Ibrutinib inhibits collagen-mediated but not ADP-mediated platelet aggregation

Ibrutinib plus Venetoclax for the Treatment of Mantle-Cell Lymphoma

BACKGROUND

Both the BTK inhibitor ibrutinib and the BCL2 inhibitor venetoclax are active as monotherapy in the treatment of mantle-cell lymphoma. Complete response rates of 21% have been observed for each agent when administered as long-term continuous therapy. Preclinical models predict synergy in combination.

METHODS

We conducted a single-group, phase 2 study of daily oral ibrutinib and venetoclax in patients, as compared with historical controls. Patients commenced ibrutinib monotherapy at a dose of 560 mg per day. After 4 weeks, venetoclax was added in stepwise, weekly increasing doses to 400 mg per day. Both drugs were continued until progression or an unacceptable level of adverse events. The primary end point was the rate of complete response at week 16. Minimal residual disease (MRD) was assessed by flow cytometry in bone marrow and by allele-specific oligonucleotide-polymerase chain reaction (ASO-PCR) in blood.

RESULTS

The study included 24 patients with relapsed or refractory mantle-cell lymphoma (23 patients) or previously untreated mantle-cell lymphoma (1 patient). Patients were 47 to 81 years of age, and the number of previous treatments ranged from none to six. Half the patients had aberrations of TP53, and 75% had a high-risk prognostic score. The complete response rate according to computed tomography at week 16 was 42%, which was higher than the historical result of 9% at this time point with ibrutinib monotherapy (P<0.001). The rate of complete response as assessed by positron-emission tomography was 62% at week 16 and 71% overall. MRD clearance was confirmed by flow cytometry in 67% of the patients and by ASO-PCR in 38%. In a time-to-event analysis, 78% of the patients with a response were estimated to have an ongoing response at 15 months. The tumor lysis syndrome occurred in 2 patients. Common side effects were generally low grade and included diarrhea (in 83% of the patients), fatigue (in 75%), and nausea or vomiting (in 71%).

CONCLUSIONS

In this study involving historical controls, dual targeting of BTK and BCL2 with ibrutinib and venetoclax was consistent with improved outcomes in patients with mantle-cell lymphoma who had been predicted to have poor outcomes with current therapy. (Funded by Janssen and others; AIM ClinicalTrials.gov number, NCT02471391 .).

Oral Bruton tyrosine kinase inhibitors selectively block atherosclerotic plaque-triggered thrombus formation in humans

Interaction of von Willebrand factor (VWF) with platelet glycoprotein Ib (GPIb) and interaction of collagen with GPVI are essential for thrombus formation on ruptured or eroded atherosclerotic plaques (atherothrombosis). GPIb and GPVI signal through Bruton tyrosine kinase (Btk), which can be blocked irreversibly by oral application of ibrutinib, an established therapy for chronic lymphocytic leukemia (CLL) with long-term safety. We found that ibrutinib and the novel Btk inhibitors acalabrutinib and ONO/GS-4059 block GPVI-dependent static platelet aggregation in blood exposed to human plaque homogenate and collagen but not to ADP or arachidonic acid. Moreover, Btk inhibitors prevented platelet thrombus formation on human atherosclerotic plaque homogenate and plaque tissue sections from arterially flowing blood, whereas integrin α₂β₁ and VWF-dependent platelet adhesion to collagen, which is important for physiologic hemostasis, was not affected. This plaque-selective platelet inhibition was also observed in CLL patients taking 450 mg of ibrutinib and in volunteers after much lower and intermittent dosing of the drug. We conclude that Btk inhibitors, by targeting GPIb and GPVI signal transduction, suppress platelet thrombus accretion from flowing blood on atherosclerotic plaque but spare hemostatic platelet function. Btk inhibitors hold promise as the first culprit lesion-focused oral antiplatelet drugs and are effective at low doses.

Platelet function is disturbed by the angiogenesis inhibitors sunitinib and sorafenib, but unaffected by bevacizumab

INTRODUCTION

At the clinical introduction of antiangiogenic agents as anticancer agents, no major toxicities were expected as merely just endothelial cells (ECs) in tumors would be affected. However, several (serious) toxicities became apparent, of which underlying mechanisms are largely unknown. We investigated to what extent sunitinib (multitargeted antiangiogenic tyrosine kinase inhibitor (TKI)), sorafenib (TKI) and bevacizumab [specific antibody against vascular endothelial growth factor (VEGF)] may impair platelet function, which might explain treatment-related bleedings.

MATERIALS AND METHODS

In vitro, the influence of sunitinib, sorafenib, and bevacizumab on platelet aggregation, P-selectin expression and fibrinogen binding, platelet-EC interaction, and tyrosine phosphorylation of c-Src was studied by optical aggregation, flow cytometry, real-time perfusion, and western blotting. Ex vivo, platelet aggregation was analyzed in 25 patients upon sunitinib or bevacizumab treatment. Concentrations of sunitinib, VEGF, and platelet and EC activation markers were measured by LC-MS/MS and ELISA.

RESULTS

In vitro, sunitinib and sorafenib significantly inhibited platelet aggregation (20 μM sunitinib: 71.3%, p < 0.001; 25 μM sorafenib: 55.8%, p = 0.042). Sorafenib and sunitinib significantly inhibited P-selectin expression on platelets. Exposure to both TKIs resulted in a reduced tyrosine phosphorylation of c-Src. Ex vivo, within 24 h sunitinib impaired platelet aggregation (83.0%, p = 0.001, N = 8). Plasma concentrations of sunitinib, VEGF, and platelet/EC activation markers were not correlated with disturbed aggregation. In contrast, bevacizumab only significantly impaired platelet aggregation in vitro at high concentrations, but not ex vivo.

CONCLUSION

Sunitinib significantly inhibits platelet aggregation in patients already after 24 h of first administration, whereas bevacizumab had no effect on aggregation. These findings may explain the clinically observed bleedings during treatment with antiangiogenic TKIs.

Acalabrutinib in relapsed or refractory mantle cell lymphoma (ACE-LY-004): a single-arm, multicentre, phase 2 trial

BACKGROUND

Bruton tyrosine kinase is a clinically validated target in mantle cell lymphoma. Acalabrutinib (ACP-196) is a highly selective, potent Bruton tyrosine kinase inhibitor developed to minimise off-target activity.

METHODS

In this open-label, phase 2 study, oral acalabrutinib (100 mg twice per day) was given to patients with relapsed or refractory mantle cell lymphoma, until disease progression or unacceptable toxicity. The primary endpoint was overall response assessed according to the Lugano classification, and safety analyses were done in all participants. This trial is registered with ClinicalTrials.gov, number NCT02213926.

FINDINGS

From March 12, 2015, to Jan 5, 2016, 124 patients with relapsed or refractory mantle cell lymphoma were enrolled and all patients received treatment; median age 68 years. Patients received a median of two (IQR 1-2) previous therapies. At a median follow-up of 15·2 months, 100 (81%) patients achieved an overall response and 49 (40%) patients achieved a complete response. The Kaplan-Meier estimated medians for duration of response, progression-free survival, and overall survival were not reached; the 12-month rates were 72% (95% CI 62-80), 67% (58-75), and 87% (79-92%), respectively. The most common adverse events were primarily grade 1 or 2 and were headache (47 [38%]), diarrhoea (38 [31%]), fatigue (34 [27%]), and myalgia (26 [21%]). The most common grade 3 or worse adverse events were neutropenia (13 [10%]), anaemia (11 [9%]), and pneumonia (six [5%]). There were no cases of atrial fibrillation and one case of grade 3 or worse haemorrhage. The median duration of treatment was 13·8 months. Treatment was discontinued in 54 (44%) patients, primarily due to progressive disease (39 [31%]) and adverse events (seven [6%]).

INTERPRETATION

Acalabrutinib treatment provided a high rate of durable responses and a favourable safety profile in patients with relapsed or refractory mantle cell lymphoma. These findings suggest an important role for acalabrutinib in the treatment of this disease population.

FUNDING

Acerta Pharma, a member of the AstraZeneca Group.

Neurological complications of new chemotherapy agents

This last decade has yielded more robust development of cancer treatments and first-in-class agents than ever before. Since 2006, nearly one hundred new drugs have received regulatory approval for the treatment of hematological and solid organ neoplasms. Moreover, older conventional therapies have received approval for new clinical indications and are being used in combination with these newer small-molecule targeted treatments. The nervous system is vulnerable to many of the traditional cancer therapies, manifesting both already well-described acute and chronic toxicities. However, newer agents may produce toxicities that may seem indistinguishable from the underlying cancer. Early recognition of neurotoxicities from new therapeutics is vital to avoid irreversible neurological injury. This review focuses on cancer therapies in use in the last 10 years and approved by the FDA from January 2006 through January 1, 2017.

Experience with ibrutinib for first-line use in patients with chronic lymphocytic leukemia

Ibrutinib is the first in-class, orally administered, Bruton's tyrosine kinase (BTK) inhibitor that abrogates the critical signaling downstream of the B-cell receptor (BCR). This signaling is required for B-cell survival, proliferation and interaction with the microenvironment. Ibrutinib proved active in preclinical models of lymphoproliferative diseases and achieved impressive response rates in heavily pretreated relapsed and refractory (R/R) patients with chronic lymphocytic leukemia (CLL). Ibrutinib prolonged survival compared to standard therapy and mitigated the effect of most poor prognostic factors in CLL, thus becoming the main therapeutic option in high-risk populations. Moreover, compared with standard chemoimmunotherapy (CIT) for adults, ibrutinib causes fewer cytopenias and infections, while having its own unique toxicity profile. Its efficacy in relapsed patients as well as its tolerability have led to its increased use in previously untreated patients, especially in those with poor prognostic markers and/or the elderly. This review elaborates on ibrutinib's unique toxicity profile and the mechanisms of acquired resistance leading to progression on ibrutinib, since both are critical for understanding the obstacles to its first-line use. We will further evaluate the data from ongoing clinical trials in this setting and explore future options for combination therapy.

Ibrutinib

Abnormal B-cell receptor (BCR) signalling is a key mechanism of disease progression in B-cell malignancy. Bruton's tyrosine kinase (BTK) has a pivotal role in BCR signalling. Ibrutinib (PCI-32765) is a small molecule which serves as a covalent irreversible inhibitor of BTK. It is characterized by high selectivity for BTK and high potency. Ibrutinib is currently approved by the FDA and EMA for use in chronic lymphocytic leukaemia in any line of treatment, for treatment of Waldenstrom macroglobulinemia in patients who have received previous treatments or are not suitable to receive immunochemotherapy as well as for second line treatment of mantle cell lymphoma and for patients with marginal zone lymphoma who have received at least one prior anti-CD20-based therapy. In addition, there is emerging clinical data on its efficacy in ABC subtype diffuse large B-cell lymphoma, multiple myeloma and primary central nervous system lymphoma. Ibrutinib has opened new options for treatment of those patients that have relapsed or have been refractory to more classical modes of treatment. Moreover, Ibrutinib has been shown to be effective in patients that have been known to have little sensitivity to classical immunochemotherapy. Having a favourable risk profile, the substance is, unlike conventional immunochemotherapy, also suitable for the less physical fit patients. Cases of primary and secondary resistance to Ibrutinib have emerged and there is an ongoing effort to identify their mechanism and develop strategies to overcome them. Beyond its direct effects on survival and apoptosis of malignant B-cells, there is increasing evidence that Ibrutinib is able to modulate the tumour microenvironment to overcome mechanisms of immune evasion. This has sparked interest in use of the substance beyond lymphoid malignancy. This chapter discusses structure, mechanism of action and toxicities of Ibrutinib and also presents important preclinical and clinical data as well as mechanisms of Ibrutinib resistance. Combination strategies with immunotherapeutic strategies such as immune checkpoint blockade and CAR T-cell therapy may be synergistic and are currently under investigation.

How I treat CLL patients with ibrutinib

Ibrutinib is a transformative therapy for high-risk and relapsed refractory chronic lymphocytic leukemia (CLL) patients. In clinical trials in relatively healthy younger patients, ibrutinib has been well tolerated. As its use has become more widespread in the community, however, its full adverse event profile has emerged and proven more challenging than was initially anticipated. Reports of community-based use have estimated discontinuation rates as high as 40% in the first year of therapy. This article therefore reviews my approach to the evaluation and management of a CLL patient starting on ibrutinib, with the goal of minimizing and managing toxicity to maintain patients on ibrutinib. Key topics discussed include bleeding risk; cardiac complications, particularly atrial fibrillation; drug interactions; and infections.

Ibrutinib and its use in the treatment of chronic lymphocytic leukemia

Ibrutinib represents a revolution in chronic lymphocytic leukemia treatment scenario providing results never seen before and offering an effective therapy even in high-risk patients with really poor outcome after chemoimmunotherapy. Thanks to longer updates, on one hand, ibrutinib has confirmed its efficacy continuing to show clinical benefits over time; on the other hand, resistance mechanisms are slowly emerging. Moreover, clinicians should be aware of ibrutinib-related side effects, paying attention to screen patients that could benefit more from the drug and try to prevent adverse events. While ibrutinib approval indication is expanding, high treatment costs will shortly require a selection of those who can really draw advantage from Bruton's tyrosine kinase inhibition and those who could continue to be treated with chemoimmunotherapy.

Severe platelet dysfunction in NHL patients receiving ibrutinib is absent in patients receiving acalabrutinib

The Bruton tyrosine kinase (Btk) inhibitor ibrutinib induces platelet dysfunction and causes increased risk of bleeding. Off-target inhibition of Tec is believed to contribute to platelet dysfunction and other side effects of ibrutinib. The second-generation Btk inhibitor acalabrutinib was developed with improved specificity for Btk over Tec. We investigated platelet function in patients with non-Hodgkin lymphoma (NHL) receiving ibrutinib or acalabrutinib by aggregometry and by measuring thrombus formation on collagen under arterial shear. Both patient groups had similarly dysfunctional aggregation responses to collagen and collagen-related peptide, and comparison with mechanistic experiments in which platelets from healthy donors were treated with the Btk inhibitors suggested that both drugs inhibit platelet Btk and Tec at physiological concentrations. Only ibrutinib caused dysfunctional thrombus formation, whereas size and morphology of thrombi following acalabrutinib treatment were of normal size and morphology. We found that ibrutinib but not acalabrutinib inhibited Src family kinases, which have a critical role in platelet adhesion to collagen that is likely to underpin unstable thrombus formation observed in ibrutinib patients. We found that platelet function was enhanced by increasing levels of von Willebrand factor (VWF) and factor VIII (FVIII) ex vivo by addition of intermediate purity FVIII (Haemate P) to blood from patients, resulting in consistently larger thrombi. We conclude that acalabrutinib avoids major platelet dysfunction associated with ibrutinib therapy, and platelet function may be enhanced in patients with B-cell NHL by increasing plasma VWF and FVIII.

Optimizing frontline therapy of CLL based on clinical and biological factors

The heterogeneity of the clinical course of chronic lymphocytic leukemia (CLL) ranges from an indolent course, where patients do not require therapy for many years, to a very aggressive disease, where treatment is required soon after diagnosis and relapses may occur early. The improved tools for prognostication allow predicting the outcome of patients with increasing reliability. Some markers also allow selecting more specific therapies with improved activity in the presence of certain genetic or clinical features of CLL. Of these markers, TP53 dysfunction, age, the presence of comorbidities and the immunoglobulin heavy-chain variable region gene mutational status, or serum markers such as β2-microglobulin have shown independent prognostic value in multiple prospective trials. During the last 10 years, multiple novel agents have become available. The advent of oral kinase inhibitors or Bcl-2 antagonists has provided highly effective options with acceptable toxicity. This manuscript summarizes the current evidence of the available treatment options and proposes an integrated algorithm for the frontline therapy of CLL.

Bruton's tyrosine kinase inhibitors: first and second generation agents for patients with Chronic Lymphocytic Leukemia (CLL)

INTRODUCTION

The BTK inhibitor ibrutinib is effective in both low- and high-risk CLL patients, achieving durable remissions with continuous therapy in the majority of patients. Ibrutinib lacks myelotoxicity and is generally well tolerated by older and unfit patients; however, side effects, such as atrial fibrillation or hemorrhage, can result in treatment interruption or discontinuation. Given the high efficacy and overall safety, ibrutinib is increasingly used in untreated and previously treated CLL patients. Second-generation BTK inhibitors are being developed, with different and generally more BTK-selective kinase inhibition profiles, which may increase the safety and/or efficacy.

AREAS COVERED

We review key features of ibrutinib, along with problems of its use, discuss the potential and drawbacks of second generation molecules, and discuss combination therapies currently in development.

EXPERT OPINION

BTK inhibitors have been a major therapeutic advance in older/unfit patients and those with high-risk and/or relapsed CLL, but require indefinite maintenance therapy and risk of developing treatment resistance or adverse events requiring treatment cessation increases over time. Novel combination strategies are currently being evaluated (e.g. the combination of ibrutinib with venetoclax), which may achieve greater depth of remission, remove the need for indefinite maintenance treatment and potentially replace chemoimmunotherapy in the first-line setting.

Bruton's Tyrosine Kinase: An Emerging Key Player in Innate Immunity

Bruton’s tyrosine kinase (BTK) was initially discovered as a critical mediator of B cell receptor signaling in the development and functioning of adaptive immunity. Growing evidence also suggests multiple roles for BTK in mononuclear cells of the innate immune system, especially in dendritic cells and macrophages. For example, BTK has been shown to function in Toll-like receptor-mediated recognition of infectious agents, cellular maturation and recruitment processes, and Fc receptor signaling. Most recently, BTK was additionally identified as a direct regulator of a key innate inflammatory machinery, the NLRP3 inflammasome. BTK has thus attracted interest not only for gaining a more thorough basic understanding of the human innate immune system but also as a target to therapeutically modulate innate immunity. We here review the latest developments on the role of BTK in mononuclear innate immune cells in mouse versus man, with specific emphasis on the sensing of infectious agents and the induction of inflammation. Therapeutic implications for modulating innate immunity and critical open questions are also discussed.

Recent therapeutic advances in chronic lymphocytic leukemia

The last several years have witnessed a paradigm shift in the management of patients with chronic lymphocytic leukemia (CLL). The course of this very heterogeneous disease, traditionally treated with chemotherapeutic agents usually in combination with rituximab, typically has been characterized by remissions and relapses, and survival times vary greatly, depending on intrinsic biological attributes of the leukemia. The developments of the last few years have been transformative, ushering in an era of novel, molecularly targeted therapies, made possible by extensive efforts to elucidate the biology of the disease that predated the new targeted drugs. Thus, successful therapeutic targeting of the B-cell receptor signaling pathway and of the Bcl-2 anti-apoptotic protein with small molecules has now made chemotherapy-free approaches possible, hopefully mitigating the risk of development of therapy-related myeloid neoplasms and making eventual cure of CLL with the use of optimal drug combinations a realistic goal. Most importantly, these therapies have demonstrated unprecedented efficacy in patients with deletion 17p/TP53 mutation, a subset that historically has been very difficult to treat. However, as we gain more experience with the newer agents, unique safety concerns and resistance mechanisms have emerged, as has the issue of cost, as these expensive drugs are currently administered indefinitely. Accordingly, novel laboratory-based strategies and clinical trial designs are being explored to address these issues. The availability of whole exome/genome sequencing has given us profound insights into the mutational landscape of CLL. In this article, we highlight some of the most impactful advances since this topic was last reviewed in this journal.

Current Status of Bruton's Tyrosine Kinase Inhibitor Development and Use in B-Cell Malignancies

The B-cell receptor (BCR) pathway plays an important role in the survival, proliferation and trafficking of cancer cells in a variety of B-cell malignancies. Recently, a number of agents have been developed to target various components of the BCR pathway. One such target is Bruton's tyrosine kinase (BTK), a Tec family kinase member found near the cell membrane that is involved in upstream BCR signaling. The biological function of BTK in several B-cell lymphoid malignancies has led to the development of the oral BTK inhibitor ibrutinib. In chronic lymphocytic leukemia (CLL), ibrutinib has demonstrated durable clinical responses in relapsed/refractory (R/R) patients, including those with the high-risk del(17p) cytogenetic abnormality. These findings have paved the way for trials evaluating ibrutinib in previously untreated CLL patients, and also in combination with chemoimmunotherapy or other novel agents. Durable clinical responses have also been demonstrated in mantle cell lymphoma (MCL) and Waldenström's macroglobulinemia (WM) patients treated with ibrutinib. Ibrutinib is generally well tolerated, although current follow-up remains short and patients of advanced age are more likely to discontinue treatment for toxicity. Treatment-specific side effects such as bleeding and atrial fibrillation may, at least partly, be related to off-target inhibition of non-BTK kinases. Studies evaluating other potential indications for BTK inhibition are ongoing, including in post-allogeneic hematopoietic stem cell transplant patients for whom ibrutinib may be effective in modulating graft-versus-host disease. Combination trials of ibrutinib with venetoclax, a Bcl-2 inhibitor, are underway and are supported by sound preclinical rationale. Several next-generation BTK inhibitors are under development with the goal of decreasing treatment-related toxicity and resistance.

Cardiac side effects of bruton tyrosine kinase (BTK) inhibitors

The development of bruton tyrosine kinase inhibitors (BTKi) has been a significant advancement in the treatment of chronic lymphocytic leukemia and related B-cell malignancies. As experience in using ibrutinib increased, the first drug to be licensed in its class, atrial fibrillation (AF) emerged as an important side effect. The intersection between BTKi therapy for B-cell malignancies and AF represents a complex area of management with scant evidence for guidance. Consideration needs to be taken regarding the interplay of increased bleeding risk versus thromboembolic complications of AF, drug interactions between ibrutinib and anticoagulants and antiarrhythmic agents, and the potential for other, as yet seldom reported cardiac side effects. This review describes the current knowledge regarding BTKi and potential pathophysiologic mechanisms of AF and discusses the management of BTKi-associated AF. Finally, a review of the second generation BTKi is provided and gaps in knowledge in this evolving field are highlighted.

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.

Characterization of atrial fibrillation adverse events reported in ibrutinib randomized controlled registration trials

The first-in-class Bruton's tyrosine kinase inhibitor ibrutinib has proven clinical benefit in B-cell malignancies; however, atrial fibrillation (AF) has been reported in 6-16% of ibrutinib patients. We pooled data from 1505 chronic lymphocytic leukemia and mantle cell lymphoma patients enrolled in four large, randomized, controlled studies to characterize AF with ibrutinib and its management. AF incidence was 6.5% [95% Confidence Interval (CI): 4.8, 8.5] for ibrutinib at 16.6-months versus 1.6% (95%CI: 0.8, 2.8) for comparator and 10.4% (95%CI: 8.4, 12.9) at the 36-month follow up; estimated cumulative incidence: 13.8% (95%CI: 11.2, 16.8). Ibrutinib treatment, prior history of AF and age 65 years or over were independent risk factors for AF. Multiple AF events were more common with ibrutinib (44.9%; comparator, 16.7%) among patients with AF. Most (85.7%) patients with AF did not discontinue ibrutinib, and more than half received common anticoagulant/antiplatelet medications on study. Low-grade bleeds were more frequent with ibrutinib, but serious bleeds were uncommon (ibrutinib, 2.9%; comparator, 2.0%). Although the AF rate among older non-trial patients with comorbidities is likely underestimated by this dataset, these results suggest that AF among clinical trial patients is generally manageable without ibrutinib discontinuation (clinicaltrials.gov identifier: 01578707, 01722487, 01611090, 01646021).

Comparison of Acalabrutinib, A Selective Bruton Tyrosine Kinase Inhibitor, with Ibrutinib in Chronic Lymphocytic Leukemia Cells

Purpose: Ibrutinib inhibits Bruton tyrosine kinase (BTK) by irreversibly binding to the Cys-481 residue in the enzyme. However, ibrutinib also inhibits several other enzymes that contain cysteine residues homologous to Cys-481 in BTK. Patients with relapsed/refractory or previously untreated chronic lymphocytic leukemia (CLL) demonstrate a high overall response rate to ibrutinib with prolonged survival. Acalabrutinib, a selective BTK inhibitor developed to minimize off-target activity, has shown promising overall response rates in patients with relapsed/refractory CLL. A head-to-head comparison of ibrutinib and acalabrutinib in CLL cell cultures and healthy T cells is needed to understand preclinical biologic and molecular effects.Experimental Design: Using samples from patients with CLL, we compared the effects of both BTK inhibitors on biologic activity, chemokine production, cell migration, BTK phosphorylation, and downstream signaling in primary CLL lymphocytes and on normal T-cell signaling to determine the effects on other kinases.Results: Both BTK inhibitors induced modest cell death accompanied by cleavage of PARP and caspase-3. Production of CCL3 and CCL4 chemokines and pseudoemperipolesis were inhibited by both drugs to a similar degree. These drugs also showed similar inhibitory effects on the phosphorylation of BTK and downstream S6 and ERK kinases. In contrast, off-target effects on SRC-family kinases were more pronounced with ibrutinib than acalabrutinib in healthy T lymphocytes.Conclusions: Both BTK inhibitors show similar biological and molecular profile in primary CLL cells but appear different on their effect on normal T cells. Clin Cancer Res; 23(14); 3734-43. ©2016 AACR.

Cutaneous Adverse Events of Targeted Therapies for Hematolymphoid Malignancies

The identification of oncogenic drivers of liquid tumors has led to the rapid development of targeted agents with distinct cutaneous adverse event (AE) profiles. The diagnosis and management of these skin toxicities has motivated a novel partnership between dermatologists and oncologists in developing supportive oncodermatology clinics. In this article we review the current state of knowledge of clinical presentation, mechanisms, and management of the most common and significant cutaneous AEs observed during treatment with targeted therapies for hematologic and lymphoid malignancies. We systematically review according to drug-targeting pathway the cutaneous AE profiles of these drugs, and offer insight when possible into whether pharmacologic target versus immunologic modulation primarily underlie presentation. We include discussion of tyrosine kinase inhibitors (imatinib, dasatinib, nilotinib, bosutinib, ponatinib), blinatumomab, ibrutinib, idelalisib, anti-B cell antibodies (rituximab, ibritumomab, obinutuzumab, ofatumumab, tositumomab), immune checkpoint inhibitors (nivolumab, pembrolizumab), alemtuzumab, brentuximab, and proteasome inhibitors (bortezomib, carfilzomib, ixazomib). We highlight skin reactions seen with antiliquid but not solid tumor agents, draw attention to serious cutaneous AEs that might require therapy modification or cessation, and offer management strategies to permit treatment tolerability. We emphasize the importance of early diagnosis and treatment to minimize disruptions to care, optimize prognosis and quality of life, and promptly address life-threatening skin or infectious events. This evolving partnership between oncologists and dermatologists in the iterative characterization and management of skin toxicities will contribute to a better understanding of these drugs' cutaneous targets and improved patient care.

Atrial fibrillation as a complication of ibrutinib therapy: clinical features and challenges of management

Ibrutinib is a Bruton's tyrosine kinase (BTK) inhibitor finding increasingly widespread use in non-Hodgkin lymphoma. Evidence of an increased risk of atrial fibrillation (AF) emerged in Phase III studies with a median incidence of approximately 6%. The mechanism remains unknown, but inhibition of a cardioprotective pathway has been proposed. Ibrutinib induces a platelet function defect, increasing the bleeding risk of anticoagulation for AF stroke prophylaxis. Multiple potential drug interactions are an added complication. In this review we examine the characteristics and management of the reported cases of AF with ibrutinib and where possible make recommendations. The evidence suggests dose reduction or temporary suspension of drug, are feasible alternative to discontinuation. The optimum choice of thromboprophylaxis has not been determined, but we propose the use of novel anticoagulants (NOACs) and avoidance of anti-platelet agents where possible. Further research and consensus guidelines are required.

Extended follow-up and impact of high-risk prognostic factors from the phase 3 RESONATE study in patients with previously treated CLL/SLL

In the phase 3 RESONATE study, ibrutinib demonstrated superior progression-free survival (PFS), overall survival (OS) and overall response rate (ORR) compared with ofatumumab in relapsed/refractory CLL patients with high-risk prognostic factors. We report updated results from RESONATE in these traditionally chemotherapy resistant high-risk genomic subgroups at a median follow-up of 19 months. Mutations were detected by Foundation One Heme Panel. Baseline mutations in the ibrutinib arm included TP53 (51%), SF3B1 (31%), NOTCH1 (28%), ATM (19%) and BIRC3 (14%). Median PFS was not reached, with 74% of patients randomized to ibrutinib alive and progression-free at 24 months. The improved efficacy of ibrutinib vs ofatumumab continues in all prognostic subgroups including del17p and del11q. No significant difference within the ibrutinib arm was observed for PFS across most genomic subtypes, although a subset carrying both TP53 mutation and del17p had reduced PFS compared with patients with neither abnormality. Reduced PFS or OS was not evident in patients with only del17p. PFS was significantly better for ibrutinib-treated patients in second-line vs later lines of therapy. The robust clinical activity of ibrutinib continues to show ongoing efficacy and acceptable safety consistent with prior reports, independent of various known high-risk mutations.

The Bruton Tyrosine Kinase (BTK) Inhibitor Acalabrutinib Demonstrates Potent On-Target Effects and Efficacy in Two Mouse Models of Chronic Lymphocytic Leukemia

Purpose: Acalabrutinib (ACP-196) is a novel, potent, and highly selective Bruton tyrosine kinase (BTK) inhibitor, which binds covalently to Cys481 in the ATP-binding pocket of BTK. We sought to evaluate the antitumor effects of acalabrutinib treatment in two established mouse models of chronic lymphocytic leukemia (CLL).Experimental Design: Two distinct mouse models were used, the TCL1 adoptive transfer model where leukemic cells from Eμ-TCL1 transgenic mice are transplanted into C57BL/6 mice, and the human NSG primary CLL xenograft model. Mice received either vehicle or acalabrutinib formulated into the drinking water.Results: Utilizing biochemical assays, we demonstrate that acalabrutinib is a highly selective BTK inhibitor as compared with ibrutinib. In the human CLL NSG xenograft model, treatment with acalabrutinib demonstrated on-target effects, including decreased phosphorylation of PLCγ2, ERK, and significant inhibition of CLL cell proliferation. Furthermore, tumor burden in the spleen of the mice treated with acalabrutinib was significantly decreased compared with vehicle-treated mice. Similarly, in the TCL1 adoptive transfer model, decreased phosphorylation of BTK, PLCγ2, and S6 was observed. Most notably, treatment with acalabrutinib resulted in a significant increase in survival compared with mice receiving vehicle.Conclusions: Treatment with acalabrutinib potently inhibits BTK in vivo, leading to on-target decreases in the activation of key signaling molecules (including BTK, PLCγ2, S6, and ERK). In two complementary mouse models of CLL, acalabrutinib significantly reduced tumor burden and increased survival compared with vehicle treatment. Overall, acalabrutinib showed increased BTK selectivity compared with ibrutinib while demonstrating significant antitumor efficacy in vivo on par with ibrutinib. Clin Cancer Res; 23(11); 2831-41. ©2016 AACR.

Practical recommendations for the choice of anticoagulants in the management of patients with atrial fibrillation on ibrutinib

The management of AF represents a major challenge in patients with CLL, especially in elderly patients with multiple comorbidities who are representative of the majority of patients with CLL. This is especially complex in the case of ibrutinib. Many anticoagulants have potential for pharmacological interaction with ibrutinib, and ibrutinib itself has antiplatelet properties. Use of ibrutinib therapy in these patients mandates review and revision of the need for anticoagulation and best anticoagulant to use. Herein, we review the current knowledge of the metabolism of common anticoagulants and how they may interact with ibrutinib.

Ibrutinib-associated bleeding: pathogenesis, management and risk reduction strategies

Ibrutinib is an irreversible inhibitor of Bruton's tyrosine kinase (Btk) that has proven to be an effective therapeutic agent for multiple B-cell-mediated lymphoproliferative disorders. Ibrutinib, however, carries an increased bleeding risk compared with standard chemotherapy. Bleeding events range from minor mucocutaneous bleeding to life-threatening hemorrhage, due in large part to the effects of ibrutinib on several distinct platelet signaling pathways. There is currently a minimal amount of data to guide clinicians regarding the use of ibrutinib in patients at high risk of bleeding or on anticoagulant or antiplatelet therapy. In addition, the potential cardiovascular protective effects of ibrutinib monotherapy in patients at risk of vascular disease are unknown. Patients should be cautioned against using non-steroidal anti-inflammatory drugs, fish oils, vitamin E and aspirin-containing products, and consider replacing ibrutinib with a different agent if dual antiplatelet therapy is indicated. Patients should not take vitamin K antagonists concurrently with ibrutinib; direct oral anticoagulants should be used if extended anticoagulation is strongly indicated. In this review, we describe the pathophysiology of ibrutinib-mediated bleeding and suggest risk reduction strategies for common clinical scenarios associated with ibrutinib.

Use of anticoagulants and antiplatelet in patients with chronic lymphocytic leukaemia treated with single-agent ibrutinib

Bleeding events have been observed among a subgroup of chronic lymphocytic leukaemia (CLL) patients treated with ibrutinib. We analysed data from two studies of single‐agent ibrutinib to better characterize bleeding events and pattern of anticoagulation and antiplatelet use. Among 327 ibrutinib‐treated patients, concomitant anticoagulation (11%) or antiplatelet use (34%) was common, but major bleeding was infrequent (2%). Bleeding events were primarily grade 1, and infrequently (1%) led to discontinuation. Among 175 patients receiving concomitant anticoagulant or antiplatelet agents, 5 had major bleeding events (3%). These events were typically observed in conjunction with other factors, such as coexisting medical conditions and/or concurrent medications.

Profile of venetoclax and its potential in the context of treatment of relapsed or refractory chronic lymphocytic leukemia

Over the last few years, dramatic changes have occurred in the treatment of chronic lymphocytic leukemia (CLL). The current standard for young and fit patients with CLL remains chemoimmunotherapy, namely the fludarabine, cyclophosphamide, and rituximab (FCR) regimen. However, novel oral therapies are presently being introduced and represent a considerable breakthrough concerning effectiveness and safety profile. In particular, the very high-risk group of CLL patients, defined by the genetic aberration del(17p) and/or TP53 mutation, benefit from the new agents. These genetic abnormalities are the most relevant negative prognostic markers in the context of chemoimmunotherapy. New targeted therapies allow different approaches to improve outcomes.

Novel agents versus chemotherapy as frontline treatment of CLL

Chronic lymphocytic leukemia (CLL) is a neoplastic disorder of mature B lymphocytes. While traditionally treated with combinations of chemoimmunotherapy, the therapeutic options for CLL have expanded in recent years with the emergence of novel oral agents, such as the Bruton tyrosine kinase inhibitor ibrutinib, that are well tolerated and highly efficacious. The role of novel agents in the first-line setting is now being investigated in head-to-head clinical trials. In this discussion paper, we consider the role of novel agents in the up-front setting, using three case studies of treatment-naive patients to highlight how choice of therapy may be individualized depending on the characteristics of the patient and the disease, as well as patient preferences.

Risk of Atrial Fibrillation and Bleeding Diathesis Associated With Ibrutinib Treatment: A Systematic Review and Pooled Analysis of Four Randomized Controlled Trials

BACKGROUND

Clinical trials raised concern that ibrutinib may increase the risk of atrial fibrillation/flutter (Afib/Aflutter) and major bleeding. However, the association has not been statistically validated, and there is no consensus regarding optimal management of anticoagulation among patients receiving ibrutinib who develop Afib/Aflutter. We performed a systematic review and pooled analysis to precisely assess the risk of Afib/Aflutter and bleeding associated with ibrutinib treatment in patients with hematologic malignancies.

PATIENTS AND METHODS

We searched PubMed, EMBASE, Cochrane Database, and meeting abstracts up to May 15, 2016, for randomized controlled trials comparing ibrutinib to chemotherapy, monoclonal antibody, or a combination. Primary outcomes were serious Afib/Aflutter and major bleeding. Secondary outcomes were all-grade Afib/Aflutter and bleeding. We calculated the Mantel-Haenszel risk ratio (RR) and estimated the effect of the treatments using a fixed-effects model.

RESULTS

Ibrutinib treatment was associated with a significantly higher incidence of serious Afib/Aflutter (3.03% vs. 0.80%, RR = 3.80, 95% confidence interval [CI] = 1.56-9.29, P = .003), all-grade Afib/Aflutter (8.18% vs. 0.93%, RR = 8.81, 95% CI = 2.70-28.75, P = .0003), and all-grade bleeding (4.85% vs. 1.55%, RR = 2.93, 95% CI = 1.14-7.52, P = .03) compared to control treatments. The observed between-treatment difference in major bleeding rates was not statistically significant (3.69% vs. 2.13%, RR = 1.72, 95% CI = 0.95-3.11, P = .07). The risk of these adverse events was not different between subgroups on the basis of pathology, treatment setting, dose, and duration of ibrutinib exposure.

CONCLUSION

The risks of Afib/Aflutter and all-grade bleeding were significantly higher in the ibrutinib group. These results indicate the need for vigilant monitoring while the patient is receiving ibrutinib therapy, and careful assessment of the risks and benefits of anticoagulation is required.

The NLRP3 inflammasome and bruton's tyrosine kinase in platelets co-regulate platelet activation, aggregation, and in vitro thrombus formation

Cleavage of interleukin-1β (IL-1β) is a key inflammatory event in immune cells and platelets, which is mediated by nucleotide-binding domain leucine rich repeat containing protein (NLRP3)-dependent activation of caspase-1. In immune cells, NLRP3 and caspase-1 form inflammasome complexes with the adaptor proteins apoptosis-associated speck-like protein containing a CARD (ASC) and bruton's tyrosine kinase (BTK). In platelets, however, the regulatory triggers and the functional effects of the NLRP3 inflammasome are unknown. Here, we show in vitro that the platelet NLRP3 inflammasome contributes to platelet activation, aggregation, and thrombus formation. NLRP3 activity, as monitored by caspase-1 activation and cleavage and secretion of IL-1β, was upregulated in activated platelets, which was dependent on platelet BTK. Pharmacological inhibition or genetic ablation of BTK in platelets led to decreased platelet activation, aggregation, and in vitro thrombus formation. We identify a functionally relevant link between BTK and NLRP3 in platelets, with potential implications in disease states associated with abnormal coagulation and inflammation.

[Advances in the treatment of chronic lymphocytic leukaemia]

Chronic lymphocytic leukemia (CLL), a proliferation of mature B cells, is one of the most prevalent haematological malignancies. Progress has been made in its treatment during the last few decades, and chemoimmunotherapy based on fludarabine, cyclophosphamide and rituximab is considered the treatment of choice for patients with standard-risk CLL and good performance status. However, due to the characterization of high-risk biological subgroups and its presentation in elderly patients and/or with comorbidities, targeted therapies, such as B-cell receptor inhibitors, have been developed and approved during the last few years. The current review examines traditional therapeutic strategies and focuses on new small molecules that already represent promising elements of the CLL treatment landscape.

Pharmacovigilance during ibrutinib therapy for chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) in routine clinical practice

Due to Cytochrome P450 3A (CYP3A) metabolism, clinical trials of ibrutinib-treated chronic lymphocytic leukemia (CLL) patients prohibited concurrent medications metabolized by CYP3A. We evaluated concomitant medication use in 118 ibrutinib-treated CLL patients outside the context of clinical trials. Seventy-five (64%) patients were on medications that could increase ibrutinib toxicity and 4 (3%) were on drugs that could decrease ibrutinib efficacy. Nineteen (16%) patients were on concomitant CYP3A inhibitors (11 moderate, 8 strong), and 4 (3%) were on CYP3A inducers (two patients were on both CYP3A inhibitors and inducers). Although the ibrutinib starting dose was changed in 18 patients on CYP3A interacting medications, no difference in 18-month progression-free survival or rate of ibrutinib discontinuation was observed in patients who were not. In routine clinical practice, 2 of 3 CLL patients commencing ibrutinib are on a concomitant medication with potential to influence ibrutinib metabolism. Formal medication review by a pharmacist should be considered in all patients initiating ibrutinib.

Ristocetin-induced platelet aggregation for monitoring of bleeding tendency in CLL treated with ibrutinib

Bleeding because of impaired platelet function is a major side effect of the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib. We quantitatively assessed ristocetin-induced platelet aggregation (RIPA) in 64 patients with chronic lymphocytic leukemia (CLL) under ibrutinib at 287 time points. Eighty-seven bleeding episodes in 39 patients were registered (85 Common Toxicity Criteria (CTC) grade 1 or 2, 2 CTC grade 3) during a median observation period of 10.9 months. At times of bleeding, RIPA values were significantly lower (14 vs 28 U; P<0.0001). RIPA was impaired in patients receiving concomitant antiplatelet therapy or anticoagulation (14 vs 25 U, P=0.005). A gradual decline of median RIPA values was observed with increasing bleeding severity. Importantly, no CTC grade 2 or 3 bleeding were observed with RIPA values of >36 U. Sequential monitoring indicated a decrease of RIPA values from a median of 17 to 9 U within 2 weeks after initiation of treatment as well as an increase above the critical threshold of 36 U within 7 days when ibrutinib was paused. Low RIPA values were similar during treatment with another BTK inhibitor, CC292. Quantitative assessment of platelet function is a practical tool to monitor bleeding tendency under BTK-inhibitor therapy.

Pharmacokinetic and pharmacodynamic evaluation of ibrutinib for the treatment of chronic lymphocytic leukemia: rationale for lower doses

INTRODUCTION

Ibrutinib, a first-in-class covalent inhibitor of Bruton's tyrosine kinase (BTK), is approved in many countries for the treatment of relapsed/refractory chronic lymphocytic leukemia (CLL) and for previously untreated disease with a 17p deletion and, most recently, as a frontline therapy for CLL. In controlled trials in CLL, ibrutinib produced high response rates and improved survival in both the frontline and relapsed settings. While ibrutinib controls CLL with impressive efficacy, it only infrequently induces complete remissions, particularly of relapsed CLL, and does not eradicate minimal residual disease. Finally, ibrutinib is extremely expensive, has off-target toxicities, and requires indefinite therapy. Areas covered: In this article, we provide an overview of the CLL therapeutic landscape and discuss the pharmacokinetic and pharmacodynamic aspects of ibrutinib. Major clinical trials of ibrutinib in CLL are summarized, and its safety profile explored. Expert opinion: Ibrutinib represents a transformative advance in CLL management and has validated BTK as a therapeutic target in this disease, but has some limitations, leading to the emergence of other BTK inhibitors and mechanism-based combination strategies. Given complete BTK occupancy at lower doses of ibrutinib and declining levels of BTK on ibrutinib therapy, lower doses of ibrutinib in CLL are being explored.

The role of B-cell receptor inhibitors in the treatment of patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia is a malignancy of mature auto-reactive B cells. Genetic and functional studies implicate B-cell receptor signaling as a pivotal pathway in its pathogenesis. Full B-cell receptor activation requires tumor-microenvironment interactions in lymphoid tissues. Spleen tyrosine kinase, Bruton's tyrosine kinase, and the phosphatidylinositol 3-kinase (PI3K) δ isoform are essential for B-cell receptor signal transduction but also mediate the effect of other pathways engaged in chronic lymphocytic leukemia cells in the tissue-microenvironment. Orally bioavailable inhibitors of spleen tyrosine kinase, Bruton's tyrosine kinase, or PI3Kδ, induce high rates of durable responses. Ibrutinib, a covalent inhibitor of Bruton's tyrosine kinase, and idelalisib, a selective inhibitor of PI3Kδ, have obtained regulatory approval in chronic lymphocytic leukemia. Ibrutinib and idelalisib are active in patients with high-risk features, achieving superior disease control in difficult-to-treat patients than prior best therapy, making them the preferred agents for chronic lymphocytic leukemia with TP53 aberrations and for patients resistant to chemoimmunotherapy. In randomized trials, both ibrutinib, versus ofatumumab, and idelalisib in combination with rituximab, versus placebo with rituximab improved survival in relapsed/refractory chronic lymphocytic leukemia. Responses to B-cell receptor inhibitors are mostly partial, and within clinical trials treatment is continued until progression or occurrence of intolerable side effects. Ibrutinib and idelalisib are, overall, well tolerated; notable adverse events include increased bruising and incidence of atrial fibrillation on ibrutinib and colitis, pneumonitis and transaminase elevations on idelalisib. Randomized trials investigate the role of B-cell receptor inhibitors in first-line therapy and the benefit of combinations. This review discusses the biological basis for targeted therapy of chronic lymphocytic leukemia with B-cell receptor inhibitors, and summarizes the clinical experience with these agents.

Sunitinib uptake inhibits platelet function in cancer patients

BACKGROUND

Sunitinib is an oral tyrosine kinase inhibitor used for cancer treatment. Patients treated with sunitinib are at higher bleeding risk. As tyrosine kinases are essential for platelet signalling, the effects of sunitinib on platelet function in vitro and in cancer patients on treatment were investigated.

PATIENTS AND METHODS

Blood samples were collected from eight healthy volunteers and eight patients diagnosed with metastatic renal cell cancer (RCC) before and 2 weeks on treatment with sunitinib. Platelets from 15 additional healthy individuals were preincubated with sunitinib or vehicle to perform in vitro experiments. Immunofluorescence imaging, western blotting, light transmission aggregometry, whole blood perfusion over collagen, flow cytometry and ELISA were performed.

RESULTS

Confocal microscopy indicated that platelets sequester sunitinib in vitro and in patients. In platelets from healthy controls, tyrosine phosphorylation was inhibited by sunitinib. Also, sunitinib dose dependently reduced collagen- and ADP-induced aggregation, collagen-dependent thrombus formation and collagen-induced secretion of platelet-derived growth factor and β-thromboglobulin. In blood from RCC patients before treatment, thrombus formation and procoagulant activity under flow were 47% and 80% higher than in healthy controls. After 14 d of sunitinib treatment, platelet count was moderately, but significantly decreased (from 243 to 144 × 10(9)/l). At the same time, collagen-induced platelet aggregation as well as thrombus formation and phosphatidylserine exposure under flow were significantly reduced (by 45%, 16% and 61%, respectively).

CONCLUSIONS

Sunitinib uptake by platelets inhibits collagen receptor-induced aggregation and thrombus formation via reduction of protein tyrosine phosphorylation and α-granule secretion. This dysfunction may contribute to the higher bleeding tendency observed in sunitinib-treated patients.

Waldenström macroglobulinemia: biology, genetics, and therapy

Waldenström macroglobulinemia (WM) is a distinct clinicopathologic entity characterized by the presence of a lymphoplasmacytic lymphoma, a non-Hodgkin lymphoma, and IgM monoclonal gammopathy. WM is an indolent, uncommon malignancy mostly affecting the elderly. Patient outcomes have modestly improved since the introduction of rituximab to conventional cytotoxic chemotherapy more than 20 years ago. However, the pivotal discovery of the somatic MYD88 L265P mutation, harbored by most patients with WM, and the somatic CXCR4 WHIM mutations, similar to germline CXCR4 mutations seen in the warts, hypogammaglobulinemia, immunodeficiency, and myelokathexis (WHIM) syndrome, present in approximately one-third of patients with WM, has fundamentally changed our understanding of this disease and expanded the potential therapeutic targets. Within this new paradigm, ibrutinib emerged as a promising new drug. Ibrutinib targets Bruton’s tyrosine kinase, a downstream protein in the B-cell receptor pathway that is overactivated by the MYD88 L265P mutation. A seminal Phase II trial of ibrutinib in previously treated WM patients showed impressive response rates and confirmed the effects of MYD88 L265P and CXCR4 WHIM mutations in response to therapy. Ibrutinib is the first and only US Food and Drug Administration–approved drug specifically for the treatment of WM. However, before ibrutinib can be established as the standard of care for WM, long-term data regarding efficacy and safety are required. Further research to address ibrutinib resistance and cost-effectiveness is also imperative before ibrutinib can gain widespread acceptance. This review will cover the present pathophysiologic understanding of WM in light of the recent MYD88 and CXCR4 discovery, as well as current and emergent treatment regimens with focus on ibrutinib.

Successful treatment of ibrutinib-associated central nervous system hemorrhage with platelet transfusion support

Ibrutinib is a novel targeted therapy for B-cell malignancies. Hemorrhagic events were reported in the original trials, however the mechanism of bleeding is just being elucidated. Recent studies have demonstrated platelet dysfunction as a mechanism of bleeding. Currently we report two patients who developed life-threatening central nervous system hemorrhage while receiving ibrutinib for chronic lymphoid leukemia (CLL) and mantle cell lymphoma, respectively. Both patients improved rapidly after platelet transfusions even though their platelet counts were normal or only mildly reduced at the time of hemorrhage. We suggest that platelet transfusions can ameliorate the platelet dysfunction defect of ibrutinib and can support the patient through the critical period until new platelet production occurs.