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.
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.
Kaur
Manjinder
M
Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
Agarwal
Chapla
C
Singh
Rana P
RP
Guan
Xiangming
X
Dwivedi
Chandradhar
C
Agarwal
Rajesh
R
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
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