Effect of Rapamycin on Mouse Chronic Lymphocytic Leukemia and the Development of Nonhematopoietic Malignancies in Eμ-TCL1 Transgenic Mice

B Cell Chronic Lymphocytic Leukemia Development in Mice with Chronic Lung Exposure to Coccidioides Fungal Arthroconidia

Links between repeated microbial infections and B cell chronic lymphocytic leukemia (B-CLL) have been proposed but not tested directly. This study examines how prolonged exposure to a human fungal pathogen impacts B-CLL development in Eµ-hTCL1-transgenic mice. Monthly lung exposure to inactivated Coccidioides arthroconidia, agents of Valley fever, altered leukemia development in a species-specific manner, with Coccidioides posadasii hastening B-CLL diagnosis/progression in a fraction of mice and Coccidioides immitis delaying aggressive B-CLL development, despite fostering more rapid monoclonal B cell lymphocytosis. Overall survival did not differ significantly between control and C. posadasii-treated cohorts but was significantly extended in C. immitis-exposed mice. In vivo doubling time analyses of pooled B-CLL showed no difference in growth rates of early and late leukemias. However, within C. immitis-treated mice, B-CLL manifests longer doubling times, as compared with B-CLL in control or C. posadasii-treated mice, and/or evidence of clonal contraction over time. Through linear regression, positive relationships were noted between circulating levels of CD5+/B220low B cells and hematopoietic cells previously linked to B-CLL growth, albeit in a cohort-specific manner. Neutrophils were positively linked to accelerated growth in mice exposed to either Coccidioides species, but not in control mice. Conversely, only C. posadasii-exposed and control cohorts displayed positive links between CD5+/B220low B cell frequency and abundance of M2 anti-inflammatory monocytes and T cells. The current study provides evidence that chronic lung exposure to fungal arthroconidia affects B-CLL development in a manner dependent on fungal genotype. Correlative studies suggest that fungal species differences in the modulation of nonleukemic hematopoietic cells are involved.

Understanding CLL biology through mouse models of human genetics

Rapid advances in large-scale next-generation sequencing studies of human samples have progressively defined the highly heterogeneous genetic landscape of chronic lymphocytic leukemia (CLL). At the same time, the numerous challenges posed by the difficulties in rapid manipulation of primary B cells and the paucity of CLL cell lines have limited the ability to interrogate the function of the discovered putative disease "drivers," defined in human sequencing studies through statistical inference. Mouse models represent a powerful tool to study mechanisms of normal and malignant B-cell biology and for preclinical testing of novel therapeutics. Advances in genetic engineering technologies, including the introduction of conditional knockin/knockout strategies, have opened new opportunities to model genetic lesions in a B-cell-restricted context. These new studies build on the experience of generating the MDR mice, the first example of a genetically faithful CLL model, which recapitulates the most common genomic aberration of human CLL: del(13q). In this review, we describe the application of mouse models to the studies of CLL pathogenesis and disease transformation from an indolent to a high-grade malignancy (ie, Richter syndrome [RS]) and treatment, with a focus on newly developed genetically inspired mouse lines modeling recurrent CLL genetic events. We discuss how these novel mouse models, analyzed using new genomic technologies, allow the dissection of mechanisms of disease evolution and response to therapy with greater depth than previously possible and provide important insight into human CLL and RS pathogenesis and therapeutic vulnerabilities. These models thereby provide valuable platforms for functional genomic analyses and treatment studies.

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.

Dissecting the Prognostic Significance and Functional Role of Progranulin in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is known for its strong dependency on the tumor microenvironment. We found progranulin (GRN), a protein that has been linked to inflammation and cancer, to be upregulated in the serum of CLL patients compared to healthy controls, and increased GRN levels to be associated with an increased hazard for disease progression and death. This raised the question of whether GRN is a functional driver of CLL. We observed that recombinant GRN did not directly affect viability, activation, or proliferation of primary CLL cells in vitro. However, GRN secretion was induced in co-cultures of CLL cells with stromal cells that enhanced CLL cell survival. Gene expression profiling and protein analyses revealed that primary mesenchymal stromal cells (MSCs) in co-culture with CLL cells acquire a cancer-associated fibroblast-like phenotype. Despite its upregulation in the co-cultures, GRN treatment of MSCs did not mimic this effect. To test the relevance of GRN for CLL in vivo, we made use of the Eμ-TCL1 CLL mouse model. As we detected strong GRN expression in myeloid cells, we performed adoptive transfer of Eμ-TCL1 leukemia cells to bone marrow chimeric Grn-/- mice that lack GRN in hematopoietic cells. Thereby, we observed that CLL-like disease developed comparable in Grn-/- chimeras and respective control mice. In conclusion, serum GRN is found to be strongly upregulated in CLL, which indicates potential use as a prognostic marker, but there is no evidence that elevated GRN functionally drives the disease.

Exome sequencing of the TCL1 mouse model for CLL reveals genetic heterogeneity and dynamics during disease development

The TCL1 mouse model is widely used to study pathophysiology, clonal evolution, and drug sensitivity or resistance of chronic lymphocytic leukemia (CLL). By performing whole exome sequencing, we present the genetic landscape of primary tumors from TCL1 mice and of TCL1 tumors serially transplanted into wild-type recipients to mimic clonal evolution. We show that similar to CLL patients, mutations in mice are frequently subclonal and heterogenous among different primary TCL1 mice. We further describe that this molecular heterogeneity mirrors heterogenous disease characteristics such as organ infiltration or CLL dependent T cell skewing. Similar to human CLL, we further observed the occurrence of novel mutations and structural variations during clonal evolution and found plasticity in the expansion of B cell receptor specific subclones. Thus, our results uncover that the genetic complexity, pathway dependence and clonal dynamics in mouse CLL are in relevant agreement to human CLL, and they are important to consider in future research using the TCL1 mouse for studying CLL.

T Cell Leukemia/Lymphoma 1A is essential for mouse epidermal keratinocytes proliferation promoted by insulin-like growth factor 1

T Cell Leukemia/Lymphoma 1A is expressed during B-cell differentiation and, when over-expressed, acts as an oncogene in mouse (Tcl1a) and human (TCL1A) B-cell chronic lymphocytic leukemia (B-CLL) and T-cell prolymphocytic leukemia (T-PLL). Furthermore, in the murine system Tcl1a is expressed in the ovary, testis and in pre-implantation embryos, where it plays an important role in blastomere proliferation and in embryonic stem cell (ESC) proliferation and self-renewal. We have also observed that Tcl1-/- adult mice exhibit alopecia and deep ulcerations. This finding has led us to investigate the role of TCL1 in mouse skin and hair follicles. We have found that TCL1 is expressed in the proliferative structure (i.e. the secondary hair germ) and in the stem cell niche (i.e. the bulge) of the hair follicle during regeneration phase and it is constitutively expressed in the basal layer of epidermis where it is required for the correct proliferative–differentiation program of the keratinocytes (KCs). Taking advantage of the murine models we have generated, including the Tcl1-/- and the K14-TCL1 transgenic mouse, we have analysed the function of TCL1 in mouse KCs and the molecular pathways involved. We provide evidence that in the epidermal compartment TCL1 has a role in the regulation of KC proliferation, differentiation, and apoptosis. In particular, the colony-forming efficiency (CFE) and the insulin-like growth factor 1 (IGF1)-induced proliferation are dramatically impaired, while apoptosis is increased, in KCs from Tcl1-/- mice when compared to WT. Moreover, the expression of differentiation markers such as cytokeratin 6 (KRT6), filaggrin (FLG) and involucrin (IVL) are profoundly altered in mutant mice (Tcl1-/-). Importantly, by over-expressing TCL1A in basal KCs of the K14-TCL1 transgenic mouse model, we observed a significant rescue of cell proliferation, differentiation and apoptosis of the mutant phenotype. Finally, we found TCL1 to act, at least in part, via increasing phospho-ERK1/2 and decreasing phospho-P38 MAPK. Hence, our data demonstrate that regulated levels of Tcl1a are necessary for the correct proliferation and differentiation of the interfollicular KCs.

Splicing modulation sensitizes chronic lymphocytic leukemia cells to venetoclax by remodeling mitochondrial apoptotic dependencies

The identification of targetable vulnerabilities in the context of therapeutic resistance is a key challenge in cancer treatment. We detected pervasive aberrant splicing as a characteristic feature of chronic lymphocytic leukemia (CLL), irrespective of splicing factor mutation status, which was associated with sensitivity to the spliceosome modulator, E7107. Splicing modulation affected CLL survival pathways, including members of the B cell lymphoma-2 (BCL2) family of proteins, remodeling antiapoptotic dependencies of human and murine CLL cells. E7107 treatment decreased myeloid cell leukemia-1 (MCL1) dependence and increased BCL2 dependence, sensitizing primary human CLL cells and venetoclax-resistant CLL-like cells from an Eμ-TCL1-based adoptive transfer murine model to treatment with the BCL2 inhibitor venetoclax. Our data provide preclinical rationale to support the combination of venetoclax with splicing modulators to reprogram apoptotic dependencies in CLL for treating venetoclax-resistant CLL cases.

Targeting Macrophages Sensitizes Chronic Lymphocytic Leukemia to Apoptosis and Inhibits Disease Progression

The role of monocytes/macrophages in the development and progression of chronic lymphocytic leukemia (CLL) is poorly understood. Transcriptomic analyses show that monocytes/macrophages and leukemic cells cross talk during CLL progression. Macrophage depletion impairs CLL engraftment, drastically reduces leukemic growth, and favorably impacts mouse survival. Targeting of macrophages by either CSF1R signaling blockade or clodrolip-mediated cell killing has marked inhibitory effects on established leukemia also. Macrophage killing induces leukemic cell death mainly via the TNF pathway and reprograms the tumor microenvironment toward an antitumoral phenotype. CSF1R inhibition reduces leukemic cell load, especially in the bone marrow, and increases circulating CD20(+) leukemic cells. Accordingly, co-targeting TAMs and CD20-expressing leukemic cells provides a survival benefit in the mice. These results establish the important role of macrophages in CLL and suggest therapeutic strategies based on interfering with leukemia-macrophage interactions.

TCL1 transgenic mouse model as a tool for the study of therapeutic targets and microenvironment in human B-cell chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy with a mature phenotype. In spite of its relatively indolent nature, no radical cure is as yet available. CLL is not associated with either a unique cytogenetic or a molecular defect, which might have been a potential therapeutic target. Instead, several factors are involved in disease development, such as environmental signals which interact with genetic abnormalities to promote survival, proliferation and an immune surveillance escape. Among these, PI3-Kinase signal pathway alterations are nowadays considered to be clearly important. The TCL1 gene, an AKT co-activator, is the cause of a mature T-cell leukemia, as well as being highly expressed in all B-CLL. A TCL1 transgenic mouse which reproduces leukemia with a distinct immunophenotype and similar to the course of the human B-CLL was developed several years ago and is widely used by many groups. This is a review of the CLL biology arising from work of many independent investigators who have used TCL1 transgenic mouse model focusing on pathogenetic, microenviroment and therapeutic targets.

Depletion of CLL-associated patrolling monocytes and macrophages controls disease development and repairs immune dysfunction in vivo

Chronic lymphocytic leukemia (CLL) is characterized by apoptosis resistance and a dysfunctional immune system. Previous reports suggested a potential role of myeloid cells in mediating these defects. However, the composition and function of CLL-associated myeloid cells have not been thoroughly investigated in vivo. Using the Eμ-TCL1 mouse model, we observed severe skewing of myeloid cell populations with CLL development. Monocytes and M2-like macrophages infiltrated the peritoneal cavity of leukemic mice. Monocytes also accumulated in the spleen in a CCR2-dependent manner, and were severely skewed toward Ly6C(low) patrolling or nonclassical phenotype. In addition, the percentage of MHC-II(hi) dendritic cells and macrophages significantly dropped in the spleen. Gene expression profiling of CLL-associated monocytes revealed aberrantly high PD-L1 expression and secretion of multiple inflammatory and immunosuppressive cytokines like interleukin-10, tumor necrosis factor-α and CXCL9. In vivo myeloid cell depletion using liposomal Clodronate resulted in a significant control of CLL development accompanied by a pronounced repair of innate immune cell phenotypes and a partial resolution of systemic inflammation. In addition, CLL-associated skewing of T cells toward antigen-experienced phenotypes was repaired. The presented data suggest that targeting nonmalignant myeloid cells might serve as a novel immunotherapeutical strategy for CLL.

miR-181b as a therapeutic agent for chronic lymphocytic leukemia in the Eµ-TCL1 mouse model

The involvement of microRNAs (miRNAs) in chronic lymphocytic leukemia (CLL) pathogenesis suggests the possibility of anti-CLL therapeutic approaches based on miRNAs. Here, we used the Eµ-TCL1 transgenic mouse model, which reproduces leukemia with a similar course and distinct immunophenotype as human B-CLL, to test miR-181b as a therapeutic agent.In vitro enforced expression of miR-181b mimics induced significant apoptotic effects in human B-cell lines (RAJI, EHEB), as well as in mouse Eµ-TCL1 leukemic splenocytes. Molecular analyses revealed that miR-181b not only affected the expression of TCL1, Bcl2 and Mcl1 anti-apoptotic proteins, but also reduced the levels of Akt and phospho-Erk1/2. Notably, a siRNA anti-TCL1 could similarly down-modulate TCL1, but exhibited a reduced or absent activity in other relevant proteins, as well as a reduced effect on cell apoptosis and viability. In vivo studies demonstrated the capability of miR-181b to reduce leukemic cell expansion and to increase survival of treated mice.These data indicate that miR-181b exerts a broad range of actions, affecting proliferative, survival and apoptotic pathways, both in mice and human cells, and can potentially be used to reduce expansion of B-CLL leukemic cells.

Role of B cell receptor signaling in IL-10 production by normal and malignant B-1 cells

B-1 cells are considered innate immune cells, which produce the majority of natural antibodies. B-1 cell responses to B cell receptor (BCR) and Toll-like receptor ligation are tightly regulated owing to the cross-reactivity to self-antigens. CD5 has been shown to play a major role in downregulation of BCR responses in B-1 cells. Here, we provide evidence for another mechanism by which BCR response is regulated in B-1 cells. B-1 cells, as well as their malignant counterpart, B cell chronic lymphocytic leukemia (B-CLL) cells, produce interleukin-10 (IL-10) constitutively. IL-10 secretion by normal B-1 cells downregulates their proliferation responses to BCR ligation. However, we found that CLL cells appear to be unique in not responding to IL-10-mediated feedback-suppressive effects in comparison to normal B-1 cells. In addition, we describe a novel role of the BCR signaling pathway in constitutive IL-10 secretion by normal and malignant B-1 cells. We found that inhibition of Src family kinases, spleen tyrosine kinase, Syk, or Bruton's tyrosine kinase reduces constitutive IL-10 production by both normal and malignant B-1 cells.

The long journey of TCL1 transgenic mice: lessons learned in the last 15 years

The first transgenic mouse of the TCL1 oncogene was described more than 15 years ago, and since then, the overexpression of the gene in T- and B-cells in vivo has been extensively studied to reveal the molecular details in the pathogenesis of some lymphocytic leukemias. This review discusses the main features of the original TCL1 models and the different lines of research successively developed with particular attention to genetically compound mice and the therapeutic applications in drug development.

PTPROt-mediated regulation of p53/Foxm1 suppresses leukemic phenotype in a CLL mouse model

The gene encoding PTPROt is methylated and suppressed in Chronic Lymphocytc Leukemia. PTPROt exhibits in vitro tumor suppressor characteristics through the regulation of B-cell receptor signaling. Here, we generated transgenic (Tg) mice with B-cell specific expression of PTPROt. While lymphocyte development is normal in these mice, crossing them with TCL1 Tg mouse model of CLL results in a survival advantage compared to the TCL1 Tg mice. Gene expression profiling of splenic B-lymphocytes before detectable signs of CLL followed by Ingenuity Pathway Analysis revealed that the most prominently regulated functions in TCL1 Tg vs non-transgenic (NTg) and TCL1 Tg vs PTPROt/TCL1 double Tg are the same and also biologically relevant to this study. Further, enhanced expression of the chemokine Ccl3, the oncogenic transcription factor Foxm1 and its targets in TCL1 Tg mice were significantly suppressed in the double Tg mice suggesting a protective function of PTPROt against leukemogenesis. This study also showed that PTPROt mediated regulation of Foxm1 involves activation of p53, a transcriptional repressor of Foxm1, which is facilitated through suppression of B-cell receptor signaling. These results establish the in vivo tumor suppressive function of PTPROt, and identify p53/Foxm1 axis as a key downstream effect of PTPROt-mediated suppression of BCR signaling.

Mouse models in the study of chronic lymphocytic leukemia pathogenesis and therapy

Mouse models that recapitulate human malignancy are valuable tools for the elucidation of the underlying pathogenetic mechanisms and for preclinical studies. Several genetically engineered mouse models have been generated, either mimicking genetic aberrations or deregulated gene expression in chronic lymphocytic leukemia (CLL). The usefulness of such models in the study of the human disease may potentially be hampered by species-specific biological differences in the target cell of the oncogenic transformation. Specifically, do the genetic lesions or the deregulated expression of leukemia-associated genes faithfully recapitulate the spectrum of lymphoproliferations in humans? Do the CLL-like lymphoproliferations in the mouse have the phenotypic, histological, genetic, and clinical features of the human disease? Here we compare the various CLL mouse models with regard to disease phenotype, penetrance, and severity. We discuss similarities and differences of the murine lymphoproliferations compared with human CLL. We propose that the Eμ-TCL1 transgenic and 13q14-deletion models that have been comprehensively studied at the levels of leukemia phenotype, antigen-receptor repertoire, and disease course show close resemblance to the human disease. We conclude that modeling CLL-associated genetic dysregulations in mice can provide important insights into the molecular mechanisms of disease pathogenesis and generate valuable tools for the development of novel therapies.

Murine genetically engineered and human xenograft models of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a genetically complex disease, with multiple factors having an impact on onset, progression, and response to therapy. Genetic differences/abnormalities have been found in hematopoietic stem cells from patients, as well as in B lymphocytes of individuals with monoclonal B-cell lymphocytosis who may develop the disease. Furthermore, after the onset of CLL, additional genetic alterations occur over time, often causing disease worsening and altering patient outcomes. Therefore, being able to genetically engineer mouse models that mimic CLL or at least certain aspects of the disease will help us understand disease mechanisms and improve treatments. This notwithstanding, because neither the genetic aberrations responsible for leukemogenesis and progression nor the promoting factors that support these are likely identical in character or influences for all patients, genetically engineered mouse models will only completely mimic CLL when all of these factors are precisely defined. In addition, multiple genetically engineered models may be required because of the heterogeneity in susceptibility genes among patients that can have an effect on genetic and environmental characteristics influencing disease development and outcome. For these reasons, we review the major murine genetically engineered and human xenograft models in use at the present time, aiming to report the advantages and disadvantages of each.

Inhibition of ER stress-associated IRE-1/XBP-1 pathway reduces leukemic cell survival

Activation of the ER stress response is associated with malignant progression of B cell chronic lymphocytic leukemia (CLL). We developed a murine CLL model that lacks the ER stress-associated transcription factor XBP-1 in B cells and found that XBP-1 deficiency decelerates malignant progression of CLL-associated disease. XBP-1 deficiency resulted in acquisition of phenotypes that are disadvantageous for leukemic cell survival, including compromised BCR signaling capability and increased surface expression of sphingosine-1-phosphate receptor 1 (S1P1). Because XBP-1 expression requires the RNase activity of the ER transmembrane receptor IRE-1, we developed a potent IRE-1 RNase inhibitor through chemical synthesis and modified the structure to facilitate entry into cells to target the IRE-1/XBP-1 pathway. Treatment of CLL cells with this inhibitor (B-I09) mimicked XBP-1 deficiency, including upregulation of IRE-1 expression and compromised BCR signaling. Moreover, B-I09 treatment did not affect the transport of secretory and integral membrane-bound proteins. Administration of B-I09 to CLL tumor-bearing mice suppressed leukemic progression by inducing apoptosis and did not cause systemic toxicity. Additionally, B-I09 and ibrutinib, an FDA-approved BTK inhibitor, synergized to induce apoptosis in B cell leukemia, lymphoma, and multiple myeloma. These data indicate that targeting XBP-1 has potential as a treatment strategy, not only for multiple myeloma, but also for mature B cell leukemia and lymphoma.

Protooncogene TCL1b functions as an Akt kinase co-activator that exhibits oncogenic potency in vivo

Protooncogene T-cell leukemia 1 (TCL1), which is implicated in human T-cell prolymphocytic leukemia (T-PLL), interacts with Akt and enhances its kinase activity, functioning as an Akt kinase co-activator. Two major isoforms of TCL1 Protooncogenes (TCL1 and TCL1b) are present adjacent to each other on human chromosome 14q.32. In human T-PLL, both TCL1 and TCL1b are activated by chromosomal translocation. Moreover, TCL1b-transgenic mice have never been created. Therefore, it remains unclear whether TCL1b itself, independent of TCL1, exhibits oncogenicity. In co-immunoprecipitation assays, both ectopic and endogenous TCL1b interacted with Akt. In in vitro Akt kinase assays, TCL1b enhanced Akt kinase activity in dose- and time-dependent manners. Bioinformatics approaches utilizing multiregression analysis, cluster analysis, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway mapping, Venn diagrams and Gene Ontology (GO) demonstrated that TCL1b showed highly homologous gene-induction signatures similar to Myr-Akt or TCL1. TCL1b exhibited oncogenicity in in vitro colony-transformation assay. Further, two independent lines of β-actin promoter-driven TCL1b-transgenic mice developed angiosarcoma on the intestinal tract. Angiosarcoma is a rare form of cancer in humans with poor prognosis. Using immunohistochemistry, 11 out of 13 human angiosarcoma samples were positively stained with both anti-TCL1b and anti-phospho-Akt antibodies. Consistently, in various cancer tissues, 69 out of 146 samples were positively stained with anti-TCL1b, out of which 46 were positively stained with anti-phospho-Akt antibodies. Moreover, TCL1b structure-based inhibitor 'TCL1b-Akt-in' inhibited Akt kinase activity in in vitro kinase assays and PDGF (platelet-derived growth factor)-induced Akt kinase activities-in turn, 'TCL1b-Akt-in' inhibited cellular proliferation of sarcoma. The current study disclosed TCL1b bears oncogenicity and hence serves as a novel therapeutic target for human neoplastic diseases.

Targeting the LYN/HS1 signaling axis in chronic lymphocytic leukemia

HS1 protein activation is differentially regulated by LYN kinase in CLL subsets. Dasatinib targets cytoskeletal activity, BCR signaling and survival of a sizable portion of patients with activated LYN/HS1.

Accelerated progression of chronic lymphocytic leukemia in Eμ-TCL1 mice expressing catalytically inactive RAG1

Chronic lymphocytic leukemia (CLL) is a prevalent B-cell neoplasia that is often preceded by a more benign monoclonal CD5(+) B-cell lymphocytosis. We previously generated transgenic mice expressing catalytically inactive RAG1 (dominant-negative recombination activating gene 1 [dnRAG1] mice) that develop an early-onset indolent CD5(+) B-cell lymphocytosis attributed to a defect in secondary V(D)J rearrangements initiated to edit autoreactive B-cell receptor (BCR) specificity. Hypothesizing that CD5(+) B cells in these animals represent potential CLL precursors, we crossed dnRAG1 mice with CLL-prone Eμ-TCL1 mice to determine whether dnRAG1 expression in Eμ-TCL1 mice accelerates CLL onset. Consistent with this hypothesis, CD5(+) B-cell expansion and CLL progression occurred more rapidly in double-transgenic mice compared with Eμ-TCL1 mice. Nevertheless, CD5(+) B cells in the 2 mouse strains exhibited close similarities in phenotype, immunoglobulin gene usage, and mutation status, and expression of genes associated with immune tolerance and BCR signaling. Gene expression profiling further revealed a potential role for prolactin signaling in regulating BCR editing. These results suggest a model in which benign accumulation of CD5(+) B cells can be initiated through a failure to successfully edit autoreactive BCR specificity and may, in turn, progress to CLL upon introduction of additional genetic mutations.

Protein kinase c-β-dependent activation of NF-κB in stromal cells is indispensable for the survival of chronic lymphocytic leukemia B cells in vivo

Tumor cell survival critically depends on heterotypic communication with benign cells in the microenvironment. Here, we describe a survival signaling pathway activated in stromal cells by contact to B cells from patients with chronic lymphocytic leukemia (CLL). The expression of protein kinase C (PKC)-βII and the subsequent activation of NF-κB in bone marrow stromal cells are prerequisites to support the survival of malignant B cells. PKC-β knockout mice are insusceptible to CLL transplantations, underscoring the in vivo significance of the PKC-βII-NF-κB signaling pathway in the tumor microenvironment. Upregulated stromal PKC-βII in biopsies from patients with CLL, acute lymphoblastic leukemia, and mantle cell lymphoma suggests that this pathway may commonly be activated in a variety of hematological malignancies.

Novel Agents and Emerging Strategies for Targeting the B-Cell Receptor Pathway in CLL

Chronic lymphocytic leukemia (CLL) is a disease of malignant CD5+ B lymphocytes that are characterized by frequent expression of autoreactive B-cell receptors (BCRs) and marked dependence on microenvironmental signals for proliferation and survival. Among the latter, signals propagated through the BCR are believed to play a key role in leukemia initiation, maintenance and evolution. Drugs that can disrupt these signals have recently emerged as potential therapeutic agents in CLL and several of them are currently being evaluated in clinical trials. Particularly promising clinical responses have been obtained with inhibitors of the kinases SYK, BTK, and PI3Kδ, which function by blocking BCR signal transduction. In addition, recent studies focusing on the phosphatase PTPN22, which is involved in the pathogenesis of multiple autoimmune diseases and is markedly overexpressed in CLL cells, suggest that it may be possible in the future to develop strategies that will selectively reprogram BCR survival signals into signals that induce leukemic cell death. This review focuses on the biological basis behind these strategies and highlights some of the most promising BCR-targeting agents in ongoing preclinical and clinical studies.

Actinomycin D induces p53-independent cell death and prolongs survival in high-risk chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most prevalent lymphoid malignancy in the elderly of the Western world. Although treatment options have improved over the past two decades, 10-15% of patients still have a poor prognosis and are often resistant to therapy. Aberrations in the p53 pathway, such as a deleted (del17p13) or mutated p53 gene, are highly enriched in this class of patients. In an extensive screen for p53-independent apoptosis inducers, actinomycin D was identified from 1496 substances and shown to induce apoptosis in primary CLL cells derived from high-risk patients including those with aberrant p53, revealing a novel p53-independent mechanism of action. Both pro-survival genes BCL2 and MCL1 are targeted by actinomycin D, in contrast to fludarabine the backbone of current treatment schedules. In the well-established TCL1 transgenic mouse model for high-risk CLL, actinomycin D treatment was more effective in reducing tumor load than fludarabine, with no evidence of resistance after three treatment cycles and an overall survival increase of over 300%. Tumor load reduction was coupled to BCL2 downregulation. Our results identify the clinically approved compound actinomycin D as a potentially valuable treatment option for CLL high-risk patients.

The Aurora A and B kinases are up-regulated in bone marrow-derived chronic lymphocytic leukemia cells and represent potential therapeutic targets

BACKGROUND

The malignant B cells in chronic lymphocytic leukemia receive signals from the bone marrow and lymph node microenvironments which regulate their survival and proliferation. Characterization of these signals and the pathways that propagate them to the interior of the cell is important for the identification of novel potential targets for therapeutic intervention.

DESIGN AND METHODS

We compared the gene expression profiles of chronic lymphocytic leukemia B cells purified from bone marrow and peripheral blood to identify genes that are induced by the bone marrow microenvironment. Two of the differentially expressed genes were further studied in cell culture experiments and in an animal model to determine whether they could represent appropriate therapeutic targets in chronic lymphocytic leukemia.

RESULTS

Functional classification analysis revealed that the majority of differentially expressed genes belong to gene ontology categories related to cell cycle and mitosis. Significantly up-regulated genes in bone marrow-derived tumor cells included important cell cycle regulators, such as Aurora A and B, survivin and CDK6. Down-regulation of Aurora A and B by RNA interference inhibited proliferation of chronic lymphocytic leukemia-derived cell lines and induced low levels of apoptosis. A similar effect was observed with the Aurora kinase inhibitor VX-680 in primary chronic lymphocytic leukemia cells that were induced to proliferate by CpG-oligonucleotides and interleukin-2. Moreover, VX-680 significantly blocked leukemia growth in a mouse model of chronic lymphocytic leukemia.

CONCLUSIONS

Aurora A and B are up-regulated in proliferating chronic lymphocytic leukemia cells and represent potential therapeutic targets in this disease.

Protein phosphatase-2A activation is a critical step for enzastaurin activity in chronic lymphoid leukemia cells

Targeting B-cell receptor (BCR) downstream pathways may be of therapeutic importance in eradicating chronic lymphocytic leukemia (CLL) cells. Since protein kinase C-β(II) (PKC-β(II)) is a key element of BCR signaling, we evaluated the impact of enzastaurin on cell survival. Enzastaurin classically activates glycogen synthase kinase-3β through inhibition of PKC-β, Akt and target of rapamycin pathways in cancer cell lines. Here, we show that in primary CLL cells, enzastaurin activates protein phosphatase-2A (PP-2A) to mediate dephosphorylating events in responding patients. In patients' cells, both PP-2A activation and Bcl-2 dephosphorylation are statistically linked to enzastaurin-induced CLL death. Protein phosphatase-2A inhibition, through pharmacological agents or siRNA, significantly hampers cell death induced by the drug. Despite limited activity in in vitro culture, enzastaurin is able to sensitize CLL cells to fludarabine, even in patients refractory to either agent used alone. These results argue for the use of enzastaurin in combination therapy in patients with CLL.

Is miR-29 an oncogene or tumor suppressor in CLL?

B-cell chronic lymphocytic leukemia (CLL) is the most common leukemia in the Western world. CLL occurs in two forms, aggressive and indolent. Aggressive CLL is characterized by high ZAP-70 expression and unmutated IgH V_H; indolent CLL shows low ZAP-70 expression and mutated IgH V_H. We recently found that miR-29 is upregulated in indolent human B-CLL, compared to aggressive B-CLL and normal CD19+ B-cells. To determine the role of miR-29 in CLL, we generated transgenic mice overexpressing miR-29 in mouse B-cells. Recently we reported that miR-29 transgenic mice develop indolent CLL phenotype. Interestingly, our previous findings suggest that miR-29 targets expression of TCL1, a critical oncogene in aggressive CLL, indicating that miR-29 might function as a tumor suppressor in CLL. Here we discuss these results and provide additional insights into function of miR-29 in CLL.

AP-1 elements and TCL1 protein regulate expression of the gene encoding protein tyrosine phosphatase PTPROt in leukemia

We previously demonstrated that the gene encoding PTPROt, the truncated form of protein tyrosine phosphatase receptor type O expressed predominantly in hematopoietic cells, is a candidate tumor suppressor and is down-regulated in chronic lymphocytic leukemia (CLL). Here, we show that PTPROt expression is significantly reduced in CD19(+) spleen B cells from Eμ-T cell leukemia 1 (TCL1) transgenic mice relative to the wild-type mice. Strikingly, as much as a 60% decrease in PTPROt expression occurs at 7 weeks independently of promoter methylation. To elucidate the potential mechanism for this early suppression of PTPROt in these mice, we explored the role of activating protein-1 (AP-1) in its expression. We first demonstrate that AP-1 activation by 12-O-tetradecanoylphorbol-13-acetate induces PTPROt expression with concurrent recruitment of c-fos and c-jun to its promoter. The PTPROt promoter is also responsive to over- and underexpression of AP-1, confirming the role of AP-1 in PTPROt expression. Next, we demonstrate that TCL1 can repress the PTPROt promoter by altering c-fos expression and c-jun activation state. Finally, using primary CLL cells we have shown an inverse relationship between TCL1 and PTPROt expression. These findings further substantiate the role of TCL1 in PTPROt suppression and its importance in the pathogenesis of CLL.

Investigating the role of CD38 and functionally related molecular risk factors in the CLL NOD/SCID xenograft model

We explored the role of CD38 and functionally associated molecular risk factors in a recently described chronic lymphocytic leukemia (CLL) nonobese diabetic/ severe combined immunodeficient xenograft model. Intravenous injection of peripheral blood mononuclear cells from 73 patients with CLL into 244 mice resulted in robust engraftment of leukemic cells into the murine spleens detected 4 wks after transplantation. Leukemic cell engraftment correlated significantly (P < 0.05) with markers reflecting disease activity, e.g., Binet stage and lymphocyte doubling time, and the expression of molecular risk factors including CD38, CD49d, ZAP-70, and IgVH mutational status. Increased engraftment levels of CD38+ as compared to CD38- CLL cells could be attributed, in part, to leukemic cell proliferation as evidenced by combined immunostaining of murine spleen sections for Ki-67 and CD20. In short-term (24 h) homing assays, CD38+ CLL cells migrated more efficiently to the bone marrow of the recipient animals than their CD38- counterparts. Finally, CD38 expression by the leukemic cells was found to be dynamic in that it was regulated not only by elements of the murine microenvironment but also by co-engrafting non-malignant human T cells. This model could be useful for evaluating the biological basis of CLL growth in the context of the hematopoietic microenvironment as well as preclinical testing of novel compounds.

Aberrantly activated anti-apoptotic signalling mechanisms in chronic lymphocytic leukaemia cells: clues to the identification of novel therapeutic targets

Chronic lymphocytic leukaemia (CLL) is the commonest haematological malignancy in the western world and is incurable by cytotoxic therapy. Considerable research effort has identified the signal transduction pathways in CLL cells that contribute to anti-apoptotic signalling. Some pathways are constitutively activated in CLL cells but upregulated in normal cells only when protein tyrosine kinases (PTKs) are activated by ligands. This review describes which PTKs are aberrantly activated in CLL cells and are potential targets for inhibition. Additional potential targets within pathways downstream of these PTKs include Mek/Erk, mTorc1, protein kinase C, PI-3 kinase/Akt, nuclear factor-κB and cyclin-dependent protein kinase. Numerous studies have identified chemical agents and antibodies that selectively kill CLL cells, irrespective of their genetic resistance to conventional chemotherapeutic agents, and which can overcome cytoprotective microenvironmental signalling. These studies have resulted in identification of novel therapies, some of which are currently undergoing clinical trials. In vitro and animal model studies and clinical trials could determine which inhibitors of which targets are the likely to be most effective and least toxic either singly or in combination.

Mammalian target of rapamycin as a target in hematological malignancies

The mammalian target of rapamycin (mTOR) regulates protein synthesis in addition to cell growth and cell proliferation. Elucidation of the roles of the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR pathway in the regulation of the pathogenesis of hematological neoplasms has led to the development and clinical evaluation of agents targeting this pathway for the treatment of leukemia and lymphomas. Clinical trials conducted to date have shown modest responses to mTOR inhibition in patients with various hematological malignancies. Novel agents that simultaneously target mTOR complex 2 (mTORC2) or AKT in addition to mTOR complex 1 (mTORC1) may offer an opportunity to improve therapeutic efficacy.

Molecular basis of CLL

B-cell chronic lymphocytic leukemia (CLL), the most common leukemia in the Western world, results from an expansion of a rare population of CD5+ mature B-lymphocytes. CLL occurs in two forms, aggressive and indolent. For the most part indolent CLL is characterized by low ZAP-70 expression and mutated IgH V(H); aggressive CLL shows high ZAP-70 expression and unmutated IgH V(H). Although clinical features and genomic abnormalities in CLL have been studied extensively, molecular mechanisms underlying disease development are still emerging. In the last few years, several important insights were reported in this area. MiR-15/16 targeting BCL2 and MCL1 and DLEU7 targeting TNF pathway were proposed as tumor suppressors at 13q14, a commonly deleted region in indolent CLL. Molecular details of how activation of TCL1, a critical oncogene in aggressive CLL, results in the initiation of this malignancy were clarified. Importance of these pathways was supported by investigations of several mouse models of CLL. Here, we present what has been learned from these new pathways, discuss mouse CLL models and how these mouse models recapitulate the molecular mechanisms of this common leukemia.

The Syk inhibitor fostamatinib disodium (R788) inhibits tumor growth in the Eμ- TCL1 transgenic mouse model of CLL by blocking antigen-dependent B-cell receptor signaling

Inhibition of antigen-dependent B-cell receptor (BCR) signaling is considered a promising therapeutic approach in chronic lymphocytic leukemia (CLL), but experimental in vivo evidence to support this view is still lacking. We have now investigated whether inhibition of BCR signaling with the selective Syk inhibitor fostamatinib disodium (R788) will affect the growth of the leukemias that develop in the Eμ-TCL1 transgenic mouse model of CLL. Similarly to human CLL, these leukemias express stereotyped BCRs that react with autoantigens exposed on the surface of senescent or apoptotic cells, suggesting that they are antigen driven. We show that R788 effectively inhibits BCR signaling in vivo, resulting in reduced proliferation and survival of the malignant B cells and significantly prolonged survival of the treated animals. The growth-inhibitory effect of R788 occurs despite the relatively modest cytotoxic effect in vitro and is independent of basal Syk activity, suggesting that R788 functions primarily by inhibiting antigen-dependent BCR signals. Importantly, the effect of R788 was found to be selective for the malignant clones, as no disturbance in the production of normal B lymphocytes was observed. Collectively, these data provide further rationale for clinical trials with R788 in CLL and establish the BCR-signaling pathway as an important therapeutic target in this disease.

Perspectives on inhibiting mTOR as a future treatment strategy for hematological malignancies

Mammalian target of rapamycin (mTOR) is a protein kinase implicated in the regulation of various cellular processes, including those required for tumor development, such as the initiation of mRNA translation, cell-cycle progression and cellular proliferation. In a wide range of hematological malignancies, the mTORC1 signaling pathway has been found to be deregulated and has been designed as a major target for tumor therapy. Given that pre-clinical studies have clearly established the therapeutic value of mTORC1 inhibition, numerous clinical trials of rapamycin and its derivates (rapalogs) are ongoing for treatment of these diseases. At this time, although disease stabilization and tumor regression have been observed, objective responses in some tumor types have been modest. Nevertheless, some of the mechanisms underlying cancer-cell resistance to rapamycin have now been described, thereby leading to the development of new strategy to efficiently target mTOR signaling in these diseases. In this review, we discuss the rationale for using mTOR inhibitors as novel therapies for a variety of hematological, malignancies with a focus on promising new perspectives for these approaches.

Chronic lymphocytic leukemia modeled in mouse by targeted miR-29 expression

B-cell chronic lymphocytic leukemia (B-CLL), the most common leukemia in the Western world, occurs in two forms, aggressive (showing for the most part high ZAP-70 expression and unmutated IgH V(H)) and indolent (showing low ZAP-70 expression and mutated IgH V(H)). We found that miR-29a is up-regulated in indolent human B-CLL as compared with aggressive B-CLL and normal CD19(+) B cells. To study the role of miR-29 in B-CLL, we generated Emu-miR-29 transgenic mice overexpressing miR-29 in mouse B cells. Flow cytometric analysis revealed a markedly expanded CD5(+) population in the spleen of these mice starting at 2 mo of age, with 85% (34/40) of miR-29 transgenic mice exhibiting expanded CD5(+) B-cell populations, a characteristic of B-CLL. On average, 50% of B cells in these transgenic mice were CD5 positive. At 2 y of age the mice showed significantly enlarged spleens and an increase in the CD5(+) B-cell population to approximately 100%. Of 20 Emu-miR-29 transgenic mice followed to 24-26 mo of age, 4 (20%) developed frank leukemia and died of the disease. These results suggest that dysregulation of miR-29 can contribute to the pathogenesis of indolent B-CLL.

microRNA-34a expression correlates with MDM2 SNP309 polymorphism and treatment-free survival in chronic lymphocytic leukemia

In chronic lymphocytic leukemia (B-CLL), aberrations along the p53 axis lead to decreased overall survival and therapy resistance. Recent studies identified microRNA-34a (miR-34a) as a major downstream target of p53. We monitored the expression of miR-34a during disease development in a murine B-CLL model. miR-34a was up-regulated more than 20-fold during the leukemic but not during the preleukemic phase. In the human system, B-CLL cells also had 4.6-fold higher miR-34a expression compared with B cells of healthy controls. In B-CLL cells of patients with p53 aberrations, miR-34a expression was consistently low. The broad distribution of miR-34a levels in p53 wild-type patients prompted us to study the correlation between single nucleotide polymorphism 309 (SNP309) in the intronic promoter of MDM2 and miR-34a expression. B-CLL cells of patients with the SNP309 GG genotype had significantly lower miR-34a expression levels compared with patients with the TT genotype (P = .002). Low miR-34a levels were able to predict shorter time to treatment (P = .003) and were associated with an abbreviated lymphocyte doubling time. Further, overexpression of miR-34a in primary B-CLL cells induced apoptosis. These findings suggest miR-34a as a possible therapeutic avenue and a sensitive indicator of the activity of the p53 axis in B-CLL.

Targeting the translational machinery as a novel treatment strategy for hematologic malignancies

The dysregulation of protein synthesis evident in the transformed phenotype has opened up a burgeoning field of research in cancer biology. Translation initiation has recently been shown to be a common downstream target of signal transduction pathways deregulated in cancer and initiated by mutated/overexpressed oncogenes and tumor suppressors. The overexpression and/or activation of proteins involved in translation initiation such as eIF4E, mTOR, and eIF4G have been shown to induce a malignant phenotype. Therefore, understanding the mechanisms that control protein synthesis is emerging as an exciting new research area with significant potential for developing innovative therapies. This review highlights molecules that are activated or dysregulated in hematologic malignancies, and promotes the transformed phenotype through the deregulation of protein synthesis. Targeting these proteins with small molecule inhibitors may constitute a novel therapeutic approach in the treatment of cancer.

Mammalian target of rapamycin inhibitors and their potential role in therapy in leukaemia and other haematological malignancies

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that functions as a key regulator of cell growth, protein synthesis, and cell-cycle progression through interactions with a number of signalling pathways, including PI3K/AKT, ras, TCL1, and BCR/ABL. Many haematological malignancies have aberrant activation of the mTOR and related signalling pathways. Accordingly, mTOR inhibitors, a class of signal transduction inhibitors that were originally developed as immunosuppressive agents, are being investigated in preclinical models and clinical trials for a number of haematological malignancies. Sirolimus and second-generation mTOR inhibitors, such as temsirolimus and everolimus, are safe and relatively well-tolerated, making them potentially attractive as single agents or in combination with conventional cytotoxics and other targeted therapies. Promising early clinical data suggests activity of mTOR inhibitors in a number of haematological diseases, including acute lymphoblastic leukaemia, chronic myeloid leukaemia, mantle cell lymphoma, anaplastic large cell lymphoma, and lymphoproliferative disorders. This review describes the rationale for using mTOR inhibitors in a variety of haematological diseases with a focus on their use in leukaemia.

Rapamycin prevents transforming growth factor-alpha-induced pulmonary fibrosis

Transforming growth factor (TGF)-alpha is a ligand for the epidermal growth factor receptor (EGFR). EGFR activation is associated with fibroproliferative processes in human lung disease and animal models of pulmonary fibrosis. Overexpression of TGF-alpha in transgenic mice causes progressive and severe pulmonary fibrosis; however, the intracellular signaling pathways downstream of EGFR mediating this response are unknown. Using a doxycycline-regulatable transgenic mouse model of lung-specific TGF-alpha expression, we observed increased PCNA protein and phosphorylation of Akt and p70S6K in whole lung homogenates in association with induction of TGF-alpha. Induction in the lung of TGF-alpha caused progressive pulmonary fibrosis over a 7-week period. Daily administration of rapamycin prevented accumulation of total lung collagen, weight loss, and changes in pulmonary mechanics. Treatment of mice with rapamycin 4 weeks after the induction of TGF-alpha prevented additional weight loss, increases in total collagen, and changes in pulmonary mechanics. Rapamycin prevented further increases in established pulmonary fibrosis induced by EGFR activation. This study demonstrates that mammalian target of rapamycin (mTOR) is a major effector of EGFR-induced pulmonary fibrosis, providing support for further studies to determine the role of mTOR in the pathogenesis and treatment of pulmonary fibrosis.

TCL1A expression delineates biological and clinical variability in B-cell lymphoma

The assembly of a collection of gene-expression signatures of the major types of B-cell non-Hodgkin's lymphoma has identified increased T-cell leukemia/lymphoma 1A (TCL1) expression in multiple lymphoma types and cases, and has enabled the investigation of the functional and clinical importance of TCL1 expression. Specifically, Burkitt's lymphoma cases show a homogeneously strong expression of TCL1, whereas diffuse large B-cell lymphoma, follicular lymphoma, mantle cell lymphoma, chronic lymphocytic leukemia, nodal marginal zone lymphoma, and splenic marginal zone lymphoma display a striking variability in the intensity of TCL1 staining. This was validated in two independent series. A Gene-Set Enrichment Analysis of the genes correlated with TCL1A expression found that variation in the level of expression of TCL1A was significantly associated with some of the most important gene signatures recognizing B-cell lymphoma pathogenesis and heterogeneity, such as germinal center, B-cell receptor, NF-kappaB (and its target genes), death, MAP kinases, TNFR1, TOLL, and IL1R. Additionally, TCL1 expression was correlated with shorter time to treatment in chronic lymphocytic leukemia cases and shorter lymphoma-specific survival in mantle cell lymphoma series, thus indicating the clinical and biological significance of TCL1 expression, and suggesting TCL1A as a potential therapeutic target.

The Tcl1 oncogene defines secondary hair germ cells differentiation at catagen-telogen transition and affects stem-cell marker CD34 expression

Overexpression of the TCL1 gene family plays a role in the onset of T-cell leukemias in mice and in humans. The Tcl1 gene is tightly regulated during early embryogenesis in which it participates in embryonic stem (ES)-cells proliferation and during lymphoid differentiation. Here, we provide evidences that Tcl1 is also important in mouse hair follicle (HF) and skin homeostasis. We found that Tcl1(-/-) adult mice exhibit hair loss, leading to alopecia with extensive skin lesions. By analysing Tcl1 expression in the wild-type (wt) skin through different stages of hair differentiation, we observe high levels in the secondary hair germ (HG) cells and hair bulges, during early anagen and catagen-telogen transition phases. The loss of Tcl1 does not result in apparent skin morphological defects during embryonic development and at birth, but its absence causes a reduction of proliferation in anagen HFs. Importantly, we show the that absence of Tcl1 induces a significant loss of the stem-cell marker CD34 (but not alpha6-integrin) expression in the bulge cells, which is necessary to maintain stem-cell characteristics. Therefore, our findings indicate that Tcl1 gene(s) might have important roles in hair formation, by its involvement in cycling and self-renewal of transient amplifying (TA) and stem-cell (SC) populations.

A pilot trial of the mTOR (mammalian target of rapamycin) inhibitor RAD001 in patients with advanced B-CLL

Although B-cell chronic lymphocytic leukemia (CLL) is treatable, it remains an incurable disease and most patients inevitably suffer relapse. Many therapeutic options exist for those requiring therapy, including monoclonal antibodies and stem cell transplantation, but remissions tend to last shorter in the course of the disease. Targeting the cell cycle has recently been realized to be an attractive therapeutic approach in solid and hematological malignancies, and the proliferative nature of B-CLL is increasingly accepted. Here, we report data on a phase II pilot trial with the oral mammalian target of rapamycin (mTOR) inhibitor RAD001 5 mg/daily in patients with advanced B-CLL who had progressive disease after at least two lines of treatment. After treatment of seven patients, this trial was stopped because of toxicity concerns, although some degree of activity was observed (one partial remission, three patients with stable disease). Interestingly, cyclin E expression decreased in responding patients. Further strategies of mTOR inhibition by RAD001 in B-CLL should focus on different treatment schedules, adequate anti-infectious prophylaxis, or combinations with cytotoxic drugs.

Mammalian target of rapamycin (mTOR) pathway signalling in lymphomas

The mammalian target of rapamycin mTOR is a central element in an evolutionary conserved signalling pathway that regulates cell growth, survival and proliferation, orchestrating signals originating from growth factors, nutrients or particular stress stimuli. Two important modulators of mTOR activity are the AKT and ERK/MAPK signalling pathways. Many studies have shown that mTOR plays an important role in the biology of malignant cells, including deregulation of the cell cycle, inactivation of apoptotic machinery and resistance to chemotherapeutic agents. The development of several mTOR inhibitors, in addition to rapamycin, has facilitated studies of the role of mTOR in cancer, and verified the antitumour effect of mTOR inhibition in many types of neoplasms, including lymphomas. Clinical trials of rapamycin derivatives in lymphoma patients are already in development and there are encouraging preliminary results, such as the substantial response of a subset of mantle cell lymphoma patients to the rapamycin analogue temsirolimus. Based on results obtained from in vitro and in vivo studies of the mTOR pathway in lymphomas, it seems that better understanding of mTOR regulation will reveal aspects of lymphomagenesis and contribute to the development of more powerful, targeted therapies for lymphoma patients.

Murine models of chronic lymphocytic leukaemia: role of microRNA-16 in the New Zealand Black mouse model

Mouse models are valuable tools in the study of human chronic lymphocytic leukaemia (CLL). The New Zealand Black (NZB) strain is a naturally occurring model of late-onset CLL characterized by B-cell hyperproliferation and autoimmunity early in life, followed by progression to CLL. Other genetically engineered models of CLL that have been developed include (NZB x NZW) F1 mice engineered to express IL5, mice expressing human TCL1A, and mice overexpressing both BCL2 and a tumour necrosis factor receptor-associated factor. The applicability to human CLL varies with each model, suggesting that CLL is a multifactorial disease. Our work with the de novo NZB model has revealed many similarities to the human situation, particularly familial CLL. In NZB, the malignant clones express CD5, zap-70, and have chromosomal instability and germline Ig sequence. We also identified a point mutation in the 3'-flanking sequence of Mirn16-1, which resulted in decreased levels of the microRNA, miR-16 in lymphoid tissue. Exogenous restoration of miR-16 to an NZB malignant B-1 cell line resulted in cell cycle alterations, suggesting that the altered expression of Mirn15a/16-1 is an important molecular lesion in CLL. Future studies utilizing the NZB mouse could ascertain the role of environmental triggers, such as low dose radiation and organic chemicals in the augmentation of a pre-existing propensity to develop CLL.

The role of microRNA and other non-coding RNA in the pathogenesis of chronic lymphocytic leukemia

New findings support the view that chronic lymphocytic leukemia (CLL) is a genetic disease in which the main alterations occur in a new class of genes named microRNAs (miRNAs). Cases with good prognostic features typically are characterized by miRNA down-regulation of genes miR-15a and miR-16-1, located at 13q14.3. Both microRNAs negatively regulate BCL2 at a post-transcriptional level. On the other hand, in CLL cases that use unmutated immunoglobulin heavy-chain variable-region genes (IgV(H)) or have high-level expression of the 70-kD zeta-associated protein (ZAP-70) have high levels of TCL1 due to low-level expression of miR-29 and miR-181, which directly target this oncogene. Conceivably, these miRNAs might be used to target BCL2 or TCL1 for therapy of this disease.

TORC2 regulates germinal center repression of the TCL1 oncoprotein to promote B cell development and inhibit transformation

Aberrant expression of the TCL1 oncoprotein promotes malignant transformation of germinal center (GC) B cells. Repression of TCL1 in GC B cells facilitates FAS-mediated apoptosis and prevents lymphoma formation. However, the mechanism for this repression is unknown. Here we show that the CREB coactivator TORC2 directly regulates TCL1 expression independent of CREB Ser-133 phosphorylation and CBP/p300 recruitment. GC signaling through CD40 or the BCR, which activates pCREB-dependent genes, caused TORC2 phosphorylation, cytosolic emigration, and TCL1 repression. Signaling via cAMP-inducible pathways inhibited TCL1 repression and reduced apoptosis, consistent with a prosurvival role for TCL1 before GC selection and supporting an initiating role for aberrant TCL1 expression during GC lymphomagenesis. Our data indicate that a novel CREB/TORC2 regulatory mode controls the normal program of GC gene activation and repression that promotes B cell development and circumvents oncogenic progression. Our results also reconcile a paradox in which signals that activate pCREB/CBP/p300 genes concurrently repress TCL1 to initiate its silencing.

Animal models for chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL), the most common leukemia in the Western world, results from an expansion of a rare population of CD5+ mature B-lymphocytes. Although clinical features and genomic abnormalities in B-CLL have been studied in considerable detail, the molecular mechanisms underlying disease development has remained unclear until recently. In the last 4 years, several transgenic mouse models for B-CLL were generated. Investigations of these mouse models revealed that deregulation of three pathways, Tcl1-Akt pathway, TNF-NF-kB pathway, and Bcl2-mediated anti-apoptotic pathway, result in the development of B-CLL. While deregulation of TCL1 alone caused a B-CLL phenotype in mice, overexpression of Bcl2 required aberrantly activated TNF-NF-kB pathway signaling to yield the disease phenotype. In this article, we present what has been learned from mice with B-CLL phenotype and how these mouse models of B-CLL were used to test therapeutic treatments for this common leukemia.