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

A pilot study of lower doses of ibrutinib in patients with chronic lymphocytic leukemia

Ibrutinib is highly efficacious and used at 420 mg/d for treatment of chronic lymphocytic leukemia (CLL). We previously demonstrated a decline in Bruton's tyrosine kinase (BTK) protein levels in CLL cells after 1 cycle of ibrutinib, suggesting ibrutinib dose could be lowered after the first cycle without loss of biological effect. To test this postulate, a pilot study (NCT02801578) was designed to systematically reduce ibrutinib dosing within the same patient with CLL over the course of three 28-day cycles. After an initial cycle of 420 mg/d, the dose was reduced to 280 mg/d in cycle 2, and then to 140 mg/d in cycle 3. Eleven patients began study treatment, and 9 completed the 3 cycles. Plasma and intracellular pharmacokinetics (PK), BTK occupancy, and pharmacodynamic (PD) response at different doses of ibrutinib were compared. Plasma and intracellular levels of ibrutinib were dose-dependent, and even the lowest dose was sufficient to occupy, on average, more than 95% of BTK protein. In concert, BTK downstream signaling inhibition was maintained with 140 mg/d ibrutinib in cycle 3, and there were comparable reductions in total and phospho-BTK (Tyr223) protein levels across 3 cycles. Reductions of plasma chemokine CCL3 and CCL4 levels, considered to be biomarkers of ibrutinib response, were similar during the 3 cycles. These PK/PD data demonstrate that after 1 cycle of ibrutinib at the standard 420 mg/d dose, the dose can be reduced without losing biological activity. Clinical efficacy of lower doses needs to be systematically evaluated. Such dose reductions would lower drug cost, lessen untoward toxicity, and facilitate rationale-based combinations. This trial was registered at www.clinicaltrials.gov as #NCT02801578.

Ibrutinib-related bleeding: pathogenesis, clinical implications and management

: Ibrutinib is the first drug of a new family of Bruton's tyrosine kinases (Btk)-inhibiting agents, which have proved to be useful for the treatment of several B-cell lymphoid malignancies. This drug is associated to an increased bleeding risk from initial clinical trials especially in association with warfarin. Although Btk plays an important role in platelet signalling, increased bleeding tendency in patients on ibrutinib is more complex than Btk inhibition alone and is because of several antiplatelet mechanisms, namely inhibition of Btk and Tec kinases, which play a key role in platelet activation downstream of the collagen GPVI and Glycoprotein Ib. This risk is increased by concomitant antiplatelet and anticoagulant therapy; both dual antiplatelet therapy and vitamin K antagonists are contraindicated in these patients. Potential ibrutinib users often have age-associated cardiovascular risk factors or conditions and the drug itself may trigger atrial fibrillation requiring antithrombotic therapy. Aspirin and direct oral anticoagulants can be regarded as the antithrombotic therapies of choice if required. Heparin and fondaparinux have also been used in clinical trials. Therefore, the need and duration of antithrombotic therapy must be carefully evaluated and treatment individualized according to clinical circumstances. Ibrutinib withdrawal and platelet transfusion are key for the management of major bleeding not involving the central nervous system.

Tyrosine Kinase Inhibitor Pazopanib Inhibits Platelet Procoagulant Activity in Renal Cell Carcinoma Patients

Pazopanib is an angiostatic tyrosine kinase inhibitor (TKI) presently used for cancer treatment, particularly in patients with renal cell carcinoma (RCC). This treatment can be accompanied by mild bleeding as an adverse effect. Given the role of protein tyrosine kinases in platelet activation processes, we investigated whether and how pazopanib can affect platelet functions in purified systems and during treatment of advanced RCC patients. In isolated platelets from healthy volunteers, pazopanib dose-dependently reduced collagen-induced integrin activation and secretion, as well as platelet aggregation. Pazopanib addition diminished glycoprotein (GP) VI-dependent tyrosine phosphorylation of multiple platelet proteins, including the tyrosine kinase Syk. Furthermore, pazopanib inhibited GPVI-induced Ca²⁺ elevation, resulting in reduced exposure of the procoagulant phospholipid phosphatidylserine (PS). Upon perfusion of control blood over a collagen surface, pazopanib inhibited thrombus size as well as PS exposure. Blood samples from 10 RCC patients were also analyzed before and after 14 days of pazopanib treatment as monotherapy. This treatment caused an overall lowering in platelet count, with 3 out of 10 patients experiencing mild bleeding. Platelets isolated from pazopanib-treated patients showed a significant lowering of PS exposure upon activation. In addition, platelet procoagulant activity was inhibited in thrombi formed under flow conditions. Control experiments indicated that higher pazopanib concentrations were required to inhibit GPVI-mediated PS exposure in the presence of plasma. Together, these results indicated that pazopanib suppresses GPVI-induced platelet activation responses in a way partly antagonized by the presence of plasma. In treated cancer patients, pazopanib effects were confined to a reduction in GPVI-dependent PS exposure. Together with the reduced platelet count, this may explain the mild bleeding tendency observed in pazopanib-treated patients.

Acquired platelet antagonism: off-target antiplatelet effects of malignancy treatment with tyrosine kinase inhibitors

Platelets can contribute to tumor progression and metastasis. Cancer patients are at increased risk of thrombosis, and advanced stages of cancer are associated with thrombocytosis or increased platelet reactivity. Tyrosine kinase inhibitors (TKIs) are widely used as a targeted strategy for cancer treatment, with the aim of prolonging progression-free survival of the patients. Because of their broad kinase target spectrum, most TKIs inevitably have off-target effects. Platelets rely on tyrosine kinase activity for their activation. Frequently observed side effects are lowering of platelet count and inhibition of platelet functions, whether or not accompanied by an increased bleeding risk. In this review, we aim to give insights into: (i) 38 TKIs that are currently used for the treatment of different types of cancer, either on the market or in clinical trials; (ii) how distinct TKIs can inhibit activation mechanisms in platelets; and (iii) the clinical consequences of the antiplatelet effects of TKI treatment. For several TKIs, the knowledge on affinity for their targets does not align with the published effects on platelets and reported bleeding events. This review should raise awareness of the potential antiplatelet effects of several TKIs, which will be enhanced in the presence of antithrombotic drugs.

The effect of Bruton's tyrosine kinase (BTK) inhibitors on collagen-induced platelet aggregation, BTK, and tyrosine kinase expressed in hepatocellular carcinoma (TEC)

OBJECTIVES

Bruton's tyrosine kinase (BTK) and tyrosine kinase expressed in hepatocellular carcinoma (TEC) are expressed by human platelets. These kinases participate in platelet activation through the collagen receptor glycoprotein VI and may perform overlapping functions. In clinical studies, BTK inhibitors (ibrutinib, acalabrutinib, tirabrutinib, zanubrutinib) have been associated with increased bleeding risk, which may result from inhibition of BTK alone or of both BTK and TEC, although the role of TEC in bleeding risk remains unclear.

METHODS

Here, in vitro catalytic and binding activities of ibrutinib and acalabrutinib were determined with four assay systems. Platelet aggregation assays determined inhibitor potency and its relationship to selectivity between BTK and TEC.

RESULTS

Neither inhibitor was substantially more selective for BTK over TEC. The potencies at which BTK inhibitors suppressed platelet aggregation correlated with the potencies in on-target BTK assays, including those in cells. At clinically relevant plasma concentration, ibrutinib, acalabrutinib, and tirabrutinib inhibited collagen-induced platelet aggregation to a similar extent, despite differing in vitro IC50 s.

CONCLUSIONS

Our results suggest BTK inhibition is the primary driver for inhibition of platelet aggregation. The subtle differences between these inhibitors suggest only randomized, double-blind, placebo-controlled clinical studies can fully address the bleeding risks of different BTK inhibitors.

Anticancer drug-induced cardiac rhythm disorders: Current knowledge and basic underlying mechanisms

Significant advances in cancer treatment have resulted in decreased cancer related mortality for many malignancies with some cancer types now considered chronic diseases. Despite these improvements, there is increasing recognition that many cancer patients or cancer survivors can develop cardiovascular diseases, either due to the cancer itself or as a result of anticancer therapy. Much attention has focused on heart failure; however, other cardiotoxicities, notably cardiac rhythm disorders, can occur without underlying cardiomyopathy. Supraventricular tachycardias occur in cancer patients treated with cytotoxic chemotherapy (anthracyclines, gemcitabine, cisplatin and alkylating-agents) or kinase-inhibitors (KIs) such as ibrutinib. Ventricular arrhythmias, with a subset of them being torsades-de-pointes (TdP) favored by QTc prolongation have been reported: this may be the result of direct hERG-channel inhibition or a more recently-described mechanism of phosphoinositide-3-kinase inhibition. The major anticancer drugs responsible for QTc prolongation in this context are KIs, arsenic trioxide, anthracyclines, histone deacetylase inhibitors, and selective estrogen receptor modulators. Anticancer drug-induced cardiac rhythm disorders remain an underappreciated complication even by experienced clinicians. Moreover, the causal relationship of a particular anticancer drug with cardiac arrhythmia occurrence remains challenging due in part to patient comorbidities and complex treatment regimens. For example, any cancer patient may also be diagnosed with common diseases such as hypertension, diabetes or heart failure which increase an individual's arrhythmia susceptibility. Further, anticancer drugs are generally usually used in combination, increasing the challenge around establishing causation. Thus, arrhythmias appear to be an underappreciated adverse effect of anticancer agents and the incidence, significance and underlying mechanisms are now being investigated.

Practical management of ibrutinib in the real life: Focus on atrial fibrillation and bleeding

The Bruton tyrosine kinase inhibitor ibrutinib (IB) has attained an important role in the treatment of patients with chronic lymphocytic leukaemia, mantle cell lymphoma, and Waldenström macroglobulinemia, significantly improving clinical outcomes. However, IB therapy has been associated with an increased risk of atrial fibrillation (AF) and bleeding. We report on the expert opinion that a group of Italian haematologists, cardiologists, and pharmacologists jointly released to improve the practical management of patients at risk for AF and bleeding during treatment with IB. A proper pretreatment assessment to identify patients who are at a higher risk, careful choice of concomitant drugs, regular monitoring, and multispecialist approach were characterized as the main principles of clinical management of these patients. For patients developing AF, anticoagulant and antiarrhythmic therapy must be guided by considerations about efficacy, safety, and risk of pharmacokinetic interactions with IB. For patients experiencing bleeding or requiring procedures that increase the risk of bleeding, considerations about platelet turnover, IB-related platelet dysfunctions, and bleeding worsening by concomitant anticoagulants or antiplatelet agents provide clues to manage bleeding. Overall, AF and bleeding are manageable clinical events in patients receiving IB, not requiring drug interruption in most cases. Preexisting AF should not represent an absolute contraindication to IB therapy. For each patient candidate for IB, strategies of risk assessment and mitigation may allow to exploit the life-saving effects of in chronic lymphocytic leukaemia and mantle cell lymphoma.

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.

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.

Acalabrutinib (ACP-196): A Covalent Bruton Tyrosine Kinase Inhibitor with a Differentiated Selectivity and In Vivo Potency Profile

Several small-molecule Bruton tyrosine kinase (BTK) inhibitors are in development for B cell malignancies and autoimmune disorders, each characterized by distinct potency and selectivity patterns. Herein we describe the pharmacologic characterization of BTK inhibitor acalabrutinib [compound 1, ACP-196 (4-[8-amino-3-[(2S)-1-but-2-ynoylpyrrolidin-2-yl]imidazo[1,5-a]pyrazin-1-yl]-N-(2-pyridyl)benzamide)]. Acalabrutinib possesses a reactive butynamide group that binds covalently to Cys481 in BTK. Relative to the other BTK inhibitors described here, the reduced intrinsic reactivity of acalabrutinib helps to limit inhibition of off-target kinases having cysteine-mediated covalent binding potential. Acalabrutinib demonstrated higher biochemical and cellular selectivity than ibrutinib and spebrutinib (compounds 2 and 3, respectively). Importantly, off-target kinases, such as epidermal growth factor receptor (EGFR) and interleukin 2-inducible T cell kinase (ITK), were not inhibited. Determination of the inhibitory potential of anti-immunoglobulin M-induced CD69 expression in human peripheral blood mononuclear cells and whole blood demonstrated that acalabrutinib is a potent functional BTK inhibitor. In vivo evaluation in mice revealed that acalabrutinib is more potent than ibrutinib and spebrutinib. Preclinical and clinical studies showed that the level and duration of BTK occupancy correlates with in vivo efficacy. Evaluation of the pharmacokinetic properties of acalabrutinib in healthy adult volunteers demonstrated rapid absorption and fast elimination. In these healthy individuals, a single oral dose of 100 mg showed approximately 99% median target coverage at 3 and 12 hours and around 90% at 24 hours in peripheral B cells. In conclusion, acalabrutinib is a BTK inhibitor with key pharmacologic differentiators versus ibrutinib and spebrutinib and is currently being evaluated in clinical trials.