Identification of Catechol-Type Diphenylbutadiene as a Tyrosinase-Activated Pro-oxidative Chemosensitizer against Melanoma A375 Cells via Glutathione S-Transferase Inhibition.

Glutathione S-transferases (GSTs) play an active role in the development of drug resistance by numerous cancer cells, including melanoma cells, which is a major cause of chemotherapy failure. As part of our continuous effort to explore why dietary polyphenols bearing the catechol moiety (dietary catechols) show usually anticancer activity, catechol-type diphenylbutadiene (3,4-DHB) was selected as a model of dietary catechols to probe whether they work as pro-oxidative chemosensitizers via GST inhibition in melanoma cells. It was found that, in human melanoma A375 cells, 3,4-DHB is easily converted to its ortho-quinone via copper-containing tyrosinase-mediated two-electron oxidation along with generation of reactive oxygen species (ROS) derived from the oxidation; the resulting ortho-quinone and ROS are responsible for its ability to sensitize the cisplatin-resistant cells by inhibiting GST, followed by induction of apoptosis in an ASK1-JNK/p38 signaling cascade and mitochondria-dependent pathway. This work provides further evidence to support that dietary catechols exhibit antimelanoma activity by virtue of their tyrosinase-dependent pro-oxidative role and gives useful information for designing polyphenol-inspired GST inhibitors and sensitizers in chemotherapy against melanoma.