Semiquantitative Methods for GFP Immunohistochemistry and In Situ Hybridization to Evaluate AAV Transduction of Mouse Retinal Cells Following Subretinal Injection.

The goal of this study was to develop methods for the evaluation of green fluorescent protein (GFP) and GFP transcript biodistribution in paraformaldehyde-fixed paraffin-embedded (PFPE) eye sections to assess the effectiveness of Adeno-associated virus (AAV) gene delivery in an experimental ocular toxicity study. Female C57BL/6NTac mice were administered AAV2-enhancedGFP vector once via subretinal injection. One group also received anti-inflammatory therapy (meloxicam). Immunohistochemistry (IHC) and RNA in situ hybridization (ISH) for GFP were performed on PFPE serial eye sections and evaluated using semiquantitative methods. On day 43, GFP labeling in both IHC and ISH sections was greatest in the retinal pigment epithelium, compared with other retinal layers in which expression was negative to moderate. Despite the presence of IHC GFP labeling in the photoreceptor layer (PRL) in some animals, only low numbers of transduced cells were detected by ISH in the PRL. Simultaneous analysis of IHC and ISH may be needed for comprehensive assessment of gene transduction and protein biodistribution. This study demonstrates approaches for semiquantitative evaluation of IHC and ISH that allow interpretation and reporting of GFP expression in toxicity studies.

Determination of a No Observable Effect Level for Endotoxin Following a Single Intravitreal Administration to Cynomolgus Monkeys.

Purpose: To characterize the inflammatory response and determine the no-observable-effect level (NOEL) in cynomolgus monkey eyes after intravitreal (ITV) injection of endotoxin. Methods: The inflammatory response to endotoxin was assessed in a single-dose study in monkeys at doses of 0.01 to 0.51 endotoxin units (EU)/eye. Tolerability was assessed by clinical ophthalmic examinations, intraocular pressure measurements, fundus color photography, optical coherence tomography, and anatomic pathology. Results: ITV injection of endotoxin at ≥0.04 EU/eye resulted in a dose-related anterior segment inflammatory response. No aqueous flare or cell was noted in the 0.01 EU/eye dose group. A more delayed posterior segment response characterized by vitreous cell was observed beginning on day 5, peaking on day 15, and decreasing in some groups. Microscopic findings of mononuclear cell infiltrates in the vitreous were observed in eyes given ≥0.21 EU/eye. Conclusion: The NOEL for ITV endotoxin in cynomolgus monkeys was 0.01 EU/eye, suggesting that this species is as sensitive as rabbits to the effects of endotoxin. The vitreous cavity also appears more sensitive to endotoxin than the anterior segment/aqueous chamber. Overall, the magnitude of the inflammatory response at ≥0.04 EU/eye suggests that dose-response curve in monkeys is steeper than in rabbits. These data highlight the importance of assessing endotoxin level in ITV formulations, as levels as low as 0.04 EU/eye may confound the safety evaluations of ITV therapeutics in cynomolgus monkeys.

Biomechanical, ultrastructural, and electrophysiological characterization of the non-human primate experimental glaucoma model.

Laser-induced experimental glaucoma (ExGl) in non-human primates (NHPs) is a common animal model for ocular drug development. While many features of human hypertensive glaucoma are replicated in this model, structural and functional changes in the unlasered portions of trabecular meshwork (TM) of laser-treated primate eyes are understudied. We studied NHPs with ExGl of several years duration. As expected, ExGl eyes exhibited selective reductions of the retinal nerve fiber layer that correlate with electrophysiologic measures documenting a link between morphologic and elctrophysiologic endpoints. Softening of unlasered TM in ExGl eyes compared to untreated controls was observed. The degree of TM softening was consistent, regardless of pre-mortem clinical findings including severity of IOP elevation, retinal nerve fiber layer thinning, or electrodiagnostic findings. Importantly, this softening is contrary to TM stiffening reported in glaucomatous human eyes. Furthermore, microscopic analysis of unlasered TM from eyes with ExGl demonstrated TM thinning with collapse of Schlemm's canal; and proteomic analysis confirmed downregulation of metabolic and structural proteins. These data demonstrate unexpected and compensatory changes involving the TM in the NHP model of ExGl. The data suggest that compensatory mechanisms exist in normal animals and respond to elevated IOP through softening of the meshwork to increase outflow.

Determination of a No-Observable Effect Level for Endotoxin Following a Single Intravitreal Administration to Dutch Belted Rabbits.

Purpose: The purpose of this study was to characterize the inflammatory response and determine a no-observable effect level (NOEL) in rabbit eyes after endotoxin intravitreal (ITV) injection. Methods: Fifty-three naïve male Dutch Belted rabbits were treated with a single 50-µL ITV injection ranging from 0.01 to 0.75 endotoxin units/eye (EU/eye) and monitored for up to 42 days post treatment. Ophthalmic examination included slit-lamp biomicroscopy and indirect ophthalmoscopy. Laser flare photometry was performed in a subset of animals. On days 2, 8, 16, and 43, a subset of animals was necropsied and eyes processed for histopathological evaluation. Results: Intravitreal injection of endotoxin at ≥0.05 EU/eye resulted in a dose-related anterior segment inflammation response. No aqueous flare or cell response was noted in the 0.01 EU/eye dose group. A more delayed posterior segment response characterized by vitreal cell response was observed beginning on day 5, peaking on day 9, and decreasing starting on day 16 that persisted at trace to a level of 1+ on day 43. Microscopy findings of infiltrates of minimal mixed inflammatory cells in the vitreous and subconjunctiva and proteinaceous fluid in the anterior chamber and/or vitreous were observed in eyes given ≥0.1 EU/eye. Conclusions: We defined the NOEL for ITV endotoxin to be 0.01 EU/eye, suggesting that the vitreal cavity is more sensitive to the effects of endotoxin than the anterior segment and aqueous chamber. These data highlight the importance of assessing endotoxin level in intravitreal formulations, as levels as low as 0.05 EU/eye may confound the safety evaluations of intravitreal therapeutics in rabbits.

90-day dietary toxicity study with esterified propoxylated glycerol (EPG) in rats.

The subchronic (90-day) toxicity of a "core" version of EPG was assessed in rats. Crl:CD-1®(ICR)BR rats (70/sex) received diets containing a constant level of 5% EPG (w/w) or adjusted to deliver 0 (control), 0.5, 1, or 2g/kg of body weight/day (g/kg bw/day). Subsets of animals from each group (20/sex) were evaluated after 30 days (interim sacrifice); the remainder after 90 days. EPG intake at all dose levels was associated with lower mean liver vitamin E levels; liver vitamin A and serum vitamin D were also lower, but less consistently. Animals given 5% EPG had higher fecal output (males) and cholesterol (males and females) without corresponding changes in serum cholesterol. Urinary pH was also mildly lower in males given 5% EPG. However, detailed evaluation of general health and assessment of blood, organs and tissues showed no evidence that EPG administration compromised the nutritional requirements of the animals, caused a state of fat-soluble vitamin deficiency, or caused' toxicity to any organ system. Based on the results of this study, it was not possible to establish a no-observable-effect level (NOEL). The possible effect of EPG on vitamin levels in the absence of any clinical signs of deficiency was not considered "adverse" per se. As such, the 2g/kg and 5% EPG level were considered to represent a no-observable-adverse-effect levels (NOAELs).

Functional and anatomic consequences of subretinal dosing in the cynomolgus macaque.

OBJECTIVE: To characterize functional and anatomic sequelae of a bleb induced by subretinal injection. METHODS: Subretinal injections (100 µL) of balanced salt solution were placed in the superotemporal macula of 1 eye in 3 cynomolgus macaques. Fellow eyes received intravitreal injections (100 µL) of balanced salt solution. Fundus photography, ocular coherence tomography, and multifocal electroretinography were performed before and immediately after injection and again at intervals up to 3 months postinjection. Histopathologic analyses included transmission electron microscopy and immunohistochemistry for glial fibrillary acidic protein, rhodopsin, M/L-cone opsin, and S-cone opsin. RESULTS: Retinas were reattached by 2 days postinjection (seen by ocular coherence tomography). Multifocal electroretinography waveforms were suppressed post-subretinal injection within the subretinal injection bleb and, surprisingly, also in regions far peripheral to this area. Multifocal electroretinography amplitudes were nearly completely recovered by 90 days. The spectral-domain ocular coherence tomography inner segment-outer segment line had decreased reflectivity at 92 days. Glial fibrillary acidic protein and S-cone opsin staining were unaffected. Rhodopsin and M/L-cone opsins were partially displaced into the inner segments. Transmission electron microscopy revealed disorganization of the outer segment rod (but not cone) discs. At all postinjection intervals, eyes with intravitreal injection were similar to baseline. CONCLUSIONS: Subretinal injection is a promising route for drug delivery to the eye. Three months post-subretinal injection, retinal function was nearly recovered, although reorganization of the outer segment rod disc remained disrupted. Understanding the functional and anatomic effects of subretinal injection is important for interpretation of the effects of compounds delivered to the subretinal space. CLINICAL RELEVANCE: Subretinal injection is a new potential route for drug delivery to the eye. Separating drug effects from the procedural effects is critical.

Prevention of experimental choroidal neovascularization and resolution of active lesions by VEGF trap in nonhuman primates.

OBJECTIVE: To evaluate the efficacy of systemic and intravitreous administration of VEGF Trap (aflibercept) in a nonhuman primate model of choroidal neovascularization (CNV). METHODS: VEGF Trap treatment on laser-induced CNV was evaluated in 48 adult cynomolgus monkeys. In the prevention arms of the study, VEGF Trap was administered by intravenous injection (3 or 10 mg/kg weekly) or intravitreous injection (50, 250, or 500 µg/eye every 2 weeks) beginning before laser injury. In the treatment arm, a single intravitreous injection (500 µg) was given 2 weeks following laser injury. Laser-induced lesions were scored from grade 1 (no hyperfluorescence) to grade 4 (clinically relevant leakage). Representative lesions were evaluated histologically. RESULTS: Grade 4 leakage developed at 32.4% and 45.4% of the laser sites in animals receiving intravitreous or intravenous administration of placebo at 2 weeks following laser injury, respectively. In contrast, the development of grade 4 lesions was completely or nearly completely prevented in all groups receiving intravenous or intravitreous injections of VEGF Trap. A single intravitreous injection of VEGF Trap (500 µg) administered following the development of CNV reduced the frequency of grade 4 lesions from 44.4% to 0% within 14 days of treatment. Intravitreous VEGF Trap was well tolerated with either no or only mild ocular inflammation. Histological evaluation showed decreased scores for morphologic features of tissue proliferation in the VEGF Trap prevention groups. CONCLUSIONS: VEGF Trap prevented the development of clinically relevant CNV leakage when administered at the lowest doses tested. Moreover, a single intravitreous injection induced inhibition of active CNV leakage. CLINICAL RELEVANCE: The animal model used in this study has an established track record as a predictor of pharmacologic efficacy of antineovascular drugs in humans having the neovascular, or wet, form of age-related macular degeneration.

Ocular inflammation in cynomolgus macaques following intravenous administration of a human monoclonal antibody.

Angiogenesis is a major component of the pathogenesis of various ocular diseases, including age-related macular degeneration (AMD). CNTO95 is a fully human monoclonal antibody against alpha(nu) integrins that has shown antiangiogenic properties in cynomolgus macaques and rats. Because angiogenesis inhibitors may have the potential to treat AMD, a proof-of-concept study was conducted in a macaque model of laser-induced choroidal neovascularization. In the course of this study, transient, intense anterior chamber ocular inflammation was observed within 24 hours following the first intravitreal or intravenous administration of the human monoclonal antibody. These animals had no outward signs of ocular toxicity or discomfort. Additional ocular safety studies demonstrated that the inflammation following intravenous administration of CNTO95 was not due to a contaminant in the vehicle, not due to endotoxin, and not a nonspecific reaction in the macaques from administration of a human monoclonal antibody. The anterior chamber ocular inflammation noted following the first dose did not recur with subsequent CNTO95 dosing. In repeated-dose toxicology studies, histopathological examination of the eyes revealed no ocular toxicity. The reason for the ocular inflammation following intravenous dosing remains unresolved but may be a secondary manifestation of a first-dose systemic infusion reaction.

Concomitant administration of bevacizumab, irinotecan, 5-fluorouracil, and leucovorin: nonclinical safety and pharmacokinetics.

Bevacizumab (Avastin) is a humanized monoclonal antibody against vascular endothelial growth factor approved for use in combination with 5-fluorouracil (5-FU)-based chemotherapy for first-line treatment of metastatic colorectal cancer. The Saltz regimen (irinotecan/5-FU/leucovorin [LV]) is a first-line treatment for this indication. The objective of this study was to evaluate the safety of bevacizumab when administered concomitantly with the Saltz regimen to cynomolgus monkeys, and to determine if the pharmacokinetics of bevacizumab, irinotecan, SN38 (the active metabolite of irinotecan), or 5-FU were affected by combined administration. Male cynomolgus monkeys were intravenously administered the Saltz regimen (125 mg/m2 irinotecan, 500 mg/m2 5-FU, 20 mg/m2 LV) alone (n = 4) or concomitantly with 10 mg/kg bevacizumab (n = 5) on days 1 and 8. All animals survived to euthanasia on day 15. Adverse effects associated with the Saltz regimen included diarrhea and neutropenia. Macroscopically, two animals from each group had small thymus glands that correlated microscopically with lymphoid depletion. Myeloid hypoplasia and/or erythroid hyperplasia was observed in the sternal bone marrow of most animals. These effects were considered to be associated with the Saltz regimen; concomitant bevacizumab administration did not alter the severity of these findings. Irinotecan and 5-FU were observed to be rapidly eliminated (t1/2 = 1 h and 0.5 h, respectively). Although the number of animals in each group was small and no statistical comparison between groups was performed, bevacizumab did not affect the disposition of either agent. These results indicate that bevacizumab can be safely administered in combination with the Saltz regimen without pharmacokinetic interaction.