Chemoresistant Cancer Stem Cells Research Articles

Withaferin a alone and in combination with cisplatin suppresses growth and metastasis of ovarian cancer by targeting putative cancer stem cells.

Currently, the treatment for ovarian cancer entails cytoreductive surgery followed by chemotherapy, mainly, carboplatin combined with paclitaxel. Although this regimen is initially effective in a high percentage of cases, unfortunately within few months of initial treatment, tumor relapse occurs because of platinum-resistance. This is attributed to chemo-resistance of cancer stem cells (CSCs). Herein we show for the first time that withaferin A (WFA), a bioactive compound isolated from the plant Withania somnifera, when used alone or in combination with cisplatin (CIS) targets putative CSCs. Treatment of nude mice bearing orthotopic ovarian tumors generated by injecting human ovarian epithelial cancer cell line (A2780) with WFA and cisplatin (WFA) alone or in combination resulted in a 70 to 80% reduction in tumor growth and complete inhibition of metastasis to other organs compared to untreated controls. Histochemical and Western blot analysis of the tumors revealed that inclusion of WFA (2 mg/kg) resulted in a highly significant elimination of cells expressing CSC markers - CD44, CD24, CD34, CD117 and Oct4 and downregulation of Notch1, Hes1 and Hey1 genes. In contrast treatment of mice with CIS alone (6 mg/kg) had opposite effect on those cells. Increase in cells expressing CSC markers and Notch1 signaling pathway in tumors exposed to CIS may explain recurrence of cancer in patients treated with carboplatin and paclitaxel. Since, WFA alone or in combination with CIS eliminates putative CSCs, we conclude that WFA in combination with CIS may present more efficacious therapy for ovarian cancer.

Enrichment for Chemoresistant Ovarian Cancer Stem Cells from Human Cell Lines

Cancer stem cells (CSCs) are defined as a subset of slow cycling and undifferentiated cells that divide asymmetrically to generate highly proliferative, invasive, and chemoresistant tumor cells. Therefore, CSCs are an attractive population of cells to target therapeutically. CSCs are predicted to contribute to a number of types of malignancies including those in the blood, brain, lung, gastrointestinal tract, prostate, and ovary. Isolating and enriching a tumor cell population for CSCs will enable researchers to study the properties, genetics, and therapeutic response of CSCs. We generated a protocol that reproducibly enriches for ovarian cancer CSCs from ovarian cancer cell lines (SKOV3 and OVCA429). Cell lines are treated with 20 µM cisplatin for 3 days. Surviving cells are isolated and cultured in a serum-free stem cell media containing cytokines and growth factors. We demonstrate an enrichment of these purified CSCs by analyzing the isolated cells for known stem cell markers Oct4, Nanog, and Prom1 (CD133) and cell surface expression of CD177 and CD133. The CSCs exhibit increased chemoresistance. This method for isolation of CSCs is a useful tool for studying the role of CSCs in chemoresistance and tumor relapse.

Enrichment for chemoresistant ovarian cancer stem cells from human cell lines.

Cancer stem cells (CSCs) are defined as a subset of slow cycling and undifferentiated cells that divide asymmetrically to generate highly proliferative, invasive, and chemoresistant tumor cells. Therefore, CSCs are an attractive population of cells to target therapeutically. CSCs are predicted to contribute to a number of types of malignancies including those in the blood, brain, lung, gastrointestinal tract, prostate, and ovary. Isolating and enriching a tumor cell population for CSCs will enable researchers to study the properties, genetics, and therapeutic response of CSCs. We generated a protocol that reproducibly enriches for ovarian cancer CSCs from ovarian cancer cell lines (SKOV3 and OVCA429). Cell lines are treated with 20 µM cisplatin for 3 days. Surviving cells are isolated and cultured in a serum-free stem cell media containing cytokines and growth factors. We demonstrate an enrichment of these purified CSCs by analyzing the isolated cells for known stem cell markers Oct4, Nanog, and Prom1 (CD133) and cell surface expression of CD177 and CD133. The CSCs exhibit increased chemoresistance. This method for isolation of CSCs is a useful tool for studying the role of CSCs in chemoresistance and tumor relapse.

Multiple blocks in the engagement of oxidative phosphorylation in putative ovarian cancer stem cells: implication for maintenance therapy with glycolysis inhibitors.

Survival rate in ovarian cancer has not improved since chemotherapy was introduced a few decades ago. The dismal prognosis is mostly due to disease recurrence where majority of the patients succumb to the disease. The demonstration that tumors are comprised of subfractions of cancer cells displaying heterogeneity in stemness potential, chemoresistance, and tumor repair capacity suggests that recurrence may be driven by the chemoresistant cancer stem cells. Thus to improve patient survival, novel therapies should eradicate this cancer cell population. We show that in contrast to the more differentiated ovarian cancer cells, the putative CD44+/MyD88+ ovarian cancer stem cells express lower levels of pyruvate dehydrogenase, Cox-I, Cox-II, and Cox-IV, and higher levels of UCP2. Together, this molecular phenotype establishes a bioenergetic profile that prefers the use of glycolysis over oxidative phosphorylation to generate ATP. This bioenergetic profile is conserved in vivo and therefore a maintenance regimen of 2-deoxyglucose administered after Paclitaxel treatment is able to delay the progression of recurrent tumors and decrease tumor burden in mice. Our findings strongly suggest the value of maintenance with glycolysis inhibitors with the goal of improving survival in ovarian cancer patients.

Caveolin-1 mediates chemoresistance in breast cancer stem cells via β-catenin/ABCG2 signaling pathway.

Accumulating evidence has suggested that cancer stem cells (CSCs) are at the root of drug resistance, and recent studies have indicated that caveolin-1, a membrane transporter protein, is involved in the regulation of cancer chemoresistance and stem cell signaling. However, the current understanding of the role of caveolin-1 in breast cancer development remains controversial. Herein, we demonstrate that caveolin-1 expression was upregulated after breast cancer chemotherapy in vitro and in vivo, accompanied by co-overexpression of β-catenin and ATP-binding cassette subfamily G member 2 (ABCG2) signaling. Additionally, breast CSCs were enriched for caveolin-1 expression. Caveolin-1 silencing sensitized breast CSCs by limiting their self-renewal ability but promoting the differentiation process. β-catenin silencing prevented the enhanced chemoresistance of CSCs induced by caveolin-1 overexpression, indicating that β-catenin is an essential molecule responsible for caveolin-1-mediated action. Further mechanistic investigation revealed that caveolin-1 silencing could downregulate the β-catenin/ABCG2 pathway through glycogen synthase kinase 3 beta activation and Akt inhibition, resulting in increased β-catenin phosphorylation and proteasomal degradation. Clinical investigation also revealed a close correlation between caveolin-1 and β-catenin/ABCG2 signaling in breast cancer samples. Notably, caveolin-1 was highly elevated in triple-negative breast cancer, and caveolin-1 silencing significantly impaired the tumorigenicity and chemoresistance of breast CSCs in in vivo models. Overall, our study not only highlights the role of caveolin-1 in mediating the chemoresistance of breast CSCs via β-catenin/ABCG2 regulation but also provides novel approaches for future therapies targeting CSCs.

Regulation of Metastasis by microRNAs in Ovarian Cancer.

Ovarian cancer (OC) is the second most common and the most fatal gynecologic cancer in the United States. Over the last decade, various targeted therapeutics have been introduced but there has been no corresponding improvement in patient survival mainly because of the lack of effective early detection methods. microRNAs (miRs) are small, non-coding RNAs that regulate gene expression post-transcriptionally. Accumulating data suggest central regulatory roles of miRs in modulating OC initiation, progression, and metastasis. More recently, aberrant miR expression has been also associated with cancer stem cell (CSC) phenotypes and development of CSC chemo-resistance. Here, we review recent advances on miRs and OC metastasis and discuss the concept that miRs are involved in both CSC transformation and subsequent OC metastasis. Finally, we describe the prevalence of circulating miRs and assess their potential utilities as biomarkers for OC diagnosis, prognosis, and therapeutics.

Cisplatin-resistant cells in malignant pleural mesothelioma cell lines show ALDH(high)CD44(+) phenotype and sphere-forming capacity.

BackgroundConventional chemotherapy in malignant pleural mesothelioma (MPM) has minimal impact on patient survival due to the supposed chemoresistance of cancer stem cells (CSCs). We sought to identify a sub-population of chemoresistant cells by using putative CSC markers, aldehyde dehydrogenase (ALDH) and CD44 in three MPM cell lines; H28, H2052 and Meso4.MethodsThe Aldefluor assay was used to measure ALDH activity and sort ALDHhigh and ALDHlow cells. Drug-resistance was evaluated by cell viability, anchorage-independent sphere formation, flow-cytometry and qRT-PCR analyses.ResultsThe ALDHhigh - and ALDHlow -sorted fractions were able to demonstrate phenotypic heterogeneity and generate spheres, the latter being less efficient, and both showed an association with CD44. Cis- diamminedichloroplatinum (II) (cisplatin) treatment failed to reduce ALDH activity and conferred only a short-term inhibition of sphere generation in both ALDHhigh and ALDHlow fractions of the three MPM cell lines. Induction of drug sensitivity by an ALDH inhibitor, diethylaminobenzaldehyde (DEAB) resulted in significant reductions in cell viability but not a complete elimination of the sphere-forming cells, suggestive of the presence of a drug-resistant subpopulation. At the transcript level, the cisplatin + DEAB-resistant cells showed upregulated mRNA expression levels for ALDH1A2, ALDH1A3 isozymes and CD44 indicating the involvement of these markers in conferring chemoresistance in both ALDHhigh and ALDHlow fractions of the three MPM cell lines.ConclusionsOur study shows that ALDHhigh CD44+ cells are implicated in conveying tolerance to cisplatin in the three MPM cell lines. The combined use of CD44 and ALDH widens the window for identification and targeting of a drug-resistant population which may improve the current treatment modalities in mesothelioma.

Glycosylated Antitumor Ether Lipids: Activity and Mechanism of Action

Glycosylated antitumor ether lipids (GAELs) are distinguished from the alkyllysophospholipids or alkylphosphocholines classes of antitumor ether lipids (AEL) by the presence of a sugar moiety. Non-phosphorus GAELs, the subject of this review, have a sugar moiety in place of the phosphobase found in alkyllysophospholipids. Analogues of non-phosphorus GAELs with glucose, maltose, arabinose, or disaccharide moieties have been synthesized. Non-phosphorus GAELs with monosaccharides have cytotoxic and antiproliferative effects against cancer cells derived from a wide range of tissues, including drug resistant cell lines. The most active compound of this group to date is 1-O-hexadecyl-2-O-methyl-3-O-(2'-amino-2'-deoxy-β-D-glucopyranosyl)-sn-glycerol (11), which displays in vitro activity similar to or greater than that of ET-18-OCH3, the AEL "gold" standard. While the detailed molecular mechanism of action of non-phosphorus GAELs is not known, the data indicate that non-phosphorus GAELs are taken up by endocytosis and incorporated into early endosomes. The presence of non-phosphorus GAELs perturbs the maturation of the endocytic vesicles, resulting in the formation of large acidic vacuoles. Cell death appears to be the result of the release of cathepsins from the vacuoles into the cytosol and subsequent activation of a death pathway that is independent of the mitochondria and independent of apoptosis. The ability of these GAELs to kill cells via an apoptosis-independent mechanism makes them prime candidates for development of effective compounds against chemo-resistant tumors and cancer stem cells. The disaccharide-linked GAELs do not have cytotoxic activity but rather inhibit cancer cell motility due to the ability of the compounds to block specific calcium-activated potassium channels in cells. The antitumor activities displayed by these experimental compounds augurs well for their eventual development into clinically useful agents for cancer treatment.

Neuroendocrine Tumors of the Lung: Hystological Classification, Diagnosis, Traditional and New Therapeutic Approaches

Lung neuroendocrine tumors are neoplasms originating from bronchopulmonary neuroendocrine cells, usually Kulchitsky cells, loaded with argentaffin granules. They account for 20-25% of all primitive lung tumors, the most common being the small-cell undifferentiated carcinoma. They include different tumors, from tumors of low-grade malignancy, especially the typical carcinoids, with high survival rates after surgical therapy, to the high-grade malignancy tumors, especially small-cell undifferentiated carcinomas. The latter have very few indications for surgical treatment with a low survival rate, even after multimodal therapy. The aim of this review is to describe the present knowledge and discuss possible new developments in the management of pulmonary neuroendocrine tumors. The authors examine and discuss in particular the role that surgical techniques should have in the treatment of small-cell lung cancer in opposition to a nihilism position that has limited therapies to non-surgical approaches. The critical review of this attitude opens the door to a more aggressive approach. In the meantime the review shows that it might be possible to include the new minimally invasive percutaneous ablative techniques as cryosurgery, thermotherapy and irreversible electroporation within a modern and flexible framework. The authors also present the hypothesis that cancer stem cells (CSC) are at the basis of recurrences of small-cell lung cancer (SCLC) and therefore that the issue is of difficult solution with the conventional oncologic approach considering the chemo-resistance of CSC to drugs. For these reasons an epigenetic therapy based on differentiation factors is proposed alongside the usual surgical and chemo-radiation protocols.

Chemoresistance in Cancer Stem Cells and Strategies to Overcome Resistance

In cancers, there exists a subpopulation of cells which are referred to as cancer stem cells (CSCs) or tumor initiating cells that have enhanced tumor-initiating capacity and metastatic potential, and drive tumor progression. Since the initial identification of acute myeloid leukemia CSCs in 1997, CSCs have been found in many types of cancer and have intrinsic resistance to the current chemotherapeutic strategies. With increased levels of detoxifying enzymes, enhanced DNA repair abilities, impressive efflux capacity, and a slower cell-cycle; CSCs present a formidable obstacle against effective chemotherapy. Several methods of specifically targeting CSCs have been developed in recent years, and these compounds have potential as adjuvant therapies. The following is a review of the mechanisms responsible for chemoresistance in CSCs, with an emphasis on potential strategies to overcome this resistance.

Synergistic Activities of MET/RON Inhibitor BMS-777607 and mTOR Inhibitor AZD8055 to Polyploid Cells Derived from Pancreatic Cancer and Cancer Stem Cells

Tyrosine kinase inhibitor BMS-777067 is an inhibitor of RON/MET receptor tyrosine kinases currently under clinical trials. Here, we report the synergistic activity of BMS-777607 in combination with mTOR inhibitor AZD8055 in killing chemoresistant pancreatic cancer and cancer stem cells. Treatment of pancreatic cancer L3.6pl cells with BMS-777607 alone inhibited clonogenic growth and moderately induced apoptotic death. However, BMS-777607 caused extensive polyploidy in L3.6pl cells through inhibition of aurora kinase B activity, independent of RON expression. In contrast, L3.6pl-derived cancer stem cells were highly resistant to BMS-777607-induced growth inhibition and apoptosis. The effect of BMS-777607 on induction of cancer stem cell polyploidy was also weak. BMS-777607-induced polyploidy features a predominant cell population with 8N chromosome content in both L3.6pl and cancer stem cells. These cells also showed decreased sensitivity toward chemotherapeutics by increased survival of IC(50) values in response to doxorubicin, cisplatin, methotrexate, 5-fluorouracial, and gemcitabine. Among a panel of chemical inhibitors that target different signaling proteins, we found that BMS-777607 in combination with mTOR inhibitor AZD8055 exerted synergistic effects on L3.6pl and cancer stem cells. More than 70% of L3.6pl and cancer stem cells lost their viability when both inhibitors were used. Specifically, BMS-777607 in combination with inhibition of mTORC2, but not mTORC1, was responsible for the observed synergism. Our findings demonstrate that BMS-777607 at therapeutic doses exerts inhibitory activities on pancreatic cancer cells but also induces polyploidy insensitive to chemotherapeutics. Combination of BMS-777607 with AZD8055 achieves the maximal cytotoxic effect on pancreatic cancer and cancer stem cells.

Tunicamycin Potentiates Cisplatin Anticancer Efficacy through the DPAGT1/Akt/ABCG2 Pathway in Mouse Xenograft Models of Human Hepatocellular Carcinoma

Hepatocellular carcinoma is highly chemoresistant, and ATP-binding cassette subfamily G member 2 (ABCG2) is thought to play a critical role in this drug resistance. The present study aims to develop effective therapeutic strategies to decrease ABCG2 expression level and to surmount drug resistance in hepatocellular carcinoma chemotherapy. First, we verified a positive correlation between the ABCG2 protein level and the drug resistance of hepatocellular carcinoma cell lines. ABCG2 was preferentially expressed in highly chemoresistant hepatocellular carcinoma cancer stem cells (CSC) enriched with CD133. In addition, ABCG2 was N-linked glycosylated in hepatocellular carcinoma cells, and this modification was involved in sustaining its protein stability. The N-linked glycosylation (NLG) inhibitor tunicamycin dramatically reduced ABCG2 expression, altered its subcellular localization, and reversed its drug efflux effect in multiple hepatocellular carcinoma cell lines. Furthermore, tunicamycin reduced the expression levels of several CSC markers and suppressed the tumorigenicity of CD133(+) CSCs. Tunicamycin combined with cisplatin (CDDP) inhibited proliferating cell nuclear antigen (PCNA) expression and increased the cleavage of PARP; this effect was partially rescued by the overexpression of ABCG2 or Akt-myr. The combination therapy more effectively suppressed tumor growth in xenograft mice than did single-agent therapy with either drug. Finally, the CDDP treatment combined with UDP-GlcNAc-dolichol-phosphate N-acetylglucosamine-1 phosphate transferase (DPAGT1) knockdown recapitulated the effect observed when CDDP was used in combination with tunicamycin. In summary, our results suggest that tunicamycin may reverse the drug resistance and improve the efficacy of combination treatments for hepatocellular carcinomas by targeting the DPAGT1/Akt/ABCG2 pathway.

Therapy-Resistant Cancer Stem Cells Have Differing Sensitivity to Photon versus Proton Beam Radiation

Cancer stem cells (CSCs) play an important role in non-small-cell lung cancer recurrence and metastasis. We sought to determine whether CSC-like cells respond differentially to proton and photon beam therapies. CSC-enriched cells from paclitaxel-resistant human H460 and A549 cell lines were irradiated with the same relative biological effectiveness dose and analyzed for cell viability, clonogenic survival, apoptosis, cell migration, cell invasiveness, tumor sphere formation, and CSC markers. The intracellular concentration of reactive oxygen species (ROS) was measured before and after irradiation. Compared with photons, protons caused significantly lower cell viability in chemoresistant cells and, in CSC-like cells, significantly lower clonogenic survival, invasiveness, and number of tumor spheres; less migration and CSC markers (coxsackievirus and adenovirus receptor, β-catenin, and side population cells); more apoptosis; and higher ROS level. CSC-like cells contained less than half the ROS levels of parental cancer cells or normal human bronchial epithelial cells. CSC-like cells may be more sensitive to irradiation with protons than photons. The increased sensitivity could be caused by the greater ROS generated by protons. Because chemoresistant CSCs play an important role in tumor recurrence, protons may be more effective than photons in eliminating recurrent or persistent non-small-cell lung cancer.

Abstract CN06-02: Breast cancer stem cells.

Abstract CN06-02: Breast cancer stem cells.

Lgr5 promotes cancer stemness and confers chemoresistance through ABCB1 in colorectal cancer

IntroductionChemotherapy failure is a major problem in patients with advanced colorectal carcinoma (CRC). Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) is a well-established target gene of the Wnt pathway and is a bona fide marker of CRC cancer stem cells (CSCs). Our previous study showed that CRC patients with higher Lgr5 level are associated with poor response to 5-fluoracil-based treatment. In this study, we investigated the mechanisms underlying Lgr5-associated chemoresistance in cancer stem cells derived from cultured CRC cells. Materials and methodsCancer stem cells were isolated from CRC cell lines by spheroid culture. The effect of Lgr5 on CRC cancer stem cell was investigated using both gain- and loss-of-function approaches. Stemness property was evaluated using sphere formation assay, side population analysis, and stem cell marker expression. Lgr5 and ABCB1 expression in CRC tissues was determined using immunohistochemical staining. ResultsForced expression of Lgr5 increased the CRC sphere-forming efficiency and spheroid size while depletion of Lgr5 reduced the stem cell property in cultured CRC cells. Over-expression of Lgr5 also reduced the sensitivity of cultured CRC cells, including adherent and spheroids, towards 5-fluoracil and oxalipatin. In addition, Lgr5 positively regulates the expression of ABCB1 in both adherent and spheroid CRC cells. Finally, in human CRC tissues, higher expression levels of Lgr5 were associated with higher ABCB1 expression. ConclusionsThe present study demonstrated that Lgr5 plays an active role in promoting the cancer stem cell property and that Lgr5 confers chemoresistance to CRC cells via ABCB1 induction.

CD147 is critical for cancer stem cell chemoresistance: what does this mean for the clinic?

In the past decade, the development of targeted cancer therapies, such as antibody-based drugs and tyrosine kinase inhibitors, has advanced the treatment of various cancers with improved antitumor ...

A bispecific EpCAM/CD133-targeted toxin is effective against carcinoma

The discovery of chemoresistant cancer stem cells (CSCs) in carcinomas has created the need for therapies that specifically target these subpopulations of cells. Here, we characterized a bispecific targeted toxin that is composed of two antibody fragments and a catalytic protein toxin allowing it to bind two CSC markers on the same cell killing this resistant subpopulation. CD133 is a well-known CSC marker and has been successfully targeted and caused regression of head and neck squamous cell carcinoma (HNSCC) in vivo. To enable it to bind a broader range of CSCs, an anti-epithelial cell adhesion molecule (EpCAM) scFv was added to create dEpCAMCD133KDEL, a deimmunized bispecific targeted toxin on a single amino acid chain. This bispecific potently inhibited protein translation and proliferation in vitro in three different types of carcinoma. Furthermore, in a CSC spheroid model dEpCAMCD133KDEL eliminated Mary-X spheroids, an inflammatory breast carcinoma. Finally, this bispecific also caused tumor regression in an in vivo model of HNSCC. This represents the first bispecific CSC-targeted toxin and warrants further development as a possible therapy for carcinoma.

Multimodal Treatment Eliminates Cancer Stem Cells and Leads to Long-Term Survival in Primary Human Pancreatic Cancer Tissue Xenografts

PurposeIn spite of intense research efforts, pancreatic ductal adenocarcinoma remains one of the most deadly malignancies in the world. We and others have previously identified a subpopulation of pancreatic cancer stem cells within the tumor as a critical therapeutic target and additionally shown that the tumor stroma represents not only a restrictive barrier for successful drug delivery, but also serves as a paracrine niche for cancer stem cells. Therefore, we embarked on a large-scale investigation on the effects of combining chemotherapy, hedgehog pathway inhibition, and mTOR inhibition in a preclinical mouse model of pancreatic cancer.Experimental DesignProspective and randomized testing in a set of almost 200 subcutaneous and orthotopic implanted whole-tissue primary human tumor xenografts.ResultsThe combined targeting of highly chemoresistant cancer stem cells as well as their more differentiated progenies, together with abrogation of the tumor microenvironment by targeting the stroma and enhancing tissue penetration of the chemotherapeutic agent translated into significantly prolonged survival in preclinical models of human pancreatic cancer. Most pronounced therapeutic effects were observed in gemcitabine-resistant patient-derived tumors. Intriguingly, the proposed triple therapy approach could be further enhanced by using a PEGylated formulation of gemcitabine, which significantly increased its bioavailability and tissue penetration, resulting in a further improved overall outcome.ConclusionsThis multimodal therapeutic strategy should be further explored in the clinical setting as its success may eventually improve the poor prognosis of patients with pancreatic ductal adenocarcinoma.

Su1730 Activation of Notch Pathway Plays a Role in Pancreatic Cancer Treatment Failure

BACKGROUND: Recurrence of colorectal cancers after surgery and chemotherapy may be partly explained by the presence of chemoresistant cancer stem cells (CSC). Given the highly heterogeneous nature of CSCs it is possible that further characterization might identify a subset of CSC that eventually develop micro-metastases. Galectin-3 (Gal3) has been implicated in tumor progression, metastasis, and drug-resistance. We have previously reported that cell surface Gal3 renders colon cancer cells resistant to TNF-related Apoptosis-Inducing Ligand (TRAIL). Here, our aim was to determine how Gal3 is related to expression of stem cell markers and chemoresistance in different colon cancer cell populations. METHODS: We used the highly metastatic colon cancer cell line LiM6 and its TRAIL-resistant derivative LIM6-TR as cellular model. CSC populations were identified and isolated based on the expression of 5 established CSC-Markers CD24, CD44, CD166, EpCAM, and ALDH. Surface Gal3 in these CSCs was monitored by flow cytometry. Self-renewal, a functional CSC hallmark of CSC, was measured in sphere-formation assays. Response to TRAIL wasmeasured by APO-BRDU TUNEL assays. RESULTS: Only 15% of LIM6 and LIM6-TR cells were CSC as defined by the 5 markers (CD24+, CD44+, CD166+, EpCAM+, ALDH+). Surface Gal3 analysis identified two subpopulations within the CSC pool of LiM6 (54% Gal3+, 46% Gal3 negative). In contrast, CSC from LIM6-TR were uniformly Gal3+. Of note, not all Gal3+ colorectal cells can be attributed with CSC properties, since only 25-30% of Gal3+ CRCs express the remaining CSC markers simultaneously. Sphere assays demonstrated that the parental LIM6-TR had a 2-fold higher sphere forming ability than LIM6. The isolated Gal3+ CSCs formed 3.3-fold more spheres than parental Lim6 cells, while a 90% decrease in sphere formation was observed in the GAL3 negative CSC subpopulation. Depletion of Gal3 in LiM6-TR cells resulted in the loss of the Gal3+ CSC subpopulation, diminished sphere formation, and resensitization to TRAIL. Sphere formation of GAL+ CSCs in the presence of the Gal3 inhibitor LacNAc [5mM] led to a 60% reduction in sphere-formation. CONCLUSIONS: Our findings indicate that surface Gal3 is responsible for high sphere formation ability and TRAIL-resistance in a subpopulation of CSC. Further experiments will determine whether surface Gal3 in combination with other CSC markers can help to identify metastatic and chemoresistant CSCs in the circulation of CRC patients.

Su1729 Targeting Both Active and Quiescent Cancer (stem) Cells Using Combined Therapy

BACKGROUND: Recurrence of colorectal cancers after surgery and chemotherapy may be partly explained by the presence of chemoresistant cancer stem cells (CSC). Given the highly heterogeneous nature of CSCs it is possible that further characterization might identify a subset of CSC that eventually develop micro-metastases. Galectin-3 (Gal3) has been implicated in tumor progression, metastasis, and drug-resistance. We have previously reported that cell surface Gal3 renders colon cancer cells resistant to TNF-related Apoptosis-Inducing Ligand (TRAIL). Here, our aim was to determine how Gal3 is related to expression of stem cell markers and chemoresistance in different colon cancer cell populations. METHODS: We used the highly metastatic colon cancer cell line LiM6 and its TRAIL-resistant derivative LIM6-TR as cellular model. CSC populations were identified and isolated based on the expression of 5 established CSC-Markers CD24, CD44, CD166, EpCAM, and ALDH. Surface Gal3 in these CSCs was monitored by flow cytometry. Self-renewal, a functional CSC hallmark of CSC, was measured in sphere-formation assays. Response to TRAIL wasmeasured by APO-BRDU TUNEL assays. RESULTS: Only 15% of LIM6 and LIM6-TR cells were CSC as defined by the 5 markers (CD24+, CD44+, CD166+, EpCAM+, ALDH+). Surface Gal3 analysis identified two subpopulations within the CSC pool of LiM6 (54% Gal3+, 46% Gal3 negative). In contrast, CSC from LIM6-TR were uniformly Gal3+. Of note, not all Gal3+ colorectal cells can be attributed with CSC properties, since only 25-30% of Gal3+ CRCs express the remaining CSC markers simultaneously. Sphere assays demonstrated that the parental LIM6-TR had a 2-fold higher sphere forming ability than LIM6. The isolated Gal3+ CSCs formed 3.3-fold more spheres than parental Lim6 cells, while a 90% decrease in sphere formation was observed in the GAL3 negative CSC subpopulation. Depletion of Gal3 in LiM6-TR cells resulted in the loss of the Gal3+ CSC subpopulation, diminished sphere formation, and resensitization to TRAIL. Sphere formation of GAL+ CSCs in the presence of the Gal3 inhibitor LacNAc [5mM] led to a 60% reduction in sphere-formation. CONCLUSIONS: Our findings indicate that surface Gal3 is responsible for high sphere formation ability and TRAIL-resistance in a subpopulation of CSC. Further experiments will determine whether surface Gal3 in combination with other CSC markers can help to identify metastatic and chemoresistant CSCs in the circulation of CRC patients.