T315I MUTATIONS ARE CLUSTERED WITH ADVANCED PHASES CONTRARY TO OTHER ABERRATIONS IN CML PATIENTS RESISTANT TO TKI THERAPY

Sborník

Background. Various mechanisms of resistance to tyrosine kinase inhibitors (TKIs) in chronic myelogenous leukemia (CML) patients were described. Among them, mutations within BCR-ABL1 kinase domain are the most frequently studied, since they affect binding of TKI molecule. However, mechanisms leading to subsequent progression are still not fully elucidated. Inhibition of BCR-ABL1 by imatinib was suggested to induce p53 pathway, therefore, p53 inactivation could possibly influence therapy response. Beside this, mutations in genes involved in myeloid transformation (e.g. ASXL11 and CBL) were identified, and their role in disease progression is under investigation. Aims. We analyzed genomic aberrations and mutations in BCR-ABL1, TP53, ASXL1 and CBL genes in patients with primary or acquired resistance to TKIs therapy. Methods. Only patients that lost or never achieved major cytogenetic response were included in the study. Mutations in BCR-ABL1 kinase domain were detected using direct sequencing and T315I-specific ligation PCR. TP53 mutational status of exons 4-10 was examined by functional analysis (FASAY) coupled to direct sequencing. Mutational analysis of ASXL1 (exon 12) and CBL (exons 8, 9) genes was performed by direct sequencing of gDNA. Genomic changes were detected using conventional metaphase cytogenetics and Affymetrix 2.7M Cytogenetic arrays. Results. In total, 26 TKI-resistant CML patients were investigated. 6 patients were examined at the time of blast crisis and 4 in the accelerated phase. In 12 patients BCR-ABL1 mutation was identified at the time of genomic analyses, among them, 6 patients carried mutation T315I. Remaining patients (n=20) were additionally examined using T315I-specific ligation PCR, and this mutation was identified in 2 patients thereafter. Remarkably, from patients with T315I mutations (n=8), 7 were in advanced disease phase. Additional genomic aberrations were identified in 13/26 of patients. The detected changes included commonly observed large alterations (+8, -Y, i(17q)), cryptic copy number changes and uniparental disomy. Disruption of the p53 pathway was observed in 3 patients: one patient had TP53 gene deletion caused by i(17q), one harbored biallelic deletion of CDKN2A that codes for a protein stabilizing p53 protein, and in one patient a TP53 mutation was detected. The TP53 mutation was present after progression to the blast crisis and was not detected in chronic phase, when TKIs resistance was manifested. Mutation in the ASXL1 gene was identified in 9/26 patients, however, no mutation in the CBL gene was detected. Distribution of observed genetic and genomic lesions in individual CML patients is shown in the Figure 1. Mutation T315I clustered with advanced phases, while other changes seem to be distributed randomly. Conclusions. Patients with primary or acquired resistance to TKIs showed different pattern of gene mutations and genomic aberrations. TKI resistance in CML patients is probably not associated with alterations in the p53 pathway. Additional changes potentially influencing treatment response were found. However, most important event facilitating disease progression is likely the presence of T315I mutation in BCR-ABL1, as this mutation was identified in almost all patients that progressed to advanced phases.This work was supported with CZ.1.05/1.1.00/02.0068, CZ.1.07/2.3.00/20.0045, CZ.1.07/2.4.00/17.0042, MSM0021622430, and MUNI/A/0784/2011.

Figure 1. Distribution of genetic and genomic alterations in TKI-resistant CML patients.

Haematologica, 2012; 97(s1):  72