The interaction between the PI3K/Akt cascade and the androgen receptor in the development and progression of castrate resistant prostate cancer

McCall, Pamela (2011) The interaction between the PI3K/Akt cascade and the androgen receptor in the development and progression of castrate resistant prostate cancer. PhD thesis, University of Glasgow.

Abstract

Prostate cancer has high cancer incidence in males and is the second highest cause of male cancer related mortality. Currently the main stay therapy for localised and metastatic disease is maximum androgen blockade (MAB). This aims to inhibit androgen production or action, thereby reducing stimulation of the androgen receptor (AR). This in turn prevents the activation of androgen-regulated genes, which normally result in on-going growth and survival. Inhibition of testicular androgen production may be achieved surgically (bilateral orchidectomy) or chemically, using gonadotropin-releasing hormone (GnRH) agonists. The latter induces castrate levels of testosterone by down-regulating pituitary GnRH receptors (and therefore gonadotropin hormone production) through constant stimulation. The action of androgen may be blocked at a peripheral level using anti androgens, which inhibit ligand binding to AR and subsequent activation. Although this approach has initial response rates of over 80% the majority of men relapse with castrate resistant prostate cancer (CRPC) and this is the cause of significant morbidity and mortality. To overcome this and to improve patients treatment options the mechanisms of castrate resistance need to be addressed.
The PI3K/Akt cascade regulates several cellular processes such as proliferation and apoptosis. Akt activation results in phosphorylation of multiple substrates and has been implicated in prostate carcinogenesis and castration resistance. Research has suggested that Akt interacts with signallingcascades implemented in carcinogenesis, in particular the NFkB cascade and AR signalling. The current study investigated the hypothesis that the expression and activation of PI3K/Akt cascade influences the progression to castrate resistant disease using clinical prostate cancer tumours. Fluorescent insitu hybridisation and Immunohistochemistry revealed that PTEN deletion was a common event in castrate resistant prostate cancer and low PTEN protein expression was significantly associated with a poor outcome. PTEN negatively regulates PI3K signalling. Consequently increased levels of PI3K and activated Akt (pAkt ser 308 and pAkt ser 473) were significantly associated with a shorter time to biochemical relapse and shorter disease specific survival. Inhibition of PI3K resulted in a significant reduction in cellular proliferation and Akt phosphorylation.
The downstream affects of Akt activation were also investigated. Akt has been reported to directly activate the NFkB signallingcascade both directly and indirectly but no correlations between Akt and NFkB were observed in the current study. Using an immunohistochemical approach NFkB, IкBα and MMP-9 expression were observed to be significantly associated with shorter time to death from relapse and disease specific death. MMP-9 and IкBα expression were also significantly associated with metastases at relapse. Using paired hormone naive and castrate resistant LNCaP cells lines allowed the functional consequences of NFkB inhibition to be investigated. Reduced NFkB activation significantly inhibited cellular proliferation and induced apoptosis in both cell lines.
Having shown a significant link between expression and activation of the PI3K cascade and progression to castrate resistant disease, the interaction between Akt and the AR was investigated in both clinical prostate tumours and cell lines. The phosphorylation of AR at the Akt consensus site serine 213 (pARser213) was significantly associated with disease progression. Patients with high expression pARser213 had a significantly shorter time to death from relapse and disease specific survival. Additionally 42% of patients displayed an increase in pARser213 expression, these patients also had a significantly shorter time to death from relapse and disease specific survival. Inhibition of PI3K resulted in a reduction of pARser213 expression in both cell lines and using siRNA knockdown to target PI3K p85 regulatory subunit reduced pARser213 expression. This research highlights the impact of both the PI3K/Akt and NFkB signallingcascades on prostate cancer progression and development of castrate resistant disease. In particular this study highlights the impact of Akt phosphorylation in castrate resistant prostate cancer patients. Therefore phosphorylation of AR at serine 213 may serve as a diagnostic tool to predict patient outcome in response to maximum androgen blockade and inhibition of AR 213 phosphorylation via the Akt cascade may be an effective therapeutic avenue to investigate for treatment of prostate cancer.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Androgen Receptor, Prostate cancer, PI3K, Akt, Castrate resistant disease
• Subjects: R Medicine > RB Pathology; Q Science > Q Science (General)
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Supervisor's Name: Edwards, Dr. Joanne
• Date of Award: 2011
• Depositing User: Dr Pamela McCall
• Unique ID: glathesis:2011-2462
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 31 Mar 2011
• Last Modified: 10 Dec 2012 13:55
• URI: https://theses.gla.ac.uk/id/eprint/2462