Expression of Apoptosis-Regulating Proteins in Chronic Lymphocytic Leukemia: Correlations With In Vitro and In Vivo Chemoresponses

Viable mutations of mouse midnolin suppress B cell malignancies

In a genetic screen, we identified two viable missense alleles of the essential gene Midnolin (Midn) that were associated with reductions in peripheral B cells. Causation was confirmed in mice with targeted deletion of four of six MIDN protein isoforms. MIDN was expressed predominantly in lymphocytes where it augmented proteasome activity. We showed that purified MIDN directly stimulated 26S proteasome activity in vitro in a manner dependent on the ubiquitin-like domain and a C-terminal region. MIDN-deficient B cells displayed aberrant activation of the IRE-1/XBP-1 pathway of the unfolded protein response. Partial or complete MIDN deficiency strongly suppressed Eμ-Myc-driven B cell leukemia and the antiapoptotic effects of Eμ-BCL2 on B cells in vivo and induced death of Sp2/0 hybridoma cells in vitro, but only partially impaired normal lymphocyte development. Thus, MIDN is required for proteasome activity in support of normal lymphopoiesis and is essential for malignant B cell proliferation over a broad range of differentiation states.

BCL-2 inhibition in haematological malignancies: Clinical application and complications

B-cell lymphoma-2 (BCL-2) family proteins are fundamental regulators of the intrinsic apoptotic pathway which modulate cellular fate. In many haematological malignancies, overexpression of anti-apoptotic factors (BCL-2, BCL-XL and MCL-1) circumvent apoptosis. To address this cancer hallmark, a concerted effort has been made to induce apoptosis by inhibiting BCL-2 family proteins. A series of highly selective BCL-2 homology 3 (BH3) domain mimetics are in clinical use and in ongoing clinical trials for acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM). These inhibitors serve as promising candidates, both as single agents or in combination therapy to improve patient outcomes. In other diseases such as follicular lymphoma, efficacy has been notably limited. There are also clinical problems with BCL-2 family inhibition, including drug resistance, disease relapse, tumour lysis syndrome, and clinically relevant cytopenias. Here, we provide a balanced view on both the clinical benefits of BCL-2 inhibition as well as the associated challenges.

Potential New Therapies "ROS-Based" in CLL: An Innovative Paradigm in the Induction of Tumor Cell Apoptosis

Chronic lymphocytic leukemia, in spite of recent advancements, is still an incurable disease; the majority of patients eventually acquire resistance to treatment through relapses. In all subtypes of chronic lymphocytic leukemia, the disruption of normal B-cell homeostasis is thought to be mostly caused by the absence of apoptosis. Consequently, apoptosis induction is crucial to the management of this illness. Damaged biological components can accumulate as a result of the oxidation of intracellular lipids, proteins, and DNA by reactive oxygen species. It is possible that cancer cells are more susceptible to apoptosis because of their increased production of reactive oxygen species. An excess of reactive oxygen species can lead to oxidative stress, which can harm biological elements like DNA and trigger apoptotic pathways that cause planned cell death. In order to upset the balance of oxidative stress in cells, recent therapeutic treatments in chronic lymphocytic leukemia have focused on either producing reactive oxygen species or inhibiting it. Examples include targets created in the field of nanomedicine, natural extracts and nutraceuticals, tailored therapy using biomarkers, and metabolic targets. Current developments in the complex connection between apoptosis, particularly ferroptosis and its involvement in epigenomics and alterations, have created a new paradigm.

Treatment of Double-Refractory Chronic Lymphocytic Leukemia-An Unmet Clinical Need

Recent years have seen significant improvement in chronic lymphocytic leukemia (CLL) management. Targeting B-cell lymphoma (BCL-2) and Bruton's kinase (BTK) have become the main strategies to restrain CLL activity. These agents are generally well tolerated, but the discontinuation of these therapies happens due to resistance, adverse effects, and Richter's transformation. A growing population of patients who have previously used both BTK inhibitors and BCL2 suffer from the constriction of the following regimens. This review explores the resistance mechanisms for both ibrutinib and venetoclax. Moreover, we present innovative approaches evaluated for treating double-refractory CLL.

Epigenetic regulation in hematopoiesis and its implications in the targeted therapy of hematologic malignancies

Hematologic malignancies are one of the most common cancers, and the incidence has been rising in recent decades. The clinical and molecular features of hematologic malignancies are highly heterogenous, and some hematologic malignancies are incurable, challenging the treatment, and prognosis of the patients. However, hematopoiesis and oncogenesis of hematologic malignancies are profoundly affected by epigenetic regulation. Studies have found that methylation-related mutations, abnormal methylation profiles of DNA, and abnormal histone deacetylase expression are recurrent in leukemia and lymphoma. Furthermore, the hypomethylating agents and histone deacetylase inhibitors are effective to treat acute myeloid leukemia and T-cell lymphomas, indicating that epigenetic regulation is indispensable to hematologic oncogenesis. Epigenetic regulation mainly includes DNA modifications, histone modifications, and noncoding RNA-mediated targeting, and regulates various DNA-based processes. This review presents the role of writers, readers, and erasers of DNA methylation and histone methylation, and acetylation in hematologic malignancies. In addition, this review provides the influence of microRNAs and long noncoding RNAs on hematologic malignancies. Furthermore, the implication of epigenetic regulation in targeted treatment is discussed. This review comprehensively presents the change and function of each epigenetic regulator in normal and oncogenic hematopoiesis and provides innovative epigenetic-targeted treatment in clinical practice.

BCL-2 protein family: attractive targets for cancer therapy

Acquired resistance to cell death is a hallmark of cancer. The BCL-2 protein family members play important roles in controlling apoptotic cell death. Abnormal over-expression of pro-survival BCL-2 family members or abnormal reduction of pro-apoptotic BCL-2 family proteins, both resulting in the inhibition of apoptosis, are frequently detected in diverse malignancies. The critical role of the pro-survival and pro-apoptotic BCL-2 family proteins in the regulation of apoptosis makes them attractive targets for the development of agents for the treatment of cancer. This review describes the roles of the various pro-survival and pro-apoptotic members of the BCL-2 protein family in normal development and organismal function and how defects in the control of apoptosis promote the development and therapy resistance of cancer. Finally, we discuss the development of inhibitors of pro-survival BCL-2 proteins, termed BH3-mimetic drugs, as novel agents for cancer therapy.

Biological relevance of ZNF224 expression in chronic lymphocytic leukemia and its implication IN NF-kB pathway regulation

Chronic lymphocytic leukemia (CLL) is a heterogeneous disease, whose presentation and clinical course are highly variable. Identification of novel prognostic factors may contribute to improving the CLL classification and providing indications for treatment options. The zinc finger protein ZNF224 plays a key role in cell transformation, through the control of apoptotic and survival pathways. In this study, we evaluated the potential application of ZNF224 as a novel marker of CLL progression and therapy responsiveness. To this aim, we analyzed ZNF224 expression levels in B lymphocytes from CLL patients at different stages of the disease and in patients showing different treatment outcomes. The expression of ZNF224 was significantly increased in disease progression and dramatically decreased in patients in complete remission after chemotherapy. Gene expression correlation analysis performed on datasets of CLL patients revealed that ZNF224 expression was well correlated with that of some prognostic and predictive markers. Moreover, bioinformatic analysis coupled ZNF224 to NF-κB pathway, and experimental data demonstrated that RNA interference of ZNF224 reduced the activity of the NF-κB survival pathway in CLL cells. Consistently with a pro-survival role, ZNF224 knockdown raised spontaneous and drug-induced apoptosis and inhibited the proliferation of peripheral blood mononuclear cells from CLL patients. Our findings provide evidence for the involvement of ZNF224 in the survival of CLL cells via NF-κB pathway modulation, and also suggest ZNF224 as a prognostic and predictive molecular marker of CLL disease.

Unraveling the mystery: How bad is BAG3 in hematological malignancies?

BAG3, also known as BIS and CAIR-1, interacts with Hsp70 via its BAG domain and with other molecules through its WW domain, PXXP repeats and IPV motifs. BAG3 can participate in major cellular pathways including apoptosis, autophagy, cytoskeleton structure, and motility by regulating the expression, location, and activity of its chaperone proteins. As a multifunctional protein, BAG3 is highly expressed in skeletal muscle, cardiomyocytes and multiple tumors, and its intracellular expression can be stimulated by stress. The functions and mechanisms of BAG3 in hematological malignancies have recently been a topic of interest. BAG3 has been confirmed to be involved in the development and chemoresistance of hematological malignancies and to act as a prognostic indicator. Modulation of BAG3 and its corresponding proteins has thus emerged as a promising therapeutic and experimental target. In this review, we consider the characteristics of BAG3 in hematological malignancies as a reference for further clinical and fundamental investigations.

Cyclin-dependent kinase inhibitor fadraciclib (CYC065) depletes anti-apoptotic protein and synergizes with venetoclax in primary chronic lymphocytic leukemia cells

Fadraciclib (CYC065) is a second-generation aminopurine CDK2/9 inhibitor with increased potency and selectivity toward CDK2 and CDK9 compared to seliciclib (R-roscovitine). In chronic lymphocytic leukemia (CLL), a disease that depends on the over-expression of anti-apoptotic proteins for its survival, inhibition of CDK9 by fadraciclib reduced phosphorylation of the C-terminal domain of RNA polymerase II and blocked transcription in vitro; these actions depleted the intrinsically short-lived anti-apoptotic protein Mcl-1 and induced apoptosis. While the simulated bone marrow and lymph node microenvironments induced Mcl-1 expression and protected CLL cells from apoptosis, these conditions did not prolong the turnover rate of Mcl-1, and fadraciclib efficiently abrogated the protective effect. Further, fadraciclib was synergistic with the Bcl-2 antagonist venetoclax, inducing more profound CLL cell death, especially in samples with 17p deletion. While fadraciclib, venetoclax, and the combination each had distinct kinetics of cell death induction, their activities were reversible, as no additional cell death was induced upon removal of the drugs. The best combination effects were achieved when both drugs were maintained together. Altogether, this study provides a rationale for the clinical development of fadraciclib in CLL, either alone or in combination with a Bcl-2 antagonist.

Rare t(X;14)(q28;q32) translocation reveals link between MTCP1 and chronic lymphocytic leukemia

Rare, recurrent balanced translocations occur in a variety of cancers but are often not functionally interrogated. Balanced translocations with the immunoglobulin heavy chain locus (IGH; 14q32) in chronic lymphocytic leukemia (CLL) are infrequent but have led to the discovery of pathogenic genes including CCND1, BCL2, and BCL3. Following identification of a t(X;14)(q28;q32) translocation that placed the mature T cell proliferation 1 gene (MTCP1) adjacent to the immunoglobulin locus in a CLL patient, we hypothesized that this gene may have previously unrecognized importance. Indeed, here we report overexpression of human MTCP1 restricted to the B cell compartment in mice produces a clonal CD5⁺/CD19⁺ leukemia recapitulating the major characteristics of human CLL and demonstrates favorable response to therapeutic intervention with ibrutinib. We reinforce the importance of genetic interrogation of rare, recurrent balanced translocations to identify cancer driving genes via the story of MTCP1 as a contributor to CLL pathogenesis.

DDX3 interacts with USP9X and participates in deubiquitination of the anti-apoptotic protein MCL1

Here, we describe a novel interaction between the RNA helicase DDX3 and the deubiquitinase ubiquitin-specific peptidase 9 X-linked (USP9X) in human cells. Domain mapping studies reveal that the C-terminal region of DDX3 interacted with the N terminus of USP9X. USP9X was predominantly localized in the cytoplasm where the interaction between DDX3 and USP9X occurred. USP9X was not visibly enriched in cytoplasmic stress granules (SGs) under oxidative stress conditions, whereas overexpression of GFP-DDX3 induced SG formation and recruited USP9X to SGs in HeLa cells. Luciferase reporter assays showed that depletion of USP9X had no significant effect on DDX3-mediated translation. Given that DDX3 is not ubiquitinated upon ubiquitin overexpression, it is unlikely that DDX3 serves as a substrate of USP9X. Importantly, we found that ubiquitinated MCL1 was accumulated upon depletion of USP9X and/or DDX3 in MG132-treated cells, suggesting that USP9X and DDX3 play a role in regulating MCL1 protein stability and anti-apoptotic function. This study indicates that DDX3 exerts anti-apoptotic effects probably by coordinating with USP9X in promoting MCL1 deubiquitination.

High Bax/Bcl-2 ratio is associated with good prognosis and better survival in patients with B cell chronic lymphocytic leukemia

Determination of Bax/Bcl-2 ratio may be a good predictive tool to recognize chronic lymphocytic leukemia (CLL) patients' outcome and prognosis to decide the time and type of therapy. This prospective study was carried out on 100 patients with newly diagnosed CLL. Bax and Bcl-2 expression in peripheral blood were measured by flow-cytometry. The association of Bax/Bcl-2 ratio with CLL laboratory markers, Rai stage, overall survival (OS) and progression-free survival (PFS) at 18 months was investigated. The sensitivity and specificity of Bax/Bcl-2 in predicting survival was evaluated. The best cut-off value of Bax/Bcl-2 ratio to predict the survival, detected by receiver operating characteristic (ROC) curve, was 1.2 with 80 % sensitivity and 60.86 % specificity. A ratio of ≤1.20 was detected in 78 % of patients and was associated with worse prognosis. A lower Bax/Bcl-2 ratio was associated with higher modified Rai stage at time of diagnosis and a significantly shorter both OS (64.1 % versus 90.9 %, p < 0.026) and PFS (66.7 % versus 90.9 %, p < 0.031) at 18 months. In multivariate analysis, bax/bcl-2 ≤ 1.2 was an independent prognostic factor for overall survival, (p = 0.025). We concluded that lower Bax /Bcl-2 ratios were associated with worse prognosis as evidenced by lower OS and PFS in CLL patients. It was also associated with markers of high tumor burden and unfavorable prognostic markers. Recognition of patients with low Bax /Bcl-2 ratio would make them good candidates for the novel Bcl-2 inhibitory targeted chemotherapy to avoid resistance to the traditional therapy.

Intrinsic and extrinsic apoptosis responses in leukaemia cells following daunorubicin treatment

BACKGROUND

Daunorubicin is used clinically in the treatment of myeloma, acute lymphatic and myelocytic leukaemia. The toxic lesions caused by daunorubicin induce various modes of cell death, including apoptosis. Apoptosis is highly regulated programmed cell death that can be initiated mainly via two pathways, through death receptors (extrinsic) or involvement of the mitochondria (intrinsic). Induction of apoptosis via these pathways has been alluded following treatment with daunorubicin, but never compared in acute lymphoblastic leukaemia over a time course.

METHODS

This study investigated the mechanisms of daunorubicin induced apoptosis in the treatment of CCRF-CEM, MOLT-4 (acute T-lymphoblastic leukaemia) and SUP-B15 (acute B-lymphoblastic leukaemia) cells. Cells were treated with daunorubicin for 4 h, and then placed in recovery medium (without daunorubicin) for 4 h, 12 h and 24 h. Apoptotic response was analysing using annexin-V expression, caspase activity, mitochondrial membrane potential change and an array to detect 43 apoptotic proteins.

RESULTS

Daunorubicin induced apoptosis in all leukemic cell lines, but with different levels and duration of response. Both apoptosis levels and caspase activity increased after four hours recovery then declined in CCRF-CEM and MOLT-4 cells. However, SUP-B15 cells displayed initially comparable levels but remained elevated over the 24 h assessment period. Changes in mitochondrial membrane potential occurred in both MOLT-4 and CCRF-CEM cells but not in SUP-B15 cells. Expression of apoptotic proteins, including Bcl-2, Bax, caspase 3 and FADD, indicated that daunorubicin potentially induced both extrinsic and intrinsic apoptosis in both CCRF-CEM and MOLT-4 cells, but only extrinsic apoptosis in SUP-B15 cells.

CONCLUSIONS

This study describes variations in sensitivities and timing of apoptotic responses in different leukaemia cell lines. These differences could be attributed to the lack of functional p53 in coordinating the cells response following cytotoxic treatment with daunorubicin, which appears to delay apoptosis and utilises alternative signalling mechanisms that need to be further explored.

The multi-kinase inhibitor TG02 induces apoptosis and blocks B-cell receptor signaling in chronic lymphocytic leukemia through dual mechanisms of action

The constitutive activation of B-cell receptor (BCR) signaling, together with the overexpression of the Bcl-2 family anti-apoptotic proteins, represents two hallmarks of chronic lymphocytic leukemia (CLL) that drive leukemia cell proliferation and sustain their survival. TG02 is a small molecule multi-kinase inhibitor that simultaneously targets both of these facets of CLL pathogenesis. First, its inhibition of cyclin-dependent kinase 9 blocked the activation of RNA polymerase II and transcription. This led to the depletion of Mcl-1 and rapid induction of apoptosis in the primary CLL cells. This mechanism of apoptosis was independent of CLL prognostic factors or prior treatment history, but dependent on the expression of BAX and BAK. Second, TG02, which inhibits the members of the BCR signaling pathway such as Lck and Fyn, blocked BCR-crosslinking-induced activation of NF-κB and Akt, indicating abrogation of BCR signaling. Finally, the combination of TG02 and ibrutinib demonstrated moderate synergy, suggesting a future combination of TG02 with ibrutinib, or use in patients that are refractory to the BCR antagonists. Thus, the dual inhibitory activity on both the CLL survival pathway and BCR signaling identifies TG02 as a unique compound for clinical development in CLL and possibly other B cell malignancies.

Co-Operativity between MYC and BCL-2 Pro-Survival Proteins in Cancer

B-Cell Lymphoma 2 (BCL-2), c-MYC and related proteins are arguably amongst the most widely studied in all of biology. Every year there are thousands of papers reporting on different aspects of their biochemistry, cellular and physiological mechanisms and functions. This plethora of literature can be attributed to both proteins playing essential roles in the normal functioning of a cell, and by extension a whole organism, but also due to their central role in disease, most notably, cancer. Many cancers arise due to genetic lesions resulting in deregulation of both proteins, and indeed the development and survival of tumours is often dependent on co-operativity between these protein families. In this review we will discuss the individual roles of both proteins in cancer, describe cancers where co-operativity between them has been well-characterised and finally, some strategies to target these proteins therapeutically.

MCL-1 inhibitors, fast-lane development of a new class of anti-cancer agents

Cell death escape is one of the most prominent features of tumor cells and closely linked to the dysregulation of members of the Bcl-2 family of proteins. Among those, the anti-apoptotic family member myeloid cell leukemia-1 (MCL-1) acts as a master regulator of apoptosis in various human malignancies. Irrespective of its unfavorable structure profile, independent research efforts recently led to the generation of highly potent MCL-1 inhibitors that are currently evaluated in clinical trials. This offers new perspectives to target a so far undruggable cancer cell dependency. However, a detailed understanding about the tumor and tissue type specific implications of MCL-1 are a prerequisite for the optimal (i.e., precision medicine guided) use of this novel drug class. In this review, we summarize the major functions of MCL-1 with a special focus on cancer, provide insights into its different roles in solid vs. hematological tumors and give an update about the (pre)clinical development program of state-of-the-art MCL-1 targeting compounds. We aim to raise the awareness about the heterogeneous role of MCL-1 as drug target between, but also within tumor entities and to highlight the importance of rationale treatment decisions on a case by case basis.

Harrison C, Eswaran J, Soundararajan M. DAP Kinase-Related Apoptosis-Inducing Protein Kinase 2 (DRAK2) Is a Key Regulator and Molecular Marker in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in the Western World and it is characterized by a marked degree of clinical heterogeneity. An impaired balance between pro- and anti-apoptotic stimuli determines chemorefractoriness and outcome. The low proliferation rate of CLL cells indicates that one of the primary mechanisms involved in disease development may be an apoptotic failure. Here, we study the clinical and functional significance of DRAK2, a novel stress response kinase that plays a critical role in apoptosis, T-cell biology, and B-cell activation in CLL. We have analyzed CLL patient samples and showed that low expression levels of DRAK2 were significantly associated with unfavorable outcome in our CLL cohort. DRAK2 expression levels showed a positive correlation with the expression of DAPK1, and TGFBR1. Consistent with clinical data, the downregulation of DRAK2 in MEC-1 CLL cells strongly increased cell viability and proliferation. Further, our transcriptome data from MEC-1 cells highlighted MAPK, NF-κB, and Akt and as critical signaling hubs upon DRAK2 knockdown. Taken together, our results indicate DRAK2 as a novel marker of CLL survival that plays key regulatory roles in CLL prognosis.

Neutralization of B-Cell Activating Factor (BAFF) by Belimumab Reinforces Small Molecule Inhibitor Treatment in Chronic Lymphocytic Leukemia

Simple Summary

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in Western countries. Despite the substantial progress achieved by the recent introduction of the novel small molecule inhibitors idelalisib, ibrutinib and venetoclax in CLL treatment, therapy resistance occurs frequently and the disease so far remains incurable. In the present study we report that BAFF, a member of the TNF protein family, protects CLL cells from treatment-induced cell death. In turn, the therapeutic effects of idelalisib, ibrutinib and venetoclax can be reinforced by neutralizing BAFF with belimumab, an antibody which presently is clinically approved for treatment of systemic lupus erythematosus. Based on the data presented in this study, a clinical study to evaluate whether drug repurposing of belimumab for BAFF neutralization can serve to improve response to small molecule inhibitor treatment in CLL is in preparation.

Abstract

The introduction of idelalisib, ibrutinib and venetoclax for treatment of chronic lymphocytic leukemia (CLL) has greatly improved long term survival of patients. However, many patients do not achieve complete remission and suffer from development of resistance upon treatment with these small molecule inhibitors. Here we report that the TNF family member B-cell activating factor (BAFF) mediates resistance of CLL cells to idelalisib, ibrutinib and venetoclax by sustaining survival and preventing apoptosis of the malignant B cells as revealed by analysis of cellular ATP levels and mitochondrial membrane integrity as well as caspase activation, respectively. As BAFF also plays a prominent role in autoimmune diseases, the BAFF-neutralizing antibody belimumab was developed and approved for treatment of systemic lupus erythematosus (SLE). When we employed belimumab in the context of CLL treatment with idelalisib, ibrutinib and venetoclax, BAFF neutralization was found to significantly increase the sensitivity of the leukemic cells to all three small molecule inhibitors. Notably, BAFF neutralization proved to be beneficial independently of clinical stage according to Binet and Rai or IgVH mutational status. Our results identify drug repurposing of belimumab for neutralization of BAFF to complement small molecule inhibitor treatment as a promising therapeutic approach in CLL that is presently undergoing clinical evaluation.

Loss of FBXW7-mediated degradation of BRAF elicits resistance to BET inhibitors in adult T cell leukemia cells

Background

Human T cell leukemia virus type 1 (HTLV-1)-associated adult T cell leukemia (ATL) has a very poor prognosis with a median survival of 8 months and a 4-year overall survival of 11% for acute ATL. Present treatment options are limited and there is no curative therapy for ATL. Ubiquitin ligase FBXW7 is commonly mutated or functionally inactivated in human cancers. Consistent with the notion that FBXW7 controls the degradation of many oncoproteins, loss of FBXW7 has been linked to increased drug resistance or sensitivity in cancer cells.

Method

In this study, we have characterized FBXW7 mutants previously identified in HTLV-I-infected ATL patient samples. TET-inducible ATL cells carrying wild type or mutated FBXW7 were analyzed for target degradation and for drug sensitivity.

Results

Our results demonstrate that mutations in FBXW7 can selectively disrupt ubiquitination and proteasome degradation of target proteins: c-MYC, cyclin E and MCL1. Both c-MYC and MYCN were highly expressed in uncultured ATL patient’s samples and ATL-derived cell lines; and ATL cells demonstrated sensitivity to BET inhibitors in vitro and in vivo. High-throughput reverse phase protein array revealed BRAF as a novel target of FBXW7 and further experiments showed that mutations in FBXW7 preventing degradation of BRAF provided resistance to BET inhibitors. In contrast to R465, hot spot FBXW7 mutations at R505C retained degradation of BRAF but not NOTCH1, c-MYC, cyclin E, or MCL1. Finally, a combination therapy using BET inhibitors along with a BRAF or an ERK inhibitor prevented tumor cell resistance and growth.

Conclusion

Our results suggest that FBXW7 status may play an important role in drug therapy resistance of cancer cells. Genetic characterization of FBXW7 may be one factor included in future personalized cancer treatment identification.

Targeting microRNA in hematologic malignancies

PURPOSE OF REVIEW

MiRNAs are critical regulators for gene expression. Numerous studies have revealed how miRNAs contribute to the pathogenesis of hematologic malignancies.

RECENT FINDINGS

The identification of novel miRNA regulatory factors and pathways crucial for miRNA dysregulation has been linked to hematologic malignancies. miRNA expression profiling has shown their potential to predict outcomes and treatment responses. Recently, targeting miRNA biogenesis or pathways has become a promising therapeutic strategy with recent miRNA-therapeutics being developed.

SUMMARY

We provide a comprehensive overview of the role of miRNAs for diagnosis, prognosis, and therapeutic potential in hematologic malignancies.

BDNF belongs to the nurse-like cell secretome and supports survival of B chronic lymphocytic leukemia cells

Evading apoptosis and sustained survival signaling pathways are two central hallmarks of B-cell chronic lymphocytic leukemia (B-CLL) cells. In this regard, nurse-like cells (NLC), the monocyte-derived type 2 macrophages, deliver stimulatory signals via B-cell activating factor (BAFF), a proliferation-inducing ligand (APRIL), and the C-X-C Motif Chemokine Ligand 12 (CXCL12). Previously, we demonstrated that brain-derived neurotrophic factor (BDNF) protects B-CLL cells from spontaneous apoptosis by activating the oncogenic complex NTSR2-TrkB (neurotensin receptor 2-tropomyosin-related kinase receptor B), only overexpressed in B-CLL cells, inducing anti-apoptotic protein Bcl-2 (B-cell lymphoma 2) expression and Src kinase survival signaling pathways. Herein, we demonstrate that BDNF belongs to the NLC secretome and promotes B-CLL survival. This was demonstrated in primary B-CLL co-cultured with their autologous NLC, compared to B-CLL cells cultured alone. Inhibition of BDNF in co-cultures, enhances B-CLL apoptosis, whereas its exogenous recombinant activates pro-survival pathways in B-CLL cultured alone (i.e. Src activation and Bcl-2 expression), at a higher level than those obtained by the exogenous recombinant cytokines BAFF, APRIL and CXCL12, the known pro-survival cytokines secreted by NLC. Together, these results showed that BDNF release from NLC trigger B-CLL survival. Blocking BDNF would support research strategies against pro-survival cytokines to limit sustained B-CLL cell survival.

Unprecedented formation of palladium(II)-pyrazole based thiourea from chromone thiosemicarbazone and [PdCl2(PPh3)2]: Interaction with biomolecules and apoptosis through mitochondrial signaling pathway

Two novel pyrazole based thiourea palladium(II) complexes, [PdCl(PPh₃)(C₉H₈NO₂S-pz)] (1) and [PdCl(PPh₃)(C₁₄H₁₀NO₂S-pz)] (2) [pz = pyrazole (C₃H₂N₂)] have been obtained unexpectedly from chromone thiosemicarbazones (L1 and L2) and [PdCl₂(PPh₃)₂]. The compounds have been fully characterized by physicochemical studies. The single crystal X-ray diffraction and spectral studies revealed square planar geometry for the complexes. The conversion of chromone thiosemicarbazone into pyrazole based thiourea might have happened through coordination to palladium(II) ion after enolization, Michael addition and ring opening followed by cyclization. To the best of our knowledge, this is the first report for the conversion of chromone thiosemicarbazone into pyrazole based thiourea moiety. Plausible mechanism was proposed based on the spectroscopic studies. Calf thymus (CT) DNA binding of the compounds was explored using various spectroscopic and molecular docking methods. DNA cleavage studies suggested that complexes 1 and 2 had the capacity to cleave the supercoiled DNA (pUC19) to its naked form. In vitro cytotoxic property of the ligands and complexes has been evaluated against three human cancer cells such as A549, HepG-2 and U937. Complex 2 exhibited potent cytotoxic activity against HepG-2 cells with the IC₅₀ value of 10.4 μM. In addition, mechanistic studies showed that complex 2 induced apoptosis through mitochondrial signaling pathway in HepG-2 cells. Beneficially, complex 2 showed less toxicity against human lung (IMR90) normal cells and hence it emerges as a potential candidate for further studies.

Current perspectives on targeting PIM kinases to overcome mechanisms of drug resistance and immune evasion in cancer

PIM kinases are a class of serine/threonine kinases that play a role in several of the hallmarks of cancer including cell cycle progression, metabolism, inflammation and immune evasion. Their constitutively active nature and unique catalytic structure has led them to be an attractive anticancer target through the use of small molecule inhibitors. This review highlights the enhanced activity of PIM kinases in cancer that can be driven by hypoxia in the tumour microenvironment and the important role that aberrant PIM kinase activity plays in resistance mechanisms to chemotherapy, radiotherapy, anti-angiogenic therapies and targeted therapies. We highlight an interaction of PIM kinases with numerous major oncogenic players, including but not limited to, stabilisation of p53, synergism with c-Myc, and notable parallel signalling with PI3K/Akt. We provide a comprehensive overview of PIM kinase's role as an escape mechanism to targeted therapies including PI3K/mTOR inhibitors, MET inhibitors, anti-HER2/EGFR treatments and the immunosuppressant rapamycin, providing a rationale for co-targeting treatment strategies for a more durable patient response. The current status of PIM kinase inhibitors and their use as a combination therapy with other targeted agents, in addition to the development of novel multi-molecularly targeted single therapeutic agents containing a PIM kinase targeting moiety are discussed.

Emerging treatment options for patients with p53-pathway-deficient CLL

Over the past 40 years, p53 has been the most widely studied protein in cancer biology. Originally thought to be an oncogene due to its stabilization in many cancers, it is now considered to be one of the most critical tumor suppressors in a cell's ability to combat neoplastic transformation. Due to its critical roles in apoptosis, cell-cycle arrest, and senescence, TP53 deletions and mutations are commonly observed and are often a portent of treatment failures and poor clinical outcomes. This is particularly true in chronic lymphocytic leukemia (CLL), as patients with p53 alterations have historically had dismal outcomes. As such, the tremendous efforts made to better understand the functions of p53 in CLL have contributed substantially to recent advances in treating patients with p53-pathway-deficient CLL.

Can ELABELA be a novel target in the treatment of chronic lymphocytic leukaemia?

BACKGROUND

It has been shown that bcl2, bcl-XL and mcl-1 protein levels are high in chronic lymphocytic leukemia cells, and resultantly, apoptosis does not occur chronic lymphocytic leukemia cells. Apelin and apela (ELABELA/ELA/Toddler) are two peptide ligands for a class A G-protein coupled receptor called apelin receptor. Studies have shown that ELA inhibits apoptosis by inhibiting apoptotic proteins and activating anti-apoptotic proteins. Proteins and genes involved in apoptosis are valuable for targeted cancer therapy. We hypothesized that serum levels may be increased in patients with chronic lymphocytic leukemia based on the antiapoptotic effect of ELA. We compared serum ELABELA levels of healthy volunteers and patients with chronic lymphocytic leukemia. We aimed to draw attention to a new molecule worthy of research in targeted cancer treatment.

METHODS

Forty two untreated CLL patients and 41 healthy volunteers were included in the study. Serum ELA levels were measured by using enzyme-linked immunosorbent assay kits (Dhanghai Sunred Biological Technology co. Ltd), automated ELISA reader (Thermo Scientific, FİNLAND) and computer program (Scanlt for Multiscan F.C.2.5.1) in accordance with the manufacturer's instructions. Statistical analysis was done by Statistical Package for Social Sciences for Windows 20 (IBM SPSS Inc., Chicago, IL) ve MedCalc programs. ELA and variables related to CLL were correlated with Spearman correlation anlysis test. ROC analysis and Youden index method were used to determine a cut off point for ELA. All p-values were 2-sided with statistical significance at 0.05 alpha levels.

RESULTS

In our study, we found that serum ELA levels were significantly higher in patients with CLL.

CONCLUSIONS

This study highlights that ELA targeting may be a potential therapeutic option for treating CLL.

Cellular demolition: Proteins as molecular players of programmed cell death

Apoptosis, a well-characterized and regulated cell death programme in eukaryotes plays a fundamental role in developing or later-life periods to dispose of unwanted cells to maintain typical tissue architecture, homeostasis in a spatiotemporal manner. This silent cellular death occurs without affecting any neighboring cells/tissue and avoids triggering of immunological response. Furthermore, diminished forms of apoptosis result in cancer and autoimmune diseases, whereas unregulated apoptosis may also lead to the development of a myriad of neurodegenerative diseases. Unraveling the mechanistic events in depth will provide new insights into understanding physiological control of apoptosis, pathological consequences of abnormal apoptosis and development of novel therapeutics for diseases. Here we provide a brief overview of molecular players of programmed cell death with discussion on the role of caspases, modifications, ubiquitylation in apoptosis, removal of the apoptotic body and its relevance to diseases.

Evolution of CLL treatment - from chemoimmunotherapy to targeted and individualized therapy

During the past 5 years, a number of highly active novel agents, including kinase inhibitors targeting BTK or PI3Kδ, an antagonist of the antiapoptotic protein BCL-2, and new anti-CD20 monoclonal antibodies, have been added to the therapeutic armamentarium for patients with chronic lymphocytic leukaemia (CLL). In these exciting times, care is needed to optimally integrate these novel agents into the traditional treatment algorithm without overlooking or compromising the benefits of established treatments, especially chemoimmunotherapy. A more personalized approach to CLL therapy that takes into account individual risk factors, patient characteristics, and their treatment preferences is now possible. Herein, we discuss the biological basis for the novel therapeutic agents and outline not only the major advantages of these agents over traditional therapies but also their adverse effects and the rationale for continued use of older versus newer types of therapy for selected patients with CLL. We conclude by providing recommendations for an individualized therapy approach for different populations of patients with CLL.

Role of Calcium Signaling in GA101-Induced Cell Death in Malignant Human B Cells

GA101/obinutuzumab is a novel type II anti-CD20 monoclonal antibody (mAb), which is more effective than rituximab (RTX) in preclinical and clinical studies when used in combination with chemotherapy. Ca²⁺ signaling was shown to play a role in RTX-induced cell death. This report concerns the effect of GA101 on Ca²⁺ signaling and its involvement in the direct cell death induced by GA101. We reveal that GA101 triggered an intracellular Ca²⁺ increase by mobilizing intracellular Ca²⁺ stores and activating Orai1-dependent Ca²⁺ influx in non-Hodgkin lymphoma cell lines and primary B-Cell Chronic Lymphocytic Leukemia (B-CLL) cells. According to the cell type, Ca²⁺ was mobilized from two distinct intracellular compartments. In Raji, BL2, and B-CLL cells, GA101 induced a Ca²⁺ release from lysosomes, leading to the subsequent lysosomal membrane permeabilization and cell death. Inhibition of this calcium signaling reduced GA101-induced cell death in these cells. In SU-DHL-4 cells, GA101 mobilized Ca²⁺ from the endoplasmic reticulum (ER). Inhibition of ER replenishment, by blocking Orai1-dependent Ca²⁺ influx, led to an ER stress and unfolded protein response (UPR) which sensitized these cells to GA101-induced cell death. These results revealed the central role of Ca²⁺ signaling in GA101’s action mechanism, which may contribute to designing new rational drug combinations improving its clinical efficacy.

A delicate balance - The BCL-2 family and its role in apoptosis, oncogenesis, and cancer therapeutics

Evasion of apoptosis is fundamental to the pathogenesis of cancer. Members of the B-cell Lymphoma 2 (BCL-2) protein family are key pro- and anti-apoptotic regulators, and in healthy cells are held in a fine, delicate balance - perturbations of which may tip a cell irreversibly towards cellular death or, conversely, allow a cell to permanently escape apoptosis and immortalize itself as a malignant clone. The restoration of this balance or, indeed, adjustment in favor of apoptosis via manipulation of the BCL-2 family, is a promising area in the realm of molecular therapeutics, and one in which breathtaking advances are currently being made. The purpose of this review is to outline the role of the BCL-2 family in apoptosis, to contrast its optimal functioning with those disruptions seen in malignancy, and to provide an overview of the medications both presently available and currently under development which selectively target members of this family.

Progesterone ameliorates the endometrial polyp by modulating the signaling pathway of Wnt and β-catenin via regulating the expression of H19 and miR-152

BACKGROUND

MicroRNAs and long noncoding RNAs are believed to play important roles in the pathogenesis of various diseases. This study aimed to explore the potential mechanism of the involvement of H19 and miR-152 in an endometrial polyp.

METHODS

Luciferase assay was conducted to determine the effect of progesterone. Real-time polymerase chain reaction (PCR) and western blot were performed to detect the influence of progesterone on miR-152 and Wnt1. MTT assay and flow cytometry (FCM) were utilized to detect the effect of progesterone on cell proliferation and apoptosis. In silicon analysis, luciferase assay, real-time PCR, and immunohistochemistry (IHC) were performed to explore the regulatory relationship between H19 and miR-152 or miR-152 and Wnt1.

RESULTS

Progesterone dose-dependently increased the H19 expression level through driving the promoter efficiency of H19. Then, progesterone upregulated Wnt1 level and downregulated miR-152 in a dose-dependent manner in ECC1 and HEC1A cells. Administration of progesterone inhibited cell viability and promoted cell apoptosis. H19 negatively regulated miR-152 expression by binding to miR-152. Furthermore, Wnt1 was identified as a virtual target gene of miR-152 and was inhibited by miR-152. Progesterone receptors mRNA and miR-152 were lowly expressed in participants with an endometrial polyp, while the levels of H19 and Wnt1 were much higher in the endometrial polyp group compared with normal controls. H19 negatively regulated miR-152 and miR-152 negatively regulated Wnt1, with the negative correlation coefficients being -0.500 and -0.500, respectively. Using IHC, it was found that Wnt1 and Bcl-2 protein were highly expressed in the endometrial polyp group compared with normal controls.

CONCLUSION

The results suggested that H19 was associated with endometrial polyp via mediating cell proliferation and apoptosis.

SLAMF receptors on normal and malignant B cells

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

Critical role of tristetraprolin and AU-rich element RNA-binding protein 1 in the suppression of cancer cell growth by globular adiponectin

Adiponectin exhibits potent antitumor activities. Herein, we examined the molecular mechanisms underlying suppression of tumor growth by globular adiponectin (gAcrp). We demonstrated that gAcrp suppressed B‐cell lymphoma 2 (Bcl‐2) expression, an anti‐apoptotic gene, by inducing its mRNA destabilization, which was accompanied with a decrease in cell viability and increased caspase‐3 activity in hepatic cancer cells. In addition, gAcrp increased expression of tristetraprolin (TTP) and AU‐rich element RNA‐binding protein 1 (AUF1), which are mRNA stability regulatory proteins. Moreover, gAcrp‐induced suppression of Bcl‐2 expression was abrogated by knockdown of TTP or AUF1. These data indicate that gAcrp induces apoptosis of hepatic cancer cells by TTP‐ and AUF1‐mediated Bcl‐2 mRNA destabilization, and further suggest that TTP and AUF1 are novel targets mediating the antitumor activity of adiponectin.

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.

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.

Targeting BCL-2 regulated apoptosis in cancer

The ability of a cell to undergo mitochondrial apoptosis is governed by pro- and anti-apoptotic members of the BCL-2 protein family. The equilibrium of pro- versus anti-apoptotic BCL-2 proteins ensures appropriate regulation of programmed cell death during development and maintains organismal health. When unbalanced, the BCL-2 family can act as a barrier to apoptosis and facilitate tumour development and resistance to cancer therapy. Here we discuss the BCL-2 family, their deregulation in cancer and recent pharmaceutical developments to target specific members of this family as cancer therapy.

Role of Mitochondria-Associated ER Membranes in Calcium Regulation in Cancer-Specific Settings

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are highly specialized subcellular compartments that are shaped by ER subdomains juxtaposed to mitochondria but are biochemically distinct from pure ER and pure mitochondria. MAMs are enriched in enzymes involved in lipid synthesis and transport, channels for calcium transfer, and proteins with oncogenic/oncosuppressive functions that modulate cell signaling pathways involved in physiological and pathophysiological processes. The term "cancer" denotes a group of disorders that result from uncontrolled cell growth driven by a mixture of genetic and environmental components. Alterations in MAMs are thought to account for the onset as well as the progression and metastasis of cancer and have been a focus of investigation in recent years. In this review, we present the current state of the art regarding MAM-resident proteins and their relevance, alterations, and deregulating functions in different types of cancer from a cell biology and clinical perspective.

Pharmacodynamics and proteomic analysis of acalabrutinib therapy: similarity of on-target effects to ibrutinib and rationale for combination therapy

Acalabrutinib, a highly selective Bruton's tyrosine kinase inhibitor, is associated with high overall response rates and durable remission in previously treated chronic lymphocytic leukemia (CLL); however, complete remissions were limited. To elucidate on-target and pharmacodynamic effects of acalabrutinib, we evaluated several laboratory endpoints, including proteomic changes, chemokine modulation and impact on cell migration. Pharmacological profiling of samples from acalabrutinib-treated CLL patients was used to identify strategies for achieving deeper responses, and to identify additive/synergistic combination regimens. Peripheral blood samples from 21 patients with relapsed/refractory CLL in acalabrutinib phase I (100-400 mg/day) and II (100 mg BID) clinical trials were collected prior to and on days 8 and 28 after treatment initiation and evaluated for plasma chemokines, reverse phase protein array, immunoblotting and pseudoemperipolesis. The on-target pharmacodynamic profile of acalabrutinib in CLL lymphocytes was comparable to ibrutinib in measures of acalabrutinib-mediated changes in CCL3/CCL4 chemokine production, migration assays and changes in B-cell receptor signaling pathway proteins and other downstream survival proteins. Among several CLL-targeted agents, venetoclax, when combined with acalabrutinib, showed optimal complementary activity in vitro, ex vivo and in vivo in TCL-1 adoptive transfer mouse model system of CLL. These findings support selective targeting and combinatorial potential of acalabrutinib.

Managing Patients With TP53-Deficient Chronic Lymphocytic Leukemia

Patients with chronic lymphocytic leukemia (CLL) having a chromosomal loss on the short arm of chromosome 17 including the TP53 gene locus (17p deletion) and/or having mutations in TP53 have a short overall survival and, until recently, limited treatment options. The recent introduction of two novel substance classes, B-cell receptor inhibitors and BH3 mimetics, into CLL treatment has provided enormous clinical progress in this previously difficult-to-treat patient subgroup characterized by high risk for treatment failure with standard chemoimmunotherapy and rapid disease progression. Compounds now approved for the treatment of TP53-deficient CLL are the two B-cell receptor inhibitors ibrutinib and idelalisib and the BH3 mimetic venetoclax. All three compounds were approved on the basis of favorable response rates that, importantly, revealed no differences between TP53-competent and TP53-deficient CLL cases. Using these compounds, longer-lasting remissions in patients with TP53-deficient CLL could be demonstrated for the first time. Whether TP53 alterations will maintain their significance as adverse prognostic factors in treatment strategies involving novel compounds needs to be assessed. This review provides an overview of current treatment options for 17p-deleted/ TP53-mutated CLL, including those compounds that are already approved by the US Food and Drug Administration or are under advanced clinical investigation. Available clinical trial data are discussed, as is the use of novel targeted treatment options in the context of transplant strategies, and an algorithm for off-study treatment of 17p-deficient CLL is suggested.

Nickel(II) bis(isatin thiosemicarbazone) complexes induced apoptosis through mitochondrial signaling pathway and G0/G1 cell cycle arrest in IM-9 cells

Three novel complexes (1, 3 and 4) ligating N-substituted isatin thiosemicarbazone derivatives have been synthesized and their structural and biological characteristics have been compared with those of the known analogs (2, 5-7 and 8). In addition, the structure of the representative ligands (L1, L3 and L4) and complex (4) was confirmed by single crystal X-ray diffraction method. All the complexes (1-8) were assessed for their cytotoxic property against a panel of four human cancer cells such as HepG-2 (liver), MOLM-14 (acute monocytic leukemia), U937 (histiocytic lymphoma). and IM-9 (myeloma). Complex 4 exhibited prominent cytotoxic property against MOLM-14, U937 and IM-9 cell lines. Moreover, the results were compared with the well-known anticancer drugs like doxorubicin, cisplatin and daunorubicin. Besides, complex 4 enhanced the apoptotic cell death in IM-9 cell line and induced cell cycle arrest at G1 phase. Western blot analysis revealed the down-regulation of Bcl-2 (b-cell lymphoma-2), up-regulation of Bax (bcl-2 associated X protein), release of cytochrome c and activation of caspases-3 in IM-9 cells by complex 4. Importantly, complex 4 was not toxic to the normal Vero cell line (IC₅₀ > 300 μM). In addition, complex 4 showed the concentration dependent cleavage of supercoiled (SC) DNA to its nicked circular (NC) form.

Obatoclax impairs lysosomal function to block autophagy in cisplatin-sensitive and -resistant esophageal cancer cells

Obatoclax, a pan-inhibitor of anti-apoptotic Bcl-2 proteins, exhibits cytotoxic effect on cancer cells through both apoptosis-dependent and -independent pathways. Here we show that obatoclax caused cytotoxicity in both cisplatin-sensitive and -resistant esophageal cancer cells. Although obatoclax showed differential apoptogenic effects in these cells, it consistently blocked autophagic flux, which was evidenced by concomitant accumulation of LC3-II and p62. Obatoclax was trapped in lysosomes and induced lysosome clustering. Obatoclax also substantially reduced the expression of lysosomal cathepsins B, D and L. Moreover, cathepsin knockdown was sufficient to induce cytotoxicity, connecting lysosomal function to cell viability. Consistent with the known function of autophagy, obatoclax caused the accumulation of polyubiquitinated proteins and showed synergy with proteasome inhibition. Taken together, our studies unveiled impaired lysosomal function as a novel mechanism whereby obatoclax mediates its cytotoxic effect in esophageal cancer cells.

Revisiting the role of interleukin-8 in chronic lymphocytic leukemia

The proliferation and survival of malignant B cells in chronic lymphocytic leukemia (CLL) depend on signals from the microenvironment in lymphoid tissues. Among a plethora of soluble factors, IL-8 has been considered one of the most relevant to support CLL B cell progression in an autocrine fashion, even though the expression of IL-8 receptors, CXCR1 and CXCR2, on leukemic B cells has not been reported. Here we show that circulating CLL B cells neither express CXCR1 or CXCR2 nor they respond to exogenous IL-8 when cultured in vitro alone or in the presence of monocytes/nurse-like cells. By intracellular staining and ELISA we show that highly purified CLL B cells do not produce IL-8 spontaneously or upon activation through the B cell receptor. By contrast, we found that a minor proportion (<0.5%) of contaminating monocytes in enriched suspensions of leukemic cells might be the actual source of IL-8 due to their strong capacity to release this cytokine. Altogether our results indicate that CLL B cells are not able to secrete or respond to IL-8 and highlight the importance of methodological details in in vitro experiments.

Neurotensin receptor type 2 protects B-cell chronic lymphocytic leukemia cells from apoptosis

B-cell chronic lymphocytic leukemia (B-CLL) cells are resistant to apoptosis, and consequently accumulate to the detriment of normal B cells and patient immunity. Because current therapies fail to eradicate these apoptosis-resistant cells, it is essential to identify alternative survival pathways as novel targets for anticancer therapies. Overexpression of cell-surface G protein-coupled receptors drives cell transformation, and thus plays a critical role in malignancies. In this study, we identified neurotensin receptor 2 (NTSR2) as an essential driver of apoptosis resistance in B-CLL. NTSR2 was highly expressed in B-CLL cells, whereas expression of its natural ligand, neurotensin (NTS), was minimal in both B-CLL cells and patient plasma. Surprisingly, NTSR2 remained in a constitutively active phosphorylated state, caused not by a mutation-induced gain-of-function but rather by an interaction with the oncogenic tyrosine kinase receptor TrkB. Functional and biochemical characterization revealed that the NTSR2-TrkB interaction acts as a conditional oncogenic driver requiring the TrkB ligand brain-derived neurotrophic factor (BDNF), which unlike NTS is highly expressed in B-CLL cells. Together, NTSR2, TrkB and BDNF induce autocrine and/or paracrine survival pathways that are independent of mutation status and indolent or progressive disease course. The NTSR2-TrkB interaction activates survival signaling pathways, including the Src and AKT kinase pathways, as well as expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL. When NTSR2 was downregulated, TrkB failed to protect B-CLL cells from a drastic decrease in viability via typical apoptotic cell death, reflected by DNA fragmentation and Annexin V presentation. Together, our findings demonstrate that the NTSR2-TrkB interaction plays a crucial role in B-CLL cell survival, suggesting that inhibition of NTSR2 represents a promising targeted strategy for treating B-CLL malignancy.

Therapeutics targeting Bcl-2 in hematological malignancies

Members of the B-cell lymphoma 2 (BCL-2) gene family are attractive targets for cancer therapy as they play a key role in promoting cell survival, a long-since established hallmark of cancer. Clinical utility for selective inhibition of specific anti-apoptotic Bcl-2 family proteins has recently been realized with the Food and Drug Administration (FDA) approval of venetoclax (formerly ABT-199/GDC-0199) in relapsed chronic lymphocytic leukemia (CLL) with 17p deletion. Despite the impressive monotherapy activity in CLL, such responses have rarely been observed in other B-cell malignancies, and preclinical data suggest that combination therapies will be needed in other indications. Additional selective antagonists of Bcl-2 family members, including Bcl-X_L and Mcl-1, are in various stages of preclinical and clinical development and hold the promise of extending clinical utility beyond CLL and overcoming resistance to venetoclax. In addition to direct targeting of Bcl-2 family proteins with BH3 mimetics, combination therapies that aim at down-regulating expression of anti-apoptotic BCL-2 family members or restoring expression of pro-apoptotic BH3 family proteins may provide a means to deepen responses to venetoclax and extend the utility to additional indications. Here, we review recent progress in direct and selective targeting of Bcl-2 family proteins for cancer therapy and the search for rationale combinations.