Functionalized pyrrolidine inhibitors of human type II alpha-mannosidases as anti-cancer agents: optimizing the fit to the active site.

Refining the chemical structure of functionalized pyrrolidine-based inhibitors of Golgi alpha-mannosidase II (GMII) to optimize binding affinity provided a lead molecule that demonstrated nanomolar competitive inhibition of alpha-mannosidases II and an optimal fit in the active site of Drosophila GMII by X-ray crystallography. Esters of this lead compound also inhibited the growth of human glioblastoma and brain-derived endothelial cells more than the growth of non-tumoral human fibroblasts, suggesting their potential for anti-cancer therapy.

Evaluation of docking programs for predicting binding of Golgi alpha-mannosidase II inhibitors: a comparison with crystallography.

Golgi alpha-mannosidase II (GMII), a zinc-dependent glycosyl hydrolase, is a promising target for drug development in anti-tumor therapies. Using X-ray crystallography, we have determined the structure of Drosophila melanogaster GMII (dGMII) complexed with three different inhibitors exhibiting IC50's ranging from 80 to 1000 microM. These structures, along with those of seven other available dGMII/inhibitor complexes, were then used as a basis for the evaluation of seven docking programs (GOLD, Glide, FlexX, AutoDock, eHiTS, LigandFit, and FITTED). We found that small inhibitors could be accurately docked by most of the software, while docking of larger compounds (i.e., those with extended aromatic cycles or long aliphatic chains) was more problematic. Overall, Glide provided the best docking results, with the most accurately predicted binding around the active site zinc atom. Further evaluation of Glide's performance revealed its ability to extract active compounds from a benchmark library of decoys.

Functionalized pyrrolidines inhibit alpha-mannosidase activity and growth of human glioblastoma and melanoma cells.

New substituted pyrrolidine-3,4-diol derivatives were prepared from d-(-)- and l-(+)-phenyl glycinol. The influence of the configuration and the substitution of the lateral side chain of these derivatives on the inhibition of 25 commercial glycosidases were determined. (2R,3R,4S)-2-({[(1R)-2-Hydroxy-1-phenylethyl]amino}methyl)pyrrolidine-3,4-diol ((+)-7a) was a potent and selective inhibitor of jack bean alpha-mannosidase (K(i) = 135 nM). However, when evaluated on human tumor cells, 7a, and the reference compound swainsonine, did not efficiently inhibit the growth of glioblastoma cells. Further derivatization of the hydroxyl group with lipophilic groups to increase bioavailability improved their growth inhibitory properties for human glioblastoma and melanoma cells. In particular, the 4-bromobenzoyl derivative 26 demonstrated high efficacy for human tumor cells whereas primary human fibroblasts were less sensitive to 26. Therefore, functionalized pyrrolidines have the potential to inhibit the growth of tumor cells and display selectivity for tumor cells when compared to normal cells.

Electron cryo-microscopy reveals mechanism of action of propranolol on artificial membranes.

The pharmacological activity of several amphiphilic drugs is often related to their ability to interact with biological membranes. Propranolol is an efficient multidrug resistance (MDR) modulator; it is a nonselective beta-blocker and is thought to reduce hypertension by decreasing the cardiac frequency and thus blood pressure. It is used in drug delivery studies in order to treat systemic hypertension. We are interested in the interaction of propranolol with artificial membranes, as liposomes of controllable size are used as biocompatible and protective structures to encapsulate labile molecules, such as proteins, nucleic acids or drugs, for pharmaceutical, cosmetic or chemical applications. We present here a study of the interaction of propranolol, a cationic surfactant, with pure egg phosphatidylcholine (EPC) vesicles. The gradual transition from liposome to micelle of EPC vesicles in the presence of propranolol was monitored by time-resolved electron cryo-microscopy (cryo-EM) under different experimental conditions. The liposome-drug interaction was studied with varying drug/lipid (D/L) ratios and different stages were captured by direct thin-film vitrification. The time-series cryo-EM data clearly illustrate the mechanism of action of propranolol on the liposome structure: the drug disrupts the lipid bilayer by perturbing the local organization of the phospholipids. This is followed by the formation of thread-like micelles, also called worm-like micelles (WLM), and ends with the formation of spherical (globular) micelles. The overall reaction is slow, with the process taking almost two hours to be completed. The effect of a monovalent salt was also investigated by repeating the lipid-surfactant interaction experiments in the presence of KCl as an additive to the lipid/drug suspension. When KCl was added in the presence of propranolol the overall reaction was the same but with slower kinetics, suggesting that this monovalent salt affects the general lipid-to-micelle transition by stabilizing the membrane, presumably by binding to the carbonyl chains of the phosphatidylcholine.