Bioanalysis

QPS Bioanalytical Scientists Contribute to New Reference Work on Regulated Bioanalytical LC-MS/MS

Last month, John Wiley & Sons, Inc. issued a new, 704-page reference work on state-of-the-art bioanalysis, the Handbook of LC-MS Bioanalysis – Best Practices, Experimental Protocol and Regulations.

An extensive list of highly renowned scientists has contributed to the 51 chapters in this book, which delivers a comprehensive review of small- and macro-molecule LC-MS bioanalysis. The text not only addresses the needs of bioanalytical scientists working on routine projects, but also explores advanced and emerging technologies, such as high-resolution mass spectrometry and dried blood spot micro sampling.

QPS is extremely proud of our bioanalytical scientists who contributed to three of the chapters in this book. Here are abstracts for the sections they worked on.

Chapter 5 - Current Understanding of Bioanalytical Assay Reproducibility: Incurred Sample Reanalysis, Incurred Sample Stability, and Incurred Sample Accuracy

The major reason for reanalysis of study samples is because an analyte and/or its labile metabolite(s) and associated matrix components tend to be unstable in biological samples. Through reanalysis of a selected portion of the study samples, incurred sample reanalysis (ISR) reflects the degree of confidence in regulated study sample analysis by determining the reproducibility of the original bioanalytical results. Incurred sample stability (ISS) is another instrument for monitoring the stability of drugs and/or their metabolite(s) of interest within a definite time frame. Incurred sample accuracy (ISA) is a relatively new approach for assessing method reproducibility, by which the possible systematic errors during ISR or ISS assessment are examined. This chapter aims to summarize the rationale for reanalysis of study samples based on these three important indicators of method reproducibility and robustness. The underlying principles of these indicators and some selected case studies are outlined to help elucidate their significance and relevance in bioanalytical research.

Chapter 7 - Metabolites in Safety Testing

This chapter summarizes the current thinking and practices across the pharmaceutical industry in support of metabolites in safety testing (MIST)-related activities. It compares two of several available options for conducting absorption, distribution, metabolism, and excretion (ADME) studies using radiolabeled materials. In the first option, radiolabeled studies are not scheduled until after the interpretation of human pharmacokinetics (PK) and metabolism in first-in-human (FIH) studies, while in the second option, preclinical radiolabeled ADME studies are initiated before the completion of FIH studies. The chapter discusses some of the liquid chromatography—mass spectrometry (LC-MS) methods available for detecting and characterizing metabolites. Bioanalytical assays, used for detection, characterization and exposure estimation of metabolites, are tiered into (i) metabolite profiling, (ii) standard free quantification/ response factor determination, (iii) qualified assays, and (iv) validated assays.

Chapter 25 – LC-MS bioanalysis of unbound drugs in plasma and serum

In blood, a drug typically exists in two forms: bound to plasma proteins, and unbound. A specific drug's affinity to plasma proteins determines the proportion that is bound. It is the unbound fraction that is responsible for the drug’s pharmacologic effects. Therefore, characteristics such as membrane permeation, (metabolic) clearance and receptor binding are currently of major interest, as the free or unbound fraction is likely to be a more accurate predictor of the relationship between plasma levels and wanted/unwanted effects of the drug of interest. Also, plasma protein binding and preferential partitioning of drugs into the erythrocytes are important factors in designing (early phase) clinical trials, and hence need to be assessed early on in the drug development process.

This chapter discusses the determination of bound and unbound drug levels. It opens with an explanation of protein binding and an overview of the regulatory background of plasma protein binding studies. The subsequent paragraphs provide an overview of the various techniques available for assessing a compound’s plasma protein binding, including the specific characteristics of each technique, and offer a series of examples from the literature. These examples highlight specific compound classes, e.g. steroids, and specific physiological areas, e.g. the CNS. Also, specific analytical challenges are addressed for elemental protein binding analysis and enantioselective challenges.

Jaap Wieling, Ph.D., Vice-President, Bioanalysis& Technology R&D
jaap.wieling@qps.com

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