Approaching sites of action of drugs in clinical pharmacology: New analytical options and their challenges

Abstract

Clinical pharmacology is an important discipline for drug development aiming to define pharmacokinetics (PK), pharmacodynamics (PD) and optimum exposure to drugs, i.e. the concentration-response relationship and its modulators. For this purpose, information on drug concentrations at the anatomical, cellular and molecular sites of action is particularly valuable. In pharmacological assays, the limited accessibility of target cells in readily available samples (i.e. blood) often hampers mass spectrometry-based monitoring of the absolute quantity of a compound and the determination of its molecular action at the cellular level. Recently, new sample collection methods have been developed for the specific capture of rare circulating cells, especially for the diagnosis of circulating tumour cells. In parallel, new advances and developments in mass spectrometric instrumentation now allow analyses to be scaled down to the cellular level. Together, these developments may permit the monitoring of minute drug quantities and show their effect at the cellular level. In turn, such PK/PD associations on a cellular level would not only enrich our pharmacological knowledge of a given compound but also expand the basis for PK/PD simulations. In this review, we describe novel concepts supporting clinical pharmacology at the anatomical, cellular and molecular sites of action, and highlight the new challenges in mass spectrometry-based monitoring. Moreover, we present methods to tackle these challenges and define future needs. K E Y W O R D S clinical pharmacology, mass spectrometry, personalized medicine, review, sites of action 1 | INTRODUCTION Clinical pharmacology studies the relevant parameters of drug fate (pharmacokinetics, PK) and efficacy (pharmacodynamics, PD) in humans in order to establish the dose-response and concentrationresponse relationship. It also defines intraindividual and interindividual modulators of these relationships, leading to different effectiveness, safety and dose requirements. Monitoring drug concentrations and effects is therefore of considerable importance during drug development, starting with the very first clinical trials. 1 Clinical pharmacology clarifies mechanisms of both beneficial and adverse drug effects in order to get closer to drug effectiveness monitoring. A drug's site of action can be defined at different scales: anatomical (the compartment the drug has to reach, e.g. tissues), cellular (the

Targeted liquid chromatography‐tandem mass spectrometry analysis of proteins: Basic principles, applications, and perspectives

“…Targeted protein analysis may also find important applications in the field of clinical pharmacology for precision medicine, in combination with discovery analyses. Monitoring the action of drugs, remotely or directly at their molecular and cellular sites of action [171] would have a great impact to determine effectiveness or possible therapy resistances and related biomarkers. In this context, shotgun proteomics would be adequate for initial discovery of biomarkers for pharmacodynamic evaluation or monitoring of the development of resistances.…”

“…Depending on the level of access to the anatomical site of action of the drugs (parameter 3 in [171]), biomarker discovery might be possible directly from the cellular site of action or would have to be performed from the circulatory system. Once biomarkers are discovered, a subset of the most significant ones could be followed by targeted protein quantification in further studies (e.g., in the context of routine therapeutic drug monitoring, or long term studies to monitor the appearance of resistances).…”

“…Once biomarkers are discovered, a subset of the most significant ones could be followed by targeted protein quantification in further studies (e.g., in the context of routine therapeutic drug monitoring, or long term studies to monitor the appearance of resistances). This monitoring may, for some applications, be performed together with the quantification of drugs, from small compounds and their metabolites (parameter 9 in [171]), to biopharmaceuticals (e.g., monoclonal antibodies (mAbs)), circulating (parameter 2 in [171]) or at the cellular sites of action (parameter 5 in [171]). This latter class of therapeutics should go through similar processes as endogenous proteins for sample preparation and analytical methods.…”

“…An additional application of target protein quantification in clinical pharmacology would consist of the quantification of the bound fraction of small therapeutic compounds covalently interacting with their protein site of action [171]. When tissues are available from surgery for quantification (e.g., in the context of the studies of resistance apparition) measuring drugs displaying a covalent interaction with a protein might only be representative when drug-targeted protein adducts are quantified (parameter 7 in [171]). This may be the case of the tyrosine kinases such as osimertinib, which has a covalent interaction with a mutant form of EGFR [172,173].…”

Microproteomic sample preparation

“…Given the central importance of proteins as biological effectors in physio-pathological processes, mass spectrometry-based proteomic approaches (MS proteomics) have been incorporated in the toolbox of life and health scientists [1,2], pathologists [3][4][5] and pharmacologists [6]. Proteomic approaches can be classified at different levels.…”