Abstract
Osteosarcoma (OS) is the most common type of primary bone tumor. Currently, there are limited treatment options for metastatic OS. Alpha-ketoglutarate (AKG), i.e., a multifunctional intermediate of the Krebs cycle, is one of the central metabolic regulators of tumor fate and plays an important role in cancerogenesis and tumor progression. There is growing evidence suggesting that AKG may represent a novel adjuvant therapeutic opportunity in anti-cancer therapy. The present study was intended to check whether supplementation of Saos-2 and HOS osteosarcoma cell lines (harboring a TP53 mutation) with exogenous AKG exerted an anti-cancer effect. The results revealed that AKG inhibited the proliferation of both OS cell lines in a concentration-dependent manner. As evidenced by flow cytometry, AKG blocked cell cycle progression at the G1 stage in both cell lines, which was accompanied by a decreased level of cyclin D1 in HOS and increased expression of p21Waf1/Cip1 protein in Saos-2 cells (evaluated with the ELISA method). Moreover, AKG induced apoptotic cell death and caspase-3 activation in both OS cell lines (determined by cytometric analysis). Both the immunoblotting and cytometric analysis revealed that the AKG-induced apoptosis proceeded predominantly through activation of an intrinsic caspase 9-dependent apoptotic pathway and an increased Bax/Bcl-2 ratio. The apoptotic process in the AKG-treated cells was mediated via c-Jun N-terminal protein kinase (JNK) activation, as the specific inhibitor of this kinase partially rescued the cells from apoptotic death. In addition, the AKG treatment led to reduced activation of extracellular signal-regulated kinase (ERK1/2) and significant inhibition of cell migration and invasion in vitro concomitantly with decreased production of pro-metastatic transforming growth factor β (TGF-β) and pro-angiogenic vascular endothelial growth factor (VEGF) in both OS cell lines suggesting the anti-metastatic potential of this compound. In conclusion, we showed the anti-osteosarcoma potential of AKG and provided a rationale for a further study of the possible application of AKG in OS therapy.
Highlights
Osteosarcoma (OS) is a malignant mesenchymal-origin primary tumor of bone
Since AKG was described to exhibit direct antiproliferative activity [22], we evaluated its influence on cell proliferation in two OS cell lines, i.e., Saos-2 (p53-null cell line) and HOS (p53 mutant)
It is worth mentioning that exogenous AKG does not penetrate into the cell, the intracellular level of this metabolite depends on the extracellular concentration [8] in an in vitro study and probably on the time required for its consumption by the cell
Summary
Osteosarcoma (OS) is a malignant mesenchymal-origin primary tumor of bone. Bone tumors are relatively rare overall (less than 1% and 3–5% of all newly diagnosed malignant cancers in adults and children, respectively), OS is the most common bone cancer in children and adolescents [2]. The 5-year overall survival rates of OS patients with distant metastasis and/or relapsed OS is low, i.e., approximately 30% in individuals with lung metastasis [5]. The current OS treatment combines surgery with chemotherapy, which was introduced in the 1980s and resulted in significant improvement in OS patients’ survival rates over the 1990s [4]. For the past 20 years, the survival rates in OS patients did not change essentially and no successful targeted therapies of this cancer have been developed so far [6]. There is still a need for novel OS treatment strategies
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