7-Ethynylcoumarins: Selective Inhibitors of Human Cytochrome P450s 1A1 and 1A2

To discover new selective mechanism-based P450 inhibitors,
eight
7-ethynylcoumarin derivatives were prepared through a facile two-step
synthetic route. Cytochrome P450 activity assays indicated that introduction
of functional groups in the backbone of coumarin could enhance the
inhibition activities toward P450s 1A1 and 1A2, providing good selectivity
against P450s 2A6 and 2B1. The most potent product 7-ethynyl-3,4,8-trimethylcoumarin
(7ETMC) showed IC50 values of 0.46 μM and 0.50 μM
for P450s 1A1 and 1A2 in the first six minutes, respectively, and
did not show any inhibition activity for P450s 2A6 and 2B1 even at
the dose of 50 μM. All of the inhibitors except 7-ethynyl-3-methyl-4-phenylcoumarin
(7E3M4PC) showed mechanism-based inhibition of P450s 1A1 and 1A2.
In order to explain this mechanistic difference in inhibitory activities,
X-ray crystallography data were used to study the difference in conformation
between 7E3M4PC and the other compounds studied. Docking simulations
indicated that the binding orientations and affinities resulted in
different behaviors of the inhibitors on P450 1A2. Specifically, 7E3M4PC
with its two-plane structure fits into the P450 1A2’s active
site cavity with an orientation leading to no reactive binding, causing
it to act as a competitive inhibitor.