The evolving role of Bruton's tyrosine kinase inhibitors in chronic lymphocytic leukemia

Ibrutinib, the first in class of the oral covalent Bruton tyrosine kinase (BTK) inhibitors, has profoundly changed the treatment landscape of chronic lymphocytic leukemia (CLL). The phase III RESONATE and RESONATE-2 trials first demonstrated the superiority of ibrutinib over ofatumumab in the relapsed/refractory setting and over chlorambucil in older patients with de novo disease. The phase III ECOG–ACRIN trial extended these results to young, fit patients, demonstrating a significant survival advantage to ibrutinib plus rituximab over fludarabine, cyclophosphamide, and rituximab. Similarly, the Alliance trial demonstrated the superiority of ibrutinib over bendamustine with rituximab as frontline in elderly patients. Challenges with ibrutinib include toxicity, development of resistance, and need for indefinite therapy. The second generation BTK inhibitor acalabrutinib may cause less off-target toxicity. The ELEVATE TN trial demonstrated the superiority of acalabrutinib with or without obinutuzumab over chlorambucil and obinutuzumab as frontline therapy for elderly or comorbid patients. Promising early results from the phase II CAPTIVATE and CLARITY trials, which combined ibrutinib with venetoclax, suggest a future role for minimal residual disease (MRD) testing to determine treatment duration. The ongoing phase III GAIA/CLL13, ECOG EA9161, Alliance A041702, CLL17, and [ClinicalTrials.gov identifier: NCT03836261] trials will assess various combinations of ibrutinib/acalabrutinib, venetoclax, and anti-CD20 antibodies. These trials will answer key questions in the treatment of CLL: should novel agents in CLL be used in combination or sequentially? What is the best frontline agent? Can treatment be safely stopped with BTK inhibitors? Can undetectable MRD be used to determine treatment duration? In this review, we will discuss these and other aspects of the evolving role of BTK inhibition in CLL.

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.

The HELIOS trial protocol: a phase III study of ibrutinib in combination with bendamustine and rituximab in relapsed/refractory chronic lymphocytic leukemia

Ibrutinib is an orally administered, covalent inhibitor of Bruton's tyrosine kinase with activity in B-cell malignancies based on Phase I/II studies. We describe the design and rationale for the Phase III HELIOS trial (trial registration: EudraCT No. 2012-000600-15; UTN No. U1111-1135-3745) investigating whether ibrutinib added to bendamustine and rituximab (BR) provides benefits over BR alone in patients with relapsed/refractory chronic lymphocytic leukemia/small lymphocytic lymphoma. Eligible patients must have relapsed/refractory disease measurable on CT scan and meet ≥ 1 International Workshop on Chronic Lymphocytic Leukemia criterion for requiring treatment; patients with del(17p) are excluded. All patients receive BR (maximum six cycles) as background therapy and are randomized 1:1 to placebo or ibrutinib 420 mg/day. Treatment with ibrutinib or placebo will start concomitantly with BR and continue until disease progression or unacceptable toxicity. The primary end point is progression-free survival. Secondary end points include safety, objective response rate, overall survival, rate of minimal residual disease-negative remissions, and patient-reported outcomes. Tumor response will be assessed using the International Workshop on Chronic Lymphocytic Leukemia guidelines.

Ibrutinib and rituximab induced rapid response in refractory Richter syndrome

We report a 53-year-old man diagnosed with Richter syndrome. He was heavily pretreated and was refractory to prior therapy. He received rituximab and ibrutinib, and achieved a significant response after 1 month of therapy. Our case illustrates the importance of investigation of rituximab and ibrutinib in Richter’s syndrome.

Entering the era of targeted therapy for chronic lymphocytic leukemia: impact on the practicing clinician

PURPOSE

Chemoimmunotherapy has been the standard of care for chronic lymphocytic leukemia (CLL). However, the introduction of B-cell receptor (BCR) kinase inhibitors such as ibrutinib has the potential to eliminate the role of chemotherapy in the treatment of CLL. How to best incorporate old and new therapies for CLL in this landscape is increasingly complex.

METHODS

This article reviews current data available to clinicians and integrates these data to provide a strategy that can be used to approach the treatment of CLL in the era of BCR signaling inhibitors.

RESULTS

Current strategies separate patients based on age or functional status as well as genetics [presence or absence of del(17)(p13.1)]. In the era of targeted therapy, this will likely continue based on current available data. Phase III studies support chemoimmunotherapy as the initial standard therapy for patients without del(17)(p13.1). Choice of chemotherapy (fludarabine plus cyclophosphamide, bendamustine, or chlorambucil) and anti-CD20 antibody (rituximab, ofatumumab, or obinutuzumab) varies based on regimen and patient status. For patients with del(17)(p13.1), no standard initial therapy exists, although several options supported by phase II clinical trials (methylprednisolone plus alemtuzumab or ibrutinib) seem better than chemoimmunotherapy. Treatment of relapsed CLL seems to be best supported by ibrutinib-based therapy. Completion of trials with ibrutinib and other new agents in the near future will offer opportunity for chemotherapy-free treatment across all groups of CLL.

CONCLUSION

Therapy for CLL has evolved significantly over the past decade with introduction of targeted therapy for CLL. This has the potential to completely transform how CLL is treated in the future.

Bruton's tyrosine kinase inhibitors and their clinical potential in the treatment of B-cell malignancies: focus on ibrutinib

Aberrant signaling of the B-cell receptor pathway has been linked to the development and maintenance of B-cell malignancies. Bruton's tyrosine kinase (BTK), a protein early in this pathway, has emerged as a new therapeutic target in a variety of such malignancies. Ibrutinib, the most clinically advanced small molecule inhibitor of BTK, has demonstrated impressive tolerability and activity in a range of B-cell lymphomas which led to its recent approval for relapsed mantle cell lymphoma and chronic lymphocytic leukemia. This review focuses on the preclinical and clinical development of ibrutinib and discusses its therapeutic potential.

Treatment of elderly patients with chronic lymphocytic leukemia: an unmet cinical need

In chronic lymphocytic leukemia (CLL), the most prevalent lymphoid malignancy in western countries, patients have a median age at diagnosis of 72 years. In the last few years, there has been remarkable progress in understanding the biology of CLL, the detection of molecular prognostic factors and the development of more effective therapies. However, many of the milestone studies were conducted in populations that were considerably younger than the average age of the CLL population. Today, the challenge is to improve management of elderly patients. In this population, outcome of treatment with newer highly effective therapies is often compromised by comorbidities and poor performance status. Decision on how elderly patients should be treated is thus a complex issue. The management of these patients should rely on the development of risk-stratified treatment strategies based on the assessment of individual functional status and the biologic characteristics of CLL. New single agents with reduced toxic effects (i.e., inhibitors of BCR signalling) that have achieved promising results in Phase I/II studies when available should modify the paradigm of the treatment of elderly patients with CLL.

Breaking good: the inexorable rise of BTK inhibitors in the treatment of chronic lymphocytic leukaemia

Although expressed in several haematological lineages and involved in multiple different signalling pathways, Bruton tyrosine kinase (BTK) plays an indispensible role in B cells in signalling from the B cell receptor (BCR) for antigen. Many B cell malignancies remain dependent on constitutive BCR signalling, making BTK a functional therapeutic target. Several BTK inhibitors (BTKi) with different kinomes and modes of action are being assessed clinically. This review documents the efficacy and toxicity of BTKi in chronic lymphocytic leukaemia (CLL). Clinically, the furthest in development is ibrutinib (trade name, Imbruvica), an irreversible BTKi, which has shown spectacular preliminary efficacy, with rapid reductions in lymph nodes accompanied by peripheral blood lymphocytosis. The lymphocytosis resolves slowly and most patients do not enter a complete remission. Nevertheless, it is possible to maintain many CLL patients, even those with adverse cytogenetic features, on drug for many months with minimal toxicities, thus potentially transforming the therapeutic paradigms for CLL. The efficacy, lack of toxicity and oral administration of BTKi will ensure their adoption in a wide range of B cell malignancies. An outstanding challenge is to incorporate BTKi with other precision medicines in a mechanism-based manner in order to dispense with conventional chemotherapy.

Ibrutinib (PCI-32765) in chronic lymphocytic leukemia

B-cell receptor (BCR) signaling is essential for chronic lymphocytic leukemia (CLL) cell survival. Many kinases in the BCR signaling pathway are being studied as potential therapeutic targets. Ibrutinib (PCI-32765) is a novel first-in-class selective inhibitor of Bruton tyrosine kinase. Preclinical evidence suggests that ibrutinib inhibits CLL cell survival and proliferation and affects CLL cell migration and homing. Early clinical data in patients with CLL and non-Hodgkin lymphoma is encouraging. It is likely that ibrutinib and other drugs targeting the BCR pathway will become an integral component of CLL therapy.

Ibrutinib: a novel Bruton's tyrosine kinase inhibitor with outstanding responses in patients with chronic lymphocytic leukemia

New treatment options are urgently needed for patients with relapsed chronic lymphocytic leukemia (CLL) who fail to respond to currently available therapies or cannot achieve a sustained response. Moreover, targeted agents with less myelotoxicity are necessary to treat patients with multiple comorbidities who would otherwise be unable to tolerate standard regimens. Ibrutinib, a Bruton's tyrosine kinase inhibitor, has shown highly encouraging results in phase I/II trials in patients with treatment-naive, relapsed and refractory CLL even in the presence of high risk disease or poor prognostic markers. In phase I/II trials, ibrutinib 420 mg or 840 mg - given continuously as single agent or at a dose of 420 mg daily in combination with a monoclonal antibody or chemoimmunotherapy - has been associated with high response rates and durable clinical remissions. Phase II and III trials are currently under way for treatment-naive patients, relapsed/refractory patients, and for those patients harboring a 17p deletion.

Ibrutinib

Abnormal B-cell receptor (BCR) signaling is a key mechanism of disease progression in B-cell malignancy. Bruton's tyrosine kinase (BTK) has a pivotal role in BCR signaling. Ibrutinib (PCI-32765) is a novel agent which serves as a covalent irreversible inhibitor of BTK. It is characterized by high selectivity for BTK and high potency. Preliminary data from phase I and ongoing phase II trials have proven very promising so far. It suggests the substance has high efficacy in B-cell malignancies such as chronic lymphocytic leukemia (CLL); diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), mantel cell lymphoma (MCL), and multiple myeloma (MM) and is very well tolerable. Most notably, the substance does not cause myelosuppression. This chapter discusses structure, mechanism of action, and toxicities of ibrutinib and also presents important preclinical and clinical data. Phase III trials will have to determine the definite role of ibrutinib in clinical practice but the data available so far suggests it may be a powerful new weapon in the battle against B-cell malignancies.

The promising impact of ibrutinib, a Bruton's tyrosine kinase inhibitor, for the management of lymphoid malignancies

Lymphoid malignancies comprise a heterogeneous group of disorders originating from clonal proliferation of B or T lymphocytes. Treatment of lymphoid neoplasms has traditionally been pursued with cytotoxic chemotherapy. To improve efficacy and ameliorate the adverse effects associated with classic chemotherapy, molecularly targeted therapy has been developed. At the forefront of clinical development is ibrutinib, an inhibitor of Bruton's tyrosine kinase (Btk). Btk is a protein tyrosine kinase that plays an important role in regulating B-cell signaling. Dysregulated Btk results in uncontrolled B-lymphocyte proliferation, differentiation, and survival. Ibrutinib is currently being studied in numerous malignancies of lymphoid origin including chronic lymphocytic leukemia, mantle cell lymphoma, non-Hodgkin lymphoma, follicular lymphoma, and multiple myeloma. Thus far, ibrutinib has demonstrated very promising results in treatment-naive patients as well as those with relapsed or refractory disease with an acceptable safety profile. In this article, we describe the pharmacology, efficacy, and toxicity profile of ibrutinib and depict the potential role that ibrutinib will play in the treatment paradigm of lymphoid neoplasms.

Ibrutinib and indolent B-cell lymphomas

Most patients with indolent B-cell lymphomas fail to achieve complete remission with current treatment approaches and invariably relapse. During the past decade, innovative immunochemotherapy strategies have substantially improved disease control rates but not survival, thus providing the rationale for development of novel agents targeting dysregulated pathways that are operable in these hematological malignancies. Ibrutinib, a novel first-in-human Bruton's tyrosine kinase (BTK) inhibitor, has progressed into phase III trials after early-phase clinical studies demonstrated effective target inhibition, increased tumor response rates, and significant improvement in survival, particularly in patients with indolent B-cell lymphomas. Recently, the compound was designated a "breakthrough therapy" by the United States Food and Drug Administration for the treatment of patients with relapsed or refractory mantle cell lymphoma and Waldenström macroglobulinemia. This review summarizes recent achievements of ibrutinib, with a focus on its emerging role in the treatment of patients with indolent B-cell lymphoid malignancies.

Bruton tyrosine kinase inhibitors: a promising novel targeted treatment for B cell lymphomas

Constitutive or aberrant signalling of the B cell receptor signalling cascade has been implicated in the propagation and maintenance of a variety of B cell malignancies. Small molecule inhibitors of Bruton tyrosine kinase (BTK), a protein early in this cascade and specifically expressed in B cells, have emerged as a new class of targeted agents. There are several BTK inhibitors, including ONO-WG-307, LFM-A13, dasatinib, CC-292, and PCI-32765 (ibrutinib), in preclinical and/or clinical development of which ibrutinib is currently in phase III trials. Recent clinical data suggest significant activity of ibrutinib as a first in class oral inhibitor of BTK. This review provides an overview of ongoing clinical studies of BTK inhibitors.

Signaling pathways in lymphoma: pathogenesis and therapeutic targets

Lymphoma is the fifth most common cancer in the USA. Most lymphomas are classified as non-Hodgkin’s lymphoma, and nearly 95% of these cancers are of B-cell origin. B-cell receptor (BCR) surface expression and BCR functional signaling are critical for survival and proliferation of both healthy B cells, as well as most B-lymphoma cells. Agents that inhibit various components of the BCR signaling pathway, as well as parallel signaling pathways, are currently in clinical trials for the treatment of various lymphoma subtypes, including those targeting isoforms of PI3K, mTOR and BTK. In this review, we describe the signaling pathways in healthy mature B cells, the aberrant signaling in lymphomatous B cells and the rationale for clinical trials of agents targeting these pathways as well as the results of clinical trials to date. We propose that the entry into a kinase inhibitor era of lymphoma therapy will be as transformative for our patients as the advent of the antibody or chemotherapy era before it.

Protein kinase inhibitors against malignant lymphoma

INTRODUCTION

Tyrosine kinases (TKs) are intimately involved in multiple signal transduction pathways regulating survival, activation, proliferation and differentiation of lymphoid cells. Deregulation or overexpression of specific oncogenic TKs is implicated in maintaining the malignant phenotype in B-lineage lymphoid malignancies. Several novel targeted TK inhibitors (TKIs) have recently emerged as active in the treatment of relapsed or refractory B-cell lymphomas that inhibit critical signaling pathways, promote apoptotic mechanisms or modulate the tumor microenvironment.

AREAS COVERED

In this review, the authors summarize the clinical outcomes of newer TKIs in various B-cell lymphomas from published and ongoing clinical studies and abstracts from major cancer and hematology conferences.

EXPERT OPINION

Multiple clinical trials have demonstrated that robust antitumor activity can be obtained with TKIs directed toward specific oncogenic TKs that are genetically deregulated in various subtypes of B-cell lymphomas. Clinical success of targeting TKIs is dependent upon on identifying reliable molecular and clinical markers associated with select cohorts of patients. Further understanding of the signaling pathways should stimulate the identification of novel molecular targets and expand the development of new therapeutic options and individualized therapies.