Irreversible Inhibitor Of Bruton Tyrosine Kinase Research Articles

Discovery of Covalent Bruton's Tyrosine Kinase Inhibitors with Decreased CYP2C8 Inhibitory Activity

Bruton's tyrosine kinase (BTK) is a member of the Tec kinase family that is expressed in cells of hematopoietic lineage. Evidence has shown that inhibition of BTK has clinical benefit for the treatment of a wide array of autoimmune and inflammatory diseases. Previously we reported the discovery of a novel nicotinamide selectivity pocket (SP) series of potent and selective covalent irreversible BTK inhibitors. The top molecule 1 of that series strongly inhibited CYP2C8 (IC50 =100 nM), which was attributed to the bridged linker group. However, our effort on the linker replacement turned out to be fruitless. With the study of the X-ray crystal structure of compound 1, we envisioned the opportunity of removal of this liability via transposition of the linker moiety in 1 from C6 to C5 position of the pyridine core. With this strategy, our optimization led to the discovery of a novel series, in which the top molecule 18 A displayed reduced CYP inhibitory activity and good potency. To further explore this new series, different warheads besides acrylamide, for example cyanamide, were also tested. However, this effort didn't lead to the discovery of molecules with better potency than 18 A. The loss of potency in those molecules could be related to the reduced reactivity of the warhead or reversible binding mode. Further profiling of 18 A disclosed that it had a strong hERG (human Ether-a-go-go Related Gene) inhibition, which could be related to the phenoxyphenyl group.

Discovery of novel BTK PROTACs for B-Cell lymphomas

Bruton's tyrosine kinase (BTK) is a key drug target for B-cell related malignancies. Irreversible covalent BTK inhibitors have been approved for the treatment of B-cell malignancies, yet BTK C481S mutation at the covalent binding site has caused drug-resistance of BTK covalent binding inhibitors. The proteolysis targeting chimera (PROTAC) technology increases the sensitivity to drug-resistant targets compared to classic inhibitors, which provides a new strategy for mutant BTK related B-cell malignancies. ARQ531, a reversible non-covalent BTK inhibitor that inhibits wild type (WT) and mutated BTK with high selectivity, could be an ideal warhead for PROTACs targeting the mutant BTK. Herein, we designed a novel series of PROTACs using the selective non-covalent BTK inhibitor ARQ531 as warhead, with the goal of improving the degradation of both wild-type and C481S mutant BTKs, and increasing the selectivity of BTK over other kinases. This effort will provide some basis for further preclinical study of BTK PROTACs as a novel strategy for treatment of B-cell lymphomas.

SY-1530, a highly selective BTK inhibitor, effectively treats B-cell malignancies by blocking B-cell activation.

Objective:B-cell antigen receptor (BCR) signaling is required to maintain the physiological functions of normal B cells and plays an important pathogenic role in B-cell malignancies. Bruton tyrosine kinase (BTK), a critical mediator of BCR signaling, is an attractive target for the treatment of B-cell malignancies. This study aimed to identify a highly potent and selective BTK inhibitor.Methods:Homogeneous time-resolved fluorescence assays were used to screen BTK inhibitors. Typhoon fluorescence imaging and Western blot analysis were used to confirm the effects of SY-1530 on the BCR signaling pathway. Additionally, the anti-tumor activities of SY-1530 were evaluated in TMD8 xenografts and spontaneous canine B-cell lymphoma.Results:We found a novel irreversible and non-competitive inhibitor of BTK, SY-1530, which provided dose-dependent and time-dependent inhibition. SY-1530 selectively bound to BTK rather than inducible T-cell kinase; consequently, it did not significantly affect T-cell receptor signaling and caused limited off-target effects. SY-1530 blocked the BCR signaling pathway through down-regulation of BTK activity, thus leading to impaired phosphorylation of BTK and its downstream kinases. Moreover, SY-1530 induced apoptosis in a caspase-dependent manner and efficaciously inhibited tumor growth in mouse xenograft models of B-cell malignancy (P < 0.001). SY-1530 also induced positive clinical responses in spontaneous canine B-cell lymphoma.Conclusions:SY-1530 is an irreversible and selective BTK inhibitor that shows inhibitory effects on B-cell malignancies by blocking the BCR signaling pathway. Therefore, it may be a promising therapeutic approach for the treatment of B-cell malignancies.

Abstract 1267: Combination therapy of JNJ-67856633, a novel, first-in-class MALT1 protease inhibitor, and JNJ-64264681, a novel BTK inhibitor, for the treatment of B-cell lymphomas

Abstract Background: Constitutive activation of the classical nuclear factor kappa-light-chain-enhancer of activated B-cells (NF-κB) pathway is a clear driver of B-cell non-Hodgkin lymphomas (NHL). Bruton's Tyrosine Kinase (BTK) and Mucosa-associated lymphoid tissue lymphoma translocation protein 1 (MALT1), which lies downstream of BTK, are key mediators of the classical NF-κB signaling pathway activated by BCR and TCR receptors. JNJ-67856633 is a first-in-class MALT1 protease inhibitor. JNJ-64264681 is a BTK inhibitor with improved selectivity against BTK. Blocking the BCR pathway at multiple points using these two orally bioavailable compounds could enhance clinical activity in B-cell lymphoma patients. Methods: JNJ-67856633 and JNJ-64264681 are currently being evaluated in phase 1 clinical trials designed to establish safety, PK, PD and the Recommended Phase 2 Dose (RP2D) of each agent. Results: JNJ-67856633 is a potent, selective, orally bioavailable, allosteric inhibitor of MALT1 protease activity. The compound inhibits proliferation of activated B-cell diffuse large B-cell lymphoma (ABC-DLBCL) cell lines bearing CD79b or CARD11 mutations as well as models mimicking resistance to covalent BTK inhibitors. JNJ-67856633 exhibits potent tumor growth inhibition in two human DLBCL xenograft models, OCI-Ly3 and OCI-Ly10, and mutation selected patient derived DLBCL xenografts. Furthermore, treatment with JNJ-67856633 leads to dose dependent inhibition of the generation of Tregs (CD4+CD25+FoxP3+) following CD3/28 stimulation in vitro, suggesting a potential immune modulatory role of MALT1 inhibition. JNJ-64264681 is an orally active small molecule that is a potent, selective, and irreversible covalent BTK inhibitor. JNJ-64264681 inhibits the growth of CD79b-mutant DLBCL cell lines in vitro and potently inhibits tumor growth in xenograft- or patient-derived DLBCL models in vivo. Treatment with JNJ-64264681 and JNJ-67856633 administered together demonstrated statistically significant tumor growth inhibition compared with vehicle control in two CD79b mutant mouse lymphoma models, one based on a DLBCL cell line (OCI-Ly10) and one based on a patient-derived DLBCL model (LY2298). In both models, the combination showed increased growth inhibition compared with single agents and tumor regression in the combination arm. Synergistic anti-proliferative activity was observed in three DLBCL cell lines carrying CD79b mutations and one MCL cell line. Conclusions: Taken together, the in vitro and in vivo data for JNJ-67856633 and JNJ-64264681 suggest that combination therapy can increase the anti-tumor effect of the monotherapies and provide a more sustained response, offering strong support for clinical investigation of the combination of these two novel agents. A phase 1b combination study is scheduled to initiate. Citation Format: Ulrike Philippar, Lorena Fontan, Ivo Cornelissen, Haopeng Rui, Sriram Balasubramanian, Marcello Gaudiano, Mariette Bekkers, Luc Van Nuffel, Tianbao Lu, Tianbao Lu, John Wiener, Mark Tichenor, Tony Greway, Kathryn Packman, Bie Verbist, Yusri Elsayed, Ricardo Attar, Jacqueline Bussolari, John Gerecitano. Combination therapy of JNJ-67856633, a novel, first-in-class MALT1 protease inhibitor, and JNJ-64264681, a novel BTK inhibitor, for the treatment of B-cell lymphomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1267.

M7583 Is a Highly Selective and Potent Second Generation BTK Inhibitor for Treatment of B-Cell Malignancies

▪The advent of ibrutinib has represented a new era in the treatment of B-cell malignancies, with remarkable clinical efficacy shown in previously difficult to treat lymphomas. Now, second generation Bruton's tyrosine kinase (BTK) inhibitors are in development with more refined pharmacologic profiles that maintain the potent anti-tumor effects of ibrutinib, but that improve upon overall tolerability and circumvent ibrutinib's inhibitory effect on antibody-dependent cell-mediated cytotoxicity (ADCC).M7583 is a potent, orally administered, highly selective, adenosine triphosphate (ATP)-competitive, second generation, irreversible inhibitor of BTK. Kinase specificity has been determined in vitro using the Merck Millipore Kinase Profiler panel. Only 3 kinases (Blk, BMX, and Txk) had IC50s within a 10-fold range of BTK (BTK IC50 = 18.5 nM; Blk IC50 = 77 nM; BMX IC50= 5 nM; Txk IC50 = 62 nM). Target inhibition was confirmed with a concentration dependent decrease in BTK auto-phosphorylation detected by western blot in the Ramos cell line (human Burkitt's B-cell lymphoma). To examine the impact of kinase selectivity on the overall efficacy of M7583, its preclinical activity was compared with that of ibrutinib in a series of in vitro studies. M7583 inhibited the growth of diffuse large B-cell lymphoma (DLBCL) cell lines and primary chronic lymphocytic leukemia (CLL) blasts. In vivo , treatment with M7583 inhibited tumor growth in mantle cell lymphoma cell line-derived xenografts and patient-derived xenograft (PDX) models of DLBCL with the activated B-cell like diffuse large B-cell lymphoma (ABC-DLBCL) subtype being the most sensitive to M7583; consistent with the findings for other BTK inhibitors. To examine the potential for inhibition of ADCC by therapeutic antibodies, M7583 and ibrutinib were combined with rituximab or an ADCC incompetent version of rituximab in ADCC cell lysis experiments. At clinically relevant concentrations, ibrutinib inhibited the ADCC mechanism of rituximab, whereas M7583 did not. Collectively, these findings show the potency and selectivity of M7583 for BTK, as well as its efficacy in models of B-cell malignancies. The safety and efficacy of M7583 is currently being investigated in Phase I/II trials in patients with B-cell malignancies. DisclosuresGoodstal:EMD Serono: Employment. Ma:EMD Serono: Employment. Lin:EMD Serono: Employment. Crandall:EMD Serono: Employment. Crowley:EMD Serono: Employment. Bender:EMD Serono: Employment. Iadevaia:EMD Serono: Employment. Clark:EMD Serono: Employment.

ESCALADE: A phase 3 study of acalabrutinib in combination with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) for patients ≤65y with untreated non-germinal center B-cell–like (non-GCB) diffuse large B-cell lymphoma (DLBCL).

TPS7572 Background: R-CHOP remains the standard of care for DLBCL. Although most patients (pts) can be cured, 35–40% will experience relapsed/refractory disease, leading to poor outcomes in the majority of pts. Covalent irreversible Bruton tyrosine kinase inhibitors (BTKi) have shown higher responses in pts with non-GCB DLBCL than with GCB DLBCL. In untreated non-GCB DLBCL pts, the phase 3 PHOENIX study (Younes et al. J Clin Oncol. 2019;37:1285-95) showed that addition of the BTKi ibrutinib to R-CHOP (R-CHOP-I) did not improve outcomes in the intent-to-treat population. However, pts age &lt; 60y treated with R-CHOP-I had significantly improved progression-free survival (PFS) and overall survival (OS) compared with those receiving R-CHOP alone. Acalabrutinib (A) is a second-generation BTKi with enhanced kinase selectivity and potential for better efficacy and tolerability than first-generation BTKis. There is a strong rationale for combining A with R-CHOP in pts with untreated DLBCL, and safety of A + R-CHOP has been shown in a phase 1b/2 study (Davies et al. ASH 2020). The aim of this study is to determine if the addition of A to R-CHOP leads to improved PFS in pts age ≤65y with untreated non-GCB DLBCL. Methods: ESCALADE (ACE-LY-312; NCT04529772) is a phase 3, randomized, global, double-blind study of A vs placebo in combination with R-CHOP for treatment of newly diagnosed non-GCB DLBCL. The study is recruiting adults ≥18y and ≤65y with previously untreated DLBCL stage II–IV disease with a Revised International Prognostic Index (R-IPI) score of 2–5. Prior to randomization, all pts will receive an initial R-CHOP cycle (cycle 1) as standard-of-care treatment to prevent delays in therapy initiation. Based on central Gene Expression Profile (GEP) testing performed after enrollment, pts with non-GCB DLBCL (activated B-cell like or unclassified) will be randomized into 2 arms to receive A 100 mg twice daily plus R-CHOP or placebo plus R-CHOP from cycle 2 to cycle 6 followed by 2 additional cycles of rituximab + A or placebo (cycles 7 and 8). All pts will receive primary prophylaxis with granulocyte colony-stimulating factors accompanying all R-CHOP cycles. The study aims to randomize 600 pts (̃300 per arm). The primary objective is to evaluate whether the addition of A to R-CHOP will prolong PFS. Secondary endpoints include event-free survival, complete response rate, OS, pharmacokinetics, and safety. Key exclusion criteria are central nervous system involvement, primary mediastinal lymphoma, high-grade B-cell lymphoma, diagnosis or treatment of malignancy other than DLBCL, and history of indolent lymphoma. Approximately 250 sites globally will enroll pts. Enrollment began in Q3 of 2020. Clinical trial information: NCT04529772.

Tirabrutinib hydrochloride for B-cell lymphomas.

Bruton tyrosine kinase (BTK) plays an important role in the B-cell receptor (BCR) signaling pathway by mediating proliferation, migration and adhesion in B-cell malignancies. Therefore, the components of BCR signaling, especially BTK, are considered to be attractive therapeutic targets. Ibrutinib, a first-in-class BTK inhibitor, has been approved for the treatment of several types of B-cell malignancies worldwide. However, ibrutinib has off-target activities on non-BTK kinase that are related to adverse effects or might translate into clinical limitations. To overcome these limitations, more specific BTK inhibitors are needed. Tirabrutinib hydrochloride (tirabrutinib) is a potent, highly selective, irreversible oral inhibitor of BTK. Tirabrutinib irreversibly and covalently binds to BTK in B cells and has demonstrated effective in vitro cytotoxicity in many types of B-cell malignancies and in vivo antitumor activity in mouse models. Here, we provide a comprehensive review of the preclinical and clinical activity of tirabrutinib, a drug approved in Japan for relapsed or refractory primary central nervous system lymphoma and all lines of Waldenström macroglobulinemia/lymphoplasmacytic lymphoma.

Efficacy and Safety of Zanubrutinib in Patients with Relapsed/Refractory Marginal Zone Lymphoma: Initial Results of the MAGNOLIA (BGB-3111-214) Trial

Efficacy and Safety of Zanubrutinib in Patients with Relapsed/Refractory Marginal Zone Lymphoma: Initial Results of the MAGNOLIA (BGB-3111-214) Trial

Long-Term Safety and Efficacy of Orelabrutinib Monotherapy in Chinese Patients with Relapsed or Refractory Mantle Cell Lymphoma: A Multicenter, Open-Label, Phase II Study

Background: In spite of years of effort, Mantle Cell Lymphoma (MCL) remains a clinical challenge. The clinical significance of Bruton's Tyrosine Kinase (BTK) inhibitor has been validated with the approvals by FDA for the treatment of multiple subtypes of NHL including refractory and relapse (r/r) MCL. However, some serious adverse events (AEs) due to poor target selectivity (inhibition of EGFR, TEC, BMX and others), such as diarrhea, sever bleeding and atrial fibrillation, remain as challenges in clinic. Orelabrutinib is a novel, potent irreversible BTK inhibitor with high selectivity for BTK. Results of early clinical study showed that it has excellent safety/tolerability profiles and favorable pharmacokinetic/pharmacodynamic properties. Sustained ~100% BTK occupancy at 24 hours was achieved with once daily dosing regimen of 50 mg and above. In this presentation, we will report an updated analysis of orelabrutinib in Chinese patients with r/r MCL with minimum of 12 cycles of treatment. Aims: To evaluate the sustained efficacy and long-term safety of orelabrutinib in Chinese patients with r/r MCL. Methods: This is an open-label, multicenter, two stages, phase II study. The primary endpoint was objective response rate (ORR) assessed per Lugano criteria (2014). Safety and other efficacy (DOR, PFS, OS) evaluations were chosen as secondary endpoints. Results: A Total 106 patients, were enrolled in this study with median follow up time of 15.0 months. 79.2% of the patients were male and median age of 62.0 years old. Most patients were at advanced stage (73.6% were at stage IV and 20.8% were at stage III). According to per protocol analysis, 87 (87.9%) patients achieved ORR and 93.9% patients achieved disease control. The median duration of response (DOR) was not reached, the DOR rate at 12 months was 73.7%, as expected the median PFS and OS were not reached, the PFS and OS rates at 12-month were 70.8% and 88.7% respectively. Comparing to the results of previous analysis, the CR rate, by conventional CT method, increased to 27.4% and it was expected a higher rate of in depth response may occur with prolonged treatment. Further analysis showed orelabrutinib was efficacious in all subgroups (age, gender, status, stage, prior therapy, etc.). Orelabrutinib demonstrated excellent safety profile in r/r MCL patients. The frequently reported treatment related adverse events (TRAE) were primarily hematological toxicities including thrombocytopenia, neutropenia, leukopenia, and hypertension. The frequently reported grade 3 or higher AEs of any cause was thrombocytopenia . No treatment related ≥grade 3 GI and cardio toxicity, nor severe bleeding, were observed. Of the 106 patients, 32 experienced serious AEs; and 17 of them, mainly hematological toxicities and / or infections were treatment-related. Comparing to the safety data of median follow up of 10.5 months, there was only a mild increase of adverse events rate after extended treatments; the safety profiles were essentially the same. These results suggested that safety events primarily occurred during early treatment and it appeared less eventful with orelabrutinib continue treatment. Conclusion: Orelabrutinib showed continuous efficacious in treating patients with r/r MCL. In addition, orelabrutinib is safe and well tolerated with no treatment related grade 3 or higher diarrhea, atrial fibrillation/flutter or severe bleeding in this study. Results of prolong treatment expected to produce a higher rate of in depth response without altering its safety profiles support orelabrutinib being a better selection for BTKi therapy. The improved safety as a resulting of high target selectivity, and the convenience of daily dosing regimen provides orelabrutinib as preferred therapeutic choice for B cell malignancy. Disclosures Zhang: Beijing InnoCare Pharma Tech Co., Ltd: Current Employment. Zhao:Beijing InnoCare Pharma Tech Co., Ltd: Current Employment. Xu:Beijing InnoCare Pharma Tech Co., Ltd: Current Employment.

Pooled Analysis of Safety Data from Clinical Trials of Orelabrutinib Monotherapy in Hematologic Malignancies

Background: Bruton tyrosine kinase (BTK) is one of the key kinases implicated in the pathogenesis of multiple B cell malignancies. Orelabrutinib is a novel, highly selective and potent irreversible BTK inhibitor with minimal activities against other kinases (ITK, EGFR, ERBB2, etc.). As thus orelabrutinib may avoid off-target related adverse events and shall have improved safety profiles comparing to other BTK inhibitors. Here we present the safety profile of orelabrutinib analyzed based on data from 5 ongoing clinical studies in B cell malignancies (Table 1). Methods: Safety data of 266 patients (pts) from 5 ongoing orelabrutinib monotherapy studies were pooled and analyzed. All pts have been treated with at least one dose of oral orelabrutinib at ≥150 mg daily. The analysis includes the frequency and severity of adverse events (AEs), AEs of special interest, and AEs leading to treatment discontinuation or dose modifications. Results: Safety data were pooled from 266 pts with median age of 60 years (range 35.0-79.0, 69.2% males). The median duration of exposure was 11.0 months (range 0.2-22.0). The most common (occurring in ≥15% of pts) AEs were neutropenia (28.6%), thrombocytopenia (25.9%), Upper respiratory tract infection (24.4%), leukopenia (18.0%), anemia (16.2%) and rash (15.8%). Treatment related serious AEs (SAEs) were reported in 14.7% pts. The most common treatment related SAEs included thrombocytopenia (3.0%), lung infection (3.0%), pneumonitis (1.9%), anemia (1.1%) and lymphadentis (0.8%), The safety profiles were comparable in pts with various subtypes of B cell malignancies. It's noted that orelabrutinib has much less frequency of BTK off-target related adverse events, such as atrial fibrillation, diarrhea, major hemorrhage etc. Among all 266 pts, only one patient was reported with one episode of transient grade 1 atrial fibrillation, and no grade ≥3 atrial fibrillation was observed. Diarrhea of any grade was 7.1% and only one case (0.4%) was reported as grade 3. The major hemorrhage, defined as serious or ≥ G3 bleeding of any site, or central nervous system bleeding of any grade, was rarely observed; as only one case of cerebral hemorrhage, in 65-year-old male patient with more than 10 years hypertension was reported; the other three cases were subcutaneous hemorrhage, vitreous hemorrhage and vitreous hemorrhage/retinal hemorrhage. The later 2 cases of vitreous hemorrhage and/or retinal hemorrhage were resulted from posterior vitreous detachment and macular degeneration and both events were assessed as unlikely related to the treatment. Among 266 pts, the second primary malignancies were reported in only one pt with r/r MCL during orelabrutinib treatment. Grade ≥3 infection occurred in 41 pts (15.4%); most common infections were upper respiratory tract infection and lung infection. Most of the AEs were occurred during the early treatment, the frequency of the new event occurrence was significantly decreased during the later cycles. Dose reductions due to AEs occurred in 15 pts (5.6%), and treatment discontinuation due to AEs in 5.3% of pts with 2.3% related to orelabrutinib. Conclusions: Orelabrutinib shows excellent safety profiles and tolerability across various B-cell malignancies in long-term treatment. These data suggested orelabrutinib as a favorable treatment choice including the combinational therapy for B-cell malignancies. . Disclosures Zhu: Beijing InnoCare Pharma Tech Co., Ltd: Current Employment. Zhao:Beijing InnoCare Pharma Tech Co., Ltd: Current Employment. Xu:Beijing InnoCare Pharma Tech Co., Ltd: Current Employment.

Abstract 3761: HSK26784: An oral PROTAC-BTK degrader for multiple B lymphocyte derived malignancies

Abstract PROteolysis TArgeting Chimeras (PROTACs) have emerged as a new and promising modality utilizing an event-driven MOA, whereby protein levels could be modulated by PROTAC-induced degradation by hijacking the ubiquitin-proteasome system. Starting from 2001, many target proteins have been studied, such as BET and kinase families as well as nuclear receptors. Bruton's tyrosine kinase (BTK) is an essential component of BCR pathway, which plays an important role in development, activation, proliferation, and survival of B lymphocytes. Ibrutinib is an irreversible inhibitor of BTK, and shows promising activity against multiple B lymphocyte derived malignancies. However, there remains a big concern about the development of Ibrutinib induced resistance by BTK C481S mutant. In our study, HSK26784 was found as a novel orally available BTK-PROTAC molecule, which could selectively degrade the BTK proteins. HSK26784 selectively degraded BTK proteins in Mino cell lines, with a half degradation concentration (DC50) of 22.9 nM. HSK26784 also effectively induced BTK degradation in mouse spleen, with a DC50 of 3.8 mg/kg. In addition, HSK26784 significantly inhibit the expression of CD69 on human PBMC cells after ex vivo BCR stimulation. HSK26784 could inhibit cell proliferation in many malignant B cell lines. In Ibrutinib sensitive cell lines, the inhibitory activity of HSK26784 is similar to that of Ibrutinib. While in the Ibrutinib non-sensitive cell lines, HSK26784 was more potent than Ibrutinib. Importantly, in the xenograft models, HSK26784 could also inhibit the tumor growth in a dose dependent manner. And HSK26784 achieved much better therapeutic effects than Ibrutinib. HSK26784 could inhibit the kinase activity of BTK wt and BTK C481S mutant, with IC50 of 11 nM and 14 nM respectively. It indicated that the efficacy of HSK26784 in BTK wt and BTK C481S mutant was comparable. HSK26784 showed good orally bioavailability in different species. The oral bio availabilities in mice, rats and dogs were 15.4 %, 11.8 % and 12.8 % respectively. In conclusion, HSK26784 is a promising BTK PROTAC degrader with better efficacy than Ibrutinib in multiple B lymphocytes. Citation Format: Meilin Qian, Fei Ye, Chen Zhang, Jianming Wang, Yuanli Zhang, Yangyang Cui, Linli Li, Xiaoli Gou, Jia Ni. HSK26784: An oral PROTAC-BTK degrader for multiple B lymphocyte derived malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3761.

Novel mouse model resistant to irreversible BTK inhibitors: a tool identifying new therapeutic targets and side effects

AbstractPharmacological inhibitors of Bruton tyrosine kinase (BTK) have revolutionized treatment of B-lymphocyte malignancies and show great promise for dampening autoimmunity. The predominant BTK inhibitors tether irreversibly by covalently binding to cysteine 481 in the BTK catalytic domain. Substitution of cysteine 481 for serine (C481S) is the most common mechanism for acquired drug resistance. We generated a novel C481S knock-in mouse model and, using a battery of tests, no overt B-lymphocyte phenotype was found. B lymphocytes from C481S animals were resistant to irreversible, but sensitive to reversible, BTK inhibitors. In contrast, irreversible inhibitors equally impaired T-lymphocyte activation in mice, mimicking the effect of treatment in patients. This demonstrates that T-lymphocyte blockage is independent of BTK. We suggest that the C481S knock-in mouse can serve as a useful tool for the study of BTK-independent effects of irreversible inhibitors, allowing for the identification of novel therapeutic targets and pinpointing potential side effects.

Discovery of quinoline-based irreversible BTK inhibitors

Bruton tyrosine kinase (BTK) is an important target in oncology and (auto)immunity. Various BTK inhibitors have been approved or are currently in clinical development. A novel BTK inhibitor series was developed starting with a quinazoline core. Moving from a quinazoline to a quinoline core provided a handle for selectivity for BTK over EGFR and resulted in the identification of potent and selective BTK inhibitors with good potency in human whole blood assay. Furthermore, proof of concept of this series for BTK inhibition was shown in an in vivo mouse model using one of the compounds identified.

Ibrutinib in Chronic Lymphocytic Leukemia: Clinical Applications, Drug Resistance, and Prospects.

Bruton’s tyrosine kinase (BTK), a pivotal component of B-cell receptor (BCR) signaling, has been recognized as an important driver of the pathogenesis of chronic lymphocytic leukemia. Ibrutinib is a highly active and selectively irreversible inhibitor of BTK, which has been approved to be effective in both frontline and recurrent therapy of CLL. Acquired resistance has become a greater problem than initially anticipated with the widespread use of ibrutinib. An ongoing exploration of the mechanisms of ibrutinib resistance (IR) in CLL has revealed potentially useful therapeutic targets. New drugs expected to overcome IR in CLL are in the early stages of clinical development. This study aimed to summarize the possible mechanisms of IR and retrospectively analyze promising therapies that might have superior efficacy in overcoming IR.

Development of PROTACs to address clinical limitations associated with BTK-targeted kinase inhibitors.

Chronic lymphocytic leukemia is a common form of leukemia and is dependent on growth-promoting signaling via the B-cell receptor. The Bruton tyrosine kinase (BTK) is an important mediator of B-cell receptor signaling and the irreversible BTK inhibitor ibrutinib can trigger dramatic clinical responses in treated patients. However, emergence of resistance and toxicity are major limitations which lead to treatment discontinuation. There remains, therefore, a clear need for new therapeutic options. In this review, we discuss recent progress in the development of BTK-targeted proteolysis targeting chimeras (PROTACs) describing how such agents may provide advantages over ibrutinib and highlighting features of PROTACs that are important for the development of effective BTK degrading agents. Overall, PROTACs appear to be an exciting new approach to target BTK. However, development is at a very early stage and considerable progress is required to refine these agents and optimize their drug-like properties before progression to clinical testing.

Results from a First-in-Human, Proof-of-Concept Phase 1 Trial in Pretreated B-Cell Malignancies for Loxo-305, a Next-Generation, Highly Selective, Non-Covalent BTK Inhibitor

Results from a First-in-Human, Proof-of-Concept Phase 1 Trial in Pretreated B-Cell Malignancies for Loxo-305, a Next-Generation, Highly Selective, Non-Covalent BTK Inhibitor

ELEVATE TN: Phase 3 Study of Acalabrutinib Combined with Obinutuzumab (O) or Alone Vs O Plus Chlorambucil (Clb) in Patients (Pts) with Treatment-Naive Chronic Lymphocytic Leukemia (CLL)

ELEVATE TN: Phase 3 Study of Acalabrutinib Combined with Obinutuzumab (O) or Alone Vs O Plus Chlorambucil (Clb) in Patients (Pts) with Treatment-Naive Chronic Lymphocytic Leukemia (CLL)

Safety and Efficacy of Orelabrutinib Monotherapy in Chinese Patients with Relapsed or Refractory Mantle Cell Lymphoma: A Multicenter, Open-Label, Phase II Study

Mantle cell lymphoma (MCL), a subtype of aggressive B-cell non-Hodgkin lymphoma (NHL), remains challenging with unsatisfied outcomes from standard therapy. The clinical significance of Bruton's Tyrosine Kinase (BTK) inhibitors has been validated in multiple subtypes of NHL. Ibrutinib, the first BTK inhibitor, has been approved by FDA for the treatment of refractory and relapse (r/r) MCL. In spite of encouraging efficacy, clinically often referred adverse events such as diarrhea, bleeding and atrial fibrillation, respectively following ibrutinib treatment. It has been hypothesized that poor target selectivity (inhibitive effect on EGFR, TEC, BMX and others) may partially explain the occurrence of these adverse events. As such, there are focused efforts to develop new BTK inhibitor with high target selectivity aiming to improve the safety. Orelabrutinib (ICP-022) is a novel, potent irreversible BTK inhibitor with high selectivity for BTK vs other kinases including TEC- and EGFR-family members. Results from Phase I study demonstrated excellent safety/tolerability profiles as well as favorable pharmacokinetic and pharmacodynamic properties. Sustained BTK occupancy at 24 hr was achieved with once daily dosing regimen. In this presentation, we describe the clinical results of orelabrutinib in Chinese patients with r/r MCL. This is an open-label, multicenter, two stages, phase II study. The primary endpoint was objective response rate (ORR) and the duration of response (DOR) and safety were chosen as secondary endpoints. The stage I was designed for regimen selection (RP2D, N=20 for 100 mg, bid and 150 mg, qd each, respectively), while the stage II for efficacy at RP2D (N=86 150 mg, qd). Response was assessed per Lugano criteria (2014). Total of 106 pts with r/r MCL were enrolled. As of 31 May 2019, sixty-two pts had completed six cycles of treatment (28 days/cycle). The median duration of treatment was 197.5 days. Safety: A total of 106 pts were enrolled and treated at 22 centers in China. The most frequent (&amp;gt;15%) adverse events (AEs) of any cause were mostly hematological toxicities including thrombocytopenia and neutropenia; and respiratory system infections as well as rash. The frequently reported (&amp;gt;10%) grade 3 or higher AEs of any cause were thrombocytopenia (12.3%). No grade 2 or higher hemorrhage was reported. No treatment related grade 3 GI or cardio toxicity was observed. Of the 106 patients, twenty-five experienced serious AEs and 13 of them were treatment-related (primarily occurred as hematologic toxicities and / or infections). Efficacy: Forty patients, divided into two cohorts (n=20 each), were enrolled in stage I. The regimen, 150 mg, qd, was selected as RP2D based on a better ORR and the convenience of once daily dosing. All patients who were enrolled in the stage I continued their treatment. At the time of reporting (the 31 May 2019), 97 patients had response assessments. The response rate was assessed by traditional CT image technology. The ORR was 82.5% (80/97) for combining both regimens with the complete response rate (CR) 24.7% (24/97), partial responses 57.7% (56/97). Stable disease was seen in 9.3% (9/97). The total disease control rate is 91.8%. Six (6.2%) patients progressed by the first response assessment. The median duration of response rate (DOR) has not been reached. Conclusion: Orelabrutinib is safe and well tolerated with no reported treatment related grade 3 or higher GI toxicity, atrial fibrillation/flutter and severe bleeding in this study. Orelabrutinib is efficacious to treat patients with r/r MCL. The improved safety, resulting from high target selectivity, and the convenience of daily dosing regimen provides orelabrutinib as the potential of preferred therapeutic choice for B cell malignancy. Disclosures Lu: Beijing InnoCare Pharma Tech. Co., Ltd.: Employment. Zhang:Beijing InnoCare Pharma Tech Co., Ltd: Employment. Zhao:Beijing InnoCare Pharma Tech Co., Ltd: Employment. Xu:Beijing InnoCare Pharma Tech Co., Ltd: Employment.

Tyrosine Kinase Inhibitors (TKIs) Targeting Syk and BTK Signaling Differentially Affect PI3K Signalosome Organization and Platelet Function

Small molecule tyrosine kinase inhibitors (TKIs) serve increasingly important roles in the treatment of hematologic malignancies and also have shown efficacy in a range of immunological and inflammatory conditions. However, many successful TKI therapies are associated with problematic effects - particularly on platelets - as bleeding complications have been reported for many TKIs, both on and off clinical trials. Bleeding risk is especially apparent for patients treated with ibrutinib and other irreversible inhibitors of Bruton's tyrosine kinase (BTK), several of which now effectively treat multiple B cell malignancies. Intriguingly, other therapeutic TKIs targeting mechanistic partners of BTK are not associated with platelet-related complications. For instance, inhibitors against the BTK-activating kinase Syk - both with selective (i.e., entospletinib) as well as promiscuous (i.e., fostamatinib) target profiles - are not associated with clinically increased bleeding, despite some reported antiplatelet effects. To gain insight into the multifaceted effects of Syk and BTK inhibitors on platelet function, we analyzed the effects of a panel of eight different clinically relevant Syk- and BTK-directed TKIs (i.e., fostamatinib/R406, entospletinib, ibrutinib, acalabrutinib, AVL-292 and others) on essential platelet responses. We first assessed the effects of TKI treatment on Syk and BTK-mediated signaling events downstream of the platelet immunoreceptor tyrosine-based activation motif (ITAM) receptor GPVI. All Syk and BTK TKIs tested inhibited the phosphorylation of phospholipase C (PLCγ2) Y1217, protein kinase Cδ (PKCδ) Y311 and Akt T308, as well as Akt substrate phosphorylation following platelet stimulation with the GPVI receptor agonist, crosslinked collagen-related peptide (CRP-XL). Independent of TKI target profile, Syk and BTK TKIs differentially inhibited the phosphorylation of DAPP1 Y132, phosphoinositide 3-kinase (PI3K) p85α Y458, Akt S473 and PKC substrates. Syk and BTK TKIs also inhibited platelet adhesion to immobilized CRP-XL in a manner matching the effects of each TKI on ITAM-mediated signaling events. However, platelet signaling and adhesion phenotypes did not match the effects of these same TKIs on GPVI-triggered dense granule secretion, which was inhibited by all TKIs tested with the exception of R406. In contrast, all Syk and BTK inhibitors tested inhibited platelet spreading on immobilized fibrinogen. Based on observations above, we hypothesized that TKIs that irreversibly bind to BTK may disrupt critical molecular interactions around BTK within the PI3K signalosome essential to the proper orchestration of platelet activation programs. To test the effects of Syk and BTK inhibitors on the organization of PI3K signaling in activating platelets, platelets were pretreated with TKIs prior to incubation on immobilized fibrinogen and processing for immunofluorescence microscopy. We found that under control conditions, PI3K p85α regulatory subunit localized to phospholipid PI(3,4)P2-rich regions in adherent platelets associated with active PKC signaling. While Syk and PI3K inhibitors abrogated platelet spreading on fibrinogen, PI3K p85α staining remained strong around undeveloped, nascent adhesions in platelets treated with Syk and PI3K inhibitors. In contrast, PI3K p85α staining was diffuse, diminished or absent in platelets adherent to fibrinogen in the presence of all irreversible BTK inhibitors tested. Our results show that clinically effective kinase inhibitors that target Syk-BTK-PI3K signaling systems have varying effects on platelet function that may offer insights to adverse effects of therapeutic TKIs in different contexts. Moreover, our findings suggest that in addition inhibiting protein kinase activities, the discrepant effects of some TKIs may be attributed to, in part, altered protein relations around BTK, PLCγ2 and other components of the PI3K signalosome in activating platelets. Ongoing studies aim to specify protein:protein interactions affected by reversible as well as irreversible TKIs; to examine patient samples for evidence of PI3K mislocalization - especially in cases of BTK inhibitor-associated bleeding; and, to determine if PI3K signalosome disorganization has roles in other physiological, therapeutic and toxic effects of TKIs. Disclosures Shatzel: Aronora, Inc.: Consultancy.

LOXO-305: Targeting C481S Bruton Tyrosine Kinase in Patients with Ibrutinib-Resistant CLL

Clinical success with the targeted Bruton Tyrosine Kinase (BTK) inhibitors ibrutinib and acalabrutinib has greatly improved the outcome of patients with relapsed chronic lymphocytic leukemia (CLL). However toxic side effects and acquired resistance due to C481S mutations in BTK remain an issue and the prognosis of those developing resistance is poor. Hence better therapeutic options are needed for these patients. Here we characterize a next generation highly selective reversible BTK inhibitor, LOXO-305, and describe its effectiveness in vitro in treatment naïve CLL patients and in those with C481S mutations. Unlike the irreversible BTK inhibitors ibrutinib and acalabrutinib, LOXO-305 does not require the C481 site for binding to the ATP binding domain of BTK. In addition, LOXO-305 is highly selective, with minimal activity against non-BTK kinase and non-kinase off targets, including ITK, TEC and EGFR. We evaluated the efficacy of LOXO-305 in BTK wild-type B cell lymphoma lines most similar to CLL, namely MEC1 and OSU-CLL, and in CLL patient samples, by determining its effect on cell viability, apoptosis and BCR signaling. In both cell lines LOXO-305 reduced cell viability and BCR mediated activation of BTK, PLCg2, ERK and AKT similar to ibrutinib. We measured cellular apoptosis in these cell lines with Annexin V APC and PI staining and showed that after 48 hours LOXO-305 treated cells had a significantly higher percentage of apoptotic cells in comparison with both DMSO (mean increase with LOXO-305: MEC1 21% (p = 0.0005) &amp; OSU-CLL 35% (p = 0.0016)) and ibrutinib (mean increase with LOXO305: MEC1 19% (p=0.0006), OSU-CLL 22% (p=0.0013)). Since LOXO-305's mechanism of BTK inhibition does not involve covalent binding to the C481 site, we tested its efficacy in in vitro ibrutinib resistant models of stably transfected HEK293 cells expressing either wild-type (WT) or C481S BTK. In WT BTK HEK cells, both LOXO-305 and ibrutinib showed comparable inhibitory activity in vitro against wild-type BTK, with IC50 values for phospho-BTK inhibition equal to 5.69 nM and 3.33 nM, respectively. LOXO-305 also inhibited phospho-BTK in BTK-C481S-expressing HEK293 cells at an IC50 equal to 21.2 nM, while ibrutinib had no inhibitory effect at concentrations as high as 300nM. When we extended our analysis to treatment naïve CLL patient cells, we observed that both LOXO-305 and ibrutinib potently inhibited IgM-induced phospho-BTK with IC50 values equal to 1.34 ± 1.23 nM for LOXO-305 (n = 7, p &amp;lt; 0.0001) and 1.04 ± 1.26 nM for ibrutinib (n = 7, p &amp;lt; 0.0001). We also found a significant reduction in phosphorylation of PLCγ2 (Y1217), the immediate downstream effector of BTK (IC50 33 nM for each agent, n = 7, p = 0.02 for LOXO-305, p = 0.0017 for ibrutinib). When we compared the cellular cytotoxicity of LOXO-305 with ibrutinib and acalabrutinib, all three agents demonstrated significant induction of apoptosis (annexin V positive) in BTK wild-type cells compared to DMSO treatment: (LOXO-305: median 63.77% n=3, p = 0.0073, ibrutinib: median 57.76%, n=3, p &amp;lt; 0.0001, acalabrutinib: median 67.11%, n=3, p = 0.0397). In CLL patient cells harboring C481S mutations, we observed a decrease in BCR signaling with 0.6 μM LOXO-305 treatment, with 95% reduction in phospho-BTK (Y223) and 50% reduction in phospho-PLCγ2 vs DMSO (n = 3, phospho-BTK p &amp;lt; 0.0001, phospho-PLCγ2 p = 0.01). In comparison ibrutinib at 0.6 μM demonstrated 50% reduction in phospho-BTK (n = 3, p = 0.01) and no significant change in phospho-PLCγ2. We also observed a 73% reduction in phospho-ERK vs DMSO with 10 μM LOXO-305 treatment (n=3, p = 0.004) while ibrutinib and acalabrutinib showed no significant change. In CLL patient cells with C481S variant allele frequencies (VAF) of 87% and 89%, LOXO-305 was 40-fold more potent at inhibiting phospho-BTK than ibrutinib (IC50 for LOXO305 0.02 μM, for ibrutinib 0.9 μM). Even in patient cells with lower C481S VAF of 9%, LOXO-305 still demonstrated 30-fold higher potency than ibrutinib (IC50 LOXO-305 0.2 μM, ibrutinib 0.6 μM). Our findings show that LOXO-305 potently inhibits cell survival and BCR signaling in both treatment naïve and C481S CLL patient cells, and therefore may prove an effective treatment in both treatment naïve and ibrutinib-resistant CLL patients. A phase 1 clinical trial is ongoing. Disclosures Ebata: LOXO Oncology Inc.: Employment, Equity Ownership. Gomez:LOXO Oncology Inc.: Employment, Equity Ownership. Brandhuber:LOXO Oncology Inc.: Employment, Equity Ownership. Rothenberg:LOXO Oncology Inc.: Employment. Brown:Janssen, Teva Pharmaceuticals: Honoraria; Gilead, Loxo, Sun Pharmaceuticals, Verastem: Research Funding; Morphosys, Invectys (Data Safety Monitoring Board): Membership on an entity's Board of Directors or advisory committees; Abbvie, Acerta, Astra-Zeneca, Beigene, Catapult Therapeutics, Dynamo Therapeutics, Genentech/Roche, Gilead, Juno/Celgene, Kite, Loxo, Octapharma, Novartis, Pfizer, Pharmacyclics, Sunesis, TG Therapeutics, Verastem: Consultancy.