Abstract
Overcoming multidrug resistance (MDR) remains a major challenge in cancer chemotherapy, largely mediated by the efflux pump P-glycoprotein (P-gp). To address this, we designed and synthesized a series of novel phenylindole-bisamide derivatives using receptor-based drug design and empirical modifications. The MDR reversal activities of target compounds were systematically evaluated in MCF-7/ADR cells. Among them, compound l1 exhibited enhanced reversal potency and significantly reduced cytotoxicity compared to the third-generation P-gp inhibitor tariquidar. Furthermore, l1 demonstrated excellent broad-spectrum chemosensitization effects when used in combination with front-line anticancer drugs. Mechanistic studies (including western blotting, cellular thermal shift assay and Rh123 accumulation assays) demonstrated that l1 effectively inhibited P-gp efflux function without affecting protein expression. Molecular docking analysis revealed that l1 binds tightly within the P-gp active pocket through π-π stacking and hydrogen-bond interactions. Importantly, in 3D tumor spheroid assays, the co-administration of l1 with doxorubicin significantly suppressed spheroid growth. Collectively, these findings identify l1 as a promising P-gp inhibitor and provide a rational scaffold for further optimization in the development of MDR inhibitors.