Quercetin as a JAK–STAT inhibitor: a potential role in solid tumors and neurodegenerative diseases

The Janus kinase–signal transducer and activator of transcription (JAK–STAT) pathway is involved in many immunological processes, including cell growth, proliferation, differentiation, apoptosis, and inflammatory responses. Some of these processes can contribute to cancer progression and neurodegeneration. Owing to the complexity of this pathway and its potential crosstalk with alternative pathways, monotherapy as targeted therapy has usually limited long-term efficacy. Currently, the majority of JAK–STAT-targeting drugs are still at preclinical stages. Meanwhile, a variety of plant polyphenols, especially quercetin, exert their inhibitory effects on the JAK–STAT pathway through known and unknown mechanisms. Quercetin has shown prominent inhibitory effects on the JAK–STAT pathway in terms of anti-inflammatory and antitumor activity, as well as control of neurodegenerative diseases. This review discusses the pharmacological effects of quercetin on the JAK–STAT signaling pathway in solid tumors and neurodegenerative diseases.