Experiences in method development for the analysis of in vitro study solutions for content

Test article concentrations in the hERG assay: losses through the perfusion, solubility and stability

INTRODUCTION

Drug-induced prolongation of the electrocardiographic QT interval (long QT syndrome) has been associated with increased risk of a serious ventricular arrhythmia, torsade de pointes. Inhibition of hERG, a cardiac potassium channel that controls action potential repolarization, is the most common cause of QT prolongation by non-cardiac drugs. The ICH S7B describes preclinical safety testing required for new drugs, including the determination of the hERG IC(50). Actual and target concentrations may differ due to solubility, stability, or loss of compound. Significant differences will invalidate quantitative concentration-response curves which may be critical to interpretation of drug safety. To examine the frequency and significance of these differences, we conducted an analysis of studies where both the electrophysiology and the dose solution analysis were conducted in-house. We have investigated the actual concentrations of test article in vehicle solution as compared to the target concentrations in an attempt to determine the reasons behind differences between the two values.

METHODS

Studies that involved both electrophysiology and dose solution analysis performed at ChanTest Corporation were evaluated. The effects of stability, solubility and loss through the perfusion apparatus on actual dosing concentrations were investigated.

RESULTS

There was a large range in the loss of the test article attributed to the perfusion apparatus (range from 0 to 74% loss). For 12 of the 22 studies evaluated, the IC(50) was>2-fold more potent when using actual values as determined by HPLC versus the target concentrations. Twenty-two percent of the test articles were not stable 24 h after room temperature storage; 16% after 24 h frozen conditions.

DISCUSSION

The best practices when considering dose solution concentration verification of test article solutions are to: determine the solubility of the compound in a physiological buffer, analyze samples collected from the perfusion chamber, and analyze samples the same day as sample collection (e.g., same day as hERG assay).

Applicability of bioanalysis of multiple analytes in drug discovery and development: review of select case studies including assay development considerations

The development of sound bioanalytical method(s) is of paramount importance during the process of drug discovery and development culminating in a marketing approval. Although the bioanalytical procedure(s) originally developed during the discovery stage may not necessarily be fit to support the drug development scenario, they may be suitably modified and validated, as deemed necessary. Several reviews have appeared over the years describing analytical approaches including various techniques, detection systems, automation tools that are available for an effective separation, enhanced selectivity and sensitivity for quantitation of many analytes. The intention of this review is to cover various key areas where analytical method development becomes necessary during different stages of drug discovery research and development process. The key areas covered in this article with relevant case studies include: (a) simultaneous assay for parent compound and metabolites that are purported to display pharmacological activity; (b) bioanalytical procedures for determination of multiple drugs in combating a disease; (c) analytical measurement of chirality aspects in the pharmacokinetics, metabolism and biotransformation investigations; (d) drug monitoring for therapeutic benefits and/or occupational hazard; (e) analysis of drugs from complex and/or less frequently used matrices; (f) analytical determination during in vitro experiments (metabolism and permeability related) and in situ intestinal perfusion experiments; (g) determination of a major metabolite as a surrogate for the parent molecule; (h) analytical approaches for universal determination of CYP450 probe substrates and metabolites; (i) analytical applicability to prodrug evaluations-simultaneous determination of prodrug, parent and metabolites; (j) quantitative determination of parent compound and/or phase II metabolite(s) via direct or indirect approaches; (k) applicability in analysis of multiple compounds in select disease areas and/or in clinically important drug-drug interaction studies. A tabular representation of select examples of analysis is provided covering areas of separation conditions, validation aspects and applicable conclusion. A limited discussion is provided on relevant aspects of the need for developing bioanalytical procedures for speedy drug discovery and development. Additionally, some key elements such as internal standard selection, likely issues of mass detection, matrix effect, chiral aspects etc. are provided for consideration during method development.