Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel and pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers. To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. .

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Key Points• KPT-9274, via its protein target NAMPT, diminishes NAD 1 levels and cellular respiration, leading to cell death.• Orally bioavailable KPT-9274 exhibits targetspecific activity in cell lines and patientderived xenograft models of AML. Treatment options for acute myeloid leukemia (AML) remain extremely limited and associated with significant toxicity. Nicotinamide phosphoribosyltransferase (NAMPT) is involved in the generation of NAD 1 and a potential therapeutic target in AML. We evaluated the effect of KPT-9274, a p21-activated kinase 4/NAMPT inhibitor that possesses a unique NAMPT-binding profile based on in silico modeling compared with earlier compounds pursued against this target. KPT-9274 elicited loss of mitochondrial respiration and glycolysis and induced apoptosis in AML subtypes independent of mutations and genomic abnormalities. These actions occurred mainly through the depletion of NAD 1 , whereas genetic knockdown of p21-activated kinase 4 did not induce cytotoxicity in AML cell lines or influence the cytotoxic effect of KPT-9274. KPT-9274 exposure reduced colony formation, increased blast differentiation, and diminished the frequency of leukemia-initiating cells from primary AML samples; KPT-9274 was minimally cytotoxic toward normal hematopoietic or immune cells. In addition, KPT-9274 improved overall survival in vivo in 2 different mouse models of AML and reduced tumor development in a patient-derived xenograft model of AML.Overall, KPT-9274 exhibited broad preclinical activity across a variety of AML subtypes and warrants further investigation as a potential therapeutic agent for AML.

Acute myeloid leukemia (AML) is a heterogeneous and complex disease, and treatments for this disease have not been curative for the majority of patients. In younger patients, internal tandem duplication of FLT3 (FLT3-ITD) is a common mutation for which two inhibitors (midostaurin and gilteritinib) with varied potency and specificity for FLT3 are clinically approved. However, the high rate of relapse or failed initial response of AML patients suggests that the addition of a second targeted therapy may be necessary to improve efficacy. Using an unbiased large-scale CRISPR screen, we genetically identified BCL2 knockout as having synergistic effects with an approved FLT3 inhibitor. Here, we provide supportive studies that validate the therapeutic potential of the combination of FLT3 inhibitors with venetoclax in vitro and in vivo against multiple models of FLT3-ITD-driven AML. Our unbiased approach provides genetic validation for co-targeting FLT3 and BCL2 and repurposes CRISPR screening data, utilizing the genome-wide scope toward mechanistic understanding.

Key Points• AEB071 demonstrates preclinical in vitro and in vivo activity against CLL independent of survival signaling and stromal cell protection.• AEB071 can either inhibit or activate the WNT pathway emphasizing the importance of pharmacodynamic monitoring in its development.Targeting B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) has been successful with durable remissions observed with several targeted therapeutics. Protein kinase C-b (PKC-b) is immediately downstream of BCR and has been shown to be essential to CLL cell survival and proliferation in vivo. We therefore evaluated sotrastaurin (AEB071), an orally administered potent PKC inhibitor, on CLL cell survival both in vitro and in vivo. AEB071 shows selective cytotoxicity against B-CLL cells in a dose-dependent manner. Additionally, AEB071 attenuates BCR-mediated survival pathways, inhibits CpG-induced survival and proliferation of CLL cells in vitro, and effectively blocks microenvironment-mediated survival signaling pathways in primary CLL cells. Furthermore, AEB071 alters b-catenin expression, resulting in decreased downstream transcriptional genes as c-Myc, Cyclin D1, and CD44. Lastly, our preliminary in vivo studies indicate beneficial antitumor properties of AEB071 in CLL. Taken together, our results indicate that targeting PKC-b has the potential to disrupt signaling from the microenvironment contributing to CLL cell survival and potentially drug resistance. Future efforts targeting PKC with the PKC inhibitor AEB071 as monotherapy in clinical trials of relapsed and refractory CLL patients are warranted. (Blood. 2014;124(9):1481-1491) IntroductionChronic lymphocytic leukemia (CLL) is one of the most common types of adult leukemia and is currently incurable. Decades of research into the biology of CLL and other B-cell malignancies has brought forth B-cell receptor (BCR) signaling as a common required driving force in the survival and proliferation of these tumor cells. Several survival pathways involved in BCR signaling, including the phosphatidylinositol 3-kinase (PI3K), nuclear factor-kB (NF-kB), and mitogen-activated protein kinase (MAPK)/extracellular signalregulated kinase (ERK), are constitutively active in the lymph node and bone marrow compartment of CLL where disease expansion occurs. [1][2][3] Efforts to target BCR signaling with therapeutic agents which reversibly inhibit PI3K-d 4,5 or irreversibly inhibit Bruton tyrosine kinase (BTK) 6-8 have shown significant clinical activity in CLL, including those with high-risk genomic disease, and are currently in phase 3 studies. Protein kinase C-b (PKC-b) is an immediate downstream target of BTK that has recently been shown to be overexpressed in CLL 9 and is essential to the in vivo development of CLL in Em-TCL1 mice. 10 In B cells, PKC-b is thought to be the predominant PKC isoform mediating BCRdependent NF-kB activation.11-13 Downstream of PKC-b, IkB kinase and caspase recruitment domain-containing protein 11 (CARD11 [also known as CARMA1]) are phosphorylated, le...