Development and characterisation of novel mouse models of human prostate cancer

To date, prostate cancer is the most common male cancer diagnosed in the United Kingdom. Our rudimentary knowledge of the aetiology and molecular pathways implicated in prostate tumourigenesis is probably responsible for its poor prognosis. To address this, a conditional transgenic approach was employed to investigate the role of the tumour suppressor Lkbl and the proto-oncogenes p-catenin and K-ras within the murine prostate. LKB1 is a tumour suppressor commonly mutated in Peutz-Jegher's syndrome (PJS), which predominantly predisposes to gastrointestinal hamartomas and various extra intestinal tumours. Using a conditional transgenic approach, recombination of a LoxP-flanked Lkbl transgene was mediated by the inducible Ah (p450 CYP1A1) promoter. Loss of Lkbl in un-induced AhCreLkb mice predisposed to prostate intra-epithelial neoplasia (PIN) within 2-4 months. Molecular analysis revealed that neoplastic foci had lost cellular polarity and showed enhanced PI3K/AKT and Wnt signalling pathway activity, ultimately leading to tumour growth. Loss of Lkbl did not result in activation of the AMPK/mTOR pathway, suggesting that a feedback mechanism suppresses mTOR in Lkbl deficient conditions. Study of disease progression in this model is limited owing to decreased longevity, which is thought to be caused by the development of bulbourethral gland cysts. Additional GU tract phenotypes were also observed in un-induced AhCre+LkbPl/J1 urethral glands and seminal vesicles and all Lkbl1 male mice were infertile. To address the problem of reduced longevity in the AhCre+Lkbl cohort, PBCre+Lkbl transgenic mice were derived. Here, Oe-recombinase expression is mediated by the composite rat Probasin promoter. All cohorts showed life-spans comparable to wild-type mice at 500 days. PBCre+Lkbl+/ prostates were normal, while mice developed low grade-PIN, demonstrating the hypomorphic nature of the Lkbl floxed allele. PBCre+Lkblm mice demonstrated atypical hyperplasia of the prostate, arguing a critical role for Lkbl levels in cancer initiation. Long-term Lkbl deficiency also predisposed to kidney abnormalities, preputial gland squamous metaplasia and PJS-linked phenotypes, including stomach hamartomas and Sertoli-cell-only syndrome at 500 days. To investigate the deregulation of Wnt signalling in the murine prostate, conditional transgenic mice carrying a dominant stable form of p-catenin in the prostate were generated (PBCre+Catnb*/lox(ex3)). At 3 months, males manifested PIN-like keratinised squamous metaplasia that advanced to adenocarcinoma by 6 months. No evidence for synergy was determined between Lkbl loss and activated P-catenin, although investigations were limited to PBCre*Lkbl*/Jl:Catnb*/lox(ex3) mice owing to a time constraint and partial embryonic lethality of Lkblm mice. Synergism between Wnt and Ras signalling has been well documented in many human cancers, including intestine, liver and kidney. To address the cooperativity of these pathways in the prostate, the PBCre transgenic line was employed to express an activated K-rasV12 mutation and a dominant stabilised form of p-catenin (PBCre+K- ras+/vl2 Catnb+/lox(ex3)). PBCre+K-ras+/v12 mice were predisposed to low grade-PIN at 16 months and demonstrated elevated MAPK signalling. Double mutants demonstrated rapid tumourigenesis to invasive carcinoma at 6 months, which displayed elevated Wnt and MAPK signalling. Further molecular analysis determined that activated K-ras and P-catenin synergise to facilitate prostate tumourigenesis by elevating the number of androgen receptor positive cells and upregulating Wnt targets, such as COX-2 and c-Myc. This evidence suggests androgen-independent tumour growth and presents a direct mechanism whereby tumour progression is accelerated via the canonical Wnt pathway. In summary, this thesis reports the first correlation between Lkbl loss and prostate neoplasia, and demonstrates synergy between Wnt and Ras signalling in murine prostate tumourigenesis. Together, these data provide a valuable resource for genetic based studies and establish the multi-step nature of tumourigenesis.