Challenges and Opportunities for the Subcutaneous Delivery of Therapeutic Proteins

Biotherapeutics is a rapidly growing drug class, and over 200 biotherapeutics have already obtained approval, with about 50 of these being approved in 2015 and 2016 alone. Several hundred protein therapeutic products are still in the pipeline, including interesting new approaches to treatment. Owing to patients' convenience of at home administration and reduced number of hospital visits as well as the reduction in treatment costs, subcutaneous (SC) administration of biologics is of increasing interest. Although several avenues for treatment using biotherapeutics are being explored, there is still a sufficient gap in knowledge regarding the interplay of formulation conditions, immunogenicity, and pharmacokinetics (PK) of the absorption of these compounds when they are given SC. This review seeks to highlight the major concerns and important factors governing this route of administration and suggest a holistic approach for effective SC delivery.     

Structure-Immunogenicity Relationships of Therapeutic Proteins

As more recombinant human proteins become available on the market, the incidence of immunogenicity problems is rising. The antibodies formed against a therapeutic protein can result in serious clinical effects, such as loss of efficacy and neutralization of the endogenous protein with essential biological functions. Here we review the literature on the relations between the immunogenicity of the therapeutic proteins and their structural properties. The mechanisms by which protein therapeutics can induce antibodies as well as the models used to study immunogenicity are discussed. Examples of how the chemical structure (including amino acid sequence, glycosylation, and pegylation) can influence the incidence and level of antibody formation are given. Moreover, it is shown that physical degradation (especially aggregation) of the proteins as well as chemical decomposition (e.g., oxidation) may enhance the immune response. To what extent the presence of degradation products in protein formulations influences their immunogenicity still needs further investigation. Immunization of transgenic animals, tolerant for the human protein, with well-defined, artificially prepared degradation products of therapeutic proteins may shed more light on the structure-immunogenicity relationships of recombinant human proteins.     

Formulation Development for Hydrophobic Therapeutic Proteins

The major challenges in formulation development for hydrophobic proteins are low solubility often combined with a strong tendency for adsorption. Human serum albumin (HSA) is frequently used as excipient to overcome these problems. Due to several drawbacks with HSA, new ways need to be found to circumvent the use of this excipient in protein formulations. One possible approach is to select an appropriate formulation pH and ionic strength in combination with excipients that provide sufficient stability and solubility for the hydrophobic protein. A reduction in adsorption can be achieved by adding surfactants or using special containers.     

合理的分子设计与工程化蛋白质药物

治疗性蛋白的分子设计与工程化已取得突破进展,基因工程药物已进入了第三代蛋白质治疗药物发展新阶段。文章重点介绍了蛋白质工程技术在优化蛋白质的疗效、稳定性、靶向性、特异性以及改善免疫原性和药代动力学等方面的分子设计策略,并结合本实验室的研究工作介绍了新近研究成功的蛋白质工程药物类型。对近年来在蛋白质工程药物研究中,常采用的的一些新技术,新方法,如点突变技术、融合蛋白技术、DNA改组技术、分子定向进化技术和蛋白质分子展示技术也作了简要讨论,同时还展望了合理的分子设计与蛋白质工程药物的发展前景。     

Controlled Delivery Systems for Proteins Using Polyanhydride Microspheres

A method to provide near-constant sustained release of high molecular weight, water-soluble proteins from polyanhydride microspheres is described. The polyanhydrides used were poly (fatty acid dimer) (PFAD), poly(sebacic acid) (PSA), and their copolymers [P(FAD-SA)]. P(FAD-SA) microspheres containing proteins of different molecular sizes—lysozyme, trypsin, heparinase, ovalbumin, albumin, and immunoglobulin—were prepared by a solvent evaporation method using a double emulsion. The microspheres containing proteins were spherical, with diameters of 50–125 µm, and encapsulated more than 80% of the protein, irrespective of the protein used. Enzymatic activity studies showed that encapsulation of enzymes inside polyanhydride microspheres can protect them from activity loss. When not placed inside polyanhydride microspheres, trypsin lost 80% of its activity in solution at 37°C at pH 7.4 in 12 hr, whereas inside the polyanhydride microspheres the activity loss was less than 10% under these conditions. About 47% of the enzymatic activity of heparinase encapsulated in the microspheres was lost at 37°C in 24 hr, while in solution it lost over 90% of its activity. The protein-loaded microspheres displayed near-zero-order erosion kinetics over 5 days as judged by the release of sebacic acid (SA) from the microspheres. The microspheres degraded to form SA and FAD monomers. All proteins were released at a near-constant rate without any large initial burst, irrespective of polymer molecular weight and protein loading. The period of protein release was longer than that of SA and continued protein release was observed even after the microsphere matrix had completely degraded. Differential scanning calorimetric studies demonstrated an interaction between protein and the FAD monomers produced with microsphere degradation. It is likely that the protein interaction with FAD monomers permits formation of water-insoluble protein aggregates which slowly dissolve and diffuse out of the matrix, leading to delayed protein release. For trypsin-loaded microspheres, trypsin lost 40% of its activity during microsphere preparation. Activity studies demonstrated that the sonication process was primarily responsible for activity loss. A reduction in the period of ultrasound exposure decreased the loss of protein activity to around 20%.     

Protein Nanoparticles for Intracellular Delivery of Therapeutic Enzymes

The use of enzymes as therapeutics is very promising because of their catalytic activity and specificity. However, intracellular delivery of active enzymes is challenging due to their low stability and large size. The production of protein-enzyme nanoparticles was investigated with the goal of developing a protein carrier for active enzyme delivery. β-Galactosidase (β-gal), an enzyme whose deficiency is the cause of some lysosomal storage disorders, was incorporated into enhanced green fluorescent protein nanoparticles prepared via desolvation. Particle size was found to be sensitive to the type of cross-linker, cross-linking time, and the presence of imidazole. The results indicate that β-gal activity is highly retained (>70%) after particle fabrication and >85% of protein is incorporated in the particles. Protein-enzyme nanoparticles exhibited higher internalization in multiple cell lines in vitro, compared with the soluble enzyme. Importantly, β-gal retained its activity following intracellular delivery. These data demonstrate that protein nanoparticles are a biocompatible, high-efficiency alternative for intracellular delivery of active enzyme therapeutics. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:1863–1871, 2014     

Microfluidic Approaches for the Characterization of Therapeutic Proteins

In the last decades, the pharmaceutical market has experienced an increase in the number of therapeutic proteins. The high activity and selectivity of these macromolecules is often achieved at the expense of complex structures, which exhibit several biophysical properties that must be carefully controlled and optimized for the successful development of these drugs as well as for guaranteeing their quality and safety. This need has motivated the application of a variety of biophysical techniques to analyze properties of therapeutic proteins and protein solutions including interactions, aggregation, solubility, viscosity, and thermal stability. After briefly summarizing currently available experimental approaches, we highlight the emerging possibilities offered by advances in microfluidic technology for the analysis of therapeutic proteins during manufacturing and formulation.     

Cytosolic Delivery of Liposomally Targeted Proteins Induced by Photochemical Internalization

Purpose The application of therapeutic proteins is often hampered by limited cell entrance and lysosomal degradation, as intracellular targets are not reached. By encapsulation of proteins into targeted liposomes, cellular uptake via endocytosis can be enhanced. To prevent subsequent lysosomal degradation and promote endosomal escape, photochemical internalization (PCI) was studied here as a tool to enhance endosomal escape. PCI makes use of photosensitising agents which localize in endocytic vesicles, inducing endosomal release upon light exposure. Materials and Methods The cytotoxic protein saporin was encapsulated in different types of targeted liposomes. Human ovarian carcinoma cells were incubated with the photosensitiser TPPS2a and liposomes. To achieve photochemical internalization, the cells were illuminated for various time periods. Cell viability was used as read-out. Illumination time and amount of encapsulated proteins were varied to investigate the influence of these parameters. Results The cytotoxic effect of liposomally targeted saporin was enhanced by applying PCI, likely due to enhanced endosomal escape. The cytotoxic effect was dependent on the amount of encapsulated saporin and the illumination time. Conclusion PCI is a promising technique for promoting cytosolic delivery of liposomally targeted saporin. PCI may also be applicable to other liposomally targeted therapeutic proteins with intracellular targets.     

Preclinical Models Used for Immunogenicity Prediction of Therapeutic Proteins

All therapeutic proteins are potentially immunogenic. Antibodies formed against these drugs can decrease efficacy, leading to drastically increased therapeutic costs and in rare cases to serious and sometimes life threatening side-effects. Many efforts are therefore undertaken to develop therapeutic proteins with minimal immunogenicity. For this, immunogenicity prediction of candidate drugs during early drug development is essential. Several in silico, in vitro and in vivo models are used to predict immunogenicity of drug leads, to modify potentially immunogenic properties and to continue development of drug candidates with expected low immunogenicity. Despite the extensive use of these predictive models, their actual predictive value varies. Important reasons for this uncertainty are the limited/insufficient knowledge on the immune mechanisms underlying immunogenicity of therapeutic proteins, the fact that different predictive models explore different components of the immune system and the lack of an integrated clinical validation. In this review, we discuss the predictive models in use, summarize aspects of immunogenicity that these models predict and explore the merits and the limitations of each of the models.     

蛋白质和肽类药物结部给药新剂型—吸入粉雾剂

蛋白质和肽类药物的常用制剂生物利用度低,因此开发这类药物的新剂型成为近年来制剂学研究的一个热点。本文综述了蛋白质和肽类药物肺部给药的新剂型－吸入粉雾剂的优点及其新产品、所用载体、物理性能评价指标、吸入装置以及生物利用度。     

Direct Cytosolic Delivery of Proteins Using Lyophilized and Reconstituted Polymer-Protein Assemblies

Pharmaceutical Research - Cytosolic delivery of proteins accesses intracellular targets for chemotherapy and immunomodulation. Current delivery systems utilize inefficient endosomal pathways of...     

Delivery Systems and Local Administration Routes for Therapeutic siRNA

With the increasing number of studies proposing new and optimal delivery strategies for the efficacious silencing of gene-related diseases by the local administration of siRNAs, the present review aims to provide a broad overview of the most important and latest developments of non-viral siRNA delivery systems for local administration. Moreover, the main disease targets for the local delivery of siRNA to specific tissues or organs, including the skin, the lung, the eye, the nervous system, the digestive system and the vagina, were explored.     

Immunogenicity of Therapeutic Proteins: The Use of Animal Models

Immunogenicity of therapeutic proteins lowers patient well-being and drastically increases therapeutic costs. Preventing immunogenicity is an important issue to consider when developing novel therapeutic proteins and applying them in the clinic. Animal models are increasingly used to study immunogenicity of therapeutic proteins. They are employed as predictive tools to assess different aspects of immunogenicity during drug development and have become vital in studying the mechanisms underlying immunogenicity of therapeutic proteins. However, the use of animal models needs critical evaluation. Because of species differences, predictive value of such models is limited, and mechanistic studies can be restricted. This review addresses the suitability of animal models for immunogenicity prediction and summarizes the insights in immunogenicity that they have given so far.     

Silicone Oil-Free Polymer Syringes for the Storage of Therapeutic Proteins

Prefilled syringes are a popular choice for the delivery of biopharmaceuticals. However, glass syringes might not be the optimal primary packaging material for all biopharmaceuticals. There is evidence that the necessary lubricant silicone oil in glass syringes can interact with proteins and can be shed from the surface into the product solution. In recent years, silicone oil-free polymer syringes were developed. Despite several advantages, however, a major shortcoming of these polymer systems is their relatively high gas permeability, which might be a limitation for the storage of oxygen sensitive biopharmaceuticals. So far, no long-term protein stability studies regarding such polymer systems have been published. In this study, 2 therapeutic proteins were stored in glass syringes and in silicone oil-free polymer syringes. In addition, polymer syringes stored in nitrogen-filled aluminum pouches or covered with oxygen-tight labels were included. Similar chemical protein stability was achieved at 4°C for all syringes. However, in contrast to the polymer syringes, high particle counts were observed in the glass syringes. Polymer syringes stored in nitrogen-filled aluminum pouches presented a promising alternative for the storage of biopharmaceuticals as they do not expose patients to silicone oil and silicone oil-protein aggregates.     

Conformational Analysis of Therapeutic Proteins by Hydroxyl Radical Protein Footprinting

Unlike small molecule drugs, therapeutic protein pharmaceuticals must not only have the correct amino acid sequence and modifications, but also the correct conformation to ensure safety and efficacy. Here, we describe a method for comparison of therapeutic protein conformations by hydroxyl radical protein footprinting using liquid chromatography-mass spectrometry (LC-MS) as an analytical platform. Hydroxyl radical protein footprinting allows for rapid analysis of the conformation of therapeutic proteins based on the apparent rate of oxidation of various amino acids by hydroxyl radicals generated in situ. Conformations of Neupogen®, a patented granulocyte colony-stimulating factor (GCSF), were compared to several expired samples of recombinant GCSF, as well as heat-treated Neupogen®. Conformations of different samples of the therapeutic proteins interferon α-2A and erythropoietin were also compared. Differences in the hydroxyl radical footprint were measured between Neupogen® and the expired or mishandled GCSF samples, and confirmed by circular dichroism spectroscopy. Samples that had identical circular dichroism spectra were also found to be indistinguishable by hydroxyl radical footprinting. The method is applicable to a wide variety of therapeutic proteins and formulations through the use of separations techniques to clean up the protein samples after radical oxidation. The reaction products are stable, allowing for flexibility in sample handling, as well as archiving and reanalysis of samples. Initial screening can be performed on small amounts of therapeutic protein with minimal training in LC-MS, but samples with structural differences from the reference can be more carefully analyzed by LC-MS/MS to attain higher spatial resolution, which can aid in engineering and troubleshooting.

Electronic supplementary material

The online version of this article (doi:10.1208/s12248-012-9336-7) contains supplementary material, which is available to authorized users.Key words: biosimilars, hydroxyl radical protein footprinting, mass spectrometry, protein conformation, therapeutic proteins