Targeting of N-Type Calcium Channels via GABA(B)-Receptor Activation by alpha-Conotoxin Vc1.1 Variants Displaying Improved Analgesic Activity

alpha-Conotoxins exhibiting analgesic activity, such as Vc1.1, have been shown to inhibit alpha 9 alpha 10 nicotinic acetylcholine receptors (nAChRs) and GABA(B)-receptor (GABA(B)R) coupled N-type (Ca(V)2.2) calcium channels. Here, we report two Vc1.1 variants, Vc1.1[N9R] and benzoyl-Vc1.1[N9R], that selectively inhibit Ca(V)2.2 channels via GABA(B)R activation but exhibit reduced inhibitory activity at alpha 9 alpha 10 and other neuronal nAChR subtypes compared with Vc1.1. Surprisingly, the analgesic activity of Vc1.1[N9R] and benzoyl-Vc1.1[N9R] was more potent than that of Vc1.1 when tested in partial sciatic nerve ligation injury and chronic constriction injury models. Vc1.1[N9R] and benzoyl-Vc1.1[N9R] exhibited either similar or tenfold higher activity of GABA(B)R-mediated Ca(V)2.2 inhibition but no activity at Ca(V)2.2 alone; however, the mechanism of increased analgesic activity is unknown. The effects on analgesic activity and alpha 9 alpha 10 nAChR of other Vc1.1 variations at position 9 and the N-terminus were also determined. Our findings provide new insights for designing potent inhibitors for GABA(B)R-coupled N-type (Ca(V)2.2) calcium channels.