Cysteine Metabolism in Tumor Redox Homeostasis

Cysteine (Cys) is a semi-essential nutrient amino acid that plays an important role in cells through endogenous production and various transport systems. Intracellular Cys can be used as a precursor of protein synthesis to maintain cell homeostasis and to generate sulfur-containing substances, including glutathione (GSH), hydrogen sulfide (H2S), and taurine. There have been quite a few reports that Cys is related to tumor occurrence and development, and its level is closely related to tumor proliferation, invasion, and metastasis. Moreover, it helps in maintaining the tumor redox balance and increasing drug resistance. This review aims to summarize the production and metabolism of Cys and its role in tumors, with special emphasis on the potential therapeutic value of Cys in tumors to improve the quality of life of cancer patients.