Mixed Ru(II)-Ir(III) Complexes as Photoactive Inhibitors of the Major Human Drug Metabolizing Enzyme CYP3A4.

Cytochrome P450 3A4 (CYP3A4) is a crucial enzyme in human drug metabolism. To garner photochemical control over the inhibition of CYP3A4, a potent Ir(III)-based inhibitor of CYP3A4 was complexed with two Ru(II)-based photocaging groups. Chemical, photochemical, and biological properties of the photocaged inhibitors were characterized. Importantly, mixed Ru(II)-Ir(III) complexes strongly absorb green light, which facilitates the photochemical release of the Ir(III) inhibitor from the Ru(II) caging fragment [Ru(tpy)(Me2bpy)]2+, where tpy = 2,2':6',2″-terpyridine and Me2bpy = 6,6'-dimethyl-2,2'-bipyridine. Emission turn on, type II heme binding, and more potent inhibition under light vs dark conditions were observed. The study also demonstrated that a Ru(II)-Ir(III) conjugate can be photoactivated to exert cytotoxic effects on MCF-7 breast cancer cells upon green light exposure. Additionally, a synthesized analogue with one [Ru(TPA)]2+ fragment (TPA = tris(pyridin-2-ylmethyl)amine) and two Ir(III) centers, although resistant to photochemical release, showed strong inhibition of CYP3A4 both in purified form and in CYP3A4-overexpressing HepG2 cells, with nanomolar potency. These mixed Ru(II)-Ir(III) compounds can permeate cell membranes and inhibit CYP3A4, presenting a new class of bioactive compounds.

Dynamic Ir(III) Photosensors for the Major Human Drug-Metabolizing Enzyme Cytochrome P450 3A4.

Probing the activity of cytochrome P450 3A4 (CYP3A4) is critical for monitoring the metabolism of pharmaceuticals and identifying drug-drug interactions. A library of Ir(III) probes that detect occupancy of the CYP3A4 active site were synthesized and characterized. These probes show selectivity for CYP3A4 inhibition, low cellular toxicity, Kd values as low as 9 nM, and are highly emissive with lifetimes up to 3.8 µs in cell growth media under aerobic conditions. These long emission lifetimes allow for time-resolved gating to distinguish probe from background autofluorescence from growth media and live cells. X-ray crystallographic analysis revealed structure-activity relationships and the preference or indifference of CYP3A4 toward resolved stereoisomers. Ir(III)-based probes show emission quenching upon CYP3A4 binding, then emission increases following displacement with CYP3A4 inhibitors or substrates. Importantly, the lead probes inhibit the activity of CYP3A4 at concentrations as low as 300 nM in CYP3A4-overexpressing HepG2 cells that accurately mimic human hepatic drug metabolism. Thus, the Ir(III)-based agents show promise as novel chemical tools for monitoring CYP3A4 active site occupancy in a high-throughput manner to gain insight into drug metabolism and drug-drug interactions.