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

Targeting PLK1 overcomes T-DM1 resistance via CDK1-dependent phosphorylation and inactivation of Bcl-2/xL in HER2-positive breast cancer.

Author information

1
Department of Molecular Biology and Genetics, Faculty of Science, Bilkent University, 06800, Ankara, Turkey.
2
Division of Molecular Genome Analysis, German Cancer Research Center (DKFZ), INF580, Heidelberg, 69120, Germany.
3
Department of Computer Engineering, Bilkent University, 06800, Ankara, Turkey.
4
Department of Pathology, Hacettepe University School of Medicine, 06410, Ankara, Turkey.
5
Department of Medical Genetics, Başkent University, 01250, Adana, Turkey.
6
Department of Molecular Biology and Genetics, Faculty of Science, Bilkent University, 06800, Ankara, Turkey. sahinozgur@gmail.com.
7
National Nanotechnology Research Center (UNAM), Bilkent University, 06800, Ankara, Turkey. sahinozgur@gmail.com.

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.

PMID:
29391599
DOI:
10.1038/s41388-017-0108-9

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