Document Type

Thesis - University Access Only

Award Date

2006

Degree Name

Master of Science (MS)

Department / School

Pharmaceutical Sciences

Abstract

Skin cancer is the most common type of cancer in the United States and its incidence is expected to increase substantially because of increased recreational exposure to sunlight and depletion of the ozone layer. More than 1 million cases of skin cancer occur in this country each year leading to an estimated 564,830 deaths this year. Chemoprevention is a strategy to prevent and control cancer. Chemoprevention involves the administration of chemical agents to prevent initiation and\or promotion, and\or progression that occurs during neoplastic development. The two major biological events that occur during tumor development are uncontrolled growth and loss of apoptotic death. Apoptosis is a controlled physiological process of cell elimination which is of fundamental importance to all multicellular organisms. The caspases, a family of cysteine proteases, are the executioners of apoptosis. Tumor suppressor gene p53 is a well studied potent regulator, whose key importance is the protection against carcinogenesis. Several studies have illustrated p53 role in apoptosis promotion by both intrinsic and extrinsic pathways. Another factor that contirbutes to UVinduced skin cancer is the cyclooxygenase-2 (COX-2), whose role in tumorigenesis is substantially proven. It plays a crucial role in the rate limiting step of inflammatory process. Cancer chemoprevention by naturally occurring agents, especially the phytochemicals, minerals and vitamins, has shown promising results against various malignancies in a number of both in vitro and in vivo conditions. One such naturally occurring phytochemical is a.-santalol, a major component of sandalwood oil that has been traditionally used in the treatment of various skin ailments. Previous studies from our laboratory have indicated skin cancer chemopreventive effects of a.-santalol in chemicallyinduced skin cancer in CD-1 and SENCAR mice. A further, mechanistic study conducted to elucidate the possible mechanism behind its chemopreventive activity has shown the potential role of apoptotic proteins, caspase-3, 8 and 9. The objective of the present investigation was to study the chemopreventive effects of a-santalol on DVB-initiated and DVB-promoted skin tumor development in female SKH-1 mice, and to determine the possible role of apoptotic proteins involved in the prevention of skin tumor development by a.-santalol. a-Santalol a major component (60%) of sandalwood oil (Santalum Album Linn) was isolated from sandalwood oil by distillation under vacuum and characterized by nuclear magn􀃿tic resonance and gas chromatography-mass spectroscopy. In the long term experiment, a total of thirty female SKH-1 mice were used which were divided into three groups; Group 1, which served as control, received 100 μL acetone (vehicle for a.-santalol) topically. Group 2 and group 3, which served as experimental groups, received 100 μL a.-santalol (5% w/v in acetone) by topical administration. Tumor initiation was done by UVB (180mJ/cm2) radiation, and after I-week promotion was carried out by UVB (180mj/cm2 ) radiation. Group 1 received topical application of acetone one hour before UVB treatment. Group 2 received a-santalol one hour before UVB treatment and Group 3 received a-santalol immediately after UVB treatment. During the initiation phase this protocol was carried out daily and during promotion phase the treatment was given twice a week. Promotion phase was continued for 30 weeks. The group weights and tumor counts of all the mice were recorded once a week. At the end of 30th week, mice were sacrificed by cervical dislocation and the dorsal skin and tumors of the mice were collected. A short term experiment was also carried out for one week using 9 mice, categorized in the same manner as the long term experiment, to study the role of various proteins under sub-chronic conditions. The mice were sacrificed by the end of one week and the dorsal skin samples were collected. The obtained skin samples were then homogenized and centrifuged (10,000 xg) to collect the cell pellet. Proteins and rnRNA were extracted from the cell pellet. Using SDS PAGE and Western Blot analysis, the extracted proteins were analyzed for the apoptotic proteins, caspase 3, 8 and 9, COX-2 and tumor suppressor protein p53. The results from the present investigation from long term experiments have shown that the tumor incidence was delayed and tumor multiplicity decreased significantly on pretreatment of a-santalol compared to control. Furthermore, these results were substantiated by Western Blot studies which have shown a significant upregulation of apoptotic proteins, caspase-3 and 8 and tumor suppressor protein p53 in the a-santalol pretreated group in comparison with control. The results from the short term experiment have illustrated that pre and post-treatment of a-santalol significantly elevated the caspase-3 and 8 levels. Furthermore, a-santalol significantly decreased the COX-2 levels. These results indicate that one possible mechanism by which a-santalol induces chemopreventive effects could be, by activating the extrinsic apoptotic pathway. It also acts by upregulating the tumor suppressor protein p53 and down regulating COX-2 thus decreasing the prostaglandins, tumor promoting agent.

Library of Congress Subject Headings

Skin -- Cancer -- Chemoprevention

Sandalwood oil

Skin -- Cancer -- Animal models

Mice -- Diseases

Format

application/pdf

Number of Pages

92

Publisher

South Dakota State University

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