Intrinsic proteotoxic stress levels vary and act as a predictive marker for sensitivity of cancer cells to Hsp90 inhibition

PLoS One. 2018 Aug 23;13(8):e0202758. doi: 10.1371/journal.pone.0202758. eCollection 2018.


Response of tumours to Hsp90 inhibitors is highly variable and their clinical effects are unpredictable, emphasising the need for a predictive marker. We postulated that sensitivity to Hsp90 inhibitors is connected to basal proteotoxic stress that makes cells dependent on Hsp90. Therefore, we assessed HSF1 as a general sensor of proteotoxic stress and correlated its activity with sensitivity to three separate small molecule Hsp90 inhibitors in seven breast cancer cell lines representing each of the different cancer subtypes. Flow cytometry was used to analyse the viability of breast cancer cell lines after Hsp90 inhibition. HSF1 activity was characterised by Ser326 phosphorylation and the transactivation capacity of HSF1 was determined by qPCR analysis of the ratios of HSF1-dependent (HOP, Hsp70) and HSF1-independent (CHIP) chaperones and cochaperone mRNAs. We show that the sensitivity of breast cancer cell lines to Hsp90 inhibition is highly variable. The basal levels of phosphorylated HSF1 also vary between cell lines and the magnitude of change in HSF1 phosphorylation after Hsp90 inhibition showed a negative correlation with sensitivity to Hsp90 inhibitors. Similarly, the basal transactivation capacity of HSF1, determined by the ratio of Hsp70 or HOP mRNA to CHIP mRNA level, is directly proportional to sensitivity to Hsp90 inhibitors. Increasing basal HSF1 activity by prior heat shock sensitised cells to Hsp90 inhibition. These results demonstrate that endogenous HSF1 activity varies between individual cancer cell lines and inversely reflects their sensitivity to Hsp90 inhibitors, suggesting that basal proteotoxic stress is an important and generalised predictor of response. Mechanistically, the data indicate that high endogenous proteotoxic stress levels sensitise to Hsp90 inhibition due to the inability to respond adequately to further proteotoxic stress. HSF1 activity therefore represents a potential biomarker for therapy with Hsp90 inhibitors, which may be useful for the rational design of future clinical studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biomarkers / metabolism*
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Female
  • HSP90 Heat-Shock Proteins / antagonists & inhibitors*
  • Heat Shock Transcription Factors / metabolism*
  • Heat-Shock Response
  • Humans
  • MCF-7 Cells
  • Molecular Chaperones / genetics
  • Phosphorylation / drug effects
  • Small Molecule Libraries / pharmacology*


  • Biomarkers
  • HSF1 protein, human
  • HSP90 Heat-Shock Proteins
  • Heat Shock Transcription Factors
  • Molecular Chaperones
  • Small Molecule Libraries

Grant support

MP, PJC, BV and PM were supported by the Czech Science Foundation by grant GACR 16-07321S. The work was partially supported by The Ministry of Education, Youth and Sports of the Czech Republic bybthe National Programme of Sustainability I, project MEYS – NPS I – LO1413 and by the Ministry of Health of the Czech Republic by the program Development of Research Organization, MH CZ - DRO (MMCI, 00209805). There was no additional external funding received for this study.