Incidence of BCR-ABL transcript variants in patients with chronic myeloid leukemia: Their correlation with presenting features, risk scores and response to treatment with imatinib mesylate

Chronic-phase chronic myeloid leukemia: Incidence of BCR/ABL transcript and its correlation with presenting features, response to treatment, and survival

Introduction

Chronic myeloid leukemia (CML) is characterized by Philadelphia chromosome resulting in the fusion between the BCR gene, located on chromosome 22, and the ABL gene on chromosome 9. The prognostic significance of BCR-ABL transcript variants in CML is controversial. The aim of the current study was to evaluate the clinico-hematological presentation and evolution of the disease, response to treatment and survival according to transcript type in chronic phase CML patients.

Results

The median age of our population was 50 years with a slight female predominance (sex-ratio 0.78). Sixty percent had the b3a2 transcript and 34% had the b2a2 type. Patients with the co-expression of these two transcripts (4.5%) and those with e19a2 were excluded from the analysis. Patients with b3a2 subtype were associated significantly with thrombocytosis (p = 0.006) and higher Sokal score (p = 0.038) compared to those with b2a2 transcript. The two isolated transcripts were not significantly associated with gender, age group, blast cell percentage or the identified ranges of spleen size. Complete cytogenetic response at 12 months for b3a2 patients and b2a2 patients was 78.6% and 21.4% respectively. This difference was statistically significant (p = 0.001, HR = 9.5, 95% CI 6.5-13.7). Patients with b3a2 transcript had a higher rate of optimal molecular response at 3 months (p = 0.04, HR = 4.2, 95% CI 1-17.3) and major molecular response at 12 months (p = 0.004, HR = 4.9, 95%CI 1.5-15.1). At the date of last follow-up, most patients achieving deep molecular response (MR4 or deeper) belonged to b3a2 group (79%) (p = 0.003, HR = 5.2, 95% CI 1.6-16.4). We did not find a significant difference in OS and EFS between the two groups.

Conclusion

Our study concluded that b2a2 transcript is a prognostic factor in cytogenetic and molecular response but further studies are needed to complete this aspect.

Association between the BCR-ABL gene transcripts and the laboratory hematological profile

Objective: This study describes the hematological parameters associated with the BCR-ABL gene transcripts in patients with chronic myeloid leukemia (CML). Methods: We reviewed the results of 100 detectable patients for one of the BCR-ABL gene transcripts. The eligibility criteria were based on the presence of one of the leukemic transcripts (b2a2, b3a2, and b2a2/b3a2) and complete epidemiological and hematological data. The data were obtained from the LabMaster computerized system. The Kruskal-Wallis test was used to compare the medians of the quantitative variables between the transcripts of the BCR-ABL gene and the chi-square test to compare the qualitative ones, adopting the p-value with a level of significance less than or equal to 0.05. Results: Forty-five patients (45%) presented the b2a2 transcript, 24 (24%) the b3a2 transcript and 31 (31%) a b2a2/b3a2 coexpression. Individuals who expressed the b3a2 transcript had higher leukocyte counts and platelet levels, but we found no differences compared with individuals who expressed the other transcript. Conclusion: In this study, the BCR-ABL gene transcripts did not influence the hematological parameters of patients with CML.

Characteristics of BCR-ABL gene variants in patients of chronic myeloid leukemia

Background

Depending on breakpoints of rearrangement different types of BCR–ABL fusion protein can be generated in patients of chronic myeloid leukemia (CML). The aim of this study is to observe frequencies of major transcripts in CML patients by reverse transcriptase polymerase chain reaction (RT-PCR) and their hematological features at the time of presentation.

Materials and methods

This cross sectional study was performed at Molecular Lab of Riphah International University, Islamabad from January to June 2019. Consecutive peripheral blood samples of 70 newly diagnosed CML patients in chronic phase were analyzed by RT-PCR to detect different BCR–ABL transcripts. Routine blood cell counts were assessed by an automated hematology analyzer.

Results

All samples expressed typical BCR–ABL rearrangement. Expression of either e14a2 or e13a2 transcript was detected in 38 (54%) and 30 (43%) patients, respectively. Coexpression of e13a2 + e14a2 was found in 2 (3%) patients. The mean total leukocyte count was higher in group expressing e13a2 (P = 0.01). Higher mean platelet count was noted in patients with e14a2 transcript, but this difference was statistically insignificant (P = 0.1). The association of male gender was observed with the group exhibiting e14a2 (P = 0.01). There was no statistically significant association between transcript type and different ranges of age, hemoglobin levels, and platelet and total leukocyte counts (P > 0.05).

Conclusion

e14a2 transcript was most common transcript in CML patients. Patients exhibiting e13a2 subgroup presented with significantly higher mean white blood cell count at the time of presentation. Significantly higher proportion of male patients was found to express e14a2 transcript over e13a2.

Assessment of BCR-ABL1 Fusion Transcripts and Their Association with Response to Imatinib Treatment in Chronic Myeloid Leukemia Patients

Objectives: BCR-ABL1 fusion transcripts with contrasting data on response to imatinib therapy have been reported from different parts of the world. Hence, the present study aimed to determine the frequencies of transcripts and their association with response to imatinib therapy in chronic myeloid leukemia (CML) patients. Methods: A total of 170 (76 follow-up and 94 imatinib-resistant) CML samples were included in the study. BCR-ABL1 fusion transcripts and expression status were analyzed in all cases using multiplex reverse transcriptase PCyR and real-time PCyR. Sanger sequencing was used for tyrosine kinase domain (TKD) mutation screening in imatinib mesylate-resistant patients. Results: Of 170 CML patients, 36.36% showed b2a2, 63.53% had b3a2, and 2.94% had b2a2 + b3a2 isoforms. Mean platelet counts and blasts were significantly lower in b2a2 carriers (P = 0.0092; P ≤ 0.0001). Patients with b2a2 transcript were found to be more in responders group (both hematological and cytogenetic), whereas b3a2 patients were more in partial responders group and death (P = 0.763; P = 0.309). In follow-up patients, mean baseline BCR-ABL1 expression levels are significantly higher in b2a2 versus b3a2 carriers (P = 0.0351). Of 94 imatinib-resistant patients, 36 (38.29%) had acquired TKD mutations. Among 36 patients, mean BCR-ABL1 levels are significantly higher in b2a2 and b2a2 + b3a2 group (P = 0.0002; P ≤ 0.0001). TKD mutation frequency was more in b3a2 (61.11%) compared to other types. With respect to follow-up status in 36 patients, 17 patients died while 19 were on imatinib higher doses or 2nd-generation tyrosine kinase inhibitors. Of 17 patients, 41.66% had b2a2 transcript and 54.54% had b3a2 transcript. Conclusion: Patients with b3a2 transcripts might be associated with poor response and worse prognosis in CML with imatinib treatment.

Serum Estrogen and its Soluble Receptor Levels in Egyptian Patients with Chronic Myeloid Leukemia: A Case–Control Study

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder. CML cells contain a BCR-ABL gene, not typically found in normal cells that produce a protein (BCR-ABL) causing CML cells to proliferate. CML occurs in three phases: chronic, accelerated and blast crisis. Disease staging is primarily based on percent of blasts in the blood and bone marrow. Most cases of CML are diagnosed in chronic phase (CP). The major objective in CML clinical management is to prevent progression from chronic to accelerated and blast crisis phases. While earlier treatments, such as cytoreductive chemo- and interferon therapies increased overall survival rates among patients, the advent of tyrosine-kinase inhibitors (TKIs) have changed the CML treatment landscape. Despite the widespread use of these therapies, there have also been associated side effects that could potentially affect its use. Also it is necessary to avoid all deaths and complications related to the treatment, by limiting as much as possible the side-effects of the treatment while ensuring the compliance of the patients. The aim of this work was to measure the serum estrogen and its soluble receptor levels in patients with chronic myeloid leukemia in order to extrapolate their possible clinical significance. The present study included 40 (20 males and 20 females) healthy volunteers clinically free from any disease, 40 (20 males and 20 females) patients of newly diagnosed CML. Blood samples were collected from all subjects and the level of serum estrogen (E2) and serum soluble estrogen receptor (ER) were measured by enzyme linked immunosorbent assay (ELISA). The level of serum E2 (pg/ml) in both male and female patients groups with CML was significantly higher than in control group. The level of serum ER (ng/ml) in both male and female patients groups with CML was significantly lower than in control group. Estimating the serum level of E2 and soluble ER is of informative diagnostic value. Estimation serum level of E2 and soluble ER in patients with CML is of value in deciding use of antiestrogen as therapeutic target in treatment protocol.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12288-021-01451-8.

Impact of the major BCR-ABL1 transcript type on clinical and biological parameters and molecular response in patients with chronic myeloid leukemia

AIM

In chronic myeloid leukemia (CML), the impact of MBCR-ABL1 major transcript type on disease phenotype and response to treatment still controversial to date. This work aims to study the influence of Mb3a2 and Mb2a2 transcripts on clinico-biological parameters and the molecular response in patients with chronic phase chronic myeloid leukemia (CP-CML) treated with Imatinib as frontline therapy.

METHODS

This is six years prospective study started in March 1 st, 2013. 67 patients with newly CP-CML were treated by Imatinib as frontline therapy. Clinical and biological characteristics disease were collected for all patients. Molecular typing was performed by multiplex RT-PCR and quantification of transcripts by real-time quantitative PCR (qRT-PCR). The cumulative incidence of deep molecular response (DMR) was estimated by the Kaplan-Meier method. The comparison was made using the parametric Log-Rank test. A value of P ≤ 0.05 is considered significant.

RESULTS

61% of patients expressed b3a2, 35.82% b2a2 and 2.98% expressed a rare transcript of type e19a2. At diagnosis, the b2a2 type had a higher level of expression than that of b3a2 (67.92 vs 53.79%; P = 0.03). This insignificant difference between the two transcript subgroups was also observed for rates below 1% at 6 months (54 vs 39; P = 0.26) and below 0.1% (54 vs 44 %; P = 0.50), (77 vs 50%; P = 0.09) and (81 vs 78 %; P = 0.52) at 12, 18 and 24 months respectively. The two types of transcript had almost the same kinetics. Nevertheless, the absolute value of the BCR-ABL1/ABL ratio decrease was faster in the group of patients expressing b3a2, than in those expressing b2a2. At 18 months post IM therapy, patients with a b3a2 transcript have a trend of better MMR that those with b2a2 (77 vs 50%; P = 0.09). The DMR was not significantly different between two groups at 24 months (50 vs 32%; P = 0.20) and 36 months (75 vs 70%; P = 0.54) respectively. The cumulative probability of achieving MRD at 5 years was higher in patients with b3a2 type but not statistically significant; (85 vs. 68%; P = 0.17).

CONCLUSION

Patients with b3a2 transcript may be associated with a better response to Imatinib therapy.

Comparison of BCR-ABL Transcript Variants Between Patients With Chronic Myeloid Leukaemia and Leukaemia Cell Lines

BACKGROUND/AIM

Chronic myeloid leukaemia (CML) is a myeloproliferative disorder characterized by the presence of breakpoint cluster region-Abelson murine leukemia (BCR-ABL1) gene fusion as a hallmark that is expressed as two major transcripts b2a2 and b3a2. The aim of this study was to compare the BCR-ABL transcripts in the blood cells of patients with CML, and in chemoresistant and chemosensitive CML cell lines to validate their use as a good method to elucidate CML biology.

MATERIALS AND METHODS

Twelve patients with CML and CML cell lines (K562, K562-LUCENA and FEPS) were analyzed by real-time polymerase chain reaction to evaluate gene expression of BCR-ABL transcripts.

RESULTS

All patients had the same expression levels of b2a2 and b3a3 transcripts, however, CML cell lines presented only b3a2 expression. There were no significant differences in absolute b3a2 expression between patients and CML cell lines.

CONCLUSION

CML cell lines provide a good in vitro alternative in that they have the same BCR-ABL expression as patients.

Association of BCR/ABL transcript variants with different blood parameters and demographic features in Iraqi chronic myeloid leukemia patients

Background

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of BCR‐ABL fusion gene (GenBank accession NC_000022.11). In the vast majority of CML patients, the typical subtype of BCR‐ABL transcript are b3a2, b2a2 or both. The aim of this study was to determine the different subtypes of BCR‐ABL transcript and their impact on the demographic and hematological parameters in Iraqi patients with CML.

Methods

One hundred patients with chronic phase CML (11 newly diagnosed and 89 imatinib‐resistant) were enrolled in this study. Ribonucleic acid (RNA) was extracted from leukocytes, and complementary DNA was created using reverse transcriptase polymerase chain reaction technique. A multiplex polymerase chain reaction with four specific primers was used to determine the BCR‐ABL fusion subtypes in each patient.

Results

Male to female ratio was 1.38:1. Fifty‐nine patients expressed b3a2 transcript, whereas 39 of the remaining cases were positive for b2a2 variant. One case expressed b2a3 transcript, while the last case coexpressed the two subtypes of mRNA b3a2/b2a2. Male and female were significantly associated with b3a2 and b2a2 subtypes, respectively. The b3a2 subtype showed higher total leukocyte count than b2a2 subgroup, while b2a2 variant demonstrated significantly elevated platelet counts compared to those with b3a2 transcript. A significantly higher plateletcrit percentage (PCT%) was found in patients with b2a2 transcript whereas.

Conclusions

The testified Iraqi group expressed M‐BCR‐ABL type with preponderance of b3a2 over b2a2 subtype. There was a gender‐skewed distribution in BCR‐ABL transcript types with b3a2 transcript more prevalent in males. The type of BCR‐ABL transcript is reflected by different leukocyte and platelet counts at diagnosis, which might represent a distinct phenotype and disease biology.

Novel mutations in the kinase domain of BCR-ABL gene causing imatinib resistance in chronic myeloid leukemia patients

Mutations in the drug binding region of BCR-ABL lead to imatinib resistance during the management of chronic myeloid leukemia (CML). In our study, 62 Philadelphia positive (Ph⁺) CML patients showing conspicuous expression of BCR-ABL gene were treated with imatinib. At the end of 3 months, 21/62 (33.87%) patients did not obtain complete hematological response (CHR) and also showed no significant decrease in BCR-ABL gene expression. In all the imatinib-resistant patients BCR-ABL gene was PCR amplified and sequenced. The sequence analysis showed four novel missense mutations p.(Leu301Ile), p.(Tyr320His), p.(Glu373Asp), p.(Asp381Asn) and six already reported mutations p.(Val256Gly), p.(Thr315Ile), p.(Gly250Glu), p.(Tyr253His), p.(Phe317Leu), p.(Met351Thr) which contributed in the formation of inactive enzyme and also two novel frameshift mutations p.(Glu281*) and p.(Tyr393*), which resulted in truncated protein formation. Further, the structural analysis revealed all these mutations affected P-loop, gatekeeper, catalytic and activation loop domain regions of the enzyme causing poor imatinib binding in the ATP region. The primary intention of the study was to find out the mutations in the BCR-ABL gene causing imatinib resistance. This study highlights the need for BCR-ABL gene sequence analysis to detect the mutations in CML patients in order to properly guide the therapy.

Molecular study of ABCB1 gene and its correlation with imatinib response in chronic myeloid leukemia

PURPOSE

The introduction and success of imatinib mesylate have become a paradigm shift in chronic myeloid leukemia (CML) treatment. However, despite its high efficiency, resistance to imatinib has emerged as a significant problem, which may in part be caused by pharmacogenetic variability. Three single-nucleotide polymorphisms (C1236T, G2677T/A, C3435T) and/or mRNA expression changes of ABCB1 gene were demonstrated to be associated with inter-individual variability of imatinib response in CML patients. In this study, we aimed to examine whether genetic variations and/or altered expression of ABCB1 gene may influence response to imatinib.

METHODS

Sixty nine CML Tunisian patients, undergoing imatinib therapy, were enrolled in this study. These were divided into two groups: responders and non-responders to imatinib. The relative transcript expression levels of ABCB1 gene and the distribution of allele and genotype frequency of ABCB1 SNPs were compared between these two categories of patients. Linkage disequilibrium tests and haplotypes analysis were also studied.

RESULTS

Our results showed that the mRNA expression level of ABCB1 gene did not differ significantly between the two categories of patients. In addition, results obtained from ABCB1 polymorphisms study and their correlation with imatinib response showed that the optimal response rate to imatinib did not differ significantly between C1236T, G2677T/A or C3435T genotypes. However, haplotype analysis showed that the 1236C-2677A-3435C haplotype was observed only in imatinib non-responders' patients suggesting that CAC haplotype was linked to higher risk of imatinib resistance.

CONCLUSION

Furthermore, analyses of ABCB1 haplotypes should be taken into account to study the relationship between ABCB1 genotypes and imatinib efficacy.

Translational progress on tumor biomarkers

There is an urgent need to apply basic research achievements to the clinic. In particular, mechanistic studies should be developed by bench researchers, depending upon clinical demands, in order to improve the survival and quality of life of cancer patients. To date, translational medicine has been addressed in cancer biology, particularly in the identification and characterization of novel tumor biomarkers. This review focuses on the recent achievements and clinical application prospects in tumor biomarkers based on translational medicine.