Hydrodynamic Radii of Ranibizumab, Aflibercept and Bevacizumab Measured by Time-Resolved Phosphorescence Anisotropy

Topical Solution for Retinal Delivery: Bevacizumab and Ranibizumab Eye Drops in Anti-Aggregation Formula (AAF) in Rabbits

PURPOSE

Wet age-related macular degeneration (AMD) is a blinding retinal disease. Monthly intravitreal anti-VEGF antibody injections of bevacizumab (off-label) and ranibizumab (FDA approved) are the standard of care. Antibody aggregation may interfere with ocular absorption/distribution. This study assessed topical delivery of dilute antibodies to the posterior segment of rabbit eyes using a novel anti-aggregation formula (AAF).

METHODS

Bevacizumab, or biosimilar ranibizumab was diluted to 5 mg/ml in AAF. All rabbits were dosed twice daily. Substudy 1 rabbits (bevacizumab, 100 µl eye drops): Group 1 (bevacizumab/AAF, n = 6); Group 2 (bevacizumab/PBS, n = 7) and Vehicle control (AAF, n = 1). Substudy 2 rabbits (ranibizumab biosimilar/AAF, 50 µl eye drops): (ranibizumab biosimilar/AAF, n = 8). At 14.5 days, serum was drawn from rabbits. Aqueous, vitreous and retina samples were recovered from eyes and placed into AAF aliquots. Tissue analyzed using AAF as diluent.

RESULTS

Bevacizumab in AAF permeated/accumulated in rabbit aqueous, vitreous and retina 10 times more, than when diluted in PBS. AAF/0.1% hyaluronic acid eye drops, dosed twice daily, provided mean tissue concentrations (ng/g) in retina (29.50), aqueous (12.34), vitreous (3.46), and serum (0.28 ng/ml). Additionally, the highest concentration (ng/g) of ranibizumab biosimilar was present in the retina (18.0), followed by aqueous (7.82) and vitreous (1.47). Serum concentration was negligible (< 0.04 ng/ml). No irritation was observed throughout the studies.

CONCLUSIONS

Bevacizumab and ranibizumab, in an AAF diluent eye drop, can be delivered to the retina, by the twice daily dosing of a low concentration mAb formulation. This may prove to be an adjunct to intravitreal injections.

Experience with the use of intravitreal bevacizumab in cases with type I retinopathy of prematurity in a Latin American country

In retinopathy of prematurity (ROP) type I, the use of intravitreal bevacizumab (IVB), which is an inhibitor of endothelial growth factor (VEGF), has become popular despite not being a therapy approved by regulatory agencies. However, IVB has shown positive effects in halting disease progression at lower costs compared to other anti-VEGF therapies (ranibizumab or aflibercept). In this report, we present the experience during the treatment with IVB of 102 Colombian children with ROP type I, with a success rate of 98% (100). Complications occurred in 3.9% (4). Finally, we conclude that a single dose of IVB is an effective therapy for the management of ROP type I, with a lower risk of complications and retreatment.

Drug Distribution After Intravitreal Injection: A Mathematical Model

Purpose

Intravitreal injection of drugs is commonly used for treatment of chorioretinal ocular pathologies, such as age-related macular degeneration. Injection causes a transient increase in the intraocular volume and, consequently, of the intraocular pressure (IOP). The aim of this work is to investigate how intravitreal flow patterns generated during the post-injection eye deflation influence the transport and distribution of the injected drug.

Methods

We present mathematical and computational models of fluid motion and mass transport in the vitreous chamber during the transient phase after injection, including the previously unexplored effects of globe deflation as ocular volume decreases.

Results

During eye globe deflation, significant fluid velocities are generated within the vitreous chamber, which can possibly contribute to drug transport. Pressure variations within the eye globe are small compared to IOP.

Conclusions

Even if significant fluid velocities are generated in the vitreous chamber after drug injection, these are found to have negligible overall effect on drug distribution.

Therapeutic Extracellular Vesicles from Tonsil-Derived Mesenchymal Stem Cells for the Treatment of Retinal Degenerative Disease

BACKGROUND

Retinal degenerative disease (RDD), one of the most common causes of blindness, is predominantly caused by the gradual death of retinal pigment epithelial cells (RPEs) and photoreceptors due to various causes. Cell-based therapies, such as stem cell implantation, have been developed for the treatment of RDD, but potential risks, including teratogenicity and immune reactions, have hampered their clinical application. Stem cell-derived extracellular vesicles (EVs) have recently emerged as a cell-free alternative therapeutic strategy; however, additional invasiveness and low yield of the stem cell extraction process is problematic.

METHODS

To overcome these limitations, we developed therapeutic EVs for the treatment of RDD which were extracted from tonsil-derived mesenchymal stem cells obtained from human tonsil tissue discarded as medical waste following tonsillectomy (T-MSC EVs). To verify the biocompatibility and cytoprotective effect of T-MSC EVs, we measured cell viability by co-culture with human RPE without or with toxic all-trans-retinal. To elucidate the cytoprotective mechanism of T-MSC EVs, we performed transcriptome sequencing using RNA extracted from RPEs. The in vivo protective effect of T-MSC EVs was evaluated using Pde6b gene knockout rats as an animal model of retinitis pigmentosa.

RESULTS

T-MSC EVs showed high biocompatibility and the human pigment epithelial cells were significantly protected in the presence of T-MSC EVs from the toxic effect of all-trans-retinal. In addition, T-MSC EVs showed a dose-dependent cell death-delaying effect in real-time quantification of cell death. Transcriptome sequencing analysis revealed that the efficient ability of T-MSC EVs to regulate intracellular oxidative stress may be one of the reasons explaining their excellent cytoprotective effect. Additionally, intravitreally injected T-MSC EVs had an inhibitory effect on the destruction of the outer nuclear layer in the Pde6b gene knockout rat.

CONCLUSIONS

Together, the results of this study indicate the preventive and therapeutic effects of T-MSC EVs during the initiation and development of retinal degeneration, which may be a beneficial alternative for the treatment of RDD.

Fast Diffusion Characterization by Multiphoton Excited Fluorescence Recovery while Photobleaching

Multiphoton-excited fluorescence recovery while photobleaching (FRWP) is demonstrated as a method for quantitative measurements of rapid molecular diffusion over microsecond to millisecond timescales. Diffusion measurements are crucial in assessing molecular mobility in cell biology, materials science, and pharmacology. Optical and fluorescence microscopy techniques enable non-invasive rapid analysis of molecular diffusion but can be challenging for systems with diffusion coefficients exceeding ∼100 μm2/s. As an example, fluorescence recovery after photobleaching (FRAP) operates on the implicit assumption of a comparatively fast photobleaching step prior to a relatively slow recovery and is not generally applicable for systems exhibiting substantial recovery during photobleaching. These challenges are exacerbated in multiphoton excitation by the lower excitation efficiency and competing effects from local heating. Herein, beam-scanning FRWP with patterned line-bleach illumination is introduced as a technique that addresses FRAP limitations and further extends its application range by measuring faster diffusion events. In FRWP, the recovery of fluorescence is continuously probed after each pass of a fast-scanning mirror, and the upper bound of measurable diffusion rates is, therefore, only limited by the mirror scanning frequency. A theoretical model describing transient fluctuations in fluorescence intensity arising as a result of combined contributions from photobleaching and localized photothermal effect is introduced along with a mathematical framework for quantifying fluorescence intensity temporal curves and recovering room-temperature diffusion coefficients. FRWP is then tested by characterization of normal diffusion of rhodamine-labeled bovine serum albumin, green fluorescence protein, and immunoglobulin G molecules in aqueous solutions of varying viscosity.

Thermo-responsive Diels-Alder stabilized hydrogels for ocular drug delivery of a corticosteroid and an anti-VEGF fab fragment

In the present study, a novel in situ forming thermosensitive hydrogel system was investigated as a versatile drug delivery system for ocular therapy. For this purpose, two thermosensitive ABA triblock copolymers bearing either furan or maleimide moieties were synthesized, named respectively poly(NIPAM-co-HEA/Furan)-PEG6K-P(NIPAM-co-HEA/Furan) (PNF) and poly(NIPAM-co-HEA/Maleimide)-PEG6K-P(NIPAM-co-HEA/-Maleimide) (PNM). Hydrogels were obtained upon mixing aqueous PNF and PNM solutions followed by incubation at 37 °C. The hydrogel undergoes an immediate (<1 min) sol-gel transition at 37 °C. In situ hydrogel formation at 37 °C was also observed after intravitreal injection of the formulation into an ex vivo rabbit eye. The hydrogel network formation was due to physical self-assembly of the PNIPAM blocks and a catalyst-free furan-maleimide Diels-Alder (DA) chemical crosslinking in the hydrophobic domains of the polymer network. Rheological studies demonstrated sol-gel transition at 23 °C, and DA crosslinks were formed in time within 60 min by increasing the temperature from 4 to 37 °C. When incubated at 37 °C, these hydrogels were stable for at least one year in phosphate buffer of pH 7.4. However, the gels degraded at basic pH 10 and 11 after 13 and 3 days, respectively, due to hydrolysis of ester bonds in the crosslinks of the hydrogel network. The hydrogel was loaded with an anti-VEGF antibody fragment (FAB; 48.4 kDa) or with corticosteroid dexamethasone (dex) by dissolving (FAB) or dispersing (DEX) in the hydrogel precursor solution. The FAB fragment in unmodified form was quantitatively released over 13 days after an initial burst release of 46, 45 and 28 % of the loading for the 5, 10 and 20 wt% hydrogel, respectively, due to gel dehydration during formation. The low molecular weight drug dexamethasone was almost quantitively released in 35 days. The slower release of dexamethasone compared to the FAB fragment can likely be explained by the solubilization of this hydrophobic drug in the hydrophobic domains of the gel. The thermosensitive gels showed good cytocompatibility when brought in contact with macrophage-like mural cells (RAW 264.7) and human retinal pigment epithelium-derived (ARPE-19) cells. This study demonstrates that PNF-PNM thermogel may be a suitable formulation for sustained release of bioactive agents into the eye for treating posterior segment eye diseases.

Biomimetic, Injectable, and Self-Healing Hydrogels with Sustained Release of Ranibizumab to Treat Retinal Neovascularization

Retinal neovascularization (RNV) is a typical feature of ischemic retinal diseases that can lead to traction retinal detachment and even blindness in patients, in which the vascular endothelial cell growth factor (VEGF) plays a pivotal role. However, most anti-VEGF drugs currently used for treating RNV, such as ranibizumab, need frequent and repeated intravitreal injections due to their short intravitreal half-life, which increases the incidence of complications. Herein, a hydrogel intravitreal drug delivery system (DDS) is prepared by a dynamic Schiff base reaction between aminated hyaluronic acid and aldehyde-functionalized Pluronic 127 for sustained release of ranibizumab. The prepared hydrogel system named HP@Ran exhibits excellent injectability, self-healing ability, structural stability, cytocompatibility, and blood compatibility. According to an in vitro drug release study, the hydrogel system continuously releases the model drug bovine serum albumin for more than 56 days. Importantly, in an in vivo rabbit persistent RNV model, the HP@Ran hydrogel system continuously releases pharmacologically active ranibizumab for more than 7 weeks and also exhibits superior anti-angiogenic efficacy over ranibizumab treatment by decreasing vascular leakage and neovascularization at 12 weeks. Thus, the developed HP@Ran hydrogel system possesses great potential for intravitreal DDS for the treatment of RNV.

Six-month sustained delivery of anti-VEGF from in-situ forming hydrogel in the suprachoroidal space

Patients with wet age-related macular degeneration (AMD) require intravitreal injections of bevacizumab (Bev) or other drugs, often on a monthly basis, which is a burden on the healthcare system. Here, we developed an in-situ forming hydrogel comprised of Bev and hyaluronic acid (HA) crosslinked with poly(ethylene glycol) diacrylate for slow release of Bev after injection into the suprachoroidal space (SCS) of the eye using a microneedle. Liquid Bev formulations were cleared from SCS within 5 days, even when formulated with high viscosity, unless Bev was conjugated to a high molecular-weight HA (2.6 MDa), which delayed clearance until 1 month. To extend release to 6 months, we synthesized in-situ forming Bev-HA hydrogel initially as a low-viscosity mixture suitable for injection and flow in the SCS to cover a large area extending to the posterior pole of the eye where the macula is located in humans. Within 1 h after injection, Bev and HA were crosslinked, which retained Bev for slow release as the hydrogel biodegraded. In vivo studies in the rabbit eye reported Bev release for >6 months, depending on gel formulation and Bev assay. The in-situ forming Bev-HA hydrogel was well tolerated, as assessed by clinical exam, fundus imaging, histological analysis, and intraocular pressure measurement. We conclude that Bev released from an in-situ forming hydrogel may enable long-acting treatments of AMD and other posterior ocular indications.

Posttransplant VEGFR1R2 Trap Eye Drops Inhibit Corneal (Lymph)angiogenesis and Improve Corneal Allograft Survival in Eyes at High Risk of Rejection

Purpose

To assess whether topical application of VEGFR1R2 Trap after corneal transplantation can impair corneal (lymph)angiogenesis and promote murine corneal allograft survival in eyes at high risk of rejection.

Methods

We used the murine model of suture-induced neovascularization and subsequent keratoplasty in eyes at high risk of rejection, which is an established model for local drug application. After transplantation, the mice were treated with either VEGFR1R2 Trap (aflibercept) or human IgG Fc as eye drops for 2 weeks (three times/d). Deposition of VEGFR1R2 Trap in corneal tissue was detected by immunohistochemistry. Two and 8 weeks after transplantation, corneal (lymph)angiogenesis was assessed morphometrically. Dendritic cells (DCs) and regulatory T cells (Tregs) in the draining lymph nodes (dLNs) were examined by flow cytometry. Allograft survival was determined by corneal graft opacity scores.

Results

Topically applied VEGFR1R2 Trap penetrated into corneal host and graft stroma after keratoplasty in eyes at high risk of rejection. Additional postsurgical corneal hemangiogenesis (P < 0.0001) and lymphangiogenesis (P < 0.01) as well as infiltrating CD45⁺ leukocytes (P < 0.001) and macrophages (P < 0.01) were significantly reduced in the VEGFR1R2 Trap group compared to controls. VEGFR1R2 Trap eye drops significantly decreased the frequency of total CD11c⁺ DCs (P < 0.01), as well as activated CD11c⁺MHC II⁺ DCs (P < 0.01) and CD11c⁺CD40⁺ DCs (P < 0.05). In contrast, the frequency of CD200R⁺ regulatory DCs (P < 0.05) and Tregs in dLNs (P < 0.01) was enhanced. Moreover, long-term allograft survival was also improved (P < 0.05).

Conclusions

Temporary, topical application of VEGFR1R2 Trap after corneal transplantation can achieve sufficient anti-VEGF activity, inhibit additional (lymph)angiogenesis, and significantly improve corneal allograft survival in eyes at high risk of rejection.

Translational Relevance

VEGFR1R2 Trap eye drops after transplantation present a new therapeutic option for patients undergoing corneal transplantation and are at high risk of graft rejection.

Determining vitreous viscosity using fluorescence recovery after photobleaching

PURPOSE

Vitreous humor is a complex biofluid whose composition determines its structure and function. Vitreous viscosity will affect the delivery, distribution, and half-life of intraocular drugs, and key physiological molecules. The central pig vitreous is thought to closely match human vitreous viscosity. Diffusion is inversely related to viscosity, and diffusion is of fundamental importance for all biochemical reactions. Fluorescence Recovery After Photobleaching (FRAP) may provide a novel means of measuring intravitreal diffusion that could be applied to drugs and physiological macromolecules. It would also provide information about vitreous viscosity, which is relevant to drug elimination, and delivery.

METHODS

Vitreous viscosity and intravitreal macromolecular diffusion of fluorescently labelled macromolecules were investigated in porcine eyes using fluorescence recovery after photobleaching (FRAP). Fluorescein isothiocyanate conjugated (FITC) dextrans and ficolls of varying molecular weights (MWs), and FITC-bovine serum albumin (BSA) were employed using FRAP bleach areas of different diameters.

RESULTS

The mean (±standard deviation) viscosity of porcine vitreous using dextran, ficoll and BSA were 3.54 ± 1.40, 2.86 ± 1.13 and 4.54 ± 0.13 cP respectively, with an average of 3.65 ± 0.60 cP.

CONCLUSIONS

FRAP is a feasible and practical optical method to quantify the diffusion of macromolecules through vitreous.

A Novel Approach for Development of Intraocular Biodegradable Ranibizumab Implant: A Solution for Stability of Protein Activity

Purpose: Ranibizumab is a monoclonal antibody fragment, targeting all isoforms of vascular endothelial growth factor A (VEGF-A), a protein involved in angiogenesis. It is used to treat age-related macular degeneration (AMD), retinal vein occlusion (RVO), and diabetic macular edema (DME), which are associated with blindness worldwide. However, proper treatment can decrease the loss of vision in about 90% of patients. Because of poor drug uptake in topical therapy and several adverse side effects of systemic irregularities and intravitreal injections, sustained-release drug delivery systems are more suitable for treatment. However, there are many challenges in the development of these systems due to the loss of protein activities.

Methods: After drug complexation by the ion pairing method and preparation of a polymeric implant, containing the drug, the characteristics of the complexes were examined by Fourier-transform infrared spectroscopy and circular dichroism spectroscopy. The stability of antibody activity and biocompatibility of the released drug from the implant were assessed by bioassays and MTT assay, respectively. Finally, the release kinetics were investigated.

Results: The bioassays showed the higher activity of the drug complex, compared to the free form, besides good biocompatibility in vitro. Also, the release data confirmed sustained and controlled release characteristics for the prepared implant.

Conclusion: In this study, for the first time, we proposed a method for developing a sustained-release intraocular implant, consisting of ranibizumab by the heating method. This method allows for the industrial production of ranibizumab by extrusion and eliminates the complications related to reservoir systems.

Time-Resolved Fluorescence Anisotropy and Molecular Dynamics Analysis of a Novel GFP Homo-FRET Dimer

Förster resonance energy transfer (FRET) is a powerful tool to investigate the interaction between proteins in living cells. Fluorescence proteins, such as the green fluorescent protein (GFP) and its derivatives, are coexpressed in cells linked to proteins of interest. Time-resolved fluorescence anisotropy is a popular tool to study homo-FRET of fluorescent proteins as an indicator of dimerization, in which its signature consists of a very short component at the beginning of the anisotropy decay. In this work, we present an approach to study GFP homo-FRET via a combination of time-resolved fluorescence anisotropy, the stretched exponential decay model, and molecular dynamics simulations. We characterize a new, to our knowledge, FRET standard formed by two enhanced GFPs (eGFPs) and a flexible linker of 15 aminoacids (eGFP15eGFP) with this protocol, which is validated by using an eGFP monomer as a reference. An excellent agreement is found between the FRET efficiency calculated from the fit of the eGFP15eGFP fluorescence anisotropy decays with a stretched exponential decay model (〈EFRETexp〉 = 0.25 ± 0.05) and those calculated from the molecular dynamics simulations (〈EFRETMD〉 = 0.18 ± 0.14). The relative dipole orientation between the GFPs is best described by the orientation factors 〈κ2〉 = 0.17 ± 0.16 and 〈|κ|〉 = 0.35 ± 0.20, contextualized within a static framework in which the linker hinders the free rotation of the fluorophores and excludes certain configurations. The combination of time- and polarization-resolved fluorescence spectroscopy with molecular dynamics simulations is shown to be a powerful tool for the study and interpretation of homo-FRET.

PET study of ocular and blood pharmacokinetics of intravitreal bevacizumab and aflibercept in rats

Intravitreal injections are the standard procedure in the treatment of retinal pathologies, such as the administration of the anti-VEGF antibodies in age-related macular degeneration. The aim of this study is to evaluate the intraocular and blood pharmacokinetics after an intravitreal injection of ⁸⁹Zr-labelled bevacizumab and ⁸⁹Zr-labelled aflibercept in Sprague-Dawley rats using Positron Emission Tomography. First, both antibodies were radiolabelled to zirconium-89 with a maximum specific activity of 15 Mbq/mg for bevacizumab and 10 Mbq/mg for aflibercept. Four µL containing 1-1.2 Mq of ⁸⁹Zr-labelled compound were injected into the vitreous through a 35 G needle. A microPET acquisition was carried out immediately after the injection and at different time points through a 12-day study and blood samples were obtained through the tail vein. Radiolabelling was successfully performed with a radiochemical purity after ultrafiltration above 95% for both agents. Both antibodies ocular curves followed a two-compartment model in which an intraocular elimination half-life of 16.44 h was found for ⁸⁹Zr-bevacizumab and 4.51 h for ⁸⁹Zr-aflibercept, considering the alpha phase as the elimination phase. Regarding the beta phase, a half-life of 3.23 days for ⁸⁹Zr-bevacizumab and 4.69 days for ⁸⁹Zr-aflibercept were observed. With regards to blood concentration, ⁸⁹Zr-bevacizumab showed a blood half-life of 7.08 days, whereas ⁸⁹Zr-aflibercept's was 3.18 days, by a one-compartment model with first-order absorption kinetics. In conclusion, this study shows for the first time the ocular and blood pharmacokinetic analysis after intravitreal injection of aflibercept and bevacizumab in rats.

Influence of molecular weight on transdermal delivery of model macromolecules using hydrogel-forming microneedles: potential to enhance the administration of novel low molecular weight biotherapeutics

With a view to improve the current monoclonal antibody-based therapies dominating the pharmaceutical market, low molecular weight (MW) protein-based macromolecules, such as recombinant antibody fragments, typically within the range of 10-70 kDa, have been developed. Previously, our group successfully delivered Avastin®, a monoclonal antibody (mAb) across the skin using hydrogel-forming microneedles (MN). However, it is thought that this delivery system can be further enhanced using novel, lower MW biomolecules. To address this perception, in the current study, FITC-dextran of different MWs (10, 70 and 150 kDa) was used to model the transdermal delivery of low MW biotherapeutics and mAbs with MWs of approximately 150 kDa. Conversely, fluorescein sodium was the compound selected to model hydrophilic, low MW drugs. As expected, fluorescein sodium produced the greatest cumulative permeation (637.4 ± 42.69 μg). The amounts of FITC-dextran 10 kDa and 150 kDa which permeated across neonatal porcine skin in vitro were 462.17 ± 65.85 μg and 213.54 ± 15.19 μg after 24 h, respectively. The results collated here suggest that the delivery of emerging novel biotherapeutics, via'super swelling' hydrogel-forming MNs, have the potential to result in greater permeation across human skin, compared to the delivery of mAbs delivered via the same route.

Comprehensive biophysical and functional study of ziv-aflibercept: characterization and forced degradation

Aflibercept (AFL) is an Fc fusion protein used in the treatment of colorectal cancers and different ophthalmological diseases. There are two medicines in which AFL is the active substance: Zaltrap and Eylea, referred as ziv-AFL and AFL respectively. No proper accelerated degradation studies were published on either AFL or ziv-AFL. These studies are essential during research, development and manufacturing stages. Here, we characterized ziv-AFL and submitted it to different stress conditions: light, 60 °C, freeze-thaw cycles, changes in pH, high hypertonic solution and strong denaturing conditions. We used an array of techniques to detect aggregation (SE-HPLC/DAD and DLS), changes in secondary structure (Far-UV circular dichroism), changes in conformation or tertiary structure (Intrinsic tryptophan fluorescence) and alterations in functionality (ELISA). Results indicate that aggregation is common degradation pathway. Two different types of aggregates were detected: dimers and high molecular weight aggregates attributed to β-amyloid-like structures. Secondary structure was maintained in most of the stress tests, while conformation was altered by almost all the tests except for the freeze-thaw cycles. Functionality, evaluated by its immunochemical reaction with VEGF, was found to be stable but with decrease when exposed to light and with likely partial inactivation of the drug when pH was altered.

Ocular Half-Life of Intravitreal Biologics in Humans and Other Species: Meta-Analysis and Model-Based Prediction

Therapeutic antibodies administered intravitreally are the current standard of care to treat retinal diseases. The ocular half-life (t_1/2) is a key determinant of the duration of target suppression. To support the development of novel, longer-acting drugs, a reliable determination of t_1/2 is needed together with an improved understanding of the factors that influence it. A model-based meta-analysis was conducted in humans and nonclinical species (rat, rabbit, monkey, and pig) to determine consensus values for the ocular t_1/2 of IgG antibodies and Fab fragments. Results from multiple literature and in-house pharmacokinetic studies are presented within a mechanistic framework that assumes diffusion-controlled drug elimination from the vitreous. Our analysis shows, both theoretically and experimentally, that the ocular t_1/2 increases in direct proportion to the product of the hydrodynamic radius of the macromolecule (3.0 nm for Fab and 5.0 nm for IgG) and the square of the radius of the vitreous globe, which varies approximately 24-fold from the rat to the human. Interspecies differences in the proportionality factors are observed and discussed in mechanistic terms. In addition, mathematical formulae are presented that allow prediction of the ocular t_1/2 for molecules of interest. The utility of these formulae is successfully demonstrated in case studies of aflibercept, brolucizumab, and PEGylated Fabs, where the predicted ocular t_1/2 values are found to be in reasonable agreement with the experimental data available for these molecules.

Fluorescence anisotropy imaging in drug discovery

Non-invasive measurement of drug-target engagement can provide critical insights in the molecular pharmacology of small molecule drugs. Fluorescence polarization/fluorescence anisotropy measurements are commonly employed in protein/cell screening assays. However, the expansion of such measurements to the in vivo setting has proven difficult until recently. With the advent of high-resolution fluorescence anisotropy microscopy it is now possible to perform kinetic measurements of intracellular drug distribution and target engagement in commonly used mouse models. In this review we discuss the background, current advances and future perspectives in intravital fluorescence anisotropy measurements to derive pharmacokinetic and pharmacodynamic measurements in single cells and whole organs.

A validated size exclusion chromatography method coupled with fluorescence detection for rapid quantification of bevacizumab in ophthalmic formulations

Bevacizumab is a full-length human monoclonal antibody used to treat various neovascular diseases such as wet age-related macular degeneration (AMD), diabetic eye disease and other problems of the retina. Monthly intravitreal injections of bevacizumab (Avastin^®) are effective in the treatment of wet AMD. However, there is a growing demand in the development of sustained release ophthalmic formulations. Therefore, this study aims, for the first time, to develop a rapid, simple, and sensitive method using size exclusion chromatography coupled with fluorescence detection for routine quantification of bevacizumab in ophthalmic formulations and during in vitro release studies. The selected chromatographic conditions included an aqueous mobile phase composed of 35 mM sodium phosphate buffer and 300 mM sodium chloride (pH 6.8), a flow rate of 0.5 mL/min, and the fluorescence detector was operated at excitation and emission wavelengths of 280 and 340 nm, respectively. The peak area-concentration relationship maintained its linearity over concentration range of 0.1-20 μg/mL (R² = 0.9993), and the quantitation limit was 100 ng/mL. The method was validated for specificity, accuracy, precision, and robustness. The developed method had a run time of 6 min at temperature 25 °C, making it a unique validated method for rapid and cost-effective quantification of bevacizumab.

Pharmaceutical Formulation Methods for Improving Retinal Drug Delivery

Clinical pharmacology training for clinicians typically focuses on a drug's Active Pharmaceutical Ingredient. However, pharmaceutical formulation, the process of optimizing manufacturing methods and excipients to make a final drug product, is a critical process in determining whether a potential drug can become a realistic, routinely used therapeutic agent. This review focuses on the formulation methods used in commonly prescribed retina drug products.

Focused ultrasound combined with microbubble-mediated intranasal delivery of gold nanoclusters to the brain

Focused ultrasound combined with microbubble-mediated intranasal delivery (FUSIN) is a new brain drug delivery technique. FUSIN utilizes the nasal route for direct nose-to-brain drug administration, thereby bypassing the blood-brain barrier (BBB) and minimizing systemic exposure. It also uses FUS-induced microbubble cavitation to enhance transport of intranasally (IN) administered agents to the FUS-targeted brain location. Previous studies have provided proof-of-concept data showing the feasibility of FUSIN to deliver dextran and the brain-derived neurotrophic factor to the caudate putamen of mouse brains. The objective of this study was to evaluate the biodistribution of IN administered gold nanoclusters (AuNCs) and assess the feasibility and short-term safety of FUSIN for the delivery of AuNCs to the brainstem. Three experiments were performed. First, the whole-body biodistribution of IN administered 64Cu-alloyed AuNCs (64Cu-AuNCs) was assessed using in vivo positron emission tomography/computed tomography (PET/CT) and verified with ex vivo gamma counting. Control mice were intravenously (IV) injected with the 64Cu-AuNCs. Second, 64Cu-AuNCs and Texas red-labeled AuNCs (TR-AuNCs) were used separately to evaluate FUSIN delivery outcome in the brain. 64Cu-AuNCs or TR-AuNCs were administered to mice through the nasal route, followed by FUS sonication at the brainstem in the presence of systemically injected microbubbles. The spatial distribution of 64Cu-AuNCs and TR-AuNCs were examined by autoradiography and fluorescence microscopy of ex vivo brain slices, respectively. Third, histological analysis was performed to evaluate any potential histological damage to the nose and brain after FUSIN treatment. The experimental results revealed that IN administration induced significantly lower 64Cu-AuNCs accumulation in the blood, lungs, liver, spleen, kidney, and heart compared with IV injection. FUSIN enhanced the delivery of 64Cu-AuNCs and TR-AuNCs at the FUS-targeted brain region compared with IN delivery alone. No histological-level tissue damage was detected in the nose, trigeminal nerve, and brain. These results suggest that FUSIN is a promising technique for noninvasive, spatially targeted, and safe delivery of nanoparticles to the brain with minimal systemic exposure.

Transient alleviation of tumor hypoxia during first days of antiangiogenic therapy as a result of therapy-induced alterations in nutrient supply and tumor metabolism - Analysis by mathematical modeling

A number of experiments on mouse tumor models, as well as certain clinical data, have demonstrated, that antiangiogenic therapy can lead to transient improvement in tumor oxygenation, that allows to increase efficiency of following radiotherapy. In the majority of works, this phenomenon has been explained by enhanced tumor perfusion due to normalization of capillaries' structure, that results in elevated oxygen inflow in tumor. However, changes in tumor perfusion often haven't been directly measured in relevant works, moreover, antiangiogenic therapy has been proven to have ambiguous effect on tumor perfusion both in mouse tumor models and in clinics. Herein, we suggest that elevation of blood perfusion may be not the only reason for transient alleviation of tumor hypoxia, and that it may manifest itself even under unchanged tumor blood flow. We propose that it may be as well caused by the decrease in tumor oxygen consumption rate (OCR) due to the reduction of tumor proliferation level, caused by nutrient shortage in result of antiangiogenic treatment. We provide detailed explanation of this hypothesis and visualize it using a specially developed mathematical model, which takes into account basic features of tumor growth and antiangiogenic therapy. We investigate the influence of the model parameters on oxygen dynamics; demonstrate, that transient alleviation of tumor hypoxia occurs in a fairly wide range of physiologically justified values of parameters; and point out the major factors, that determine oxygen dynamics during antiangiogenic therapy.

Modulating release of ranibizumab and aflibercept from thiolated chitosan-based hydrogels for potential treatment of ocular neovascularization

BACKGROUND

This paper describes the synthesis of thiolated chitosan-based hydrogels with varying degrees of crosslinking that has been utilized to modulate release kinetics of two clinically relevant FDA-approved anti-VEGF protein drugs, ranibizumab and aflibercept. These hydrogels have been fabricated into disc shaped structures for potential use as patches on ocular surface.

METHODS

Protein conformational changes and aggregation after loading and release was evaluated by circular dichroism (CD), steady-state tryptophan fluorescence spectroscopy, electrophoresis and size-exclusion chromatography (SEC). Finally, the capacity of both released proteins to bind to VEGF was tested by ELISA and surface plasmon resonance (SPR) technology.

RESULTS

The study demonstrates the versatility of thiolated chitosan-based hydrogels for delivering proteins. The effect of various parameters of the hydrogel on protein release kinetics and mechanism of protein release was studied using the Korsmeyer-Peppas release model. Furthermore, we have studied the stability of released proteins in detail while comparing it with non-entrapped proteins under physiological conditions to understand the effect of formulation conditions on protein stability.

CONCLUSIONS

The disc-shaped thiolated chitosan-based hydrogels provide a potentially useful platform to deliver ranibizumab and aflibercept for the treatments of ocular diseases such as wet AMD, DME and corneal neovascularization.

Photon counting phosphorescence lifetime imaging with TimepixCam

TimepixCam is a novel fast optical imager based on an optimized silicon pixel sensor with a thin entrance window and read out by a Timepix Application Specific Integrated Circuit. The 256 × 256 pixel sensor has a time resolution of 15 ns at a sustained frame rate of 10 Hz. We used this sensor in combination with an image intensifier for wide-field time-correlated single photon counting imaging. We have characterised the photon detection capabilities of this detector system and employed it on a wide-field epifluorescence microscope to map phosphorescence decays of various iridium complexes with lifetimes of about 1 μs in 200 μm diameter polystyrene beads.

Confocal Luminescence Lifetime Imaging with Variable Scan Velocity and Its Application to Oxygen Sensing

The dependence of the luminescence lifetime on the probe environment is the basis of a range of sensing techniques. The major advantage of using the lifetime as the sensitive parameter is its independence on the probe concentration. However, the instrumentation for lifetime measurements is complex, generally requiring time-resolved excitation and detection. Here, we present a simple method for the measurement of luminescence lifetimes on the microsecond scale based on variable excitation time determined by the scanning velocity. The technique is implemented in a confocal laser scanning microscope (CLSM), thus allowing not only simple lifetime measurement but also phosphorescence lifetime imaging. Since the method exploits the spatiotemporal dependence of sample excitation in a CLSM, there is no need for a pulsed or modulated light source or for additional time-resolved detection. The method can be realized in a standard CLSM without any modifications. The principle is demonstrated on oxygen sensing by collisional quenching of an oxygen-sensitive ruthenium(II) complex.