PB1920 BCR‐ABL GENE ABL KINASE DOMAIN MUTATIONS IN IMATINIB RESISTANT CHRONIC MYELOID LEUKEMIA PATIENTS FROM AZERBAIJAN
Authors: Asadov C. , Hasanova A. , Shirinova A. , Karimova N. , Alimirzoeva Z. 
Published: June 2019

Background:

While chronic myeloid leukemia (CML) can successfully be treated with tyrosine kinase inhibitors, point mutations within ABL kinase domain of the BCR‐ABL gene are the most common cause of resistance to Imatinib Mesylate. More than 100 BCR‐ABL1 kinase domain point mutations with various frequencies of incidence, domain positions and implications on tyrosine kinase inhibitors (TKI) response in CML are associated with TKI resistance.

Aims:

To assess the frequency and type of ABL kinase domain mutations in Imatinib resistant CML patients.

Methods:

115 Imatinib resistant CML patients having been observed during the period from 2014 to 2018. 90 patients at the time of diagnosis were in the chronic phase (78.3%), 19 patients in the acceleration phase (16.5%) and 6 patients in the blast crisis phase (5.2%). By risk groups by Socal et al., the patients were distributed as: low risk ‐ 35 patients; the average risk is 67 patients; high risk ‐ 13 patients. Total RNA was isolated from whole blood and reverse‐transcribed. The resulting cDNA was subjected to an initial round of RT‐PCR across the BCR‐ABL1 breakpoint followed by a second round to amplify the sequence. The final PCR product was pyrosequenced. A total of 14 mutations were identified. Statistical analysis was performed using SPSS 25.0 (IBM, USA) with Chi‐Square. Critical p‐value was set to 0.05.

Results:

115 Imatinib resistant CML patients were analyzed, 44.3% men (n = 51) and 55.7% women (n = 64), average age – 45.3 ± 14.8 (from 16 to 80). BCR‐ABL1 mutations were found in 16.5% (19/115) CML patients. 7 different mutation variants were identified in 19 patients (Y253H – 2, E255K – 1, F317L (TTG) – 2, F317L (TTA) – 1, T315I – 7, F359 V – 3, F359C ‐ 3). Mutations Y253F, E255 V, V299L(CTG), V299L(TTG), F317 V, F317L(CTC), T315A didn’t identified. Mutation associated resistance rate was higher in men than in women (24.5% against 7.8%, p = 0,025). Also these mutations were analyzed between the group of patients aged ≥50 and <50. The results were 20.45 % and 14.08 %, respectively, p = 0.371. In men and women, T315I mutation prevailed, which occurred in 9.8% and 3.1% of cases, respectively, p = 0.136. In addition, the mutations identified in men were Y253H ‐ 2 (3.92%), F317L (TTG) ‐ 2 (3.92%), F359 V ‐ 2 (3.92%), F359C ‐ 2 (3.92%), E255K ‐ 1 (1.96%), and in women, F317L (TTG) ‐ 1 (1.56%), F359 V ‐ 1 (1.56%), F359C ‐ 1 (1.56%). Studying the frequencies of mutations in the different phases of the disease allowed us to establish that mutations were detected in 10 patients in the chronic phase, which accounted for 11.1% of the total number of patients in this phase, and they were detected in 5 patients in the acceleration phase (26.3%), and in 4 patients in the blast crisis phase (66.7%), p = 0.0008. Studying the distribution of mutations by risk groups showed that mutations were detected in 2 patients in the high‐risk group, which accounted for 15.4% of the total number of patients in this group, in 12 patients in the medium‐risk group, (17.9%), and in 5 patients in the low‐risk group (14.3%), p = 0.890.

Summary/Conclusion:

Since different mutations of the kinase domain of BCR‐ABL1 are associated with different types of resistance to TKI, identifying trends in the distribution of mutations in CML patients receiving TKI treatment is very important for choosing treatment strategy and early prediction of therapy resistance.