Quantification of follicle stimulating hormone (follitropin alfa): is in vivo bioassay still relevant in the recombinant age?

Quantification of follicle-stimulating hormone (FSH) for clinical use has traditionally involved the use of in vivo bioassays, particularly the Steelman-Pohley bioassay. This assay has limited precision, requires large numbers of laboratory animals and involves cumbersome procedures for data generation and interpretation. Recent advances in manufacturing procedures for recombinant human FSH (r-hFSH) have resulted in a preparation (follitropin alfa; Gonal-F) that is highly consistent in both isoform profile and glycan species distribution. As a result, follitropin alfa can be reliably quantified using an optimised size exclusion high-performance liquid chromatography (SE-HPLC) method, and vials can be filled by mass. Preliminary clinical studies suggest that the fill-by-mass process results in a product that delivers a more consistent clinical response and is more effective than follitropin alfa vials filled by bioassay in women undergoing controlled ovarian stimulation. Non-bioassay methods such as SE-HPLC are likely to become increasingly important for quality testing and regulatory purposes, provided that the manufacturing process is well controlled and produces a protein of highly consistent physico-chemical properties.