Littlewood-Evans et al. demonstrate that extracellular succinate leads to the propagation of inflammatory macrophage activation, providing translational evidence to support the development of GPR91 antagonists for the treatment of rheumatoid arthritis.

FTY720, a potent immunomodulator, becomes phosphorylated in vivo (FTY-P) and interacts with sphingosine-1-phosphate (S1P) receptors. Recent studies showed that FTY-P affects vascular endothelial growth factor (VEGF)-induced vascular permeability, an important aspect of angiogenesis. We show here that FTY720 has antiangiogenic activity, potently abrogating VEGF-and S1P-induced angiogenesis in vivo in growth factor implant and corneal models. FTY720 administration tended to inhibit primary and significantly inhibited metastatic tumor growth in a mouse model of melanoma growth. In combination with a VEGFR tyrosine kinase inhibitor PTK787/ ZK222584, FTY720 showed some additional benefit. FTY720 markedly inhibited tumor-associated angiogenesis, and this was accompanied by decreased tumor cell proliferation and increased apoptosis. In transfected HEK293 cells, FTY-P internalized S1P 1 receptors, inhibited their recycling to the cell surface, and desensitized S1P receptor function. Both FTY720 and FTY-P apparently failed to impede VEGF-produced increases in mitogen-activated protein kinase activity in human umbilical vascular endothelial cells (HUVEC), and unlike its activity in causing S1PR internalization, FTY-P did not result in a decrease of surface VEGFR2 levels in HUVEC cells. Pretreatment with FTY720 or FTY-P prevented S1P-induced Ca 2+ mobilization and migration in vascular endothelial cells. These data show that functional antagonism of vascular S1P receptors by FTY720 potently inhibits angiogenesis; therefore, this may provide a novel therapeutic approach for pathologic conditions with dysregulated angiogenesis.

In dystrophic mice, a model of merosin‐deficient congenital muscular dystrophy, laminin‐2 mutations produce peripheral nerve dysmyelination and render Schwann cells unable to sort bundles of axons. The laminin receptor and the mechanism through which dysmyelination and impaired sorting occur are unknown. We describe mice in which Schwann cell‐specific disruption of beta1 integrin, a component of laminin receptors, causes a severe neuropathy with impaired radial sorting of axons. Beta1‐null Schwann cells populate nerves, proliferate, and survive normally, but do not extend or maintain normal processes around axons. Interestingly, some Schwann cells surpass this problem to form normal myelin, possibly due to the presence of other laminin receptors such as dystroglycan and α6β4 integrin. These data suggest that PI integrin links laminin in the basal lamina to the cytoskeleton in order for Schwann cells to ensheath axons, and alteration of this linkage contributes to the peripheral neuropathy of congenital muscular dystrophy.

Purpose: Comparison of the antiangiogenic/vascular properties of the oral mammalian target of rapamycin (mTOR) inhibitor RAD001 (everolimus) and the vascular endothelial growth factor receptor (VEGFR) inhibitor vatalanib (PTK/ZK). Experimental Design: Antiproliferative activity against various tumor histotypes and downstream effects on the mTOR pathway were measured in vitro. In vivo, antitumor activity, plasma, and tumor RAD001 levels were measured. Activity in several different angiogenic/ vascular assays in vitro and in vivo was assessed and compared with PTK/ZK.Results: RAD001 inhibited proliferation in vitro (IC 50 values <1 nmol/L to >1 Amol/L), and in sensitive and insensitive tumor cells, pS6 kinase and 4E-BP1were inhibited. Activity in vitro did not correlate with activity in vivo and significant responses were seen in tumors with IC 50 values >10-fold higher than tumor RAD001concentrations. In vitro, RAD001inhibited the proliferation of VEGF-stimulated and fibroblast growth factor-stimulated human endothelial cells but not dermal fibroblasts and impaired VEGF release from both sensitive and insensitive tumor cells but did not inhibit migration of human endothelial cells. In vivo, in tumor models derived from either sensitive or insensitive cells, RAD001 reduced Tie-2 levels, the amount of mature and immature vessels, total plasma, and tumorVEGF. RAD001did not affect blood vessel leakiness in normal vasculature acutely exposed to VEGF nor did it affect tumor vascular permeability (K trans ) as measured by dynamic contrast-enhanced magnetic resonance imaging. However, the pan-VEGFR inhibitor PTK/ZK inhibited endothelial cell migration and vascular permeability but had less effect on mature vessels compared with RAD001. Conclusions: VEGFR and mTOR inhibitors show similar but also distinct effects on tumor vascular biology, which has implications for their clinical activity alone or in combination.

BackgroundBlood vessels comprise endothelial cells, mural cells (pericytes/vascular smooth muscle cells) and basement membrane. During angiogenesis, mural cells are recruited to sprouting endothelial cells and define a stabilizing context, comprising cell-cell contacts, secreted growth factors and extracellular matrix components, that drives vessel maturation and resistance to anti-angiogenic therapeutics.Methods and FindingsTo better understand the basis for mural cell regulation of angiogenesis, we conducted high content imaging analysis on a microtiter plate format in vitro organotypic blood vessel system comprising primary human endothelial cells co-cultured with primary human mural cells. We show that endothelial cells co-cultured with mural cells undergo an extensive series of phenotypic changes reflective of several facets of blood vessel formation and maturation: Loss of cell proliferation, pathfinding-like cell migration, branching morphogenesis, basement membrane extracellular matrix protein deposition, lumen formation, anastamosis and development of a stabilized capillary-like network. This phenotypic sequence required endothelial-mural cell-cell contact, mural cell-derived VEGF and endothelial VEGFR2 signaling. Inhibiting formation of adherens junctions or basement membrane structures abrogated network formation. Notably, inhibition of mural cell VEGF expression could not be rescued by exogenous VEGF.ConclusionsThese results suggest a unique role for mural cell-associated VEGF in driving vessel formation and maturation.

Dysregulation of the alternative complement pathway (AP) predisposes individuals to a number of diseases including paroxysmal nocturnal hemoglobinuria, atypical hemolytic uremic syndrome, and C3 glomerulopathy. Moreover, glomerular Ig deposits can lead to complement-driven nephropathies. Here we describe the discovery of a highly potent, reversible, and selective small-molecule inhibitor of factor B, a serine protease that drives the central amplification loop of the AP. Oral administration of the inhibitor prevents KRN-induced arthritis in mice and is effective upon prophylactic and therapeutic dosing in an experimental model of membranous nephropathy in rats. In addition, inhibition of factor B prevents complement activation in sera from C3 glomerulopathy patients and the hemolysis of human PNH erythrocytes. These data demonstrate the potential therapeutic value of using a factor B inhibitor for systemic treatment of complement-mediated diseases and provide a basis for its clinical development.

Dysregulated angiogenesis and high tumor vasculature permeability, two vascular endothelial growth factor (VEGF)-mediated processes and hallmarks of human tumors, are in part phosphatidylinositol 3-kinase (PI3K) dependent. NVP-BEZ235, a dual PI3K/mammalian target of rapamycin (mTOR) inhibitor, was found to potently inhibit VEGF-induced cell proliferation and survival in vitro and VEGF-induced angiogenesis in vivo as shown with s.c. VEGF-impregnated agar chambers. Moreover, the compound strongly inhibited microvessel permeability both in normal tissue and in BN472 mammary carcinoma grown orthotopically in syngeneic rats. Similarly, tumor interstitial fluid pressure, a phenomenon that is also dependent of tumor permeability, was significantly reduced by NVP-BEZ235 in a dose-dependent manner on p.o. administration. Because RAD001, a specific mTOR allosteric inhibitor, was ineffective in the preceding experiments, we concluded that the effects observed for NVP-BEZ235 are in part driven by PI3K target modulation. Hence, tumor vasculature reduction was correlated with full blockade of endothelial nitric oxide (NO) synthase, a PI3K/Akt-dependent but mTORC1-independent effector involved in tumor permeability through NO production. In the BN472 tumor model, early reduction of permeability, as detected by Ktrans quantification using the dynamic contrast-enhanced magnetic resonance imaging contrasting agent P792 (Vistarem), was found to be a predictive marker for late-stage antitumor activity by NVP-BEZ235. [Cancer Res 2008;68(16):6598–607]

The mechanism whereby IL-17 drives rheumatoid arthritis remains incompletely understood. We demonstrate that anti–IL-17 therapy in collagen-induced arthritis ameliorates bone damage by reducing the number of osteoclasts in joints. We found equal numbers of CD4+ Th17 and IL-17 producing γδ T cells in the joints of arthritic mice, and in vitro, both populations similarly induced osteoclastogenesis. However, individual depletion and adoptive transfer studies revealed that in vivo, Th17 cells dominated with regard to bone destruction. Unlike γδ T cells, Th17 cells were found in apposition to tartrate-resistant acid phosphatase positive osteoclasts in subchondral areas of inflamed joints, a pattern reproduced in patient biopsies. This localization was caused by Ag-specific retention, because OVA-primed Th17 cells showed a γδ T cell-like diffuse distribution. Because IL-23, as produced by osteoclasts, enhanced T cell-mediated osteoclastogenesis, we propose that Ag-specific juxtaposition is key to foster the molecular cross talk of Th17 cells and osteoclasts, thus driving arthritic bone destruction.