Vitamin D decreases tumor cell growth and invasiveness in primary malignant bone tumors in vitro

Primary malignant bone tumors (PMBTs) are rare neoplasms arising from bone tissue. Limited evidence suggests an association between reduced serum 25(OH) vitamin D3 levels and PMBT incidence. The active metabolite 1,25(OH)2 vitamin D3 (1,25D3) modulates tumor cell proliferation, apoptosis, and migration through interactions with the vitamin D receptor (VDR). This study investigated the effects of 1,25D3 on osteosarcoma (MG-63, SaOS-2), chondrosarcoma (SW-1353), and Ewing's sarcoma (RD-ES) cell lines. Expression of key components of vitamin D metabolism, including 1α-hydroxylase (CYP27B1), 24-hydroxylase (CYP24A1), VDR, protein disulfide-isomerase A3 (PDIA3), and the 1,25D3-responsive bone gamma-carboxyglutamate protein (BGLAP), was analyzed at mRNA and protein levels. VDR nuclear translocation was assessed by Western blotting. Cell viability, cell cycle progression, apoptosis, and migration were evaluated using metabolic assays, flow cytometry, immunocytochemistry, wound healing, and live-cell imaging. Treatment with 1,25D3 upregulated CYP24A1 in osteosarcoma cells, while BGLAP expression was detected in both osteosarcoma and SW-1353 cells. All examined cell lines expressed VDR and PDIA3, and 1,25D3 induced VDR nuclear translocation. MG-63 cell viability decreased by 23%, whereas SW-1353 cell viability decreased by 10%, with no significant changes observed in SaOS-2 and RD-ES cells. In MG-63 cells, 1,25D3 induced a significant accumulation of cells in the G1 phase, consistent with cell-cycle arrest, whereas only minor cell-cycle alterations were observed in the other cell lines. Interestingly, 1,25D3 reduced the proportion of apoptotic osteosarcoma cells by 18–30%. The migration of MG-63 cells was significantly reduced by 1,25D3, and an inhibitory trend, albeit not statistically significant, was also observed in RD-ES cells. In conclusion, 1,25D3 modulated cell viability, apoptosis, and migration in PMBT cell models, with distinct, cell-type-specific responses. These findings suggest a potential role for 1,25D3 in regulating PMBT growth and invasiveness.