Tumor‐derived spheroids: Relevance to cancer stem cells and clinical applications

Abstract

Recently, many types of in vitro 3‐D culture systems have been developed to recapitulate the in vivo growth conditions of cancer. The cancer 3‐D culture methods aim to preserve the biological characteristics of original tumors better than conventional 2‐D monolayer cultures, and include tumor‐derived organoids, tumor‐derived spheroids, organotypic multicellular spheroids, and multicellular tumor spheroids. The 3‐D culture methods differ in terms of cancer cell sources, protocols for cell handling, and the required time intervals. Tumor‐derived spheroids are unique because they are purposed for the enrichment of cancer stem cells (CSCs) or cells with stem cell‐related characteristics. These spheroids are grown as floating spheres and have been used as surrogate systems to evaluate the CSC‐related characteristics of solid tumors in vitro. Because eradication of CSCs is likely to be of clinical importance due to their association with the malignant nature of cancer cells, such as tumorigenicity or chemoresistance, the investigation of tumor‐derived spheroids may provide invaluable clues to fight against cancer. Spheroid cultures have been established from cancers including glioma, breast, colon, ovary, and prostate cancers, and their biological and biochemical characteristics have been investigated by many research groups. In addition to the investigation of CSCs, tumor‐derived spheroids may prove to be instrumental for a high‐throughput screening platform or for the cultivation of CSC‐related tumor cells found in the circulation or body fluids.

Generation and characterization of hepatocellular carcinoma cell lines with enhanced cancer stem cell potential

“…In our present study, we successfully generated two HepG2 derived monoclonal tumour cell lines, namely clone 3 and clone 5, with enhanced CSC potential by application of the tumour sphere formation assay, which represents a commonly accepted method to enrich CSC populations, and subsequent single‐cell cloning. The established clones 3 and 5 were positive for the cell surface protein CD133, which is one of the most commonly described HCSC markers.…”

“…In our study, we aimed to generate novel CSC enriched monoclonal cell lines of the well‐established HCC cell line HepG2. For this, we utilized the spheroid formation assay, which represents a commonly accepted method to enrich CSC populations . Our strategy gave rise to three distinct HepG2 sub‐cell lines, of which two HCSC enriched subclones were selected for detailed characterization.…”

Salivary gland cell aggregates are derived from self-organization of acinar lineage cells

“…Following the discovery that single stem cells form spheres or aggregates through proliferation and differentiation, “sphere” cultures have been widely used for culture of intestine, liver, mammary gland, and neural tissue, and have also been adapted for salivary glands (Cao et al, 2011; Feng et al, 2009; Ishiguro et al, 2017; Lathia, Mack, Mulkearns-Hubert, Valentim, & Rich, 2015; Lombaert, Brunsting, Wierenga, Faber, et al, 2008; Maimets, Bron, de Haan, van Os, & Coppes, 2015; Manuel Iglesias et al, 2013; Min, Lee, Bak, & Kim, 2015; Nanduri et al, 2011; Reynolds & Weiss, 1992; Shubin, Felong, Graunke, Ovitt, & Benoit, 2015; Smart et al, 2013). Using rigorous techniques, sphere culture enables isolation and expansion of clonogenic stem/progenitor cell populations with growth only through proliferation (Chen et al, 2012; Reynolds & Weiss, 1992).…”

TGF‐β‐mediated LEFTY/Akt/GSK‐3β/Snail axis modulates epithelial‐mesenchymal transition and cancer stem cell properties in ovarian clear cell carcinomas

“…Epithelial‐mesenchymal transition (EMT) plays a central role in converting both normal and neoplastic epithelial cells into derivatives with a more mesenchymal phenotype . Current evidence supports a strong association between EMT and cancer stem cells (CSCs), as demonstrated by EMT cells that exhibit stem‐like traits including high aldehyde dehydrogenase 1 (ALDH1) high activity and spheroid formation, and CSCs that acquire mesenchymal‐like characteristics . In addition, CSC frequently exhibits a slow cycling rate which makes them inherently resistant to standard chemotherapy and radiotherapy …”