The Cdc25 phosphatases function as key regulators of the cell cycle during normal eukaryotic cell division and as mediators of the checkpoint response in cells with DNA damage. The role of Cdc25s in cancer has become increasingly evident in recent years. More than 20 studies of patient samples from diverse cancers show significant overexpression of Cdc25 with frequent correlation to clinical outcome. Recent screening and design efforts have yielded novel classes of inhibitors that show specificity for the Cdc25s over other phosphatases and cause cell cycle arrest in vivo. Herein we provide a single source for those interested in the cellular functions of Cdc25 in cell cycle progression, its role in the progress of cancer and survival of cancer patients, and recent efforts in the design of specific inhibitors.

The zinc-dependent enzyme LpxC catalyzes the deacetylation of UDP-3-O-acyl-GlcNAc, the first committed step of lipid A biosynthesis. Lipid A is an essential component of the outer membranes of most Gram-negative bacteria, including Escherichia coli, Salmonella enterica and Pseudomonas aeruginosa, making LpxC an attractive target for antibiotic design. The inhibition of LpxC by a novel N-aroyl-L-threonine hydroxamic acid (CHIR-090) from a recent patent application (International Patent WO 2004/062601 A2 to Chiron and the University of Washington) is reported here. CHIR-090 possesses remarkable antibiotic activity against both E. coli and P. aeruginosa, comparable to that of ciprofloxacin. The biological activity of CHIR-090 is explained by its inhibition of diverse LpxC orthologs at low nM concentrations, including that of Aquifex aeolicus, for which structural information is available. The inhibition of A. aeolicus LpxC by CHIR-090 occurs in two steps. The first step is rapid and reversible, with a K i of 1.0 -1.7 nM, depending on the method of assay. The second step involves the conversion of the EI complex with a half-life of about a minute to a tightly bound form. The second step is functionally irreversible but does not result in the covalent modification of the enzyme, as judged by electrospray-ionization mass spectrometry. CHIR-090 is the first example of a slow, tight-binding inhibitor for LpxC, and may be the prototype for a new generation of LpxC inhibitors with therapeutic applicability.The emergence of multi-drug resistant bacterial pathogens is a growing public health concern (1). Human and animal pathogens are developing resistance to every major class of commercial antibiotic, both natural and synthetic. New antibiotics directed against previously unexploited bacterial targets are urgently needed (2-4).Zinc-dependent hydrolases are a well-studied class of proteins, many of which have set successful precedents for mechanism-based inhibitor design (5-7). Several bacterial metalloamidases have been identified as potential antibiotic targets (7). Among them is LpxC, a zincdependent, cytoplasmic deacetylase involved in the biosynthesis of the lipid A component of lipopolysaccharide (Scheme 1) (8-11).LpxC removes the acetate group from the nitrogen atom at the glucosamine 2 position of UDP-3-O-acyl-N-acetylglucosamine (Scheme 1) (12,13). This reaction is the first committed step of lipid A biosynthesis (14) and is essential for bacterial growth (12,13 Despite its unique substrate specificity and sequence, LpxC does share some mechanistic features with other important metallo-amidases. As in thermolysin (18), angiotensinconverting enzyme (5,19), the matrix metallo-proteinases (6), and peptide N-deformylase (20), a single transition metal ion is required for LpxC catalytic activity (9) and a glutamate side chain in the LpxC active site is thought to activate the Zn 2+ -bound water (21). Selective chelation of the LpxC active site Zn 2+ ion by certain small molecules containing hydroxamic acid group...