Assessment of the quality and structural integrity of a complex glycoprotein mixture following extraction from the formulated biopharmaceutical drug product

Biological drugs represent an important and rapidly growing class of therapeutics useful in the treatment of a variety of disorders ranging from cancer to inflammation to infectious diseases. Unlike single chemical entities, the recombinant production of these drugs in living cells confers considerable structural and chemical heterogeneity to the biologically derived protein product that constitutes the active pharmaceutical ingredient (API). In mammalian based expression systems, much of this diversity is conferred through heterogeneous protein glycosylation. These post-translational modifications can have significant effects on the structure, biological function, and pharmacological properties of the API. In addition, the bulk proteins that comprise the API are further formulated through the use of multiple excipients designed to ensure product stability, solubility, and lot-to-lot consistency. Unfortunately, these matrices can interfere with commonly available analytical methods used in the thorough chemical characterization of the biological drug product. At the same time, a demonstration of the suitable extraction of the bulk drug substance in a manner and form that does not destabilize the active ingredient or introduce any structural bias with direct reference to the original drug product is both critical and necessary. Here, we use recombinant human follicle stimulating hormone (follitropin alpha for injection) from a pharmaceutical source as an example to illustrate a suitable purification strategy to effectively extract the bulk drug substance from the formulated drug product with high purity and yield. We assess the suitability of this extraction method in preserving the structural integrity and overall quality of the drug substance relative to the formulated drug product, placing a particular emphasis on glycosylation as a key product attribute. In so doing, we demonstrate that it is possible to effectively extract the active pharmaceutical ingredient from a formulated biological drug product in a manner that is consequently sufficient for its use in comparability studies.