Potent and selective inhibition of Tat-dependent HIV-1 replication in chronically infected cells by a novel naphthalene derivative JTK-101

Recent Progress in the Synthesis of Benzoxazin-4-Ones, Applications in N-Directed Ortho-Functionalizations, and Biological Significance

The development of efficient synthetic procedures to access fused N, O-heterocyclic skeletons has been a pivotal research topic in organic synthesis for several years. Owing to the applications of N, O-fused heterocycles in organic synthesis, material sciences, and medicinal chemistry, significant efforts have been dedicated to design novel methods for their construction. To this end, 1,3-benzoxazin-4-ones are privileged candidates for N, O-heterocyclic molecules often found in natural products, agrochemicals, and materials science applications. In this review, we aim to summarize the existing literature on the synthesis of 1,3-benzoxazin-4-ones from 2010 onwards. Moreover, 1,3-benzoxazin-4-ones have also been identified as an excellent native directing group for the ortho-functionalization via C-H activation, which is often a strenuous task requiring pre-functionalized substrates. In the latter part of this report, we compiled several interesting examples of N-directed functionalizations of 1,3-benzoxazin-4-ones. Additionally, to emphasize biological importance, recent developments on the anticancer evaluations of benzoxazine-4-one core are included. We believe that by harnessing the methodologies discussed herein, new possibilities could be unlocked for the synthesis of fused N, O-heterocycles, leading to the development of novel biologically active compounds and functional materials.

U1 and OM10.1. Myeloid Cell Lines as Surrogate Models of Reversible Proviral Latency

As already discussed for T cell lines, also myeloid cell lines as served as the earliest models of chronic HIV infection. They were particularly relevant in the late 1980s and early 1990s when most experimental in vitro infections were based on laboratory-adapted "T-cell tropic" strains of HIV-1, such as LAI/IIIB or others, that later were found to rely upon CXCR4 as coreceptor for viral entry in addition to CD4 as primary receptor. Although primary macrophages do express CXCR4 together with CD4, virus replication is much less efficient than that observed with CCR5-using "macrophage-tropic" strains, as discussed separately in this book. Although different myeloid cell lines have been used to generate models of chronic HIV-1 infection that could be used to investigate features of proviral reactivation, as reviewed in (Cassol et al. J Leukoc Biol 80:1018-1030, 2006), two cell lines in particular have been broadly used and will be here discussed: the U937-derived U1 and HL-60-derived OM-10.1.

ZnCl2-promoted domino reaction of 2-hydroxybenzonitriles with ketones for synthesis of 1,3-benzoxazin-4-ones

A ZnCl2-promoted synthesis of 1,3-benzoxazin-4-one from 2-hydroxybenzonitriles and ketones was developed. This method displays facile access to a diverse range of substituted 1,3-benzoxazin-4-ones in good yields. This synthetic protocol has advantages: (i) easy availability of starting material; (ii) strong corrosive acid-free condition; (iii) high yield.

Induction of E. coli-derived endonuclease MazF suppresses HIV-1 production and causes apoptosis in latently infected cells

The current antiretroviral therapy cannot cure the patients infected with human immunodeficiency virus type 1 (HIV-1) due to the existence of latently infected cells capable of virus production from harboring proviral DNA. MazF is an ACA nucleotide sequence-specific endoribonuclease derived from Escherichia coli. The conditional expression of MazF by binding of HIV-1 Tat to the promoter region of a MazF-expression vector has previously been shown to selectively inhibit HIV-1 replication in acutely infected cells. The expression of MazF significantly suppressed tumor necrosis factor (TNF)-α-induced HIV-1 production and viral RNA expression in the HIV-1 latently infected cell line OM-10.1 transduced with the MazF-expression vector (OM-10.1/MFR). Moreover, the viability of OM-10.1/MFR cells decreased with increasing concentrations of TNF-α, whereas such decrease was not observed for HL-60 cells transduced with the MazF-expression vector (HL-60/MFR), the uninfected parental cell line of OM-10.1. TNF-α increased the expression of cleaved caspase-3 and cleaved poly (ADP-ribose) polymerase in OM-10.1/MFR cells, indicating that the cell death was caused by the induction of apoptosis. TNF-α-induced expression of MazF mRNA was detected in OM-10.1/MFR but not HL-60/MFR cells, suggesting that TNF-α-induced apoptosis of latently infected cells was due to the expression of MazF. Thus, the anti-HIV-1 gene therapy using the MazF-expression vector may have potential for the cure of HIV-1 infection in combination with suitable latency reversing agents through reducing the size of latently infected cells without viral reactivation.

Galectin-3 is involved in HIV-1 expression through NF-κB activation and associated with Tat in latently infected cells

Galectin-3 (Gal-3) is involved in many biological processes and pathogenesis of diseases in part through nuclear factor (NF)-κB activation. We demonstrated that Gal-3 expression was significantly induced by tumor necrosis factor (TNF)-α or phorbol 12-myristate 13-acetate in OM-10.1 and ACH-2 cells, which are considered as a model of HIV-1 latently infected cells. The expression of Gal-3 was also associated with their viral production. However, the induction of Gal-3 by TNF-α was not observed in their uninfected parental cells. Knockdown of Gal-3 resulted in the suppression of NF-κB activation and HIV-1 replication in the latently infected cells. The expression level of Gal-3 was highly correlated with that of HIV-1 Tat in the latently infected cells stimulated with TNF-α. Furthermore, colocalization and possible interaction of Gal-3 and Tat were observed in the stimulated cells. These results suggent that Gal-3 expression is closely correlated with HIV-1 expression in latently infected cells through NF-κB activation and the interaction with Tat.

Development of a dual reporter screening assay for distinguishing the inhibition of HIV Tat-mediated transcription from off-target effects

Human immunodeficiency virus (HIV) encodes a transcription trans-activator (Tat) with an essential role in the transcriptional elongation of viral RNA based on the viral promoter long terminal repeat (LTR). Tat-mediated transcription is conserved and can be distinguished from host transcription, so it is a therapeutic target for combating HIV replication. Traditional screening assays for Tat-mediated transcriptional inhibitors are based on the biochemical properties of Tat and transactivation-responsive RNA. We developed an inducible system based on two lentiviral expression cassettes for doxycycline (Dox)-inducible Tat and Renilla luciferase (R-Luc) using TZM-bl cells harboring LTR-driven firefly luciferase (F-Luc). The cells simultaneously expressed both Tat-induced F-Luc and R-Luc, so it was possible to recognize off-target effects in the presence of Dox. The system was validated with known inhibitors: CYC202 obtained high sensitivity and specificity, whereas 6Bio and DRB had off-target effects. The MTT-based cytotoxicity test indicated the resistance of the system even at concentrations with off-target effects. The specificity of the system was confirmed using antiretroviral drugs. Our dual reporter system can simply detect Tat inhibitory effects, as well as precisely discriminate between the inhibitory and off-target effects of inhibitors, and may be useful for the development of a therapeutic anti-HIV drug.

Recent advances in the identification of Tat-mediated transactivation inhibitors: progressing toward a functional cure of HIV

The current anti-HIV combination therapy does not eradicate the virus that persists mainly in quiescent infected CD4(+) T cells as a latent integrated provirus that resumes after therapy interruption. The Tat-mediated transactivation (TMT) is a critical step in the HIV replication cycle that could give the opportunity to reduce the size of latent reservoirs. More than two decades of research led to the identification of various TMT inhibitors. While none of them met the criteria to reach the market, the search for a suitable TMT inhibitor is still actively pursued. Really promising compounds, including one in a Phase III clinical trial, have been recently identified, thus warranting an update.

Selective inhibition of HIV-1 replication by the CDK9 inhibitor FIT-039

FIT-039 has recently been identified as a novel cyclin-dependent kinase 9 inhibitor with potent antiviral activity against a broad spectrum of DNA viruses, such as herpes simplex virus type 1 (HSV-1) and human cytomegaloviruses. In this study, FIT-039 was examined for its inhibitory effect on human immunodeficiency virus type 1 (HIV-1) replication in chronically infected cells. Its 50% effective concentration was 1.4-2.1μM, irrespective of the cells used for antiviral assays, while its 50% cytotoxic concentration was >20μM, indicating that FIT-039 is a selective inhibitor of HIV-1 replication. FIT-039 also inhibited HIV-1 RNA expression in a dose-dependent fashion. Since previous studies demonstrated that FIT-039 exhibited antiviral efficacy without noticeable adverse effects in HSV-1-infected mice, the compound should be further investigated for its clinical potential against HIV-1 infection.

Identification of novel inhibitors of human immunodeficiency virus type 1 replication by in silico screening targeting cyclin T1/Tat interaction

Human immunodeficiency virus type 1 (HIV-1) transcription is essential for viral replication and the only step for viral genome amplification. Cyclin T1 (CycT1) interacts with HIV-1 Tat and transactivation-responsive (TAR) RNA, leading to the activation of viral transcription through the hyperphosphorylation of RNA polymerase II (RNAPII). Thus, the CycT1/Tat/TAR RNA interaction represents a novel target for inhibition of HIV-1 replication. In this study, we conducted in silico screening of compounds targeting the CycT1/Tat/TAR RNA complex and found that two structurally related compounds (C1 and C2) had high docking scores for a model of the complex. These compounds proved inhibitory to HIV-1 replication in tumor necrosis factor alpha-stimulated chronically infected cells. In addition, C3, a derivative of C1 and C2, was found to be a more potent inhibitor of HIV-1 replication in chronically infected cells. C3 also inhibited HIV-1 replication in acutely infected cells. The compound could suppress Tat-mediated HIV-1 long terminal repeat-driven gene expression and phosphorylation of RNAPII through inhibition of Tat binding to CycT1. Furthermore, the docking pose of C3 was defined by analyses for its in silico docking energy and in vitro antiviral activity, which indicates that C3 interacts with Tat-binding amino acids of CycT1. Thus, a series of compounds described herein are novel inhibitors of HIV-1 transcription through inhibition of CycT1/Tat interaction.

Strategies to Block HIV Transcription: Focus on Small Molecule Tat Inhibitors

After entry into the target cell, the human immunodeficiency virus type I (HIV) integrates into the host genome and becomes a proviral eukaryotic transcriptional unit. Transcriptional regulation of provirus gene expression is critical for HIV replication. Basal transcription from the integrated HIV promoter is very low in the absence of the HIV transactivator of transcription (Tat) protein and is solely dependent on cellular transcription factors. The 5' terminal region (+1 to +59) of all HIV mRNAs forms an identical stem-bulge-loop structure called the Transactivation Responsive (TAR) element. Once Tat is made, it binds to TAR and drastically activates transcription from the HIV LTR promoter. Mutations in either the Tat protein or TAR sequence usually affect HIV replication, indicating a strong requirement for their conservation. The necessity of the Tat-mediated transactivation cascade for robust HIV replication renders Tat one of the most desirable targets for transcriptional therapy against HIV replication. Screening based on inhibition of the Tat-TAR interaction has identified a number of potential compounds, but none of them are currently used as therapeutics, partly because these agents are not easily delivered for an efficient therapy, emphasizing the need for small molecule compounds. Here we will give an overview of the different strategies used to inhibit HIV transcription and review the current repertoire of small molecular weight compounds that target HIV transcription.

6-desfluoroquinolones as HIV-1 Tat-mediated transcription inhibitors

The current anti-HIV treatments fail to completely eradicate the virus in HIV-infected individuals, mainly as a result of a small pool of latently infected cells. This issue, together with the emergence of multidrug-resistant viruses, clearly highlights the need to find additional strategies. An overview of the Tat-mediated transcription inhibitors 6-desfluoroquinolones (6-DFQs), identified by our group, is given in this review along with a critical appraisal of their advantages and drawbacks. Attempts are also made to place them within the context of new potential anti-HIV therapeutics. Due to their innovative mechanism of action, the 6-DFQs could be interesting candidates for use in association with the currently used cocktail of drugs. Their potential as antivirals deserves further investigation.