Ferroptosis Inducers Erastin and RSL3 Enhance Adriamycin and Topotecan Sensitivity in ABCB1/ABCG2-Expressing Tumor Cells.

Acquired resistance to chemotherapeutic drugs is the primary cause of treatment failure in the clinic. While multiple factors contribute to this resistance, increased expression of ABC transporters-such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance proteins-play significant roles in the development of resistance to various chemotherapeutics. We found that Erastin, a ferroptosis inducer, was significantly cytotoxic to NCI/ADR-RES, a P-gp-expressing human ovarian cancer cell line. Here, we examined the effects of both Erastin and RSL3 (Ras-Selected Ligand 3) on reversing Adriamycin resistance in these cell lines. Our results show that Erastin significantly enhanced Adriamycin uptake in NCI/ADR-RES cells without affecting sensitive cells. Furthermore, we observed that Erastin enhanced Adriamycin cytotoxicity in a time-dependent manner. The selective iNOS inhibitor, 1400W, reduced both uptake and cytotoxicity of Adriamycin in P-gp-expressing NCI/ADR-RES cells only. These findings were also confirmed in a BCRP-expressing human breast cancer cell line (MCF-7/MXR), which was selected for resistance to Mitoxantrone. Both Erastin and RSL3 were found to be cytotoxic to MCF-7/MXR cells. Erastin significantly enhanced the uptake of Hoechst dye, a well-characterized BCRP substrate, sensitizing MCF-7/MXR cells to Topotecan. The effect of Erastin was inhibited by 1400W, indicating that iNOS is involved in Erastin-mediated enhancement of Topotecan cytotoxicity. RSL3 also significantly increased Topotecan cytotoxicity. Our findings-demonstrating increased cytotoxicity of Adriamycin and Topotecan in P-gp- and BCRP-expressing cells-suggest that ferroptosis inducers may be highly valuable in combination with other chemotherapeutics to manage patients' cancer burden in the clinical setting.