Microenvironment dependency in Chronic Lymphocytic Leukemia: The basis for new targeted therapies

Clinical trials, challenges, and changes in TCR-based therapeutics for hematologic malignancies

INTRODUCTION

T cells engineered to express antigen-specific T cell receptors (TCR; TCR-T) are a promising class of immunotherapeutic for patients with hematologic malignancies. Like chimeric antigen receptor-engineered T cells (CAR-T), TCR-T are cell products with defined specificity and composition. Unlike CAR-T, TCR-T can recognize targets arising both from intracellular and cell surface proteins and leverage the sensitivity of natural TCR signaling machinery. A growing number of TCR-T targeting various antigens in different hematologic malignancies are in early-phase clinical trials, and more are in preclinical development.

AREAS COVERED

This review covers results from early-phase TCR-T clinical trials for hematologic malignancies. Challenges in the field are reviewed, including identifying optimal targets, engaging CD4+ help for CD8+ T cells, and overcoming tumor-induced suppression; recent innovations to overcome these challenges are also highlighted.

EXPERT OPINION

In the future, TCR-T's promise for hematologic malignancies will be borne out in later-phase clinical trials and approvals for clinical use. Improved antigen discovery methods will help build the toolbox of targets needed for broadly applicable TCR-T. Rationally designed TCR-T modifications including incorporation of accessory receptors and gene editing will enhance TCR-T function. New hybrid receptors combining features of TCR and CAR will enter the clinic.

The survival grip-how cell adhesion promotes tumor maintenance within the microenvironment

Cell adhesion is warranted by proteins that are crucial for the maintenance of tissue integrity and homeostasis. Most of these proteins behave as receptors to link adhesion to the control of cell survival and their expression or regulation are often altered in cancers. B-cell malignancies do not evade this principle as they are sustained in relapsed niches by interacting with the microenvironment that includes cells and their secreted factors. Focusing on chronic lymphocytic leukemia and mantle cell lymphoma, this Review delves with the molecules involved in the dialog between the adhesion platforms and signaling pathways known to regulate both cell adhesion and survival. Current therapeutic strategies disrupt adhesive structures and compromise the microenvironment support to tumor cells, rendering them sensitive to immune recognition. The development of organ-on-chip and 3D culture systems, such as spheroids, have revealed the importance of mechanical cues in regulating signaling pathways to organize cell adhesion and survival. All these elements contribute to the elaboration of the crosstalk of lymphoma cells with the microenvironment and the education processes that allow the establishment of the supportive niche.

Extracellular vesicles from type-2 macrophages increase the survival of chronic lymphocytic leukemia cells ex vivo

The resistance of Chronic Lymphocytic Leukemia (CLL) B-cells to cell death is mainly attributed to interactions within their microenvironment, where they interact with various types of cells. Within this microenvironment, CLL-B-cells produce and bind cytokines, growth factors, and extracellular vesicles (EVs). In the present study, EVs purified from nurse-like cells and M2-polarized THP1 cell (M2-THP1) cultures were added to CLL-B-cells cultures. EVs were rapidly internalized by B-cells, leading to a decrease in apoptosis (P = 0.0162 and 0.0469, respectively) and an increased proliferation (P = 0.0335 and 0.0109). Additionally, they induced an increase in the resistance of CLL-B-cells to Ibrutinib, the Bruton kinase inhibitor in vitro (P = 0.0344). A transcriptomic analysis showed an increase in the expression of anti-apoptotic gene BCL-2 (P = 0.0286) but not MCL-1 and an increase in the expression of proliferation-inducing gene APRIL (P = 0.0286) following treatment with EVs. Meanwhile, an analysis of apoptotic protein markers revealed increased amounts of IGFBP-2 (P = 0.0338), CD40 (P = 0.0338), p53 (P = 0.0219) and BCL-2 (P = 0.0338). Finally, exploration of EVs protein content by mass spectrometry revealed they carry various proteins involved in known oncogenic pathways and the RNAseq analysis of CLL-B-cells treated or not with NLCs EVs show various differentially expressed genes.

Lysosome-Disrupting Agents in Combination with Venetoclax Increase Apoptotic Response in Primary Chronic Lymphocytic Leukemia (CLL) Cells Mediated by Lysosomal Cathepsin D Release and Inhibition of Autophagy

Venetoclax and obinutuzumab are becoming frontline therapies for chronic lymphocytic leukemia (CLL) patients. Unfortunately, drug resistance still occurs, and the combination could be immunosuppressive. Lysosomes have previously been identified as a target for obinutuzumab cytotoxicity in CLL cells, but the mechanism remains unclear. In addition, studies have shown that lysosomotropic agents can cause synergistic cell death in vitro when combined with the BTK inhibitor, ibrutinib, in primary CLL cells. This indicates that targeting lysosomes could be a treatment strategy for CLL. In this study, we have shown that obinutuzumab induces lysosome membrane permeabilization (LMP) and cathepsin D release in CLL cells. Inhibition of cathepsins reduced obinutuzumab-induced cell death in CLL cells. We further determined that the lysosomotropic agent siramesine in combination with venetoclax increased cell death in primary CLL cells through an increase in reactive oxygen species (ROS) and cathepsin release. Siramesine treatment also induced synergistic cytotoxicity when combined with venetoclax. Microenvironmental factors IL4 and CD40L or incubation with HS-5 stromal cells failed to significantly protect CLL cells from siramesine- and venetoclax-induced apoptosis. We also found that siramesine treatment inhibited autophagy through reduced autolysosomes. Finally, the autophagy inhibitor chloroquine failed to further increase siramesine-induced cell death. Taken together, lysosome-targeting drugs could be an effective strategy in combination with venetoclax to overcome drug resistance in CLL.

Lessons learned from the Eµ-TCL1 mouse model of CLL

The Eµ-TCL1 mouse model has been used for over 20 years to study the pathobiology of chronic lymphocytic leukemia (CLL) and for preclinical testing of novel therapies. A CLL-like disease develops with increasing age in these mice due to a B cell specific overexpression of human TCL1. The reliability of this model to mirror human CLL is controversially discussed, as none of the known driver mutations identified in patients are found in Eµ-TCL1 mice. It has to be acknowledged that this mouse model was key to develop targeted therapies that aim at inhibiting the constitutive B cell receptor (BCR) signaling, a main driver of CLL. Inhibitors of BCR signaling became standard-of-care for a large proportion of patients with CLL as they are highly effective. The Eµ-TCL1 model further advanced our understanding of CLL biology owed to studies that crossed this mouse line with various transgenic mouse models and demonstrated the relevance of CLL-cell intrinsic and -extrinsic drivers of disease. These studies were instrumental in showing the relevance of the tumor microenvironment in the lymphoid tissues for disease progression and immune escape in CLL. It became clear that CLL cells shape and rely on stromal and immune cells, and that immune suppressive mechanisms and T cell exhaustion contribute to CLL progression. Based on this knowledge, new immunotherapy strategies were clinically tested for CLL, but so far with disappointing results. As some of these therapies were effective in the Eµ-TCL1 mouse model, the question arose concerning the translatability of preclinical studies in these mice. The aim of this review is to summarize lessons we have learnt over the last decades by studying CLL-like disease in the Eµ-TCL1 mouse model. The article focuses on pitfalls and limitations of the model, as well as the gained knowledge and potential of using this model for the development of novel treatment strategies to achieve the goal of curing patients with CLL.

PYK2 is overexpressed in chronic lymphocytic leukaemia: A potential new therapeutic target

Chronic Lymphocytic Leukaemia (CLL) is the most common adult B-cell leukaemia and despite improvement in patients' outcome, following the use of targeted therapies, it remains incurable. CLL supportive microenvironment plays a key role in both CLL progression and drug resistance through signals that can be sensed by the main components of the focal adhesion complex, such as FAK and PYK2 kinases. Dysregulations of both kinases have been observed in several metastatic cancers, but their role in haematological malignancies is still poorly defined. We characterized FAK and PYK2 expression and observed that PYK2 expression is higher in leukaemic B cells and its overexpression significantly correlates with their malignant transformation. When targeting both FAK and PYK2 with the specific inhibitor defactinib, we observed a dose-response effect on CLL cells viability and survival. In vivo treatment of a CLL mouse model showed a decrease of the leukaemic clone in all the lymphoid organs along with a significant reduction of macrophages and of the spleen weight and size. Our results first define a possible prognostic value for PYK2 in CLL, and show that both FAK and PYK2 might become putative targets for both CLL and its microenvironment (e.g. macrophages), thus paving the way to an innovative therapeutic strategy.

A synthetic human 3D in vitro lymphoid model enhancing B-cell survival and functional differentiation

To investigate B-cell differentiation and maturation occurring in the germinal center (GC) using in vitro culture systems, key factors and interactions of the GC reaction need to be accurately simulated. This study aims at improving in vitro GC simulation using 3D culture techniques. Human B-cells were incorporated into PEG-4MAL hydrogels, to create a synthetic extracellular matrix, supported by CD40L cells, human tonsil-derived lymphoid stromal cells, and cytokines. The differentiation and antibody production of CD19⁺B-cells was best supported in a 5.0%-PEG-4MAL, 2.0 mM-RGD-peptide composition. The 3D culture significantly increased plasmablast and plasma cell numbers as well as antibody production, with less B-cell death compared to 2D cultures. Class switching of naive CD19⁺IgD⁺B-cells toward IgG⁺ and IgA⁺B-cells was observed. The formation of large B-cell clusters indicates the formation of GC-like structures. In conclusion, a well-characterized and controllable hydrogel-based human 3D lymphoid model is presented that supports enhanced B-cell survival, proliferation, differentiation, and antibody production.

Immune modulatory effects of Idelalisib in stromal cells of chronic lymphocytic leukemia

Molecular targets of tyrosine kinase inhibitors are not restricted to the B-cell compartment but also regulate functions in the tumor microenvironment. Increasing evidence suggests that B-cell receptor-associated kinases like protein kinase C (PKC)-β is essential for the formation of a microenvironment supporting leukemic growth. Here we describe the effect of Idelalisib on the PKCβ/NF-κB and Notch pathway in stromal cells upon contact to primary chronic lymphocytic leukemia cells (CLL). There is no Idelalisib-dependent regulation of the Notch expression in stromal cells, whereas Idelalisib induces PKCβ expression and activates the canonical NF-κB pathway. Idelalisib deregulates important immune-modulatory proteins in activated stromal cells, which might provoke the patient's side effects. Additionally, we established a 3D-stroma/leukemia model, that can give us a more defined look into the communication between tumor and stromal cells than standard cell cultures. This opens up the possibility to improve therapies, especially in the context of minimal-residual disease.

Targeting of the A2A adenosine receptor counteracts immunosuppression in vivo in a mouse model of chronic lymphocytic leukemia

Tumor immunosuppression is a major cause for treatment failure and disease relapse, both in solid tumors and leukemia. Local hypoxia is among the conditions that cause immunosuppression, acting at least in part through the upregulation of extracellular adenosine levels, which potently suppress T cell responses and skew macrophages towards an M2 phenotype. Hence, there is intense investigation to identify drugs that target this axis. By using the TCL1 adoptive transfer CLL mouse model, we show that adenosine production and signaling are upregulated in the hypoxic lymphoid niches, where intense colonization of leukemic cells occurs. This leads to a progressive remodeling of the immune system towards tolerance, with expansion of T regulatory cells (Tregs), loss of CD8+ T cell cytotoxicity and differentiation of murine macrophages towards the patrolling (M2-like) subset. In vivo administration of SCH58261, an inhibitor the A2A adenosine receptor, re-awakens T cell responses, while limiting Tregs expansion, and re-polarizes monocytes towards the inflammatory (M1-like) phenotype. These results show for the first time the in vivo contribution of adenosine signaling to immune tolerance in CLL, and the translational implication of drugs interrupting this pathway. Although the effects of SCH58261 on leukemic cells are limited, interfering with adenosine signaling may represent an appealing strategy for combination-based therapeutic approaches.

Co-expression network-based identification of biomarkers correlated with the lymph node metastasis of patients with head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is ranked as one of the most frequent malignancies worldwide with a high risk of lymph node metastasis, which serves as a main reason for cancer deaths. Identification of the potential biomarkers for lymph node metastasis in HNSCC patients may contribute to personalized treatment and better therapeutic effect. In the present study, GSE30788 microarray data and corresponding clinical parameters were downloaded from Gene Expression Omnibus (GEO) and Weighted Gene Co-expression Network Analysis (WGCNA) was performed to investigate significant modules associated with clinical traits. As a result, the genes in the blue module were determined as candidate genes related with HNSCC lymph node metastasis and ten hub genes were selected from the PPI network. Further analysis validated the close associations of hub gene expression with lymph node metastasis of HNSCC patients. Furthermore, survival analysis suggested the level of Loricrin (LOR) was statistically significantly associated with the disease-free survival of HNSCC patients, indicating the potential of utilizing it as prognosis predictor. Overall, our study conducted a co-expression network-based analysis to investigate significant genes underlying HNSCC metastasis, providing promising biomarkers and therapeutic targets.

RGDS-Modified Superporous Poly(2-Hydroxyethyl Methacrylate)-Based Scaffolds as 3D In Vitro Leukemia Model

Superporous poly(2-hydroxyethyl methacrylate-co-2-aminoethyl methacrylate) (P(HEMA-AEMA)) hydrogel scaffolds are designed for in vitro 3D culturing of leukemic B cells. Hydrogel porosity, which influences cell functions and growth, is introduced by adding ammonium oxalate needle-like crystals in the polymerization mixture. To improve cell vitality, cell-adhesive Arg-Gly-Asp-Ser (RGDS) peptide is immobilized on the N-(γ-maleimidobutyryloxy)succinimide-activated P(HEMA-AEMA) hydrogels via reaction of SH with maleimide groups. This modification is especially suitable for the survival of primary chronic lymphocytic leukemia cells (B-CLLs) in 3D cell culture. No other tested stimuli (interleukin-4, CD40 ligand, or shaking) can further improve B-CLL survival or metabolic activity. Both unmodified and RGDS-modified P(HEMA-AEMA) scaffolds serve as a long-term (70 days) 3D culture platforms for HS-5 and M2-10B4 bone marrow stromal cell lines and MEC-1 and HG-3 B-CLL cell lines, although the adherent cells retain their physiological morphologies, preferably on RGDS-modified hydrogels. Moreover, the porosity of hydrogels allows direct cell lysis, followed by efficient DNA isolation from the 3D-cultured cells. P(HEMA-AEMA)-RGDS thus serves as a suitable 3D in vitro leukemia model that enables molecular and metabolic assays and allows imaging of cell morphology, interactions, and migration by confocal microscopy. Such applications can prospectively assist in testing of drugs to treat this frequently recurring or refractory cancer.

Protein kinase C-β-dependent changes in the glucose metabolism of bone marrow stromal cells of chronic lymphocytic leukemia

Survival of chronic lymphocytic leukemia (CLL) cells critically depends on the support of an adapted and therefore appropriate tumor microenvironment. Increasing evidence suggests that B-cell receptor-associated kinases such as protein kinase C-β (PKCβ) or Lyn kinase are essential for the formation of a microenvironment supporting leukemic growth. Here, we describe the impact of PKCβ on the glucose metabolism in bone marrow stromal cells (BMSC) upon CLL contact. BMSC get activated by CLL contact expressing stromal PKCβ that diminishes mitochondrial stress and apoptosis in CLL cells by stimulating glucose uptake. In BMSC, the upregulation of PKCβ results in increased mitochondrial depolarization and leads to a metabolic switch toward oxidative phosphorylation. In addition, PKCβ-deficient BMSC regulates the expression of Hnf1 promoting stromal insulin signaling after CLL contact. Our data suggest that targeting PKCβ and the glucose metabolism of the leukemic niche could be a potential therapeutic strategy to overcome stroma-mediated drug resistance.

High M-MDSC Percentage as a Negative Prognostic Factor in Chronic Lymphocytic Leukaemia

In the current study, we analysed the role and prognostic value of myeloid-derived suppressor cells (MDSC) in chronic lymphocytic leukaemia (CLL). The frequency of circulating monocytic MDSC (M-MDSC; defined as CD14+CD11b+CD15-HLA-DR-/low cells) was assessed in correlation with clinical and laboratory parameters characterising the disease activity and patient immune status. Samples of peripheral blood from untreated CLL patients and healthy volunteers were stained with monoclonal antibodies for flow cytometry analysis. CLL patients with M-MDSC percentages above 9.35% (according to the receiver operating characteristic (ROC) analysis) had a shorter time-to-treatment and shorter survival time than the group with a lower percentage of M-MDSC. The M-MDSC percentage was higher in patients with adverse prognostic factors (i.e., 17p and 11q deletion and CD38 and ZAP-70 expression). A high M-MDSC percentage was linked to significantly lower expression of the CD3ζ in T cells. Furthermore, an analysis of immune regulatory molecules (arginase 1 (ARG1), nitric oxide synthase (NOS2), indoleamine 2,3-dioxygenase (IDO), transforming growth factor beta (TGF-β), and interleukin (IL)-10) was performed. By the means of flow cytometry and RT-qPCR, we showed an overexpression of three of them in M-MDSC of CLL patients. M-MDSC cells seem to be an important factor in the immunosuppressive microenvironment of CLL and seem to be a good and novel prognostic factor.

Chromatin mapping and single-cell immune profiling define the temporal dynamics of ibrutinib response in CLL

The Bruton tyrosine kinase (BTK) inhibitor ibrutinib provides effective treatment for patients with chronic lymphocytic leukemia (CLL), despite extensive heterogeneity in this disease. To define the underlining regulatory dynamics, we analyze high-resolution time courses of ibrutinib treatment in patients with CLL, combining immune-phenotyping, single-cell transcriptome profiling, and chromatin mapping. We identify a consistent regulatory program starting with a sharp decrease of NF-κB binding in CLL cells, which is followed by reduced activity of lineage-defining transcription factors, erosion of CLL cell identity, and acquisition of a quiescence-like gene signature. We observe patient-to-patient variation in the speed of execution of this program, which we exploit to predict patient-specific dynamics in the response to ibrutinib based on the pre-treatment patient samples. In aggregate, our study describes time-dependent cellular, molecular, and regulatory effects for therapeutic inhibition of B cell receptor signaling in CLL, and it establishes a broadly applicable method for epigenome/transcriptome-based treatment monitoring.

Ibrutinib, a Bruton tyrosine kinase inhibitor, provides effective treatment for chronic lymphocytic leukemia (CLL). Here, the authors describe time-dependent molecular changes to malignant cells and to the immune system in patients undergoing ibrutinib therapy, with can be used for therapy monitoring.

Stem cells and extracellular vesicles: biological regulators of physiology and disease

Many different subpopulations of subcellular extracellular vesicles (EVs) have been described. EVs are released from all cell types and have been shown to regulate normal physiological homeostasis, as well as pathological states by influencing cell proliferation, differentiation, organ homing, injury and recovery, as well as disease progression. In this review, we focus on the bidirectional actions of vesicles from normal and diseased cells on normal or leukemic target cells; and on the leukemic microenvironment as a whole. EVs from human bone marrow mesenchymal stem cells (MSC) can have a healing effect, reversing the malignant phenotype in prostate and colorectal cancer, as well as mitigating radiation damage to marrow. The role of EVs in leukemia and their bimodal cross talk with the encompassing microenvironment remains to be fully characterized. This may provide insight for clinical advances via the application of EVs as potential therapy and the employment of statistical and machine learning models to capture the pleiotropic effects EVs endow to a dynamic microenvironment, possibly allowing for precise therapeutic intervention.

Olaptesed pegol (NOX-A12) with bendamustine and rituximab: a phase IIa study in patients with relapsed/refractory chronic lymphocytic leukemia

Olaptesed pegol (NOX-A12) is a pegylated structured L-oligoribonucleotide that binds and neutralizes CXCL12, a chemokine tightly regulating the life cycle of chronic lymphocytic leukemia cells. The resulting inhibition of CXCR4 and CXCR7 signaling reduces the protective activity of the bone marrow and lymph node microenvironment. CXCL12 inhibition mobilizes chronic lymphocytic leukemia cells into the circulation and prevents their homing into the protective niches. In this phase I/II study, 28 patients with relapsed/refractory chronic lymphocytic leukemia were treated with olaptesed pegol in combination with bendamustine and rituximab. Combination treatment was preceded by single escalating pilot doses of olaptesed pegol in the first ten patients for evaluation of safety and pharmacokinetics. Peak concentrations and systemic exposure of olaptesed pegol were dose-linear; plasma elimination was monophasic with a 53.2 h half-life. A rapid increase in circulating chronic lymphocytic leukemia cells was observed already 1 h after administration of olaptesed pegol and lasted for at least 72 h. Single-agent treatment was well tolerated and no dose-limiting toxicity was observed. The combination regimen yielded an overall response rate of 86%, with 11% of patients achieving a complete response and 75% a partial response. Notably, all ten high-risk patients, including four with a 17p deletion, responded to treatment. The median progression-free survival was 15.4 (95% confidence interval: 12.2, 26.2) months while the median overall survival was not reached with >80% of patients alive after a median follow-up of 28 months. Olaptesed pegol was well tolerated and did not result in additional toxicity when combined with bendamustine and rituximab (ClinicalTrials.gov identifier: NCT01486797). Further clinical development of this novel CXCL12 inhibitor is thus warranted.

SLAMF receptors on normal and malignant B cells

The Signaling Lymphocyte Activation Molecule family (SLAMF) is a collection of nine surface receptors expressed mainly on hematopoietic cells, and was found to modulate the behavior of immune cells. SLAMF receptors are expressed on B cells in health and disease. Each SLAM receptor has a unique differential expression pattern during the development and activation of B cells. Furthermore, recent findings have revealed a principal role for this family of receptors in B cell malignancies, emphasizing their importance in the control of malignant cell survival, cell to cell communication within the tumor microenvironment, retention in the supporting niches and regulation of T cell anti-tumor response. This review summarizes the latest studies regarding SLAMF expression and behavior in B cells and in B cell pathologies, and discusses the therapeutic potential of these receptors.

SLAMF1/CD150 in hematologic malignancies: Silent marker or active player?

SLAMF1/CD150 receptor is a founder of signaling lymphocyte activation molecule (SLAM) family of cell-surface receptors. It is widely expressed on cells within hematopoietic system. In hematologic malignancies CD150 cell surface expression is restricted to cutaneous T-cell lymphomas, few types of B-cell non-Hodgkin's lymphoma, near half of cases of chronic lymphocytic leukemia, Hodgkin's lymphoma, and multiple myeloma. Differential expression among various types of hematological malignancies allows considering CD150 as diagnostical and potential prognostic marker. Moreover, CD150 may be a target for antibody-based or measles virus oncolytic therapy. Due to CD150 signaling properties it is involved in regulation of malignant cell fate decision and tumor microenvironment in Hodgkin's lymphoma and chronic lymphocytic leukemia. This review summarizes evidence for the important role of CD150 in pathogenesis of hematologic malignancies.

Role of CXCL12 and CXCR4 in the pathogenesis of hematological malignancies

The chemokine receptor CXCR4 and its ligand stromal cell-derived factor-1 (SDF-1/CXCL12) are important players in the cross-talk among lymphoma, myeloma and leukemia cells and their microenvironments. In hematological malignancies and solid tumors, the overexpression of CXCR4 on the cell surface has been shown to be responsible for disease progression, increasing tumor cell survival and chemoresistance and metastasis to organs with high CXCL12 levels (e.g., lymph nodes and bone marrow (BM)). Furthermore, the overexpression of CXCR4 has been found to have prognostic significance for disease progression in many type of tumors including lymphoma, leukemia, glioma, and prostate, breast, colorectal, renal, and hepatocellular carcinomas. In leukemia, CXCR4 expression granted leukemic blasts a higher capacity to seed into BM niches, thereby protecting leukemic cells from chemotherapy-induced apoptosis, and was correlated with shorter disease-free survival. In contrast, neutralizing the interaction of CXCL12/CXCR4 with a variety of antagonists induced apoptosis and differentiation and increased the chemosensitivity of lymphoma, myeloma, and leukemia cells. The role of CXCL12 and CXCR4 in the pathogenesis of hematological malignancies and the clinical therapeutic potential of CXCR4 antagonists in these diseases is discussed.

GPCRomics: GPCR Expression in Cancer Cells and Tumors Identifies New, Potential Biomarkers and Therapeutic Targets

G protein-coupled receptors (GPCRs), the largest family of targets for approved drugs, are rarely targeted for cancer treatment, except for certain endocrine and hormone-responsive tumors. Limited knowledge regarding GPCR expression in cancer cells likely has contributed to this lack of use of GPCR-targeted drugs as cancer therapeutics. We thus undertook GPCRomic studies to define the expression of endoGPCRs (which respond to endogenous molecules such as hormones, neurotransmitters and metabolites) in multiple types of cancer cells. Using TaqMan qPCR arrays to quantify the mRNA expression of ∼340 such GPCRs, we found that human chronic lymphocytic leukemia (CLL) cells/stromal cells associated with CLL, breast cancer cell lines, colon cancer cell lines, pancreatic ductal adenocarcinoma (PDAC) cells, cancer associated fibroblasts (CAFs), and PDAC tumors express 50 to >100 GPCRs, including many orphan GPCRs (which lack known physiologic agonists). Limited prior data exist regarding the expression or function of most of the highly expressed GPCRs in these cancer cells and tumors. Independent results from public cancer gene expression databases confirm the expression of such GPCRs. We propose that highly expressed GPCRs in cancer cells (for example, GPRC5A in PDAC and colon cancer cells and GPR68 in PDAC CAFs) may contribute to the malignant phenotype, serve as biomarkers and/or may be novel therapeutic targets for the treatment of cancer.

A retinoic acid-dependent stroma-leukemia crosstalk promotes chronic lymphocytic leukemia progression

In chronic lymphocytic leukemia (CLL), the non-hematopoietic stromal microenvironment plays a critical role in promoting tumor cell recruitment, activation, survival, and expansion. However, the nature of the stromal cells and molecular pathways involved remain largely unknown. Here, we demonstrate that leukemic B lymphocytes induce the activation of retinoid acid synthesis and signaling in the microenvironment. Inhibition of RA-signaling in stromal cells causes deregulation of genes associated with adhesion, tissue organization and chemokine secretion including the B-cell chemokine CXCL13. Notably, reducing retinoic acid precursors from the diet or inhibiting RA-signaling through retinoid-antagonist therapy prolong survival by preventing dissemination of leukemia cells into lymphoid tissues. Furthermore, mouse and human leukemia cells could be distinguished from normal B-cells by their increased expression of Rarγ2 and RXRα, respectively. These findings establish a role for retinoids in murine CLL pathogenesis, and provide new therapeutic strategies to target the microenvironment and to control disease progression.

The stromal microenvironment plays a key role in the expansion of chronic lymphocytic leukemia. Here, the authors use the Eµ-TCL1 mouse model to show that leukemic B-cells induce the activation of retinoic acid synthesis in stromal cells of the lymphoid microenvironment, and that impacting on retinoic acid signalling via diet or chemical inhibition prolonged survival by preventing leukemia dissemination and accumulation in lymphoid tissues.

Autologous T cells expressing the oncogenic transcription factor KLF6-SV1 prevent apoptosis of chronic lymphocytic leukemia cells

Crosstalk between leukemic cells and the tumor microenvironment is of importance in chronic lymphocytic leukemia (CLL). T cells seem to sustain the survival of CLL cells by various mechanisms. The Krüppel-like family of transcription factors (KLFs) are identified as regulators of proliferation and cell death. In the present study, we analyzed the expression of the wild type (WT) gene KLF6 and the oncogenic splice variant 1 (KLF6-SV1) at the mRNA level in subsets of T cells from CLL patients (n = 29), multiple myeloma patients (n = 6) and normal donors (n = 10). RNA Silencing was used for wtKLF6 and KLF6-SV1. Tumor cell apoptosis was measured. A significant overexpression of wtKLF6 and KLF6-SV1 in T cells of CLL patients compared to normal donors and myeloma patients was noted (p<0.002). Western blot showed that both wtKLF6 and KLF6-SV1 were expressed in purified T cells from CLL patients. KLF6-SV1 siRNA transfection induced a significant down-regulation of KLF6-SV1 in CLL T cells, which lost the capability to sustain the growth of leukemic cells. However, no such a significant effect was seen after wtKLF6 transfection of the autologous T cells. The results suggest that KLF6-SV1 may play a role in the regulation of survival CLL cells.

Circulating Tfh1 (cTfh1) cell numbers and PD1 expression are elevated in low-grade B-cell non-Hodgkin's lymphoma and cTfh gene expression is perturbed in marginal zone lymphoma

CD4⁺ T-cell subsets are found in the tumour microenvironment (TME) of low-grade B-cell non-Hodgkin’s lymphomas such as marginal zone lymphoma (MZL) or follicular lymphoma (FL). Both numbers and architecture of activating follicular helper T-cells (Tfh) and suppressive Treg in the TME of FL are associated with clinical outcomes. There has been almost no previous work on CD4⁺ T-cells in MZL. It is now recognised that circulating CD4⁺CXCR5⁺ T-cells are the memory compartment of Tfh cells. We determined differences in number of circulating Tfh (cTfh) cells and cTfh subsets between normal subjects and patients with FL or MZL. Lymphoma patients showed increased numbers of cTfh1 and reduced cTfh17 cells due to decreased expression of the subset-defining marker CCR6 in patients. PD1, a surface marker associated with Tfh cells, showed increased expression on cTfh subsets in patients. Focusing on MZL we determined expression of 96 T-cell associated genes by microfluidic qRT-PCR. Analysis of differentially expressed genes showed significant differences between normal subjects and patients both for bulk cTfh (CCL4) and the cTfh1 subset (JAK3). While our findings require confirmation in larger studies we suggest that analysis of number and gene expression of circulating T-cells might be a source of clinically useful information as is the case for T-cells within lymphoma lymph nodes.

Extracellular vesicles of bone marrow stromal cells rescue chronic lymphocytic leukemia B cells from apoptosis, enhance their migration and induce gene expression modifications

Interactions between chronic lymphocytic leukemia (CLL) B cells and the bone marrow (BM) microenvironment play a major function in the physiopathology of CLL. Extracellular vesicles (EVs), which are composed of exosomes and microparticles, play an important role in cell communication. However, little is known about their role in CLL / microenvironment interactions. In the present study, EVs purified by ultracentrifugation from BM mesenchymal stromal cell (BM-MSC) cultures were added to CLL B cells. After their integration into CLL B cells, we observed a decrease of leukemic cell spontaneous apoptosis and an increase in their chemoresistance to several drugs, including fludarabine, ibrutinib, idelalisib and venetoclax after 24 hours. Spontaneous (P=0.0078) and stromal cell-derived factor 1α -induced migration capacities of CLL B cells were also enhanced (P=0.0020). A microarray study highlighted 805 differentially expressed genes between leukemic cells cultured with or without EVs. Of these, genes involved in the B-cell receptor pathway such as CCL3/4, EGR1/2/3, and MYC were increased. Interestingly, this signature presents important overlaps with other microenvironment stimuli such as B-cell receptor stimulation, CLL/nurse-like cells co-culture or those provided by a lymph node microenvironment. Finally, we showed that EVs from MSCs of leukemic patients also rescue leukemic cells from spontaneous or drug-induced apoptosis. However, they induce a higher migration and also a stronger gene modification compared to EVs of healthy MSCs. In conclusion, we show that EVs play a crucial role in CLL B cells/BM microenvironment communication.

Targeting the CXCR4 pathway using a novel anti-CXCR4 IgG1 antibody (PF-06747143) in chronic lymphocytic leukemia

BACKGROUND

The CXCR4-CXCL12 axis plays an important role in the chronic lymphocytic leukemia (CLL)-microenvironment interaction. Overexpression of CXCR4 has been reported in different hematological malignancies including CLL. Binding of the pro-survival chemokine CXCL12 with its cognate receptor CXCR4 induces cell migration. CXCL12/CXCR4 signaling axis promotes cell survival and proliferation and may contribute to the tropism of leukemia cells towards lymphoid tissues and bone marrow. Therefore, we hypothesized that targeting CXCR4 with an IgG1 antibody, PF-06747143, may constitute an effective therapeutic approach for CLL.

METHODS

Patient-derived primary CLL-B cells were assessed for cytotoxicity in an in vitro model of CLL microenvironment. PF-06747143 was analyzed for cell death induction and for its potential to interfere with the chemokine CXCL12-induced mechanisms, including migration and F-actin polymerization. PF-06747143 in vivo efficacy was determined in a CLL murine xenograft tumor model.

RESULTS

PF-06747143, a novel-humanized IgG1 CXCR4 antagonist antibody, induced cell death of patient-derived primary CLL-B cells, in presence or absence of stromal cells. Moreover, cell death induction by the antibody was independent of CLL high-risk prognostic markers. The cell death mechanism was dependent on CXCR4 expression, required antibody bivalency, involved reactive oxygen species production, and did not require caspase activation, all characteristics reminiscent of programmed cell death (PCD). PF-06747143 also induced potent B-CLL cytotoxicity via Fc-driven antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity activity (CDC). PF-06747143 had significant combinatorial effect with standard of care (SOC) agents in B-CLL treatment, including rituximab, fludarabine (F-ara-A), ibrutinib, and bendamustine. In a CLL xenograft model, PF-06747143 decreased tumor burden and improved survival as a monotherapy, and in combination with bendamustine.

CONCLUSIONS

We show evidence that PF-06747143 has biological activity in CLL primary cells, supporting a rationale for evaluation of PF-06747143 for the treatment of CLL patients.

Targeting the CXCR4 pathway using a novel anti-CXCR4 IgG1 antibody (PF-06747143) in chronic lymphocytic leukemia

BACKGROUND

The CXCR4-CXCL12 axis plays an important role in the chronic lymphocytic leukemia (CLL)-microenvironment interaction. Overexpression of CXCR4 has been reported in different hematological malignancies including CLL. Binding of the pro-survival chemokine CXCL12 with its cognate receptor CXCR4 induces cell migration. CXCL12/CXCR4 signaling axis promotes cell survival and proliferation and may contribute to the tropism of leukemia cells towards lymphoid tissues and bone marrow. Therefore, we hypothesized that targeting CXCR4 with an IgG1 antibody, PF-06747143, may constitute an effective therapeutic approach for CLL.

METHODS

Patient-derived primary CLL-B cells were assessed for cytotoxicity in an in vitro model of CLL microenvironment. PF-06747143 was analyzed for cell death induction and for its potential to interfere with the chemokine CXCL12-induced mechanisms, including migration and F-actin polymerization. PF-06747143 in vivo efficacy was determined in a CLL murine xenograft tumor model.

RESULTS

PF-06747143, a novel-humanized IgG1 CXCR4 antagonist antibody, induced cell death of patient-derived primary CLL-B cells, in presence or absence of stromal cells. Moreover, cell death induction by the antibody was independent of CLL high-risk prognostic markers. The cell death mechanism was dependent on CXCR4 expression, required antibody bivalency, involved reactive oxygen species production, and did not require caspase activation, all characteristics reminiscent of programmed cell death (PCD). PF-06747143 also induced potent B-CLL cytotoxicity via Fc-driven antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity activity (CDC). PF-06747143 had significant combinatorial effect with standard of care (SOC) agents in B-CLL treatment, including rituximab, fludarabine (F-ara-A), ibrutinib, and bendamustine. In a CLL xenograft model, PF-06747143 decreased tumor burden and improved survival as a monotherapy, and in combination with bendamustine.

CONCLUSIONS

We show evidence that PF-06747143 has biological activity in CLL primary cells, supporting a rationale for evaluation of PF-06747143 for the treatment of CLL patients.

Plasma matrix metalloprotease 9 correlates with blood lymphocytosis, leukemic cell invasiveness, and prognosis in B-cell chronic lymphocytic leukemia

The complex biology underlying chronic lymphocytic leukemia cell migration and tissue invasiveness is not yet completely understood and might provide novel predictive markers and therapeutic targets. A total of 36 patients out of treatment from at least 3 months were enrolled and followed up for a median period of 44.2 months (range: 4.4–99.2). Matrix metalloprotease 9 and tissue inhibitor of metalloproteases 1 plasma levels and production/release from lymphoid cells were measured by zymography and enzyme-linked immunosorbent assay (ELISA) analysis. Malignant and normal lymphocyte mobility and matrix-degradation capability were studied using a Boyden chamber system, with and without autologous plasma. Free matrix metalloprotease 9 plasma levels were related with blood lymphocytosis, especially in more advanced stages (p = 0.003), and higher concentrations were associated with an increased disease progression risk (hazard ratio = 9.0, 95% confidence interval = 1.5–13.8). Leukemic cells expressed and secreted very little matrix metalloprotease 9. On the contrary, normal lymphocytes derived from the same leukemic patients showed matrix metalloprotease 9 intracellular levels that were lower in subjects with higher blood lymphocytosis (p = 0.024) and more advanced stages (p = 0.03); the released quantities were inversely associated with matrix metalloprotease 9 plasma concentrations (p = 0.035). Leukemic cells had a reduced spontaneous mobility and matrix-degradation capability that were stimulated by autologous plasma (p = 0.001) and normal lymphocytes (p = 0.005), respectively. Matrix metalloprotease 9 affected cell invasiveness depending on concentration and disease stage. In conclusion, chronic lymphocytic leukemia cells have a reduced mobility, matrix-degradation capability, and matrix metalloprotease 9 production compared to their own autologous normal lymphocytes. They are exposed to matrix metalloprotease 9 of prevalently systemic origin whose higher levels are associated with both leukemic and normal lymphocyte accumulation in the peripheral blood and have a negative prognostic value.

Bone marrow stroma-induced resistance of chronic lymphocytic leukemia cells to arsenic trioxide involves Mcl-1 upregulation and is overcome by inhibiting the PI3Kδ or PKCβ signaling pathways

CLL remains an incurable disease in spite of the many new compounds being studied. Arsenic trioxide (ATO) induces apoptosis in all CLL cell types and could constitute an efficient therapy. To further explore this, we have studied the influence of stromal cells, key components of the CLL microenvironment, on the response of CLL cells to ATO. Bone marrow stromal cells induced CLL cell resistance to 2 μM ATO and led to activation of Lyn, ERK, PI3K and PKC, as well as NF-κB and STAT3. Mcl-1, Bcl-xL, and Bfl-1 were also upregulated after the co-culture. Inhibition experiments indicated that PI3K and PKC were involved in the resistance to ATO induced by stroma. Moreover, idelalisib and sotrastaurin, specific inhibitors for PI3Kδ and PKCβ, respectively, inhibited Akt phosphorylation, NF-κB/STAT3 activation and Mcl-1 upregulation, and rendered cells sensitive to ATO. Mcl-1 was central to the mechanism of resistance to ATO, since: 1) Mcl-1 levels correlated with the CLL cell response to ATO, and 2) blocking Mcl-1 expression or function with specific siRNAs or inhibitors overcame the protecting effect of stroma. We have therefore identified the mechanism involved in the CLL cell resistance to ATO induced by bone marrow stroma and show that idelalisib or sotrastaurin block this mechanism and restore sensibility to ATO. Combination of ATO with these inhibitors may thus constitute an efficient treatment for CLL.

Lipoprotein lipase in chronic lymphocytic leukemia: function and prognostic implications

Chronic lymphocytic leukemia (CLL) is a clinically heterogeneous disease characterized by the accumulation of a clonal population of B cells in peripheral blood, bone marrow, and lymphoid organs. More than 10 years ago, lipoprotein lipase (LPL) mRNA was identified as being strongly expressed in patients experiencing a more aggressive phenotype, while CLL patients with an indolent disease course lack expression of this marker. Since then, several reports confirmed the capability of LPL to predict CLL disease evolution at the moment of diagnosis. In contrast, data on the functional implications of LPL in CLL are scarce. LPL exerts a central role in overall lipid metabolism and transport, but plays additional, non-catalytic roles as well. Which of those is more important in the pathogenesis of CLL remains largely unclear. Here, we review the current knowledge on the prognostic and biological relevance of LPL in CLL.

Expression and function of the TL1A/DR3 axis in chronic lymphocytic leukemia

TNF-like ligand 1A (TL1A) and its unique receptor death receptor 3 (DR3) acts as broad T-cell costimulator involved in regulatory mechanisms of adaptive immune response under physiological and pathological settings. Moreover, we have recently shown that TL1A negatively regulates B-cell proliferation. Despite increasing interest on the TL1A/DR3-axis functions, very little is known on its expression and role in leukemia. In this study, we investigated the expression and function of TL1A/DR3 axis in chronic lymphocytic leukemia (CLL). DR3 was differentially expressed in activated CLL cells and predominantly detected in patients with early clinical stage disease. Soluble TL1A has been revealed in the sera of CLL patients where higher TL1A levels were associated with early stage disease. T cells, monocytes and leukemic B cells have been identified as major sources of TL1A in CLL. The relevance of these findings has been sustained by functional data showing that exogenous TL1A reduces CLL proliferation induced by stimulation of the B cell receptor. Overall, these data document the expression of the TL1A/DR3 axis in early-stage CLL. They also identify a novel function for TL1A as a negative regulator of leukemic cell proliferation that may influence the CLL physiopathology and clinical outcome at an early-stage disease.

Key Molecular Drivers of Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is an adult neoplastic disease of B cells characterized by variable clinical outcomes. Although some patients have an aggressive form of the disease and often encounter treatment failure and short survival, others have more stable disease with long-term survival and little or no need for theraphy. In the past decade, significant advances have been made in our understanding of the molecular drivers that affect the natural pathology of CLL. The present review describes what is known about these key molecules in the context of their role in tumor pathogenicity, prognosis, and therapy.

CD84 mediates CLL-microenvironment interactions

Chronic lymphocytic leukemia (CLL) is a malignant disease of small mature lymphocytes. Signals from the CLL microenvironment promote progression of the disease and induce drug resistance. This phenomenon is largely dependent on direct contact between the malignant B cells and stromal cells. CD84 belongs to the signaling lymphocyte activation molecule family of immunoreceptors, which self-associates, forming an orthogonal homophilic dimer. We therefore hypothesized that CD84 may bridge between CLL cells and their microenvironment, promoting cell survival. Our in vitro results show that CD84 expressed on CLL cells interact with CD84 expressed on cells in their microenvironment, inducing cell survival in both sides. Blocking CD84 in vitro and in vivo disrupt the interaction of CLL cells with their microenvironment, resulting in induced cell death. Thus, our findings suggest novel therapeutic strategies based on the blockade of this CD84-dependent survival pathway.

Targeted therapies for CLL: Practical issues with the changing treatment paradigm

Chemoimmunotherapy (CIT) such as FCR (fludarabine, cyclophosphamide, rituximab) has been the standard first-line therapy for younger patients with CLL. In the last few years, several novel targeted therapies have been developed for patients with CLL. These include B-cell receptor (BCR) inhibitors such as Bruton tyrosine kinase (BTK) inhibitors, PI3 kinase inhibitors, and Syk inhibitors, novel anti-CD20 monoclonal antibodies such as ofatumumab and obinutuzumab, and Bcl-2 antagonists such as venetoclax (ABT-199). Strategies targeting the immune system such as lenalidomide, chimeric antigen receptor (CAR) T cells, and more recently, checkpoint inhibitors, are in clinical development. Ibrutinib and idelalisib are already approved for patients with relapsed and refractory CLL. Ibrutinib is also approved for first-line treatment of CLL patients with del(17p). Several ongoing phase III clinical trials with novel therapies will further define the role of targeted agents in CLL.

Bruton's tyrosine kinase inhibitor restrains Wnt signaling in chronic lymphocytic leukemia

The B-cell receptor (BCR) signaling pathway serves an important role in the pathogenesis of chronic lymphocytic leukemia (CLL), and has been identified as a novel and effective therapeutic target of CLL, with particular focus its kinase factor, BTK. Previous studies have focused on combining the BTK inhibitor with additional chemotherapeutic agents to improve the prognosis of patients with CLL. Further investigation into the mechanism of the BTK inhibitor would promote an understanding of the pathogenesis of CLL. The current study investigated the association between ibrutinib and the Wnt signaling pathway, additionally focussing upon one of its regulators, metadherin (MTDH), which has been identified to be overexpressed in CLL and is considered a promoter of the Wnt pathway. The experiments in the current study were performed in the MEC-1 CLL cell line. Results indicated that MTDH, β-catenin and lymphoid-enhancing factor-1 were inhibited subsequent to ibrutinib treatment. The results indicate that in CLL, ibrutinib is likely to possess an inhibitory role in Wnt signaling.

Preclinical modeling of novel therapeutics in chronic lymphocytic leukemia: the tools of the trade

In the last decade our understanding of chronic lymphocytic leukemia (CLL) biology and pathogenesis has increased substantially. These insights have led to the development of several new agents with novel mechanisms of action prompting a change in therapeutic approaches from chemotherapy-based treatments to targeted therapies. Multiple preclinical models for drug development in CLL are available; however, with the advent of these targeted agents, it is becoming clear that not all models and surrogate readouts of efficacy are appropriate for all drugs. In this review we discuss in vitro and in vivo preclinical models, with a particular focus on the benefits and possible pitfalls of different model systems in the evaluation of novel therapeutics for the treatment of CLL.

Ulocuplumab (BMS-936564 / MDX1338): a fully human anti-CXCR4 antibody induces cell death in chronic lymphocytic leukemia mediated through a reactive oxygen species-dependent pathway

The CXCR4 receptor (Chemokine C-X-C motif receptor 4) is highly expressed in different hematological malignancies including chronic lymphocytic leukemia (CLL). The CXCR4 ligand (CXCL12) stimulates CXCR4 promoting cell survival and proliferation, and may contribute to the tropism of leukemia cells towards lymphoid tissues. Therefore, strategies targeting CXCR4 may constitute an effective therapeutic approach for CLL. To address that question, we studied the effect of Ulocuplumab (BMS-936564), a fully human IgG4 anti-CXCR4 antibody, using a stroma--CLL cells co-culture model. We found that Ulocuplumab (BMS-936564) inhibited CXCL12 mediated CXCR4 activation-migration of CLL cells at nanomolar concentrations. This effect was comparable to AMD3100 (Plerixafor--Mozobil), a small molecule CXCR4 inhibitor. However, Ulocuplumab (BMS-936564) but not AMD3100 induced apoptosis in CLL at nanomolar concentrations in the presence or absence of stromal cell support. This pro-apoptotic effect was independent of CLL high-risk prognostic markers, was associated with production of reactive oxygen species and did not require caspase activation. Overall, these findings are evidence that Ulocuplumab (BMS-936564) has biological activity in CLL, highlight the relevance of the CXCR4-CXCL12 pathway as a therapeutic target in CLL, and provide biological rationale for ongoing clinical trials in CLL and other hematological malignancies.

Ofatumumab and Lenalidomide for Patients with Relapsed or Refractory Chronic Lymphocytic Leukemia: Correlation between Responses and Immune Characteristics

PURPOSE

We evaluated efficacy and tolerability of the combination of ofatumumab and lenalidomide in patients with relapsed/refractory chronic lymphocytic leukemia (CLL), and explored whether immune system characteristics could influence the response to treatment.

EXPERIMENTAL DESIGN

Thirty-four patients were enrolled in this phase II study. Ofatumumab was administered at a dose of 300 mg on day 1, 1,000 mg on days 8, 15, and 22 during course 1, 1,000 mg on day 1 during courses 3-6, and once every other course during courses 7-24 (28-day courses). Oral lenalidomide (10 mg daily) was started on day 9 and continued for as long as a clinical benefit was observed.

RESULTS

The overall response rate was 71%. Eight patients (24%) achieved a complete remission (CR) or CR with incomplete recovery of blood counts, including 9% with minimal residual disease-negative CR. The median progression-free survival was 16 months, and the estimated 5-year survival was 53%. The most common treatment-related toxicity was neutropenia (grade >2 in 18% of the 574 patient courses). The most frequent infectious complications were pneumonia and neutropenic fever (24% and 9% of patients, respectively). We observed that patients who achieved a CR had at baseline higher numbers and a better preserved function of T cells and natural killer cells compared with non-responders.

CONCLUSIONS

The combination of ofatumumab and lenalidomide is a well-tolerated regimen that induces durable responses in the majority of patients with relapsed/refractory CLL. Our correlative data suggest a role of competent immune system in supporting the efficacy of this treatment. Clin Cancer Res; 22(10); 2359-67. ©2016 AACR.

In vivo adhesion of malignant B cells to bone marrow microvasculature is regulated by α4β1 cytoplasmic-binding proteins

Multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) cells must attach to the bone marrow (BM) microvasculature before lodging in the BM microenvironment. Using intravital microscopy (IVM) of the BM calvariae we demonstrate that the α4β1 integrin is required for MM and CLL cell firm arrest onto the BM microvasculature, while endothelial P-selectin and E-selectin mediate cell rolling. Talin, kindlin-3 and ICAP-1 are β1-integrin-binding partners that regulate β1-mediated cell adhesion. We show that talin and kindlin-3 cooperatively stimulate high affinity and strength of α4β1-dependent MM and CLL cell attachment, whereas ICAP-1 negatively regulates this adhesion. A functional connection between talin/kindlin-3 and Rac1 was found to be required for MM cell attachment mediated by α4β1. Importantly, IVM analyses with talin- and kindlin-3-silenced MM cells indicate that these proteins are needed for cell arrest on the BM microvasculature. Instead, MM cell arrest is repressed by ICAP-1. Moreover, MM cells silenced for talin and kindlin-3, and cultured on α4β1 ligands showed higher susceptibility to bortezomib-mediated cell apoptosis. Our results highlight the requirement of α4β1 and selectins for the in vivo attachment of MM and CLL cells to the BM microvasculature, and indicate that talin, kindlin-3 and ICAP-1 differentially control physiological adhesion by regulating α4β1 activity.

Disruption of in vivo Chronic Lymphocytic Leukemia Tumor-Microenvironment Interactions by Ibrutinib--Findings from an Investigator-Initiated Phase II Study

PURPOSE

Chronic lymphocytic leukemia (CLL) cells depend on microenvironmental interactions for proliferation and survival that are at least partially mediated through B-cell receptor (BCR) signaling. Ibrutinib, a Bruton tyrosine kinase inhibitor, disrupts BCR signaling and leads to the egress of tumor cells from the microenvironment. Although the on-target effects on CLL cells are well defined, the impact on the microenvironment is less well studied. We therefore sought to characterize the in vivo effects of ibrutinib on the tumor microenvironment.

EXPERIMENTAL DESIGN

Patients received single-agent ibrutinib on an investigator-initiated phase II trial. Serial blood and tissue samples were collected pretreatment and during treatment. Changes in cytokine levels, cellular subsets, and microenvironmental interactions were assessed.

RESULTS

Serum levels of key chemokines and inflammatory cytokines decreased significantly in patients on ibrutinib. Furthermore, ibrutinib treatment decreased circulating tumor cells and overall T-cell numbers. Most notably, a reduced frequency of the Th17 subset of CD4(+)T cells was observed concurrent with reduced expression of activation markers and PD-1 on T cells. Consistent with direct inhibition of T cells, ibrutinib inhibited Th17 differentiation of murine CD4(+)T cells in vitro Finally, in the bone marrow microenvironment, we found that ibrutinib disaggregated the interactions of macrophages and CLL cells, inhibited secretion of CXCL13, and decreased the chemoattraction of CLL cells.

CONCLUSIONS

In conjunction with inhibition of BCR signaling, these changes in the tumor microenvironment likely contribute to the antitumor activity of ibrutinib and may impact the efficacy of immunotherapeutic strategies in patients with CLL. See related commentary by Bachireddy and Wu, p. 1547.

Lyn sustains oncogenic signaling in chronic lymphocytic leukemia by strengthening SET-mediated inhibition of PP2A

Cytosolic HSP90-bound Lyn mediates resistance to apoptosis by strengthening PP2A/SET interaction in CLL cells. FTY720-analogues antagonizing the PP2A/SET interaction and Lyn inhibitors may provide a therapeutic approach of CLL.

Initial treatment of CLL: integrating biology and functional status

A better understanding of the biology of chronic lymphocytic leukemia (CLL) has led to significant advances in therapeutic strategies for patients with CLL. Chemoimmunotherapy (CIT) has been the standard first-line therapy for CLL. Age and comorbidities can help decide which patients may benefit from a CIT approach. FCR (fludarabine, cyclophosphamide, and rituximab) is the current standard treatment option for younger patients with CLL. For older patients and for patients with renal dysfunction, bendamustine and rituximab may be a better option. For older patients with comorbidities who may not be able to tolerate intensive CIT, the combination treatment of chlorambucil and obinutuzumab or ofatumumab is an option. For patients with del(17p), ibrutinib is the treatment of choice. Several ongoing phase 3 clinical trials with novel therapies will further refine the frontline therapy of CLL.

The STAT3 inhibitor WP1066 reverses the resistance of chronic lymphocytic leukemia cells to histone deacetylase inhibitors induced by interleukin-6

Interleukin-6 (IL-6) is a pleiotropic cytokine produced by a variety of cell types, including fibroblasts, endothelial cells, lymphocytes, and bone marrow stromal cells (BMSCs). Levels of IL-6 are increased in serum of CLL patients and correlated with adverse clinical features and short survival. In our study, we observed that IL-6 induced the resistance of CLL cells to pan-histone deacetylase (HDAC) inhibitors vorinostat (SAHA) and panobinostat (LBH589). Furthermore, low concentrations of SAHA and LBH589 enhanced the activation of the signal transducer and activator of transcription 3 (STAT3) signaling pathway induced by IL-6 in CLL cells. All of these effects were blocked by the STAT3-selective inhibitor, WP1066. Meanwhile, WP1066 decreased the expressions of Mcl-1 and Bcl-xL protein induced by IL-6 with or without low concentrations of HDAC inhibitors. Co-culture of CLL cells with BMSCs could also facilitate the activation of STAT3 and protected CLL cells from apoptosis when treated with HDAC inhibitors, and this cytoprotection was reversed by WP1066. The present study indicated that IL-6 or co-culture with BMSCs prevented HDAC inhibitor-induced apoptosis of CLL cells. This prevention was mediated by activation of the STAT3 signaling pathway. Moreover, WP1066 reversed the resistance of CLL cells to SAHA and LBH589 induced by either IL-6 or co-culture with BMSCs. Our findings suggest that targeting the STAT3 pathway may be a novel way to improve the efficacy of the HDAC inhibitor in CLL patients by overcoming antiapoptotic signaling of the microenvironment.