Joachim K. Seydel

Drug-membrane interactions : analysis, drug distribution, modeling

Preface. Foreword. INTRODUCTION Function, Composition, and Organization of Membranes OCTANOL--WATER PARTITION VERSUS PARTITIONING INTO MEMBRANES ANALYTICAL TOOLS FOR THE ANALYSIS AND QUANTIFICATION OF DRUG--MEMBRANE INTERACTIONS High--performance Liquid Chromatography (HPLC) Displacement of 45Ca from Phospholipid Head Groups Differential Scanning Calorimetry (DSC) Fluorescence Techniques Fourier Transform Infrared Spectroscopy (FT--IR) Electron Spin Resoncance (ESR) Small Angle Neutron and X--ray Diffraction Nuclear Magnetic Resonance (NMR) Circular Dichroism (CD) UV Spectroscopy DRUG--MEMBRANE INTERACTIONS AND PHARMACOKINETICS OF DRUGS Drug Transport Drug Distribution Uptake into and Distribution within Bacterial Cells Drug Accumulation, Toxicity, and Selectivity DRUG--MEMBRANE INTERACTIONS AND PHARMACODYNAMICS Drug Efficacy Drug Resistance COMPUTER SIMULATION OF PHOSPHOLIPIDS AND DRUG--PHOSPHOLIPID INTERACTIONS Modeling Strategies for Studying Phospholipids and Drug--Phospholipid Interactions Computer Simulations with Phospholipids Concluding Remarks INDEX

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- andcis-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 oftrans- andcis-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.

Effect of cyclodextrin derivatives on indomethacin stability in aqueous solution

The effect of various cyclodextrins (CD) and cyclodextrin derivatives on indomethacin stability in phosphate buffer, pH 7.4, was investigated. The influence of CD-ring size, type of substituent, degree of substitution, substitution pattern, and influence of CD concentration were monitored. The indomethacin complex in solution was studied by 1H-NMR spectroscopy to develop a molecular inclusion model. The most favorable ring size for the stabilization of indomethacin was the β-CD. The β-CD derivatives inhibited the hydrolysis of indomethacin more effectively than the parent CD. Among the studied CD derivatives, those with lipophilic substituents, such as ethyl or methyl, were superior to those with hydrophilic substitutents. The more hydroxyl groups of the glucose moiety are substituted, the better is the stabilizing effect. Further, the p-chlorobenzoic part of the indomethacin molecule is included in the CD channel.

Pyrimethamin-resistantPlasmodium falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines

Methotrexate resistance induced in culturedPlasmodium falciparum depends on an altered dihydrofolate reductase with decreased affinity for methotrexate as well as for pyrimethamine. In contrast, pyrimethamine-resistant field isolates ofP. falciparum lack cross-resistance to methotrexate and 2,4-diamino-5-(substituted benzyl) pyrimidines. The structure of the latter class was optimized by the use of trimethoprim as a lead and the substitution of methoxy groups at the benzyl ring by 3-(4′-aminophenyl-4-sulfonylphenylamino)propoxy or by (4′-aminophenyl-4-sulfonylphenyl)methoxy, which resulted in antimalarials of high potency. The efficiency of these newly designed 2,4-diamino-5-(substituted benzyl) pyrimidines was confirmed by their strong inhibitory effect on plasmodial dihydrofolate reductase as well as by in vitro screening against drug-sensitive and-resistant strains ofP. falciparum.

Synthesis of new 2,4-diamino-5-benzylpyrimidines active against various bacterial species

Abstract New inhibitors of mycobacterial dihydrofolate reductase (DHFR) have been developed. These compounds show high inhibitory activities against Gram-negative and mycobacterial DHFR exceeding that for the commercially available DHFR blockers. Amongst these compounds K-130 shows a 100-fold lower MIC against M lufu than the most active derivatives known so far (TMP, BDP). Mycobacterium lufu was used as a model for the non cultivable strain M leprae . K-130 is also very active against other mycobacterial strains. Besides the higher affinity to the isolated enzyme, the increase in lipophilicity favours permeation of the mycobacterial cell wall and is responsible for the high inhibitory power of K-130 against mycobacteria. The lower activity against Gram-negative bacteria ( E coli ), despite high affinity to the enzyme, is explained by the hydrophilic nature of the outer score of the cell-wall components.

New benzylpyrimidines: inhibition of DHFR from various species. QSAR, CoMFA and PC analysis

Summary To further analyze the structural requirements responsible for the enhanced activity of the newly developed, highly active benzylpyrimidine K-130, a series of trimethoprim analogues with various 4-anilinoalkoxy moieties has been synthesized and tested against dihydrofolate reductase (DHFR) derived from various species (Mycobacterium lufu, Escherichia coli, Candida albicans and rats). The importance of the secondary amino group for binding affinity could be shown by varying the substituent in the para position to the sec-amino moiety. This finding could be supported by multiple linear regression and comparative molecular field analysis (CoMFA). The polarized SO2 group, which was thought to be responsible for the increased activity of K-130, seems not to be the only group important for receptor binding. Additionally, a high selectivity of the new compounds for DHFR derived from the various bacteria and C albicans compared with DHFR derived from rat liver is shown by PC analysis.

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.

Development of effective drug combinations for the inhibition of multiply resistant Mycobacteria, especially of the Mycobacterium avium complex

Rationally designed combinations of rifampicin (RAMP) and thiacetazone plus isonicotinic acid hydrazide and/or ethambutol are highly effective in the treatment of patients (including HIV-positive) infected with multiply resistant mycobacteria of the Mycobacterium avium complex (MAC). Clinical results are very promising. The high efficacy of these combinations is due to the synergistic potentiation of single-drug activities. As soon as rifabutin is marketed, it should replace RAMP in the combination treatment of patients with highly RAMP-resistant MAC bacteria.

Bacterial Growth Kinetics of Escherichia coli and Mycobacteria in the Presence of Brodimoprim and Metioprim Alone and in Combination with Sulfamerazine and Dapsone (VI)

Bacterial growth kinetics and checkerboard titration experiments have been performed to determine the inhibitory power of metioprim (I) and brodimoprim (II) alone and in combination with diaminodiphenylsulfone (DDS) using Escherichia coli and mycobacteria as test organisms. The evaluated potency of the new TMP derivatives alone and in combination is compared to TMP and other derivatives. A strongly synergistic activity of I and II in combination with DDS against E. coli and various mycobacteria is observed which is also operative in case of highly DDS-resistant mycobacterial strains. The implication of these findings for the development of a combined chemotherapy with these drugs against atypical mycobacterial infections - especially leprosy - is discussed.

Model-based relationship between the microbial transformation rate of organic chemicals and their physicochemical properties

Abstract Using the time hierarchy of the processes, determining the fate of foreign compounds in microbial cell suspensions, a simple kinetic description of biotransformation was derived considering both the boundary cases in the rate-concentration dependence of the pertinent enzymic reaction, namely the first and zero order kinetics. The decisive drug properties turned out to be hydrophobicity and the rate parameters of the transformation reaction. In accord with the results of the uptake experiments and contrary to the previous approaches, transport of organic molecules into the cell is not considered as the rate limiting step. The resulting equations are consistent with the literature data.