ABCC1 promotes GSH-dependent iron transport and resistance to Fe(II) and Cu(II) chelators.

Therapy resistance is a major challenge in cancer treatment, with multidrug resistance (MDR) being a well-characterized phenomenon wherein cancer cells develop resistance not only to the administered drug but also to structurally diverse compounds. Metal chelators, including quinolines and thiosemicarbazones, have shown broad antitumor activity and potential in overcoming MDR by modulating metal metabolism. However, predicting whether chelators increase or decrease toxicity in MDR cells remains complex, especially as chelator-metal complexes may become substrates for ATP-binding cassette (ABC) transporters, leading to resistance or hypersensitivity. In this study, we developed cell lines with comparable expression levels of the three major MDR ABC transporters (ABCB1, ABCC1, and ABCG2). Our findings demonstrated distinct transporter-specific influences on chelator toxicity. Cells expressing ABCC1 displayed significant resistance to thiosemicarbazones (Dp44mT, COTI-2, DpC) in both their metal-free and metal-bound forms. Vesicular transport assays further demonstrated that ABCC1 actively transports the Fe-GSH complex, formed under physiological glutathione levels, indicating its role in regulating the labile iron pool and reducing intracellular iron toxicity. These findings underscore the importance of transporter-chelator interactions in shaping drug resistance and sensitivity and highlight the intricate roles of ABC transporters in modulating chelator activity.