N-(3,4-dimethoxyphenethyl)-4-(6,7-dimethoxy-3,4-dihydroisoquinolin-2[1H]-yl)-6,7-dimethoxyquinazolin-2-amine (CP-100,356) as a "chemical knock-out equivalent" to assess the impact of efflux transporters on oral drug absorption in the rat.

The utility of the diaminoquinazoline derivative CP-100,356 as an in vivo probe to selectively assess MDR1/BCRP-mediated drug efflux was examined in the rat. CP-100,356 was devoid of inhibition (IC(50) >50 microM) against major human P450 enzymes including P4503A4. In human MDR1-transfected MDCKII cells, CP-100,356 inhibited acetoxymethyl calcein (calcein-AM) uptake (IC(50) approximately 0.5 +/- 0.07 microM) and digoxin transport (IC(50) approximately 1.2 +/- 0.1 microM). Inhibition of prazosin transport (IC(50) approximately 1.5 +/- 0.3 microM) in human BCRP-transfected MDCKII cells by CP-100,356 confirmed the dual MDR1/BCRP inhibitory properties. CP-100,356 was a weak inhibitor of OATP1B1 (IC(50) approximately 66 +/- 1.1 microM) and was devoid of MRP2 inhibition (IC(50) >15 microM). In vivo inhibitory effects of CP-100,356 in rats were examined after coadministration with MDR1 substrate fexofenadine and dual MDR1/BCRP substrate prazosin. Coadministration with increasing doses of CP-100,356 resulted in dramatic increases in systemic exposure of fexofenadine (36- and 80-fold increase in C(max) and AUC at a CP-100,356 dose of 24 mg/kg). Significant differences in prazosin pharmacokinetics were also discernible in CP-100,356-pretreated rats as reflected from a 2.6-fold increase in AUC. Coadministration of CP-100,356 and P4503A substrate midazolam did not result in elevations in systemic exposure of midazolam in the rat. The in vivo methodology should have utility in drug discovery in selective and facile assessment of the role of MDR1 and BCRP efflux transporters in oral absorption of new drug candidates.