Poster Sessions

MOLBIO/BIOCHEM/BIOPHYS-6

Shinobu Ohnuma

S. Ohnuma, W. Chanmahasathien, P. Limtrakul, S.V. Ambudkar

Stemofoline is a Potent Natural Product Modulator of the Multidrug-resistance-linked P-glycoprotein (ABCB1)

Stemofoline is a plant alkaloid isolated form 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 (Pgp), 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 Pgp function. Stemofoline stimulated Pgp-mediated ATP hydrolysis (conc. required for 50% stimulation = 10-12, uM), suggesting that this alkaloid seems to interact with drug-binding site of Pgp. Consistent with this view, stemofoline inhibited the photo-crosslinking of Pgp with [125I]-iodoarylazidoprazosin (IAAP), which is a transport substrate. Interestingly, stemofoline instead of inhibiting verapamil-stimulated ATP hydrolysis, it further enhanced the ATPase activity suggesting that stemofoline and verapamil bind simultaneously to Pgp in the drug-binding pocket. In addition, the efflux of the fluorescent substrate calcein-AM from P-gp expressing cells was blocked by stemofoline in a concentration-dependent manner. These studies indicate that stemofoline could be developed as a potent modulator to overcome MDR in cancer cells.