BACKGROUND The treatment of relapsed chronic lymphocytic leukemia (CLL) has resulted in few durable remissions. Bruton's tyrosine kinase (BTK), an essential component of B-cell–receptor signaling, mediates interactions with the tumor microenvironment and promotes the survival and proliferation of CLL cells. METHODS We conducted a phase 1b–2 multicenter study to assess the safety, efficacy, pharmacokinetics, and pharmacodynamics of ibrutinib (PCI-32765), a first-in-class, oral covalent inhibitor of BTK designed for treatment of B-cell cancers, in patients with relapsed or refractory CLL or small lymphocytic lymphoma. A total of 85 patients, the majority of whom were considered to have high-risk disease, received ibrutinib orally once daily; 51 received 420 mg, and 34 received 840 mg. RESULTS Toxic effects were predominantly grade 1 or 2 and included transient diarrhea, fatigue, and upper respiratory tract infection; thus, patients could receive extended treatment with minimal hematologic toxic effects. The overall response rate was the same in the group that received 420 mg and the group that received 840 mg (71%), and an additional 20% and 15% of patients in the respective groups had a partial response with lymphocytosis. The response was independent of clinical and genomic risk factors present before treatment, including advanced-stage disease, the number of previous therapies, and the 17p13.1 deletion. At 26 months, the estimated progression-free survival rate was 75% and the rate of overall survival was 83%. CONCLUSIONS Ibrutinib was associated with a high frequency of durable remissions in patients with relapsed or refractory CLL and small lymphocytic lymphoma, including patients with high-risk genetic lesions. (Funded by Pharmacyclics and others; ClinicalTrials.gov number, NCT01105247.)

BACKGROUND Ibrutinib is an irreversible inhibitor of Bruton’s tyrosine kinase (BTK) and is effective in chronic lymphocytic leukemia (CLL). Resistance to irreversible kinase inhibitors and resistance associated with BTK inhibition have not been characterized. Although only a small proportion of patients have had a relapse during ibrutinib therapy, an understanding of resistance mechanisms is important. We evaluated patients with relapsed disease to identify mutations that may mediate ibrutinib resistance. METHODS We performed whole-exome sequencing at baseline and the time of relapse on samples from six patients with acquired resistance to ibrutinib therapy. We then performed functional analysis of identified mutations. In addition, we performed Ion Torrent sequencing for identified resistance mutations on samples from nine patients with prolonged lymphocytosis. RESULTS We identified a cysteine-to-serine mutation in BTK at the binding site of ibrutinib in five patients and identified three distinct mutations in PLCγ2 in two patients. Functional analysis showed that the C481S mutation of BTK results in a protein that is only reversibly inhibited by ibrutinib. The R665W and L845F mutations in PLCγ2 are both potentially gain-of-function mutations that lead to autonomous B-cell–receptor activity. These mutations were not found in any of the patients with prolonged lymphocytosis who were taking ibrutinib. CONCLUSIONS Resistance to the irreversible BTK inhibitor ibrutinib often involves mutation of a cysteine residue where ibrutinib binding occurs. This finding, combined with two additional mutations in PLCγ2 that are immediately downstream of BTK, underscores the importance of the B-cell–receptor pathway in the mechanism of action of ibrutinib in CLL. (Funded by the National Cancer Institute and others.)

Background Irreversible inhibition of Bruton tyrosine kinase (Btk) by ibrutinib represents a significant therapeutic advance for chronic lymphocytic leukemia (CLL). However, ibrutinib also irreversibly inhibits alternative kinase targets, which potentially compromise its therapeutic index. Acalabrutinib (ACP-196) is a more selective irreversible Btk inhibitor specifically designed to improve upon the safety and efficacy of first generation Btk inhibitors. Methods Sixty-one patients with relapsed CLL were treated in a phase 1–2 multicenter study designed to assess the safety, efficacy, pharmacokinetics and pharmacodynamics of oral acalabrutinib. Patients were continuously treated with acalabrutinib 100 to 400 mg once daily in the dose-escalation portion of the study, and 100 mg twice daily in the expansion portion. Results Patient demographics include a median age of 62 years; median of 3 prior therapies; 31% del(17)(p13.1) and 75% unmutated immunoglobulin heavy chain variable genes. No dose-limiting toxicities occurred. The most common adverse events observed were headache (43%), diarrhea (39%) and increased weight (26%). Most adverse events were Grade 1–2. At a median follow-up of 14.3 months, the best overall response rate was 95%, including 85% partial response, 10% partial response with lymphocytosis and 5% stable disease. In patients with del(17)(p13.1), the best overall response was 100%. No cases of Richter’s transformation and only 1 CLL progression have occurred. Conclusions Acalabrutinib is a highly selective Btk inhibitor that provides effective and well tolerated treatment for patients with relapsed CLL, including those with del(17)(p13.1).

Key Points Ibrutinib is the first clinically viable irreversible ITK inhibitor. Ibrutinib inhibits the formation of Th2 but not Th1 immunity.

B-cell receptor (BCR) signaling is aberrantly activated in chronic lymphocytic leukemia (CLL). Bruton tyrosine kinase (BTK) is essential to BCR signaling and in IntroductionChronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia with an immunophenotype expressing the T-cell marker CD5 together with CD19, CD20, CD23, and dim-surface immunoglobulin. 1 Although immunophenotypically similar to the normal B1 lymphocytes, CLL cells have a distinct mRNA gene expression profile that most approximates a postgerminal memory B cell. 2 For many years CLL has been viewed as a nonproliferating leukemia based on the nonproliferating blood compartment; however, as with normal B cells, it has come to be recognized that CLL cell proliferation probably occurs in sites where microenvironmental stimulation occurs such as the lymph nodes and spleen. In such sites, proliferation centers are observed with a high proportion of dividing CLL cells expressing survivin that are often surrounded by either T cells or accessory stromal cells capable of providing cytokine costimulation. 3,4 Studies administering heavy water allow accurate measurement of all body compartments of CLL and assess the birth rate of CLL tumor cells in vivo. 5 These studies have demonstrated a broad range of proliferation of CLL cells that varies based on disease state and also immunoglobulin heavy chain variable (IVGH) mutational status. 5,6 In particular, a higher tumor birth rate is noted in CLL patients with IVGH unmutated disease and ZAP-70 expression. Multiple studies have documented evidence of enhanced B-cell receptor (BCR) signaling in patients with IVGH unmutated disease or those with increased ZAP-70 expression. [7][8][9] Thus, accessory cytokines, cell-cell contact in the microenvironment, and also BCR-signaling coupled to B-cell proliferation appear sentinel to CLL progression and pathogenesis.While understanding of CLL biology has improved dramatically, until very recently integration of these findings to treatment interventions has been lacking. Specifically, treatment has included alkylators, nucleoside analogs, and their combination where small advances in improved response and progression-free survival (PFS) have been noted. 10,11 However, these therapies have had very little impact on overall survival of CLL. The addition of the chimeric CD20 antibody, rituximab, perhaps represents the most significant advance in CLL therapy. Rituximab single agent activity 12 and phase 2 studies combining it with fludarabine (FR) or fludarabine and cyclophosphamide (FCR) have demonstrated improved overall survival (OS) over historical controls. 13,14 A randomized trial of FCR versus fludarabine or cyclophosphamide alone 15 demonstrated significant improvement in response; PFS and OS. While the presumptive mechanism of rituximab in CLL has been assumed to be immunologic (reviewed in Jaglowski and Byrd 16 ), a recent study demonstrated a direct effect on BCR-signaling in both normal and malignant B cells via perturbation of membrane rafts by CD20 anti...

• Three-year follow-up of ibrutinib in CLL demonstrated continued activity with durable responses that improve in quality with extended treatment.• Toxicity diminished over time with respect to grade $3 cytopenias, fatigue, infections, and adverse events leading to discontinuation.Ibrutinib is an orally administered inhibitor of Bruton tyrosine kinase that antagonizes B-cell receptor, chemokine, and integrin-mediated signaling. In early-phase studies, ibrutinib demonstrated high response rates and prolonged progression-free survival (PFS) in chronic lymphocytic leukemia (CLL). The durable responses observed with ibrutinib relate in part to a modest toxicity profile that allows the majority of patients to receive continuous therapy for an extended period. We report on median 3-year follow-up of 132 patients with symptomatic treatment-naïve and relapsed/ refractory CLL or small lymphocytic lymphoma. Longer treatment with ibrutinib was associated with improvement in response quality over time and durable remissions. Toxicity with longer follow-up diminished with respect to occurrence of grade 3 or greater cytopenias, fatigue, and infections. Progression remains uncommon, occurring primarily in some patients with relapsed del(17)(p13.1) and/or del(11)(q22.3) disease. Treatment-related lymphocytosis remains largely asymptomatic even when persisting >1 year and does not appear to alter longer-term PFS and overall survival compared with patients with partial response or better. Collectively, these data provide evidence that ibrutinib controls CLL disease manifestations and is well tolerated for an extended period; this information can help direct potential treatment options for different subgroups to diminish the long-term risk of relapse. (Blood. 2015;125(16):2497-2506

Importance The Bruton’s Tyrosine Kinase inhibitor ibrutinib is effective in patients with chronic lymphocytic leukemia (CLL). Reasons for discontinuation from this drug and outcomes following discontinuation have not been evaluated outside of clinical trials with relatively short follow-up. Objective To determine features associated with discontinuation of ibrutinib and outcomes. Design 308 patients participating in four sequential trials of ibrutinib were included. These trials accrued patients included in this analysis from May 2010 until April 2014, and data were locked in June 2014. Setting The Ohio State University Comprehensive Cancer Center Participants Patients with CLL enrolled on 4 sequential clinical trials. Main Outcome Measure Patients were evaluated for time to discontinuation, reasons for discontinuation, and survival following discontinuation. For patients who discontinued due to progression, targeted deep sequencing was performed in samples at baseline and relapse. Results With a median follow-up of 20 months, 232 patients remain on therapy, 31 have discontinued because of progression, and 45 have discontinued for other reasons. Disease progression includes Richter’s transformation or progressive CLL. Richter’s appeared to occur early and CLL progressions later (cumulative incidence at 12 months: 4.5% (95% CI: 2.0% to 7.0%) and 0.3% (95% CI: 0% to 1.0%), respectively). Median survival following Richter’s transformation was 3.5 months (95% CI: 0.3–6.0), and 17.6 months (95% CI: 4.7-not reached) following CLL progression. Sequencing on peripheral blood from 8 patients with Richter’s transformation revealed 2 with mutations in BTK, and a lymph node sample showed no mutations in BTK or PLCγ2. Deep sequencing on 11 patients with CLL progression revealed BTK or PLCγ2 mutations in all. These mutations were not identified pre-treatment in any patient. Conclusions and Relevance This single institution experience with ibrutinib confirms it to be an effective therapy and identifies, for the first time, baseline factors associated with ibrutinib discontinuation. Outcomes data show poor prognosis after discontinuation, especially for those patients with Richter’s transformation. Finally, sequencing data confirm initial reports associating mutations in BTK and PLCγ2 with progression and clearly show that CLL progressions are associated with these mutations, while Richter’s transformation is likely not.

Cancer is associated with immune deficiency, but the biologic basis of this is poorly defined. Here we demonstrate that impaired actin polymerization results in CD4 + and CD8 + T cells from patients with chronic lymphocytic leukemia (CLL) exhibiting defective immunological synapse formation with APCs. Although this synapse dysfunction was in part a result of the CLL cells having poor APC function, defective actin polymerization was also identified in T cells from patients with CLL. We further demonstrate that, following contact with CLL cells, defects in immune synapse formation were induced in healthy allogeneic T cells. This required direct contact and was inhibited by blocking adhesion molecules on CLL B cells. In T cells from patients with CLL and in T cells from healthy individuals that had been in contact with CLL cells, recruitment of key regulatory proteins to the immune synapse was inhibited. Treatment of autologous T cells and CLL cells with the immunomodulating drug lenalidomide resulted in improved synapse formation.These results define what we believe to be a novel immune dysfunction in T cells from patients with CLL that has implications for both autologous and allogeneic immunotherapy approaches and identifies repair of immune synapse defects as an essential step in improving cancer immunotherapy approaches.