Destroying c-Jun Messenger: New Insights into Biological Mechanisms of DNAzyme Function
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Skin cancer is the commonest cancer in light-skinned Caucasians and non-melanoma skin cancer accounts for over 90% of these malignancies . Basal cell carcinoma (BCC) generally do not metastasize, but can be locally invasive. Squamous cell carcinomas (SCC) typically occur on chronically sun-exposed sites such as face and forearms and are at increased risk of metastatic spread particularly in immunosuppressed individuals. Surgery, the principal treatment for these non-melanoma skin cancers, can cause disfiguring scars while other therapeutic options are limited by side effects or lack of efficacy.
Work by our group and others has demonstrated that immediate-early genes can serve as key targets in a range of cancer types. The c-jun gene is mapped to 1p32-p31 and encodes the 45kDa bZIP-domain-containing transcription factor c-Jun that, in combination with protein partners, forms AP-1. Protein partners of c-Jun are many and include c-Fos, pRb, BRCA1, ATF-2 and ERG. c-Jun/AP-1 is dynamically regulated by growth factors and cytokines, is overexpressed in a range of cancers including BCC, SCC and melanoma, and stimulates the expression of numerous genes [2-4].
DNAzymes are single-stranded synthetic DNA-based catalytic molecules that can be engineered to bind and destroy target messenger RNA . These agents have been used as inhibitors of biological processes in a range of animal models of human disease including ocular neovascularization, kidney disease and spinal cord injury . The first in vivo demonstration of efficacy was the use of DNAzymes targeting the transcription factor early growth response (Egr)-1 as inhibitors of intimal thickening in a rat model of balloon angioplasty . The wider use of DNAzymes as therapeutic agents has been hampered by delivery issues, particularly the limitation in target tissue delivery associated with systemic administration . This notwithstanding, it has been suggested that oligonucleotides in vivo do not necessarily require a delivery vehicle for endosomal/lysosomal sequestration .
Our recent work with local administration of liposomal formulation of c-Jun-targeting DNAzymes (Dz13)  has overcome some of these systemic delivery issues. Dz13 inhibited human BCC growing as intradermal tumors in SCID mice, and blocked the growth of SCC as intradermal and subcutaneous implants [2, 3]. Inhibition of tumor growth was Dz13 dose-dependent and sustained. At the highest dose used, Dz13-treated BCC did not regrow even 3 weeks after the cessation of treatment. A control DNAzyme with scrambled binding arms or single point mutation in the catalytic domain did not affect tumor growth. Dz13 inhibited the expression of c-Jun in vivo, demonstrating that it acted on its target, and this resulted in a decrease in CD31+ staining in the tumors, an indicator of tumor angiogenesis . In addition, Dz13 reduced lung nodule formation in a model of SCC metastasis.
The study by Cai and co-workers provided novel insights into the mechanism of action of DNAzymes . Dz13 rendered c-jun mRNA unstable, reduced growth factor expression and increased apoptosis in the tumors without apparent induction of oxidative stress. Interestingly, Dz13-mediated tumor decay was more profound in immunocompetent mice syngeneic to the tumor compared with immunocompromised animals. Immunohistological inspection revealed increased immune and inflammatory cells in Dz13-treated tumors in the immunocompetent mice. In addition, Dz13 mediated tumor regression was prevented by the administration of CD4 or CD8 antibodies, which depleted the mice of the respective T cell subsets. Thus, inhibition of tumor growth by a DNAzyme involves the induction of tumor immunity. These findings suggest that c-Jun inhibition in tumors stimulates apoptosis and adaptive immune mechanisms that attack the tumor. Underpinned by a favorable preclinical safety profile, DNAzymes could provide a new treatment option combining both direct and indirect mechanisms to prevent the growth and spread of non-melanoma skin cancer.
Levon M. Khachigian: Centre for Vascular Research, University of New South Wales, Sydney, Australia
Hong Cai: Centre for Vascular Research, University of New South Wales, Sydney, Australia
Fergal J. Moloney: Dermatology Research Laboratories, University of Sydney, Australia and Dermatology Department, Mater Misericordiae University Hospital, Dublin, Ireland
Christopher R. Parish: Centre for Vascular Research, John Curtin School of Medical Research, Canberra, Australia
Beng H. Chong: Centre for Vascular Research, University of New South Wales, Sydney, Australia
Roland Stocker: Centre for Vascular Research, University of Sydney, Sydney NSW Australia and Victor Chang Cardiac Research Institute, Sydney, Australia
Ross St.C. Barnetson: Dermatology Research Laboratories, University of Sydney, Australia
Gary M. Halliday: Dermatology Research Laboratories, University of Sydney, Australia
Levon Khachigian, email:
Received: July 11,2012;
Published: July 13,2012;
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