Theranostics 2020; 10(18):8098-8110. doi:10.7150/thno.45363

Research Paper

Mcl-1 inhibition overcomes intrinsic and acquired regorafenib resistance in colorectal cancer

Xiangping Song1,2,3, Lin Shen1,3,4, Jingshan Tong1,3, Chaoyuan Kuang1, Shan Zeng4, Robert E. Schoen1,5, Jian Yu1,6, Haiping Pei2✉, Lin Zhang1,3✉

1. UPMC Hillman Cancer Center, Pittsburgh, PA 15213, USA.
2. Department of Gastrointestinal Surgery, Xiangya Hospital, Central South University, Changsha, Hunan, 410008, P.R. China.
3. Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
4. Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, 410008, P.R. China.
5. Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213. USA.
6. Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213. USA.

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Citation:
Song X, Shen L, Tong J, Kuang C, Zeng S, Schoen RE, Yu J, Pei H, Zhang L. Mcl-1 inhibition overcomes intrinsic and acquired regorafenib resistance in colorectal cancer. Theranostics 2020; 10(18):8098-8110. doi:10.7150/thno.45363. Available from http://www.thno.org/v10p8098.htm

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Abstract

Intrinsic and acquired resistance to targeted therapies is a significant clinical problem in cancer. We previously showed that resistance to regorafenib, a multi-kinase inhibitor for treating colorectal cancer (CRC) patients, can be caused by mutations in the tumor suppressor FBW7, which block degradation of the pro-survival Bcl-2 family protein Mcl-1. We tested if Mcl-1 inhibition can be used to develop a precision combination therapy for overcoming regorafenib resistance.

Methods: Small-molecule Mcl-1 inhibitors were tested on CRC cells with knock-in (KI) of a non-degradable Mcl-1. Effects of Mcl-1 inhibitors on regorafenib sensitivity were determined in FBW7-mutant and -wild-type (WT) CRC cells and tumors, and in those with acquired regorafenib resistance due to enriched FBW7 mutations. Furthermore, translational potential was explored by establishing and analyzing FBW7-mutant and -WT patient-derived organoid (PDO) and xenograft (PDX) tumor models.

Results: We found that highly potent and specific Mcl-1 inhibitors such as S63845 overcame regorafenib resistance by restoring apoptosis in multiple regorafenib-resistant CRC models. Mcl-1 inhibition re-sensitized CRC tumors with intrinsic and acquired regorafenib resistance in vitro and in vivo, including those with FBW7 mutations. Importantly, Mcl-1 inhibition also sensitized FBW7-mutant PDO and PDX models to regorafenib. In contrast, Mcl-1 inhibition had no effect in FBW7-WT CRCs.

Conclusions: Our results demonstrate that Mcl-1 inhibitors can overcome intrinsic and acquired regorafenib resistance in CRCs by restoring apoptotic response. FBW7 mutations might be a potential biomarker predicting for response to the regorafenib/Mcl-1 inhibitor combination.

Keywords: Mcl-1, FBW7, regorafenib, colorectal cancer, apoptosis