Maria Rosaria Ricciardi

ATM-ATR-dependent up-regulation of DNAM-1 and NKG2D ligands on multiple myeloma cells by therapeutic agents results in enhanced NK-cell susceptibility and is associated with a senescent phenotype.

There is much evidence to support a role for natural killer (NK) cells in controlling the progression of multiple myeloma (MM), a malignancy characterized by an abnormal plasma cell proliferation in the bone marrow (BM). Induction of DNA damage response has been recently shown capable of enhancing NKG2D ligand (NKG2DL) expression, but nothing is known about DNAM-1 ligand (DNAM-1L) regulation. In this study, we show that myeloma cells treated with low doses of therapeutic agents commonly used in the management of patients with MM, such as doxorubicin, melphalan, and bortezomib, up-regulate DNAM-1 and NKG2D ligands. Accordingly, therapeutic drug treatment of MM cells increases NK-cell degranulation, the NKG2D and DNAM-1 receptors being the major triggering molecules. Similar data were also obtained using ex vivo primary plasma cells derived from MM patients. Drug-induced DNAM-1 and NKG2D ligand expression was abolished after treatment with the ATM (ataxia telangiectasia mutated) and ATR (ATM- and RAD3-related) pharmacologic inhibitors caffeine and KU-55933, and was preferentially associated with senescent cells arrested in the G2 phase of the cell cycle. Altogether, our findings have identified a common pathway that can trigger the up-regulation of different NK cell-activating ligands and suggest that NK cells represent an immunosurveillance mechanism toward cells undergoing stress-induced senescent programs.

BCR ligation induced by IgM stimulation results in gene expression and functional changes only in IgVH unmutated chronic lymphocytic leukemia (CLL) cells

Chronic lymphocytic leukemia (CLL) patients exhibit a variable clinical course. To investigate the association between clinicobiologic features and responsiveness of CLL cells to anti-IgM stimulation, we evaluated gene expression changes and modifications in cell-cycle distribution, proliferation, and apoptosis of IgV(H) mutated (M) and unmutated (UM) samples upon BCR cross-linking. Unsupervised analysis highlighted a different response profile to BCR stimulation between UM and M samples. Supervised analysis identified several genes modulated exclusively in the UM cases upon BCR cross-linking. Functional gene groups, including signal transduction, transcription, cell-cycle regulation, and cytoskeleton organization, were up-regulated upon stimulation in UM cases. Cell-cycle and proliferation analyses confirmed that IgM cross-linking induced a significant progression into the G(1) phase and a moderate increase of proliferative activity exclusively in UM patients. Moreover, we observed only a small reduction in the percentage of subG(0/1) cells, without changes in apoptosis, in UM cases; contrariwise, a significant increase of apoptotic levels was observed in stimulated cells from M cases. These results document that a differential genotypic and functional response to BCR ligation between IgV(H) M and UM cases is operational in CLL, indicating that response to antigenic stimulation plays a pivotal role in disease progression.

MEK Inhibition Enhances ABT-737-Induced Leukemia Cell Apoptosis via Prevention of ERK activated MCL-1 induction and Modulation of MCL-1/BIM Complex

Recently, strategies for acute myeloid leukemia (AML) therapy have been developed that target anti-apoptotic BCL2 family members using BH3-mimetic drugs such as ABT-737. Though effective against BCL2 and BCL-XL, ABT-737 poorly inhibits MCL-1. Here we report that, unexpectedly, ABT-737 induces activation of the extracellular receptor activated kinase and induction of MCL-1 in AML cells. MEK inhibitors such as PD0325901 and CI-1040 have been used successfully to suppress MCL-1. We report that PD0325901 blocked ABT-737-induced MCL-1 expression, and when combined with ABT-737 resulted in potent synergistic killing of AML-derived cell lines, primary AML blast and CD34+38-123+ progenitor/stem cells. Finally, we tested the combination of ABT-737 and CI-1040 in a murine xenograft model using MOLM-13 human leukemia cells.Whereas control mice and CI-1040-treated mice exhibited progressive leukemia growth, ABT-737, and to a significantly greater extent, ABT-737+CI-1040 exerted major anti-leukemia activity. Collectively, results demonstrated unexpected anti-apoptotic interaction between the BCL2 family-targeted BH3-mimetic ABT-737 and mitogen-activated protein kinase signaling in AML cells: the BH3 mimetic is not only restrained in its activity by MCL-1, but also induces its expression. However, concomitant inhibition by BH3 mimetics and MEK inhibitors could abrogate this effect and may be developed into a novel and effective therapeutic strategy for patients with AML.

Bortezomib and zoledronic acid on angiogenic and vasculogenic activities of bone marrow macrophages in patients with multiple myeloma

Bone marrow neovascularisation supports plasma cell tumour progression in patients with multiple myeloma (MM), and is partially sustained by bone marrow macrophages through their angiogenic and vasculogenic activities. As such, macrophages may be a target for antivascular treatment in MM. Here, we show that bortezomib (BZ) and zoledronic acid (ZOL) display distinct and synergistic inhibitory effects on cell proliferation, adhesion, migration and expression of angiogenic cytokines (i.e.: VEGF, bFGF, HGF and PDGF). Similar effects were found on capillarogenic organisation and expression of vascular markers in cells which became vasculogenic. VEGFR2 and ERK1/2 phosphoactivation as well as NF-kappaB activity were also inhibited. Overall these data provide evidence that the exposure of bone marrow macrophages in MM during the treatment with ZOL and BZ, alone and or in combination, impacts their angiogenic and vasculogenic properties, suggesting that these cells may be considered as a target of both drugs in MM patients.

Targeting the leukemia cell metabolism by the CPT1a inhibition: functional preclinical effects in leukemias

Cancer cells are characterized by perturbations of their metabolic processes. Recent observations demonstrated that the fatty acid oxidation (FAO) pathway may represent an alternative carbon source for anabolic processes in different tumors, therefore appearing particularly promising for therapeutic purposes. Because the carnitine palmitoyl transferase 1a (CPT1a) is a protein that catalyzes the rate-limiting step of FAO, here we investigated the in vitro antileukemic activity of the novel CPT1a inhibitor ST1326 on leukemia cell lines and primary cells obtained from patients with hematologic malignancies. By real-time metabolic analysis, we documented that ST1326 inhibited FAO in leukemia cell lines associated with a dose- and time-dependent cell growth arrest, mitochondrial damage, and apoptosis induction. Data obtained on primary hematopoietic malignant cells confirmed the FAO inhibition and cytotoxic activity of ST1326, particularly on acute myeloid leukemia cells. These data suggest that leukemia treatment may be carried out by targeting metabolic processes.

Reactive Oxygen Species– and DNA Damage Response–Dependent NK Cell Activating Ligand Upregulation Occurs at Transcriptional Levels and Requires the Transcriptional Factor E2F1

Increasing evidence indicates that cancer cell stress induced by chemotherapeutic agents promote antitumor immune responses and contribute to their full clinical efficacy. In this article, we identify the signaling events underlying chemotherapy-induced NKG2D and DNAM-1 ligand expression on multiple myeloma (MM) cells. Our findings indicate that sublethal doses of doxorubicin and melphalan initiate a DNA damage response (DDR) controlling ligand upregulation on MM cell lines and patient-derived malignant plasma cells in Chk1/2-dependent and p53-independent manner. Drug-induced MICA and PVR gene expression are transcriptionally regulated and involve DDR-dependent E2F1 transcription factor activity. We also describe the involvement of changes in the redox state in the control of DDR-dependent upregulation of ligand surface expression and gene transcriptional activity by using the antioxidant agent N-acetyl-l-cysteine. Finally, in accordance with much evidence indicating that DDR and oxidative stress are major determinants of cellular senescence, we found that redox-dependent DDR activation upon chemotherapeutic treatment is critical for MM cell entry in premature senescence and is required for the preferential ligand upregulation on senescent cells, which are preferentially killed by NK cells and trigger potent IFN-γ production. We propose immunogenic senescence as a mechanism that promotes the clearance of drug-treated tumor cells by innate effector lymphocytes, including NK cells.

Inhibition of Glycogen Synthase Kinase-3 Increases NKG2D Ligand MICA Expression and Sensitivity to NK Cell–Mediated Cytotoxicity in Multiple Myeloma Cells: Role of STAT3

Engagement of NKG2D and DNAX accessory molecule-1 (DNAM-1) receptors on lymphocytes plays an important role for anticancer response and represents an interesting therapeutic target for pharmacological modulation. In this study, we investigated the effect of inhibitors targeting the glycogen synthase kinase-3 (GSK3) on the expression of NKG2D and DNAM-1 ligands in multiple myeloma (MM) cells. GSK3 is a pleiotropic serine–threonine kinase point of convergence of numerous cell-signaling pathways, able to regulate the proliferation and survival of cancer cells, including MM. We found that inhibition of GSK3 upregulates both MICA protein surface and mRNA expression in MM cells, with little or no effects on the basal expression of the MICB and DNAM-1 ligand poliovirus receptor/CD155. Moreover, exposure to GSK3 inhibitors renders myeloma cells more efficient to activate NK cell degranulation and to enhance the ability of myeloma cells to trigger NK cell–mediated cytotoxicity. We could exclude that increased expression of β-catenin or activation of the heat shock factor-1 (transcription factors inhibited by active GSK3) is involved in the upregulation of MICA expression, by using RNA interference or viral transduction of constitutive active forms. On the contrary, inhibition of GSK3 correlated with a downregulation of STAT3 activation, a negative regulator of MICA transcription. Both Tyr705 phosphorylation and binding of STAT3 on MICA promoter are reduced by GSK3 inhibitors; in addition, overexpression of a constitutively active form of STAT3 significantly inhibits MICA upregulation. Thus, we provide evidence that regulation of the NKG2D-ligand MICA expression may represent an additional immune-mediated mechanism supporting the antimyeloma activity of GSK3 inhibitors.

The mitogen-activated protein kinase (MAPK) cascade controls phosphatase and tensin homolog (PTEN) expression through multiple mechanisms

The mitogen-activated protein kinase (MAPK) and PI3K pathways are regulated by extensive crosstalk, occurring at different levels. In tumors, transactivation of the alternate pathway is a frequent “escape” mechanism, suggesting that combined inhibition of both pathways may achieve synergistic antitumor activity. Here we show that, in the M14 melanoma model, simultaneous inhibition of both MEK and mammalian target of rapamycin (mTOR) achieves synergistic effects at suboptimal concentrations, but becomes frankly antagonistic in the presence of relatively high concentrations of MEK inhibitors. This observation led to the identification of a novel crosstalk mechanism, by which either pharmacologic or genetic inhibition of constitutive MEK signaling restores phosphatase and tensin homolog (PTEN) expression, both in vitro and in vivo, and inhibits downstream signaling through AKT and mTOR, thus bypassing the need for double pathway blockade. This appears to be a general regulatory mechanism and is mediated by multiple mechanisms, such as MAPK-dependent c-Jun and miR-25 regulation. Finally, PTEN upregulation appears to be a major effector of MEK inhibitors’ antitumor activity, as cancer cells in which PTEN is inactivated are consistently more resistant to the growth inhibitory and anti-angiogenic effects of MEK blockade.

Reduced susceptibility to apoptosis correlates with kinetic quiescence in disease progression of chronic lymphocytic leukaemia.

The role of apoptosis and cell kinetics in the mechanisms of disease progression of chronic lymphocytic leukaemia (CLL) is still unclear. In the present study, we investigated the susceptibility of leukaemic cells taken from 75 CLL patients with either stable (STD) or progressive disease (PRD) to enter apoptosis. Particular attention was paid to the relationship between cell cycle status and autologous serum (AS). The susceptibility to enter apoptosis was significantly greater in STD than in PRD, both in standard medium (mean = 23·62% ± 14·7 versus 14·23% ± 7·2; P = 0·02) and in the presence of AS (mean = 23·03% ± 17·9 versus 11·27% ± 7·6; P = 0·01). Furthermore, cell kinetics studies revealed a higher quiescence in PRD than in STD cases, both in terms of a lower RNA content (P = 0·04) and of higher expression of the negative cell cycle regulator p27kip1 (P = 0·03). These kinetic differences were confirmed by short‐term in vitro culture both in fetal calf serum and in AS. The results of this study indicate that CLL cells from PRD cases are characterized by a higher degree quiescence and much lower susceptibility to apoptosis when compared with STD ones. In this context, AS does not appear to play a specific role. The association between these kinetic characteristics and disease progression in CLL prompts further studies to establish whether higher quiescence may be responsible for the decreased susceptibility of PRD cells to enter apoptosis.

Che-1-induced inhibition of mTOR pathway enables stress-induced autophagy

Mammalian target of rapamycin (mTOR) is a key protein kinase that regulates cell growth, metabolism, and autophagy to maintain cellular homeostasis. Its activity is inhibited by adverse conditions, including nutrient limitation, hypoxia, and DNA damage. In this study, we demonstrate that Che‐1, a RNA polymerase II‐binding protein activated by the DNA damage response, inhibits mTOR activity in response to stress conditions. We found that, under stress, Che‐1 induces the expression of two important mTOR inhibitors, Redd1 and Deptor, and that this activity is required for sustaining stress‐induced autophagy. Strikingly, Che‐1 expression correlates with the progression of multiple myeloma and is required for cell growth and survival, a malignancy characterized by high autophagy response.