Kinetic Evidence for the Existence and Mechanism of Formation of a Barrel Stave Structure from Pore-Forming Dendrimers

Cholesterol-stabilized membrane-active nanopores with anticancer activities

Cholesterol-enhanced pore formation is one evolutionary means cholesterol-free bacterial cells utilize to specifically target cholesterol-rich eukaryotic cells, thus escaping the toxicity these membrane-lytic pores might have brought onto themselves. Here, we present a class of artificial cholesterol-dependent nanopores, manifesting nanopore formation sensitivity, up-regulated by cholesterol of up to 50 mol% (relative to the lipid molecules). The high modularity in the amphiphilic molecular backbone enables a facile tuning of pore size and consequently channel activity. Possessing a nano-sized cavity of ~ 1.6 nm in diameter, our most active channel Ch-C1 can transport nanometer-sized molecules as large as 5(6)-carboxyfluorescein and display potent anticancer activity (IC₅₀ = 3.8 µM) toward human hepatocellular carcinomas, with high selectivity index values of 12.5 and >130 against normal human liver and kidney cells, respectively.

Bacterial cells utilize cholesterol-enhanced pore formation to specifically target eukaryotic cells. Here, the authors present a class of bio-inspired, cholesterol-enhanced nanopores which display anticancer activities in vitro.

Inducement of G-quadruplex DNA forming and down-regulation of oncogene c-myc by bile acid-amino acid conjugate-BAA

Human c-myc gene is a central regulator of cellular proliferation and cell growth, and G-quadruplexes have been proven to be the transcriptional controller of this gene. In this study, the interaction of bile acid-amino acid conjugate (BAA) with G-quadruplexes in c-myc was investigated by circular dichroism spectroscopy, nuclear magnetic resonance (NMR) measurement, and quantitative real-time polymerase chain reaction (PCR) assay. The experimental results indicated that BAA has the ability to selectively induce the formation of parallel G-quadruplexes in c-myc, which leads to down-regulation of c-myc transcription in the human breast cancer cell MCF-7.

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.

Lipophilic lysine-spermine conjugates are potent polyamine transport inhibitors for use in combination with a polyamine biosynthesis inhibitor

Cancer cells can overcome the ability of polyamine biosynthesis inhibitors to completely deplete their internal polyamines by the importation of polyamines from external sources. This paper discusses the development of a group of lipophilic polyamine analogues that potently inhibit the cellular polyamine uptake system and greatly increase the effectiveness of polyamine depletion when used in combination with DFMO, a well-studied polyamine biosynthesis inhibitor. The attachment of a length-optimized C(16) lipophilic substituent to the epsilon-nitrogen atom of an earlier lead compound, D-Lys-Spm (5), has produced an analogue, D-Lys(C(16)acyl)-Spm (11) with several orders of magnitude more potent cell growth inhibition on a variety of cultured cancer cell types including breast (MDA-MB-231), prostate (PC-3), melanoma (A375), and ovarian (SK-OV-3), among others. These results are discussed in the context of a possible membrane-catalyzed interaction with the extracellular polyamine transport apparatus. The resulting novel two-drug combination therapy targeting cellular polyamine metabolism has shown exceptional efficacy against cutaneous squamous cell carcinomas (SCC) in a transgenic ornithine decarboxylase (ODC) mouse model of skin cancer. A majority (88%) of large, aggressive SCCs exhibited complete or nearly complete remission to this combination therapy, whereas responses to each agent alone were poor. The availability of a potent polyamine transport inhibitor allows, for the first time, for a real test of the hypothesis that starving cells of polyamines will lead to objective clinical response.

Synthetic ion channels in bilayer membranes

Natural ion channels are large protein complexes that regulate key functions of cells. Supramolecular chemists have been able to take hints from Nature to design and prepare completely synthetic ion channel systems that reproduce many of the fundamental functions of natural channels. This tutorial review introduces the field to non-specialists. It examines the design, synthesis, incorporation, and characterization of synthetic ion channels in bilayer membranes, and points to potential applications of synthetic ion channels.

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

A series of molecular umbrella conjugates, derived from cholic acid, deoxycholic acid, spermidine, lysine, and 5-mercapto-2-nitrobenzoic acid, have been synthesized and found capable of transporting an attached 16-mer oligonucleotide (S-dT16) across liposomal membranes made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidyldglycerol (POPG), and cholesterol [POPC/POPG/cholesterol (65/5/30; mol/mol/mol, v/v/v)] at 37 degrees C. Those molecular umbrellas containing four choloyl (or deoxycholoyl) groups resulted in significantly faster rates of transport as compared to those containing only two such moieties. A model that accounts for these membrane transport processes is proposed.

Ligand-Gated Synthetic Ion Channels

Supramolecular pi-stack architecture is fundamental in DNA chemistry but absent in biological and synthetic ion channels and pores. Here, a novel rigid-rod pi-stack architecture is introduced to create synthetic ion channels with characteristics that are at the forefront of rational design, that is, ligand gating by a conformational change of the functional supramolecule. Namely, the intercalation of electron-rich aromatics is designed to untwist inactive electron-poor helical pi-stacks without internal space into open barrel-stave ion channels. Conductance experiments in planar lipid bilayers corroborate results from spherical bilayers and molecular modeling: Highly cooperative and highly selective ligand gating produces small, long-lived, weakly anion selective, ohmic ion channels. Structural studies conducted under conditions relevant for function provide experimental support for helix-barrel transition as origin of ligand gating. Control experiments demonstrate that minor structural changes leading to internal decrowding suffice to cleanly annihilate chiral self-organization and function.