Exposure to hypomethylating agent 5-aza-2’-deoxycytidine (decitabine) causes rapid, severe DNA damage, telomere elongation and mitotic dysfunction in human WIL2-NS cells

Background 5-aza-2’-deoxycytidine (5azadC, decitabine) is a DNA hypomethylating agent used in the treatment of myelodysplastic syndromes. Due to cytotoxic side effects dose optimization is essential. This study defines and quantifies the effects of 5azadC on chromosomal stability and telomere length, at clinically relevant dosages. Methods Human WIL2-NS cells were maintained in complete medium containing 0, 0.2 or 1.0μM 5azadC for four days, and analysed daily for telomere length (flow cytometry), chromosomal stability (cytokinesis-block micronucleus cytome (CBMN-cyt) assay), and global methylation (%5me-C). Results DNA methylation decreased significantly in 1.0 μM 5azadC, relative to control (p<0.0001). Exposure to 1.0μM 5azadC resulted in 170% increase in telomere length (p<0.0001), in parallel with rapid increase in biomarkers of DNA damage; (micronuclei (MN, 6-fold increase), nucleoplasmic bridges (NPB, a 12-fold increase), and nuclear buds (NBud, a 13-fold increase) (all p<0.0001). Fused nuclei (FUS), indicative of mitotic dysfunction, showed a 5- and 13-fold increase in the 0.2μM and 1.0μM conditions, respectively (p = 0.001) after 4 days. Conclusions These data show that (i) clinically relevant concentrations of 5azadC are highly genotoxic; (ii) hypomethylation was associated with increased TL and DNA damage; and (iii) longer TL was associated with chromosomal instability. These findings suggest that lower doses of 5azdC may be effective as a hypomethylating agent, while potentially reducing DNA damage and risk for secondary disease.