Targeting PLK1 Overcomes T-DM1 Resistance via CDK1-dependent Phosphorylation and Inactivation of Bcl-2/xL in HER2-positive Breast Cancer

Oncogene. 2018 Apr;37(17):2251-2269. doi: 10.1038/s41388-017-0108-9. Epub 2018 Feb 2.

Abstract

Trastuzumab-refractory, HER2 (human epidermal growth factor receptor 2)-positive breast cancer is commonly treated with trastuzumab emtansine (T-DM1), an antibody-drug conjugate of trastuzumab and the microtubule-targeting agent, DM1. However, drug response reduces greatly over time due to acquisition of resistance whose molecular mechanisms are mostly unknown. Here, we uncovered a novel mechanism of resistance against T-DM1 by combining whole transcriptome sequencing (RNA-Seq), proteomics and a targeted small interfering RNA (siRNA) sensitization screen for molecular level analysis of acquired and de novo T-DM1-resistant models of HER2-overexpressing breast cancer. We identified Polo-like kinase 1 (PLK1), a mitotic kinase, as a resistance mediator whose genomic as well as pharmacological inhibition restored drug sensitivity. Both acquired and de novo resistant models exhibited synergistic growth inhibition upon combination of T-DM1 with a selective PLK1 inhibitor, volasertib, at a wide concentration range of the two drugs. Mechanistically, T-DM1 sensitization upon PLK1 inhibition with volasertib was initiated by a spindle assembly checkpoint (SAC)-dependent mitotic arrest, leading to caspase activation, followed by DNA damage through CDK1-dependent phosphorylation and inactivation of Bcl-2/xL. Furthermore, we showed that Ser70 phosphorylation of Bcl-2 directly regulates apoptosis by disrupting the binding to and sequestration of the pro-apoptotic protein Bim. Importantly, T-DM1 resistance signature or PLK1 expression correlated with cell cycle progression and DNA repair, and predicted a lower sensitivity to taxane/trastuzumab combination in HER2-positive breast cancer patients. Finally, volasertib in combination with T-DM1 greatly synergized in models of T-DM1 resistance in terms of growth inhibition both in three dimensional (3D) cell culture and in vivo. Altogether, our results provide promising pre-clinical evidence for potential testing of T-DM1/volasertib combination in T-DM1 refractory HER2-positive breast cancer patients for whom there is currently no treatment available.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ado-Trastuzumab Emtansine
  • Animals
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology*
  • CDC2 Protein Kinase / metabolism
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm / drug effects*
  • Drug Synergism
  • Female
  • Humans
  • Maytansine / analogs & derivatives*
  • Maytansine / therapeutic use
  • Mice
  • Phosphorylation / drug effects
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Proto-Oncogene Proteins / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-bcl-2 / genetics
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Pteridines / pharmacology*
  • Receptor, ErbB-2 / metabolism
  • Signal Transduction / drug effects
  • Trastuzumab / therapeutic use*
  • Xenograft Model Antitumor Assays
  • bcl-X Protein / genetics
  • bcl-X Protein / metabolism

Substances

  • BCL2 protein, human
  • BI 6727
  • Cell Cycle Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Pteridines
  • bcl-X Protein
  • Maytansine
  • Receptor, ErbB-2
  • Protein-Serine-Threonine Kinases
  • polo-like kinase 1
  • CDC2 Protein Kinase
  • CDK1 protein, human
  • Trastuzumab
  • Ado-Trastuzumab Emtansine