Cisplatin (CDDP) triggers cell death of MCF-7 cells following disruption of intracellular calcium ([Ca²⁺]_i) homeostasis

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Breast cancer (BC) is a public health problem all over the world. Cisplatin (CDDP) is an antineoplastic agent with high rate of success in treating cancers. The down side of CDDP treatment is the development of chemo-resistance. Beside DNA damage and activation of p53 signaling pathway, CDDP induces tumor-cell death due to elevation in the intracellular calcium concentration ([Ca²⁺]_i).However, the role of [Ca²⁺]_i in CDDP induced apoptosis of breast cancer cells (MCF-7) is not well understood. Here we investigate the cytotoxic effects of CDDP in relation to [Ca²⁺]_i homeostasis in MCF-7-sensitive and -resistant cell lines. Live-cell imaging using [Ca²⁺]_i sensitive fluorescent dyes was employed to monitor [Ca²⁺]_i CDDP treated MCF-7 cells (0.001-10 µM) and [Ca²⁺]_i modulators i.e. Caffeine (10 mM); Nimodipine (10 µM); Ionomycin (10 µM); Thapsigargin (500 nM). A concentration-dependent increase of[Ca²⁺]_i was observed in CDDP MCF-7 treated cells. From the concentration range tested 100 nM CDDP triggered the highest [Ca²⁺]_i increase (120%; n = 19)while in drug resistant MCF-7 cells the effects of CDDP on [Ca²⁺]_i were reduced as compared with the drug sensitive MCF-7 cells. Furthermore, the CDDP induced cell death correlates with the increase of [Ca²⁺]_i, and thus, significantly lower in the CDDP desensitized cells (p < 0.05). Pre-application of the calcium channel blocker, Nimodipine reduced [Ca²⁺]_i elevation significantly (46.6% increase; n = 26) as well as when a pre-application of Caffeine, Ionomycin or Thapsigargin occurred followed by the subsequent application of CDDP (n = 15; 37.8%, n = 32; 34.9%, n = 21; 53.7% increase respectively).