Tolerability and activity of ublituximab, umbralisib, and ibrutinib in patients with chronic lymphocytic leukaemia and non-Hodgkin lymphoma: a phase 1 dose escalation and expansion trial

Small-molecule agents for cancer immunotherapy

Cancer immunotherapy, exemplified by the remarkable clinical benefits of the immune checkpoint blockade and chimeric antigen receptor T-cell therapy, is revolutionizing cancer therapy. They induce long-term tumor regression and overall survival benefit in many types of cancer. With the advances in our knowledge about the tumor immune microenvironment, remarkable progress has been made in the development of small-molecule drugs for immunotherapy. Small molecules targeting PRR-associated pathways, immune checkpoints, oncogenic signaling, metabolic pathways, cytokine/chemokine signaling, and immune-related kinases have been extensively investigated. Monotherapy of small-molecule immunotherapeutic drugs and their combinations with other antitumor modalities are under active clinical investigations to overcome immune tolerance and circumvent immune checkpoint inhibitor resistance. Here, we review the latest development of small-molecule agents for cancer immunotherapy by targeting defined pathways and highlighting their progress in recent clinical investigations.

Discovery of novel pyrido[3,2-d]pyrimidine derivatives as selective and potent PI3Kδ inhibitors

The δ isoform of class I PI3K (PI3Kδ) has been shown as a promising target for the treatment of hematologic malignancies and immune diseases. Herein, a series of pyrido[3,2-d]pyrimidine derivatives were designed, synthesized and evaluated for the preliminary bioactivity. Compared with idelalisib, compound S5 exhibited excellent enzyme activity against PI3Kδ (IC50  = 2.82 nM) and strong antiproliferation activity against SU-DHL-6 cells (IC50  = 0.035 μM). Besides, S5 inhibited the phosphorylation of Akt, which is downstream of PI3Kδ, in concentration-dependent manner. In view of the significant improvement in potency of PI3Kδ and selectivity over other PI3K isoforms, Compound S5 deserved further investigation as a promising PI3Kδ inhibitor.

Targeting casein kinase 1 for cancer therapy: current strategies and future perspectives

Casein Kinase 1 (CK1) is a family of serine/threonine protein kinases that play a crucial role in various cellular processes, including cell proliferation, survival, and metabolism. The dysregulation of CK1 expression has been implicated in the development and progression of several types of cancer, making it an attractive target for anticancer therapy. In this review, we provide an overview of the current strategies employed to target CK1 for cancer therapy and discuss the future perspectives in this field. We highlight the different approaches, including small molecule inhibitors, RNA interference, genome editing, and immunotherapies, which hold immense potential for targeted modulation of CK1 activity in cancer cells. Furthermore, we discuss the challenges associated with targeting CK1 and propose potential strategies to overcome these hurdles. Overall, targeting CK1 holds great promise as a therapeutic strategy for cancer treatment, and further research in this area is warranted.

PI3K/Akt/mTOR Signaling Pathway in Blood Malignancies-New Therapeutic Possibilities

Blood malignancies remain a therapeutic challenge despite the development of numerous treatment strategies. The phosphatidylinositol-3 kinase (PI3K)/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway plays a central role in regulating many cellular functions, including cell cycle, proliferation, quiescence, and longevity. Therefore, dysregulation of this pathway is a characteristic feature of carcinogenesis. Increased activation of PI3K/Akt/mTOR signaling enhances proliferation, growth, and resistance to chemo- and immunotherapy in cancer cells. Overactivation of the pathway has been found in various types of cancer, including acute and chronic leukemia. Inhibitors of the PI3K/Akt/mTOR pathway have been used in leukemia treatment since 2014, and some of them have improved treatment outcomes in clinical trials. Recently, new inhibitors of PI3K/Akt/mTOR signaling have been developed and tested both in preclinical and clinical models. In this review, we outline the role of the PI3K/Akt/mTOR signaling pathway in blood malignancies' cells and gather information on the inhibitors of this pathway that might provide a novel therapeutic opportunity against leukemia.

Ublituximab-xiiy as a treatment option for relapsing multiple sclerosis

INTRODUCTION

B cell depletion has been established as an efficacious anti-inflammatory therapy in people with relapsing forms of multiple sclerosis (MS). Ublituximab (ublituximab-xiiy) is the latest approved chimeric glycoengineered anti-CD20 monoclonal antibody (mAb) for the treatment of relapsing forms of MS.

AREAS COVERED

In this narrative review, the authors explore the safety and effectiveness of data derived from the Phase 2 and Phase 3 ublituximab trials and from their respective post-hoc analyses. Moreover, they consider the similarities and differences between the currently available anti-CD20 antibodies for treatment of relapsing MS. Lastly, the authors discuss the role and place of ublituximab in the current disease modifying therapy landscape.

EXPERT OPINION

Ublituximab is a rapid-acting and effective anti-inflammatory option as a treatment in people with relapsing MS that significantly reduced the annualized relapse rate and MRI-based disease activity. When compared to the Phase III trials of the other two anti-CD20 mAbs (ocrelizumab and ofatumumab), ublituximab did not result with reduction of 3 or 6-month confirmed disability progression. These differences may be attributed to the overall low rate of progression in both the ublituximab and the active comparator teriflunomide arm. Future data from open-label extensions are warranted. There was no significant reduction of ublituximab on whole-brain atrophy compared to teriflunomide.

The Non-Hodgkin Lymphoma Treatment and Side Effects: A Systematic Review and Meta-Analysis

OBJECTIVE

This paper aims to review studies regarding side effects found during Non-Hodgkin Lymphoma treatment, to suggest the drug class most associated with these effects, as well as the most prevalent side effect grade.

METHODS

This review is registered in PROSPERO (IDCRD42022295774) and followed the PICOS strategy and PRISMA guidelines. The search was carried out in the databases PubMed/MEDLINE, Scientific Electronic Library Online, and DOAJ. Medical Subject Headings Terms were used and quantitative studies with conclusive results regarding side effects during the non-Hodgkin lymphoma treatment were selected. Patent information was obtained from google patents.

RESULTS

Monoclonal antibodies were the main drug class associated with side effects during NHL therapy. The combination of Rituximab (Rituxan®; patent EP1616572B) and iInotuzumab (Besponsa®; patent EP1504035B3) was associated with a higher incidence of thrombocytopenia (p<0.05), while the combination of Rituximab and Venetoclax (Venclexta®; patent CN107089981A) was associated with a higher incidence of neutropenia (p<0.05) when compared to Bendamustine combinations (Treanda ™; patent US20130253025A1). Meta-analysis revealed a high prevalence of grade 3-4 neutropenia and thrombocytopenia in men. Finally, Americans and Canadians experienced a higher prevalence of these side effects, when compared to others nationalities (p<0.05).

CONCLUSION

Patents regarding the use of monoclonal antibodies in NHL treatment were published in the last year. Monoclonal antibodies associated with neutropenia (grade 3-4) and thrombocytopenia, especially in North American men treated for NHL, and with an average age of 62 years demonstrated importance in this study.

Development and safety of PI3K inhibitors in cancer

The phosphatidylinositol 3-kinase (PI3K) signalling pathway regulates cell survival, proliferation, migration, metabolism and other vital cellular life processes. In addition, activation of the PI3K signalling pathway is important for cancer development. As a result, a variety of PI3K inhibitors have been clinically developed to treat malignancies. Although several PI3K inhibitors have received approval from the Food and Drug Administration (FDA) for significant antitumour activity, frequent and severe adverse effects have greatly limited their clinical application. These toxicities are mostly on-target and immune-mediated; nevertheless, the underlying mechanisms are still unclear. Current management usually involves intervention through symptomatic treatment, with discontinuation if toxicity persists. Therefore, it is necessary to comprehensively understand these adverse events and ensure the clinical safety application of PI3K inhibitors by establishing the most effective management guidelines, appropriate intermittent dosing regimens and new combination administration. Here, the focus is on the development of PI3K inhibitors in cancer therapy, with particular emphasis on isoform-specific PI3K inhibitors. The most common adverse effects of PI3K inhibitors are also covered, as well as potential mechanisms and management approaches.

Assessing chemotherapy dosing strategies in a spatial cell culture model

Predicting patient responses to chemotherapy regimens is a major challenge in cancer treatment. Experimental model systems coupled with quantitative mathematical models to calculate optimal dose and frequency of drugs can enable improved chemotherapy regimens. Here we developed a simple approach to track two-dimensional cell colonies composed of chemo-sensitive and resistant cell populations via fluorescence microscopy and coupled this to computational model predictions. Specifically, we first developed multiple 4T1 breast cancer cell lines resistant to varying concentrations of doxorubicin, and demonstrated how heterogeneous populations expand in a two-dimensional colony. We subjected cell populations to varied dose and frequency of chemotherapy and measured colony growth. We then built a mathematical model to describe the dynamics of both chemosensitive and chemoresistant populations, where we determined which number of doses can produce the smallest tumor size based on parameters in the system. Finally, using an in vitro model we demonstrated multiple doses can decrease overall colony growth as compared to a single dose at the same total dose. In the future, this system can be adapted to optimize dosing strategies in the setting of heterogeneous cell types or patient derived cells with varied chemoresistance.

BTK inhibitors in the treatment of hematological malignancies and inflammatory diseases: mechanisms and clinical studies

Bruton's tyrosine kinase (BTK) is an essential component of multiple signaling pathways that regulate B cell and myeloid cell proliferation, survival, and functions, making it a promising therapeutic target for various B cell malignancies and inflammatory diseases. Five small molecule inhibitors have shown remarkable efficacy and have been approved to treat different types of hematological cancers, including ibrutinib, acalabrutinib, zanubrutinib, tirabrutinib, and orelabrutinib. The first-in-class agent, ibrutinib, has created a new era of chemotherapy-free treatment of B cell malignancies. Ibrutinib is so popular and became the fourth top-selling cancer drug worldwide in 2021. To reduce the off-target effects and overcome the acquired resistance of ibrutinib, significant efforts have been made in developing highly selective second- and third-generation BTK inhibitors and various combination approaches. Over the past few years, BTK inhibitors have also been repurposed for the treatment of inflammatory diseases. Promising data have been obtained from preclinical and early-phase clinical studies. In this review, we summarized current progress in applying BTK inhibitors in the treatment of hematological malignancies and inflammatory disorders, highlighting available results from clinical studies.

Integrin Signaling Shaping BTK-Inhibitor Resistance

Integrins are adhesion molecules that function as anchors in retaining tumor cells in supportive tissues and facilitating metastasis. Beta1 integrins are known to contribute to cell adhesion-mediated drug resistance in cancer. Very late antigen-4 (VLA-4), a CD49d/CD29 heterodimer, is a beta1 integrin implicated in therapy resistance in both solid tumors and haematological malignancies such as chronic lymphocytic leukemia (CLL). A complex inside-out signaling mechanism activates VLA-4, which might include several therapeutic targets for CLL. Treatment regimens for this disease have recently shifted towards novel agents targeting BCR signaling. Bruton’s tyrosine kinase (BTK) is a component of B cell receptor signaling and BTK inhibitors such as ibrutinib are highly successful; however, their limitations include indefinite drug administration, the development of therapy resistance, and toxicities. VLA-4 might be activated independently of BTK, resulting in an ongoing interaction of CD49d-expressing leukemic cells with their surrounding tissue, which may reduce the success of therapy with BTK inhibitors and increases the need for alternative therapies. In this context, we discuss the inside-out signaling cascade culminating in VLA-4 activation, consider the advantages and disadvantages of BTK inhibitors in CLL and elucidate the mechanisms behind cell adhesion-mediated drug resistance.

Evaluation of vecabrutinib as a model for noncovalent BTK/ITK inhibition for treatment of chronic lymphocytic leukemia

Covalent Bruton tyrosine kinase (BTK) inhibitors, such as ibrutinib, have proven to be highly beneficial in the treatment of chronic lymphocytic leukemia (CLL). Interestingly, the off-target inhibition of IL-2-inducible T-cell kinase (ITK) by ibrutinib may also play a role in modulating the tumor microenvironment, potentially enhancing the treatment benefit. However, resistance to covalently binding BTK inhibitors can develop as the result of a mutation in cysteine 481 of BTK (C481S), which prevents irreversible binding of the drugs. In the present study we performed preclinical characterization of vecabrutinib, a next-generation noncovalent BTK inhibitor that has ITK-inhibitory properties similar to those of ibrutinib. Unlike ibrutinib and other covalent BTK inhibitors, vecabrutinib showed retention of the inhibitory effect on C481S BTK mutants in vitro, similar to that of wild-type BTK. In the murine Eμ-TCL1 adoptive transfer model, vecabrutinib reduced tumor burden and significantly improved survival. Vecabrutinib treatment led to a decrease in CD8+ effector and memory T-cell populations, whereas the naive populations were increased. Of importance, vecabrutinib treatment significantly reduced the frequency of regulatory CD4+ T cells in vivo. Unlike ibrutinib, vecabrutinib treatment showed minimal adverse impact on the activation and proliferation of isolated T cells. Lastly, combination treatment with vecabrutinib and venetoclax augmented treatment efficacy, significantly improved survival, and led to favorable reprogramming of the microenvironment in the murine Eμ-TCL1 model. Thus, noncovalent BTK/ITK inhibitors, such as vecabrutinib, may be efficacious in C481S BTK mutant CLL while preserving the T-cell immunomodulatory function of ibrutinib.

Regulation of B-Cell Receptor Signaling and Its Therapeutic Relevance in Aggressive B-Cell Lymphomas

The proliferation and survival signals emanating from the B-cell receptor (BCR) constitute a crucial aspect of mature lymphocyte's life. Dysregulated BCR signaling is considered a potent contributor to tumor survival in different subtypes of B-cell non-Hodgkin lymphomas (B-NHLs). In the last decade, the emergence of BCR-associated kinases as rational therapeutic targets has led to the development and approval of several small molecule inhibitors targeting either Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (SYK), or phosphatidylinositol 3 kinase (PI3K), offering alternative treatment options to standard chemoimmunotherapy, and making some of these drugs valuable assets in the anti-lymphoma armamentarium. Despite their initial effectiveness, these precision medicine strategies are limited by primary resistance in aggressive B-cell lymphoma such as diffuse large B-cell lymphoma (DLBCL) and mantle cell lymphoma (MCL), especially in the case of first generation BTK inhibitors. In these patients, BCR-targeting drugs often fail to produce durable responses, and nearly all cases eventually progress with a dismal outcome, due to secondary resistance. This review will discuss our current understanding of the role of antigen-dependent and antigen-independent BCR signaling in DLBCL and MCL and will cover both approved inhibitors and investigational molecules being evaluated in early preclinical studies. We will discuss how the mechanisms of action of these molecules, and their off/on-target effects can influence their effectiveness and lead to toxicity, and how our actual knowledge supports the development of more specific inhibitors and new, rationally based, combination therapies, for the management of MCL and DLBCL patients.

Ibrutinib reduces neutrophil infiltration, preserves neural tissue and enhances locomotor recovery in mouse contusion model of spinal cord injury

Following acute spinal cord injury (SCI), excessive recruitment of neutrophils can result in inflammation, neural tissue loss and exacerbation of neurological outcomes. Ibrutinib is a bruton's tyrosine kinase inhibitor in innate immune cells such as the neutrophils that diminishes their activation and influx to the site of injury. The present study evaluated the efficacy of ibrutinib administration in the acute phase of SCI on neural tissue preservation and locomotor recovery. Ibrutinib was delivered intravenously at 3.125 mg/kg either immediately, 12 hours after, or both immediately and 12 hours after SCI induction in adult male C57BL/6 mice. Neutrophil influx into the lesion area was evaluated 24 hours following SCI using light microscopy and immunohistochemistry methods. Animals' body weight changes were recorded, and their functional motor recovery was assessed based on the Basso mouse scale during 28 days after treatment. Finally, spinal cord lesion volume was estimated by an unbiased stereological method. While animals' weight in the control group started to increase one week after injury, it stayed unchanged in treatment groups. However, the double injection of ibrutinib led to a significantly lower body weight compared to the control group at 4 weeks post-injury. Mean neutrophil counts per visual field and the lesion volume were significantly decreased in all ibrutinib-treated groups. In addition, ibrutinib significantly improved locomotor functional recovery in all treated groups, especially in immediate and double-injection groups. Neural tissue protection and locomotor functional recovery suggest ibrutinib treatment as a potent immunotherapeutic intervention for traumatic SCI that warrants clinical testing.

Integrated safety analysis of umbralisib, a dual PI3Kδ/CK1ε inhibitor, in relapsed/refractory lymphoid malignancies

Umbralisib is a unique PI3Kδ/casein kinase-1ε inhibitor with a tolerable safety profile in relapsed/refractory lymphoid malignancies.

Low rates of immune-mediated toxicities were observed with umbralisib.

Phosphoinositide 3-kinase-δ (PI3Kδ) inhibitors are active in lymphoid malignancies, although associated toxicities can limit their use. Umbralisib is a dual inhibitor of PI3Kδ and casein kinase-1ε (CK1ε). This study analyzed integrated comprehensive toxicity data from 4 open-label, phase 1 and 2 studies that included 371 adult patients (median age, 67 years) with relapsed/refractory non-Hodgkin lymphoma (follicular lymphoma [n = 147]; marginal zone lymphoma [n = 82]; diffuse large B-cell lymphoma/mantle cell lymphoma [n = 74]; chronic lymphocytic leukemia [n = 43]; and other tumor types [n = 25]) who were treated with the recommended phase 2 dose of umbralisib 800 mg or higher once daily. At data cutoff, median duration of umbralisib treatment was 5.9 months (range, 0.1-75.1 months), and 107 patients (28.8%) received umbralisib for ≥12 months. Any-grade treatment-emergent adverse events (AEs) occurred in 366 (98.7%) of 371 patients, with the most frequent being diarrhea (52.3%), nausea (41.5%), and fatigue (31.8%). Grade 3 or higher treatment-emergent AEs occurred in 189 (50.9%) of 371 patients and included neutropenia (11.3%), diarrhea (7.3%), and increased aminotransferase levels (5.7%). Treatment-emergent serious AEs occurred in 95 (25.6%) of 371 patients. AEs of special interest were limited and included pneumonia (29 of 371 [7.8%]), noninfectious colitis (9 of 371 [2.4%]), and pneumonitis (4 of 371 [1.1%]). AEs led to discontinuation of umbralisib in 51 patients (13.7%). Four patients (1.1%) died of AEs, none of which was deemed related to umbralisib. No cumulative toxicities were reported. The favorable long-term tolerability profile and low rates of immune-mediated toxicities support the potential use of umbralisib for the benefit of a broad population of patients with lymphoid malignancies.

The Evolving Use of Phosphatidylinositol 3-Kinase Inhibitors for the Treatment of Chronic Lymphocytic Leukemia

B cells express 4 phosphatidylinositol 3-kinase (PI3K) isoforms and have a dependence on p110δ for survival. The design of isoform-selective inhibitors is possible, and pharmacologic inhibition of p110δ is toxic to neoplastic chronic lymphocytic leukemia (CLL) cells for both cell-intrinsic and cell-extrinsic reasons. Idelalisib is a first-in-class p110δ inhibitor that exhibits efficacy for the treatment of relapsed CLL irrespective of adverse prognostic features. Duvelisib is a p110γ/δ inhibitor with a similar efficacy and safety profile to idelalisib. Recent data indicate that umbralisib, a p110δ/CK-1ε dual inhibitor, is safe and effective when administered to patients with CLL.

Ibrutinib combinations in CLL therapy: scientific rationale and clinical results

Ibrutinib has revolutionized the treatment of chronic lymphocytic leukemia (CLL). This drug irreversibly inhibits Bruton tyrosine kinase (BTK) by covalently binding to the C481 residue in the BTK kinase domain. BTK is a pivotal protein for B cell receptor signaling and tissue homing of CLL cells. Preclinical investigations have established the importance of the B cell receptor pathway in the maintenance and survival of normal and malignant B cells, underscoring the importance of targeting this axis for CLL. Clinical trials demonstrated overall and progression-free survival benefit with ibrutinib in multiple CLL subgroups, including patients with relapsed or refractory disease, patients with 17p deletion, elderly patients, and treatment-naïve patients. Consequently, ibrutinib was approved by the US Food and Drug Administration for newly diagnosed and relapsed disease. Ibrutinib has transformed the treatment of CLL; however, several limitations have been identified, including low complete remission rates, development of resistance, and uncommon substantial toxicities. Further, ibrutinib must be used until disease progression, which imposes a financial burden on patients and society. These limitations were the impetus for the development of ibrutinib combinations. Four strategies have been tested in recent years: combinations of ibrutinib with immunotherapy, chemoimmunotherapy, cell therapy, and other targeted therapy. Here, we review the scientific rationale for and clinical outcome of each strategy. Among these strategies, ibrutinib with targeted agent venetoclax results in high complete response rates and, importantly, high rates of undetectable minimal residual disease. Although we concentrate here on ibrutinib, similar combinations are expected or ongoing with acalabrutinib, tirabrutinib, and zanubrutinib, second-generation BTK inhibitors. Future investigations will focus on the feasibility of discontinuing ibrutinib combinations after a defined time; the therapeutic benefit of adding a third agent to ibrutinib-containing combinations; and profiling of resistant clones that develop after combination treatment. A new standard of care for CLL is expected to emerge from these investigations.

Current and future treatment strategies in chronic lymphocytic leukemia

Treatment decisions for patients with chronic lymphocytic leukemia (CLL) are dependent on symptoms and classification into high-, medium-, or low-risk categories. The prognosis for CLL hinges, in part, on the presence or absence of less-favorable genetic aberrations, including del(17p), del(11q), TP53 dysfunction, and IGHV mutations, as these markers are associated with worse treatment response. Promising results from multiple clinical trials show emerging therapies targeting Burton tyrosine kinase, B-cell leukemia/lymphoma 2, and phosphatidylinositol 4,5-bisphosphate 3-kinase catalytic subunit delta result in better outcomes and prolonged progression-free survival for patients both with and without certain high-risk aberrations. Favorable outcomes using these novel oral targeted therapies, either alone or in combination with other treatments such as anti-CD20 antibodies, has led to their use almost entirely supplanting chemoimmunotherapy in the treatment of CLL. In this narrative review, we summarize the current clinical evidence for the use of targeted mono- and combination therapies for CLL, discuss new and next-generation treatment approaches currently in development, and provide insight into areas of unmet need for the treatment of patients with CLL.

When to Use Targeted Therapy for the Treatment of Follicular Lymphoma

PURPOSE OF REVIEW

Follicular lymphoma is a common indolent non-Hodgkin lymphoma with survival improving in the modern era. Despite favorable responses and improving remission duration, FL remains largely incurable with patterns of relapsing and remitting disease with many patients requiring multiple lines of therapy. As our understanding of the malignant B-cell biology evolves, more targeted therapies have emerged for the treatment of follicular lymphoma.

RECENT FINDINGS

Targeted therapies entering the treatment landscape of follicular lymphoma include lenalidomide in combination with rituximab based on the randomized AUGMENT. Tazemetostat, an EZH2 inhibitor, joins the list of targeted therapies approved based on single-arm phase 2 studies in the relapsed setting. There are three PI3K inhibitors currently approved and more under development. Herein, I will review the available evidence that supports the use of targeted therapy across the disease course of follicular lymphoma.

Umbralisib: First Approval

Umbralisib (UKONIQ™) is an oral, first-in-class dual phosphatidylinositol 3-kinase delta (PI3Kδ) and casein kinase 1 epsilon (CK1ε) inhibitor being developed by TG Therapeutics for the treatment of various haematological malignancies. In February 2021, umbralisib received its first approval in the USA for the treatment of adults with relapsed or refractory marginal zone lymphoma (MZL) who have received ≥ 1 prior anti-CD20-based regimen, and relapsed or refractory follicular lymphoma (FL) who have received ≥ 3 prior lines of systemic therapy. Clinical studies in various haematological malignancies, including chronic lymphocytic leukaemia and non-Hodgkin's lymphoma, are underway in multiple countries. This article summarizes the milestones in the development of umbralisib leading to this first approval.

PI3K Inhibitors in Cancer: Clinical Implications and Adverse Effects

The phospatidylinositol-3 kinase (PI3K) pathway is a crucial intracellular signaling pathway which is mutated or amplified in a wide variety of cancers including breast, gastric, ovarian, colorectal, prostate, glioblastoma and endometrial cancers. PI3K signaling plays an important role in cancer cell survival, angiogenesis and metastasis, making it a promising therapeutic target. There are several ongoing and completed clinical trials involving PI3K inhibitors (pan, isoform-specific and dual PI3K/mTOR) with the goal to find efficient PI3K inhibitors that could overcome resistance to current therapies. This review focuses on the current landscape of various PI3K inhibitors either as monotherapy or in combination therapies and the treatment outcomes involved in various phases of clinical trials in different cancer types. There is a discussion of the drug-related toxicities, challenges associated with these PI3K inhibitors and the adverse events leading to treatment failure. In addition, novel PI3K drugs that have potential to be translated in the clinic are highlighted.

Novel Agents in Chronic Lymphocytic Leukemia: New Combination Therapies and Strategies to Overcome Resistance

Simple Summary

Nowadays, many patients with chronic lymphocytic leukemia (CLL) are treated with so-called novel agents, including BTK inhibitors, Bcl-2 inhibitors and PI3K inhibitors. As CLL is a chronic disease, most patients will relapse on or after treatment with these drugs and various mechanisms behind this resistance to novel agents have been described. In this review, we present the current evidence on resistance to novel agents, discuss approaches to prevent its development and provide guidance on the treatment of patients who have already acquired resistance.

Abstract

The approval of Bruton’s tyrosine kinase (BTK) inhibitors such as ibrutinib and acalabrutinib and the Bcl-2 inhibitor venetoclax have revolutionized the treatment of chronic lymphocytic leukemia (CLL). While these novel agents alone or in combination induce long lasting and deep remissions in most patients with CLL, their use may be associated with the development of clinical resistance. In this review, we elucidate the genetic basis of acquired resistance to BTK and Bcl-2 inhibition and present evidence on resistance mechanisms that are not linked to single genomic alterations affecting these target proteins. Strategies to prevent resistance to novel agents are discussed in this review with a special focus on new combination therapies.

Umbralisib, a Dual PI3Kδ/CK1ε Inhibitor in Patients With Relapsed or Refractory Indolent Lymphoma

PURPOSE

Phosphatidylinositol-3-kinase (PI3K) inhibitors have shown activity in relapsed or refractory (R/R) indolent non-Hodgkin lymphoma (iNHL). PI3K inhibitors have been hampered by poor long-term tolerability and toxicity, which interfere with continuous use. Umbralisib, a dual inhibitor of PI3Kδ/casein kinase-1ε, exhibits improved selectivity for PI3Kδ compared with other PI3K inhibitors. This phase IIb trial was designed to evaluate the efficacy and safety of umbralisib in patients with R/R iNHL.

PATIENTS AND METHODS

In this multicohort, open-label, phase IIb study, 208 patients with R/R marginal zone, follicular, or small lymphocytic lymphoma (MZL, FL, or SLL) unresponsive to prior treatments (≥ 1 MZL; ≥ 2 FL/SLL), including ≥ 1 anti-CD20-based therapy, were administered umbralisib 800 mg orally once daily until disease progression, unacceptable toxicity, or study withdrawal. Primary end point is overall response rate; secondary end points include time to response, duration of response, progression-free survival, and safety.

RESULTS

The median follow-up is 27.7 months (efficacy) and 21.4 months (safety). The overall response rate was 47.1%, and tumor reduction occurred in 86.4% of patients. The median time to response was 2.7-4.6 months. The median duration of response was not reached for MZL, 11.1 months for FL, and 18.3 months for SLL. Median progression-free survival was not reached for MZL, 10.6 months for FL, and 20.9 months for SLL. At least one grade ≥ 3 treatment-emergent adverse event (TEAE) was reported in 53.4% of patients. TEAEs led to umbralisib discontinuation in 32 patients (15.4%). A total of 31 patients (14.9%) discontinued because of a treatment-related adverse event. Grade ≥ 3 TEAEs reported in ≥ 10% of patients: neutropenia (11.5%) and diarrhea (10.1%). Increased ALT/AST (grade ≥ 3) occurred in 6.7%/7.2% of patients.

CONCLUSION

Umbralisib achieved meaningful clinical activity in heavily pretreated patients with iNHL. The safety profile was manageable, with a relatively low incidence of immune-mediated toxicities and adverse event-related discontinuations.

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.

Discovery of a Potent and Selective PI3Kδ Inhibitor (S)-2,4-Diamino-6-((1-(7-fluoro-1-(4-fluorophenyl)-4-oxo-3-phenyl-4H-quinolizin-2-yl)ethyl)amino)pyrimidine-5-carbonitrile with Improved Pharmacokinetic Profile and Superior Efficacy in Hematological Cancer Models

PI3Kδ inhibitors have been approved for B-cell malignancies like CLL, small lymphocytic lymphoma, and so forth. However, currently available PI3Kδ inhibitors are nonoptimal, showing weakness against at least one of the several important properties: potency, isoform selectivity, and/or pharmacokinetic profile. To come up with a PI3Kδ inhibitor that overcomes all these deficiencies, a pharmacophoric expansion strategy was employed. Herein, we describe a systematic transformation of a "three-blade propeller" shaped lead, 2,3-disubstituted quinolizinone 11, through a 1,2-disubstituted quinolizinone 20 to a novel "four-blade propeller" shaped 1,2,3-trisubstituted quinolizinone 34. Compound 34 has excellent potency, isoform selectivity, metabolic stability across species, and exhibited a favorable pharmacokinetic profile. Compound 34 also demonstrated a differentiated efficacy profile in human germinal center B and activated B cell-DLBCL cell lines and xenograft models. Compound 34 qualifies for further evaluation as a candidate for monotherapy or in combination with other targeted agents in DLBCLs and other forms of iNHL.

Managing toxicities of phosphatidylinositol-3-kinase (PI3K) inhibitors

Despite the proven effective approach to targeting the phosphatidylinositol-3-kinase (PI3K) pathway in B-cell malignancies, the approved PI3K inhibitors idelalisib and duvelisib have been less commonly selected for patients with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), given the availability of other more tolerable agents. However, patients with CLL/SLL can experience a disease course that is multiply relapsed, refractory, or intolerant to treatment, and PI3K inhibitors can achieve meaningful responses. This article reviews the common early- and late-onset (considered immune-mediated) toxicities with PI3K inhibitors, including infections, hepatotoxicity, diarrhea and/or colitis, and pneumonitis. Data on pretreatment considerations, toxicity management, and drug rechallenge are presented. In addition, next-generation PI3K inhibitors and novel treatment approaches with PI3K inhibitors, including combinations, time-limited treatments, and intermittent dosing, are highlighted.

Standard treatment approaches for relapsed/refractory chronic lymphocytic leukemia after frontline chemoimmunotherapy

Despite the effectiveness of chemoimmunotherapy (CIT), in most cases the clinical course of chronic lymphocytic leukemia (CLL) is characterized by consecutive episodes of disease progression and need for therapy. Treatment possibilities for patients with CLL in whom CIT fails whose disease progresses after initial CIT include pathway inhibitors (PIs) and, for selected patients, cellular therapy (ie, allogeneic stem cell transplant, chimeric antigen receptor T cells). PIs (ie, Bruton tyrosine kinase inhibitors, phosphatidylinositol 3-kinase inhibitors, and BCL2 inhibitors) are revolutionizing the treatment of CLL. PIs have proved to be more effective than CIT, both as upfront therapy and for relapsed/refractory disease, largely because they may overcome the negative impact of adverse biomarkers (eg, TP53 aberrations, unmutated IGHV) on outcomes and because of their acceptable toxicity. In this article, the management of patients with relapsed/refractory CLL is discussed, with a particular emphasis on the role of PIs.

Targeting Casein Kinase 1 (CK1) in Hematological Cancers

The casein kinase 1 enzymes (CK1) form a family of serine/threonine kinases with seven CK1 isoforms identified in humans. The most important substrates of CK1 kinases are proteins that act in the regulatory nodes essential for tumorigenesis of hematological malignancies. Among those, the most important are the functions of CK1s in the regulation of Wnt pathways, cell proliferation, apoptosis and autophagy. In this review we summarize the recent developments in the understanding of biology and therapeutic potential of the inhibition of CK1 isoforms in the pathogenesis of chronic lymphocytic leukemia (CLL), other non-Hodgkin lymphomas (NHL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and multiple myeloma (MM). CK1δ/ε inhibitors block CLL development in preclinical models via inhibition of WNT-5A/ROR1-driven non-canonical Wnt pathway. While no selective CK1 inhibitors have reached clinical stage to date, one dual PI3Kδ and CK1ε inhibitor, umbralisib, is currently in clinical trials for CLL and NHL patients. In MDS, AML and MM, inhibition of CK1α, acting via activation of p53 pathway, showed promising preclinical activities and the first CK1α inhibitor has now entered the clinical trials.

Immune Dysfunctions and Immune-Based Therapeutic Interventions in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy characterized by a wide range of tumor-induced alterations, which affect both the innate and adaptive arms of the immune response, and accumulate during disease progression. In recent years, the development of targeted therapies, such as the B-cell receptor signaling inhibitors and the Bcl-2 protein inhibitor venetoclax, has dramatically changed the treatment landscape of CLL. Despite their remarkable anti-tumor activity, targeted agents have some limitations, which include the development of drug resistance mechanisms and the inferior efficacy observed in high-risk patients. Therefore, additional treatments are necessary to obtain deeper responses and overcome drug resistance. Allogeneic hematopoietic stem cell transplantation (HSCT), which exploits immune-mediated graft-versus-leukemia effect to eradicate tumor cells, currently represents the only potentially curative therapeutic option for CLL patients. However, due to its potential toxicities, HSCT can be offered only to a restricted number of younger and fit patients. The growing understanding of the complex interplay between tumor cells and the immune system, which is responsible for immune escape mechanisms and tumor progression, has paved the way for the development of novel immune-based strategies. Despite promising preclinical observations, results from pilot clinical studies exploring the safety and efficacy of novel immune-based therapies have been sometimes suboptimal in terms of long-term tumor control. Therefore, further advances to improve their efficacy are needed. In this context, possible approaches include an earlier timing of immunotherapy within the treatment sequencing, as well as the possibility to improve the efficacy of immunotherapeutic agents by administering them in combination with other anti-tumor drugs. In this review, we will provide a comprehensive overview of main immune defects affecting patients with CLL, also describing the complex networks leading to immune evasion and tumor progression. From the therapeutic standpoint, we will go through the evolution of immune-based therapeutic approaches over time, including i) agents with broad immunomodulatory effects, such as immunomodulatory drugs, ii) currently approved and next-generation monoclonal antibodies, and iii) immunotherapeutic strategies aiming at activating or administering immune effector cells specifically targeting leukemic cells (e.g. bi-or tri-specific antibodies, tumor vaccines, chimeric antigen receptor T cells, and checkpoint inhibitors).

The role of PI3K inhibitors in the treatment of malignant lymphomas

Deregulated phosphatidylinositide 3-kinase (PI3K) signaling plays a crucial role in the biology of different lymphoma entities leading to the proliferation and survival of the malignant cells. Due to novel treatment options and modern supportive care, the outcome of patients with lymphomas has significantly improved in the past years. However, patients with relapsed or refractory disease still have a limited prognosis. PI3K inhibitors represent a modern and effective therapeutic option for patients with different types of lymphoma. However, the efficacy of PI3K inhibitors varies among lymphoma entities. Additionally, severe toxicity including infectious and autoimmune complications leading to therapy-related deaths has been observed. Next-generation PI3K inhibitors show promising efficacy and manageable toxicity profiles. Future research might identify effective combinatorial therapy approaches for PI3K inhibitors to further improve response rates. This review discusses the most recent developments in the field of PI3K inhibition in different subtypes of lymphoma.

Toxicity patterns of novel PI3K combinations in patients with non-Hodgkin lymphoma

Phosphoinositide-3-kinase (PI3K) inhibitors have efficacy in lymphoid malignancies; however, inflammatory and infectious toxicities can compromise the treatment course. An improved understanding of these toxicities will guide clinical use and further development. We evaluated the occurrence of treatment-related adverse events (AEs) in a retrospective review of 79 patients treated in standard fashion with PI3K inhibitor monotherapy or with anti-CD20 monoclonal antibodies or as part of a novel combination regimen. Patients treated with a novel combination were at a higher risk of developing a severe AE compared to those treated with standard therapy (HR 1.89, 95% CI 1.02, 3.49; p = .04). Additionally, previously untreated patients were at higher risk of developing a severe AE compared to previously treated patients (HR 3.19, 95% CI 1.48, 6.84; p = .003). These results caution against the use of untested PI3K inhibitor combinations in routine practice and suggest that early phase clinical trials should utilize conservative treatment schemas.

Ibrutinib in B-cell lymphoma: single fighter might be enough?

Background

In recent years, the B cell receptor (BCR) signaling pathway has become a "hot point" because it plays a critical role in B-cell proliferation and function. Bruton's tyrosine kinase (BTK) is overexpressed in many subtypes of B-cell lymphoma as a downstream kinase in the BCR signaling pathway. Ibrutinib, the first generation of BTK inhibitor, has shown excellent antitumor activity in both indolent and aggressive B-cell lymphoma.

Main body

Ibrutinib monotherapy has been confirmed to be effective with a high response rate (RR) and well-tolerated in many B-cell lymphoma subgroups. To achieve much deeper and faster remission, combination strategies contained ibrutinib were conducted to evaluate their synergistic anti-tumor effect.

Conclusions

For patients with indolent B-cell lymphoma, most of them respond well with ibrutinib monotherapy. Combination strategies contained ibrutinib might be a better choice to achieve deeper and faster remission in the treatment of aggressive subtypes of B-cell lymphoma. Further investigations on the long-term efficacy and safety of the ibrutinib will provide novel strategies for individualized treatment of B-cell lymphoma.

Lights and Shade of Next-Generation Pi3k Inhibitors in Chronic Lymphocytic Leukemia

The treatment (i.e. therapy and management) of chronic lymphocytic leukemia (i.e. the disease) has been improved thanks to the introduction (i.e. approval) of kinase inhibitors during the last years. PI3K is one of the most important kinases at the crossroad to the B-cell receptor and cytokine receptor which play a key role in CLL cell survival, proliferation and migration. Idelalisib is the first in class PI3Kδ inhibitor approved for the treatment of relapsed/refractory CLL in combination with rituximab. Idelalisib activity in heavily treated patients is balanced by recurrent adverse events which limit its long-term use. These limitations prompt the investigation on novel PI3K inhibitors, also targeting different protein isoforms, and alternative schedule strategies. In this regard, duvelisib is the only PI3K γ and δ inhibitor approved as single agent for relapsed CLL. In this review, we will address novel insights on PI3K structure, isoforms, regulating signaling and the most updated data of next-generation PI3K inhibitors in CLL.

Can Next-Generation PI3K Inhibitors Unlock the Full Potential of the Class in Patients With B-Cell Lymphoma?

Although outcomes after first-line therapy for patients with indolent or aggressive non-Hodgkin lymphoma (NHL) are continually improving, relapse is still common. Current treatment options for patients with relapsed or refractory disease have limited efficacy, and various targeted therapies are under investigation to help improve outcomes in this patient population. The phosphatidylinositol 3-kinase (PI3K) pathway was identified as being involved in hematologic malignancies, leading to significant research for potential therapeutic agents. This has led to 3 PI3K inhibitors (idelalisib, copanlisib, and duvelisib) being approved for the treatment of patients with relapsed or refractory follicular lymphoma who have received at least 2 prior systemic therapies, with reported response rates of 40% to 59%. With potential class-specific and PI3K isoform-related toxicities that may limit clinical utility, the safety of the approved PI3K inhibitors has been carefully evaluated to weigh the risk/benefit ratio of therapy. Currently, there are no approved PI3K inhibitors for patients with aggressive NHL. A number of newer PI3K inhibitors are in clinical development for the treatment of relapsed or refractory NHL, aiming to improve treatment benefit for patients. We discuss a number of attributes that are important to increase the therapeutic potential of newer PI3K inhibitors. More promising results may come from combination trials with these newer PI3K inhibitors, developed to limit toxicities (including long-term adverse events), and other antitumor agents.

Phosphatidylinositol 3 Kinase δ Inhibitors: Present and Future

Inhibitors of PI3Kδ hold great potential for the therapy of chronic lymphocytic leukemia and B-cell malignancies. After initially exciting efficacy results with idelalisib, the first-in-class inhibitor, the emergence of unexpected and unpredictable autoimmune toxicities, worse in less heavily treated and younger patients, has decreased the use of the currently available inhibitors. Newer drugs in development are attempting to reduce toxicity with novel schedules and/or combinations. This article reviews the clinical data on efficacy and toxicity across the class and discusses ongoing efforts to understand and mitigate the likely on-target autoimmune toxicity.

Research advances on selective phosphatidylinositol 3 kinase δ (PI3Kδ) inhibitors

PI3Kδ in B cells mediates antigen receptor signaling and promote neutrophil chemotaxis. The activation of PI3Kδ can cause mast cell maturation and degranulation, myeloid cell dysfunction, and cytokine release. As a key signal molecule, PI3Kδ interacts with the lipid binding domain of a variety of cellular proteins as a secondary messenger, ultimately affecting a series of significant cellular pathways in disease pathology. Therefore, many research organizations and pharmaceutical companies have studied it to develop effectively selective PI3Kδ inhibitors as therapeutics. This review summarizes research advances in varying chemical classes of selective PI3Kδ inhibitors and the structure-activity relationship, and it mainly focuses on the propeller- versus flat-type class of inhibitors.

Exploring a Future for PI3K Inhibitors in Chronic Lymphocytic Leukemia

PURPOSE OF REVIEW

Treatment for chronic lymphocytic leukemia has changed substantially in the past decade with an increasing shift towards use of targeted therapies, in particular agents targeting the B cell receptor pathway. Inhibition of PI3K, downstream of the B cell receptor pathway, represents an active therapeutic strategy in CLL. Here, we explore the relevance of PI3K inhibition in CLL, examine efficacy and toxicity of approved PI3K inhibitors in CLL, examine barriers to use of PI3K inhibitors, and explore strategies to optimize use of PI3K inhibitors in CLL.

RECENT FINDINGS

Current generation PI3K inhibitors are active agents in CLL but their use may be limited by immune-mediated toxicities. Clinical trials of next generation PI3K inhibitors are ongoing and early data suggests these agents are highly active with potentially differentiated toxicity profiles. Furthermore, alternative dosing schedules may reduce toxicities of these agents. Inhibition of PI3K remains an important strategy in management of CLL and novel approaches to limit toxicities of PI3K inhibitors represent an important area of clinical research in CLL.

Investigational treatments for chronic lymphocytic leukemia: a focus on phase 1 and 2 clinical trials

Introduction: During recent years, the introduction of novel drugs, particularly small molecule inhibitors, has led to remarkable progress in both previously untreated and relapsed/refractory (RR) patients in chronic lymphocytic leukemia (CLL). However, further research is necessary to find an optimal cure that responds to the individual needs of the patient. Areas covered: This review discusses new agents in phase 1 and 2 clinical trials currently underway in CLL patients. A literature review of the MEDLINE database for articles in English concerning novel drugs, clinical trials, phase 1, phase 2 and CLL was conducted via PubMed. Publications from 2000 through January 2020 were scrutinized. Conference proceedings from the previous five years of the American Society of Hematology, European Hematology Association and American Society of Clinical Oncology were searched manually. Additional relevant publications were obtained by reviewing the references from the chosen articles. The search also included clinical trials registered in clinicaltrials.gov. Expert opinion: The use of BTK and PI3Kδ inhibitors and BCL-2 antagonist have changed the treatment strategy of CLL. Several clinical trials with novel, unapproved agents are currently ongoing. Their findings should define the role of these novel drugs in the treatment of patients with previously untreated and RR CLL.

Promises and pitfalls of targeted agents in chronic lymphocytic leukemia

Targeted agents have significantly improved outcomes for patients with chronic lymphocytic leukemia, particularly high-risk subgroups for whom chemoimmunotherapy previously offered limited efficacy. Two classes of agent in particular, the Bruton tyrosine kinase inhibitors (e.g., ibrutinib) and the B-cell lymphoma 2 inhibitor, venetoclax, induce high response rates and durable remissions in the relapsed/refractory and frontline settings. However, maturing clinical data have revealed promises and pitfalls for both agents. These drugs induce remissions and disease control in the majority of patients, often in situations where modest efficacy would be expected with traditional chemoimmunotherapy approaches. Unfortunately, in the relapsed and refractory setting, both agents appear to be associated with an inevitable risk of disease relapse and progression. Emerging patterns of resistance are being described for both agents but a common theme appears to be multiple sub-clonal drivers of disease progression. Understanding these mechanisms and developing effective and safe methods to circumvent the emergence of resistance will determine the longer-term utility of these agents to improve patients' quality and length of life. Rational drug combinations, optimised scheduling and sequencing of therapy will likely hold the key to achieving these important goals.

Drug Review: Ibrutinib

Ibrutinib is an irreversible BTK inhibitor, characterized by high selectivity and potency. It has revolutionized the therapy of B-cell lymphomas, especially chronic lymphocytic leukemia (CLL) and mantle cell lymphoma. Importantly, it has expanded the armamentarium for those patients who are refractory to conventional chemoimmunotherapy. This small-molecule inhibitor has shown efficacy in this difficult-to-treat subset – those with del(17p)/TP53-mutated CLL. Its immunomodulatory properties make it an excellent choice for combining with other immunotherapeutic agents such as venetoclax. The drug is not without drawbacks. The need for indefinite therapy and the presence of adverse effects such as infection, bleeding, hypertension, and arrhythmia temper our enthusiasm for this versatile drug. But overall, ibrutinib's favorable risk profile and lack of myelosuppression make it an ideal therapy for the elderly and those with multiple comorbidities.

PI3K Inhibitors and Their Role as Novel Agents for Targeted Therapy in Lymphoma

OPINION STATEMENT

Phosphatidylinositol 3-kinase (PI3K) inhibitors represent a novel class of agents targeting the key cellular regulatory PI3K/AKT/mTOR pathway involved in crucial functions such as cellular proliferation, cell cycle regulation, protein synthesis, and cell motility. This review starts with an overview of the PI3K pathway and the rationale for its targeting in lymphoma and potential on-target side effects of PI3K inhibition. With three agents now FDA approved for the treatment of relapsed and refractory (R/R) indolent non-Hodgkin lymphoma (iNHL), idelalisib, copanlisib, and duvelisib, we aim to review the pivotal trials leading to their approval as well as their clinical applications according to lymphoma subtypes. Important treatment-related adverse events are also reviewed and a perspective on the clinical role of these agents is provided, as well as some practical guidance on how to prevent, monitor, and manage potential adverse events in the clinic. PI3K inhibitors have an established role in the management of R/R iNHL, but their use and development are hampered by adverse events, particularly when used in combination with other anti-lymphoma therapies. Finally, this review highlights areas in need of more research in order to optimally use these agents in the care of patients with lymphoma.

The evolving treatment landscape of chronic lymphocytic leukemia

PURPOSE OF REVIEW

This review provides guidance in the rapidly changing scenario of chronic lymphocytic leukemia (CLL) treatment. New studies as well as updates of other seminal ones have been recently presented and are likely to change the management of patients with CLL in everyday clinical practice.

RECENT FINDINGS

Kinase inhibitors (e.g. ibrutinib and idelalisib) have transformed the treatment paradigm in CLL in both front-line and relapsed/refractory patients. Longer follow-up data are now available supporting the safety of ibrutinib and the continuous administration required per current label. Novel studies show the superiority of the drug alone or in combination with monoclonal antibodies compared with standard chemoimmunotherapy. The combination of venetoclax and obinutuzumab (treatment-naïve, only in United States) or rituximab (relapsed/refractory) has granted approval from the regulatory authorities in United States and Europe, based on phase 3 randomized studies. These novel chemo-free combinations allow for fixed-duration treatment and undetectable minimal residual disease. Novel targeted strategies including second and third generation BTK and PI3K inhibitors are currently under investigation and promise to further improve the CLL treatment armamentarium. The chimeric-antigen receptor (CAR) T cells are coming to the stage with promising efficacy and new challenges.

SUMMARY

A bright chemo-free era for CLL patients is just around the corner. A deep knowledge of currently available evidences is key to tailor treatment choice and optimize long-term tolerability and disease control. Fixed-duration combinations are investigated to allow treatment holidays and avoid the emergence of resistant clones under the selective pressure of continuous treatment.

Approved and emerging PI3K inhibitors for the treatment of chronic lymphocytic leukemia and non-Hodgkin lymphoma

INTRODUCTION

PI3K inhibition with idelalisib (at that time CAL-101) was at the forefront of the development of molecularly targeted therapies in Chronic Lymphocytic Leukemia (CLL)/Small Lymphocytic Leukemia (SLL) and follicular lymphoma. However, after initial approval, subsequent trials identified specific immune-mediated and infectious toxicity that led to a reduced use and stopped the further development of this agent. PI3K inhibition as a treatment paradigm fell out of favor compared to other developments such as BTK or BCL2 inhibitors.

AREAS COVERED

This review provides an overview of the experience with approved PI3Ki, including long-term experience, and highlights the current PI3Ki developments in CLL, B-cell and T-Cell Non-Hodgkin's Lymphoma.

EXPERT OPINION

With careful monitoring and prophylaxis usage of the first-generation PI3K inhibitor, idelalisib, in the approved indications, it is safe and remains an option in higher line therapy after the failure of other novel agents and/or chemoimmunotherapy. New developments with next-generation PI3K inhibitors of improved tolerability and sustained efficacy reignited the treatment principle and already led to newly approved therapeutic options for patients. Certainly, the authors here believe that PI3K inhibitors as a monotherapy and in combination with other agents is currently a rapidly evolving field in cancer treatment.

Phase Ib Study of Tirabrutinib in Combination with Idelalisib or Entospletinib in Previously Treated Chronic Lymphocytic Leukemia

PURPOSE

Bruton tyrosine kinase (BTK) inhibition alone leads to incomplete responses in chronic lymphocytic leukemia (CLL). Combination therapy may reduce activation of escape pathways and deepen responses. This open-label, phase Ib, sequential dose-escalation and dose-expansion study evaluated the safety, tolerability, pharmacokinetics, and preliminary efficacy of the selective BTK inhibitor tirabrutinib alone, in combination with the PI3K delta (PI3Kδ) inhibitor idelalisib, or with the spleen tyrosine kinase (SYK) inhibitor entospletinib in patients with relapsed/refractory CLL.

PATIENTS AND METHODS

Patients received either tirabrutinib monotherapy (80 mg every day) or tirabrutinib 20-150 mg every day in combination with either idelalisib (50 mg twice a day or 100 mg every day) or entospletinib (200 mg or 400 mg every day).

RESULTS

Fifty-three patients were included. Systemic tirabrutinib exposure was comparable between monotherapy and combination therapy. No MTD was identified. Across all treatment groups, the most common adverse event was diarrhea (43%, 1 patient grade ≥3); discontinuation due to adverse events was uncommon (13%). Objective response rates were 83%, 93%, and 100%, and complete responses were 7%, 7%, and 10% in patients receiving tirabrutinib, tirabrutinib/idelalisib, and tirabrutinib/entospletinib, respectively. As of February 21, 2019, 46 of 53 patients continue to receive treatment on study.

CONCLUSIONS

Tirabrutinib in combination with idelalisib or entospletinib was well tolerated in patients with CLL, establishing an acceptable safety profile for concurrent selective inhibition of BTK with either PI3Kδ or SYK. This small study did not establish a superior efficacy of the combinations over tirabrutinib alone. This trial is registered at www.clinicaltrials.gov (NCT02457598).

Advances in targeted therapy for malignant lymphoma

The incidence of lymphoma has gradually increased over previous decades, and it ranks among the ten most prevalent cancers worldwide. With the development of targeted therapeutic strategies, though a subset of lymphoma patients has become curable, the treatment of refractory and relapsed diseases remains challenging. Many efforts have been made to explore new targets and to develop corresponding therapies. In addition to novel antibodies targeting surface antigens and small molecular inhibitors targeting oncogenic signaling pathways and tumor suppressors, immune checkpoint inhibitors and chimeric antigen receptor T-cells have been rapidly developed to target the tumor microenvironment. Although these targeted agents have shown great success in treating lymphoma patients, adverse events should be noted. The selection of the most suitable candidates, optimal dosage, and effective combinations warrant further investigation. In this review, we systematically outlined the advances in targeted therapy for malignant lymphoma, providing a clinical rationale for mechanism-based lymphoma treatment in the era of precision medicine.

Ublituximab and umbralisib in relapsed/refractory B-cell non-Hodgkin lymphoma and chronic lymphocytic leukemia

Targeting both CD20 and phosphatidylinositol 3-kinase (PI3K), a protein that is critically involved in B-cell maturation, could be an efficacious strategy for treating B-cell malignancies. The safety of the next-generation compounds umbralisib, a PI3K-δ inhibitor, plus ublituximab, an anti-CD20 monoclonal antibody (combination referred to as U2), was evaluated in patients with chronic lymphocytic lymphoma (CLL) or non-Hodgkin lymphoma (NHL) in this phase 1/1b study. Phase 1 dose escalation was performed with a 3 + 3 design to establish the maximum tolerated dose. In this portion, ublituximab was given intravenously (NHL, 900 mg; CLL, 600 or 900 mg) for 12 cycles. Umbralisib was given orally once daily at 800 or 1200 mg (initial formulation) or 400 to 1200 mg (micronized formulation) in the phase 1 dose escalation portion, and at 800 to 1200 mg in the phase 1b portion until progression, toxicity, or study removal. The maximum tolerated dose was not reached in either the CLL or NHL cohort, and only 1 dose-limiting toxicity was observed. U2 had low instances of grade 3 or higher diarrhea (8%), pneumonia (8%), or hepatic toxicity (4%). Treatment discontinuation due to adverse events occurred in 13% of patients, and umbralisib dose reductions occurred in 15% of patients. The overall response rate for all patients was 46% with 17% complete responses. The median duration of response was 20 months (95% confidence interval, 11.3-not reached). U2 was well tolerated, and no new safety signals were observed over single-agent umbralisib. Preliminary efficacy with this combination is promising and warrants further investigation. This study was registered at www.clinicaltrials.gov as #NCT02006485.

Inhibiting Bruton's Tyrosine Kinase in CLL and Other B-Cell Malignancies

Inhibitors of Bruton's tyrosine kinase (BTK), a major kinase in the B-cell receptor (BCR) signaling pathway, mediating B-cell proliferation and apoptosis, have substantially altered the management, clinical course, and outcome of patients with B-cell malignancies. This is especially true for patients with previously limited treatment options due to disease characteristics or coexisting diseases. Ibrutinib was the first orally available, nonselective and irreversible inhibitor of BTK approved for the treatment of patients with various B-cell malignancies. Newer and more selective BTK inhibitors are currently in clinical development, including acalabrutinib, which is currently US FDA approved for previously treated mantle cell lymphoma. Significant efforts are underway to investigate the optimal combinations, timing, and sequencing of BTK inhibitors with other regimens and targeted agents, and to capitalize on the immunomodulatory modes of action of BTK inhibitors to correct tumor-induced immune defects and to achieve long-lasting tumor control. This review describes the major milestones in the clinical development of BTK inhibitors in chronic lymphocytic leukemia and other B-cell malignancies, highlights the most recent long-term follow-up results, and evaluates the role of BTK inhibitors and their combination with other agents in B-cell malignancies and other indications.

Ibrutinib in the treatment of chronic lymphocytic leukemia: 5 years on

A major revolution in the treatment of chronic lymphocytic leukemia (CLL) began with the approval of ibrutinib, a first-in-class oral inhibitor of Bruton tyrosine kinase (BTK), for the treatment of relapsed/refractory (R/R) and/or TP53 mutated patients with CLL. However, 5 years later, some issues relating to this disorder still remain including the fact that with ibrutinib only a relatively small proportion of patients achieve complete remission and that ibrutinib-resistant CLL clones can develop in about 20% of patients. In addition, therapy must still be given continuously, and toxicities leading to drug discontinuation occur in about 30% of patients. In the meantime second-generation BTK inhibitors have already aroused considerable interest and gathered momentum. A possible strategy to overcome some of these obstacles is to combine ibrutinib with other targeted agents especially in high-risk disease, such as previously treated refractory patients or those with TP53 aberrations or complex karyotypes, in whom rapid eradication of disease is most desirable. Therapy with single agent ibrutinib should be part of a sequential approach for patients with low risk disease, especially in older patients (aged >70 years) with a higher burden of comorbidities. Long-term results of ongoing studies combining Ibrutinib with (chemo)-immunotherapy or other targeted agents are eagerly awaited. Future clinical trials are indeed still needed to provide answers to these open questions.