Prospective identification of resistance mechanisms to HSP90 inhibition in KRAS mutant cancer cells

Oncotarget. 2017 Jan 31;8(5):7678-7690. doi: 10.18632/oncotarget.13841.


Inhibition of the HSP90 chaperone results in depletion of many signaling proteins that drive tumorigenesis, such as downstream effectors of KRAS, the most commonly mutated human oncogene. As a consequence, several small-molecule HSP90 inhibitors are being evaluated in clinical trials as anticancer agents. To prospectively identify mechanisms through which HSP90-dependent cancer cells evade pharmacologic HSP90 blockade, we generated multiple mutant KRAS-driven cancer cell lines with acquired resistance to the purine-scaffold HSP90 inhibitor PU-H71. All cell lines retained dependence on HSP90 function, as evidenced by sensitivity to short hairpin RNA-mediated suppression of HSP90AA1 or HSP90AB1 (also called HSP90α and HSP90β, respectively), and exhibited two types of genomic alterations that interfere with the effects of PU-H71 on cell viability and proliferation: (i) a Y142N missense mutation in the ATP-binding domain of HSP90α that co-occurred with amplification of the HSP90AA1 locus, (ii) genomic amplification and overexpression of the ABCB1 gene encoding the MDR1 drug efflux pump. In support of a functional role for these alterations, exogenous expression of HSP90α Y142N conferred PU-H71 resistance to HSP90-dependent cells, and pharmacologic MDR1 inhibition with tariquidar or lowering ABCB1 expression restored sensitivity to PU-H71 in ABCB1-amplified cells. Finally, comparison with structurally distinct HSP90 inhibitors currently in clinical development revealed that PU-H71 resistance could be overcome, in part, by ganetespib (also known as STA9090) but not tanespimycin (also known as 17-AAG). Together, these data identify potential mechanisms of acquired resistance to small molecules targeting HSP90 that may warrant proactive screening for additional HSP90 inhibitors or rational combination therapies.

Keywords: HSP90 inhibition; MDR1; PU-H71; drug resistance; mutant KRAS.

MeSH terms

  • A549 Cells
  • ATP Binding Cassette Transporter, Subfamily B / antagonists & inhibitors
  • ATP Binding Cassette Transporter, Subfamily B / genetics
  • ATP Binding Cassette Transporter, Subfamily B / metabolism
  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects
  • Benzodioxoles / pharmacology*
  • Benzoquinones / pharmacology
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Dose-Response Relationship, Drug
  • Drug Resistance, Neoplasm* / genetics
  • Gene Amplification
  • Genetic Predisposition to Disease
  • HSP90 Heat-Shock Proteins / antagonists & inhibitors*
  • HSP90 Heat-Shock Proteins / genetics
  • HSP90 Heat-Shock Proteins / metabolism
  • Humans
  • Lactams, Macrocyclic / pharmacology
  • Mutation*
  • Mutation, Missense
  • Neoplasms / drug therapy*
  • Neoplasms / genetics
  • Neoplasms / metabolism
  • Neoplasms / pathology
  • Phenotype
  • Proto-Oncogene Proteins p21(ras) / genetics*
  • Purines / pharmacology*
  • RNA Interference
  • Transfection
  • Triazoles / pharmacology


  • ABCB1 protein, human
  • ATP Binding Cassette Transporter, Subfamily B
  • Antineoplastic Agents
  • Benzodioxoles
  • Benzoquinones
  • HSP90 Heat-Shock Proteins
  • HSP90AA1 protein, human
  • HSP90AB1 protein, human
  • KRAS protein, human
  • Lactams, Macrocyclic
  • Purines
  • STA 9090
  • Triazoles
  • 9H-purine-9-propanamine, 6-amino-8-((6-iodo-1,3-benzodioxol-5-yl)thio)-N-(1-methylethyl)-
  • tanespimycin
  • Proto-Oncogene Proteins p21(ras)