title: Skin cancer chemopreventive agent, {alpha}-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.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
authors.forename: Manjinder
authors.initials: M
authors.lastname: Kaur
authors.forename: Chapla
authors.initials: C
authors.lastname: Agarwal
authors.forename: Rana P
authors.initials: RP
authors.lastname: Singh
authors.forename: Xiangming
authors.initials: X
authors.lastname: Guan
authors.forename: Chandradhar
authors.initials: C
authors.lastname: Dwivedi
authors.forename: Rajesh
authors.initials: R
authors.lastname: Agarwal
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D002277:Carcinoma / Q000517:prevention & control; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D010938:Plant Oils / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D000081223:Polycyclic Sesquiterpenes; D012717:Sesquiterpenes / Q000494:pharmacology*; D012878:Skin Neoplasms / Q000517:prevention & control*; D014407:Tumor Cells, Cultured
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D010938:Plant Oils; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D000081223:Polycyclic Sesquiterpenes; D012717:Sesquiterpenes; C043206:santalol; D045304:Cytochromes c; D003513:Cycloheximide; D011065:Poly(ADP-ribose) Polymerases; D020169:Caspases; C076763:sandalwood oil