The Mechanism of Safrole-Induced [Ca^(2+)]_i Rises and Non-Ca^(2+)-Triggered Cell Death in SCM1 Human Gastric Cancer Cells

Safrole is a carcinogen found in plants. The effect of safrole on cytosolic free Ca^(2+) concentrations ([Ca^(2+)]_i) and viability in SCM1 human gastric cancer cells was explored. The Ca2+-sensitive fluorescent dye fura-2 was applied to measure [Ca^(2+)]_i. Safrole at concentrations of 150-450 μM induced a [Ca^(2+)]_i rise in a concentration-dependent manner. The response was reduced by 60% by removing extracellular Ca^(2+). Safrole-evoked Ca^(2+) entry was not altered by nifedipine, econazole, SKF96365, and protein kinase C activator or inhibitor. In Ca^(2+)-free medium, treatment with the endoplasmic reticulum Ca^(2+) pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) abolished safrole-evoked [Ca^(2+)]_i rises. Conversely, treatment with safrole abolished thapsigargin or BHQ-evoked [Ca^(2+)]i rises. Inhibition of phospholipase C (PLC) with U73122 abolished safrole-induced [Ca2+]i rises. At 250-550 μM, safrole decreased cell viability concentration-dependently, which was not reversed by chelating cytosolic Ca^(2+) with 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid/acetoxy methyl (BAPTA/AM). Annexin V/propidium iodide staining data suggest that safrole (350-550 μM) induced apoptosis concentration- dependently. These studies suggest that in SCM1 human gastric cancer cells, safrole induced [Ca^(2+)]_i rises by inducing PLC-dependent Ca^(2+) release from the endoplasmic reticulum and Ca^(2+) influx via non-store-operated Ca^(2+) entry pathways. Safrole-induced cell death may involve apoptosis.