Abstract 829: Targeted antizyme expression impairs HER2/neu-induced tumorigenesis but not normal mammary gland development

The objective of these studies was to utilize a novel transgenic mouse model with inducible and mammary gland-specific antizyme (AZ) expression to test the hypothesis that AZ will prevent mammary tumorigenesis and restrict the growth of established mammary tumors. AZ is a negative regulator of cellular polyamine levels that inhibits ornithine decarboxylase (ODC) activity, stimulates ODC degradation and suppresses exogenous polyamine uptake. Mouse lines were generated harboring a transgene construct (tetO-AZ) containing Tet operon repeat sequences upstream of an AZ cDNA followed by an internal ribosome entry site and a luciferase coding region. The tetO-AZ mice were crossed with MMTV-rtTA (MTB) mice to achieve AZ expression within the mammary gland that is induced by doxycycline (Dox). Bioluminescent imaging and in vitro assays of luciferase activity and AZ protein demonstrate tissue-specific and Dox-dependent transgene expression. Morphometric and immunohistochemical analysis of the mammary epithelial tree verified that normal development is unaffected by elevated levels of AZ. Next, we examined the ability of AZ to prevent tumor appearance in a widely used model of human breast cancer. TetO-AZ/MTB mice were crossed with MMTV-neu mice that develop spontaneous mammary tumors and Dox-treated animals were monitored for up to 1 year. Tumor-free survival was greatly extended in tetO-AZ/MTB/neu mice relative to controls (348 vs. 234 days, p=0.0003). In vivo imaging of the luciferase reporter revealed a pronounced absence of transgene expression within all 19 tumors detected in Dox-treated tetO-AZ/MTB/neu mice, therefore these tumors developed from cells that initially lacked AZ expression or lost AZ expression at a very early stage of tumor growth. The Dox-regulated transgenic model also allowed us to examine the effect of AZ on the maintenance and growth of established tumors in Dox-naïve mice. Once tumors reached 5 mm in diameter, Dox treatment was initiated to induce AZ expression in tetO-AZ/MTB/neu mice and tumor growth was evaluated. The established primary tumors from Dox-treated controls grew very rapidly and 34/45 (76%) exceeded 2000 mm3 within the monitoring period of 8 weeks, whereas only 6/16 (38%) of the tumors from tetO-AZ/MTB/neu mice reached that size. In vivo imaging of transgene-derived luciferase reporter expression allows us to compare transgene expression levels with tumor growth rate over time. This analysis has revealed several classes of response including a) reduced tumor growth in the presence of strong AZ expression, b) evolutionary loss of AZ expression and subsequent increased growth rate and c) occasional rapidly growing tumors that tolerate high levels of AZ expression. In summary, our studies indicate that elevated AZ expression prevents the appearance of HER2/neu-induced mammary tumors and suppresses the growth of established mammary tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 829. doi:10.1158/1538-7445.AM2011-829