Identification of CBX3 and ABCA5 as Putative Biomarkers for Tumor Stem Cells in Osteosarcoma

Recently, there has been renewed interest in the role of tumor stem cells (TSCs) in tumorigenesis, chemoresistance, and relapse of malignant tumors including osteosarcoma. The potential exists to improve osteosarcoma treatment through characterization of TSCs and identification of therapeutic targets. Using transcriptome, proteome, immunophenotyping for cell-surface markers, and bioinformatic analyses, heterogeneous expression of previously reported TSC or osteosarcoma markers, such as CD133, nestin, POU5F1 (OCT3/4), NANOG, SOX2, and aldehyde dehydrogenase, among others, was observed in vitro. However, consistently significantly lower CD326, CD24, CD44, and higher ABCG2 expression in TSC-enriched as compared with un-enriched osteosarcoma cultures was observed. In addition, consistently higher CBX3 expression in TSC-enriched osteosarcoma cultures was identified. ABCA5 was identified as a putative biomarker of TSCs and/or osteosarcoma. Lastly, in a high-throughput screen we identified epigenetic (5-azacytidine), anti-microtubule (vincristine), and anti-telomerase (3,11-difluoro-6,8,13-trimethyl- 8H-quino [4,3,2-kl] acridinium methosulfate; RHPS4)-targeted therapeutic agents as candidates for TSC ablation in osteosarcoma.近年来，肿瘤干细胞（Tumor Stem Cells, TSCs）在包括骨肉瘤在内的恶性肿瘤的发生、化疗耐药及复发过程中的作用，重新受到学界的广泛关注。通过对肿瘤干细胞进行特征鉴定并筛选治疗靶点，有望提升骨肉瘤的临床治疗水平。本研究通过转录组学、蛋白质组学、细胞表面标志物免疫表型分析及生物信息学分析，在体外实验中观察到：既往报道的肿瘤干细胞或骨肉瘤相关标志物（如CD133、巢蛋白（nestin）、POU5F1（OCT3/4）、NANOG、SOX2及醛脱氢酶等）存在异质性表达。不过，与未富集肿瘤干细胞的骨肉瘤培养体系相比，富集肿瘤干细胞的培养体系中CD326、CD24、CD44的表达水平持续显著降低，而ABCG2的表达水平则持续显著升高，且该差异具有一致性。此外，本研究还发现，富集肿瘤干细胞的骨肉瘤培养体系中CBX3的表达水平持续显著升高。ABCA5被鉴定为肿瘤干细胞及/或骨肉瘤的潜在生物标志物。最后，通过高通量筛选，本研究鉴定出三类可用于骨肉瘤肿瘤干细胞消融的靶向治疗候选药物，分别为表观遗传调控类药物（5-氮胞苷）、抗微管类药物（长春新碱）以及抗端粒酶类药物（3,11-二氟-6,8,13-三甲基-8H-喹诺[4,3,2-kl]吖啶鎓甲硫酸盐；RHPS4）。