Abstract A60: Germline genetic variation modulates tumor progression and metastasis in mouse prostate neuroendocrine carcinoma
Authors: Patel Shashank , Kollins Erin , Bell Katie , Cardiff Robert , Molinolo Alfredo , Crawford Nigel 
Published: May 2013

Conventional assessment of prognosis in prostate cancer (PC) relies heavily upon Gleason grading, which suffers from significant interobserver variability. Consequently, there is a need for additional means of assessing prognosis. Neuroendocrine differentiation (NED) has been gaining increasing attention as a potential prognostic marker. Pure NE PC, which is associated with a poor outcome, is rare and comprises &lt;1% of all tumors. Additionally, conventional prostate adenocarcinomas displaying NED are associated with a poorer prognosis, with NED increased in high-grade and high-stage tumors, and particularly in hormonally treated and castration resistant disease.

The aim of this study is to determine whether host germline genetic variation influences tumor progression and metastasis in C57BL/6-Tg(TRAMP)8247Ng/J (TRAMP) mouse model of aggressive NE PC. We crossed TRAMP mice to the eight progenitor strains of the Collaborative Cross (CC) recombinant inbred (RI) panel to address this. Transgene-positive F1 males were aged to whichever of the following were achieved first: 30 weeks of age or humane endpoints. Tumor growth and metastasis burden were quantified in these mice.

These experiments conclusively demonstrate that the introduction of germline variation by breeding significantly modulates tumor growth, local metastasis burden and distant metastasis frequency in this model of NE PC. Compared to wildtype TRAMP males (TRAMP × C57BL/B6J F1; av. tumor burden = 1.40g, n=35) both TRAMP × NOD/ShiLtJ (n=42) and TRAMP × NZO/HlLtJ (n=57) F1 males displayed a significant increase in tumor growth (av. tumor burden = 8.01g and 4.71g, respectively; p&lt;0.0001). Conversely, both TRAMP × WSB/EiJ (n=68) and TRAMP × PWK/PhJ (n=40) F1 males displayed a significant reduction in tumor growth (av. tumor burden = 0.71g and 0.01g, respectively; p&lt;0.0001). Strikingly, only 6 of 40 TRAMP × PWK/PhJ males developed macroscopic tumors, which implies that polymorphisms carried by this strain play a significant role in NED.

In those mice with local dissemination, nodal metastasis burden was quantified by normalizing nodal metastasis weight to total prostate tumor weight. In spite of TRAMP × NZO/HlLtJ F1 males (n=41) having an increased tumor burden compared to wildtype TRAMP mice (n=25), a less metastatic phenotype was evident in this strain with normalized metastasis burden being reduced (met burden = 0.23g/g tumor vs. 0.40g/g tumor in wildtype TRAMP mice; p=0.002). Conversely, TRAMP × WSB/EiJ males (n=14), which displayed a reduced tumor burden, had an increased nodal metastasis burden (met burden = 3.20g/g tumor; p=0.009). Patterns of distant metastasis to lung tended to follow the same patterns as for local dissemination in each of the strains. Tumor-associated morbidity was also significantly higher in four F1 strains (A/J, CAST/EiJ, NOD/LtJ and NZO/HlLtJ) compared to control mice, implying that the excess tumor burden in these strains has a deleterious effect upon survival. All tumors and metastases displayed positive staining for NE markers, and quantification of the expression of these is ongoing to determine strain-specific differences.

The eventual aim of this work is to identify quantitative trait loci associated with the development of NED and aggressive disease development in PC. We are therefore performing F2 intercrosses between TRAMP mice and a number of the strains described above. Additionally, TRAMP mice are being bred to Diversity Outbred stock, which is a genetically diverse mouse resource used as a tool for high resolution genetic mapping. Candidate gene characterization within these loci will facilitate an improved understanding of this aspect of PC pathogenesis and potentially facilitate the identification of individuals at increased risk of NED.

Citation Format: Shashank Patel, Erin Kollins, Katie Bell, Robert Cardiff, Alfredo Molinolo, Nigel Crawford. Germline genetic variation modulates tumor progression and metastasis in mouse prostate neuroendocrine carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr A60.