Abstract 2337: ADAM17 mediation of cancer stem cell-ness and chemo-resistance in colorectal cancer

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA INTRODUCTION: Despite the multitude of drug options, most patients with metastatic colorectal cancer (mCRC) die within 3 years of diagnosis. Response to systemic therapy is not durable (< 1year) and drug resistance is inevitable. There is accumulating evidence for the existence of cancer stem cells (CSCs) in CRC, which are now believed to mediate chemo-resistance. The molecular mechanisms that regulate the CSC phenotype in CRC have not been fully elucidated. The metalloproteinase ADAM17 [also known as TNFα-converting enzyme (TACE)], an enzyme involved in Notch pathway activation, has been shown to be overexpressed in CRC and mediate cell proliferation and chemo-resistance in CRC cells. However, the role of ADAM17 in mediating the CSC phenotype in CRC has not been characterized. The present study sought to determine the role of CRC-associated ADAM17 in mediating chemo-resistance of CRC cells by regulating the CSC phenotype. METHODS: Most preclinical studies used established cancer cell lines that have been cultured in vitro for decades. Our laboratory has shown that these cell lines are not suitable for consistent isolation of CSCs (Fan et al, 2014, BJC in press). To circumvent this problem, we developed a new model using CRC cells either freshly isolated from patient-derived xenografts (PDX) or early passage of newly established Human CRC Primary cell lines (HCP) derived from the PDXs. With this newly established HCP cell line model, we used siRNA knockdown or a synthetic peptide inhibitor TAPI-2, to determine the effect of blocking ADAM17 on the CSC phenotype and chemo-resistance in CRC cells. RESULTS: ADAM17 inhibition, either by siRNA or by TAPI-2, reduced the protein levels of cleaved Notch1 (NICD) and its downstream target HES-1 in CRC cells. Levels of proteins that are involved in other CSC-associated pathways were not altered by ADAM17 inhibition, suggesting that the Notch pathway is the major stem-cell pathway activated by ADAM17. Furthermore, ADAM17 inhibition caused a decrease in the CSC-phenotype in CRC cells as determined by the sphere formation assay and the Aldefluor assay (a standard assay for identifying CSCs). In addition, the lethal dose 50 (LD50) of 5-fluorouracil (5-FU) was decreased by 3 fold when pre-incubating CRC cells with the ADAM17 inhibitor TAPI-2. We also showed that the protein levels of ADAM17 were higher in our chemo-resistant cells (cells that survive continuous exposure to chemotherapy) compared to control. CONCLUSION: Our studies demonstrated the role of ADAM17 in promoting the CSC phenotype and chemo-resistance in CRC cells. Utilization of drugs that inhibit ADAM17 activity may increase the therapeutic benefit to patients with mCRC, and potentially other solid malignancies. Citation Format: Rui Wang, Fan Fan, Delphine Boulbes, Rajat Bhattacharya, Xiang-Cang Ye, Ling Xia, Lee Ellis. ADAM17 mediation of cancer stem cell-ness and chemo-resistance in colorectal cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2337. doi:10.1158/1538-7445.AM2015-2337