The molecular determinants of R-roscovitine block of hERG channels

Human ether-à-go-go-related gene (Kv11.1, or hERG) is a potassium channel that conducts the delayed rectifier potassium current (IKr) during the repolarization phase of cardiac action potentials. hERG channels have a larger pore than other K+channels and can trap many unintended drugs, often resulting in acquired LQTS (aLQTS). R-roscovitine, a cyclin-dependent kinase (CDK) inhibitor that also inhibits L-type calcium channels, inhibits open hERG channels but does not become trapped in the pore. Two-electrode voltage clamp recordings from Xenopus oocytes expressing wild-type (WT) or mutant (T623A, S624A, Y652A, F656A) hERG channels demonstrated that, compared to WT hERG, T623A, Y652A, and F656A inhibition by 200 μM R-roscovitine was ~ 48 %, 29 %, and 73 % weaker, respectively. In contrast, S624A hERG was inhibited more potently than WT hERG, with an ~ 34 % stronger inhibition. These findings were further supported by the IC50 values, which were increased for T623A, Y652A and F656A (by ~5.5, 2.75, and 42 fold respectively) and reduced 1.3 fold for the S624A mutant. Our data suggest that while T623, Y652, and F656 are critical for R-roscovitine-mediated inhibition, S624 may not be. This relatively unique feature, coupled with R-roscovitine’s tolerance in clinical trials, could guide future drug screens. We discuss our findings and how they lend support for the recent Comprehensive In Vitro Proarrhythmia Assay (CiPA) guidelines on the re-evaluation of potentially useful drugs that had failed testing due to unintended interactions with hERG.