Bruton's Tyrosine Kinase Expression Research Articles

Abstract 2578: Synthetic lethal approaches to aurora inhibition in aggressive B-cell non-Hodgkin lymphoma

Abstract We explored synthetic lethality in the context of aurora inhibition with novel combination therapies for aggressive B-NHL. Aurora A and B are serine/threonine kinases and when amplified dysregulate the mitotic phase of the cell cycle. Pre-clinical and clinical evidence demonstrate that aurora inhibition has therapeutic benefit in aggressive B-NHL. Alisertib, an aurora inhibitor has single agent activity in B-NHL mouse xenograft tumors and clinical trials. Pre-clinical studies demonstrate Bruton's tyrosine kinase (BTK) is persistently expressed despite alisertib therapy. TMAs for DLBCL (S0313, S0515, N = 60) and MCL (S0213, S0601, N = 45) were generated to evaluate aurora A, B and BTK expression by IHC. We developed B-NHL cell lines resistant to alisertib to evaluate mechanisms of acute and chronic resistance and knock down of aurora A and B to evaluate Myc, Bcl2 and BTK expression. Mouse B-NHL xenograft models were conducted to demonstrate synthetic lethality of aurora plus BTK inhibition. We demonstrate synergistic inhibition of cell proliferation associated with apoptosis, particularly in ABC and double hit DLBCL and mantle cell lymphoma (MCL) cells. Ibrutinib completely inhibited BTK and AKT activity at 3.0μM without affecting BTK or AKT protein level in B-NHL cells that co-over-express Myc and Bcl-2. Aurora A and B knockdown show compromised oncogene expression. IHC indicated in DLBCL and MCL aurora B to be differentially over-expressed versus aurora A and BTK. Alisertib plus ibrutinib was highly synergistic in inhibiting cell proliferation and inducing apoptosis in B-NHL cells. Moreover, this effect was amplified with the addition of rituximab. Acute and chronic resistance to alisertib was due to ERK1/2 activation. Significantly greater apoptosis was induced in the triplet combination (alisertib + ibrutinib + rituximab) compared to doublet combinations (ibrutinib + rituximab or alisertib + ibrutinib or alisertib + rituximab). Mouse xenograft models of MCL (Granta-519) and double hit DLBCL (U2932) showed ibrutinib alone had no anti-B-NHL activity. Ibrutinib + alisertib lead to tumor growth inhibition (TGI) of ∼50% in MCL and ∼30% in DLBCL (p = 0.005). Interestingly, ibrutinib + rituximab lead to a TGI of ∼60% (p = 0.005) in both B-NHL mouse models. In contrast, triplet therapy with alisertib plus ibrutinib plus rituximab demonstrated a statistically significant tumor TGI of ∼70-90% (p = 0.005) in both B-NHL mouse models with an associated enhanced overall survival (>70 days). Harvested tumors at the end of treatment(s) demonstrated target inhibition and increased apoptosis with triple therapy. Inhibition of BTK plus rituximab in the presence of aurora inhibition is synthetic lethal in B-NHL and warrant clinical trial evaluation. Citation Format: Daruka Mahadevan, Carla Morales, Laurence Cooke, Manjari Pandey, Catherine Spier, Wenqing Qi. Synthetic lethal approaches to aurora inhibition in aggressive B-cell non-Hodgkin lymphoma. [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 2578. doi:10.1158/1538-7445.AM2015-2578

Role of Bruton's tyrosine kinase inhibitors in HIV-1-infected cells.

Many cellular cofactors have been documented to be critical for various stages of viral replication. Using high-throughput proteomic assays, we have previously identified Bruton's tyrosine kinase (BTK) as a host protein that was uniquely upregulated in the plasma membrane of human immunodeficiency virus (HIV-1)-infected T cells. Here, we have further characterized the BTK expression in HIV-1 infection and show that this cellular factor is specifically expressed in infected myeloid cells. Significant upregulation of the phosphorylated form of BTK was observed in infected cells. Using size exclusion chromatography, we found BTK to be virtually absent in the uninfected U937 cells; however, new BTK protein complexes were identified and distributed in both high molecular weight (∼600 kDa) and a small molecular weight complex (∼60-120 kDa) in the infected U1 cells. BTK levels were highest in cells either chronically expressing virus or induced/infected myeloid cells and that BTK translocated to the membrane following induction of the infected cells. BTK knockdown in HIV-1-infected cells using small interfering RNA (siRNA) resulted in selective death of infected, but not uninfected, cells. Using BTK-specific antibody and small-molecule inhibitors including LFM-A13 and a FDA-approved compound, ibrutinib (PCI-32765), we have found that HIV-1-infected cells are sensitive to apoptotic cell death and result in a decrease in virus production. Overall, our data suggests that HIV-1-infected cells are sensitive to treatments targeting BTK expressed in infected cells.

A novel BTK gene mutation creates a de-novo splice site in an X-linked agammaglobulinemia patient

Bruton's tyrosine kinase (BTK), encoded by the BTK gene, is a cytoplasmic protein critical in B cell development. Mutations in the BTK gene cause X-linked agammaglobulinemia (XLA), a primary immunodeficiency with characteristically low or absent B cells and antibodies. This report describes a five year-old boy who presented with otitis externa, arthritis, reduced immunoglobulins and no B cells. Flow cytometry showed undetectable monocyte BTK expression. Sequencing revealed a novel mutation at exon 13 of the BTK gene which created a de novo splice site with a proximal 5 nucleotide loss resulting in a truncated BTK protein. The patient still suffered from ear infection despite intravenous immunoglobulin replacement therapy. In this study, mosaicism was seen only in the mother's genomic DNA. These results suggest that a combination of flow cytometry and BTK gene analysis is important for XLA diagnosis and carrier screening.

Mutations in Bruton’s tyrosine kinase impair IgA responses

X-linked agammaglobulinemia (XLA) is a primary immunodeficiency caused by mutations in Bruton's tyrosine kinase (BTK), and is characterized by markedly decreased numbers of blood B cells and an absence of all immunoglobulin isotypes. We performed whole exome sequencing in a male pediatric patient with dysgammaglobulinemia with IgA deficiency. Genetic analysis revealed a BTK missense mutation (Thr316Ala). To investigate whether a BTK mutation underlay this antibody deficiency with marked decrease of IgA in this patient, we performed functional analyses of B cells and phagocytes, and molecular analyses of somatic hypermutation and class switch recombination. The BTK missense mutation resulted in B cells with reduced BTK and high IgM expression. Equal proportions of CD19(low) and CD19(normal) fractions were observed, and both included naïve and memory B cells. Calcium influx and phospholipase Cγ2 phosphorylation upon IgM stimulation were marginally impaired in CD19(low), but not in CD19(+) B cells. Similar to XLA patients, IgA transcripts showed low SHM levels, whereas IgG transcripts were hardly affected. Our analyses suggest that the BTK mutation likely underlies the disease in this case, and that hypomorphic BTK mutations can result in normal circulating B cell numbers, but specifically impair IgA responses.

Ibrutinib, Single Agent or in Combination with Dexamethasone, in Patients with Relapsed or Relapsed/Refractory Multiple Myeloma (MM): Preliminary Phase 2 Results

Introduction: Multiple myeloma (MM) remains an incurable disease in need of new therapies with unique targets. Ibrutinib is a first-in-class, once-daily, oral, covalent inhibitor of Bruton’s tyrosine kinase (BTK), an essential enzyme in the B-cell receptor signaling pathway. While BTK is essential for the development and function of B cells and is down-regulated in plasma cells, the expression of BTK in malignant plasma cells is increased 4-fold and comparable to BTK expression levels in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). In addition, pre-clinical models show that BTK inhibition with ibrutinib led to direct inhibition of both osteoclast bone resorption and the release of osteoclast-derived tumor growth factors (Tai et al, Blood 2012). Taken together these data suggest that ibrutinib may have a role in the treatment of MM.Methods: This open label phase 2 dose escalation study was designed to enroll patients in 4 cohorts (Figure) to evaluate efficacy (≥MR) and secondary endpoints of safety, PK, ORR and DOR. Patients must have had documented non-responsive/progressive disease at the time of study entry following at least 2 prior lines of therapy including at least one immunomodulatory agent. Efficacy and safety were assessed at 4 weeks intervals using the IMWG response criteria for efficacy assessments (Rajkumar et al, Blood 2011), while safety was assessed according to CTCAE v4.0 criteria.Results: As of 15 May 2014 and a median follow up of 15.2 months, 69 patients with a median age of 64 years (range 43-81) were dosed, of which 20% had either a del 17p or p53 deletion. The number of median prior therapies was 4 (range, 2-14), 41% had ≥ 5 prior therapies and 80% had undergone autologous stem cell transplant. Sixty-two percent of patients were refractory to their last line of therapy and of the 65 patients that had received prior therapy with both an immunomodulatory agent and a proteasome inhibitor, 44% were refractory to both.Anti-tumor activity was noted across all cohorts. The highest activity with a clinical benefit rate (CBR) of 25% including 1 PR, 4 MR and 5 sustained (>4 cycles) SD was observed in Cohort 4. (Table) This led to expansion of Cohort 4 per protocol design. In Cohorts 1 and 3, 14 patients had dex added following PD, resulting in 1 PR and 9 SD.Overall, 57% experienced a Grade 3 or higher adverse event. The most commonly reported non-hematologic toxicities (any grade) were diarrhea (51%), fatigue (41%), nausea (35%), dizziness (25%), and muscle spasms (23%). The majority were Grade 1 and 2. Myelosuppression had a reported overall incidence of any grade anemia (29%), thrombocytopenia (23%), and neutropenia (7%) with 16%, 9% and 4% being Grade 3, respectively. There were no clinically meaningful differences among dose levels. Twenty-three patients experienced a SAE for a total of 47 reported events with 16 assessed as possibly/definitely related to ibrutinib per investigator. At least one dose modification occurred in 22% of patients, with 6 discontinuing due to an adverse event.At the time of the data cut-off 7 patients remain on study treatment. The most common reason for treatment discontinuation was PD in 47% of patients, with additional patients discontinuing due to investigator discretion (18%), patient decision (7%) and non-compliance (3%).Conclusions: In this heavily pre-treated patient population ibrutinib, as a single agent and in combination with dex, demonstrated evidence of anti-tumor activity. There was a trend toward improved efficacy (≥MR) in Cohort 4 and treatment was well tolerated with manageable toxicities. Ongoing correlative studies are being conducted to determine changes in cytokines, chemokines and indices of bone metabolism and to determine the effect of dex, a known CYP3A4/5 inducer, on the pharmacokinetic profile of ibrutinib. In addition, ibrutinib is currently being evaluated in combination with carfilzomib in an ongoing Phase1/2b study. (NCT01962792) [Display omitted] TableConfirmed Response by Assigned TreatmentCohortResponse, n (%)1 (n=13)2 (n=18)3 (n=18)4 (n=20)PR11-1MR1--4SD ≥ 4 cycles2465SD < 4 cycles5641PD4575Not evaluable-214Not evaluable – no post-baseline assessments [Display omitted] DisclosuresOff Label Use: Discussion of efficacy and safety data with ibrutinib as single-agent and in combination with dexamethasone in patients with relapsed and relapsed/refractory multiple myeloma treated in a phase 2 clinical trial. Huff:Celgene, Millenium: Consultancy. Bensinger:Pharmacyclics, Novartis, Celgene, Millenium, Sanofi, Acetylon: Consultancy, Research Funding. Siegel:Celgene, Millennium, Onyx: Honoraria, Membership on an entity’s Board of Directors or advisory committees, Speakers Bureau. Jagannath:Celgene, BMS, Jansen, Sanofi-Aventis: Honoraria. Lebovic:Onyx, Celgene: Speakers Bureau. Anderson:Celgene, Millenium, Onyx, : Speakers Bureau. Elias:Pharmacyclics, Inc.: Employment. Clow:Pharmacyclics, Inc.: Employment. Fardis:Pharmacyclics: Employment. Graef:Pharmacyclics: Employment. Bilotti:Pharmacyclics: Employment. Richardson:Celgene, Millennium, Johnson&Johnson: Membership on an entity’s Board of Directors or advisory committees.

Splice-correcting oligonucleotides restore BTK function in X-linked agammaglobulinemia model.

X-linked agammaglobulinemia (XLA) is an inherited immunodeficiency that results from mutations within the gene encoding Bruton's tyrosine kinase (BTK). Many XLA-associated mutations affect splicing of BTK pre-mRNA and severely impair B cell development. Here, we assessed the potential of antisense, splice-correcting oligonucleotides (SCOs) targeting mutated BTK transcripts for treating XLA. Both the SCO structural design and chemical properties were optimized using 2'-O-methyl, locked nucleic acid, or phosphorodiamidate morpholino backbones. In order to have access to an animal model of XLA, we engineered a transgenic mouse that harbors a BAC with an authentic, mutated, splice-defective human BTK gene. BTK transgenic mice were bred onto a Btk knockout background to avoid interference of the orthologous mouse protein. Using this model, we determined that BTK-specific SCOs are able to correct aberrantly spliced BTK in B lymphocytes, including pro-B cells. Correction of BTK mRNA restored expression of functional protein, as shown both by enhanced lymphocyte survival and reestablished BTK activation upon B cell receptor stimulation. Furthermore, SCO treatment corrected splicing and restored BTK expression in primary cells from patients with XLA. Together, our data demonstrate that SCOs can restore BTK function and that BTK-targeting SCOs have potential as personalized medicine in patients with XLA.

Role of Bruton's tyrosine kinase (BTK) in growth and metastasis of INA6 myeloma cells.

Bruton's tyrosine kinase (BTK) and the chemokine receptor CXCR4 are linked in various hematologic malignancies. The aim of the study was to understand the role of BTK in myeloma cell growth and metastasis using the stably BTK knockdown luciferase-expressing INA6 myeloma line. BTK knockdown had reduced adhesion to stroma and migration of myeloma cells toward stromal cell-derived factor-1. BTK knockdown had no effect on short-term in vitro growth of myeloma cells, although clonogenicity was inhibited and myeloma cell growth was promoted in coculture with osteoclasts. In severe combined immunodeficient-rab mice with contralaterally implanted pieces of bones, BTK knockdown in myeloma cells promoted their proliferation and growth in the primary bone but suppressed metastasis to the contralateral bone. BTK knockdown myeloma cells had altered the expression of genes associated with adhesion and proliferation and increased mammalian target of rapamycin signaling. In 176 paired clinical samples, BTK and CXCR4 expression was lower in myeloma cells purified from a focal lesion than from a random site. BTK expression in random-site samples was correlated with proportions of myeloma cells expressing cell surface CXCR4. Our findings highlight intratumoral heterogeneity of myeloma cells in the bone marrow microenvironment and suggest that BTK is involved in determining proliferative, quiescent or metastatic phenotypes of myeloma cells.

Single cell imaging of Bruton's tyrosine kinase using an irreversible inhibitor.

A number of Bruton's tyrosine kinase (BTK) inhibitors are currently in development, yet it has been difficult to visualize BTK expression and pharmacological inhibition in vivo in real time. We synthesized a fluorescent, irreversible BTK binder based on the drug Ibrutinib and characterized its behavior in cells and in vivo. We show a 200 nM affinity of the imaging agent, high selectivity, and irreversible binding to its target following initial washout, resulting in surprisingly high target-to-background ratios. In vivo, the imaging agent rapidly distributed to BTK expressing tumor cells, but also to BTK-positive tumor-associated host cells.

The bruton tyrosine kinase inhibitor ibrutinib (PCI‐32765) blocks hairy cell leukaemia survival, proliferation and B cell receptor signalling: a new therapeutic approach

B cell receptor (BCR) signalling plays a critical role in the progression of several B-cell malignancies, but its role in hairy cell leukaemia (HCL) is ambiguous. Bruton tyrosine kinase (BTK), a key player in BCR signalling, as well as B cell migration and adhesion, can be targeted with ibrutinib, a selective, irreversible BTK inhibitor. We analysed BTK expression and function in HCL and analysed the effects of ibrutinib on HCL cells. We demonstrated uniform BTK protein expression in HCL cells. Ibrutinib significantly inhibited HCL proliferation and cell cycle progression. Accordingly, ibrutinib also reduced HCL cell survival after BCR triggering with anti-immunoglobulins and abrogated the activation of kinases downstream of the BCR (PI3K and MAPK). Ibrutinib also inhibited BCR-dependent secretion of the chemokines CCL3 and CCL4 by HCL cells. Interestingly, ibrutinib inhibited also CXCL12-induced signalling, a key pathway for bone marrow homing. Collectively, our data support the clinical development of ibrutinib in patients with HCL.

Inhibition Of BTK Activity In Myeloma Cells Within a Supportive Microenvironment Promotes Their Growth But Suppresses Metastasis

Bruton’s Tyrosine Kinase (BTK), a TEC family kinase, is expressed by hematopoietic cells and is indispensable for B cell maturation and migration. We and others recently demonstrated that BTK is expressed in MM cells and mediates their homing to bone through chemotaxis to SDF-1, a chemokine highly produced in the bone marrow (BM) (Tai et al,Blood 2012; Bam et al.,AJH 2013). The aim of this study was to unravel the role of BTK in MM cell adhesion, growth and metastasis in our in vitro and in vivo experimental systems. BTK activity was suppressed using lentiviral particles containing BTK or scramble shRNA, or using the clinical BTK inhibitor, ibrutinib. Primary MM cells passaged in our animal model or IL6-dependent INA6 MM line were also infected with EGFP/luciferase construct for tracking purposes and monitoring tumor growth. Knockdown of BTK in INA6 cells diminished their homotypic cell aggregation growth pattern and reduced adhesion to fibronectin compared to control cells by 38±6% (p&lt;0.01). In vivo we exploited our SCID-rab model whereby SCID mice were implanted with a piece of rabbit femur on each flank and luciferase-expressing INA6 MM cells containing scramble or BTK shRNA were injected directly into the right-side implanted bone. We previously demonstrated that MM cells grow restrictively in the implanted bone area and are capable of metastasis to the secondary implanted bone but not murine organs (Yata et al, Leukemia 2004). MM growth in the primary bone site of BTK shRNA group (n=13) was higher than in the scramble shRNA group (n=12) by 4±1 folds (p&lt;0.04) assessed by live-animal imaging. Overall MM burden was also higher in the BTK shRNA group by 4.3 folds (p&lt;0.03) and 2.3 folds (p&lt;0.002) detected by measurement of circulating human immunoglobulins and soluble syndecan-1 levels, respectively. In contrast, metastasis to the secondary implanted bones assessed by ex-vivo imaging 10 weeks after engraftment was lower by 37±11 folds (p&lt;0.002) in the BTK shRNA group compared to control scramble shRNA group. In both groups, metastatic tumor cells were identified only in the secondary implanted bones. MM cells extracted from the primary myelomatous bones retained their differences in BTK expression between the two groups. Cell cycle analysis on extracted MM cells revealed decreased sub-G phase (apoptotic cells) and increased in vivo BrdU labeling index in the BTK knockdown MM cells compared to control MM cells. Gene array analysis revealed BTK target genes including upregulation of factors associated with lymphoid malignancies (e.g. BCL11A, TIAM1, RAB31) and underexpression of genes mediating cell adhesion and migration (e.g. LPXN, DBN1, F11R, CT45) in the BTK knockdown cells compared to control cells. In vitro, we established a novel coculture system of MM cells with healthy adult human BM that first has been cultivated with MM patients’ serum for 7 days. Primary MM cells (n=20) were consistently capable of long-term (7 days) survival and growth in this coculture system. Growth of BTK-expressing MM cells (n=7) in the coculture was significantly increased by 61%-90% in the presence of 5 μM (p&lt;0.02) or 10 μM (p&lt;0.01) ibrutinib. Cocultured MM cells treated with 5 μM Ibrutinib had increased BrdU labeling index compared to control MM cells as assessed by flow cytometry. We also observed reduced expression of BTK in MM cells from focal lesion compared to interstitial marrow in paired clinical samples (n=106, p&lt;3.24E-05). These data suggest that BTK plays a role in MM cell homotypic and heterotypic adhesion, and that inhibition of BTK activity in MM cells within a supportive microenvironment promotes their proliferation and growth but suppresses metastasis. Disclosures: No relevant conflicts of interest to declare.

Targeting BTK As a Treatment For Multiple Myeloma Stem Cells

BackgroundMultiple myeloma stem cells (MMSCs), characterized by drug-resistance and self-renewal, are very likely responsible for relapse. Though the phenotypic features of MMSCs are still controversial, it is believed that MMSCs are enriched in plasma cell progenitors. Bruton's tyrosine kinase (BTK) plays a central role in B-cell development and plasma cell differentiation. BLAB/c. CBA/N mice carrying the defective BTK gene are resistant to pristine-induced plasmacytomagenesis suggesting activation of BTK is essential for plasma tumor initiation. In this study, we explore the role of BTK in maintaining MMSCs. Materials and methodsReal-time-PCR was used to detect the BTK expression in MMSCs and compared to the bulk cells. BTK-related self-renewal and drug resistance were evaluated by clonogenic formation assays, using 10,000 MM cells from the BTK over-expressing ARP1 and OPM2 MM cell lines, treated with bortezomib (1nM, 10nM), as well as doxorubicin (50nM, 100nM), etoposide (50nM, 100nM), and verapamil (50nM). Flow cytometry was performed to detect the side population (SP) fraction and apoptosis in MM cells. Co-immunoprecipitation assay and western blot were utilized for the mechanistic BTK studies. Effect of BTK on MM progression in vivo was assessed in the 5TGM1 myeloma mice and NOD/SCID mice models. ResultsOur results revealed that BTK, iPS genes, Wnt and Hedgehog signaling pathways were significantly increased in MMSCs (CD138- and SP fraction) compared to bulk myeloma cells in both MM cell lines and primary MM cells. We also demonstrated that over-expression of BTK in the low-expressing MM cell lines, ARP1 and OPM2 increased the SP fraction, clonogenic potential and drug-resistance, while knockdown of BTK in high-expressing MM cell lines, OCI-MY5 and H929 abrogated these characteristics. Our in vivo study indicated that over-expression of BTK in ARP1 cells accelerates tumor formation in NOD/SCID mice compared to the EV control cells. Targeting BTK by shRNA or BTK inhibitor, CGI-1747 delayed MM tumor formation and MM progression in NOD/SCID mice and 5TGM1 model, respectively. Mechanistic studies identified that BTK activates the AKT pathway, inducing the drug-resistant genes, p-Bcl-2 and ABCB1, and inhibiting GSK3β leading to activation of the Wnt/ β-Catenin pathway. Inhibition of AKT by a specific inhibitor decreased Wnt and Hh proteins by western blot. ConclusionBTK plays an important role on maintaining MM stemness and drug-resistance through activating AKT, Wnt and Hh signaling pathways. Targeting BTK in MM may be a promising strategy to eliminate MMSCs. Disclosures:No relevant conflicts of interest to declare.

Bruton tyrosine kinase is commonly overexpressed in mantle cell lymphoma and its attenuation by Ibrutinib induces apoptosis

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy that characteristically shows overexpression of cyclin-D1 due to an alteration in the t(11;14)(q13;q32) chromosomal region. Although there are some promising treatment modalities, great majority of patients with this disease remain incurable. The B-cell antigen receptor (BCR) signaling plays a crucial role in B-cell biology and lymphomagenesis. Bruton tyrosine kinase (BTK) has been identified as a key component of the BCR signaling pathway. Evidence suggests that the blockade of BTK activity by potent pharmacologic inhibitors attenuates BCR signaling and induces cell death. Notably, the expression levels and the role of BTK in MCL survival are still elusive. Here, we demonstrated a moderate to strong BTK expression in all MCL cases (n=19) compared to benign lymphoid tissues. Treatment of MCL cell lines (Mino or Jeko-1) with a potent BTK pharmacologic inhibitor, Ibrutinib, decreased phospho-BTK-Tyr(223) expression. Consistent with this observation, Ibrutinib inhibited the viability of both Mino and JeKo-1 cells in concentration- and time-dependent manners. Ibrutinib also induced a concentration-dependent apoptosis in both cell lines. Consistently, Ibrutinib treatment decreased the levels of anti-apoptotic Bcl-2, Bcl-xL, and Mcl-1 protein. These findings suggest that BTK signaling plays a critical role in MCL cell survival, and the targeting of BTK could represent a promising therapeutic modality for aggressive lymphoma.

Bruton's tyrosine kinase: potential target in human multiple myeloma

Bruton's tyrosine kinase (BTK), a Tec family non-receptor tyrosine kinase that is required for B cell development, is critical for the initiation and maintenance of human B-cell malignancies. However, the expression of BTK and the role that BTK plays in the pathogenesis of multiple myeloma (MM) remain seldom reported. In this study we examined the expression and screened for gene mutations of BTK in MM cells. We showed that BTK was elevated and activated in a dexamethasone-resistant cell line and in two out of nine (22.2%) patients’ cells. Interestingly, patients with higher BTK expression had a poorer prognosis. In addition, a single nucleotide polymorphism (SNP) at cDNA position 2062 (T2062C) in the BTK gene was recorded in six out of eight (75%) patients and in U266 cells. This SNP in MM cells was not detected in other malignant hematopoietic cells of different lineages. These results suggest that the function of BTK warrants further investigation, and BTK expression might be used as a prognostic indicator for patients with MM.

Abstract LB-303: Small molecule inhibitor of the BTK pathway disrupts BCR signaling and demonstrates antitumor efficacy in a xenograft model.

Abstract Despite the recent advances made in the treatment and management of B cell malignancies, these diseases are not curable and overall survival is limited. Bruton's Tyrosine Kinase (BTK) is a member of the Tec family of intracellular kinases first identified for its signaling via the B-cell Receptor (BCR) and its role in the immune system. More recently, BTK was found to play an important role in B cell malignancies and select solid tumors. Preclinical and clinical results with selective irreversible BTK inhibitors provide validation for BTK as a therapeutic target in B cell malignancies. Aiming to leverage the contribution of the BTK signaling pathway to tumor growth, and its role in progression and drug resistance, we have developed a series of relatively selective, reversible, small molecule BTK inhibitors and evaluated their activity in enzyme, cell-based, and in vivo studies. Data obtained with the orally available MKC4659 compound illustrates our findings. In biochemical assays, compound MKC4659 demonstrated a relatively select targeting profile focused on a narrow group of PTKs including significant activity against BTK with IC50 less than 25 nM. In cellular assays the compound demonstrated significant in vitro potency against B cell lymphoma cell lines, inhibiting the growth of several B cell tumor cell lines including ones unresponsive to currently known BTK inhibitors. Importantly, MKC4659 showed a differential effect on B cell lymphoma, with no significant activity detected in control cells lacking detectable BTK expression. In vitro mode of action studies demonstrated that MKC4659 induces apoptosis and PARP cleavage in B cell lymphoma but not in control cells. Assays evaluating the in vitro on-target effect of compounds showed significant inhibition of the B cell receptor-mediated activation of the BTK pathway. In addition to inhibiting the phosphorylation of BTK, MKC4659 inhibited the phosphorylation of PLCγ in several B cell lymphoma cell lines. With in vitro potency demonstrated, and PK and ADMET profiles amenable to in vivo dosing, MKC4659 was evaluated for in vivo efficacy in a xenograft model of B cell lymphoma. In vivo dosing of MKC4659 inhibited growth of DOHH2 xenograft tumors in a dose dependent manner. In summary, our team has identified BTK pathway inhibitors with demonstrated on-target and anti-tumor activity in cellular assays, and efficacy in a preclinical model of B cell malignancy. This effort provides a platform for compound development and evaluation for the treatment of hematologic malignancies. Optimization efforts on the MKC4659 series are ongoing and have yielded potent and drug-like preclinical candidates that are now moving into advanced animal studies. Citation Format: Mary Faris, Uriel M. Malyankar, Victor Tam, Colleen Schweitzer, Diljeet Joea, Alexis Mollard, Bret Stephens, Steven L. Warner, David J. Bearss, Qingping Zeng. Small molecule inhibitor of the BTK pathway disrupts BCR signaling and demonstrates antitumor efficacy in a xenograft model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-303. doi:10.1158/1538-7445.AM2013-LB-303

Role of Bruton's tyrosine kinase in myeloma cell migration and induction of bone disease

Myeloma cells typically grow in bone, recruit osteoclast precursors and induce their differentiation and activity in areas adjacent to tumor foci. Bruton's tyrosine kinase (BTK), of the TEC family, is expressed in hematopoietic cells and is particularly involved in B-lymphocyte function and osteoclastogenesis. We demonstrated BTK expression in clinical myeloma plasma cells, interleukin (IL)-6- or stroma-dependent cell lines and osteoclasts. SDF-1 induced BTK activation in myeloma cells and BTK inhibition by small hairpin RNA or the small molecule inhibitor, LFM-A13, reduced their migration toward stromal cell-derived factor-1 (SDF-1). Pretreatment with LFM-A13 also reduced in vivo homing of myeloma cells to bone using bioluminescence imaging in the SCID-rab model. Enforced expression of BTK in myeloma cell line enhanced cell migration toward SDF-1 but had no effect on short-term growth. BTK expression was correlated with cell-surface CXCR4 expression in myeloma cells (n = 33, r = 0.81, P < 0.0001), and BTK gene and protein expression was more profound in cell-surface CXCR4-expressing myeloma cells. BTK was not upregulated by IL-6 while its inhibition had no effect on IL-6 signaling in myeloma cells. Human osteoclast precursors also expressed BTK and cell-surface CXCR4 and migrated toward SDF-1. LFM-A13 suppressed migration and differentiation of osteoclast precursors as well as bone-resorbing activity of mature osteoclasts. In primary myeloma-bearing SCID-rab mice, LFM-A13 inhibited osteoclast activity, prevented myeloma-induced bone resorption and moderately suppressed myeloma growth. These data demonstrate BTK and cell-surface CXCR4 association in myeloma cells and that BTK plays a role in myeloma cell homing to bone and myeloma-induced bone disease. Am. J. Hematol. 88:463-471, 2013. © 2013 Wiley Periodicals, Inc.

Bruton’s Tyrosine Kinase: Structure and Functions, Expression and Mutations

Bruton’s tyrosine kinase (BTK), a member of the Tec family of protein tyrosine kinases (PTKs), plays a vital and diverse function in many cellular processes. BTK is expressed throughout B cell development, widely participating in multiple signal pathways including PI3K, PLCγ, and PKC. Those pathways play critical functions in cell proliferation, development, differentiation, survival, and apoptosis. The expression of BTK is selectively down-regulated in T lymphocytes and plasma cells and the relative level of BTK expression may be modulated in different developmental populations of B cells. Mutations in the gene for BTK are responsible for X-linked agammaglobulinemia (XLA) in human and X-inked immunodeficiency (xid) in mice. Both of these diseases are characterized by blocks in B-cell development at multiple stages and impaired function of residual mature B cells. To date, more than 1252 mutations have been identified in human BTK gene associating with XLA. Targeting BTK has achieved remarkable efficacy in B cell malignancies, multiple myeloma and related bone disease. The present review discusses the recent data regarding the role of BTK in B cell development and its structure, regulation, functions, expression and mutations.

Cell Surface CXCR4 and BTK Expression Are Associated in Myeloma Cells and Osteoclast Precursors and Mediate Myeloma Cell Homing and Clonogenicity, and Osteoclastogenesis

Abstract 884Myeloma cells typically grow in bone, recruit osteoclast precursors and induce their differentiation and activity in areas adjacent to tumor foci. Clonal B-lymphocytes and plasma cells harboring lymphocytic phenotypes have a proposed role in sustaining myeloma. Bruton’s tyrosine kinase (BTK) is expressed in hematopoietic cells and is particularly involved in B-lymphocyte function and osteoclastogenesis. The SDF-1/CXCR4 signaling pathway is reportedly involved in homing to bone of myeloma cells and osteoclast precursors. The aims of the study were to investigate the possible association between CXCR4 and BTK signaling in myeloma cells and osteoclast precursors, and the consequences of BTK inhibition on myeloma cell migration and clonogenicity, and osteoclastogenesis. By global gene expression profiling (GEP), BTK expression was moderately higher in clinical myeloma cells (n=559) than normal plasma cells (n=25, p<0.05). BTK was also detected in IL6–dependent cell lines and myeloma cell lines that can passage in vivo (n=7), using GEP, qRT-PCR and Western Blot analyses. Cell surface CXCR4 determined by flow cytometry was variably expressed in myeloma cells (5%–95%) and was significantly correlated with BTK gene expression (r=0.75, p<0.002, n=14). Most myeloma cell lines grown independently in vitro expressed very low levels of BTK; however, even in such cell lines (e.g. CAG), enrichment of myeloma cells expressing cell-surface CXCR4 by FACS analysis resulted in detectable BTK expression. BTK inhibition by shRNA in IL6–dependent INA6 cells inhibited their migration toward SDF-1 by >50% (p<0.006) and diminished their ability to form colonies in a 2-weeks clonogenic assay (p<0.0002). The BTK small molecule inhibitor LFM-A13 (25–50 μM) consistently reduced SDF-1-induced migration of primary myeloma cells and myeloma lines (n=6, p<0.03), and clonogenicity (colonies number and size) of 3 BTK-expressing myeloma lines by >50% (p<0.03). Using kinase immunoprecipitation assay, SDF-1 rapidly induced BTK phosphorylation (activation) in myeloma cells, an effect that was blocked by LFM-A13. In vivo, pretreatment of luciferase-expressing myeloma cells with LFM-A13 lessened their homing to bone following intravenous injection into SCID-rab mice as determined by live-animal imaging. BTK was highly expressed in osteoclast precursors while cell surface CXCR4 was detected in 5% of this cell population. LFM-A13 also reduced osteoclast precursor migration toward SDF-1 and suppressed osteoclast formation and bone resorption activity on dentine slices (p<0.002). In myeloma-bearing SCID-rab mice, LFM-A13 (n=10, 40 mg/kg, twice daily for 3 weeks, i.p.) reduced osteoclast number by 45% (p<0.004), prevented reduction of bone mineral density (BMD, p<0.04) and attenuated myeloma growth at near significant level (p<0.07). These data indicate that CXCR4 and BTK signaling are linked in myeloma cells and osteoclast precursors and that BTK has potential as a targeted myeloma therapy because of its roles in myeloma cell homing and clonogenicity and myeloma-induced osteolysis. Disclosures:Barlogie:Celgene, Genzyme, Novartis, Millennium: Consultancy, Honoraria, Patents & Royalties. Shaughnessy:Myeloma Health, Celgene, Genzyme, Novartis: Consultancy, Employment, Equity Ownership, Honoraria, Patents & Royalties.

Bruton's Tyrosine Kinase (BTK) Is Indispensable for Myeloma Cell Migration towards SDF-1 and Induction of Osteoclastogenesis and Osteolytic Bone Disease

AbstractAbstract 447Bruton's tyrosine kinase (BTK), a nonreceptor tyrosine kinase of the TEC family of protein tyrosine kinases, is preferentially expressed in the hematopoietic cells and involved in B-lymphocytes survival and differentiation, and their migration towards SDF-1 gradient. BTK is also expressed in osteoclast precursors and plays indispensable role in osteoclastogenesis (Shinohara et al., Cell 2008). LFM-A13 is small molecule inhibitor of BTK and TEC, and can be tolerated even when animals are given daily dose of 100 mg/kg. The aims of the study were to investigate the effect of LFM-A13 on myeloma cell migration and growth in vitro, and on myeloma bone disease and tumor growth in the SCID-rab model. Our clinical gene expression profiling data indicate that in contrast to most myeloma cell lines, primary myeloma cells express BTK and that relative to normal plasma cells, BTK expression is upregulated in myeloma cells molecularly classified in the CD-1, CD-2, HY, LB and MF subtypes. Expression of BTK at the RNA and proteins levels in myeloma cells and osteoclast precursors was validated using qRT-PCR and Western Blot. To test effect on migration, myeloma cells expressing BTK and cell surface CXCR4 (n=5) were placed in the top of transwell inserts in the absence and presence of LFM-A13 (50 μM) and their migration towards SDF-1 (30 nM) was evaluated after 18 hours. SDF-1 induced migration of myeloma cells by >2.5 folds, an effect that was markedly inhibited by LFM-A13 (p<0.01). At similar concentration, this agent modestly reduced growth of BTK-expressing myeloma cells by 20%, assessed by MTT assay. LFM-A13 dose dependently inhibited osteoclast formation by 25% at 10 μM (p<0.0005) and by 80% at 40 μM (p<0.0001). In vivo, SCID-rab mice engrafted with a novel myeloma cell line, DAS, established through sequential passaging in this animal model (Xin et al., BJH 2007). DAS cells do not grow in culture, are molecularly classified as MF subtype and express high level of BTK. Upon establishment of myeloma growth, 2 weeks after tumor cell injection, hosts were intraperitoneally treated with 40 mg/kg LFM-A13 or vehicle (10 mice/group) twice a day for 3 weeks. Myeloma bone disease was evaluated by x-rays and analysis of bone mineral density (BMD). Tumor growth was analyzed by measurement of circulating human Ig and histologically. Whereas in the control group BMD of the implanted bone was reduced by 15±4% from pretreatment levels, it remained unchanged (0.8±4% change from pretreatment level) in the LFM-A13 treated hosts (p<0.01 versus control). X-ray radiographs revealed induction of osteolytic lesions in implanted bones of control hosts and that LFM-A13 effectively prevented these effects. LFM-A13 reduced the number of TRAP-expressing osteoclasts in myelomatous bones by >43% (p<0.004). At the end of the experiment, tumor burden was insignificantly lower in hosts treated with the LFM-A13 (Ig levels 42±15 and 19±5 μg/ml in control and LFM-A13 groups, respectively). We conclude that BTK is indispensable for SDF-1-indcued myeloma cell migration and stimulation of osteoclastogenesis, and that pharmacologic inhibition of BTK effectively inhibits myeloma-induced bone resorption and may interrupt with myeloma cell homing and metastasis to bone. Disclosures:No relevant conflicts of interest to declare.

Mutations of Bruton's tyrosine kinase gene in Brazilian patients with X-linked agammaglobulinemia

Mutations in Bruton's tyrosine kinase (BTK) gene are responsible for X-linked agammaglobulinemia (XLA), which is characterized by recurrent bacterial infections, profound hypogammaglobulinemia, and decreased numbers of mature B cells in peripheral blood. We evaluated 5 male Brazilian patients, ranging from 3 to 10 years of age, from unrelated families, whose diagnosis was based on recurrent infections, markedly reduced levels of IgM, IgG and IgA, and circulating B cell numbers <2%. BTK gene analysis was carried out using PCR-SSCP followed by sequencing. We detected three novel (Ala347fsX55, I355T, and Thr324fsX24) and two previously reported mutations (Q196X and E441X). Flow cytometry revealed a reduced expression of BTK protein in patients and a mosaic pattern of BTK expression was obtained from mothers, indicating that they were XLA carriers.

Correction of B-cell development in Btk-deficient mice using lentiviral vectors with codon-optimized human BTK

X-linked agammaglobulinemia (XLA) is the most common primary immunodeficiency (PID) in man and caused by mutations in the Bruton's tyrosine kinase (BTK) gene. XLA is characterized by a B-cell differentiation arrest in bone marrow, absence of mature B cells and immunoglobulins (Igs), and recurrent bacterial infections. We used self-inactivating lentiviral vectors expressing codon-optimized human BTK under the control of three different ubiquitous or B cell-specific promoters. Btk-/- mice engrafted with transduced cells showed correction of both precursor B-cell and peripheral B-cell development. Lentiviral vectors containing the wildtype BTK sequence did not correct the phenotype. All treated mice with codon-optimized BTK exhibited the recovery of B1 cells in the peritoneal cavity, and of serum IgM and IgG3 levels. Calcium mobilization responses upon B-cell receptor stimulation as well as in vivo responses to T cell-independent antigens were restored. Viral promoters overexpressing BTK >100-fold above normal resulted in erythro-myeloid proliferations independent of insertional mutagenesis. However, transplantation into secondary Btk-/- recipients using cellular promoters resulted in functional restoration of peripheral B cells and IgM levels, without any adverse effects. In conclusion, transduction of human BTK corrects B-cell development and antigen-specific antibody responses in Btk-/- mice, thus indicating the feasibility of lentiviral gene therapy for XLA, provided that BTK expression does not vastly exceed normal levels.