Research Papers:

Acquisition of a single EZH2 D1 domain mutation confers acquired resistance to EZH2-targeted inhibitors

Theresa Baker, Sujata Nerle, Justin Pritchard, Boyang Zhao, Victor M. Rivera, Andrew Garner and Francois Gonzalvez _

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Oncotarget. 2015; 6:32646-32655. https://doi.org/10.18632/oncotarget.5066

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Theresa Baker1, Sujata Nerle1, Justin Pritchard1, Boyang Zhao1, Victor M. Rivera1, Andrew Garner1,*, Francois Gonzalvez1,*

1ARIAD Pharmaceuticals, Inc., Cambridge, MA 02139, USA

*These authors have contributed equally to this work

Correspondence to:

Francois Gonzalvez, e-mail: [email protected]

Keywords: EZH2, drug resistance, mutation, epigenetics, cancer

Received: July 17, 2015     Accepted: August 20, 2015     Published: September 02, 2015


Although targeted therapies have revolutionized cancer treatment, overcoming acquired resistance remains a major clinical challenge. EZH2 inhibitors (EZH2i), EPZ-6438 and GSK126, are currently in the early stages of clinical evaluation and the first encouraging signs of efficacy have recently emerged in the clinic. To anticipate mechanisms of resistance to EZH2i, we used a forward genetic platform combining a mutagenesis screen with next generation sequencing technology and identified a hotspot of secondary mutations in the EZH2 D1 domain (Y111 and I109). Y111D mutation within the WT or A677G EZH2 allele conferred robust resistance to both EPZ-6438 and GSK126, but it only drove a partial resistance within the Y641F allele. EZH2 mutants required histone methyltransferase (HMT) catalytic activity and the polycomb repressive complex 2 (PRC2) components, SUZ12 and EED, to drive drug resistance. Furthermore, D1 domain mutations not only blocked the ability of EZH2i to bind to WT and A677G mutant, but also abrogated drug binding to the Y641F mutant. These data provide the first cellular validation of the mechanistic model underpinning the oncogenic function of WT and mutant EZH2. Importantly, our findings suggest that acquired-resistance to EZH2i may arise in WT and mutant EZH2 patients through a single mutation that remains targetable by second generation EZH2i.

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