Abstract B32: Transgenic model for early prostate cancer metastasis to the lymph nodes
Authors: Ko Hyun-Kyung , AKakura Shin , Peresie Jennifer , Goodrich David , Foster Barbara , Gelman Irwin H. 
Published: May 2019

Abstract
The emergence of castration-recurrent (CR), metastatic prostate cancer (PC) following the failure of androgen-deprivation therapy represents the lethal phenotype of this disease. However, the genes and pathways that drive metastasis, and whether metastasis is an early or late event, remain poorly understood. Early dissemination of PC to the bones (10) and lymph nodes (8,13) has been described, and at least one study shows that a lower-grade focus, rather than high-grade foci in the same primary PC, was the source for metastases in one patient (7), suggesting collectively that metastatic dissemination is likely early event. Thus, we sought to develop a transgenic model to study early metastatic dissemination of PC. Although PTEN loss, associated with activation of AKT signaling, occurs frequently in PC, there is no increased association with metastatic disease (6,12,14), strongly suggesting that it is not sufficient as a driver of metastasis. Moreover, prostate-specific Pten loss in most mouse transgenic (Tg) models induces prostatic intraepithelial neoplasia (PIN), whereas its combination with a second relevant event, such as Myc amplification (5) or Smad4 loss (3), results in the production of aggressive primary and metastatic lesions. To address what might be the genetic drivers of early PC metastasis, we produced a transgenic mouse model containing losses of the tumor suppressor, Rb1, and the metastasis-suppressor, SSeCKS/Akap12. The loss of Rb1 signaling, resulting from either mutation or deletion of Rb1, or from the downregulation of Rb1 mediators, occurs in at least 40% of PC metastases, whereas its loss in primary PC is under 10% (6,11,12). Additionally, the downregulation AKAP12 is greater in PC metastases compared to primary PC (4,14), and the loss of Akap12 in Tg mice causes AKT activation (1) as well as Rb-dependent premature senescence (2). Whereas the loss of Rb1 or Akap12 alone resulted in prostatic hyperplasia (1,9), their combined loss resulted in high-grade (HG) PIN that fails to progress to malignancy after 18 months. Most significantly, mice with HG-PIN lesions exhibited metastases to draining lymph nodes, marked by relatively differentiated tumor cells co-expressing markers of basal (p63, cytokeratin 14) and luminal (cytokeratin 8 and androgen receptor) epithelial cells, and although none expressed the basal marker, cytokeratin 5, about 40% expressed vimentin, a marker of epithelial-to-mesenchymal transition. These cells likely arose from small, rare foci of p63-positive basal cells in the HG-PIN lesions showing similar sets of transitional markers as well as increased co-staining with nuclear androgen receptor. Interestingly, although all the PIN lesion and metastatic cells expressed upregulated levels of activated AKT (increased AKTpoS473 relative to total AKT) compared to prostate epithelial cells from Rb- or Akap12-deficient mice, the double Rb/Akap12 knockout cells did not progress to malignancy, as do Pten/Rb-deficient prostate cells, suggesting that Pten loss affects drivers in addition to AKT. Lastly, the double Rb/Akap12-deficient metastatic cells exhibited increased levels of Smad4 protein compared to single Rb- or Akap12-deficient cells, suggesting that its continued expression suppressed malignant progression. Taken together, these data suggest that in the context of Rb loss, Akap12 suppresses the oncogenic proliferation and early metastatic spread of basal-luminal prostate tumor cells. Experiments will be described to use this model to dissect the genomic drivers of early prostate cancer metastatic dissemination, and following the loss of Smad4, to identify drivers of prostate cancer malignant progression.
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Citation Format: Hyun-Kyung Ko, Shin AKakura, Jennifer Peresie, David Goodrich, Barbara Foster, Irwin H. Gelman. Transgenic model for early prostate cancer metastasis to the lymph nodes. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B32.