AMD1 is required for the maintenance of leukemic stem cells and promotes chronic myeloid leukemic growth.

Polyamines are critical elements in mammals, but it remains unknown whether adenosyl methionine decarboxylase (AMD1), a rate-limiting enzyme in polyamine synthesis, is required for myeloid leukemia. Here, we found that leukemic stem cells (LSCs) were highly differentiated, and leukemia progression was severely impaired in the absence of AMD1 in vivo. AMD1 was highly upregulated as chronic myeloid leukemia (CML) progressed from the chronic phase to the blast crisis phase, and was associated with the poor prognosis of CML patients. In addition, the pharmacological inhibition of AMD1 by AO476 treatment resulted in a robust reduction of the progression of leukemic cells both in vitro and in vivo. Mechanistically, AMD1 depletion induced loss of mitochondrial membrane potential and accumulation of reactive oxygen species (ROS), resulting in the differentiation of LSCs via oxidative stress and aberrant activation of unfolded protein response (UPR) pathway, which was partially rescued by the addition of polyamine. These results indicate that AMD1 is an essential element in the progression of myeloid leukemia and could be an attractive target for the treatment of the disease.

Integrative genomic analysis reveals cancer-associated mutations at diagnosis of CML in patients with high-risk disease.

Genomic events associated with poor outcome in chronic myeloid leukemia (CML) are poorly understood. We performed whole-exome sequencing, copy-number variation, and/or RNA sequencing for 65 patients to discover mutations at diagnosis and blast crisis (BC). Forty-six patients with chronic-phase disease with the extremes of outcome were studied at diagnosis. Cancer gene variants were detected in 15 (56%) of 27 patients with subsequent BC or poor outcome and in 3 (16%) of 19 optimal responders (P = .007). Frequently mutated genes at diagnosis were ASXL1, IKZF1, and RUNX1 The methyltransferase SETD1B was a novel recurrently mutated gene. A novel class of variant associated with the Philadelphia (Ph) translocation was detected at diagnosis in 11 (24%) of 46 patients comprising fusions and/or rearrangement of genes on the translocated chromosomes, with evidence of fragmentation, inversion, and imperfect sequence reassembly. These were more frequent at diagnosis in patients with poor outcome: 9 (33%) of 27 vs 2 (11%) of 19 optimal responders (P = .07). Thirty-nine patients were tested at BC, and all had cancer gene variants, including ABL1 kinase domain mutations in 58%. However, ABL1 mutations cooccurred with other mutated cancer genes in 89% of cases, and these predated ABL1 mutations in 62% of evaluable patients. Gene fusions not associated with the Ph translocation occurred in 42% of patients at BC and commonly involved fusion partners that were known cancer genes (78%). Genomic analysis revealed numerous relevant variants at diagnosis in patients with poor outcome and all patients at BC. Future refined biomarker testing of specific variants will likely provide prognostic information to facilitate a risk-adapted therapeutic approach.

Comprehensive therapeutic outcomes of frontline imatinib mesylate in newly diagnosed chronic phase chronic myeloid leukemia patients in Korea: feasibility assessment of current ELN recommendation.

Optimal responses during imatinib therapy are commonly defined following the European LeukemiaNet (ELN) recommendations. Achievements of these optimal responses have not, however, been comprehensively tested as response-related prognostic factors using single center data sets. We evaluated the parameters using long-term (median 63 months) outcomes from 363 chronic phase chronic myeloid leukemia patients treated with imatinib as frontline therapy at our center. Intention-to-treat analysis showed comparable rates of complete cytogenetic response (86 %), major molecular response (MMR, 54 %), and complete molecular response (MR(4.5), 8 %). Estimated overall survival, progression-free survival, and event-free survival at 7 years were 94, 88 and 84 %, respectively. Achievement of recommended optimal response at 6 months (major cytogenetic response) and 12 months (complete cytogenetic response) yielded significantly better overall, progression-free, and event-free survival. However, achievement of recommended optimal response at 18 months (MMR) provided marginal benefit only in event-free survival. Most ELN criteria were predictive of long-term outcomes, with the exception of the clinical significance of achieving MMR at 18 months. Treatment adherence in the early treatment period was one of the important independent predictors of favorable long-term outcome. Durable cytogenetic and molecular responses were maintained in a majority of patients treated with optimal dose intensity.

Dynamic change of T315I BCR-ABL kinase domain mutation in Korean chronic myeloid leukaemia patients during treatment with Abl tyrosine kinase inhibitors.

We analysed the dynamic change of imatinib-resistant mutations in BCR-ABL kinase domain focusing on T315I mutation during dasatinib or nilotinib therapy. Fifty-five imatinib-resistant chronic myeloid leukaemia patients (32 patients with imatinib-resistant mutations and 23 patients without mutation) in different disease phases were treated with dasatinib (median 17.3 months) or nilotinib (median 6.8 months). Among the 32 patients with baseline mutation, mutations including M244V, G250E, E255K, M351T, H396R, S417Y, E450K and E459K disappeared in 8 patients and new mutations were detected in 9 patients, all of which were T315I. Among the 23 patients without baseline mutation, 4 patients showed newly developed mutations including T315I, T315I + E459K, M244V and F359V. The T315I was the most frequently detected mutation in imatinib therapy (16%, 9 of 55) as well as in dasatinib or nilotinib therapy (24%, 11 of 44). Patients with imatinib resistant baseline mutations had a higher rate of mutation development during dasatinib or nilotinib treatment compared to patients without baseline mutations (28% vs. 17%).

Previous best responses can be re-achieved by resumption after imatinib discontinuation in patients with chronic myeloid leukemia: implication for intermittent imatinib therapy.

Although imatinib is considered as a front line therapy in patients with chronic myeloid leukemia (CML), it is still unclear whether transient imatinib discontinuation may adversely affect the outcome. This study was conducted to investigate long-term outcome after discontinuation and resumption of imatinib, and to determine whether intermittent imatinib therapy can be employed in patients with CML. Twenty six Philadelphia chromosome positive (Ph+) patients with CML discontinued imatinib when they achieved complete cytogenetic response (CCyR) or complete molecular response (CMR), and they were retreated with imatinib in case of hematologic, cytogenetic or molecular relapse. Except one patient who progressed and two patients who are in persistent molecular remission without imatinib resumption, all of 23 patients are maintaining the best response achieved after imatinib resumption with a median follow-up of 44 months. This study shows that although imatinib cannot be discontinued completely, intermittent therapy can be considered for the treatment of patients with CML in particular situations.

Analysis of Bcr-Abl kinase domain mutations in Korean chronic myeloid leukaemia patients: poor clinical outcome of P-loop and T315I mutation is disease phase dependent.

Despite durable responses to imatinib in chronic myeloid leukaemia (CML), mutations in Bcr-Abl kinase domain (KD) are known to induce imatinib resistance and cause poor clinical outcome. We characterized Bcr-Abl KD mutations in 137 Korean CML patients with imatinib resistance (n = 111) or intolerance (n = 26) using allele specific oligonucleotide polymerase chain reaction (PCR) and direct sequencing. Seventy (51%) patients harboured 81 mutations of 20 different types with increasing prevalence in advanced phase. Nine (13%) patients had multiple mutations. No mutation was found in intolerant patients. T315I was the most common mutation and P-loop was the hottest spot in Bcr-Abl KD. Patients harbouring P-loop mutation, T315I, or multiple mutations showed poor overall survival and progression free survival compared with patients harbouring other mutations. Survival analysis according to disease phase of mutation being detected and type of mutations provided correlation between P-loop or T315I mutation and poor overall survival in blast crisis, but not in accelerated phase (AP) or chronic phase (CP), indicating poor clinical outcome of particular mutations depends on disease phase. CML patients with imatinib resistance showed high rate (63%) of mutations in Bcr-Abl KD and therefore CML patients who do not respond to imatinib should be the candidates for mutation screening as molecular monitoring.

Structural modeling of V299L and E459K Bcr-Abl mutation, and sequential therapy of tyrosine kinase inhibitors for the compound mutations.

Sequential treatment with different tyrosine kinase inhibitors (TKIs) is one of the strategies for handling chronic myeloid leukemia (CML) in which dynamic change in Bcr-Abl kinase domain mutation is often an obstacle faced during TKI therapy. Here we report successful sequential therapy with different TKIs for the CML patient harboring V299L and E459K compound mutations. Molecular monitoring including quantitative analysis of BCR-ABL transcript level and mutation analysis were performed regularly for successful treatment. Additionally a drug-target complex was structurally modeled to investigate influence of amino acid substitutions on drug resistance, and to choose alternative TKI in sequential therapy, suggesting protein structural modeling can be useful approach in selecting alternative TKIs.