Inhibition of BET recruitment to chromatin as an effective treatment for MLL-fusion leukaemia.

Recurrent chromosomal translocations involving the mixed lineage leukaemia (MLL) gene initiate aggressive forms of leukaemia, which are often refractory to conventional therapies. Many MLL-fusion partners are members of the super elongation complex (SEC), a critical regulator of transcriptional elongation, suggesting that aberrant control of this process has an important role in leukaemia induction. Here we use a global proteomic strategy to demonstrate that MLL fusions, as part of SEC and the polymerase-associated factor complex (PAFc), are associated with the BET family of acetyl-lysine recognizing, chromatin 'adaptor' proteins. These data provided the basis for therapeutic intervention in MLL-fusion leukaemia, via the displacement of the BET family of proteins from chromatin. We show that a novel small molecule inhibitor of the BET family, GSK1210151A (I-BET151), has profound efficacy against human and murine MLL-fusion leukaemic cell lines, through the induction of early cell cycle arrest and apoptosis. I-BET151 treatment in two human leukaemia cell lines with different MLL fusions alters the expression of a common set of genes whose function may account for these phenotypic changes. The mode of action of I-BET151 is, at least in part, due to the inhibition of transcription at key genes (BCL2, C-MYC and CDK6) through the displacement of BRD3/4, PAFc and SEC components from chromatin. In vivo studies indicate that I-BET151 has significant therapeutic value, providing survival benefit in two distinct mouse models of murine MLL-AF9 and human MLL-AF4 leukaemia. Finally, the efficacy of I-BET151 against human leukaemia stem cells is demonstrated, providing further evidence of its potent therapeutic potential. These findings establish the displacement of BET proteins from chromatin as a promising epigenetic therapy for these aggressive leukaemias.

IL-33-ST2 signaling promotes stemness in subtypes of myeloid leukemia cells through the Wnt and Notch pathways.

Cell stemness is characterized by quiescence, pluripotency, and long-term self-renewal capacity. Therapy-resistant leukemic stem cells (LSCs) are the primary cause of relapse in patients with chronic and acute myeloid leukemia (CML and AML). However, the same signaling pathways frequently support stemness in both LSCs and normal hematopoietic stem cells (HSCs), making LSCs difficult to therapeutically target. In cell lines and patient samples, we found that interleukin-33 (IL-33) signaling promoted stemness only in leukemia cells in a subtype-specific manner. The IL-33 receptor ST2 was abundant on the surfaces of CD34+ BCR/ABL1 CML and CD34+ AML cells harboring AML1/ETO and DEK/NUP214 translocations or deletion of chromosome 9q [del(9q)]. The cell surface abundance of ST2, which was lower or absent on other leukemia subtypes and HSCs, correlated with stemness, activated Wnt signaling, and repressed Notch signaling. IL-33-ST2 signaling promoted the maintenance and expansion of AML1/ETO-, DEK/NUP214-, and BCR/ABL1-positive LSCs in culture and in mice by activating Wnt, MAPK, and NF-κB signaling. Wnt signaling and its inhibition of the Notch pathway up-regulated the expression of the gene encoding ST2, thus forming a cell-autonomous loop. IL-33-ST2 signaling promoted the resistance of CML cells to the tyrosine kinase inhibitor (TKI) nilotinib and of AML cells to standard chemotherapy. Thus, inhibiting IL-33-ST2 signaling may target LSCs to overcome resistance to chemotherapy or TKIs in these subtypes of leukemia.

DNA Damage-Induced HSPC Malfunction Depends on ROS Accumulation Downstream of IFN-1 Signaling and Bid Mobilization.

Mouse mutants with an impaired DNA damage response frequently exhibit a set of remarkably similar defects in the HSPC compartment that are of largely unknown molecular basis. Using Mixed-Lineage-Leukemia-5 (Mll5)-deficient mice as prototypical examples, we have identified a mechanistic pathway linking DNA damage and HSPC malfunction. We show that Mll5 deficiency results in accumulation of DNA damage and reactive oxygen species (ROS) in HSPCs. Reduction of ROS efficiently reverses hematopoietic defects, establishing ROS as a major cause of impaired HSPC function. The Ink4a/Arf locus also contributes to HSPC phenotypes, at least in part via promotion of ROS. Strikingly, toxic ROS levels in Mll5-/- mice are critically dependent on type 1 interferon (IFN-1) signaling, which triggers mitochondrial accumulation of full-length Bid. Genetic inactivation of Bid diminishes ROS levels and reverses HSPC defects in Mll5-/- mice. Overall, therefore, our findings highlight an unexpected IFN-1 > Bid > ROS pathway underlying DNA damage-associated HSPC malfunction.

Myeloproliferative neoplasm (MPN) symptom assessment form total symptom score: prospective international assessment of an abbreviated symptom burden scoring system among patients with MPNs.

PURPOSE: Myeloproliferative neoplasm (MPN) symptoms are troublesome to patients, and alleviation of this burden represents a paramount treatment objective in the development of MPN-directed therapies. We aimed to assess the utility of an abbreviated symptom score for the most pertinent and representative MPN symptoms for subsequent serial use in assessing response to therapy. PATIENTS AND METHODS: The Myeloproliferative Neoplasm Symptom Assessment Form total symptom score (MPN-SAF TSS) was calculated as the mean score for 10 items from two previously validated scoring systems. Questions focus on fatigue, concentration, early satiety, inactivity, night sweats, itching, bone pain, abdominal discomfort, weight loss, and fevers. RESULTS: MPN-SAF TSS was calculable for 1,408 of 1,433 patients with MPNs who had a mean score of 21.2 (standard deviation [SD], 16.3). MPN-SAF TSS results significantly differed among MPN disease subtypes (P<.001), with a mean of 18.7 (SD, 15.3), 21.8 (SD, 16.3), and 25.3 (SD, 17.2) for patients with essential thrombocythemia, polycythemia vera, and myelofibrosis, respectively. The MPN-SAF TSS strongly correlated with overall quality of life (QOL; r=0.59; P<.001) and European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30) functional scales (all P<.001 and absolute r≥0.50 except social functioning r=0.48). No significant trends were present when comparing therapy subgroups. The MPN-SAF TSS had excellent internal consistency (Cronbach's α=.83). Factor analysis identified a single underlying construct, indicating that the MPN-SAF TSS is an appropriate, unified scoring method. CONCLUSION: The MPN-SAF TSS is a concise, valid, and accurate assessment of MPN symptom burden with demonstrated clinical utility in the largest prospective MPN symptom study to date. This new prospective scoring method may be used to assess MPN symptom burden in both clinical practice and trial settings.