Establishment of highly tumorigenic human colorectal cancer cell line (CR4) with properties of putative cancer stem cells.

BACKGROUND: Colorectal cancer (CRC) has the third highest mortality rates among the US population. According to the most recent concept of carcinogenesis, human tumors are organized hierarchically, and the top of it is occupied by malignant stem cells (cancer stem cells, CSCs, or cancer-initiating cells, CICs), which possess unlimited self-renewal and tumor-initiating capacities and high resistance to conventional therapies. To reflect the complexity and diversity of human tumors and to provide clinically and physiologically relevant cancer models, large banks of characterized patient-derived low-passage cell lines, and especially CIC-enriched cell lines, are urgently needed. PRINCIPAL FINDINGS: Here we report the establishment of a novel CIC-enriched, highly tumorigenic and clonogenic colon cancer cell line, CR4, derived from liver metastasis. This stable cell line was established by combining 3D culturing and 2D culturing in stem cell media, subcloning of cells with particular morphology, co-culture with carcinoma associated fibroblasts (CAFs) and serial transplantation to NOD/SCID mice. Using RNA-Seq complete transcriptome profiling of the tumorigenic fraction of the CR4 cells in comparison to the bulk tumor cells, we have identified about 360 differentially expressed transcripts, many of which represent stemness, pluripotency and resistance to treatment. Majority of the established CR4 cells express common markers of stemness, including CD133, CD44, CD166, EpCAM, CD24 and Lgr5. Using immunocytochemical, FACS and western blot analyses, we have shown that a significant ratio of the CR4 cells express key markers of pluripotency markers, including Sox-2, Oct3/4 and c-Myc. Constitutive overactivation of ABC transporters and NF-kB and absence of tumor suppressors p53 and p21 may partially explain exceptional drug resistance of the CR4 cells. CONCLUSIONS: The highly tumorigenic and clonogenic CIC-enriched CR4 cell line may provide an important new tool to support the discovery of novel diagnostic and/or prognostic biomarkers as well as the development of more effective therapeutic strategies.

New-generation taxoid SB-T-1214 inhibits stem cell-related gene expression in 3D cancer spheroids induced by purified colon tumor-initiating cells.

BACKGROUND: Growing evidence suggests that the majority of tumors are organized hierarchically, comprising a population of tumor-initiating, or cancer stem cells (CSCs) responsible for tumor development, maintenance and resistance to drugs. Previously we have shown that the CD133high/CD44high fraction of colon cancer cells is different from their bulk counterparts at the functional, morphological and genomic levels. In contrast to the majority of colon cancer cells expressing moderate levels of CD133, CD44 and CD166, cells with a high combined expression of CD133 and CD44 possessed several characteristic stem cell features, including profound self-renewal capacity in vivo and in vitro, and the ability to give rise to different cell phenotypes. The present study was undertaken for two aims: a) to determine stem cell-related genomic characteristics of floating 3D multicellular spheroids induced by CD133high/CD44high colon cancer cells; and b) to evaluate CSC-specific alterations induced by new-generation taxoid SB-T-1214. RESULTS: Selected CSC phenotype was isolated from three independent invasive colon cancer cell lines, HCT116, HT29 and DLD-1. A stem cell-specific PCR array assay (SABiosciences) revealed that colonospheres induced by purified CD133high/CD44high expressing cells display profound up-regulation of stem cell-related genes in comparison with their bulk counterparts. The FACS analysis has shown that the 3D colonospheres contained some minority cell populations with high levels of expression of Oct4, Sox2, Nanog and c-Myc, which are essential for stem cell pluripotency and self-renewal. Single administration of the SB-T-1214 at concentration 100 nM-1 microM for 48 hr not only induced growth inhibition and apoptotic cell death in these three types of colon cancer spheroids in 3D culture, but also mediated massive inhibition of the stem cell-related genes and significant down-regulation of the pluripotency gene expression. PCR array and FACS data were confirmed with western blotting. Importantly, viable cells that survived this treatment regimen were no longer able to induce secondary floating spheroids and exhibited significant morphological abnormalities. CONCLUSIONS: We report here that a new-generation taxoid SB-T-1214 possesses significant activity against colon cancer spheroids induced by and enriched with drug resistant tumorigenic CD133high/CD44high cells and efficiently inhibited expression of the majority of stem cell-related genes. Our data indicates that the previously observed long-term efficacy of SB-T-1214 against drug resistant colon tumors in vivo may be explained by the down-regulation of multiple stem cell-related genes in the tumorigenic cell population, in addition to its known efficacy as a mitotic poison against proliferating cancer cells.

Phenotypic subpopulations of metastatic colon cancer stem cells: genomic analysis.

BACKGROUND: Human cancer is characterized by high heterogeneity in gene expression, varieties of differentiation phenotypes and tumor-host interrelations. Growing evidence suggests that tumor-initiating, or cancer stem cells (CSCs), may also represent a heterogeneous population. The present study was undertaken to isolate and characterize the different phenotypic subpopulations of metastatic colon cancer and to develop a working colon CSC model for obtaining highly tumorigenic and clonogenic cells in sufficient numbers. MATERIALS AND METHODS: Different phenotypic cell subpopulations were isolated based on differential levels and patterns of expression of several stemness markers, including CD133, CD44, CD166 and CD49b. Stemness properties of isolated cells were tested by analysis of their ability to form floating colonospheres in vitro, to induce tumors in NOD/SCID mice after transplantation at relatively low cell numbers, and to produce progenitors of different phenotypes. RESULTS: The metastatic colon cancer HCT116 cell line, which expressed a majority of known CSC markers, closely resembling the patterns of expression in exfoliated peritoneal cells from several metastatic colon cancer patients, was selected as a reference material. Genome-wide microarray analysis (Affymetrix; DAVID) of CD133(high) CSC-enriched versus CSC-depleted cell populations revealed 4,351 differentially expressed genes with an overrepresentation of those responsible for apoptosis resistance, regulation of cell cycle, proliferation, stemness and developmental pathways. Simultaneous analysis of 84 stem cell- and metastasis-related genes with corresponding PCR arrays identified genes differentially expressed in several colon CSC phenotypic populations versus bulk tumor cells, and in relation to each other. It was found that colonospheres induced by tumorigenic cells with the highest expression of CD133 and those which were induced by CD133/CD44-negative cells possessed profoundly different stem cell-related gene expression profiles. CONCLUSION: The proposed approaches allow for reliable isolation and propagation of highly tumorigenic and clonogenic cells of different phenotypes. Genomic analysis of several candidate CSC phenotypic populations may contribute to the identification of novel targets for colon cancer stem cell-targeted drug development and treatment.

Genomic analysis of prostate cancer stem cells isolated from a highly metastatic cell line.

BACKGROUND: Tumor-initiating or cancer stem cells (CSCs) were recently isolated from all major human cancers, including prostate cancer. However, the extreme heterogeneity of tumor cells in terms of biological behavior and gene expression patterns and difficulties isolating a pure population of CSCs from tumor tissues significantly impede a comparative analysis of CSCs. MATERIALS AND METHODS: Different phenotypic populations were isolated from a metastatic derivative of PC-3 cell line, PC3-MM2, and tested for their ability to form tumors in NOD/SCID mice and floating spheroids in 3D culture systems. RESULTS: All tested cell lines possessed minor populations of cells with highest expression of CD133, CD44 and CD166, whereas the vast majority of cells were CD133-negative. Several experimental approaches promoted a higher proportion of CD133-positive cells with increased in vivo tumorigenicity and the ability to produce floating spheres. Genome-wide microarray analysis (Affymetrix; DAVID) of CSC-enriched versus CSC-depleted cell populations revealed 213 genes with 10-100 fold increased activity out of 8994 differentially expressed ones and 87 genes with 5-50 fold decreased activity. CONCLUSIONS: The proposed in vitro prostate CSC model allows for reliable isolation and propagation of highly tumorigenic cells. This study may contribute to the identification of novel targets for CSC-targeted prostate cancer treatment.