In vitro activity: AP-III-a4 (also known as ENOblock) is a novel and potent small molecule inhibitor of enolase which is isolated by small molecule screening in a cancer cell assay to detect cytotoxic agents that function in hypoxic conditions, which has previously been shown to induce drug resistance. AP-III-a4 is the first, nonsubstrate analogue that directly binds to enolase and inhibits its activity (IC50=0.576 uM); inhibit cancer cell metastasis in vivo. In HCT116 cells, AP-III-a4 induces cell death under hypoxia, and inhibits cancer cell migration and invasion by down-regulation of AKT and Bcl-xL expression. In Huh7 hepatocytes and HEK kidney cells, AP-III-a4 induces glucose uptake and inhibits phosphoenolpyruvate carboxykinase (PEPCK) expression. Thus, ENOblock is the first reported enolase inhibitor that is suitable for biological assays. This new chemical tool may also be suitable for further study as a cancer and diabetes drug candidate. In HCT116 cells, AP-III-a4 induces cell death under hypoxia, and inhibits cancer cell migration and invasion by down-regulation of AKT and Bcl-xL expression. In Huh7 hepatocytes and HEK kidney cells, AP-III-a4 induces glucose uptake and inhibits phosphoenolpyruvate carboxykinase (PEPCK) expression.

Kinase Assay: A single unit of enolase is defined as the amount of enzyme that produces 1 μmol of phosphoenol pyruvate from phospho-D-glycerate/min in standard assay. Enolase activity assay is measured at 37°C by incubating pure enolase (3–9 U) in a buffer containing 50 mM imidazole-HCl (pH 6.8), 2.0 mM MgSO4 and 400 mM KCl in the absence or presence of ENOblock or NaF. The reaction is initiated by adding 1 μmol of 2-phospho-D-glycerate, and the OD is measured after 10 min of reaction time with a spectrophometer at 240 nm.

Cell Assay: 3 x 105 HCT116 cells are seeded in a 6 well plate. 24 h later, cells are treated with compound of interest (with or without prior induction of hypoxia for 4 h) for 24 h using triplicate wells. Cells are then trypsinized and resuspended in 2.5 mL PBS. A 100 μL aliquot is taken for staining with 0.2% trypan blue solution and counted using a hemocytometer. 150 cells are counted and dead cells are classified as those that could not exclude trypan blue.