Novel thioredoxin inhibitors paradoxically increase hypoxia-inducible factor-alpha expression but decrease functional transcriptional activity, DNA binding

Abstract Purpose:Hypoxia-inducible factor-a (HIF-a) is a transcription factor that regulates the response to hypoxia. HIF-a protein is found at high levels in many cancers, and the redox protein thiore-doxin-1 (Trx-1) increases both aerobic and hypoxia-induced HIF-a. Therefore, Trx-1and HIF-a are attractive molecular targets for novel cancer therapeutics. Experimental Design:We investigated whether two novel anticancer drugs AJM290 and AW464 (quinols), which inhibitTrx-1function, can inhibit the HIF pathway. Results:Treatment of several cancer cell lines with AJM290 orAW464 prevented the hypoxia-induced increase of vascular endothelial growth factor (VEGF) at subtoxic concentrations. AJM290 and AW464 also decreasedVEGF in pVHLmutant renal cell carcinoma cells that consti-tutively overexpress HIF-a protein. They surprisingly up-regulated HIF-a expression in breast cancer cell lines in normoxia and hypoxia as well as in pVHL mutant cells. In the MDA-MB-468 breast cancer cell line, the compounds inhibited RNA and protein expression of the HIF-a target genes, carbonic anhydrase IX,VEGF, and BNIP3, concordantly with HIF-a up-regulation. Both compounds specifically inhibited HIF-a-dependent induction of hypoxia regulatory element-luciferase and HIF-1ahypoxia regulatory element-DNA binding. To analyze the HIF-1adomai