Physicochemical Differences Observed in Photostability Studies of Lyophilized, Reconstituted, and Diluted Somatropin

While photostability testing conditions for biologics are often based on small molecule standards, the unique characteristics of proteins necessitate a deeper understanding of appropriate testing and controls. This study examines the effects of light stress on various presentations of somatropin, a therapeutic growth hormone.

Somatropin was exposed to light in lyophilized, reconstituted, and diluted forms. Quality attribute changes were analyzed using size exclusion chromatography, micro-fluidic imaging, imaged capillary isoelectric focusing, and liquid chromatography mass spectrometry (LC-MS).

Light stress increased high molecular weight species (HMWS), particularly in liquid formulations, as shown by size exclusion chromatography (Lyophilized + 0.4%, Reconstituted + 2.7%, Diluted + 4.7%). Micro-fluidic imaging revealed no change in particle formation. All presentations exhibited shifts in charge variants, with increases in acidic species (Lyophilized + 2.8%, Reconstituted + 7.8%, Diluted + 6.2%) and basic (Lyophilized + 0.4%, Reconstituted + 0.7%, Diluted + 0.8%) . Liquid chromatography-tandem mass spectrometry (LC-MS/MS) peptide mapping detected increased methionine oxidation in light-exposed samples, correlating with higher protein concentration (M14- Lyophilized + 2.3%, Reconstituted + 7.4%, Diluted + 2.7%, M125- Lyophilized + 2.5%, Reconstituted + 2.9%). Diluted somatropin showed higher HMWS levels but reduced methionine-125 oxidation susceptibility compared to reconstituted formulations.

Light exposure altered product quality attributes, with more pronounced effects on liquid presentations. These findings provide insights into the distinct impacts of light exposure on different drug presentations throughout their lifecycle, highlighting the importance of tailored photostability testing for different product presentations of biologic drugs.