Search

PML-RARα perturbs the normal epigenetic setting, which is essential to oncogenic transformation in acute promyelocytic leukemia (APL). Transcription induction and recruitment of DNA methyltransferases (DNMTs) by PML-RARα and subsequent hypermethylation are components of this perturbation. Arsenic trioxide (ATO), an important drug in APL therapy, concurrent with degradation of PML-RARα induces cell cycle change and apoptosis. How ATO causes cell cycle alteration has remained largely unexplained. Here, we investigated DNA methylation patterns of cell cycle regulatory genes promoters, the effects of ATO on the methylated genes and cell cycle distribution in an APL cell line, NB4. Analysis of promoter methylation status of 22 cell cycle related genes in NB4 revealed that CCND1, CCNE1, CCNF, CDKN1A, GADD45α, and RBL1 genes were methylated 60.7, 84.6, 58.6, 8.7, 33.4, and 73.7%, respectively, that after treatment with 2 μM ATO for 48 h, turn into 0.6, 13.8, 0.1, 6.6, 10.7, and 54.5% methylated. ATO significantly reduced the expression of DNMT1, 3A, and 3B. ATO induced the expression of CCND1, CCNE1, and GADD45α genes, suppressed the expression of CCNF and CDKN1A genes, which were consistent with decreased number of cells in G1 and S phases and increased number of cells in G2/M phase. In conclusion, demethylation and alteration in the expression level of the cell cycle related genes may be possible mechanisms in ATO-induced cell cycle arrest in APL cells. It may suggest that ATO by demethylation of CCND1 and CCNE1 and their transcriptional activation accelerates G1 and S transition into the G2/M cell cycle arrest. [ABSTRACT FROM AUTHOR]

Aim Survivin, an inhibitor of apoptosis protein, is overexpressed in most cancers and is associated with chemotherapy resistance, increased tumor recurrence and shorter patient survival. Several survivin splice variants have been described, and none of their expressions have been defined in acute promyelocytic leukemia (APL). Methods Expression of the survivin gene isoforms (survivin, -2α, -2B, -ΔΕx3 and -3B) were analyzed in 50 peripheral blood and 19 bone marrow samples that were collected at different phases of the disease (diagnostic, remission and relapse) in APL patients treated with arsenic trioxide (ATO) as a front-line therapy. In addition, the human APL-derived cell line (NB4) was analyzed for the expression of survivin isoforms and capsase-3 in response to the ATO. Results Survivin and its variants were overexpressed significantly in patient's bone marrow samples compared to peripheral blood or normal samples. Their expression was decreased after ATO treatment in both NB4 cells (except survivin-2α) and APL patients along with PML-RARα copy number reduction. Downregulation of survivin isoforms was associated with an increase in both caspase-3 gene expression and its enzymatic activity levels. In a patient who did not respond to ATO treatment, expression of survivin isoforms (except survivin-2α) were highly increased during the induction therapy. Conclusion Survivin isoforms are upregulated in APL patients, and their expression is diminished during the ATO treatment. In addition, overexpression of survivin and its variants (except survivin-2α) are associated with unfavorable results, suggesting that they may play an important role in mechanisms underlying the resistance of APL cells to ATO. [ABSTRACT FROM AUTHOR]

Acute promyelocytic leukemia (APL) is characterized by specific t(15;17), distinct morphologic picture, and clinical coagulopathy that contributes to the morbidity and mortality of the disease. This study was purposed to dissect the molecular mechanisms underlying telomerase-dependent arsenic trioxide (ATO)-induced cytotoxic and anti-proliferative effects in NB4 cells. ATO exposure was associated with transcriptional repression of Pin1, survivin, c-Myc, hTERT, and PinX1 along with an expressive enhancement in p73 mRNA level. Moreover, ATO treatment suppressed cell growth, viability and metabolic activity, exerted apoptosis, hindered telomerase activity, shortened telomere length, and dampened NF-κB activation. On aggregate, these issues indicate that ATO might preempt cell growth and proliferation in NB4 cells through suppression of Pin1-mediated NF-κB-dependent stimulation of telomerase and survivin. [ABSTRACT FROM AUTHOR]

The intertwining between cancer pathogenesis and perturbation of multitude signaling pathways ushered the cancer therapeutic approaches into an unbounded route of targeted therapies. For the nonce and among the plethora of promising inhibitors, intense interest has focused on small molecules targeting different component of PI3K axis. Intrigued by the constant activation of PI3K in leukemia, this study aimed to investigate the effects of BKM120, as the excelled member of pan PI3K inhibitors, in a panel of hematologic malignant cell lines. The resulting data showed that BKM120 exerted a concentration-dependent growth suppressive effect; however, IC 50 values varied among the tested cells. Our results outlined that the blockage of PI3K in NB4, as the most sensitive cell line, resulted in a caspase-3-dependent apoptosis probably through NFκB-mediated suppression of c-Myc and hTERT. As far we are aware, to date, there have been no reports of BKM120 effect on enzymatic repression of telomerase, and this study represents for the first time that the anti-proliferative effect of the inhibitor on NB4 is mediated by down-regulation of telomerase; shedding new light on the novel mechanism of action of BKM120. [ABSTRACT FROM AUTHOR]

Genetic and laboratory experiments have brought remarkable advances in management of human malignancies, which not only revolutionized the understanding of the disease, but also led to development of novel and effective targeted therapies against specific deregulated pathways. This study aimed to investigate anti-cancer effects of Idelalisib, a potent PI3K-δ inhibitor, in a panel of hematological cell lines. The resulting data showed that Idelalisib decreased cell survival in all the tested cell lines; however, as compared to NB4, viability of other cell lines, irrespective of their molecular characteristics or even the compensatory activation of MEK/ERK pathway, was inhibited at higher concentrations. This study suggests for the first time that there is a significant correlation between relative response to Idelalisib and basal expression levels of anti-apoptotic genes, in particular survivin and MCL-1. Intriguingly, we found that Idelalisib-induced apoptosis in NB4, as the most sensitive cell line with the lowest expression level of the aforementioned genes, is executed probably via alteration in the transcriptional level of apoptosis-related genes coupled with p21-mediated caspase-3 activation. Moreover, the lower concentrations of Idelalisib combined with arsenic trioxide (ATO) produced synergistic anti-cancer effect in APL-derived NB4 cells. Overall, due to the pharmacologic safety of Idelalisib and its broad clinical effectiveness in chronic lymphoproliferative disorders, our study suggests that this inhibitor is a promising agent for the treatment of acute promyelocytic leukemia, either as single agent or in a combined-modality strategy. [ABSTRACT FROM AUTHOR]