DNA damage dependent activation of checkpoint kinase-1 and mitogen-activated protein kinase-p38 are required in malabaricone C-induced mitochondrial cell death

Background: Given that lung cancer is the second leading cause of cancer-related deaths with low survival rates, the project was aimed to formulate an efficient drug with minimum side effects, and rationalize its action mechanistically. Methods: Mitochondria deficient cells, shRNA-mediated BCL2 and ATM depleted cells and pharmacological inhibition of DNA-damage response proteins were employed to explore the signaling mechanism governed between nucleus and mitochondria in response to mal C. Results: Mal C decreased cell viability in three lung carcinoma cells, associated with DNA damage, p38-MAPK activation, imbalance in BAX/BCL2 expression, mitochondrial dysfunction and cytochrome-c release. Mitochondria depletion and p38-MAPK inhibition made A549 cells extremely resistant, but BCL2 knock-down partially sensitized the cells to mal C treatment. The mal C-induced apoptosis in A549 cells was initiated by DNA single strand breaks that led to double strand breaks (DSBs). DSB generation paralleled the induction of ATM- and ATR-mediated CHK1 phosphorylation. ATM silencing and ATR inhibition partially attenuated the mal C-induced p38-MAPK activation, CHK1 phosphoiylation and apoptosis, which were completely suppressed by CHK1 inhibition. Conclusions: Mal C activates the ATM-CHK1-p38 MAPK cascade to cause mitochondrial cell death in lung carcinoma cells. General significance: Given that mal C has appreciable natural abundance and is non-toxic to mice, further in vivo evaluation would help in establishing its anti-cancer property. (C) 2013 Elsevier B.V. All rights reserved.