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 Chronic lymphocytic leukemia (CLL) primarily affects older persons who often have coexisting conditions in addition to disease-related immunosuppression and myelosuppression. We conducted an international, open-label, randomized phase 3 trial to compare two oral agents, ibrutinib and chlorambucil, in previously untreated older patients with CLL or small lymphocytic lymphoma. METHODS We randomly assigned 269 previously untreated patients who were 65 years of age or older and had CLL or small lymphocytic lymphoma to receive ibrutinib or chlorambucil. The primary end point was progression-free survival as assessed by an independent review committee. RESULTS The median age of the patients was 73 years. During a median follow-up period of 18.4 months, ibrutinib resulted in significantly longer progression-free survival than did chlorambucil (median, not reached vs. 18.9 months), with a risk of progression or death that was 84% lower with ibrutinib than that with chlorambucil (hazard ratio, 0.16; P<0.001). Ibrutinib significantly prolonged overall survival; the estimated survival rate at 24 months was 98% with ibrutinib versus 85% with chlorambucil, with a relative risk of death that was 84% lower in the ibrutinib group than in the chlorambucil group (hazard ratio, 0.16; P=0.001). The overall response rate was higher with ibrutinib than with chlorambucil (86% vs. 35%, P<0.001). The rates of sustained increases from baseline values in the hemoglobin and platelet levels were higher with ibrutinib. Adverse events of any grade that occurred in at least 20% of the patients receiving ibrutinib included diarrhea, fatigue, cough, and nausea; adverse events occurring in at least 20% of those receiving chlorambucil included nausea, fatigue, neutropenia, anemia, and vomiting. In the ibrutinib group, four patients had a grade 3 hemorrhage and one had a grade 4 hemorrhage. A total of 87% of the patients in the ibrutinib group are continuing to take ibrutinib. CONCLUSIONS Ibrutinib was superior to chlorambucil in previously untreated patients with CLL or small lymphocytic lymphoma, as assessed by progression-free survival, overall survival, response rate, and improvement in hematologic variables. (Funded by Pharmacyclics and others; RESONATE-2 ClinicalTrials.gov number, NCT01722487.)

Signals from the microenvironment have a profound influence on the maintenance and/or progression of hematopoietic and epithelial cancers. Mesenchymal or marrowderived stromal cells, which constitute a large proportion of the non-neoplastic cells within the tumor microenvironment, constitutively secrete the chemokine stromal cellderived factor-1 (SDF-1/CXCL12). CXCL12 secretion by stromal cells attracts cancer cells, acting through its cognate receptor, CXCR4, which is expressed by both hematopoietic and nonhematopoietic tumor cells. Chemokine system overviewThe human chemokine system currently includes more than 40 chemokines and 18 chemokine receptors. Chemokine receptors are defined by their ability to induce directional migration of cells toward a gradient of a chemotactic cytokine (chemotaxis). Chemokine receptors are a family of 7 transmembrane domain, G-proteincoupled cell surface receptors that are designated CXCR1 through CXCR5, CCR1 through CCR11, XCR1, and CX3CR1, based on their specific preference for certain chemokines. Chemokines are small secreted proteins that can be segregated into 2 main subfamilies based on whether the 2 conserved cysteine residues present in all chemokines are separated by an intervening amino acid, respectively accounting for CXC or CC chemokines.Chemokine receptors are present on many different cell types. Initially, these receptors were identified on leukocytes, where they were found to play an important role in the homing of such cells to sites of inflammation. 1 However, during the past few years, hematopoietic and nonhematopoietic cells have been found to express receptors for various chemokines that are constitutively expressed in distinct tissue microenvironments. The interactions between such receptors and their respective chemokines help coordinate the trafficking and organization of cells within various tissue compartments. 2,3 Lymphocytes trafficking between blood and secondary lymphoid tissues, for example, is a nonrandom process that is regulated by tissue-specific expression of chemokines. 4 Circulating blood lymphocytes interact transiently and reversibly with vascular endothelium through adhesion molecules (selectins, integrins) in a process called rolling. Chemokines on the luminal endothelial surface can activate chemokine receptors on the rolling cells, which triggers integrin activation. 5 This results in the arrest, firm adhesion, and transendothelial migration into tissues where chemokine gradients direct localization and retention of the cells. 6 These steps, collectively referred to as "homing," are essential for normal development of the organism, organization and function of the immune system, and tissue replacement. There is growing evidence that these physiologic mechanisms of tissue-specific recruitment also are functional in neoplastic cells. CXCR4 chemokine receptor and its ligand, SDF-1 (CXCL12)Stromal cell-derived factor-1 (SDF-1), which now is designated as CXCL12, 7 is a homeostatic chemokine that signals through CXCR4, 8 which in turn pla...

• 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

B-cell receptor (BCR) signaling is a critical pathway in the pathogenesis of several B-cell malignancies, including chronic lymphocytic leukemia (CLL), and can be targeted by inhibitors of BCRassociated kinases, such as Bruton tyrosine kinase (Btk). PCI-32765, a selective, irreversible Btk inhibitor, is a novel, molecularly targeted agent for patients with B-cell malignancies, and is particularly active in patients with CLL. In this study, we analyzed the mechanism of action of PCI-32765 in CLL, using in vitro and in vivo models, and performed correlative studies on specimens from patients receiving therapy with PCI-32765. PCI-32765 significantly inhibited CLL cell survival, DNA synthesis, and migration in response to tissue homing chemokines (CXCL12, CXCL13 IntroductionChronic lymphocytic leukemia (CLL), the most common leukemia in western societies, is characterized by the accumulation of mature, CD5 ϩ CD23 ϩ monoclonal B lymphocytes in the blood, secondary lymphatic tissues, and the bone marrow. 1 Proliferating CLL cells, which account for approximately 0.1% to 1% of the CLL clone, 2 are typically found within microanatomical structures called proliferation centers or pseudofollicles, 3 where CLL cells interact with accessory cells (ie, stromal cells or T cells), thereby receiving survival and growth signals. 4 Such external signals from the leukemia microenvironment can supplement intrinsic oncogenic lesions, thereby promoting maintenance and expansion of the CLL clone. 3,5,6 Among the various external stimuli in the tissue microenvironments, B-cell receptor (BCR) activation and signaling, particularly in lymphatic tissues, 6 is a central pathologic mechanism, even though the precise mechanism of BCR stimulation and the nature of the antigen(s) that activate the BCRs remain obscure. 1,7 The most direct evidence for the importance of BCR signaling in CLL comes from recent comparative gene expression profiling (GEP) data that revealed BCR signaling as the most prominent pathway activated in CLL cells isolated from lymphatic tissues. 6 These GEP changes displayed remarkable similarity to GEP changes of CLL cells cocultured with monocyte-derived nurselike cells (NLC), 8 a system for studying the impact of the lymphatic tissue microenvironment in CLL in vitro. Additional evidence for the importance of BCR signaling in CLL comes from the observation that important CLL risk factors have functional links to the BCRs. The mutation status of the IgV H segments of the BCR distinguishes "mutated" (M-CLL) from "unmutated" CLL (U-CLL), with a low or high risk for disease progression, respectively, each accounting for approximately 50% of the patients. ZAP-70 is predominantly expressed in U-CLL cases, 9 and ZAP-70 expression is associated with enhanced BCR signaling. 10 Furthermore, CLL patients express restricted sets of BCRs, as determined by BCR sequencing. These BCRs have immunoglobulin (Ig) heavy-chain variable (V) gene sequences that are identical or stereotyped in subsets of patients, 11,12 suggesting that these BCR...

In lymphocytes, the phosphoinositide 3-kinase (PI3K) isoform p110␦ (PI3K␦) transmits signals from surface receptors, including the B-cell receptor (BCR). CAL-101, a selective inhibitor of PI3K␦, displays clinical activity in CLL, causing rapid lymph node shrinkage and a transient lymphocytosis. Inhibition of pro-survival pathways, the presumed mechanism of CAL-101, does not explain this characteristic pattern of activity. Therefore, we tested CAL-101 in assays that model CLLmicroenvironment interactions in vitro.We found that CAL-101 inhibits CLL cell chemotaxis toward CXCL12 and CXCL13 and migration beneath stromal cells (pseudoemperipolesis) . IntroductionChronic lymphocytic leukemia (CLL), the most common leukemia in Western countries, is characterized by the accumulation of CD5 ϩ /CD23 ϩ monoclonal B cells in the blood and tissue compartments (marrow and secondary lymphatic tissues). 1 CLL cells are resistant to cell death in vivo. However, they rapidly die from spontaneous apoptosis once removed from the patient unless they are cocultured with accessory stromal cells, such as marrow stromal cells (MSCs) 2 or monocyte-derived nurse-like cells (NLCs). 3 Cross-talk between CLL cells and these supporting cells in tissue microenvironments comprises a complex signaling network that may be critical for disease progression and drug resistance. Interference with this cross-talk may constitute a new therapeutic target. Several molecular pathways related to leukemia cell migration, B-cell receptor (BCR) signaling, and interactions between CLL cells and T cells have been identified over recent years (reviewed in Burger et al 4 ).The chemokines, CXCL12 and CXCL13, are constitutively secreted by MSCs and NLCs 5,6 and attract CLL cells via their respective cognate chemokine receptors, CXCR4, CXCR5, thereby regulating homing and retention of the leukemia cells in the tissue compartments. In addition, BCR signaling in the lymphatic tissue microenvironment promotes the clonal expansion of normal and malignant B cells. 1,7,8 CLL cells isolated from lymph nodes 8 or high-risk patients 9 display gene expression profiles that indicate BCR activation. In response to BCR activation and in NLC cocultures, CLL cells secrete the chemokines CCL3 and CCL4 (also called MIP-1␣ and ␤), 10 presumably for recruitment of accessory cells, such as regulatory T cells. 11,12 We proposed that the secretion of CCL3 and CCL4 by CLL cells correlates with the responsiveness of the BCR, based on higher secretion of CCL3/4 in ZAP-70 ϩ cases, 10 and a close correlation between CCL3 plasma levels and ZAP-70, IgHV mutational status, and prognosis. 13 Phosphoinositide 3Ј-kinases (PI3Ks) integrate and transmit signals from diverse surface molecules, such as the BCR, 14 chemokine receptors, and adhesion molecules, thereby regulating key cellular functions, including growth, survival, and migration. 15 The PI3Ks are divided into 3 classes; I, II, and III. The class I kinases contain 4 isoforms designated PI3K␣, ␤, ␥, and ␦. While the PI3K␣ and ␤ isoforms are ...

Despite major therapeutic advances, most mature B-cell malignancies remain incurable. Compelling evidence suggests that crosstalk with accessory stromal cells in specialized tissue microenvironments, such as the bone marrow and secondary lymphoid organs, favors disease progression by promoting malignant B-cell growth and drug resistance. Therefore, disrupting the crosstalk between malignant B cells and their milieu is an attractive novel strategy for treating selected mature B-cell malignancies. Here we summarize the current knowledge about the cellular and molecular interactions between neoplastic B lymphocytes and accessory cells that shape a supportive microenvironment, and the potential therapeutic targets that are emerging, together with the new problems they raise. We discuss clinically relevant aspects and provide an outlook into future biologically oriented therapeutic strategies. We anticipate a paradigm shift in the treatment of selected B-cell malignancies, moving from targeting primarily the malignant cells toward combining cytotoxic drugs with agents that interfere with the microenvironment's proactive role. Such approaches hopefully will help eliminating residual disease, thereby improving our current therapeutic efforts. (Blood. 2009;114:3367-3375) IntroductionThe microenvironment is the compilation of accessory cells that within individual organs work as a team through cell-cell contacts and active molecular crosstalk to provide a functional scaffolding to parenchymal cells. In solid tumors, a microenvironment instrumental to the survival and propagation of malignant cells is built up by the concurrence of inflammatory cells that produce growth factors, new vessel formation that provides nutrients, and immune tolerance that avoids immune-mediated elimination. Conceivably, this conducive microenvironment may be an appropriate soil to host cancer stem cells (CSCs). Signals from the tumor microenvironment are a major hurdle to cancer cell eradication, and its neoangiogenetic component has become an attractive target for treatment strategies that aim at perturbing the nurturing capacity of the tumor cell milieu. 1 Blood cancers develop in specialized tissue microenvironments, such as bone marrow (BM) and secondary lymphoid organs. These microenvironments are characterized by different populations of accessory stromal and T cells that interact with malignant cells and promote tumor growth and drug resistance. 2,3 Malignant blood cells apparently have highly variable degrees of dependency on signals from the microenvironment. To make matters more complex, the affinity and dependency on accessory stromal cells for tumor growth and progression can change over time, with the evolution of stroma-dependent or stroma-independent subclones.The issue of microenvironment-targeted treatment has recently gained increasing attention in hemato-oncology, and the enthusiasm in this field is justified by a number of new drugs that are targeted toward the microenvironment, such as thalidomide and lenalidomide, plerixaf...

Key Points Our 5-year experience shows sustained single-agent efficacy of ibrutinib in CLL patients, with complete response rates increasing over time. Long-term ibrutinib was well tolerated with no new safety signals; rates of grade ≥3 cytopenias decreased with continued therapy.