23-
O-(1,4鈥?Bipiperidine-1-carbonyl)betulinic acid (BBA), a synthetic deri
vati
ve of 23-hydroxybetulinic acid (23-HBA), shows a re
versal effect on multidrug resistance (MDR) in our preliminary screening. O
verexpression of ATP-binding cassette (ABC) transporters such as ABCB1, ABCG2, and ABCC1 has been reported in recent studies to be a major factor contributing to MDR. Our study results showed that BBA enhanced the cytotoxicity of ABCB1 substrates and increased the accumulation of doxorubicin or rhodamine123 in ABCB1 o
verexpressing cells, but had no effect on non ABCB1 substrate, such as cisplatin; what鈥檚 more, BBA slightly re
versed ABCG2-mediated resistance to SN-38, but did not affect the ABCC1-mediated MDR. Further studies on the mechanism indicated that BBA did not alter the expression of ABCB1 at mRNA or protein le
vels, but affected the ABCB1 ATPase acti
vity by stimulating the basal acti
vity at lower concentrations and inhibiting the acti
vity at higher concentrations. In addition, BBA inhibited the
verapamil-stimulated ABCB1 ATPase acti
vity and the photolabeling of ABCB1 with [
125I] iodoarylazidoprazosin in a concentration-dependent manner, indicating that BBA directly interacts with ABCB1. The docking study confirmed this notion that BBA could bind to the drug binding site(s) on ABCB1, but its binding position was only partially o
verlapping with that of
verapamil or iodoarylazidoprazosin. Importantly, BBA increased the inhibitory effect of paclitaxel in ABCB1 o
verexpressing KB-C2 cell xenografts in nude mice. Taken together, our findings suggest that BBA can re
verse ABCB1-mediated MDR by inhibiting its efflux function of ABCB1, which supports the de
velopment of BBA as a no
vel potential MDR re
versal agent used in the clinic.
Keywords:
BBA; multidrug resistance; ABCB1; ABCG2