PX-12(IV-2) is an irreversible inhibitor of Thioredoxin-1 (Trx-1); inhibits the growth of MCF-7 and HT-29 cells with IC₅₀ values of 1.9 and 2.9 μM, respectively. IC50 & Target: IC50: 1.9 (MCF-7), 2.9 μM (HT-29 cells)^[1] In Vitro: PX-12 inhibits the growth of MCF-7 and HT-29 cells with IC₅₀ values of 1.9 and 2.9 μM, respectively^[1]. PX-12 particularly reduces the activity of Trx-1 by means of thio-alkylating critical cysteine residue (Cys73) which is located in the outside the conserved redox catalytic site of Trx-1. PX-12 affects the oxidation state of thiols in a number of cell surface proteins. Key surface receptors for platelet adhesion and activation are affected, including the collagen receptor GPVI and the von Willebrand factor receptor, GPIb. PX-12 inhibits thrombus formation over Type I collagen in whole blood under flow conditions^[2]. Thioredoxin-1 (Trx-1) is a cellular redox protein that promotes tumor growth, inhibits apoptosis, and up-regulates hypoxia-inducible factor-1α and vascular endothelial growth factor^[3]. PX-12 inhibits the growth of colorectal cancer DLD-1 and SW620 cells in a dose- and time-dependent manner. PX-12 reduces cell colony formation and induced a G2/M phase arrest of the cell cycle. PX-12 treatment induces apoptosis. PX-12 inhibits colorectal cancer cell migration and invasion. Treatment of cancer cells with PX-12 reduces NOX1, CDH17 and S100A4 mRNA expression, and increases KLF17 mRNA expression. PX-12 decreases S100A4 protein expression in the colorectal cancer cells^[4]. In Vivo: PX-12 has been shown to have in vivo antitumor activity against human tumor xenografts including HT-29 colon cancer in SCID mice and has been tested in a phase I clinical trial in patients^[3].