MECHANISMS AND MODULATION OF MULTIDRUG RESISTANCE IN PRIMARY HUMAN RENAL-CELL CARCINOMA

Human renal cell carcinomas show a high degree of intrinsic multidrug resistance. In experimental cell lines, the membrane bound P-170 glycoprotein and the glutathione redox cycle seem to contribute to this phenomenon. P-170 may be inactivated by calcium antagonists; the glutathione redox cycle by buthionine sulfoximine. We studied the resistance patterns of 35 human renal cell carcinomas against vinblastine, doxorubicin and carboplatinum in a tetrazolium-based microculture assay. Concomitantly, P-170 expression was traced immunohistochemically using moab C219 and the glutathione content was determined enzymatically. Reversal of multidrug resistance was examined by applying the R-stereoisomer of verapamil and/or by addition of buthionine sulfoximine. A high degree of chemoresistance was seen in 27 tumors against vinblastine, in 30 tumors against doxorubicin and in 31 tumors against carboplatinum. Chemoresponse was found in eight, five or four cases respectively. P-170 was detected in 70% of highly vinblastine resistant and in 63% of highly doxorubicin resistant tumors, but in none of the less resistant cases. Resistance against carboplatinum and doxorubicin was significantly associated with elevated glutathione levels as compared to less resistant renal cell carcinomas. R-verapamil lead to a strong reversal of vinblastine resistance and to a distinct circumvention of doxorubicin resistance, but revealed no effect in carboplatinum resistance. Buthionine sulfoximine overcame carboplatinum resistance and modified doxorubicin resistance, but had no influence on vinblastine resistance. The combined application of R-verapamil and buthionine sulfoximine reversed doxorubicin resistance but did not act synergistically in vinblastine or carboplastinum resistance. Both mechanisms, P-170 and glutathione, occurred independently of each other and may well explain multidrug resistance of human renal cell carcinomas.