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

Simultaneous Inhibition of PI3Kgamma and PI3Kdelta Deteriorates T-cell Function With Implications for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a common and incurable B-cell malignancy. Recent therapeutic approaches that target the B-cell receptor signaling pathway include inhibition of phosphatidylinositol-3-kinase (PI3K). The PI3K isoform delta is constitutively active in CLL, making it an attractive therapeutic target. However, the expression of PI3K isoforms is not exclusive to leukemic cells, as other immune cells in the tumor microenvironment also rely on PI3K activity. Subsequently, therapeutic inhibition of PI3K causes immune-related adverse events (irAEs). Here, we analyzed the impact of the clinically approved PI3Kδ inhibitors idelalisib and umbralisib, the PI3Kγ inhibitor eganelisib, and the dual-γ and -δ inhibitor duvelisib on the functional capacity of T cells. All investigated inhibitors reduced T-cell activation and proliferation in vitro, which is in line with PI3K being a crucial signaling component of the T-cell receptor signaling. Further, dual inhibition of PI3Kγ and PI3Kδ showed strong additive effects suggesting a role also for PI3Kγ in T cells. Extrapolation of this data to a clinical setting could provide an explanation for the observed irAEs in CLL patients undergoing treatment with PI3K inhibitors. Consequently, this highlights the need for a close monitoring of patients treated with PI3K inhibitors, and particularly duvelisib, due to their potentially increased risk of T-cell deficiencies and associated infections.

Novel targeted treatments in hairy cell leukemia and other hairy cell-like disorders

In the category of mature B-cell neoplasms, splenic B-cell lymphoma and leukemia were clearly identified and include four distinct entities: hairy cell leukemia (HCL), splenic marginal zone lymphoma (SMZL), splenic diffuse red pulp lymphoma (SDRPL) and the new entity named splenic B-cell lymphoma/leukemia with prominent nucleoli (SBLPN). The BRAF^V600E mutation is detected in nearly all HCL cases and offers a possibility of targeted therapy. BRAF inhibitors (BRAFi) represent effective and promising therapeutic approaches in patients with relapsed/refractory HCL. Vemurafenib and dabrafenib were assessed in clinical trials. The BRAF^V600E mutation is missing in SDRPL and SBLPN: mitogen-activated protein kinase 1 (MAP2K1) mutations were found in 40% of SBLPN and VH4-34+ HCL patients, making possible to use MEK inhibitors (MEKi) such as trametinib, cobimetinib or binimetinib in monotherapy or associated with BRAFi. Other mutations may be associated and other signaling pathways involved, including the B-cell receptor signaling (BCR), cell cycle, epigenetic regulation and/or chromatin remodeling. In SDRPL, cyclin D3 (CCND3) mutations were found in 24% of patients, offering the possibility of using cell cycle inhibitors. Even if new emerging drugs, particularly those involved in the epigenetic regulation, have recently been added to the therapeutic armamentarium in HCL and HCL-like disorders, purine nucleoside analogs more and more associated with anti-CD20 monoclonal antibodies, are still used in the frontline setting. Thanks to the recent discoveries in genetics and signaling pathways in HCL and HCL-like disorders, new targeted therapies have been developed, have proven their efficacy and safety in several clinical trials and become essential in real life: BRAFi, MEKi, Bruton Tyrosine Kinase inhibitors (BTKi) and anti-CD22 immunotoxins. New other drugs emerged and have to be assessed in the future. In this article, we will discuss the main mutations identified in HCL and HCL-like disorders and the signaling pathways potentially involved in the pathogenesis of the different hairy cell disorders. We will discuss the results of the recent clinical trials, which will help us to propose an algorithm useful in clinical practice and we will highlight the different new drugs that may be used in the near future.

Efficacy and safety of phosphatidylinositol 3-kinase inhibitors in patients with chronic lymphocytic leukemia: a meta-analysis and systematic review

BACKGROUND

Phosphatidylinositol 3-kinase (PI3K) inhibitors demonstrate promising effects in the treatment of relapsed/refractory chronic lymphocytic leukemia (CLL). Emerging evidence of the therapeutic effects of the PI3K inhibitors in various aspects remains controversial.

RESEARCH DESIGN AND METHODS

This meta-analysis was to evaluate the efficacy and safety of PI3K inhibitors based on a synthesis of the data generated by randomized controlled trials (RCTs) of patients with CLL, by searching PubMed, EMBASE, Cochrane Central Register of Controlled Trials, and ClinicalTrials.gov registry.

RESULTS

Five RCTs with 1593 patients were included. The PI3K inhibitors significantly improved progression-free survival (PFS), the chance of overall response, and partial response than the control arm. Regarding adverse events (AEs), the PI3K inhibitors increased the risk of pyrexia, chills, diarrhea, decreased appetite, vomiting, rash, pneumonia, and upper respiratory tract infection.

CONCLUSIONS

Available evidence showed significant improvements over conventional therapy in PFS of the PI3K inhibitors in patients with CLL, with relatively manageable AEs.

Adverse events in lymphoma patients treated with phosphoinositide 3 kinase Inhibitor in clinical trials: a meta-analysis

BACKGROUND

Malignant lymphomas are one of the most common cancers worldwide and with high biologic heterogeneity, while the phosphoinositide 3 kinase (PI3K)/mTOR pathway is crucial in maintaining cell growth and survival both in physiological and in pathological conditions (i.e., lymphoma). PI3K inhibitors have been proven to be effective in several subtypes of lymphomas. However, the high incidence of treatment-related adverse events as well as the special safety profile in PI3K inhibitors draws great attention. Thus, this meta-analysis was conducted to compare adverse events in PI3K inhibitors to conventional regimens in lymphoma patients.

METHODS

Articles were retrieved from PubMed, Cochrane, and Embase to identify randomized controlled trials and phase III clinical trials that used PI3K inhibitors comparing with non-PI3K inhibitors in lymphoma patients. To achieve the appropriate results, we calculated the risk ratio and 95% confidence intervals.

RESULTS

Four trials with 1399 patients that met our criteria were included. The PI3K inhibitors group significantly increased the risk of all-grade adverse events (AEs) (RR 0.95, 95% CI: 0.92-0.98) and high-grade AEs (RR 0.63, 95% CI: 0.57-0.70), compared with the non-PI3K inhibitors group. Besides, the incidence of neutropenia (RR 0.81, 95% CI: 0.74-0.90), pneumonia (RR 0.62, 95% CI: 0.46-0.83), and diarrhea (RR 0.40, 95% CI: 0.32-0.49) were significantly high in the PI3Ki group, while the incidence of anemia (RR 0.78, 95% CI: 0.50-1.20) and thrombocytopenia (RR 0.85, 95% CI: 0.51-1.42) had no statistic significant.

CONCLUSION

PI3K inhibitors increased the risk of certain AEs in lymphoma patients.

Parsaclisib in Japanese patients with relapsed or refractory B-cell lymphoma (CITADEL-111): A phase Ib study

Parsaclisib, a potent, selective, next-generation PI3Kδ inhibitor, has shown clinical benefit in patients with relapsed or refractory B-cell lymphoma. We undertook a phase Ib study (CITADEL-111) evaluating safety, pharmacokinetics, and efficacy of parsaclisib in Japanese patients with relapsed or refractory B-cell malignancies. Patients received oral parsaclisib daily for 8 weeks then once weekly (10-mg dose, n = 3; 20-mg dose, n = 14). Pharmacokinetic samples were collected on days 1, 8, and 15, and efficacy was monitored according to Lugano criteria. At data cut-off (August 14, 2020), 6 patients (35.3%) remained on study treatment and 11 (64.7%) discontinued due to progressive disease (9 [52.9%]) or adverse events (2 [11.8%]). Median duration of treatment was 8.3 (range, 0.3-24.4) months. The most commonly reported nonhematologic adverse events were constipation (6 [35.3%]), nausea, and pyrexia (each 4 [23.5%]). Five patients (29.4%) experienced treatment-emergent new or worsening decreased neutrophils to grade 3 or 4. No treatment-emergent worsening in aminotransferase elevations to grade 3 or 4 were observed. Ten patients (58.8%) required dose interruption and 5 (29.4%) dose reduction. Body weight-normalized parsaclisib exposure was comparable between Japanese and Western patients. Objective response rate was 100% in follicular lymphoma (9 of 9 patients, including complete response in 2 patients [22.2%]) and marginal zone lymphoma (2 of 2 patients), and 16.7% in diffuse large B-cell lymphoma (1 of 6 patients). Results observed in Japanese patients with relapsed or refractory follicular or marginal zone lymphoma support further clinical development of parsaclisib in these patient populations.

Updates in hairy cell leukemia (HCL) and variant-type HCL (HCL-V): rationale for targeted treatments with a focus on ibrutinib

Hairy cell leukemia (HCL) and HCL-like disorders such as hairy cell leukemia variant (HCL-V) and splenic diffuse red pulp lymphoma (SDRPL) are rare indolent B-cell malignancies. Purine analogs (PNAs), alone or in association with rituximab (R), are the standard of care for HCL in the first-line setting. However, PNAs are toxic and patients may become resistant to these drugs. Therefore, new therapeutic strategies are needed. Several recent in vitro studies highlighted the importance of the interactions between HCL cells and their microenvironment, in particular with bone marrow stromal cells, endothelial cells, and the extracellular matrix. In these interactions, chemokine receptors and adhesion molecules play a major role. Moreover, the importance of signaling pathways, like BRAF, BCR, and CXCR4 has been underlined. Bruton's tyrosine kinase (BTK) is a fundamental signal transmitter of BCR and CXCR4 in HCL. Preclinical and recent clinical data showed an efficacy of ibrutinib, a BTK inhibitor (BTKi), in HCL and HCL-V. These promising results joined those of other emerging drugs like BRAF or MEK inhibitors and anti-CD22 immunotoxins.

Plain Language Summary

Bruton's tyrosine kinase (BTK) inhibitors (BTKi) in hairy cell leukemia (HCL) and variant-type HCL The treatment of hairy cell leukemia (HCL) has changed significantly in recent years. In the first-line settings, treatment with purine analogs (PNAs) with or without anti-CD20 monoclonal antibodies remains the gold standard in 2022. In relapsed/refractory HCL, other drugs are needed: BRAF inhibitors: vemurafenib monotherapy with or without rituximab or dabrafenib in combination with trametinib, an MEK inhibitor (MEKi), as well as the anti-CD22 antibody drug conjugate moxetumomab pasudotox.There are arguments for the use of Bruton's tyrosine kinase inhibitors (BTKi). Ibrutinib was recently tested in a multisite phase 2 study in 37 patients with either HCL (28 patients: 76%) or HCL-V (nine patients: 24%) including two who were previously untreated. Patients received single-agent ibrutinib at 420 mg daily (24 patients) or 840 mg daily (13 patients) until disease progression or unacceptable toxicity. The overall response rate (ORR) at 32 weeks was 24%, increasing to 36% at 48 weeks and reaching 54% at any time since starting ibrutinib. Seven patients achieved a complete response (CR) as the best response at any time on study, while 13 patients had a partial response (PR) and 10 patients had stable disease (SD). Interestingly, the response rate was not statistically different between HCL and HCL-V patients, suggesting that ibrutinib could be an option in both entities. The estimated 36-month progression-free survival (PFS) was 73% and the estimated 36-month overall survival (OS) was 85%, with no differences between HCL and HCL-V. The frequency of cardiovascular grade 1-2 adverse events (AEs) was 16% for atrial fibrillation; 3% for atrial flutter; 32% for hypertension; and 0%, 3%, and 11%, respectively, for grade ⩾ 3 AEs. Unlike in chronic lymphocytic leukemia (CLL), where the mechanism of action of ibrutinib is well known, the mechanism of action of ibrutinib in HCL appears to be unclear. No mutations were identified in patients with progressive disease, suggesting that the mechanisms of resistance could be different between HCL and CLL. The BTKi that are not yet approved are challenged by the new other targeted treatments.

Real-world management of targeted therapies in chronic lymphocytic leukemia

The advent of novel targeted therapies, including B-cell receptor (BCR) pathway and B-cell lymphoma 2 (BCL2) inhibitors, has substantially changed the treatment paradigm for chronic lymphocytic leukemia (CLL). Although targeted therapies have improved outcomes compared to traditional chemoimmunotherapy in the front-line and relapsed or refractory settings, they are associated with resistance mutations and suboptimal outcomes in certain high-risk patients. Additionally, targeted therapies are associated with drug interactions and unique adverse effect profiles which can be challenging for patients and clinicians to manage. Ongoing studies continue to address questions regarding optimal sequencing of therapies, the role of treatment combinations, and the efficacy of next-generation novel agents. This review provides a comprehensive overview regarding the clinical management of targeted therapies for CLL and applies current literature to clinical practice.

Preclinical Evaluation of a Novel Dual Targeting PI3Kδ/BRD4 Inhibitor, SF2535, in B-Cell Acute Lymphoblastic Leukemia

The PI3K/Akt pathway—and in particular PI3Kδ—is known for its role in drug resistant B-cell acute lymphoblastic leukemia (B-ALL) and it is often upregulated in refractory or relapsed B-ALL. Myc proteins are transcription factors responsible for transcribing pro-proliferative genes and c-Myc is often overexpressed in cancers. The chromatin regulator BRD4 is required for expression of c-Myc in hematologic malignancies including B-ALL. Previously, combination of BRD4 and PI3K inhibition with SF2523 was shown to successfully decrease Myc expression. However, the underlying mechanism and effect of dual inhibition of PI3Kδ/BRD4 in B-ALL remains unknown. To study this, we utilized SF2535, a novel small molecule dual inhibitor which can specifically target the PI3Kδ isoform and BRD4. We treated primary B-ALL cells with various concentrations of SF2535 and studied its effect on specific pharmacological on-target mechanisms such as apoptosis, cell cycle, cell proliferation, and adhesion molecules expression usingin vitro and in vivo models. SF2535 significantly downregulates both c-Myc mRNA and protein expression through inhibition of BRD4 at the c-Myc promoter site and decreases p-AKT expression through inhibition of the PI3Kδ/AKT pathway. SF2535 induced apoptosis in B-ALL by downregulation of BCL-2 and increased cleavage of caspase-3, caspase-7, and PARP. Moreover, SF2535 induced cell cycle arrest and decreased cell counts in B-ALL. Interestingly, SF2535 decreased the mean fluorescence intensity (MFI) of integrin α4, α5, α6, and β1 while increasing MFI of CXCR4, indicating that SF2535 may work through inside-out signaling of integrins. Taken together, our data provide a rationale for the clinical evaluation of targeting PI3Kδ/BRD4 in refractory or relapsed B-ALL using SF2535.

PI3Kδ Inhibitors as Immunomodulatory Agents for the Treatment of Lymphoma Patients

The development of small molecules able to block specific or multiple isoforms of phosphoinositide 3-kinases (PI3K) has already been an active field of research for many years in the cancer field. PI3Kδ inhibitors are among the targeted agents most extensively studied for the treatment of lymphoma patients and PI3Kδ inhibitors are already approved by regulatory agencies. More recently, it became clear that the anti-tumor activity of PI3K inhibitors might not be due only to a direct effect on the cancer cells but it can also be mediated via inhibition of the kinases in non-neoplastic cells present in the tumor microenvironment. T-cells represent an important component of the tumor microenvironment and they comprise different subpopulations that can have both anti- and pro-tumor effects. In this review article, we discuss the effects that PI3Kδ inhibitors exert on the immune system with a particular focus on the T-cell compartment.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

Mining the Microenvironment for Therapeutic Targets in Chronic Lymphocytic Leukemia

ABSTRACT

The leukemia cells of patients with chronic lymphocytic leukemia (CLL) are highly fastidious, requiring stimulation by soluble factors and interactions with accessory cells within the supportive niches of lymphoid tissue that comprise the leukemia microenvironment. The advent of therapies that can disrupt some of the stimulatory signaling afforded by the microenvironment has ushered in a new era of targeted therapy, which has dramatically improved clinical outcome and patient survival. Future advances are required for patients who develop intolerance or resistance to current targeted therapies. These may be found by investigating novel drugs that can inhibit identified targets, such as the pathways involved in B-cell receptor signaling, or by developing agents that inhibit additional targets of the leukemia microenvironment. This review describes some of the molecules involved in promoting the growth and/or survival of CLL cells and discusses targeting strategies that may become tomorrow's therapy for patients with CLL.

Lessons, Challenges and Future Therapeutic Opportunities for PI3K Inhibition in CLL

Simple Summary

The phosphoinositide 3-kinase (PI3K) is a family of kinases that play a key role in the biology of chronic lymphocytic leukemia (CLL). Inhibitors of PI3K demonstrated efficacy in the treatment of CLL, associated with significant adverse events that limited the clinical use of this drugs. In this review, we underlined the relevance of PI3K inhibitors in CLL, we collected recent data about the use of these molecules in clinical practice and in clinical trial discussing strategies for the management of adverse events, which could help to improve the use of these therapies in the treatment of CLL.

Abstract

Chronic lymphocytic leukemia (CLL) shows constitutive phosphatidylinositol 3-kinase (PI3K) activation resulting from aberrant regulation of the B-cell receptor (BCR) signaling. PI3K inhibitors have been evaluated in CLL therapy, bringing a new treatment opportunity for patients with this disease. Despite the proven therapeutic efficacy, the use of approved PI3K inhibitors is limited by severe immune-mediated toxicities and given the availability of other more tolerable agents. This article reviews the relevance of PI3K signaling and pharmacologic inhibition in CLL. Data on efficacy and toxicity of PI3K inhibitors are also presented, as well as strategies for overcoming barriers for their clinical use in CLL treatment.

Phosphoinositide 3-Kinase Signaling in the Tumor Microenvironment: What Do We Need to Consider When Treating Chronic Lymphocytic Leukemia With PI3K Inhibitors?

Phosphoinositide 3-kinases (PI3Ks) and their downstream proteins constitute a signaling pathway that is involved in both normal cell growth and malignant transformation of cells. Under physiological conditions, PI3K signaling regulates various cellular functions such as apoptosis, survival, proliferation, and growth, depending on the extracellular signals. A deterioration of these extracellular signals caused by mutational damage in oncogenes or growth factor receptors may result in hyperactivation of this signaling cascade, which is recognized as a hallmark of cancer. Although higher activation of PI3K pathway is common in many types of cancer, it has been therapeutically targeted for the first time in chronic lymphocytic leukemia (CLL), demonstrating its significance in B-cell receptor (BCR) signaling and malignant B-cell expansion. The biological activity of the PI3K pathway is not only limited to cancer cells but is also crucial for many components of the tumor microenvironment, as PI3K signaling regulates cytokine responses, and ensures the development and function of immune cells. Therefore, the success or failure of the PI3K inhibition is strongly related to microenvironmental stimuli. In this review, we outline the impacts of PI3K inhibition on the tumor microenvironment with a specific focus on CLL. Acknowledging the effects of PI3K inhibitor-based therapies on the tumor microenvironment in CLL can serve as a rationale for improved drug development, explain treatment-associated adverse events, and suggest novel combinatory treatment strategies in CLL.

Identification of a potent and selective phosphatidylinositol 3-kinase δ inhibitor for the treatment of non-Hodgkin's lymphoma

PI3Kδ has proved to be an effective target for anti-lymphoma drugs. However, the application of current approved PI3Kδ inhibitors has been greatly limited due to their specific immune-mediated toxicity and increased risk of infection, it is necessary to develop more PI3Kδ inhibitors with new scaffold. In this study, SAR study with respect to piperazinone-containing purine derivatives led to the discovery of a potent and selective PI3Kδ inhibitor, 4-(cyclobutanecarbonyl)-1-((2-(2-ethyl-1H-benzo[d]imidazol-1-yl)-9-methyl-6-morpholino-9H-purin-8-yl)methyl)piperazin-2-one (WNY1613). WNY1613 exhibits good antiproliferative activity against a panel of non-Hodgkin's lymphoma (NHL) cell lines by inducing cancer cell apoptosis and inhibiting the phosphorylation of PI3K and MAPK downstream components. In addition, it can also prevent the tumor growth in both SU-DHL-6 and JEKO-1 xenograft models without observable toxicity. WNY1613 thus could be developed as a promising candidate for the treatment of NHL after subsequent extensive pharmacodynamics and pharmacokinetics investigation.

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.

Inositol Polyphosphate-Based Compounds as Inhibitors of Phosphoinositide 3-Kinase-Dependent Signaling

Signaling pathways regulated by the phosphoinositide 3-kinase (PI3K) enzymes have a well-established role in cancer development and progression. Over the past 30 years, the therapeutic potential of targeting this pathway has been well recognized, and this has led to the development of a multitude of drugs, some of which have progressed into clinical trials, with few of them currently approved for use in specific cancer settings. While many inhibitors compete with ATP, hence preventing the catalytic activity of the kinases directly, a deep understanding of the mechanisms of PI3K-dependent activation of its downstream effectors led to the development of additional strategies to prevent the initiation of this signaling pathway. This review summarizes previously published studies that led to the identification of inositol polyphosphates as promising parent molecules to design novel inhibitors of PI3K-dependent signals. We focus our attention on the inhibition of protein-membrane interactions mediated by binding of pleckstrin homology domains and phosphoinositides that we proposed 20 years ago as a novel therapeutic strategy.