Abstract
Hereditary diffuse gastric cancer (HDGC) is a cancer syndrome caused by germline mutations in the tumour suppressor gene CDH1, which encodes the cell-cell adhesion protein E-cadherin. Mutations in CDH1 lead to increased proliferation, invasiveness and loss of cell polarity. Patients with germline CDH1 mutations have a 70% lifetime risk of developing gastric cancer. Female carriers also have a 42% lifetime risk of developing lobular breast cancer.
The current optimal treatment for HDGC is a prophylactic gastrectomy as surveillance through endoscopy is imperfect and tumours can be discovered at a late stage. This project aims to utilise the synthetic lethal (SL) approach to find a chemopreventative treatment for HDGC. The SL approach aims to manipulate cell viability by exploiting the relationships between related genes. Synthetic lethality is a gene relationship in which an inactivation of either of two genes alone allows cell survival, however when both are inactivated it leads to cell death.
Previous work within the laboratory has identified potential SL targets for CDH1 via high throughput drug screening. This was carried out in an isogenic pair of non-tumourigenic breast epithelial MCF-10A cell lines, one lacking CDH1 function. This identified histone de-acetylase inhibitors (HDACi) and statins as promising SL therapies for HDGC as they can selectively inhibit growth of CDH1-/- cells. Epigenetic changes, such as histone acetylation and deacetylation, modify expression patterns and are linked to cancer progression. Statins are widely used, well tolerated drugs that lower cholesterol levels and impact on plasma membrane organisation.
This project has validated successful SL compounds from the MCF-10A drug screen in a gastric cancer model, using isogenic NCI-N87 CDH1+/+ and CDH1-/- cell lines. Promising compounds that have shown the best SL effect in 2D cell culture models, were then analysed for clinical trial data to find drugs that have minimal adverse effects. The compounds with minimal side effects and strong SL relationship with CDH1, were then assessed in a gastric organoid model of HDGC. This organoid model called the air-liquid interface (ALI) model, is a 3D representation of the gastric gland and contains all gastric cell lineages. As such it is a more accurate pre-clinical model for drug screening than 2D cultures. A second organoid model, the submerged model, was also further developed as it is a higher throughput model and will be more efficient for future drug compound testing. Mocetinostat, the compound identified to have the best synthetic lethal effect, will now undergo further preclinical testing as a potential chemopreventative compound for families affected by HDGC.