Rapid biocompatible solid phase microextraction: Nirogacestat protein binding in post dose human serum samples

Protein binding can influence the ability of a drug to permeate biologic membranes and can therefore be a limiting factor in the passage of drugs across a membrane. Most drugs must be unbound (free) to have a pharmacological effect. To quantitate free active drug in blood plasma, protein binding is typically assessed based on permeation techniques using devices such as a rapid equilibrium dialysis (RED) device. Caveats to this approach include the time to equilibration, which can introduce drug instability, and/or non-specific binding that confound accurate estimation of protein binding. Initial experiments with a RED device showed nirogacestat in clinical samples had non-specific binding in the buffer chamber which resulted in a low percent bound of 24.1 %. Clearly a different approach is needed to accurately characterize the protein binding of nirogacestat in clinical samples. For this reason, adsorption-based technologies, such as biocompatible solid phase microextraction (BioSPME), provide a potentially suitable alternative to permeation-based protein binding for highly bound drugs like nirogacestat. BioSPME was used to measure protein binding for nirogacestat for both in vitro and clinical samples. A biocompatible sorbent material selectively extracts unbound analytes from a sample matrix as sample passes through the BioSPME cartridge, where the analyte is adsorbed onto the solid phase while the sample's base liquid passes through then eluted with a solvent. This approach allows for control of equilibration/incubation times and container types. The results show that BioSPME provides an accurate and reliable method for measuring protein binding in both in vitro and clinical samples. SIGNIFICANCE STATEMENT: BioSPME accurately measures the protein binding of nirogacestat in clinical serum samples and is an alternative to RED for measuring protein binding in vitro and in clinical samples.