Mutational analysis of ProTx I and the novel venom peptide Pe1b provide insight into residues responsible for selective inhibition of the analgesic drug target NaV1.7.
Management of chronic pain presents a major challenge, since many currently available treatments lack efficacy and have problems such as addiction and tolerance. Loss of function mutations in the SCN9A gene lead to a congenital inability to feel pain, with no other sensory deficits aside from anosmia. SCN9A encodes the voltage gated sodium (NaV) channel 1.7 (NaV1.7) which has been identified as a primary pain target. However, in developing NaV1.7 targeted analgesics, extreme care must to be taken to avoid off target activity on other NaV subtypes that are critical for survival. Since spider venoms are an excellent source of NaV channel modulators, we screened a panel of spider venoms to identify selective NaV1.7 inhibitors. This led to identification of two novel NaV modulating venom peptides (b/m theraphotoxin Pe1a and b/m theraphotoxin Pe1b (Pe1b) from the arboreal tarantula Phormingochilus everetti. A third peptide isolated from the tarantula Bumba pulcherrimaklaasi was identical to the well known ProTx I (b/o theraphotoxin Tp1a) from the tarantula Thrixopelma pruriens. A tethered toxin (t toxin) based alanine scanning strategy was used to determine the NaV1.7 pharmacophore of ProTx I. We designed several ProTx I and Pe1b analogues, and tested them for activity and NaV channel subtype selectivity. Several analogues had improved potency against NaV1.7, and altered specificity against other NaV channels. These analogues provide a foundation for development of Pe1b as a lead molecule for therapeutic inhibition of NaV1.7.
Biochemical pharmacology