New Research Reveals a Promising Functional Alternative to Surfactants within Biologic Formulations
One of the most common challenges when formulating biological molecules for therapeutic use is overcoming the molecules’ tendency to aggregate. Currently, the nonionic surfactants polysorbate 80 and polysorbate 20 are widely used to stabilize proteins in liquid preparations for parenteral administration, but there are concerns about both their composition and stability. In small-molecule formulations, cyclodextrins and their derivatives are well established, enabling excipients, and are already approved for parenteral use. New research points to these excipients as a promising alternative to surfactants for biologics.
Protein Formulation Issues
The inherent instability of proteins, especially those that are genetically engineered and far removed from their native environment, makes them challenging to work with. Proteins are sensitive to temperature changes, shearing, shaking, solvents, ionic strength, purity, protein concentration, pressure, and freeze/thaw cycles; they only remain stable within a narrow pH range and are susceptible to adsorption. Of the various degradation pathways that occur, aggregation is one of the most common and is a significant cause for concern since protein aggregates reduce drug efficacy and can induce immunogenicity. Effective formulation plays a critical role in successfully producing a stable protein drug.
The Excipient Challenge
A biological formulation contains multiple excipients, each one contributing to a different desired outcome. A wide range of excipient materials is approved for parenteral applications, and in liquid formulations, polysorbates are often used to protect against interface-induced protein aggregation and surface adsorption. Some 70% of marketed formulations of monoclonal antibody products contain either polysorbate 20 or polysorbate 80.
However, there are two main concerns when formulating a protein drug product using polysorbate. Firstly, the excipient itself is not a discrete molecule, and secondly, there are worries about excipient stability. Polysorbates 20 and 80 are chemically diverse mixtures that contain mainly sorbitan polyoxyethylene esters of fatty acids. These esters are prone to degradation by autoxidation and hydrolysis with the generation of peroxides that can promote protein instability. Therefore, degradation of polysorbates raises questions about both the lowered ability of the surfactant to protect the formulation against interfacial stresses and the impact of the degradation products on the stability of the protein.
Cyclodextrins and their derivatives are widely employed as excipients within small-molecule applications in which they are used to enhance solubility and bioavailability, improve drug chemical and physical stability, and deliver taste-masking. When formulating for parenteral delivery, it is necessary to use a modified cyclodextrin in order to achieve the required water solubility, and hydroxypropyl-β-cyclodextrin (HPβCD) is well established here. Its unique structure, which includes a hydrophilic exterior and a hydrophobic cavity, enables the formation of inclusion complexes in which lipophilic compounds such as Active Pharmaceutical Ingredients (APIs) are non-covalently bound within the cavity. This increases the API solubility and may improve the taste or create a higher bioavailability for the drug. Extensive toxicological and pharmacological studies have shown that HPßCD is safe for parenteral application and it is currently used in approved products such as itraconazol (Sporanox®) and Mitomycin (MitoExtra®). However, all of these are exclusively low-molecular weight drugs.
Previous work on HPßCD in protein formulations suggests a mechanism of action in which the hydrophobic interior of the HPßCD cavity complexes to the exposed hydrophobic amino acid residues on the protein . Since the exterior of HPßCD is hydrophilic, this effectively shields hydrophobic interactions and blocks the protein-protein interactions that lead to aggregation. It is also thought that HPßCD can inhibit protein aggregation induced by exposure to the air-water interface by acting in a manner similar to nonionic surfactants and displacing proteins from that interface.
Assessing HPßCD for Protein Applications
Scientists at Roquette have carried out experimental work to further explore the properties of HPßCD and examine its utility for real-world protein formulations. Two biopharmaceutical grade products were used throughout the studies—Roquette’s KLEPTOSE® HP and KLEPTOSE® HPB. Both products exhibit surface-active properties in addition to other key physical properties. Continue reading more including the following case studies:
Case Study 1: Arresting Rate of Aggregation during Agitation and Thermal Stress Using IgG as a Model Protein
Case Study 2: Reverting Reversible Aggregates into Monomers and Arresting Rate of Aggregation of Bevacizumab