Gene therapy for sporadic ovarian cancer
Ovarian cancer accounts for more deaths than all other gynaecological cancers taken together. The 5 year survival rate can be as high as 80% for cases diagnosed early, but the asymptomatic nature of the disease means that it is most frequently detected in the later stages. By this time, disease has invariably spread beyond the ovaries and the survival rate drops to around 30%. Treatment of ovarian cancer often fails due to a high rate of chemoresistance and novel methods of treatment and detection are required to increase the survival chances of patients. This study sought to determine whether gene therapy for sporadic ovarian cancer could offer a novel and more successful treatment option for the disease. Mutation or abnormal expression of the p53 gene has already been shown to be the most common genetic even in ovarian cancer, being involved in up to 70% of cases. Wild-type p53 was delivered, using liposomes, into p53 mutant ovarian cancer cell lines and this resulted in a restoration of the wild-type functions of the gene, namely cell cycle arrest and apoptosis. The results from the cell line studies suggested that restoration of the wild-type p53 function limit or reduce tumour progression and increase the sensitivity of the tumour to chemotherapy. A mouse model of human peritoneal ovarian cancer was then constructed and the wild-type p53 gene was administered in liposomes into the peritoneum. The results suggested that p53 gene therapy prevents tumours from growing in the mice, when compared to a control gene. It is now known that p53 gene therapy for humans is being clinically assessed. There are a proportion of tumours that do not harbour an abnormal p53 gene, raising the possibility that other tumour suppressor gene mutations may play a role in the molecular genetic control of growth arrest and apoptosis. P53-dependent, apoptosis-regulating family members bcl-2 and bax were analysed immunohistochemically to determine their involvement in ovarian cancer. Both proteins were significantly associated with malignancy and also with overall length of survival, but not associated with the various prognostic factors such as stage and differentiation of tumour. It is unlikely that these genes will become targets for gene therapy in ovarian cancer. Mutation, deletion and hypermethylation of the p53-independent pi6 gene, alter its function, resulting in loss of G1 cell cycle arrest control. The status of methylation of the pi 6 promoter in ovarian tumours was determined and combined with mutation data, resulting in the conclusion that abnormal pi 6 was not a common event in ovarian cancer and is therefore not a likely candidate for gene therapy. This study has contributed to the evergrowing wealth of knowledge on the molecular genetic events of ovarian cancer, and has shown that gene therapy for sporadic ovarian cancer as a clinical application is feasible.