Discovery of spiroindolediketopiperazine alkaloids from Penicillium sp. KYS-32 as dual inhibitors of ABCB1 and ABCG2 to reverse multidrug resistance.

Chemical investigation of the fungus Penicillium sp. KYS-32 afforded eleven spiroindolediketopiperazine alkaloids (1-11), including seven previously unreported compounds penispiroketins A-G (1-7). Compounds 2, 3, 6, and 7 are characterized by an oxidation at C-12, a structural feature that is exceptionally rare among this chemical family. Their structures were elucidated through a combination of spectroscopic analyses, X-ray crystallography, and ECD calculations. In the first assessment of this chemical class as multidrug resistance (MDR) reversers, compounds 10 and 11 effectively resensitized HCT-15/Taxol cells to both paclitaxel and mitoxantrone. Preliminary structure-activity relationship studies indicated that the N-1 prenyl and C-18 isobutenyl substituents are critical for the observed activity. Subsequent biological studies identified 11 as a dual-target inhibitor that directly binds to and inhibits both ABCB1/P-gp and ABCG2/BCRP transporters. Molecular docking simulations revealed that 11 occupies the substrate-binding pockets of both proteins, forming pivotal hydrogen bonds with Tyr941 in ABCB1 and Thr542 in ABCG2. These findings establish compound 11 as a novel dual inhibitor of ABCB1 and ABCG2, offering a promising chemical scaffold for developing next-generation MDR reversal agents.