Dr Sebastian Zeki

Title: Clonal competition and genetic evolution of Barrett’s Oesophagus

Project Start Date: 1 August 2011

Completion Date: 31 July 2014

Summary:

Barrett’s oesophagus (BO) is a common condition in which the cells lining the oesophagus change type in response to acid and bile reflux. This change is an important risk factor for oesophageal cancer development as the cells in BO can develop cancer associated DNA mutations; as a result BO is considered to be a precancerous condition. We know that different cells develop different mutations but we do not know whether these cells compete against or co-operate with one other to drive progression to cancer. My project aims to investigate whether such interactions occur and which mechanisms are involved by studying mutations in small areas of tissue and determining how different populations of cells may interfere with other populations in tissue from patients with BO.

The first project seeks to show that competition does exists by showing that although the tissue that has pre-cancerous changes is made of many cell populations, the cancer that subsequently develops is made up only of one selected population- the ‘winning’ cell population. This is good evidence for a competitive process occurring. The detailed dissection of individual portions of the oesophagus will also allow us to understand the geography of interfering precancerous populations- important so that we can understand how interfering populations may interact.

The subject of the second project is ‘radiofrequency ablation’ therapy. This is a technique whereby areas within the oesophagus which look cancerous or have dysplasia can be accessed using an endoscope through the mouth and removed using a device which heats and destroys the areas. This has been very successful but there are still patients who develop recurrent cancer after treatment. The hypothesis of this project is that these patients have persistent genetic mutations that are causing recurrence and that these mutations may be expressing survival factors that make them more resistant to treatment and therefore a more ‘competitive’ cell population. This is important so that we can understand recurrent cancers and better optimize RFA to get better cure rates.

The third project will look at the possible types of interactions different cell populations may have at a molecular level. Specifically I will be assessing the role that partially damaged cells which don’t die and still secrete signals (called senescent cells) have on their neighbours. The proposition is that these cells may enhance tumour like behaviour.

Using detailed microdissection techniques, I have demonstrated that cancers contain only one of the mutations that are present in the surrounding precancerous tissue which indicates that the cancer evolves from a mix of mutated cells. I have also shown that the populations in the precancerous tissue are well mixed rather than containing borders, indicating that interactions between populations are likely to be very local. This is important so that we can tailor further investigations for the types of interactions to local signals rather than more distant types of signalling.

The second project has demonstrated the following points. Firstly, that patients with cancer undergoing RFA need to have all Barrett’s removed, even the tissue that shows no suspicious changes. Secondly that patients with all Barrett’s tissue removed can rarely still have cancer associated mutations in the new and supposedly normal tissue which indicates that these patients may still need to be surveyed with an endoscope even after a potential cure. Thirdly that cancer associated mutations can be found in areas potentially beyond the reach of RFA suggesting that RFA should be combined with other endoscopic treatment such as mucosal resections.

The third project has demonstrated that Barrett’s cells which have been damaged are able to cause neighbouring cells to proliferate. This potentially gives a mechanism by which areas of damage in Barrett’s oesophagus can still promote tumour growth

Clinical implications:

• Patients who have traditionally thought to be cured after RFA treatment may still need surveillance- this may increase the cost of this treatment.
• All patients should continue to have sessions of RFA until all BO is removed- patients in whom BO tissue is left, even if not suspicious, are at risk of getting recurrent cancer.
• Molecular assessment of tissue may be more useful than examination under a microscope to understand the risk of an individual patient of developing cancer.
• Cells containing cancer associated mutations may be present in areas beyond the reach of RFA alone, justifying the use of combined therapies.
• Identifying pathways that encourage tumour growth can help target further investigation into targeted therapies.

The work will be augmented by the arrival of technologies that give greater genetic detail. My work has indicated that in BO cancers evolve from one population of many. Using newer technologies we should be able to add detail to this evolution and assess which mutations provide this evolutionary advantage. Furthermore we should be able to get a more detailed understanding about how different cell populations migrate out across BO and what this is determined by.

The application of RFA is extremely topical at present and as a result of my work , the University of San Francisco (Helen Diller Unit, Dept Surgery, UCSF) will be performing deep genetic analysis of samples from patients who have undergone RFA to see if we can predict who will respond to treatment which should greatly reduce both the cost of therapies and the burden to the patient.

The possibility that damaged cells can cause their neighbours to proliferate and the understanding that this may be mediated by inflammatory proteins can allow further investigation as to how these inflammatory pathways work and which constituents of inflammation are the main targets.