Thimerosal, a competitive thioredoxin reductase 1 (TrxR1) inhibitor discovered via high-throughput screening.

Thioredoxin reductase 1 (TrxR1) is considered as an important anti-cancer drug target, inhibition of which can induce reactive oxygen species (ROS)-mediated apoptosis of human cancer cells. Here, we developed and optimized a high-throughput screening (HTS) assay based on enzyme kinetics for the discovery of TrxR1 inhibitors. By utilizing this assay, we performed a HTS for 2500 compounds from an in-house library against TrxR1. We found that a vaccine preservative, thimerosal, strongly inhibited TrxR1 in a competitive and reversible manner with an IC of 24.08 ± 0.86 nM. In addition, we determined that thiomersal has an inhibitory effect on the proliferation of A549 lung cancer cell line, with a GI of 6.81 ± 0.09 μM, slightly more potent than auranofin (GI = 11.85 ± 0.56 μM). Furthermore, we showed by flow cytometer that thimerosal effectively increased the content of ROS in A549 cells. Therefore, our work provided a high-throughput screening assay to quickly and effectively discover TrxR1 inhibitors, identifying thiomersal as a novel TrxR1 inhibitor and chemical probe.