Light exacerbates local and global effects induced by pH unfolding of Ipilimumab

Monoclonal antibodies (mAbs) are an essential class of therapeutic proteins for the treatment of cancer, auto- immune and rare diseases. During their production, storage, and administration processes, these proteins encounter various stressors such as temperature fluctuations, vibrations, and light exposure, able to induce chemico-physical modifications to their structure. Viral inactivation is a key step in downstream processes, and it is achieved by titration of the mAb at low pH, followed by neutralization. The changes of the pH pose a sig- nificant risk of unfolding and subsequent aggregation to proteins, thereby affecting their manufacturing. This study aims to investigate whether a combined exposure to light during the viral inactivation process can further affect the structural integrity of Ipilimumab, a mAb primarily used in the treatment of metastatic mel- anoma. The biophysical and biochemical characterization of Ipilimumab revealed that pH variation is a considerable risk for its stability with irreversible unfolding at pH 2. The threshold for Ipilimumab denaturation lies between pH 2 and 3 and is correlated with the loss of the protein structural cooperativity, which is the most critical factor determining the protein refolding. Light has demonstrated to exacerbate some local and global effects making pH-induced exposed regions more vulnerable to structural and chemical changes. Therefore, specific precautions to real-life exposure to ambient light during the sterilization process of mAbs should be considered to avoid loss of the therapeutic activity and to increase the yield of production. Our findings underscore the critical role of pH optimization in preserving the structural integrity and therapeutic efficacy of mAbs. Moreover, a detailed conformational study on the structural modifications of Ipilimumab may improve the chemico-physical knowledge of this effective drug and suggest new production strategies for more stable products under some kind of stress conditions.