Functional comparison of anoctamin 1 antagonists on human uterine smooth muscle contractility and excitability

Background: Pre-term birth is a major health care challenge throughout the world, and preterm labor represents a potentially reversible component of this problem. Current tocolytics do not improve preterm labor beyond 48 h. We have previously shown that anoctamin 1 (ANO1) channel blockade results in relaxation of pre-contracted human uterine smooth muscle (USM). Three drug classes with reported medicinal effects in humans also have members with ANO1 antagonism. In this study, we compared the ability of representatives from these 3 classes to reduce human USM contractility and excitability. Objective: This study sought to examine the comparative potency of 3 ANO1 antagonists on pregnant human USM relaxation, contraction frequency reduction, inhibition of intracellular calcium release and membrane hyperpolarization. Methods: Experiments were performed using: 1) Ex vivo organ bath (human pregnant tissue), 2) Oxytocin-induced calcium flux (in vitro human USM cells) and 3) Membrane potential assay (in vitro human USM cells). Results: Benzbromarone (BB) demonstrated the greatest potency among the compounds tested with respect to force, frequency inhibition, reducing calcium elevation and depolarizing membrane potential. Conclusion: While all 3 ANO1 antagonists attenuate pregnant human uterine tissue contractility and excitability, BB is the most potent tocolytic drug. Our findings may serve as a foundation for future structure-function analyses for novel tocolytic drug development.