Abstract
Background and Objectives
One of the most important mechanisms of hematologic malignancies is DNA methylation in the promoter region of tumor suppressor genes such as P15. Harmalin is one of the alkaloids derived from plants that show anti-proliferative activity on leukemic cell lines. The effect of harmalin on Dnmt1 gene expression and hypomethylation of P15 promoter in NB4 cell line was evaluated.
 
Materials and Methods
In this experimental study, cytotoxic effects of harmaline were investigated until 72 hours on the NB4 cell line using MTT. Flow cytometry was performed in order to evaluate the cell cycle of NB4 cell line after treatment with harmalin. Gene promoter methylation status of P15 was evaluated by Methylation Specific PCR. Dnmt1 and P15 gene expression was analyzed by Real-time PCR technique.
 
Results
15μg/ml harmalin after 48 hours showed a dose and time-dependent anti-proliferative properties on NB4 cell line, cell cycle analysis would stop NB4 cells in G0G1 phase of the cell cycle. Real-time PCR results showed that 15μg/ml harmalin reduced gene expression of Dnmt1, induced hypomethylation of P15 gene promoter and increased P15 gene expression in NB4 cell line.
 
Conclusions 
According to our data, the effect of harmalin on reduction of Dnmt1 expression, P15 promoter hypomethylation and P15 reactivation in this cell line showed that it could be suggested as a therapeutic strategy, suitable for monotherapy or supplement for medication which is commonly used for APL (Acute Promyeloid Leukemia).