Skin cancer is the commonest cancer in light-skinned Caucasians and non-melanoma skin cancer accounts for over 90% of these malignancies [1]. 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 [5]. 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 [6]. 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 [7]. 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 [8]. This notwithstanding, it has been suggested that oligonucleotides in vivo do not necessarily require a delivery vehicle for endosomal/lysosomal sequestration [9].
Our recent work with local administration of liposomal formulation of c-Jun-targeting DNAzymes (Dz13) [2] 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 [2]. 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 [2]. 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.
REFERENCES
- 1.Leiter U, Garbe C. Adv Exp Med Biol. 2008;624:89–103. doi: 10.1007/978-0-387-77574-6_8. [DOI] [PubMed] [Google Scholar]
- 2.Cai H, Santiago F S, Prado-Lourenco L, Patrikakis M, Wang B, Chong B H, Parish C R, Stocker R, Lieschke G, Davenport M P, Wong K T W, Chesterman C N, Francis D F, Moloney F, Barnetson R, Halliday G M, Khachigian L M. Science Translational Medicine. 2012;4:139ra182. doi: 10.1126/scitranslmed.3003960. [DOI] [PubMed] [Google Scholar]
- 3.Zhang G, Luo X, Sumithran E, Pua V S C, Barnetson R S, Halliday G M, Khachigian L M. Oncogene. 2006;25:7260–7266. doi: 10.1038/sj.onc.1209726. [DOI] [PubMed] [Google Scholar]
- 4.Zhang G, Dass C R, Sumithran E, Di Girolimo N R, Sun L-Q, Khachigian L M. Journal of National Cancer Institute. 2004;96:683–696. doi: 10.1093/jnci/djh120. [DOI] [PubMed] [Google Scholar]
- 5.Santoro S W, Joyce G F. Proc. Natl. Acad. Sci. USA. 1997;94:4262–4266. doi: 10.1073/pnas.94.9.4262. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Bhindi R, Fahmy R G, Lowe H C, Chesterman C N, Dass C R, Cairns M J, Saravolac E G, Sun L Q, Khachigian L M. Am J Pathol. 2007;171:1079–1088. doi: 10.2353/ajpath.2007.070120. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Santiago F S, Lowe H C, Kavurma M M, Chesterman C N, Baker A, Atkins D G, Khachigian L M. Nature Med. 1999;5:1264–1269. doi: 10.1038/15215. [DOI] [PubMed] [Google Scholar]
- 8.Rossi J J. Sci Transl Med. 2012;4:139fs120. doi: 10.1126/scitranslmed.3004080. [DOI] [PubMed] [Google Scholar]
- 9.Dias N, Stein C A. Mol Cancer Ther. 2002;1:347–355. [PubMed] [Google Scholar]