Prediction of intraocular antibody drug stability using ex-vivo ocular model

Assessing Physicochemical Stability of Monoclonal Antibodies in a Simulated Subcutaneous Environment

Monoclonal antibodies (mAbs) are being increasingly administered by the subcutaneous (SC) route compared to the traditional intravenous route. Despite the growing popularity of the subcutaneous route, our current knowledge regarding the intricate mechanistic changes happening in the formulation after injection in the subcutaneous space, as well as the in vivo stability of administered mAbs, remains quite limited. Changes in the protein environment as it transitions from a stabilized, formulated drug product in an appropriate container closure to the SC tissue environment can drastically impact the structural stability and integrity of the injected protein. Interactions of the protein with components of the extracellular matrix can lead to changes in its structure, potentially impacting both safety and efficacy. Investigating protein stability in the SC space can enable early assessment of risk and performance of subcutaneously administered proteins influencing clinical decisions and formulation development strategies. The Subcutaneous Injection Site Simulator (SCISSOR) is a novel in vitro system that mimics the subcutaneous injection site and models the events that a protein goes through as it transitions from a stabilized formulation environment to the dynamic physiological space. In this paper, we utilize the SCISSOR to probe for biophysical and chemical changes in seven mAbs post SC injection using a variety of analytical techniques. After 24 h, all mAbs demonstrated a relative decrease in conformational stability, an increase in fragmentation, and elevated acidic species. Higher order structure analysis revealed a deviation in the secondary structure from the standard and an increase in the number of unordered species. Our findings suggest an overall reduced stability of mAbs after subcutaneous administration. This reduced stability could have a potential impact on safety and efficacy. In vitro systems such as the SCISSOR combined with downstream analyses have potential to provide valuable information for assessing the suitability of lead molecules and aid in formulation design optimized for administration in the intended body compartment, thus improving chances of clinical success.

Intraocular delivery considerations of ocular biologic products and key preclinical determinations

INTRODUCTION

Ophthalmic diseases of the retina are a significant cause of vision loss globally. Despite much progress, there remains an unmet need for durable, long-acting treatment options. While biologic therapies show great promise, they present many challenges, including complexities in biochemical properties, mechanism of action, manufacturing considerations, preclinical evaluation, and delivery mechanism; these are confounded by the unique anatomy and physiology of the eye itself.

AREAS COVERED

This review describes the current development status of intravitreally administered drugs for the treatment of ophthalmic disease, outlines the range of approaches that can be considered for sustained drug delivery to the eye, and discusses key preclinical considerations for the evaluation of ocular biologics.

EXPERT OPINION

The required frequency of dosing in the eye results in a great burden on both patients and the health care system, with direct intraocular administration remaining the most reliable and predictable route. Sustained and controlled ophthalmic drug delivery systems will go a long way in reducing this burden. Sustained delivery can directly dose target tissues, improving bioavailability and reducing off-target systemic effects. Maintaining stability and activity of compounds can prevent aggregation and enable extended duration of release, while sustaining dosage and preventing residual polymer after drug depletion.

Protein Stability After Administration: A Physiologic Consideration

Regulatory authorities and the scientific community have identified the need to monitor the in vivo stability of therapeutic proteins (TPs). Due to the unique physiologic conditions in patients, the stability of TPs after administration can deviate largely from their stability under drug product (DP) conditions. TPs can degrade at substantial rates once immersed in the in vivo milieu. Changes in protein stability upon administration to patients are critical as they can have implications on patient safety and clinical effectiveness of DPs. Physiologic conditions are challenging to simulate and require dedicated in vitro models for specific routes of administration. Advancements of in vitro models enable to simulate the exposure to physiologic conditions prior to resource demanding pre-clinical and clinical studies. This enables to evaluate the in vivo stability and thus may allow to improve the safety/efficacy profile of DPs. While in vitro-in vivo correlations are challenging, benchmarking DP candidates enables to identify liabilities and optimize molecules. The in vivo stability should be an integral part of holistic stability assessments during early development. Such assessments can accelerate development timelines and lead to more stable DPs for patients.

Analytical Challenges Assessing Protein Aggregation and Fragmentation Under Physiologic Conditions

Therapeutic proteins are administered by injection or infusion. After administration, the physiologic environment in the desired body compartment - fluid or tissue - can impact protein stability and lead to changes in the safety and/or efficacy profile. For example, protein aggregation and fragmentation are critical quality attributes of the drug product and can occur after administration to patients. In this context, the in vivo stability of therapeutic proteins has gained increasing attention. However, in vivo protein aggregation and fragmentation are difficult to assess and have been rarely investigated. This mini-review summarizes analytical approaches to assess the stability of therapeutic proteins using simulated physiologic conditions. Furthermore, we discuss factors potentially causing in vivo protein aggregation, precipitation, and fragmentation in complex biological fluids. Different analytical approaches are evaluated with respect to their applicability and possible shortcomings when it comes to these degradation events in biological fluids. Tracking protein stability in biological fluids typically requires purifying or labeling the protein of interest to circumvent matrix interference of biological fluids. Improved analytical methods are strongly needed to gain knowledge on in vivo protein aggregation and fragmentation. In vitro models can support the selection of lead candidates and accelerate the pre-clinical development of therapeutic proteins.

Stability of monoclonal antibodies after simulated subcutaneous administration

Changes in the environment from the drug product to the human physiology might lead to physical and/or chemical modifications of the protein drug, such as in vivo aggregation and fragmentation. Although subcutaneous (SC) injection is a common route of administration for therapeutic proteins, knowledge on in vivo stability in the SC tissue is limited. In this study, we developed a physiologic in vitro model simulating the SC environment in patients. We assessed the stability of two monoclonal antibodies (mAbs) in four different protein-free fluids under physiologic conditions. We monitored protein stability over two weeks using a range of analytical methods, in analogy to testing purposes of a drug product. Both mAbs showed an increase of protein aggregates, fragments, and acidic species. mAb1 was consistently more stable in this in vitro model than mAb2, highlighting the importance of comparing the stability of different mAbs under physiologic conditions. Throughout the study, both mAbs were substantially less stable in bicarbonate buffers as compared to phosphate-buffered saline. In summary, our developed model was able to differentiate stability between molecules. Bicarbonate buffers were more suitable compared to phosphate-buffered saline in regards to simulating the in vivo conditions and evaluating protein liabilities.

Long-Term Stability of Anti-Vascular Endothelial Growth Factor (a-VEGF) Biologics Under Physiologically Relevant Conditions and Its Impact on the Development of Long-Acting Delivery Systems

The port delivery system with ranibizumab (PDS) is an investigational long-acting drug delivery system for the continuous release of ranibizumab, an anti-VEGF biologic, in the vitreous humor. The efficacy of the PDS implant relies on the maintenance of long-term drug stability under physiological conditions. Herein, the long-term stability of three anti-VEGF biologics - ranibizumab, bevacizumab and aflibercept - was investigated in phosphate buffered saline (PBS) at 37 °C for several months. Comparison of stability profiles shows that bevacizumab and aflibercept are increasingly prone to aggregation whereas ranibizumab undergoes minimal aggregation. Ranibizumab also shows the smallest loss in antigen binding capacity after long-term incubation in PBS. Even though the aggregated forms of bevacizumab and aflibercept bind to VEGF, the consequences of aggregation on immunogenicity, implant function and efficacy are unknown. These results highlight the importance of maintaining long-term drug stability under physiologically relevant conditions which is necessary for achieving efficacy with an in vivo continuous drug delivery device such as the PDS implant.

Role of Formulation Parameters on Intravitreal Dosing Accuracy Using 1 mL Hypodermic Syringes

PURPOSE

Evaluation of product viscosity, density and aeration on the dose delivery and accuracy for intravitreal injections with commonly used commercially available hypodermic 1 mL syringes.

METHODS

Six commercially available hypodermic 1 mL syringes with different specifications were used for the study. Syringes were filled with the test solutions with different densities and viscosities. Syringes were also subjected to shaking stress to introduce aeration in the test solutions in the presence of different surfactant concentrations with and without high antibody concentration. Target intravitreal volumes of 100 μL, 50 μL and 30 μL were tested to assess dosing accuracy in a controlled simulated administration setup using DIN ISO 11040-4 guidelines and Zwick/Roell Z010 TN instrument.

RESULTS

With increasing product viscosity, higher volumes and hence doses were delivered especially for very low volumes like 50 μL and 30 μL. No impact of increasing product density was found on the delivered dose. The presence of surfactants or high protein concentration can lead to aeration, which also negatively affects the dose accuracy and precision.

CONCLUSION

Formulation parameters like viscosity can have an impact on dose delivery using hypodermic syringes for intravitreal injections and on the resulting glide force.

Characterization, Stability, and in Vivo Efficacy Studies of Recombinant Human CNTF and Its Permeation into the Neural Retina in ex Vivo Organotypic Retinal Explant Culture Models

Ciliary neurotrophic factor (CNTF) is one of the most studied neuroprotective agents with acknowledged potential in treating diseases of the posterior eye segment. Although its efficacy and mechanisms of action in the retina have been studied extensively, it is still not comprehensively understood which retinal cells mediate the therapeutic effects of CNTF. As with therapeutic proteins in general, it is poorly elucidated whether exogenous CNTF administered into the vitreous can enter and distribute into the retina and hence reach potentially responsive target cells. Here, we have characterized our purified recombinant human CNTF (rhCNTF), studied the protein’s in vitro bioactivity in a cell-based assay, and evaluated the thermodynamic and oligomeric status of the protein during storage. Biological activity of rhCNTF was further evaluated in vivo in an animal model of retinal degeneration. The retinal penetration and distribution of rhCNTF after 24 h was studied utilizing two ex vivo retina models. Based on our characterization findings, our rhCNTF is correctly folded and biologically active. Moreover, based on initial screening and subsequent follow-up, we identified two buffers in which rhCNTF retains its stability during storage. Whereas rhCNTF did not show photoreceptor preservative effect or improve the function of photoreceptors in vivo, this could possibly be due to the used disease model or the short duration of action with a single intravitreal injection of rhCNTF. On the other hand, the lack of in vivo efficacy was shown to not be due to distribution limitations; permeation into the retina was observed in both retinal explant models as in 24 h rhCNTF penetrated the inner limiting membrane, and being mostly observed in the ganglion cell layer, distributed to different layers of the neural retina. As rhCNTF can reach deeper retinal layers, in general, having direct effects on resident CNTF-responsive target cells is plausible.

Ocular Drug Delivery: A Special Focus on the Thermosensitive Approach

The bioavailability of ophthalmic therapeutics is reduced because of the presence of physiological barriers whose primary function is to hinder the entry of exogenous agents, therefore also decreasing the bioavailability of locally administered drugs. Consequently, repeated ocular administrations are required. Hence, the development of drug delivery systems that ensure suitable drug concentration for prolonged times in different ocular tissues is certainly of great importance. This objective can be partially achieved using thermosensitive drug delivery systems that, owing to their ability of changing their state in response to temperature variations, from room to body temperature, may increase drug bioavailability. In the case of topical instillation, in situ forming gels increase pre-corneal drug residence time as a consequence of their enhanced adhesion to the corneal surface. Otherwise, in the case of intraocular and periocular, i.e., subconjunctival, retrobulbar, peribulbar administration, among others, they have the undoubted advantage of being easily injectable and, owing to their sudden thickening at body temperature, have the ability to form an in situ drug reservoir. As a result, the frequency of administration can be reduced, also favoring the patient’s adhesion to therapy. In the main section of this review, we discuss some of the most common treatment options for ocular diseases, with a special focus on posterior segment treatments, and summarize the most recent improvement deriving from thermosensitive drug delivery strategies. Aside from this, an additional section describes the most widespread in vitro models employed to evaluate the functionality of novel ophthalmic drug delivery systems.

Advancements in Understanding Immunogenicity of Biotherapeutics in the Intraocular Space

Therapeutic breakthroughs in a number of retinal degenerative diseases have come about through the development of biotherapeutics administered directly into the eye. As a consequence of their use, we have gained more insight into the immune privileged status of the eye and the various considerations that development, manufacturing, and use of these drugs require. It has been observed that therapeutic proteins injected into the vitreous can elicit an immune response resulting in the production of anti-drug antibodies (ADAs) which can have clinical consequences. This review includes discussion of the anatomy, physiology, and specific area of the eye that are targeted for drug administration. The various immunologic mechanisms involved in the immune responses to intraocularly administered protein are discussed. This review entails discussion on chemistry, manufacturing, and control (CMC) and formulation-related issues that may influence the risk of immunogenicity. Based on the available immunogenicity profile of the marketed intraocular drugs and their reported adverse events, the animal models and the translational gap from animals to human are discussed. Thus, the objective of this review article is to assess the factors that influence immunogenicity in relation to intraocular administration and the steps taken for mitigating immunogenicity risks.