Therapeutic glycoprotein hormones: Considerations for the use of in vitro alternatives to in vivo potency assays

Abstract

Therapeutic protein hormones such as Erythropoietin and Gonadotrophins have historically utilised in vivo bioassays for potency assignment. In line with 3 R’s principles for animal research, manufacturers and regulatory authorities alike are continually seeking to implement in vitro alternatives to animal assays wherever possible. However, these proteins are heavily glycosylated, giving rise to an inverse correlation of in vivo and in vitro biological activities, which complicates the transition away from in vivo bioassays for potency assignment. Whilst manufacturers are actively pursuing the development of alternatives to in vivo bioassays for product quality control, these efforts inevitably result in product-specific approaches, which are unlikely to be representative of all versions of the same product from different manufacturers. This presents a further challenge for organisations tasked with ensuring harmonisation of dosage between products from different manufacturers, through provision of documentary (pharmacopoeial monographs) and physical (assay calibrators) standards, as such resources must be suitable for all licensed versions of a product. This review will describe these challenges, and the product-specific approaches which have been implemented by manufacturers, and propose a framework aimed at mitigating the risks associated with the wider introduction of in vitro alternatives to in vivo potency assays.