Membrane Perturbations and Assay Interferences by Ivermectin Explain Its In Vitro SARS-CoV‑2 Antiviral Activities and Lack of Translatability

The antiparasitic
drug ivermectin was proposed as a repurposed
drug for the treatment of SARS-CoV-2 infection based on in vitro studies,
but proved ineffective in high-quality clinical trials. When exploring
possible reasons for this disconnect, we found that ivermectin interferes
with AlphaScreen assays by quenching singlet oxygen transmission,
calling into question the original justifications for pursuing ivermectin
as an antiviral agent. Furthermore, at the low micromolar concentrations
where ivermectin reduced SARS-CoV-2 viral burden in vitro, ivermectin
decreased cell viability, modified membrane bilayer properties, and
nonspecifically dysregulated membrane protein functions. In this Perspective, we provide molecular-level rationale for why
ivermectin, an effective and safe antiparasitic drug at low nanomolar
concentrations, becomes cytotoxic at low micromolar concentrations
and, in turn, why ivermectin has not translated into an effective
antiviral agent. We highlight lessons learned from the failed ivermectin
repurposing effort and provide a workflow for identifying membrane-perturbing
bioactivity early in drug development.