Discovery and mode of action of a novel analgesic β-toxin from the African spider Ceratogyrus darlingi

Spider venoms are rich sources of peptidic ion channel modulators with important therapeutical potential. We screened a panel of 60 spider venoms to find modulators of ion channels involved in pain transmission. We isolated, synthesized and pharmacologically characterized Cd1a, a novel peptide from the venom of the spider Ceratogyrus darlingi. Cd1a reversibly paralysed sheep blowflies (PD(50) of 1318 pmol/g) and inhibited human Ca(v)2.2 (IC(50) 2.6 μM) but not Ca(v)1.3 or Ca(v)3.1 (IC(50) > 30 μM) in fluorimetric assays. In patch-clamp electrophysiological assays Cd1a inhibited rat Ca(v)2.2 with similar potency (IC(50) 3 μM) without influencing the voltage dependence of Ca(v)2.2 activation gating, suggesting that Cd1a doesn’t act on Ca(v)2.2 as a classical gating modifier toxin. The Cd1a binding site on Ca(v)2.2 did not overlap with that of the pore blocker ω-conotoxin GVIA, but its activity at Ca(v)2.2-mutant indicated that Cd1a shares some molecular determinants with GVIA and MVIIA, localized near the pore region. Cd1a also inhibited human Na(v)1.1–1.2 and Na(v)1.7–1.8 (IC(50) 0.1–6.9 μM) but not Na(v)1.3–1.6 (IC(50) > 30 μM) in fluorimetric assays. In patch-clamp assays, Cd1a strongly inhibited human Na(v)1.7 (IC(50) 16 nM) and produced a 29 mV depolarising shift in Na(v)1.7 voltage dependence of activation. Cd1a (400 pmol) fully reversed Na(v)1.7-evoked pain behaviours in mice without producing side effects. In conclusion, Cd1a inhibited two anti-nociceptive targets, appearing to interfere with Ca(v)2.2 inactivation gating, associated with the Ca(v)2.2 α-subunit pore, while altering the activation gating of Na(v)1.7. Cd1a was inactive at some of the Na(v) and Ca(v) channels expressed in skeletal and cardiac muscles and nodes of Ranvier, apparently contributing to the lack of side effects at efficacious doses, and suggesting potential as a lead for development of peripheral pain treatments.