Recognizing Unmet Need in the Era of Targeted Therapy for CLL/SLL: "What's Past Is Prologue" (Shakespeare)

Real-world patterns and sequences of targeted therapy use in chronic lymphocytic leukemia and small lymphocytic lymphoma in the United States: a longitudinal study

With increasing focus on novel targeted therapies for chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), this longitudinal claims-based study evaluated real-world CLL/SLL treatment sequences, particularly sequential targeted therapy. Among patients with first-line (1 L) treatment in 2014-2017 (N = 2,612; median follow-up = 3 years), the most common 1 L treatment was chemoimmunotherapy (CIT; 44.6%), followed by CD20 (25.2%) and Bruton's tyrosine kinase inhibitors (BTKi; 21.7%). Among those with 1 L in 2018-2021 (N = 4,534; median follow-up = 1 year), these were BTKi (45.5%), CD20 (20.4%), CIT (17.5%), and B-cell lymphoma 2 inhibitor (8.3%). In 2014-2017, the proportion of patients receiving sequential targeted therapy in the first 2 LOTs was 11.2% (80.2% was BTKi→BTKi); in 2018-2021, this proportion was 34.3% (66.4% was BTKi→BTKi). Over time, there was a substantial increase in targeted therapy use in 1 L and sequential targeted therapy, particularly with BTKi→BTKi. Future studies should assess clinical outcomes to determine optimal sequences for CLL/SLL and reasons for restarting BTKi.

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.

Non-Covalent Bruton's Tyrosine Kinase Inhibitors in the Treatment of Chronic Lymphocytic Leukemia

Covalent Bruton's tyrosine kinase inhibitors (cBTKi) have led to a paradigm shift in the treatment of chronic lymphocytic leukemia (CLL). These targeted oral therapies are administered as standard treatments in both the front-line and relapsed and/or refractory settings. Given their administration as a continuous therapy with a "treat-to-progression" strategy, limitations of their use include discontinuation due to toxicity or from progression of the disease. Non-covalent Bruton's tyrosine kinase inhibitors (ncBTKi) distinguish themselves by binding reversibly to the BTK target, which may address the limitations of toxicity and acquired resistance seen with cBTKi. Several ncBTKis have been studied preclinically and in clinical trials, including pirtobrutinib and nemtabrutinib. Pirtobrutinib, which is now FDA approved for relapsed and/or refractory mantle cell lymphoma (MCL), has shown outstanding safety and preliminary efficacy in CLL in phase 1 and 2 clinical trials, with phase 3 trials underway. This agent may fill an unmet medical need for CLL patients requiring treatment after a cBTKi. Pirtobrutinib is particularly promising for the treatment of "double exposed" CLL, defined as CLL requiring treatment after both a cBTKi and venetoclax. Some patients have now developedacquired resistance to pirtobrutinib, and resistance mechanisms (including novel acquired mutations in BTK outside of the C481 position) have been recently described. Further study regarding the mechanisms of resistance to pirtobrutinib in patients without prior cBTKi exposure, as well as the potential for cross-resistance between cBTKi and ncBTKis, may be important to help inform where ncBTKis will ultimately fit in the treatment sequencing paradigm for CLL. An emerging clinical challenge is the treatment of CLL after ncBTKi discontinuation. Novel therapeutic strategies are being investigated to address the treatment of patients following disease progression on ncBTKis. Such strategies include novel agents (BTK degraders, bispecific antibody therapy, CAR T-cell therapy, PKC-beta inhibitors) as well as combination approaches incorporating a ncBTKi (e.g., pirtobrutinib and venetoclax) that may help overcome this acquired resistance.

Zanubrutinib or Ibrutinib in Relapsed or Refractory Chronic Lymphocytic Leukemia

BACKGROUND

In a multinational, phase 3, head-to-head trial, ibrutinib, a Bruton's tyrosine kinase (BTK) inhibitor, was compared with zanubrutinib, a BTK inhibitor with greater specificity, as treatment for relapsed or refractory chronic lymphocytic leukemia (CLL) or small lymphocytic lymphoma (SLL). In prespecified interim analyses, zanubrutinib was superior to ibrutinib with respect to overall response (the primary end point). Data from the final analysis of progression-free survival are now available.

METHODS

We randomly assigned, in a 1:1 ratio, patients with relapsed or refractory CLL or SLL who had received at least one previous course of therapy to receive zanubrutinib or ibrutinib until the occurrence of disease progression or unacceptable toxic effects. In this final analysis, progression-free survival (a key secondary end point) was assessed with the use of a hierarchical testing strategy to determine whether zanubrutinib was noninferior to ibrutinib. If noninferiority was established, the superiority of zanubrutinib was assessed and claimed if the two-sided P value was less than 0.05.

RESULTS

At a median follow-up of 29.6 months, zanubrutinib was found to be superior to ibrutinib with respect to progression-free survival among 652 patients (hazard ratio for disease progression or death, 0.65; 95% confidence interval, [CI], 0.49 to 0.86; P = 0.002), as assessed by the investigators; the results were similar to those as assessed by an independent-review committee. At 24 months, the investigator-assessed rates of progression-free survival were 78.4% in the zanubrutinib group and 65.9% in the ibrutinib group. Among patients with a 17p deletion, a TP53 mutation, or both, those who received zanubrutinib had longer progression-free survival than those who received ibrutinib (hazard ratio for disease progression or death, 0.53; 95% CI, 0.31 to 0.88); progression-free survival across other major subgroups consistently favored zanubrutinib. The percentage of patients with an overall response was higher in the zanubrutinib group than in the ibrutinib group. The safety profile of zanubrutinib was better than that of ibrutinib, with fewer adverse events leading to treatment discontinuation and fewer cardiac events, including fewer cardiac events leading to treatment discontinuation or death.

CONCLUSIONS

In patients with relapsed or refractory CLL or SLL, progression-free survival was significantly longer among patients who received zanubrutinib than among those who received ibrutinib, and zanubrutinib was associated with fewer cardiac adverse events. (Funded by BeiGene; ALPINE ClinicalTrials.gov number, NCT03734016.).

Novel therapies and combinations in CLL refractory to BTK inhibitors and venetoclax

Patients with chronic lymphocytic leukemia (CLL) refractory to covalent BTK and BCL2 inhibitors have a new unmet clinical need. Standard treatment options are able to obtain only limited and short-lasting disease control associated with reduced overall survival, and thus these patients have become ideal candidates for enrollment in clinical trials. Favorable results have been obtained with the use of noncovalent BTK inhibitors (roughly 70% overall response rate regardless of the actual resistance or intolerance to previous covalent BTK inhibitors) and anti-CD19 chimeric antigen receptor (CAR) T-cell therapy (with complete responses in up to 45% of cases and an undetectable measurable residual disease rate of 65% in the bone marrow). These 2 approaches should be considered valid options in this setting, although not yet approved. For young fit patients achieving remissions with salvage treatments, the option of allogeneic stem cell transplantation should be discussed as the outcome appears to be unaffected by number and type of previous targeted agents. Novel treatment strategies interfering with different mechanisms of CLL cell survival and proliferation are warranted, including small molecules with novel targets (eg, CDK9, MCL1, ERK inhibitors), CAR T cells targeting different antigens, CAR natural killer cells, or bispecific antibodies.

Management of relapsed/refractory Chronic Lymphocytic Leukemia

The therapeutic landscape for chronic lymphocytic leukemia (CLL) has changed dramatically over the past decade as our understanding of the biology of CLL has advanced, allowing the development of oral therapies targeting key drivers of CLL. Currently, inhibitors of Bruton's Tyrosine Kinase and the BH3 mimetic venetoclax are standards of care for both frontline and relapsed/refractory CLL. Sequencing of available therapies, therefore, has become a major challenge of therapy. In this review, we will focus on the current landscape for the treatment of relapsed/refractory CLL. We will also discuss important considerations when sequencing these available treatments. The recent advances in this disease are significant steps forward, and raise new questions of how these available drugs should be given as well as how we can continue to improve the treatment of CLL.

Cellular Therapy in High-Risk Relapsed/Refractory Chronic Lymphocytic Leukemia and Richter Syndrome

Despite the development of highly effective, targeted inhibitors of B-cell proliferation and anti-apoptotic pathways in chronic lymphocytic leukemia (CLL), these treatments are not curative, and many patients will develop either intolerance or resistance to these treatments. Transformation of CLL to high-grade lymphoma—the so-called Richter syndrome (RS)—remains a highly chemoimmunotherapy-resistant disease, with the transformation occurring following targeted inhibitors for CLL treatment being particularly adverse. In light of this, cellular therapy in the form of allogenic stem cell transplantation and chimeric antigen receptor T-cell therapy continues to be explored in these entities. We reviewed the current literature assessing these treatment modalities in both high-risk CLL and RS. We also discussed their current limitations and place in treatment algorithms.