Determination of FoxM1 gene expresssion level in acute lymphoblastic leukemia cell line and targeting FoxM1 by deksametazon and FoxM1 inhibitor Siomycin A

Introduction-Objective: FoxM1 is a transcriptional factor that takes play in regulation of cell cyle and promotes cell proliferation. Recent studies show that the FoxM1 signaling network is frequently deregulated in human malignancies with up-regulated expression of FoxM1 in lung cancer, glioblastomas, prostate cancer, basal cell carcinomas, hepatocellular carcinoma, and primary breast cancer and pancreatic cancer. Siomycin A, a thiazol antibiotic, is known to inhibit FoxM1 transcriptional activity. Dexamethasone is a glucocorticoid that is very important in treatment of acute lymphoblastic leukemia (ALL) and is known to be more potent compared to other steroids in the treatment of T-cell ALL. In this study, we aimed to determine the gene expression levels of FoxM1 in Jurkat cells (T-ALL cell line) and to investigate the changes in gene expression levels and the effects on cellular proliferation by targeting FoxM1 with siomycin A and dexamethasone. Materials and methods: The gene expression levels of FoxM1 were studied with reverse transcriptase polymerase chain reaction (RT-PCR). The antiproliferative effects of siomycin A and dexamethasone on Jurkat cells were studied with MTT cell proliferation test. The possible synergistic, additive, neutral, and antagonistic effect of combination of dexamethasone and siomycin A was determined with isobologram analysis. The apoptotic effects of these two agents were evaluated by Caspase-3 activity, disturbances in mitochondrial membrane potential and localisation of phospatidilserine in cellular membrane. For this purpose, Caspase-3 calorimetric assay kit, JC-1 mitochondrial membrane potential assay kit, and Annexin V-FITC apoptosis detection kit were used, respectively. For cell cycle analysis, siomycin A and dexamethasone treated Jurkat cells were stained with propidium iodide and analysed in flow-cytometer. Results: We found that FoxM1 gene is overexpressed in T-ALL cell line and dexamethasone and siomycin A caused a reduction in gene expression levels of FoxM1 in Jurkat cells. Eight to 13 % decrease in proliferation of Jurkat cells were observed when these cells were treated with 1 and 10 µM doses of dexamethasone for 72 hours, respectively. On the other hand, the same doses of dexamethasone combined with siomycin A caused 74% and 75% decrease in proliferation of Jurkat cells. Isobologram analysis revealed very strong synergy between dexamethasone and siomycin A. Apoptotic tests showed no apoptotic activity of dexamethasone and siomycin A on Jurkat cells. Cell cycle analysis showed that, reduction of FOXM1 expression by combination of dexamethasone and siomycin A in Jurkat cells inhibited cell proliferation through induction of G1 phase arrest. Conclusion: It is demonstrated that FoxM1 gene is strongly overexpressed in T-ALL cell line and targeting FoxM1 by siomycin A and dexamethasone caused a significant decrease in TALL cell proliferation through induction of G1 cell cycle arrest. All these findings suggest a possible role for FoxM1 in T-ALL pathogenesis and represent FoxM1 as an attractive target for T-ALL therapy. Key words: FoxM1, acute lymphoblastic leukemia, siomycin A