A Contaminant Impurity, Not Rigosertib, Is a Tubulin Binding Agent

Stacey J. Baker, Stephen C. Cosenza, Saikrishna Athuluri-Divakar, M. V.Ramana Reddy, Rodrigo Vasquez-Del Carpio, Rinku Jain, Aneel K. Aggarwal, E. Premkumar Reddy

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Rigosertib is a styryl benzyl sulfone that inhibits growth of tumor cells and acts as a RAS mimetic by binding to Ras binding domains of RAS effectors. A recent study attributed rigosertib's mechanism of action to microtubule binding. In that study, rigosertib was obtained from a commercial vendor. We compared the purity of clinical-grade and commercially sourced rigosertib and found that commercially sourced rigosertib contains approximately 5% ON01500, a potent inhibitor of tubulin polymerization. Clinical-grade rigosertib, which is free of this impurity, does not exhibit tubulin-binding activity. Cell lines expressing mutant β-tubulin have also been reported to be resistant to rigosertib. However, our study showed that these cells failed to proliferate in the presence of rigosertib at concentrations that are lethal to wild-type cells. Rigosertib induced a senescence-like phenotype in the small percentage of surviving cells, which could be incorrectly scored as resistant using short-term cultures.

Original languageEnglish (US)
Pages (from-to)180-190.e4
JournalMolecular cell
Issue number1
StatePublished - Jul 2 2020


  • ON01500
  • ON01910
  • RAS
  • Ras binding domain
  • rigosertib
  • tubulin polymerization

ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology


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