417. Intratumoral Delivery of Oncolytic Adenovirus Expressing Decorin Inhibits Growth and Metastases of 4T1 Breast Tumors in Syngeneic Immune Competent BALB/c Mice Model

During the advanced stage of breast cancer, majority of the patients develop distal metastases that eventually lead to mortality. Unfortunately, conventional strategies generally invoke limited therapeutic responses in patients with tumor metastases. Therefore, the development of novel and highly effective therapies for the treatment of distal metastases of breast cancer is an unmet need in medicine. Decorin (DCN) is a small leucine-rich proteoglycan and is often down-regulated in tumor stroma of breast cancer patients. Our previous work demonstrated that systemic delivery of Ad.dcn, an oncolytic adenovirus expressing DCN, significantly inhibited skeletal metastases and the tumor induced bone destruction in MDA-MB-231 bone metastasis model. However, the therapeutic responses of Ad.dcn in immune-competent models have never been examined. In this study, we showed that non-replicated adenovirus Ad(E1-). dcn mediated high level expression of human DCN in 4T1 cells, and inhibited the expression of tyrosine kinase receptor MET, β-catenin and vascular endothelial growth factor A. To examine the anti-tumor responses of Ad.dcn, we established subcutaneous 4T1 tumors in BALB/c mice. Ad.dcn was delivered intratumorallly (2.5×1010VPs) on day 7 post-cell inoculation, and a repeat dose was given on day 10. Our data showed that Ad.dcn inhibited the growth of local tumors as measured by the caliper as well as by the Bioluminescence Imaging (BLI). At the terminal time point (day 25) we also observed a significant reduction in the tumor weight. Analysis of BLI in real time also demonstrated that Ad.dcn significantly reduced the tumor metastases to lung. On day 25 Ad.dcn group had fewer metastases (2/8 mice), compared to buffer treated group (7/8 mice). Similar reductions in lung metastases were observed by H&E staining. Moreover, Ad.dcn treatment reduced the expression of Th2 cytokines (IL-2, IL-4 and IL-10) in the tumors, which will potentially activate the antitumor immune responses. Furthermore, Ad.dcn also reduced the expression of N-cadherin and vimentin in the tumors, indicating Ad.dcn could also potentially reduce tumor metastases by inhibiting epithelial-mesenchymal transition (EMT) of the tumor cells. Taken together, our results suggested that Ad.dcn not only inhibited the growth of local tumor, but also prevented the distal metastases of tumor. Combining these results in the 4T1 tumor model, and previously examined MB-MDA-231 bone metastases model, we propose the following model of Ad.dcn-mediated inhibition of tumor growth and metastases. Ad.dcn is taken up by tumor cells after systemic or intratumoral delivery, and then replicates in tumor cells and kills them. Tumor cells produce and release high level of decorin protein into tumor microenvironment. Decorin then targets multiple tumor and stromal components to activate anti-tumor immune responses, decrease angiogenesis, and inhibit EMT. Therefore, Ad.dcn is a potential therapeutic strategy for the treatment of breast cancer and its distal metastases.Y.Y. and W.X. made equal contribution. L.W. and P.S. are the corresponding Authors.