Michael Platten

Toll‐Like Receptor Engagement Enhances the Immunosuppressive Properties of Human Bone Marrow‐Derived Mesenchymal Stem Cells by Inducing Indoleamine‐2,3‐dioxygenase‐1 via Interferon‐β and Protein Kinase R

Mesenchymal stem cells (MSC) display unique suppressive properties on T‐cell immunity, thus representing an attractive vehicle for the treatment of conditions associated with harmful T‐cell responses such as organ‐specific autoimmunity and graft‐versus‐host disease. Toll‐like receptors (TLR) are primarily expressed on antigen‐presenting cells and recognize conserved pathogen‐derived components. Ligation of TLR activates multiple innate and adaptive immune response pathways to eliminate and protect against invading pathogens. In this work, we show that TLR expressed on human bone marrow‐derived MSC enhanced the immunosuppressive phenotype of MSC. Immunosuppression mediated by TLR was dependent on the production of immunosuppressive kynurenines by the tryptophan‐degrading enzyme indoleamine‐2,3‐dioxygenase‐1 (IDO1). Induction of IDO1 by TLR involved an autocrine interferon (IFN)‐β signaling loop, which was dependent on protein kinase R (PKR), but independent of IFN‐γ. These data define a new role for TLR in MSC immunobiology, which is to augment the immunosuppressive properties of MSC in the absence of IFN‐γ rather than inducing proinflammatory immune response pathways. PKR and IFN‐β play a central, previously unidentified role in orchestrating the production of immunosuppressive kynurenines by MSC. STEM CELLS 2009;27:909–919

N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast) inhibits transforming growth factor-β release and reduces migration and invasiveness of human malignant glioma cells

Extensive infiltration of normal brain tissue and suppression of anti‐tumor immune surveillance mediated by molecules such as transforming growth factor‐β (TGF‐β) are key biological features that contribute to the malignant phenotype of human gliomas. Tranilast (N‐[3,4‐dimethoxycinnamoyl]‐anthranilic acid) is an anti‐allergic compound used clinically to control atopic and fibrotic disorders. These effects are attributed to the suppression of TGF‐β1 synthesis and interference with growth factor–mediated proliferation and migration of fibroblasts and vascular smooth muscle cells. Here, we show that tranilast inhibits DNA synthesis and proliferation of human malignant glioma cells and promotes p21 accumulation in the absence of cytotoxicity. Further, tranilast reduces the release of TGF‐β1 and TGF‐β2 by glioma cells and inhibits migration, chemotactic responses and invasiveness. These effects are not associated with a reduction of αvβ3 integrin expression at the cell surface but appear to involve inhibition of matrix metalloproteinase‐2 expression and activity. Neither the tranilast‐mediated inhibition of proliferation nor the inhibition of migration was counteracted by supplementation with exogenous TGF‐β. Finally, tranilast administered orally inhibited the growth of experimental 9L rat gliomas and reduced expression of TGF‐β2 in vivo. We conclude that tranilast might be a useful therapeutic agent for the treatment of human malignant glioma because of a TGF‐β‐independent abrogation of the malignant phenotype of proliferation, migration and invasiveness and because of the antagonism of TGF‐β‐associated immunosuppression.

N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast) suppresses microglial inducible nitric oxide synthase (iNOS) expression and activity induced by interferon-γ (IFN-γ)

Microglial cells up‐regulate inducible nitric oxide synthase (iNOS) expression in response to various pro‐inflammatory stimuli including interferon‐γ (IFN‐γ), allowing for the release of nitric oxide (NO). Tranilast (N‐[3,4‐dimethoxycinnamoyl]‐anthranilic acid) is an antiallergic compound with suppressive effects on the activation of monocytes. Here, we show that N9 murine microglial cells express iNOS mRNA and protein and release nitric oxide into the culture medium in response to IFN‐γ (200u2003uu2003ml−1) as measured by Northern and Western blot analyses and Griess assay. Exposure to non‐toxic doses of tranilast (30u2003–u2003300u2003μM) leads to a concentration‐dependent inhibition of IFN‐γ‐induced (200u2003uu2003ml−1) iNOS mRNA and protein expression. This is paralleled by a suppression of NO‐release into the cell culture medium. Inhibition of IFN‐γ‐induced iNOS mRNA expression by tranilast is paralleled by an inhibition of nuclear factor‐κB (NF‐κB) activation and phosphorylation of inhibitory κB (IκB) as determined by Western blot analyses and NF‐κB reporter gene assay. These results suggest that tranilast‐mediated suppression of microglial iNOS activity induced by IFN‐γ involves the inhibition of NF‐κB‐dependent iNOS mRNA expression.

Moderne Therapiestrategien bei hirneigenen glialen Tumoren

ZusammenfassungDie Kombination von Radio- und Chemotherapie kann das Gesamtüberleben von Patienten mit Gliomen signifikant verbessern. Dabei stehen heute neben der lokalen Kontrolle vor allem auch die Erhaltung der Lebensqualität und der neurokognitiven Funktion im Langzeitverlauf im Vordergrund.