Skin cancer chemopreventive agent,  -santalol, induces apoptotic death of human epidermoid carcinoma A431 cells via caspase activation together with dissipation of mitochondrial membrane potential and cytochrome c release

Abstract

alpha-Santalol, an active component of sandalwood oil, has been studied in detail in recent years for its skin cancer preventive efficacy in murine models of skin carcinogenesis; however, the mechanism of its efficacy is not defined. Two major biological events responsible for the clonal expansion of transformed/initiated cells into tumors are uncontrolled growth and loss of apoptotic death. Accordingly, in the present study, employing human epidermoid carcinoma A431 cells, we assessed whether alpha-santalol causes cell growth inhibition and/or cell death by apoptosis. Treatment of cells with alpha-santalol at concentrations of 25-75 microM resulted in a concentration- and a time-dependent decrease in cell number, which was largely due to cell death. Fluorescence-activated cell sorting analysis of Annexin V/propidium iodide (PI) stained cells revealed that alpha-santalol induces a strong apoptosis as early as 3 h post-treatment, which increases further in a concentration- and a time-dependent manner up to 12 h. Mechanistic studies showed an involvement of caspase-3 activation and poly(ADP-ribose) polymerase cleavage through activation of upstream caspase-8 and -9. Further, the treatment of cells with alpha-santalol also led to disruption of the mitochondrial membrane potential and cytochrome c release into the cytosol, thereby implicating the involvement of the mitochondrial pathway. Pre-treatment of cells with caspase-8 or -9 inhibitor, pan caspase inhibitor or cycloheximide totally blocked alpha-santalol-caused caspase-3 activity and cleavage, but only partially reversed apoptotic cell death. This suggests involvement of both caspase-dependent and -independent pathways, at least under caspase inhibiting conditions, in alpha-santalol-caused apoptosis. Together, this study for the first time identifies the apoptotic effect of alpha-santalol, and defines the mechanism of apoptotic cascade activated by this agent in A431 cells, which might be contributing to its overall cancer preventive efficacy in mouse skin cancer models.

Bromelain inhibits nuclear factor kappa‐B translocation, driving human epidermoid carcinoma A431 and melanoma A375 cells through G2/M arrest to apoptosis

“…Researchers like Liang et al [53] using a series of caspase inhibitors with overlapping specificities, enzyme-specific chromogenic substrates, determined that apoptosis pathway bypassed the need for activated caspase-3 and proceeded via caspase-9, -7 and -6. Lack of sole involvement of caspases in a-santalol-induced apoptosis in A431 cells was also shown by Kaur et al [54]. They showed that pre-treatment of cells with caspase-8 or -9 inhibitor, pan caspase inhibitor or cycloheximide totally blocked a-santalolcaused caspase-3 activity and cleavage, but only partially reversed apoptotic cell death which therefore indicated the involvement of both caspasedependent and independent pathways in a-santalol-caused apoptosis.…”

Anticancerous Potential of Medicinal Plants- A Review

“…[57] It has also been shown to act as a skin cancer chemoprotective agent. [58] It induces apoptosis in human epidermoid carcinoma A431 cells by activation of caspase 8 and 9 which in turn activate caspase 3 and are responsible for the cleavvge of the poly (ADP-ribose) polymerase. [59] It also affects the intrinsic pathway of apoptosis as it dysfunctions the mitochondria by decreasing its membrane potential which marks the release of cytochrome c into the cytosol and results into the activation of caspase and hence apoptosis.…”

Recent Developments in Pharmaceutical and Therapeutic Applications of Sandalwood Oil

“…In addition to these effects of α-santalol, it induces apoptotic death of human epidermoid carcinoma A431 cells via caspases activation through both extrinsic and intrinsic pathways. [24] This study identified the apoptotic effect of α-santalol and defined the mechanism of apoptotic cascade activated by this agent in A431 cells, which might be contributing to its overall cancer preventive efficacy in mouse skin cancer models. Although α -santalol is a major component (61%) of sandalwood oil and may be a major contributor to its skin cancer chemo-preventive effects, the effects of other components of sandalwood oil could not be ruled out.…”

“…Mechanistic studies showed an involvement of caspase-3 activation and poly (ADP-ribose) polymerase cleavage & disruption of the mitochondrial membrane potential and cytochrome-C release into the cytoso l, thereby suggesting involvement of both caspase -dependant and independent pathways. [24] www.wjpps.com…”