QSAR study on the contribution of log P and E(s) to the in vitro antiprotozoal activity of glutathione derivatives.

A series of N-S-blocked glutathione monoester and diester derivatives based on N-benzyloxycarbonyl-S-(2,4-dinitrophenyl)glutathione were evaluated for activity against the pathogenic parasites Trypanosoma brucei brucei, Trypanosoma cruzi, and Leishmania donovani in vitro.Only monoesters 7-9 with a log P value of >2.7 were active inhibitors of T.b. brucei bloodstream form trypomastigotes. Diester compounds 10-15 and 17-27 in most cases were better inhibitors of T.b. brucei than monoester compounds, and some displayed high activity against T. cruzi 14 and L. donovani 17, 19, 29. Compounds 14, 24, and 25 were the most active compounds identified against T.b. brucei having ED(50) values of <0.4 microM. Analysis of the inhibition data (ED(50)) vs calculated log P and E(s) values provided evidence to support membrane penetration and steric factors as the key component in the activity of these compounds. The optimum values for log P and E(s) determined were 5.8 and -0.70, respectively. A QSAR equation relating log(1/ED(50)) vs log P and E(s) was determined and interpreted within the proposed mechanism of activity for these compounds.

Structure-activity study on the in vitro antiprotozoal activity of glutathione derivatives.

A series of N-, S-, and COOH-blocked glutathione derivatives were evaluated against the pathogenic parasites Trypanosoma brucei, Trypanosoma cruzi, and Leishmania donovani in vitro, to identify the determinants necessary for activity and for further development into an active lead structure. The results show that N,S-blocked glutathione diesters are the most effective inhibitors of T. brucei with structures 14-16 being the most active, 14 having an IC(50) approximately 1.9 microM. The toxicity effects observed for glutathione derivatives 12, 14, and 16 have been correlated to the K562 antileukemic activity of these compounds and their inhibitory effects on the glyoxalase system of the host. Diester compounds based on S-2,4-dinitrophenylglutathione (17-22) were found to be significantly better inhibitors of T. brucei with ED(50)'s in the range 16-0.19 microM. Compounds 19 and 20 were the two best inhibitors, with an ED(50) of approximately 1.07 and 0.19 microM, respectively; however 20 displayed toxicity in parasitic assays. Monoesters, monoamides, and diamides tested generally exhibited low in vitro activity. The compounds did not inhibit glutathionylspermidine synthetase and trypanothione reductase enzyme targets in the unique trypanothione pathway of these parasites. Diester compounds per se were considered to be ineffective inhibitors of trypanothione metabolism suggesting that these compounds might act as prodrugs, being hydrolyzed in situ into a variety of glutathione derivatives which include combinations of monoesters, free acids, and amines, some of which are inhibitors of trypanothione metabolism.

Structural similitudes between cytotoxic antiestrogen-binding site (AEBS) ligands and cytotoxic sigma receptor ligands. Evidence for a relationship between cytotoxicity and affinity for AEBS or sigma-2 receptor but not for sigma-1 receptor.

1-Benzyl-4-(N-2-pyrrolidinylethoxy)benzene (PBPE) is a cytotoxic derivative of the antitumoral drug tamoxifen. PBPE binds with high-affinity and specificity to the microsomal antiestrogen-binding site (AEBS). PBPE, as well as some other high-affinity AEBS ligands, shares structural features with high-affinity and selective sigma receptor ligands in the N-(arylethyl)-N-alkyl-2-(1-pyrrolidinyl)ethylamine class, such as BD1008, which are cytotoxic against tumoral cells. Based on these structural and pharmacological similitudes, we set out to examine whether AEBS and sigma receptors could be related binding sites. We showed that BD1008 had a high affinity for AEBS. However, prototypical sigma receptor ligands were very low-affinity competitors on AEBS. Surprisingly, AEBS ligands displayed a high affinity for sigma-1 and sigma-2 receptor subtypes, showing that AEBS and sigma receptor-binding sites were not mutually exchangeable. Moreover, phenytoin, which is an allosteric modulator of sigma-1 receptor, was a competitive inhibitor of [3H]tamoxifen on AEBS. These results suggest that the tamoxifen-binding site on AEBS and the sigma ligand-binding site on sigma receptors were not identical but related entities. We also showed here that the high-affinity and specific AEBS ligands also bound sigma receptors with high affinity. Moreover, the compounds that were capable of displacing tamoxifen from AEBS were cytotoxic against tumoral cells but not against the AEBS-deficient cell line Rtx-6. These results confirm that AEBS and sigma receptors might belong to the same family of proteins, and that the tamoxifen-binding site might be involved in the cytotoxicity of AEBS ligands and some classes of sigma compounds.

Estrogens modulate bovine vascular endothelial cell permeability and HSP 25 expression concomitantly.

The atheroprotective properties of estrogens are supported by clinical data from postmenopausal women who use estrogen replacement therapy. However, the mechanisms mediating activity remain unknown, and it has been suggested that estrogens may help to modulate endothelial permeability to atherogenic lipoproteins. In these studies we used bovine vascular endothelial cells as an in vitro model to show that estrogens were able to regulate low-density lipoprotein transport and permeability of the endothelial monolayer. Macromolecular transport was observed to be a second-order polynomial function of estrogen concentration. Moreover, this regulation was correlated with expression of heat shock protein (HSP) 25, which is known to influence fluid phase pinocytosis and cytoskeleton remodeling, thus suggesting a role for HSP 25 in the estrogenic control of transcellular permeability of the endothelium monolayer.