Global DNA methylation status of colorectal cancer cells exposed to photodynamic therapy

Introduction: DNA methylation and histone modifications are epigenetic mechanisms that allow heritable silencing of genes without introducing mutations or alterations to the coding sequences of the genes. Being an important regulator of gene transcription, DNA methylation and its role in carcinogenesis has received considerable attention recently. Although hypermethylation represses transcription of promoter regions of tumour suppressor genes has been extensively studied, global hypomethylation has also been identified as an oncogenic inducer. Photodynamic therapy (PDT) is the use of low intensity laser irradiation (LILI) in conjunction with a photosensitiser (PS), in this instance Zinc (II) Phthalocyanine (ZnPc), to treat cancer cells. A single wavelength is used to activate the PS, which in turn causes changes in cellular functions. DNA methhylation is an epigenetic regulator. The methylation status of a gene determines if it is expressed or silenced. Aim: This study aimed to determine if DNA methylation has an effect on PDT. Method: Cancer cells, demethylated and normal, were exposed to PDT with different incubation times. Cell viability, proliferation and morphology were measured. Results: The results indicate that when cells are exposed to PDT, a statistical significant decrease (P< 0.001) in viability is achieved with an incubation time of 24 hours. The viability of cells treated with a high concentration of the demethylating agent showed a statistical significant decrease (P<0.01) in viability when incubated for 24 hours. Conclusion: DNA methylation does have an effect on the efficiency of PDT depending on the incubation time of the PS.