Abstract 311: AR splice variant, ARv567es, enhances proliferation and induces tumor formation in a novel transgenic mouse model of prostate cancer, Pb-ARv567es.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Castration-resistant prostate cancer (CRPC) is the leading cause of death in men with prostate cancer. Development of CRPC has been attributed to a variety of mechanisms, including expression of constitutively active androgen receptor splice variants (AR-Vs). ARv567es, in which exons 5, 6, and 7 are deleted, is one of the two AR variants frequently found in human CRPC xenografts and human metastases. Currently, the limited studies on ARv567es are confined to expression testing with xenografts and functional exploration in in vitro cell lines. To evaluate the role of ARv567es in the autonomous state we developed an ARv567es transgenic mouse, Pb-ARv567es, in which the ARv567es coding sequence is targeted to the prostate epithelium of the C57BL/6 mouse under the drive of the minimal rat probasin (rPb) promoter. RT-PCR and immunohistochemistry, using a human specific AR antibody, demonstrated that ARv567es was expressed specifically in prostate but not by other tissues. Endogenous mouse AR levels were not affected. Serial evaluation of prostate histology revealed foci hyperplasia by 16 weeks with a gradual progression to PIN lesions by 10 months and well-differentiated adenocarcinoma at one year of age. To investigate whether androgen deprivation affects ARv567es function, we performed castration and sham surgery on Pb-ARv567es and Wt mice at 16 weeks of age. Three weeks post-castration, the prostate and genitourinary organs (GU) were harvested and weighed. In both the castrated and sham Pb-ARv567es mice, the prostate and GU organs showed significantly higher relative weights compared with those of Wt littermates (p<0.01), even though castrate Pb-ARv567es mice still did not maintain normal columnar epithelium. Pb-ARv567es mouse prostates had a significantly higher Ki-67 index compared with Wt littermates (p<0.01). These data show that ARv567es increases the proliferative rate of the prostate epithelium. In line with this, a recent study demonstrated that AR-Vs activate a novel mitotic transcriptome in vitro that is different from the canonical AR induced gene profile. To investigate whether a similar transcriptome was present in the Pb-ARv567es transgenic mouse, we ran real-time PCR on prostates from intact and castrate Pb-ARv567es and Wt mice; transgenic prostates showed increased expression of mitotic genes seen in CRPC patients and in vitro AR-Vs studies, including Ube2c. Up-regulated protein levels were confirmed by IHC. Our Pb-ARv567es mouse demonstrates that the distinct AR variant transcriptome is a consequence when AR-Vs occur and suggests that activation of this transcriptome enhances prostate epithelial proliferation. The Pb-ARv567es mouse is a novel model in which the role of AR variants in prostate cancer can be examined. Citation Format: Gang Liu, Cynthia Sprenger, Shihua Sun, Kathryn Soriano Epilepsia, Stephen Plymate. AR splice variant, ARv567es, enhances proliferation and induces tumor formation in a novel transgenic mouse model of prostate cancer, Pb-ARv567es. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 311. doi:10.1158/1538-7445.AM2013-311