A novel ω-conotoxin Bu8 inhibiting N-type voltage-gated calcium channels displays potent analgesic activity

omega-Conotoxins inhibit N-type voltage-gated calcium (CaV2.2) channels and exhibit efficacy in attenuating neuropathic pain but have a low therapeutic index. Here, we synthesized and characterized a novel omega-conotoxin, Bu8 from Conus bullatus, which consists of 25 amino acid residues and three disulfide bridges. Bu8 selectively and potently inhibits depolarization-activated Ba2+ currents mediated by rat CaV2.2 expressed in HEK293T cells (IC50 = 89 nmol/L). Bu8 is two-fold more potent than w-conotoxin MVIIA, a omega-conotoxin currently used for the treatment of severe chronic pain. It also displays potent analgesic activity in animal pain models of hot plate and acetic acid writhing but has fewer side effects on mouse motor function and lower toxicity in goldfish. Its lower side effects may be attributed to its faster binding rate and higher recovery ratios. The NMR structure demonstrates that Bu8 contains a small irregular triple beta-strand. The structure-activity relationships of Bu8 Ala mutants and Bu8/MVIIA hybrid mutants demonstrate that the binding mode of CaV2.2 with the amino acid residues in loop 1 and loop 2 of Bu8 is different from that of MVIIA. This study characterizes a novel, more potent omega-conotoxin and provides new insights for designing CaV2.2 antagonists. (C) 2021 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V.

Automated summary

Bu8 is a novel omega-conotoxin that is more potent than MVIIA, showing strong analgesic effects in animal pain models with fewer side effects. Its faster binding rate and higher recovery ratios contribute to its lower side effects, and its structure-activity relationships provide new insights for designing CaV2.2 antagonists.