Tyrosine Kinase Btk Research Articles

Oral administration of Bruton's tyrosine kinase inhibitors impairs GPVI-mediated platelet function.

The Tec family kinase Bruton's tyrosine kinase (Btk) plays an important signaling role downstream of immunoreceptor tyrosine-based activation motifs in hematopoietic cells. Mutations in Btk are involved in impaired B-cell maturation in X-linked agammaglobulinemia, and Btk has been investigated for its role in platelet activation via activation of the effector protein phospholipase Cγ2 downstream of the platelet membrane glycoprotein VI (GPVI). Because of its role in hematopoietic cell signaling, Btk has become a target in the treatment of chronic lymphocytic leukemia and mantle cell lymphoma; the covalent Btk inhibitor ibrutinib was recently approved by the US Food and Drug Administration for treatment of these conditions. Antihemostatic events have been reported in some patients taking ibrutinib, although the mechanism of these events remains unknown. We sought to determine the effects of Btk inhibition on platelet function in a series of in vitro studies of platelet activation, spreading, and aggregation. Our results show that irreversible inhibition of Btk with two ibrutinib analogs in vitro decreased human platelet activation, phosphorylation of Btk, P-selectin exposure, spreading on fibrinogen, and aggregation under shear flow conditions. Short-term studies of ibrutinib analogs administered in vivo also showed abrogation of platelet aggregation in vitro, but without measurable effects on plasma clotting times or on bleeding in vivo. Taken together, our results suggest that inhibition of Btk significantly decreased GPVI-mediated platelet activation, spreading, and aggregation in vitro; however, prolonged bleeding was not observed in a model of bleeding.

Chystallographic Evidence of Autologous Recognition By a Clonotypic B Cell Receptor in Chronic Lymphocytic Leukemia

Abstract Chronic lymphocytic leukemia (CLL) leukemic cells express B-cell receptor immunoglobulin (BcR IG) whose signaling is of paramount importance throughout the natural history of the disease. Indeed, signaling pathways downstream of the BcR are constitutively active in all cases of CLL and inhibitors of the Bruton's tyrosine kinase BTK (Ibrutinib) or PI3Kδ (Idelalisib), two downstream signaling effectors, are clinically effective. This functional evidence complements earlier molecular observations supporting antigen drive in CLL ontogeny, including the distinction of CLL into cases with somatically hypermutated BcR IG (M-CLL) that have a significantly better outcome compared to those with unmutated, germline-like receptors (U-CLL). CLL also displays a remarkably skewed BcR IG gene repertoire, culminating in the existence of highly homologous, stereotyped BcR IG in >30% of cases, indicating selection by a limited set of antigenis. A number of potential antigenic elements have been described, being recognized by the monoclonal receptors and able to deliver intracellular signals. More recently, it has been reported that CLL cells are endowed with the apparently unique property of autonomous signaling, since individual CLL-derived BcR IG can promote Ca2+ influx and NF-κB target gene transcription in a reconstituted B cell system upon self-recognition of common BcR-intrinsic epitopes. However, the precise molecular details of such process are unknown. In order to gain insight into the molecular interactions, particularly to further understand the role played by autonomous signaling, we determined the crystal structures of two BcR IG of CLL cases assigned to subset #4. This is a CLL subset expressing stereotyped, G(κ)-switched BcR IG encoded by the IGHV4-34/IGKV2-30 gene combination. Subset #4 accounts for ~1% of all CLL and is the largest within M-CLL, distinctive for a particularly indolent clinical course. BcR IG derived from two subset #4 cases were found to bind autologously via their VH CDR3 loops to a composite surface spanning the variable and constant regions of the heavy chain; the relevant epitope is conserved in all cases belonging to subset #4 and differs from other non-subset #4 BcR IG. This specific self-recognition was identified as dependent on the individual IG gene usage in the BcR, and is functionally relevant as it occurs in solution and leads to intracellular signalling in B cells. Analysis of epitope and paratope mutants revealed that the interactions observed in the crystal structures are mediated by a few critical amino acid residues. Indeed, the distinctively conserved amino acid residues in the VH CDR3 loop of the BcR IG both dictate a specific VH-VK pairing and shape the combining site for autologous recognition. Moreover, the epitope comprises specific amino acids from the CH1 domain that restrict the autologous recognition to IgG molecules. Finally, we found persisting long-lived interaction occurring between subset #4 BcR IGs, thus recalling high affinity receptor-cognate antigen interactions associated with the induction of anergy. This scenario well fits with the anergic phenotype of the subset #4 leukemic cells, and thus provides a biochemical explanation for the indolent clinical course of this subset. In conclusion, though focusing on a particular CLL subset, the structural and biochemical analysis here presented describes a general model for autologous recognition that may epitomize the molecular events leading to the expansion of CLL B lymphocytes at large. It is conceivable that CLL-associated BcR IGs can each bind to a distinct internal epitope with the specific nature of the interaction dictated by diverse factors e.g. VDJ recombination, heavy and light chain pairing, SHM, and isotype switch. The strength and persistence of the autologous recognition can then lead to a specific outcome in the intracellular signaling process, ranging from proliferation to anergy. The structural diversity thus produced in the BcR IG development may be linked to and underlie the heterogeneity characterizing CLL at the biological and clinical level. Disclosures Stamatopoulos: Gilead Sciences: Research Funding; Janssen Pharmaceuticals: Research Funding. Ghia:Pharmacyclics: Honoraria; Gilead: Honoraria, Research Funding, Speakers Bureau; Janssen: Honoraria; Roche: Research Funding; GSK: Research Funding; AbbVie: Honoraria; Celgene: Honoraria; Adaptive Biotechnologies: Consultancy.

First-in-Class ROR1 Small Molecule Inhibitor (KAN0439834) Downregulated Wnt-Canonical and Non-Canonical Signaling Pathways and Induced Apoptosis of CLL Cells

Background: The receptor tyrosine kinase (RTK) ROR1 is detected during embryogenesis but downregulated in adult normal tissues. However, it is expressed in several solid tumors and hematological malignancies. Targeting ROR1 with specific siRNAs in chronic lymphocytic leukemia (CLL) induced apoptosis of the leukemic cells. Moreover, ROR1 specific monoclonal antibodies (mAbs) dephosphorylated ROR1 followed by apoptosis of the CLL cells. Furthermore, ROR1 tyrosine kinase inhibitors (ROR1-TKI) (small molecule inhibitors) have been shown to dephosphorylate ROR1, downregulate the activated PI3K/AKT/mTOR signaling pathway and induce specific apoptosis of CLL cells.Aim: In the present report we analysed the effects of a ROR1-TKI drug candidate (KAN0439834) on other intracellular signaling pathways involved in cell survival, differentiation and migration in addition to the PI3K/AKT/mTOR pathway in CLL cells.Methods: KAN0439834 ROR1-TKI was derived from a high-throughput screening (HTS) and a chemical synthesis program, including cellular assays for CLL specific cytotoxicity. The compound was also tested for ADME and in vivo pharmacokinetics characteristics. Peripheral blood mononuclear cells (PBMC) were derived from patients with CLL and normal healthy donors. Intracellular signaling molecules were analysed by Western blot (WB) after 30 min incubation of the cells with the ROR1-TKI (50-1000 nM). Apoptosis/necrosis was determined by the MTT cytotoxicity assay and Annexin V/PI staining in flowcytometry after 24 h of incubation.Results: CLL cells expressed ROR1 as determined by WB and flowcytometry. ROR1 was shown to be phosphorylated using a polyclonal anti-phospho-ROR1 (pROR1) antibody (WB). After 30 min of incubation with 50-1000 nM of KAN0439834, ROR1 was dephosphorylated in a dose-dependent manner. KAN0439834 also dephosphorylated LRP6, GSK3β, JNK, MAPK/ERK/p42,44, PKC, Src, and c-Jun and decreased the β-catenin concentration as well as deactivated BCL-2 and Bax proteins. KAN0439834 had no effect on Bruton tyrosine kinase (Btk) phosphorylation involved in B-cell receptor (BCR) signaling. Incubation of CLL cells with KAN0439834 (50-1000 nM) showed a dose dependent induction of apoptosis/necrosis of leukemic cells with more than 80% specific killing of CLL cells after 24 h and an IC50 value of 250 nM.Conclusions: Our data show that KAN0439834 downregulated the activity of various signaling pathways in CLL cells suggested to be connected with ROR1 signaling, including the Wnt-canonical associated molecule as LRP6, GSK3β and β-catenin as well as several Wnt non-canonical associated proteins as Src, MAPK/ERK p42,44, JNK, and PKC and inactivation of c-Jun that was followed by apoptosis of the CLL cells in a dose dependent manner. Further studies are ongoing to study the effects of the ROR1 specific TKIs on ROR1 downstream signaling as well as in preclinical in vivo animal models using human fresh tumors and cell lines to evaluate the anti-tumor effects. Available data suggest a specific ROR1-mediated cytotoxic effect of KAN0439834 on CLL cells, which represents a first-in-class of a novel CLL drug candidate targeting ROR1. DisclosuresMoshfegh:Kancera AB: Employment. Vågberg:Kancera AB: Employment. Styrbjörn:Kancera AB: Employment. Schultz:Kancera AB: Employment. Olsson:Kancera AB: Employment. Löfberg:Kancera AB: Employment. Norström:Kancera AB: Employment. Norin:Kancera AB: Employment. Olin:Kancera AB: Employment, Equity Ownership. Österborg:Janssen Cilag: Research Funding.

Microenvironmental-Mediated Regulation of L-Selectin in Chronic Lymphocytic Leukaemia

Abstract Chronic Lymphocytic Leukaemia (CLL) is characterized by the accumulation of CD5/19+ve B cells in the blood, bone marrow and lymph nodes. The tumour microenvironment of the bone marrow and secondary lymphoid organs promotes cell proliferation, survival and protection from drug induced apoptosis. Selectins, integrins and chemokines mediate the trafficking of CLL cells to these protective niches. An important adhesion molecule in this process is L-selectin (CD62L) which is involved in initial tethering and rolling of CLL cells in the high endothelial venules, allowing migration between the blood and the secondary lymphoid organs. It has been shown that CLL cell expression of CD62L increases during in vitro culture and blocking antibodies cause an increase in apoptosis, suggesting a role for CD62L in cell survival (Burgess et al., Clin Cancer Res. 2013). The B-cell receptor (BCR) signalling pathway is the most important pathway involved in micro-environmental crosstalk and CLL cell survival, and has recently been shown to interact with the STAT3 signalling pathway (Rozovski et al., Blood 2014). In this study, Hs5 Bone Marrow Stromal Cell (BMSC), Human Umbilical Vein Endothelial cells (HUVEC) and patient derived BMSC co-cultures were used to mimic pro-survival microenvironmental signals and investigate the effect on the expression of a panel of cell surface adhesion molecules. These coculture models resulted in a significant increase in CD62L positive CLL cells (p<0.01, n=7). Stimulation of the BCR using immunoglobulin F(ab´)2fragments induced tyrosine phosphorylation of STAT3 and resulted in a significant increase in CD62L expression, which was abrogated by pre-treatment with the Bruton tyrosine kinase (btk) inhibitor Ibrutinib prior to BCR stimulation. (p<0.05, n=5). siRNA mediated STAT3 knockdown and treatment with STAT3 inhibitors, including Cucurbitacin I, resulted in a significant decrease in CD62L positive CLL cells (p<0.0001, n=14). Co-culture with Hs5 cells, HUVECs, patient derived BMSC or BCR stimulation did not overcome Cucurbitacin I induced downregulation of CD62L. The effect of STAT3 inhibition on CLL cell adhesion and chemotaxis was also investigated. A microfluidic system including a neMESYS Low Pressure syringe pump system (Cetoni GmbH) and Cellix Vena8Endothelial+biochips coated with Human Umbilical Vein Endothelial cells (HUVECs) or Human Dermal Lymphatic Endothelial cells (HDLEC) was utilised to investigate CLL cell adhesion under fluid shear flow conditions. Flow rates of0.5 dynes/cm2 for the HUVEC-coated biochips and 0.08 dynes/cm2 for the HDLEC coated biochips were used to model the fluid shear of blood and lymphatic flow respectively. Treatment with Cucurbitacin I resulted in a mean decrease of 50% in CLL cell adhesion to HUVEC but not HDLEC in this system (p<0.05, n=3). Chemotaxis of CLL cells was investigated using Neuroprobe 96-well ChemoTx plates. Treatment with Cucurbitacin I resulted in a mean decrease of 87% of CLL cells migrated in response to the chemokine CXCL12 compared to control (p<0.0001, n=4). In conclusion, this study shows microenvironmental signals mediate the expression of CD62L in CLL cells. Our data suggest that the STAT3 pathway regulates the expression of CD62L and the adhesion and chemotaxis of CLL cells. The down-regulation of CD62L expression through inhibition of BCR signalling or direct inhibition of STAT3 may have implications for the trafficking of CLL cells and treatment of CLL. Disclosures No relevant conflicts of interest to declare.

Ibrutinib-Treated Platelets Secure Vascular Integrity in Inflammation

Background: Ibrutinib is a potent and irreversible inhibitor of Bruton's tyrosine kinase (Btk), and has been approved for treatment of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). In recent clinical trials, Ibrutinib has shown high efficacy with an excellent safety profile. However, bleeding events have been observed in a subset of patients in several of these trials. While these bleeding events are generally low grade and have not led to interruption or dose reduction of treatment, the origin of bleeding remains incompletely understood. In the setting of thrombocytopenia, inflammation can induce robust vascular permeability and hemorrhage, and our lab has previously shown that immunoreceptor tyrosine-based activation motif (ITAM) signaling is necessary for the protective effects of platelets against hemorrhage. In platelets Btk acts downstream of ITAM receptors, therefore we hypothesized that bleeding in Ibrutinib-treated patients may be, at least in part, the result of hemorrhage at sites of inflammation.Methods: To investigate the possibility that bleeding events in Ibrutinib-treated patients are due to inflammatory hemorrhage, we used two inflammatory models - the dermal reverse passive Arthus reaction (rpA) and P. aeruginosa LPS-induced lung inflammation, both of which have been shown to induce hemorrhage in the absence of platelet ITAM signaling. To selectively inhibit Btk in platelets, thrombocytopenic mice were reconstituted with Ibrutinib- or vehicle-treated wild-type platelets and challenged in rpA or LPS model. Bleeding in the dermis or broncho-alveolar lavage (BAL) fluid was assessed by analysis of hemoglobin. In the clinic, patients generally receive once-a-day doses of 420-560 mg of the Btk inhibitor Ibrutinib, and plasma concentrations can transiently reach 0.5-1 µM. Thus, during their lifetime, circulating platelets are exposed to compounding doses of Ibrutinib, which may have greater inhibitory effects than a single dose, a phenomenon which we have observed in mice (see results below). Therefore, we treated mouse platelets in vitro with 0.5 µM Ibrutinib (low dose, equal to a single dose) or 5 µM Ibrutinib (high dose, comparable to multiple dose exposure) before adoptive transfer into mice.Results: While low dose Ibrutinib did not prevent αIIbβ3 integrin activation induced by collagen or convulxin (Cvx), high dose Ibrutinib abolished collagen-induced aggregation. This dose-dependent inhibition of aggregation was also observed in platelets isolated from mice which had received a single vs. multiple doses of Ibrutinib in vivo. αIIbβ3 activation induced by the stronger GPVI agonist, Cvx, however was only partially impaired, suggesting that Ibrutinib may not completely inhibit ITAM-dependent platelet activation. We next tested whether platelets treated ex vivo with Ibrutinib and transfused into thrombocytopenic mice were able to secure vascular integrity at sites of inflammation. In both models, platelet depletion without transfusion of wild-type platelets induced substantial bleeding. However, transfusion of Ibrutinib-treated platelets was able to rescue bleeding to the same extent as vehicle-treated platelets.Summary: Our findings demonstrate that Ibrutinib-treated platelets are capable of securing vascular integrity at sites of inflammation in mice. Our studies suggest that bleeding events in patients treated with Ibrutinib are not due to inflammation-associated hemorrhage. DisclosuresBergmeier:AHA: Research Funding; NIH: Research Funding.

The Bruton Tyrosine Kinase (Btk) Inhibitor ACP-196: Marked Activity in Relapsed/Refractory CLL with a Favorable Safety Profile

The Bruton Tyrosine Kinase (Btk) Inhibitor ACP-196: Marked Activity in Relapsed/Refractory CLL with a Favorable Safety Profile

Hemophagocytic Lymphohistiocytosis in a Patient with Relapsed Chronic Lymphocytic Leukemia Treated with Ibrutinib

▪Introduction Hemophagocytic Lymphohistiocytosis (HLH) is a rare disorder characterized by an ineffective T-cell and NK response resulting in an exuberant cytokine production. Ibrutinib is an oral irreversible inhibitor of Bruton Tyrosine Kinase (Btk) significantly improving objective responses in patients with relapsed/refractory Chronic Lymphocytic Leukemia (CLL). We report the diagnostic work up and the clinical course of a case of HLH occurring in a patient with relapsed CLL during treatment with ibrutinib. Case report: the patient was a 77-years-old male diagnosed with CLL at the age of 70. At time diagnosis, the disease presented with unfavorable prognostic markers (CD38pos, ZAP70pos and unmutated IGVH). Two years later, the patient developed progressive lymphoadenopathy and a fludarabine-based regimen was administered. No objective response was observed and multiple lines of treatment attained only partial short lasting responses. In the presence of refractory disease with del17p Ibrutinib at a daily dose of 420 mg was started. On day 7 of treatment, febrile neutropenia occurred that did not benefit from antibiotics therapy. Due to persistent fever and deterioration of the clinical picture on day 16, Ibrutinib was hold and the patient hospitalized. Blood counts progressively dropped and disseminated intravascular coagulation complicated the clinical course. Additionaly, splenomegaly, hypertriglyceridemia and unexplainable severe hyperferritinemia (23,023 ng/mL) were encountered. The occurrence of 5 out of 8 diagnostic criteria allowed for a diagnosis of HLH to be made and treatment with dexamethasone, in combination with cyclosporin A and intravenous immunoglobulin, was started (Figure 1). We performed viral genome load and cytokine dosage tests on sera samples, showing high serum EBV genome title. In consideration of the activity of anticytokine treatment in the setting of HLH, the patient was treated by anti-interleukin(IL)-6 receptor Tocilizumab. Despite intensive supportive treatment, irreversible multiorgan failure developed with life-threatening bleeding and death.We retrospectively measured at two different time points the levels of interleukin (IL)1beta, IL2, IL6, IL10, IL12, IL18 and TNFalfa. In both samples, the IL1beta, IL6, IL10 and IL18 were significantly elevated compared with two healthy controls (Figure 2). Conclusion: HLH is a rare occurrence in CLL and the relationship with ibrutinib treatment is uncertain in this patient. However it is worth noting that off-target effects of ibrutinib may include downregulation of CD8/NK activity which may be involved in initiating HLH. The demonstration of IL6 elevated levels confirmed that Tocilizumb may be effective in the treatment of HLH. [Display omitted] [Display omitted] DisclosuresOff Label Use: Tocilizumab for the treatment of HLH. Cuneo:Roche: Speakers Bureau; Gilead: Speakers Bureau; Jannsen: Speakers Bureau; Celgene: Speakers Bureau; Novartis: Speakers Bureau.

CD25 (IL2RA) Orchestrates Negative Feedback Control and Stabilizes Oncogenic Signaling Strength in Acute Lymphoblastic Leukemia

Background and hypothesis: CD25 (IL2RA) represents the α chain of the interleukin 2 receptor on T cells and plays an important role in the maintenance of regulatory T (Treg) cells, hence preventing T cell autoimmunity. In a comprehensive gene expression analysis, we found that CD25 is specifically upregulated by pre-B cell receptor (pre-BCR) signaling during early B cell development and oncogenic tyrosine kinase that mimic pre-BCR signaling (e.g. in Ph+ ALL and Ph-like ALL). In adults with Ph+ ALL (ECOG; MDACC) and children with Ph-like ALL (P9906) patients with CD25 expression at the time of diagnosis have a particularly poor outcome (n=416; P =0.005). For these reasons, we studied the function of CD25 in B cell development and leukemia in a series of genetic experiments.Results: Unlike T cells, CD25 (IL2RA) does not function as IL2 receptor chain in B cells and B-lineage ALL: CD25 expressed on B-lineage cells did not pair with IL2Rb and g-chains and was not responsive to IL2. Il2ra-/- B cells were arrested at the pre-B cell stage with hyperactive pre-BCR downstream signaling including SRC, BTK and ERK. In the presence of CD25, Il2ra+/+ B cells responded to engagement of the pre-BCR with phosphorylation of pre-BCR downstream tyrosine kinases and coordinated release of Ca2+ from cytoplasmic stores. In the absence of CD25 (Il2ra-/-), the pre-BCR signals autonomously, resulting in uncoordinated Ca2+ oscillations of variable duration. While CD25 does not function as IL2 receptor chain in B cells, it coordinates pre-BCR-dependent signal transduction and regulates its intensity.The pre-BCR related tyrosine kinase BTK is phosphorylated by BCR-ABL1 in Ph+ ALL and other tyrosine kinase oncogenes in Ph-like ALL (Chen et al., 2015). Interestingly, overexpression of a constitutively active form of BTK resulted in strong upregulation of CD25 surface expression. Conversely, the BTK-inhibitor ibrutinib abolished CD25 expression suggesting that feedback control between pre-BCR signaling and CD25 requires BTK.The ability of CD25 to stabilize oncogenic signaling strength in Ph+ ALL and Ph-like ALL was important for leukemia-initiation and development of fatal disease. In the absence of CD25, Il2ra-/- ALL cells showed impaired proliferation and colony formation. Serial transplantation experiments revealed a profound defect of Il2ra-/- ALL cells to initiate leukemia. 100-times more cells were required to cause fatal disease. In addition, CD25 expression mediated drug-resistance in ALL cells: In patient-derived pre-B ALL cells with heterogeneous CD25 expression, vincristine selectively induced apoptosis in CD25Low cells but spared CD25High ALL cells. Combination with an anti-CD25 immunotoxin efficiently eradiated CD25High leukemia cells and sensitized the ALL cell population to treatment with vincristine.To elucidate the mechanism of how CD25 coordinates negative feedback control of pre-BCR signaling or its oncogenic mimics, we focused on its short (13aa) cytoplasmic tail, which includes two phosphorylation sites (S268 and T271) that are known substrates for serine/threonine protein kinase, PKCα. To identify cytoplasmic interaction partners of CD25, we overexpressed a Flag-tagged truncated form of CD25 including a myristoylation signal for constitutive membrane localization, transmembrane domain and cytoplasmic tail. Immunoprecipitation (IP; Flag) followed by 2D mass spectrometry revealed strong interactions of PP2A with cytoplasmic tail of CD25. Western blots showed additional strong interactions of the cytoplasmic tail of CD25 with inhibitory phosphatases PTEN, SHP1 and SHIP1. Importantly, reconstitution of myristoylated CD25 tail but not a mutant construct lacking the serine/threonine motif (S268A/T271A) rescued proliferation and survival defects of Il2ra-/- ALL cells.Conclusion: We identified CD25 as a surface receptor that mediates membrane recruitment of PP2A, PTEN, SHP1 and SHIP1, which balances fluctuations in signaling output from a pre-B cell receptor or its oncogenic mimic in ALL cells (e.g. BCR-ABL1 in Ph+ ALL). We propose that CD25-mediated negative feedback control stabilizes oncogenic tyrosine kinase signaling and mediates drug-resistance in Ph+ ALL and Ph-like ALL cells. Targeted inhibition using CD25-directed immunotoxins may be useful in new approaches to overcome drug-resistance in Ph+ ALL and Ph-like ALL. DisclosuresNo relevant conflicts of interest to declare.

Nonreceptor tyrosine kinases ITK and BTK negatively regulate mast cell proinflammatory responses to lipopolysaccharide

Mast cells are indispensable for LPS-induced septic hypothermia, in which TNF-α plays an essential role to initiate septic responses. ITK and BTK regulate mast cell responses to allergens, but their roles in mast cell responses in LPS-induced sepsis are unclear. We sought to investigate the roles of ITK and BTK in mast cell responses during LPS-induced septic inflammation. Mice (genetically modified or bone marrow-derived mast cell-reconstituted Sash) were given LPS to induce septic hypothermia in the presence or absence of indicated inhibitors. Flow cytometry was used to determine LPS-induced cell influx and TNF-α production in peritoneal cells. Microarray was used for genomewide gene expression analysis on bone marrow-derived mast cells. Quantitative PCR and multiplex were used to determine transcribed and secreted proinflammatory cytokines. Microscopy and Western blotting were used to determine activation of signal transduction pathways. The absence of ITK and BTK leads to exacerbation of LPS-induced septic hypothermia and neutrophil influx. Itk(-/-)Btk(-/-) mast cells exhibit hyperactive preformed and LPS-induced TNF-α production, and lead to more severe LPS-induced septic hypothermia when reconstituted into mast cell-deficient Sash mice. LPS-induced nuclear factor kappa B, Akt, and p38 activation is enhanced in Itk(-/-)Btk(-/-) mast cells, and blockage of phosphatidylinositol-4,5-bisphosphate 3-kinase, Akt, or p38 downstream mitogen-activated protein kinase interacting serine/threonine kinase 1 activation significantly suppresses TNF-α hyperproduction and attenuates septic hypothermia. ITK and BTK regulate thermal homeostasis during septic response through mast cell function in mice. They share regulatory function downstream of Toll-like receptor 4/LPS in mast cells, through regulating the activation of canonical nuclear factor kappa B, phosphatidylinositol-4,5-bisphosphate 3-kinase/Akt, and p38 signaling pathways.

A novel 2,5-diaminopyrimidine-based affinity probe for Bruton's tyrosine kinase.

As a critical regulator of the B-cell receptor signaling pathway, Bruton’s tyrosine kinase (Btk) has attracted intensive drug discovery efforts for treating B-cell lineage cancers and autoimmune disorders. In particular, covalent inhibitors targeting Cys481 in Btk have demonstrated impressive clinical benefits, and their companion affinity probes have been crucial in the drug development process. Recently, we have discovered a novel series of 2,5-diaminopyrimidine-based covalent irreversible inhibitors of Btk. Here, we present the discovery of a novel affinity Btk probe based on the aforementioned scaffold and demonstrate its usage in evaluating the target engagement of Btk inhibitors in live cells.

Conditional knockdown of BCL2A1 reveals rate-limiting roles in BCR-dependent B-cell survival.

Bcl2 family proteins control mitochondrial apoptosis and its members exert critical cell type and differentiation stage-specific functions, acting as barriers against autoimmunity or transformation. Anti-apoptotic Bcl2a1/Bfl1/A1 is frequently deregulated in different types of blood cancers in humans but its physiological role is poorly understood as quadruplication of the Bcl2a1 gene locus in mice hampers conventional gene targeting strategies. Transgenic overexpression of A1, deletion of the A1-a paralogue or constitutive knockdown in the hematopoietic compartment of mice by RNAi suggested rate-limiting roles in lymphocyte development, granulopoiesis and mast cell activation. Here we report on the consequences of conditional knockdown of A1 protein expression using a reverse transactivator (rtTA)-driven approach that highlights a critical role for this Bcl2 family member in the maintenance of mature B-cell homeostasis. Furthermore, we define the A1/Bim (Bcl-2 interacting mediator of cell death) axis as a target of key kinases mediating B-cell receptor (BCR)-dependent survival signals, such as, spleen tyrosine kinase (Syk) and Brutons tyrosine kinase (Btk). As such, A1 represents a putative target for the treatment of B-cell-related pathologies depending on hyperactivation of BCR-emanating survival signals and loss of A1 expression accounts, in part, for the pro-apoptotic effects of Syk- or Btk inhibitors that rely on the ‘BH3-only' protein Bim for cell killing.

Bruton’s tyrosine kinase in chronic inflammation: from pathophysiology to therapy

Bruton's tyrosine kinase (Btk) not only plays a role in differentiation and activa- tion of B-cells but is also involved in regulating signaling in myeloid cell populations, mast cells, platelets, and osteoclasts. Btk plays a critical role in B-cell receptor signaling and has been shown to be involved in CD40 ligation, Toll-like receptor triggering, and Fc-receptor signaling as well, suggesting that targeting Btk might be particularly useful in autoimmune diseases characterized by pathologic antibodies, macrophage activation, and myeloid-derived type I interferon responses. Btk knockout and X-linked immunodeficiency mouse material and X-linked agammaglobulinemia patient samples are powerful tools to examine the role of Btk in health and disease. In addition, the recent development of several covalent and noncovalent small-molecule inhibitors specifically targeting Btk can contribute to our understanding of the functional role of Btk in several cell types and disease mechanisms. Specific Btk inhibitors have been used in both in vitro and in vivo models for autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis, systemic sclerosis, and Sjogren's syndrome. The current small-molecule Btk inhibitors have demonstrated potent and selective Btk inhibition in preclinical studies, and some inhibitors have propelled the clinical develop- ment of such molecules toward clinical trials in patients with rheumatoid arthritis. Future studies on the effectiveness of Btk inhibition in other autoimmune diseases could further broaden the understanding of the disease mechanisms as well as lead to new targeted therapies.

Abstract IA11: Monoclonal antibodies and in situ vaccination.

Abstract Traditional therapies for lymphoma have targeted features of the tumor, itself, such as cell surface molecules and intracellular signaling pathways. Increasingly, we are gaining therapeutic approaches that target the host microenvironment, and especially the host immune system. An exciting challenge is to combine these therapies in ways that are at least additive, and hopefully synergistic. We will present recent examples that combine therapies that target both the tumor and the host. Small molecule inhibitors of survival pathways in lymphoma cells, such as B cell receptor signaling, also have effects on the immune system. A case is point is Ibrutinib, a covalent inhibitor of Bruton's tyrosine kinase (Btk), recently approved for the treatment of CLL and MCL and with significant clinical activity in other lymphoid malignancies. Ibrutinib inhibits other members of the Tec kinase family, such as Itk, an important signaling molecule in subsets of T cells. By doing so, it can sculpt the T cell immune response and direct it against the tumor. Recent preclinical experiments indicate that Ibrutinib can enhance the T cell immune response induced by in situ vaccination as well as other immunotherapeutic maneuvers. These results imply a greater role for Ibrutinib than currently envisioned, one where it may be employed as an immune enhancer in addition to a targeted anti-tumor agent. Abscopal tumor responses can be induced in patients with lymphoma by local in situ vaccination. CpG ologonucleotide, a ligand for a Toll-like receptor, is injected into one site of tumor and low dose radiation is directed to the same site (Brody et. al. J Clin Oncol. 2010;28(28):4324). In preclinical animal models this treatment generates an anti-tumor T cell immune response. Such T cell responses can be enhanced by additional intra-tumoral injections of antibodies against immune checkpoints, such as CTLA4 and OX40 (Marabelle et al. J Clin Invest. 2013;123(6):2447). These antibodies work by depleting the negative T regulatory cells (Tregs) in the local tumor microenvironment, unleasing T effector cells to attack tumor at distant sites. Very low doses of checkpoint antibodies can be used to avoid autoimmune adverse effects. Such combinations of low dose radiation with immune enhancing agents may change the way we employ radiotherapy in the future- to help trigger immune responses rather than to sterilize the local tumor site. The therapeutic power of antibodies can be enhanced by stimulating ADCC, a primary mechanism of anti-tumor effect. One way to accomplish this is to target CD137, an activation molecule that appears on host NK cells after they encounter tumor cells coated by an anti-tumor antibody. In preclinical models the combination of an anti-CD20 with an anti-CD137 antibody is impressively synergistic (Kohrt et. al. Blood. 2011,117(8):2423). CD137 is also expressed on activated T cells and therefore the antibody against CD137 might also enhance an underlying host anti tumor T cell immune response. Two clinical trials are now under way to test the effect of an antibody against CD137 as a single agent and in combination with rituximab in patients with relapsed/refractory lymphoma. Citation Format: Ronald Levy. Monoclonal antibodies and in situ vaccination. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr IA11.

WHI-131 Promotes Osteoblast Differentiation and Prevents Osteoclast Formation and Resorption in Mice.

The small molecule WHI-131 is a potent therapeutic agent with anti-inflammatory, antiallergic, and antileukemic potential. However, the regulatory effects of WHI-131 on osteoblast and osteoclast activity are unclear. We examined the effects of WHI-131 on osteoblast and osteoclast differentiation with respect to bone remodeling. The production of receptor activator of nuclear factor kappa-B ligand (RANKL) by osteoblasts in response to interleukin (IL)-1 or IL-6 stimulation decreased by 56.8% or 50.58%, respectively, in the presence of WHI-131. WHI-131 also abrogated the formation of mature osteoclasts induced by IL-1 or IL-6 stimulation. Moreover, WHI-131 treatment decreased RANKL-induced osteoclast differentiation of bone marrow-derived macrophages, and reduced the resorbing activity of mature osteoclasts. WHI-131 further decreased the mRNA and protein expression levels of c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) by almost twofold, and significantly downregulated the mRNA expression of the following genes: tartrate-resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR), DC-STAMP, OC-STAMP, ATP6v0d2, and cathepsin K (CtsK) compared with the control group. WHI-131 further suppressed the phosphorylation of protein kinase B (Akt) and degradation of inhibitor of kappa B (IκB); Ca(2+) oscillation was also affected, and phosphorylation of the C-terminal Src kinase (c-Src)-Bruton agammaglobulinemia tyrosine kinase (Btk)-phospholipase C gamma 2 (PLCγ2) (c-Src-Btk-PLCg2 calcium signaling pathway) was inhibited following WHI-131 treatment. The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway was activated by WHI-131, accompanied by phosphorylation of STAT3 Ser727 and dephosphorylation of STAT6. In osteoblasts, WHI-131 caused an approximately fourfold increase in alkaline phosphatase activity and Alizarin Red staining intensity. Treatment with WHI-131 increased the mRNA expression levels of genes related to osteoblast differentiation, and induced the phosphorylation of Akt, p38, and Smad1/5/8. Furthermore, 5-week-old ICR mice treated with WHI-131 exhibited antiresorbing effects in a lipopolysaccharide-induced calvaria bone loss model in vivo and increased bone-forming activity in a calvarial bone formation model. Therefore, the results of this study show that WHI-131 plays a dual role by inhibiting osteoclast differentiation and promoting osteoblast differentiation. Thus, WHI-131 could be a useful pharmacological agent to treat osteoporosis by promoting bone growth and inhibiting resorption.

Abstract 2596: ACP-196: a novel covalent Bruton's tyrosine kinase (Btk) inhibitor with improved selectivity and in vivo target coverage in chronic lymphocytic leukemia (CLL) patients

Abstract Ibrutinib, a first generation Btk inhibitor, is approved for the treatment of CLL and mantle cell lymphoma; known toxicities include atrial fibrillation, diarrhea, rash, arthralgia and bleeding events (1). Recent reports show ibrutinib's off target effects may negatively impact its potential for combined therapy with anti-CD20 antibodies (2,3). Here we describe the pharmacologic characterization of ACP-196 a potent, novel second generation Btk inhibitor, which binds covalently to Cys481 with improved selectivity and in vivo target coverage. Compared to ibrutinib and CC-292, ACP-196 demonstrated higher selectivity for Btk when profiled against a panel of 395 non-mutant kinases (1 μM) in a competitive binding assay. IC50 determinations on 9 kinases with a Cys in the same position as Btk showed ACP-196 to be the most selective. The improved selectivity is related to the reduced intrinsic reactivity of ACP-196's electrophile. Importantly, unlike ibrutinib, ACP-196 did not inhibit EGFR, Itk or Txk. Phosphoflow assays on EGFR expressing cell lines confirmed ibrutinib's EGFR inhibition (EC50: 47-66 nM) with no inhibition observed for ACP-196 at 10 μM. These data may explain the ibrutinib-related incidence of diarrhea and rash. Ibrutinib's potency on Itk and Txk may explain why it interferes with cell-mediated anti-tumor activities of therapeutic CD20 antibodies and immune-mediated killing in the tumor microenvironment (2,3). In human whole blood, ACP-196 and ibrutinib showed robust and equipotent inhibitory activity on B-cell receptor induced responses in the low nM range, whereas CC-292 was 10-20 fold less potent. In vivo, oral administration of ACP-196 in mice resulted in dose-dependent inhibition of anti-IgM-induced CD86 expression in CD19+ splenocytes with an ED50 of 0.34 mg/kg compared to 0.91 mg/kg for ibrutinib. A similar model was used to compare the duration of Btk inhibition after a single oral dose of 25 mg/kg. ACP-196 and ibrutinib inhibited CD86 expression >90% at 3h and ∼50% at 24h postdose. In contrast, CC-292 inhibited ∼50% at 3h and ∼20% at 24h postdose. An ELISA based Btk target occupancy assay was developed to measure target coverage in preclinical and clinical studies. In healthy volunteers, ACP-196 at an oral dose of 100 mg QD showed >90% target coverage over a 24h period. Btk occupancy and regulation of the PD markers (CD69 and CD86) correlated with PK parameters for exposure. In CLL patients, after 7 days of dosing with ACP-196 at 200 mg QD, 94% Btk target occupancy was observed compared with ∼80% reported for ibrutinib at 420 mg QD (4). In conclusion, ACP-196 is a novel Btk inhibitor with key pharmacologic differentiators versus ibrutinib and CC-292. ACP-196 is currently being evaluated in clinical trials. 1. IMBRUVICA package insert 2014 2. Rajasekaran Blood 2014 Abstr # 3118 3. Da Roit Haematologica 2014 4. Byrd NEJM 2013 Citation Format: Todd Covey, Tjeerd Barf, Michael Gulrajani, Fanny Krantz, Bart van Lith, Elena Bibikova, Bas van de Kar, Edwin de Zwart, Ahmed Hamdy, Raquel Izumi, Allard Kaptein. ACP-196: a novel covalent Bruton's tyrosine kinase (Btk) inhibitor with improved selectivity and in vivo target coverage in chronic lymphocytic leukemia (CLL) patients. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2596. doi:10.1158/1538-7445.AM2015-2596

Abstract 408: ACP-196, an orally bioavailable covalent selective inhibitor of Btk, modulates the innate tumor microenvironment, exhibits antitumor efficacy and enhances gemcitabine activity in pancreatic cancer

Abstract Pancreatic ductal adenocarcinoma exists in a complex desmoplastic microenvironment that provides stromal support for tumor growth and conceals the tumor from immune surveillance. Tumor-associated stroma comprises a mix of fibroblasts, immunosuppressive T regulatory cells (Tregs), myeloid suppressive monocytes (MDSCs) and tumor-associated macrophages (TAMs) that promote tumor growth and restrain immune-mediated tumor cell killing. The targeting of immune infiltrates may impair stromal support and enhance immune-mediated killing of pancreatic cancer cells. Bruton's tyrosine kinase (Btk) is a nonreceptor enzyme in the Tec kinase family expressed among cells of hematopoietic origin including B cells, myeloid cells, mast cells and platelets, but not T cells, where it regulates multiple cellular processes. Here we describe an unexpected finding of ACP-196, a potent, novel, second generation Btk inhibitor with improved selectivity and target coverage that binds covalently to a cysteine residue (Cys481) in the front position of the ATP-binding pocket. In an orthotopic mouse model of pancreatic cancer, KPC derived pancreatic cancer cells (KrasG12D; Trp53R172H; Pdx1-Cre) were injected into the pancreases. Vehicle, single agent ACP-196 (15 mg/kg/BID, gavage), single agent gemcitabine (50 mg/kg, IV) and combination ACP-196 with gemcitabine were evaluated for efficacy. By 4 weeks of treatment, mice in the vehicle group showed signs of health deterioration and all mice were euthanized, tumors were collected and measured. Relative to the vehicle treatment, ACP-196 monotherapy resulted in a >2-fold reduction in tumor growth compared with less than a 2-fold reduction with gemcitabine alone. The combination of ACP-196 and gemcitabine resulted in a further reduction in tumor growth when compared to each single agent. Interestingly, analysis of tumor tissues showed that single agent ACP-196 inhibited immunosuppressive populations of TAMs and MDSCs. Surprisingly, Treg populations were also reduced with a robust expansion of CD8+ T cells in the tumors. None of these effects were observed with gemcitabine alone. Although Btk is not expressed in T cells, this finding maybe the result of inhibiting the MDSC and TAM populations within the tumor microenvironment, a mechanism of action which is currently under investigation. Taken together, these data identify Btk as a novel target for modulating tumor immune escape and suggest that pharmacologic targeting of suppressive myeloid cells by ACP-196 induces therapeutic benefit. ACP-196 is currently being evaluated in clinical trials including frontline and salvage pancreatic cancer. Citation Format: Brian J. Lannutti, Michael Gulrajani, Fanny Krantz, Elena Bibikova, Todd Covey, Katti Jessen, Wayne Rothbaum, David M. Johnson, Roger Ulrich. ACP-196, an orally bioavailable covalent selective inhibitor of Btk, modulates the innate tumor microenvironment, exhibits antitumor efficacy and enhances gemcitabine activity in pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 408. doi:10.1158/1538-7445.AM2015-408

Abstract 2599: Discovery and pharmacological characterization of the second generation of Btk inhibitors with improved target selectivity and enhanced in vivo efficacy

Abstract Bruton's tyrosine kinase (Btk) is an essential component of the B-cell receptor (BCR) signaling pathways regulating survival, activation, proliferation, and differentiation of B lymphocytes. The first Btk inhibitor, Ibrutinib, has demonstrated a significant clinical efficacy in a variety of B-cell malignancies. Through structure-guided approach, we have discovered two series of novel and potent Btk inhibitors, represented by EBI-1266 and EBI-1367, respectively. Both of these compounds showed high potency in inhibiting Btk kinase activity and growth of a number of aggressive lymphoma cell lines driven by aberrant BCR signaling, with IC50 value within low nanomolar range. Mechanistic studies examining BCR signaling pathway in related B cell lymphoma cell lines revealed that both EBI-1266 and EBI-1367 potently inhibited Btk phosphorylation and downstream Erk phosphorylation, similar to Ibrutinib. Furthermore, each compound showed unique and significant superiority over Ibrutinib: EBI-1266 had a cleaner selectivity profile against a panel of kinases with a cysteine residue in the conserved catalytic domain, and EBI-1367 exhibited >10-fold higher in vivo exposure in multiple preclinical species. In a tumor xenograft mouse model where tumor growth is dependent on Btk activity, both EBI-1266 and EBI-1367 showed significant oral anti-tumor activities, with EBI-1367 being more efficacious than Ibrutinib, consistent with a higher exposure of EBI-1367 in both blood and tumor tissues. No evidence of overt toxicities was observed in rodents with prolonged oral administration for two weeks with doses at least 3-fold above a highly efficacious dose. In summary, the pharmacological profiles of EBI-1266 and EBI-1367 indicate that these compounds have a great potential to become the next generation of Btk inhibitors, offering advantages in pharmaceutical development, enhanced in vivo efficacy and reduced toxicities. We are currently performing IND-enabling studies aiming to initiate phase I clinical trials for these Btk inhibitors. Citation Format: Jiayin Zhang, Dong Liu, Ru Shen, Yinfa Yan, Liuqing Yang, Minsheng Zhang, Jun Feng, Beibei Fu, Jerry Hu, Biao Lu, Hong Wan, Lei Zhang, Weikang Tao, Lianshan Zhang, Jingsong Cao. Discovery and pharmacological characterization of the second generation of Btk inhibitors with improved target selectivity and enhanced in vivo efficacy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2599. doi:10.1158/1538-7445.AM2015-2599

Abstract 259: Ibrutinib enhances the anti-tumor efficacy of CTLA-4 blockade in lymphoma and colon cancer models

Abstract The anti-CTLA-4 antibody ipilimumab was the first immune checkpoint blockade antibody to show significant clinical efficacy. However, only a subset of the treated melanoma patients had long-term survival benefits (Schadendorf, D., et al. ECCO 2013). Combining ipilimumab with an agent that modulates immunity by a different mechanism may improve efficacy. Ibrutinib is a first-in-class, oral, covalent inhibitor of Bruton's tyrosine kinase (Btk), an essential enzyme in the B-cell receptor signaling pathway. Ibrutinib also inhibits the interleukin-2-inducible Tec kinase (Itk) that is required for the activation/survival of Th2 T cells. This activity is consistent with preclinical studies that demonstrated ibrutinib could potentiate Th1 immunity (Dubovsky, JA., et al. Blood 2013). We investigated whether ibrutinib could enhance the anti-tumor effect of CTLA-4 blockade using the A20 B-cell lymphoma and the CT26 colon carcinoma mouse models. BALB/c mice (9-11/group) were implanted with tumor cells subcutaneously on the hind flanks. Animals bearing 80-100 mm3 (D x d2 x 0.4) tumors were dosed daily with oral ibrutinib (24 mg/kg) with or without the anti-mouse CTLA-4 antibody 9D9 (100 μg/mouse) given every 2 days by intraperitoneal injections. Animals in the lymphoma and colon cancer models were treated for 13 and 37 days, respectively. Tumor volume was measured and survival recorded for up to 2 months after tumor inoculation. Neither the A20 tumors, which express Btk, nor the CT26 tumors were inhibited by ibrutinib. In the A20 model, although 9D9 alone resulted in complete tumor regression in 7 of 9 treated animals, tumors in 2 of the 7 mice relapsed after treatment had ended. In contrast, 9D9 in combination with ibrutinib led to rapid, complete, and durable responses in 7 of 9 treated animals that lasted until the end of the study. In the CT26 model, treatment with 9D9 alone had minimal effects on tumor growth, but the addition of ibrutinib led to complete tumor regression in 6 of 10 treated animals. Thus, ibrutinib enhanced the anti-tumor efficacy of an anti-CTLA-4 antibody in B-cell lymphoma and colon carcinoma mouse models. The mechanism of tumor eradication by the combination therapy is under investigation and will be discussed at presentation. Citation Format: Patrick Ng, Daniel Lu, Betty Chang. Ibrutinib enhances the anti-tumor efficacy of CTLA-4 blockade in lymphoma and colon cancer models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 259. doi:10.1158/1538-7445.AM2015-259

Bruton's Tyrosine Kinase Synergizes with Notch2 To Govern Marginal Zone B Cells in Nonobese Diabetic Mice.

Expansion of autoimmune-prone marginal zone (MZ) B cells has been implicated in type 1 diabetes. To test disease contributions of MZ B cells in NOD mice, Notch2 haploinsufficiency (Notch2(+/-)) was introduced but failed to eliminate the MZ, as it does in C57BL/6 mice. Notch2(+/-)/NOD have MZ B cell numbers similar to those of wild-type C57BL/6, yet still develop diabetes. To test whether BCR signaling supports Notch2(+/-)/NOD MZ B cells, Bruton's tyrosine kinase (Btk) deficiency was introduced. Surprisingly, MZ B cells failed to develop in Btk-deficient Notch2(+/-)/NOD mice. Expression of Notch2 and its transcriptional target, Hes5, was increased in NOD MZ B cells compared with C57BL/6 MZ B cells. Btk deficiency reduced Notch2(+/-) signaling exclusively in NOD B cells, suggesting that BCR signaling enhances Notch2 signaling in this autoimmune model. The role of BCR signaling was further investigated using an anti-insulin transgenic (Tg) BCR (125Tg). Anti-insulin B cells in 125Tg/Notch2(+/-)/NOD mice populate an enlarged MZ, suggesting that low-level BCR signaling overcomes reliance on Notch2. Tracking clonotypes of anti-insulin B cells in H chain-only VH125Tg/NOD mice showed that BTK-dependent selection into the MZ depends on strength of antigenic binding, whereas Notch2-mediated selection does not. Importantly, anti-insulin B cell numbers were reduced by Btk deficiency, but not Notch2 haploinsufficiency. These studies show that 1) Notch2 haploinsufficiency limits NOD MZ B cell expansion without preventing type 1 diabetes, 2) BTK supports the Notch2 pathway in NOD MZ B cells, and 3) autoreactive NOD B cell survival relies on BTK more than Notch2, regardless of MZ location, which may have important implications for disease-intervention strategies.

Optimized Near-IR Fluorescent Agents for in Vivo Imaging of Btk Expression.

Bruton's tyrosine kinase (Btk) is intricately involved in anti-apoptotic signaling pathways in cancer and in regulating innate immune response. A number of Btk inhibitors are in development for use in treating B-cell malignancies and certain immunologic diseases. To develop robust companion imaging diagnostics for in vivo use, we set out to explore the effects of red wavelength fluorochrome modifications of two highly potent irreversible Btk inhibitors, Ibrutinib and AVL-292. Surprisingly, we found that subtle chemical differences in the fluorochrome had considerable effects on target localization. Based on iterative designs, we developed a single optimized version with superb in vivo imaging characteristics enabling single cell Btk imaging in vivo. This agent (Ibrutinib-SiR-COOH) is expected to be a valuable chemical tool in deciphering Btk biology in cancer and host cells in vivo.