Current Drug Discovery Technologies - Volume 5, Issue 2, 2008

One of the prerequisite processes in living cells is the ability to maintain the simultaneous, hierarchical and selective transmembrane transport of ions, molecules and waste products employing highly evolved proteins, self-organized in the form of specific and sophisticated ion channels or biomolecule nanocarriers. The examples of synthetic approach to the preparation of such supramolecular transporters include natural protein scaffolds, abiotic structures, peptide-abiotic hybrids, nanotubular cyclic peptides, hydraphiles and their variants. In many cases these synthetic ion channels exhibiting a selective and specific in vitro activity as antibiotics acting by disruption of cellular ion balance of various microbials. Similarly, free and macrocycle encapsulated chloride channels blockers have been found to be useful to promote therapy induced apoptosis. These both examples show that synthetic biomembrane nanocarriers would be applied in near perspective as the promising targeted and/or triggered therapeutics. Thus, in recent years efforts of supramolecular chemist evolving continuously from the traditional target-directed to the more complete property-oriented strategies of synthesis to enable design, preparation and screening of more substantial, selective, and pharmacoactive molecules with enhanced transporters mimicking ability. The significance of these supramolecular nanocarrier approaches still increasing by the demands of modern gene delivery and cell transfection technologies. Examples of such novel solutions offered by a potential supramolecular nanocarrier system will be illustrated in this special issue of Current Drug Discovery Technologies. The introductory review paper by Tecilla et al. focuses on the currently designed supramolecular synthetic systems, both artificial channels and nanocarriers, promoting selective anion transport, thus enabling development of new therapeutics for variable anion channelopathies, a commonly diagnosed genetic disease in humans. This approach is continued in the minireview paper by Mutihac describing the potential applications of calixarenes and their derivatives in transport of diverse low-molecular biologically relevant substances through liquid membranes and for development of new drug formulations with enhanced drug-target specificity. Basing on a typical supramolecular function of immobilized chiral stationary phase (CSP) involving dynamic enantiorecognition of the analyte during the translocation process in bilayer interphase comprising of each HPLC systems Bazylak et al. discussed chiral separation of profens, as the well known non-selective NSAIDs and recently recognized potential anticancer agents, with use of past-developed polysaccharide-, cyclodextrin-, glycoantibiotics-CSPs and currently proposed bimodal, combinatorial, monolithic and polymeric modes. Similar approach is also elaborated in the last minireview paper by Bielecki and Wasiak et al. presenting some recent results on use of various supramolecular nanocarrier molecules in design of range of analytical devices applicable in drug screening procedures employing membrane mimicking processes. In the first research paper by de Villiers et al. the results of extended study on solubility, stability and availability of nifedipine encapsulated in various nanocavity sized para-sulfonato-calixarenes have been described. Similarly, Bazylak et al. have illustrated separation abilities of currently available HPLC techniques employing supramolecular host-guest stationary phases, e.g. octadecylsilica versus calixarene bonded silica with variable nanosize of their cavity and upper-rim modification, for screening of the 1,3,4-oxadiazolureas with potent analgesic activity. The highly selective separation of positional and E/Z isomers of these analytes were described in this report as well as some preliminary data indicating on especially attractive possibility of use calixarenes as the future nanocarriers for these compounds. The next four research papers by Torres- Labandeira et al., Diaz et al., Jiang et al. and Terekhova deal with detailed thermodynamic, spectral, kinetic, and computational studies on the solubilization process of the water insoluble sodium dicloxacillin, benzimidazolic antihelmintics, purine alkaloids and insecticide intermediates, respectively, with different cyclodextrins. In addition, the series of highly innovative divalent metal complexes of moensin A, a polyether-type antibiotic and anticoccidial agent, have been described and characterized in research paper by Pantcheva et al. which enabled to obtain the new kind of antimicrobials with increased membrane permeabilizing properties and enhanced activity against Gram-positive bacteria. In last research paper by Przybylo et al. the results of study by fluorescence resonance energy transfer (FRET) method on the oligonucleotide orientation and binding with the lipid bilayer, used as the carrier of genetic material and mimicking a gene delivery system, has been reported.......

Anion transport across phospholipid membrane is a typical supramolecular function involving dynamic recognition of the substrate during the whole translocation process. Supramolecular chemists, taking inspiration by the natural anion transporters, have designed artificial systems able to mimic, at the functional level, several features of the natural ion channels. The scope of this research is twofold: on one hand to get insight on the molecular basis of recognition and transport, and on the other hand to get control of the biomedical relevant processes. The present review focuses on the synthetic systems promoting anion transport, covering both artificial channels and carriers that operate in phospholipid membrane. The design principles of such systems will be discussed together with the potential biomedical applications.

The present minireview summarizes some potential applications of calix[n]arenes family in binding and transport through liquid membranes of various biological compounds. In this respect, some specific aspects of their applications as carriers through liquid membrane are discussed in view of their potential for development of new drug formulation. The place of calix[n]arenes in the interesting and challenging field of transmembrane ion transport as synthetic ionophores is briefly outlined.

The permanent world-wide increase in therapeutic administration of racemic profens as easy available non-prescribed analgesic drugs and a common first-choice anti-inflammatory agents was recently linked with renewed interest in their beneficial use, also as enantiopure formulations, to treat and/or prevent a variety of human malignancies including its four major types as colorectal, breast, lung, and prostate cancer. This underlies the continuous need of selecting perfectly suited chiral separation methods of profens capable to determine nanolevels of a distomer in presence of the eutomer in a variety of complex biological and environmental media. Thus, current improvements for direct enantiomeric separations of profens by well defined supramolecular-based chiral HPLC and recently developed monolithic, combinatorial, bimodal and polymeric chiral stationary phases employing a modern supramolecular chirality concepts has been outlined in this review. The use of diverse supramolecular approaches for chiral HPLC as an easy accessible tool enabling fast development of nanoscale enantioselective, high-throughput and gradient screening procedures for in situ monitoring of stereoselective ADME properties of profens in range of anticancer drug discovery technologies has been also addressed.

The paper gives a short review of the most important research results published recently in the field of the applications of supramolecular nanocarriers in modern pharmaceutical and analytical chemistry. The main attention has been paid to the fast developing technology of chemical sensors, ion-selective electrodes and separation methods, in particular to newly designed packing in highperformance liquid chromatography employing supramolecularly aided and membrane mimicking processes.

This study reports the use of para-sulphonato calix[8]arene to produce stable complexes with improved bioavailability for nifedipine, a calcium-channel blocker that is practically insoluble in water. Thermal analysis and electrospray ionisation mass spectroscopy confirmed that nifedipine formed complexes with the calixarenes in a size dependent way. The most stable, soluble complexes was formed with para-sulphonato calix[8]arene. Complexation was weakest with the calix[4]arene while complexation with the calix[6]arene was intermediate. However, the calix[4 and 6]arenes changed the chemical stability of the drug in solution because significant amounts of the nitroso-pyridine derivative was produced, proposing an interaction between the nifedipine bearing a H substituent at the N-1 position and the calixarenes. This oxidative degradation of the drug was greatest when combined with the calix[6]arene. Simultaneous oral ingestion of the calix[6 or 8]arenes significantly increased the bioavailability of the drug after oral administration in male Sprague-Dawley rats while not influencing CYP3A activities in the liver. The pharmacokinetic parameters of the nifedipine: para-sulfonato calix[8]arene complexes showed it was bioequivalent to a nifedipine PEG-solution. The absolute bioavailability for both formulations was ca. 60 %.

The aim of this work is to analyze the effect of cyclodextrin (CD) complexation on the solubilization and stabilization of sodium dicloxacillin in acid aqueous solutions. The effect of four cyclodextrins α-, β-,γ- and hydroxypropyl-β-CD was studied. Phase solubility diagrams obtained are AL or BS type, depending on the cyclodextrin used and on the pH of the solution. The highest stability constants of the inclusion complexes are obtained with γ-CD at pH 1 and 2 and HPβ-CD at pH 3. The structure of the inclusion complex in solution is characterized by nuclear magnetic resonance (1H-NMR). This study suggests that the 7-oxo-4-thia-1-azabicyclo group is located in the CD cavity. Nevertheless, molecular modelling calculations predict two different orientations of dicloxacillin in the γ-CD cavity in vacuum and in aqueous solution. In vacuum, the results predict the inclusion of the dichlorophenyl ring of dicloxacillin instead of 7-oxo-4-thia-1-azabicyclo group into the γ-CD cavity. However, the results are different in aqueous solution and this conformation is confirmed by the NMR study. The effect of γ-CD and HPβ-CD in the stability of the drug in solution was studied. The degradation of sodium dicloxacillin in solution follows a pseudo-first-order kinetics and the cyclodextrin do not change this fact. Both cyclodextrins increase the stability of the drug but the efficacy is higher with γ-CD.

The main purpose of this work was to accomplish a comparative study about cyclodextrins complexation equilibria with three benzimidazolic antihelmintics: albendazole (Alb), mebendazole (Meb) and thiabendazole (Thiab).The complexation process with four different cyclodextrins (α-, β-, γ-, and HP-β-CDs) was investigated under various temperatures and different reaction media (aqueous solution buffered at pH 7.5, dimethylsulfoxide (DMSO) and DMSO/water at 25/75, 50/50, 75/50 (w/w) mixtures). It was studied by electronic absorption and 1H NMR (NOESY) spectroscopy. Binding constants were determined by electronic absorption spectroscopic method, the ΔH and ΔS complexation values were evaluated and discussed according to the diverse factors that affect the chemical interactions in these systems. Solubility has also been determined by the Higuchi and Connors method. In general, albendazole and mebendazole exhibit similar complexation behavior, while thiabendazole acts differently. Classic and non-classic solvophobic effects are mainly the driving and stabilizing forces for complex formation, with the exception in some Thiab-CDs interactions. In all cases, DMSO, an aprotic solvent, should be considered as an active component of the reaction systems.

The complexation of carboxylic acid Monensin A (MonH, 1a) with CoCl2.6H2O and MnCl2.4H2O leads to the formation of mononuclear complexes [Co(Mon)2(H2O)2], 2a and [Mn(Mon)2(H2O)2], 2b, respectively. The unique crystal structures of 2a and 2b were determined by X-ray crystallography. The complexes crystallize in the monoclinic space group P21 with an octahedrally coordinated transition metal center forming the crystallographically centrosymmetric chromophore CoO6 or MnO6, respectively. Two molecules of Monensin A act bidentately through their carboxylate moiety and a hydroxyl group, and two water molecules are additionally transcoordinated. Although the transition metal ions are not bound into the cavity of the ligand, the unusual bidentate coordination mode of the ionophore induces its “pseudo-cyclization” forming 22-membered cycles further stabilized by a number of H-bonds. The complexes are the first example of divalent metal complexes of the monovalent polyether ionophore. The parallel study on the complexation ability of the potassium complex of Monensin A (MonK, 1b) towards Co(II) and Mn(II) showed the formation of the isostructural complexes 2a and 2b accompanied by loss of the potassium ion due to the new coordination mode of the ligand. The biological tests performed with the antibiotic MonH and the corresponding metal(II) complexes show greatly enhanced antimicrobial activity of complexes 2a-b against Gram(+)-bacteria.

Complex molecular ensembles are frequently considered an element of new pharmacological formulations. This is especially evident in the therapies based on genetic information. In order to obtain an effective drug, it is necessary to associate a nucleic acid molecule with the components to ensure the desired aggregate structure and properties. To evaluate the progress of the supromolecular aggregate formation a range of methodologies and techniques are needed to test the quality and uniformity of the formulations. In this paper we propose a procedure which measures the association of a small molecule with nucleic acid using propidium iodide and oligonucleotides as an example. To measure propidium iodide binding constant the oligonucleotide was covalently labeled with fluorescein and then the changes in fluorescence resonance energy transfer (FRET) were determined and handled according to the acceptor-donor titration methodology. The calculated binding constants were in a good agreement with the values published previously. The developed method was then used to evaluate the extent of an oligonucleotide association with the lipid aggregates. It was found that two populations of oligonucleotides are present in all lipid samples studied. The fraction of oligonucleotides associated with liposomes rises with the increase of a cationic lipid content, reaching the constant value when the fraction of cationic lipid exceeded 20 mol%. Energy transfer data combined with these obtained in quenching experiments show that the orientation of the oligonucleotide associated with a lipid bilayer depends on the amount of surface charge.

The effect of native and hydroxypropylated β-cyclodextrin on the solubility and activity of some purine alkaloids was examined. For this purpose, the solubility of purine alkaloids in pure water and in aqueous solutions of mentioned β-cyclodextrins was determined at 298.15 K. Stability constants of inclusion complexes and their stoichiometry were obtained from solubility diagrams. Enthalpic characteristics of interactions occurring between β-cyclodextrins and purine alkaloids in aqueous solution were calculated from the direct calorimetric measurements. It was found, that β-cyclodextrin forms with purine alkaloids weak complexes which are stabilized only by the entropy term. Due to very low complexing affinity of both β-cyclodextrins to studied purine alkaloids their solubilizing effect is insignificant. The influence of structure of purine alkaloids and β-cyclodextrin on the thermodynamic parameters of interaction was discussed.

β-Cyclodextrin (β-CD) forms a series of supramolecular complexes with aromatic or aliphatic guest molecules such as benzaldehyde, butyl acrylate, etc. Remarkable blue shifts (λmax) of the UV-vis absorption peaks of the guest molecules are observed after the formation of inclusion complexes. The congestion lines appearing in the guest molecules are reduced in a remarkable extent accordingly. The mechanisms of the blue shifts are investigated herein.

Retention profiles in series of the neutral and highly hydrophobic 1,3,4-oxadiazoles containing chlorophenylurea and halogenobenzamide moiety and indicating analgesic activity were determined in the isocratic standard- and narrow-bore HPLC systems employing, respectively, various octadecylsilica and different calixarene bonded stationary phases. When acetonitrile - 2.65 mM phosphoric acid (55 : 45, %, v/v), pH* 3.25, mobile phase was applied retention of these compounds increased with decline of their overall hydrophobicity according to the general preference of more polar compounds by calixarene cavity in time of its non-specific host-guest supramolecular interactions with halogenated substances. The size of calixarene nanocavity and its upper-rim substitution did not change the observed retention order, resolution and selectivity of separation for oxadiazoles. Compared to the retention on the non-end-capped and the highly-end-capped octadecylsilica HPLC column a most improved separation of some regioisomers of halogenated 1,3,4- oxadiazoles were observed on both used calixarene-type HPLC supports. In addition, preliminary data on the self-assembled supramolecular crystal structure of exemplary 1,3,4-oxadiazolchlorophenylurea with cis-elongated conformation was reported and formation of the monovalent inclusion host-guest complexes between 1,3,4-oxadiazoles and each calixarene-type stationary phase was studied with molecular modelling MM+ and AM1 methods. The structural, isomeric and energetic factors leading to the hydrogen bond stabilized inclusion complexes between these species were considered and used for explanation of observed retention sequence and selectivity of 1,3,4-oxadiazoles separation in applied calixarene-based HPLC systems. All these data would be useful in future development of optimized procedures enabling encapsulation of 1,3,4-oxadiazolurea-type drugs with calixarenes.