MICA: Targeting the Wnt Receptor Frizzled-7 for the Treatment of Gastric Cancer

Gastric cancer is the third most common cause of death due to cancer, with approximately 700,000 cases diagnosed annually, and accounts for substantial morbidity and mortality worldwide. Compared to other organs such as the intestine or breast, the cellular and molecular events that regulate the stomach during normal conditions (homeostasis) and cancer are poorly understood. This is reflected in the relatively few targeted therapies available to treat gastric cancer, and highlights an urgent need to identify new therapeutic targets for this disease, by gaining insight into the cell signaling that regulates gastric tumour initiation, growth and progression.

Cell signaling plays critical roles in regulating cellular decisions including whether a cell divides, differentiates into a specialized cell type, migrates, or dies. These cellular fates are tightly controlled during development of the embryo and during early life to ensure that cells grow, and differentiate into all the cell types required for the many different tissue types of the adult body. In adults cell signaling controls the homeostasis of tissues, and consequently when this signaling becomes deregulated it can re-activate the cues to trigger cell growth and thus transform a normal cell into a cancer cell which can divide unregulated into a tumour. One of the pathways in which this has been demonstrated by myself and others is the Wnt signaling pathway. This pathway is required for the normal development of embryos, and is also critical for the function of stem cells in several organs including the intestine and the stomach. Although we have a good knowledge of the signal transduction from the cell surface through to activating the expression of target genes for the Wnt pathway, very little is known about which of the ten different Frizzled (Fzd), Wnt receptors transmit this signal. Indeed, we were the first to demonstrate recently that Fzd7 is the predominant Wnt receptor transmitting critical Wnt signals to regulate stem cell function in the intestine and the stomach.

This project grant application will determine the therapeutic benefit of inhibiting Fzd7 for the treatment of gastric cancer. I have generated a body of strong preliminary data which shows that genetic deletion of Fzd7 in two mouse model of gastric cancer is able to block the growth of gastric tumors. This application aims to build on these exciting results by first investigating if deletion of Fzd7 can also block the growth of large, established gastric tumors. Then we shall employ a technology called shRNA in which we can switch on or off the expression of Fzd7. This will enable us to determine what happens to gastric tumor growth once the levels of Fzd7 are first reduced and then returned to normal levels. These experiments will be performed in human gastric cancer cells and complimented with additional experiments using a blocking antibody targeting a sunset of Wnt receptors including Fzd7. This antibody is already in clinical trials for other cancers including lung, breast and pancreas, and thus the results of this project will directly inform new potential clinical trials using this Fzd antibody to treat gastric cancer.

The final aim of this project will be a comprehensive study into how gastric cancer cells can respond to inhibition of Fzd7 even in gastric cancer cells which are thought to activate the Wnt pathway at a level downstream of the receptor. This will not only provide new insight into the mechanism of how Wnt receptors can regulate gastric cancer cells, but will also help select which patients will be most suitable to this therapeutic approach.

Frizzled (Fzd) proteins are co-receptors for Wnt ligands, several of which are upregulated in many cancers, including gastric cancer (GC), and thus offer novel therapeutic targets. This project will determine the therapeutic benefit of inhibiting Fzd receptors for the treatment of GC. We have recently identified that Fzd7 is required to transmit Wnt signalling in the stems cells located in the gastric and intestinal epithelium. Cell signalling that regulates stem cell activity is often deregulated in cancer, supporting the hypothesis that Fzd7 could be an attractive target for therapy. We shall establish the requirement for Fzd7 in gastric cancer using gastric specific inducible Cre recombinase technology to genetically delete Fzd7 in several mouse models of GC. To investigate if Fzd7 is also important for human GC cells we shall use inducible shRNA technology to target Fzd7 in human GC cell lines, and using colony forming assays and xenografts. To target Fzd7 pharmacologically we shall employ a monoclonal antibody which is already in clinical trials for breast and lung cancer, which targets the conserved extra cellular domain of Fzd1/2/7, in our mouse models of GC and in xenografts, thus directly informing future clinical trials. Finally we shall perform comprehensive cellular and molecular characterisation of GC cells after Fzd7 inhibition and investigate how GC cells with mutant APC are able to respond to inhibition of Fzd7, thus providing valuable mechanistic insight to help select which patients may respond to this therapeutic approach. This application is based on strong preliminary data showing that genetic inhibition of Fzd7, can block the growth of gastric tumours in mouse models of GC and human GC cells. The data generated in this project will represent a significant advance in the field, as presently the therapeutic benefit of targeting Fzd7, and Wnt receptors in general, for the treatment of GC has not be studied in vivo.

The overall goals of this research are to establish the therapeutic benefit of targeting the Wnt receptor Fzd7 for the treatment of gastric cancer (GC). Fz7 has attracted significant interest recently as it is upregulated in several different cancer types including GC (GC) and is an attractive therapeutic target. GLOBOCAN estimate that by 2035 almost 100,000 people in the UK will be diagnosed with GC every year, leading to almost 7000 mortalities. One of the most commonly associated risk factors for GC is age, with people >65 years old being 30 times more likely to develop or die of GC. Thus, new therapeutic strategies to treat GC will directly benefit GC patients, and importantly our rapidly increasing population of people over 65 years of age. Incidence and mortality from GC are strongly related to social class and measures of deprivation, with socially and economically deprived groups almost twice likely to die of GC compared to the least deprived. Thus, finding new treatments for GC will enhance the quality of life and health of the most vulnerable and deprived populations in the UK. GC is also the 4th leading cause of cancer mortality worldwide and therefore not only will this research benefit the UK but also GC patients worldwide. My well established reputation in the field of cancer research, and particularly my long spell working in Australia provides a solid foundation of people who I can engage with regarding this project. The level of engagement will cover a large spectrum of target audiences, from academics in my direct research field right through to secondary school students, the general public and research clinicians. Indeed I already give an annual workshop to second year undergraduate students at Cardiff University, in which I describe what cancer researchers do and explain the basic concepts of cancer biology including my own work. This is a two way process in which the students also tell me what they know about cancer - often with surprising results, as they realise that cancer is hard to explain. This subsequently feeds back into why researchers are still trying to understand the basic biology behind cancer, and inspires the next generation of researchers and potential investors to help us. I am also regularly invited to present my work at national and international conferences and institute seminars, and have also been interviewed on live radio and by national newspapers in UK and Australia. I also make regular use of the Facebook page for the European Cancer Stem Cell Research Institute to engage with friends, family and colleagues, and intend to continue using these forums to disseminate the results from this project to a large population of the general public. In addition to helping improve the health and quality of life for GC patients, this work will also impact on academic researchers. Discoveries in the intestine, including some of my own, have greatly increased our knowledge of the biology of this organ resulting in a deeper understanding of the events leading to transformation and progression of colon cancer. Our understanding of gastric biology lags significantly behind and is reflected in the low number of treatment options available for GC compared to colon cancer. Thus, this project will identify the requirement of the Wnt receptor Fzd during the very early stage of tumorigenesis, providing valuable information on the biology of this organ. In addition to the powerful genetic experiments in this project we shall also employ a pharmacological approach to speed up clinical translation. Indeed, I have already established an MTA with Oncomed Pharmaceuticals (USA) to conduct preclinical trials with their monoclonal antibody against Fzd1/2/5/7 (described in the research plan) which is currently in clinical trials for breast, pancreatic and lung cancer. Thus, Oncomed will also benefit from this project as they will potentially identify additional cancer patients who will respond to this treatment.