Novel Thioredoxin Inhibitors Paradoxically Increase Hypoxia-Inducible Factor-α Expression but Decrease Functional Transcriptional Activity, DNA Binding, and Degradation

Abstract Purpose: Hypoxia-inducible factor-α (HIF-α) is a transcription factor that regulates the response to hypoxia. HIF-α protein is found at high levels in many cancers, and the redox protein thioredoxin-1 (Trx-1) increases both aerobic and hypoxia-induced HIF-α. Therefore, Trx-1 and HIF-α are attractive molecular targets for novel cancer therapeutics. Experimental Design: We investigated whether two novel anticancer drugs AJM290 and AW464 (quinols), which inhibit Trx-1 function, can inhibit the HIF pathway. Results: Treatment of several cancer cell lines with AJM290 or AW464 prevented the hypoxia-induced increase of vascular endothelial growth factor (VEGF) at subtoxic concentrations. AJM290 and AW464 also decreased VEGF in pVHL mutant renal cell carcinoma cells that constitutively overexpress HIF-α protein. They surprisingly up-regulated HIF-α 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-α target genes, carbonic anhydrase IX, VEGF, and BNIP3, concordantly with HIF-α up-regulation. Both compounds specifically inhibited HIF-α-dependent induction of hypoxia regulatory element-luciferase and HIF-1α hypoxia regulatory element-DNA binding. To analyze the HIF-1α domain inhibited by AJM290, we transfected cells with plasmids expressing a fusion protein of Gal linked to HIF-1α or HIF-1α COOH-terminal transactivation domain (CAD) with a Gal4-responsive luciferase reporter gene. AJM290 inhibited both the full-length HIF-1α and HIF-1α CAD transcriptional activity. Conclusions: AJM290 and AW464 are inhibitors of HIF-1α CAD transcription activity and DNA binding, but they also inhibit degradation of HIF, in contrast to other Trx inhibitors.