Cooperative inhibitory effects of uremic toxins and other serum components on OATP1B1-mediated transport of SN-38

Purpose Half-life of SN-38, an active metabolite of irinotecan, remarkably increases in patients with end-stage kidney disease (ESKD), even though SN-38 is excreted in bile. Uremic toxins (UTs), which accumulate in the serum of ESKD patients, were reported to inhibit organic anion-transporting polypeptide (OATP) 1B1-mediated uptake of SN-38; however, the relevance of this finding in a clinical setting is unknown. This study focused on cooperative effects of serum components and UTs on OATP1B1-mediated transport of SN-38. Methods Uptake of SN-38 by OATP1B1 was evaluated using cells stably expressing OATP1B1. Serum was obtained from > 400 ESKD patients undergoing hemodialysis. Deproteinized serum was combined with human serum albumin (HSA) to explore the effects of albumin-bound and unbound serum compounds. Results Uptake clearance of SN-38 in OATP1B1 cells decreased by 40% in the presence of uremic serum residue with albumin compared to that in the presence of normal serum residue. Additional UTs (3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, hippuric acid, indole-3-acetic acid, and 3-indoxyl sulfate) combined with normal serum residue in HSA decreased OATP1B1-mediated SN-38 transport by 32.1% compared to that in the presence of normal serum residue. The inhibitory effect of albumin-unbound fraction with UTs and normal serum residue was comparable to that of uremic serum residue, with an uptake decrease of 17.2% compared to that reported in the presence of normal serum residue. Conclusions Hepatic uptake of SN-38 via OATP1B1 decreases in ESKD patients through cooperative inhibitory effects of UTs and serum components.