Drug Metabolism and Pharmacokinetics, Genentech Inc., South San Francisco, CA 94080.
Drug Metabolism and Pharmacokinetics, Genentech Inc., South San Francisco, CA 94080.
J Pharm Sci. 2021 Jan;110(1):536-542. doi: 10.1016/j.xphs.2020.09.012. Epub 2020 Sep 15.
Fraction unbound (f) is an important consideration when characterizing the ADME properties of drug candidates. For highly bound compounds, there can be low confidence in quantifying f introducing uncertainty in certain parameter estimations. Specifically, predictions of clearance (CL) rely on accurate f values measured in plasma (f) and microsomes (f) to scale in vitro intrinsic CL to in vivo CL. However, determining the ratio of f/f may circumvent the need to measure discrete binding values. The purpose of this study was to evaluate a plasma-to-microsome competitive equilibrium dialysis (cED) method to determine f/f ratio (fuR) for nine physiochemically-distinct compounds, and to investigate the impact of altering microsomal concentrations on fuR. The values of fuR were comparable to ratios calculated from discretely measured f and f values. Furthermore, increasing microsomal concentrations increased fuR for basic and neutral compounds. When using fuR values, there was a good in vitro-in vivo correlation (IVIVC) (≤3-fold observed in vivo CL). These results suggest that the cED method used to determine fuR may be an appropriate, alternative IVIVC approach. Application of cED may extend beyond IVIVC of CL to evaluate other parameters such as species differences in protein binding and free tissue to plasma ratios.
当描述候选药物的 ADME 性质时，未结合分数（f）是一个重要的考虑因素。对于高度结合的化合物，在量化 f 时可能缺乏信心，这会导致某些参数估计出现不确定性。具体来说，清除率（CL）的预测依赖于在血浆（f）和微粒体（f）中测量的准确 f 值，以将体外内在 CL 转化为体内 CL。然而，确定 f/f 的比值可以避免测量离散结合值的需要。本研究的目的是评估一种血浆-微粒体竞争性平衡透析（cED）方法，以确定九种生理化学上不同的化合物的 f/f 比值（fuR），并研究改变微粒体浓度对 fuR 的影响。fuR 的值与从离散测量的 f 和 f 值计算得出的比值相当。此外，增加微粒体浓度会增加碱性和中性化合物的 fuR。当使用 fuR 值时，具有良好的体外-体内相关性（IVIVC）（体内 CL 的观察倍数≤3 倍）。这些结果表明，用于确定 fuR 的 cED 方法可能是一种合适的替代 IVIVC 方法。cED 的应用可能不仅限于 CL 的 IVIVC，还可以评估其他参数，如蛋白结合和游离组织与血浆比的种间差异。
