isolated from OAW42-SR. Expressi on of the MDR-associated protein P-170, the more recently discovered L RP (lung resistance-related protein) and MRP (multidrug resistance-ass ociated protein), topoisomerase II alpha and beta, GST pi and the cyto skeletal proteins, cytokeratin 8 and vimentin, were studied (using imm unocytochemistry and Western blotting techniques) in conjunction with drug (doxorubicin) accumulation and subcellular distribution. Expressi on of mRNA for P-170, MRP, topoisomerase 11 alpha and beta and GST pi was studied using RT-PCR (reverse transcriptase polymerase chain react ion). Results indicate differential co-expression of four MDR-associat ed parameters (P-170, MRP, LRP and reduced topoisomerase II alpha and beta) in the OAW42-SR and OAW42-A1 variants, whereas resistance in the OAW42-A variant appeared to be mainly P-170 mediated. Comparable amou nts of MRP and greater amounts of LRP were detected in the OAW42-S cel ls compared to the OAW42-SR variant (which showed increased resistance compared to the OAW42-S cells), but all cell lines expressed similar low-level amounts of MRP mRNA (by RT-PCR). GST pi levels did not diffe r markedly between variants. Increased levels of the cytoskeletal prot eins were observed with increasing levels of resistance. The relative resistance of the variants, OAW42-SR and OAW42-A1, compared with OAW42 -S was seen to change during increased serial passaging of the cells. There was greater drug accumulation by the sensitive OAW42-S cell line compared with that of the resistant variants, particularly the most h ighly resistant OAW42-A cells. Both verapamil and cyclosporin A effect ively restored the accumulation defects seen in the resistant variants , cyclosporin A being the more effective of the two. Subcellular locat ion of drug was predominantly in the nucleus with maximum levels seen in the sensitive OAW42-S variant and minimum levels in the most resist ant OAW42-A clone. (C) 1997 Elsevier Science Ltd.