(438d) Towards the Generation of a Predictive Model of Protein Desorption Behavior

An important consideration during the storage and delivery of biologically active therapeutic agents is the interaction of protein molecules with the various surfaces present in the delivery device. In a pre-filled system, these therapeutic proteins encounter such solid/liquid interfaces, often for extended periods of time under sub-optimal conditions. Due to the intrinsic surface-activity of proteins, spontaneous adsorption can occur, and due to surface-related events discussed below, conformational unfolding, activity loss, and population of non-native, aggregate-prone states may results, ultimately compromising the clinical safety and efficacy of the therapeutic. A central paradigm that underpins our understanding of protein adsorption is that bound proteins tend to denature, and these non-native, perturbed structures are likely stabilized through the loss of α-helices with the concomitant formation of intermolecular b-sheets. It is believed that these unfolding events on the surface have a significant effect on the subsequent desorption behavior of these proteins. An equally important determinant of desorption behavior is related to protein/surface affinity and structuring and orientation of the adsorbed protein layer. The goal of this research is to understand the impact of each of these aforementioned parameters on desorption behavior, and to define a general rule to predict this behavior given specific system parameters. To this end, we screen the adsorption, desorption and secondary structure behavior of various model proteins of varying size, structure and structural stability, on nanoparticles surfaces on varying levels of hydrophobicity, as a function of surface coverage. Our results indicate that for hydrophilic surfaces, parameters related to the Langmuir adsorption isotherm are fairly good predictors of desorption behavior, and that structural unfolding on the surface, albeit important in determining characteristics of the adsorbed layer, has little impact on determining desorption behavior.