Structure-activity relationships in platelet activating factor. 9. From PAF-antagonism to PLA2 inhibition

The anticancer/cytotoxic effect of a novel gallic acid derivative in non-small cell lung carcinoma A549 cells and peripheral blood mononuclear cells from healthy individuals and lung cancer patients

Gallic acid (GA) is a naturally occurring polyphenol with a strong antioxidant capacity. GA stimulates the apoptosis of cancer cells, thereby suppressing cancer cell invasion. However, the low oral permeability of GA limits its therapeutic use. In order to enhance the antioxidant capacity and oral permeability of GA, a series of compounds analogous to GA were synthesized: 4-methoxybenzenesulfonamide (MBS), 3,4-dimethoxybenzenesulfonamide (DMBS) and 3,4,5-trimethoxybenzenesulfonamide (TMBS). In the new compounds, hydroxyl groups were replaced with various numbers of methoxy groups (stronger electron-donating groups), to increase hydrophobicity and oral permeability compared to GA. In addition, the carboxylic group was replaced with a sulfonyl group (a stronger electron-withdrawing group), to increase the molecular polarity and antioxidative activities of the compounds. The cell counting kit-8 (CCK-8) assay was used to detect the effect of GA, MBS, DMBS, and TMBS on cell proliferation and apoptosis in peripheral blood mononuclear cells (PBMCs) from healthy individuals and non-small cell lung carcinoma A549 cells. Additionally, the comet assay was used to assess the genotoxicity of these compounds in PBMCs from healthy individuals, lung cancer patients, and A549 cells. Compared to untreated cells, TMBS reduced DNA damage more effectively than GA in PBMCs from lung cancer patients and healthy donors. Furthermore, in comparison to GA, TMBS was more cytotoxic in A549 cells. Moreover, TMBS was not cytotoxic in healthy PBMCs, suggesting that TMBS demonstrates therapeutic potential in cancer.

Synthesis and evaluation of nitrostyrene derivative compounds, new snake venom phospholipase A2 inhibitors

Several nitrostyrene derivatives were synthesized and their inhibitive activities on phospholipase A(2) (PLA(2)) from Bothrops jararacussu venom were evaluated. Some compounds were very efficient as inhibition agents against edema-inducing, enzymatic and myotoxic activities. Data revealed that the size of the substitute and substitution position in the nitrostyrene moiety had important influence on the inhibition capacities. The enzymatic kinetic studies show that the nitrostyrene derivatives compounds inhibit PLA(2) in a non-competitive manner. The electronic, molecular and topologic parameters were calculated using ab initio quantum calculations (density functional theory-DFT) and analyzed by chemometric methods (principal component analysis (PCA) and hierarchical cluster analysis (HCA)) in order to build models able to establish relationships between the electronic features and the structure-activity presented by the target compound. Compounds with the nitro group in the ortho, meta and para position (compounds 2-4) on the aromatic ring were more efficient in the inhibition of PLA(2) activity in all tests. These results indicate that the influence of the nitro group in the aromatic ring is, in fact, important. In addition, quantum chemistry calculations show that compounds with a higher capacity of inhibiting PLA(2) present lower values of highest occupied molecular orbital (HOMO) energy and polarizability, suggesting the formation of a charge-transferring complex between the nitrostyrene compounds and PLA(2).

Inhibition of Secreted Phospholipase A2. 4-Glycerol Derivatives of 4,5-Dihydro-3-(4-tetradecyloxybenzyl)-1,2,4-4H-oxadiazol-5-one with Broad Activities

Secreted phospholipases A2 (sPLA2s) have been reported to play an important role in various inflammatory conditions and thus represent an attractive therapeutic target. Previous SAR studies from our laboratory have revealed certain important features of our recently discovered specific hGIIA sPLA2 inhibitors, and we report here the synthesis and biological activities of glycerol-containing derivatives of our lead compound III (Figure 1). Efficient and selective synthesis methods have been developed to make glycerol trisubstituted by different groups on desired positions. In terms of biological activities, the best compounds (A3, A6, and A15) are more active than III (Figure 1), as potent as Me-Indoxam, an sPLA2s inhibitor of reference, against hGIIA, hGV, and hGX sPLA2s and at least 10 times less active toward the GIB enzymes in two in vitro assay systems. By synthesis of enantiopure (S)-A6, we demonstrated that no important improvement of the inhibitory potency could be achieved by this approach. Furthermore, the results show that the global lipophilicity is likely responsible for the anti-PLA2 activity and two oxadiazolone moieties seem too big to be accommodated by the active site of the hGIIA enzyme.

Inhibition of secretory phospholipase A2. 2-Synthesis and structure–activity relationship studies of 4,5-dihydro-3-(4-tetradecyloxybenzyl)-1,2,4-4H-oxadiazol-5-one (PMS1062) derivatives specific for group II enzyme

We have recently reported the discovery of a series of specific inhibitors of human group IIA phospholipase A(2) (hGIIA PLA(2)) to display promising in vitro and in vivo properties. Here we describe the influence of different structural modifications on the specificity and potency against hGIIA PLA(2) versus porcine group IB PLA(2). The SAR results, as well as the logP and pK(a) values of oxadiazolone determined in this work, provide important information towards the comprehension of the mode of action of this kind of compounds.

A new phospholipase A2 inhibitor, unrelated to substrate analogues: kinetic characterization of the inhibition of secretory phospholipases A2 by PMS 832

Starting from a series of compounds which were known to be PAF antagonists, we have synthesized molecules that are good inhibitors of PLA2s of groups I or II, with IC50 in the micromolar range (Binisti et al., 1997). In this report we investigate the mechanism of inhibition of bovine and porcine pancreatic phospholipases A2 (group I), and platelet lysate phospholipase A2 (group II) by one of these compounds, 1-(4'-methoxybenzoyl)-2-n-tridecylpiperazine (PMS 832). We show that PMS 832 behaves as a reversible, competitive inhibitor, with Ki values of 4.1 +/- 1.2 and 1.5 +/- 0.4 microM for porcine pancreatic phospholipase A2 and platelet lysate phospholipase A2, respectively. PMS 832 failed to inhibit platelet activation induced by several agonists and was also found to be inactive towards phospholipase C from Bacillus cereus, indicating a high specificity for phospholipase A2 inactivation. Thus, PMS 832 and its derivatives could serve as interesting tools to investigate the role of extracellular phospholipases A2 in inflammatory processes, and may be useful in the development of new anti-inflammatory agents.