Refining Covalent Warhead Reactivity: A New Look At GSH Reactivity Assays

By Stéphane Turcotte, Senior Principal Scientist

Covalent drugs continue to deliver therapeutic impact, but concerns around warhead reactivity often discourage their early use in drug discovery. A clearer understanding of how irreversible and reversible warheads behave—and how to measure that behavior accurately—can meaningfully reduce risk later in development. Traditional glutathione (GSH) reactivity assays provide a starting point, yet their concentration‑dependent design, limited reproducibility, and inability to distinguish between warhead classes create gaps in assessing true toxicological risk.

A new kinetic‑focused GSH assay offers an improved path forward. By measuring koff for reversible warheads and extracting kinact/KI for irreversible ones, teams can evaluate toxicity through residence time and targeted reactivity rather than simple half‑life decay. These insights support smarter warhead selection, more refined covalent building blocks, and better‑informed hit optimization.

If you’re looking to strengthen covalent screening strategies from day one, access the full application note to gain practical guidance.