Comparative Analysis of Proximal Tubule Cell Sources for In Vitro Studies of Renal Proximal Tubule Toxicity

Background/Objectives: The kidneys are essential for eliminating drugs and chemicals from the human body and renal epithelial cells are particularly vulnerable to damage caused by xenobiotics and their metabolites. Drug-induced kidney toxicity is a major cause of drug attrition during preclinical and clinical development and the ability to predict renal toxicity remains a pressing challenge, necessitating more predictive in vitro models. However, the abundance of commercially available renal proximal tubule epithelial cell (RPTEC) sources complicates the selection of the most predictive cell types. Methods: This study compared a wide range of RPTEC sources, including primary cells (Lonza) and various RPTEC lines from different vendors, such as ciPTECs (Cell4Pharma), TERT1/RPTECs (ATCC), and HEK293 (GenoMembrane), including OAT1-overexpressing variants. HepG2 cells were included for a comparison of organ specificity. The different cells were cultured in 96- or 384-well plates and exposed to 12 drugs for 72 h at a concentration yielding a response (0.3–300 µM) to evaluate their ability to predict clinical outcomes. The CellTiterGlo^® assay was used to measure cell viability, and transcriptome data from unexposed cells was analyzed using the TempO-seq^® S1500+ platform. Results: Gene expression data showed that the primary kidney cells most closely matched the transcriptome of the human kidney medulla, followed by the TERT1 and ciPTEC lines, with the HEK lines showing the lowest similarity. The RPTEC sources showed clustering by cell type, with OAT1 overexpression driving changes in metabolic, detoxification, and immune pathways, especially in TERT1 cells. Cell viability data were used to determine points of departure (PODs) which were compared to human serum Cmax values to assess safety margins. The TERT1 and ciPTEC RPTEC lines demonstrated the highest predictive performance for nephrotoxicity, with OAT1 overexpression significantly enhancing sensitivity, accuracy, and overall predictive power (MCC scores: 0.764 and 0.667, respectively). In contrast, HepG2 cells showed the lowest performance across all metrics, highlighting the critical role of cell type and transporter expression in nephrotoxicity prediction. Conclusions: This study highlights important differences among RPTEC sources and their utility in drug safety studies of the renal proximal tubule. We show that while improved cell options for renal proximal tubule are needed, OAT1-overexpressing RPTECs are a superior model to the background cell type.