Pharmaceutical-Grade Rigosertib Is a Microtubule-Destabilizing Agent.

We recently used CRISPRi/a-based chemical-genetic screens and cell biological, biochemical, and structural assays to determine that rigosertib, an anti-cancer agent in phase III clinical trials, kills cancer cells by destabilizing microtubules. Reddy and co-workers (Baker et al., 2020, this issue of Molecular Cell) suggest that a contaminating degradation product in commercial formulations of rigosertib is responsible for the microtubule-destabilizing activity. Here, we demonstrate that cells treated with pharmaceutical-grade rigosertib (>99.9% purity) or commercially obtained rigosertib have qualitatively indistinguishable phenotypes across multiple assays. The two formulations have indistinguishable chemical-genetic interactions with genes that modulate microtubule stability, both destabilize microtubules in cells and in vitro, and expression of a rationally designed tubulin mutant with a mutation in the rigosertib binding site (L240F TUBB) allows cells to proliferate in the presence of either formulation. Importantly, the specificity of the L240F TUBB mutant for microtubule-destabilizing agents has been confirmed independently. Thus, rigosertib kills cancer cells by destabilizing microtubules, in agreement with our original findings.

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Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.

Déclaration de conflit d'intérêts

Declaration of Interests M.A.H., L.A.G., M.K., and J.S.W. have filed a patent application related to CRISPRi and CRISPRa screening (PCT/US15/40449). M.E.T., L.A.G., and J.S.W. have filed a patent application for the SunTag technology (PCT/US2015/040439). J.S.W. consults for and holds equity in KSQ Therapeutics, Maze Therapeutics, and Tenaya Therapeutics. J.S.W. is a venture partner at 5AM Ventures and a member of the Amgen Scientific Advisory Board. M.J. and M.A.H. consult for Maze Therapeutics.