Partial resistance of E. coli mutants against 2, 4-diamino-5-benzylpyrimidines by interactions with bacterial membrane lipopolysaccharides. Derivation of quantitative structure-binding relationships.

A series of previously synthesized 2,4-diamino-5-benzylpyrimidines, inhibitors of bacterial dihydrofolate reductase (DHFR) showed decreased inhibition of E. coli cultures, despite increased inhibitory activity against DHFR. Preliminary studies using E. coli mutants with different degrees of outer membrane deficiencies suggested that the decrease in activity was partly due to inactivation because of binding to outer membrane constituents. In the present study antibacterial activities of the benzylpyrimidines have been systematically determined as a function of cell membrane defects in E. coli using bacterial growth kinetic techniques. It has been shown that the observed differences in activity were not due to different binding affinities to the target enzyme of the mutants. Lipopolysaccharides have been extracted from the mutants and used in binding studies by ultrafiltration, photometric and NMR techniques. The observed differences in binding affinity to the lipopolysaccharides have been related to the differences in the lipophilic properties and molecular weight of the substituents. Quantitative structure-activity relationships have been derived. The results of the study show the importance of drug-membrane interactions for the rational development of antibacterials.

Structure-activity relationship studies on benzofuran analogs of propafenone-type modulators of tumor cell multidrug resistance.

A series of benzofurylethanolamine analogs of propafenone (1a) have been prepared and evaluated for multidrug resistance-reversing activity in two in vitro assay systems. As for propafenones, an excellent correlation of biological data with calculated lipophilicity values was found for benzofurans, whereby the latter generally had lower activity/lipophilicity ratios. Almost identical slopes of the regression lines were obtained for both propafenones and benzofurans. Multiple linear regression analysis of the complete data set yielded an equation with excellent predictive power (r2 cross-valid = 0.968). Interaction measurements with artificial membranes indicated that the differences in activity between these two series of compounds are not due to differences in the interaction pattern with biological membranes.

Membrane interactions of some catamphiphilic drugs and relation to their multidrug-resistance-reversing ability.

The multidrug-resistance (MDR)-reversing ability of the catamphiphilic drugs could be mediated through their interaction with the membrane phospholipids. This could lead directly (through changes in membrane permeability and fluidity) and/or indirectly (through inhibition of P-glycoprotein phosphorylation via inhibition of the phosphatidylserine-dependent protein kinase C or changes in the conformation and functioning of the membrane-integrated proteins via changes in the structure organization of the surrounding membrane bilayer) to the reversal of MDR. Using differential scanning calorimetry and NMR techniques and artificial membranes composed of phosphatidylcholine or phosphatidylserines we found a significant correlation between the MDR-reversing activity of the drugs in doxorubicin-resistant human breast carcinoma MCF-7/DOX and murine leukaemia P388/DOX tumour cells (data taken from the literature) and their ability to interact with phosphatidylserines. Trans- and cis-flupentixol were found to interact most strongly with both the phospholipids, followed by trifluoperazine, chlorpromazine, triflupromazine, flunarizine, imipramine, quinacrine and lidocaine. Differences in the interaction of trans- and cis-flupentixol with the phospholipids studied are suggested to be responsible for their different MDR-reversing ability. Verapamil showed moderate membrane activity, assuming that the membrane interactions are not the only reason for its high MDR-reversing ability. Amiodarone showed very strong interactions with phosphatidylserines and is recommended for further MDR-reversal studies.

Drug membrane interaction and the importance for drug transport, distribution, accumulation, efficacy and resistance.

Some aspects of drug membrane interaction and its influence on drug transport, accumulation, efficacy and resistance have been discussed. The interactions manifest themselves macroscopically in changes in the physical and thermodynamic properties of "pure membranes" or bilayers. As various amounts of foreign molecules enter the membrane, in particular the main gel to liquid crystalline phase transition can be dramatically changed. This may change permeability, cell-fusion, cell resistance and may also lead to changes in conformation of the embedded receptor proteins. Furthermore, specific interactions with lipids may lead to drug accumulation in membranes and thus to much larger concentrations at the active site than present in the surrounding water phase. The lipid environment may also lead to changes in the preferred conformation of drug molecules. These events are directly related to drug efficacy. The determination of essential molecular criteria for the interaction could be used to design new and more selective therapeutics. This excursion in some aspects of drug membrane interaction underlines the importance of lipids and their interaction with drug molecules for our understanding of drug action, but this is not really a new thought but has been formulated in 1884 by THUDICUM: "Phospholipids are the centre, life and chemical soul of all bioplasm whatsoever, that of plants as well as of animals".

Synthesis and quantitative structure-activity relationships of anticonvulsant 2,3,6-triaminopyridines.

The synthesis of 2,3,6-triaminopyridine derivatives, representing a unique chemical structure for anticonvulsants, is described. The synthetic program was performed (a) to identify more potent analogs, (b) to determine structural properties controlling potency as well as neurotoxicity, and (c) to reduce the requirements for animal testing. As a result, besides other structural properties, the overall molecular lipophilicity (log k', octanol-coated column) explained changes in anticonvulsant potency and neurotoxicity. Mimicking the interaction of the amphiphilic triaminopyridines with biological membranes, NMR experiments in the presence of lecithin vesicles were conducted in order to measure the phospholipid-binding parameter log delta (1/T2). Replacement of log k' with log delta (1/T2) in the correlation analysis afforded a more significant equation describing the anticonvulsant activity of 21 derivatives.

Interaction of prostaglandin E1 with alpha-cyclodextrin in aqueous systems: stability of the inclusion complex.

Prostavasin, an inclusion complex of prostaglandin E1 (PGE1) with alpha-cyclodextrin (alpha-CD), is used in the therapy of thrombosis. Nuclear magnetic resonance measurements have been made to study the interaction of PGE1 with alpha-CD. The observed interaction (chemical shift) and the derived dissociation constant prove that only weak interaction forces are operative and that complete dissociation occurs upon dilution.

Quantitative structure-pharmacokinetic relationships derived on antibacterial sulfonamides in rats and its comparison to quantitative structure-activity relationships.

Quantitative structure-pharmacokinetic relationships have been derived for a series of substituted 2-sulfapyridines. Pharmacokinetic parameters, such as elimination rate constant (ke), clearance (Cl), and protein-binding constant (Kassoc), have been determined in rats. The observed variation is statistically significant, explained by changes in the lipophilic (deltaRm), electronic (pKa), and steric effects (I, ES) of the substituents. The obtained correlations are discussed with respect to the previously derived correlations for the antibacterial activity of these compounds. A scale up of the results opens up the possibility of a rational synthesis of highly active sulfonamides with special pharmacokinetic properties because lipophilicity influences strongly the pharmacokinetic properties, whereas no influence on the degree of antibacterial effect is observed. Steric substituent influence is opposite on specific binding to bacterial enzymes and unspecific binding to serum proteins.

Mode of action and quantitative structure-activity correlations of tuberculostatic drugs of the isonicotinic acid hydrazide type.

Quantitative structure-activity studies have been performed for a series of 2-substituted isonicotinic acid hydrazides by correlating electronic, steric, and lipophilic properties of the substituents with the biological activity date (MIC) from serial dilution tests with Mycobacterium tuberculosis (strain H 37 Rv). The reaction rates for the quaternization of 2-substituted pyridines with methyl iodide were also determined. The rate constants show a similar dependence on the steric and electronic effects of the substituents as the antibacterial activities of the corresponding pyridine-4-carboxylic acid hydrazides. The obtained correlations give evidence that the reactivity of the pyridine nitrogen atom is essential for the biological activity of 2-substituted isonicotinic acid hydrazides and seem to support the hypothesis that isonicotinic acid derivatives are incorporated into an NAD analogue.