Functional characterization of age-dependent p16 epimutation reveals biological drivers and therapeutic targets for colorectal cancer

Therapeutic targeting of DNA methylation alterations in cancer

DNA methylation is a critical component of gene regulation and plays an important role in the development of cancer. Hypermethylation of tumor suppressor genes and silencing of DNA repair pathways facilitate uncontrolled cell growth and synergize with oncogenic mutations to perpetuate cancer phenotypes. Additionally, aberrant DNA methylation hinders immune responses crucial for antitumor immunity. Thus, inhibiting dysregulated DNA methylation is a promising cancer therapy. Pharmacologic inhibition of DNA methylation reactivates silenced tumor suppressors and bolster immune responses through induction of viral mimicry. Now, with the advent of immunotherapies and discovery of the immune-modulatory effects of DNA methylation inhibitors, there is great interest in understanding how targeting DNA methylation in combination with other therapies can enhance antitumor immunity. Here, we describe the role of aberrant DNA methylation in cancer and mechanisms by which it promotes tumorigenesis and modulates immune responses. Finally, we review the initial discoveries and ongoing efforts to target DNA methylation as a cancer therapeutic.

Dietary Folate and Cofactors Accelerate Age-dependent p16 Epimutation to Promote Intestinal Tumorigenesis

The extent to which non-genetic environmental factors, such as diet, contribute to carcinogenesis has been long debated. One potential mechanism for the effects of environmental factors is through epigenetic modifications that affect gene expression without changing the underlying DNA sequence. However, the functional cooperation between dietary factors and cancer-causing epigenetic regulation is largely unknown. Here, we use a mouse model of age-dependent p16 epimutation, in which the p16 gene activity is directly controlled by promoter DNA methylation. We show p16 epimutation is modulated by folate and cofactors in dietary supplementation, which leads to increased colon cancer risk. Importantly, our findings provide functional evidence concerning the safety of folate fortification in the general population.

SIGNIFICANCE

Our study demonstrates that dietary folate and cofactors modulate tumor-suppressor gene methylation to increase intestinal tumorigenesis. Our findings highlight the need for monitoring the long-term safety of folate fortification in high-risk individuals.

Adjuvant chemotherapy decision-making in stage II colon adenocarcinoma associated with patients' age and high-risk factors

PURPOSE

To clarify whether the combination of age and high-risk factors (HRFs) was preferable for adjuvant chemotherapy (AC) decision-making in patients with stage II colon adenocarcinoma.

METHODS

We conducted a retrospective study analyzing eligible colon cancer patients from the Surveillance, Epidemiology, and End Results (SEER) database between 2010 and 2017. A nomogram was used to predict patient prognosis. Decision curve analysis (DCA) predicted model clinical benefit. Restricted cubic spline calculated the optimal cut-off value.

RESULTS

A total of 8570 patients with stage II colon adenocarcinoma were included in this study; 25.2% received AC. A nomogram predicting the prognosis of patients with stage II colon adenocarcinoma was constructed with age and HRFs, and scores were assigned to the relevant variables. DCA showed that age combined with HRFs was superior to treatment decision-making based on HRFs alone. Patients were grouped according to their total score with the cut-off value of 100. AC did not significantly improve overall survival (OS) in low-score group (hazard ratios (HRs) 1.01, 95% confidence intervals (CIs) 0.86-1.18, p = 0.918). In high-score group, AC improved 5-year OS by about 7.6% (HR 0.73, 95% CI 0.61-0.88, p = 0.001). And high-score group mainly included patients aged < 50 years with two or more HRFs and patients aged ≥ 50 years with at least one HRF.

CONCLUSION

Age and HRFs could be preferable for determining the group of stage II colon adenocarcinoma patients who would benefit from AC. Patients aged < 50 years with two or more HRFs might be a potential benefit population for AC.

Association of APC Expression with Its Promoter Methylation Status and the Prognosis of Hepatocellular Carcinoma

OBJECTIVE

The present study was aimed to investigate the APC expression, its promoter methylation status, the expression of β-Catenin, c-Myc and Cyclin D1 and further explore their prognostic value in Hepatocellular carcinoma (HCC).

PATIENTS AND METHODS

Serum samples from 90 HCC patients and 27 healthy donors were collected in this study. The methylation-specific PCR (MSP) was performed to evaluate promoter methylation status of APC gene. RT-qPCR was used to detect the mRNA expression of APC, β-Catenin, c-Myc and Cyclin D1, meanwhile the protein expression were analyzed by Western blot.

RESULTS

The positive rate of APC gene methylation in HCC patients (46.67%) was higher than healthy donors (11.11%). APC gene exhibited marked hypermethylation in the patients of TNM III-IV stage when compared to the patients of TNM I-II stage , the methylation status of APC gene was correlated with tumor size and lymph node metastasis whereas the APC gene methylation showed no relationship with the patient's sex and age. APC methylation may be associated with APC expression level, APC expression in HCC cells is silenced by aberrant promoter hypermethylation. In HCC patients with methylated APC, the mRNA and protein expression of β-Catenin, c-Myc and Cyclin D1 were higher than the unmethylated patient subgroup and healthy donors.

CONCLUTIONS

The downregulation of APC in HCC samples was associated with promoter hypermethylation. APC methylation could be used as a novel diagnostic biomarker in HCC, which was associated with regulation of Wnt/β-Catenin signal pathway.