Molecular Pharmacology, Vol 13, 883-891, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics

Binding of the Nucleoside Transport Inhibitor Nitrobenzylthioinosine to HeLa Cells

¹ Cancer Research Unit (McEachern Laboratory), University of Alberta, Edmonton, Alberta, Canada T6G 2H7

Nitrobenzylthioinosine (NBMPR), a potent inhibitor of nucleoside transport, was bound tightly but reversibly to HeLa cell membrane sites associated with the nucleoside transport mechanism. Site-specific binding was assayed with [³³S]NBMPR and a competing, nonisotopic congener. Mass law analysis of the binding data indicated that each HeLa cell possessed about 1O³ binding sites of a single class which bound NBMPR tightly; the bound inhibitor had a dissociation constant of about 0.1 nM. Occupancy of these binding sites by NBMPR correlated with inhibition of uridine and thymidine uptake; however, the relationship between these parameters was not simple because, as binding saturation was approached (at about 5 nM NBMPR), a substantial fraction (25-30%) of the transport capability remained active but inhibitable by 5 µM NBMPR.

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