Mechanisms underlying the effect of an oral antihyperglycaemic agent glyburide on calcium ion (Ca²⁺) movement and its related cytotoxicity in prostate cancer cells

Glyburide is an agent commonly used to treat type 2 diabetes and also affects various physiological responses in different models. However, the effect of glyburide on Ca²⁺ movement and its related cytotoxicity in prostate cancer cells is unclear. This study examined whether glyburide altered Ca²⁺ signalling and viability in PC3 human prostate cancer cells and investigated those underlying mechanisms. Intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in suspended cells were measured by using the fluorescent Ca²⁺-sensitive dye fura-2. Cell viability was examined by WST-1 assay. Glyburide at concentrations of 100–1000 μM induced [Ca²⁺]_i rises. Ca²⁺ removal reduced the signal by approximately 60%. In Ca²⁺-containing medium, glyburide-induced Ca²⁺ entry was inhibited by 60% by protein kinase C (PKC) activator (phorbol 12-myristate 13 acetate, PMA) and inhibitor (GF109203X), and modulators of store-operated Ca²⁺ channels (nifedipine, econazole and SKF96365). Furthermore, glyburide induced Mn²⁺ influx suggesting of Ca²⁺ entry. In Ca²⁺-free medium, inhibition of phospholipase C (PLC) with U73122 significantly inhibited glyburide-induced [Ca²⁺]_i rises. Treatment with the endoplasmic reticulum (ER) Ca²⁺ pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished glyburide-evoked [Ca²⁺]_i rises. Conversely, treatment with glyburide abolished BHQ-evoked [Ca²⁺]_i rises. Glyburide at 100–500 μM decreased cell viability, which was not reversed by pretreatment with the Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Together, in PC3 cells, glyburide induced [Ca²⁺]_i rises by Ca²⁺ entry via PKC-sensitive store-operated Ca²⁺ channels and Ca²⁺ release from the ER in a PLC-dependent manner. Glyburide also caused Ca²⁺-independent cell death. This study suggests that glyburide could serve as a potential agent for treatment of prostate cancer.