Genetic Medicine for Hearing Loss: OTOF as Exemplar.

Millions of people worldwide have disabling hearing loss because one of their genes generates an incorrect version of some specific protein the ear requires for hearing. In many of these cases, delivering the correct version of the gene to a specific target cell within the inner ear has the potential to restore cochlear function to enable high-acuity physiologic hearing. Purpose: In this review, we outline our strategy for the development of genetic medicines with the potential to treat hearing loss. We will use the example of otoferlin gene (OTOF)-mediated hearing loss, a sensorineural hearing loss due to autosomal recessive mutations of the OTOF gene.

Characterization of gene-activated human acid-beta-glucosidase: crystal structure, glycan composition, and internalization into macrophages.

Gaucher disease, the most common lysosomal storage disease, can be treated with enzyme replacement therapy (ERT), in which defective acid-beta-glucosidase (GlcCerase) is supplemented by a recombinant, active enzyme. The X-ray structures of recombinant GlcCerase produced in Chinese hamster ovary cells (imiglucerase, Cerezyme) and in transgenic carrot cells (prGCD) have been previously solved. We now describe the structure and characteristics of a novel form of GlcCerase under investigation for the treatment of Gaucher disease, Gene-Activated human GlcCerase (velaglucerase alfa). In contrast to imiglucerase and prGCD, velaglucerase alfa contains the native human enzyme sequence. All three GlcCerases consist of three domains, with the active site located in domain III. The distances between the carboxylic oxygens of the catalytic residues, E340 and E235, are consistent with distances proposed for acid-base hydrolysis. Kinetic parameters (K(m) and V(max)) of velaglucerase alfa and imiglucerase, as well as their specific activities, are similar. However, analysis of glycosylation patterns shows that velaglucerase alfa displays distinctly different structures from imiglucerase and prGCD. The predominant glycan on velaglucerase alfa is a high-mannose type, with nine mannose units, while imiglucerase contains a chitobiose tri-mannosyl core glycan with fucosylation. These differences in glycosylation affect cellular internalization; the rate of velaglucerase alfa internalization into human macrophages is at least 2-fold greater than that of imiglucerase.

Simultaneous but not prior inhibition of VEGF165 enhances the efficacy of photodynamic therapy in multiple models of ocular neovascularization.

PURPOSE: To investigate the effect of the combined treatment of photodynamic therapy and specific VEGF165 inhibition with pegaptanib sodium (Macugen; Eyetech Pharmaceuticals, Lexington, MA) on ocular neovascularization. METHODS: Photodynamic therapy's (PDT's) effects on the integrity of pegaptanib sodium were analyzed by HPLC, a VEGF165-binding assay, and a VEGF165-induced tissue factor gene expression assay. The effects of mono- or combined treatment on vessel growth and regression were determined in a murine corneal neovascularization model. The effects of combined treatment on vessel growth were also determined in a murine choroidal neovascularization model. RESULTS: PDT did not affect the chemical composition of pegaptanib sodium nor the efficacy of pegaptanib sodium in the inhibition of VEGF165 binding to Flt-1 and VEGF165-induced gene expression. In an animal model of effects on existing ocular neovascular lesions (corneal neovascularization), PDT monotherapy yielded an initial regression of these vessels, but there followed a rapid regrowth. In contrast, pegaptanib sodium monotherapy yielded little regression but potently abrogated further vessel growth. The combination of pegaptanib sodium and PDT resulted in the regression of the neovascular lesions, as observed with PDT alone, but also prevented significant vessel regrowth, leading to a significantly greater reduction in lesion size than did each monotherapy. In addition, there was a significantly greater effect of the combination of pegaptanib sodium and PDT on lesion size in choroidal neovascularization than with each monotherapy. Pretreatment with pegaptanib sodium appeared to decrease the efficacy of PDT-induced vessel regression in corneal neovascularization, and as such the enhanced efficacy over monotherapy when the agents were delivered simultaneously was not observed. CONCLUSIONS: Although the combined simultaneous treatment of ocular neovascularization with PDT and pegaptanib sodium may provide a more effective approach for the regression and overall treatment of CNV associated with AMD, the order of addition of these treatments may play a role in achieving optimal efficacy.

Erythropoietin promotes survival of retinal ganglion cells in DBA/2J glaucoma mice.

PURPOSE: Retinal ganglion cell (RGC) loss occurs in response to increased intraocular pressure (IOP) and/or retinal ischemia in glaucoma and leads to impairment of vision. This study was undertaken to test the efficacy of erythropoietin (EPO) in providing neuroprotection to RGCs in vivo. METHODS: The neuroprotective effects of EPO were studied in the DBA/2J mouse model of glaucoma. Mice were intraperitoneally injected with control substances or various doses of EPO, starting at the age of 6 months and continuing for an additional 2, 4, or 6 months. RGCs were labeled retrogradely by a gold tracer. IOP was measured with a microelectric-mechanical system, and EPO receptor (EPOR) expression was detected by immunohistochemistry. Axonal death in the optic nerve was quantified by para-phenylenediamine staining, and a complete blood count system was used to measure the number of erythrocytes. RESULTS: In DBA/2J mice, the average number of viable RGCs significantly decreased from 4 months to 10 months, with an inverse correlation between the number of dead optic nerve axons and viable RGCs. Treatment with EPO at doses of 3000, 6000, and 12,000 U/kg body weight per week all prevented significant RGC loss, compared with untreated DBA/2J control animals. EPO effects were similar to those of memantine, a known neuroprotective agent. IOP, in contrast, was unchanged by both EPO and memantine. Finally, EPOR was expressed in the RGC layer in both DBA/2J and C57BL/6J mice. CONCLUSIONS: EPO promoted RGC survival in DBA/2J glaucomatous mice without affecting IOP. These results suggest that EPO may be a potential therapeutic neuroprotectant in glaucoma.

Inhibitory effect of an antibody to cryptic collagen type IV epitopes on choroidal neovascularization.

PURPOSE: The wet form of age-related macular degeneration (AMD) occurs as a consequence of abnormal blood vessel growth from the choroid into the retina. Pathological angiogenesis during tumor growth and ocular disease has been associated with specific exposure of cryptic extracellular matrix epitopes. We investigated the presence of cryptic collagen IV epitopes in a murine model of choroidal neovascularization (CNV), and tested the effect on blood vessel growth of H8, a humanized antibody directed against a cryptic collagen type IV epitope. METHODS: To induce experimental CNV in adult C57BL/6 mice, Bruch's membrane was ruptured using a diode laser. Subsequently, mice were treated with daily intraperitoneal (i.p.) injections of either H8 (10 mg/kg or 30 mg/kg) or an isotype-matched antibody control. Two weeks postinjection, choroidal flat mounts were immunostained with the blood vessel marker platelet/endothelial cell adhesion molecule-1 (PECAM-1) and H8. CNV was visualized using fluorescence microscopy and the CNV lesion area measured using Open Lab software. RESULTS: Collagen type IV and the cryptic epitope were observed at the site of laser-induced lesions. Staining with H8 was first observed three days post injury, two days after MMP2 expression in CNV lesions, becoming most intense five days following laser injury and extending beyond the area of neovascularization. At 14 days post injury, H8 staining was reduced in intensity, colocalized with the area of CNV, and was nearly absent from the underlying choroidal vessels. In addition, mice treated with H8 had a significant dose-dependent decrease in the area of CNV as compared to isotype-matched antibody controls. CONCLUSIONS: Results suggest that exposure of cryptic collagen type IV epitopes is associated with the incidence of CNV and that the humanized antibody H8 may provide a new treatment for CNV.

An antisense oligodeoxynucleotide against vascular endothelial growth factor in a nonhuman primate model of iris neovascularization.

OBJECTIVE: To evaluate an antisense oligodeoxynucleotide (AS-ODN) targeted against vascular endothelial growth factor for its effects on ocular angiogenesis and its intraocular localization in a nonhuman primate model of iris neovascularization. METHODS: Bilateral laser retinal vein occlusion was performed in monkeys, followed by intravitreal injections of a vascular endothelial growth factor-specific AS-ODN or control. Serial fluorescein angiograms were graded in a masked manner to measure iris neovascularization. Localization was determined using a fluorescent-labeled AS-ODN and confocal microscopy on fixed tissue. RESULTS: Intravitreally injected vascular endothelial growth factor-specific AS-ODN localized to the retina, in the ganglion cell layer, inner nuclear layer, outer plexiform layer, photoreceptor outer segments, and retinal pigment epithelium. In 8 animals tested with 3microM ODN, AS-ODN-treated eyes had a significant reduction in iris neovascularization compared with control fellow eyes (P = .006, MIXOR analysis). Overall, in 17 animals tested across a range of ODN concentrations (0.1-50.0microM), AS-ODN-treated eyes were more likely to have lower iris neovascularization grades (P = .006, McNemar test) and the absence of iris neovascularization (P< .001, mixed-effects logistic regression model). CONCLUSION: Antisense ODNs that target vascular endothelial growth factor delivered to the retina via intravitreal injection reduced iris neovascularization in this model. Clinical Relevance Antisense ODNs against vascular endothelial growth factor may have therapeutic potential for neovascular eye diseases.

Melanoma-associated antigens in esophageal adenocarcinoma: identification of novel MAGE-A10 splice variants.

PURPOSE: The melanoma-associated antigens (MAGEs) are tumor-specific antigens recognized by cytotoxic T lymphocytes. In this study, expression of MAGE family A members was evaluated during the development of esophageal adenocarcinoma (EA) as potential targets for immunotherapy. EXPERIMENTAL DESIGN: MAGE-A mRNA expression was evaluated in 46 samples including Barrett's metaplasia (BM), dysplasia, and EA using oligonucleotide microarrays. Expression of MAGE-A proteins was confirmed by immunohistochemistry on tissue microarrays containing 59 EA, 11 dysplasia, and 9 BM samples and by Western blot. To further evaluate MAGE-A10 expression, reverse transcription-polymerase chain reaction (RT-PCR) products were sequenced, and protein expression was determined using a specific antibody. RESULTS: Overexpression of MAGE-A1, MAGE-A2b, MAGE-A3, MAGE-A4, MAGE-A6, MAGE-A9, MAGE-A10, and MAGE-A12 was found in EAs relative to BM on oligonucleotide microarrays. MAGE-A3 overexpression was confirmed by real-time RT-PCR in 21.4% (6 of 28) of esophageal tumors. Immunohistochemistry on tissue microarray revealed MAGE-A proteins in 20.3% (12 of 59) of EAs and MAGE-A10 staining in 16.9% (10 of 59) of EAs. MAGE-A expression was confirmed by Western blot in several esophageal tumors and in two EA cell lines, Flo-1 and Seg-1, whereas Flo-1 also expressed MAGE-A10. Tumors produced from these cell lines in nude mice retained MAGE-A expression. Interestingly, RT-PCR in primary tumors expressing MAGE-A10 protein revealed additional PCR products that were identified as novel MAGE-A10 alternative splice variants using DNA sequencing. CONCLUSIONS: This is the first report of these MAGE-A10 alternative splice sequences, and characterization of MAGE-A expression may provide potential targets for immunotherapy in patients with EA.

L-type amino acid transporter-1 overexpression and melphalan sensitivity in Barrett's adenocarcinoma.

The L-type amino acid transporter-1 (LAT-1) has been associated with tumor growth. Using cDNA microarrays, overexpression of LAT-1 was found in 87.5% (7/8) of esophageal adenocarcinomas relative to 12 Barrett's samples (33% metaplasia and 66% dysplasia) and was confirmed in 100% (28/28) of Barrett's adenocarcinomas by quantitative reverse transcription polymerase chain reaction. Immunohistochemistry revealed LAT-1 staining in 37.5% (24/64) of esophageal adenocarcinomas on tissue microarray. LAT-1 also transports the amino acid-related chemotherapeutic agent, melphalan. Two esophageal adenocarcinoma and one esophageal squamous cell line, expressing LAT-1 on Western blot analysis, were sensitive to therapeutic doses of melphalan (P <.001). Simultaneous treatment with the competitive inhibitor, BCH [2-aminobicyclo-(2,1,1)-heptane-2-carboxylic acid], decreased sensitivity to melphalan (P <.05). In addition, confluent esophageal squamous cultures were less sensitive to melphalan (P <.001) and had a decrease in LAT-1 protein expression. Tumors from two esophageal adenocarcinoma cell lines grown in nude mice retained LAT-1 mRNA expression. These results demonstrate that LAT-1 is highly expressed in a subset of esophageal adenocarcinomas and that Barrett's adenocarcinoma cell lines expressing LAT-1 are sensitive to melphalan. LAT-1 expression is also retained in cell lines grown in nude mice providing a model to evaluate melphalan as a chemotherapeutic agent against esophageal adenocarcinomas expressing LAT-1.

In situ gene expression analysis of cancer using laser capture microdissection, microarrays and real time quantitative PCR.

The simultaneous development of laser capture microdissection (LCM) and high-throughput mRNA analysis platforms has provided a significant technological advance in the world of cancer biology. The combination of such technologies provides a unique and powerful opportunity to directly assess the in situ molecular genetic events that are associated with initiation and progression of human malignancies. Despite these technological advances, the integration of LCM with high-throughput gene expression analysis has been met with various challenges. The goal of this review is to highlight some of the obstacles that we have faced and continue to face as we try to optimally apply LCM to in situ gene expression analysis.

RGS5 expression is a quantitative measure of pericyte coverage of blood vessels.

Pericytes play a key role in the process of vascular maturation and stabilization however, the current methods for quantifying pericyte coverage of the neovasculature are laborious and subjective in nature. In this study, we have developed an objective, sensitive, and high-throughput method for quantifying pericyte coverage of angiogenic vessels by analyzing the expression of the pericyte-specific gene, the regulator of G-protein signaling 5 (RGS5). We determined that RGS5 expression was up-regulated during a defined developmental time period in which nascent vessel sprouts acquired a pericyte covering. Furthermore, RGS5 expression was dramatically reduced in vessels with poor pericyte coverage compared to normal angiogenic vasculature. Finally, we determined that the susceptibility of nascent vessels to regression by vascular endothelial growth factor (VEGF) inhibition was significantly reduced following RGS5 up-regulation, further implicating RGS5 in pericyte-endothelial cell interactions and the vascular maturation process. These studies establish the use of RGS5 gene expression as a quantitative and robust measure of pericyte coverage of neovasculature. This method provides a tool for vascular biologists studying pericyte-endothelial cell interactions and vascular maturation in both normal and pathological conditions, such as diabetic retinopathy and cancer.

Combination therapy for the treatment of ocular neovascularization.

The growth of inappropriately regulated, leaky blood vessels is a prominent component of several debilitating eye diseases, such as age-related macular degeneration (AMD), proliferative diabetic retinopathy (PDR), and retinopathy of prematurity (ROP). New pharmacological therapies that target vascular endothelial growth factor-A (VEGF-A) have significantly enhanced the treatment of AMD by limiting the progression of the disease, and in some cases, by improving vision. Although anti-VEGF therapy will undoubtedly prove valuable in the treatment of other neovascular diseases of the eye, improvements with this type of therapy are still required. At present, anti-VEGF therapy requires intravitreal injection and a relatively frequent dosing regimen (4-6 weeks). Furthermore, in experimental models of neovascularization, anti-VEGF treatment becomes less effective at blocking vessel growth and at regressing vessels as the neovascularization develops over time. As such, the use of anti-VEGF therapy in late-stage AMD may be limited. An important strategy for improved treatment of neovascular diseases of the eye could be combination therapy. Combination therapy of anti-VEGF drugs with established treatments, such as photodynamic therapy with verteporfin (PDT-V), or with newly-developed drugs targeting specific kinases, presents opportunities for increased efficacy and improved therapeutic outcome. In this review, we evaluate the opportunities for combination therapy for the treatment of neovascular diseases of the eye.

Molecular mapping and functional characterization of the VEGF164 heparin-binding domain.

The longer splice isoforms of vascular endothelial growth factor-A (VEGF-A), including mouse VEGF164, contain a highly basic heparin-binding domain (HBD), which imparts the ability of these isoforms to be deposited in the heparan sulfate-rich extracellular matrix and to interact with the prototype sulfated glycosaminoglycan, heparin. The shortest isoform, VEGF120, lacks this highly basic domain and is freely diffusible upon secretion. Although the HBD has been attributed significant relevance to VEGF-A biology, the molecular determinants of the heparin-binding site are unknown. We used site-directed mutagenesis to identify amino acid residues that are critical for heparin binding activity of the VEGF164 HBD. We focused on basic residues and found Arg-13, Arg-14, and Arg-49 to be critical for heparin binding and interaction with extracellular matrix in tissue samples. We also examined the cellular and biochemical consequences of abolishing heparin-binding function, measuring the ability of the mutants to interact with VEGF receptors, induce endothelial cell gene expression, and trigger microvessel outgrowth. Induction of tissue factor expression, vessel outgrowth, and binding to VEGFR2 were unaffected by the HBD mutations. In contrast, the HBD mutants showed slightly decreased binding to the NRP1 (neuropilin-1) receptor, and analyses suggested the heparin and NRP1 binding sites to be distinct but overlapping. Finally, mutations that affect the heparin binding activity also led to an unexpected reduction in the affinity of VEGF164 binding specifically to VEGFR1. This finding provides a potential basis for previous observations suggesting enhanced potency of VEGF164 versus VEGF120 in VEGFR1-mediated signaling in inflammatory cells.

Vascular endothelial growth factor-A is a survival factor for retinal neurons and a critical neuroprotectant during the adaptive response to ischemic injury.

Vascular endothelial growth factor-A (VEGF-A) has recently been recognized as an important neuroprotectant in the central nervous system. Given its position as an anti-angiogenic target in the treatment of human diseases, understanding the extent of VEGF's role in neural cell survival is paramount. Here, we used a model of ischemia-reperfusion injury and found that VEGF-A exposure resulted in a dose-dependent reduction in retinal neuron apoptosis. Although mechanistic studies suggested that VEGF-A-induced volumetric blood flow to the retina may be partially responsible for the neuroprotection, ex vivo retinal culture demonstrated a direct neuroprotective effect for VEGF-A. VEGF receptor-2 (VEGFR2) expression was detected in several neuronal cell layers of the retina, and functional analyses showed that VEGFR2 was involved in retinal neuroprotection. VEGF-A was also shown to be involved in the adaptive response to retinal ischemia. Ischemic preconditioning 24 hours before ischemia-reperfusion injury increased VEGF-A levels and substantially decreased the number of apoptotic retinal cells. The protective effect of ischemic preconditioning was reversed after VEGF-A inhibition. Finally, chronic inhibition of VEGF-A function in normal adult animals led to a significant loss of retinal ganglion cells yet had no observable effect on several vascular parameters. These findings have implications for both neural pathologies and ocular vascular diseases, such as diabetic retinopathy and age-related macular degeneration.

Inhibition of platelet-derived growth factor B signaling enhances the efficacy of anti-vascular endothelial growth factor therapy in multiple models of ocular neovascularization.

'Vascular endothelial growth factor-A (VEGF-A) blockade has been recently validated as an effective strategy for the inhibition of new blood vessel growth in cancer and ocular pathologies. However, several studies have also shown that anti-VEGF therapy may not be as effective in the treatment of established unwanted blood vessels, suggesting they may become less dependent on VEGF-A for survival. The VEGF-A dependence of vessels may be related to the presence of vascular mural cells (pericytes or smooth muscle cells). Mural cell recruitment to the growing endothelial tube is regulated by platelet-derived growth factor-B (PDGF-B) signaling, and interference with this pathway causes disruption of endothelial cell-mural cell interactions and loss of mural cells. We have investigated the basis of blood vessel dependence on VEGF-A in models of corneal and choroidal neovascularization using a combination of reagents (an anti-VEGF aptamer and an anti-PDGFR-beta antibody) to inhibit both the VEGF-A and PDGF-B signaling pathways. We demonstrate that neovessels become refractory to VEGF-A deprivation over time. We also show that inhibition of both VEGF-A and PDGF-B signaling is more effective than blocking VEGF-A alone at causing vessel regression in multiple models of neovascular growth. These findings provide insight into blood vessel growth factor dependency and validate a combination therapy strategy for enhancing the current treatments for ocular angiogenic disease.

Molecular profiling of angiogenesis markers.

The goal of this study was to develop a sensitive, simple, and widely applicable assay to measure copy numbers of specific mRNAs using real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and identify a profile of gene expression closely associated with angiogenesis. We measured a panel of nine potential angiogenesis markers from a mouse transgenic model of prostate adenocarcinoma (TRAMP) and a mouse skin model of vascular endothelial growth factor (VEGF)-driven angiogenesis. In both models, expression of VEGF correlated with expression of mRNAs encoding other angiogenic cytokines (angiopoietin-1 and angiopoietin-2), endothelial cell receptor tyrosine kinases (Flt-1, KDR, Tie-1), and endothelial cell adhesion molecules (VE-cadherin, PECAM-1). Relative to control, in dermis highly stimulated by VEGF, the Ang-2 mRNA transcript numbers increased 35-fold, PECAM-1 and VE-cadherin increased 10-fold, Tie-1 increased 8-fold, KDR and Flt-1 each increased 4-fold, and Ang-1 increased 2-fold. All transcript numbers were correspondingly reduced in skin with less VEGF expression, indicating a relationship of each of these seven markers with VEGF. Thus, this study identifies a highly efficient method for precise quantification of a panel of seven specific mRNAs that correlate with VEGF expression and VEGF-induced neovascularization, and it provides evidence that real-time quantitative RT-PCR offers a highly sensitive strategy for monitoring angiogenesis.