B-cell Receptor Inhibitors Research Articles

Chronic Lymphocytic Leukemia: Chemoimmunotherapy is over? No

Chemotherapeutic agents have been the backbone for treatment of CLL during the past decades. Fifteen years ago combinations consisting of chemotherapy plus CD20 antibody (rituximab, ofatumumab or obinutuzumab) or other antibodies (for example the CD52 antibody alemtuzumab) have been introduced into CLL treatment treatment successfully (1, 2). Particularly in CLL patients without unfavorable genetic aberrations administration of frontline chemoimmunotherapy (CIT) achieved remarkable results with regard to response rates, progression-free survival (PFS) and overall survival (OS). However, in relapse treatment of CLL novel agents as B-cell receptor inhibitors (BCRi) or Bcl2 inhibitors showed superior response, PFS and OS in comparison to different chemotherapeutic and antibody- based approaches (3-6). In addition to that, patients with unfavorable genetic aberrations, as TP53 alterations, clearly benefit from initial therapy with novel agents (7). In contrast to chemoimmunotherapy, which is given for defined period, most oral inhibitors are so far administered continuously. With regard to this background arguments for the position “NO – time for chemoimmunotherapies is not yet over” are listed here.

Rituximab primarily targets an intra-clonal BCR signaling proficient CLL subpopulation characterized by high CD20 levels

The use of the anti-CD20 antibody rituximab has improved the outcome of patients with chronic lymphocytic leukemia (CLL). Rituximab was shown to act via various mechanisms, such as antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), direct apoptosis, or sensitization to chemotherapy (reviewed in ref. [1]). However, the biological function of CD20 and the reasons for the impressive activity of rituximab and other anti-CD20 antibodies remain elusive. It has been suggested, but remains controversial, whether CD20 functions as a calcium channel, couples with CD40 and MHCII, or B-cell receptor (BCR), and whether it has a role in T cell-dependent and -independent immunity [1,2,3,4]. This is also of great clinical interest for the design of combinatorial treatment of rituximab with BCR inhibitors, DNA damaging or immunomodulatory drugs, or CAR T cells. We have previously shown that microenvironmental interactions upregulate the CD20 levels on CLL cells through the CXCR4/SDF-1 axis [5]. Here we describe that higher CD20 expression has a direct role in the BCR signaling in CLL cells, and a BCR-proficient intra-clonal CLL cell subpopulation is more efficiently eliminated by rituximab in vivo due to higher CD20 levels.

A multiprotein supercomplex controlling oncogenic signalling in lymphoma.

SummaryB cell receptor (BCR) signaling has emerged as a therapeutic target in B cell lymphomas, but inhibiting this pathway in diffuse large B cell lymphoma (DLBCL) has benefited only a subset of patients1. Gene expression profiling identified two major DLBCL subtypes, known as germinal center (GC) B cell-like (GCB) and activated B cell-like (ABC)2,3, with inferior outcomes following immunochemotherapy in ABC. Autoantigens drive BCR-dependent activation of NF-κB in ABC DLBCL through a kinase cascade of SYK, BTK and PKCβ to promote the assembly of the CARD11-BCL10-MALT1 (CBM) adapter complex that recruits and activates IκB kinase (IKK)4,5,6. Genome sequencing revealed gain-of-function mutations targeting the CD79A and CD79B BCR subunits and the Toll-like receptor (TLR) signaling adapter MYD885,7, with MYD88L265P being the most prevalent isoform. In a clinical trial, the BTK inhibitor, ibrutinib, produced responses in 37% of ABC cases1. The most striking response rate (80%) was observed in tumors with both CD79B and MYD88L265P mutations, but how these mutations cooperate to promote dependence on BCR signaling remains unclear. Herein, we used genome-wide CRISPR-Cas9 screening and functional proteomics to understand the molecular basis for exceptional clinical responses to ibrutinib. We discovered a new mode of oncogenic BCR signaling in ibrutinib-responsive cell lines and biopsies, coordinated by a multiprotein supercomplex formed by MYD88, TLR9, and the BCR (My-T-BCR). The My-T-BCR co-localizes with mTOR on endolysosomes, where it drives pro-survival NF-κB and mTOR signaling. Inhibitors of BCR and mTOR signaling cooperatively decreased My-T-BCR supercomplex formation and function, providing mechanistic insight into their synergistic toxicity for My-T-BCR+ DLBCL cells. My-T-BCR complexes characterized ibrutinib-responsive malignancies and distinguished ibrutinib responders from non-responders. Our data provide a roadmap for the rational deployment of oncogenic signaling inhibitors in molecularly-defined subsets of DLBCL.

CX-4945, a Selective Inhibitor of Casein Kinase 2, Synergizes with B Cell Receptor Signaling Inhibitors in Inducing Diffuse Large B Cell Lymphoma Cell Death.

Approximately one third of Diffuse Large B cell Lymphomas (DLBCL) are refractory or relapse. Novel therapeutic approaches under scrutiny include inhibitors of B-cell receptor (BCR) signaling. Protein kinase CK2 propels survival, proliferation and stress response in solid and hematologic malignancies and promotes a "non-oncogene addiction" phenotype. Whether this kinase regulates BCR signaling, being a suitable pharmacological target in DLBCL, is unknown. The objective was to establish if CK2 controls DLBCL cell survival and the BCR signaling, to check if the combination of CK2 inhibitor CX-4945 and BCR blockers Ibrutinib and Fostamatinib is more effectively cytotoxic for DLBCL cells than the single agents and to survey the changes in signaling molecules downstream BCR upon CK2 inhibition. A panel of GC and ABC DLBCL cells was treated with CX-4945 and Fostamatinib or Ibrutinib. BCR signaling was assayed by intracellular Ca++ measurement and looking at the phosphorylation of signaling molecules. The effects on cell survival were assessed by flow cytometry, western blot and MTT assays. CK2 inhibition with CX-4945 causes DLBCL cell death. CX-4945 impaired AKT phosphorylation and intracellular Ca++ mobilization upon BCR engagement. The CK2 inhibitor acted synergistically with either the SYK inhibitor Fostamatinib or the BTK inhibitor Ibrutinib in inducing DLBCL cell death. CX-4945 was equally effective in GC and ABC DLBCL subtypes as well as in "double hit" DLBCL cell lines. These findings suggest a role for CK2 downstream of the BCR in controlling survival pathways crucial for cell growth of different DLBCL subtypes. Also, the use of CX-4945 in combination with BCR signaling blockers could represent a novel rational therapeutic approach in the DLBCL.

Novel agents in the Canadian therapeutic landscape of chronic lymphocytic leukemia

In this brief commentary, we discuss oral novel agents within in the armementarium of therapeutic options for Canadian patients with chronic lymphocytic leukemia (CLL). Previously limited to chemotherapy, the Canadian patient with relapsed or refractory CLL has the option of treatment with B-cell receptor inhibitors ibrutinib or idelalisib (combined with rituximab), both individually showing superiority to anti-CD20 monoclonal antibody comparators regardless of high-risk deletion 17p (del(17p)) status in phase 3 clinical trials. BCL2-inhibitor venetoclax shows impressive efficacy for previously-treated patients with del(17p), but though approved, it is not yet funded. For treatment-naïve patients, ibrutinib has proven superior to chemotherapy for those over 65 with comorbidities, but its role remains to be seen for the young and/or fit. Whereas oral novel agents are generally well-tolerated, some side effects, such as infection, hemorrhage, cardiac arrhythmias and tumour lysis syndrome, can be severe, therefore expert clinical vigilance is essential. Regarding sequencing of these agents, most patients failing ibrutinib or idelalisib do respond to venetoclax. While future studies using combinations of novel agents may eventually obviate the use of chemotherapy for CLL, regimens that can be stopped when minimal residual disease is achieved, such as venetoclax, are particularly relevant for our publicly-funded health care system. For Canadian CLL patients, the availability of oral novel agents has greatly expanded treatment options and is improving outcomes.

Casein kinase 1 is a therapeutic target in chronic lymphocytic leukemia

AbstractCasein kinase 1δ/ε (CK1δ/ε) is a key component of noncanonical Wnt signaling pathways, which were shown previously to drive pathogenesis of chronic lymphocytic leukemia (CLL). In this study, we investigated thoroughly the effects of CK1δ/ε inhibition on the primary CLL cells and analyzed the therapeutic potential in vivo using 2 murine model systems based on the Eµ-TCL1–induced leukemia (syngeneic adoptive transfer model and spontaneous disease development), which resembles closely human CLL. We can demonstrate that the CK1δ/ε inhibitor PF-670462 significantly blocks microenvironmental interactions (chemotaxis, invasion and communication with stromal cells) in primary CLL cells in all major subtypes of CLL. In the mouse models, CK1 inhibition slows down accumulation of leukemic cells in the peripheral blood and spleen and prevents onset of anemia. As a consequence, PF-670462 treatment results in a significantly longer overall survival. Importantly, CK1 inhibition has synergistic effects to the B-cell receptor (BCR) inhibitors such as ibrutinib in vitro and significantly improves ibrutinib effects in vivo. Mice treated with a combination of PF-670462 and ibrutinib show the slowest progression of disease and survive significantly longer compared with ibrutinib-only treatment when the therapy is discontinued. In summary, this preclinical testing of CK1δ/ε inhibitor PF-670462 demonstrates that CK1 may serve as a novel therapeutic target in CLL, acting in synergy with BCR inhibitors. Our work provides evidence that targeting CK1 can represent an alternative or addition to the therapeutic strategies based on BCR signaling and antiapoptotic signaling (BCL-2) inhibition.

Chronic lymphocytic leukemia: update on pathophysiology and management

Chronic lymphocytic leukemia (CLL) is the most common hematological malignancy in the Western countries. Although a multi-step model has been proposed for the pathogenesis of CLL as well as other malignancies, the precise mechanism underlying the development of CLL remains complicated and unclear. In addition, several studies have investigated adverse prognostic factors, including gene abnormalities and the evolution of clones with the disease progression. FCR (fludarabine, cyclophosphamide, and rituximab) has been the standard first-line therapy for "fit" younger patients without TP53 abnormality/17p deletion. Patients with CLL with TP53 abnormality/17p deletion exhibit poor prognosis because of the resistance to chemoimmunotherapy such as FCR. However, several novel targeted therapies such as B-cell receptor inhibitors including Bruton's tyrosine kinase inhibitors, PI3 kinase inhibitors, and Bcl-2 antagonists have been developed and have proven effective for high-risk patients with CLL with TP53 dysfunction. Moreover, in patients with CLL with the IGHV somatic mutation, FCR therapy offers long-term disease-free survival. These promising findings suggest the possibility of a cure. Although the aim of CLL treatment has been disease control, it is gradually changing to the possibility of a cure. Furthermore, the evaluation of minimal residual disease is important for the cure of CLL.

CD40L mediated alternative NF\u03baB-signaling induces resistance to BCR-inhibitors in patients with mantle cell lymphoma

Drug resistance is a significant obstacle in cancer treatment and therefore a frequent subject of research. Developed or primary resistance limits the treatment success of inhibitors of the B cell receptor (BCR) pathway in mantle cell lymphoma (MCL) patients. Recent research has highlighted the role of the nuclear factor-kappa B (NFκB) pathway in the context of resistance to BCR inhibitors in MCL. In this study, we analyzed the dependency of MCL cell lines on NFκB signaling and illustrated the ability of CD40L to activate the alternative NFκB pathway in MCL. This activation leads to independency of classical NFκB signaling and results in resistance to BCR inhibitors. Therefore, ligands (such as CD40L) and their activation of the alternative NFκB pathway have a major impact on the drug response in MCL. Furthermore, this study indicates a protective role for cells expressing specific ligands as microenvironmental niches for MCL cells and underlines the significance of therapeutically targeting alternative NFκB signaling in MCL.

Functional and clinical relevance of VLA-4 (CD49d/CD29) in ibrutinib-treated chronic lymphocytic leukemia.

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, which antagonizes B cell receptor (BCR) signals, demonstrates remarkable clinical activity in chronic lymphocytic leukemia (CLL). The lymphocytosis experienced by most patients under ibrutinib has previously been attributed to inhibition of BTK-dependent integrin and chemokine cues operating to retain the tumor cells in nodal compartments. Here, we show that the VLA-4 integrin, as expressed by CD49d-positive CLL, can be inside-out activated upon BCR triggering, thus reinforcing the adhesive capacities of CLL cells. In vitro and in vivo ibrutinib treatment, although reducing the constitutive VLA-4 activation and cell adhesion, can be overcome by exogenous BCR triggering in a BTK-independent manner involving PI3K. Clinically, in three independent ibrutinib-treated CLL cohorts, CD49d expression identifies cases with reduced lymphocytosis and inferior nodal response and behaves as independent predictor of shorter progression-free survival, suggesting the retention of CD49d-expressing CLL cells in tissue sites via activated VLA-4. Evaluation of CD49d expression should be incorporated in the characterization of CLL undergoing therapy with BCR inhibitors.

Guidelines for Diagnosis and Treatment of Chronic Lymphocytic Leukemia. Krohem B-Cll 2017.

SUMMARY – Recent developments in the diagnosis and treatment of chronic lymphocytic leukemia (B-CLL) have led to change of approach in clinical practice. New treatments have been approved based on the results of randomized multicenter trials for first line and for salvage therapy, and the results of numerous ongoing clinical trials are permanently providing new answers and further refining of therapeutic strategies. This is paralleled by substantial increase in understanding the disease genetics due to major advances in the next generation sequencing (NGS) technology. We define current position of the Croatian Cooperative Group for Hematologic Disease on diagnosis and treatment of CLL in the transition from chemo-immunotherapy paradigm into a new one that is based on new diagnostic stratification and unprecedented therapeutic results of B-cell receptor inhibitors (BRI) and Bcl-2 antagonists. This is a rapidly evolving field as a great number of ongoing clinical trials constantly accumulate and provide new knowledge. We believe that novel therapy research including genomic diagnosis is likely to offer new options that will eventually lead to time limited therapies without chemotherapy and more effective clinical care for B-CLL based on individualized precision medicine.

Primary central nervous system lymphoma.

Primary central nervous system lymphoma (PCNSL) is a rare and aggressive extranodal non-Hodgkin lymphoma (NHL), confined to the brain, eyes, spinal cord or leptomeninges without systemic involvement. Overall prognosis, diagnosis and management of PCNSL differ from other types of NHL. Prompt diagnosis and initiation of treatment are vital to improving clinical outcomes. PCNSL is responsive to radiation therapy, however whole-brain radiotherapy (WBRT) inadequately controls the disease when used alone and its delayed neurotoxicity causes neurocognitive impairment, especially in elderly patients. High-dose methotrexate (HD-MTX)-based induction chemotherapy with or without autologous stem cell transplantation (ASCT) or reduced-dose WBRT leads to durable disease control and less neurotoxicity. The optimal treatment has yet to be defined, however HD-MTX-based induction chemotherapy is considered standard for newly diagnosed PCNSL. Ongoing randomized trials address the role of rituximab, and of consolidative treatment using ASCT or reduced-dose WBRT. Despite high tumor response rates to initial treatment, many patients have relapsing disease with very poor prognosis. The optimal treatment for refractory or relapsed PCNSL is poorly defined. The choice of salvage treatment depends on age, previous treatment and response, performance status and comorbidities at the time of relapse. Novel therapeutics targeting underlying tumor biology include small molecule inhibitors of B-cell receptor, cereblon, and mammalian target of rapamycin signaling, and immunotherapy programmed cell death 1 receptor inhibitors and chimeric antigen receptor T cells.

Venetoclax: a chance for patients with chronic lymphocytic leukaemia previously treated with ibrutinib

In recent years, biological and clinical research has identified several targeted agents that are changing the management of patients with chronic lymphocytic leukaemia. In clinical trials, 1 Jain N O'Brien S Targeted therapies for CLL: practical issues with the changing treatment paradigm. Blood Rev. 2016; 30: 233-244 Crossref PubMed Scopus (55) Google Scholar the B-cell receptor inhibitor ibrutinib has led to durable responses and longer survival (overall and progression-free) than chemotherapy in patients with this disease. Ibrutinib is now largely used in clinical practice in patients with chromosome 17p deletions or TP53 mutations and relapsed or refractory chronic lymphocytic leukaemia. More recently, the drug has also been approved in the USA and European Union as a front-line therapy for chronic lymphocytic leukaemia. 1 Jain N O'Brien S Targeted therapies for CLL: practical issues with the changing treatment paradigm. Blood Rev. 2016; 30: 233-244 Crossref PubMed Scopus (55) Google Scholar However, many patients discontinue ibrutinib because of adverse events such as atrial fibrillation, infections, and cytopenias. Another common reason for treatment discontinuation is disease progression, which is observed most frequently in patients with TP53 mutations or complex karyotypes. 2 Jain P Keating M Wierda W et al. Outcomes of patients with chronic lymphocytic leukemia after discontinuing ibrutinib. Blood. 2015; 125: 2062-2067 Crossref PubMed Scopus (284) Google Scholar , 3 Mato AR Nabhan C Barr PM et al. Outcomes of CLL patients treated with sequential kinase inhibitor therapy: a real world experience. Blood. 2016; 128: 2199-2205 Crossref PubMed Scopus (142) Google Scholar Mutations conferring resistance to ibrutinib are also commonly found in patients with high-risk genetic landscapes or who have disease progression during ibrutinib treatment. 4 Woyach JA Ruppert AS Guinn D et al. BTKC481S-mediated resistance to ibrutinib in chronic lymphocytic leukemia. J Clin Oncol. 2017; 35: 1437-1443 Crossref PubMed Scopus (267) Google Scholar , 5 Jones D Woyach JA Zhao W et al. PLCG2 C2 domain mutations co-occur with BTK and PLCG2 resistance mutations in chronic lymphocytic leukemia undergoing ibrutinib treatment. Leukemia. 2017; 31: 1645-1647 Crossref PubMed Scopus (40) Google Scholar Outcomes after ibrutinib discontinuation are poor, 2 Jain P Keating M Wierda W et al. Outcomes of patients with chronic lymphocytic leukemia after discontinuing ibrutinib. Blood. 2015; 125: 2062-2067 Crossref PubMed Scopus (284) Google Scholar , 3 Mato AR Nabhan C Barr PM et al. Outcomes of CLL patients treated with sequential kinase inhibitor therapy: a real world experience. Blood. 2016; 128: 2199-2205 Crossref PubMed Scopus (142) Google Scholar and few treatment options are available for such patients. Therefore, treatment options for patients with relapsed or refractory disease previously treated with ibrutinib are a primary unmet medical need in the management of chronic lymphocytic leukaemia, especially given the increasing use of this drug in clinical practice. Venetoclax for chronic lymphocytic leukaemia progressing after ibrutinib: an interim analysis of a multicentre, open-label, phase 2 trialThe results of this interim analysis show that venetoclax has durable clinical activity and favourable tolerability in patients with relapsed or refractory chronic lymphocytic leukaemia whose disease progressed during or after discontinutation of ibrutinib therapy. The durability of response to venetoclax will be assessed in the final analysis in 2019. Full-Text PDF

Venetoclax for Treating Chronic Lymphocytic Leukaemia: An Evidence Review Group Perspective of a NICE Single Technology Appraisal.

Venetoclax for Treating Chronic Lymphocytic Leukaemia: An Evidence Review Group Perspective of a NICE Single Technology Appraisal.

Introduction to the symposium 'Targeted therapy in B-cell malignancies'.

Content List ‐ Read more articles from the symposium: Targeted therapy in B‐cell malignancies.

Incidence and management of toxicity associated with ibrutinib and idelalisib: a practical approach

The use of novel B-cell receptor signaling inhibitors results in high response rates and long progression-free survival in patients with indolent B-cell malignancies, such as chronic lymphocytic leukemia, follicular lymphoma, mantle cell lymphoma and Waldenström macroglobulinemia. Ibrutinib, the first-in-class inhibitor of Bruton tyrosine kinase, and idelalisib, the first-in-class inhibitor of phosphatidylinositol 3-kinase δ, have recently been approved for the treatment of several indolent B-cell malignancies. These drugs are especially being used for previously unmet needs, i.e., for patients with relapsed or refractory disease, high-risk cytogenetic or molecular abnormalities, or with comorbidities. Treatment with ibrutinib and idelalisib is generally well tolerated, even by elderly patients. However, the use of these drugs may come with toxicities that are distinct from the side effects of immunochemotherapy. In this review we discuss the most commonly reported and/or most clinically relevant adverse events associated with these B-cell receptor inhibitors, with special emphasis on recommendations for their management.

Abstract 4057: Inhibition of polyploidy and senescence induces intrinsic apoptosis in double hit or double expresser DLBCL

Abstract Introduction: Double Hit (DH) or Double Expresser (DE) DLBCL are aggressive Non-Hodgkin’s Lymphomas (NHLs) with translocation or over-expression of MYC and BCL-2 which are incurable with current therapies. MYC is a critical driver of oncogenic phenotypes and regulates expression of numerous genes including aurora kinases (AKs), which are validated drug targets. AKs are over-expressed in DLBCL and AK inhibition in two Phase-II trials of relapsed and refractory B/T-NHL resulted in 20%-30% overall response rate. Bruton’s tyrosine kinase (BTK) plays a central role in B-cell receptor (BCR) signaling and inhibitors of BTK have shown efficacy in B-NHL clinical trials. Targeting CD20 (rituximab) in DLBCL inhibits BCL-2 and induces apoptosis via caspase-3 activation. We hypothesized that DH/DE-DLBCL are amenable to a novel therapeutic strategy of AK, BTK and CD20 inhibition. Methods: Four DH/DE DLBCL cell lines were evaluated for viability by MTS; polyploidy, senescence and apoptosis by flow cytometry; DNA damage by TUNEL assay. Phospho-BCL-2, -AK and -BTK analysis by western. Safety and efficacy of drug combinations in a mouse xenograft model. Analysis of patient samples and mouse tumors by IHC. Results: DH/DE-DLBCL cell lines and patient samples displayed over-expression of MYC, BCL-2, BTK and AK-A proteins. Cell viability assays with alisertib alone showed ~30% cell death, while majority of remaining ~70% cells were polyploid and senescent at day-4 (a mechanism of treatment failure). These polyploid and senescent cells (PASC) showed increased levels of phospho-BTK indicating increased BCR signaling (a rationale for combination therapy). We show that alisertib + ibrutinib + rituximab significantly reduced PASCs leading to intrinsic cell death compared to single/double combinations. Dual inhibition of AK + BTK reduced phospho-ERK-1/2, -Bcl-6 and -MYC with increased DNA breaks indicated by up regulation of phospho-H2A-X, -Chk-2, and pro-apoptotic Noxa and Puma proteins. Triple therapy reduced Bcl-2, Bcl-xL and increased Noxa and Puma compromising the mitochondrial outer membrane potential, release of Cyt-C, activation of caspase-3 and induction apoptosis by PARP cleavage. A DLBCL SCID mouse xenograft model showed ibrutinib alone is inactive while alisertib + ibrutinib was additive with a tumor growth inhibition (TGI) rate of ~25%. TGI for ibrutinib + rituximab was ~50-60%. However, triple therapy showed a TGI of >90% and was well tolerated. Survival analysis: 67% of mice alive at day-89 with triple therapy versus 20% with ibrutinib + rituximab. Other treatments showed no survival past day-52. Conclusions: A novel triple therapy consisting of alisertib + ibrutinib + rituximab inhibits PASCs induced by AK inhibition in DH/DE-DLBCL leading to a significant anti-proliferative signal and intrinsic apoptosis. Our work provides a rationale for exploring these combinations in the clinic. Citation Format: Shariful Islam, Wenqing Qi, Carla Morales, Laurence Cooke, Catherine M. Spier, Daruka Mahadevan. Inhibition of polyploidy and senescence induces intrinsic apoptosis in double hit or double expresser DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4057. doi:10.1158/1538-7445.AM2017-4057

Abstract LB-303: Substrate-mimetic covalent inhibitor of MALT1 is most effective against CARD11 mutant ABC-DLBCL

Abstract Diffuse Large B-cell lymphoma is the most common subtype of B-cell non Hodgkin Lymphoma (B-NHL) representing 30% of all B-NHL. There are three molecular subtypes: germinal center B cell-like (GCB) DLBCL, activated B cell-like (ABC) DLBCL, and primary mediastinal B cell lymphoma (PMBL). Of those, Activated B-cell like Diffuse Large B-cell Lymphoma (ABC-DLBCL) represents a third of the patients and is characterized by constitutive NF-κB activity due to mutations in various proteins of the B-cell receptor (BCR) as well as Toll-like receptor (TLR) pathways. Mutations in the BCR pathway include: activating mutations of CD79A/B (20% of ABC-DLBCLs) and CARD11 (10%) and deletion or inactivating mutation of A20 (20-30%). In the TLR pathway, MYD88 is mutated in 37% of ABC-DLBCL patients. Given this scenario, numerous therapeutic strategies targeting proteins signaling downstream of the BCR pathway have been proposed for ABC-DLBCL -including inhibitors targeting kinases SYK, BTK, PI3K, PKC, MAPKs and AKT or the protease MALT1. MALT1 inhibition provides advantages to other targets because it is downstream of most of the BCR pathway mutations present in patients, including CARD11. Patients with CARD11 mutations do not respond to BTK inhibitors. However, none of the MALT1 inhibitors reported to date are good candidates for clinical use. Here we report a new class of substrate mimetic MALT1 inhibitors based on Z-VRPR-fmk. Our lead compound, SCM-02-138 displayed nanomolar potency in biochemical and cellular MALT1 protease reporter assays. Crystallography shows covalent binding of the compound to MALT1 active site Cys residue. SCM-02-138 was highly selective for MALT1 and showed over 100-fold differential killing in sensitive vs resistant cell lines. MALT1 inhibition was most effective in CARD11 mutant cells. SCM-02-138 was active in vivo, as assessed by hIL10 inhibition in xenografted models of ABC-DLBCL cell lines. Moreover it was effective against ABC-DLBCL xenografts and PDX DLBCL ex vivo. Combination of SCM-02-138 with other BCR inhibitors revealed PI3K delta inhibition as the most synergistic combination. Combination of SCM-02-138 and CAL-101 potentiated both proliferation inhibition and apoptosis. In summary, we have developed a new class of MALT1 peptidic inhibitor characterized by nanomolar potency, irreversibility and high specificity. This inhibitor will be particularly useful against CARD11 mutant ABC-DLBCL, which are resistant to BTK inhibitors. Citation Format: Lorena Fontan, David Scott, John Hatcher, Qi Qiao, Ilkay Us, Gabriella Casalena, Mariette Bekkers, Ulrike Philippar, Matthew Durant, Spandan Chennamadhavuni, Hao Wu, Nathaniel Gray, Ari Melnick. Substrate-mimetic covalent inhibitor of MALT1 is most effective against CARD11 mutant ABC-DLBCL [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-303. doi:10.1158/1538-7445.AM2017-LB-303

Managing Patients With TP53-Deficient Chronic Lymphocytic Leukemia.

Patients with chronic lymphocytic leukemia (CLL) having a chromosomal loss on the short arm of chromosome 17 including the TP53 gene locus (17p deletion) and/or having mutations in TP53 have a short overall survival and, until recently, limited treatment options. The recent introduction of two novel substance classes, B-cell receptor inhibitors and BH3 mimetics, into CLL treatment has provided enormous clinical progress in this previously difficult-to-treat patient subgroup characterized by high risk for treatment failure with standard chemoimmunotherapy and rapid disease progression. Compounds now approved for the treatment of TP53-deficient CLL are the two B-cell receptor inhibitors ibrutinib and idelalisib and the BH3 mimetic venetoclax. All three compounds were approved on the basis of favorable response rates that, importantly, revealed no differences between TP53-competent and TP53-deficient CLL cases. Using these compounds, longer-lasting remissions in patients with TP53-deficient CLL could be demonstrated for the first time. Whether TP53 alterations will maintain their significance as adverse prognostic factors in treatment strategies involving novel compounds needs to be assessed. This review provides an overview of current treatment options for 17p-deleted/ TP53-mutated CLL, including those compounds that are already approved by the US Food and Drug Administration or are under advanced clinical investigation. Available clinical trial data are discussed, as is the use of novel targeted treatment options in the context of transplant strategies, and an algorithm for off-study treatment of 17p-deficient CLL is suggested.

MYC Protein-positive Diffuse Large B-Cell Lymphoma Features an Activated B-Cell Receptor Signal Pathway.

Components of the B-cell receptor (BCR) signaling pathway represent promising therapeutic targets in diffuse large B-cell lymphoma (DLBCL) and other B-cell malignancies. MYC, a transcriptional factor and oncoprotein, is overexpressed in a fraction of DLBCL and indicates poor prognosis and aggressive clinical course when treated with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). However, BCR signaling status in MYC-positive DLBCL cases and the potential efficacy of BCR signal inhibitors in treating this aggressive disease are unknown. To further elucidate the BCR signaling pathway in MYC-positive DLBCL, we analyzed the levels of BCR-associated genes according to MYC gene status, detected phosphorylated protein with primary DLBCL samples, and estimated the patient survival with MYC expression. In addition, we manipulated MYC gene expression and tested its effects on BCR signaling in vitro. We found that CD19, SYK, and BLK were highly expressed in DLBCL with MYC gene overexpression. MYC-positive DLBCL had higher levels of pSYK and pBLK, but only pSYK level correlated with patient survival. The in vitro studies demonstrated that overexpression of the MYC gene augmented BCR signaling, whereas MYC gene knockdown attenuated BCR signaling. Thus, MYC protein-positive DLBCL features highly activated BCR signaling and may represent a potential candidate for BCR inhibitor therapy.

Targeting of B-cell receptor signalling in B-cell malignancies.

Pharmacological agents that inhibit enzymes of the B-cell receptor (BCR) pathway are of increasing importance in the treatment of B-cell malignancies. These include inhibitors of Bruton tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K), splenic tyrosine kinase and protein kinase Cβ. Two agents are already approved in the USA and Europe: ibrutinib, a BTK inhibitor, for the treatment of chronic lymphatic leukaemia (CLL), mantle cell lymphoma (MCL) and Waldenström's macroglobulinemia; and idelalisib, a PI3Kδ inhibitor, for the treatment of CLL and follicular lymphoma. In addition, the role of these drugs in diffuse large B-cell lymphoma and marginal zone lymphoma is under investigation, as single agents and in combination with chemotherapy. In CLL, both ibrutinib and idelalisib have an established role as first-line therapy in patients with del(17p), and in MCL, ibrutinib is a standard option for patients relapsing after chemoimmunotherapy. Unexpected toxicities have been encountered when combining these potent new agents with other drugs, including chemotherapy and lenalidomide, and based on this experience the risks and benefits of novel combinations must be evaluated carefully. In this review, we summarize the efficacy and safety results with these inhibitors and discuss novel combinations that are under study and the future role of BCR inhibitors in these disorders.