Development and characterization of cancer stem cell-based tumoroids as an osteosarcoma model

Three-dimensional (3D) cancer tumor models are becoming vital approaches for high-throughput drug screening, drug targeting, development of novel theranostic systems, and personalized medicine. Yet, it is becoming more evident that the tumor progression and metastasis is fueled by a subpopulation of stem-like cells within the tumor that are also called cancer stem cells (CSCs). This study aimed to develop a tumoroid model using CSCs. For this purpose CD133⁺ cells were isolated from SaOS-2 osteosarcoma cell line with magnetic-activated cell sorting. To evaluate tumoroid formation ability, the cells were incubated in different cell numbers in agar gels produced by 3D Petri Dish® method. Subsequently, CD133⁺ cells and CD133^- cells were co-cultured to investigate CD133⁺ cell localization in tumoroids. The characterization of tumoroids was performed using Live&Dead staining, immunohistochemistry, and quantitative polymerase chain reaction analysis. The results showed that, CD133⁺ , CD133^- and SaOS-2 cells were all able to form 3D tumoroids regardless of the initial cell number, but, while 72 hr were needed for CD133⁺ cells to self-assemble, 24 hr were enough for CD133^- and SaOS-2 cells. CD133⁺ cells were located within tumoroids randomly with high cell viability. Finally, when compared to two-dimensional (2D) cultures, there were 5.88, 4.14, 6.95, and 1.68-fold higher messenger RNA expressions for Sox2, OCT3/4, Nanog, and Nestin, respectively, in CD133⁺ cells that were cultured within 3D tumoroids, showing longer maintenance of stem cell phenotype in 3D, that can allow more relevant screening and targeting efficiency in pharmaceutical testing. It was concluded that CSC-based tumoroids are propitious as 3D tumor models to fill the gap between conventional 2D in vitro culture and in vivo animal experiments for cancer research.

MicroRNA-29b-1 impairs in vitro cell proliferation, self‑renewal and chemoresistance of human osteosarcoma 3AB-OS cancer stem cells

Osteosarcoma (OS) is the most common type of bone cancer, with a peak incidence in the early childhood. Emerging evidence suggests that treatments targeting cancer stem cells (CSCs) within a tumor can halt cancer and improve patient survival. MicroRNAs (miRNAs) have been implicated in the maintenance of the CSC phenotype, thus, identification of CSC-related miRNAs would provide information for a better understanding of CSCs. Downregulation of miRNA-29 family members (miR-29a/b/c; miR-29s) was observed in human OS, however, little is known about the functions of miR-29s in human OS CSCs. Previously, during the characterization of 3AB-OS cells, a CSC line selected from human OS MG63 cells, we showed a potent downregulation of miR-29b. In this study, after stable transfection of 3AB-OS cells with miR-29b-1, we investigated the role of miR-29b-1 in regulating cell proliferation, sarcosphere-forming ability, clonogenic growth, chemosensitivity, migration and invasive ability of 3AB-OS cells, in vitro. We found that, miR-29b-1 overexpression consistently reduced both, 3AB-OS CSCs growth in two- and three-dimensional culture systems and their sarcosphere- and colony-forming ability. In addition, while miR-29b-1 overexpression sensitized 3AB-OS cells to chemotherapeutic drug-induced apoptosis, it did not influence their migratory and invasive capacities, thus suggesting a context-depending role of miR-29b-1. Using publicly available databases, we proceeded to identify potential miR-29b target genes, known to play a role in the above reported functions. Among these targets we analyzed CD133, N-Myc, CCND2, E2F1 and E2F2, Bcl-2 and IAP-2. We also analyzed the most important stemness markers as Oct3/4, Sox2 and Nanog. Real-time RT-PCR and western-blot analyses showed that miR-29b-1 negatively regulated the expression of these markers. Overall, the results show that miR-29b-1 suppresses stemness properties of 3AB-OS CSCs and suggest that developing miR-29b-1 as a novel therapeutic agent might offer benefits for OS treatment.

Mutant p53 gain of function can be at the root of dedifferentiation of human osteosarcoma MG63 cells into 3AB-OS cancer stem cells

Osteosarcoma is a highly metastatic tumor affecting adolescents, for which there is no second-line chemotherapy. As suggested for most tumors, its capability to overgrow is probably driven by cancer stem cells (CSCs), and finding new targets to kill CSCs may be critical for improving patient survival. TP53 is the most frequently mutated tumor suppressor gene in cancers and mutant p53 protein (mutp53) can acquire gain of function (GOF) strongly contributing to malignancy. Studies thus far have not shown p53-GOF in osteosarcoma. Here, we investigated TP53 gene status/role in 3AB-OS cells-a highly aggressive CSC line previously selected from human osteosarcoma MG63 cells-to evaluate its involvement in promoting proliferation, invasiveness, resistance to apoptosis and stemness. By RT-PCR, methylation-specific PCR, fluorescent in situ hybridization, DNA sequence, western blot and immunofluorescence analyses, we have shown that-in comparison with parental MG63 cells where TP53 gene is hypermethylated, rearranged and in single copy-in 3AB-OS cells, TP53 is unmethylated, rearranged and in multiple copies, and mutp53 (p53-R248W/P72R) is post-translationally modified and with nuclear localization. p53-R248W/P72R-knockdown by short-interfering RNA reduced the growth and replication rate of 3AB-OS cells, markedly increasing cell cycle inhibitor levels and sensitized 3AB-OS cells to TRAIL-induced apoptosis by DR5 up-regulation; moreover, it strongly decreased the levels of stemness and invasiveness genes. We have also found that the ectopic expression of p53-R248W/P72R in MG63 cells promoted cancer stem-like features, as high proliferation rate, sphere formation, clonogenic growth, high migration and invasive ability; furthermore, it strongly increased the levels of stemness proteins. Overall, the findings suggest the involvement of p53-R248W/P72R at the origin of the aberrant characters of the 3AB-OS cells with the hypothesis that its GOF can be at the root of the dedifferentiation of MG63 cells into CSCs.