Persulfated molecular umbrellas as anti-HIV and anti-HSV agents

Signed, Sealed, Delivered: Conjugate and Prodrug Strategies as Targeted Delivery Vectors for Antibiotics

Innate and developed resistance mechanisms of bacteria to antibiotics are obstacles in the design of novel drugs. However, antibacterial prodrugs and conjugates have shown promise in circumventing resistance and tolerance mechanisms via directed delivery of antibiotics to the site of infection or to specific species or strains of bacteria. The selective targeting and increased permeability and accumulation of these prodrugs not only improves efficacy over unmodified drugs but also reduces off-target effects, toxicity, and development of resistance. Herein, we discuss some of these methods, including sideromycins, antibody-directed prodrugs, cell penetrating peptide conjugates, and codrugs.

Bis(sulfonamide) transmembrane carriers allow pH-gated inversion of ion selectivity

Bis(sulfonamide) based synthetic carriers are reported for inversion of ion selectivity upon deviation of pH within a narrow window. A liposomal membrane potential is also generated when potassium ions are passively transported by these carriers.

Crystal structure of head-to-head dimers of cholic and deoxycholic acid derivatives with different symmetric bridges

The crystal structure of three head-to-head dimers (having two cholic acid or deoxycholic acid units) linked at carbon atoms C3 by aromatic or alkyl bridges is studied. An internal coordinates system is necessary for describing the relative orientation in the space of the two bile acid residues. Five angles (three torsion and two common ones) are necessary for defining the relative position of both steroid residues in space. Carbon atoms C3 (which always carries a α-hydroxy group in natural bile acids), and C10 and C13 (which always carry β-methyl groups) of each steroid residue are suitable for this purpose. Furthermore, the distance between each C3 carbon atoms of both steroid residues will allow one to locate the steroids in space. The three dimers selected provide a large range of values for these angles. The packing, hydrogen bond network, and location of guest in the three crystals are discussed.

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.

Microbicides: chemistry, structure, and strategy

PURPOSE OF REVIEW

To highlight promising areas of research and preview future generations of microbicides, this review will focus on reports that described new cellular or viral targets, drug substances, or strategies that are specifically intended for topical microbicides. Those reports that dealt with the design, discovery, and synthesis of anti-HIV agents for use in oral or parenteral formulations, while important for the microbicide field, are beyond the scope of this review.

RECENT FINDINGS

Drug substances intended for topical microbicides are becoming increasingly target specific and, structurally, more complex. New production methods might reduce the cost of microbicides that contain these complex molecules. Genetically engineered probiotic vaginal bacteria express an even wider range of antiviral compounds, perhaps resulting in uninterrupted, coitally independent protection. Combination microbicides that contain two or more drug substances frequently act synergistically. The discovery of new cellular targets such as syndecan-3 might lead to more effective microbicides.

SUMMARY

Future generations of microbicides will likely contain one or more complex or highly specific drug substances, resulting in safer and more effective products. Since compliance issues continue to confound HIV and herpes simplex virus trials, efforts to bring practical, coitally independent microbicides to developing countries will become a top priority.

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.

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.

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.

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.

Molecular umbrellas: a novel class of candidate topical microbicides to prevent human immunodeficiency virus and herpes simplex virus infections

Molecular umbrella compounds may function as novel topical microbicides to prevent human immunodeficiency virus (HIV) and herpes simplex virus (HSV) infections. In a preliminary structure-activity investigation, one umbrella compound, designated Spm8CHAS, was identified which inhibited both HIV and HSV infections with no cellular toxicity. The objectives of the current studies were to define its spectrum of antiviral activity, characterize its mechanism of action, and explore the possibility of combining Spm8CHAS with HIV-specific reverse transcriptase inhibitors. Spm8CHAS inhibited infections by laboratory and clinical R5 and X4 clade B and clade C HIV strains in cell culture. Ectocervical tissue explants exposed to HIV-1(BaL) in the presence of Spm8CHAS were completely protected (50% inhibitory concentration [IC(50)], 13.6 microg/ml), and transfer of virus to target T cells via migratory cells was abolished (IC(50), 3.8 microg/ml). Spm8CHAS inhibited HSV-2 infection of epithelial cells 10,000-fold if present throughout the infection. Notably, adding Spm8CHAS to cultures following HSV entry significantly reduced viral infection, indicating that the drug also acts postentry. Subsequent studies indicated that Spm8CHAS blocks cell-to-cell spread of HSV. Confocal microscopy using a fluorescently labeled analog of Spm8CHAS demonstrated that this conjugate crosses the plasma cell membrane and is transported to the nucleus. Combinations of Spm8CHAS with UC-781 or 9-[R-2-(phosphonylmethoxy)propyl] adenine monohydrate in vitro exhibited additive anti-HIV activity with preserved anti-HSV activity. The abilities of Spm8CHAS to inhibit primary isolates of HIV, block HSV infection postentry, and cross cell membranes support the development of a combination microbicide containing Spm8CHAS with an HIV-specific reverse transcriptase inhibitor to prevent both HIV and HSV infections by multiple mechanisms.

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.

Molar mass of main-chain bile acid-based oligo-esters measured by SEC, MALDI-TOF spectrometry and NMR spectroscopy: A comparative study

Bile acid-based polymers are promising new materials for biomedical applications. The determination of their molar mass, as for other novel polymers, has been difficult, due to the lack of suitable standards for size exclusion chromatography (SEC). In order to solve this problem, a family of main-chain bile acid-based oligo-esters has been synthesized by acyclic diene metathesis to be used as analogues in such analysis. These oligomers have been characterized by SEC, MALDI-TOF mass spectrometry and NMR spectroscopy. The results show that SEC with polystyrene standards tends to overestimate the molar mass of these materials and that a correction factor between 0.50 and 0.60 should be used for more accuracy.

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.

Topical microbicides for the prevention of genital herpes infection

Genital herpes is one of the most prevalent sexually transmitted infections worldwide and is the most common cause of genital ulcers. Despite increased public awareness and the initiation of efforts to prevent transmission, the prevalence of herpes simplex virus (HSV) type 2 continues to increase. What makes HSV so difficult to control is that most sexual and perinatal transmission occurs during unrecognized or asymptomatic shedding. The impact of genital herpes as a public health threat is amplified because of its epidemiological synergy with HIV/AIDS. Thus, there is an urgent need for novel prophylactic methods, such as topical microbicides designed for genital application, to prevent both HSV and HIV transmission. Several candidate microbicides are being advanced to clinical trials based on in vitro activity and animal studies. These include compounds that inactivate virus directly, those that enhance innate immunity, and drugs that block viral binding and entry. A more vigorous evaluation of the safety of these and other candidate topical microbicides in development should include assessment of the impact of repeated application on innate host defences in the genital tract.