Human organic cation transporter 2 (hOCT2/SLC22A2) is a key drug transporter that facilitates the transport of endogenous and exogenous organic cations. Because hOCT2 is responsible for the development of adverse effects caused by platinum-based anti-cancer agents, drugs with OCT2 inhibitory effects may serve as prophylactic agents against the toxicity of platinum-based anti-cancer agents. In the present study, we established a machine learning-based quantitative structure-activity relationship (QSAR) model for hOCT2 inhibitors based on the public ChEMBL database and explored novel hOCT2 inhibitors among the FDA-approved drugs. Using our QSAR model, we identified 162 candidate hOCT2 inhibitors among the FDA-approved drugs registered in the DrugBank database. After manual selection and in vitro assays, we found that dequalinium, a quaternary ammonium cation antimicrobial agent, is a potent hOCT2 inhibitor (IC50 = 88.16 ± 7.14 nM). Moreover, dequalinium inhibited hOCT2-mediated transport of platinum anti-cancer agents (cisplatin and oxaliplatin) in a concentration-dependent manner. Our study is the first to demonstrate the construction of a novel machine learning-based QSAR model for hOCT2 inhibitors and identify a novel hOCT2 inhibitor among FDA-approved drugs using this model.
© 2025. The Author(s).

The mineralocorticoid receptor (MR) is a member of the steroid-thyroid hormone receptor superfamily of ligand-dependent transcription factors with diverse functions including the biological actions of aldosterone. Identification of the various transcriptional coregulators of MR is essential for understanding the complexity of MR signaling pathways under physiological and pathological conditions. We used a yeast two-hybrid system to find proteins that interact with a full-length MR and found, among other proteins, that MR interacted specifically with receptor for activated C kinase 1 (RACK1), a scaffolding protein. Overexpression of RACK1 using a tetracycline-inducible lentivirus in mouse cortical collecting duct M1 cells stably expressing the rat MR and a Gaussia luciferase gene reporter under a hormone-response element promoter resulted in enhanced agonist-dependent MR transactivation. Knockdown of RACK1 protein expression by short hairpin RNAs led to a significant reduction in MR activation of the reporter gene and the endogenous genes Ctla2α and Psca. We also demonstrated that RACK1 regulation of MR action is mediated through phosphorylation by the PKC-β signaling pathway. MR and RACK1 were coimmunoprecipitated using an MR antibody in male Sprague-Dawley brain tissue and M1-rMR cells, and colocalization in M1-rMR cells and male rat brains was confirmed by immunofluorescence and immunohistochemistry. The scaffolding protein RACK1 is associated with MR under basal and agonist-stimulated conditions and facilitates agonist-stimulated MR actions through PKC-β. These findings indicate that RACK1 is a newly described coactivator of MR.