Abstract SY01-01: Genetic and epigenetic mechanisms linking diet and bowel cancer
Authors: Mathers John C. , Willis Naomi , McCallum Iain , Belshaw Nigel J. , Johnson Ian T. 
Published: August 2012

Genetic basis of colorectal cancer Tumours in the large bowel arise though unrepaired genomic damage in individual stem cells located at the base of the crypts within this columnar epithelium. In the hereditary forms of bowel cancer, familial adenomatous polyposis (FAP) and Lynch Syndrome (LS), risk is increased greatly through germ-line defects in tumour suppressor genes notably the APC gene and in genes encoding the DNA mismatch repair consortium, respectively. Despite these potent genetic influences on bowel cancer development in FAP and LS, there is now good evidence that cancer risk in such patients can be reduced or delayed significantly by chemopreventive agents 1-3. Defects in the same genes are acquired through genomic damage in the much more common sporadic bowel cancer.

Diet and colorectal cancer risk There is compelling evidence that lifestyle factors, especially diet, are major modulators of bowel cancer risk. For example, a recent meta-analysis demonstrated a dose-dependent reduction in bowel cancer risk with increasing intake of dietary fiber, in particular cereal fiber and whole grains.4 In addition, bowel cancer risk increases with increasing adiposity (obesity). Whilst there is evidence for cancer-related phenotypic changes in response to some dietary interventions5, the molecular mechanisms through which dietary factors modulate the acquisition or repair of the genomic damage which is fundamental for tumorigenesis remains poorly understood.

Epigenetic mechanisms We have hypothesised that poor dietary choices and/or increased adiposity may enhance bowel cancer risk through increased inflammation in the colorectal epithelium. This inflammatory load, together with other stressors e.g. altered redox state, may be responsible for aberrant gene expression though epigenetic mechanisms. Epigenetics describes the nature and application of the information overlaid on the primary genetic sequence which is used to regulate gene expression under specific circumstances. The constellation of marks and molecules which is encompassed by epigenetics includes DNA methylation, histone modifications, DNA/histone binding proteins and small (non-coding) RNAs. Importantly, epigenetic marks and molecules are plastic in response to a wide range of environmental exposures, including dietary factors,6 and provide a clear mechanistic link between such exposures and the aberrant gene expression which is a cardinal feature of tumours.

Diet-responsive biomarkers of bowel cancer risk Using both proteomic and sensitive gene methylation approaches, we have demonstrated that the macroscopically normal mucosa of those at higher bowel cancer risk (i.e. patients with adenomatous polyps or carcinoma) can be distinguished from that of normal (low risk) individuals.7,8 The genes showing differential patterns of methylation in those at greater bowel cancer risk included genes in the WNT signalling pathway e.g. APC, SFRP4 and WIF1 and other tumour suppressor (or putative tumour suppressor genes) i.e. HPP1, P16 and ESR1.8 Such observations suggest that there may be field changes in the vulnerable large bowel epithelium which are i) detectable long in advance of any evidence of colorectal mucosal pathology and ii) potential biomarkers of risk which could be used as surrogate endpoints in dietary intervention studies.

Developing diet-related epigenetic biomarkers of bowel cancer risk We have undertaken a randomised controlled trial (the DISC Study) in which 75 healthy volunteers were given food supplements of resistant starch (RS) and polydextrose (PD) for 50 days in a 2*2 factorial design. RS and PD are non-digestible carbohydrates which show bioactivity in the large bowel where they appear to have beneficial effects on gut physiology and immune function including anti-inflammatory effects. These beneficial effects may be mediated by short-chain fatty acids (SCFA) which are produced by bacterial fermentation of the ingested RS and PD. One of the SCFA, butyrate, has potent antineoplastic actions which may be attributed to epigenetically-mediated changes in gene expression since butyrate is a powerful histone deacetylase inhibitor.9 We are assessing systemic and local inflammation in the colon using the biomarkers hsCRP in blood and calprotectin in stool, respectively. Bioactivity of the RS and PD in the colon will be monitored by measurement of SCFAs in stool and urine.

We collected colo-rectal mucosal biopsies before and after the intervention for biomarker assessment. These biomarker studies include measurement of the methylation status of genes (those involved in WNT signalling and other tumour suppressor genes) known to be important in the early stages of cancer development and which may be modifiable by diet. In addition we will assess functional outcomes including expression of marker proteins identified though our earlier proteomic studies7 and mucosal cell kinetics.5 This work is on-going and recent data will be reported.

Summary A wealth of epidemiological evidence provides assurance that much bowel cancer can be attributed adverse environmental exposures and this is a firm basis for the development of dietary (and other lifestyle-based) interventions which aim to reduce or delay colorectal cancer development. However, the lack of robust, validated biomarkers of bowel cancer risk is a significant impediment to the conduct of such interventions since studies with cancer as the endpoint3 are costly in both time and other resources. Epigenetic markers, especially patterns of DNA methylation, are an attractive target for development of surrogate endpoints for nutritional intervention studies since they are plastic in response to dietary exposures and provide a clear mechanistic link with the aberrant gene expression which is a cardinal feature of cancer development.

Acknowledgement

The DISC Study is funded by the Biotechnology and Biological Sciences Research Council (BBSRC) (Grant no. BH090948). References

1. Burn J et al. (2008) N Engl J Med 359, 2567-2578. Effect of Aspirin or Resistant Starch on colorectal neoplasia in the Lynch Syndrome.

2. Burn J et al. (2011) Cancer Prevention Research 4, 655-665. A Randomized Placebo-Controlled Prevention Trial of Aspirin and/or Resistant Starch in Young People with Familial Adenomatous Polyposis.

3. Burn J et al. (2011) Lancet 378, 2081-2087. Long-term effect of aspirin on cancer risk in carriers of hereditary colorectal cancer: an analysis from the CAPP2 randomised controlled trial.

4. Aune D et al. (2011) BMJ 343; d6617. Dietary fibre, whole grains, and risk of colorectal cancer: systematic review and dose-response meta-analysis of prospective studies.

5. Dronamraju SS et al. (2008) Gut 58, 413-420. Cell kinetics and gene expression changes in colorectal cancer patients given resistant starch - A randomised controlled trial.

6. Mathers JC et al. (2010) Adv. Genet. 71, 3-39. Induction of epigenetic alterations by dietary and other environmental factors.

7. Polley AC et al. (2006) Cancer Res. 66, 6553-6562. Proteomic analysis reveals field-wide changes in protein expression in the morphologically normal mucosa of patients with colorectal neoplasia.

8. Belshaw NJ et al. (2008) Br J Cancer 99, 136-42. Profiling CpG island field methylation in both morphologically normal and neoplastic human colonic mucosa.

9. Williams EA et al. (2003) Proc Nutr Soc 62, 107-115. Anti-cancer effects of butyrate: use of micro-array technology to investigate mechanisms.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr SY01-01. doi:1538-7445.AM2012-SY01-01