Exploration of the effect of the alkaloid colchicine on Ca handling and its related physiology in human oral cancer cells.

Objective: Colchicine, extracted from plants of the genus Colchicum, is a commonly prescribed drug for inflammatory diseases. It has been shown that colchicine affected various physiological responses in different models. However, the effect of colchicine on cytosolic free Ca levels ([Ca]) and its related physiology in human oral cancer cells is unknown. This study examined whether colchicine altered Ca homeostasis and caused cytotoxicity in OC2 human oral cancer cells.

Methods: The Ca-sensitive fluorescent dye fura-2 was used to measure [Ca]. Cell viability was measured by the fluorescent reagent 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay.

Results: Colchicine at concentrations of 250-650 μM induced [Ca] rises concentration-dependently. The response was reduced by approximately 40% by removing extracellular Ca. In Ca-free medium, treatment with the endoplasmic reticulum Ca pump inhibitor thapsigargin inhibited colchicine-evoked [Ca] rises. Conversely, treatment with colchicine inhibited thapsigargin-evoked [Ca] rises. Inhibition of phospholipase C (PLC) with U73122 abolished colchicine-induced Ca release. In Ca-containing medium, colchicine-induced Ca entry was supported by Mn-caused quenching of fura-2 fluorescence and the entry was partly inhibited by protein kinase C (PKC) modulators (phorbol 12-myristate 13 acetate, PMA; and GF109203X) and by three modulators of store-operated Ca channels (nifedipine, econazole and SKF96365). Colchicine at 250-650 μM decreased cell viability, which was not reversed by pretreatment with the Cachelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM).

Conclusions: In OC2 cells, colchicine induced [Ca] rises by evoking PLC-dependent Ca release from the endoplasmic reticulum and Ca entry via PKC-sensitive store-operated Ca entry. Furthermore, colchicine caused cell death that was not triggered by preceding [Ca] rises.