Therapeutics , Targets , and Chemical Biology De fi nition of PKC-a , CDK 6 , and MET as Therapeutic Targets in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a highly heterogeneous and recurrent subtype of breast cancer that lacks an effective targeted therapy. To identify candidate therapeutic targets, we profiled global gene expression in TNBC and breast tumor-initiating cells with a patient survival dataset. Eight TNBC-related kinases were found to be overexpressed in TNBC cells with stem-like properties. Among them, expression of PKC-a, MET, and CDK6 correlated with poorer survival outcomes. In cases coexpressing two of these three kinases, survival rates were lower than in cases where only one of these kinases was expressed. In functional tests, two-drug combinations targeting these three kinases inhibited TNBC cell proliferation and tumorigenic potential in a cooperative manner. A combination of PKC-a-MET inhibitors also attenuated tumor growth in a cooperative manner in vivo. Our findings define three kinases critical for TNBC growth and offer a preclinical rationale for their candidacy as effective therapeutic targets in treating TNBC. Cancer Res; 74(17); 1–14. 2014 AACR. Introduction Breast cancers are typically classified into several subtypes: Luminal A and B subtypes of breast cancer that correspond to pathologic estrogen receptor (ER)-positive tumors, the HER2 subtype that corresponds toHER2-overexpressing tumors, and triple-negative/basal-like breast cancer (TNBC/BLBC). BLBC makes up about 15% to 20% of breast cancers. Recent studies using clinical samples indicate that BLBC shares more than 80% similarity with TNBC, which is negative for ER, progesterone receptor (PR), andHER2 expression (1). In addition, two major subgroups of TNBC characterized on the basis of gene ontologies and differential gene expression profile have been reported: basal-like TNBC driven by genes enriched in cell cycle, cell division, and DNA damage response; and mesenchymal-like driven by genes involved in cell motility, cell differentiation, and growth factor pathways (2). These findings indicate that TNBCs are highly heterogeneous. Although subtyping allows for better prediction of the response of each subtype to specific molecular targets, the therapeutic benefits in clinical trial are still unclear. Here, we will use TNBC as a general term to broadly represent the TNBC/BLBC subtype. Patients with TNBC initially respond to conventional chemotherapy, but the disease frequently relapses and leads to worse outcome than patients with hormone receptor-positive subtypes (3). The low survival rate of patientswith TNBC is also due to high metastasis rates and lack of effective treatment after a relapse (4). Currently, no effective targeted therapies are available for patients with TNBC because of TNBC's lack of expressionof hormone receptors andHER2amplification (1, 5). A cancer stem cell (CSC) or tumor-initiating cell (TIC) hypothesis has been proposed to account for treatment failure and recurrence in patients with TNBC (6). Breast TICs (BTIC) make up a small subpopulation of cells inside tumors that are resistant to conventional therapy and are capable of reinitiating tumor growth after treatment (7–9); these cells can be enriched by flow cytometry using specific cell-surface markers such as CD44þ and CD24 /low (10) and ALDH1 (11). Accumulating evidence suggests that BTICs are responsible for tumor initiation, progression, and drug resistance (12, 13). Residual breast tumor cells that survive after conventional Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas. The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, Texas. Department ofGeneral Surgery, ChangGungMemorialHospital at Linkou, Chang Gung University College of Medicine, Taipei, Taiwan. Graduate Institute for Cancer Biology and Center for Molecular Medicine, China Medical University, Taichung, Taiwan. Department of Biotechnology, Asia University, Taichung, Taiwan. Department of Internal Medicine, Chang Gung Memorial Hospital at Linkou, Chang Gung University College of Medicine, Taipei, Taiwan. Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston, Texas. Department of Surgery, Mackay Memorial Hospital, Mackay Junior College of Medicine, Nursing, and Management, Taipei, Taiwan. Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan. Department of Gynecologic Oncology and Reproductive Medicine, The University of Texas MD Anderson Cancer Center, Houston, Texas. Department of Systems Biology, The University of Texas MD Anderson Cancer Center, Houston, Texas. Department of Breast Medical Oncology, TheUniversity of Texas MD Anderson Cancer Center, Houston, Texas. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/). Corresponding Author: Mien-Chie Hung, Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 108, Houston, TX 77030. Phone: 713-7923668; Fax: 713-794-3270; E-mail: mhung@mdanderson.org doi: 10.1158/0008-5472.CAN-14-0584 2014 American Association for Cancer Research. Cancer Research www.aacrjournals.org OF1 Research. on May 1, 2017. © 2014 American Association for Cancer cancerres.aacrjournals.org Downloaded from Published OnlineFirst June 26, 2014; DOI: 10.1158/0008-5472.CAN-14-0584