Effect of Human Plasma on Hepatic Uptake of Organic Anion-Transporting Polypeptide 1B Substrates: Studies Using Transfected Cells and Primary Human Hepatocytes.

Abstract

Current challenges with the in vitro-in vivo extrapolation (IVIVE) of hepatic uptake clearance involving organic anion-transporting polypeptide (OATP) 1B1/1B3 hinder drug design strategies. Here we evaluated the effect of 100% human plasma on the uptake clearance using transfected human embryonic kidney (HEK) 293 cells and primary human hepatocytes and assessed IVIVE. Apparent unbound uptake clearance (PSinf,u) increased significantly (P < 0.05) in the presence of plasma (vs. buffer incubations) for about 50% of compounds in both OATP1B1-transfected and wild-type HEK cells. Thus, plasma showed a minimal effect on the uptake ratios. With cultured human hepatocytes, plasma significantly (P < 0.05) increased PSinf,u for 11 of 19 OATP1B substrates (median change of 2.1-fold). Cell accumulation in HEK cells and hepatocytes was also increased for tolbutamide, which is not an OATP substrate. Plasma-to-buffer ratio of PSinf,u obtained in hepatocytes showed a good correlation with unbound fraction in plasma, and the relationship was best described by a "facilitated-dissociation" model. IVIVE was evaluated for the 19 OATP1B substrates using hepatocyte data in the presence of buffer and plasma. PSinf,u from buffer incubations markedly underpredicted hepatic intrinsic clearance (calculated via well stirred and parallel tube models) with an estimated bias of 0.10-0.13. Predictions improved when using PSinf,u from plasma incubations; however, considerable systemic underprediction was still apparent (0.19-0.26 bias). Plasma data with a global scaling factor of 3.8-5.3 showed good prediction accuracy (95% predictions within 3-fold; average fold error = 1.7, bias = 1). In summary, this study offers insight into the effect of plasma on the uptake clearance and its scope in improving IVIVE. SIGNIFICANCE STATEMENT: Our study using diverse anionic compounds shows that human plasma facilitates organic anion-transporting polypeptide 1B-mediated as well as passive uptake clearance, particularly for the highly bound compounds. Leveraging data from transfected human embryonic kidney 293 cells and primary human hepatocytes, we further evaluated mechanisms involved in the observed plasma-facilitated uptake transport. Enhanced hepatic uptake rate in the presence of plasma could be of relevance, as such mechanisms likely prevail in vivo and emphasize the need to maintain physiologically relevant assay conditions to achieve improved translation of transport data.