SciCombinator

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Concept: Imatinib

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Imatinib mesylate (Gleevec) inhibits Abl1, c-Kit, and related protein tyrosine kinases (PTKs) and serves as a therapeutic for chronic myelogenous leukemia and gastrointestinal stromal tumors. Imatinib also has efficacy against various pathogens, including pathogenic mycobacteria, where it decreases bacterial load in mice, albeit at doses below those used for treating cancer. We report that imatinib at such low doses unexpectedly induces differentiation of hematopoietic stem cells and progenitors in the bone marrow, augments myelopoiesis but not lymphopoiesis, and increases numbers of myeloid cells in blood and spleen. Whereas progenitor differentiation relies on partial inhibition of c-Kit by imatinib, lineage commitment depends upon inhibition of other PTKs. Thus, imatinib mimics “emergency hematopoiesis,” a physiological innate immune response to infection. Increasing neutrophil numbers by adoptive transfer sufficed to reduce mycobacterial load, and imatinib reduced bacterial load of Franciscella spp., which do not utilize imatinib-sensitive PTKs for pathogenesis. Thus, potentiation of the immune response by imatinib at low doses may facilitate clearance of diverse microbial pathogens.

Concepts: Innate immune system, Gastrointestinal stromal tumor, Imatinib, Cancer, Bacteria, Tyrosine kinase, Bone marrow, Immune system

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BACKGROUND: BCR-ABL kinase domain mutations are infrequently detected in newly diagnosed chronic-phase chronic myeloid leukemia (CML) patients. Recent studies indicate the presence of pre-existing BCR-ABL mutations in a higher percentage of CML patients when CD34+ stem/progenitor cells are investigated using sensitive techniques, and these mutations are associated with imatinib resistance and disease progression. However, such studies were limited to smaller number of patients. METHODS: We investigated BCR-ABL kinase domain mutations in CD34+ cells from 100 chronic-phase CML patients by multiplex allele-specific PCR and sequencing at diagnosis. Mutations were re-investigated upon manifestation of imatinib resistance using allele-specific PCR and direct sequencing of BCR-ABL kinase domain. RESULTS: Pre-existing BCR-ABL mutations were detected in 32/100 patients and included F311L, M351T, and T315I. After a median follow-up of 30 months (range 8-48), all patients with pre-existing BCR-ABL mutations exhibited imatinib resistance. Of the 68 patients without pre-existing BCR-ABL mutations, 24 developed imatinib resistance; allele-specific PCR and BCR-ABL kinase domain sequencing detected mutations in 22 of these patients. All 32 patients with pre-existing BCR-ABL mutations had the same mutations after manifestation of imatinib-resistance. In imatinib-resistant patients without pre-existing BCR-ABL mutations, we detected F311L, M351T, Y253F, and T315I mutations. All imatinib-resistant patients except T315I and Y253F mutations responded to imatinib dose escalation. CONCLUSION: Pre-existing BCR-ABL mutations can be detected in a substantial number of chronic-phase CML patients by sensitive allele-specific PCR technique using CD34+ cells. These mutations are associated with imatinib resistance if affecting drug binding directly or indirectly. After the recent approval of nilotinib, dasatinib, bosutinib and ponatinib for treatment of chronic myeloid leukemia along with imatinib, all of which vary in their effectiveness against mutated BCR-ABL forms, detection of pre-existing BCR-ABL mutations can help in selection of appropriate first-line drug therapy. Thus, mutation testing using CD34+ cells may facilitate improved, patient-tailored treatment.

Concepts: Dasatinib, Mutation, Enzyme, DNA, Philadelphia chromosome, Leukemia, Imatinib, Chronic myelogenous leukemia

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We analyzed the cost-effectiveness of treating incident chronic myeloid leukemia in chronic phase (CML-CP) with generic imatinib when it becomes available in United States in 2016. In the year following generic entry, imatinib’s price is expected to drop 70% to 90%. We hypothesized that initiating treatment with generic imatinib in these patients and then switching to the other tyrosine-kinase inhibitors (TKIs), dasatinib or nilotinib, because of intolerance or lack of effectiveness (“imatinib-first”) would be cost-effective compared with the current standard of care: “physicians' choice” of initiating treatment with any one of the three TKIs.

Concepts: Philadelphia chromosome, Leukemia, Tyrosine kinase, Signal transduction, Protein kinase, United States, Imatinib, Chronic myelogenous leukemia

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Resistance to tyrosine kinase inhibitors in patients with chronic myeloid leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph-positive ALL) is frequently caused by mutations in the BCR-ABL kinase domain. Ponatinib (AP24534) is a potent oral tyrosine kinase inhibitor that blocks native and mutated BCR-ABL, including the gatekeeper mutant T315I, which is uniformly resistant to tyrosine kinase inhibitors.

Concepts: Imatinib, Blood disorders, Protein kinase, Protein kinase inhibitor, Cancer, Leukemia, Chronic myelogenous leukemia, Acute lymphoblastic leukemia

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The introduction of imatinib, a tyrosine kinase inhibitor (TKI), has greatly increased survival for patients with chronic myeloid leukemia (CML). Conversely, nonadherence to imatinib and other TKIs undoubtedly results in disease progression and treatment resistance. We examined trends in imatinib expenditures from 2002 to 2011 and assessed the association between copayment requirements for imatinib and TKI adherence.

Concepts: Leukemia, Tyrosine kinase, Signal transduction, Chronic myelogenous leukemia, Cancer, Protein kinase, Imatinib, Protein kinase inhibitor

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BACKGROUND: A large number of chronic myeloid leukemia (CML) patients are treated with imatinib mesylate outside of clinical trials, which may not be representative of common clinical practice. The age of CML patients enrolled within controlled clinical studies is lower with respect to patients included in population-based registries. PATIENTS AND METHODS: To describe the safety and tolerability of imatinib in very elderly CML patients in chronic phase, 211 chronic-phase CML patients aged >75 years were retrospectively analyzed using data collected from 31 institutions in Italy. RESULTS: The median age at imatinib start was 78.6 years [interquartile range (IR) 76.3-81.4], median time from diagnosis to imatinib start was 1.2 months (IR 0.5-3.7). The starting dose of imatinib was 400 mg/day in 144 patients (68.2 %), >400 mg/day in 4 patients (2.0 %), and <400 mg/day in 63 patients (29.8 %); overall, 94 patients (44.5 %) needed a dose reduction and 27 (12.7 %) discontinued imatinib for toxicity. Grade 3-4 hematologic and extrahematologic toxicities were observed in 40 (18.9 %) and 45 (21.3 %) patients, respectively. After a median observation of 29.8 months (IR 13.0-55.6), 203/211 patients had at least 6 months of observation on imatinib or discontinued before and were evaluable for response and outcome; of them, 183 patients (90.2 %) achieved a complete hematologic response (CHR). Among these 183 patients in CHR, 14 refused any other karyotypic or molecular evaluation, 24 achieved CHR only, and 145 (71.4 %) achieved a cytogenetic response (CyR) of any grade, which was complete (CCyR) in 129 (63.5 %). Among the 129 patients with CCyR, 95 (46.7 %) achieved a major molecular response (MMolR). By multivariate regression analysis, late chronic phase (p = 0.001) and grade 3-4 extrahematologic toxicity (p = 0.007) maintained a negative independent prognostic impact for CCyR, while late chronic phase (p = 0.026), grade 3-4 extrahematologic toxicity (p = 0.007), and lower initial dose of imatinib (p = 0.044) maintained a negative independent prognostic impact for MMolR. The 2-year and 4-year overall survival were 92.6 % (95 % CI 88.7-96.5) and 78.0 % (95 % CI 71.2-84.8), respectively. CONCLUSIONS: Results from this large cohort of patients show that no upper age limit should be applied for the administration of imatinib to patients with chronic-phase CML; the very elderly, including those with concomitant severe diseases, should be offered this treatment. The role of a reduced starting dose of imatinib warrants further studies.

Concepts: Mesylate, Regression analysis, Blood disorders, Philadelphia chromosome, Imatinib, Leukemia, Clinical trial, Chronic myelogenous leukemia

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OBJECTIVES: The validity of the three currently used chronic myeloid leukemia (CML) scoring systems (Sokal CML prognostic scoring system, Euro/Hasford CML scoring system, and the EUTOS CML prognostic scoring system) were compared in the CML patients receiving frontline imatinib mesylate. PATIENTS AND METHODS: One hundred and fourty-three chronic phase CML patients (71 males, 72 females) taking imatinib as frontline treatment were included in the study. The median age was 44 (16-82) years. Median total and on-imatinib follow-up durations were 29 (3.8-130) months and 25 (3-125) months, respectively. RESULTS: The complete hematological response (CHR) rate at 3 months was 95%. The best cumulative complete cytogenetic response (CCyR) rate at 24 months was 79.6%. Euro/Hasford scoring system was well-correlated with both Sokal and EUTOS scores (r = 0.6, P < 0.001 and r = 0.455, P < 0.001). However, there was only a weak correlation between Sokal and EUTOS scores (r = 0.2, P = 0.03). The 5-year median estimated event-free survival for low and high EUTOS risk patients were 62.6 (25.7-99.5) and 15.3 (7.4-23.2) months, respectively (P < 0.001). This performance was better than Sokal (P = 0.3) and Euro/Hasford (P = 0.04) scoring systems. Overall survival and CCyR rates were also better predicted by the EUTOS score. DISCUSSION: EUTOS CML prognostic scoring system, which is the only prognostic system developed during the imatinib era, predicts European LeukemiaNet (ELN)-based event-free survival better than Euro/Hasford and Sokal systems in CML patients receiving frontline imatinib mesylate. This observation might have important clinical implications.

Concepts: Scores, Mesylate, Philadelphia chromosome, Leukemia, Imatinib, Chronic myelogenous leukemia

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STAT5 fulfills essential roles in hematopoietic stem cell (HSC) self-renewal and chronic myeloid leukaemia (CML), a prototypical stem cell malignancy. However, the specific contributions of the two related genes STAT5A and STAT5B have not been determined. In this study, we used an RNAi-based strategy to establish participation of these genes to CML disease and persistence following targeted therapy. We showed that STAT5A/STAT5B double knockdown triggers CML cell apoptosis and suppresses both normal and CML HSC long-term clonogenic potential. STAT5A and STAT5B exhibited similar pro-survival activity, but STAT5A attenuation alone was ineffective at impairing growth of normal and CML CD34+ cells isolated at diagnosis. In contrast, STAT5A attenuation was sufficient to enhance basal oxidative stress and DNA damage of normal CD34+ and CML cells. Further, it weakened the ability to manage exogenous oxidative stress, increased p53 (TRP53)/CHK-2 (CHEK2) stress pathway activation and enhanced prolyl hydroxylase domain (PHD)-3 (EGLN3) mRNA expression. Only STAT5A and its transactivation domain-deficient mutant STAT5AD749 specifically rescued these activities. STAT5A attenuation was also active at inhibiting growth of CML CD34+ cells from patients with acquired resistance to imatinib. Our findings demonstrate that STAT5A has a selective role in contributing to stress resistance through unconventional mechanisms, offering new opportunities to eradicate the most primitive and TKI- resistant CML cells with an additional potential to eradicate persistent stem cell populations.

Concepts: Adenosine triphosphate, Imatinib, Gene, Signal transduction, DNA, Chronic myelogenous leukemia, Leukemia, Cancer

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Treatment of chronic myeloid leukemia (CML) with imatinib mesylate and other second- and/or third-generation c-Abl-specific tyrosine kinase inhibitors (TKIs) has substantially extended patient survival. However, TKIs primarily target differentiated cells and do not eliminate leukemic stem cells (LSCs). Therefore, targeting minimal residual disease to prevent acquired resistance and/or disease relapse requires identification of new LSC-selective target(s) that can be exploited therapeutically. Considering that malignant transformation involves cellular metabolic changes, which may in turn render the transformed cells susceptible to specific assaults in a selective manner, we searched for such vulnerabilities in CML LSCs. We performed metabolic analyses on both stem cell-enriched (CD34(+) and CD34(+)CD38(-)) and differentiated (CD34(-)) cells derived from individuals with CML, and we compared the signature of these cells with that of their normal counterparts. Through combination of stable isotope-assisted metabolomics with functional assays, we demonstrate that primitive CML cells rely on upregulated oxidative metabolism for their survival. We also show that combination treatment with imatinib and tigecycline, an antibiotic that inhibits mitochondrial protein translation, selectively eradicates CML LSCs both in vitro and in a xenotransplantation model of human CML. Our findings provide a strong rationale for investigation of the use of TKIs in combination with tigecycline to treat patients with CML with minimal residual disease.

Concepts: Mitochondrion, Cellular respiration, Chronic myelogenous leukemia, Imatinib, Cancer, Metabolism, Oxidative phosphorylation, Adenosine triphosphate

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After identification of activating mutations of the KIT gene in gastrointestinal stromal tumor (GIST)-the most common sarcomaof the gastrointestinal tract-a phase 2 study demonstrated efficacy of imatinib mesylate in patients with metastatic GIST harboring a KIT exon 11 mutation. Initial results of long-term follow-up have found a survival benefit in this subgroup of patients.

Concepts: Evolution, DNA repair, Mesylate, Oncology, DNA, Imatinib, Cancer, Gastrointestinal stromal tumor