Chronic lymphoproliferative disorders of natural killer cells (CLPD-NKs

Key Points• Key biological features of MDSs are explained by NLRP3 inflammasome activation, which drives pyroptotic cell death and b-catenin activation.• Alarmin signals and founder gene mutations license this redox-sensitive inflammasome platform.Despite genetic heterogeneity, myelodysplastic syndromes (MDSs) share features of cytological dysplasia and ineffective hematopoiesis. We report that a hallmark of MDSs is activation of the NLRP3 inflammasome, which drives clonal expansion and pyroptotic cell death. Independent of genotype, MDS hematopoietic stem and progenitor cells (HSPCs) overexpress inflammasome proteins and manifest activated NLRP3 complexes that direct activation of caspase-1, generation of interleukin-1b (IL-1b) and IL-18, and pyroptotic cell death. Mechanistically, pyroptosis is triggered by the alarmin S100A9 that is found in excess in MDS HSPCs and bone marrow plasma. Further, like somatic gene mutations, S100A9-induced signaling activates NADPH oxidase (NOX), increasing levels of reactive oxygen species (ROS) that initiate cation influx, cell swelling, and b-catenin activation. Notably, knockdown of NLRP3 or caspase-1, neutralization of S100A9, and pharmacologic inhibition of NLRP3 or NOX suppress pyroptosis, ROS generation, and nuclear b-catenin in MDSs and are sufficient to restore effective hematopoiesis. Thus, alarmins and founder gene mutations in MDSs license a common redox-sensitive inflammasome circuit, which suggests new avenues for therapeutic intervention. (Blood. 2016;128(25):2960-2975

PURPOSE Approximately 20% of patients with TP53-mutant myelodysplastic syndromes (MDS) achieve complete remission (CR) with hypomethylating agents. Eprenetapopt (APR-246) is a novel, first-in-class, small molecule that restores wild-type p53 functions in TP53-mutant cells. METHODS This was a phase Ib/II study to determine the safety, recommended phase II dose, and efficacy of eprenetapopt administered in combination with azacitidine in patients with TP53-mutant MDS or acute myeloid leukemia (AML) with 20%-30% marrow blasts (ClinicalTrials.gov identifier: NCT03072043 ). RESULTS Fifty-five patients (40 MDS, 11 AML, and four MDS/myeloproliferative neoplasms) with at least one TP53 mutation were treated. The overall response rate was 71% with 44% achieving CR. Of patients with MDS, 73% (n = 29) responded with 50% (n = 20) achieving CR and 58% (23/40) a cytogenetic response. The overall response rate and CR rate for patients with AML was 64% (n = 7) and 36% (n = 4), respectively. Patients with only TP53 mutations by next-generation sequencing had higher rates of CR (69% v 25%; P = .006). Responding patients had significant reductions in TP53 variant allele frequency and p53 expression by immunohistochemistry, with 21 (38%) achieving complete molecular remission (variant allele frequency < 5%). Median overall survival was 10.8 months with significant improvement in responding versus nonresponding patients by landmark analysis (14.6 v 7.5 months; P = .0005). Overall, 19/55 (35%) patients underwent allogeneic hematopoietic stem-cell transplant, with a median overall survival of 14.7 months. Adverse events were similar to those reported for azacitidine or eprenetapopt monotherapy, with the most common grade ≥ 3 adverse events being febrile neutropenia (33%), leukopenia (29%), and neutropenia (29%). CONCLUSION Combination treatment with eprenetapopt and azacitidine is well-tolerated yielding high rates of clinical response and molecular remissions in patients with TP53-mutant MDS and oligoblastic AML.

Although next-generation sequencing has allowed for the detection of somatic mutations in myelodysplastic syndromes (MDS), the clinical relevance of variant allele frequency (VAF) for the majority of mutations is unknown. We profiled TP53 and 20 additional genes in our training set of 219 patients with MDS or secondary acute myeloid leukemia with findings confirmed in a validation cohort. When parsed by VAF, TP53 VAF predicted for complex cytogenetics in both the training (P=0.001) and validation set (P<0.0001). MDS patients with a TP53 VAF > 40% had a median overall survival (OS) of 124 days versus an OS that was not reached in patients with VAF <20% (hazard ratio (HR), 3.52; P=0.01) with validation in an independent cohort (HR, 4.94, P=0.01). TP53 VAF further stratified distinct prognostic groups independent of clinical prognostic scoring systems (P=0.0005). In multivariate analysis, only a TP53 VAF >40% was an independent covariate (HR, 1.61; P<0.0001). In addition, SRSF2 VAF predicted for monocytosis (P=0.003), RUNX1 VAF with thrombocytopenia (P=0.01) and SF3B1 with ringed sideroblasts (P=0.001). Together, our study indicates that VAF should be incorporated in patient management and risk stratification in MDS.

Key Points• GM-CSF-dependent STAT5 hypersensitivity is detected in 90% of CMML samples and is enhanced by signaling mutations.• Treatment with a GM-CSF-neutralizing antibody and JAK2 inhibitors reveals therapeutic potential.Granulocyte-macrophage-colony-stimulating factor (GM-CSF) hypersensitivity is a hallmark of juvenile myelomonocytic leukemia (JMML) but has not been systematically shown in the related human disease chronic myelomonocytic leukemia (CMML). We find that primary CMML samples demonstrate GM-CSF-dependent hypersensitivity by hematopoietic colony formation assays and phospho-STAT5 (pSTAT5) flow cytometry compared with healthy donors. Among CMML patients, the pSTAT5 hypersensitive response positively correlated with high-risk disease, peripheral leukocytes, monocytes, and signalingassociated mutations. When compared with IL-3 and G-CSF, GM-CSF hypersensitivity was cytokine specific and thus a possible target for intervention in CMML. To explore this possibility, we treated primary CMML cells with KB003, a novel monoclonal anti-GM-CSF antibody, and JAK2 inhibitors. We found that an elevated proportion of immature GM-CSF receptor-a(R) subunit-expressing cells were present in the bone marrow myeloid compartment of CMML. In survival assays, we found that myeloid and monocytic progenitors were sensitive to GM-CSF signal inhibition. Our data indicate that a committed myeloid precursor expressing CD38 may represent the progenitor population with enhanced GM-CSF dependence in CMML, consistent with results in JMML. These preclinical data indicate that GM-CSF signaling inhibitors merit further investigation in CMML and that GM-CSFR expression on myeloid progenitors may be a biomarker for this therapy. (Blood. 2013;121(25):5068-5077)