By Samuel Pine, Alison Joyce, and Mauricio Maia
Measuring drug levels in blood is part and parcel for clinical trials, but what do drug development scientists do when the drug is not present in blood? Or when the site of pharmacological action is such that systemic levels of drug may not directly predict how much drug is in there? Instead of a swallowed pill or an injection into the blood or muscle, some drugs are administered in the eye or the knee joints, for example. Measurement of drug or target levels at the site of action is important for modeling drug target coverage and determining safe and effective clinical doses. How would you measure drug levels in those inner parts of the eye or the synovial fluid of the joints? What if there is a useful biomarker that is present only in urine or the cerebrospinal fluid which could show that an experimental drug is working as expected?
One of the reasons drugs and biomarkers are commonly measured in a blood matrix such as serum or plasma is that they are relatively easy to access for most study participants. But when a measurement is required in other biological fluids and tissues matrices, the process of obtaining and testing samples can present rather unique challenges. This is especially true when the analyte of interest is a protein or other large molecule that requires a ligand-binding assay (LBA) technique or is not amenable to harsh extraction processes. Large-molecule bionalysis by LBA is critical for drug development at biopharma companies and is widely implemented in the drug development process for pharmacokinetic, immunogenicity, and biomarker measurements. Standardized processes have been largely worked out for using LBAs to test serum and plasma samples, but there remains much to learn about matrix effects for the less-oft-used matrices, such as urine, synovial fluid, mucosal samples, and solid tissues. Putting aside the challenges of actually collecting some of these tissues, once a sample is in a collection tube the bioanalytical challenges begin, including stability, handling, matrix effects in the assay, limited volumes, and data normalization. All of these combine to present new hurdles for the bioanalytical lab tasked with developing the methods that will need to be validated.
If you have you ever worked in or wondered what life is like on these outer edges of the bioanalytical trenches, then the roundtable discussion Bioanalysis in Challenging Matrices at the upcoming AAPS National Biotechnology Conference in Boston on May 17 will be a great opportunity for you to ask and answer questions. It will be a forum to commiserate and share your own learnings with your colleagues and learn new techniques for dealing with odd, uneven, and finicky matrices and samples. The roundtable will support a deep-dive into this topic by focusing on all the aspects of quantitating large molecules in nontraditional matrices including matrix characteristics, collection and sample processing effects, modeling data, LBA platforms, and normalization approaches. Case studies from bioanalysis studies in synovial fluid, urine, vitreous humor, tears, and solid tissues will be used to illustrate approaches to overcome the unique properties of different matrices. The session will provide an opportunity to gain insight on current practices from real-world examples and facilitate a discussion on best practices and strategies for implementing sampling protocols and bioanalysis in nontraditional matrices.
Come and see what types of techniques are working, flex those creative muscles, and come up with strategies that may suit a challenging project. Don’t sweat it: Working with unique matrices may be challenging, but it doesn’t have to be painful!