RT Journal Article SR Electronic T1 Does Addition of Protein to Hepatocyte or Microsomal In Vitro Incubations Provide A Useful Improvement in In Vitro-In Vivo Extrapolation (IVIVE) Predictability? JF Drug Metabolism and Disposition JO Drug Metab Dispos FD American Society for Pharmacology and Experimental Therapeutics SP DMD-AR-2021-000677 DO 10.1124/dmd.121.000677 A1 Tsubasa Kameyama A1 Jasleen Sodhi, Ph.D. A1 Leslie Z. Benet YR 2022 UL http://dmd.aspetjournals.org/content/early/2022/01/27/dmd.121.000677.abstract AB Accurate prediction of in vivo hepatic clearance is an essential part of successful and efficient drug development; however, many investigators have recognized that there are significant limitations in the predictability of clearance with a tendency for underprediction for primarily metabolized drugs. Here, we examine the impact of adding serum or albumin into hepatocyte and microsomal incubations on the predictability of in vivo hepatic clearance. The addition of protein into hepatocyte incubations has been reported to improve the predictability for high clearance (extraction ratio) drugs and highly protein bound drugs. Analyzing published data for 60 different drugs and 97 experimental comparisons (with 17 drugs being investigated from 2-7 times) we confirmed the marked underprediction of clearance. However, we could not validate any relevant improved predictability within 2-fold by the addition of serum to hepatocyte incubations or albumin to microsomal incubations. This was the case when investigating all measurements, or when subdividing analyses by extraction ratio, degree of protein binding, BDDCS class, examining ECCS class 1B drugs only or drug charge. Manipulating characteristics of small data sets of like compounds and adding scaling factors can appear to yield good predictability, but the carryover of these methods to alternate drug classes and different laboratories is not evident. Improvement in predictability of poorly soluble compounds is greater than that for soluble compounds but not to a meaningful extent. Overall, we cannot confirm that protein addition improves IVIVE predictability to any clinically meaningful degree when considering all drugs and different subsets. Significance Statement The addition of protein into microsomal or hepatocyte incubations has been widely proposed to improve hepatic clearance predictions. To date, studies examining this phenomenon have not included appropriate negative controls where predictability is achieved without protein addition and have been conducted with small datasets of similar compounds that do not apply to alternate drug classes. Here, extensive analysis of published data for 60 drugs and 97 experimental comparisons could not validate any relevant clinically improved clearance predictability with protein addition.