Rigid amphipathic fusion inhibitors, small molecule antiviral compounds against enveloped viruses

TLDR

Antiviral drugs that target viral proteins quickly select for resistance, and the limited number of viral targets makes it difficult to develop new therapies, so the unique fusion mechanics of enveloped viruses offer a promising alternative target. The study seeks novel antiviral targets by exploiting the fusion step of enveloped viruses. RAFIs are synthetic rigid amphiphiles that mimic phospholipids with larger hydrophilic heads, increasing positive curvature in the outer leaflet and raising the activation energy barrier beyond what viral proteins can provide, thereby blocking fusion. RAFIs inhibit the infectivity of diverse enveloped viruses, including hepatitis C and HSV‑1/2, with an IC50 of 48 nM, a selectivity index over 3,000, and no cytotoxic or cytostatic effects, by preventing the negative curvature required for initial fusion.

Abstract

Antiviral drugs targeting viral proteins often result in prompt selection for resistance. Moreover, the number of viral targets is limited. Novel antiviral targets are therefore needed. The unique characteristics of fusion between virion envelopes and cell membranes may provide such targets. Like all fusing bilayers, viral envelopes locally adopt hourglass-shaped stalks during the initial stages of fusion, a process that requires local negative membrane curvature. Unlike cellular vesicles, however, viral envelopes do not redistribute lipids between leaflets, can only use the energy released by virion proteins, and fuse to the extracellular leaflets of cell membranes. Enrichment in phospholipids with hydrophilic heads larger than their hydrophobic tails in the convex outer leaflet of vesicles favors positive curvature, therefore increasing the activation energy barrier for fusion. Such phospholipids can increase the activation barrier beyond the energy provided by virion proteins, thereby inhibiting viral fusion. However, phospholipids are not pharmacologically useful. We show here that a family of synthetic rigid amphiphiles of shape similar to such phospholipids, RAFIs (rigid amphipathic fusion inhibitors), inhibit the infectivity of several otherwise unrelated enveloped viruses, including hepatitis C and HSV-1 and -2 (lowest apparent IC 50 48 nM), with no cytotoxic or cytostatic effects (selectivity index > 3,000) by inhibiting the increased negative curvature required for the initial stages of fusion.