Characterization of the Preclinical in Vitro and in Vivo Pharmacokinetic Properties of the Cyclic Oligomeric Depsipeptide Ryanodine Receptor 2 Inhibitor ent-Verticilide

ent-Verticilide is a synthetic cyclic oligomeric depsipeptide that inhibits ryanodine receptor 2 (RyR2)-mediated calcium (Ca) leak and has demonstrated antiarrhythmic activity in mice. This study characterized the preclinical absorption, distribution, metabolism, and pharmacokinetic properties of ent-verticilide and investigated factors affecting its oral exposure. ent-Verticilide was stable in rat plasma and simulated gastric and intestinal fluids but exhibited extensive plasma protein binding (>94%) and low apparent permeability in Caco-2 cells, with no evidence of pronounced net efflux. In rat and human liver microsomes, ent-verticilide underwent rapid NADPH-dependent metabolism, with an in vitro half-life of 5.43 min and 4.35 min, respectively, and a predicted hepatic extraction ratio of 0.90 and 0.92, respectively. Following intravenous administration in rats, ent-verticilide exhibited a systemic clearance of 25.5 mL/min/kg and a large steady-state volume of distribution (4.72 L/kg). Absolute oral bioavailability was approximately 16%. Simultaneous portal and systemic sampling estimated intestinal availability (FaFg) at 0.25 and hepatic availability (Fh) at 0.64, suggesting that processes occurring before hepatic entry are a major limitation to oral exposure. Pretreatment with the CYP inhibitor 1-aminobenzotriazole increased portal and systemic exposure approximately 10.6- and 18.5-fold, respectively, and increased apparent Fh to approximately 1. Collectively, these findings identify limited intestinal availability and CYP-mediated presystemic metabolism as important determinants of ent-verticilide exposure and provide a framework for its continued development as an RyR2-targeted therapeutic.