Exploratory studies on CA-15L, an anti-HIV active HIV-1 capsid fragment

Low-molecular-weight anti-HIV-1 agents targeting HIV-1 capsid proteins

The HIV-1 capsid is a shell that encapsulates viral RNA, and forms a conical structure by assembling oligomers of capsid (CA) proteins. Since the CA proteins are highly conserved among many strains of HIV-1, the inhibition of the CA function could be an appropriate goal for suppression of HIV-1 replication, but to date, no drug targeting CA has been developed. Hydrophobic interactions between two CA molecules through Trp184 and Met185 in the protein are known to be indispensable for conformational stabilization of the CA multimer. In our previous study, a small molecule designed by in silico screening as a dipeptide mimic of Trp184 and Met185 in the interaction site was synthesized and found to have significant anti-HIV-1 activity. In the present study, molecules with different scaffolds based on a dipeptide mimic of Trp184 and Met185 have been designed and synthesized. Their significant anti-HIV activity and their advantages compared to the previous compounds were examined. The present results should be useful in the design of novel CA-targeting anti-HIV agents.

Hybrids of small CD4 mimics and gp41-related peptides as dual-target HIV entry inhibitors

Hybrid molecules containing small CD4 mimics and gp41-C-terminal heptad repeat (CHR)-related peptides have been developed. A YIR-821 derivative was adopted as a CD4 mimic, which inhibits the interaction of gp120 with CD4. SC-peptides, SC34 and SC22EK, were also used as CHR-related peptides, which inhibit the interaction between the N-terminal heptad repeat (NHR) and CHR and thereby membrane fusion. Therefore, these hybrid molecules have dual-targets of gp120 and gp41. In the synthesis of the hybrid molecules of CD4 mimic-SC-peptides with different lengths of linkers, two conjugating methods, Cu-catalyzed azide-alkyne cycloaddition and direct cysteine alkylation, were performed. The latter reaction caused simpler operation procedures and higher synthetic yields than the former. The synthesized hybrid molecules of CD4 mimic-SC22EK have significantly higher anti-HIV activity than each sole agent. The present data should be useful in the future design of anti-HIV agents as dual-target entry inhibitors.

An insight on medicinal aspects of novel HIV-1 capsid protein inhibitors

A capsid is the protein shell of a virus, encircling its genetic material. The HIV capsid is erected from a single protein, known as capsid protein. The capsid of HIV-1 significantly involved in many processes of the virus life cycle, which makes it as a novel target for the new inhibitors. Recently many novel HIV-1 inhibitors binding to capsid proteins have been reported successfully. Most of these inhibitors can inhibit or accelerate the disassembly or assembly of the capsid, and some of them can inhibit reverse transcription. Unfortunately, none of them are currently approved by U.S. FDA. However, GS-6207, an inhibitor binds to the NTD-CTD interface with potent antiviral activity and the long metabolic cycle, is expected to be the first approved drug targeting HIV-1 capsid. Herein, we provide a concise report focusing on the recent prospective of HIV-1 capsid inhibitors in medicinal chemistry in order to enlighten drug design.

Small-Molecule Anti-HIV-1 Agents Based on HIV-1 Capsid Proteins

The capsid of human immunodeficiency virus type 1 (HIV-1) is a shell that encloses viral RNA and is highly conserved among many strains of the virus. It forms a conical structure by assembling oligomers of capsid (CA) proteins. CA dysfunction is expected to be an important target of suppression of HIV-1 replication, and it is important to understand a new mechanism that could lead to the CA dysfunction. A drug targeting CA however, has not been developed to date. Hydrophobic interactions between two CA molecules via Trp184/Met185 in CA were recently reported to be important for stabilization of the multimeric structure of CA. In the present study, a small molecule designed by in silico screening as a dipeptide mimic of Trp184 and Met185 in the interaction site, was synthesized and its significant anti-HIV-1 activity was confirmed. Structure activity relationship (SAR) studies of its derivatives were performed and provided results that are expected to be useful in the future design and development of novel anti-HIV agents targeting CA.

Hybrids of Small-Molecule CD4 Mimics with Polyethylene Glycol Units as HIV Entry Inhibitors

CD4 mimics are small molecules that inhibit the interaction of gp120 with CD4. We have developed several CD4 mimics. Herein, hybrid molecules consisting of CD4 mimics with a long alkyl chain or a PEG unit attached through a self-cleavable linker were synthesized. In anti-HIV activity, modification with a PEG unit appeared to be more suitable than modification with a long alkyl chain. Thus, hybrid molecules of CD4 mimics, with PEG units attached through an uncleavable linker, were developed and showed high anti-HIV activity and low cytotoxicity. In investigation of pharmacokinetics in a rhesus macaque, a hybrid compound had a more effective PK profile than that of the parent compound, and intramuscular injection was a more useful administration route to maintain the high blood concentration of the CD4 mimic than intravenous injection. The presented hybrid molecules of CD4 mimics with a PEG unit would be practically useful when combined with a neutralizing antibody.

Potent leads based on CA-19L, an anti-HIV active HIV-1 capsid fragment

Several anti-HIV-1 peptides have previously been found among overlapping fragment peptide libraries that contain an octa-arginyl moiety and cover the whole sequence of an HIV-1 capsid (CA) protein. Several derivatives based on a potent CA fragment peptide CA-19L have been synthesized. CA-19L overlaps with the Helix 9 region of the CA protein, which could be important for oligomerization of the CA proteins. Derivatives of CA-19L in which several amino acid residues were added to the N- and C-termini according to the natural CA sequence, were synthesized and their anti-HIV activity was evaluated. Some potent compounds were found, and these potential new anti-HIV agents are expected to be useful as new tools for elucidation of CA functions.

Bivalent HIV-1 fusion inhibitors based on peptidomimetics

Membrane fusion is a valid target for inhibition of HIV-1 replication. A 34-mer fragment peptide (C34), which is contained in the HIV-1 envelope protein gp41, has significant anti-HIV activity. Previously, a dimeric derivative of C34 linked by a disulfide bridge at its C-terminus was found to have more potent anti-HIV activity than the C34 peptide monomer. To date, several peptidomimetic small inhibitors have been reported, but most have lower potency than peptide derivatives related to C34. In the present study we applied this dimerization concept to these peptidomimetic small inhibitors and designed several bivalent peptidomimetic HIV-1 fusion inhibitors. The importance of the length of linkers crosslinking two peptidomimetic compounds was demonstrated and several potent bivalent inhibitors containing tethered peptidomimetics were produced.