Loss-of-function mutations of NaV1.7 lead to congenital insensitivity to pain, a rare condition resulting in individuals who are otherwise normal except for the inability to sense pain, making pharmacological inhibition of NaV1.7 a promising therapeutic strategy for the treatment of pain. We characterized a novel mouse model of NaV1.7-mediated pain based on intraplantar injection of the scorpion toxin OD1, which is suitable for rapid in vivo profiling of NaV1.7 inhibitors. Intraplantar injection of OD1 caused spontaneous pain behaviors, which were reversed by co-injection with NaV1.7 inhibitors and significantly reduced in NaV1.7−/− mice. To validate the use of the model for profiling NaV1.7 inhibitors, we determined the NaV selectivity and tested the efficacy of the reported NaV1.7 inhibitors GpTx-1, PF-04856264 and CNV1014802 (raxatrigine). GpTx-1 selectively inhibited NaV1.7 and was effective when co-administered with OD1, but lacked efficacy when delivered systemically. PF-04856264 state-dependently and selectively inhibited NaV1.7 and significantly reduced OD1-induced spontaneous pain when delivered locally and systemically. CNV1014802 state-dependently, but non-selectively, inhibited NaV channels and was only effective in the OD1 model when delivered systemically. Our novel model of NaV1.7-mediated pain based on intraplantar injection of OD1 is thus suitable for the rapid in vivo characterization of the analgesic efficacy of NaV1.7 inhibitors.

SH-SY5Y human neuroblastoma cells provide a useful in vitro model to study the mechanisms underlying neurotransmission and nociception. These cells are derived from human sympathetic neuronal tissue and thus, express a number of the Cav channel subtypes essential for regulation of important physiological functions, such as heart contraction and nociception, including the clinically validated pain target Cav2.2. We have detected mRNA transcripts for a range of endogenous expressed subtypes Cav1.3, Cav2.2 (including two Cav1.3, and three Cav2.2 splice variant isoforms) and Cav3.1 in SH-SY5Y cells; as well as Cav auxiliary subunits α2δ1–3, β1, β3, β4, γ1, γ4–5, and γ7. Both high- and low-voltage activated Cav channels generated calcium signals in SH-SY5Y cells. Pharmacological characterisation using ω-conotoxins CVID and MVIIA revealed significantly (∼ 10-fold) higher affinity at human versus rat Cav2.2, while GVIA, which interacts with Cav2.2 through a distinct pharmacophore had similar affinity for both species. CVID, GVIA and MVIIA affinity was higher for SH-SY5Y membranes vs whole cells in the binding assays and functional assays, suggesting auxiliary subunits expressed endogenously in native systems can strongly influence Cav2.2 channels pharmacology. These results may have implications for strategies used to identify therapeutic leads at Cav2.2 channels.

This study established a novel animal model of cisplatin-induced mechanical allodynia consistent with the A-fiber neuropathy seen clinically. Systematic assessment of a range of therapeutics identified several candidates that warrant further clinical investigation.

Cav2.2 is a calcium channel subtype localized at nerve terminals, including nociceptive fibers, where it initiates neurotransmitter release. Cav2.2 is an important contributor to synaptic transmission in ascending pain pathways, and is up-regulated in the spinal cord in chronic pain states along with the auxiliary α2δ1 subunit. It is therefore not surprising that toxins that inhibit Cav2.2 are analgesic. Venomous animals, such as cone snails, spiders, snakes, assassin bugs, centipedes and scorpions are rich sources of remarkably potent and selective Cav2.2 inhibitors. However, side effects in humans currently limit their clinical use. Here we review Cav2.2 inhibitors from venoms and their potential as drug leads.

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 (PD50 of 1318 pmol/g) and inhibited human Cav2.2 (IC50 2.6 μM) but not Cav1.3 or Cav3.1 (IC50 > 30 μM) in fluorimetric assays. In patch-clamp electrophysiological assays Cd1a inhibited rat Cav2.2 with similar potency (IC50 3 μM) without influencing the voltage dependence of Cav2.2 activation gating, suggesting that Cd1a doesn’t act on Cav2.2 as a classical gating modifier toxin. The Cd1a binding site on Cav2.2 did not overlap with that of the pore blocker ω-conotoxin GVIA, but its activity at Cav2.2-mutant indicated that Cd1a shares some molecular determinants with GVIA and MVIIA, localized near the pore region. Cd1a also inhibited human Nav1.1–1.2 and Nav1.7–1.8 (IC50 0.1–6.9 μM) but not Nav1.3–1.6 (IC50 > 30 μM) in fluorimetric assays. In patch-clamp assays, Cd1a strongly inhibited human Nav1.7 (IC50 16 nM) and produced a 29 mV depolarising shift in Nav1.7 voltage dependence of activation. Cd1a (400 pmol) fully reversed Nav1.7-evoked pain behaviours in mice without producing side effects. In conclusion, Cd1a inhibited two anti-nociceptive targets, appearing to interfere with Cav2.2 inactivation gating, associated with the Cav2.2 α-subunit pore, while altering the activation gating of Nav1.7. Cd1a was inactive at some of the Nav and Cav 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.