Metastatic colorectal cancer (CRC) is one of the most deadly cancers, characterized by poor prognosis and low survival rate. The multi-kinase inhibitor regorafenib can improve patient survival and has recently been approved for the treatment of metastatic CRC. Regorafenib inhibits the RAS/RAF/MEK/ERK pathway, which is aberrantly activated in most CRCs due to prevalent RAS and RAF mutations. However, the anticancer mechanism of regorafenib is not well understood. No genetic alteration has been linked to regorafenib sensitivity or resistance in CRC cells. The sometimes serious side effects of regorafenib observed in clinical studies make identifying responder patients a critical mission of precision medicine, to avoid unnecessary treatment. Our preliminary studies reveal that the therapeutic activity of regorafenib in CRC cells is associated with apoptosis induction and proteasomal degradation of Mcl-1, a pro-survival Bcl-2 family protein. CRC cells that are intrinsically insensitive to regorafenib lack Mcl-1 degradation and contain inactivating mutations of FBW7, a tumor suppressor and E3 ubiquitin ligase that is frequently mutated in CRCs. In response to regorafenib treatment, FBW7 binds to phosphorylated Mcl-1 and is required for its ubiquitination and subsequent degradation. Blocking Mcl-1 phosphorylation by a genetic knock-in approach abrogates its binding to FBW7 and degradation, and suppresses regorafenib-induced killing of CRC cells. Furthermore, CRC cells with acquired regorafenib resistance were found to have blocked Mcl-1 degradation and enrichment of FBW7 mutations. We hypothesize that FBW7-mediated Mcl-1 degradation is crucial for the anticancer effects of regorafenib and that FBW7 mutations disrupt regorafenib-induced Mcl-1 degradation, resulting in regorafenib resistance in CRCs. We propose to test this hypothesis and its translational implications by using genetic and biochemical approaches.
Aim 1 : Delineate how Mcl-1 degradation mediates the anticancer activity of regorafenib in CRC cells.
Aim 2 : Determine the effects of oncogenic mutations on regorafenib sensitivity and Mcl-1 stability.
Aim 3 : Elucidate the roles of FBW7 mutations and Mcl-1 stability in acquired resistance to regorafenib. In parallel with ongoing clinical studies on regorafenib, these studies may establish FBW7 mutational status and Mcl-1 stability as key determinants of regorafenib sensitivity in CRCs. They may also provide a rationale for effective combinations of regorafenib with other drugs, as well as new tools for investigating the broad functional roles of Mcl-1 and FBW7 in targeted anticancer therapies, and for overcoming therapeutic resistance caused by genomic instability in CRC cells.

Public Health Relevance

Colorectal cancer is one of the leading causes of cancer-related death in the United States. The proposed studies will help to understand the antitumor mechanism of a recently approved targeted drug against colorectal cancer. In the long run, the results of these studies could be useful for rational design of more effective strategies and agents to improve treatment of colorectal cancer.

National Institute of Health (NIH)
National Cancer Institute (NCI)
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Basic Mechanisms of Cancer Therapeutics Study Section (BMCT)
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Forry, Suzanne L
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University of Pittsburgh
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Chen, Dongshi; Ni, Hong-Min; Wang, Lei et al. (2018) PUMA induction mediates acetaminophen-induced necrosis and liver injury. Hepatology :
Tong, Jingshan; Zheng, Xingnan; Tan, Xiao et al. (2018) Mcl-1 Phosphorylation without Degradation Mediates Sensitivity to HDAC Inhibitors by Liberating BH3-Only Proteins. Cancer Res 78:4704-4715
Leibowitz, Brian J; Yang, Liheng; Wei, Liang et al. (2018) Targeting p53-dependent stem cell loss for intestinal chemoprotection. Sci Transl Med 10:
Knickelbein, Kyle; Tong, Jingshan; Chen, Dongshi et al. (2018) Restoring PUMA induction overcomes KRAS-mediated resistance to anti-EGFR antibodies in colorectal cancer. Oncogene 37:4599-4610
Wei, Liang; Leibowitz, Brian J; Epperly, Michael et al. (2018) The GS-nitroxide JP4-039 improves intestinal barrier and stem cell recovery in irradiated mice. Sci Rep 8:2072
Fletcher, Rochelle; Wang, Yi-Jun; Schoen, Robert E et al. (2018) Colorectal cancer prevention: Immune modulation taking the stage. Biochim Biophys Acta Rev Cancer 1869:138-148
Wang, Yi-Jun; Fletcher, Rochelle; Yu, Jian et al. (2018) Immunogenic effects of chemotherapy-induced tumor cell death. Genes Dis 5:194-203
Chen, Dongshi; Tong, Jingshan; Yang, Liheng et al. (2018) PUMA amplifies necroptosis signaling by activating cytosolic DNA sensors. Proc Natl Acad Sci U S A 115:3930-3935
Tong, Jingshan; Tan, Shuai; Nikolovska-Coleska, Zaneta et al. (2017) FBW7-Dependent Mcl-1 Degradation Mediates the Anticancer Effect of Hsp90 Inhibitors. Mol Cancer Ther 16:1979-1988
Tong, Jingshan; Wang, Peng; Tan, Shuai et al. (2017) Mcl-1 Degradation Is Required for Targeted Therapeutics to Eradicate Colon Cancer Cells. Cancer Res 77:2512-2521

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