Calcium-dependence of Hydrogen Peroxide-induced C-fos Expression and Growth Stimulation of Multicellular Prostate Tumor Spheroids

Hydrogen peroxide (H2O2) in nanomolar concentrations (20-100 nM) stimulated the growth of small (diameter 100 +/- 30 microm) multicellular prostate cancer spheroids and increased c-fos expression. H2O2 transiently raised [Ca2+]i by Ca2+ release from intracellular stores as the transient persisted in low (10 nM) Ca2+ solution but was abolished when intracellular Ca2+ stores were depleted by thapsigargin or chelation of [Ca2+]i with BAPTA. The H2O2-induced [Ca2+]i transient was furthermore inhibited by the P2-purinoreceptor antagonists suramin and basilen blue, indicating that H2O2 may act via purinergic receptor stimulation. Treatment of spheroids with either suramin, basilen blue or BAPTA inhibited the H2O2-induced growth stimulation and c-fos expression, indicating that the H2O2-mediated growth stimulation of multicellular spheroids is mediated via a Ca2+-dependent pathway.