Novel survival factors and approaches to the treatment of hypoxic prostate cancer

Abstract

Tumour hypoxia has been demonstrated to cause development of an aggressive tumour phenotype and is associated with increased patient mortality and poorer response to treatments such as chemotherapy and radiotherapy. Previous studies have established that hypoxia exists within a nidus of prostate cancer. Based on the importance of the tumour microenvironment, especially hypoxia, in prostate cancer, the major aims of this thesis were to establish: (a) the role of a novel putative survival factor, dermcidin, in prostate cancer survival under hypoxia/oxidative stress; and (b) the effect of nitric oxide-donating non-steroidal anti-inflammatory drugs (NO-NSAIDS), a new class of drugs, on the killing of prostate cancer cells subjected to hypoxia. A wide-range of confirmatory, cellular and molecular biology techniques were employed in this thesis. The PC-3 hormone-insensitive prostate cancer cell line was used for the majority of studies as this cell line represents hormone-independent prostate cancer, treatment of which is currently palliative. Cell incubation at 0.2% oxygen for 48 hours was established as suitable conditions to stimulate the development of the hypoxia response. Upregulation of nuclear hypoxia-inducible factor-1α protein was the main marker used to assess the hypoxia response. Dermcidin messenger RNA production was found to occur in a range of prostate cancer cell lines; was upregulated in cell lines by both hypoxic and oxidative stress; and found to act as a proliferation, survival and pro-invasion factor under hypoxia and oxidative stress in immortalised prostate cancer cell lines. Furthermore, the portion of the dermcidin molecule responsible for the survival advantage was localised to the proteolysis-inducing factor core peptide subunit. However, subsequent analysis of primary cancer samples from prostate cancer patients revealed that dermcidin was not expressed in these tumours, although dermcidin mRNA was identified in analysis of other primary tumours. As such, the role of dermcidin in prostate cancer was not evaluated further in this thesis. Investigation of NO-sulindac (a NO-NSAID drug) in hypoxic PC-3 cells showed that these agents were significantly more pro-necrotic, pro-apoptotic and anti-invasive than traditional, unnitrated sulindac. NO-sulindac was found to downregulate the hypoxia response mounted by PC-3 cells under hypoxia via the Akt signalling pathway. Finally, analysis of the role of NO-sulindac in radiosensitising hypoxic PC-3 cells showed that NO-sulindac caused significant radiosensitisation under normoxia, but particularly in hypoxic conditions. As such, NO-NSAIDs show great promise as neoadjuvant, concurrent and adjuvant treatments for patients with hypoxic prostate cancer. The findings of this thesis illustrate several potential novel strategies for treatment of hormone-independent prostate cancer.