Primary B-chronic Lymphocytic Leukemia Research Articles

Overcoming of Microenvironment Protection on Primary Chronic Lymphocytic Leukemia Cells after Treatment with BTK and MDM2 Pharmacological Inhibitors.

In B-chronic lymphocytic leukemia (B-CLL), the interaction between leukemic cells and the microenvironment promotes tumor cell survival. The Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib is one of the first-in-class molecules for the treatment of B-CLL patients; however, the emerging mechanisms of resistance to ibrutinib call for new therapeutic strategies. The purpose of the current study was to investigate the ability of ibrutinib plus the MDM2-inhibitor nutlin-3 to counteract the tumor microenvironment protective effect. We observed that primary B-CLL cells cultivated in microenvironment mimicking conditions were protected from apoptosis by the up-regulation of c-MYC and of p53. In the same setting, combined treatments with ibrutinib plus nutlin-3 led to significantly higher levels of apoptosis compared to the single treatments, counteracting the c-MYC up-regulation. Moreover, the combination induced high p53 levels and a significant dissipation of the mitochondrial membrane potential, together with BAX cleavage in the more active p18 form and phospho-BAD down-regulation, that are key components of the mitochondrial apoptotic pathway, enhancing the apoptosis level. Our findings propose a new therapeutic strategy to overcome the tumor microenvironment protection involved in B-CLL resistance to drugs, with possible clinical implications also for other hematologic and solid tumors for which ibrutinib is considered a therapeutic option.

Ibrutinib synergizes with MDM-2 inhibitors in promoting cytotoxicity in B chronic lymphocytic leukemia.

ObjectiveThe aim of this study was to investigate the anti-leukemic activity of the Bruton tyrosine kinase inhibitor Ibrutinib in combination with the small molecule MDM-2 inhibitor Nutlin-3 in preclinical models.MethodsThe potential efficacy of the Ibrutinib/Nutlin-3 combination was evaluated in vitro in a panel of B leukemic cell lines (EHEB, JVM-2, JVM-3, MEC-1, MEC-2) and in primary B-chronic lymphocytic leukemia (B-CLL) patient samples, by assessing cell viability, cell cycle profile, apoptosis and intracellular pathway modulations. Validation of the combination therapy was assessed in a B leukemic xenograft mouse model.ResultsIbrutinib exhibited variable anti-leukemic activity in vitro and the combination with Nutlin-3 synergistically enhanced the induction of apoptosis independently from the p53 status. Indeed, the Ibrutinib/Nutlin-3 combination was effective in promoting cytotoxicity also in primary B-CLL samples carrying 17p13 deletion and/or TP53 mutations, already in therapy with Ibrutinib. Molecular analyses performed on both B-leukemic cell lines as well as on primary B-CLL samples, while confirming the switch-off of the MAPK and PI3K pro-survival pathways by Ibrutinib, indicated that the synergism of action with Nutlin-3 was independent by p53 pathway and was accompanied by the activation of the DNA damage cascade signaling through the phosphorylation of the histone protein H2A.X. This observation was confirmed also in the JVM-2 B leukemic xenograft mouse model.ConclusionsTaken together, our data emphasize that the Ibrutinib/Nutlin-3 combination merits to be further evaluated as a therapeutic option for B-CLL.

Metformin combined with sodium dichloroacetate promotes B leukemic cell death by suppressing anti-apoptotic protein Mcl-1.

Metformin and the mitochondrial targeting dichloroacetate (DCA) have recently received attention due to their ability to inhibit anaerobic glycolysis, which renders most cancer cells resistant to apoptosis induction. We observed that Metformin alone exhibited a dose-dependent anti-leukemic activity in both B leukemic cell lines and primary B-chronic lymphocytic leukemia (B-CLL) patients' cells and its anti-leukemic activity was enhanced when used in combination with DCA. In order to overcome the problems of poor bioavailability and cellular uptake, which limit DCA efficacy, we have designed and synthetized cocrystals consisting of Metformin and DCA (Met-DCA) at different stoichiometric ratios. Of note, the MetH2++•2DCA− cocrystal exhibited enhanced in vitro anti-leukemic activity, with respect to the treatment with the mix consisting of Metformin plus DCA. In particular, the treatment with the cocrystal MetH2++•2DCA− induced a synergistic apoptotic cell death coupled to a marked down-modulation of the anti-apoptotic Mcl-1 protein. Taken together, our data emphasize that innovative compounds based on Metformin-DCA combination merit to be further evaluated as chemotherapeutic agents for the treatment of B-CLL.

The p53 transcriptional pathway is preserved in ATMmutated and NOTCH1mutated chronic lymphocytic leukemias.

By using next generation sequencing, we have analyzed 108 B chronic lymphocytic leukemia (B-CLL) patients. Among genes involved in the TP53 pathway, we found frequent mutations in ATM (n=18), TP53 (n=10) and NOTCH1 (n=10) genes, rare mutations of NOTCH2 (n=2) and CDKN1A/p21 (n=1) and no mutations in BAX, MDM2, TNFRSF10A and TNFRSF10B genes. The in vitro treatment of primary B-CLL cells with the activator of p53 Nutlin-3 induced the transcription of p53 target genes, without significant differences between the B-CLL without mutations and those harboring either ATM or NOTCH1mutations. On the other hand, the subgroup of TP53mutated B-CLL exhibited a significantly lower induction of the p53 target genes in response to Nutlin-3 as compared to the other B-CLL samples. However, among the TP53mutated B-CLL, those showing mutations in the high hot spot region of the DNA binding domain [273-280 aa] maintained a significantly higher p53-dependent transcriptional activity as compared to the other TP53mutated B-CLL samples. Since the ability to elicit a p53-dependent transcriptional activity in vitro has a positive prognostic significance, our data suggest that ATMmutated, NOTCH1mutated and surprisingly, also a subset of TP53mutated B-CLL patients might benefit from therapeutic combinations including small molecule activator of the p53 pathway.

Sodium dichloroacetate exhibits anti-leukemic activity in B-chronic lymphocytic leukemia (B-CLL) and synergizes with the p53 activator Nutlin-3.

The anti-leukemic activity of the mitochondria-targeting small molecule sodium dichloroacetate (DCA), used alone and in association with the small molecule inhibitor of the p53/MDM2 interaction Nutlin-3, was analyzed in primary B-chronic lymphocytic leukemia (B-CLL) samples (n=22), normal peripheral blood cells (n=10) and in p53wild-type EHEB, JVM-2, JVM-3 B lymphoblastoid cell lines. DCA exhibited a dose-dependent anti-leukemic activity in both primary B-CLL and B leukemic cell lines with a functional p53 status and showed a synergistic cytotoxic activity when used in combination with Nutlin-3. At the molecular level, DCA positively regulated p53 activity, as documented by post-transcriptional modifications of p53 protein and synergized with Nutlin-3 in increasing the expression of the p53-target genes MDM2, PUMA, TIGAR and in particular p21. The potential role of p21 in mediating the DCA+Nutlin-3 anti-leukemic activity was underscored in knocking-down experiments. Indeed, transfection of leukemic cells with p21 siRNAs significantly decreased the DCA+Nutlin-3-induced cytotoxicity. Taken together, our data emphasize that DCA is a molecule that merits to be further evaluated as a chemotherapeutic agent for B-CLL, likely in combination with other therapeutic compounds.

The phosphatidylinositol‐3 kinase I inhibitor BKM120 induces cell death in B‐chronic lymphocytic leukemia cells in vitro

BKM120, a pan class I PI3K inhibitor, was cytotoxic in the majority of primary B-chronic lymphocytic leukemia (CLL) lymphocytes, including samples from patients who have a high-risk for poor response to treatment (patient with del11 and del17) at clinically obtainable concentrations. The PI3Kδ inhibitor Cal-101 is cytotoxic in B-CLL lymphocytes in vitro and is active in the treatment of CLL in vivo. Interestingly, we demonstrated that BKM120 is 3.6 fold more toxic than Cal-101 in malignant B-CLL lymphocytes in vitro. BKM120 cytotoxicity correlated with the basal expression of proteins involved in the PI3K/Akt pathway. A protein signature of PI3K pathway proteins predicts the response to BKM120 treatment. In the primary B-CLL lymphocytes tested in vitro, BKM120 decreased the phosphorylation status of molecular biomarkers used as indicators of PI3K pathway inhibition in vivo. Also, BKM120 induced apoptosis in primary B-CLL cells culture in the presence and absence of stromal cell support. Our findings suggest that BKM120 should be tested clinically in CLL.

The non-genotoxic activator of the p53 pathway Nutlin-3 shifts the balance between E2F7 and E2F1 transcription factors in leukemic cells

The effect of Nutlin-3, a small molecule inhibitor of the MDM2/p53 interaction, was investigated on the steady-state mRNA levels of the transcription factors E2F1 and E2F7 in a cohort of primary B-chronic lymphocytic leukemia (B-CLL) patient samples (n = 15) and normal peripheral blood mononuclear cells (PBMC). A 24-h treatment with Nutlin-3 significantly down-regulated E2F1 and promoted the concomitant up-regulation of E2F7 in both leukemic and normal cells. Our data suggest that the ability of Nutlin-3 to up-regulate E2F7 likely represents an important molecular determinant in the anti-proliferative activity of Nutlin-3.

Merkel-cell polyomavirus (MCPyV) is rarely associated to B-chronic lymphocytic leukemia (1 out of 50) samples and occurs late in the natural history of the disease

BackgroundPrevious studies have reported conflicting results on the frequency and potential pathogenetic role of Merkel-cell polyomavirus (MCPyV) in B-chronic lymphocytic leukemia (B-CLL). ObjectivesTo evaluate the association of MCPyV to B-CLL and to investigate the occurrence of MCPyV infection in relationship to the natural history of B-CLL. Study designSamples of primary B-CLL peripheral blood mononuclear cells were obtained from two distinct University Hospitals of Italy from January 2010. For one B-CLL patient, it was possible to retrospectively examine the blood sample at diagnosis of B-CLL (March 2004) and several pathological tissues of cutaneous tumors occurring during the course of the disease. ResultsOnly one out of 50 B-CLL blood samples examined was positive for MCPyV DNA. Retrospective analysis revealed that MCPyV DNA was absent in peripheral blood sample at diagnosis, becoming present only in advanced disease stages also in tonsil tissue as well as in a biopsy of differentiated squamous cell carcinoma. ConclusionsThe association with MCPyV seems to represent a rare and late event during the natural history of B-CLL.

SOCS1 is significantly up-regulated in Nutlin-3-treated p53wild-type B chronic lymphocytic leukemia (B-CLL) samples and shows an inverse correlation with miR-155

The basal SOCS1 mRNA levels were significantly lower in p53(mutated) BJAB and MAVER leukemic cell lines with respect to p53(wild-type) SKW6.4 and JVM-2 leukemic cell lines, p53(wild-type) primary B chronic lymphocytic leukemia (B-CLL) cells and primary normal peripheral blood mononuclear cells (PBMC). Moreover, the MDM2 small molecule inhibitor Nutlin-3 significantly increased the levels of SOCS1 mRNA in both primary p53(wild-type) B-CLL cells as well as in p53(wild-type) B leukemic cell lines, but not in p53(mutated) B leukemic cell lines nor in primary PBMC. Of note, a significant inverse correlation was observed between SOCS1 mRNA and miR-155 levels in Nutlin-3-treated primary B-CLL cells and PBMC, suggesting that the miRNA-155/SOCS1 axis represents a potentially important therapeutic target of Nutlin-3 in B-CLL.

Nutlin-3 Downregulates the Expression of the Oncogene TCL1 in Primary B Chronic Lymphocytic Leukemic Cells

The oncogene TCL1 plays a key role in the development of B chronic lymphocytic leukemia (B-CLL), but it is not known whether TCL1 could be modulated by therapeutic approaches. B-CLL patient samples (n = 35) and B leukemic cell lines (EHEB, JVM2, JVM3, MEC1, MEC2, and BJAB) with different p53 status were exposed to Nutlin-3, a small-molecule inhibitor of the p53-MDM2 interaction. Modulations of the steady-state mRNA levels of TCL1 were analyzed by quantitative real-time PCR and Western blotting in both primary B-CLL samples and leukemic cell lines. In addition, transfection experiments with either p53 siRNA or with a TCL1 expression plasmid were carried out in the EHEB B-CLL cell line. Upon ex vivo treatment with Nutlin-3, TCL1 was significantly (P < 0.05) decreased in 23 of 28 B-CLL p53(wild-type). The functionality of the p53 pathway in the same leukemic cell samples was underscored by the concomitant ability of Nutlin-3 to significantly (P < 0.05) upregulate the p53 target gene MDM2 in the p53(wild-type) leukemic cells. The dependence of TCL1 downregulation by a functional p53 pathway was confirmed in a panel of B lymphoblastoid cell lines and by p53 knockdown experiments with p53 siRNA. The importance of TCL1 in promoting leukemic cell survival was underscored in transfection experiments, in which TCL1 overexpression significantly counteracted the Nutlin-3-mediated induction of apoptosis in EHEB. Our data indicate that the Nutlin-3 downregulates TCL1 mRNA and protein, which likely represents an important molecular determinant in the proapoptotic activity of Nutlin-3.

Dasatinib Plus Nutlin-3 Shows Synergistic Antileukemic Activity in Both p53wild-type and p53mutated B Chronic Lymphocytic Leukemias by Inhibiting the Akt Pathway

To analyze the effect of the combination of Dasatinib, a multikinase inhibitor, plus Nutlin-3, a nongenotoxic activator of the p53 pathway, in primary B chronic lymphocytic leukemia (B-CLL) patient samples and B leukemic cell line models. The induction of cytotoxicity was evaluated in both primary B-CLL cell samples (n = 20) and in p53(wild-type) (EHEB, JVM-2) and p53(deleted/mutated) (MEC-2, BJAB) B leukemic cell lines. The role of Akt in modulating leukemic cell survival/apoptosis in response to Dasatinib or Dasatinib + Nutlin-3 was documented by functional experiments carried out using specific pharmacological inhibitors and by overexpression of membrane-targeted constitutively active form of Akt. The combination of Dasatinib + Nutlin-3 exhibited a synergistic cytotoxicity in the majority (19 out of 20) of B-CLL samples, including patients carrying 17p- (n = 4), and in both p53(wild-type) and p53(deleted/mutated) B leukemic cell lines. At the molecular level, Dasatinib significantly counteracted the Nutlin-3-mediated induction of the p53 transcriptional targets MDM2 and p21 observed in p53(wild-type) leukemic cells. Conversely, Nutlin-3 did not interfere with the ability of Dasatinib to decrease the phosphorylation levels of ERK1/2, p38/MAPK, and Akt in both p53(wild-type) and p53(deleted/mutated) B leukemic cell lines. A critical role of Akt downregulation in mediating the antileukemic activity of Dasatinib and Dasatinib + Nutlin-3 was demonstrated in experiments carried out by specifically modulating the Akt pathway. These findings suggest that Dasatinib + Nutlin-3 might represent an innovative therapeutic combination for both p53(wild-type) and p53(deleted/mutated) B-CLL.

The Oncogene DEK Promotes Leukemic Cell Survival and Is Downregulated by both Nutlin-3 and Chlorambucil in B-Chronic Lymphocytic Leukemic Cells

To characterize the role of the oncogene DEK in modulating the response to either Nutlin-3, a small-molecule inhibitor of the MDM2/p53 interaction, or chlorambucil in primary B-chronic lymphocytic leukemia (B-CLL) cells. DEK mRNA and protein levels were evaluated in primary B-CLL samples (n = 21), p53(wild-type) SKW6.4, p53(mutated) BJAB lymphoblastoid cell lines, and normal CD19(+) B lymphocytes-treated Nutlin-3 or chlorambucil (10 micromol/L, each). Knocking down experiments with either p53 or DEK small interfering RNA (siRNA) were done to investigate the potential role of p53 in controlling the expression of DEK and the role of DEK in leukemic cell survival/apoptosis. Both Nutlin-3 and chlorambucil downregulated DEK in primary B-CLL samples (n = 21) and SKW6.4 but not in BJAB cells. Knocking down p53 attenuated the effect of Nutlin-3 on DEK expression, whereas knocking down DEK significantly increased both spontaneous and Nutlin-3-induced apoptosis. Conversely, counteracting DEK downmodulation by using p53 small interfering RNA reduced Nutlin-3-mediated apoptosis. On the other hand, Nutlin-3 potently induced p53 accumulation, but it did not affect DEK levels in normal CD19(+) B lymphocytes. These data show that the downregulation of DEK in response to either Nutlin-3 or chlorambucil represents an important molecular determinant in the cytotoxic response of leukemic cells, and suggest that strategies aimed to downregulate DEK might improve the therapeutic potential of these drugs.

Nutlin-3 up-regulates the expression of Notch1 in both myeloid and lymphoid leukemic cells, as part of a negative feedback antiapoptotic mechanism

AbstractThe small molecule inhibitor of the MDM2/p53 interaction Nutlin-3 significantly up-regulated the steady-state mRNA and protein levels of Notch1 in TP53wild-type (OCI, SKW6.4) but not in TP53deleted (HL-60) or TP53mutated (BJAB) leukemic cell lines. A direct demonstration that NOTCH1 was a transcriptional target of p53 in leukemic cells was obtained in experiments carried out with siRNA for p53. Moreover, inhibition of Notch1 expression using Notch1-specific siRNA significantly increased cytotoxicity in TP53wild-type leukemic cells. Of note, Nutlin-3 up-regulated Notch1 expression also in primary TP53wild-type B-chronic lymphocytic leukemia (B-CLL) cells and the combined use of Nutlin-3 plus pharmacological γ-secretase inhibitors of the Notch signaling showed a synergistic cytotoxicity in both TP53wild-type leukemic cell lines and primary B-CLL cells. A potential drawback of γ-secretase inhibitors was their ability to enhance osteoclastic maturation of normal circulating preosteoclasts induced by RANKL + M-CSF. Notwithstanding, Nutlin-3 completely suppressed osteoclastogenesis irrespective of the presence of γ-secretase inhibitors. Taken together, these data indicate that the p53-dependent up-regulation of Notch1 in response to Nutlin-3 represents an antiapoptotic feedback mechanism able to restrain the potential therapeutic efficacy of Nutlin-3 in hematologic malignancies. Therefore, therapeutic combinations of Nutlin-3 + γ-secretase inhibitors might potentiate the cytotoxicity of Nutlin-3 in p53wild-type leukemic cells.

A Novel Raji-Burkitt's Lymphoma Model for Preclinical and Mechanistic Evaluation of CD52-Targeted Immunotherapeutic Agents

To date, efforts to study CD52-targeted therapies, such as alemtuzumab, have been limited due to the lack of stable CD52 expressing transformed B-cell lines and animal models. We describe generation and utilization of cell lines that stably express CD52 both in vitro and in vivo. By limiting dilution, we have established several clones of Raji-Burkitt's lymphoma cell line that express surface CD52. Immunophenotype and cytogenetic characterization of these clones was done. In vivo usefulness of the CD52(high) cell line to evaluate the therapeutic efficacy of CD52-directed antibody was investigated using a SCID mouse xenograft model. Stable expression of CD52 was confirmed in cells cultured in vitro up to 52 weeks of continuous growth. The functional integrity of the expressed CD52 molecule was shown using alemtuzumab, which induced cytotoxic effects in vitro in the CD52(high) but not the CD52(low) clone. Compared with control antibody, alemtuzumab treatment in CD52(high) inoculated mice resulted in significantly increased median survival. Comparable levels of CD52-targeted direct cytotoxicity, complement-dependent cytotoxicity, and antibody-dependent cytotoxicity and anti-CD52 immunoliposome-mediated delivery of synthetic oligodeoxyribo nucleotides in CD52(high) clone and primary B-chronic lymphocytic leukemia cells implicated potential in vivo application of this model for evaluation of CD52-targeted antibody and immunoliposomes encapsulating therapeutic agents. These results show the in vitro utility of the cloned Raji cell lines that stably express high levels CD52. The disseminated leukemia-lymphoma mouse model described herein using these stable cell lines can serve as an excellent system for in vivo therapeutic and mechanistic evaluation of existing and novel antibodies directed against CD52 molecule.

Homeostatic chemokines increase survival of B-chronic lymphocytic leukemia cells through inactivation of transcription factor FOXO3a

B-chronic lymphocytic leukemia (B-CLL) cell is characterized by the accumulation of long-lived CD5+ B lymphocytes, whose survival in vivo is in part dependent on exogenous factors such as cytokines and/or extracellular matrix proteins. Homeostatic chemokines are critical mediators of lymphoid cell trafficking. However, how they function in cell signaling and survival remains ill-defined. In this study, we have investigated the role of the homeostatic chemokines, CXCL12, CCL21, CCL19 and CXCL13, in B-CLL cell survival. Using primary leukemic cells isolated from 26 patients, we observed that each chemokine enhances cell survival. Chemokines induced the phosphorylation of ERK1/2 and p90RSK, and of Akt and its effectors GSK3 and FOXO3a. Consistently, inhibitors against mitogen-activated protein kinase/extracellular signal-regulated kinase and phosphatidylinositol 3-kinase inhibited chemokine-induced survival. Moreover, using a constitutively active mutated form of FOXO3a or siRNAs against FOXO3a in transfection experiments performed in primary B-CLL cells, we directly demonstrated the critical role of FOXO3a in both spontaneous and chemokine-induced B-CLL cell survival. Overall, our data support the notion that homeostatic chemokines contribute to B-CLL resistance to cell death through inactivation of the transcription factor FOXO3a, which may represent a novel therapeutic target in this hematopoietic malignancy.

Rapid and efficient nonviral gene delivery of CD154 to primary chronic lymphocytic leukemia cells

Interactions between CD40 and CD40 ligand (CD154) are essential in the regulation of both humoral and cellular immune responses. Forced expression of human CD154 in B chronic lymphocytic leukemia (B-CLL) cells can upregulate costimulatory and adhesion molecules and restore antigen-presenting capacity. Unfortunately, B-CLL cells are resistant to direct gene manipulation with most currently available gene transfer systems. In this report, we describe the use of a nonviral, clinical-grade, electroporation-based gene delivery system and a standard plasmid carrying CD154 cDNA, which achieved efficient (64+/-15%) and rapid (within 3 h) transfection of primary B-CLL cells. Consistent results were obtained from multiple human donors. Transfection of CD154 was functional in that it led to upregulated expression of CD80, CD86, ICAM-I and MHC class II (HLA-DR) on the B-CLL cells and induction of allogeneic immune responses in MLR assays. Furthermore, sustained transgene expression was demonstrated in long-term cryopreserved transfected cells. This simple and rapid gene delivery technology has been validated under the current Good Manufacturing Practice conditions, and multiple doses of CD154-expressing cells were prepared for CLL patients from one DNA transfection. Vaccination strategies using autologous tumor cells manipulated ex vivo for patients with B-CLL and perhaps with other hematopoietic malignancies could be practically implemented using this rapid and efficient nonviral gene delivery system.