Abstract 729: A novel cancer-stem-cell biomarker, DCLK1-S, traffics to nuclei of colon cancer cells: potential use as a biomarker for assessing colon cancer risk after screening colonoscopy
Authors: Shubhashish Sarkar, Vsevolod L. L. Popov, Malany O'Connell, Heather L. Stevenson, Brian S. Lee, Robert A. Obeid, Pomila Singh
Journal: Cancer Research (2017)

Abstract DCLK1 expression is critically required for maintaining growth of human colon cancer cells (hCCCs). We and others recently reported that the 5’promoter of hDCLK1-gene gets hypermethylated and silenced in human colorectal tumors (hCRCs) during adenoma-carcinoma sequence of colon carcinogenesis (Reviewed by Singh et al. SCI, 2016). We also made the discovery that hCRCs and hCCCs express a novel short isoform of DCLK1 (DCLK1-S) (isoform2) from β-promoter in intron V of hDCLK1-gene, while normal-colons express the canonical long-isoform (DCLK1-L) (isoform1) from 5’(α)-promoter, suggesting that DCLK1-S, and not DCLK1-L, marks cancer-stem-cells (CSCs) (O’Connell et al, Sci Rep, 2015). Even though DCLK1-S differs from DCLK1-L by only six amino-acids, we succeeded in generating a mono-specific DCLK1-S-Antibody (PS41014), which does not cross-react with DCLK1-L, and specifically detects DCLK1-S in several assay platforms, including westerns and IHC. Sub-cellular localization of S/L isoforms was examined by immune-electron-microscopy (IEM). Surprisingly, besides plasma membrane and cytosolic fractions, S/L also localized to nuclear/mitochondrial fractions, with pronounced localization of S-isoform in the nuclei and mitochondria of hCCCs. Sporadic CRCs develop from adenomas (Ads). Screening colonoscopy is used for detection/resection of growths, and morphological/pathological criteria are used for risk assessment and recommendations for follow-up colonoscopy. But, these features are not precise and majority of the patients with adenomas will never develop CRC. We hypothesized that antibody-based assay(s), which identify CSCs, will significantly improve prognostic value of morphological/pathological criteria. We conducted a pilot retrospective study with PS41014-Ab, by staining archived adenoma specimens from patients who developed (High-risk) or did not develop (Low-risk) adenocarcinomas within 10-15 years. PS41014-Ab stained adenomas from initial and follow-up colonoscopies of high-risk patients, at significantly higher levels (3-5X) than adenomas from low-risk patients, suggesting that PS41014-Ab could be used as an additional tool for assessing CRC-risk. We previously reported that CRC-patients, whose colonic tumors were positive for relatively high levels of DCLK1-S expression (by qRT-PCR), had a worse overall survival and disease free interval than low-expressers (O’Connell et al, Sci Rep 2015). We now report that DCLK1-S-Antibody may help to identify patients at high-risk for developing CRCs within 10-15 years, at the time of index/screening colonoscopy, and thus serve as a useful biomarker at early time points of colon carcinogenesis, unlike the currently available fecal/blood tests. Citation Format: Shubhashish Sarkar, Vsevolod L. L. Popov, Malany O'Connell, Heather L. Stevenson, Brian S. Lee, Robert A. Obeid, Pomila Singh. A novel cancer-stem-cell biomarker, DCLK1-S, traffics to nuclei of colon cancer cells: potential use as a biomarker for assessing colon cancer risk after screening colonoscopy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 729. doi:10.1158/1538-7445.AM2017-729