P-glycoprotein induction in Caco-2 cells by newly synthetized thioxanthones prevents paraquat cytotoxicity

Abstract

The induction of P-glycoprotein (P-gp), an ATP-dependent efflux pump, has been proposed as a strategy against the toxicity induced by P-gp substrates such as the herbicide paraquat (PQ). The aim of this study was to screen five newly synthetized thioxanthonic derivatives, a group known to interact with P-gp, as potential inducers of the pump's expression and/or activity and to evaluate whether they would afford protection against PQ-induced toxicity in Caco-2 cells. All five thioxanthones (20 µM) caused a significant increase in both P-gp expression and activity as evaluated by flow cytometry using the UIC2 antibody and rhodamine 123, respectively. Additionally, it was demonstrated that the tested compounds, when present only during the efflux of rhodamine 123, rapidly induced an activation of P-gp. The tested compounds also increased P-gp ATPase activity in MDR1-Sf9 membrane vesicles, indicating that all derivatives acted as P-gp substrates. PQ cytotoxicity was significantly reduced in the presence of four thioxanthone derivatives, and this protective effect was reversed upon incubation with a specific P-gp inhibitor. In silico studies showed that all the tested thioxanthones fitted onto a previously described three-feature P-gp induction pharmacophore. Moreover, in silico interactions between thioxanthones and P-gp in the presence of PQ suggested that a co-transport mechanism may be operating. Based on the in vitro activation results, a pharmacophore model for P-gp activation was built, which will be of further use in the screening for new P-gp activators. In conclusion, the study demonstrated the potential of the tested thioxanthonic compounds in protecting against toxic effects induced by P-gp substrates through P-gp induction and activation.

Effect of MDR1 gene polymorphisms on mortality in paraquat intoxicated patients

“…Some reports have shown that inducing P-gp can protect cells against PQ induced toxicity in vivo and in vitro 91012131415. Silva et al have demonstrated that inducing P-gp in Caco-2 cells using newly synthesized thioxanthones can prevent PQ cytotoxicity15. Mice treated with dexamethasone display increased MDR1 expression in the lungs associated with decreased PQ accumulation and pneumotoxicity9.…”

“…One study has shown that P-gp is involved in removing PQ from the kidneys and attenuating toxicity enhanced in MDR 1a/1b knockout mice12. Some reports have suggested that inducing P-gp might be used as a therapeutic approach to treat PQ intoxication13141516.…”

Quantification of 1‐(propan‐2‐ylamino)‐4‐propoxy‐9H‐thioxanthen‐9‐one (TX5), a newly synthetized P‐glycoprotein inducer/activator, in biological samples: method development and validation

“…Xanthones (Xs) and thioxanthones (TXs) are two families of heterocyclic compounds with several known biological activities and recognized therapeutic potential (Masters & Brase, ; Pinto et al ., ; Silva et al ., ). In fact, in recent years, the interaction of Xs and TXs with membrane transporters, like P‐gp, has been an important research target for medicinal chemists, who describe these classes as privileged structures given their pronounced biological effects (Silva et al ., ; Sousa & Pinto, ).…”

“…The authors demonstrated that all tested Xs and TXs have the ability to significantly increase both P‐gp expression and activity, 24 h after incubation, and also that these compounds can immediately activate the pump, as demonstrated by the increased efflux of Rhodamine 123, a P‐gp fluorescent substrate, after a short period of incubation. Importantly, the authors also showed that the tested compounds increased P‐gp ATPase activity, indicating that all derivatives act as P‐gp substrates (Silva et al ., ). Among the tested compounds, 1‐(propan‐2‐ylamino)‐4‐propoxy‐9 H ‐thioxanthen‐9‐one (TX5, Figure ) was the most effective compound in protecting Caco‐2 cells against toxic effects induced by the P‐gp substrate paraquat, through a P‐gp induction and activation mechanism.…”

“…Recently, Silva et al . () tested several newly synthesized dihydroxylated xanthones and thioxanthones to evaluate whether they would afford protection against paraquat‐induced toxicity in Caco‐2 cells (paraquat is a known toxic P‐gp substrate). The authors demonstrated that all tested Xs and TXs have the ability to significantly increase both P‐gp expression and activity, 24 h after incubation, and also that these compounds can immediately activate the pump, as demonstrated by the increased efflux of Rhodamine 123, a P‐gp fluorescent substrate, after a short period of incubation.…”