Bruton's tyrosine kinase inhibition increases BCL-2 dependence and enhances sensitivity to venetoclax in chronic lymphocytic leukemia

BCL-2 dependence is a favorable predictive marker of response to therapy for chronic lymphocytic leukemia

BACKGROUND

Established genetic biomarkers in chronic lymphocytic leukemia (CLL) have been useful in predicting response to chemoimmunotherapy but are less predictive of response to targeted therapies. With several such targeted therapies now approved for CLL, identifying novel, non-genetic predictive biomarkers of response may help to select the optimal therapy for individual patients.

METHODS

We coupled data from a functional precision medicine technique called BH3-profiling, which assesses cellular cytochrome c loss levels as indicators for survival dependence on anti-apoptotic proteins, with multi-omics data consisting of targeted and whole-exome sequencing, genome-wide DNA methylation profiles, RNA-sequencing, protein and functional analyses, to identify biomarkers for treatment response in CLL patients.

RESULTS

We initially studied 73 CLL patients from a discovery cohort. We found that greater dependence on the anti-apoptotic BCL-2 protein was associated with prognostically favorable genetic biomarkers. Furthermore, BCL-2 dependence was strongly associated with gene expression patterns and signaling pathways that suggest a more targeted drug-sensitive milieu and was predictive of drug responses. We subsequently demonstrated that these associations were causal in cell lines and additional CLL patient samples. To validate the findings from our discovery cohort and in vitro studies, we utilized primary CLL cells from 54 additional patients treated on a prospective, phase-2 clinical trial of the BTK inhibitor ibrutinib given in combination with chemoimmunotherapy (fludarabine, cyclophosphamide, rituximab) and confirmed in this independent dataset that higher BCL-2 dependence predicted favorable clinical response, independent of the genetic background of the CLL cells.

CONCLUSION

We comprehensively defined BCL-2 dependence as a potential functional and predictive biomarker of treatment response in CLL, underscoring the importance of characterizing apoptotic signaling in CLL to stratify patients beyond genetic markers and identifying novel combinations to exploit BCL-2 dependence therapeutically. Our approach has the potential to help optimize targeted therapy combinations for CLL patients.

Phase II Study of Acalabrutinib, Venetoclax, and Obinutuzumab in a Treatment-Naïve Chronic Lymphocytic Leukemia Population Enriched for High-Risk Disease

PURPOSE

The AMPLIFY trial recently established fixed-duration acalabrutinib, venetoclax, and obinutuzumab (AVO) as a new standard-of-care option for patients with previously untreated chronic lymphocytic leukemia (CLL) with wild-type TP53; however, due to the chemoimmunotherapy control arm, AMPLIFY excluded patients with high-risk TP53 aberration, for whom current standards of care are continuous Bruton tyrosine kinase inhibitor therapy or alternatively fixed-duration venetoclax-based doublets. AVO has not previously been evaluated in patients with CLL with TP53 aberration.

METHODS

This investigator-sponsored, multicenter, phase II study enrolled patients with treatment-naïve CLL enriched for high-risk CLL, defined by TP53 aberration (ClinicalTrials.gov identifier: NCT03580928). Patients received acalabrutinib, obinutuzumab, and then venetoclax, with each treatment introduced sequentially and in combination, with the duration guided by measurable residual disease (MRD). Patients who achieved undetectable MRD (uMRD) after either 15 or 24 cycles could discontinue treatment. The primary end point was complete remission (CR) with bone marrow uMRD (BM-uMRD) at the start of cycle 16.

RESULTS

Seventy-two patients were accrued, including 45 patients with TP53 aberration. The CR with BM-uMRD rates at the start of cycle 16 were 42% in patients with TP53 aberration and 42% in all-comers, and the BM-uMRD rates were 71% and 78%, respectively. Hematologic toxicities were mainly low grade, and cardiovascular toxicities and bleeding complications were infrequent. After a median follow-up of 55.2 months, 10 patients had progressed, including four with transformation, and three patients died. Four-year progression-free survival and overall survival for patients with or without TP53 aberration were 70%/96% and 88%/100%, respectively.

CONCLUSION

AVO was highly active and well tolerated in patients with previously untreated high-risk CLL, supporting its use as a new standard-of-care treatment option.

The preclinical discovery and development of zanubrutinib for the treatment of chronic lymphocytic leukemia

INTRODUCTION

The history of treating chronic lymphocytic leukemia (CLL) inflected in 2014 with the Food and Drug Administration's (FDA) approval of ibrutinib, the first-in-class small molecule inhibitor of the Bruton's tyrosine kinase (BTK). Zanubrutinib is a 2nd generation covalent BTK inhibitor developed and manufactured by BeiGene.

AREAS COVERED

In this review, the authors trace the arc of zanubrutinib development from the preclinical phase through the two landmark phase 3 studies in the CLL space, ALPINE and SEQUOIA. The authors cover contemporary management strategies in CLL and highlight the areas of need that zanubrutinib was designed to mitigate.

EXPERT OPINION

Zanubrutinib entered a fray of novel, exciting therapies for CLL. As the second of two 2nd generation covalent BTK inhibitors its path to prominence in CLL management was narrow. Emphasis during development on kinase selectivity and enhanced bioavailability identified a molecule with superior efficacy and tolerability; hierarchical endpoints in trial design allowed for efficient acquisition of comparative data. Zanubrutinib is endorsed by the National Comprehensive Cancer Network as a preferred, category 1 recommended treatment choice for CLL. Future efforts in combination therapies and response-directed treatment breaks will hopefully lead to still further improvements in use.

SOHO State of the Art Updates and Next Questions | Covalent Bruton's Tyrosine Kinase Inhibitors in Chronic Lymphocytic Leukemia

Inhibitors of Bruton's tyrosine kinase (BTK) are among the most widely used therapies for chronic lymphocytic leukemia (CLL) and established a new expectation for efficacy and safety in the treatment of this disease. Currently there are 3 covalent inhibitors of BTK approved for the treatment of CLL: ibrutinib, acalabrutinib, and zanubrutinib. The first-in-class covalent BTK inhibitor is ibrutinib, which as monotherapy has excellent efficacy in the front-line setting with a 7-year progression free survival (PFS) of 59%. Ibrutinib-based therapies have also demonstrated superiority over standard chemoimmunotherapy in the front-line and the relapsed/refractory setting. Acalabrutinib is a second-generation BTK inhibitor that has higher selectivity to BTK. Acalabrutinib has efficacy in both frontline and relapsed CLL and is associated with a decreased incidence of atrial fibrillation and hypertension when compared to ibrutinib. Like acalabrutinib, zanubrutinib was designed to be more selective for BTK than ibrutinib and to maximize BTK inhibition in tissues. Zanubrutinib has demonstrated clinical efficacy in first line and relapsed/refractory setting. These agents are indicated as monotherapy, with dosing until disease progression or intolerable toxicity, and are mainly differentiated by safety profile, although efficacy differences may exist as well. Combination with CD20 monoclonal antibodies and/or BCL2 inhibitors are alternative options for use. Here we will review efficacy and safety considerations with these agents.

SOHO State of the Art Updates and Next Questions | Venetoclax + Obinutuzumab Therapy in Chronic Lymphocytic Leukemia

In the past decade, the treatment paradigm for chronic lymphocytic leukemia (CLL) has markedly shifted from traditional chemoimmunotherapy towards targeted therapies.1 A fixed-duration, targeted regimen with venetoclax, a potent oral BCL-2 inhibitor, combined with obinutuzumab, a glycoengineered type II anti-CD20 monoclonal antibody (Ven-Obi), has become the standard to beat for time-limited therapy in CLL. Ven-Obi allows for the rapid induction of remissions with high rates of undetectable minimal residual disease (uMRD) in patients across different treatment settings. This strategy enables the discontinuation of therapy while maintaining treatment-free remissions for several years in many patients. With up to 6-year data now available from the pivotal phase 3 trial of this combination in CLL, this review aims to examine the evolving role of this strategy in CLL management, including updated data for safety and efficacy in randomized trials in both the frontline and relapsed/refractory (R/R) settings. We also explore real-world data for this combination, and review related issues, such as MRD monitoring, the potential for venetoclax retreatment or consolidative strategies and evaluate ongoing trials comparing this regimen as a standard of care control arm versus novel (including all-oral) therapeutic combinations.

Molecular Composition and Kinetics of B Cells During Ibrutinib Treatment in Patients with Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of B cells due to constitutive B-cell receptor (BCR) signaling, leading to apoptosis resistance and increased proliferation. This study evaluates the effects of the Bruton Tyrosine Kinase (BTK) inhibitor ibrutinib on the molecular composition, clonality, and kinetics of B cells during treatment in CLL patients. Employing a multi-omics approach of up to 3.2 years of follow-up, we analyzed data from 24 CLL patients, specifically focusing on nine patients treated with ibrutinib monotherapy. In this study, clonal stability was observed within the ibrutinib-treated group following an effective initial clinical response, where clonotype frequencies of residual CLL cells remained high and stable, ranging from 74.9% at 1.5 years to 87.7% at approximately 3 years. In contrast, patients treated with the B-cell lymphoma 2 (BCL2) inhibitor venetoclax exhibited substantial reductions in clonal frequencies, approaching molecular eradication. Deep whole-exome sequencing revealed minimal genomic progression in the ibrutinib group, maintaining somatic drivers and variant allele frequencies (VAF) above 0.2 throughout treatment. At the single-cell level, the NF-κB pathway inhibition and apoptotic signals were detected or even augmented during treatment in ibrutinib-treated patients. These findings may corroborate the role of ibrutinib in stabilizing the genomic landscape of CLL cells, preventing significant genomic evolution despite maintaining a high clonal burden within the residual B-cell compartment.

Current Approaches and Novel Agents in the Treatment of Chronic Lymphocytic Leukemia

The treatment of CLL has evolved from traditional chemoimmunotherapy (CIT) to an increasing number of targeted and biologic approaches. Randomized trials have demonstrated superiority of covalent bruton tyrosine kinase inhibitors (cBTKis) over CIT, and second-generation compounds such as acalabrutinib and zanubrutinib appear to have a more favorable efficacy/safety profile than ibrutinib. The noncovalent BTKi, pirtobrutinib, has shown impressive activity after failure of the cBTKis and is quite tolerable. The Bcl-2 inhibitor venetoclax plus a CD20, generally obinutuzumab, provides a high level of efficacy as initial treatment or after failure on a cBTKi, with many patients achieving a state of undetectable minimal residual disease. Promising novel approaches include BTK degraders, bispecific antibodies, and chimeric antigen receptor T-cell (CAR-T)-cell therapy. What is clear is that CIT is archaic, and current and future targeted approaches will continue to improve the outcome for patients with chronic lymphocytic leukemia.

Pharmacological management of chronic lymphocytic leukemia: current and emerging therapies

INTRODUCTION

Chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL), characterized by its monoclonal lymphoproliferative nature, is an indolent but incurable malignancy. The treatment landscape of CLL/SLL has drastically transformed in the last decade since the introduction of targeted therapy and immune-effector T-cell therapy. The paradigm shift from chemoimmunotherapy to targeted and cellular therapies was largely driven by improved efficacy and safety. With the success of targeted therapies, novel agents and combinations are rapidly emerging on the horizon.

AREAS COVERED

In this review, we will summarize clinical evidence supporting current and emerging therapies with emphasis on investigational therapies and novel combinations of commercial agents. Clinical trials were identified via clinicaltrials.gov, and a PubMed literature search was last performed in June 2024.

EXPERT OPINION

With the availability of more effective and better-tolerated treatments for CLL/SLL, the role of early intervention should be further investigated due to its potential to alter disease course, delay progression, and improve overall survival rates. With many highly effective agents and combinations expected to become commercially available, attention to safety profiles and careful selection of patients for each treatment will be critical, with consideration of comorbidities, logistical issues, and financial burden of treatment.

Ibrutinib and venetoclax in combination for chronic lymphocytic leukemia: synergy in practice

The combination of ibrutinib and venetoclax has emerged as a promising therapeutic strategy for patients with chronic lymphocytic leukemia (CLL). Preclinical investigations demonstrated a synergistic antitumor effect through multiple mechanisms, providing a robust foundation for translating this regimen into clinical trials. Beyond the dual inhibition by 2 small molecules, another innovative concept being tested with this combination is the use of measurable residual disease (MRD)-driven treatment vs fixed-duration treatment to meet the escalating demand for oral, convenient, cost-effective, and time-limited therapeutic approaches. The clinical translation of this combination has yielded remarkable outcomes with significant improvements in the progression-free survival and overall survival rates for both treatment-naïve patients and those with relapsed/refractory CLL. Notably, a substantial proportion of patients achieved undetectable MRD. Clinical trial updates following the initial published results have shown consistency and durability of responses over time. In this review, the initial investigator-initiated trial results for ibrutinib and venetoclax are discussed, several multicenter clinical trial designs and outcomes are examined, variables such as chromosome 17p deletion that influence treatment responses are addressed, and the safety of the regimen is discussed. In addition, we reviewed the usage of this combination in other B-cell malignancies and discussed how current knowledge can be used for shaping the future CLL treatment regimens.

BTK inhibitors: past, present, and future

Bruton's tyrosine kinase (BTK) inhibitors have revolutionized the treatment landscape for B cell lymphomas such as chronic lymphocytic leukemia (CLL). The first-in-class BTK inhibitor ibrutinib has recently been succeeded by covalent BTK inhibitors that are safer but still face challenges of resistance mutations. The noncovalent BTK inhibitor pirtobrutinib was recently approved for relapsed and refractory CLL, and whether noncovalent BTK inhibitors will supplant covalent BTK inhibitors as upfront treatment options either alone or in combination will be determined. Meanwhile, newer BTK inhibitors and BTK degraders are vying for their place in the potential future landscape of B cell cancers as well as autoimmune diseases. This review will cover the latest progress in BTK inhibitor development and where the field is moving in light of these recent discoveries.

Combination of BCL-2 inhibitors and immunotherapy: a promising therapeutic strategy for hematological malignancies

The rapid development of high-throughput sequencing in recent years has facilitated great progress in the molecular-targeted therapy of hematological malignancies, including leukemia, lymphoma, and multiple myeloma. BCL-2 inhibitors are among the most important molecular-targeted agents. Immunotherapy for hematologic malignancy has rapidly increased in popularity in recent years and has been proven to improve the overall survival rate. However, few clinical studies have investigated combination therapy with BCL-2 inhibitors and immunotherapies, such as immune molecule-targeted drugs or immune cell adoptive therapy. In this review, we discuss the drug discovery process, current clinical application status, and resistance and tolerance issues associated with BCL-2 inhibitors. We emphasize their important role in regulating the immune system and propose that the combination of BCL-2 inhibitors with immunotherapy may be one of the most promising treatment methods for hematologic malignancies.

Therapeutic targeting of apoptosis in chronic lymphocytic leukemia

Therapeutic targeting of apoptosis with small molecule B-cell lymphoma 2 (BCL-2) inhibition with venetoclax is highly efficacious in CLL, leading to sustained deep responses, particularly among patients with treatment-naïve disease with favorable prognostic markers. Patients with unfavorable genetic characteristics such as TP53 aberration and unmutated IGHV may also derive durable benefits, but their remission duration after time-limited venetoclax-containing combination therapy is shorter, particularly in patients with relapsed/refractory disease. Emerging data indicate that the context of disease progression after initial treatment with venetoclax may define the success of re-treatment with venetoclax. Specifically, continuous venetoclax exposure may select for resistant disease due to genetic mechanisms such as BCL2 mutations and functional resistance mechanisms such as hyperphosphorylation of BCL-2 family proteins, which decrease the affinity of venetoclax binding to the target or lead to increased MCL-1 dependence and concomitant decrease in BCL-2 dependence. These patients may be best served by switching to a different class of targeted agents at the time of progression. In contrast, relapsed CLL that arises while being off therapy after a period of time-limited venetoclax-based regimens maintains sensitivity to re-treatment with venetoclax for the majority of patients. Novel strategies related to therapeutic targeting of apoptosis include next-generation BCL-2 inhibitors with improved potency and pharmacokinetic profiles, direct targeting of anti-apoptotic BH3 family proteins beyond BCL-2 such as MCL-1, and indirect targeting of MCL-1 through mechanisms such as small molecule cyclin-dependent kinase 9 inhibitors.

Prognostication in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common type of leukemia in Western countries. CLL is a highly heterogeneous disease: some patients may never require therapy and others relapse several times after different therapeutic strategies. Therefore, in CLL, prognostic markers are essential to capture high-risk patients for different clinical endpoints including early treatment requirement, early progression after BTK or BCL2 inhibitors and Richter transformation. In early stage CLL, different biological and clinical biomarkers have been identified to predict time to treatment requirement that could be used to identify the most appropriate population for early intervention clinical trial. However, at the moment, the standard of care for early stage CLL remains watch & wait since no survival benefit has been identified in clinical trials with chemoimmunotherapy and with BTK inhibitors. In patients requiring treatment TP53 disruptions identify high-risk patients who benefit the most from long-term continuous therapy with BTKi. On the opposite side of the spectrum, IGHV mutated patients devoid of TP53 disruption benefit the most from fixed-duration therapy with venetoclax-obinutuzumab. In between, the highly heterogenous subgroup of patients with IGHV unmutated genes represents the group in which further efforts are needed to identify additional prognostic biomarkers aimed at selecting patients who can benefit from fixed-duration and patients who can benefit from long term BTKi therapy. In the context of the aggressive transformation of CLL, namely Richter syndrome, the clonal relationship to the CLL counterpart represents the strongest prognostic biomarker. Clonally related Richter syndrome still represents an unmet clinical need which requires further efforts to identify new therapeutic strategies.

Taking the Next Step in Double Refractory Disease: Current and Future Treatment Strategies for Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a monoclonal B-cell lymphoproliferative disease with a high annual incidence in Western countries. As B-cell receptor (BCR) signaling and intrinsic apoptotic resistance play critical roles in the development and survival of CLL cells, therapeutic approaches targeting these pathways have been extensively investigated to tackle this incurable disease. Over the last decade, several Phase 3 trials have confirmed the superior efficacy of covalent Bruton tyrosine kinase inhibitors (cBTKis) and venetoclax, a selective B-cell lymphoma 2 (BCL2) inhibitor, over chemoimmunotherapy. This has been demonstrated in both the treatment-naïve and relapsed/refractory (RR) settings and includes patients with high-risk molecular features. However, these drugs are not curative, with patients continuing to relapse after treatment with both cBTKis and BCL2is, and the optimal treatment strategy for these patients has not been defined. Several novel agents with distinct mechanisms have recently been developed for CLL which have demonstrated efficacy in patients who have previously received cBTKis and BCL2i. In particular, novel BCR-signaling targeting agents have shown promising efficacy in early-phase clinical trials for RR-CLL. Furthermore, cancer immunotherapies such as bispecific antibodies and chimeric antigen receptor T-cells have also shown anti-tumor activity in patients with heavily pretreated RR-CLL. Personalised approaches with these novel agents and combination strategies based on the understanding of resistance mechanisms have the potential to overcome the clinical challenge of what to do next for a patient who has already had a cBTKi and venetoclax.

Five-year follow-up of a phase 2 study of ibrutinib plus fludarabine, cyclophosphamide, and rituximab as initial therapy in CLL

ABSTRACT

We previously reported high rates of undetectable minimal residual disease <10-4 (uMRD4) with ibrutinib plus fludarabine, cyclophosphamide, and rituximab (iFCR) followed by 2-year ibrutinib maintenance (I-M) in treatment-naïve chronic lymphocytic leukemia (CLL). Here, we report updated data from this phase 2 study with a median follow-up of 63 months. Of 85 patients enrolled, including 5 (6%) with deletion 17p or TP53 mutation, 91% completed iFCR and 2-year I-M. Five-year progression-free survival (PFS) and overall survival were 94% (95% confidence interval [CI], 89%-100%) and 99% (95% CI, 96%-100%), respectively. No additional deaths have occurred with this extended follow-up. No difference in PFS was observed by immunoglobulin heavy-chain variable region gene status or duration of I-M. High rates of peripheral blood (PB) uMRD4 were maintained (72% at the end of iFCR, 66% at the end of 2-year I-M, and 44% at 4.5 years from treatment initiation). Thirteen patients developed MRD conversion without clinical progression, mostly (77%) after stopping ibrutinib. None had Bruton tyrosine kinase (BTK) mutations. One patient had PLCG2 mutation. Six of these patients underwent ibrutinib retreatment per protocol. Median time on ibrutinib retreatment was 34 months. The cumulative incidence of atrial fibrillation was 8%. Second malignancy or nonmalignant hematologic disease occurred in 13%, mostly nonmelanoma skin cancer. Overall, iFCR with 2-year I-M achieved durably deep responses in patients with diverse CLL genetic markers. Re-emergent clones lacked BTK mutation and retained sensitivity to ibrutinib upon retreatment. This trial is registered at www.clinicaltrials.gov as #NCT02251548.

First-in-Human Study with Preclinical Data of BCL-2/BCL-xL Inhibitor Pelcitoclax in Locally Advanced or Metastatic Solid Tumors

PURPOSE

B-cell lymphoma-extra-large (BCL-xL) regulates apoptosis and is an attractive anticancer therapeutic target. However, BCL-xL inhibition also kills mature platelets, hampering clinical development. Using an innovative prodrug strategy, we have developed pelcitoclax (APG-1252), a potent, dual BCL-2 and BCL-xL inhibitor. Aims of this study were to characterize the antitumor activity and safety of pelcitoclax and explore its underlying mechanisms of action (MOA).

PATIENTS AND METHODS

Cell line-derived xenograft and patient-derived xenograft (PDX) models were tested to evaluate antitumor activity and elucidate MOA. Subjects (N = 50) with metastatic small-cell lung cancer and other solid tumors received intravenous pelcitoclax once or twice weekly. Primary outcome measures were safety and tolerability; preliminary efficacy (responses every 2 cycles per RECIST version 1.1) represented a secondary endpoint.

RESULTS

Pelcitoclax exhibited strong BAX/BAK‒dependent and caspase-mediated antiproliferative and apoptogenic activity in various cancer cell lines. Consistent with cell-based apoptogenic activity, pelcitoclax disrupted BCL-xL:BIM and BCL-xL:PUMA complexes in lung and gastric cancer PDX models. Levels of BCL-xL complexes correlated with tumor growth inhibition by pelcitoclax. Combined with taxanes, pelcitoclax enhanced antitumor activity by downregulating antiapoptotic protein myeloid cell leukemia-1 (MCL-1). Importantly, pelcitoclax was well tolerated and demonstrated preliminary therapeutic efficacy, with overall response and disease control rates of 6.5% and 30.4%, respectively. Most common treatment-related adverse events included transaminase elevations and reduced platelets that were less frequent with a once-weekly schedule.

CONCLUSIONS

Our data demonstrate that pelcitoclax has antitumor activity and is well tolerated, supporting its further clinical development for human solid tumors, particularly combined with agents that downregulate MCL-1.

Absence of BTK, BCL2, and PLCG2 Mutations in Chronic Lymphocytic Leukemia Relapsing after First-Line Treatment with Fixed-Duration Ibrutinib plus Venetoclax

PURPOSE

Mutations in BTK, PLCG2, and BCL2 have been reported in patients with progressive disease (PD) on continuous single-agent BTK or BCL2 inhibitor treatment. We tested for these mutations in samples from patients with PD after completion of first-line treatment with fixed-duration ibrutinib plus venetoclax for chronic lymphocytic leukemia (CLL) in the phase II CAPTIVATE study.

PATIENTS AND METHODS

A total of 191 patients completed fixed-duration ibrutinib plus venetoclax (three cycles of ibrutinib then 12-13 cycles of ibrutinib plus venetoclax). Genomic risk features [del(11q), del(13q), del(17p), trisomy 12, complex karyotype, unmutated IGHV, TP53 mutated] and mutations in genes recurrently mutated in CLL (ATM, BIRC3, BRAF, CHD2, EZH2, FBXW7, MYD88, NOTCH1, POT1, RPS15, SF3B1, XPO1) were assessed at baseline in patients with and without PD at data cutoff; gene variants and resistance-associated mutations in BTK, PLCG2, or BCL2 were evaluated at PD.

RESULTS

Of 191 patients completing fixed-duration ibrutinib plus venetoclax, with median follow-up of 38.9 months, 29 (15%) developed PD. No baseline risk feature or gene mutation was significantly associated with development of PD. No previously reported resistance-associated mutations in BTK, PLCG2, or BCL2 were detected at PD in 25 patients with available samples. Of the 29 patients with PD, 19 have required retreatment (single-agent ibrutinib, n = 16, or ibrutinib plus venetoclax, n = 3); 17 achieved partial response or better, 1 achieved stable disease, and 1 is pending response assessment.

CONCLUSIONS

First-line fixed-duration combination treatment with ibrutinib plus venetoclax may mitigate development of resistance mechanisms associated with continuous single-agent targeted therapies, allowing for effective retreatment. See related commentary by Al-Sawaf and Davids, p. 471.

Treatment of Double-Refractory Chronic Lymphocytic Leukemia-An Unmet Clinical Need

Recent years have seen significant improvement in chronic lymphocytic leukemia (CLL) management. Targeting B-cell lymphoma (BCL-2) and Bruton's kinase (BTK) have become the main strategies to restrain CLL activity. These agents are generally well tolerated, but the discontinuation of these therapies happens due to resistance, adverse effects, and Richter's transformation. A growing population of patients who have previously used both BTK inhibitors and BCL2 suffer from the constriction of the following regimens. This review explores the resistance mechanisms for both ibrutinib and venetoclax. Moreover, we present innovative approaches evaluated for treating double-refractory CLL.

Chronic Lymphocytic Leukemia Therapy Guided by Measurable Residual Disease

BACKGROUND

The combination of ibrutinib and venetoclax has been shown to improve outcomes in patients with chronic lymphocytic leukemia (CLL) as compared with chemoimmunotherapy. Whether ibrutinib-venetoclax and personalization of treatment duration according to measurable residual disease (MRD) is more effective than fludarabine-cyclophosphamide-rituximab (FCR) is unclear.

METHODS

In this phase 3, multicenter, randomized, controlled, open-label platform trial involving patients with untreated CLL, we compared ibrutinib-venetoclax and ibrutinib monotherapy with FCR. In the ibrutinib-venetoclax group, after 2 months of ibrutinib, venetoclax was added for up to 6 years of therapy. The duration of ibrutinib-venetoclax therapy was defined by MRD assessed in peripheral blood and bone marrow and was double the time taken to achieve undetectable MRD. The primary end point was progression-free survival in the ibrutinib-venetoclax group as compared with the FCR group, results that are reported here. Key secondary end points were overall survival, response, MRD, and safety.

RESULTS

A total of 523 patients were randomly assigned to the ibrutinib-venetoclax group or the FCR group. At a median of 43.7 months, disease progression or death had occurred in 12 patients in the ibrutinib-venetoclax group and 75 patients in the FCR group (hazard ratio, 0.13; 95% confidence interval [CI], 0.07 to 0.24; P<0.001). Death occurred in 9 patients in the ibrutinib-venetoclax group and 25 patients in the FCR group (hazard ratio, 0.31; 95% CI, 0.15 to 0.67). At 3 years, 58.0% of the patients in the ibrutinib-venetoclax group had stopped therapy owing to undetectable MRD. After 5 years of ibrutinib-venetoclax therapy, 65.9% of the patients had undetectable MRD in the bone marrow and 92.7% had undetectable MRD in the peripheral blood. The risk of infection was similar in the ibrutinib-venetoclax group and the FCR group. The percentage of patients with cardiac serious adverse events was higher in the ibrutinib-venetoclax group than in the FCR group (10.7% vs. 0.4%).

CONCLUSIONS

MRD-directed ibrutinib-venetoclax improved progression-free survival as compared with FCR, and results for overall survival also favored ibrutinib-venetoclax. (Funded by Cancer Research UK and others; FLAIR ISRCTN Registry number, ISRCTN01844152; EudraCT number, 2013-001944-76.).

Expression of "DNA damage response" pathway genes in diffuse large B-cell lymphoma: The potential for exploiting synthetic lethality

Diffuse large B-cell lymphoma (DLBCL) and follicular lymphoma (FL) are two of the most prevalent non-Hodgkin's lymphoma subtypes. Despite advances, treatment resistance and patient relapse remain challenging issues. Our study aimed to scrutinize gene expression distinctions between DLBCL and FL, employing a cohort of 53 DLBCL and 104 FL samples that underwent rigorous screening for genetic anomalies. The NanoString nCounter assay evaluated 730 cancer-associated genes, focusing on densely tumorous areas in diagnostic samples. Employing the Lymph2Cx method, we determined the cell-of-origin (COO) for DLBCL cases. Our meticulous analysis, facilitated by Qlucore Omics Explorer software, unveiled a substantial 37% of genes with significantly differential expression patterns between DLBCL and FL, pointing to nuanced mechanistic disparities. Investigating the impact of FL disease stage and DLBCL COO on gene expression yielded minimal differences, prompting us to direct our attention to consistently divergent genes in DLBCL. Intriguingly, our Gene Set Enrichment Analysis spotlighted 21% of these divergent genes, converging on the DNA damage response (DDR) pathway, vital for cell survival and cancer evolution. Strong positive correlations among most DDR genes were noted, with key genes like BRCA1, FANCA, FEN1, PLOD1, PCNA, and RAD51 distinctly upregulated in DLBCL compared to FL and normal tissue controls. These findings were subsequently validated using RNA seq data on normal controls and DLBCL samples from public databases like The Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) databases, enhancing the robustness of our results. Considering the established significance of these DDR genes in solid cancer therapies, our study underscores their potential applicability in DLBCL treatment strategies. In conclusion, our investigation highlights marked gene expression differences between DLBCL and FL, with particular emphasis on the essential DDR pathway. The identification of these DDR genes as potential therapeutic targets encourages further exploration of synthetic lethality-based approaches for managing DLBCL.

Immune restoration with ibrutinib plus venetoclax in first-line chronic lymphocytic leukemia: the phase 2 CAPTIVATE study

We evaluated immune cell subsets in patients with chronic lymphocytic leukemia (CLL) who received first-line therapy with 3 cycles of ibrutinib then 13 cycles of ibrutinib plus venetoclax in the minimal residual disease (MRD) cohort of the CAPTIVATE study (NCT02910583). Patients with Confirmed undetectable MRD (uMRD) were randomly assigned to placebo or ibrutinib groups; patients without Confirmed uMRD were randomly assigned to ibrutinib or ibrutinib plus venetoclax groups. We compared immune cell subsets in samples collected at 7 time points with age-matched healthy donors. CLL cells decreased within 3 cycles after venetoclax initiation; from cycle 16 onward, levels were similar to healthy donor levels (HDL; ≤0.8 cells per μL) in patients with Confirmed uMRD and slightly above HDL in patients without Confirmed uMRD. By 4 months after cycle 16, normal B cells had recovered to HDL in patients randomly assigned to placebo. Regardless of randomized treatment, abnormal counts of T cells, classical monocytes, and conventional dendritic cells recovered to HDL within 6 months (median change from baseline -49%, +101%, and +91%, respectively); plasmacytoid dendritic cells recovered by cycle 20 (+598%). Infections generally decreased over time regardless of randomized treatment and were numerically lowest in patients randomly assigned to placebo within 12 months after cycle 16. Sustained elimination of CLL cells and recovery of normal B cells were confirmed in samples from patients treated with fixed-duration ibrutinib plus venetoclax in the GLOW study (NCT03462719). These results demonstrate promising evidence of restoration of normal blood immune composition with ibrutinib plus venetoclax.

First-Line Treatment of Older Patients with CLL: A New Approach in the Chemo-Free Era

Bruton tyrosine kinase inhibitors (BTKi) and the BCL2 inhibitor venetoclax, with or without the anti-CD20 monoclonal antibody Obinutuzumab, represent the preferred options for the first-line therapy of CLL because they are more effective and may improve quality of life. However, patient inclusion criteria are heterogeneous across trials designed for older patients, and the identification of CLL-specific parameters identifying unfit patients at risk of developing drug-specific adverse events is required to guide treatment choice. Due to inclusion/exclusion criteria in trials, higher discontinuation rates with BTKi were reported in real-world studies, and registry analyses provided useful information on factors predicting earlier discontinuation in a real-world setting. Though targeted agents were shown to be cost-effective treatments in high-income countries, the out-of-pocket expenses may limit accessibility to these drugs, and the overall expenditure for new drugs in CLL is projected to increase substantially, posing an issue for sustainability. This being said, the choice of a finite-duration treatment based on venetoclax-containing regimens or treatment until progression with BTKi is today possible in high-income countries, and the therapy choice drivers are represented by coexisting medical conditions rather than age, patient expectations, logistics, and sustainability.

Outcomes in Patients with High-Risk Features after Fixed-Duration Ibrutinib plus Venetoclax: Phase II CAPTIVATE Study in First-Line Chronic Lymphocytic Leukemia

PURPOSE

The CAPTIVATE study investigated first-line ibrutinib plus venetoclax for chronic lymphocytic leukemia in 2 cohorts: minimal residual disease (MRD)-guided randomized discontinuation (MRD cohort) and Fixed Duration (FD cohort). We report outcomes of fixed-duration ibrutinib plus venetoclax in patients with high-risk genomic features [del(17p), TP53 mutation, and/or unmutated immunoglobulin heavy chain (IGHV)] in CAPTIVATE.

PATIENTS AND METHODS

Patients received three cycles of ibrutinib 420 mg/day then 12 cycles of ibrutinib plus venetoclax (5-week ramp-up to 400 mg/day). FD cohort patients (n = 159) received no further treatment. Forty-three MRD cohort patients with confirmed undetectable MRD (uMRD) after 12 cycles of ibrutinib plus venetoclax received randomized placebo treatment.

RESULTS

Of 195 patients with known status of genomic risk features at baseline, 129 (66%) had ≥1 high-risk feature. Overall response rates were >95% regardless of high-risk features. In patients with and without high-risk features, respectively, complete response (CR) rates were 61% and 53%; best uMRD rates: 88% and 70% (peripheral blood) and 72% and 61% (bone marrow); 36-month progression-free survival (PFS) rates: 88% and 92%. In subsets with del(17p)/TP53 mutation (n = 29) and unmutated IGHV without del(17p)/TP53 mutation (n = 100), respectively, CR rates were 52% and 64%; uMRD rates: 83% and 90% (peripheral blood) and 45% and 80% (bone marrow); 36-month PFS rates: 81% and 90%. Thirty-six-month overall survival (OS) rates were >95% regardless of high-risk features.

CONCLUSIONS

Deep, durable responses and sustained PFS seen with fixed-duration ibrutinib plus venetoclax are maintained in patients with high-risk genomic features, with similar PFS and OS to those without high-risk features. See related commentary by Rogers, p. 2561.

Unresolved questions in selection of therapies for treatment-naïve chronic lymphocytic leukemia

BACKGROUND

The treatment landscape for chronic lymphocytic leukemia (CLL) continues to undergo considerable evolution. Optimal selection of initial therapy from multiple effective options provides a major challenge for clinicians, who need to consider both disease and patient factors in conjunction with a view to sequencing available therapies in event of disease relapse.

REVIEW

We explore the most topical clinically relevant unresolved questions through discussion of important available pertinent literature and propose expert opinion based on these data. (1) Shrinking role of chemoimmunotherapy (CIT); while novel therapies are generally superior, we highlight the utility of FCR for IGHV-mutated CLL. (2) Choosing between inhibitors of Bruton's tyrosine kinase (BTKi); while efficacy between agents is likely similar there are important differences in toxicity profiles, including the incidence of cardiac arrhythmia and hypertension. (3) BTKi with or without anti-CD20 monoclonal antibodies (mAb); while obinutuzumab-acalabrutinib (AO) may confer superior progression-free survival to acalabrutinib (Acala), this is not true of rituximab (Ritux) to ibrutinib (Ib)-we highlight that potential for increased side effects should be carefully considered. (4) Continuous BTKi versus time-limited venetoclax-obinutuzumab (VenO); we propose that venetoclax (Ven)-based therapy is generally preferable to BTKi with exception of TP53 aberrant disease. (5) BTKi-Ven versus VenO as preferred time-limited therapy; we discuss comparable efficacies and the concerns about simultaneous 1L exposure to both BTKi and Ven drug classes. (6) Utility of triplet therapy (BTKi-Ven-antiCD20 mAb) versus VenO; similar rates of complete response are observed yet with greater potential for adverse events. (7) Optimal therapy for TP53 aberrant CLL; while limited data are available, there are likely effective novel therapy combinations for TP53 aberrant disease including BTKi, BTKi-Ven ± antiCD20 mAb.

CONCLUSION

Frontline therapy for CLL should be selected based on efficacy considering the patient specific biologic profile of their disease and potential toxicities, considering patient comorbidities and preferences. With the present paradigm of sequencing effective agents, 1L combinations of novel therapies should be used with caution in view of potential adverse events and theoretical resistance mechanism concerns in the absence of compelling randomized data to support augmented efficacy.

Novel BCL-2 Inhibitor Lisaftoclax in Relapsed or Refractory Chronic Lymphocytic Leukemia and Other Hematologic Malignancies: First-in-Human Open-Label Trial

PURPOSE

This global phase I trial investigated the safety, efficacy, pharmacokinetics, and pharmacodynamics of lisaftoclax (APG-2575), a novel, orally active, potent selective B-cell lymphoma 2 (BCL-2) inhibitor, in patients with relapsed or refractory chronic lymphocytic leukemia or small lymphocytic lymphoma (R/R CLL/SLL) and other hematologic malignancies (HMs).

PATIENTS AND METHODS

Maximum tolerated dose (MTD) and recommended phase II dose were evaluated. Outcome measures were safety and tolerability (primary) and pharmacokinetic variables and antitumor effects (secondary). Pharmacodynamics in patient tumor cells were explored.

RESULTS

Among 52 patients receiving lisaftoclax, MTD was not reached. Treatment-emergent adverse events (TEAEs) included diarrhea (48.1%), fatigue (34.6%), nausea (30.8%), anemia and thrombocytopenia (28.8% each), neutropenia (26.9%), constipation (25.0%), vomiting (23.1%), headache (21.2%), peripheral edema and hypokalemia (17.3% each), and arthralgia (15.4%). Grade ≥ 3 hematologic TEAEs included neutropenia (21.2%), thrombocytopenia (13.5%), and anemia (9.6%), none resulting in treatment discontinuation. Clinical pharmacokinetic and pharmacodynamic results demonstrated that lisaftoclax had a limited plasma residence and systemic exposure and elicited rapid clearance of malignant cells. With a median treatment of 15 (range, 6-43) cycles, 14 of 22 efficacy-evaluable patients with R/R CLL/SLL experienced partial responses, for an objective response rate of 63.6% and median time to response of 2 (range, 2-8) cycles.

CONCLUSIONS

Lisaftoclax was well tolerated, with no evidence of tumor lysis syndrome. Dose-limiting toxicity was not reached at the highest dose level. Lisaftoclax has a unique pharmacokinetic profile compatible with a potentially more convenient daily (vs. weekly) dose ramp-up schedule and induced rapid clinical responses in patients with CLL/SLL, warranting continued clinical investigation.

Impact of Minimal Residual Disease on Progression-Free Survival Outcomes After Fixed-Duration Ibrutinib-Venetoclax Versus Chlorambucil-Obinutuzumab in the GLOW Study

PURPOSE

In GLOW, fixed-duration ibrutinib + venetoclax showed superior progression-free survival (PFS) versus chlorambucil + obinutuzumab in older/comorbid patients with previously untreated chronic lymphocytic leukemia (CLL). The current analysis describes minimal residual disease (MRD) kinetics and any potential predictive value for PFS, as it has not yet been evaluated for ibrutinib + venetoclax treatment.

METHODS

Undetectable MRD (uMRD) was assessed by next-generation sequencing at <1 CLL cell per 10,000 (<10^-4) and <1 CLL cell per 100,000 (<10^-5) leukocytes. PFS was analyzed by MRD status at 3 months after treatment (EOT+3).

RESULTS

Ibrutinib + venetoclax achieved deeper uMRD (<10^-5) rates in bone marrow (BM) and peripheral blood (PB), respectively, in 40.6% and 43.4% of patients at EOT+3 versus 7.6% and 18.1% of patients receiving chlorambucil + obinutuzumab. Of these patients, uMRD (<10^-5) in PB was sustained during the first year post-treatment (EOT+12) in 80.4% of patients receiving ibrutinib + venetoclax and 26.3% receiving chlorambucil + obinutuzumab. Patients with detectable MRD (dMRD; ≥10^-4) in PB at EOT+3 were more likely to sustain MRD levels through EOT+12 with ibrutinib + venetoclax versus chlorambucil + obinutuzumab. PFS rates at EOT+12 were high among patients treated with ibrutinib + venetoclax regardless of MRD status at EOT+3: 96.3% and 93.3% in patients with uMRD (<10^-4) and dMRD (≥10^-4) in BM, respectively, versus 83.3% and 58.7% for patients receiving chlorambucil + obinutuzumab. PFS rates at EOT+12 also remained high in patients with unmutated immunoglobulin heavy-chain variable region (IGHV) receiving ibrutinib + venetoclax, independent of MRD status in BM.

CONCLUSION

Molecular and clinical relapses were less frequent during the first year post-treatment with ibrutinib + venetoclax versus chlorambucil + obinutuzumab regardless of MRD status at EOT+3 and IGHV status. Even for patients not achieving uMRD (<10^-4), PFS rates remained high with ibrutinib + venetoclax; this is a novel finding and requires additional follow-up to confirm its persistence over time.

Ibrutinib sensitizes CLL cells to venetoclax by interrupting TLR9-induced CD40 upregulation and protein translation

Chronic lymphocytic leukemia (CLL) cells upregulate Bcl-2 proteins within the lymph node (LN) microenvironment. Signaling via B-cell receptor, Toll-like receptors and CD40 collectively reduce sensitivity to the BCL-2 inhibitor venetoclax. Time-limited treatment with venetoclax plus the BTK-inhibitor ibrutinib results in deep remissions, but how this combination affects LN-related signaling is not yet completely clear. Therefore, samples obtained from the HOVON141/VISION phase 2 clinical trial were used to analyze this. Two cycles of lead-in ibrutinib monotherapy resulted in decreased protein expression of Bcl-2 proteins in circulating CLL cells. Strikingly, at this timepoint CD40-induced venetoclax resistance was strongly attenuated, as was expression of CD40. Since CD40 signaling occurs within the CLL LN, we tested various LN-related signals that could affect CD40 signaling. While BCR stimulation had only a minor effect, TLR9 stimulation via CpG led to significantly increased CD40 expression and importantly, reverted the effects of ibrutinib treatment on venetoclax sensitivity by inducing overall protein translation. Together, these findings identify a novel effect of ibrutinib: interruption of TLR9-induced CD40 upregulation and translation of pro-survival proteins. This mechanism may potentially further inhibit priming of CLL cells in the LN microenvironment for venetoclax resistance.

Synergistic disruption of BTK and BCL-2 causes apoptosis while inducing ferroptosis in double-hit lymphoma

Double-hit lymphoma (DHL) is an aggressive subset of Diffuse Large B-cell Lymphoma (DLBCL) with poor outcomes and without satisfying treatment options. BTK inhibitor monotherapy is ineffective to suppress aggressive lymphoma. Hence, combination with other potential agents is warranted. Here, we demonstrated the second generation of BTK inhibitor, zanubrutinib, and a BCL-2 inhibitor, navitoclax, worked in synergistic manner to suppress DHL. Comprehensive in silico approach by interrogating single-cell to bulk-level profiling was employed along with in vitro and in vivo validation in DHL cell lines. Ablation of BTK enhanced sensitivity to navitoclax and suppressed proliferation of DHL cells. Combination of second generation of BTK inhibitor with navitoclax synergistically suppressed DLBCL cells with higher synergy score in DHL subset. The drug combination triggered apoptosis and ferroptosis, with the latter being characterized by reactive oxygen species (ROS) accumulation, extensive lipid peroxidation, and depletion of reduced glutathione. Moreover, ablation of BTK sensitized DHL cells to ferroptosis. Mechanistically, disruption of BTK and BCL-2 triggered ferroptosis by downregulating NRF2 and HMOX1, while deactivating GPX4. Combination of zanubrutinib and navitoclax effectively suppressed tumor growth in vivo. Our data suggest that zanubrutinib and navitoclax synergistically suppressed DHL by inducing apoptosis and ferroptosis.

A retrospective assessment of real-world experience with venetoclax and azacitidine therapy in elderly acute myeloid leukemia

This study aimed to examine the effect of venetoclax coupled with azacytidine in treating older adults with relapsed and refractory (R/R) acute myeloid leukemia (AML). The clinical data of 10 senior patients with AML over 65 years old who were treated with venetoclax and azacytidine, including six patients with R/R AML, were retrospectively evaluated. This study comprised seven males and three females with a median age of 71 years. Five patients had at least one relapse, and one patient did not achieve remission after four cycles of azacytidine monotherapy, considering it resistant. AML with myelodysplasia-related changes was found in four cases. One of the 10 patients died early after 1-13 cycles of venetoclax plus azacytidine treatment due to a protracted period of neutropenia and severe lung infection induced by medications. Six of the remaining nine patients, including six R/R patients, achieved a complete remission (CR) or a CR with incomplete hematologic recovery (CRi). After two cycles of therapy, one patient did not react. Neutropenia lasted an average of 10.5 (6-15) days in all patients, with the most severe cases occurring in the second and third weeks of therapy. Three patients who tested positive for the TP53 gene mutation had the following outcomes: One relapsed patient has been in progression-free remission (PFS) for the past 24 months, whereas another has been in full remission but relapsed 2 months later. Another patient experienced complete remission in myelology for 4 months, but the variable allele fraction (VAF) value steadily rose, suggesting that the illness was on the verge of progressing. IDH2 gene alterations were found in three of four patients who obtained maintained CR for more than 18 months following recurrence. Venetoclax in combination with azacytidine is a successful and well-tolerated therapy for R/R AML in the elderly. Venetoclax and azacytidine may help patients with TP53 mutations and reduce VAF. The IDH2 mutation might be a good predictor of veneclax sensitivity. A notable adverse response in the treatment phase of the regimen is severe infection induced by neutropenia.

Next Generation BTK Inhibitors in CLL: Evolving Challenges and New Opportunities

Ibrutinib revolutionized the CLL treatment approach and prognosis demonstrating its efficacy and safety even at extended follow-up. During the last few years, several next-generation inhibitors have been developed to overcome the occurrence of toxicity or resistance in patients on continuous treatment. In a head-to-head comparison of two phase III trials, both acalabrutinib and zanubrutinib demonstrated a lower incidence of adverse events in respect to ibrutinib. Nevertheless, resistance mutations remain a concern with continuous therapy and were demonstrated with both first- and next-generation covalent inhibitors. Reversible inhibitors showed efficacy independently of previous treatment and the presence of BTK mutations. Other strategies are currently under development in CLL, especially for high-risk patients, and include BTK inhibitor combinations with BCl2 inhibitors with or without anti-CD20 monoclonal antibodies. Finally, new mechanisms for BTK inhibition are under investigations in patients progressing with both covalent and non-covalent BTK and BCl2 inhibitors. Here we summarize and discuss results from main experiences on irreversible and reversable BTK inhibitors in CLL.

A phase 1b study of ibrutinib in combination with obinutuzumab in patients with relapsed or refractory chronic lymphocytic leukemia

This study investigated ibrutinib plus obinutuzumab in relapsed/refractory CLL, evaluating tolerability of 3 sequencing regimens as well as overall safety and efficacy. Fifty-two patients were initially randomized 1:1:1 to receive either obinutuzumab 1 month before ibrutinib initiation, ibrutinib 1 month prior to obinutuzumab initiation, or to start both drugs concomitantly. Higher rates of infusion-related reactions were observed with the first sequence, and only the latter 2 cohorts were expanded. Grade 4 hematologic toxicity was uncommon, and notable all-grade non-hematologic toxicities included bruising (58%), hypertension (46%), arthralgia (38%), diarrhea (37%), transaminitis (35%), atrial fibrillation (21%), and serious infection (17%). Best overall response rate was 96% (including 40% CR and 56% PR). Best rates of undetectable minimal residual disease in peripheral blood and bone marrow were 27% and 19%, respectively. With a median follow-up of 41.5 months, four-year progression-free and overall survival rates are 74% and 93%, respectively. Correlative studies demonstrated that serum CCL4 and CXCL13 levels were associated with clinical response, and BH3 profiling revealed increased BCL-2 and BCL-xL dependence in CLL cells from patients on treatment. Overall, ibrutinib plus obinutuzumab was highly active, with a manageable safety profile, supporting further investigation of this type of approach in relapsed/refractory CLL.

Novel combination approaches with targeted agents in frontline chronic lymphocytic leukemia

Targeted therapies have revolutionized the frontline treatment landscape for patients with chronic lymphocytic leukemia (CLL) and have largely displaced a reliance on chemoimmunotherapy when treating this disease. Multiple randomized trials have documented the efficacy of oral therapy with the Bruton tyrosine kinase inhibitors ibrutinib and acalabrutinib (and zanubrutinib, pending a supplemental new drug application in CLL), as well as BCL2 inhibition using venetoclax. In this review, the authors highlight novel therapeutic strategies for using these agents in combination, either as doublet therapy or as triplet therapy, with anti-CD20 antibodies. First, the current treatment landscape is outlined, and the data are reviewed for continuous and time-limited therapeutic approaches, which constitute the current standard of care. Then, more recent reports are described from phase 2 and 3 studies exploring different combination strategies of Bruton tyrosine kinase and BCL2 inhibition for treatment-naive patients. In addition, relevant differences are emphasized between patient characteristics (e.g., patient fitness and the presence of high-risk disease features) and study methodology (e.g., dosing schedule, randomization, and assessment of measurable residual disease) across trials. Finally, the authors revisit the currently available data for these approaches in the context of ongoing studies and future planned trials, evaluating their potential impact on the frontline treatment landscape for CLL in the years to come.

The path to venetoclax resistance is paved with mutations, metabolism, and more

Venetoclax is a B cell lymphoma 2 (BCL-2)-selective antagonist used to treat chronic lymphocytic leukemia (CLL) and acute myelogenous leukemia (AML). Although this has been a promising therapeutic option for these patients, many of these patients develop resistance and relapsed disease. Here, we summarize the emerging mechanisms of resistance to venetoclax treatment, discuss the promising combination strategies, and highlight the combinations that are currently in clinical trials. Efforts to understand mechanisms of resistance are critical to advance the development of new targeted therapeutic strategies and further our understanding of the biological functions of BCL-2 in tumor cells.

Microfluidic-based dynamic BH3 profiling predicts anticancer treatment efficacy

Precision medicine is starting to incorporate functional assays to evaluate anticancer agents on patient-isolated tissues or cells to select for the most effective. Among these new technologies, dynamic BH3 profiling (DBP) has emerged and extensively been used to predict treatment efficacy in different types of cancer. DBP uses synthetic BH3 peptides to measure early apoptotic events ('priming') and anticipate therapy-induced cell death leading to tumor elimination. This predictive functional assay presents multiple advantages but a critical limitation: the cell number requirement, that limits drug screening on patient samples, especially in solid tumors. To solve this problem, we developed an innovative microfluidic-based DBP (µDBP) device that overcomes tissue limitations on primary samples. We used microfluidic chips to generate a gradient of BIM BH3 peptide, compared it with the standard flow cytometry based DBP, and tested different anticancer treatments. We first examined this new technology's predictive capacity using gastrointestinal stromal tumor (GIST) cell lines, by comparing imatinib sensitive and resistant cells, and we could detect differences in apoptotic priming and anticipate cytotoxicity. We then validated µDBP on a refractory GIST patient sample and identified that the combination of dactolisib and venetoclax increased apoptotic priming. In summary, this new technology could represent an important advance for precision medicine by providing a fast, easy-to-use and scalable microfluidic device to perform DBP in situ as a routine assay to identify the best treatment for cancer patients.

Minimal residual disease-driven treatment intensification with sequential addition of ibrutinib to venetoclax in R/R CLL

Undetectable measurable residual disease (uMRD) is achievable in patients with chronic lymphocytic leukemia (CLL) with the BCL2-inhibitor venetoclax alone or combined with the Bruton's tyrosine kinase inhibitor ibrutinib. This phase 2, multicenter, MRD-driven study was designed to discontinue treatment upon reaching uMRD4 (<10-4) in patients with relapsed/refractory CLL receiving venetoclax monotherapy or after the addition of ibrutinib. Primary end point of the study was proportion of uMRD4 with venetoclax ± ibrutinib. Secondary end points were overall response rate, partial response, complete response, progression-free survival, duration of response, overall survival, and safety of venetoclax ± ibrutinib. Patients with uMRD4 at Cycle 12 Day 1 discontinued venetoclax. MRD+ patients added ibrutinib and continued both drugs up to Cycle 24 Day 28/uMRD4/progression/toxicity. After Cycle 24 Day 28, MRD+ patients continued ibrutinib. Thirty-eight patients (29% with TP53 aberrations; 79% with unmutated IGHV) started venetoclax. Overall response rate with venetoclax was 36 (95%) of 38 patients (20 complete; 16 partial response). Seventeen patients (45%) with uMRD4 at Cycle 12 Day 1 discontinued venetoclax. Nineteen (55%) MRD+ subjects added ibrutinib. After a median of 7 months (range, 3-10 months) of combined treatment, 16 (84%) of 19 achieved uMRD4, thus stopping both drugs. Two MRD+ patients at Cycle 24 Day 28 continued ibrutinib until progression/toxicity. After a median follow-up of 36.5 months, median progression-free survival was not reached; 10 patients progressed (4 restarted venetoclax, 3 without treatment need, 2 developed Richter transformation, and 1 dropped out). Seven (22%) of 32 patients remain uMRD4 after 3 years of follow-up. Neutropenia was the most frequent grade 3 to 4 adverse event; no grade 5 events occurred on study. This sequential MRD-guided approach led to uMRD4 in 33 (87%) of 38 patients, with venetoclax monotherapy or combined with ibrutinib, delivering treatment combination only in a fraction, and ultimately identifying the few patients benefiting from continuous therapy. This trial was registered at www.clinicaltrials.gov as # NCT04754035.

Preclinical evaluation of combination nemtabrutinib and venetoclax in chronic lymphocytic leukemia

Inhibitors of B cell receptor (BCR) signaling such as the Bruton's tyrosine kinase (BTK) inhibitors are effective therapeutics for chronic lymphocytic leukemia (CLL). The first-in-class covalent BTK inhibitor, ibrutinib, produces durable responses in most CLL patients; however, complete responses are only observed in a minority of patients. B cell lymphoma 2 (BCL2), an anti-apoptotic protein that contributes to CLL cell survival, has also been investigated as a therapeutic target. The BCL2 inhibitor venetoclax is effective in patients with CLL and can produce undetectable minimal residual disease, allowing discontinuation of therapy. In combination, ibrutinib and venetoclax have shown preclinical synergy and clinical efficacy. Nemtabrutinib is a next generation, reversible inhibitor of BTK that potently inhibits BCR signaling in treatment-naïve and ibrutinib-refractory CLL cells ex vivo. The clinical efficacy of combining BTK inhibitors with BCL2 inhibitors motivated us to evaluate the novel combination of nemtabrutinib and venetoclax. In vitro studies show that nemtabrutinib and venetoclax are not antagonistic to each other. In an adoptive transfer CLL mouse model, mice treated with nemtabrutinib and venetoclax had prolonged survival compared to mice treated with ibrutinib and venetoclax. Our preclinical studies further validate the combination of BTK inhibitors with venetoclax and justify further investigation of combining nemtabrutinib with venetoclax in CLL.

Effective Tumor Debulking with Ibrutinib Before Initiation of Venetoclax: Results from the CAPTIVATE Minimal Residual Disease and Fixed-Duration Cohorts

PURPOSE

The phase II CAPTIVATE study investigated first-line treatment with ibrutinib plus venetoclax for chronic lymphocytic leukemia in two cohorts: minimal residual disease (MRD)-guided randomized treatment discontinuation (MRD cohort) and fixed duration (FD cohort). We report tumor debulking and tumor lysis syndrome (TLS) risk category reduction with three cycles of single-agent ibrutinib lead-in before initiation of venetoclax using pooled data from the MRD and FD cohorts.

PATIENTS AND METHODS

In both cohorts, patients initially received three cycles of ibrutinib 420 mg/day then 12 cycles of ibrutinib plus venetoclax (5-week ramp-up to 400 mg/day).

RESULTS

In the total population (N = 323), the following decreases from baseline to after ibrutinib lead-in were observed: percentage of patients with a lymph node diameter ≥5 cm decreased from 31% to 4%, with absolute lymphocyte count ≥25 × 109/L from 76% to 65%, with high tumor burden category for TLS risk from 23% to 2%, and with an indication for hospitalization (high TLS risk, or medium TLS risk and creatinine clearance <80 mL/minute) from 43% to 18%. Laboratory TLS per Howard criteria occurred in one patient; no clinical TLS was observed.

CONCLUSIONS

Three cycles of ibrutinib lead-in before venetoclax initiation provides effective tumor debulking, decreases the TLS risk category and reduces the need for hospitalization for intensive monitoring for TLS.

MAJIC: a phase III trial of acalabrutinib + venetoclax versus venetoclax + obinutuzumab in previously untreated chronic lymphocytic leukemia or small lymphocytic lymphoma

Here we describe the rationale and design of MAJIC, a phase III, prospective, multicenter, randomized trial comparing the combination of the BTK inhibitor acalabrutinib plus the BCL2 inhibitor venetoclax versus the combination of venetoclax plus obinutuzumab as frontline treatment for chronic lymphocytic leukemia or small lymphocytic lymphoma. In both treatment arms, disease response (assessed by International Workshop on Chronic Lymphocytic Leukemia criteria) and minimal residual disease will be used to guide therapy duration, with all patients ultimately discontinuing treatment after a maximum of 2 years. The primary end point is progression-free survival. Key secondary end points include rates of undetectable minimal residual disease, overall response and overall survival. This study will address key unanswered questions in frontline chronic lymphocytic leukemia/small lymphocytic lymphoma therapy by investigating the optimal duration of finite treatment and identifying the optimal venetoclax doublet regimen.

Obinutuzumab, acalabrutinib, and venetoclax, after an optional debulking with bendamustine in relapsed or refractory chronic lymphocytic leukaemia (CLL2-BAAG): a multicentre, open-label, phase 2 trial

BACKGROUND

Although BTK inhibitors provide long-term disease-control in patients with chronic lymphocytic leukaemia, they need to be combined with BCL2 inhibitors or antibodies to achieve deep responses with undetectable minimal residual disease (uMRD), which allows for time-limited treatment. This trial aims to evaluate the triple combination of obinutuzumab, acalabrutinib, and venetoclax after an optional debulking with bendamustine.

METHODS

This multicentre, open-label, investigator-initiated, phase 2 study evaluates a sequential treatment consisting of a debulking with two cycles of bendamustine for patients with a higher tumour load (70 mg/m² intravenously on days 1 and 2, repeated after 28 days), followed by an induction and a maintenance with obinutuzumab (1000 mg intravenously on days 1-2, 8, and 15 of the first induction cycle, every 4 weeks in induction cycles 2-6 and every 12 weeks in the maintenance phase), acalabrutinib (100 mg orally twice daily continuously from induction cycle 2 day 1 onwards) and venetoclax (starting in induction cycle 3 with 20 mg per day with a weekly dose ramp-up over 5 weeks to the target dose of 400 mg per day). Eligible patients were aged 18 years or older with an ECOG performance score 0-2 and had relapsed or refractory chronic lymphocytic leukaemia requiring treatment according to the 2018 International Workshop on Chronic Lymphocytic Leukemia criteria. The primary endpoint was uMRD (<10^-4) in peripheral blood at the end of induction treatment assessed centrally at the final restaging, 12 weeks after the start of the last induction cycle. As per protocol, all patients with more than two induction cycles were included in the analyses. This study is registered with ClinicalTrials.gov, number NCT03787264, and is ongoing.

FINDINGS

Between Jan 14, 2019, and June 25, 2020, 45 evaluable patients with relapsed or refractory chronic lymphocytic leukaemia were enrolled; 13 (29%) were female, 32 (71%) were male, 21 (47%) had already received a targeted agent, and 14 (32%) had del(17)(p13.1) or TP53 mutation. Ethnicity-race data was not collected. At data cutoff (Feb 25, 2021), all patients had completed the induction treatment. 34 patients (76%; 95% CI 61-87, p=0·26) had uMRD in peripheral blood after 6 months of triple therapy. Until data cutoff, 32 (71%) patients started maintenance and nine (28%) were able to stop with uMRD. After a median observation time of 13·8 months (IQR 10·4-18·4), there were two (4%) Richter transformations, but no progressions and no deaths observed. The most common adverse events of grade 3 and 4 during the entire treatment were thrombocytopenia and neutropenia (12 [27%] of 45 patients each), tumour lysis syndrome and infections (five [11%] of 45 patients each, grade 3 adverse events only), infusion-associated reactions (four [9%] of 45 patients) and anaemia (four [9%] of 45 patients).

INTERPRETATION

With 76% of patients achieving uMRD in peripheral blood, this trial did not reach the prespecified activity threshold. Triple therapy with obinutuzumab, acalabrutinib, and venetoclax after an optional debulking with bendamustine regimen requires further evaluation in larger trials to define its value compared with double treatment with a BTK or BCL2 inhibitor combined with obinutuzumab or a combination of the two oral targeted drugs. Until these trials show a clear benefit, the use of the triple combination in routine practice cannot be recommended.

FUNDING

Acerta, AstraZeneca, F Hoffmann-La Roche, and AbbVie.

Tipping the balance: toward rational combination therapies to overcome venetoclax resistance in mantle cell lymphoma

Mantle cell lymphoma (MCL), an aggressive, but incurable B-cell lymphoma, is genetically characterized by the t(11;14) translocation, resulting in the overexpression of Cyclin D1. In addition, deregulation of the B-cell lymphoma-2 (BCL-2) family proteins BCL-2, B-cell lymphoma-extra large (BCL-XL), and myeloid cell leukemia-1 (MCL-1) is highly common in MCL. This renders these BCL-2 family members attractive targets for therapy; indeed, the BCL-2 inhibitor venetoclax (ABT-199), which already received FDA approval for the treatment of chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML), shows promising results in early clinical trials for MCL. However, a significant subset of patients show primary resistance or will develop resistance upon prolonged treatment. Here, we describe the underlying mechanisms of venetoclax resistance in MCL, such as upregulation of BCL-XL or MCL-1, and the recent (clinical) progress in the development of inhibitors for these BCL-2 family members, followed by the transcriptional and (post-)translational (dys)regulation of the BCL-2 family proteins, including the role of the lymphoid organ microenvironment. Based upon these insights, we discuss how rational combinations of venetoclax with other therapies can be exploited to prevent or overcome venetoclax resistance and improve MCL patient outcome.

Fixed-Duration Ibrutinib-Venetoclax in Patients with Chronic Lymphocytic Leukemia and Comorbidities

BACKGROUND: GLOW is a phase 3 trial evaluating the efficacy and safety of ibrutinib-venetoclax in older patients and/or those with comorbidities with previously untreated chronic lymphocytic leukemia (CLL). METHODS: We randomly assigned (1:1) patients 65 years of age or older or those 18 to 64 years of age who also had a Cumulative Illness Rating Scale (CIRS) score greater than 6 (CIRS scores range from 0 to 56, with higher scores indicating more impaired function of organ systems) or creatinine clearance of less than 70 ml/min, to ibrutinib-venetoclax (3 cycles ibrutinib lead-in, then 12 cycles ibrutinib-venetoclax) or chlorambucil-obinutuzumab (6 cycles). The primary end point was progression-free survival (PFS) assessed by an independent review committee. Secondary end points included undetectable minimal residual disease (uMRD), response rates, and safety. RESULTS: This study enrolled 211 patients, with 106 randomly assigned to ibrutinib-venetoclax and 105 to chlorambucil-obinutuzumab. With a median follow-up of 27.7 months, there were 22 PFS events for ibrutinib-venetoclax and 67 events for chlorambucil-obinutuzumab. PFS was significantly longer for ibrutinib-venetoclax than for chlorambucil-obinutuzumab (hazard ratio, 0.216; 95% confidence interval [CI], 0.131 to 0.357; P<0.001). The improvement in PFS with ibrutinib-venetoclax was consistent across predefined subgroups, including patients 65 years of age or older or with a CIRS score greater than 6. The best uMRD rate in bone marrow by next-generation sequencing was significantly higher for ibrutinib-venetoclax (55.7%) than for chlorambucil-obinutuzumab (21.0%; P<0.001). The proportion of patients with sustained uMRD in peripheral blood from 3 to 12 months after end of treatment was 84.5% for ibrutinib-venetoclax and 29.3% for chlorambucil-obinutuzumab. Four patients treated with ibrutinib-venetoclax required subsequent therapy compared with 27 patients receiving chlorambucil-obinutuzumab (hazard ratio, 0.143; 95% CI, 0.050 to 0.410). Adverse events grade 3 or greater occurred for 80 (75.5%) and 73 (69.5%) patients receiving ibrutinib-venetoclax and chlorambucil-obinutuzumab, respectively, with neutropenia being most common in both arms (37 [34.9%] and 52 [49.5%]). There were 11 (10.4%) and 12 (11.4%) all-cause deaths in the ibrutinib-venetoclax and chlorambucil-obinutuzumab arms, respectively. CONCLUSIONS: Ibrutinib-venetoclax, an all-oral, once-daily, fixed-duration combination, demonstrated superior PFS and deeper and better sustained responses versus chlorambucil-obinutuzumab as first-line CLL treatment in older patients and/or those with comorbidities. (Funded by Janssen Research & Development, LLC, and Pharmacyclics; ClinicalTrials.gov number, NCT03462719.)

Fixed-duration ibrutinib plus venetoclax for first-line treatment of CLL: primary analysis of the CAPTIVATE FD cohort

CAPTIVATE (NCT02910583) is an international phase 2 study in patients aged ≤70 years with previously untreated chronic lymphocytic leukemia (CLL). Results from the cohort investigating fixed-duration (FD) treatment with ibrutinib plus venetoclax are reported. Patients received 3 cycles of ibrutinib lead-in then 12 cycles of ibrutinib plus venetoclax (oral ibrutinib [420 mg/d]; oral venetoclax [5-week ramp-up to 400 mg/d]). The primary endpoint was complete response (CR) rate. Hypothesis testing was performed for patients without del(17p) with prespecified analyses in all treated patients. Secondary endpoints included undetectable minimal residual disease (uMRD) rates, progression-free survival (PFS), overall survival (OS), and safety. Of the 159 patients enrolled and treated, 136 were without del(17p). The median time on study was 27.9 months, and 92% of patients completed all planned treatment. The primary endpoint was met, with a CR rate of 56% (95% confidence interval [CI], 48-64) in patients without del(17p), significantly higher than the prespecified 37% minimum rate (P < .0001). In the all-treated population, CR rate was 55% (95% CI, 48-63); best uMRD rates were 77% (peripheral blood [PB]) and 60% (bone marrow [BM]); 24-month PFS and OS rates were 95% and 98%, respectively. At baseline, 21% of patients were in the high tumor burden category for tumor lysis syndrome (TLS) risk; after ibrutinib lead-in, only 1% remained in this category. The most common grade ≥3 adverse events (AEs) were neutropenia (33%) and hypertension (6%). First-line ibrutinib plus venetoclax represents the first all-oral, once-daily, chemotherapy-free FD regimen for patients with CLL. FD ibrutinib plus venetoclax achieved deep, durable responses and promising PFS, including in patients with high-risk features.

Progress in understanding the mechanisms of resistance to BCL-2 inhibitors

Venetoclax is a new type of BH3 mimetic compound that can target the binding site in the BCL-2 protein and induce apoptosis in cancer cells by stimulating the mitochondrial apoptotic pathway. Venetoclax is especially used to treat haematological malignancies. However, with the recent expansion in the applications of venetoclax, some cases of venetoclax resistance have appeared, posing a major problem in clinical treatment. In this article, we explored several common mechanisms of venetoclax resistance. Increased expression of the antiapoptotic proteins MCL-1 and BCL-XL plays a key role in conferring cellular resistance to venetoclax. These proteins can bind to the released BIM in the context of venetoclax binding to BCL-2 and thus continue to inhibit mitochondrial apoptosis. Structural mutations in BCL-2 family proteins caused by genetic instability lead to decreased affinity for venetoclax and inhibit the intrinsic apoptosis pathway. Mutation or deletion of the BAX gene renders the BAX protein unable to anchor to the outer mitochondrial membrane to form pores. In addition to changes in BCL-2 family genes, mutations in other oncogenes can also confer resistance to apoptosis induced by venetoclax. TP53 mutations and the expansion of FLT3-ITD promote the expression of antiapoptotic proteins MCL-1 and BCL-XL through multiple signalling pathways, and interfere with venetoclax-mediated apoptosis processes depending on their affinity for BH3-only proteins. Finally, the level of mitochondrial oxidative phosphorylation in venetoclax-resistant leukaemia stem cells is highly abnormal. Not only the metabolic pathways but also the levels of important metabolic components are changed, and all of these alterations antagonize the venetoclax-mediated inhibition of energy metabolism and promote the survival and proliferation of leukaemia stem cells. In addition, venetoclax can change mitochondrial morphology independent of the BCL-2 protein family, leading to mitochondrial dysfunction. However, mitochondria resistant to venetoclax antagonize this effect, forming tighter mitochondrial cristae, which provide more energy for cell survival.

Adapted to Survive: Targeting Cancer Cells with BH3 Mimetics

A hallmark of cancer is cell death evasion, underlying suboptimal responses to chemotherapy, targeted agents, and immunotherapies. The approval of the antiapoptotic BCL2 antagonist venetoclax has finally validated the potential of targeting apoptotic pathways in patients with cancer. Nevertheless, pharmacologic modulators of cell death have shown markedly varied responses in preclinical and clinical studies. Here, we review emerging concepts in the use of this class of therapies. Building on these observations, we propose that treatment-induced changes in apoptotic dependency, rather than pretreatment dependencies, will need to be recognized and targeted to realize the precise deployment of these new pharmacologic agents.

SIGNIFICANCE

Targeting antiapoptotic family members has proven efficacious and tolerable in some cancers, but responses are infrequent, particularly for patients with solid tumors. Biomarkers to aid patient selection have been lacking. Precision functional approaches that overcome adaptive resistance to these compounds could drive durable responses to chemotherapy, targeted therapy, and immunotherapies.

MEK and MCL-1 sequential inhibition synergize to enhance rhabdomyosarcoma treatment

Targeted agents have emerged as promising molecules for cancer treatment, but most of them fail to achieve complete tumor regression or attain durable remissions due to tumor adaptations. We used dynamic BH3 profiling to identify targeted agents effectiveness and anti-apoptotic adaptations upon targeted treatment in rhabdomyosarcoma. We focused on studying the use of BH3 mimetics to specifically inhibit pro-survival BCL-2 family proteins, overwhelm resistance to therapy and prevent relapse. We observed that the MEK1/2 inhibitor trametinib rapidly depleted the pro-apoptotic protein NOXA, thus increasing MCL-1 availability. Indeed, we found that the MCL-1 inhibitor S63845 synergistically enhanced trametinib cytotoxicity in rhabdomyosarcoma cells in vitro and in vivo. In conclusion, our findings indicate that the combination of a BH3 mimetic targeting MCL-1 with trametinib improves efficiency on rhabdomyosarcoma by blocking tumor adaptation to treatment.

Combining BTK inhibitors with BCL2 inhibitors for treating chronic lymphocytic leukemia and mantle cell lymphoma

The advent of BTK inhibitors has changed the treatment of patients with chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). The first-in-class BTK inhibitor ibrutinib has shown remarkable therapeutic effects and manageable toxicities in multiple clinical trials. The second-generation BTK inhibitors, including acalabrutinib and zanubrutinib, also show remarkable efficacies. However, using BTK inhibitors as monotherapies requires continuous treatment. Resistance to BTK inhibitors and severe side effects unavoidably occur during BTK inhibitor monotherapy, frequently resulting in treatment failure. The addition of the BCL2 inhibitor venetoclax to BTK inhibitor may improve the therapeutic effects and result in deeper responses, providing a potential fixed-duration treatment, especially for patients with CLL. In this review, by focusing on CLL and MCL, we discussed the rationale for the combinational use and summarized the current data on the combinations of BTK inhibitors and venetoclax in patients with CLL and MCL.

The mitochondrial anti-apoptotic dependencies of hematologic malignancies: from disease biology to advances in precision medicine

Mitochondria are critical organelles in the regulation of intrinsic apoptosis. As a general feature of blood cancers, different antiapoptotic members of the BCL-2 protein family localize at the outer mitochondrial membrane to sequester variable amounts of proapoptotic activators, and hence protect cancer cells from death induction. However, the impact of distinct anti-apoptotic members on apoptosis prevention, a concept termed anti-apoptotic dependence, differs remarkably across disease entities. Over the last two decades, several genetic and functional methodologies have been established to uncover the anti-apoptotic dependencies of the majority of blood cancers, inspiring the development of a new class of small molecules called BH3 mimetics. In this review, we highlight the rationale of targeting mitochondrial apoptosis in hematology, and provide a comprehensive map of the anti-apoptotic dependencies that are currently guiding novel therapeutic strategies. Cell-extrinsic and -intrinsic mechanisms conferring resistance to BH3 mimetics are also examined, with insights on potential strategies to overcome them. Finally, we discuss how the field of mitochondrial apoptosis might be complemented with other dimensions of precision medicine for more successful treatment of 'highly complex' hematologic malignancies.

New Treatment Options for Newly-Diagnosed and Relapsed Chronic Lymphocytic Leukemia

OPINION STATEMENT

The better understanding of the biology of chronic lymphocytic leukemia (CLL) gained over the past decade has led to the development and introduction of several targeted drugs, with an demonstrable improvement in the prognosis for this currently incurable condition. Currently, Bruton's tyrosine kinase (BTK) inhibitors, phosphoinositide 3-kinase (PI3K) inhibitors, venetoclax, and CD20 monoclonal antibodies are the key elements in the treatment of both previously untreated and relapsed/refractory CLL patients. Ibrutinib was the first BTK inhibitor approved for clinical use, and showed excellent efficacy and an acceptable safety profile. Following this, the better-tolerated second-generation irreversible BTK inhibitors acalabrutinib and zanubrutinib have been introduced for the treatment of lymphoid malignancies, and acalabrutinib was approved for CLL. When used as single drugs, BTK inhibitors are given continuously until unacceptable toxicity or disease progression; however, when combined with venetoclax and/or CD20 antibodies, they induce deeper response and can be given for a limited time. Recently, promising new reversible BTK inhibitors pirtobrutinib and nemtabrutinib were discovered, and these seem to be more active and better tolerated than their irreversible predecessors. However, they are in an early phase of development and are not currently approved for CLL. The phosphatidylinositol 3-kinase (PI3K) inhibitors idelalisib and duvelisib are highly effective in patients with relapsed CLL, including high-risk disease. The major limitations for their use are adverse events, mostly of autoimmune origin (hepatitis, enteritis/colitis, and pneumonitis). Otherwise, cellular therapies like allogeneic hematopoietic stem cell transplantation and chimeric antigen receptor (CAR) T cells and bispecific monoclonal antibodies offer promise for patients who have failed BTK inhibitors and venetoclax treatment. In the coming years, it is likely that novel targeted therapies will replace immunochemotherapy regimens in most patients.