Quercetin Interrupts the Positive Feedback Loop Between STAT3 and IL-6, Promotes Autophagy, and Reduces ROS, Preventing EBV-Driven B Cell Immortalization.

The oncogenic gammaherpesvirus Epstein-Barr virus (EBV) immortalizes in vitro B lymphocytes into lymphoblastoid cell lines (LCLs), a model that gives the opportunity to explore the molecular mechanisms driving viral tumorigenesis. In this study, we addressed the potential of quercetin, a widely distributed flavonoid displaying antioxidant, anti-inflammatory, and anti-cancer properties, in preventing EBV-driven B cell immortalization. The results obtained indicated that quercetin inhibited thectivation of signal transducer and activator of transcription 3 (STAT3) induced by EBV infection and reduced molecules such as interleukin-6 (IL-6) and reactive oxidative species (ROS) known to be essential for the immortalization process. Moreover, we found that quercetin promoted autophagy and counteracted the accumulation of sequestosome1/p62 (SQSTM1/p62), ultimately leading to the prevention of B cell immortalization. These findings suggest that quercetin may have the potential to be used to counteract EBV-driven lymphomagenesis, especially if its stability is improved.

Tumor stroma engraftment of gene-modified mesenchymal stem cells as anti-tumor therapy against ovarian cancer.

BACKGROUND AIMS: Many ovarian cancers originate from ovarian surface epithelium, where they develop from cysts intermixed with stroma. The stromal layer is critical to the progression and survival of the neoplasm and consequently is recruited into the tumor microenvironment. METHODS: Using both syngeneic mouse tumors (ID8-R) and human xenograft (OVCAR3, SKOV3) tumor models, we first confirmed that intraperitoneally injected circulating mesenchymal stem cells (MSCs) could target, preferentially engraft and differentiate into α-smooth muscle actin-positive myofibroblasts, suggesting their role as "reactive stroma" in ovarian carcinoma development and confirming their potential as a targeted delivery vehicle for the intratumoral production of interferon-ß (IFN-ß). Mice with ovarian carcinomas then received weekly intraperitoneal injections of IFN-ß expressing MSCs. RESULTS: Intraperitoneal injections of IFN-ß expressing MSCs resulted in complete eradication of tumors in 70% of treated OVCAR3 mice (P = 0.004) and an increased survival of treated SKOV3 mice compared with controls (P = 0.01). Similar tumor growth control was observed using murine IFN-ß delivered by murine MSCs in ID8-R ovarian carcinoma. As a potential mechanism of tumor killing, MSCs produced IFN-ß-induced caspase-dependent tumor cell apoptosis. CONCLUSIONS: Our results demonstrate that ovarian carcinoma engrafts MSCs to participate in myofibrovascular networks and that IFN-ß produced by MSCs intratumorally modulates tumor kinetics, resulting in prolonged survival.

Mesenchymal stem cells: potential precursors for tumor stroma and targeted-delivery vehicles for anticancer agents.

BACKGROUND: High concentrations of interferon beta (IFN-beta) inhibit malignant cell growth in vitro. However, the therapeutic utility of IFN-beta in vivo is limited by its excessive toxicity when administered systemically at high doses. Mesenchymal stem cells (MSC) can be used to target delivery of agents to tumor cells. We tested whether MSC can deliver IFN-beta to tumors, reducing toxicity. METHODS: Human MSC were transduced with an adenoviral expression vector carrying the human IFN-beta gene (MSC-IFN-beta cells). Flow cytometry was used to measure tumor cell proliferation among in vitro co-cultures of MSC-IFN-beta cells and human MDA 231 breast carcinoma cells or A375SM melanoma cells. We used a severe combined immunodeficiency mouse xenograft model (4-10 mice per group) to examine the effects of injected MSC-IFN-beta cells and human recombinant IFN-beta on the growth of MDA 231- and A375SM-derived pulmonary metastases in vivo and on survival. All statistical tests were two-sided. RESULTS: Co-culture of MSC-IFN-beta cells with A375SM cells or MDA 231 cells inhibited tumor cell growth as compared with growth of the tumor cells cultured alone (differences in mean percentage of control cell growth: -94.0% [95% confidence interval [CI] = -81.2% to -106.8%; P<.001] and -104.8% [95% CI = -82.1% to -127.5%; P<.001], respectively). Intravenous injection of MSC-IFN-beta cells into mice with established MDA 231 or A375SM pulmonary metastases led to incorporation of MSC in the tumor architecture and, compared with untreated control mice, to prolonged mouse survival (median survival for MDA 231-injected mice: 60 and 37 days for MSC-injected and control mice, respectively [difference = 23.0 days (95% CI = 14.5 to 34.0 days; P<.001]; median survival for A375SM-injected mice: 73.5 and 30.0 days for MSC-injected and control mice, respectively [difference = 43.5 days (95% CI = 37.0 to 57.5 days; P<.001]). By contrast, intravenous injection of recombinant IFN-beta did not prolong survival in the same models (median survival for MDA 231-injected mice: 41.0 and 37.0 days for IFN-beta-injected and control mice, respectively [difference = 4 days, 95% CI = -5 to 10 days; P = .308]; median survival for A375SM-injected mice: 32.0 and 30.0 days for IFN-beta-injected and control mice, respectively [difference = 2 days, 95% CI = 0 to 4.5 days; P = .059]). CONCLUSIONS: Injected MSC-IFN-beta cells suppressed the growth of pulmonary metastases, presumably through the local production of IFN-beta in the tumor microenvironment. MSC may be an effective platform for the targeted delivery of therapeutic proteins to cancer sites.

Infection of HHV-8+ primary effusion lymphoma cells with a recombinant Epstein-Barr virus leads to restricted EBV latency, altered phenotype, and increased tumorigenicity without affecting TCL1 expression.

To investigate the role of Epstein-Barr virus (EBV) in the pathogenesis of primary effusion lymphoma (PEL), we infected human herpesvirus 8 (HHV-8+) but EBV- PEL lines BC-3, CRO-AP/6, and CRO-AP/3 cells with the recombinant Akata EBV strain. All EBV-infected clones expressed EBER-1, EBNA-1, and LMP2A. The expression of LMP1 and LMP2B was variable. None, however, expressed EBNA2-6. The surface markers CD30, CD74, and syndecan-1 were down-regulated in EBV convertants. EBV-infected BC-3 and CRO-AP/6 cells were highly tumorigenic in severe combined immunodeficiency (SCID) mice in contrast to their respective EBV- parental cells. However, neither the parental cells nor the virus-converted counterparts expressed TCL1. The results showing that PEL cells on in vitro EBV infection do not sustain latency III despite the absence of immune pressure indicate that the choice of EBV latent gene expression program is cell dependent. The data suggest an important role of EBV in the pathogenesis of PEL.

PML-RARalpha is associated with leptin-receptor induction: the role of mesenchymal stem cell-derived adipocytes in APL cell survival.

Leptin is secreted by bone marrow (BM) adipocytes and stromal cells and was shown to stimulate myeloid proliferation. We here report that primary acute promyelocytic leukemia (APL) cells express high levels of the leptin-receptor (OB-R) long isoform. In cells with regulated promyelocytic leukemia-retinoic acid receptor (PML-RARalpha) expression, inducing PML-RARalpha was found to increase OB-R levels. We then investigated the effects of leptin produced by BM adipocytes on APL cells using a coculture system with mesenchymal stem cell (MSC)-derived adipocytes. In PML-RARalpha-expressing cells, all-trans retinoic acid (ATRA)- and doxorubicin-induced apoptosis were significantly reduced by coculture with adipocyte-differentiated MSCs. This antiapoptotic effect required direct cell-to-cell interactions, was associated with phosphorylation of signal transducer and activator of transcription-3 (STAT3) and mitogen-activated protein kinase (MAPK), and was reduced by blocking OB-R. This report provides a mechanistic basis for the BM adipocyte-leukemia cell interaction and suggests that OB-R receptor blockade may have therapeutic use in APL.

Human herpesvirus 6 and multiple sclerosis: a study of T cell cross-reactivity to viral and myelin basic protein antigens.

Several reports have suggested an association of human herpesvirus 6 (HHV-6) with multiple sclerosis. Autoreactive T lymphocytes directed against myelin components seem to contribute to the pathogenesis of the disease. It has been suggested that molecular mimicry between viral and self-antigens might be one of the mechanisms that determine the onset of several autoimmune diseases. Following this hypothesis, the purpose of the present study was to evaluate if HHV-6 could play a role in activating T cells capable of cross-reaction with an important myelin component, the myelin basic protein. T cell lines were established from 22 multiple sclerosis patients and from 16 healthy controls, and their capability to react to both virus and myelin basic protein antigens was compared. The analysis of T cell cross-reactivity in patients and controls did not show significant differences in the HHV-6 ability to activate myelin basic protein-reactive T cells. Similarly, the evaluation of the humoral immune response to HHV-6 in patients and controls did not mirror any abnormality in the HHV-6 status in multiple sclerosis patients. Therefore, although the findings of activity in vitro of T cell lines with dual specificity are consistent with the hypothesis of molecular mimicry, the lack of differences in cross-reactivity between patients and controls do not support molecular mimicry as an important mechanism in the physiopathology of this disease.

Bone marrow-derived mesenchymal stem cells as vehicles for interferon-beta delivery into tumors.

Molecules that physiologically control cell proliferation are often produced locally in tissues and are rapidly destroyed when they enter circulation. This allows local effects while avoiding interference with other systems. Unfortunately, it also limits the therapeutic use of these molecules via systemic delivery. We here demonstrate that, for the purpose of anticancer therapy, bone marrow-derived mesenchymal stem cells (MSCs) can produce biological agents locally at tumor sites. We show that the tumor microenvironment preferentially promotes the engraftment of MSCs as compared with other tissues. MSCs with forced expression of IFN-beta inhibited the growth of malignant cells in vivo. Importantly, this effect required the integration of MSCs into the tumors and could not be achieved by systemically delivered IFN-beta or by IFN-beta produced by MSCs at a site distant from the tumors. Our results indicate that MSCs may serve as a platform for delivery of biological agents in tumors.