Sensitivity to PI3K and AKT inhibitors is mediated by divergent molecular mechanisms in subtypes of DLBCL.

Activated B-cell-like (ABC) and germinal center B-cell-like diffuse large B-cell lymphoma (DLBCL) represent the 2 major molecular DLBCL subtypes. They are characterized by differences in clinical course and by divergent addiction to oncogenic pathways. To determine activity of novel compounds in these 2 subtypes, we conducted an unbiased pharmacologic in vitro screen. The phosphatidylinositol-3-kinase (PI3K) α/δ (PI3Kα/δ) inhibitor AZD8835 showed marked potency in ABC DLBCL models, whereas the protein kinase B (AKT) inhibitor AZD5363 induced apoptosis in PTEN-deficient DLBCLs irrespective of their molecular subtype. These in vitro results were confirmed in various cell line xenograft and patient-derived xenograft mouse models in vivo. Treatment with AZD8835 induced inhibition of nuclear factor κB signaling, prompting us to combine AZD8835 with the Bruton's tyrosine kinase inhibitor ibrutinib. This combination was synergistic and effective both in vitro and in vivo. In contrast, the AKT inhibitor AZD5363 was effective in PTEN-deficient DLBCLs through downregulation of the oncogenic transcription factor MYC. Collectively, our data suggest that patients should be stratified according to their oncogenic dependencies when treated with PI3K and AKT inhibitors.

B-cell receptor-driven MALT1 activity regulates MYC signaling in mantle cell lymphoma.

Mantle cell lymphoma (MCL) is a mature B-cell lymphoma characterized by poor clinical outcome. Recent studies revealed the importance of B-cell receptor (BCR) signaling in maintaining MCL survival. However, it remains unclear which role MALT1, an essential component of the CARD11-BCL10-MALT1 complex that links BCR signaling to the NF-κB pathway, plays in the biology of MCL. Here we show that a subset of MCLs is addicted to MALT1, as its inhibition by either RNA or pharmacologic interference induced cytotoxicity both in vitro and in vivo. Gene expression profiling following MALT1 inhibition demonstrated that MALT1 controls an MYC-driven gene expression network predominantly through increasing MYC protein stability. Thus, our analyses identify a previously unappreciated regulatory mechanism of MYC expression. Investigating primary mouse splenocytes, we could demonstrate that MALT1-induced MYC regulation is not restricted to MCL, but represents a common mechanism. MYC itself is pivotal for MCL survival because its downregulation and pharmacologic inhibition induced cytotoxicity in all MCL models. Collectively, these results provide a strong mechanistic rationale to investigate the therapeutic efficacy of targeting the MALT1-MYC axis in MCL patients.

Mouse models of mantle cell lymphoma, complex changes in gene expression and phenotype of engrafted MCL cells: implications for preclinical research.

Mantle cell lymphoma (MCL) is an aggressive type of B-cell non-Hodgkin lymphoma (NHL) associated with poor prognosis. Animal models of MCL are scarce. We established and characterized various in vivo models of metastatic human MCL by tail vein injection of either primary cells isolated from patients with MCL or established MCL cell lines (Jeko-1, Mino, Rec-1, Hbl-2, and Granta-519) into immunodeficient NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ mice. MCL infiltration was assessed with immunohistochemistry (tissues) and flow cytometry (peripheral blood). Engraftment of primary MCL cells was observed in 7 out of 12 patient samples. The pattern of engraftment of primary MCL cells varied from isolated involvement of the spleen to multiorgan infiltration. On the other hand, tumor engraftment was achieved in all five MCL cell lines used and lymphoma involvement of murine bone marrow, spleen, liver, and brain was observed. Overall survival of xenografted mice ranged from 22 ± 1 to 54 ± 3 days depending on the cell line used. Subsequently, we compared the gene expression profile (GEP) and phenotype of the engrafted MCL cells compared with the original in vitro growing cell lines (controls). We demonstrated that engrafted MCL cells displayed complex changes of GEP, protein expression, and sensitivity to cytotoxic agents when compared with controls. We further demonstrated that our MCL mouse models could be used to test the therapeutic activity of systemic chemotherapy, monoclonal antibodies, or angiogenesis inhibitors. The characterization of MCL murine models is likely to aid in improving our knowledge in the disease biology and to assist scientists in the preclinical and clinical development of novel agents in relapsed/refractory MCL patients.

Downregulation of deoxycytidine kinase in cytarabine-resistant mantle cell lymphoma cells confers cross-resistance to nucleoside analogs gemcitabine, fludarabine and cladribine, but not to other classes of anti-lymphoma agents.

BACKGROUND: Mantle cell lymphoma (MCL) is an aggressive type of B-cell non-Hodgkin lymphoma associated with poor prognosis. Implementation of high-dose cytarabine (araC) into induction therapy became standard-of-care for all newly diagnosed younger MCL patients. However, many patients relapse even after araC-based regimen. Molecular mechanisms responsible for araC resistance in MCL are unknown and optimal treatment strategy for relapsed/refractory MCL patients remains elusive. METHODS: Five araC-resistant (R) clones were derived by long-term culture of five MCL cell lines (CTRL) with increasing doses of araC up to 50 microM. Illumina BeadChip and 2-DE proteomic analysis were used to identify gene and protein expression changes associated with araC resistance in MCL. In vitro cytotoxicity assays and experimental therapy of MCL xenografts in immunodeficient mice were used to analyze their relative responsiveness to a set of clinically used anti-MCL drugs. Primary MCL samples were obtained from patients at diagnosis and after failure of araC-based therapies. RESULTS: Marked downregulation of deoxycytidine-kinase (DCK) mRNA and protein expression was identified as the single most important molecular event associated with araC-resistance in all tested MCL cell lines and in 50% primary MCL samples. All R clones were highly (20-1000x) cross-resistant to all tested nucleoside analogs including gemcitabine, fludarabine and cladribine. In vitro sensitivity of R clones to other classes of clinically used anti-MCL agents including genotoxic drugs (cisplatin, doxorubicin, bendamustine) and targeted agents (bortezomib, temsirolimus, rituximab) remained unaffected, or was even increased (ibrutinib). Experimental therapy of immunodeficient mice confirmed the anticipated loss of anti-tumor activity (as determined by overall survival) of the nucleoside analogs gemcitabine and fludarabine in mice transplanted with R clone compared to mice transplanted with CTRL cells, while the anti-tumor activity of cisplatin, temsirolimus, bortezomib, bendamustine, cyclophosphamide and rituximab remained comparable between the two cohorts. CONCLUSIONS: Acquired resistance of MCL cells to araC is associated with downregulation of DCK, enzyme of the nucleotide salvage pathway responsible for the first phosphorylation (=activation) of most nucleoside analogs used in anti-cancer therapy. The data suggest that nucleoside analogs should not be used in the therapy of MCL patients, who relapse after failure of araC-based therapies.

The plant alkaloid and anti-leukemia drug homoharringtonine sensitizes resistant human colorectal carcinoma cells to TRAIL-induced apoptosis via multiple mechanisms.

TNF-related apoptosis-inducing ligand (TRAIL) is a pro-apoptotic ligand from the TNF-alpha family that is under consideration, along with agonistic anti-TRAIL receptor antibodies, as a potential anti-tumor agent. However, most primary human tumors are resistant to monotherapy with TRAIL apoptogens, and thus the potential applicability of TRAIL in anti-tumor therapy ultimately depends on its rational combination with drugs targeting these resistances. In our high-throughput screening for novel agents/drugs that could sensitize TRAIL-resistant colorectal cancer cells to TRAIL-induced apoptosis, we found homoharringtonine (HHT), a cephalotaxus alkaloid and tested anti-leukemia drug, to be a very effective, low nanomolar enhancer of TRAIL-mediated apoptosis/growth suppression of these resistant cells. Co-treatment of TRAIL-resistant RKO or HT-29 cells with HHT and TRAIL led to the effective induction of apoptosis and the complete elimination of the treated cells. HHT suppressed the expression of the anti-apoptotic proteins Mcl-1 and cFLIP and enhanced the TRAIL-triggered activation of JNK and p38 kinases. The shRNA-mediated down-regulation of cFLIP or Mcl-1 in HT-29 or RKO cells variably enhanced their TRAIL-induced apoptosis but it did not markedly sensitize them to TRAIL-mediated growth suppression. However, with the notable exception of RKO/sh cFLIP cells, the downregulation of cFLIP or Mcl-1 significantly lowered the effective concentration of HHT in HHT + TRAIL co-treatment. Combined HHT + TRAIL therapy also led to the strong suppression of HT-29 tumors implanted into immunodeficient mice. Thus, HHT represents a very efficient enhancer of TRAIL-induced apoptosis with potential application in TRAIL-based, anti-cancer combination therapy.

The diagnostic performance of whole-body MRI in the staging of lymphomas in adult patients compared to PET/CT and enhanced reference standard-systematic review and meta-analysis.

BACKGROUND: Morphology highlighted by diffusion weighted imaging (DWI) is the basis of whole-body MRI (wbMRI). The aim of this study was to analyze current knowledge on the diagnostic performance of wbMRI in the pretreatment staging of patients with lymphoma. METHODS: A search for original articles reporting the diagnostic performance (sensitivity, specificity) of pretreatment (first staging or staging in relapsed patients after complete remission) wbMRI in nodal and extranodal involvement by extracranial lymphoma and the agreement of stage by the Cotswolds-modified Ann Arbor classification in adult patients compared to the reference standard (PET/CT or enhanced reference standard) was conducted in PubMed, EMBASE, Cochrane Library, ClinicalTrials.gov. RESULTS: Altogether 15 studies with 519 patients were included in the meta-analysis. The pooled sensitivity and specificity for nodal involvement were 0.93 (95% CI: 0.90 to 0.96) and 0.99 (95% CI: 0.98 to 1.00). For nodal staging, most studies used the size criterion of 10 mm in the short diameter (n=10) and the absence of prominent fatty hilum (n=4). Restricted diffusion on diffusion-weighted imaging as a sign of nodal involvement was either not used (n=5), used for detection (n=4), semi-quantitatively (n=4), or quantitatively (n=1). Only one study (7) relied solely on restricted diffusion as the main criterion for nodal involvement. The pooled sensitivity and specificity for extranodal involvement were 0.89 (95% CI: 0.79 to 0.98) and 0.99 (95% CI: 0.99 to 1.00). Seven studies considered diffuse splenic involvement when its long or vertical axis was greater than 13 cm regardless of the patient's physiognomy. The pooled agreement in staging (Cohen's kappa) was almost perfect (0.90, 95% CI: 0.84 to 0.95). DISCUSSION: The sensitivity and specificity of wbMRI in the assessment of the nodal and extranodal involvement by lymphoma is high. The agreement of wbMRI with the reference standard is almost perfect.

CD31/PECAM-1 impacts engraftment, growth and spread of mantle cell lymphoma cells and positively correlates with extramedullary involvement.

Platelet/endothelial cell adhesion molecule 1 (PECAM-1, CD31) is an immunoglobulin superfamily member expressed on the surface of platelets, leukocytes and endothelial cells. The role of CD31 in biology of lymphomas has not yet been systemically studied. Expression of cell surface CD31 was analyzed by flow cytometry on primary MCL cells isolated from peripheral blood, bone marrow or malignant effusions obtained from 29 newly diagnosed MCL patients. CD31 was significantly more expressed in patients with documented extranodal involvement. Knock-down of CD31 expression in JEKO1 and MINO MCL cell lines hampered their subcutaneous engraftment in immunodeficient mice and prolonged overall survival of intravenously-xenografted animals. In contrast, transgenic overexpression of CD31 accelerated growth of subcutaneous JEKO1 and MINO tumors, shortened overall survival of intravenously-xenografted mice, and resulted in significantly increased frequency of extramedullary murine tissue infiltration Our observations suggest that CD31 facilitate survival and regulate extranodal spread of MCL cells.

Deciphering the complex circulating immune cell microenvironment in chronic lymphocytic leukaemia using patient similarity networks.

The tissue microenvironment in chronic lymphocytic leukaemia (CLL) plays a key role in the pathogenesis of CLL, but the complex blood microenvironment in CLL has not yet been fully characterised. Therefore, immunophenotyping of circulating immune cells in 244 CLL patients and 52 healthy controls was performed using flow cytometry and analysed by multivariate Patient Similarity Networks (PSNs). Our study revealed high inter-individual heterogeneity in the distribution and activation of bystander immune cells in CLL, depending on the bulk of the CLL cells. High CLL counts were associated with low activation on circulating monocytes and T cells and vice versa. The highest activation of immune cells, particularly of intermediate and non-classical monocytes, was evident in patients treated with novel agents. PSNs revealed a low activation of immune cells in CLL progression, irrespective of IgHV status, Binet stage and TP53 disruption. Patients with high intermediate monocytes (> 5.4%) with low activation were 2.5 times more likely (95% confidence interval 1.421-4.403, P = 0.002) to had shorter time-to-treatment than those with low monocyte counts. Our study demonstrated the association between the activation of circulating immune cells and the bulk of CLL cells. The highest activation of bystander immune cells was detected in patients with slow disease course and in those treated with novel agents. The subset of intermediate monocytes showed predictive value for time-to-treatment in CLL.

TRAIL-induced apoptosis of HL60 leukemia cells: two distinct phenotypes of acquired TRAIL resistance that are accompanied with resistance to TNFalpha but not to idarubicin and cytarabine.

TNF-related apoptosis-inducing ligand (TRAIL) is a proapoptotic cytokine implicated in cancer cell surveillance. A potential of TRAIL as a cancer-specific therapeutic agent has been proposed, either as a single agent or in combination with chemotherapy. Prolonged exposure of TRAIL-sensitive leukemia cell line, wild-type (WT) HL60 cells to recombinant soluble TRAIL or to cytostatic agents, cytarabine and idarubicin, resulted in the establishment of resistant subclones with distinct phenotypic features. The TRAIL resistant HL60 subclones were characterized by decreased expression of TRAIL and TNFalpha death receptors. These resistant subclones had impaired activation of caspases 8 and 10 in response to TRAIL and TNFalpha, decreased TRAIL-induced nuclear translocation of NFkappaB RelA/p65, and dysregulation of the expression of several apoptosis regulators. Among the TRAIL resistant HL60 subclones we identified two separate phenotypes that differed in the expression of CD14, osteoprotegerin, and several apoptosis regulators. Both these TRAIL resistant HL60 subclones were resistant to TNFalpha, suggesting disruption of the extrinsic apoptotic pathway, but not to cytostatic agents, cytarabine and idarubicin. The concurrently derived HL60 subclones were cytarabine and idarubicin-resistant but remained sensitive to TRAIL-induced apoptosis. We identified distinct pathways for the development of HL60 leukemia cell resistance to apoptosis induction. These findings are relevant for the design of more effective strategies for leukemia therapy.

Prospective observational study in comorbid patients with chronic lymphocytic leukemia receiving first-line bendamustine with rituximab.

Chemoimmunotherapy with bendamustine and rituximab is an alternative treatment for elderly patients with CLL. The aim of this observational multicenter study was to prospectively assess efficacy and safety of bendamustine and rituximab in front-line therapy in patients with CLL and significant comorbidities in real hematological practice. Eighty-three consecutive patients with cumulative illness rating scale (CIRS) >6 who received at least one cycle of BR as first-line treatment were included in the study. The median age was 71 years (range, 53-83), the median CIRS was 8 (range, 7-17), and 60.2% of patients had a creatinine clearance ≤70 mL/min. FISH analysis, available for 78 cases, showed a del(17p) in 11.5% and del(11q) in 20.5% of patients. Overall response rate was 88.0% with a complete response rate of 20.5%. With median follow-up time of 22 months, the estimated median progression free survival was 35.9 months. Progression free survival and overall survival rates at 2 years were 69.9% and 96.2%, respectively. Grade 3 or 4 neutropenia, thrombocytopenia, and anemia were documented in 40 (48.2%), 14 (16.9%), and 8 (9.6%) patients, respectively. Grade 3 or 4 infections occurred in 14.5% of patients. Chemoimmunotherapy with BR is an effective therapeutic option with manageable toxicity for the initial treatment of CLL patients with significant comorbidities. ClinicalTrials.gov Identifier: NCT02381899.

Targeting of BCL2 Family Proteins with ABT-199 and Homoharringtonine Reveals BCL2- and MCL1-Dependent Subgroups of Diffuse Large B-Cell Lymphoma.

PURPOSE: To investigate the roles of BCL2, MCL1, and BCL-XL in the survival of diffuse large B-cell lymphoma (DLBCL). EXPERIMENTAL DESIGNS: Immunohistochemical analysis of 105 primary DLBCL samples, and Western blot analysis of 18 DLBCL cell lines for the expression of BCL2, MCL1, and BCL-XL. Pharmacologic targeting of BCL2, MCL1, and BCL-XL with ABT-199, homoharringtonine (HHT), and ABT-737. Analysis of DLBCL clones with manipulated expressions of BCL2, MCL1, and BCL-XL. Immunoprecipitation of MCL1 complexes in selected DLBCL cell lines. Experimental therapy aimed at inhibition of BCL2 and MCL1 using ABT-199 and HHT, single agent, or in combination, in vitro and in vivo on primary cell-based murine xenograft models of DLBCL. RESULTS: By the pharmacologic targeting of BCL2, MCL1, and BCL-XL, we demonstrated that DLBCL can be divided into BCL2-dependent and MCL1-dependent subgroups with a less pronounced role left for BCL-XL. Derived DLBCL clones with manipulated expressions of BCL2, MCL1, and BCL-XL, as well as the immunoprecipitation experiments, which analyzed MCL1 protein complexes, confirmed these findings at the molecular level. We demonstrated that concurrent inhibition of BCL2 and MCL1 with ABT-199 and HHT induced significant synthetic lethality in most BCL2-expressing DLBCL cell lines. The marked cytotoxic synergy between ABT-199 and HHT was also confirmed in vivo using primary cell-based murine xenograft models of DLBCL. CONCLUSIONS: As homoharringtonine is a clinically approved antileukemia drug, and ABT-199 is in advanced phases of diverse clinical trials, our data might have direct implications for novel concepts of early clinical trials in patients with aggressive DLBCL.

Roscovitine sensitizes leukemia and lymphoma cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a death ligand with selective antitumor activity. However, many primary tumors are TRAIL resistant. Previous studies reported that roscovitine, a cyclin-dependent kinase inhibitor, sensitized various solid cancer cells to TRAIL. We show that roscovitine and TRAIL demonstrate synergistic cytotoxicity in hematologic malignant cell lines and primary cells. Pretreatment of TRAIL-resistant leukemia cells with roscovitine induced enhanced cleavage of death-inducing signaling complex-bound proximal caspases after exposure to TRAIL. We observed increased levels of both pro- and antiapoptotic BCL-2 proteins at the mitochondria following exposure to roscovitine. These results suggest that roscovitine induces priming of cancer cells for death by binding antiapoptotic BCL-2 proteins to proapoptotic BH3-only proteins at the mitochondria, thereby decreasing the threshold for diverse proapoptotic stimuli. We propose that the mitochondrial priming and enhanced processing of apical caspases represent major molecular mechanisms of roscovitine-induced sensitization to TRAIL in leukemia/lymphoma cells.