DETECTION OF P-GLYCOPROTEIN-170 IN OVARIAN-CARCINOMA CELL-LINES AND ENHANCEMENT OF ITS EXPRESSION AFTER INDUCTION OF IN-VITRO RESISTANCE

Background: After the clinical introduction of platinum-containing regimens for the primary treatment of ovarian cancer we obtain partial and complete remissions in 60-70% of the patients. Upon subsequent treatment, however, most tumors develop resistance. For a number of substances such resistance is often associated with overexpression of a MW 170,000 membrane glycoprotein. The exact clinical relevance of overexpression of Pgp still awaits clarification. Material and Methods: More than 40 new permanent ovarian cancer cell lines were established in our laboratory over the past years. They originated from pretreated and from untreated patients. Permanent cell lines are suitable objects for the detection of Pgp and the influence on its expression by resistance induction. In this paper we compared two antibodies (JSB-1 and MRK-16), which are directed against an internal and external epitope, respectively. The data were obtained by flow cytometry analysis. Furthermore, we tried to induce in vitro resistance to doxorubicin, etoposide and cisplatinum in two chemotherapeutically sensitive cell lines. Results: We found no correlation between the pretreatment of the patient of whom the cell line was established and the expression of Pgp in the cell culture. In vitro resistance could be induced against doxorubicin and etoposide but not against cisplatinum. Pgp expression was measured simultaneously; its expression strongly correlated with resistance induction. Although directed against different epitopes, the two antibodies JSB-1 and MRK-16 show a high degree of correlation (r = 0.67). Up to now the application of the two antibodies was mainly restricted to western blotting and immunohistochemical tests. We have shown that, after adequate permeabilization of the cell membrane for JSB-1, both antibodies yield comparable results. Conclusion: Our results suggest a causal relationship between resistance induction against doxorubicin and etoposide, and enhanced Pgp expression. Both antibodies are applicable to the detection of Pgp by flow cytometric analysis.