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

Aim: Photodynamic therapy (PDT) is the use of low intensity laser irradiation (LILT) 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. This study aims to determine if DNA methylation has an effect on the effectiveness of PDT. Method: Cancer cells, demethylated with aza-5-dc and normal, were exposed to PDT with different incubation times. Cell viability, proliferation and morphology were measured. Results: Cells that underwent PDT and aza-5-dc treatment showed a statistically significant decrease in viability when compared to control cells. A significant decrease was also shown when cells, demethylated with a high concentration of aza-5-dc were compared to cells exposed to PDT. Conclusion: The DNA methylation status of cells does have an effect on PDT effectiveness.