Combined targeting of Raf and Mek synergistically inhibits tumorigenesis in triple negative breast cancer model systems
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Teddy S. Nagaria1,2, Changnian Shi1, Charles Leduc2, Victoria Hoskin1,2, Soma Sikdar2, Waheed Sangrar1,2,* and Peter A. Greer1,2,*
1Division of Cancer Biology and Genetics, Cancer Research Institute, Queen’s University, Kingston, ON, Canada
2Department of Pathology and Molecular Medicine, Queen’s University, Kingston, ON, Canada
Peter A. Greer, email: [email protected]
Keywords: triple negative breast cancer, Raf, Mek, selumitinib, synergy
Received: December 01, 2016 Accepted: August 04, 2017 Published: August 24, 2017
Aberrant Ras-MAPK signaling from receptor tyrosine kinases (RTKs), including epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor-2 (HER2), is a hallmark of triple negative breast cancer (TNBC); thus providing rationale for targeting the Ras-MAPK pathway. Components of this EGFR/HER2-Ras-Raf-Mek-Erk pathway were co-targeted in the MDA-MB-231 and MDA-MB-468 human TNBC cell lines, and in vitro effects on signaling and cytotoxicity, as well as in vivo effects on xenograft tumor growth and metastasis were assessed. The dual EGFR/HER2 inhibitor lapatinib (LPN) displayed greater cytotoxic potency and MAPK signaling inhibition than the EGFR inhibitor erlotinib, suggesting both EGFR and HER2 contribute to MAPK signaling in this TNBC model. The Raf inhibitor sorafenib (SFN) or the Mek inhibitor U0126 suppressed MAPK signaling to a greater extent than LPN; which correlated with greater cytotoxic potency of SFN, but not U0126. However, U0126 potentiated the cytotoxic efficacy of LPN and SFN in an additive and synergistic manner, respectively. This in-series Raf-Mek co-targeting synergy was recapitulated in orthotopic mouse xenografts, where SFN and the Mek inhibitor selumitinib (AZD6244) inhibited primary tumor growth and pulmonary metastasis. Raf and Mek co-inhibition exhibits synergy in TNBC models and represent a promising combination therapy for this aggressive breast cancer type.
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