Exploration of Niflumic Acid’s Action on Ca²⁺ Movement and Cell Viability in Human Osteosarcoma Cells

Niflumic acid, a drug used for joint and muscular pain, affected Ca²⁺ signaling in different models. However, the effect of niflumic acid on Ca²⁺ homeostasis and Ca²⁺-related physiology in human osteosarcoma cells is unknown. This study examined the effect of niflumic acid on cytosolic free Ca²⁺ concentrations ([Ca²⁺]i) in MG63 human osteosarcoma cells. Intracellular Ca²⁺ concentrations in suspended cells were monitored by using the fluorescent Ca²⁺-sensitive dye fura- 2. Cell viability was examined by using 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio- 1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1). In MG63 cells, niflumic acid at concentrations of 250-750 μM evoked [Ca²⁺]i rises concentration-dependently. Niflumic acid-evoked Ca²⁺ entry was confirmed by Mn²⁺-induced quenching of fura-2 fluorescence. This entry was inhibited by nifedipine, econazole, SKF96365, the protein kinase C (PKC) activator phorbol 12-myristate 13 acetate (PMA), but was not affected by the PKC inhibitor GF109203X. In Ca²⁺- free medium, treatment with the endoplasmic reticulum Ca²⁺ pump inhibitor thapsigargin (TG) inhibited niflumic acid-evoked [Ca²⁺]i rises. Conversely, treatment with niflumic acid abolished TG-evoked [Ca²⁺]i rises. Inhibition of phospholipase C (PLC) with U73122 also partly reduced niflumic acid-evoked [Ca²⁺]i rises. Niflumic acid killed cells at 200-500 μM in a concentration-dependent fashion. Chelating cytosolic Ca²⁺ with 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid/ AM (BAPTA/AM) did not reverse niflumic acid-induced cytotoxicity. Collectively, our data suggest that in MG63 cells, niflumic acid induced [Ca²⁺]i rises by evoking PLC-dependent Ca²⁺ release from the endoplasmic reticulum, and Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ entry. Niflumic acid also induced Ca²⁺-independent cell death.