Calpain and Caspase Orchestrated Death Signal to Accomplish Apoptosis Induced by Resveratrol and Its Novel Analog Hydroxstilbene-1 in Cancer Cells

Stomach ulceration is a major side effect of most chemopreventive drugs. We have established that although resveratrol is a promising chemopreventive compound, it delays the ulcer healing process. However, its analog hydroxystilbene-1 (HST-1) was devoid of such an ulcerogenic side effect. Consequently, here we tried to explore the chemopreventive efficacy of HST-1 compared with resveratrol in different cancer cell lines and identified the probable signaling pathways responsible for cell death. Our cell viability study established that HST-1, compared with resveratrol, showed better chemopreventive potential in all of the cell lines tested, with U937 and MCF-7 being the cells most affected. Furthermore, in U937 and MCF-7 cell lines, terminal deoxynucleotidyl transferase dUTP nick end labeling assay, cell cycle analysis, and nuclear fragmentation by confocal microscopy established that both HST-1 and resveratrol switched on the apoptotic death cascade to execute cell death. The initiator signal was Fas-independent but synchronized in terms of cytosolic Ca2+ influx, dissipation of mitochondrial membrane potential, and oxidative burst. It is noteworthy that the executioner signal was cell-specific as in U937 cells; HST-1 and resveratrol treatment induced mitochondrial permealization followed by cardiolipin depletion and cytochrome c release, which eventually activated downstream caspases 9 and 3 to execute the death process. In contrast, in MCF-7 cells the death process was executed in a caspase-independent but calpain-dependent manner as calpain activation induced cleavage of cytosolic alpha-fodrin, stimulated mitochondrial release of apoptotic inducing factor and endonuclease G, and thus harmonized cytosolic and mitochondrial death signals to accomplish apoptosis.