Discovery of novel coumarin-containing triazolo[1,5-a]pyrimidine derivatives as potent ABCB1 inhibitor for modulation of multidrug resistance.

ABCB1-mediated drug efflux is a key determinant of multidrug resistance (MDR) in cancer. To overcome this mechanism, a series of thiol-substituted aminocoumarin-derived, coumarin-containing triazolo[1,5-a]pyrimidine derivatives (5a-5s) was synthesised, and compound 5r (NYH-707) was identified as the most potent ABCB1 inhibitor. NYH-707 markedly restored paclitaxel sensitivity in SW620/Ad300 MDR cells, reducing the IC(50) from 4.55 ± 0.73 µM to 0.011 ± 0.002 µM (reversal factor = 413.6). Molecular docking predicted strong binding (-9.7 kcal/mol) through hydrogen bonding with LYS-826 and SER-880 and π-π stacking with PHE-994. CETSA confirmed direct ABCB1 engagement, while drug-accumulation assays demonstrated inhibition of ABCB1-mediated efflux. In vivo, co-administration of NYH-707 and paclitaxel significantly suppressed SW620/Ad300 xenograft growth without detectable systemic toxicity. These findings indicate that NYH-707 acts as a potent and selective ABCB1 modulator capable of reversing MDR likely by modulating ABCB1 conformational dynamics, thereby enhancing chemotherapeutic efficacy in resistant tumours.