Xanthines Down-Regulate the Drug Transporter ABCG2 and Reverse Multidrug Resistance

Abstract

ABCG2 is an ATP-binding-cassette (ABC) transporter that confers multidrug resistance (MDR) to tumor cells by extruding a broad variety of chemotherapeutic agents, ultimately leading to failure of cancer therapy. Thus, the down-regulation of ABCG2 expression and/or function has been proposed as part of a regimen to improve cancer therapeutic efficacy. In this study, we found that a group of xanthines including caffeine, theophylline, and dyphylline can dramatically decrease ABCG2 protein in cells that have either moderate (BeWo, a placental choriocarcinoma cell line) or high (MCF-7/MX100, a breast cancer drug-resistant cell subline) levels of ABCG2 expression. This down-regulation is time-dependent, dose-dependent, and reversible. Using lysosomal inhibitors, we found that xanthines decreased ABCG2 by inducing its rapid internalization and lysosome-mediated degradation. As a consequence, caffeine treatment significantly increased the retention of an established ABCG2 substrate in MCF-7/MX100 cells but not in parental MCF-7 cells and sensitized the MDR cells to the chemotherapeutic agent mitoxantrone (MX); combination treatment with MX and caffeine decreased the IC 50 of MX ϳ10-fold and induced a greater degree of apoptotic cell death than MX treatment alone. Taken together, our results describe a novel function for this large class of therapeutically relevant compounds and suggest that a subset of xanthines could be developed as combination therapy to improve the efficacy of anticancer drugs that are ABCG2 substrates.

ABCG2/BCRP: Specific and Nonspecific Modulators

“…21) has been shown to downregulate the expression of ABCG2 in cancer cell lines in a time-and dose-dependent and reversible way. 126 Also, theophylline and dyphylline decreased ABCG2 expression significantly in MCF-7/MX100 cells in a time-dependent, dose-dependent, and reversible manner. Caffeine treatment was shown to increase the retention of MX.…”

Effect of Paullinia cupana on MCF-7 breast cancer cell response to chemotherapeutic drugs

“…As regards MCF-7, the line used in the present study, previous studies demonstrated the effect of caffeine on enhancing cell apoptosis caused by exposure to paclitaxel (14) and increasing the cytotoxic effect of alkylating drugs, such as cyclophosphamide (36). In addition, caffeine and other xanthines, including theophylline and dyphylline, significantly decreased the expression of the ABCG2 protein in the MCF-7/MX100 subline, which exhibits a high resistance to anti-breast cancer drugs (37).…”

A role for ABCG2 beyond drug transport: Regulation of autophagy

“…1A) were utilized for these studies. During the course of our investigations on the regulation of ABCG2 expression by methylxanthines in these cells 18 we observed that both cell lines were more resistant to this class of compounds than their drug-sensitive parent lines. This result was unexpected, since methylxanthines are not ABCG2 substrates.…”

“…Western blot assays for the autophagy markers LC3B (this is the only isoform of LC3 tested, referred as LC3 in this study) and SQSTM1 were conducted according to the protocol described previously, 18 with specific modifications for LC3. Immunoblotting was accomplished using a rabbit monoclonal antibody against LC3 (1:1,000; Cell Signaling Technology, 2775) and immunoreactive proteins were visualized using an enhanced chemiluminescent system (Super Signal West Femto Chemiluminescent Substrate; Thermo Scientific, 34095) according to the manufacturer's recommendations.…”