Epigallocatechin-3-gallate mobilizes intracellular Ca ²⁺ in prostate cancer cells through combined Ca ²⁺ entry and Ca ²⁺-induced Ca ²⁺ release

Aims: To elucidate the mechanism by which (-)-epigallocatechin-3-gallate (EGCG) mediates intracellular Ca increase in androgen-independent prostate cancer (PCa) cells.

Main methods: Following exposure to different doses of EGCG, viability of DU145 and PC3 PCa cells was evaluated by MTT assay and the intracellular Ca²⁺ dynamics by the fluorescent Ca²⁺ chelator Fura-2. The expression of different channels was investigated by qPCR analysis and sulfhydryl bonds by Ellman's assay.

Key findings: EGCG inhibited PC3 and DU145 proliferation with IC₅₀ = 46 and 56 μM, respectively, and induced dose-dependent peaks of internal Ca²⁺ that were dependent on extracellular Ca²⁺. The expression of TRPC4 and TRPC6 channels was revealed by qPCR in PC3 cells, but lack of effect modulators and blockers ruled out an exclusive role for these, as well as for voltage-dependent T-type, Ca²⁺ channels. Application of dithiothreitol and catalase and sulfhydryl (SH) measurements showed that EGCG-induced Ca²⁺ rise depends on SH oxidation, while the effect of EGTA, dantrolene, and the PLC inhibitor U73122 suggested that EGCG-induced Ca²⁺ influx acts as a trigger for Ca²⁺-induced Ca²⁺ release, involving both ryanodine and IP₃ receptors. Different from EGCG, ATP caused a rapid Ca²⁺ increase, which was independent of external Ca²⁺, but sensitive to U73122.

Significance: EGCG induces an internal Ca²⁺ increase in PCa cells by a multi-step mechanism. As dysregulation of cytosolic Ca²⁺ is directly linked to apoptosis in PCa cells, these data confirm the possibility of using EGCG as a synergistic adjuvant in combined therapies for recalcitrant malignancies like androgen-independent PCa.

Keywords: ATP-induced Ca(2+) release; Androgen-resistant prostate cancer cells; Ca(2+)-induced Ca(2+) release; Cytotoxicity; DU145 cell; Fura2; Green tea; PC3 cells; SH oxidation.