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

The prognostic importance of BCR-ABL transcripts in Chronic Myeloid Leukemia: A systematic review and meta-analysis

BACKGROUND

Chronic Myeloid Leukemia (CML) is characterized by the overproduction of BCR-ABL, a tyrosine kinase with constitutive activity, in which the majority of CML patients have e13a2 or e14a2 transcripts. Reckoned the possible associations between the hematologic and molecular features of the disease, a profound understanding of different aspects of this neoplasm would be provided.

METHOD

The authors implemented a systematic literature search, utilizing the terms published articles or internationally accepted abstracts from PubMed, Embase, Medline, Cochrane library before January 2019. Weighted mean proportion and 95 % confidence intervals (CIs) of CML prevalence calculated using a fixed-effects and a random-effects model. Statistical heterogeneity was evaluated using the I2 statistic.

RESULTS

34 studies for a total of 54,034 Patients were selected and included in the review. Results revealed that compared to e13a2 group, the overall estimated prevalence is much higher in the e14a2 (39 % and 54 %, respectively). Besides, the overall estimated prevalence ratio of male to female was higher in the e13a2 group in comparison to e14a2 (1.08 and 0.856 respectively). The overall estimated prevalence of dual transcription of e13a2/e14a2 was 1.11 %, and male/female overall estimated prevalence ratio was 1.18.

CONCLUSION

This meta-analysis of CML patients demonstrated the e14a2 as the more common transcript type. Usually, the e14a2 transcript is prevalent in females, whereas e13a2 and dual transcription of e13a2/e14a2 are more common in men. These data explicate that the differences in proportion are not by chance. This is crucial, as the transcript type is a variable suspected to be of prognostic importance for the treatment-related response, the outcome of treatment, and the rate of treatment-free remission.

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.

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.