Abstract C49: Activating Wnt/B-catenin signaling in luminal epithelial stem cells in the murine prostate induces carcinoma in situ

Prostate cancer is the most diagnosed non-skin cancer in American men, and results in the second highest amount of cancer-related deaths. Because prostate cancer is generally dependent on androgens, it can often be successfully treated via androgen deprivation therapy. However, prostate cancer often becomes resistant to the effects of androgen deprivation, which is commonly coupled with advanced metastatic disease which is lethal. When prostate cancer cells metastasize, they go preferentially to bone. There are few experimental models of castration-resistant metastatic prostate cancer. Our lab is interested in the progression of prostate cancer to castration-resistant disease and in its predilection to bone during metastasis, and we strive to create a genetically engineered mouse model that recapitulates the human disease. To that end, we turned our interest to the Wnt/B-catenin signaling pathway. Wnt/B-catenin signaling is up-regulated in prostate cancer (compared to normal prostate tissue) and is correlated with prostate cancer progression and skeletal metastasis. An endogenous negative regulator of Wnt/B-catenin signaling, adenomatous polyposis coli (APC), is frequently hypermethylated at sites in its gene promoter, and the resulting reduced expression is correlated with prostate cancer progression, as well. Wnt/B-catenin signaling may also be important in skeletal metastasis, due to its role in osteoblastogenesis. Based on this information, we conditionally deleted Apc in the murine prostate by crossing prostate-specific Cre recombinase mice (Probasin-Cre and Nkx3.1-CreERT) to mice containing loxP sites flanking Apc, causing its recombination in luminal epithelial cells. Using a double fluorescent reporter model, we showed first that Probasin-Cre is active in almost 100% of luminal epithelial cells in the prostate, whereas Nkx3.1creERT is active in approximately 45% of these cells. Abate-Shen et al. showed that Nkx3.1 marks a specific luminal cell type that acts as a stem cell and can survive castration conditions. Because Nkx3.1creERT was reported to be active in a more primitive cell type than Probasin-Cre, we hypothesized that loss of Apc in the Nkx3.1-driven model would induce a more aggressive carcinoma. However, we showed that these two models phenocopy one another, in that both develop aggressive hyperplasia that leads to carcinoma in situ. In castration conditions prior to Apc recombination, no carcinoma developed, but castration after tumors developed resulted in focal regions of hyperplasia, indicating some level of castration resistance. Neither model developed metastasis, indicating that at least a second genetic hit is likely required to induce metastasis. Based on data from DePinho et al., which showed that combinatorial loss of Pten and Smad4 resulted in metastatic cancer, we showed that upon Apc loss, Smad4 levels do indeed increase. To this end, we crossed mice to develop a double conditional Apc-Smad4 knockout. This work is in progress, but thus far, a fraction of these mice have developed more aggressive tumors than the Apc knockout alone. Citation Format: Kenneth C. Valkenburg, Bart O. Williams. Activating Wnt/B-catenin signaling in luminal epithelial stem cells in the murine prostate induces carcinoma in situ. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr C49.