Adaphostin-induced oxidative stress overcomes BCR/ABL mutation-dependent and -independent imatinib resistance

The BCR/ABL kinase has been targeted for the treatment of chronic myelogenous leukemia (CML) by imatinib mesylate. While imatinib has been extremely effective for chronic phase CML, blast crisis CML and Ph+ acute lymphoblastic leukemia (ALL) are often resistant. In particular, mutation of the T315 residue in the bcr/abl activation loop renders cells highly resistant to imatinib and to second-generation kinase inhibitors such as BMS-354825 or AMN107. Adaphostin is a tyrphostin that was originally intended to inhibit the BCR/ABL kinase by competing with its peptide substrates. Recent findings have in addition implicated reactive oxygen species (ROS) in the cytotoxic mechanism of adaphostin. In view of this unique mode of action, we examined the effects of adaphostin on numerous imatinib-resistant leukemia models, including imatinib-resistant CML and Ph+ ALL cell lines, cells harboring point mutations in BCR/ABL, and specimens from imatinib-resistant CML patients, using assays for intracellular ROS, apoptosis, and clonogenicity. Every model of imatinib resistance examined remained fully sensitive to adaphostin-induced cell death. Collectively, these data suggest that ROS generation by adaphostin overcomes even the most potent imatinib resistance in CML and Ph+ ALL.     

Clofarabine and cytarabine combination as induction therapy for acute myeloid leukemia (AML) in patients 50 years of age or older

Outcome of patients with acute myeloid leukemia (AML) who are older than 60 years of age remains unsatisfactory, with low remission rates and poor overall survival. We have previously established the activity of clofarabine plus cytarabine in AML relapse. We have now conducted a phase 2 study of clofarabine plus cytarabine in patients aged 50 years or older with previously untreated AML. Clofarabine was given at 40 mg/m2 as a 1-hour intravenous infusion for 5 days (days 2 to 6) followed 4 hours later by cytarabine at 1 g/m2/d as a 2-hour intravenous infusion for 5 days (days 1 to 5). Of 60 patients, 29 (48%) had secondary AML, 30 (50%) had abnormal karyotypes (monosomy 5 and/or 7 in 15 [25%]), and 11 (21%) showed FLT3 abnormalities. The overall response (OR) rate was 60% (52% CR, 8% CRp). Four patients (7%) died during induction. Adverse events were mainly grade 2 or lower and included diarrhea, nausea, vomiting, mucositis, skin reactions, liver test abnormalities, and infusion-related facial flushing and headaches. Myelosuppression was common. Clofarabine plus cytarabine has activity in adult AML, achieving a good CR rate. However, survival does not appear to be improved compared with other regimens. Modifications of this combination in AML therapy of older patients warrant further evaluation.     

Altered T-cell subset repertoire affects treatment outcome of patients with myelofibrosis

Phenotypic characterization of T cells in myelofibrosis is intriguing because of increased inflammation, markedly elevated pro-inflammatory cytokines, and altered distribution of T-cell subsets. Constitutive activation of Janus kinase-2 (JAK2) in the majority of patients with myelofibrosis contributes to the expression of the programmed cell death protein-1 (PD1) and T-cell exhaustion. We wondered whether T-cell activation affects treatment outcome of patients with myelofibrosis and sought to determine whether the JAK1/2 inhibitor ruxolitinib affects the activation of T-cell subsets. T cells from 47 myelofibrosis patients were analyzed and the percentages of either helper (CD4+) or cytotoxic (CD8+) naïve, central memory, effector memory, or effector T cells; and fractions of PD1-expressing cells in each subset were assessed. Higher numbers of T cells co-expressing CD4/PD1 and CD8/PD1 were found in myelofibrosis patients than in healthy controls (n=28), and the T cells were significantly skewed toward an effector phenotype in both CD4+ and CD8+ subsets, consistent with a shift from a quiescent to an activated state. Over the course of ruxolitinib treatment, the distribution of aberrant T-cell subsets significantly reversed towards resting cell phenotypes. CD4+ and CD8+ subsets at baseline correlated with monocyte and platelet counts, and their PD1+ fractions correlated with leukocyte counts and spleen size. Low numbers of PD1+/CD4+ and PD1+/CD8+ cells were associated with complete resolution of palpable splenomegaly and improved survival rate, suggesting that low levels of exhausted T cells confer a favorable response to ruxolitinib treatment.     

Clinical significance of cultures collected from fine-needle aspiration biopsy

The rate of positive cultures in fine-needle aspiration biopsy (FNAB) specimens is evaluated, and the value of submitting FNAB culture is assessed. Review of 3,300 FNAB specimens from 2,416 patients were tabulated for culture results, when obtained from the FNAB material. For positive culture results, clinical impact was assessed. Of 3,300 FNAB specimens and 2,416 patients, 185 had cultures performed (6% of specimens, 8% of patients). Of the 185 cultured specimens, 63 (34%) were positive and 122 (66%) were negative. Of the 63 positive cultures, 23 (12% of all FNAB cultures) had a significant impact on patient care. In our institution the FNA culture rate is 6%. When cases with clinical or microscopic suspicion of infection are cultured, 34% are positive for aerobic or anaerobic bacteria, mycobacteria or fungus. Culture in FNA specimens is a useful adjunct to diagnosis and impacts care in 12% of patients cultured at FNAB. This method can be used to triage patients with suspected infectious diseases and can aid in managing patients who may have recurrent infections.     

Superior efficacy of co-targeting GFI1/KDM1A and BRD4 against AML and post-MPN secondary AML cells

There is an unmet need to overcome nongenetic therapy-resistance to improve outcomes in AML, especially post-myeloproliferative neoplasm (MPN) secondary (s) AML. Studies presented describe effects of genetic knockout, degradation or small molecule targeted-inhibition of GFI1/LSD1 on active enhancers, altering gene-expressions and inducing differentiation and lethality in AML and (MPN) sAML cells. A protein domain-focused CRISPR screen in LSD1 (KDM1A) inhibitor (i) treated AML cells, identified BRD4, MOZ, HDAC3 and DOT1L among the codependencies. Our findings demonstrate that co-targeting LSD1 and one of these co-dependencies exerted synergistic in vitro lethality in AML and post-MPN sAML cells. Co-treatment with LSD1i and the JAKi ruxolitinib was also synergistically lethal against post-MPN sAML cells. LSD1i pre-treatment induced GFI1, PU.1 and CEBPα but depleted c-Myc, overcoming nongenetic resistance to ruxolitinib, or to BETi in post-MPN sAML cells. Co-treatment with LSD1i and BETi or ruxolitinib exerted superior in vivo efficacy against post-MPN sAML cells. These findings highlight LSD1i-based combinations that merit testing for clinical efficacy, especially to overcome nongenetic therapy-resistance in AML and post-MPN sAML.Subject terms: Acute myeloid leukaemia, Targeted therapies     

Investigational Janus kinase inhibitors in development for myelofibrosis

Introduction: Since the discovery of the activating V617F mutation in Janus kinase 2 (JAK2), a number of pharmacologic inhibitors of JAK2 have entered clinical trials for patients with myelofibrosis. However, ruxolitinib, approved in 2011, remains the only one currently available for treatment of myelofibrosis, with many others having been discontinued for toxicity, and considerable uncertainty surrounding the future of those still in development.

Areas covered: The available clinical data on pacritinib and momelotinib, the two agents in the most advanced phases of clinical testing in myelofibrosis, are examined in detail. NS-018 and INCB039110, selective inhibitors of JAK2 and JAK1, respectively, are also discussed. Finally, the JAK2 inhibitors no longer in clinical development are summarized in tabular form.

Expert opinion: The different agents evaluated clearly differ in their kinomes, toxicity profiles and potential for myelosuppression. If approved, the JAK2-specific non-myelosuppressive inhibitor pacritinib could fulfill a major unmet need, that of patients with significant cytopenias. However, toxicity concerns persist. The data from the pivotal trials of momelotinib do not support its approval, although improvement of anemia is an important benefit. Selective JAK1 inhibition alone is unlikely to succeed in myelofibrosis. In these circumstances, rational ruxolitinib-based combinations may represent the best way forward.