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

Disrupting pro-survival and inflammatory pathways with dimethyl fumarate sensitizes chronic lymphocytic leukemia to cell death

Microenvironmental signals strongly influence chronic lymphocytic leukemia (CLL) cells through the activation of distinct membrane receptors, such as B-cell receptors, and inflammatory receptors, such as Toll-like receptors (TLRs). Inflammatory pathways downstream of these receptors lead to NF-κB activation, thus protecting leukemic cells from apoptosis. Dimethyl fumarate (DMF) is an anti-inflammatory and immunoregulatory drug used to treat patients with multiple sclerosis and psoriasis in which it blocks aberrant NF-κB pathways and impacts the NRF2 antioxidant circuit. Our in vitro analysis demonstrated that increasing concentrations of DMF reduce ATP levels and lead to the apoptosis of CLL cells, including cell lines, splenocytes from Eµ-TCL1-transgenic mice, and primary leukemic cells isolated from the peripheral blood of patients. DMF showed a synergistic effect in association with BTK inhibitors in CLL cells. DMF reduced glutathione levels and activated the NRF2 pathway; gene expression analysis suggested that DMF downregulated pathways related to NFKB and inflammation. In primary leukemic cells, DMF disrupted the TLR signaling pathways induced by CpG by reducing the mRNA expression of NFKBIZ, IL6, IL10 and TNFα. Our data suggest that DMF targets a vulnerability of CLL cells linked to their inflammatory pathways, without impacting healthy donor peripheral blood mononuclear cells.

Expression and Activity of the NF-κB Subunits in Chronic Lymphocytic Leukaemia: A Role for RelB and Non-Canonical Signalling

BACKGROUND

Canonical NF-κB signalling by p65 (RelA) confers chemo-resistance and poor survival in chronic lymphocytic leukaemia (CLL). The role of non-canonical NF-κB signalling (leading to RelB and p52 subunit activation) in CLL is less understood, but given its importance in other B-cell tumour types, we theorised that RelB and p52 may also contribute to the pathology of CLL.

METHODS

DNA binding activity of all five NF-kB subunits, p65, p50, RelB, p52, and c-Rel, was quantified using ELISA and correlated to ex vivo chemoresistance, CD40L-stimulated signalling (to mimic the lymph node microenvironment), and clinical data.

RESULTS

Importantly, we show for the first time that high basal levels of RelB DNA binding correlate with nuclear RelB protein expression and are associated with del(11q), ATM dysfunction, unmutated IGHV genes, and shorter survival. High levels of nuclear p65 are prevalent in del(17p) cases (including treatment-naïve patients) and also correlate with the outcome. CD40L-stimulation resulted in rapid RelB activation, phosphorylation and processing of p100, and subsequent CLL cell proliferation.

CONCLUSIONS

These data highlight a role for RelB in driving CLL cell tumour growth in a subset of patients and therefore strategies designed to inhibit non-canonical NF-κB signalling represent a novel approach that will have therapeutic benefit in CLL.

The role of SF3B1 and NOTCH1 in the pathogenesis of leukemia

The discovery of new genes/pathways improves our knowledge of cancer pathogenesis and presents novel potential therapeutic options. For instance, splicing factor 3b subunit 1 (SF3B1) and NOTCH1 genetic alterations have been identified at a high frequency in hematological malignancies, such as leukemia, and may be related to the prognosis of involved patients because they change the nature of malignancies in different ways like mediating therapeutic resistance; therefore, studying these gene/pathways is essential. This review aims to discuss SF3B1 and NOTCH1 roles in the pathogenesis of various types of leukemia and the therapeutic potential of targeting these genes or their mutations to provide a foundation for leukemia treatment.

The Pt(S-pr-thiosal)2 and BCL1 Leukemia Lymphoma: Antitumor Activity In Vitro and In Vivo

B cell malignancies are, despite the development of targeted therapy in a certain percentage of the patients still a chronic disease with relapses, requiring multiple lines of therapy. Regimens that include platinum-based drugs provide high response rates in different B cell lymphomas, high-risk chronic lymphocytic leukemia (CLL), and devastating complication of CLL, Richter’s syndrome. The aim of this study was to explore the potential antitumor activity of previously synthetized platinum(IV) complex with alkyl derivatives of thyosalicilc acid, PtCl2(S-pr-thiosal)2, toward murine BCL1 cells and to delineate possible mechanisms of action. The PtCl2(S-pr-thiosal)2 reduced the viability of BCL1 cells in vitro but also reduced the growth of metastases in the leukemia lymphoma model in BALB/c mice. PtCl2(S-pr-thiosal)2 induced apoptosis, inhibited proliferation of BCL1 cells, and induced cell cycle disturbance. Treatment of BCL1 cells with PtCl2(S-pr-thiosal)2 inhibited expression of cyclin D3 and cyclin E and enhanced expression of cyclin-dependent kinase inhibitors p16, p21, and p27 resulting in cell cycle arrest in the G1 phase, reduced the percentage of BCL1 cells in the S phase, and decreased expression of Ki-67. PtCl2(S-pr-thiosal)2 treatment reduced expression of phosphorylated STAT3 and downstream-regulated molecules associated with cancer stemness and proliferation, NANOG, cyclin D3, and c-Myc, and expression of phosphorylated NFκB in vitro and in vivo. In conclusion, PtCl2(S-pr-thiosal)2 reduces STAT3 and NFκB phosphorylation resulting in inhibition of BCL1 cell proliferation and the triggering of apoptotic cell death.

miRNAs in Lymphocytic Leukaemias-The miRror of Drug Resistance

Refractory disease and relapse remain the main causes of cancer therapy failure. Refined risk stratification, treatment regimens and improved early diagnosis and detection of minimal residual disease have increased cure rates in malignancies like childhood acute lymphoblastic leukaemia (ALL) to 90%. Nevertheless, overall survival in the context of drug resistance remains poor. The regulatory role of micro RNAs (miRNAs) in cell differentiation, homeostasis and tumorigenesis has been under extensive investigation in different cancers. There is accumulating data demonstrating the significance of miRNAs for therapy outcomes in lymphoid malignancies and some direct demonstrations of the interplay between these small molecules and drug response. Here, we summarise miRNAs' impact on chemotherapy resistance in adult and paediatric ALL and chronic lymphocytic leukaemia (CLL). The main focus of this review is on the modulation of particular signaling pathways like PI3K-AKT, transcription factors such as NF-κB, and apoptotic mediators, all of which are bona fide and pivotal elements orchestrating the survival of malignant lymphocytic cells. Finally, we discuss the attractive strategy of using mimics, antimiRs and other molecular approaches pointing at miRNAs as promising therapeutic targets. Such novel strategies to circumvent ALL and CLL resistance networks may potentially improve patients' responses and survival rates.

Targeting the Non-Canonical NF-κB Pathway in Chronic Lymphocytic Leukemia and Multiple Myeloma

In this study, we evaluated an NF-κB inducing kinase (NIK) inhibitor, CW15337, in primary chronic lymphocytic leukemia (CLL) cells, CLL and multiple myeloma (MM) cell lines and normal B- and T-lymphocytes. Basal NF-κB subunit activity was characterized using an enzyme linked immunosorbent assay (ELISA), and the effects of NIK inhibition were then assessed in terms of cytotoxicity and the expression of nuclear NF-κB subunits following monoculture and co-culture with CD40L-expressing fibroblasts, as a model of the lymphoid niche. CW15337 induced a dose-dependent increase in apoptosis, and nuclear expression of the non-canonical NF-κB subunit, p52, was correlated with sensitivity to CW15337 (p = 0.01; r² = 0.39). Co-culture on CD40L-expressing cells induced both canonical and non-canonical subunit expression in nuclear extracts, which promoted in vitro resistance against fludarabine and ABT-199 (venetoclax) but not CW15337. Furthermore, the combination of CW15337 with fludarabine or ABT-199 showed cytotoxic synergy. Mechanistically, CW15337 caused the selective inhibition of non-canonical NF-κB subunits and the transcriptional repression of BCL2L1, BCL2A1 and MCL1 gene transcription. Taken together, these data suggest that the NIK inhibitor, CW15337, exerts its effects via suppression of the non-canonical NF-κB signaling pathway, which reverses BCL2 family-mediated resistance in the context of CD40L stimulation.

Bortezomib in combination with fludarabine plus cyclophosphamide for patients with relapsed or refractory mantle-cell lymphoma: results of the LYM-4003 study

This study aimed to identify the maximum-tolerated dose (MTD) of cyclophosphamide when combined with bortezomib and fludarabine (B-FC) in a phase 1b trial, and to assess the efficacy and safety of this combination in a phase 2 trial in patients with relapsed or refractory MCL (rrMCL). Forty patients were enrolled between April 8, 2011, and October 10, 2015. The MTD of cyclophosphamide was identified to be 250 mg/m² days 1-2. At a median follow-up of 31.6 months (13.5-47.4), among 32 patients in phase 2, 10 (31%) had a complete response and 13 (41%) had a partial response. The median progression-free survival was 21 months (95% CI 7.3-34.7), and the median overall survival was 32.4 months (95% CI 17.8-47.0). Grade 3-4 hematologic AEs included neutropenia (27%) and thrombocytopenia (39%). The B-FC regimen has satisfactory responses and manageable toxicities in rrMCL patients (ClinicalTrials.gov NCT01322776).

TLR9 expression in chronic lymphocytic leukemia identifies a promigratory subpopulation and novel therapeutic target

Chronic lymphocytic leukemia (CLL) remains incurable despite B-cell receptor-targeted inhibitors revolutionizing treatment. This suggests that other signaling molecules are involved in disease escape mechanisms and resistance. Toll-like receptor 9 (TLR9) is a promising candidate that is activated by unmethylated cytosine guanine dinucleotide-DNA. Here, we show that plasma from patients with CLL contains significantly more unmethylated DNA than plasma from healthy control subjects (P < .0001) and that cell-free DNA levels correlate with the prognostic markers CD38, β2-microglobulin, and lymphocyte doubling time. Furthermore, elevated cell-free DNA was associated with shorter time to first treatment (hazard ratio, 4.0; P = .003). We also show that TLR9 expression was associated with in vitro CLL cell migration (P < .001), and intracellular endosomal TLR9 strongly correlated with aberrant surface expression (sTLR9; r = 0.9). In addition, lymph node-derived CLL cells exhibited increased sTLR9 (P = .016), and RNA-sequencing of paired sTLR9hi and sTLR9lo CLL cells revealed differential transcription of genes involved in TLR signaling, adhesion, motility, and inflammation in sTLR9hi cells. Mechanistically, a TLR9 agonist, ODN2006, promoted CLL cell migration (P < .001) that was mediated by p65 NF-κB and STAT3 transcription factor activation. Importantly, autologous plasma induced the same effects, which were reversed by a TLR9 antagonist. Furthermore, high TLR9 expression promoted engraftment and rapid disease progression in a NOD/Shi-scid/IL-2Rγnull mouse xenograft model. Finally, we showed that dual targeting of TLR9 and Bruton's tyrosine kinase (BTK) was strongly synergistic (median combination index, 0.2 at half maximal effective dose), which highlights the distinct role for TLR9 signaling in CLL and the potential for combined targeting of TLR9 and BTK as a more effective treatment strategy in this incurable disease.

Novel pyrrolobenzodiazepine benzofused hybrid molecules inhibit NF-κB activity and synergise with bortezomib and ibrutinib in hematological cancers

Chronic lymphocytic leukemia (CLL) and multiple myeloma are incurable hematologic malignancies that are pathologically linked with aberrant nuclear factor-kappa B (NF-κB) activation. In this study, we identified a group of novel C8-linked benzofused pyrrolo[2,1- c][1,4]benzodiazepine monomeric hybrids capable of sequence-selective inhibition of NF-κB with low nanomolar LD50 values in CLL (n=46) and multiple myeloma cell lines (n=5). The lead compound, DC-1-192, significantly inhibited NF-κB DNA binding after just 4 h of exposure, demonstrating inhibitory effects on both canonical and non-canonical NF-κB subunits. In primary CLL cells, sensitivity to DC-1-192 was inversely correlated with RelA subunit expression (r²=0.2) and samples with BIRC3 or NOTCH1 mutations showed increased sensitivity (P=0.001). RNAsequencing and gene set enrichment analysis confirmed the over-representation of NF-κB regulated genes in the downregulated gene list. Furthermore, in vivo efficacy studies in NOD/SCID mice, using a systemic RPMI 8226 human multiple myeloma xenograft model, showed that DC- 1-192 significantly prolonged survival (P=0.017). In addition, DC1-192 showed synergy with bortezomib and ibrutinib; synergy with ibrutinib was enhanced when CLL cells were co-cultured on CD40L-expressing fibroblasts in order to mimic the cytoprotective lymph node microenvironment (P=0.01). Given that NF-κB plays a role in both bortezomib and ibrutinib resistance mechanisms, these data provide a strong rationale for the use of DC-1-192 in the treatment of NF-κB-driven cancers, particularly in the context of relapsed/refractory disease.

Molecular Action of Polyphenols in Leukaemia and Their Therapeutic Potential

Leukaemia is a malignant disease of the blood. Current treatments for leukaemia are associated with serious side-effects. Plant-derived polyphenols have been identified as potent anti-cancer agents and have been shown to work synergistically with standard chemotherapy agents in leukaemia cell lines. Polyphenols have multiple mechanisms of action and have been reported to decrease cell proliferation, arrest cell cycle and induce apoptosis via the activation of caspase (3, 8 and 9); the loss of mitochondrial membrane potential and the release of cytochrome c. Polyphenols have been shown to suppress activation of transcription factors, including NF-kB and STAT3. Furthermore, polyphenols have pro-oxidant properties, with increasing evidence that polyphenols inhibit the antioxidant activity of glutathione, causing oxidative DNA damage. Polyphenols also induce autophagy-driven cancer cell death and regulate multidrug resistance proteins, and thus may be able to reverse resistance to chemotherapy agents. This review examines the molecular mechanism of action of polyphenols and discusses their potential therapeutic targets. Here, we discuss the pharmacological properties of polyphenols, including their anti-inflammatory, antioxidant, anti-proliferative, and anti-tumour activities, and suggest that polyphenols are potent natural agents that can be useful therapeutically; and discuss why data on bioavailability, toxicity and metabolism are essential to evaluate their clinical use.

HELQ and EGR3 expression correlate with IGHV mutation status and prognosis in chronic lymphocytic leukemia

Background

IGHV mutation status is a crucial prognostic biomarker for CLL. In the present study, we investigated the transcriptomic signatures associating with IGHV mutation status and CLL prognosis.

Methods

The co-expression modules and hub genes correlating with IGHV status, were identified using the GSE28654, by ‘WGCNA’ package and R software (version 4.0.2). The over-representation analysis was performed to reveal enriched cell pathways for genes of correlating modules. Then 9 external cohorts were used to validate the correlation of hub genes expression with IGHV status or clinical features (treatment response, transformation to Richter syndrome, etc.). Moreover, to elucidate the significance of hub genes on disease course and prognosis of CLL patients, the Kaplan–Meier analysis for the OS and TTFT of were performed between subgroups dichotomized by the median expression value of individual hub genes.

Results

2 co-expression modules and 9 hub genes ((FCRL1/FCRL2/HELQ/EGR3LPL/LDOC1/ZNF667/SOWAHC/SEPTIN10) correlating with IGHV status were identified by WGCNA, and validated by external datasets. The modules were found to be enriched in NF-kappaB, HIF-1 and other important pathways, involving cell proliferation and apoptosis. The expression of hub genes was revealed to be significantly different, not only between CLL and normal B cell, but also between various types of lymphoid neoplasms. HELQ expression was found to be related with response of immunochemotherapy treatment significantly (p = 0.0413), while HELQ and ZNF667 were expressed differently between stable CLL and Richter syndrome patients (p < 0.0001 and p = 0.0278, respectively). By survival analysis of subgroups, EGR3 expression was indicated to be significantly associated with TTFT by 2 independent cohorts (GSE39671, p = 0.0311; GSE22762, p = 0.0135). While the expression of HELQ and EGR3 was found to be associated with OS (p = 0.0291 and 0.0114 respectively).The Kras, Hedgehog and IL6-JAK-STAT3 pathways were found to be associating with the expression of hub genes, resulting from GSEA.

Conclusions

The expression of HELQ and EGR3 were correlated with IGHV mutation status in CLL patients. Additionally, the expression of HELQ/EGR3 were prognostic markers for CLL associating with targetable cell signaling pathways.

Mechanisms of B Cell Receptor Activation and Responses to B Cell Receptor Inhibitors in B Cell Malignancies

The B cell receptor (BCR) pathway has been identified as a potential therapeutic target in a number of common B cell malignancies, including chronic lymphocytic leukemia, diffuse large B cell lymphoma, Burkitt lymphoma, follicular lymphoma, mantle cell lymphoma, marginal zone B cell lymphoma, and Waldenstrom's macroglobulinemia. This finding has resulted in the development of numerous drugs that target this pathway, including various inhibitors of the kinases BTK, PI3K, and SYK. Several of these drugs have been approved in recent years for clinical use, resulting in a profound change in the way these diseases are currently being treated. However, the response rates and durability of responses vary largely across the different disease entities, suggesting a different proportion of patients with an activated BCR pathway and different mechanisms of BCR pathway activation. Indeed, several antigen-dependent and antigen-independent mechanisms have recently been described and shown to result in the activation of distinct downstream signaling pathways. The purpose of this review is to provide an overview of the mechanisms responsible for the activation of the BCR pathway in different B cell malignancies and to correlate these mechanisms with clinical responses to treatment with BCR inhibitors.

Biological and clinical implications of BIRC3 mutations in chronic lymphocytic leukemia

BIRC3 is a recurrently mutated gene in chronic lymphocytic leukemia (CLL) but the functional implications of BIRC3 mutations are largely unexplored. Furthermore, little is known about the prognostic impact of BIRC3 mutations in CLL cohorts homogeneously treated with first-line fludarabine, cyclophosphamide, and rituximab (FCR). By immunoblotting analysis, we showed that the non-canonical nuclear factor-κB pathway is active in BIRC3-mutated cell lines and in primary CLL samples, as documented by the stabilization of MAP3K14 and by the nuclear localization of p52. In addition, BIRC3-mutated primary CLL cells are less sensitive to flu-darabine. In order to confirm in patients that BIRC3 mutations confer resistance to fludarabine-based chemoimmunotherapy, a retrospective multicenter cohort of 287 untreated patients receiving first-line FCR was analyzed by targeted next-generation sequencing of 24 recurrently mutated genes in CLL. By univariate analysis adjusted for multiple comparisons BIRC3 mutations identify a poor prognostic subgroup of patients in whom FCR treatment fails (median progression-free survival: 2.2 years, P<0.001) similar to cases harboring TP53 mutations (median progression-free survival: 2.6 years, P<0.0001). BIRC3 mutations maintained an independent association with an increased risk of progression with a hazard ratio of 2.8 (95% confidence interval 1.4-5.6, P=0.004) in multivariate analysis adjusted for TP53 mutation, 17p deletion and IGHV mutation status. If validated, BIRC3 mutations may be used as a new molecular predictor to select high-risk patients for novel frontline therapeutic approaches.

Derivatisation of parthenolide to address chemoresistant chronic lymphocytic leukaemia

Parthenolide is a natural product that exhibits anti-leukaemic activity, however, its clinical use is limited by its poor bioavailability. It may be extracted from feverfew and protocols for growing, extracting and derivatising it are reported. A novel parthenolide derivative with good bioavailability and pharmacological properties was identified through a screening cascade based on in vitro anti-leukaemic activity and calculated "drug-likeness" properties, in vitro and in vivo pharmacokinetics studies and hERG liability testing. In vitro studies showed the most promising derivative to have comparable anti-leukaemic activity to DMAPT, a previously described parthenolide derivative. The newly identified compound was shown to have pro-oxidant activity and in silico molecular docking studies indicate a prodrug mode of action. A synthesis scheme is presented for the production of amine 7 used in the generation of 5f.

Effects of Systematic Shortening of Noncovalent C8 Side Chain on the Cytotoxicity and NF-κB Inhibitory Capacity of Pyrrolobenzodiazepines (PBDs)

The systematic shortening of the noncovalent element of a C8-linked pyrrolobenzodiazepine (PBD) conjugate (13) led to the synthesis of a 19-member library of C8-PBD monomers. The critical elements of 13, which were required to render the molecule cytotoxic, were elucidated by an annexin V assay. The effects of shortening the noncovalent element of the molecule on transcription factor inhibitory capacity were also explored through an enzyme-linked immunosorbent assay-based measurement of nuclear NF-κB upon exposure of JJN-3 cells to the synthesized molecules. Although shortening the noncovalent interactive element of 13 had a less than expected effect upon compound cytotoxicity due to reduced DNA interaction, the transcription factor inhibitory capacity of the molecule was notably altered. This study suggests that a relatively short noncovalent side chain at the C8 position of PBD is sufficient to confer cytotoxicity. The shortened PBD monomers provide a new ADC payload scaffold because of their potent cytotoxicity and drug-like properties.

Identification of novel lncRNAs involved in the pathogenesis of childhood acute lymphoblastic leukemia

This study aimed to explore novel long non-coding RNAs (lncRNAs) and the underlying mechanisms involved in childhood acute lymphoblastic leukemia (cALL). The GSE67684 dataset was downloaded from the Gene Expression Omnibus. Differentially expressed genes (DEGs) and lncRNAs (DELs) between Days 0, 8, 15 and 33 were isolated using random variance model corrective analysis of variance. Overlapping DEGs and DELs were clustered using Cluster 3.0. Bio-functional enrichment analysis was performed using Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG). Interactions between lncRNAs and mRNAs were calculated using dynamic simulations, and interactions among mRNAs were predicted using the STRING database. lncRNA-mRNA and protein-protein interaction (PPI) networks were visualized using Cytoscape. Subsequently, the expression levels of lncRNAs in biological samples from children with or without cALL were validated using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). A total of 593 overlapping DEGs and 21 DELs were identified. After clustering, Profile 26 exhibited a continuously increasing temporal trend, whereas Profile 1 exhibited a continuous decreasing trend. Upregulated DEGs were significantly enriched in 1,825 GO terms and 166 KEGG pathways, whereas downregulated DEGs were significantly enriched in 196 GO terms and 90 KEGG pathways. The lncRNAs NONHSAT027612.2 and NONHSAT134556.2 were the top two regulators in the lncRNA-mRNA network. Toll-like receptor 4, cathepsin G, nucleotide-binding oligomerization domain containing 2 and cathepsin S may be considered the hub genes of the PPI network. RT-qPCR results indicated that the expression levels of the lncRNAs NONHSAT027612.2 and NONHSAT134556.2 were significantly elevated in the blood and bone marrow of patients with cALL compared with the controls. In conclusion, the lncRNAs NONHSAT027612.2 and NONHSAT134556.2 may serve important roles in the pathogenesis of cALL via regulating immune response-associated pathways.

Aberrant Activation of NF-κB Signalling in Aggressive Lymphoid Malignancies

Lymphoid malignancies frequently harbor genetic mutations leading to aberrant activation of nuclear factor-κB (NF-κB) signaling; in normal cells, this pathway has important roles in the control of cell growth, survival, stress responses, and inflammation. Malignancies with mutations in NF-κB pathway components can derive from all cell stages of mature B-cell development; however, aberrant NF-κB activity is particularly prevalent in aggressive subtypes of non-Hodgkin lymphoma and myeloma. NF-κB activation is mediated by two separate pathways, the canonical and alternative pathway, and five downstream transcription factor subunits. Recent findings implicate a predominant role for distinct NF-κB pathways and subunits in certain lymphoma subtypes and myeloma; findings which are complemented by the realization that individual NF-κB subunits can have unique, non-redundant biological roles in the putative tumor precursor cells, including activated B cells, germinal center B cells and plasma cells. The knowledge gained from these studies may be exploited for the development of therapeutic strategies to inhibit aberrant NF-κB activity at the level of the transcription-factor subunits and their target genes, as global inhibition of the pathway is toxic. Here, we provide an overview on the role of aberrant NF-κB activation in aggressive lymphoid malignancies and discuss the potential importance of individual NF-κB subunits in the pathogenesis of tumor subtypes.

CUDC-907 blocks multiple pro-survival signals and abrogates microenvironment protection in CLL

CUDC‐907, a dual PI3K/HDAC inhibitor, has been proposed to have therapeutic potential in hematopoietic malignancies. However, the molecular mechanisms of its effects in chronic lymphocytic leukaemia (CLL) remain elusive. We show that CLL cells are sensitive to CUDC‐907, even under conditions similar to the protective microenvironment of proliferation centres. CUDC‐907 inhibited PI3K/AKT and HDAC activity, as expected, but also suppressed RAF/MEK/ERK and STAT3 signalling and reduced the expression of anti‐apoptotic BCL‐2 family proteins BCL‐2, BCL‐xL, and MCL‐1. Moreover, CUDC‐907 downregulated cytokines BAFF and APRIL and their receptors BAFFR, TACI, and BCMA, thus blocking BAFF‐induced NF‐κB signalling. T cell chemokines CCL3/4/17/22 and phosphorylation of CXCR4 were also reduced by CUDC‐907. These data indicated that CUDC‐907 abrogates different protective signals and suggested that it might sensitize CLL cells to other drugs. Indeed, combinations of low concentrations of CUDC‐907 with inhibitors of BCL2, BTK, or the NF‐κB pathway showed a potent synergistic effect. Our data indicate that, apart from its known functions, CUDC‐907 blocks multiple pro‐survival pathways to overcome microenvironment protection in CLL cells. This provides a rationale to evaluate the clinical relevance of CUDC‐907 in combination therapies with other targeted inhibitors.

Inhibitory-κB Kinase (IKK) α and Nuclear Factor-κB (NFκB)-Inducing Kinase (NIK) as Anti-Cancer Drug Targets

The cellular kinases inhibitory-κB kinase (IKK) α and Nuclear Factor-κB (NF-κB)-inducing kinase (NIK) are well recognised as key central regulators and drivers of the non-canonical NF-κB cascade and as such dictate the initiation and development of defined transcriptional responses associated with the liberation of p52-RelB and p52-p52 NF-κB dimer complexes. Whilst these kinases and downstream NF-κB complexes transduce pro-inflammatory and growth stimulating signals that contribute to major cellular processes, they also play a key role in the pathogenesis of a number of inflammatory-based conditions and diverse cancer types, which for the latter may be a result of background mutational status. IKKα and NIK, therefore, represent attractive targets for pharmacological intervention. Here, specifically in the cancer setting, we reflect on the potential pathophysiological role(s) of each of these kinases, their associated downstream signalling outcomes and the stimulatory and mutational mechanisms leading to their increased activation. We also consider the downstream coordination of transcriptional events and phenotypic outcomes illustrative of key cancer 'Hallmarks' that are now increasingly perceived to be due to the coordinated recruitment of both NF-κB-dependent as well as NF-κB⁻independent signalling. Furthermore, as these kinases regulate the transition from hormone-dependent to hormone-independent growth in defined tumour subsets, potential tumour reactivation and major cytokine and chemokine species that may have significant bearing upon tumour-stromal communication and tumour microenvironment it reiterates their potential to be drug targets. Therefore, with the emergence of small molecule kinase inhibitors targeting each of these kinases, we consider medicinal chemistry efforts to date and those evolving that may contribute to the development of viable pharmacological intervention strategies to target a variety of tumour types.

NOTCH1 Aberrations in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is an incurable B-cell neoplasm characterized by highly variable clinical outcomes. In recent years, genomic and molecular studies revealed a remarkable heterogeneity in CLL, which mirrored the clinical diversity of this disease. These studies profoundly enhanced our understanding of leukemia cell biology and led to the identification of new biomarkers with potential prognostic and therapeutic significance. Accumulating evidence indicates a key role of deregulated NOTCH1 signaling and NOTCH1 mutations in CLL. This review highlights recent discoveries that improve our understanding of the pathophysiological NOTCH1 signaling in CLL and the clinical impact of NOTCH1 mutations in retrospective and prospective trials. In addition, we discuss the rationale for a therapeutic strategy aiming at inhibiting NOTCH1 signaling in CLL, along with an overview on the currently available NOTCH1-directed approaches.

NF-κB signaling and its relevance to the treatment of mantle cell lymphoma

Mantle cell lymphoma is an aggressive subtype of non-Hodgkin B cell lymphoma that is characterized by a poor prognosis determined by Ki67 and Mantle Cell International Prognostic Index scores, but it is becoming increasingly treatable. The majority of patients, especially if young, achieve a progression-free survival of at least 5 years. Mantle cell lymphoma can initially be treated with an anti-CD20 antibody in combination with a chemotherapy backbone, such as VR-CAP (the anti-CD20 monoclonal antibody rituximab administered with cyclophosphamide, doxorubicin, and prednisone) or R-CHOP (the anti-CD20 monoclonal antibody rituximab administered with cyclophosphamide, doxorubicin, vincristine, and prednisone). While initial treatment can facilitate recovery and complete remission in a few patients, many patients experience relapsed or refractory mantle cell lymphoma within 2 to 3 years after initial treatment. Targeted agents such as ibrutinib, an inhibitor of Bruton’s tyrosine kinase, which has been approved only in the relapsed setting, can be used to treat patients with relapsed or refractory mantle cell lymphoma. However, mantle cell lymphoma cells often acquire resistance to such targeted agents and continue to survive by activating alternate signaling pathways such as the PI3K-Akt pathway or the NF-κB pathways.

NF-κB is a transcription factor family that regulates the growth and survival of B cells; mantle cell lymphoma cells depend on NF-κB signaling for continued growth and proliferation. The NF-κB signaling pathways are categorized into canonical and non-canonical types, wherein the canonical pathway prompts inflammatory responses, immune regulation, and cell proliferation, while the non-canonical leads to B cell maturation and lymphoid organogenesis. Since these pathways upregulate survival genes and tumor-promoting cytokines, they can be activated to overcome the inhibitory effects of targeted agents, thereby having profound effects on tumorigenesis. The NF-κB pathways are also highly targetable in that they are interconnected with numerous other pathways, including B cell receptor signaling, PI3K/Akt/mTOR signaling, and toll-like receptor signaling pathways. Additionally, elements of the non-canonical NF- κB pathway, such as NF-κB-inducing kinase, can be targeted to overcome resistance to targeting of the canonical NF- κB pathway.

Targeting the molecular mechanisms of the NF-κB pathways can facilitate the development of novel agents to treat malignancies and overcome drug resistance in patients with relapsed or refractory mantle cell lymphoma.

Cooperative down-regulation of ribosomal protein L10 and NF-κB signaling pathway is responsible for the anti-proliferative effects by DMAPT in pancreatic cancer cells

Dimethylaminoparthenolide (DMAPT), a water-soluble analogue of natural product parthenolide, possesses anti-inflammatory and anti-tumor activities. Despite that the anti-inflammatory mechanism of DMAPT has been well studied, specific target(s) for DMPAT and its anti-tumor mechanism remain poorly understood. In this study, to assess the anti-proliferative effects of DMAPT in pancreatic cancer cell lines and exploit its anti-tumor mechanism, serial affinity chromatograph was implemented to probe potential targets for DMAPT, revealing that ribosomal protein L10 (RPL10) is a specific binding protein of DMAPT in PANC-1 cells. DMAPT could decrease the expression of RPL10 accompanying its anti-proliferative effects. Mechanistically, in both PANC-1 cells and MiaPaca-2 cells, reduced expression of RPL10 triggered by DMAPT binding decreased the expression of either p65 or IKKγ through the direct binding between RPL10 and p65 or IKKγ. Together, the present study strongly implies that RPL10 is a novel target with therapeutic potential for the treatment of pancreatic cancer.

Cooperation of imipramine blue and tyrosine kinase blockade demonstrates activity against chronic myeloid leukemia

The use of tyrosine kinase inhibitors (TKI), including nilotinib, has revolutionized the treatment of chronic myeloid leukemia (CML). However current unmet clinical needs include combating activation of additional survival signaling pathways in persistent leukemia stem cells after long-term TKI therapy. A ubiquitous signaling alteration in cancer, including CML, is activation of reactive oxygen species (ROS) signaling, which may potentiate stem cell activity and mediate resistance to both conventional chemotherapy and targeted inhibitors. We have developed a novel nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, imipramine blue (IB) that targets ROS generation. ROS levels are known to be elevated in CML with respect to normal hematopoietic stem/progenitor cells and not corrected by TKI. We demonstrate that IB has additive benefit with nilotinib in inhibiting proliferation, viability, and clonogenic function of TKI-insensitive quiescent CD34⁺ CML chronic phase (CP) cells while normal CD34⁺ cells retained their clonogenic capacity in response to this combination therapy in vitro. Mechanistically, the pro-apoptotic activity of IB likely resides in part through its dual ability to block NF-κB and re-activate the tumor suppressor protein phosphatase 2A (PP2A). Combining BCR-ABL1 kinase inhibition with NADPH oxidase blockade may be beneficial in eradication of CML and worthy of further investigation.

In vitro and in vivo evidence for uncoupling of B-cell receptor internalization and signaling in chronic lymphocytic leukemia

B-cell receptor activation, occurring within lymph nodes, plays a key role in the pathogenesis of chronic lymphocytic leukemia and is linked to prognosis. As well as activation of downstream signaling, receptor ligation triggers internalization, transit to acidified endosomes and degradation of ligand-receptor complexes. Herein, we investigated the relationship between these two processes in normal and leukemic B cells. We found that leukemic B cells, particularly anergic cases lacking the capacity to initiate downstream signaling, internalize and accumulate ligand in acidified endosomes more efficiently than normal B cells. Furthermore, ligation of either surface CD79B, a B-cell receptor component required for downstream signaling, or surface Immunoglobulin M (IgM) by cognate agonistic antibody, showed that the two molecules internalize independently of each other in leukemic but not normal B cells. Since association with surface CD79B is required for surface retention of IgM, this suggests that uncoupling of B-cell receptor internalization from signaling may be due to the dissociation of these two molecules in leukemic cells. A comparison of lymph node with peripheral blood cells from chronic lymphocytic leukemia patients showed that, despite recent B-cell receptor activation, lymph node B cells expressed higher levels of surface IgM. This surprising finding suggests that the B-cell receptors of lymph node- and peripheral blood-derived leukemic cells might be functionally distinct. Finally, long-term therapy with the Bruton’s tyrosine kinase inhibitors ibrutinib or acalabrutinib resulted in a switch to an anergic pattern of B-cell receptor function with reduced signaling capacity, surface IgM expression and more efficient internalization.

Microenvironmental stromal cells abrogate NF-κB inhibitor-induced apoptosis in chronic lymphocytic leukemia

Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) is known to play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL). Several NF-κB inhibitors were shown to successfully induce apoptosis of CLL cells in vitro Since the microenvironment is known to be crucial for the survival of CLL cells, herein, we tested whether NF-κB inhibition may still induce apoptosis in these leukemic cells in the presence of protective stromal interaction. We used the specific NF-κB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ). Microenvironmental support was mimicked by co-culturing CLL cells with bone marrow-derived stromal cell lines (HS-5 and M2-10B4). NF-κB inhibition by DHMEQ in CLL cells could be confirmed in both the monoculture and co-culture setting. In line with previous reports, NF-κB inhibition induced apoptosis in the monoculture setting by activating the intrinsic apoptotic pathway resulting in poly (ADP-ribose) polymerase (PARP)-cleavage; however, it was unable to induce apoptosis in leukemic cells co-cultured with stromal cells. Similarly, small interfering ribonucleic acid (siRNA)-mediated RELA downregulation induced apoptosis of CLL cells cultured alone, but not in the presence of supportive stromal cells. B-cell activating factor (BAFF) was identified as a microenvironmental messenger potentially protecting the leukemic cells from NF-κB inhibition-induced apoptosis. Finally, we show improved sensitivity of stroma-supported CLL cells to NF-κB inhibition when combining the NF-κB inhibitor with the SYK inhibitor R406 or the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, agents known to inhibit the stroma-leukemia crosstalk. We conclude that NF-κB inhibitors are not promising as monotherapies in CLL, but may represent attractive therapeutic partners for ibrutinib and R406.

Targeting metabolism and survival in chronic lymphocytic leukemia and Richter syndrome cells by a novel NF-κB inhibitor

IT-901 is a novel and selective NF-κB inhibitor with promising activity in pre-clinical models. Here we show that treatment of chronic lymphocytic leukemia cells (CLL) with IT-901 effectively interrupts NF-κB transcriptional activity. CLL cells exposed to the drug display elevated mitochondrial reactive oxygen species, which damage mitochondria, limit oxidative phosphorylation and ATP production, and activate intrinsic apoptosis. Inhibition of NF-κB signaling in stromal and myeloid cells, both tumor-supportive elements, fails to induce apoptosis, but impairs NF-κB-driven expression of molecules involved in cell-cell contacts and immune responses, essential elements in creating a pro-leukemic niche. The consequence is that accessory cells do not protect CLL cells from IT-901-induced apoptosis. In this context, IT-901 shows synergistic activity with ibrutinib, arguing in favor of combination strategies. IT-901 is also effective in primary cells from patients with Richter syndrome (RS). Its anti-tumor properties are confirmed in xenograft models of CLL and in RS patient-derived xenografts, with documented NF-κB inhibition and significant reduction of tumor burden. Together, these results provide pre-clinical proof of principle for IT-901 as a potential new drug in CLL and RS.

Treatment of relapsed extranodal natural killer/T-cell lymphoma with bortezomib plus fludarabine

Extranodal NK/T cell lymphoma (ENKL) is a rare entity, associated with an aggressive clinical behavior and poor prognosis. The optimal treatment strategies, particularly for relapsed patients, have not been clearly determined. A 40-year-old female ENKL patient with orbital involvement as the first presentation was initially suspected to have an orbital pseudotumor. When the patient developed disease progression following treatment with methylprednisolone, biopsy of the orbital mass was performed. Histopathological examination of the biopsy specimen was consistent with the diagnosis of ENKL (Ann Arbor stage IE). The patient was then treated with radiotherapy followed by chemotherapy with dexamethasone, methotrexate, ifosfamide, L-asparaginase and etoposide (SMILE regimen). Despite an initial good response, the patient developed disease relapse and progression (stage IIIE). Subsequently, treatment was switched to a novel regimen comprising bortezomib and fludarabine as salvage therapy for two courses. A positron emission tomography scan revealed disappearance of the orbital tumor. The patient then received autologous hematopoietic stem cell transplantation. At the last follow-up (March 2017), the patient remained disease-free.

Succinamide derivatives of melampomagnolide B and their anti-cancer activities

A series of succinamide derivatives of melampomagnolide B have been synthesized by coupling MMB monosuccinate (2) with various heterocyclic amines to afford compounds 3a-3l. MMB monosuccinate was also reacted with terminal diaminoalkanes to afford dimeric succinamido analogs of MMB (4a-4h). These succinamide analogs of MMB were evaluated for their anti-cancer activity against a panel of sixty human cancer cell lines. Analogs 3d-3i and dimers 4f-4g exhibited promising anti-cancer activity with GI50 values ranging from 0.28 to 33.5µM against most of the cell lines in the panel. The dimeric analogs 4f and 4g were identified as lead compounds with GI50 values in the nanomolar range (GI50=280-980nM) against several cell lines in the panel; i.e. leukemia cell lines CCRF-CEM, HL-60(TB), K-562, MOLT-4, RPMI-8226 and SR; and solid tumor cell lines NCI-H522 (non-small cell lung cancer), SW-620 and HCT-116 (colon cancer), LOX IMVI (melanoma), RXF 393 (renal cancer), and MCF7, BT-549 and MDA-MB-468 (breast cancer). Succinamide analogs 3a, 3c-3l and 4b-4h were also evaluated for their apoptotic activity against M9-ENL1 acute myelogenous leukemia cells; compounds 3h-3j and 4g were equipotent with parthenolide, exhibiting LC50 values in the range 4.1-8.1μM. Molecular docking studies indicate that these molecules interact covalently with the highly conserved Cys-46 residue of the N-terminal lobe (1-109) of human IKKβ to inhibit the NFκB transcription factor complex, resulting in down-regulation of anti-apoptotic genes under NFκB control.

NF-κB in Hematological Malignancies

NF-κB (Nuclear Factor Κ-light-chain-enhancer of activated B cells) transcription factors are critical regulators of immunity, stress response, apoptosis, and differentiation. Molecular defects promoting the constitutive activation of canonical and non-canonical NF-κB signaling pathways contribute to many diseases, including cancer, diabetes, chronic inflammation, and autoimmunity. In the present review, we focus our attention on the mechanisms of NF-κB deregulation in hematological malignancies. Key positive regulators of NF-κB signaling can act as oncogenes that are often prone to chromosomal translocation, amplifications, or activating mutations. Negative regulators of NF-κB have tumor suppressor functions, and are frequently inactivated either by genomic deletions or point mutations. NF-κB activation in tumoral cells is also driven by the microenvironment or chronic signaling that does not rely on genetic alterations.

Indole carboxylic acid esters of melampomagnolide B are potent anticancer agents against both hematological and solid tumor cells

A series of novel, heteroaryl carboxylic acid conjugates of the sesquiterpene melampomagnolide-B (MMB, 3) has been evaluated as antitumor agents against an NCI panel of 64 human hematopoetic and solid tumor cell lines. The indole-3-acrylic acid conjugate 7j and the indole-3-carboxylic acid conjugate 7k were found to be the most potent analogs in the series. Compounds 7j and 7k exhibited remarkable growth inhibition, with GI₅₀ values in the range 0.03-0.30 μM and 0.04-0.28 μM, respectively, against the cell lines in the leukemia sub-panel, and GI₅₀ values of 0.05-0.40 μM and 0.04-0.61 μM, respectively, against 90% of the solid tumor cell lines in the NCI panel. Compound 7a was particularly effective against the sub-panel of breast cancer cell lines with GI₅₀ values in the range <0.01-0.30 μM. Compounds 7j, 7a and its water soluble analog 7p also exhibited potent anticancer activity against rat 9L-SF gliosarcoma cells in culture. Compound 7j was the most potent compound in the series in the M9-ENL1 AML cell assay with a lethal dose concentration EC₅₀ value of 720 nM, and exhibited the greatest cytotoxicity against a collection of primary AML stem cell specimens, which included a specimen that was unresponsive to PTL, affording EC₅₀ values in the range 0.33-1.0 μM in three out of four specimens. The results from this study provide further evidence that analogs of the sesquiterpene MMB can be designed to afford molecules with significantly improved anticancer activity. Thus, both 7j and 7k are considered potential lead molecules in the search for new anticancer agents that can be used as treatments for both hematopoetic and solid tumors.

Chronic Lymphocytic Leukemia: Exploiting Vulnerabilities with Targeted Agents

The field of oncology has been transformed over the course of the last 20 years in large part due to the enhanced understanding of cellular biology and cellular signaling. The indolent natural history of chronic lymphocytic leukemia (CLL) has permitted extensive study of cancer biology and can in some ways be thought of a model for understanding and translating concepts to other diseases. By systematically probing the biology of CLL cells and working out in stepwise fashion the transduction of signals from the surface immunoglobulin to nuclear transcription factors, investigators have paved the way for rational targeting of therapies at natural vulnerabilities that mimic oncogene addiction. These key targets include Bruton's tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K), Src, Bcl2, and cyclin-dependent kinases (CDKs). In this review, we will consider these proteins and describe the current and future molecules designed to target them in CLL.

Class I histone deacetylases regulate p53/NF-κB crosstalk in cancer cells

The transcription factors NF-κB and p53 as well as their crosstalk determine the fate of tumor cells upon therapeutic interventions. Replicative stress and cytokines promote signaling cascades that lead to the co-regulation of p53 and NF-κB. Consequently, nuclear p53/NF-κB signaling complexes activate NF-κB-dependent survival genes. The 18 histone deacetylases (HDACs) are epigenetic modulators that fall into four classes (I-IV). Inhibitors of histone deacetylases (HDACi) become increasingly appreciated as anti-cancer agents. Based on their effects on p53 and NF-κB, we addressed whether clinically relevant HDACi affect the NF-κB/p53 crosstalk. The chemotherapeutics hydroxyurea, etoposide, and fludarabine halt cell cycle progression, induce DNA damage, and lead to DNA fragmentation. These agents co-induce p53 and NF-κB-dependent gene expression in cell lines from breast and colon cancer and in primary chronic lymphatic leukemia (CLL) cells. Using specific HDACi, we find that the class I subgroup of HDACs, but not the class IIb deacetylase HDAC6, are required for the hydroxyurea-induced crosstalk between p53 and NF-κB. HDACi decrease the basal and stress-induced expression of p53 and block NF-κB-regulated gene expression. We further show that class I HDACi induce senescence in pancreatic cancer cells with mutant p53.

The Phospholipase Cγ2 Mutants R665W and L845F Identified in Ibrutinib-resistant Chronic Lymphocytic Leukemia Patients Are Hypersensitive to the Rho GTPase Rac2 Protein

Mutations in the gene encoding phospholipase C-γ2 (PLCγ2) have been shown to be associated with resistance to targeted therapy of chronic lymphocytic leukemia (CLL) with the Bruton's tyrosine kinase inhibitor ibrutinib. The fact that two of these mutations, R665W and L845F, imparted upon PLCγ2 an ∼2-3-fold ibrutinib-insensitive increase in the concentration of cytosolic Ca2+ following ligation of the B cell antigen receptor (BCR) led to the assumption that the two mutants exhibit constitutively enhanced intrinsic activity. Here, we show that the two PLCγ2 mutants are strikingly hypersensitive to activation by Rac2 such that even wild-type Rac2 suffices to activate the mutant enzymes upon its introduction into intact cells. Enhanced "basal" activity of PLCγ2 in intact cells is shown using the pharmacologic Rac inhibitor EHT 1864 and the PLCγ2F897Q mutation mediating Rac resistance to be caused by Rac-stimulated rather than by constitutively enhanced PLCγ2 activity. We suggest that R665W and L845F be referred to as allomorphic rather than hypermorphic mutations of PLCG2 Rerouting of the transmembrane signals emanating from BCR and converging on PLCγ2 through Rac in ibrutinib-resistant CLL cells may provide novel drug treatment strategies to overcome ibrutinib resistance mediated by PLCG2 mutations or to prevent its development in ibrutinib-treated CLL patients.

Metformin inhibits cell cycle progression of B-cell chronic lymphocytic leukemia cells

B-cell chronic lymphocytic leukemia (CLL) was believed to result from clonal accumulation of resting apoptosis-resistant malignant B lymphocytes. However, it became increasingly clear that CLL cells undergo, during their life, iterative cycles of re-activation and subsequent clonal expansion. Drugs interfering with CLL cell cycle entry would be greatly beneficial in the treatment of this disease.

1, 1-Dimethylbiguanide hydrochloride (metformin), the most widely prescribed oral hypoglycemic agent, inexpensive and well tolerated, has recently received increased attention for its potential antitumor activity. We wondered whether metformin has apoptotic and anti-proliferative activity on leukemic cells derived from CLL patients.

Metformin was administered in vitro either to quiescent cells or during CLL cell activation stimuli, provided by classical co-culturing with CD40L-expressing fibroblasts.

At doses that were totally ineffective on normal lymphocytes, metformin induced apoptosis of quiescent CLL cells and inhibition of cell cycle entry when CLL were stimulated by CD40-CD40L ligation. This cytostatic effect was accompanied by decreased expression of survival- and proliferation-associated proteins, inhibition of signaling pathways involved in CLL disease progression and decreased intracellular glucose available for glycolysis.

In drug combination experiments, metformin lowered the apoptotic threshold and potentiated the cytotoxic effects of classical and novel antitumor molecules.

Our results indicate that, while CLL cells after stimulation are in the process of building their full survival and cycling armamentarium, the presence of metformin affects this process.

Simvastatin and downstream inhibitors circumvent constitutive and stromal cell-induced resistance to doxorubicin in IGHV unmutated CLL cells

The immunoglobulin heavy-chain variable region (IGHV) mutational status is a strong determinant of remission duration in chronic lymphocytic leukemia (CLL). The aim of this work was to compare the multidrug resistance (MDR) signature of IGHV mutated and unmutated CLL cells, identifying biochemical and molecular targets potentially amenable to therapeutic intervention.

We found that the mevalonate pathway-dependent Ras/ERK1–2 and RhoA/RhoA kinase signaling cascades, and the downstream HIF-1α/P-glycoprotein axis were more active in IGHV unmutated than in mutated cells, leading to a constitutive protection from doxorubicin-induced cytotoxicity. The constitutive MDR phenotype of IGHV unmutated cells was partially dependent on B cell receptor signaling, as shown by the inhibitory effect exerted by ibrutinib. Stromal cells further protected IGHV unmutated cells from doxorubicin by upregulating Ras/ERK1–2, RhoA/RhoA kinase, Akt, HIF-1α and P-glycoprotein activities. Mevalonate pathway inhibition with simvastatin abrogated these signaling pathways and reversed the resistance of IGHV unmutated cells to doxorubicin, also counteracting the protective effect exerted by stromal cells. Similar results were obtained via the targeted inhibition of the downstream molecules ERK1–2, RhoA kinase and HIF-1α.

Therefore, targeting the mevalonate pathway and its downstream signaling cascades is a promising strategy to circumvent the MDR signature of IGHV unmutated CLL cells.

Key Molecular Drivers of Chronic Lymphocytic Leukemia

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

NF-κB activation in chronic lymphocytic leukemia: A point of convergence of external triggers and intrinsic lesions

The nuclear factor-κB (NF-κB) pathway is constitutively activated in chronic lymphocytic leukemia (CLL) patients, and hence plays a major role in disease development and evolution. In contrast to many other mature B-cell lymphomas, only a few recurrently mutated genes involved in canonical or non-canonical NF-κB activation have been identified in CLL (i.e. BIRC3, MYD88 and NFKBIE mutations) and often at a low frequency. On the other hand, CLL B cells seem 'addicted' to the tumor microenvironment for their survival and proliferation, which is primarily mediated by interaction through a number of cell surface receptors, e.g. the B-cell receptor (BcR), Toll-like receptors and CD40, that in turn activate downstream NF-κB. The importance of cell-extrinsic triggering for CLL pathophysiology was recently also highlighted by the clinical efficacy of novel drugs targeting microenvironmental interactions through the inhibition of BcR signaling. In other words, CLL can be considered a prototype disease for studying the intricate interplay between external triggers and intrinsic aberrations and their combined impact on disease evolution. In this review, we will discuss the current understanding of mechanisms underlying NF-κB deregulation in CLL, including micro-environmental, genetic and epigenetic events, and summarize data generated in murine models resembling human CLL. Finally, we will also discuss different strategies undertaken to intervene with the NF-κB pathway and its upstream mediators.

Pro-survival signal inhibition by CDK inhibitor dinaciclib in Chronic Lymphocytic Leukaemia

Dinaciclib is a cyclin-dependent kinase inhibitor with clinical potential in different cancers, including chronic lymphocytic leukaemia (CLL). In order to better understand its cytotoxic action, we characterized its effects on signalling pathways important for the survival of CLL cells. We found that dinaciclib induced apoptosis through the activation of caspases 8 and 9, which was independent of the presence of cytokines to mimic the environment of proliferation centres or IGVH mutation status. Moreover, treatment with dinaciclib led to the inhibition of oncogenic pathways normally activated in stimulated CLL cells, such as STAT3, NF-κB, p38, PI3K/AKT and RAF/MEK/ERK. Dinaciclib was also able to block the expression of anti-apoptotic proteins of the BCL2 family such as MCL1 and BCL-xL (also termed BCL2L1). Finally, we showed that low concentrations of dinaciclib enhanced cell sensitivity to ibrutinib and the BCL2 inhibitor ABT-199, two drugs with known effects on CLL. Taken together, our data show that dinaciclib targets multiple pro-survival signalling pathways in CLL, which provides a mechanistic explanation for its potent induction of apoptosis. They also support a therapeutic application of cyclin-dependent kinase inhibitors in CLL in combination with other relevant targeted therapies.

SLP76 integrates into the B-cell receptor signaling cascade in chronic lymphocytic leukemia cells and is associated with an aggressive disease course

I In the last decade, the B-cell receptor has emerged as a pivotal stimulus in the pathogenesis of chronic lymphocytic leukemia, and a very feasible therapeutic target in this disease. B-cell receptor responsiveness in chronic lymphocytic leukemia cells is heterogeneous among patients and correlates with aggressiveness of the disease. Here we show, for the first time, that SLP76, a key scaffold protein in T-cell receptor signaling, is ectopically expressed in chronic lymphocytic leukemia cells, with variable levels among patients, and correlates positively with unmutated immunoglobulin heavy chain variable gene status and ZAP-70 expression. We found that SLP76 was functionally active in chronic lymphocytic leukemia cells. A SYK-dependent basal level of phosphorylated SLP76 exists in the cells, and upon B-cell receptor engagement, SLP76 tyrosine phosphorylation is significantly enhanced concomitantly with increased physical association with BTK. B-cell receptor-induced SLP76 phosphorylation is mediated by upstream signaling events involving LCK and SYK. Knockdown of SLP76 in the cells resulted in decreased induction of BTK, PLCγ2 and IκB phosphorylation, as well as cell viability after B-cell receptor activation with anti-IgM. Consistent with our biochemical findings, high total SLP76 expression in chronic lymphocytic leukemia cells correlated with a more aggressive disease course.

IN CONCLUSION

SLP76 is ectopically expressed in chronic lymphocytic leukemia cells where it plays a role in B-cell receptor signaling.

Association of Bax Expression and Bcl2/Bax Ratio with Clinical and Molecular Prognostic Markers in Chronic Lymphocytic Leukemia

Background

In chronic lymphocytic leukemia (CLL), in vivo apoptotic resistance of malignant B lymphocytes results, in part, from the intrinsic defects of their apoptotic machinery. These include genetic alterations and aberrant expression of many apoptosis regulators, among which the Bcl2 family members play a central role.

Aim

The aim of this study was to investigate the association of pro-apoptotic Bax gene expression and Bcl2/Bax ratio with the clinical features of CLL patients as well as with molecular prognostic markers, namely the mutational status of rearranged immunoglobulin heavy variable (IGHV) genes and lipoprotein lipase (LPL) gene expression.

Methods

We analyzed the expression of Bax mRNA and Bcl2/Bax mRNA ratio in the peripheral blood mononuclear cells of 58 unselected CLL patients and 10 healthy controls by the quantitative reverse-transcriptase polymerase chain reaction.

Results

We detected significant Bax gene overexpression in CLL samples compared to non-leukemic samples (p=0.003), as well as an elevated Bcl2/Bax ratio (p=<0.001). Regarding the association with prognostic markers, the Bcl2/Bax ratio showed a negative correlation to lymphocyte doubling time (r=-0.307; p=0.0451), while high-level Bax expression was associated with LPL-positive status (p=0.035). Both the expression of Bax and Bcl2/Bax ratio were higher in patients with unmutated vs. mutated IGHV rearrangements, but this difference did not reach statistical significance.

Conclusions

Our results suggest that dysregulated expression of Bcl2 and Bax, which leads to a high Bcl2/Bax ratio in leukemic cells, contributes to the pathogenesis and clinical course of CLL.

At High Levels, Constitutively Activated STAT3 Induces Apoptosis of Chronic Lymphocytic Leukemia Cells

In chronic lymphocytic leukemia (CLL), the increment in PBLs is slower than the expected increment calculated from the cells' proliferation rate, suggesting that cellular proliferation and apoptosis are concurrent. Exploring this phenomenon, we found overexpression of caspase-3, higher cleaved poly (ADP-ribose) polymerase levels (p < 0.007), and a higher apoptosis rate in cells from patients with high counts compared with cells from patients with low counts. Although we previously found that STAT3 protects CLL cells from apoptosis, STAT3 levels were significantly higher in cells from patients with high counts than in cells from patients with low counts. Furthermore, overexpression of STAT3 did not protect the cells. Rather, it upregulated caspase-3 and induced apoptosis. Remarkably, putative STAT3 binding sites were identified in the caspase-3 promoter, and a luciferase assay, chromatin immunoprecipitation, and an EMSA revealed that STAT3 activated caspase-3 However, caspase-3 levels increased only when STAT3 levels were sufficiently high. Using chromatin immunoprecipitation and EMSA, we found that STAT3 binds with low affinity to the caspase-3 promoter, suggesting that at high levels, STAT3 activates proapoptotic mechanisms and induces apoptosis in CLL cells.

Unexpected functions of nuclear factor-κB during germinal center B-cell development: implications for lymphomagenesis

PURPOSE OF REVIEW

B-cell tumors originating from the transformation of germinal center B cells frequently harbor genetic mutations, leading to constitutive activation of the nuclear factor-κB (NF-κB) signaling pathway. The present review highlights recent insights into the roles of separate NF-κB transcription factors in germinal center B-cell development and discusses implications of the results for germinal center lymphomagenesis.

RECENT FINDINGS

Understanding how aberrant NF-κB activation promotes tumorigenesis requires the understanding of the role of NF-κB in the tumor-precursor cells. Despite extensive knowledge on NF-κB biology, the function of this complex signaling pathway in the differentiation of germinal center B cells is largely unknown. The present review will discuss recent findings that revealed distinct roles of separate NF-κB transcription factors during the germinal center reaction in the context of germinal center lymphomagenesis. Most notably, a single NF-κB subunit, c-REL, was found to be required for the maintenance of the germinal center reaction and was associated with the activation of a metabolic program that promotes cell growth.

SUMMARY

Identifying the biological roles of the separate NF-κB transcription factor subunits in germinal center biology will help to better understand the pathogenic consequences of their constitutive activation in B-cell tumors. This knowledge may be exploited for the development of targeted antitumor therapies aimed at inhibiting selectively those components of aberrant NF-κB activity which contribute to pathogenesis.

Dimers of Melampomagnolide B Exhibit Potent Anticancer Activity against Hematological and Solid Tumor Cells

Novel carbamate (7a-7h) and carbonate (7i, 7j, and 8) dimers of melampomagnolide B have been synthesized by reaction of the melampomagnolide-B-triazole carbamate synthon 6 with various terminal diamino- and dihydroxyalkanes. Dimeric carbamate products 7b, 7c, and 7f exhibited potent growth inhibition (GI50 = 0.16-0.99 μM) against the majority of cell lines in the NCI panel of 60 human hematological and solid tumor cell lines. Compound 7f and 8 exhibited anticancer activity that was 300-fold and 1 × 10(6)-fold more cytotoxic than DMAPT, respectively, at a concentration of 10 μM against rat 9L-SF gliosarcoma cells. Compounds 7a-7j and 8 were also screened against M9-ENL1 and acute myelogenous leukemia (AML) primary cell lines and exhibited 2- to 10-fold more potent antileukemic activity against M9-ENL1 cells (EC50 = 0.57-2.90 μM) when compared to parthenolide (EC50 = 6.0) and showed potent antileukemic activity against five primary AML cell lines (EC50 = 0.76-7.3 μM).

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.