Chronic lymphocytic leukaemia--the role of the microenvironment pathogenesis and therapy

B cell receptor signaling and associated pathways in the pathogenesis of chronic lymphocytic leukemia

B cell antigen receptor (BCR) signaling is a key driver of growth and survival in both normal and malignant B cells. Several lines of evidence support an important pathogenic role of the BCR in chronic lymphocytic leukemia (CLL). The significant improvement of CLL patients' survival with the use of various BCR pathway targeting inhibitors, supports a crucial involvement of BCR signaling in the pathogenesis of CLL. Although the treatment landscape of CLL has significantly evolved in recent years, no agent has clearly demonstrated efficacy in patients with treatment-refractory CLL in the long run. To identify new drug targets and mechanisms of drug action in neoplastic B cells, a detailed understanding of the molecular mechanisms of leukemic transformation as well as CLL cell survival is required. In the last decades, studies of genetically modified CLL mouse models in line with CLL patient studies provided a variety of exciting data about BCR and BCR-associated kinases in their role in CLL pathogenesis as well as disease progression. BCR surface expression was identified as a particularly important factor regulating CLL cell survival. Also, BCR-associated kinases were shown to provide a crosstalk of the CLL cells with their tumor microenvironment, which highlights the significance of the cells' milieu in the assessment of disease progression and treatment. In this review, we summarize the major findings of recent CLL mouse as well as patient studies in regard to the BCR signalosome and discuss its relevance in the clinics.

A Novel Triple-Action Inhibitor Targeting B-Cell Receptor Signaling and BRD4 Demonstrates Preclinical Activity in Chronic Lymphocytic Leukemia

B-cell chronic lymphocytic leukemia (CLL) results from intrinsic genetic defects and complex microenvironment stimuli that fuel CLL cell growth through an array of survival signaling pathways. Novel small-molecule agents targeting the B-cell receptor pathway and anti-apoptotic proteins alone or in combination have revolutionized the management of CLL, yet combination therapy carries significant toxicity and CLL remains incurable due to residual disease and relapse. Single-molecule inhibitors that can target multiple disease-driving factors are thus an attractive approach to combat both drug resistance and combination-therapy-related toxicities. We demonstrate that SRX3305, a novel small-molecule BTK/PI3K/BRD4 inhibitor that targets three distinctive facets of CLL biology, attenuates CLL cell proliferation and promotes apoptosis in a dose-dependent fashion. SRX3305 also inhibits the activation-induced proliferation of primary CLL cells in vitro and effectively blocks microenvironment-mediated survival signals, including stromal cell contact. Furthermore, SRX3305 blocks CLL cell migration toward CXCL-12 and CXCL-13, which are major chemokines involved in CLL cell homing and retention in microenvironment niches. Importantly, SRX3305 maintains its anti-tumor effects in ibrutinib-resistant CLL cells. Collectively, this study establishes the preclinical efficacy of SRX3305 in CLL, providing significant rationale for its development as a therapeutic agent for CLL and related disorders.

Bone marrow dendritic cells support the survival of chronic lymphocytic leukemia cells in a CD84 dependent manner

Chronic lymphocytic leukemia (CLL) is a malignancy of mature B lymphocytes. The microenvironment of the CLL cells is a vital element in the regulation of the survival of these malignant cells. CLL cell longevity is dependent on external signals, originating from cells in their microenvironment including secreted and surface-bound factors. Dendritic cells (DCs) play an important part in tumor microenvironment, but their role in the CLL bone marrow (BM) niche has not been studied. We show here that CLL cells induce accumulation of bone marrow dendritic cells (BMDCs). Depletion of this population attenuates disease expansion. Our results show that the support of the microenvironment is partly dependent on CD84, a cell surface molecule belonging to the Signaling Lymphocyte Activating Molecule (SLAM) family of immunoreceptors. Our results suggest a novel therapeutic strategy whereby eliminating BMDCs or blocking the CD84 expressed on these cells may reduce the tumor load.

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.

Microenvironment-induced PIM kinases promote CXCR4-triggered mTOR pathway required for chronic lymphocytic leukaemia cell migration

Lymph node microenvironment provides chronic lymphocytic leukaemia (CLL) cells with signals promoting their survival and granting resistance to chemotherapeutics. CLL cells overexpress PIM kinases, which regulate apoptosis, cell cycle and migration. We demonstrate that BCR crosslinking, CD40 stimulation, and coculture with stromal cells increases PIMs expression in CLL cells, indicating microenvironment‐dependent PIMs regulation. PIM1 and PIM2 expression at diagnosis was higher in patients with advanced disease (Binet C vs. Binet A/B) and in those, who progressed after first‐line treatment. In primary CLL cells, inhibition of PIM kinases with a pan‐PIM inhibitor, SEL24‐B489, decreased PIM‐specific substrate phosphorylation and induced dose‐dependent apoptosis in leukaemic, but not in normal B cells. Cytotoxicity of SEL24‐B489 was similar in TP53‐mutant and TP53 wild‐type cells. Finally, inhibition of PIM kinases decreased CXCR4‐mediated cell chemotaxis in two related mechanisms‐by decreasing CXCR4 phosphorylation and surface expression, and by limiting CXCR4‐triggered mTOR pathway activity. Importantly, PIM and mTOR inhibitors similarly impaired migration, indicating that CXCL12‐triggered mTOR is required for CLL cell chemotaxis. Given the microenvironment‐modulated PIM expression, their pro‐survival function and a role of PIMs in CXCR4‐induced migration, inhibition of these kinases might override microenvironmental protection and be an attractive therapeutic strategy in this disease.

BRD4 Profiling Identifies Critical Chronic Lymphocytic Leukemia Oncogenic Circuits and Reveals Sensitivity to PLX51107, a Novel Structurally Distinct BET Inhibitor

Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or de novo expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel in vitro and in vivo pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers.Significance: To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. Cancer Discov; 8(4); 458-77. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 371.

The possible role of maintenance treatment for primary central nervous system lymphoma

Primary central nervous system lymphoma (PCNSL) is a rare and aggressive brain tumor. The prognosis is poor, with high rates of relapse and disease progression after treatment. In addition, PCNSL affects a largely older population, so that a significant proportion of patients are ineligible for intensive therapies and high-dose chemotherapy. The elderly patients are also susceptible to the accelerated and detrimental cognitive side effects of whole-brain irradiation which is an alternative consolidation to high-dose chemotherapy. Maintenance therapy has been shown to be a promising strategy to prolong remission time in other hematopoietic malignancies. Herein, we discuss the place of maintenance treatment in PCNSL in view of perspective obtained from hematological malignancies and non-Hodgkin's lymphoma.

Role of Bruton's tyrosine kinase in B cells and malignancies

Bruton’s tyrosine kinase (BTK) is a non-receptor kinase that plays a crucial role in oncogenic signaling that is critical for proliferation and survival of leukemic cells in many B cell malignancies. BTK was initially shown to be defective in the primary immunodeficiency X-linked agammaglobulinemia (XLA) and is essential both for B cell development and function of mature B cells. Shortly after its discovery, BTK was placed in the signal transduction pathway downstream of the B cell antigen receptor (BCR). More recently, small-molecule inhibitors of this kinase have shown excellent anti-tumor activity, first in animal models and subsequently in clinical studies. In particular, the orally administered irreversible BTK inhibitor ibrutinib is associated with high response rates in patients with relapsed/refractory chronic lymphocytic leukemia (CLL) and mantle-cell lymphoma (MCL), including patients with high-risk genetic lesions. Because ibrutinib is generally well tolerated and shows durable single-agent efficacy, it was rapidly approved for first-line treatment of patients with CLL in 2016. To date, evidence is accumulating for efficacy of ibrutinib in various other B cell malignancies. BTK inhibition has molecular effects beyond its classic role in BCR signaling. These involve B cell-intrinsic signaling pathways central to cellular survival, proliferation or retention in supportive lymphoid niches. Moreover, BTK functions in several myeloid cell populations representing important components of the tumor microenvironment. As a result, there is currently a considerable interest in BTK inhibition as an anti-cancer therapy, not only in B cell malignancies but also in solid tumors. Efficacy of BTK inhibition as a single agent therapy is strong, but resistance may develop, fueling the development of combination therapies that improve clinical responses. In this review, we discuss the role of BTK in B cell differentiation and B cell malignancies and highlight the importance of BTK inhibition in cancer therapy.

Cell lines generated from a chronic lymphocytic leukemia mouse model exhibit constitutive Btk and Akt signaling

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature CD5⁺ B cells in blood. Spontaneous apoptosis of CLL cells in vitro has hampered in-depth investigation of CLL pathogenesis. Here we describe the generation of three monoclonal mouse cell lines, EMC2, EMC4 and EMC6, from the IgH.TEμ CLL mouse model based on sporadic expression of SV40 large T antigen. The cell lines exhibit a stable CD5⁺CD43⁺IgM⁺CD19⁺ CLL phenotype in culture and can be adoptively transferred into Rag1^−/− mice. RNA-seq analysis revealed only minor differences between the cell lines and their primary tumors and suggested that NF-κB and mTOR signaling pathways were involved in cell line outgrowth. In vitro survival and proliferation was dependent on constitutive phosphorylation of Bruton's tyrosine kinase (Btk) at Y551/Y223, and Akt(S473). Treatment of the cell lines with small molecule inhibitors specific for Btk (ibrutinib) or PI3K (idelalisib), which is upstream of Akt, resulted in reduced viability, proliferation and fibronectin-dependent cell adhesion. Treatment of cell line-engrafted Rag1^−/− mice with ibrutinib was associated with transient lymphocytosis, reduced splenomegaly and increased overall survival. Thus, by generating stable cell lines we established a novel platform for in vitro and in vivo investigation of CLL signal transduction and treatment modalities.

Immune checkpoint blockade: the role of PD-1-PD-L axis in lymphoid malignancies

The co-inhibitory receptor programmed cell death (PD)-1, expressed by immune effector cells, is credited with a protective role for normal tissue during immune responses, by limiting the extent of effector activation. Its presently known ligands, programmed death ligands (PD-Ls) 1 and 2, are expressed by a variety of cells including cancer cells, suggesting a role for these molecules as an immune evasion mechanism. Blocking of the PD-1-PD-L signaling axis has recently been shown to be effective and was clinically approved in relapsed/refractory tumors such as malignant melanoma and lung cancer, but also classical Hodgkin’s lymphoma. A plethora of trials exploring PD-1 blockade in cancer are ongoing. Here, we review the role of PD-1 signaling in lymphoid malignancies, and the latest results of trials investigating PD-1 or PD-L1 blocking agents in this group of diseases. Early phase studies proved very promising, leading to the clinical approval of a PD-1 blocking agent in Hodgkin’s lymphoma, and Phase III clinical studies are either planned or ongoing in most lymphoid malignancies.

The mutational signature of chronic lymphocytic leukemia

Advances in next-generation sequencing technologies continue to unravel the cancer genome, identifying key biological pathways important for disease pathogenesis and clinically relevant genetic lesions. These studies have provided unprecedented resolution of the cancer genome, facilitating significant advances in the ability to detect many cancers, and predict patients who will develop an aggressive disease or respond poorly to treatment. The mature B-cell neoplasm chronic lymphocytic leukaemia remains at the forefront of these genomic analyses, largely due its protracted natural history and the accessibility to suitable material for study. We now possess a comprehensive view of the genomic copy number mutational landscape of the disease, as well as a detail description of clonal evolution, and the molecular mechanisms that drive the acquisition of genomic lesions and more broadly, genomic complexity. Here, recent genomic insights with associated biological and clinical implications will be reviewed.

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.

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.

Development, Maintenance, and Reversal of Multiple Drug Resistance: At the Crossroads of TFPI1, ABC Transporters, and HIF1

Early detection and improved therapies for many cancers are enhancing survival rates. Although many cytotoxic therapies are approved for aggressive or metastatic cancer; response rates are low and acquisition of de novo resistance is virtually universal. For decades; chemotherapeutic treatments for cancer have included anthracyclines such as Doxorubicin (DOX); and its use in aggressive tumors appears to remain a viable option; but drug resistance arises against DOX; as for all other classes of compounds. Our recent work suggests the anticoagulant protein Tissue Factor Pathway Inhibitor 1α (TFPI1α) plays a role in driving the development of multiple drug resistance (MDR); but not maintenance; of the MDR state. Other factors; such as the ABC transporter drug efflux pumps MDR-1/P-gp (ABCB1) and BCRP (ABCG2); are required for MDR maintenance; as well as development. The patient population struggling with therapeutic resistance specifically requires novel treatment options to resensitize these tumor cells to therapy. In this review we discuss the development, maintenance, and reversal of MDR as three distinct phases of cancer biology. Possible means to exploit these stages to reverse MDR will be explored. Early molecular detection of MDR cancers before clinical failure has the potential to offer new approaches to fighting MDR cancer.

Targeting Bruton's tyrosine kinase signaling as an emerging therapeutic agent of B-cell malignancies

It is becoming increasingly evident that B-cell receptor (BCR) signaling is central to the development and function of B cells. BCR signaling has emerged as a pivotal pathway and a key driver of numerous B-cell lymphomas. Disruption of BCR signaling can be lethal to malignant B cells. Recently, kinase inhibitors that target BCR signaling have induced notable clinical responses. These inhibitors include spleen tyrosine kinase, mammalian target of rapamycin, phosphoinositide 3'-kinase and Bruton's tyrosine kinase (BTK). Ibrutinib, an oral irreversible BTK inhibitor, has emerged as a promising targeted therapy for patients with B-cell malignancies. The present review discusses the current understanding of BTK-mediated BCR signaling in the biology and pathobiology of normal and malignant B cells, and the cellular interaction with the tumor microenvironment. The data on ibrutinib in the preclinical and clinical settings is also discussed, and perspectives for the future use of ibrutinib are outlined.

Transcriptomic profile induced in bone marrow mesenchymal stromal cells after interaction with multiple myeloma cells: implications in myeloma progression and myeloma bone disease

Despite evidence about the implication of the bone marrow (BM) stromal microenvironment in multiple myeloma (MM) cell growth and survival, little is known about the effects of myelomatous cells on BM stromal cells. Mesenchymal stromal cells (MSCs) from healthy donors (dMSCs) or myeloma patients (pMSCs) were co-cultured with the myeloma cell line MM.1S, and the transcriptomic profile of MSCs induced by this interaction was analyzed. Deregulated genes after co-culture common to both d/pMSCs revealed functional involvement in tumor microenvironment cross-talk, myeloma growth induction and drug resistance, angiogenesis and signals for osteoclast activation and osteoblast inhibition. Additional genes induced by co-culture were exclusively deregulated in pMSCs and predominantly associated to RNA processing, the ubiquitine-proteasome pathway, cell cycle regulation, cellular stress and non-canonical Wnt signaling. The upregulated expression of five genes after co-culture (CXCL1, CXCL5 and CXCL6 in d/pMSCs, and Neuregulin 3 and Norrie disease protein exclusively in pMSCs) was confirmed, and functional in vitro assays revealed putative roles in MM pathophysiology. The transcriptomic profile of pMSCs co-cultured with myeloma cells may better reflect that of MSCs in the BM of myeloma patients, and provides new molecular insights to the contribution of these cells to MM pathophysiology and to myeloma bone disease.

Targeted antisense radiotherapy and dose fractionation using a (177)Lu-labeled anti-bcl-2 peptide nucleic acid-peptide conjugate

INTRODUCTION

The overall goal of these studies was to test the hypothesis that simultaneous down-regulation of a tumor survival gene and delivery of internally emitted cytotoxic radiation will be more effective than either treatment modality alone. The objectives were to evaluate the therapeutic efficacy of a (177)Lu-labeled anti-bcl-2-PNA-Tyr(3)-octreotate antisense conjugate in a mouse model bearing human non-Hodgkin's lymphoma (NHL) tumor xenografts and to optimize targeted antisense radiotherapy by dose fractionation.

METHODS

In the initial therapy studies, tumor-bearing mice were given saline, nonradioactive DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate, (177)Lu-DOTA-Tyr(3)-octreotate, (177)Lu-DOTA-PNA-peptide alone, or (177)Lu-DOTA-PNA-peptide followed by a chase dose of nonradioactive PNA-peptide. The MTD of (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate was then determined. Subsequently single dose MTD and four weekly fractionated doses were directly compared, followed by histopathologic evaluation.

RESULTS

Antisense radiotherapy using 4.44 MBq of the (177)Lu-DOTA-PNA-peptide followed by nonradioactive PNA-peptide was significantly more effective than other low dose treatment regimens. A dose of 18.5 MBq of (177)Lu-DOTA-PNA-peptide was determined to be the approximate maximum tolerated dose (MTD). The median times to progression to a 1cm(3) tumor volume were 32 and 49 days for single dose MTD and fractionated dose (4 × 4.63 MBq) groups, respectively. Histopathology revealed metastases in the single dose groups, but not in the dose fractionation group.

CONCLUSIONS

Targeted antisense radiotherapy using (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate and DOTA-PNA-peptide conjugate effectively inhibited tumor progression in a mouse model of NHL. Furthermore, a dose fractionation regimen had a significant advantage over a single high dose, in terms of tumor growth inhibition and prevention of metastasis.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Down-regulating bcl-2, an anti-apoptotic proto-oncogene, is a mechanism to reverse chemotherapy resistance or failure in humans with NHL. We have developed a (177)Lu-DOTA-anti-bcl-2-PNA-Tyr(3)-octreotate conjugate for targeted antisense radiotherapy, in which down-regulation of bcl-2 and delivery of cytotoxic radiation occur simultaneously. Our previous studies have shown highly specific inhibition of bcl-2 protein, additive in vitro cytotoxic effects on human lymphoma cells, and favorable biodistribution and dosimetric properties. Lutetium-177 targeted antisense radiotherapy demonstrates a significant advantage over conventional (177)Lu-peptide receptor radionuclide therapy in a mouse model of NHL. Our preclinical studies identified an effective combination of antisense and radionuclide therapy, with the goal of future clinical trials in patients.

Arsenic trioxide synergistically potentiates the cytotoxic effect of fludarabine in chronic lymphocytic leukemia cells by further inactivating the Akt and ERK signaling pathways

CLL remains an incurable disease, making it crucial to continue searching for new therapies efficient in all CLL cases. We have studied the effect of combining arsenic trioxide (ATO) with fludarabine, a frontline drug in CLL. We have found a synergistic interaction between 1 μM ATO and 5 μM fludarabine that significantly enhanced the cytotoxic effect of the individual drugs. Importantly, ATO sensitized fludarabine-resistant cells to the action of this drug. The mechanism behind this effect included the downregulation of phospho-Akt, phospho-ERK, and the Mcl-1/Bim and Bcl-2/Bax ratios. The combination of ATO and fludarabine partially overcame the survival effect induced by co-culturing CLL cells with stromal cells. Therefore, low concentrations of ATO combined with fludarabine may be an efficient therapeutic strategy in CLL patients.

Decreased dickkopf-1 levels in chronic lymphocytic leukemia and increased osteopontin levels in non-Hodgkin's lymphoma at initial diagnosis: Could they be playing roles in pathogenesis?

Aims We determined plasma levels of dickkopf-1 (DKK-1) and osteopontin (OPN) which have roles in the Wnt pathway in chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL) patients and in healthy controls. We also tested whether DKK-1 and OPN levels could be of clinical or prognostic significance in CLL and NHL. Methods We included 36 CLL, 24 NHL patients, and 21 healthy controls. Patients' clinical and demographic features, treatment modalities, and response to treatment were recorded. DKK-1 and OPN levels in plasma obtained at initial diagnosis were determined with enzyme-linked immunosorbent assay. Results CLL patients had significantly lower DKK-1 levels than NHL and control groups (P levels, respectively, 0.048 and 0.017). OPN level was significantly higher in NHL group than in CLL and control groups (P values, 0.017 and <0.001). CLL patients with early and late Rai stages of disease had similar DKK-1 and OPN levels. After a median follow-up of 48 months, 13 CLL patients died. Univariate analysis showed that advanced Rai stages and older age were significantly poor prognostic factors. DKK-1 level in CLL patients who have died was significantly lower than those who were alive (P = 0.035). NHL patients with extranodal involvement had significantly higher OPN levels than those with no involvement (P = 0.04). Conclusions Our results demonstrated that the Wnt pathway inhibitor DKK-1 was decreased in CLL. OPN was increased in NHL and associated with extranodal involvement. In order to reveal the pathogenic and clinical roles of DKK-1 and OPN in CLL and NHL, larger studies need to be conducted.

Targeted therapy with MXD3 siRNA, anti-CD22 antibody and nanoparticles for precursor B-cell acute lymphoblastic leukaemia

Conventional chemotherapy for precursor B-cell (preB) acute lymphoblastic leukaemia (ALL) has limitations that could be overcome by targeted therapy. Previously, we discovered a potential therapeutic molecular target, MDX3 (MAX dimerization protein 3), in preB ALL. In this study, we hypothesize that an effective siRNA therapy for preB ALL can be developed using antiCD22 antibody (αCD22 Ab) and nanoparticles. We composed nanocomplexes with super paramagnetic iron oxide nanoparticles (SPIO NPs), αCD22 Abs and MXD3 siRNA molecules based on physical interactions between the molecules. We demonstrated that the MXD3 siRNA-αCD22 Ab-SPIO NP complexes entered leukaemia cells and knocked down MXD3, leading the cells to undergo apoptosis and resulting in decreased live cell counts in the cell line Reh and in primary preB ALL samples in vitro. Furthermore, the cytotoxic effects of the MXD3 siRNA-αCD22 Ab-SPIO NP complexes were significantly enhanced by addition of the chemotherapy drugs vincristine or doxorubicin. We also ruled out potential cytotoxic effects of the MXD3 siRNA-αCD22 Ab-SPIO NP complexes on normal primary haematopoietic cells. Normal B cells were affected while CD34-positive haematopoietic stem cells and non-B cells were not. These data suggest that MXD3 siRNA-αCD22 Ab-SPIO NP complexes have the potential to be a new targeted therapy for preB ALL.

FCR and bevacizumab treatment in patients with relapsed chronic lymphocytic leukemia

BACKGROUND

Patients with relapsed chronic lymphocytic leukemia (CLL) often achieve response with chemoimmunotherapy but have short remission durations. Studies have shown that patients with CLL have increased angiogenesis in the microenvironment; levels of proangiogenic growth factors such as VEGF and/or angiopoietin-2 are also elevated. Increased angiogenesis correlates with poor outcome in CLL. Bevacizumab (B) is a humanized monoclonal antibody targeting VEGF-A.

METHODS

In this study, we analyzed whether a combination of bevacizumab with fludarabine, cyclophosphamide, and rituximab chemoimmunotherapy (FCR-B) could improve outcomes in patients with relapsed CLL. Sixty-two patients were enrolled. The median age of the patients was 60 years (range, 31-84 years) and 40% had received >1 prior therapy for CLL. Sixty-one patients were evaluable for toxicity, and 57 were evaluable for response. Six cycles were planned; 36 patients (59%) completed ≥4-6 cycles of the regimen.

RESULTS

The overall response rate was 79%, with 13 (23%) complete remissions (CRs), 8 nodular partial remissions (14%), and 24 partial remissions (43%). The median progression-free survival and overall survival rates were 13.5 and 45 months, respectively. Grade 3 or 4 toxicities included febrile neutropenia (n = 40), infections (n = 21), thrombocytopenia (n = 18) and anemia (n = 9).

CONCLUSIONS

Results with FCR-B were similar to those observed with an historical cohort of relapsed patients treated with FCR.

Chronic lymphocytic leukemia cells in a lymph node microenvironment depict molecular signature associated with an aggressive disease

Chronic lymphocytic leukemia (CLL) cells survive longer in vivo than in vitro, suggesting that the tissue microenvironment provides prosurvival signals to tumor cells. Primary and secondary lymphoid tissues are involved in the pathogenesis of CLL, and the role of these tissue microenvironments has not been explored completely. To elucidate host-tumor interactions, we performed gene expression profiling (GEP) of purified CLL cells from peripheral blood (PB; n = 20), bone marrow (BM; n = 18), and lymph node (LN; n = 15) and validated key pathway genes by real-time polymerase chain reaction, immunohistochemistry and/or TCL1 trans-genic mice. Gene signatures representing several pathways critical for survival and activation of B cells were altered in CLL cells from different tissue compartments. Molecules associated with the B-cell receptor (BCR), B cell-activating factor/a proliferation-inducing ligand (BAFF/APRIL), nuclear factor (NF)-κB pathway and immune suppression signature were enriched in LN-CLL, suggesting LNs as the primary site for tumor growth. Immune suppression genes may help LN-CLL cells to modulate antigen-presenting and T-cell behavior to suppress antitumor activity. PB CLL cells overexpressed chemokine receptors, and their cognate ligands were enriched in LN and BM, suggesting that a chemokine gradient instructs B cells to migrate toward LN or BM. Of several chemokine ligands, the expression of CCL3 was associated with poor prognostic factors. The BM gene signature was enriched with antiapoptotic, cytoskeleton and adhesion molecules. Interestingly, PB cells from lymphadenopathy patients shared GEP with LN cells. In Eμ-TCL1 transgenic mice (the mouse model of the disease), a high percentage of leukemic cells from the lymphoid compartment express key BCR and NF-κB molecules. Together, our findings demonstrate that the lymphoid microenvironment promotes survival, proliferation and progression of CLL cells via chronic activation of BCR, BAFF/APRIL and NF-κB activation while suppressing the immune response.

PKC-β as a therapeutic target in CLL: PKC inhibitor AEB071 demonstrates preclinical activity in CLL

Targeting B-cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL) has been successful with durable remissions observed with several targeted therapeutics. Protein kinase C-β (PKC-β) is immediately downstream of BCR and has been shown to be essential to CLL cell survival and proliferation in vivo. We therefore evaluated sotrastaurin (AEB071), an orally administered potent PKC inhibitor, on CLL cell survival both in vitro and in vivo. AEB071 shows selective cytotoxicity against B-CLL cells in a dose-dependent manner. Additionally, AEB071 attenuates BCR-mediated survival pathways, inhibits CpG-induced survival and proliferation of CLL cells in vitro, and effectively blocks microenvironment-mediated survival signaling pathways in primary CLL cells. Furthermore, AEB071 alters β-catenin expression, resulting in decreased downstream transcriptional genes as c-Myc, Cyclin D1, and CD44. Lastly, our preliminary in vivo studies indicate beneficial antitumor properties of AEB071 in CLL. Taken together, our results indicate that targeting PKC-β has the potential to disrupt signaling from the microenvironment contributing to CLL cell survival and potentially drug resistance. Future efforts targeting PKC with the PKC inhibitor AEB071 as monotherapy in clinical trials of relapsed and refractory CLL patients are warranted.

Matrix metalloproteinase-9 is involved in chronic lymphocytic leukemia cell response to fludarabine and arsenic trioxide

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) contributes to chronic lymphocytic leukemia (CLL) pathology by regulating cell migration and preventing spontaneous apoptosis. It is not known if MMP-9 is involved in CLL cell response to chemotherapy and we address this in the present study, using arsenic trioxide (ATO) and fludarabine as examples of cytotoxic drugs.

METHODS

We used primary cells from the peripheral blood of CLL patients and MEC-1 cells stably transfected with an empty vector or a vector containing MMP-9. The effect of ATO and fludarabine was determined by flow cytometry and by the MTT assay. Expression of mRNA was measured by RT-PCR and qPCR. Secreted and cell-bound MMP-9 was analyzed by gelatin zymography and flow cytometry, respectively. Protein expression was analyzed by Western blotting and immunoprecipitation. Statistical analyses were performed using the two-tailed Student's t-test.

RESULTS

In response to ATO or fludarabine, CLL cells transcriptionally upregulated MMP-9, preceding the onset of apoptosis. Upregulated MMP-9 primarily localized to the membrane of early apoptotic cells and blocking apoptosis with Z-VAD prevented MMP-9 upregulation, thus linking MMP-9 to the apoptotic process. Culturing CLL cells on MMP-9 or stromal cells induced drug resistance, which was overcome by anti-MMP-9 antibodies. Accordingly, MMP-9-MEC-1 transfectants showed higher viability upon drug treatment than Mock-MEC-1 cells, and this effect was blocked by silencing MMP-9 with specific siRNAs. Following drug exposure, expression of anti-apoptotic proteins (Mcl-1, Bcl-xL, Bcl-2) and the Mcl-1/Bim, Mcl-1/Noxa, Bcl-2/Bax ratios were higher in MMP-9-cells than in Mock-cells. Similar results were obtained upon culturing primary CLL cells on MMP-9.

CONCLUSIONS

Our study describes for the first time that MMP-9 induces drug resistance by modulating proteins of the Bcl-2 family and upregulating the corresponding anti-apoptotic/pro-apoptotic ratios. This is a novel role for MMP-9 contributing to CLL progression. Targeting MMP-9 in combined therapies may thus improve CLL response to treatment.

IgM peak independently predicts treatment-free survival in chronic lymphocytic leukemia and correlates with accumulation of adverse oncogenetic events

We examined the significance of IgM peaks in chronic lymphocytic leukemia (CLL), including its association with newly reported MYD88, BIRC3, NOTCH1 and SF3B1 mutations. A total of 27, 25, 41 and 57 patients with monoclonal IgM or IgG peaks (IgM and IgG groups), hypogammaglobulinemia (Hypo-γ group) and normal immunoglobulin serum levels (normal-γ group) were, respectively, included. IgM peaks were mainly associated with Binet stage C and the del(17p). Biased usage of IGHV3-48 was shared by both IgM and IgG groups. IGHV3-74 and IGHV4-39 gene rearrangements were specific for IgM and IgG peaks, respectively. SF3B1, NOTCH1, MYD88 and BIRC3 mutation frequencies were 12%, 4%, 2% and 2%, respectively, being over-represented in IgM, IgG and Hypo-γ groups for SF3B1, and being equal between normal-γ and IgM groups for MYD88. Overall, 76%, 87%, 49% and 42% of cases from IgM, IgG, Hypo-γ and normal-γ groups had at least one intermediate or poor prognosis genetic marker, respectively. By multivariate analysis, IgM peaks were associated with shorter treatment-free survival independently from any other univariate poor prognosis biological parameters, including IgG peaks, Hypo-γ, IGHV status, SF3B1 mutations, cytogenetics and lymphocytosis. Therefore, as with IgG peaks, IgM peaks aggravated the natural course of CLL, with increased accumulation of adverse genetic events.

Genetic and cytokine changes associated with symptomatic stages of CLL

The pathogenesis and drug resistance of symptomatic CLL patients involves genetic changes associated with the CLL clone as well as changes within the microenvironment. To further understand these processes, we compared early stage CLL to symptomatic late stage using gene expression and serum cytokine profiling to gain insight of the genetic and microenvironment changes associated with the most severe form of the disease. Patients were classified into low stage (Rai stage 0/I/II) and high stage (Rai stage III/IV). Gene expression profiles were obtained on pretreatment samples using the HG-U133A 2.0 Affymetrix platform. A comparison of low versus high stage CLL revealed a set of 21 genes differentially expressed genes. 15 genes were up regulated in the high stage compared to low stage while 6 genes were down regulated. Analysis of GO molecular function revealed 9 of 21 genes were involved in transcription factor activity. Serum cytokine profiles showed six cytokines to be significantly different in high stage patients. Two chemokines, SDF-1/CXCL12 and uPAR known to be involved in stem cell mobilization and homing were increased in serum of high stage patients. This study has identified therapeutic targets for symptomatic CLL patients.

Treatment of older patients with chronic lymphocytic leukemia: key questions and current answers

Despite the advanced age at onset, chronic lymphocytic leukemia (CLL) shortens the life expectancy of the majority of newly diagnosed patients. The management of elderly patients with CLL is more complex than that of younger patients due to the greater frequency of comorbidities and functional impairment as well as reduced organ function. Many of the recent advances in the care of CLL patients (prognostication, more intense combination therapy regimens) are of unclear relevance for elderly patients. This review addresses 5 key questions in the management of elderly patients with CLL: (1) why is classifying the “fitness” of CLL patients necessary; (2) what criteria should be used to classify patient fitness; (3) when should elderly patients be treated; (4) how should therapy be selected for elderly patients; and (5) which therapy is best (for this patient)?

"Role of the B-cell receptor and the microenvironment in chronic lymphocytic leukemia''

Despite significant progress in treatment, chronic lymphocytic leukemia (CLL) remains an incurable disease. Advances have been made to understand the molecular pathogenesis underlying CLL progression and treatment resistance. We here review the available evidences concerning the role of the B-cell receptor (BCR) and the tumor microenvironment interactions in CLL pathogenesis. Antigen likely has a key role in the selection of the tumoral clone, the mutational status of immunoglobulin genes is a strong prognostic predictor and BCR signaling has been postulated to have a role for CLL trafficking and interaction with the stromal microenvironment. There is also important evidence, favoring a role for the microenvironment in CLL pathogenesis. Most, if not all, proliferative events occur in the lymph nodes and bone marrow, where leukemic cells receive through microenvironment interactions survival signals aiming to avoid apoptosis and acquire favorable tumoral growing conditions. In addition, the tumoral microenvironment appears to be the site where the acquisition of additional genetic lesions in the clone occur, which should greatly influence clinical outcome. The advent of new tyrosine kinase inhibitors which seem to be able to modulate microenvironment interactions and circumvent the p53 deletion have generated significant promise by raising the possibility that they could provide significant progress in disease treatment.