Role of beta2 integrins in the prevention of apoptosis induction in chronic lymphocytic leukemia B cells

The Role of the Microenvironment and Cell Adhesion Molecules in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy whose progression largely depends on the lymph node and bone marrow microenvironment. Indeed, CLL cells actively proliferate in specific regions of these anatomical compartments, known as proliferation centers, while being quiescent in the blood stream. Hence, CLL cell adhesion and migration into these protective niches are critical for CLL pathophysiology. CLL cells are lodged in their microenvironment through a series of molecular interactions that are mediated by cellular adhesion molecules and their counter receptors. The importance of these adhesion molecules in the clinic is demonstrated by the correlation between the expression levels of some of them, in particular CD49d, and the prognostic likelihood. Furthermore, novel therapeutic agents, such as ibrutinib, impair the functions of these adhesion molecules, leading to an egress of CLL cells from the lymph nodes and bone marrow into the circulation together with an inhibition of homing into these survival niches, thereby preventing disease progression. Several adhesion molecules have been shown to participate in CLL adhesion and migration. Their importance also stems from the observation that they are involved in promoting, directly or indirectly, survival signals that sustain CLL proliferation and limit the efficacy of standard and novel chemotherapeutic drugs, a process known as cell adhesion-mediated drug resistance. In this respect, many studies have elucidated the molecular mechanisms underlying cell adhesion-mediated drug resistance, which have highlighted different signaling pathways that may represent potential therapeutic targets. Here, we review the role of the microenvironment and the adhesion molecules that have been shown to be important in CLL and their impact on transendothelial migration and cell-mediated drug resistance. We also discuss how novel therapeutic compounds modulate the function of this important class of molecules.

αvβ3 Integrin Expression and Mitogenic Effects by Thyroid Hormones in Chronic Lymphocytic Leukemia

Background: Chronic lymphocytic leukemia (CLL) is the most common adult leukemia. The thyroid hormones, T3 and T4, bind the αvβ3 integrin and activate phosphorylates ERK (pERK). These tumor-promoting actions were reported in a number of malignancies, but not in CLL. Methods: Primary cells from 22 CLL patients were verified for disease markers (CD5/CD19/CD23) and analyzed for αvβ3 by flow cytometry (FC), ImageStream, Western blots (WB), and immunohistochemistry (IHC) in archival bone marrow (BM, n = 6) and lymph node (LN, n = 5) tissues. Selected samples (n = 8) were incubated with T3 (1–100 nM) or T4 (0.1–10 µM) for 30 min, and the expression levels of αvβ3, pERK and PCNA (cell proliferation marker) were determined (WB). Results: αvβ3 was detected on the membrane of circulating CLL cells and in the BM but not in the LN. T3 and T4 enhanced αvβ3 protein levels in primary CLL cells. Similarly, pERK and PCNA were rapidly induced in response to T3 and T4 exposure. Conclusions: αvβ3 integrin is expressed on primary CLL cells and is induced by thyroid hormones. We further suggest that the hormones are mitogenic in these cells, presumably via αvβ3-mediated signaling.

EphrinA4 plays a critical role in α4 and αL mediated survival of human CLL cells during extravasation

A role of endothelial cells in the survival of CLL cells during extravasation is presently unknown. Herein we show that CLL cells but not normal B cells can receive apoptotic signals through physical contact with TNF-α activated endothelium impairing survival in transendothelial migration (TEM) assays. In addition, the CLL cells of patients having lymphadenopathy (LApos) show a survival advantage during TEM that can be linked to increased expression of α4 and αL integrin chains. Within this context, ephrinA4 expressed on the surface of CLL cells sequestrates integrins and inactivates them resulting in reduced adhesion and inhibition of apoptotic/survival signals through them. In agreement, ephrinA4 silencing resulted in increased survival of CLL cells of LApos patients but not LA neg patients. Similarly was observed when a soluble ephrinA4 isoform was added to TEM assays strongly suggesting that accumulation of this isoform in the serum of LApos patients could contribute to CLL cells dissemination and survival in vivo. In supporting, CLL lymphadenopathies showed a preferential accumulation of apoptotic CLL cells around high endothelial venules lacking ephrinA4. Moreover, soluble ephrinA4 isolated from sera of patients increased the number and viability of CLL cells recovered from the lymph nodes of adoptively transferred mice. Finally, we present evidence suggesting that soluble ephrinA4 mediated survival during TEM could enhance a transcellular TEM route of the CLL cells. Together these findings point to an important role of ephrinA4 in the nodal dissemination of CLL cells governing extravasation and survival.

Functional studies of chronic lymphocytic leukemia B cells expressing β2-integrin type complement receptors CR3 and CR4

The expression and role of CR3 (CD11b/CD18) and CR4 (CD11c/CD18) in B cells are not yet explored in contrast to myeloid cells, where these β₂-integrin type receptors are known to participate in various cellular functions, including phagocytosis, adherence and migration. Here we aimed to reveal the expression and role of CR3 and CR4 in human B cells. In B cells of healthy donors CR3 and CR4 are scarcely expressed. However, two patients with chronic lymphocytic leukemia (CLL) characterized by a peculiar immune-phenotype containing both CD5-positive and CD5-negative B cell populations made possible to study these molecules in distinct B cell subsets. We found that CD11b and CD11c were expressed on both CD5-positive and CD5-negative B cells, albeit to different extents. Our data suggest that these receptors are involved in spreading, since this activity of CpG-activated B cells on fibrinogen could be partially blocked by monoclonal antibodies specific for CD11b or CD11c. CpG-stimulation lead to proliferation of both CD5-positive and CD5-negative B cells of the patients with a less pronounced effect on the CD5-positive cells. In contrast to normal B cells, CLL B cells of both patients reacted to CpG-stimulation with robust IL-10 production. The concomitant, suboptimal stimulus via the BCR and TLR9 exerted either a synergistic enhancing effect or resulted in inhibition of proliferation and IL-10 production of patients' B cells. Our data obtained studying B cells of leukemic patients point to the role of CR3 and probably CR4 in the interaction of tumor cells with the microenvironment and suggest the involvement of IL-10 producing B cells in the pathologic process.

Proteome analysis of sheep B lymphocytes in the course of bovine leukemia virus-induced leukemia

Presented are the results of a study of the expression pattern of different proteins in the course of bovine leukemia virus-induced leukemia in experimental sheep and I discuss how the obtained data may be useful in gaining a better understanding of the pathogenesis of the disease, diagnosis, and for the selection of possible therapeutic targets. In cattle, the disease is characterized by life-long persistent lymphocytosis leading to leukemia/lymphoma in about 5% of infected animals. In sheep, as opposed to cattle, the course of the disease is always fatal and clinical symptoms usually occur within a three-year period after infection. For this reason, sheep are an excellent experimental model of retrovirus-induced leukemia. This model can be useful for human pathology, as bovine leukemia virus is closely related to human T-lymphotropic virus type 1. The data presented here provide novel insights into the molecular mechanisms of the bovine leukemia virus-induced tumorigenic process and indicate the potential marker proteins both for monitoring progression of the disease and as possible targets of pharmacological intervention. A study of the proteome of B lymphocytes from four leukemic sheep revealed 11 proteins with altered expression. Among them, cytoskeleton and intermediate filament proteins were the most abundant, although proteins belonging to the other functional groups, i.e. enzymes, regulatory proteins, and transcription factors, were also present. It was found that trypsin inhibitor, platelet factor 4, thrombospondin 1, vasodilator-stimulated phosphoprotein, fibrinogen alpha chain, zyxin, filamin-A, and vitamin D-binding protein were downregulated, whereas cleavage and polyadenylation specificity factor subunit 5, non-POU domain-containing octamer-binding protein and small glutamine-rich tetratricopeptide repeat-containing protein alpha were upregulated. Discussed are the possible mechanisms of their altered expression and its significance in the bovine leukemia virus-induced leukemogenic process. Impact statement The submitted manuscript provides new data on the molecular mechanisms of BLV-induced tumorigenic process indicating the potential marker proteins both for monitoring the progression of the disease and as possible targets of pharmacological intervention. This is to my knowledge the first study of the proteome of the transformed lymphocytes in the course of bovine leukemia virus-induced leukemia in susceptible animals. BLV can be considered as useful model for related human pathogen - HTLV-1, another member of the deltaretrovirus genus evolutionary closely related to BLV. Information gathered in this study can be useful to speculate on possible shared mechanisms of deltaretrovirus-induced carcinogenesis.

Potential of the dietary antioxidants resveratrol and curcumin in prevention and treatment of hematologic malignancies

Despite considerable improvements in the tolerance and efficacy of novel chemotherapeutic agents, the mortality of hematological malignancies is still high due to therapy relapse, which is associated with bad prognosis. Dietary polyphenolic compounds are of growing interest as an alternative approach, especially in cancer treatment, as they have been proven to be safe and display strong antioxidant properties. Here, we provide evidence that both resveratrol and curcumin possess huge potential for application as both chemopreventive agents and anticancer drugs and might represent promising candidates for future treatment of leukemia. Both polyphenols are currently being tested in clinical trials. We describe the underlying mechanisms, but also focus on possible limitations and how they might be overcome in future clinical use – either by chemically synthesized derivatives or special formulations that improve bioavailability and pharmacokinetics.

Curcumin inhibits prosurvival pathways in chronic lymphocytic leukemia B cells and may overcome their stromal protection in combination with EGCG

PURPOSE

Chronic lymphocytic leukemia (CLL) is incurable with current chemotherapy treatments. Curcumin (diferuloylmethane), an active ingredient in the spice turmeric, inhibits tumor metastasis, invasion, and angiogenesis in tumor cell lines. We evaluated the effects of curcumin on the viability of primary CLL B cells and its ability to overcome stromal mediated protection.

EXPERIMENTAL DESIGN

The in vitro effect of curcumin on primary CLL B cells was evaluated using fluorescence activated cell sorter analysis and Western blotting. For some experiments, CLL B cells were cocultured with human stromal cells to evaluate the effects of curcumin on leukemia cells cultured in their microenvironment. Finally, the effect of curcumin in combination with the green tea extract epigallocatechin-3 gallate (EGCG) was evaluated.

RESULTS

Curcumin induced apoptosis in CLL B cells in a dose-dependent (5-20 micromol/L) manner and inhibited constitutively active prosurvival pathways, including signal transducers and activators of transcription 3 (STAT3), AKT, and nuclear factor kappaB. Moreover, curcumin suppressed expression of the anti-apoptotic proteins Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP), and up-regulated the pro-apoptotic protein BIM. Coculture of CLL B cells with stromal cells resulted in elevated levels of STAT3, increased expression of Mcl-1 and XIAP, and decreased sensitivity to curcumin. When curcumin was administered simultaneously with EGCG, antagonism was observed for most patient samples. In contrast, sequential administration of these agents led to substantial increases in CLL B-cell death and could overcome stromal protection.

CONCLUSIONS

Curcumin treatment was able to overcome stromal protection of CLL B cells on in vitro testing and to synergize with EGCG when administered in a sequential fashion. Additional evaluation of curcumin as a potential therapeutic agent for treatment of CLL seems warranted.

CD49d expression is an independent predictor of overall survival in patients with chronic lymphocytic leukaemia: a prognostic parameter with therapeutic potential

In vitro studies have demonstrated that surface expression of CD49d on chronic lymphocytic leukaemia (CLL) B cells facilitates leukaemic cell-stromal interactions by binding to fibronectin. This interaction reduces both spontaneous and drug-induced apoptosis. The present study measured CD49d expression by flow cytometry in a cohort of untreated CLL patients previously accrued to a prospective observational study and evaluated the relationship with overall survival (OS). Among the 158 CLL patients tested, the percentage of leukaemic B cells expressing CD49d ranged from 0 to 100%. When all risk factors were treated as continuous variables, CD49d expression showed moderate correlation with expression of ZAP-70 (r = 0.54; P < 0.0001) and CD38 (r = 0.58; P < 0.0001) but not %IGHV mutation. As a continuous variable, CD49d expression strongly correlated with OS (P < 0.0001). Recursive partitioning analysis suggested the 45% threshold of CD49d expression best predicted OS. Multivariate analysis, controlling for disease stage, ZAP-70, IGHV status and fluorescent in situ hybridization defects identified CD49d as an independent predictor of OS and was a better predictor of clinical outcome than ZAP-70, IGHV, or cytogenetics. This observational cohort study suggests that CLL B-cell expression of CD49d is an easily measurable and independent predictor of OS and CD49d expression in CLL. Importantly, anti-CD49d antibodies are already approved for treatment of other human diseases. Clinical testing of anti-CD49d therapy in CLL appears warranted.

Adhesion molecule profiles of B-cell non-Hodgkin's lymphomas in the leukemic phase

We evaluated the expression of 10 adhesion molecules on peripheral blood tumor cells of 17 patients with chronic lymphocytic leukemia, 17 with mantle-cell lymphoma, and 13 with nodal or splenic marginal B-cell lymphoma, all in the leukemic phase and before the beginning of any therapy. The diagnosis of B-cell non-Hodgkin's lymphomas was based on cytological, histological, immunophenotypic, and molecular biology methods. The mean fluorescence intensity of the adhesion molecules in tumor cells was measured by flow cytometry of CD19-positive cells and differed amongst the types of lymphomas. Comparison of chronic lymphocytic leukemia and mantle-cell lymphoma showed that the former presented a higher expression of CD11c and CD49c, and a lower expression of CD11b and CD49d adhesion molecules. Comparison of chronic lymphocytic leukemia and marginal B-cell lymphoma showed that the former presented a higher expression of CD49c and a lower expression of CD11a, CD11b, CD18, CD49d, CD29, and CD54. Finally, comparison of mantle-cell lymphoma and marginal B-cell lymphoma showed that marginal B-cell lymphoma had a higher expression of CD11a, CD11c, CD18, CD29, and CD54. Thus, the CD49c/CD49d pair consistently demonstrated a distinct pattern of expression in chronic lymphocytic leukemia compared with mantle-cell lymphoma and marginal B-cell lymphoma, which could be helpful for the differential diagnosis. Moreover, the distinct profiles of adhesion molecules in these diseases may be responsible for their different capacities to invade the blood stream.

Apoptosis induction by hypercross-linking of the surface antigen CD5 with anti-CD5 monoclonal antibodies in B cell chronic lymphocytic leukemia

We evaluated cells from 24 patients with B cell chronic lymphocytic leukemia (B-CLL) to determine apoptosis induced by CD5 hypercross-linking. Following the CD5 hypercross-linking with anti-CD5 monoclonal antibodies (MoAbs), we identified 10 patients where CD5 hypercross-linking induced apoptosis (group A) and 14 patients whose cells were resistant to the anti-CD5 MoAbs (group B). The programmed cell death pathway of the cells from patient group A was caspase-3 and poly (ADP-ribose) polymerase (PARP)-dependent, involved a reduction of the mitochondrial transmembrane potential DeltaPsi and a down-regulation of the anti-apoptotic Bcl-2, Mcl-1 and iNOS proteins. Early activation-associated molecules such as CD25 and CD69 were expressed at higher levels than in controls after 6 h of culture with anti-CD5 MoAb. The expression of CD5 and of CD72, the ligand for CD5, were significantly lower in group A compared with group B. Anti-CD20 MoAb had similar activity with anti-CD5 MoAb and the combination of the two MoAbs seemed to be additive. In this study, it is suggested that the cells from some B-CLL patients can be induced into programmed cell death by CD5 hypercross-linking with anti-CD5 MoAbs.

Non-malignant leukocytes delay spontaneous B-CLL cell apoptosis

Malignant B cells from chronic lymphocytic leukemia (B-CLL) patients have a long survival in vivo, although, in culture, they spontaneously die by apoptosis. Here, we analyzed the capacity of accessory leukocytes to modulate apoptosis of B-CLL cells in vitro. To this end, we performed long-term cultures using total mononuclear cells (TMC) from B-CLL patients and TMC depleted from monocytes, NK cells and T lymphocytes (B-CLL cells). In all the patients studied (n = 25) the presence of accessory leukocytes markedly prolonged the survival of B-CLL cells. The anti-apoptotic effect was exerted by monocytes and, to a lesser degree, NK cells, partially through the release of soluble factors. Indeed, accessory leukocytes separated from leukemic cells by semipermeable membranes were still able to prolong B-CLL cell survival. By flow cytometric analysis we found that the protective effect of non-malignant cells was associated with delayed down-regulation of Bcl-2 expression on leukemic cells. By contrast, the expression of Fas and Fas ligand proteins was unchanged in most samples. Our findings suggest that monocytes and NK cells, by delaying leukemic cell apoptosis, may play a role in B-CLL cell accumulation in vivo.

Gene expression in chronic lymphocytic leukemia B cells and changes during induction of apoptosis

Our studies in chronic lymphocytic leukemia (CLL) are directed at understanding which signals maintain viability in vivo and become lost upon removal of leukemic cells from the body, such that they immediately begin to undergo apoptosis ex vivo. In this report, we examine changes in gene expression observed between freshly isolated CLL B cells and after maintenance in vitro with and without Fludara. We compare these effects with an Epstein-Barr virus (EBV)-transformed cell line treated similarly. Kinetic effects of drug treatment on apoptosis and cell division were examined with DNA laddering, radioisotopic labeling, and flow cytometry using the fluorescent dye carboxyfluorescein diacetate succinimidyl ester. Reverse transcriptase polymerase chain reaction and hybridization blots of microarray cDNA analyses were performed to examine gene expression. We demonstrate that many genes, especially cyclin D1, were downregulated after culture of CLL cells. Anti-apoptotic genes BAG-1 and Akt2 were upregulated. The greatest positive effect with Fludara was the upregulation of JNK1. The EBV-transformed cell line was resistant to classic DNA laddering induced with Fludara. Although DNA synthesis was blocked, the EBV-transformed cell line had some ability to recover from treatment following drug washout. CLL cells express cell cycle regulatory genes that are specific for activated cells in the G(1)-S phase of the cell cycle. Growth regulatory signals are lost when the leukemic cells are isolated from the body. Fludara enhances kinetics of apoptosis and induces expression of a gene responsive to stress that regulates expression of a kinase involved in initiation of the apoptotic pathway.