Molecular umbrella-assisted transport of an oligonucleotide across cholesterol-rich phospholipid bilayers

Quasi-Podands with 1,2,3-Triazole Rings from Bile Acid Derivatives: Synthesis, and Spectroscopic and Theoretical Studies

An innovative approach to producing derivatives of bile acids has been devised, utilizing the principles of "click" chemistry. By employing intermolecular [3 + 2] cycloaddition between the newly developed acyl propiolic esters of bile acids and the azide groups of 1,3,5-tris(azidomethyl)benzene, a novel class of quasi-podands featuring 1,2,3-triazole rings has been synthesized. Identifying and characterizing these six compounds involved comprehensive analysis through spectral techniques (1H NMR, 13C NMR, and FT-IR), mass spectrometry, and the PM5 semiempirical method. The synthesized compounds' pharmacotherapeutic potential has been evaluated, employing the Prediction of Activity Spectra for Substances (PASS) methodology. Additionally, molecular docking was performed for all molecules.

Investigating bolalipids as solubilizing agents for poorly soluble drugs: Effects of alkyl chain length on solubilization and cytotoxicity

Synthetic single-chain bolalipids with symmetrical headgroups have shown potential in various pharmaceutical applications, such as the stabilization of liposome bilayers. Despite their amphiphilic character, synthetic bolalipids have not yet been investigated for their suitability as solubilizing agents for poorly soluble drug compounds. In this study, three synthetic single-chain bolalipids with increasing alkyl chain lengths (C22, C24 and C26) were investigated. All three bolalipids were able to achieve an increased solubility of the model drug, mefenamic acid, by approximately 180% in a pH 7.4 buffer compared to only a 102-105% increase achieved by sodium dodecyl sulfate (SDS) or the non-ionic surfactant pegylated hydroxystearate (PEG-HS). Subsequently, interfacial activity of bolalipids and their ability to destabilize liposomal bilayers were investigated. The C22 bolalipid exhibited a consistently lower interfacial activity, which was consistent with its significantly lower cytotoxicity in the macrophage-like cell line, J774. A1, compared to C24 and C26 counterparts. The mean IC₅₀ values of the bolalipids tested (0.035-0.093 mM) were approximately 4-100-fold lower than that of SDS (0.401 mM) or PEG-HS (0.922 mM), with the mechanism of toxicity linked to increased cell membrane permeability, as is expected for surfactants. In summary, evidence from this study shows that decreasing the length of the bolalipid alkyl linker from C26 to C22 resulted in a significantly decreased cytotoxicity with no loss in drug solubilization efficiency.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

In this review, we outline the growing role that molecular dynamics simulation is able to play as a design tool in drug delivery. We cover both the pharmaceutical and computational backgrounds, in a pedagogical fashion, as this review is designed to be equally accessible to pharmaceutical researchers interested in what this new computational tool is capable of and experts in molecular modeling who wish to pursue pharmaceutical applications as a context for their research. The field has become too broad for us to concisely describe all work that has been carried out; many comprehensive reviews on subtopics of this area are cited. We discuss the insight molecular dynamics modeling has provided in dissolution and solubility, however, the majority of the discussion is focused on nanomedicine: the development of nanoscale drug delivery vehicles. Here we focus on three areas where molecular dynamics modeling has had a particularly strong impact: (1) behavior in the bloodstream and protective polymer corona, (2) Drug loading and controlled release, and (3) Nanoparticle interaction with both model and biological membranes. We conclude with some thoughts on the role that molecular dynamics simulation can grow to play in the development of new drug delivery systems.

Oxyanion transport across lipid bilayers: direct measurements in large and giant unilamellar vesicles

A simple di(thioamido)carbazole 1 serves as a potent multispecific transporter for various biologically relevant oxyanions, such as drugs, metabolites and model organic phosphate. The transport kinetics of a wide range of oxyanions can be easily quantified by a modified lucigenin assay in both large and giant unilamellar vesicles.

(Some) current concepts in antibacterial drug discovery

The rise of multidrug resistance in bacteria rendering pathogens unresponsive to many clinical drugs is widely acknowledged and considered a critical global healthcare issue. There is broad consensus that novel antibacterial chemotherapeutic options are extremely urgently needed. However, the development pipeline of new antibacterial drug lead structures is poorly filled and not commensurate with the scale of the problem since the pharmaceutical industry has shown reduced interest in antibiotic development in the past decades due to high economic risks and low profit expectations. Therefore, academic research institutions have a special responsibility in finding novel treatment options for the future. In this mini review, we want to provide a broad overview of the different approaches and concepts that are currently pursued in this research field.

Synthesis and anticancer activity of bile acid dendrimers with triazole as bridging unit through click chemistry

Triazole-based novel dendrimers with bile acid surface groups have been synthesized through click chemistry by divergent approach and characterized by spectral data. All the dendrimers exhibit excellent anticancer activity. Higher-generation dendrimers exhibit better anticancer activity than the lower-generation dendrimers.

Synthesis, spectroscopic and theoretical studies of new quasi-podands from bile acid derivatives linked by 1,2,3-triazole rings

A novel method for the synthesis of bile acid derivatives has been developed using "click chemistry". Intermolecular 1,3-dipolar cycloaddition of the propargyl ester of bile acids and azide groups of 1,3,5-tris(azidomethyl)benzene gave a new quasi-podands with 1,2,3-triazole rings. The structures of the products were confirmed by spectral (1H-NMR, 13C-NMR, and FT-IR) analysis, mass spectrometry and PM5 semiempirical methods. Estimation of the pharmacotherapeutic potential has been accomplished for synthesized compounds on the basis of Prediction of Activity Spectra for Substances (PASS).

Peptide nucleic acid (PNA) cell penetrating peptide (CPP) conjugates as carriers for cellular delivery of antisense oligomers

We have explored the merits of a novel delivery strategy for the antisense oligomers based on cell penetrating peptide (CPP) conjugated to a carrier PNA with sequence complementary to part of the antisense oligomer. The effect of these carrier CPP-PNAs was evaluated by using antisense PNA targeting splicing correction of the mutated luciferase gene in the HeLa pLuc705 cell line, reporting cellular (nuclear) uptake of the antisense PNA via luciferase activity measurement. Carrier CPP-PNA constructs were studied in terms of construct modification (with octaarginine and/or decanoic acid) and carrier PNA length (to adjust binding affinity). In general, the carrier CPP-PNA constructs including the ones with decanoyl modification provided significant increase of the activity of unmodified antisense PNA as well as of antisense octaarginine-PNA conjugates. Antisense activity, and by inference cellular delivery, of unmodified antisense PNA was enhanced at least 20-fold at 6 μM upon the complexation with an equimolar amount of nonamer carrier decanoyl-CPP-PNA (Deca-cPNA1(9)-(D-Arg)8). The antisense activity of a CPP-PNA ((D-Arg)8-asPNA) (at 2 μM) was improved 6-fold and 8-fold by a heptamer carrier CPP-PNA (cPNA1(7)-(D-Arg)8) and hexamer carrier decanoyl-CPP-PNA (Deca-cPNA1(6)-(D-Arg)8), respectively, without showing significant additional cellular toxicity. Most interestingly, the activity reached the same level obtained by enhancement with endosomolytic chloroquine (CQ) treatment, suggesting that the carrier might facilitate endosomal escape. Furthermore, 50% downregulation of luciferase expression at 60 nM siRNA was obtained using this carrier CPP-PNA delivery strategy (with CQ co-treatment) for a single stranded antisense RNA targeting normal luciferase mRNA. These results indicated that CPP-PNA carriers may be used as effective cellular delivery vectors for different types of antisense oligomers and also allows use of combinations of (at least two) different CPP ligands.

Tuning the efficiency of dendritic nanocarriers using conformational constraints

A series of deoxycholic and cholic acid-derived oligomers were synthesized and their ability to extract hydrophilic dye molecules of different structure, size, and functional groups into nonpolar media was studied. The structure of the dye and "dendritic effect" in the extraction process was examined using absorption spectroscopy and dynamic light scattering (DLS). The efficiency of structurally preorganized oligomers in the aggregation process was evaluated by 1-anilinonaphthalene-8-sulfonic acid (ANS) fluorescence studies. The possible formation of globular structures for higher-generation molecules was investigated by molecular modeling studies and the results were correlated with the anomaly observed in the extraction process with this molecule. The ability of these molecules for selective extraction of specific dyes from blended colors is also reported.

Nanomolar cellular antisense activity of peptide nucleic acid (PNA) cholic acid ("umbrella") and cholesterol conjugates delivered by cationic lipids

Limited cellular uptake and low bioavailability of peptide nucleic acids (PNAs) have restricted widespread use of PNAs as antisense/antigene agents for cells in culture and not least for in vivo applications. We now report the synthesis and cellular antisense activity in cultured HeLa pLuc705 cells of cholesterol and cholic acid ("umbrella") derivatives of splice correction antisense PNA oligomers. While the conjugates alone were practically inactive up to 1 μM, their activity was dramatically improved when delivered by a cationic lipid transfection agent (LipofectAMINE2000). In particular, PNAs, conjugated to cholesterol through an ester hemisuccinate linker or to cholic acid, exhibited low nanomolar activity (EC(50) ∼ 25 nM). Excellent sequence specificity was retained, as mismatch PNA conjugates did not show any significant antisense activity. Furthermore, we show that increasing the transfection volume improved transfection efficiency, suggesting that accumulation (condensation) of the PNA/lipid complex on the cellular surface is part of the uptake mechanism. These results provide a novel, simple method for very efficient cellular delivery of PNA oligomers, especially using PNA-cholic acid conjugates which, in contrast to PNA-cholesterol conjugates, exhibit sufficient water solubility. The results also question the generality of using cholic acid "umbrella" derivatives as a delivery modality for antisense oligomers.

Functional star polymers with a cholic acid core and their thermosensitive properties

Star polymers derived from cholic acid with poly(allyl glycidyl ether) arms have been prepared via anionic polymerization, yielding polymers with well-defined molecular weight and low polydispersity. The double bonds of the allyl groups on the polymer are used to introduce either amine or carboxylic acid groups to obtain amphiphilic polymers with cationic and anionic groups, respectively. The polymers can aggregate in water above a certain critical concentration, which was found to vary with the arm length of the star polymers. The star polymers bearing amino groups showed interesting thermosensitivity, which also depends on the pH of the media. A simple acetylation of the amine groups can sharpen the transition and vary the cloud point from 15 to 48 degrees C, depending on the degree of acetylation. Such polymers offer useful alternatives to the existing thermosensitive polymers.

Molecular pockets derived from cholic acid as chemosensors for metal ions

Molecular pockets in the form of a tripod made of cholic acid were found to be able to solubilize pyrene in polar media as a result of the facial amphiphilicity of bile acids. The trimer containing 1,2,3-triazole groups can complex with heavy metal ions, as clearly shown by electron paramagnetic resonance spectroscopy. Both the metal cation and the pyrene molecule can be brought close together in the cavity formed by the cholic acid trimer, resulting in significantly improved efficiency for fluorescence quenching of pyrene. The decrease of fluorescence intensity can be used for the detection of heavy metal ions, and the detection limit is about 1 microM in water, suggesting the usefulness of such molecules as chemosensors for such metal ions. A different trimer without the coordinating triazole groups is shown to shield pyrene away from metal ions, causing a much reduced fluorescence quenching.

A fine line between molecular umbrella transport and ionophoric activity

A persulfated molecular umbrella derived from one spermine, four lysine, and eight deoxycholic acid molecules was found to exhibit ionophoric activity, as shown by pH discharge and Na(+) and Cl(-) transport experiments. In sharp contrast, a moderately more hydrophilic analogue derived from cholic acid showed no such ionophoric activity. Both molecular umbrellas crossed liposomal membranes by passive transport with experimental rates that were similar. These findings show how the interactions between such amphomorphic molecules and phospholipid bilayers are a sensitive function of the umbrella's hydrophilic/lipophilic balance (HLB). They also raise the possibility of exploiting molecular umbrellas in fundamentally new ways.

Invertible amphiphilic molecular pockets made of cholic acid

A trimer of cholic acid was prepared via a simple isocyanate linkage. Fluorescence and UV-vis spectroscopic studies showed that the same cholane trimer can form either a hydrophobic cavity in aqueous solutions or a hydrophilic cavity in an apolar solvent using pyrene and a derivative of pyrene as probes. The dynamic inversion of the cavities was demonstrated for the first time by a simple change of the polarity of the solvent media by adjusting from an aqueous buffer to tetrahydrofuran and vice versa. The NMR study of a dimer model compound of cholic acid indicated a restricted conformation exist in the solvent mixture of chloroform and methanol.

Molecular umbrella transport: exceptions to the classic size/lipophilicity rule

The ability of a series of molecular umbrellas, derived from cholic acid, L-lysine, spermidine, and Cascade Blue, to cross fluid liposomal membranes made from 1-palmitoyl-2-oleyol-sn-glycero-3-phosphocholine (POPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) (95/5, mol/mol) has been determined. In sharp contrast to the classic "size/lipophilicity" rule of membrane transport, those molecular umbrellas that were larger in size and less lipophilic crossed these liposomal membranes more readily. The likely origin for this unusual behavior is briefly discussed.

Bioconjugate-based molecular umbrellas

Molecular umbrellas are "amphomorphic" compounds that can produce a hydrophobic or hydrophilic exterior when exposed to a hydrophobic or hydrophilic microenvironment, respectively. Such molecules are composed of two or more facial amphiphiles that are connected to a central scaffold. Molecular umbrellas that have been synthesized to date, using bile acids as umbrella "walls", polyamines such as spermidine and spermine as scaffold material, and l-lysine as "branches", have been found capable of transporting certain hydrophilic peptides, nucleotides, and oligonucleotides across liposomal membranes by passive diffusion. They have also have been shown to increase water solubility and hydrolytic stability of a hydrophobic drug, and to exhibit significant antiviral activity. The ability of a fluorescently labeled molecular umbrella to readily enter live HeLa cells suggests that such conjugates could find use as drug carriers.

Viewing membrane-bound molecular umbrellas by parallax analyses

Fluorescence quenching measurements have been made for a series of di-walled and tetra-walled molecular umbrellas having moderate (i.e., hydroxyl-) and strong (i.e., sulfate-) facial hydrophilicity, using Cascade Blue as the fluorophore. Through the use of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphotempocholine, 1-palmitoyl-2-stearoyl-(5-DOXYL)-sn-glycero-3-phosphocholine, and 1-palmitoyl-2-stearoyl-(12-DOXYL)-sn-glycero-3-phosphocholine as fluorescence quenchers, evidence has been obtained for a membrane-bound state in which the umbrella molecules lie on the surface of the lipid bilayer. In the case of the sulfated molecular umbrellas, evidence has also been obtained for a subpopulation in which the fluorophore lies deeper within the membrane. Probable structures for the shallow-lying and deep-lying molecular umbrellas are discussed.

Ceragenins: cholic acid-based mimics of antimicrobial peptides

The prevalence of drug-resistant bacteria drives the quest for new antimicrobials, including those that are not expected to readily engender resistance. One option is to mimic Nature's most ubiquitous means of controlling bacterial growth, antimicrobial peptides, which have evolved over eons. In general, bacteria remain susceptible to these peptides. Human antimicrobial peptides play a central role in innate immunity, and deficiencies in these peptides have been tied to increased rates of infection. However, clinical use of antimicrobial peptides is hampered by issues of cost and stability. The development of nonpeptide mimics of antimicrobial peptides may provide the best of both worlds: a means of using the same mechanism chosen by Nature to control bacterial growth without the problems associated with peptide therapeutics. The ceragenins were developed to mimic the cationic, facially amphiphilic structures of most antimicrobial peptides. These compounds reproduce the required morphology using a bile-acid scaffolding and appended amine groups. The resulting compounds are actively bactericidal against both gram-positive and gram-negative organisms, including drug-resistant bacteria. This antimicrobial activity originates from selective association of the ceragenins with negatively charged bacterial membrane components. Association has been studied with synthetic models of bacterial membrane components, with bacterial lipopolysaccharide, with vesicles derived from bacterial phospholipids, and with whole cells. Comparisons of the antimicrobial activities of ceragenins and representative antimicrobial peptides suggest that these classes of compounds share a mechanism of action. Rapid membrane depolarization is caused by both classes as well as blebbing of bacterial membranes. Bacteria express the same genes in response to both classes of compounds. On the basis of the antibacterial activities of ceragenins and preliminary in vivo studies, we expect these compounds to find use in augmenting or replacing antimicrobial peptides in treating human disease.

Synthesis and biological evaluation of bile acid dimers linked with 1,2,3-triazole and bis-beta-lactam

We report herein the synthesis and biological evaluation of bile acid dimers linked through 1,2,3-triazole and bis-beta-lactam. The dimers were synthesized using 1,3-dipolar cycloaddition reaction of diazido bis-beta-lactams , and terminal alkynes derived from cholic acid/deoxycholic acid in the presence of Cu(i) catalyst (click chemistry). These novel molecules were evaluated in vitro for their antifungal and antibacterial activity. Most of the compounds exhibited significant antifungal as well as antibacterial activity against all the tested fungal and bacterial strains. Moreover, their in vitro cytotoxicities towards HEK-293 and MCF-7 cells were also established.

Cellular entry and nuclear targeting by a highly anionic molecular umbrella

A fluorescently labeled, persulfated molecular umbrella ( 1) has been synthesized from cholic acid, lysine, spermine, and Coumarin 343 and found capable of entering live HeLa cells. The distributions of 1 throughout the cytoplasm and the nucleus were diffuse and punctate, respectively. This finding, together with its ability to cross liposomal membranes by passive diffusion, suggests that passive diffusion plays a significant role in the ability of 1 to enter cells. The fact that 1 is concentrated at the nucleus raises the possibility that molecular umbrellas of this type could be used for the nuclear targeting of drugs.

Fluorescence study of inclusion complexes between star-shaped cholic acid derivatives and polycyclic aromatic fluorescent probes and the size effects of host and guest molecules

Star-shaped host molecules containing two, three, and four cholic acid moieties have been used to form inclusion complexes with polycyclic aromatic hydrocarbon probes (guests) varying in size from four (pyrene) to five (benzo(e)pyrene) and seven aromatic rings (coronene) and investigated by steady-state fluorescence measurements and fluorescence lifetime techniques. The results indicated that these hydrophobic guest probes prefer to locate in the hydrophobic cavities formed by the host molecules in an aqueous solution. Further studies showed that the stoichiometric ratios of the complexes depended on the relative size of both the host and the guest. The complexes of 1:1 ratio (guest:host) were formed between pyrene and the host molecules of different sizes, while the complexes of 1:2 ratio (guest:host) were found for coronene in all cases. For benzo(e)pyrene with an intermediate size, the complexes with 1:1 and 1:2 ratios (guest:host) were formed depending on the relative sizes of the host molecules. The stability of the inclusion complexes was observed to change with the solvent polarity, indicative of an adaptation of the hydrophobicity of the host pockets to the polarity of the solvent. The formation of the complexes was driven by the solvophobic interactions.

Mechanical control of enantioselectivity of amino acid recognition by cholesterol-armed cyclen monolayer at the air-water interface

Monolayers of the cholesterol-armed cyclen Na+ complex at the air-water interface display a remarkable, surface pressure dependent enantioselectivity of amino acid recognition. Upon compression of the monolayer, the binding constants of amino acids increase accompanying an inversion of chiral selectivity from the d- to l-form in the case of valine.

Mechanism of Internalization of an ICAM-1-Derived Peptide by Human Leukemic Cell Line HL-60: Influence of Physicochemical Properties on Targeted Drug Delivery

Peptide-mediated targeted delivery offers an attractive strategy for selective delivery of cytotoxic drugs to cancer cells. In this work, we have investigated the mechanism of internalization of cIBR peptide [cyclo(1,12)PenPRGGSVLVTGC] that is conjugated with fluorescein isothiocyanate (FITC) and doxorubicin (DOX) to give FITC-cIBR and DOX-cIBR conjugates, respectively. Internalization mechanisms of FITC-cIBR and DOX-cIBR were studied in LFA-1-expressing cells (HL-60) and LFA-1-deficient cells (HUVEC) under the following conditions: (a) at two different temperatures (4 and 37 degrees C), (b) in the presence of ATP-depleting agents (sodium azide and 2-deoxy- d-glucose), and (c) in the presence of a microtubule-disrupting agent (nocodazole). At 37 degrees C, FITC-cIBR was internalized by HL-60 cells and located in the endosomes; however, it was not internalized by LFA-1-deficient HUVEC. Incubation of FITC-cIBR at 4 degrees C or in the presence of nocodazole inhibited its endocytosis in HL-60 cells. The ATP inhibitors inhibited the internalization of FITC-cIBR but maintained its binding to cell surface receptors. In contrast, DOX-cIBR was diffusely distributed in the cytoplasm of LFA-1-expressing HL-60 cells following incubation at 37 degrees C. No inhibitory processes could block the entry or change the distribution pattern of DOX-cIBR into HL-60 cells, suggesting that DOX-cIBR uptake was not mediated by receptors such as LFA-1. DOX-cIBR was still found inside HUVEC, but with a distribution pattern somewhat different from that in HL-60 cells. The major entry mechanism of DOX-cIBR could be via passive diffusion because DOX-cIBR has an octanol/water distribution coefficient (Log D) of 1.15. Thus, DOX-cIBR is more lipophilic than FITC-cIBR with a Log D of 0.57. Therefore, the change in the hydrophobicity of the conjugate may alter the mechanism of entry of DOX-cIBR compared to that of FITC-cIBR. This study suggests that alteration of the physicochemical properties of drug-peptide conjugates can change the mode of uptake from receptor-mediated uptake to passive diffusion.

Design, synthesis, and antitumor activity of bile acid–polyamine–nucleoside conjugates

A series of bile acid-polyamine amides conjugated with 3'-azido-3'-deoxythymidine (AZT) as potential antitumor prodrugs in the form of phosphoramidates were synthesized in good yields and their antitumor activities were assayed against two human cancer cells in vitro: cervix cancer HeLa cells and renal cancer 7860 cells. The improved antitumor activity probably derived from the enhanced delivery efficiency of AZT due to bile acid-polyamine conjugates.

Recent Advances in Synthetic Membrane Transporters

It is 25 years since the first report of a synthetic ion channel transporter. Today, dozens of molecular and supramolecular designs have been developed to facilitate ion and small molecule transport across a bilayer membrane. Presented here is a concise summary of the advances made over the past four years. The transporters are grouped into three mechanistic classes: mobile carrier, monomeric channel, and self-assembled pore. Common building blocks are crown ethers, steroids, cyclodextrins, peptides, curcubiturils, and calixarenes. The eventual goal is to produce functional supramolecular devices such as sensors, enzyme assays, and lead candidates for pharmaceutical development.

Synthesis, characterization, and saccharide binding studies of bile acid-porphyrin conjugates

Synthesis and characterization of bile acid-porphyrin conjugates (BAPs) are reported. Binding of saccharides with BAPs in aqueous methanol was studied by monitoring changes in the visible absorption spectral of the porphyrin-moieties. Although these studies clearly showed absorbance changes, suggesting quite high if non-selective binding, the mass spectral studies do not unambiguously support these results.

Synthetic ion channels and pores (2004-2005)

This critical review covers synthetic ion channels and pores created between January 2004 and December 2005 comprehensively. The discussion of a rich collection of structural motifs may particularly appeal to organic, biological, supramolecular and polymer chemists. Functions addressed include ion selectivity and molecular recognition, as well as responsiveness to light, heat, voltage and membrane composition. The practical applications involved concern certain topics in medicinal chemistry (antibiotics, drug delivery), catalysis and sensing. An introduction to principles and methods is provided for the non-specialist; some new sources of inspiration from fields beyond chemistry are highlighted.