JCI - Targeting ER stress–induced autophagy overcomes BRAF inhibitor resistance in melanoma

JCI - Targeting ER stress–induced autophagy overcomes BRAF inhibitor resistance in melanoma

J Clin Invest. doi:10.1172/JCI70454. 
Copyright © 2014, The American Society for Clinical Investigation.

Research Article

Targeting ER stress–induced autophagy overcomes BRAF inhibitor resistance in melanoma

Xiao-Hong Ma1, Sheng-Fu Piao1, Souvik Dey2, Quentin Mcafee1,Giorgos Karakousis3, Jessie Villanueva4, Lori S. Hart2, Samuel Levi5,Janice Hu1, Gao Zhang4, Rossitza Lazova6, Vincent Klump6, John M. Pawelek6,Xiaowei Xu7, Wei Xu1, Lynn M. Schuchter1,8, Michael A. Davies9,Meenhard Herlyn4, Jeffrey Winkler5,8, Constantinos Koumenis2,8 andRavi K. Amaravadi1,8

1Department of Medicine, 
2Department of Radiation Oncology, and 
3Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania, USA. 
4Molecular and Cellular Oncogenesis Program, Wistar Institute, Philadelphia, Pennsylvania, USA. 
5Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA. 
6Department of Dermatology, Yale University, New Haven, Connecticut, USA. 
7Department of Pathology and Laboratory Medicine and 
8Abramson Cancer Center, University of Pennsylvania, Philadelphia, Pennsylvania, USA. 
9MD Anderson Cancer Center, University of Texas, Houston, Texas, USA.

Address correspondence to: Ravi Amaravadi, Department of Medicine and Abramson Cancer Center Perelman School of Medicine, University of Pennsylvania, 16 Penn Tower, 3400 Spruce Street, Philadelphia, Pennsylvania 19104, USA. Phone: 215.662.7402; Fax: 215.349.8550; E-mail: Ravi.amaravadi@uphs.upenn.edu.

Authorship note: Xiao-Hong Ma and Sheng-Fu Piao contributed equally to this work.

Published February 24, 2014
Received for publication July 27, 2013, and accepted in revised form November 22, 2013.

Melanomas that result from mutations in the gene encoding BRAF often become resistant to BRAF inhibition (BRAFi), with multiple mechanisms contributing to resistance. While therapy-induced autophagy promotes resistance to a number of therapies, especially those that target PI3K/mTOR signaling, its role as an adaptive resistance mechanism to BRAFi is not well characterized. Using tumor biopsies from BRAFV600E melanoma patients treated either with BRAFi or with combined BRAF and MEK inhibition, we found that BRAFi-resistant tumors had increased levels of autophagy compared with baseline. Patients with higher levels of therapy-induced autophagy had drastically lower response rates to BRAFi and a shorter duration of progression-free survival. In BRAFV600Emelanoma cell lines, BRAFi or BRAF/MEK inhibition induced cytoprotective autophagy, and autophagy inhibition enhanced BRAFi-induced cell death. Shortly after BRAF inhibitor treatment in melanoma cell lines, mutant BRAF bound the ER stress gatekeeper GRP78, which rapidly expanded the ER. Disassociation of GRP78 from the PKR-like ER-kinase (PERK) promoted a PERK-dependent ER stress response that subsequently activated cytoprotective autophagy. Combined BRAF and autophagy inhibition promoted tumor regression in BRAFi-resistant xenografts. These data identify a molecular pathway for drug resistance connecting BRAFi, the ER stress response, and autophagy and provide a rationale for combination approaches targeting this resistance pathway.

See the related Commentary Dangerous liaisons: flirtations between oncogenic BRAF and GRP78 in drug-resistant melanomas.