Nami Ohashi

CD4 mimics targeting the mechanism of HIV entry.

A structure-activity relationship study was conducted of several CD4 mimicking small molecules which block the interaction between HIV-1 gp120 and CD4. These CD4 mimics induce a conformational change in gp120, exposing its co-receptor-binding site. This induces a highly synergistic interaction in the use in combination with a co-receptor CXCR4 antagonist and reveals a pronounced effect on the dynamic supramolecular mechanism of HIV-1 entry.

Cell-Permeable Stapled Peptides Based on HIV-1 Integrase Inhibitors Derived from HIV-1 Gene Products

HIV-1 integrase (IN) is an enzyme which is indispensable for the stable infection of host cells because it catalyzes the insertion of viral DNA into the genome and thus is an attractive target for the development of anti-HIV agents. Earlier, we found Vpr-derived peptides with inhibitory activity against HIV-1 IN. These Vpr-derived peptides are originally located in an α-helical region of the parent Vpr protein. Addition of an octa-arginyl group to the inhibitory peptides caused significant inhibition against HIV replication associated with an increase in cell permeability but also relatively high cytotoxicity. In the current study, stapled peptides, a new class of stabilized α-helical peptidomimetics were adopted to enhance the cell permeability of the above lead peptides. A series of stapled peptides, which have a hydrocarbon link formed by a ruthenium-catalyzed ring-closing metathesis reaction between successive turns of α-helix, were designed, synthesized, and evaluated for biological activity. In cell-based assays some of the stapled peptides showed potent anti-HIV activity comparable with that of the original octa-arginine-containing peptide (2) but with lower cytotoxicity. Fluorescent imaging experiments revealed that these stapled peptides are significantly cell permeable, and CD analysis showed they form α-helical structures, whereas the unstapled congeners form β-sheet structures. The application of this stapling strategy to Vpr-derived IN inhibitory peptides led to a remarkable increase in their potency in cells and a significant reduction of their cytotoxicity.

CD4 mimics targeting the HIV entry mechanism and their hybrid molecules with a CXCR4 antagonist

Small molecules behaving as CD4 mimics were previously reported as HIV-1 entry inhibitors that block the gp120-CD4 interaction and induce a conformational change in gp120, exposing its co-receptor-binding site. A structure-activity relationship (SAR) study of a series of CD4 mimic analogs was conducted to investigate the contribution from the piperidine moiety of CD4 mimic 1 to anti-HIV activity, cytotoxicity, and CD4 mimicry effects on conformational changes of gp120. In addition, several hybrid molecules based on conjugation of a CD4 mimic analog with a selective CXCR4 antagonist were also synthesized and their utility evaluated.

Fluorogenically Active Leucine Zipper Peptides as Tag–Probe Pairs for Protein Imaging in Living Cells†

Artificial functional peptides are valuable tools in variousfields of chemical biology. Small peptides, such as anoligohistidine tag (His tag), can be genetically incorporatedinto target proteins and used for purification of recombinantproteins, immobilization of proteins on microplates, andbioimaging of proteins on the surface of living cells with theircomplementary partner molecules, such as Ni

CD4 mimics as HIV entry inhibitors: Lead optimization studies of the aromatic substituents

Several CD4 mimics have been reported as HIV-1 entry inhibitors that can intervene in the interaction between a viral envelope glycoprotein gp120 and a cell surface protein CD4. Our previous SAR studies led to a finding of a highly potent analogue 3 with bulky hydrophobic groups on a piperidine moiety. In the present study, the aromatic ring of 3 was modified systematically in an attempt to improve its antiviral activity and CD4 mimicry which induces the conformational changes in gp120 that can render the envelope more sensitive to neutralizing antibodies. Biological assays of the synthetic compounds revealed that the introduction of a fluorine group as a meta-substituent of the aromatic ring caused an increase of anti-HIV activity and an enhancement of a CD4 mimicry, and led to a novel compound 13a that showed twice as potent anti-HIV activity compared to 3 and a substantial increase in a CD4 mimicry even at lower concentrations.

Azamacrocyclic Metal Complexes as CXCR4 Antagonists

The chemokine receptor CXCR4 is a member of the seven transmembrane GPCR family, which is implicated in multiple diseases, including HIV infection, cancers, and rheumatoid arthritis. Low‐molecular‐weight nonpeptidic compounds, including AMD3100 and various pyridyl macrocyclic zinc(II) complexes, have been identified as selective antagonists of CXCR4. In the present study, structure–activity relationship studies were performed by combining the common structural features of alkylamino and pyridiyl macrocyclic antagonists. Several new zinc(II) or copper(II) complexes demonstrated potent anti‐HIV activity, strong CXCR4‐binding activity, and significant inhibitory activity against Ca2+ mobilization induced by CXCL12 stimulation. These results may prove useful in the design of novel CXCR4 antagonists, and the compounds described could potentially be developed as therapeutics against CXCR4‐relevant diseases or chemical probes to study the biological activity of CXCR4.

Peptidic HIV integrase inhibitors derived from HIV gene products: structure-activity relationship studies.

Structure-activity relationship studies were conducted on HIV integrase (IN) inhibitory peptides which were found by the screening of an overlapping peptide library derived from HIV-1 gene products. Since these peptides located in the second helix of Vpr are considered to have an alpha-helical conformation, Glu-Lys pairs were introduced into the i and i+4 positions to increase the helicity of the lead compound possessing an octa-arginyl group. Ala-scan was also performed on the lead compound for the identification of the amino acid residues responsible for the inhibitory activity. The results indicated the importance of an alpha-helical structure for the expression of inhibitory activity, and presented a binding model of integrase and the lead compound.

Synthetic Caged DAG‐lactones for Photochemically Controlled Activation of Protein Kinase C

Switching on kinases: Synthetic caged DAG-lactones have been developed and showed decreases of two orders of magnitude, relative to the corresponding parent compounds, in their binding affinities towards PKC. The caged compounds had no effect on the translocation of PKC until after photoactivation. This approach is a potentially powerful tool for probing the PKC signaling cascade.

A CD4 mimic as an HIV entry inhibitor: Pharmacokinetics

To date, several small molecules of CD4 mimics, which can suppress competitively the interaction between an HIV-1 envelope glycoprotein gp120 and a cellular surface protein CD4, have been reported as viral entry inhibitors. A lead compound 2 (YYA-021) with relatively high potency and low cytotoxicity has been identified previously by SAR studies. In the present study, the pharmacokinetics of the intravenous administration of compound 2 in rats and rhesus macaques is reported. The half-lives of compound 2 in blood in rats and rhesus macaques suggest that compound 2 shows wide tissue distribution and relatively high distribution volumes. A few hours after the injection, both plasma concentrations of compound 2 maintained micromolar levels, indicating it might have promise for intravenous administration when used combinatorially with anti-gp120 monoclonal antibodies.

Multimerized CHR-derived peptides as HIV-1 fusion inhibitors

To date, several HIV-1 fusion inhibitors based on the carboxy-terminal leucine/isoleucine heptad repeat (CHR) region of an HIV-1 envelope protein gp41 have been discovered. We have shown that a synthetic peptide mimetic of a trimer form of the CHR-derived peptide C34 has potent inhibitory activity against the HIV-1 fusion mechanism, compared to a monomer C34 peptide. The present study revealed that a dimeric form of C34 is evidently structurally critical for fusion inhibitors, and that the activity of multimerized CHR-derived peptides in fusion inhibition is affected by the properties of the unit peptides C34, SC34EK, and T20. The fluorescence-based study suggested that the N36-interactive sites of the C34 trimer, including hydrophobic residues, are exposed outside the trimer and that trimerization of C34 caused a remarkable increase in fusion inhibitory activity. The present results could be useful in the design of fusion inhibitors against viral infections which proceed via membrane fusion with host cells.