The thioredoxin system, composed of thioredoxin reductase (TrxR), thioredoxin (Trx), and NADPH (Nicotinamide adenine dinucleotide compounds were found to induce antiproliferative effects towards several human cancer cells some of which endowed with cisplatin or multidrug resistance. In addition, they were able to activate caspase-3 and induce apoptosis observed as nucleosome formation and sub-G1 cell accumulation. The complexes with thiocyanate and xanthate ligands were particularly effective in inhibiting thioredoxin reductase and inducing apoptosis.Pharmacodynamic studies in human ovarian cancer cells allowed for the correlatation of intracellular drug accumulation with TrxR inhibition that leads to the induction of apoptosis via the mitochondrial pathway.

The seleno-enzyme thioredoxin reductase (TrxR) is a putative target for cytotoxic gold complexes. We investigated the mechanism of TrxR inhibition by a group of structurally diverse gold(III) compounds; the antiarthritic gold(I) drugs auranofin and aurothiomalate were also studied for comparison purposes. The tested compounds -either gold(III) or gold(I) -were found to produce potent enzyme inhibition only after pre-reduction of the enzyme with NADPH, indicating that TrxR inhibition is the result of protein structure modifications occurring upon cofactor binding. MALDI-ToF MS experiments on the intact enzyme provided evidence for extensive enzyme metallation, while experiments on trypsinized gold(III)-protein adducts identified a specific protein fragment -namely 236 IGEHMEEHGIK 246 -bearing an attached gold(I) ion. Independent mechanistic information on the system was derived from BIAM assays capable of monitoring selective metal binding to cysteine and/or selenocysteine residues. While the effects produced by auranofin could be essentially ascribed to gold(I) coordination to the active site selenol, the effects caused by the various gold(III) compounds were better interpreted in terms of oxidative protein damage.

No abstract