Recent studies have shown that microRNAs (miRNAs) play important roles in the development of cancer, and that epigenetic mechanisms are deeply involved in their dysregulation. Technological advances that enable comprehensive analysis of miRNA expression profiles and the epigenome in cancer cells have led to the identification of a large number of epigenetically regulated miRNAs. As with protein-coding genes, it appears that miRNA genes involved in regulating cancer-related pathways are silenced in association with CpG island hypermethylation and altered histone modification. Aberrant DNA methylation of miRNA genes is a potentially useful biomarker for detecting cancer or predicting its outcome, and re-expression of the miRNAs could be an effective approach to cancer therapy. In this symposium, I will present our recent studies on epigenetic dysregulation of miRNA in gastrointestinal cancer and its clinical application.

Epigenetic changes are closely associated with various types of diseases including cancer, diabetes and hypertension. Growing evidences demonstrate the strong relationships between the environmental/lifestyle factors and risk for the diseases. Epigenetic approaches in cancer epidemiology, so-called the “epigenetic epidemiology”, are used, and it has been reported that several lifestyle factors, such as diet, smoking, alcohol consumption and physical activity, may influence DNA methylation patterns. We studied the DNA methylation status of tumor-related genes in gastric cancer tissues, and then compared to past lifestyle of the patients. DNA methylation levels were inversely related to green tea intakes and physical activity. It has been known that DNA methylation changes are also found in blood leukocyte DNA from the cancer patients, in which alterations were significantly associated with some environmental/lifestyle factors. Thus, methylation of leukocyte DNA is possible to be one of the useful surrogate markers for predicting the risk for cancers. In addition to the development of newly epigenetic drugs, the strategies involving a lifestyle improvement might be beneficial in preventing epigenetic alterations and counteracting cancer.

The standard treatment for cancer is multidisciplinary therapy combining surgery, anticancer drugs, radiation and molecular-targeting therapies, and a certain degree of success has been achieved. On the other hand, the toxicity and effectiveness of multidisciplinary therapy have almost reached their limits and a new therapeutic modality with low toxicity is needed for the future. In regard to genetic changes, epigenetic changes are more frequent than genomic changes in cancer and expectations for epigenetic therapy have increased. In order to use epigenetic therapy as a new cancer treatment tool, we started a study focusing on the anticancer effect of phenylbutyrate (PB), which possessed histone deacetylases (HDAC)-inhibitory effect. A satisfactory anticancer effect of PB at clinical doses was confirmed in breast cancer cell lines. However, the effect varied among the cell lines. In the study of the gene expression profiles, remarkable differences were observed among the cells in the expressions of chemotherapy-resistant molecules such as AKRD1, AXL and caveolin-1/2, as well as in the expressions of methylated tumor suppressor genes such as TFAP2B. We propose to study about the reactivities of these genes to PB and to other epigenetic therapeutics, in an attempt to contribute to identification of the most important molecule. In addition, these data may be applied as a PB therapy sensitivity prediction marker and also as practical data from the aspect of clinical application.

Phenylbutyrate is one of HDAC inhibitors with histone deacetylase inhibiting activity that has been used for the treatment of an infant congenital disease (urea cycle disorder). It is a stable substance classified as an aromatic fatty acid and is characterized by a low likelihood of interaction with other drugs, fewer side effects, availability for oral use, availability for use in combination with standard therapy, and its expected curative effect in non-responders to standard treatment with a single drug.
At our clinic, phenylbutyrate is mainly applied for the treatment of patients with solid carcinomas. Among the 49 evaluable cases, 94% (46) were classified as having stage 4 disease and 61% (30) were treated with the drug administered in combination with the standard treatment. Most of the side effects observed pertained to the digestive symptom, including symptoms such as heartburn, stomach retching and a feeling of fullness, and in all cases, the symptoms were classified into grade 1. Some complete responses were observed in the phenylbutyrate monotherapy group, and some relatively better responses were also observed in the cases receiving combination therapy with phenylbutyrate than in those receiving monotherapies with other anticancer agents. Therefore, therapy with phenylbutyrate may be a promising treatment option for intractable cases.