HSP90 inhibition potentiates oxidant-based antimelanoma action of novel thioquercetin derivatives by compromising AhR/CYP1A1 pathway

Quercetin, a plant-derived dietary flavonoid, has multifunctional biological activities, including anticancer action; however, its applications may be restricted due to limited bioavailability. Thus, novel synthetic quercetin derivatives (QDs) with improved properties and/or drug combinations should be designed and tested. In the present study, anticancer activity of fourteen newly synthesized QDs was investigated using four cellular models of melanoma, namely A375, MM370, G-361, and SH-4 cells. Thioquercetins (thioQ, thioQ(OAc)₄, and thioQ(OAc)₅), when used at low micromolar range, induced apoptotic cell death in melanoma cells compared to normal cells. Thioquercetins also reduced the population of spheroid-forming cells and suppressed the growth of A375 cells in 3D spheroid models. Thioquercetin-mediated antimelanoma action was potentiated upon heat shock protein 90 (HSP90) inhibition. Co-treatment with the HSP90 inhibitor 17-DMAG and thioquercetins augmented oxidative stress (increased superoxide production, decreased levels of antioxidant proteins SOD1, and PRDX1-2), and impaired the aryl hydrocarbon receptor (AhR)/cytochrome P450 1A1 (CYP1A1) signaling pathway-based detoxification of thioquercetins by the inhibition of AhR translocation to the nucleus and AhR-mediated stimulation of CYP1A1 expression leading to enhanced cytotoxic effects against melanoma cells. The senolytic activity of thioQ(OAc)₄ with four acetylated hydroxy groups against cisplatin-induced senescent melanoma cells was also revealed in selected experimental settings. We suggest that the use of novel thioquercetin-based derivatives along with HSP90 inhibitors should be further validated in vivo and considered for the design of more effective antimelanoma strategies in the future.