The NF-κB subunit Rel A is associated with in vitro survival and clinical disease progression in chronic lymphocytic leukemia and represents a promising therapeutic target

Gene expression of INPP5F as an independent prognostic marker in fludarabine-based therapy of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease. Various disease-related and patient-related factors have been shown to influence the course of the disease. The aim of this study was to identify novel biomarkers of significant clinical relevance. Pretreatment CD19-separated lymphocytes (n=237; discovery set) and peripheral blood mononuclear cells (n=92; validation set) from the REACH trial, a randomized phase III trial in relapsed CLL comparing rituximab plus fludarabine plus cyclophosphamide with fludarabine plus cyclophosphamide alone, underwent gene expression profiling. By using Cox regression survival analysis on the discovery set, we identified inositol polyphosphate-5-phosphatase F (INPP5F) as a prognostic factor for progression-free survival (P<0.001; hazard ratio (HR), 1.63; 95% confidence interval (CI), 1.35-1.98) and overall survival (P<0.001; HR, 1.47; 95% CI, 1.18-1.84), regardless of adjusting for known prognostic factors. These findings were confirmed on the validation set, suggesting that INPP5F may serve as a novel, easy-to-assess future prognostic biomarker for fludarabine-based therapy in CLL.

The Nedd8-activating enzyme inhibitor MLN4924 thwarts microenvironment-driven NF-κB activation and induces apoptosis in chronic lymphocytic leukemia B cells

BACKGROUND

Stromal-mediated signaling enhances NF-κB pathway activity in chronic lymphocytic leukemia (CLL) B cells, leading to cell survival and chemoresistance. Ubiquitination of IκBα may partially account for constitutive activation of NF-κB. MLN4924 is an investigational agent that inhibits the Nedd8-activating enzyme, thereby neutralizing Cullin-RING ubiquitin ligases and preventing degradation of their substrates.

EXPERIMENTAL DESIGN

We conducted a preclinical assessment of MLN4924 in CLL. Primary CLL cells were cocultured in vitro with CD40L-expressing stroma to mimic the prosurvival conditions present in lymphoid tissue. The effect of MLN4924 on CLL cell apoptosis, NF-κB pathway activity, Bcl-2 family members, and cell cycle was assessed by flow cytometry, Western blotting, PCR, and immunocytochemistry.

RESULTS

CD40L-expressing stroma protected CLL cells from spontaneous apoptosis and induced resistance to multiple drugs, accompanied by NF-κB activation and Bim repression. Treatment with MLN4924 induced CLL cell apoptosis and circumvented stroma-mediated resistance. This was accompanied by accumulation of phospho-IκBα, decreased nuclear translocation of p65 and p52 leading to inhibition of both the canonical and noncanonical NF-κB pathways, and reduced transcription of their target genes, notably chemokines. MLN4924 promoted induction of Bim and Noxa in the CLL cells leading to rebalancing of Bcl-2 family members toward the proapoptotic BH3-only proteins. siRNA-mediated knockdown of Bim or Noxa decreased sensitivity to MLN4924. MLN4924 enhanced the antitumor activity of the inhibitors of B-cell receptor (BCR)-associated kinases.

CONCLUSIONS

MLN4924 disrupts NF-κB activation and induces Bim expression in CLL cells, thereby preventing stroma-mediated resistance. Our data provide rationale for further evaluation of MLN4924 in CLL.

The gene expression response of chronic lymphocytic leukemia cells to IL-4 is specific, depends on ZAP-70 status and is differentially affected by an NFκB inhibitor

Interleukin 4 (IL-4), an essential mediator of B cell development, plays a role in survival of chronic lymphocytic leukemia (CLL) cells. To obtain new insights into the function of the IL-4 pathway in CLL, we analyzed the gene expression response to IL-4 in CLL and in normal B cells (NBC) by oligonucleotide microarrays, resulting in the identification of 232 non-redundant entities in CLL and 146 in NBC (95 common, 283 altogether), of which 189 were well-defined genes in CLL and 123 in NBC (83 common, 229 altogether) (p<0.05, 2-fold cut-off). To the best of our knowledge, most of them were novel IL-4 targets for CLL (98%), B cells of any source (83%), or any cell type (70%). Responses were significantly higher for 54 and 11 genes in CLL and NBC compared to each other, respectively. In CLL, ZAP-70 status had an impact on IL-4 response, since different sets of IL-4 targets correlated positively or negatively with baseline expression of ZAP-70. In addition, the NFκB inhibitor 6-Amino-4-(4-phenoxyphenethylamino)quinazoline, which reversed the anti-apoptotic effect of IL-4, preferentially blocked the response of genes positively correlated with ZAP-70 (e.g. CCR2, SUSD2), but enhanced the response of genes negatively correlated with ZAP-70 (e.g. AUH, BCL6, LY75, NFIL3). Dissection of the gene expression response to IL-4 in CLL and NBC contributes to the understanding of the anti-apoptotic response. Initial evidence of a connection between ZAP-70 and NFκB supports further exploration of targeting NFκB in the context of the assessment of inhibition of the IL-4 pathway as a therapeutic strategy in CLL, especially in patients expressing bad prognostic markers.

Anti-cancer activity of carbamate derivatives of melampomagnolide B

Melampomagnolide B (MMB) is a natural sesquiterpene structurally related to parthenolide (PTL). We have shown that MMB exhibits anti-leukemic properties similar to PTL. Unlike PTL, the presence of a primary hydroxyl group in the MMB molecule allows the opportunity for examining the biological activity of a variety of conjugated analogs of MMB. We have now synthesized a series of carbamate analogs of MMB and evaluated these derivatives for anti-cancer activity against a panel of sixty human cancer cell lines. Analogs 6a and 6e exhibited promising anti-leukemic activity against human leukemia cell line CCRF-CEM with GI50 values of 680 and 620 nM, respectively. Analog 6a also showed GI50 values of 1.98 and 1.38 μM respectively, against RPMI-8226 and SR leukemia cell lines and GI50 values of 460 and 570 nM against MDA-MB-435 melanoma and MDA-MB-468 breast cancer cell lines, respectively. Analog 6e had GI50 values of 650 and 900 nM against HOP-92 non-small cell lung and RXF 393 renal cancer cell lines.

The arachidonic acid-LTB4-BLT2 pathway enhances human B-CLL aggressiveness

Deregulation of the oxidative cascade of poly-unsaturated fatty acids (PUFAs) has been associated with several cancers, including chronic lymphocytic leukemia (B-CLL). Leukotriene B4 (LTB4), a metabolite of arachidonic acid (AA), is produced by B-CLL and contributes to their survival. The aim of the present study was to analyze the activity of the oxidative cascade of PUFAs in B-CLL. Purified B cells from patients and normal B CD5 positive cells were subjected to flow cytometry, Western-blot and RT-qPCR analyses. LTB4 plasma and intracellular concentrations were determined by ELISA. Our results showed that aggressive B-CLL tumor cells, i.e. cells with an annual proliferation index above 2, over-expressed calcium-dependent and calcium-independent phospholipases A2 (cPLA2-alpha and iPLA2-beta, respectively), 5-lipoxygenase (5LOX) and leukotriene A4 hydroxylase (LTA4H). Intracellular LTB4 levels were lower in the most aggressive cells than in cells with a smaller proliferation index, despite equivalent plasma levels, and lower expression of cytochrome P450 4F3A (CYP4F3A), one major enzyme involved in LTB4 inactivation. Since BLT2, a LTB4 membrane receptor was also more often expressed on aggressive tumor cells, and since a BLT2 inhibitor significantly impaired B-CLL viability in vitro, we propose that LTB4 was efficiently trapped onto BLT2 present on aggressive tumors, thereby eliciting an autocrine response. Taken together our results demonstrate a major deregulation of the pathway leading to LTB4 synthesis and degradation in B-CLL cells, and provide a framework for understanding how these modifications promote cell survival and proliferation, especially in the most aggressive BCLL.

Telomere dysfunction accurately predicts clinical outcome in chronic lymphocytic leukaemia, even in patients with early stage disease

Defining the prognosis of individual cancer sufferers remains a significant clinical challenge. Here we assessed the ability of high-resolution single telomere length analysis (STELA), combined with an experimentally derived definition of telomere dysfunction, to predict the clinical outcome of patients with chronic lymphocytic leukaemia (CLL). We defined the upper telomere length threshold at which telomere fusions occur and then used the mean of the telomere 'fusogenic' range as a prognostic tool. Patients with telomeres within the fusogenic range had a significantly shorter overall survival (P < 0·0001; Hazard ratio [HR] = 13·2, 95% confidence interval [CI] = 11·6-106·4) and this was preserved in early-stage disease patients (P < 0·0001, HR=19·3, 95% CI = 17·8-802·5). Indeed, our assay allowed the accurate stratification of Binet stage A patients into those with indolent disease (91% survival at 10 years) and those with poor prognosis (13% survival at 10 years). Furthermore, patients with telomeres above the fusogenic mean showed superior prognosis regardless of their IGHV mutation status or cytogenetic risk group. In keeping with this finding, telomere dysfunction was the dominant variable in multivariate analysis. Taken together, this study provides compelling evidence for the use of high-resolution telomere length analysis coupled with a definition of telomere dysfunction in the prognostic assessment of CLL.

Loss of cooperativity of secreted CD40L and increased dose-response to IL4 on CLL cell viability correlates with enhanced activation of NF-kB and STAT6

Chronic lymphocytic leukemia (CLL) cells fail to enter apoptosis in vivo as opposed to their non-malignant B-lymphocyte counterparts. The ability of CLL cells to escape apoptosis is highly dependent on their microenvironment. Compared to non-malignant B cells, CLL cells are more responsive to complex stimuli that can be reproduced in vitro by the addition of cytokines. To understand the molecular mechanism of the environment-dependent anti-apoptotic signaling circuitry of CLL cells, we quantified the effect of the SDF-1, BAFF, APRIL, anti-IgM, interleukin-4 (IL4) and secreted CD40L (sCD40L) on the survival of in vitro cultured CLL cells and found IL4 and sCD40L to be most efficient in rescuing CLL cells from apoptosis. In quantitative dose-response experiments using cell survival as readout, the binding affinity of IL4 to its receptor was similar between malignant and non-malignant cells. However, the downstream signaling in terms of the amount of STAT6 and its degree of phosphorylation was highly stimulated in CLL cells. In contrast, the response to sCD40L showed a loss of cooperative binding in CLL cells but displayed a largely increased ligand binding affinity. Although a high-throughput microscopy analysis did not reveal a significant difference in the spatial CD40 receptor organization, the downstream signaling showed an enhanced activation of the NF-kB pathway in the malignant cells. Thus, we propose that the anti-apoptotic phenotype of CLL involves a sensitized response for IL4 dependent STAT6 phosphorylation, and an activation of NF-kB signaling due to an increased affinity of sCD40L to its receptor.

STAT3-activated GM-CSFRα translocates to the nucleus and protects CLL cells from apoptosis

Here, it was determined that chronic lymphocytic leukemia (CLL) cells express the α subunit, but not the β subunit, of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR/CSF2R). GM-CSFRα was detected on the surface, in the cytosol, and in the nucleus of CLL cells via confocal microscopy, cell fractionation, and GM-CSFRα antibody epitope mapping. Because STAT3 is frequently activated in CLL and the GM-CSFRα promoter harbors putative STAT3 consensus binding sites, MM1 cells were transfected with truncated forms of the GM-CSFRα promoter, then stimulated with IL6 to activate STAT3 and to identify STAT3-binding sites. Chromatin immunoprecipitation (ChIP) and an electoromobility shift assay (EMSA) confirmed STAT3 occupancy to those promoter regions in both IL6-stimulated MM1 and CLL cells. Transfection of MM1 cells with STAT3-siRNA or CLL cells with STAT3-shRNA significantly downregulated GM-CSFRα mRNA and protein levels. RNA transcripts, involved in regulating cell survival pathways, and the proteins KAP1 (TRIM28) and ISG15 coimmunoprecipitated with GM-CSFRα. GM-CSFRα-bound KAP1 enhanced the transcriptional activity of STAT3, whereas GM-CSFRα-bound ISG15 inhibited the NF-κB pathway. Nevertheless, overexpression of GM-CSFRα protected MM1 cells from dexamethasone-induced apoptosis, and GM-CSFRα knockdown induced apoptosis in CLL cells, suggesting that GM-CSFRα provides a ligand-independent survival advantage.

IMPLICATIONS

Constitutively, activation of STAT3 induces the expression of GM-CSFRα that protects CLL cells from apoptosis, suggesting that inhibition of STAT3 or GM-CSFRα may benefit patients with CLL.

Targeted therapy in chronic lymphocytic leukemia: past, present, and future

BACKGROUND

Chronic lymphocytic leukemia (CLL) is the most prevalent leukemia in the western world. Recent advances in understanding the biology of B-cell malignancies have resulted in the development of novel agents targeting key prosurvival pathways in the neoplastic B cell.

OBJECTIVE

The goal of this article was to summarize current literature on the emerging therapeutic approaches in CLL and B-cell malignancies.

METHODS

A literature review was performed, identifying pathways and key clinical trials involving novel therapies in CLL, with special emphasis on B-cell receptor (BCR)-targeting agents.

RESULTS

Understanding the biology of the BCR-signaling pathway has led to identification of novel molecular targets. Most notably, inhibitors of Bruton tyrosine kinase and phosphatidylinositide 3-kinase-δ have entered clinical trials and demonstrated high response rates in CLL, including high-risk disease. Cyclin-dependent kinase inhibitors may evolve into an alternative therapeutic approach in CLL. New drugs that target molecules within and outside of the BCR-signaling pathway have shown promise in preclinical studies.

CONCLUSIONS

Both preclinical and early clinical trial results involving novel targeted therapies suggest that the standard treatment paradigm in CLL and B-cell malignancies will soon change. Particular attention should be paid to the BCR-targeting agents, whose favorable adverse effect profile may improve the lives of elderly patients with CLL.

B-cell antigen receptor signaling in chronic lymphocytic leukemia: therapeutic targets and translational opportunities

B-cell chronic lymphocytic leukemia (CLL) is characterized by clonally expanded and molecularly heterogeneous populations of B lymphocytes with impaired apoptotic mechanisms. This occurs as a result of multiple genetic and epigenetic abnormalities, including chromosomal aberrations and enhancer region hypomethylation, often impinging on intracellular signaling pathways that are essential to normal B-cell activation, proliferation, and survival. The B-cell antigen receptor (BCR) signaling is one such pathway usurped by malignant B cells, as exemplified by the early phase clinical success achieved by small-molecule agents targeting key players involved in the pathway. Such new targeted agents, including those that inhibit the function of Spleen tyrosine kinase (SYK), Bruton's tyrosine kinase (BTK), phosphatidylinositol 3-kinases (PI3K), and B-cell lymphoma 2 (BCL-2), along with the current standard therapy comprising chemo-immunotherapies with or without B-cell depleting biologic agent rituximab (anti-CD20 monoclonal antibody), should expand the armamentarium for CLL therapy. We review the therapeutic agents currently in clinical development which target different effectors of the malignant BCR signaling, and discuss their overlapping and discriminating translational opportunities in the context of CLL treatment.

Dasatinib in combination with fludarabine in patients with refractory chronic lymphocytic leukemia: a multicenter phase 2 study

Resistance to chemotherapy-induced apoptosis in CLL is associated with overexpression of antiapoptotic proteins induced by signals from the microenvironment. In vitro, dasatinib effectively inhibits expression of anti-apoptotic regulators and restores fludarabine sensitivity in activated CLL. The aim of this study was to evaluate efficacy of one cycle of dasatinib monotherapy (100mg/day, days 1-28) followed by combination of dasatinib with fludarabine (40mg/m²/day, days 1-3 every 28 day) for a total of 6 cycles in fludarabine-refractory CLL. The primary endpoint was overall response rate according to the IWCLL'08 criteria. 20 patients were enrolled: 18 completed at least one cycle of treatment of which 67% finished at least 2 cycles of combination treatment. 3 of these 18 patients reached a formal PR (16.7%). Majority of patients obtained some reduction in lymph node (LN) size. Most frequent toxicity was related to myelosuppression. NF-κB RNA expression levels of circulating CLL cells decreased whereas the levels of pro-apoptotic NOXA increased during treatment. In conclusion, dasatinib/fludarabine combination has modest clinical efficacy in fludarabine-refractory patients.

RelB, together with RelA, sustains cell survival and confers proteasome inhibitor sensitivity of chronic lymphocytic leukemia cells from bone marrow

Although the biological factors that contribute to the pathogenesis of chronic lymphocytic leukemia (CLL) remain widely unresolved, it has been suggested that dysregulated cell survival and proliferation are fundamental to this process. Constitutive classical nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation protects CLL B-cells from cell death and plays a critical role in the acquisition of chemoresistance. RelB, representing the alternative NF-κB activity, functions specifically in lymphoid organogenesis and B-cell maturation. RelB indeed plays a tumor-supportive role and confers radiation resistance in tumors. However, the involvement of RelB in CLL has not been addressed. Here, we analyzed the NF-κB activation in 67 of CLL bone marrow (BM). Both the RelA and RelB activity were detected in CLL B-cells from BM, in spite of inevitable variability. Low RelB activity was linked to a favorable prognosis of CLL. The migration and adhesion abilities of CLL B-cells were not affected by the RelB activity. High RelB activity, together with the RelA activity, maintained basal survival of cells. The induction of RelA and RelB expression in the nucleus was responsible for better survival of CLL B-cells supported by bone marrow stromal cells. In addition, the presence of high RelB activity in CLL B-cells was correlated with sensitivity to proteasome inhibitor but not fludarabine. Taken together, we provided evidences that not only RelA but also RelB, subunits of NF-κB family, played an important role in the cellular behaviors of CLL cells from BM. The strength of RelB activity influenced the prognosis of CLL patients.

KEY MESSAGE

RelB, with RelA activity, maintained the basal survival of CLL cells from BM. RelB, with RelA, conferred the proteasome inhibitor sensitivity of CLL cells. Induction of RelA and RelB was responsible for the better survival of CLL B-cells. The strength of RelB activity influenced the prognosis of CLL patients.

B cell receptor signaling in chronic lymphocytic leukemia

B cell receptor (BCR) signaling plays an important pathogenic role in chronic lymphocytic leukemia (CLL) and B cell lymphomas, based on structural restrictions of the BCR, and BCR-dependent survival and growth of the malignant B cells. In CLL and lymphoma subtypes, ligand-independent ('tonic') and ligand-dependent BCR signaling have been characterized, which can involve mutations of BCR pathway components or be triggered by (auto)antigens present in the tissue microenvironment. In CLL, based on high response rates and durable remissions in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR-associated kinases [Bruton's tyrosine kinase (BTK), phosphoinositide 3-kinase (PI3K)δ], which will change treatment paradigms in CLL and other B cell malignancies. Here, we discuss the evolution of this field, from BCR-related prognostic markers, to mechanisms of BCR activation, and targeting of BCR-associated kinases, the emerging Achilles' heel in CLL pathogenesis.

Molecular genetics of high-risk chronic lymphocytic leukemia

In an optimized management algorithm of chronic lymphocytic leukemia (CLL), the early identification of high-risk patients, ideally prior to treatment, is a prerequisite for designing strategies tailored at overcoming therapy resistance. TP53 abnormalities play a central role in our current understanding of the poor prognosis of high-risk CLL patients, but fail to explain the molecular basis of 50% of high-risk CLL. Next-generation sequencing studies have revealed several novel genetic alterations in high-risk CLL, including NOTCH1, SF3B1 and BIRC3 mutations. Alterations of these genes occur in 5-10% of CLL at diagnosis, show a prevalence that increases in the more advanced phases of the disease, and confer poor prognosis in consecutive CLL series.

Clinical implications of the molecular genetics of chronic lymphocytic leukemia

Genetics and molecular genetics have contributed to clarify the biological bases of the clinical heterogeneity of chronic lymphocytic leukemia. In recent years, our knowledge of the molecular genetics of chronic lymphocytic leukemia has significantly broadened, offering potential new clinical implications. Mutations of TP53 and ATM add prognostic information independently of fluorescence in situ hybridization cytogenetic stratification. In addition, next generation sequencing technologies have allowed previously unknown genomic alterations in chronic lymphocytic leukemia to be identified. Mutations of NOTCH1, SF3B1 and BIRC3 have been associated with short time to progression and survival. Each of these lesions recognizes a different distribution across different clinical phases and biological subgroups of the disease. The clinical implications of these molecular lesions are in some instances well established, such as in the case of patients with TP53 disruption, who should be considered for alternative therapies/allogeneic stem cell transplant upfront, or in patients with ATM disruption, who are candidates to rituximab-based immunochemotherapy. On the contrary, NOTCH1, SF3B1 and BIRC3 mutations appear to have a specific significance, the clinical value of which is currently being validated, i.e. association to Richter syndrome transformation for NOTCH1 mutations, and short progression-free survival after treatment for SF3B1 mutations. Certainly, these new lesions have helped clarify the molecular bases of chronic lymphocytic leukemia aggressiveness beside TP53 disruption. This review covers the recent advancements in our understanding of the molecular genetics of chronic lymphocytic leukemia and discusses how they are going to translate into clinical implications for patient management.

Epigenetic upregulation of lncRNAs at 13q14.3 in leukemia is linked to the In Cis downregulation of a gene cluster that targets NF-kB

Non-coding RNAs are much more common than previously thought. However, for the vast majority of non-coding RNAs, the cellular function remains enigmatic. The two long non-coding RNA (lncRNA) genes DLEU1 and DLEU2 map to a critical region at chromosomal band 13q14.3 that is recurrently deleted in solid tumors and hematopoietic malignancies like chronic lymphocytic leukemia (CLL). While no point mutations have been found in the protein coding candidate genes at 13q14.3, they are deregulated in malignant cells, suggesting an epigenetic tumor suppressor mechanism. We therefore characterized the epigenetic makeup of 13q14.3 in CLL cells and found histone modifications by chromatin-immunoprecipitation (ChIP) that are associated with activated transcription and significant DNA-demethylation at the transcriptional start sites of DLEU1 and DLEU2 using 5 different semi-quantitative and quantitative methods (aPRIMES, BioCOBRA, MCIp, MassARRAY, and bisulfite sequencing). These epigenetic aberrations were correlated with transcriptional deregulation of the neighboring candidate tumor suppressor genes, suggesting a coregulation in cis of this gene cluster. We found that the 13q14.3 genes in addition to their previously known functions regulate NF-kB activity, which we could show after overexpression, siRNA-mediated knockdown, and dominant-negative mutant genes by using Western blots with previously undescribed antibodies, by a customized ELISA as well as by reporter assays. In addition, we performed an unbiased screen of 810 human miRNAs and identified the miR-15/16 family of genes at 13q14.3 as the strongest inducers of NF-kB activity. In summary, the tumor suppressor mechanism at 13q14.3 is a cluster of genes controlled by two lncRNA genes that are regulated by DNA-methylation and histone modifications and whose members all regulate NF-kB. Therefore, the tumor suppressor mechanism in 13q14.3 underlines the role both of epigenetic aberrations and of lncRNA genes in human tumorigenesis and is an example of colocalization of a functionally related gene cluster.

Inhibition of NF-κB-mediated signaling by the cyclin-dependent kinase inhibitor CR8 overcomes prosurvival stimuli to induce apoptosis in chronic lymphocytic leukemia cells

PURPOSE

Chronic lymphocytic leukemia (CLL) is currently incurable with standard chemotherapeutic agents, highlighting the need for novel therapies. Overcoming proliferative and cytoprotective signals generated within the microenvironment of lymphoid organs is essential for limiting CLL progression and ultimately developing a cure.

EXPERIMENTAL DESIGN

We assessed the potency of cyclin-dependent kinase (CDK) inhibitor CR8, a roscovitine analog, to induce apoptosis in primary CLL from distinct prognostic subsets using flow cytometry-based assays. CLL cells were cultured in in vitro prosurvival and proproliferative conditions to mimic microenvironmental signals in the lymphoid organs, to elucidate the mechanism of action of CR8 in quiescent and proliferating CLL cells using flow cytometry, Western blotting, and quantitative real-time PCR.

RESULTS

CR8 was 100-fold more potent at inducing apoptosis in primary CLL cells than roscovitine, both in isolated culture and stromal-coculture conditions. Importantly, CR8 induced apoptosis in CD40-ligated CLL cells and preferentially targeted actively proliferating cells within these cultures. CR8 treatment induced downregulation of the antiapoptotic proteins Mcl-1 and XIAP, through inhibition of RNA polymerase II, and inhibition of NF-κB signaling at the transcriptional level and through inhibition of the inhibitor of IκB kinase (IKK) complex, resulting in stabilization of IκBα expression.

CONCLUSIONS

CR8 is a potent CDK inhibitor that subverts pivotal prosurvival and proproliferative signals present in the tumor microenvironment of CLL patient lymphoid organs. Our data support the clinical development of selective CDK inhibitors as novel therapies for CLL.

Apoptosis deregulation in CLL

The description of apoptosis and the identification of the genes that regulate it have proved pivotal to our understanding of how cancer cells accumulate and ultimately cause morbidity and mortality. It has become increasingly clear that in CLL the balance between the pro- and anti-apoptotic members of the BCL2 family of apoptotic regulatory proteins is critical in the development and clinical progression of CLL. Furthermore, the apoptotic potential of the CLL cell determines chemotherapy sensitivity and ultimately progression-free and overall survival. The unravelling of the BCL2 story in CLL has led to the development of a whole new class of therapeutic agents-the BH3 mimetics-which are significantly more targeted than conventional chemo-immunotherapy and therefore promise potent clinical activity coupled with reduced toxicity.

Parthenolide eliminates leukemia-initiating cell populations and improves survival in xenografts of childhood acute lymphoblastic leukemia

Approximately 20% of children with acute lymphoblastic leukemia (ALL) relapse because of failure to eradicate the disease. Current drug efficacy studies focus on reducing leukemia cell burden. However, if drugs have limited effects on leukemia-initiating cells (LICs), then these cells may expand and eventually cause relapse. Parthenolide (PTL) has been shown to cause apoptosis of LIC in acute myeloid leukemia. In the present study, we assessed the effects of PTL on LIC populations in childhood ALL. Apoptosis assays demonstrated that PTL was effective against bulk B- and T-ALL cells, whereas the CD34(+)/CD19(-), CD34(+)/CD7(-), and CD34(-) subpopulations were more resistant. However, functional analyses revealed that PTL treatment prevented engraftment of multiple LIC populations in NOD/LtSz-scid IL-2Rγ(c)-null mice. PTL treatment of mice with established leukemias from low- and high-risk patients resulted in survival and restoration of normal murine hemopoiesis. In only 3 cases, disease progression was significantly slowed in mice engrafted with CD34(+)/CD19(-) or CD34(+)/CD7(-) and CD34(-) cells, but was not prevented, demonstrating that individual LIC populations within patients have different responses to therapy. These observations indicate that PTL may have therapeutic potential in childhood ALL and provide a basis for developing effective therapies that eradicate all LIC populations to prevent disease progression and reduce relapse.

Inhibition of nuclear factor kappa B activation in early-stage chronic lymphocytic leukemia by omega-3 fatty acids

Targeting the nuclear factor kappa B (NFκB) pathway is proposed as therapy for chronic lymphocytic leukemia (CLL). We hypothesized that an omega-3 fatty acids (n-3) supplement would suppress NFκB activation in lymphocytes of Rai Stage 0-1 CLL patients. The initial dose of 2.4 g n-3/day was gradually increased to 7.2 g n-3/day. After n-3 consumption: 1) plasma n-3 increased; 2) NFκB activation was suppressed in lymphocytes; 3) in vitro sensitivity of lymphocytes to doxorubicin was increased; and 4) expression of 32 genes in lymphocytes was significantly decreased.

Signaling pathways activated by the B-cell receptor in chronic lymphocytic leukemia

Over the past decade, several features of the B-cell receptor (BCR) complex have emerged as major markers for prognostic classification of B-cell chronic lymphocytic leukemia (B-CLL). In particular, the absence of somatic mutations within the immunoglobulin variable heavy chain genes (IGHV), the presence of ZAP-70 and a higher ability of the BCR to translate signals within the cell have been associated with an aggressive clinical course. Indeed, the stratification of patients with B-CLL based on BCR features suggests that heterogeneity of B-CLL clinical courses may reflect BCR signaling differences that have arisen during the evolution of leukemia. Therefore, characterizing BCR signaling profiles may help to identify signaling markers useful for patient stratification, disease monitoring and therapeutic targeting in B-CLL.

Phospho-specific flow cytometry identifies aberrant signaling in indolent B-cell lymphoma

Background

Knowledge about signaling pathways in malignant cells may provide prognostic and diagnostic information in addition to identify potential molecular targets for therapy. B-cell receptor (BCR) and co-receptor CD40 signaling is essential for normal B cells, and there is increasing evidence that signaling via BCR and CD40 plays an important role in the pathogenesis of B-cell lymphoma. The aim of this study was to investigate basal and induced signaling in lymphoma B cells and infiltrating T cells in single-cell suspensions of biopsies from small cell lymphocytic lymphoma/chronic lymphocytic leukemia (SLL/CLL) and marginal zone lymphoma (MZL) patients.

Methods

Samples from untreated SLL/CLL and MZL patients were examined for basal and activation induced signaling by phospho-specific flow cytometry. A panel of 9 stimulation conditions targeting B and T cells, including crosslinking of the B cell receptor (BCR), CD40 ligand and interleukins in combination with 12 matching phospho-protein readouts was used to study signaling.

Results

Malignant B cells from SLL/CLL patients had higher basal levels of phosphorylated (p)-SFKs, p-PLCγ, p-ERK, p-p38, p-p65 (NF-κB), p-STAT5 and p-STAT6, compared to healthy donor B cells. In contrast, anti-BCR induced signaling was highly impaired in SLL/CLL and MZL B cells as determined by low p-SFK, p-SYK and p-PLCγ levels. Impaired anti-BCR-induced p-PLCγ was associated with reduced surface expression of IgM and CD79b. Similarly, CD40L-induced p-ERK and p-p38 were also significantly reduced in lymphoma B cells, whereas p-p65 (NF-κB) was equal to that of normal B cells. In contrast, IL-2, IL-7 and IL-15 induced p-STAT5 in tumor-infiltrating T cells were not different from normal T cells.

Conclusions

BCR signaling and CD40L-induced p-p38 was suppressed in malignant B cells from SLL/CLL and MZL patients. Single-cell phospho-specific flow cytometry for detection of basal as well as activation-induced phosphorylation of signaling proteins in distinct cell populations can be used to identify aberrant signaling pathways.

The Hsp90 inhibitor NVP-AUY922-AG inhibits NF-κB signaling, overcomes microenvironmental cytoprotection and is highly synergistic with fludarabine in primary CLL cells

Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stability and function of multiple over-expressed signaling proteins that promote growth and survival in cancer cells. Chronic lymphocytic leukaemia (CLL) is characterized by increased expression of several Hsp90 client proteins making it a potentially susceptible to Hsp90 inhibition. In this study we showed that the novel Hsp90 inhibitor NVP-AUY922-AG was cytotoxic to primary CLL cells in vitro (LD₅₀=0.18μM±0.20). Importantly, its toxicity was preserved under cytoprotective co-culture conditions that rendered fludarabine ineffective. At the molecular level, NVP-AUY922-AG depleted the expression of multiple Hsp90 client proteins including Akt and activators of NF-κB, IKKα and IKKβ. Consistent with this inhibition profile, NVP-AUY922-AG resulted in decreased transcription of the NF-B target genes MCL1, CFLAR, BIRC5. In contrast, fludarabine significantly induced the transcription of MCL1 and BIRC5. Given the anti-apoptotic nature of these genes and the role they play in fludarabine resistance, we considered that the combination of NVP-AUY922-AG with fludarabine might resensitize CLL cells to the effects of fludarabine. In keeping with this hypothesis, the combination of NVP-AUY922-AG and fludarabine was highly synergistic (mean CI=0.110.06) and this synergy was enhanced in co-culture (mean CI=0.06±0.08). Furthermore, the combination maintained the decrease in MCL1, CFLAR and BIRC5 transcription suggesting that the ability of NVP-AUY922-AG to modulate expression of these genes may contribute to the efficacy of this drug under cytoprotective co-culture conditions and for its remarkable synergy with fludarabine. Taken together these findings indicate that Hsp90 inhibition is an attractive therapeutic strategy in CLL.

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.

Targeting the microenvironment in chronic lymphocytic leukemia offers novel therapeutic options

Chronic lymphocytic leukemia (CLL) cells display features consistent with a defect in apoptosis and exhibit prolonged survival in vivo. Survival of these malignant cells is influenced by interactions with non-leukemic cells located in permissive niches in lymphoid organs. Leukemic cells subvert the normal architecture of the lymphoid organs, recruiting stromal cells, dendritic cells and T lymphocytes, all reported as playing active roles in the survival and proliferation of CLL. The same survival-promoting environment also rescues/protects leukemic cells from cytotoxic therapies, giving way to disease relapse. This review summarizes and discusses current knowledge about the intricate network of soluble and cell-bound signals regulating the life and death of CLL cells in different districts. At the same time, it seeks to hone in on which discrete molecular elements are best suited as targets for treating this still incurable disease.

Glucocorticoid resistance in chronic lymphocytic leukaemia is associated with a failure of upregulated Bim/Bcl-2 complexes to activate Bax and Bak

Glucocorticoids (GCs) represent an important component of modern treatment regimens for fludarabine-refractory or TP53-defective chronic lymphocytic leukemia (CLL). However, GC therapy is not effective in all patients. The molecular mechanisms responsible for GC-induced apoptosis and resistance were therefore investigated in primary malignant cells obtained from a cohort of 46 patients with CLL. Dexamethasone-induced apoptosis was unaffected by p53 dysfunction and more pronounced in cases with unmutated IGHV genes. Cross-resistance was observed between dexamethasone and other GCs but not fludarabine, indicating non-identical resistance mechanisms. GC treatment resulted in the upregulation of Bim mRNA and protein, but to comparable levels in both GC-resistant and sensitive cells. Pre-incubation with Bim siRNAs reduced GC-induced upregulation of Bim protein and conferred resistance to GC-induced apoptosis in previously GC-sensitive cells. GC-induced upregulation of Bim was associated with the activation of Bax and Bak in GC-sensitive but not -resistant CLL samples. Co-immunoprecipitation experiments showed that Bim does not interact directly with Bax or Bak, but is almost exclusively bound to Bcl-2 regardless of GC treatment. Taken together, these findings suggest that the GC-induced killing of CLL cells results from the indirect activation of Bax and Bak by upregulated Bim/Bcl-2 complexes, and that GC resistance results from the failure of such activation to occur.

The B-cell receptor signaling pathway as a therapeutic target in CLL

Targeted therapy with imatinib and other selective tyrosine kinase inhibitors has transformed the treatment of chronic myeloid leukemia. Unlike chronic myeloid leukemia, chronic lymphocytic leukemia (CLL) lacks a common genetic aberration amenable to therapeutic targeting. However, our understanding of normal B-cell versus CLL biology points to differences in properties of B-cell receptor (BCR) signaling that may be amenable to selective therapeutic targeting. The application of mouse models has further expanded this understanding and provides information about targets in the BCR signaling pathway that may have other important functions in cell development or long-term health. In addition, overexpression or knockout of selected targets offers the potential to validate targets genetically using new mouse models of CLL. The initial success of BCR-targeted therapies has promoted much excitement in the field of CLL. At the present time, GS-1101, which reversibly inhibits PI3Kδ, and ibrutinib (PCI-32765), an irreversible inhibitor of Bruton tyrosine kinase, have generated the most promising early results in clinical trials including predominately refractory CLL where durable disease control has been observed. This review provides a summary of BCR signaling, tools for studying this pathway relevant to drug development in CLL, and early progress made with therapeutics targeting BCR-related kinases.

TCL1A and ATM are co-expressed in chronic lymphocytic leukemia cells without deletion of 11q

Chronic lymphocytic leukemia is characterized by the accumulation of B cells that are resistant to apoptosis. This resistance is induced by pro-survival stimuli from the microenvironment. TCL1 and ATM are central to the pathogenesis of the disease and associated with more aggressive disease. Their protein products have recently been shown to physically interact in leukemic cells and to impact on NF-κB signaling, which is a key regulator of apoptosis. In the present study we show that TCL1 and ATM are significantly co-expressed and up-regulated in malignant cells compared to non-malignant B cells, and that expression of TCL1 is partially deregulated by aberrant DNA-methylation. In addition, complex external stimuli induce essentially similar TCL1 and ATM time-course kinetics. In line with a coordinative regulation of NF-κB signaling by TCL1, its knockdown induced apoptosis in primary leukemia cells. These findings suggest that both genes functionally cooperate to modulate similar apoptosis-related cellular pathways.

Regulation of cell death and autophagy by IKK and NF-κB: critical mechanisms in immune function and cancer

The cellular response to survive or to undergo death is fundamental to the benefit of the organism, and errors in this process can lead to autoimmunity and cancer. The transcription factor nuclear factor κB (NF-κB) functions to block cell death through transcriptional induction of genes encoding anti-apoptotic and antioxidant proteins. This is essential for survival of activated cells of the immune system and for cells undergoing a DNA damage response. In Ras-transformed cells and tumors as well as other cancers, NF-κB functions to suppress apoptosis--a hallmark of cancer. Critical prosurvival roles for inhibitor of NF-κB kinase (IKK) family members, including IKKε and TBK1, have been reported, which are both NF-κB-dependent and -independent. While the roles of NF-κB in promoting cell survival in lymphocytes and in cancers is relatively clear, evidence has been presented that NF-κB can promote cell death in particular contexts. Recently, IKK was shown to play a critical role in the induction of autophagy, a metabolic response typically associated with cell survival but which can lead to cell death. This review provides an historical perspective, along with new findings, regarding the roles of the IKK and NF-κB pathways in regulating cell survival.

The B-cell receptor signaling pathway as a therapeutic target in CLL

Targeted therapy with imatinib and other selective tyrosine kinase inhibitors has transformed the treatment of chronic myeloid leukemia. Unlike chronic myeloid leukemia, chronic lymphocytic leukemia (CLL) lacks a common genetic aberration amenable to therapeutic targeting. However, our understanding of normal B-cell versus CLL biology points to differences in properties of B-cell receptor (BCR) signaling that may be amenable to selective therapeutic targeting. The application of mouse models has further expanded this understanding and provides information about targets in the BCR signaling pathway that may have other important functions in cell development or long-term health. In addition, overexpression or knockout of selected targets offers the potential to validate targets genetically using new mouse models of CLL. The initial success of BCR-targeted therapies has promoted much excitement in the field of CLL. At the present time, GS-1101, which reversibly inhibits PI3Kδ, and ibrutinib (PCI-32765), an irreversible inhibitor of Bruton tyrosine kinase, have generated the most promising early results in clinical trials including predominately refractory CLL where durable disease control has been observed. This review provides a summary of BCR signaling, tools for studying this pathway relevant to drug development in CLL, and early progress made with therapeutics targeting BCR-related kinases.

N-(4-hydroxyphenyl)retinamide promotes apoptosis of resting and proliferating B-cell chronic lymphocytic leukemia cells and potentiates fludarabine and ABT-737 cytotoxicity

The in vitro effects of the synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR, fenretinide) on primary B-cell chronic lymphocytic leukemia (CLL) cells from previously untreated CLL patients were investigated. 4HPR promoted the intrinsic apoptotic pathway by reactive oxygen species (ROS) generation and was accompanied by drop of Mcl-1 protein expression. The latter was not attributable to transcriptional downregulation but to protein degradation mediated by jun N-terminal kinase activation, and likely by NF-kB downregulation and Noxa upregulation. CLL cells stimulated in vitro with CD40L did not increase 4HPR chemoresistance if activation was accompanied by proliferation. Intra-patient analysis confirmed that the proliferating pool of CLL cells was more sensitive to the cytotoxic action of 4HPR than the activated but resting CLL subpopulation. The different 4HPR susceptibility of the two subpopulations was associated with higher Noxa expression in proliferating CLLs. Combination experiments revealed that 4HPR strongly potentiated ABT-737 cytotoxicity, especially in proliferating CLL cells that displayed amplified chemoresistance to ABT-737 alone. Synergic cytotoxicity was also demonstrated in combination with fludarabine, in both resting and stimulated CLL samples. This study entitles 4HPR to be assayed as a chemotherapeutic adjuvant for the treatment of CLL.

Disruption of BIRC3 associates with fludarabine chemorefractoriness in TP53 wild-type chronic lymphocytic leukemia

The genetic lesions identified to date do not fully recapitulate the molecular pathogenesis of chronic lymphocytic leukemia (CLL) and do not entirely explain the development of severe complications such as chemorefractoriness. In the present study, BIRC3, a negative regulator of noncanonical NF-κB signaling, was investigated in different CLL clinical phases. BIRC3 lesions were absent in monoclonal B-cell lymphocytosis (0 of 63) and were rare in CLL at diagnosis (13 of 306, 4%). Conversely, BIRC3 disruption selectively affected 12 of 49 (24%) fludarabine-refractory CLL cases by inactivating mutations and/or gene deletions that distributed in a mutually exclusive fashion with TP53 abnormalities. In contrast to fludarabine-refractory CLL, progressive but fludarabine-sensitive patients were consistently devoid of BIRC3 abnormalities, suggesting that BIRC3 genetic lesions associate specifically with a chemorefractory phenotype. By actuarial analysis in newly diagnosed CLL (n = 306), BIRC3 disruption identified patients with a poor outcome similar to that associated with TP53 abnormalities and exerted a prognostic role that was independent of widely accepted clinical and genetic risk factors. Consistent with the role of BIRC3 as a negative regulator of NF-κB, biochemical studies revealed the presence of constitutive noncanonical NF-κB activation in fludarabine-refractory CLL patients harboring molecular lesions of BIRC3. These data identify BIRC3 disruption as a recurrent genetic lesion of high-risk CLL devoid of TP53 abnormalities.

Exploiting biological diversity and genomic aberrations in chronic lymphocytic leukemia

There is remarkable heterogeneity in the clinical course and biological characteristics of patient subgroups with chronic lymphocytic leukemia (CLL). Mutations of key tumor suppressors (ATM, miR-15a/16-1 and TP53) have been identified in CLL, and these aberrations are important "drivers" of the disease and some of its clinical characteristics. While some mutations are associated with poor outcome [particularly del(17p) and TP53 mutation], others are linked to a favorable clinical course [e.g. del(13q) as sole aberration]. In addition to genetic aberrations, antigen drive and microenvironmental interactions contribute to the pathogenesis of CLL. How the genetic aberrations impact on the process of antigen drive or microenvironmental interactions is currently unclear. Our improved understanding of the biology and clinical course of specific genetic subgroups is beginning to be translated into more specific and targeted treatment approaches. As a result, genetic subgroups are treated in distinct protocols. This review summarizes the contribution of the microenvironment and the most important genetic aberrations in CLL and how our improved knowledge of the biology of CLL may translate into improved treatment results.

Surface IgM stimulation induces MEK1/2-dependent MYC expression in chronic lymphocytic leukemia cells

Although long considered as a disease of failed apoptosis, it is now clear that chronic lymphocytic leukemia (CLL) cells undergo extensive cell division in vivo, especially in progressive disease. Signaling via the B-cell receptor is thought to activate proliferation and survival pathways in CLL cells and also has been linked to poor outcome. Here, we have analyzed the expression of the proto-oncoprotein MYC, an essential positive regulator of the cell cycle, after stimulation of surface IgM (sIgM). MYC expression was rapidly increased after sIgM stimulation in a subset of CLL samples. The ability of sIgM stimulation to increase MYC expression was correlated with sIgM-induced intracellular calcium fluxes. MYC induction was partially dependent on the MEK/ERK signaling pathway, and MYC and phosphorylated ERK1/2 were both expressed within proliferation centers in vivo. Although stimulation of sIgD also resulted in ERK1/2 phosphorylation, responses were relatively short lived compared with sIgM and were associated with significantly reduced MYC induction, suggesting that the kinetics of ERK1/2 activation is a critical determinant of MYC induction. Our results suggest that ERK1/2-dependent induction of MYC is likely to play an important role in antigen-induced CLL cell proliferation.

Leflunomide induces apoptosis in fludarabine-resistant and clinically refractory CLL cells

PURPOSE

Environmental conditions in lymph node proliferation centers protect chronic lymphocytic leukemia (CLL) cells from apoptotic triggers. This situation can be mimicked by in vitro stimulation with CD40 ligand (CD40L) and interleukin 4 (IL-4). Our study investigates the impact of the drug leflunomide to overcome apoptosis resistance of CLL cells.

EXPERIMENTAL DESIGN

CLL cells were stimulated with CD40L and IL-4 and treated with fludarabine and the leflunomide metabolite A771726.

RESULTS

Resistance to fludarabine-mediated apoptosis was induced by CD40 activation alone stimulating high levels of BCL-XL and MCL1 protein expression. Apoptosis resistance was further enhanced by a complementary Janus-activated kinase (JAK)/STAT signal induced by IL-4. In contrast, CLL proliferation required both a CD40 and a JAK/STAT signal and could be completely blocked by pan-JAK inhibition. Leflunomide (A771726) antagonized CD40L/IL-4-induced proliferation at very low concentrations (3 μg/mL) reported to inhibit dihydroorotate dehydrogenase. At a concentration of 10 μg/mL, A771726 additionally attenuated STAT3/6 phosphorylation, whereas apoptosis of CD40L/IL-4-activated ("resistant") CLL cells was achieved with higher concentrations (IC(50): 80 μg/mL). Apoptosis was also effectively induced by A771726 in clinically refractory CLL cells with and without a defective p53 pathway. Induction of apoptosis involved inhibition of NF-κB activity and loss of BCL-XL and MCL1 expression. In combination with fludarabine, A771726 synergistically induced apoptosis (IC(50): 56 μg/mL).

CONCLUSION

We thus show that A771726 overcomes CD40L/IL-4-mediated resistance to fludarabine in CLL cells of untreated as well as clinically refractory CLL cells. We present a possible novel therapeutic principle for attacking chemoresistant CLL cells.

Association of reactive oxygen species-mediated signal transduction with in vitro apoptosis sensitivity in chronic lymphocytic leukemia B cells

BACKGROUND

Chronic lymphocytic leukemia (CLL) is a B cell malignancy with a variable clinical course and unpredictable response to therapeutic agents. Single cell network profiling (SCNP) utilizing flow cytometry measures alterations in signaling biology in the context of molecular changes occurring in malignancies. In this study SCNP was used to identify proteomic profiles associated with in vitro apoptotic responsiveness of CLL B cells to fludarabine, as a basis for ultimately linking these with clinical outcome.

METHODOLOGY/PRINCIPAL FINDING

SCNP was used to quantify modulated-signaling of B cell receptor (BCR) network proteins and in vitro F-ara-A mediated apoptosis in 23 CLL samples. Of the modulators studied the reactive oxygen species, hydrogen peroxide (H₂O₂), a known intracellular second messenger and a general tyrosine phosphatase inhibitor stratified CLL samples into two sub-groups based on the percentage of B cells in a CLL sample with increased phosphorylation of BCR network proteins. Separately, in the same patient samples, in vitro exposure to F-ara-A also identified two sub-groups with B cells showing competence or refractoriness to apoptotic induction. Statistical analysis showed that in vitro F-ara-A apoptotic proficiency was highly associated with the proficiency of CLL B cells to undergo H₂O₂-augmented signaling.

CONCLUSIONS/SIGNIFICANCE

This linkage in CLL B cells among the mechanisms governing chemotherapy-induced apoptosis increased signaling of BCR network proteins and a likely role of phosphatase activity suggests a means of stratifying patients for their response to F-ara-A based regimens. Future studies will examine the clinical applicability of these findings and also the utility of this approach in relating mechanism to function of therapeutic agents.

B-cell receptor signaling in chronic lymphocytic leukemia

The B-cell receptor (BCR) is a key survival molecule for normal B cells and for most B-cell malignancies. Recombinatorial and mutational patterns in the clonal immunoglobulin (Ig) of chronic lymphocytic leukemia (CLL) have revealed 2 major IgMD-expressing subsets and an isotype-switched variant, each developing from distinct B-cell populations. Tracking of conserved stereotypic features of Ig variable regions characteristic of U-CLL indicate circulating naive B cells as the likely cells of origin. In CLL, engagement of the BCR by antigen occurs in vivo, leading to down-regulated expression and to an unanticipated modulation of glycosylation of surface IgM, visible in blood cells, especially in U-CLL. Modulated glycoforms of sIgM are signal competent and could bind to environmental lectins. U-CLL cases express more sIgM and have increased signal competence, linking differential signaling responses to clinical behavior. Mapping of BCR signaling pathways identifies targets for blockade, aimed to deprive CLL cells of survival and proliferative signals. New inhibitors of BCR signaling appear to have clinical activity. In this Perspective, we discuss the functional significance of the BCR in CLL, and we describe strategies to target BCR signaling as an emerging therapeutic approach.

NF-κB mediates radio-sensitization by the PARP-1 inhibitor, AG-014699

The stress inducible transcription factor, NF-κB induces genes involved in proliferation and apoptosis. Aberrant NF-κB activity is common in cancer and contributes to therapeutic-resistance. Poly(ADP-ribose) polymerase-1 (PARP-1) is activated during DNA strand break repair and is a known transcriptional co-regulator. Here, we investigated the role of PARP-1 function during NF-κB activation using p65 siRNA, PARP siRNA or the potent PARP-1 inhibitor, AG-014699. Survival and apoptosis assays showed that NF-κB p65^−/− cells were more sensitive to ionizing radiation (IR) than p65^+/+ cells. Co-incubation with p65 siRNA, PARP siRNA or AG-014699 radio-sensitized p65^+/+, but not p65^−/− cells, demonstrating that PARP-1 mediates its effects on survival via NF-κB. Single strand break (SSB) repair kinetics, and the effect SSB repair inhibition by AG-014699 were similar in p65^+/+ and p65^−/− cells. Since preventing SSB repair did not radio-sensitize p65^−/− cells, we conclude that radio-sensitization by AG-014699 is due to downstream inhibition of NF-κB activation, and independent of SSB repair inhibition. PARP-1 catalytic activity was essential for IR-induced p65 DNA binding and NF-κB-dependent gene transcription, whereas for TNF-α treated cells, PARP-1 protein alone was sufficient. We hypothesize that this stimulus-dependent differential is mediated via stimulation of the Poly(ADP-ribose) polymer, which was induced following IR, not TNF-α. Targeting DNA-damage activated NF-κB using AG-014699 may therefore overcome toxicity observed with classical NF-κB inhibitors without compromising other vital inflammatory functions. These data highlight the potential of PARP-1 inhibitors to overcome NF-κB-mediated therapeutic resistance and widens the spectrum of cancers in which these agents may be utilized.

Two novel aspirin analogues show selective cytotoxicity in primary chronic lymphocytic leukaemia cells that is associated with dual inhibition of Rel A and COX-2

OBJECTIVES

Non-steroidal anti-inflammatory drugs have been shown to induce apoptosis in primary B-cell chronic lymphocytic leukaemia (CLL) cells, but the molecular mechanisms that underpin this observation have not been fully elucidated. Here, we have analysed the effect two novel aspirin analogues, 2-hydroxy benzoate zinc (2HBZ) and 4-hydroxy benzoate zinc (4HBZ), on primary CLL samples.

MATERIALS AND METHODS

Cytotoxic effects of 2HBZ and 4HBZ were analysed in primary CLL cells derived from 52 patients, and normal B- and T-lymphocytes. Mechanisms of action of these agents were also elucidated.

RESULTS

Both analogues induced apoptosis in a dose-dependent and time-dependent manner. Apoptosis was associated with activation of caspase-3 that could be partially abrogated by the caspase-9 inhibitor (Z-LEHD.fmk). Importantly, both agents demonstrated preferential cytotoxicity in CLL cells when compared to normal B- and T-lymphocytes. In terms of their molecular mechanisms of action, 4HBZ and 2HBZ inhibited COX-2 transcription and protein expression and this was associated with upstream inhibition of transcription factor Rel A. Co-culture of CLL cells with CD40 ligand-expressing mouse fibroblasts significantly increased COX-2 expression and inhibited spontaneous apoptosis. Importantly, the most potent analogue, 4HBZ, overcame pro-survival effects of the co-culture system and significantly repressed COX-2. Finally, elevated COX-2 expression was associated with poor prognostic subsets and increased sensitivity to 4HBZ.

CONCLUSIONS

Our results demonstrate therapeutic potential of 4HBZ and are consistent with a mechanism involving suppression of Rel A nuclear translocation and inhibition of COX-2 transcription.

Personalizing treatment for chronic lymphocytic leukemia

Over the past few years, more effective therapies have emerged in the treatment of chronic lymphocytic leukemia (CLL); these are mainly combinations of immunotherapy with fludarabine-based regimens. Despite the higher response rates obtained with these more intensive treatments, they may not always be applicable. Patients with several comorbidities have an increased toxicity with these newer therapies. Effective tools to distinguish between fit and nonfit patients and new therapeutic approaches suitable for fragile patients with CLL are therefore necessary. Moreover, there is still a subset of patients who are refractory to standard fludarabine-based treatments who continue to have very poor survival. Efforts to understand the mechanisms of resistance to treatment in order to develop new therapeutic agents for those patients are mandatory. Finally, advances in the knowledge of the pathogenesis of CLL are promoting the emergence of drugs directed to new biological targets of this disease. Consequently, trials exploring the toxicity profile and efficacy of these new therapeutic agents, alone or in combination with standard treatments, are warranted.

A water soluble parthenolide analog suppresses in vivo tumor growth of two tobacco-associated cancers, lung and bladder cancer, by targeting NF-κB and generating reactive oxygen species

Dimethylaminoparthenolide (DMAPT) is a water soluble parthenolide analog with preclinical activity in hematologic malignancies. Using non-small lung cancer (NSCLC) cell lines (A549 and H522) and an immortalized human bronchial epithelial cell line (BEAS2B) and TCC cell lines (UMUC-3, HT-1197 and HT-1376) and a bladder papilloma (RT-4), we aimed to characterize DMAPT's anticancer activity in tobacco-associated neoplasms. Flow cytometric, electrophoretic mobility gel shift assays (EMSA), and Western blot studies measured generation of reactive oxygen species (ROS), inhibition of NFκB DNA binding, and changes in cell cycle distribution and apoptotic proteins. DMAPT generated ROS with subsequent JNK activation and also decreased NFκB DNA binding and antiapoptotic proteins, TRAF-2 and XIAP. DMAPT-induced apoptotic cell death and altered cell cycle distribution with upregulation of p21 and p73 levels in a cell type-dependent manner. DMAPT suppressed cyclin D1 in BEAS2B. DMAPT retained NFκB and cell cycle inhibitory activity in the presence of the tobacco carcinogen nitrosamine ketone, 4(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Using a BrdU accumulation assay, 5-20 μM of DMAPT was shown to inhibit cellular proliferation of all cell lines by more than 95%. Oral dosing of DMAPT suppressed in vivo A549 and UMUC-3 subcutaneous xenograft growth by 54% (p = 0.015) and 63% (p < 0.01), respectively, and A549 lung metastatic volume by 28% (p = 0.043). In total, this data demonstrates DMAPT's novel anticancer properties in both early and late stage tobacco-associated neoplasms as well as its significant in vivo activity. The data provides support for the conduct of clinical trials in TCC and NSCLC.

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.

MicroRNA expression profiling identifies activated B cell status in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (CLL) is thought to be a disease of resting lymphocytes. However, recent data suggest that CLL cells may more closely resemble activated B cells. Using microRNA (miRNA) expression profiling of highly-enriched CLL cells from 38 patients and 9 untransformed B cells from normal donors before acute CpG activation and 5 matched B cells after acute CpG activation, we demonstrate an activated B cell status for CLL. Gene set enrichment analysis (GSEA) identified statistically-significant similarities in miRNA expression between activated B cells and CLL cells including upregulation of miR-34a, miR-155, and miR-342-3p and downregulation of miR-103, miR-181a and miR-181b. Additionally, decreased levels of two CLL signature miRNAs miR-29c and miR-223 are associated with ZAP70(+) and IgV(H) unmutated status and with shorter time to first therapy. These data indicate an activated B cell status for CLL cells and suggest that the direction of change of individual miRNAs may predict clinical course in CLL.