Anti-neoplastic Effect of Adjuvant Epigenetic Therapy of Decitabine and Suberoylanilide Hydroxamic Acid on U937 Acute Myeloid Leukemia Cell Line

Abstract

Acute myeloid leukemia is a heterogeneous malignant disorder characterized by rapid buildup of abnormal myeloid blasts in the blood and the bone marrow. This uncontrolled accumulation eventually interferes with the normal functioning of healthy blasts. Despite major advances in AML research, high incidence and death rates persist. Recently the role of epigenetic modifications in leukemogenesis has been well acknowledged, including histone deacetylation and DNA methylation, which frequently target the promoters of key genes involved in pathways such as apoptosis and cell cycle. Several studies have reported that combining different epigenetic modulators significantly boosts the effects of each one when used individually. In this study, the effects of a histone deacetylase inhibitor and a DNA methyl transferase inhibitor, suberoylanilide hydroxamic acid and Decitabine, respectively, were evaluated using U937 cells as an AML model cell line. Once having determined their growth inhibitory effects, and cell cycle arresting and apoptotic powers, two strategies of combining SAHA and DAC were assessed: simultaneous and sequential treatments. The sequential combination treatment, which consisted of priming the cells with DAC and then adding SAHA, was shown to enhance the effects of each epigenetic modulator, unlike the simultaneous treatment strategy. The effects were observed for growth inhibition, apoptosis stimulation and cell cycle arrest. Lastly, the changes incurred upon the sequential treatment were evaluated at the level of protein expression. The results revealed that, relative to controls and cells treated with only one drug, both intrinsic and extrinsic apoptotic pathways were activated by the sequential combination of SAHA and DAC. Further studies should be conducted to decipher the complete molecular mechanisms and pathways involved in the growth inhibitory effects of the combined SAHA and DAC treatment.