AML1-ETO Needs a Partner: New Insights into the Pathogenesis of t(8;21) Leukemia

The detailed characterization of genetic and molecular aberrations in acute myeloid leukemia (AML) has substantially improved our understanding of the pathogenesis of this disease. With an incidence of up to 12% in all AML cases, the translocation t(8;21), forming the AML1-ETO fusion gene, is one of the most common genetic aberrations in AML. Experimental data have shown that AML1-ETO is not sufficient to induce leukemia by itself, but has to collaborate with other genetic alterations for leukemic transformation. These data are supported by observations in AML patients, who recurrently show activating mutations of the receptor tyrosine kinase FLT3 or c-KIT together with the AML1-ETO fusion gene. These findings might have clinical implications and provide a rationale to test RTK inhibitors in the treatment of patients with core binding factor AML and concurrent activating RTK mutations.     

Minimal residual disease monitoring via AML1-ETO breakpoint tracing in childhood acute myeloid leukemia

Relapse of childhood AML1-ETO (AE) acute myeloid leukemia is the most common cause of treatment failure. Optimized minimal residual disease monitoring methods is required to prevent relapse. In this study, we used next-generation sequencing to identify the breakpoints in the fusion gene and the DNA-based droplet digital PCR (ddPCR) method was used for dynamic monitoring of AE-DNA. The ddPCR technique provides more sensitive and precise quantitation of the AE gene during disease progression and relapse. Quantification of the AE fusion gene by ddPCR further contributes to improved prognosis. Our study provides valuable methods for dynamic surveillance of AE fusion DNA and assistance in determining the prognosis.     

Eriocalyxin B induces apoptosis of t(8;21) leukemia cells through NF-kappaB and MAPK signaling pathways and triggers degradation of AML1-ETO oncoprotein in a caspase-3-dependent manner

Diterpenoids isolated from Labiatae family herbs have strong antitumor activities with low toxicity. In this study, Eriocalyxin B (EriB), a diterpenoid extracted from Isodon eriocalyx, was tested on human leukemia/lymphoma cells and murine leukemia models. Acute myeloid leukemia cell line Kasumi-1 was most sensitive to EriB. Significant apoptosis was observed, concomitant with Bcl-2/Bcl-XL downregulation, mitochondrial instability and caspase-3 activation. AML1-ETO oncoprotein was degraded in parallel to caspase-3 activation. EriB-mediated apoptosis was associated with NF-kappaB inactivation by preventing NF-kappaB nuclear translocation and inducing IkappaBalpha cleavage, and disturbance of MAPK pathway by downregulating ERK1/2 phosphorylation and activating AP-1. Without affecting normal hematopoietic progenitor cells proliferation, EriB was effective on primary t(8;21) leukemia blasts and caused AML1-ETO degradation. In murine t(8;21) leukemia models, EriB remarkably prolonged the survival time or decreased the xenograft tumor size. Together, EriB might be a potential treatment for t(8;21) leukemia by targeting AML1-ETO oncoprotein and activating apoptosis pathways.     

Geographic heterogeneity of the AML1-ETO fusion gene in Iranian patients with acute myeloid leukemia

Background:

The human AML1 gene, located on chromosome 21, can be fused to the AML1- eight-twenty-one (ETO) oncoprotein on chromosome eight, resulting in a t(8;21)(q22;q22) translocation. Acute myeloid leukemia (AML) associated with this translocation is considered a distinct AML with a favorable prognosis. Due to the various incidences of the translocation, which is associated with geographic diversities, investigation of molecular epidemiology is important to increase the awareness of physicians and hematologists regarding the frequency this chromosomal aberration.

Methods:

The patients were classified according to the French–American–British classification into eight groups: M0–M7. Determination of the prevalence of the AML1-ETO fusion gene was accomplished by TaqMan real-time PCR. Bone marrow samples from 113 patients with newly-diagnosed, untreated AML -M1, -M2, and -M4, and 20 healthy controls admitted to the Ghaem Hospital in Mashhad, Iran were studied.

Results:

The AML1-ETO fusion gene was detected up 50% of the M2 subgroup and absent in the M1 and M4 subtypes and healthy controls. Comparison of the prevalence of the t(8;21) translocation with results of previous studies showed that it varies between countries. This result may be due to geographic or ethnic differences, or both.

Conclusions:

The relatively high prevalence of the t(8;21) translocation in Iran was similar to that found in other Asian countries. It was closely associated with female gender, relatively young age, and FAB-M2 subtype. Its distribution varied considerably with geographic area. Therefore, further studies are needed to provide epidemiological data important for the establishment of optimal therapeutic strategies applicable to patients of each region. Key Words: Acute myeloid leukemia, AML1-ETO, M2, Prevalence, t(8;21)     

Acute myeloid leukemia with translocation (1;21)

Advancement in genetic and molecular biology techniques has greatly helped our understanding of various diseases, especially hematological disorders. We describe a case of primary myelofibrosis (PMF) that transformed into acute myeloid leukemia with a very rare and unusual genetic translocation of (1;21). There are only five reported cases of this translocation in acute myeloid leukemia (AML) or myelodysplastic syndrome but none of them transformed from PMF. This case not only highlights the importance of rare genetic translocations but also provides the natural history of the disease and its poor prognosis. To the best of our knowledge our patient is the first reported case of AML transformed from PMF to have this unique translocation of (1;21).     

Systemic mastocytosis associated with t(8;21)(q22;q22) acute myeloid leukemia

Although KIT mutations are present in 20–25% of cases of t(8;21)(q22;q22) acute myeloid leukemia (AML), concurrent development of systemic mastocytosis (SM) is exceedingly rare. We examined the clinicopathologic features of SM associated with t(8;21)(q22;q22) AML in ten patients (six from our institutions and four from published literature) with t(8;21) AML and SM. In the majority of these cases, a definitive diagnosis of SM was made after chemotherapy, when the mast cell infiltrates were prominent. Deletion 9q was an additional cytogenetic abnormality in four cases. Four of the ten patients failed to achieve remission after standard chemotherapy and seven of the ten patients have died of AML. In the two patients who achieved durable remission after allogeneic hematopoietic stem cell transplant, recipient-derived neoplastic bone marrow mast cells persisted despite leukemic remission. SM associated with t(8;21) AML carries a dismal prognosis; therefore, detection of concurrent SM at diagnosis of t(8;21) AML has important prognostic implications.     

C/EBPalpha S248A mutation reduces granulocytic differentiation in human leukemic K562 cells

Phosphorylation of C/EBPα can either lead to granulocytic differentiation or a block in granulopoiesis. This dichotomy in effect is dependent on the upstream signaling pathway and the phosphorylation site in C/EBPα. Ras signaling induced phosphorylation of S248 residue of C/EBPα is known to enhance granulocytic differentiation. In this study, using β-estradiol inducible stable cell lines we show that the point mutation of phosphorylation site S248 in C/EBP disrupts the CD11b and GCSFr expression and subsequently reduces the differentiation of leukemic K562 cells. Based on our observations in the present study, we conclude that S248A mutation of C/EBPα leads to a reduction of granulocytic differentiation markers and a block in differentiation at the morphological level.     

Altered chromatin modifications in AML1/RUNX1 breakpoint regions involved in (8;21) translocation

The RUNX1/AML1 gene is the most frequent target for chromosomal translocation, and often identified as a site for reciprocal rearrangement of chromosomes 8 and 21 in patients with acute myelogenous leukemia. Virtually all chromosome translocations in leukemia show no consistent homologous sequences at the breakpoint regions. However, specific chromatin elements (DNase I and topoisomerase II cleavage) have been found at the breakpoints of some genes suggesting that structural motifs are determinant for the double strand DNA-breaks. We analyzed the chromatin organization at intron 5 of the RUNX1 gene where all the sequenced breakpoints involved in t(8;21) have been mapped. Using chromatin immunoprecipitation assays we show that chromatin organization at intron 5 of the RUNX1 gene is different in HL-60 and HeLa cells. Two distinct features mark the intron 5 in cells expressing RUNX1: a complete lack or significantly reduced levels of Histone H1 and enrichment of hyperacetylated histone H3. Strikingly, induction of DNA damage resulted in formation of t(8;21) in HL-60 but not in HeLa cells. Taken together, our results suggest that H1 depletion and/or histone H3 hyperacetylation may have a linkage with an increase susceptibility of specific chromosomal regions to undergo translocations.     

Complex chromosome abnormality mimicking t(8;21)in an acute myeloblastic leukemia

A patient with acute myeloblastic leukemia (AML) and karyotypic abnormality mimicking t(8;21) is reported. Because of the uncommon morphology of blasts for AML with t(8;21), and absence of AML1-ETO fusion in the RT-PCR analysis, fluorescence in situ hybridization (FISH) was applied to precise the abnormality. FISH revealed a complex rearrangement involving chromosomes 7, 21 and 8, and involvement of the AML1 gene without evidence of AML1-ETO fusion. This case of unusual AML illustrates the necessity of collecting all hematologic, cytogenetic, and eventual FISH and RT-PCR data to analyse genetic rearrangements in leukemic patients.     

Ring chromosome 8 and translocation t(8;21) in a patient with acute myeloblastic leukemia

Recurrent translocation t(8;21)(q22;q22) acute myeloid leukemia (AML) is often associated with secondary chromosome changes of which the clinical significance is not clear since they do not seem to impair the prognosis. Uncommon chromosome changes may lead to the identification of leukemogenetic factors associated with t(8;21) since the AML1/RUNX1-ETO fusion gene resulting from the translocation is thought to be unable alone to induce leukemia. We here report a patient with AML, t(8;21) and ring chromosome 8 resulting in partial chromosome 8 deletion. Another patient with partial 8q deletion has been previously reported. It is suggested that more attention be paid to the genes located in distal 8q in relation to leukemogenesis.     

Efficacy of a combination therapy targeting CDK4/6 and autophagy in a mouse xenograft model of t(8;21) acute myeloid leukemia

One of the most frequent cytogenetic abnormalities in acute myeloid leukemia (AML) is t(8;21). Although patients with t(8;21) AML have a more favorable prognosis than other cytogenetic subgroups, relapse is still common and novel therapeutic approaches are needed. A recent study showed that t(8;21) AML is characterized by CCND2 deregulation and that co-inhibition of CDK4/6 and autophagy induces apoptosis in t(8;21) AML cells. In this study, we examined the in vivo effects of co-inhibiting CDK4/6 and autophagy. We used a mouse model in which t(8;21)-positive Kasumi-1 cells were subcutaneously inoculated into NOD/Shi-scid IL2Rg^null mice. The mice were treated with the autophagy inhibitor chloroquine (CQ), a CDK4/6 inhibitor (either abemaciclib or palbociclib), or a CDK4/6 inhibitor plus CQ. After 20 days of treatment, tumor volume was measured, and immunostaining and transmission electron microscopy observations were performed. There was no change in tumor growth in CQ-treated mice. However, mice treated with a CDK4/6 inhibitor plus CQ had significantly less tumor growth than mice treated with a CDK4/6 inhibitor alone. CDK4/6 inhibitor treatment increased the formation of autophagosomes. The number of single-strand DNA-positive (apoptotic) cells was significantly higher in the tumors of mice treated with a CDK4/6 inhibitor plus CQ than in mice treated with either CQ or a CDK4/6 inhibitor. These results show that CDK4/6 inhibition induces autophagy, and that co-inhibition of CDK4/6 and autophagy induces apoptosis in t(8;21) AML cells in vivo. The results suggest that inhibiting CDK4/6 and autophagy could be a novel and promising therapeutic strategy in t(8;21) AML.     

In vitro catalytic activities of DNA/RNA chimeric hammerhead ribozymes against AML1-MTG8 mRNA, a fused gene transcript in acute myeloid leukemia with t(8;21)

In order to design the best construct for therapeutic hammerhead ribozymes against AML1-MTG8, the t(8;21)-associated fusion mRNA of acute myeloid leukemia, we synthesized DNA/RNA chimeric ribozymes directed to the area adjacent to the fusion point between AML1 and MTG8. Catalytic efficiency and fusion gene specificity of ribozymes were examined by kinetic studies of the cleavage reactions of AML1-MTG8, AML1, and MTG8 RNAs transcribed in vitro. Ribozyme 2 (Rz2) specifically cleaved AML1-MTG8 RNA at three nucleotides downstream of the fusion junction with high efficiency. The highest cleavage efficiency was achieved by Rz4.3, which targeted non-contiguous sequences and cleaved at 19 nucleotides downstream of the fusion junction. Rz4.3 also cleaved MTG8 RNA but the cleavage efficiency was three orders of magnitude lower than that for AML1-MTG8 RNA. Therefore, Rz4.3 and Rz2 are the proper ribozymes for in vivo application to modulate gene expression of the AML1-MTG8.     

A case of acute myeloid leukemia-M2 with trisomy 4 in addition to t(8;21)

t(8;21)(q22;q22) is the most frequently observed karyotypic abnormality associated with acute myeloid leukemia (AML), specifically in FAB-M2. Short-term unstimulated bone marrow (BM) and peripheral blood lymphocyte culture showed 47,XX, +4,t(8;21) in all metaphase plates; and interphase and metaphase results of AML-ETO fusion was positive and trisomy of 4 was confirmed with WCP probes. Trisomy 4 in AML with t(8;21) is a rare numerical abnormality. Here we present such case of patient which may constitute a distinctive subtype.