Aim: 

[Pt(O,O'-acac)(g-acac)(DMS)] (Pt-2acac), a new Pt(II) complex, is able to induce apoptosis in cisplatin-resistant human breast carcinoma MCF-7 cells [1]. The aim of this study was to assess the effect of Pt-2acac on intracellular calcium ([Ca²⁺]_i) homeostasis in MCF-7 cells.

Methods: 

(a) [Ca²⁺]_i was monitored by Fura-2; (b) Mn²⁺ uptake (Mn²⁺ is a good Ca²⁺-entry tracer, since it is not actively pumped out of the cell) was estimated by the Fura-2 quenching technique; (c) the activation of PKC-a was assessed by western blot and (d) the enzymatic activity of PMCA was measured using a coupled enzyme assay.

Results: 

In MCF-7 cells Pt-2acac caused the increase of [Ca⁺]_i, and the alteration of the overall [Ca²⁺]_i response after UTP stimulation of the purinergic receptor. In order to understand the mechanisms of Pt-2acac-altered Ca²⁺ homeostasis, some aspects of the [Ca²⁺]_i response were assessed obtaining the following Results:

(1) Pt-2acac did not affect the capacitative Ca²⁺ entry in cells treated with 1 mM thapsigargin; (2) Pt-2acac reduced the Mn²⁺ cell influx both in the absence or presence of purinergic stimulation; (3) Pt-acac provoked a cytosol-to-membrane translocation of PKC-a (note that PKC-a is the only conventional PKC expressed by MCF-7 cells); (4) Pt-2acac provoked the inhibition of PMCA activity, as demonstrated by enzymatic assay; (5) cell pre-incubation with Gö6976, a conventional PKC inhibitor, abolished the Pt-2acac effects on both Mn²⁺ cell influx and PMCA activity.

Conclusion: 

In MCF-7 cells, Pt-2acac caused an increase of [Ca²⁺]_i potentially responsible for apoptotic process; this increase appears to be due to the inhibition of PMCA activity overcaming the decrease of Ca²⁺ plasma membrane permeability. Both effects were mediated through PKC-a isoform activation.

References: 

[1] A. Muscella et al. Br J Pharmacol 2008, 153:34–49.