Photosensitive Ru(II) Complexes as Inhibitors of the Major Human Drug Metabolizing Enzyme CYP3A4

We report the synthesis and photochemical and biological characterization of the first selective and potent metal-based inhibitors of cytochrome P450 3A4 (CYP3A4), the major human drug metabolizing enzyme. Five Ru­(II)-based derivatives were prepared from two analogs of the CYP3A4 inhibitor ritonavir, 4 and 6: [Ru­(tpy)­(L)­(6)]­Cl₂ (tpy = 2,2′:6′,2″-terpyridine) with L = 6,6′-dimethyl-2,2′-bipyridine (Me₂bpy; 8), dimethylbenzo­[i]­dipyrido­[3,2-a:2′,3′-c]­phenazine (Me₂dppn; 10) and 3,6-dimethyl-10,15-diphenylbenzo­[i]­dipyrido­[3,2-a:2′,3′-c]­phenazine (Me₂Ph₂dppn; 11), [Ru­(tpy)­(Me₂bpy)­(4)]­Cl₂ (7) and [Ru­(tpy)­(Me₂dppn)­(4)]­Cl₂ (9). Photochemical release of 4 or 6 from 7–11 was demonstrated, and the spectrophotometric evaluation of 7 showed that it behaves similarly to free 4 (type II heme ligation) after irradiation with visible light but not in the dark. Unexpectedly, the intact Ru­(II) complexes 7 and 8 were found to inhibit CYP3A4 potently and specifically through direct binding to the active site without heme ligation. Caged inhibitors 9–11 showed dual action properties by combining photoactivated dissociation of 4 or 6 with efficient ¹O₂ production. In prostate adenocarcinoma DU-145 cells, compound 9 had the best synergistic effect with vinblastine, the anticancer drug primarily metabolized by CYP3A4 in vivo. Thus, our study establishes a new paradigm in CYP inhibition using metalated complexes and suggests possible utilization of photoactive CYP3A4 inhibitory compounds in clinical applications, such as enhancement of therapeutic efficacy of anticancer drugs.