Ocular Pharmacokinetics of Brimonidine Drug Delivery System in Monkeys and Translational Modeling for Selection of Dose and Frequency in Clinical Trials.

Brimonidine, a selective α 2-adrenoceptor agonist, displays putative retinal cyto- and neuroprotective activity in vitro and in vivo. An intravitreal sustained-release brimonidine implant, Brimonidine Posterior Segment Drug Delivery System (brimonidine DDS), allowing targeted drug delivery to the retina has been developed for potential clinical application. This study evaluates the in vivo posterior segment pharmacokinetics of brimonidine DDS implant in the monkey eye and applies translational pharmacokinetic modeling to predict tissue exposure in the human eye. Anesthetized cynomolgus monkeys received a single intravitreal injection of brimonidine DDS 400 µg implant before removal of study eyes at days 7, 30, 60, 92, 120, and 150 postimplant (three to four animals per time point) for assay of brimonidine in aqueous humor, vitreous, and retina samples. Brimonidine concentrations in the human eye were modeled using a linear, three-compartment model assuming bidirectional distribution to/from the aqueous humor and retina and elimination from the aqueous humor. Monkey tissue volumes were scaled up to human values; intercompartmental and elimination rate constants were assumed to be identical in the two species. Modeling and simulations were performed using NONMEM v. 7.3, R 3.5.1. Brimonidine exposure was highest in the monkey vitreous and retina; concentrations in the central (macula) and peripheral retina were maintained at high levels (>100 ng/g) for 3 to 4 months. Simulated brimonidine concentration-time profiles in human macula indicated that brimonidine DDS 400 µg implant would deliver effective drug concentrations (20.7‒82.2 ng/g, based on animal pharmacology) for approximately 3 months. Accordingly, administration of the 400 µg implant at 3-month intervals is recommended. SIGNIFICANCE STATEMENT: Brimonidine, an α 2-adrenoceptor agonist, is cyto- and neuroprotective in animal models of retinal/optic nerve injury. Brimonidine Posterior Segment Drug Delivery System (brimonidine DDS) is an intravitreal sustained-release implant with potential ophthalmological applications. This study explores the pharmacokinetics of brimonidine DDS 400 µg implant in the monkey eye and uses compartmental modeling to predict human ocular tissue exposure. Targeted retinal brimonidine delivery from vitreous was demonstrated in monkeys. Simulated tissue concentration-time profiles indicated persistence of pharmacologically effective brimonidine concentrations for ≈3 months in human retina.

A nonhuman primate model of blue light-induced progressive outer retina degeneration showing brimonidine drug delivery system-mediated cyto- and neuroprotection.

Geographic atrophy (GA) is an advanced form of age-related macular degeneration (AMD) characterized by atrophy of the retinal pigment epithelium (RPE), loss of photoreceptors, and disruption of choriocapillaris. Excessive light exposure is toxic to the retina and is a known risk factor for AMD. We first investigated the effects of blue light-induced phototoxicity on RPE and photoreceptors in nonhuman primates (NHPs, a model of progressive retinal degeneration) and then evaluated the potential cyto- and neuroprotective effects of the brimonidine drug delivery system (Brimo DDS). In the first set of experiments related to model development, parafoveal lesions of varying severity were induced using blue light irradiation of the retina of cynomolgus monkeys to evaluate the level of phototoxicity in the RPE and photoreceptors. RPE damage was assessed using fundus autofluorescence imaging to quantify areas of hypofluorescence, while thinning of the outer nuclear layer (ONL, photoreceptor nuclei) was quantified using optical coherence tomography (OCT). Photoreceptor function was assessed using multifocal electroretinography (mfERG). RPE damage progressively increased across all lesion severities from 2 to 12 weeks, as did the extent of ONL thinning. Lesions of high severity continued to show reduction in mfERG amplitude, reaching a statistically significant maximum reduction at 12 weeks. Collectively, the first set of experiments showed that blue light irradiation of the NHP eye resulted in progressive retinal degeneration identified by damage to RPE, ONL thinning, and disrupted photoreceptor function - hallmarks of GA in humans. We then used the model to evaluate the cyto- and neuroprotective effects of Brimo DDS, administered as a therapeutic after allowing the lesions to develop for 5 weeks. Placebo DDS or Brimo DDS were administered intravitreally and a set of untreated animals were used as an additional control. In the placebo DDS group, hypofluorescence area continued to increase from baseline, indicating progressive RPE damage, while progression was significantly slowed in eyes receiving Brimo DDS. Likewise, ONL thinning continued to progress over time in eyes that received the placebo DDS, but was reduced in Brimo DDS-treated eyes. Pharmacologically relevant brimonidine concentrations were sustained in the retina for up to 26 weeks following Brimo DDS administration. In summary, Brimo DDS demonstrated cyto- and neuroprotective effects in a novel NHP GA model of progressive retinal degeneration.

Review of Biomarkers in Ocular Matrices: Challenges and Opportunities.

Biomarkers provide a powerful and dynamic approach to improve our understanding of the mechanisms underlying ocular diseases with applications in diagnosis, disease modulation or for predicting and monitoring of clinical response to treatment. Defined as measurable indicator of normal or pathological processes, biomarker evaluation has been used extensively in drug development within clinical settings to better comprehend effectiveness of treatment in ocular diseases. Biomarkers in the eye have the advantage of access to multiple ocular matrices via minimally invasive methods. Repeat sampling for biomarker assessment has enabled reproducible objective measures of disease process or biological responses to a drug treatment. This review describes the usage of biomarkers with respect to four commonly sampled ocular matrices in clinic: tears, conjunctiva, aqueous humor and vitreous. Issues that affect the evaluation of biomarkers are discussed along with opportunities to leverage biomarkers such that ultimately, they can be used for customized targeted therapy.

Comparative renal excretion of VX-702, a novel p38 MAPK inhibitor, and methotrexate in the perfused rat kidney model.

CONTEXT: VX-702 is a novel p38 mitogen-activated protein kinase inhibitor being developed to treat rheumatoid arthritis. OBJECTIVE: To characterize the renal excretion profile of VX-702 using the isolated perfused rat kidney (IPRK) model. METHODS: Studies were performed to assess the dose linearity of VX-702 excretion and to evaluate the effect of inhibitors of organic anion (probenecid) and organic cation (cimetidine) transport systems on VX-702 disposition. VX-702 excretion was studied over a range of doses targeting concentrations between 100 and 600 ng/mL. VX-702 (600 ng/mL) was also co-perfused with probenecid (1 mM) and cimetidine (2 mM). The results were compared to parallel experiments performed with methotrexate (MTX). RESULTS: VX-702 excretion was linear over the range of doses studied, and clearance data were consistent with net reabsorption by the kidney. Transport inhibition studies indicate that VX-702 is not a substrate for renal organic anion and organic cation transport systems. MTX (500 ng/mL) also displayed net reabsorption in the IPRK, but secretory transport was inhibited upon co-administration with probenecid. This finding is consistent with previous IPRK studies that demonstrated inhibitory effects of NSAIDS on MTX excretion. CONCLUSION: Overall, this study suggests that a renal drug-drug interaction between VX-702 and MTX would be unlikely if these medications were co-administered.

Disposition of ON 01210.Na (Ex-RAD(R)), a novel radioprotectant, in the isolated perfused rat liver: probing metabolic inhibition to increase systemic exposure.

ON 01210.Na (Ex-RAD) is a novel benzyl styryl sulfone analog, developed as a radioprotectant by Onconova Therapeutics Inc. The objectives of this research were to evaluate the hepatobiliary disposition of ON 01210.Na in the isolated perfused rat liver (IPRL) and to determine the effect of coadministration of ethacrynic acid (EA) on the pharmacokinetic profile of ON 01210.Na. EA acid was used as a prototypical inhibitor of glutathione-S-transferase inhibitor. ON 01210.Na was highly bound in IPRL perfusate proteins, and binding was significantly lower in the presence of EA. Dose-escalation studies (bolus dose, target concentrations 10-250 µg/mL) showed that ON 01210.Na followed nonlinear pharmacokinetics with hepatic clearance decreasing from 3.14 to 1.99 mL/min with increasing dose. ON 01210.Na underwent extensive metabolic degradation to its glutathione (GSH) adduct in liver. The GSH metabolite was mainly excreted into the bile. Coadministration of EA (1 mM) significantly inhibited the conversion of ON 01210.Na to its GSH conjugate, resulting in decreased clearance (approx. fivefold lower), and prolonged elimination from the perfusate. These preclinical studies suggest that EA is a potential pharmacoenhancer that can reduce the metabolism of ON 01210.Na in vivo, thereby increasing drug exposure and boosting radioprotective activity.

Pharmacokinetics, lymph node uptake, and mechanistic PK model of near-infrared dye-labeled bevacizumab after IV and SC administration in mice.

Our objective was to determine the pharmacokinetics, bioavailability and lymph node uptake of the monoclonal antibody bevacizumab, labeled with the near-infrared (IR) dye 800CW, after intravenous (IV) and subcutaneous (SC) administration in mice. Fluorescence imaging and enzyme-linked immunosorbent assay (ELISA) assays were developed and validated to measure the concentration of bevacizumab in plasma. The bevacizumab-IRDye conjugate remained predominantly intact in plasma and in lymph node homogenate samples over a 24-h period, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and size exclusion chromatography. The plasma concentration vs. time plots obtained by fluorescence and ELISA measurements were similar; however, unlike ELISA, fluorescent imaging was only able to quantitate concentrations for 24 h after administration. At a low dose of 0.45 mg/kg, the plasma clearance of bevacizumab was 6.96 mL/h/kg after IV administration; this clearance is higher than that reported after higher doses. Half-lives of bevacizumab after SC and IV administration were 4.6 and 3.9 days, respectively. After SC administration, bevacizumab-IRDye800CW was present in the axillary lymph nodes that drain the SC site; lymph node uptake of bevacizumab-IRDye 800CW was negligible after IV administration. Bevacizumab exhibited complete bioavailability after SC administration. Using a compartmental pharmacokinetic model, the fraction absorbed through the lymphatics after SC administration was estimated to be about 1%. This is the first report evaluating the use of fluorescent imaging to determine the pharmacokinetics, lymphatic uptake, and bioavailability of a near-infrared dye-labeled antibody conjugate.

Noninvasive real-time fluorescence imaging of the lymphatic uptake of BSA-IRDye 680 conjugate administered subcutaneously in mice.

The goal of our studies was to determine lymphatic uptake of bovine serum albumin (BSA) using real-time noninvasive fluorescence imaging. BSA labeled with near-infrared dye (IRDye) 680 was used as a model protein-dye conjugate. The conjugation of BSA with IRDye 680 was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Size-exclusion high-performance liquid chromatography and SDS-PAGE demonstrated that the IRDye 680-labeled BSA conjugate in the lymph node (LN) homogenate samples was stable at physiological temperature (37°C) for at least 5 days. Whole-body noninvasive optical imaging of hairless SKH-1 mice was performed after subcutaneous (s.c.) injection (dose = 0.1 mg/kg) into the front footpad. Noninvasive fluorescence imaging demonstrated that BSA-IRDye 680 conjugates were dynamically taken up by the lymphatic system, accumulated in the axillary LNs and then cleared, indicating that lymphatic transport plays a role in the absorption of BSA. Ex vivo tissue imaging of LN homogenates provided confirmatory data with respect to the uptake of fluorescent-labeled BSA determined by in vivo imaging. Noninvasive real-time imaging of LNs provides a novel tool for evaluating uptake and accumulation of fluorescent-labeled proteins by the lymphatic system after s.c. injection in a mouse model.