Characterization of breast cancer resistance protein (BCRP) in epithelial ovarian cancer (EOC)

Abstract

2020 Purpose: While the majority of patients with advanced EOC achieve an initial response with current chemotherapy regimens, most eventually relapse with resistant disease. One of the cellular mechanisms of drug resistance is over-expression of BCRP, a drug efflux pump that selectively pumps chemotherapeutic drugs out of cells. The objectives of this study are to characterize BCRP in EOC cell lines and investigate the relationship between BCRP expression and clinicopathological parameters in advanced EOC. Methodology: BCRP expression and cellular localization were evaluated in 10 EOC cell lines using QRT-PCR and fluorescence microscopy. Functional analysis was performed measuring topotecan efflux by flow cytometry in the presence and absence of Trypostatin-A, a specific BCRP inhibitor. A topotecan-resistant cell line was treated with DES (a known inhibitor of BCRP) and efflux of topotecan was measured by flow cytometry. BCRP expression was measured in 101 untreated primary EOC tissues using QRT-PCR. Statistical correlations between BCRP expression and clinicopathological parameters were analyzed using chi square test, log-rank test, and Cox proportional hazards models. Results: EOC cell lines exhibited varying degrees of BCRP expression. mRNA expression was correlated with protein levels and function. DES was able to reverse BCRP-mediated topotecan resistance in EOC cell lines. BCRP mRNA expression in EOC patient tissues was widely dispersed. No correlation was found between BCRP expression and age, stage, grade or debulking status. A significant correlation was demonstrated between BCRP expression and chemotherapeutic response (CR/PR vs. SD/PD, p=2.75x10–14). Comparison of survival (<24 vs. >24 months) showed a trend of decreased survival with high BCRP expression (p=0.076). Conclusions: BCRP is both present and functionally active in EOC cell lines. Further, preliminary studies with DES have shown a dose-dependent reversal of topotecan uptake. Additionally, we have demonstrated a highly significant association between elevated BCRP expression and poor chemotherapeutic response in patient samples. BCRP may serve as a molecular target for reducing drug resistance to chemotherapy in advanced EOC. No significant financial relationships to disclose.