Synthesis and evaluation of bifunctional anti-HIV agents based on specific CXCR4 antagonists-AZT conjugation

Leveraging the therapeutic, biological, and self-assembling potential of peptides for the treatment of viral infections

Peptides and peptide-based materials have an increasing role in the treatment of viral infections through their use as active pharmaceutical ingredients, targeting moieties, excipients, carriers, or structural components in drug delivery systems. The discovery of peptide-based therapeutic compounds, coupled with the development of new stabilization and formulation strategies, has led to a resurgence of antiviral peptide therapeutics over the past two decades. The ability of peptides to bind cell receptors and to facilitate membrane penetration and subsequent intracellular trafficking enables their use in various antiviral systems for improved targeting efficiency and treatment efficacy. Importantly, the self-assembly of peptides into well-defined nanostructures provides a vast library of discrete constructs and supramolecular biomaterials for systemic and local delivery of antiviral agents. We review here the recent progress in exploiting the therapeutic, biological, and self-assembling potential of peptides, peptide conjugates, and their supramolecular assemblies in treating human viral infections, with an emphasis on the treatment strategies for Human Immunodeficiency Virus (HIV).

miR‑146a‑5p expression is upregulated by the CXCR4 antagonist TN14003 and attenuates SDF‑1‑induced cartilage degradation

Osteoarthritis (OA) is an aseptic inflammatory disease which is associated with the stromal cell-derived factor 1/C-X-C chemokine receptor type 4 (SDF-1/CXCR4) axis. Accumulating studies have identified numbers of microRNAs (miRNAs) that serve important roles in the pathogenesis of OA. However, whether and how the inhibition of the SDF-1/CXCR4 axis induces alterations in miRNA expression remains largely unclear. miRNA profiling was performed in OA chondrocytes stimulated with SDF-1 alone, or SDF-1 with the CXCR4 antagonist TN14003 by miRNA microarray. Candidate miRNAs were verified by reverse transcription quantitative polymerase chain reaction. Bioinformatic analyses including target prediction, gene ontology (GO) and pathway analysis were performed to explore the potential functions of candidate miRNAs. Notably, 7 miRNAs (miR-146a-5p, miR-221-3p, miR-126-3p, miR-185-5p, miR-155-5p, miR-124-3p and miR-130a-3p) were significantly differentially expressed. GO analysis indicated that miR-146a-5p and its associated genes were enriched in receptor regulatory activity, nuclear factor-kappa-light-chain-enhancer of activated B cells (NF-κB)-inducing kinase activity, cellular response to interleukin-1, cytokine-cytokine receptor interaction, NF-κB signaling pathway and osteoclast differentiation pathways. CXCR4 was predicted to be a target of miR-146a-5p with high importance. The mRNA and protein levels of key factors involved in cartilage degeneration were measured following manipulation of the expression levels of miR-146a-5p in OA chondrocytes. CXCR4 and MMP-3 levels were negatively associated with miR-146a-5p expression, while the levels of type II collagen and aggrecan were positively associated. These data reveal that TN14003 upregulates miR-146a-5p expression, and also pinpoints a novel role of miR-146a-5p in inhibiting cartilage degeneration by directly targeting the SDF-1/CXCR4 axis.

Identification of novel bifunctional HIV-1 reverse transcriptase inhibitors

Objectives

The increasing prevalence of mutations in HIV-1 reverse transcriptase (RT) that confer resistance to existing NRTIs and NNRTIs underscores the need to develop RT inhibitors with novel mode-of-inhibition and distinct resistance profiles.

Methods

Biochemical assays were employed to identify inhibitors of RT activity and characterize their mode of inhibition. The antiviral activity of the inhibitors was assessed by cell-based assays using laboratory HIV-1 isolates and MT4 cells. RT variants were purified via avidin affinity columns.

Results

Compound A displayed equal or greater potency against many common NNRTI-resistant RTs (K103N and Y181C RTs) relative to WT RT. Despite possessing certain NNRTI-like properties, such as being unable to inhibit an engineered variant of RT lacking an NNRTI-binding pocket, we found that compound A was dependent on Mg2+ for binding to RT. Optimization of compound A led to more potent analogues, which retained similar activities against WT and K103N mutant viruses with submicromolar potency in a cell-based assay. One of the analogues, compound G, was crystallized in complex with RT and the structure was determined at 2.6 Å resolution. The structure indicated that compound G simultaneously interacts with the active site (Asp186), the highly conserved primer grip region (Leu234 and Trp229) and the NNRTI-binding pocket (Tyr188).

Conclusions

These findings reveal a novel class of RT bifunctional inhibitors that are not sensitive to the most common RT mutations, which can be further developed to address the deficiency of current RT inhibitors.

Design, Synthesis, and Antiviral Evaluation of Chimeric Inhibitors of HIV Reverse Transcriptase

In a continuing study of potent bifunctional anti-HIV agents, we rationally designed a novel chimeric inhibitor utilizing thymidine (THY) and a TMC derivative (a diarylpyrimidine NNRTI) linked via a polymethylene linker (ALK). The nucleoside, 5'-hydrogen-phosphonate (H-phosphonate), and 5'-triphosphate forms of this chimeric inhibitor (THY-ALK-TMC) were synthesized and the antiviral activity profiles were evaluated at the enzyme and cellular level. The nucleoside triphosphate (11) and the H-phosphonate (10) derivatives inhibited RT polymerization with an IC50 value of 6.0 and 4.3 nM, respectively. Additionally, chimeric nucleoside (9) and H-phosphonate (10) derivatives reduced HIV replication in a cell-based assay with low nanomolar antiviral potencies.

CXCR4, inhibitors and mechanisms of action

In this review, the author discusses recent advances in anti-HIV inhibitors, targeting CXCR4, including natural and modified chemokines, peptides and organic compounds, their mechanisms of action, and the molecular process of virus invasion of immune cells. Peptides with strong anti-HIV activity exhibit several common features, such as electrostatic charges, cyclization, beta-turns and dimerization induced by a sulphide bond. Organic compounds, such as cyclams, display a unique metal-mediated mechanism in the binding process to its target CXCR4. Understanding of their mechanisms of action may be useful for the design of more effective drugs. Consecutive interactions of viral glycoprotein gp120 with CD4 and the co-receptor, CXCR4 or another co-receptor CCR5 on the cell surface leads to virus invasion into host cells. The molecular details of the binding between HIV glycoproteins and the co-receptors also provide a basis for anti-HIV therapy.

AZT and AZT-monophosphate prodrugs incorporating HIV-protease substrate fragment: synthesis and evaluation as specific drug delivery systems

With the view to deliver anti-HIV nucleoside and nucleoside-monophosphate (MP) analogues specifically into HIV-infected cells, we synthesized a series of ester and phosphoramidate peptide conjugates of zidovudine (AZT) and of AZT-MP, respectively, wherein the peptide sequences derive from a HIV-protease (PR) hydrolysable substrate. Their in vitro stability with respect to hydrolysis, anti-HIV activity and cytotoxicity, and ability to inhibit the HIV-PR activity were investigated. Concerning the ester AZT-peptide conjugates, their antiviral activity level in thymidine kinase-expressing (TK+) CEM-SS and MT-4 cells was in most cases closely correlated to their hydrolysis rate: the faster the hydrolysis, the closer the anti-HIV activity to that of AZT. None of them was a HIV-PR substrate, indicating that their antiviral activity was not related to their intracellular hydrolysis by this enzyme. None of them inhibited HIV in TK-deficient (TK-) CEM cells, demonstrating that they probably act as prodrugs of AZT. Most of the phosphoramidate peptide conjugates of AZT-MP were rapidly degraded in a physiological buffer into several metabolites including AZT. Their anti-HIV activity in TK+ CEM-SS and MT-4 cells was much lower than that of AZT, indicating that only low amounts of AZT or AZT-MP were released into cells during incubation. Antiviral activities measured on TK- CEM cells for some phosphoramidates suggest that low amounts of AZT-MP could be released intracellularly. However, this AZT-MP release was not initiated by a HIV-PR hydrolysis, as no evidence for peptide cleavage was obtained by HPLC analysis of one representative compound after incubation with HIV-PR.

A new class of 5-fluoro-2'-deoxyuridine prodrugs conjugated with a tumor-homing cyclic peptide CNGRC by ester linkers: synthesis, reactivity, and tumor-cell-selective cytotoxicity

PURPOSE

Tumor-targeting prodrugs of 5-fluoro-2'-deoxyuridine (5-FdUrd), which are chemical conjugations of 5-FdUrd with a tumor-homing cyclic peptide CNGRC by succinate and glutarate linkers, were synthesized to investigate the structural effects of linkers on the hydrolytic release of 5-FdUrd and the tumor-cell-selective cytotoxicity.

METHODS

A solid phase synthesis method was used to produce 5-FdUrd prodrugs. The kinetics and efficiency of hydrolytic 5-FdUrd release from the prodrugs were investigated in phosphate buffer (PB), fetal bovine serum (FBS), HT-1080 cell lysate, MDA-MB-231 cell lysate, and MEM containing 10% FBS. The tumor-cell-selective cytotoxicity of prodrugs was evaluated by an MTT method.

RESULTS

Two tumor-targeting prodrugs CNF1 and CNF2 bearing 5-FdUrd conjugated with a common cyclic peptide CNGRC by succinate and glutarate linkers, respectively, and their control compounds CN1 and CN2 without 5-FdUrd moiety were synthesized and identified. CNF1 underwent hydrolysis to release 5-FdUrd more rapidly and efficiently than CNF2. Both prodrugs were of lower cytotoxicity compared to 5-FdUrd, showing more selective cytotoxicity toward APN/CD13 positive cells (HT-1080) than toward APN/CD13 negative cells (HT-29, MDA-MB-231).

CONCLUSIONS

A new class of tumor-targeting 5-FdUrd prodrugs CNF1 and CNF2 were successfully synthesized. These prodrugs targeted a tumor marker APN/CD13 to cause tumor-cell-selective cyctotoxicity due to 5-FdUrd release, the rate of which could be controlled by the structure of ester linker.

Tuftsin-AZT conjugate: potential macrophage targeting for AIDS therapy

The IgG-derived immunomodulating peptide tuftsin, Thr-Lys-Pro-Arg, is recognized by specific receptors on phagocytic cells, notably macrophages, and is capable of targeting proteins and peptides to these sites. Aiming to target 3'-azido-3'-deoxythymidine (AZT) to HIV-infected macrophages, a conjugate of AZT with tuftsin was synthesized. The AZT-tuftsin chimera possesses the characteristic capacities of its two components. Thus, like AZT, it inhibits reverse transcriptase activity and HIV-antigen expression, and similarly to tuftsin, it stimulates IL-1 release from mouse macrophages and augments the immunogenic function of the cells. Importantly, the conjugate is not cytotoxic to T-cells. The results suggest that the AZT-tuftsin conjugate might have potential use in AIDS therapy.

Chemoenzymatic syntheses of homo- and heterodimers of AZT and d4T, and evaluation of their anti-HIV activity

Homo- and heterodimers of AZT and d4T, possessing carbonate and carbamate linkers, have been synthesized with the aim to enhance the antiviral activity of their components. Homo- and heterodimer carbamates showed weak anti-HIV activity. On the other hand, dinucleoside carbonates showed marked antiviral activity.

New bicyclam-GalCer analogue conjugates: synthesis and in vitro anti-HIV activity

The synthesis of bipharmacophore anti-HIV compounds which, in a single molecule, combine two ligands, that is, the bicyclam AMD3100 and a GalCer analogue, that might inhibit several steps of the complex virus/cell cascade interactions has been performed. The 'double-drug' Gal-AMD3100 conjugates elicited inhibitory effects on T (or X4)-tropic HIV-1 replication in all CXCR4 expressing cell lines with EC(50) values ranging from 0.25 to 6.0 microM which were however approximately 40- to 125-fold lower than that of AMD3100. Concerning the mechanism of inhibition of the Gal-AMD3100 conjugates, experiments performed with X4 or R5HIV-1 strains and GHOST cells genetically modified to express CD4 and CXCR4 or CCR5 indicated clearly that the conjugates interact with CXCR4 and not with CCR5.

The therapeutic potential of CXCR4 antagonists in the treatment of HIV

Since the identification of the chemokine receptors CXCR4 and CCR5 as co-receptors for HIV-1 entry, several antagonists against these receptors have been synthesised. A highly selective CXCR4 antagonist, T22, and its downsized analogues T140 and TC14012, which inhibit X4-HIV-1 infection through their specific binding to CXCR4, have been identified. Besides T22 analogues, several other CXCR4 antagonists have been reported, such as AMD3100, ALX40-4C, KRH-1120 and AMD8664. Discovery of entry inhibitors, such as chemokine antagonists, may lead to the development of a new generation of antiHIV agents, since these inhibitors are thought to be useful for the clinical treatment of HIV-1-infected patients, especially at the late stage of treatment for AIDS patients developing multi-drug-resistant strains. In this review, recent research into CXCR4 antagonists in comparison with development of other antagonists is summarised.

[Development of selective antagonists against an HIV second receptor]

The authors have discovered a highly selective CXCR4 antagonist, T22 ([Tyr5,12, Lys7]-polyphemusin II), and its shortened potent analogs, T140 and TC14012, which strongly inhibit the T-cell line-tropic HIV-1 (X4-HIV-1) infection through their specific binding to a chemokine receptor, CXCR4. CXCR4 is a major coreceptor (second receptor) for the entry of X4-HIV-1 into T-cells. These peptides have been found through the structure-activity relationship (SAR) study on tachyplesins and polyphemusins, which function as self-defense peptides of horseshoe crabs with immature immune systems. T140 and TC14012 showed the highest level of anti-HIV activity and antagonism of target cell entry by X4-HIV-1 among all the CXCR4 antagonists that have been reported to date. Additionally, bifunctional anti-HIV agents based on the specific CXCR4 antagonists (T140 analogs)-3'-azido-3'-deoxythymidine (AZT) conjugation have been synthesized and evaluated, since T140 analogs can possibly work as a carrier of AZT targeting T-cells due to their specific affinity for CXCR4 on T-cells. T22 have two disulfide bonds and a Trp residue in the molecule. In connection with this study, novel facile and side-reaction-free methodologies for disulfide bond formation have been established for the increase of the efficiency of SAR studies. Furthermore, the completely stereocontrolled synthetic process for a couple of (E)-alkene dipeptide isosteres starting from L-amino acid has been established in order to facilitate nonpeptidylation studies on peptide-lead candidates. In this review, the authors wish to summarize our recent research on the development of specific antagonists against the HIV second receptor CXCR4, involving studies on the establishment of efficient methodologies for the facile synthesis of peptides and peptide mimetics.