Effect of NPC-14686 (Fmoc-l-homophenylalanine) on Ca ²⁺ homeostasis and viability in OC2 human oral cancer cells

The effect of the anti-inflammatory compound NPC-14686 on intracellular Ca ²⁺ concentration ([Ca ²⁺ ] _i ) and viability in OC2 human oral cancer cells was investigated. The Ca ²⁺ -sensitive fluorescent probe fura-2 was used to examine [Ca ²⁺ ] _i . NPC-14686 induced [Ca ²⁺ ] _i rises in a concentration-dependent fashion. The effect was reduced approximately by 10% by removing extracellular Ca ²⁺ . NPC-14686- elicited Ca ²⁺ signal was decreased by nifedipine, econazole, SKF96365, and GF109203X. In Ca ²⁺ -free medium, incubation with the endoplasmic reticulum Ca ²⁺ pump inhibitor thapsigargin or 2,5-di-tertbutylhydroquinone (BHQ) abolished NPC-14686-induced [Ca ²⁺ ]i rises. Conversely, pretreatment with NPC-14686 abolished thapsigargin or BHQ-induced [Ca ²⁺ ] _i rises. Inhibition of phospholipase C with U73122 abolished NPC-14686-induced [Ca ²⁺ ] _i rises. At 20-100 μM, NPC-14686 inhibited cell viability, which was not reversed by chelating cytosolic Ca ²⁺ with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). NPC-14686 between 20 μM and 40 μM also induced apoptosis. Collectively, in OC2 cells, NPC-14686 induced [Ca ²⁺ ]i rises by evoking phospholipase C-dependent Ca ²⁺ release from the endoplasmic reticulum and Ca ²⁺ entry via protein kinase C-regulated store-operated Ca ²⁺ channels. NPC-14686 also caused Ca ²⁺ -independent apoptosis.