Changes in expression of apoptosis-related genes are linked to the molecular response to imatinib treatment in chronic-phase chronic myeloid leukemia patients

Prevalence of Abelson murine leukemia viral oncogene homolog-breakpoint cluster region fusions and correlation with peripheral blood parameters in chronic myelogenous leukemia patients in Lorestan Province, Iran

Context:

Chronic myelogenous leukemia (CML) is a chronic malignancy of myeloid linage associated with a significant increase in granulocytes in bone marrow and peripheral blood. CML diagnosis is based on detection of Philadelphia chromosome and “Abelson murine leukemia viral oncogene homolog” (ABL)-“breakpoint cluster region protein” fusions (ABL-BCR fusions).

Aims:

In this study, patients with CML morphology were studied according to ABL-BCR fusions and the relationship between the fusions and peripheral blood cell changes was examined.

Materials and Methods:

All patients suspected to chronic myeloproliferative disorders in Lorestan Province visiting subspecialist hematology clinics who were confirmed by oncologist were studied over a period of 5 years. After completing basic data questionnaire, blood samples were obtained with informed consent from the patients. Blood cell count and morphology were investigated and RNA was extracted from blood samples. cDNA was synthesized from RNA and ABL-BCR fusions including b3a2 and b2a2 (protein 210 kd or p210), e1a2 (protein 190 kdor p190), and e19a2 (protein 230 kdor p230) were studied by multiplex reverse transcription polymerase chain reaction method. Coexistence of e1a2 and b2a2 (p210/p190) fusions was also studied. The prevalence of mutations and their correlation with the blood parameters were statistically analyzed.

Results:

Of 58 patients positive for ABL-BCR fusion, 18 (30.5%) had b2a2 fusion, 37 (62.71%) had b3a2 fusion and three (3.08%) had e1a2 fusion. Coexistence of e1a2 and b2a2 (p210/p190) was not observed. There was no significant correlation between ABL-BCR fusions and white blood cell count, platelet count, and hemoglobin concentration.

Conclusions:

The ABL-BCR fusions in Lorestan Province were similar to other studies in Iran, and b3a2 fusion had the highest prevalence in the studied patients studied.

BCL2 gene polymorphisms and splicing variants in chronic myeloid leukemia

Recent data suggest that constitutional genetic variation in the antiapoptotic BCL2 gene could be associated with the susceptibility to develop chronic myeloid leukemia (CML) and the clinical outcome in several hematological malignancies. The present study examines whether BCL2 single nucleotide polymorphisms (SNPs) predispose to CML or may potentially influence the disease characteristics at diagnosis. Notably, no association was observed between the four candidate BCL2 SNPs and the risk of developing CML. Instead, the 4777C>A (rs2279115) and the 5735A>G (rs1801018) SNPs were significantly associated with the disease risk profile as determined by the Sokal score. We found that such polymorphisms correlated with the expression of BCL2 alternative splicing transcripts (BCL2-α, BCL2-β) in healthy donors, but not in CML patients, although the relative levels of BCL2 mRNA splicing variants were shown to change during the clinical course of CML. Our findings suggest that BCL2 polymorphisms could influence the clinical features of CML patients at diagnosis. However, the pathogenic mechanisms involved in such association remain to be ascertained.

BAX/BCL-XL gene expression ratio inversely correlates with disease progression in chronic myeloid leukemia

BCR-ABL fusion gene is implicated in the pathogenesis of chronic myeloid leukemia (CML), encoding the oncoprotein p210(BCR-ABL) with anti-apoptotic activity. The inability to undergo apoptosis is an important mechanism of drug resistance and neoplastic evolution in CML. The gene transcript expression of mitochondrial apoptotic related genes BAX and BCL-XL was evaluated by quantitative Real Time PCR (qPCR) in vitro in K562 cells and in vivo in peripheral blood of 66 CML patients in different stages of the disease: 13 cases at diagnosis, 34 in chronic phase (CP), 10 in accelerated phase (AP) and 9 in blast crisis (BC). Our results in K562 cells showed that all treatments with different tyrosine kinase inhibitors (TKIs) induced a decreased expression of the antiapoptotic oncogene BCL-XL, whereas the proapoptotic gene BAX remains constant with minor modifications. A significantly lower BAX/BCL-XL expression ratio (mean±SEM) than a group of healthy individuals (4.8±0.59) were observed in CML patients at diagnosis (1.28 ± 0.16), in AP (1.14±0.20), in BC (1.16±0.30) and in 18% of cases of patients in CP (2.71±0.40). Most CP cases (82%) showed a significantly increased ratio (10.03±1.30), indicating that the treatment with TKIs efficiently inhibited the expression of BCL-XL by blocking BCR-ABL oncoprotein. The BAX/BCL-XL ratio showed a significant inverse correlation (Spearman P<0.0001) with BCR-ABL/ABL relative expression indicating that low BAX/BCL-XL was associated with disease progression. Accordingly, the follow up of a cohort of eight cases during 6months from diagnosis showed that while the BAX/BCL-XL ratio rapidly increased after treatment in seven cases with good evolution, it decreased in the single case that showed rapid evolution and short survival. Our data suggest that BAX/BCL-XL expression ratio may be a sensitive monitor of disease progression and an early predictor of TKI therapy responsiveness in CML patients.

Genetic variants in the candidate genes of the apoptosis pathway and susceptibility to chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder, characterized by the presence of BCR/ABL fusion gene. It is unclear which cellular events drive BCR/ABL gene translocation or initiate leukemogenesis in CML. Bcl-2 promotes survival of hematopoietic stem cells. Accordingly, apoptosis-related pathway may involve in the leukemogenesis of CML. In the current study, we evaluated 80 single nucleotide polymorphism (SNP) markers involved in the pathways of apoptosis (n = 30), angiogenesis (n = 7), myeloid cell growth (n = 14), xenobiotic metabolism (n = 13), WT1 signaling (n = 7), interferon signaling (n = 4), and others (n = 5) in 170 CML patients and 182 healthy controls. In a single-marker analysis, the following SNPs were identified including VEGFA, BCL2, CASP7, JAK3, CSF3, and HOCT1. In the multivariate logistic model with these SNPs and covariates, only BCL2 (rs1801018) was significantly associated with the susceptibility to CML (P = .05; odds ratio [OR] 2.16 [1.00-4.68]). In haplotype analyses, haplotype block of BCL2 consistently showed significant association with the susceptibility to CML. Risk allele analysis showed that a greater number of risk alleles from BCL2 SNP correlated to increasing risk of CML (overall P = .1, OR 1.84 [1.06-3.22] for 3-4 risk alleles vs 0-1 risk alleles). The current study indicated that BCL2 SNP seemed to be associated with increasing susceptibility to CML.