An experimental design for a single-time-point microsomal stability assay was evaluated as compared with multiple-time-point studies. Results obtained from single-time-point experiments are in excellent agreement with those from multiple time points. First-order reaction kinetics revealed rapid changes of predicted half-life from percent remaining of the parent compound at the inflection points, suggesting a maximum predictive limit for half-life. Selection of the incubation time in single-time-point assays is important to obtain balanced information for stable and unstable compounds. A short incubation time (e.g., 5 min) is most useful for differentiating between unstable compounds, which is beneficial to direct the synthetic efforts in projects with poor metabolic stability. A long incubation time (e.g., 30 min) is more applicable to a compound series with high metabolic stability. For screening purposes, a moderate incubation time (e.g., 15 min) is recommended to achieve good resolution and a sufficiently high maximum predictive limit for half-life. This study suggests that a single-time-point assay is sufficient for ranking compounds in early drug discovery. It increases throughput and reduces turnaround time and cost.
Copyright 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:1537-1544, 2004