Gallium compound GaQ(3) -induced Ca(2+) signalling triggers p53-dependent and -independent apoptosis in cancer cells

BACKGROUND AND PURPOSE A novel anti-neoplastic gallium complex GaQ(3) (KP46), earlier developed by us, is currently in phase I clinical trial. GaQ(3) induced S-phase arrest and Apoptosis via Caspase/PARP cleavage in a variety of cancers. However, the underlying mechanism of Apoptosis is unknown. Here, we have explored the mechanism(s) of GaQ(3) -induced Apoptosis in Cancer cells, focusing on p53 and intracellular CA(2+) signalling. EXPERIMENTAL APPROACH GaQ(3) -induced cytotoxicity and Apoptosis were determined in Cancer cell lines, with different p53 status (p53(+/+) , p53(-/-) and p53 mutant). Time course analysis of intracellular CA(2+) calcium release, p53 promoter activation, p53-nuclear/cytoplasmic movements and Reactive Oxygen Species (ROS) were conducted. CA(2+) -dependent formation of the p53-p300 transcriptional complex was analysed by co-immunoprecipitation and chromatin immunoprecipitation. CA(2+) signalling, p53, p300 and ROS were serially knocked down to study CA(2+) -p53-ROS ineractions in GaQ(3) -induced Apoptosis. KEY RESULTS GaQ(3) triggered intracellular CA(2+) release stabilizing p53-p300 complex and recruited p53 to p53 promoter, leading to p53 mRNA and protein synthesis. p53 induced higher intracellular CA(2+) release and ROS followed by activation of p53 downstream genes including those for the micro RNA mir34a. In p53(-/-) and p53 mutant cells, GaQ(3) -induced CA(2+) -signalling generated ROS. ROS further increased membrane translocation of FAS and FAS-mediated extrinsic Apoptosis. CONCLUSIONS AND IMPLICATIONS This study disclosed a novel mechanism of CA(2+) -signalling-mediated p53 activation and ROS up-regulation. Understanding the mechanism of GaQ(3) -induced Apoptosis will help establish this gallium-based organic compound as a potent anti-cancer drug.