Differential modulation of angiogenesis by erythropoiesis-stimulating agents in a mouse model of ischaemic retinopathy

Background: Erythropoiesis stimulating agents (ESAs) are widely used to treat anaemia but concerns exist about their potential to promote pathological angiogenesis in some clinical scenarios. In the current study we have assessed the angiogenic potential of three ESAs; epoetin delta, darbepoetin alfa and epoetin beta using in vitro and in vivo models.

Methodology/Principal Findings: The epoetins induced angiogenesis in human microvascular endothelial cells at high doses, although darbepoetin alfa was pro-angiogenic at low-doses (1-20 IU/ml). ESA-induced angiogenesis was VEGF-mediated. In a mouse model of ischaemia-induced retinopathy, all ESAs induced generation of reticulocytes but only epoetin beta exacerbated pathological (pre-retinal) neovascularisation in comparison to controls (p<0.05). Only epoetin delta induced a significant revascularisation response which enhanced normality of the vasculature (p<0.05). This was associated with mobilisation of haematopoietic stem cells and their localisation to the retinal vasculature. Darbepoetin alfa also increased the number of active microglia in the ischaemic retina relative to other ESAs (p<0.05). Darbepoetin alfa induced retinal TNF alpha and VEGF mRNA expression which were up to 4 fold higher than with epoetin delta (p<0.001).

Conclusions: This study has implications for treatment of patients as there are clear differences in the angiogenic potential of the different ESAs.

Inhibition of platelet-derived growth factor promotes pericyte loss and angiogenesis in ischemic retinopathy

We investigated whether inhibition of platelet-derived growth factor (PDGF) receptor tyrosine kinase activity would affect pericyte viability, vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor-2 (VEGFR-2) expression and angiogenesis in a model of retinopathy of prematurity (ROP). ROP was induced in Sprague Dawley rats by exposure to 80% oxygen from postnatal (P) days 0 to 11 (with 3 hours/day in room air), and then room air from P12-18 (angiogenesis period). Shams were neonatal rats in room air from P0-18. STI571, a potent inhibitor of PDGF receptor tyrosine kinase, was administered from P12-18 at 50 or 100 mg/kg/day intraperitoneal (i.p.). Electron microscopy revealed that pericytes in the inner retina of both sham and ROP rats appeared normal; however STI571 induced a selective pericyte and vascular smooth muscle degeneration. Immunolabeling for caspase-3 and a-smooth muscle cell actin in consecutive paraffin sections of retinas confirmed that these degenerating cells were apoptotic pericytes. In all groups, VEGF and VEGFR-2 gene expression was located in ganglion cells, the inner nuclear layer, and retinal pigment epithelium. ROP was associated with an increase in both VEGF and VEGFR-2 gene expression and blood vessel profiles in the inner retina compared to sham rats. STI571 at both doses increased VEGF and VEGFR-2 mRNA and exacerbated angiogenesis in ROP rats, and in sham rats at 100 mg/kg/day. In conclusion, PDGF is required for pericyte viability and the subsequent prevention of VEGF/VEGFR-2 overexpression and angiogenesis in ROP.

Increased endocytosis in retinal vascular endothelial cells grown in high glucose medium is modulated by inhibitors of nonenzymatic glycosylation

We sought to determine if hyperglycaemia is responsible for increased retinal vascular endothelial-cell (RVEC) endocytosis in diabetes and to assess the role of nonenzymatic glycosylation in mediation of this novel endothelial-cell pathology. RVECs were propagated in media containing either 5 or 25 mmol/l glucose for up to 10 days after which they were exposed to the protein tracer horseradish peroxidase for 30 min. The level of RVEC endocytosis was quantified in intact cell monolayers by electron microscopic stereology, and in cell lysates by a simple spectrophotometric method. The effect of the nonenzymatic glycosylation inhibitors, aminoguanidine and D-lysine, on high-glucose medium induced changes in RVEC endocytosis was tested by inclusion of these agents in the culture medium. RVECs exposed to 25 mmol/l glucose showed a stepwise increase in endocytosis of horseradish peroxidase culminating in a two- to threefold increase after 10 days. Endocytosis returned to normal levels after a further 10 days in 5 mmol/l glucose medium. The increase in RVEC endocytosis was markedly reduced, but not completely normalised, by aminoguanidine and D-lysine. Exposure of cultured RVECs to 25 mmol/l glucose causes an increase in endocytosis of similar magnitude to that experienced by RVEC in early diabetes, and implicates hyperglycaemia in the latter situation. A significant component of the increase in RVEC endocytosis appears to be mediated by nonenzymatic glycosylation.

FKBPL and Peptide Derivatives: Novel Biological Agents That Inhibit Angiogenesis by a CD44-Dependent Mechanism

Purpose: Antiangiogenic therapies can be an important adjunct to the management of many malignancies. Here we investigated a novel protein, FKBPL, and peptide derivative for their antiangiogenic activity and mechanism of action.

Experimental Design: Recombinant FKBPL (rFKBPL) and its peptide derivative were assessed in a range of human microvascular endothelial cell (HMEC-1) assays in vitro. Their ability to inhibit proliferation, migration, and Matrigel-dependent tubule formation was determined. They were further evaluated in an ex vivo rat model of neovascularization and in two in vivo mouse models of angiogenesis, that is, the sponge implantation and the intravital microscopy models. Antitumor efficacy was determined in two human tumor xenograft models grown in severe compromised immunodeficient (SCID) mice. Finally, the dependence of peptide on CD44 was determined using a CD44-targeted siRNA approach or in cell lines of differing CD44 status.

Results: rFKBPL inhibited endothelial cell migration, tubule formation, and microvessel formation in vitro and in vivo. The region responsible for FKBPL's antiangiogenic activity was identified, and a 24-amino acid peptide (AD-01) spanning this sequence was synthesized. It was potently antiangiogenic and inhibited growth in two human tumor xenograft models (DU145 and MDA-231) when administered systemically, either on its own or in combination with docetaxel. The antiangiogenic activity of FKBPL and AD-01 was dependent on the cell-surface receptor CD44, and signaling downstream of this receptor promoted an antimigratory phenotype.

Conclusion: FKBPL and its peptide derivative AD-01 have potent antiangiogenic activity. Thus, these agents offer the potential of an attractive new approach to antiangiogenic therapy.

Probing the mid-gorge of cholinesterases with spacer-modified bivalent quinazolinimines leads to highly potent and selective butyrylcholinesterase inhibitors

The spacer structure of homobivalent quinazolinimes acting as potent acetyl-(AChE)- and butyrylcholinesterase (BChE) inhibitors was chemically modified introducing tertiary amine and acyl-amide moieties, and the activities at both ChEs were evaluated. Molecular docking was applied to explain the data and probe the capacity of the mid-gorge site of both ChEs. The novel spacer structures considerably alter the biological profile of bivalent quinazolinimines with regard to both inhibitory activity and selectivity. Mutual interaction of binding to the various sites of the enzymes was further investigated by applying also different spacer lengths and ring sizes of the alicycle of the tricyclic quinazolinimines. In order to achieve selectivity toward BChE and to improve inhibitory activities, the spacer structure was optimized and identified a highly potent and selective BChE inhibitor. (C) 2010 Elsevier Ltd. All rights reserved.

Differential expression of steroid 5 alpha-reductase isozymes and association with disease severity and angiogenic genes predict their biological role in prostate cancer

The biological role of steroid 5 alpha-reductase isozymes (encoded by the SRD5A1 and SRD5A2 genes) and angiogenic factors that play important roles in the pathogenesis and vascularization of prostate cancer (PC) is poorly understood. The sub-cellular expression of these isozymes and vascular endothelial growth factor (VEGF) in PC tissue microarrays (n=62) was examined using immunohistochemistry. The effect of SRD5A inhibition on the angiogenesis pathway genes in PC was also examined in prostate cell lines, LNCaP, PC3, and RWPE-1, by treating them with the SRD5A inhibitors finasteride and dutasteride, followed by western blot, quantitative PCR, and ELISA chip array techniques. In PC tissues, nuclear SRD5A1 expression was strongly associated with higher cancer Gleason scores (P=0.02), higher cancer stage (P=0.01), and higher serum prostate specific antigen (PSA) levels (P=0.01), whereas nuclear SRD5A2 expression was correlated with VEGF expression (P=0.01). Prostate tumor cell viability was significantly reduced in dutasteride-treated PC3 and RWPE-1 cells compared with finasteride-treated groups. Expression of the angiogenesis pathway genes transforming growth factor beta 1 (TGFB1), endothelin (EDN1), TGF alpha (TGFA), and VEGFR1 was upregulated in LNCaP cells, and at least 7 out of 21 genes were upregulated in PC3 cells treated with finasteride (25 mu M). Our findings suggest that SRD5A1 expression predominates in advanced PC, and that inhibition of SRD5A1 and SRD5A2 together was more effective in reducing cell numbers than inhibition of SRD5A2 alone. However, these inhibitors did not show any significant difference in prostate cell angiogenic response. Interestingly, some angiogenic genes remained activated after treatment, possibly due to the duration of treatment and tumor resistance to inhibitors. Endocrine-Related Cancer (2010) 17 757-770

Proteasome inhibitors in cancer therapy

The ubiquitin proteasome pathway plays a critical role in regulating many processes in the cell which are important for tumour cell growth and survival. Inhibition of proteasome function has emerged as a powerful strategy for anti-cancer therapy. Clinical validation of the proteasome as a therapeutic target was achieved with bortezomib and has prompted the development of a second generation of proteasome inhibitors with improved pharmacological properties. This review summarises the main mechanisms of action of proteasome inhibitors in cancer, the development of proteasome inhibitors as therapeutic agents and the properties and progress of next generation proteasome inhibitors in the clinic.

Novel Inhibitors of the Pseudomonas aeruginosa Virulence Factor LasB: a Potential Therapeutic Approach for the Attenuation of Virulence Mechanisms in Pseudomonal Infection

Pseudomonas elastase (LasB), a metalloprotease virulence factor, is known to play a pivotal role in pseudomonal infection. LasB is secreted at the site of infection, where it exerts a proteolytic action that spans from broad tissue destruction to subtle action on components of the host immune system. The former enhances invasiveness by liberating nutrients for continued growth, while the latter exerts an immunomodulatory effect, manipulating the normal immune response. In addition to the extracellular effects of secreted LasB, it also acts within the bacterial cell to trigger the intracellular pathway that initiates growth as a bacterial bio?lm. The key role of LasB in pseudomonal virulence makes it a potential target for the development of an inhibitor as an antimicrobial agent. The concept of inhibition of virulence is a recently established antimicrobial strategy, and such agents have been termed “second-generation” antibiotics. This approach holds promise in that it seeks to attenuate virulence processes without bactericidal action and, hence, without selection pressure for the emergence of resistant strains. A potent inhibitor of LasB,N-mercaptoacetyl-Phe-Tyr-amide (Ki 41 nM) has been developed, and its ability to block these virulence processes has been assessed. It has been demonstrated that thes compound can completely block the action of LasB on protein targets that are instrumental in bio?lm formation and immunomodulation. The novel LasB inhibitor has also been employed in bacterial-cell-based assays, to reduce the growth of pseudomonal bio?lms, and to eradicate bio?lm completely when used in combination with conventional antibiotics.