Predicting accelerated aggregation rates for monoclonal antibody formulations, and challenges for low-temperature predictions

Orthogonal high-throughput thermal scanning method for rank ordering protein formulations

A high-throughput thermal-scanning method to rank-order formulation conditions for therapeutic proteins is described. Apparent transition temperatures for unfolding and aggregation of four different proteins are determined using the dyes SYPRO Orange and thioflavin T (ThT) under a variety of buffer conditions. The results indicate that the ThT-based thermal scanning method offers several advantages over the previously described SYPRO Orange-based thermal scanning and allows rapid rank ordering of solution conditions relevant toward long-term storage of therapeutic molecules. The method is also amenable to high protein concentration and does not require sample dilution or extensive preparation. Additionally, this parallel use of SYPRO Orange and ThT can be readily applied to the screening of mutants for their unfolding and aggregation propensities.

Non-Arrhenius protein aggregation

Protein aggregation presents one of the key challenges in the development of protein biotherapeutics. It affects not only product quality but also potentially impacts safety, as protein aggregates have been shown to be linked with cytotoxicity and patient immunogenicity. Therefore, investigations of protein aggregation remain a major focus in pharmaceutical companies and academic institutions. Due to the complexity of the aggregation process and temperature-dependent conformational stability, temperature-induced protein aggregation is often non-Arrhenius over even relatively small temperature windows relevant for product development, and this makes low-temperature extrapolation difficult based simply on accelerated stability studies at high temperatures. This review discusses the non-Arrhenius nature of the temperature dependence of protein aggregation, explores possible causes, and considers inherent hurdles for accurately extrapolating aggregation rates from conventional industrial approaches for selecting accelerated conditions and from conventional or more advanced methods of analyzing the resulting rate data.

Accelerated stability studies of abatacept formulations: comparison of freeze-thawing- and agitation-induced stresses

Accelerated degradation studies are frequently used to screen for formulation conditions that confer adequate shelf life for therapeutic proteins. To speed development cycles, degradation is often accelerated by application of conditions that expose proteins to elevated temperatures, dynamic air-water interfaces created by agitation, or stresses induced by freeze-thaw cycling. The purpose of this case study was to compare freeze-thaw- and agitation-induced aggregations with aggregation previously studied at elevated temperatures (Fast J, Cordes AA, Carpenter JF, Randolph TW. 2009. Biochemistry 48:11724-11736) using the therapeutic fusion protein abatacept as a model. The stability of abatacept against aggregation induced by the freeze-thaw and agitation degradation methods was assessed by size-exclusion chromatography (SEC) and microflow imaging (MFI) analysis. pH conditions that were previously found to increase conformational stability of abatacept and reduce aggregation during incubation at elevated temperature (Fast J, Cordes AA, Carpenter JF, Randolph TW. 2009. Biochemistry 48:11724-11736) also reduced aggregation induced by freeze-thaw cycling and by agitation in this study. Especially in the case of the freeze-thaw cycling, wherein the formation of aggregates was not readily detectable by SEC, MFI proved to be a useful method to characterize the stability of the formulations against aggregation.

Engineering aggregation-resistant antibodies

The ability of antibodies to bind to target molecules with high affinity and specificity has led to their widespread use in diagnostic and therapeutic applications. Nevertheless, a limitation of antibodies is their propensity to self-associate and aggregate at high concentrations and elevated temperatures. The large size and multidomain architecture of full-length monoclonal antibodies have frustrated systematic analysis of how antibody sequence and structure regulate antibody solubility. In contrast, analysis of single and multidomain antibody fragments that retain the binding activity of mono-clonal antibodies has provided valuable insights into the determinants of antibody aggregation. Here we review advances in engineering antibody frameworks, domain interfaces, and antigen-binding loops to prevent aggregation of natively and nonnatively folded antibody fragments. We also highlight advances and unmet challenges in developing robust strategies for engineering large, multidomain antibodies to resist aggregation.