The involvement of microRNAs in dietary reduction of cancer risk in Familial Adenomatous Polyposis patients

  • Topic:
  • Institution: Flinders University
  • Country: Australia
  • Status: Ongoing

Scientific abstract

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Background

Colorectal cancer (CRC) is a major cause of cancer related death in Western nations. Butyrate, produced by fermentation of dietary fibre, induces apoptosis in colorectal cancer cells, while serving as an energy source for normal colonocytes. Known as the “Butyrate Paradox”, this is thought to explain some of the benefit of high-fibre diets, in protecting against CRC. MicroRNAs (miRNAs) are short non-coding RNAs that inhibit the expression of target genes, including cancer-associated genes, and may thereby play roles as tumour suppressors, or oncogenes, depending on the cellular context. We have shown that an oncogenic subset of microRNAs, the miR-17~92 cluster, are repressed by butyrate in cultured CRC cells. Further, the same study showed that members of this miRNA cluster regulate the butyrate response in these cells. More recently, we have reported the in vivo regulation of this oncogenic miR-17~92 cluster, by dietary butyrate, in a randomised human trial which explored the effects of butyrylated resistant (high-amylose) starch (HAMSB) on high red meat diets. We now seek to address the fundamental question of whether butyrate regulates miRNAs and gene expression in colorectal neoplasia in vivo, and may thereby prevent tumour initiation or progression.

Hypothesis

Butyrate regulates microRNA expression and thereby limits the expression of intestinal genes involved in tumour progression.

Objectives

  • To profile mature microRNA levels in “normal” and neoplastic epithelia of volunteers with Familial Adenomatous Polyposis (FAP), who have received butyrylated resistant starch as a dietary supplement.
  • To define changes in the transcriptome of FAP intestinal epithelia and neoplasms, as a result of ingesting butyrylated resistant starch.
  • Using network analysis, to predict the cellular pathways that are regulated by butyrate, in both “normal” and neoplastic tissues, and correlate molecular changes with observed responses to the dietary supplement.

Settings and methods

We have initiated a trial to investigate the effects of butyrylated resistant starch on the colorectal epithelium of individuals with Familial Adenomatous Polyposis (FAP). The proposed study will add enormous value to an existing project by investigating the effect of butyrate on gene (especially miRNA) activity in the mucosae and neoplasms of FAP volunteers. MicroRNAs will be profiled in “normal” mucosae, adenomas and possibly carcinomas of 20 FAP patients, before and after HAMSB supplementation, using Next Generation Sequencing (small RNA-seq). New, low-input, RNA-seq methods will also be adapted to enable global transcriptome profiling of RNA samples from limited biopsy specimens. A variety of bioinformatics packages, including Ingenuity Pathway Analysis, will be employed to integrate miRNA and transcript data, and define cellular pathways that are differentially affected by butyrate. These pathways will be manipulated in vitro to model in vivo observations and test nutritional benefits.

Impact

This project will leverage a nation-wide study, to define the transcriptional and epigenetic changes that accompany butyrate responses in neoplasms. Data from this FAP cohort will suggest a mechanism for the expected nutritional responses in a vulnerable population, but also identify nutritional mechanisms, and likely drug targets, that can be extended to CRC in the broader population.

Plain language abstract

Background

High fibre diets are known to have a protective effect against bowel cancer. Along with rapid intestinal transit, one of the major reasons for this protective effect is the production of a fatty acid called butyrate, which is produced when intestinal bacteria ferment the fibre in your bowels. Butyrate provides a major energy source for normal gut cells, however it specifically causes cancerous bowel cells to die. We have shown in cultured cells that specific gene products called microRNAs, some of which are more active in cancers, are responsible for the specific killing effect in cancer cells. This project will determine if the same butyrate inducing mechanism occurs in the polyps of people who have a genetic predisposition to bowel cancer.

Aims and objectives

  1. To determine whether human intestinal microRNA levels change following prolonged exposure to a diet that contains a butyrate releasing supplement, called HAMSB.
  2. To correlate any observed changes in microRNA levels with a reduction in polyp size or number.
  3. To identify any genes that might be controlled by the butyrate influenced microRNAs.
  4. To use cancer cell cultures, and manipulate the activities of the microRNAs (identified in people), to test if they have a direct role in the butyrate induced killing of cancer cells, and prove that specific target genes are responsible.

How it will be done

A clinical trial is currently underway in Australia, to test the ability of HAMSB (also called StarPlus) to shrink the polyps in patients who are predisposed to bowel cancer. After six months on the diet (or a control diet), the subjects will provide a small sample of their rectal lining, which we will analyse for the levels of human gut microRNAs. We will also measure the activity of all human genes in the same tissues, using new genomic technologies. We will then attempt to match the microRNA activities with the genes that they are thought to regulate (actually, suppress) and see if we can identify some specific cellular mechanisms that are responsible.

Potential impact

By understanding how cancer cells respond to butyrate, society will benefit in the following ways:

  1. This knowledge will help to sell the message that high fibre diets (or nutritional supplements) are beneficial in reducing bowel cancer risk.
  2. The clinical trial, itself, will determine if patients who have a strong genetic risk of developing bowel cancer will benefit from the HAMSB supplement. The importance of this can't be overstated for these unfortunate people.
  3. The study will identify new molecules in polyp cells that can be targeted by specific drugs to develop new anti-cancer therapies.