Multidrug resistance (MDR) mediated by
ATP binding cassette subfamily B member 1 (ABCB1) is significantly hindering effective
cancer chemotherapy. However, currently, no ABCB1-inhibitory drugs have been approved to treat MDR
cancer clinically, mainly due to the inhibitor specificity, toxicity, and drug interactions. Here, we reported that three polyoxypregnanes (POPs) as the most abundant constituents of Marsdenia tenacissima (M. tenacissima) were novel ABCB1-modulatory
pro-drugs, which underwent intestinal microbiota-mediated biotransformation in vivo to generate active metabolites. The metabolites at non-toxic concentrations restored chemosensitivity in ABCB1-overexpressing
cancer cells via inhibiting ABCB1 efflux activity without changing
ABCB1 protein expression, which were further identified as specific non-competitive inhibitors of ABCB1 showing multiple binding sites within ABCB1 drug cavity. These POPs did not exhibit ABCB1/drug metabolizing
enzymes interplay, and their repeated administration generated predictable pharmacokinetic interaction with
paclitaxel without obvious toxicity in vivo. We further showed that these POPs enhanced the accumulation of
paclitaxel in
tumors and overcame ABCB1-mediated chemoresistance. The results suggested that these POPs had the potential to be developed as safe, potent, and specific
pro-drugs to reverse ABCB1-mediated MDR. Our work also provided scientific evidence for the use of M. tenacissima in combinational
chemotherapy.