Elucidation of Thioredoxin as a Molecular Target for Antitumor Quinols

Abstract

Heteroaromatic quinols 4-(benzothiazol-2-yl)-4-hydroxycyclohexa-2,5-dienone (1) and 4-(1-benzenesulfonyl-1H-indol-2-yl)-4-hydroxycyclohexa-2,5-dienone (2) exhibit potent and selective antitumor activity against colon, renal, and breast carcinoma cell lines in vitro (GI 50 < 500 nmol/L). In vivo growth inhibition of renal, colon, and breast xenografts has been observed. Profound G 2 -M cell cycle block accompanied down-regulation of cdk1 gene transcription was corroborated by decreased CDK1 protein expression following treatment of HCT 116 cells with growth inhibitory concentrations of 1 or 2. The chemical structure of the quinol pharmacophore 4-(hydroxycyclohexa-2,5-dienone) suggested that these novel agents would readily react with nucleophiles in a double Michael (B-carbon) addition. Indeed, COMPARE analysis within the National Cancer Institute database revealed a number of chemically related quinone derivatives that could potentially react with sulfur nucleophiles in a similar manner and suggested that thioredoxin/ thioredoxin reductase signal transduction could be a putative target. Molecular modeling predicted covalent irreversible binding between quinol analogues and cysteine residues 32 and 35 of thioredoxin, thereby inhibiting enzyme activity. Binding has been confirmed, via mass spectrometry, between reduced human thioredoxin and 1. Microarray analyses of untreated HCT 116 cells and those exposed to either 1 (1 Mmol/L) or 2 (500 nmol/L and 1 Mmol/L) determined that of z z10,000 cancer-related genes, expression of thioredoxin reductase was up-regulated > >3-fold. Furthermore, quinols 1 and 2 inhibited insulin reduction, catalyzed by thioredoxin/thioredoxin reductase signaling in a dose-dependent manner (IC 50 < < 6 Mmol/L). Results are consistent with a mechanism of action of novel antitumor quinols involving inhibition of the small redox protein thioredoxin. (Cancer Res 2005; 65(9): 3911-9)

High Throughput Screening against the Peroxidase Cascade of African Trypanosomes Identifies Antiparasitic Compounds That Inactivate Tryparedoxin

“…Indeed, compounds that interact with Trx do not necessarily react with Tpx. The antitumor benzothiazole-substituted quinole PMX464 inhibits Trx (21)(22)(23). A recent study on the T. brucei peroxidase system revealed that the quinole reacts with T(SH) 2 as well as Px and Prx but not with Tpx or TR (20).…”

“…Recently the effect of the antitumor quinol PMX 464 on the parasite peroxidase systems has been studied (20). In mammalian and yeast cells, the quinol inhibits thioredoxin (21)(22)(23). Toward T. brucei, PMX 464 showed cytocidal activity and caused depletion of cellular T(SH) 2 .…”

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

“…AW464 is a benzothiazole-substituted quinol compound that has been shown by mass spectrometry to bind to Trx-1 and has been proposed to cross-link irreversibly to cysteine residues 32 and 35 of Trx-1 active site via its two h-carbon atoms; the first link is reversible, whereas the second cross-link is thought to be irreversible (36,41). AW464 can inhibit VEGF expression in hypoxic colorectal cells, and hypoxia has been shown to sensitize colorectal cancer cells to antiproliferative effect of AW464 (35).…”

“…AW464 can inhibit VEGF expression in hypoxic colorectal cells, and hypoxia has been shown to sensitize colorectal cancer cells to antiproliferative effect of AW464 (35). Further chemical syntheses and structure activity screening uncovered AJM290, an indole-substituted quinol that possess enhanced potency in vitro against human derived colon, renal, and mammary carcinoma cell lines and in vivo antitumor activity against breast, colon, and renal mouse xenografts (36,42).…”

Structure of Mycobacterium tuberculosis thioredoxin in complex with quinol inhibitor PMX464

“…15,16 Hydroxycyclohexadienone analogues, of which PMX464 is the parent compound, have encouraging results in inhibitory trials against Mtb H 37 Rv strains in vitro 17 and studies showed that MtbTrxC catalyzed reduction of insulin is inhibited by PMX464 in a potent and dose-dependent manner consistent with irreversible inhibition of Trx (IC 50 < 6 lM). 18 To investigate how the inhibitor binds and thus provide a template for design and development we have determined the structure of PMX464 in complex with a catalytically inactive MtbTrxC.…”