It is known that human thioredoxin (hTrx), an antioxidant protein, is essential for cellular functions as this ubiquitous 12 KDa protein has oxidoreductase activities. An increased generation of hTrx and an elevated oxidative stress status, which results in dimer formation of hTrx, have been observed in cancer cells. However, the physiological role, if any, of Trx dimer formation in cancer remains unknown. Human Trx has been studied as an anticancer target and the development of hTrx system inhibitors for therapeutic purposes is of increasing interest, which ultimately requires appropriate animal models to evaluate these potential anti-cancer drugs.
Mouse or rats are common vertebrate species used to test potential drugs. Therefore, for testing of hTrx inhibitors in an animal model the regulation of the mouse thioredoxin (mTrx) protein structure must be compared to the hTrx protein. We are currently studying mTrx in order to understand the mechanism of dimer formation in response to various compounds compared to hTrx. It is known that mTrx contains an extra Cys46 residue compared to hTrx, and we are using site-directed mutagenesis to study the role of this cysteine residue in dimer formation under oxidising conditions. Initially hydrogen peroxide and diamide have been used as oxidative stressors to induce dimer formation in various hTrx and mTrx mutated proteins to compare the outcomes, such as an assessment of insulin reductase activity. This knowledge will allow us to test and evaluate anticancer drugs that target hTrx in the mouse as an animal model.