The relative efficacy of chemically diverse small-molecule enzyme-inhibitors against anticoagulant activities of Black Snake (Pseudechis spp.) venoms.

Snakebite remains a worldwide public health burden and a severely neglected tropical disease. Recent research has begun to focus on the potential use of repurposed small-molecule enzyme-inhibitors as early treatments to neutralise the effects of snake venoms. Black snakes (Pseudechis spp.) are a widespread and dangerously venomous group found throughout Australia and New Guinea. Utilising validated coagulation assays, our study assessed the efficacy of two chemically different small molecule inhibitors, a phospholipase A inhibitor (varespladib) and a metalloproteinase inhibitor (prinomastat), in vitro neutralisation of the anticoagulant prothrombinase-inhibiting activity of venom from seven species within the Pseudechis genus (P. australis, P. butleri, P. coletti, P. guttatus, P. papuanus, P.rossignolii, P. sp (NT).). Varespladib was shown to be highly effective at neutralising this anticoagulant activity for all seven species, but with P. coletti notably less so than the others. In contrast, prinomastat showed strong neutralisation for five out of the seven species, but was ineffective at neutralising the activity of P. coletti or P. rossignolii venoms. This suggests that varespladib binds to a highly conserved site but that prinomastat binds to a more variable site. These results build upon recent literature indicating that metalloproteinase inhibitors have cross-neutralising potential towards snake venom phospholipase A toxins, but with higher degrees of variability that PLA2-specific inhibitors. An important caveat is that these are in vitro tests and while suggestive of potential clinical utility, in vivo animal testing and clinical trials are required as future work.