MuLK, a eukaryotic multi-substrate lipid kinase.

We report the identification and characterization of a novel lipid kinase that phosphorylates multiple substrates. This enzyme, which we term MuLK for multi-substrate lipid kinase, does not belong to a previously described lipid kinase family. MuLK has orthologs in many organisms and is broadly expressed in human tissues. Although predicted to be a soluble protein, MuLK co-fractionates with membranes and localizes to an internal membrane compartment. Recombinant MuLK phosphorylates diacylglycerol, ceramide, and 1-acylglycerol but not sphingosine. Although its affinity for diacylglycerol and ceramide are similar, MuLK exhibits a higher V(max) toward diacylglycerol in vitro, consistent with it acting primarily as a diacylglycerol kinase. MuLK activity was inhibited by sphingosine and enhanced by cardiolipin. It was stimulated by calcium when magnesium concentrations were low and inhibited by calcium when magnesium concentrations were high. The effects of charged lipids and cations on MuLK activity in vitro suggest that its activity in vivo is tightly regulated by cellular conditions.

Dipeptidyl aspartyl fluoromethylketones as potent caspase-3 inhibitors: SAR of the P2 amino acid.

This article describes the synthesis and biological evaluation of a series of dipeptidyl aspartyl fluoromethylketones as caspase-3 inhibitors. Structure-activity relationship (SAR) studies showed that for caspase-3 inhibition, Val is the best P(2) amino acid. The SAR studies also showed that the Asp free carboxylic acid in P(1) is important for caspase inhibiting activities, as well as for selectivity over other proteases.

Discovery, characterization and SAR of gambogic acid as a potent apoptosis inducer by a HTS assay.

Gambogic acid (2), a natural product isolated from the resin of Garcinia hurburyi tree, was discovered to be a potent apoptosis inducer using our cell- and caspase-based high-throughput screening assays. Gambogic acid was found to have an EC(50) of 0.78 microM in the caspase activation assay in T47D breast cancer cells. The apoptosis-inducing activity of gambogic acid was further characterized by a nuclear fragmentation assay and flow cytometry analysis in human breast tumor cells T47D. Gambogic acid was found to induce apoptosis independent of cell cycle, which is different from paclitaxel that arrests cells in the G2/M phase. To understand the structure-activity relationship (SAR) of gambogic acid, derivatives of 2 with modifications to different function groups were prepared. SAR studies of gambogic acid, as measured by the caspase activation assay, showed that the 9,10 carbon-carbon double bond of the alpha,beta-unsaturated ketone is important for biological activity, while the 6-hydroxy and 30-carboxy group can tolerate a variety of modifications. The importance of the 9,10 carbon-carbon double bond was confirmed by the traditional growth inhibition assay. The high potency of 2 as an inducer of apoptosis, its novel mechanism of action, easy isolation and abundant supply, as well as the fact that it is amenable to chemical modification, makes gambogic acid an attractive molecule for the development of anticancer agents.

MX1013, a dipeptide caspase inhibitor with potent in vivo antiapoptotic activity.

1. Caspases play a critical role in apoptosis, and are considered to be key targets for the design of cytoprotective drugs. As part of our antiapoptotic drug-discovery effort, we have synthesized and characterized Z-VD-fmk, MX1013, as a potent, irreversible dipeptide caspase inhibitor. 2. MX1013 inhibits caspases 1, 3, 6, 7, 8, and 9, with IC50 values ranging from 5 to 20 nm. MX1013 is selective for caspases, and is a poor inhibitor of noncaspase proteases, such as cathepsin B, calpain I, or Factor Xa (IC50 values >10 microm). 3. In several cell culture models of apoptosis, including caspase 3 processing, PARP cleavage, and DNA fragmentation, MX1013 is more active than tetrapeptide- and tripeptide-based caspase inhibitors, and blocked apoptosis at concentrations as low as 0.5 microm. 4. MX1013 is more aqueous soluble than tripeptide-based caspase inhibitors such as Z-VAD-fmk. 5. At a dose of 1 mg kg-1 i.v., MX1013 prevented liver damage and the lethality caused by Fas death receptor activation in the anti-Fas mouse-liver apoptosis model, a widely used model of liver failure. 6. At a dose of 20 mg kg-1 (i.v. bolus) followed by i.v. infusion for 6 or 12 h, MX1013 reduced cortical damage by approximately 50% in a model of brain ischemia/reperfusion injury. 7. At a dose of 20 mg kg-1 (i.v. bolus) followed by i.v. infusion for 12 h, MX1013 reduced heart damage by approximately 50% in a model of acute myocardial infarction. 8. Based on these studies, we conclude that MX1013, a dipeptide pan-caspase inhibitor, has a good combination of in vitro and in vivo properties. It has the ability to protect cells from a variety of apoptotic insults, and is systemically active in three animal models of apoptosis, including brain ischemia.

Discovery of substituted N-phenyl nicotinamides as potent inducers of apoptosis using a cell- and caspase-based high throughput screening assay.

By applying a novel cell- and caspase-based HTS assay, a series of N-phenyl nicotinamides has been identified as a new class of potent inducers of apoptosis. Through SAR studies, a 20-fold increase in potency was achieved from a screening hit N-(4-methoxy-2-nitrophenyl)pyridine-3-carboxamide (1) to lead compound 6-methyl-N-(4-ethoxy-2-nitrophenyl)pyridine-3-carboxamide (10), with an EC(50) of 0.082 microM in the caspase activation assay in T47D breast cancer cells. The N-phenyl nicotinamides also were found to be active in the growth inhibition assay where compound 10 had a GI(50) value of 0.21 microM in T47D cells. More importantly, compound 10 was found to be equipotent in MES-SA cells and paclitaxel-resistant, p-glycoprotein overexpressed MES-SA/DX5 cells. Compounds 1 and 6-chloro-N-(4-ethoxy-2-nitrophenyl)pyridine-3-carboxamide (8), a more potent analogue, were found to arrest T47D cells in G(2)/M phase of the cell cycle followed by induction of apoptosis as measured by flow cytometry. Compound 8, which was more potent than 1 in the caspase activation assay, also was found to be more potent in G(2)/M arrest and apoptosis assay. These data confirm that the cell-based caspase activation assay is useful for screening for inducers of apoptosis, as well as for SAR studies and lead optimization. Upon further characterization, N-phenyl nicotinamides were found to be inhibitors of microtubule polymerization in vitro. The identification of N-phenyl nicotinamides as a novel series of inducers of apoptosis demonstrates that our cell- and caspase-based HTS assay is useful for the discovery and optimization of potentially novel anticancer agents.

N-Ac-DEVD-N'-(Polyfluorobenzoyl)-R110: novel cell-permeable fluorogenic caspase substrates for the detection of caspase activity and apoptosis.

N-Pentafluorobenzoyl-R110 (1a) and N-(2,3,4,5-tetrafluorobenzoyl)-R110 (1b) with enhanced cell retention properties, were prepared from rhodamine 110 (R-110) and the corresponding polyfluorobenzoyl chloride. N-Ac-DEVD-N'-pentafluorobenzoyl-R110 (3a) and N-Ac-DEVD-N'-(2,3,4,5-tetrafluorobenzoyl)-R110 (3b) were prepared as tetrapeptide substrates for caspases. Substrate 3b was efficiently cleaved by human recombinant caspase-3 in an enzyme assay. Substrate 3b also was efficiently cleaved in cell-based apoptosis assays. After cleavage in apoptotic cells by activated caspases, the substrate becomes fluorescent as measured by flow cytometry. These substrates should prove useful in cell-based assays for studying apoptosis inducers and inhibitors.