Abstract 1532: Stemofoline is a potent natural product modulator of the multidrug resistance-linked P-glycoprotein (ABCB1)

Abstract

Abstract Stemofoline is a plant alkaloid isolated from Stemona, which is native to Eastern and Southeastern Asia and Northern Australasia. The extract from the tuberous roots of Stemona is used to treat respiratory disorders, including pulmonary tuberculosis and bronchitis, and different insect pests. P-glycoprotein (P-gp, ABCB1), a member of the ATP-binding cassette (ABC) transporter superfamily is implicated in multidrug resistance (MDR) in cancer cells. We investigated the effect of stemofoline on P-gp function aiming to overcome P-gp-mediated MDR. Stemofoline stimulated P-gp-mediated ATP hydrolysis (conc. required for 50% stimulation = 10-12 micro M). In addition, Stemofoline did not change the Km for ATP, suggesting that this alkaloid seems to interact with drug-binding site of P-gp. Consistent with this view, stemofoline inhibited the photo-crosslinking of P-gp with [125I]-iodoarylazidoprazosin (IAAP; IC 50 = 7 micro M), which is a transport substrate of P-gp. Interestingly, stemofoline instead of inhibiting substrate-stimulated ATP hydrolysis (such as verapamil and vinblastine), it further enhanced the ATPase activity suggesting that stemofoline and these drugs (verapamil and vinblasine) bind simultaneously to P-gp in the drug-binding pocket. In addition, the efflux of the fluorescent substrates such as calcein-AM and Bodipy-verapamil from P-gp expressing cells was blocked by stemofoline in a concentration-dependent manner. Furthermore, stemofoline was not cytotoxic to P-gp expressing KB-V1 or parental KB-3-1 cells up to 100 micro M concentration, but this compound at non-toxic concentration (1 − 5 micro M) sensitized KB-V1 cells to vinblastine. Stemofoline does not appear to interact with ABCG2 transporter, which is also linked to development of MDR. These studies indicate that stemofoline could be developed as a specific potent modulator to overcome P-gp-mediated MDR in cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1532.