Analgesic Buxus alkaloids with Enhanced Selectivity for the Low‐Voltage‐Gated Calcium Channel Ca_v3.2 over Ca_v3.1 through a New Binding Mode

Abstract

Low‐voltage‐gated calcium channels (LVGCCs; Cav3.1‐3.3) represent promising drug targets for epilepsy, pain, and essential tremor. At present, modulators with heightened selectivity for a subtype of LVGCCs are still highly desired. In this study we explored three classes of Buxus alkaloids and identified 9(10/19)abeo‐artanes Buxusemine H and Buxusemine L (BXSL) as an unprecedented type of Cav3.2 inhibitors. Particularly, BXSL exhibited Cav3.2 inhibition comparable to Z944, a non‐subtype‐selective LVGCCs inhibitor under clinical trial. While lacking specificity for Cav3.3, BXSL showed a 30‐fold selectivity of Cav3.2 over Cav3.1. As compared to several well‐known inhibitors, the experimental and computational studies suggested BXSL exhibits a distinct binding mode to Cav3.2, notably through the essential interaction with serine‐1543 in domain III. Furthermore, BXSL showed minimal impact on various recombinant and native nociceptive ion channels, while significantly reducing the excitability of isolated mouse dorsal root ganglion neurons. Animal studies in wild‐type and Cav3.2 knock‐out mice revealed that BXSL (5 mg/kg), by inhibiting Cav3.2, exhibits an analgesic effect equivalent to Z944 (10 mg/kg) or mibefradil (10 mg/kg). Moreover, we proposed a structural rationale for the high selectivity of 9(10/19)abeo‐artane‐type alkaloids towards Cav3.2 over Cav3.1. This study introduces a novel analgesic agent and valuable molecular insight for structure‐based innovative Cav3.2 drug development.