TGFβ1 Induces Senescence and Attenuated VEGF Production in Retinal Pericytes

Diabetic retinopathy (DR) is a microvascular disease of the retina and a serious complication of type I and type II diabetes mellitus. DR affects working-age populations and can cause permanent vision loss if left untreated. The standard of care for proliferative DR is inhibiting VEGF. However, the mechanisms that induce excessive VEGF production in the retina remain elusive, although some evidence links elevated VEGF in the diabetic retina with local and systemic TGFβ1 upexpression. Here, we present evidence from animal models of disease suggesting that excessive TGFβ1 production in the early DR is correlated with VEGF mRNA and protein production by senescent pericytes and other retinal cells. Collectively, these results confirm that TGFβ1 is strongly implicated in the vascular complications of DR.

ScFvs as Allosteric Inhibitors of VEGFR-2: Novel Tools to Harness VEGF Signaling

Vascular Endothelial Growth Factor Receptor 2 (VEGFR-2) is the main mediator of angiogenic signaling in endothelial cells and a primary responder to VEGF. VEGF dependent VEGFR-2 activation regulates endothelial cell migration and proliferation, as well as vessel permeability. VEGF is presented as an antiparallel homodimer, and its binding to VEGFR-2 brings two receptors in close proximity. Downstream signaling is triggered by receptor dimerization, kinase activation, and receptor internalization. Our aim was to further investigate allosteric inhibition using binders targeting extracellular subdomains 4⁻7 of VEGFR-2 as an alternative to existing anti-angiogenic therapies, which rely on neutralizing VEGF or blocking of the ligand-binding site on the receptor. We applied phage display technology to produce single chain antibody fragments (scFvs) targeting VEGFR-2. Selected antibody fragments were characterized using biophysical and biological assays. We characterized several antibody fragments, which exert their inhibitory effect of VEGFR-2 independent of ligand binding. These reagents led to rapid clearance of VEGFR-2 from the cell surface without kinase activation, followed by an increase in intracellular receptor-positive vesicles, suggesting receptor internalization. Our highly specific VEGFR-2 binders thus represent novel tools for anti-angiogenic therapy and diagnostic applications.

Characterization of a drug-targetable allosteric site regulating vascular endothelial growth factor signaling

Vascular endothelial growth factors (VEGFs) regulate blood and lymph vessel development upon activation of three receptor tyrosine kinases (VEGFRs). The extracellular domain of VEGFRs consists of seven Ig-homology domains, of which D2-3 form the ligand-binding site, while the membrane proximal domains D4-7 are involved in homotypic interactions in ligand-bound receptor dimers. Based on low-resolution structures, we identified allosteric sites in D4-5 and D7 of vascular endothelial growth factor receptor 2 (VEGFR-2) accomplishing regulatory functions. Allosteric inhibition of VEGFR-2 signaling represents an attractive option for the treatment of neovascular diseases. We showed earlier that DARPin^® binders to domains D4 or D7 are potent VEGFR-2 inhibitors. Here we investigated in detail the allosteric inhibition mechanism of the domain D4 binding inhibitor D4b. The 2.38 Å crystal structure of D4b in complex with VEGFR-2 D4-5, the first high-resolution structure of this VEGFR-2 segment, indicates steric hindrance by D4b as the mechanism of inhibition of receptor activation. At the cellular level, D4b triggered quantitative internalization of VEGFR-2 in the absence of ligand and thus clearance of VEGFR-2 from the surface of endothelial cells. The allosteric VEGFR-2 inhibition was sufficiently strong to efficiently inhibit the growth of human endothelial cells at suboptimal dose in a mouse xenograft model in vivo, underlining the therapeutic potential of the approach.

In vitro induction of apoptotic cell death in chronic lymphocytic leukemia by two natural products: preliminary study

PURPOSE

B cell chronic lymphocytic leukemia (B-CLL) is an neoplastic disorder characterized by alterations in the pathways of programmed cell death (apoptosis). Deregulation of apoptosis pathways also contributes to chemoresistance of B-CLL cells. Therefore, it is not surprising that induction and acceleration of apoptosis represent key point in novel B-CLL therapeutic protocols. The present study was designed to investigate the effects of two natural products, Immunarc forte and Korbazol on the in vitro survival of leukemic cells.

METHODS

peripheral blood mononuclear cells (PBMC) from 20 B-CLL patients and 20 healthy donors were used for cytotoxicity studies. Cytotoxic activity of the tested products were assessed by the MTT colorimetric assay and the type of cell death was determined by flow cytometry.

RESULTS

we found that Korbazol was selectively cytotoxic against B-CLL cells, but the cytotoxic activity of Immunarc forte was much weaker. Of note, synergy was shown between these two drugs, and this effect was also selective, without affecting the normal mononuclear cells. According to Annexin-V binding, Korbazol and Immunarc forte induced apoptotic type of cell death in B-CLL cells. Moreover, treatment with Korbazol, but not with Immunarc forte, decreased spontaneous apoptosis in cultured normal polymorphonuclear cells.

CONCLUSION

our findings imply that Korbazol is as potential therapeutic agent that induces apoptosis of B-CLL cells. The resistance of normal mononuclear cells and anti-apoptotic effects on normal polymorphonuclear cells, as well as its ability to synergize with Immunarc forte, warrants further investigation and supports their therapeutic application in the treatment of B-CLL.

Endoplasmic reticulum stress associated with caspases-4 and -2 mediates korbazol-induced B-chronic lymphocytic leukemia cell apoptosis

PURPOSE

B-cell chronic lymphocytic leukemia (B-CLL) is an incurable disease that rapidly develops drug resistance. Therefore there is a need for identifying new agents that will improve the therapeutic outcome. Korbazol is a natural product known to exert cytotoxic effect on the in vitro survival of leukemic cells. The aim of this study was to investigate the mechanism of korbazol-induced apoptosis in B-CLL leukemic cells.

METHODS

peripheral blood mononuclear cells from 10 B-CLL patients were used for assessing the effect of caspase inhibitors and chelator of intracellular Ca(2)+.

RESULTS

cell death rate induced by the tested compound was decreased with the caspase-3 inhibitor Ac-DEVD-CHO, and the inhibitors of caspase-2 (Z-VDVAD-FMK) and -4 (ZYVAD- FMK), but not with the caspase-9 inhibitor z-LEHD-FMK and caspase-8 inhibitor z-IETD-FMK. No significant release of cytochrome C (cyt C) from mitochondria to the cytosol of B-CLL cells treated with korbazol was observed. Moreover, chelating of intracellular Ca(2)+ with BAPTA-AM almost completely abolished the cytotoxic effect of korbazol.

CONCLUSION

engagement of caspases-2 and -4 and mobilization of intracellular Ca(2)+ indicate involvement of endoplasmic reticulum (ER) stress in apoptosis induced by korbazol.