Applications of enzyme activity assays in clinical development for rare disease therapeutics.

Many rare diseases, such as lysosomal storage diseases, are caused by genetically driven enzyme deficiencies. Treatment strategies for these diseases have expanded from substrate reduction and enzyme replacement therapies to more recent gene- and cell-based approaches. As therapeutic modalities for treating rare diseases evolve, bioanalytical assays for measuring enzyme activity have been developed in parallel to support a variety of contexts of use (COUs). In this review, we examine the major contexts in which enzyme activity assays are applied to generate reliable data supporting patient selection, pharmacokinetic, pharmacodynamic, and immunogenicity assessments. Examples from ongoing clinical studies and approved product development are used to illustrate these applications. In particular, we highlight the growing role of enzyme activity assays in pharmacodynamic biomarker assessment and challenges related to preanalytical variability and maintaining assay performance during longitudinal clinical studies. Technical considerations associated with enzyme activity assays for different COUs are also discussed. As therapeutic strategies for rare enzyme deficiency disorders continue to advance, the various COUs that enzyme activity assays support and the corresponding analytical validation approaches may further evolve to inform clinical development and regulatory decision-making.