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Adenanthin has been recently shown to inhibit the enzymatic activities of peroxiredoxins (Prdx) I and II through its functional α,β-unsaturated ketone group serving as a Michael acceptor. A similar group is found in SK053, a compound recently developed by our group to target the thioredoxin-thioredoxin reductase (Trx-TrxR) system. This work provides evidence that next to Prdx I and II adenanthin targets additional proteins including thioredoxin-thioredoxin reductase system as well as protein disulfide isomerase (PDI) that contain a characteristic structural motif, referred to as a thioredoxin fold. Adenanthin inhibits the activity of Trx-TR system and PDI in vitro in the insulin reduction assay and decreases the activity of Trx in cultured cells. Moreover, we identified Trx-1 as an adenanthin binding protein in cells incubated with biotinylated adenanthin as an affinity probe. The results of our studies indicate that adenanthin is a mechanism-selective, rather than an enzyme-specific inhibitor of enzymes containing readily accessible, nucleophilic cysteines. This observation might be of importance in considering potential therapeutic applications of adenanthin to include a range of diseases, where aberrant activity of Prdx, Trx-TrxR and PDI is involved in their pathogenesis., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The effect of deferoxamine on nucleotide metabolism in HL-60 leukemic cells was studied to explore the mechanism of its antiproliferation activity. It was found that in intact cells deferoxamine markedly inhibited the ribonucleotide reduction and incorporation of bases (adenine, hypoxanthine), ribonucleosides (inosine, guanosine) and deoxyribonucleosides (thymidine, deoxyadenosine, deoxyguanosine) into nucleic acids. Although deferoxamine did not inhibit thymidine and uridine incorporation into free nucleotides, inhibition of hypoxanthine and adenine incorporation into nucleotides as well as inhibition of nucleotide biosynthesis de novo was found. Nucleotide catabolism, protein synthesis, and intracellular levels of ribonucleotides were not affected significantly by deferoxamine. These results showed that deferoxamine selectively affects several specific reactions of nucleotide metabolism. Inhibition of ribonucleotide reduction, inhibition of ribonucleotide and deoxyribonucleotide incorporation into nucleic acids, as well as inhibition of purine biosynthesis, may alter significantly cellular physiology and, therefore, contribute significantly to the antiproliferative activity of deferoxamine.