Thioxanthone-Mediated Cytoprotection Against Cisplatin Toxicity: Exploring the Potential Involvement of P-Glycoprotein Through Computational and Experimental Approaches.

P-glycoprotein (P-gp), an efflux transporter highly expressed in renal tubules, plays a crucial role in the detoxification and protection of barrier/excretory tissues from harmful xenobiotics. Xanthones and thioxanthones (TXs) are known for their antimicrobial and antitumor activities and for their ability to modulate membrane transporters such as P-gp. Previous studies have reported that (thio)xanthonic derivatives enhance P-gp expression and/or activity in intestinal cells, reducing the intracellular accumulation of toxic substrates; however, their capacity to modulate P-gp in renal cells remains poorly explored. This study aimed to predict, in silico, TXs' binding sites within P-gp and to evaluate, in vitro, in human kidney (HK)-2 cells, the effects of selected TXs (TX1-5) on P-gp activity and expression, and protection against cisplatin-induced cytotoxicity. Computational studies identified preferential TX1-5 binding to the drug-binding pocket, particularly the rhodamine 123 (R) or modulator (M) sites, and to nucleotide-binding domain 1. In vitro, rhodamine 123 accumulation assays revealed increased P-gp transport activity after 120 min or 24 h exposure to TX1-5, except TX4. TX2 elicited the strongest effect (141% increase, p < 0.0001), upregulated P-gp expression (24 h, p < 0.0001), and significantly protected HK-2 cells from cisplatin-induced cytotoxicity (increased IC50, p < 0.0001). Altogether, these findings position thioxanthones as promising scaffolds for the development of P-gp-targeted strategies to mitigate drug-induced nephrotoxicity.