Curcumin is known to induce apoptosis of cancer cells by different mechanisms, but its effects on cancer stem-like cells have been less investigated. Here we report that curcumin promotes the survival of DCLK1-positive colon cancer stem-like cells (CSC), potentially confounding application of its anticancer properties. At optimal concentrations, curcumin greatly reduced expression levels of stem cell markers (DCLK1/CD44/ALDHA1/Lgr5/Nanog) in 3D spheroid cultures and tumor xenografts derived from colon cancer cells. However, curcumin unexpectedly induced proliferation and autophagic survival of a subset of DCLK1-positive CSCs. Spheroid cultures were disintegrated by curcumin in vitro but re-grew within 30–40 days of treatment, suggesting a survival benefit from autophagy, permitting long-term persistence of CRC. Notably, RNAi-mediated silencing of DCLK1 triggered apoptotic cell death of colon cancer cells in vitro and in vivo, and abolished CRC survival in response to curcumin; combination of DCLK1-siRNA and curcumin dramatically reversed CSC phenotype, contributing to attenuation of the growth of spheroid cultures and tumor xenografts. Taken together, our findings confirm a role of DCLK1 in colon cancer stem cells and highlight DCLK1 as a target to enhance antitumor properties of curcumin.

Background & Aims Prograstrin induces proliferation in colon crypts by activating p65NF-κ B and β-catenin. We investigated whether Annexin A2 (AnxA2), a progastrin receptor, activates NF-κB and β-catenin in vivo. Method ANXA2-null (ANXA2− /−) and wild-type (ANXA2+/+) mice were studied, along with clones of progastrin-responsive HEK-293 cells that stably expressed full-length progastrin (HEK-mGAS) or an empty-vector (HEK-C). Small interfering RNA was used to downregulate AnxA2, p65NF-κB, and β-catenin in cells. Results Proliferation and activation of p65 and β-catenin increased significantly in HEK-mGAS, compared with HEK-C clones. HEK-mGAS cells had a 2–4-fold increase in relative levels of c-Myc, COX-2, CyclinD1, DCAMKL+1, and CD44, compared with HEK-C clones. Down-regulation of AnxA2 in HEK-mGAS clones reduced activation of NF-κB and β-catenin, as well as levels of DCAMKL+1. Surprisingly, downregulation of β-catenin had no effect on activation of p65NF-κB, whereas down-regulation of p65 significantly reduced activation of β-catenin in HEK-mGAS clones. Loss of either p65 or β-catenin significantly reduced proliferation of HEK-mGAS clones, indicating that both factors are required for the proliferative effects of progastrin. Lengths of colon crypts and levels of p65, β-catenin, DCAMKL+1, and CD44 were significantly higher in ANXA2+/+ mice compared to corresponding values measured in either ANXA2− /− mice injected with progastrin or ANXA2+/+ and ANXA2− /− mice injected with saline. Conclusions AnxA2 expression is required for the biological effects of progastrin in vivo and in vitro, and mediates the stimulatory effect of progastrin on p65NF-κ, β-catenin, and the putative stem-cell markers DCAMKL+1 and CD44. AnxA2 might therefore mediate the hyperproliferative and co-carcinogenic effects of progastrin.

We recently reported that overexpression of progastrin in embryonic epithelial cells (HEKmGAS-cells) increased proliferation of the cells, compared to that of control HEKC-cells. Here we report the novel finding that tumorigenic and metastatic potential of HEKmGAS cells is also increased significantly, compared to that of HEKC cells. Cell-surface associated annexinA2 (CS-ANXA2) binds progastrin and is over-expressed on cancer-cells, allowing us to successfully use fluorescently-labeled progastrin-peptide for enumerating metastatic lesions of transformed/cancer cells in vivo. Next, we examined the hypothesis that increased tumorigenic/metastatic potential of isogenic HEKmGAS vs HEKC cells maybe due to transformed-phenotype of stem-cells. FACSorting/FACScanning of cells demonstrated significant increases in percent DCLK1/Lgr5 positive stem-cells, co-expressing CD44/CS-ANXA2, in HEKmGAS vs HEKC-cells. Distinct differences were noted in morphology of HEKC vs HEKmGAS spheroidal growths on non-adherent cultures (selective for stem cells). HEKC-spheroids were rounded with distinct perimeters (basement membranes?), while HEKmGAS-spheroids were amorphous, with no perimeters. Relative levels of DCLK1/Lgr5/CD44 and AnnexinA2/β-catenin/pNFκBp65/metalloproteinases were significantly increased in HEKmGAS vs HEKC-cells, growing either as mono-layer cultures, 3D-spheroids (in vitro), or xenografts (in vivo). Interestingly, HEKC-cells enriched for CS-ANXA2, developed amorphous spheroids, while down-regulation of ANXA2 in HEKmGAS-clones, resulted in loss of matrixmetalloproteinases and re-formation of rounded spheroids, suggesting high levels of CS-ANXA2/matrixmetalloproteinases may impact spheroid morphology. Down-regulation of DCLK1 significantly attenuated activation of β-catenin, with loss of proliferation of HEKmGAS and HEKC-cells, suggesting DCLK1 is required for maintaining proliferation of cells. Conclusions Our results suggest the novel possibility that transformed stem-cells, unlike non-transformed stem-cells, co-express stem-cell-markers DCLK1 and CD44 with CS-ANXA2.

Cancer stem cells (CSCs) are believed to be resistant to currently available therapies and maybe responsible for relapse of cancer in patients. Measuring circulating tumor cells (CTCs) in blood of patients has emerged as a non-invasive diagnostic procedure for screening patients who may be at high risk for developing metastatic cancers or relapse of the cancer disease. However, accurate detection of CTCs has remained a problem, since epithelial-cell-markers used to-date, are not always reliable for detecting CTCs, especially during epithelial-mesenchymal-transition. Since CSCs are required to initiate metastatic tumors, our goal was to optimize and standardize a method for identifying circulating CSCs (CCSCs) in patients, using established CSC markers. Here, we report for the first time the detection of CCSCs in blood of athymic nude mice, bearing metastatic tumors, and in the blood of patients positive for colonic adenocarcinomas. Using a simple and non-expensive method, we isolated a relatively pure population of CSCs (CD45−/CK19+), free of red blood cells and largely free of contaminating CD45+ white blood cells. Enriched CCSCs from patients with colon adenocarcinomas had a malignant phenotype and co-expressed CSC markers (DCLK1/LGR5) with CD44/Annexin A2. CSCs were not found in the blood of non-cancer patients, free of colonic growths. Enriched CCSCs from colon cancer patients grew primary spheroids, suggesting presence of tumor-initiating cells in the blood of these patients. In conclusion, we have developed a novel diagnostic assay for detecting CSCs in circulation, which may more accurately predict the risk of relapse or metastatic disease in patients. Since CSCs can potentially initiate metastatic growths, patients positive for CCSCs can be treated with inhibitory agents that selectively target CSCs, besides conventional treatments, to reduce the risk of relapse/metastatic disease for improving clinical outcomes.

Cell-surface-associated annexin A2 (CS-ANXA2) is a nonconventional "receptor" for progastrin; expression levels of both are elevated in colon cancers, and downregulation of either reduces tumorigenic potential of cells. We recently reported internalization of progastrin in target cells. Here, mechanisms mediating internalization of progastrin were examined. Initially, we confirmed that cell-surface ANXA2 mediates binding and internalization of progastrin in intestinal cells. Progastrin, covalently linked to sepharose beads, failed to activate p38MAPK/ERKs, suggesting internalization of progastrin was required for eliciting biological effects; importantly annexin A2 expression and availability of CS-ANXA2 were required for internalization of progastrin. Clathrin expression and formation of clathrin-coated pits were critically required for endocytotic internalization of progastrin; in the absence of clathrin, progastrin failed to activate p38MAPK/ERKs. Downregulation of caveolin had no effect on binding or internalization of progastrin. We therefore demonstrate for the first time that progastrin binds CS-ANXA2 and is rapidly internalized via clathrin-mediated endocytotic pathway, resulting in activation of MAPKinases. Targeting clathrin-mediated endocytosis of progastrin may thus inhibit previously reported co-carcinogenic/tumorigenic effects of progastrin on intestinal cells.