In vivo characterization of therapeutic monoclonal antibodies

Therapeutic monoclonal antibodies (mAbs) are complex drug molecules with a high degree of heterogeneity, including charge variants, aggregates, fragments, and post-translational modifications (PTMs). PTMs can be introduced by chemical or enzymatic modifications over the lifespan of mAbs during production, storage, and in vivo circulation. Common PTMs in mAbs include glycosylation, deamidation, oxidation, glycation, N-terminal glutamine cyclization, and C-terminal lysine processing. These product-related modifications are termed as product quality attributes (PQAs). A given PQA has the potential to impact the safety and/or efficacy of a therapeutic mAb. A PQA may enhance immunogenicity or off-target bindings, resulting in changes of the safety profile of a therapeutic mAb. A PQA may change the interaction of a therapeutic mAb to its target antigen, and therefore alter the efficacy. The PQAs that impact on drug safety and/or efficacy are considered as critical quality attributes (CQAs). Control of PQAs, especially CQAs, within predefined acceptance criteria is required by regulatory agencies to ensure product quality, consistency, and stability. During drug development, manufacturing processes aim to maximize the production of a desired product in high purity with minimal and consistent levels of variant forms. Formulation development seeks to stabilize mAb products and minimize additional formation of variants during storage. The modifications occurred during mAb production and storage can be reliably monitored and controlled. However, additional modifications can occur after a mAb is administered to patients. mAbs are typically administered intravenously or subcutaneously, and quickly get into the circulation of patients. The circulating half-life of a typical mAb in human blood system is 2-3 weeks. The blood environment is remarkably different from formulation buffers and storage temperatures. Typical mAb drug products are formulated at a pH of 5-6 with multiple excipients, such as sugars, salts, amino acids, and surfactants. The formulation buffer, pH, and excipients are optimized to enhance mAb solubility/stability and to reduce viscosity as well as the formation of aggregates/particulates. In contrast, blood is a dynamic environment with thousands of proteins including many protein-modifying enzymes, and is tightly regulated at a pH of 7.4 and a temperature of 37 °C. The clearance and modification of a mAb in blood circulation may result in changes of the PQA profile, leading to increased attribute exposure and decreased effective drug exposure to patients, and therefore causing the concerns of immune responses and loss of efficacy. To this end, a recent FDA guidance for industry recommends sponsors to evaluate susceptibilities of therapeutic protein products to modifications in the in vivo milieu as early as in product design and development, in order to facilitate product engineering for enhancing the product stability under in vivo conditions [1]. Therefore, in vitro and in vivo characterization of PQAs can monitor the attribute stability before and after drug administration and JOURNAL OF APPLIED BIOANALYSIS, January 2016, p. 10-15. http://dx.doi.org/10.17145/jab.16.003 (ISSN 2405-710X) Vol. 2, No. 1