Selectivity of the Multidrug Resistance Modulator, LY335979, for P-Glycoprotein and Effect on Cytochrome P-450 Activities

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 290; no. 2; pp. 854 - 862
• Main Authors: Dantzig, A H, Shepard, R L, Law, K L, Tabas, L, Pratt, S, Gillespie, J S, Binkley, S N, Kuhfeld, M T, Starling, J J, Wrighton, S A
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.08.1999
• Subjects: ATP-Binding Cassette Transporters - biosynthesis; ATP-Binding Cassette Transporters - drug effects; ATP-Binding Cassette Transporters - metabolism; ATP-Binding Cassette, Sub-Family B, Member 1 - biosynthesis; ATP-Binding Cassette, Sub-Family B, Member 1 - drug effects; ATP-Binding Cassette, Sub-Family B, Member 1 - metabolism; Caco-2 Cells; Cell Membrane - metabolism; Cell Survival - drug effects; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System - drug effects; Cytochrome P-450 Enzyme System - metabolism; Dibenzocycloheptenes - metabolism; Dibenzocycloheptenes - pharmacology; Drug Resistance, Multiple; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; HeLa Cells; Humans; Isoenzymes - biosynthesis; Isoenzymes - drug effects; Kinetics; Leukotriene C4 - metabolism; Mixed Function Oxygenases - metabolism; Multidrug Resistance-Associated Proteins; Quinolines - metabolism; Quinolines - pharmacology
• ISSN: 0022-3565; 1521-0103

Overexpression of ATP-dependent drug efflux pumps, P-glycoprotein (Pgp) or multidrug resistance-associated protein (MRP), confers multidrug resistance to tumor cells. Modulators of multidrug resistance block the action of these pumps, thereby sensitizing cells to oncolytics. A potent Pgp modulator is LY335979, which fully sensitizes Pgp-expressing cells at 0.1 μM in cytotoxicity assays and for which Pgp has an affinity of 59 nM. The present study examines its effect on MRP1-mediated drug resistance and cytochrome P-450 (CYP) activity and its ability to serve as a Pgp substrate. Drug resistance was examined with HL60/ADR and MRP1-transfected HeLa-T5 cells. Drug cytotoxicity was unaffected by 1 μM LY335979; leukotriene C4 uptake into HeLa-T5 membrane vesicles was unaffected. Because the substrate specificity of Pgp and CYP3A overlap, the effect of LY335979 on the 1′-hydroxylation of midazolam by CYP3A in human liver microsomes was examined. The apparent K i was 3.8 μM, ∼60-fold higher than the affinity of Pgp for LY335979. The modulator’s effect on Pgp was evaluated with Pgp-overexpressing CEM/vinblastine (VLB) 100 and parental CCRF-CEM cells. Both cell lines accumulated [ 3 H]LY335979 equally well and did not efflux [ 3 H]LY335979 during a 3-h incubation, indicating that it is not a substrate of Pgp. Equilibrium-binding studies with CEM/VLB 100 plasma membranes and [ 3 H]LY335979 showed that Pgp had a K d of 73 nM, which is in good agreement with the previously determined K i value. Thus, LY335979 is an extremely potent Pgp, and not MRP1 or MRP2, modulator and has a significantly lower affinity for CYP3A than for Pgp.