Reactive oxygen species and its role in pathogenesis and resistance to therapy in acute myeloid leukemia.

Relapse following a short clinical response to therapy is the major challenge for the management of acute myeloid leukemia (AML) patients. Leukemic stem cells (LSC), as the source of relapse, have been investigated for their metabolic preferences and their alterations at the time of relapse. As LSC rely on oxidative phosphorylation (OXPHOS) for energy requirement, reactive oxygen species (ROS), as by-products of OXPHOS, have been investigated for their role in the effectiveness of the standard AML therapy. Increased levels of non-mitochondrial ROS, generated by nicotinamide adenine dinucleotide phosphate oxidase, in a subgroup of AML patients add to the complexity of studying ROS. Although there are various studies presenting the contribution of ROS to AML pathogenesis, resistance, and its inhibition or activation as a target, a model that can clearly explain its role in AML has not been conceptualized. This is due to the heterogeneity of AML, the dynamics of ROS production, which is influenced by factors such as the type of treatment, cell differentiation state, mitochondrial activity, and also the heterogeneous generation of non-mitochondrial ROS and limited available data on their interaction with the microenvironment. This review summarizes these challenges and the recent progress in this field.

BCR-ABL1 kinase domain mutations: methodology and clinical evaluation.

The introduction of tyrosine kinase inhibitors (TKIs), starting with imatinib and followed by second and third generation TKIs, has significantly changed the clinical management of patients with chronic myeloid leukemia (CML). Despite their unprecedented clinical success, a proportion of patients fail to achieve complete cytogenetic remission by 12 months of treatment (primary resistance) while others experience progressive resistance after an initial response (secondary resistance). BCR-ABL1 kinase domain (KD) mutations have been detected in a proportion of patients at the time of treatment failure, and therefore their identification and monitoring plays an important role in therapeutic decisions particularly when switching TKIs. When monitoring KD mutations in a clinical laboratory, the choice of method should take into account turnaround time, cost, sensitivity, specificity, and ability to accurately quantify the size of the mutant clone. In this article, we describe in a "manual" style the methods most widely used in our laboratory to monitor KD mutations in patients with CML including direct sequencing, D-HPLC, and pyrosequencing. Advantages, disadvantages, interpretation of results, and their clinical applications are reviewed for each method.

EVI-1 oncogene expression predicts survival in chronic-phase CML patients resistant to imatinib treated with second-generation tyrosine kinase inhibitors.

Activation of the EVI-1 oncogene has been reported in acute myeloid leukemia, chronic myeloid leukemia (CML) in blast crisis, and less commonly, in chronic-phase CML patients. We screened an unselected cohort of 75 chronic-phase CML patients who had failed imatinib for expression of EVI-1 and sought a correlation with subsequent outcome on the second-generation tyrosine kinase inhibitors dasatinib (n = 61) or nilotinib (n = 14). The 8 patients (10.7%) who expressed EVI-1 transcripts detectable by real-time polymerase chain reaction had significantly lower event-free survival, progression-free survival, and overall survival than patients with undetectable transcript. The predictive value of EVI-1 expression was validated in an independent cohort. In a multivariate analysis, EVI-1 expression status and the best cytogenetic response obtained on imatinib were the only independent predictors for overall survival, progression-free survival, and event-free survival. Our data suggest that screening for EVI-1 expression at the time of imatinib failure may predict for response to second-line TKI therapy and consequently aid clinical management.

Technical aspects and clinical applications of measuring BCR-ABL1 transcripts number in chronic myeloid leukemia.

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by a triphasic clinical course, the morphologic expansion of a terminally differentiated myeloid cell and the presence of the BCR-ABL1 fusion gene, the hallmark of CML. The fusion gene is usually, but not always, associated with a Philadelphia chromosome, the result of a reciprocal exchange of genetic material between chromosome 22 and chromosome 9, which leads to the production of the activated BCR-ABL1 gene and oncoprotein. The breakpoint in the BCR gene occurs commonly downstream of exons e13 or e14 (M-BCR) and less frequently downstream of exons e1 and e2 (m-BCR). Less than 1% of cases carry a breakpoint downstream of exon 6 or 8 ("variant fusion genes") or exon 19 (mu-BCR). Breakpoints in the ABL1 gene cluster upstream of exon a2 (or of exon a3 in less than 5% of patients with CML). Conventional cytogenetic, fluorescence in situ hybridization, and molecular testing for the BCR-ABL1 fusion gene are key investigations for the diagnosis and monitoring of CML. Treatment using tyrosine kinase inhibitors has revolutionized the management of CML with hematologic and cytogenetic response within 12-18 months observed in >85% of patients. Nevertheless, between 15 and 20% of patients may evolve to blastic phase. Measurement of low level or "minimal" residual disease using molecular tests is becoming the gold-standard approach to measure response to therapy due to its higher sensitivity compared to other routine techniques. The technical aspects and clinical applications of molecular monitoring will be the main focus of this article.

The level of BCR-ABL1 kinase activity before treatment does not identify chronic myeloid leukemia patients who fail to achieve a complete cytogenetic response on imatinib.

Imatinib is currently the first line therapy for newly diagnosed patients with chronic myeloid leukemia. However, 20-25% of patients do not achieve durable complete cytogenetic responses. The mechanism underlying this primary resistance is unknown, but variations in BCR-ABL1 kinase activity may play a role and can be investigated by measuring the autophosphorylation levels of BCR-ABL1 or of a surrogate target such as Crkl. In this study we used flow cytometry to investigate the in vitro inhibition of Crkl phosphorylation by imatinib in CD34(+) cells in diagnostic samples from two groups of patients distinguished by their cytogenetic response. No difference in inhibition of Crkl phosphorylation was observed in the two groups. The observation that increasing the dose of imatinib in vivo did not increase the level of cytogenetic response in some non-responders suggests that in at least a proportion of patients imatinib resistance may be due to activation of BCR-ABL1-independent pathway.