Structure modifications of 6-aminoquinolones with potent anti-HIV activity

N-Heterocycles as Promising Antiviral Agents: A Comprehensive Overview

Viruses are a real threat to every organism at any stage of life leading to extensive infections and casualties. N-heterocycles can affect the viral life cycle at many points, including viral entrance into host cells, viral genome replication, and the production of novel viral species. Certain N-heterocycles can also stimulate the host's immune system, producing antiviral cytokines and chemokines that can stop the reproduction of viruses. This review focused on recent five- or six-membered synthetic N-heterocyclic molecules showing antiviral activity through SAR analyses. The review will assist in identifying robust scaffolds that might be utilized to create effective antiviral drugs with either no or few side effects.

Grignard Reagent Utilization Enables a Practical and Scalable Construction of 3-Substituted 5-Chloro-1,6-naphthyridin-4-one Derivatives

A robust, practical, and scalable approach for the construction of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 via the addition of Grignard reagents to 4-amino-2-chloronicotinonitrile (15) was developed. Starting with various Grignard reagents, a wide range of 3-substituted 5-chloro-1,6-naphthyridin-4-one derivatives 13 were conveniently synthesized in moderate-to-good yields through addition–acidolysis–cyclocondensation. In addition, the robustness and applicability of this synthetic route was proven on a 100 g scale, which would enable convenient sample preparation in the preclinical development of 1,6-naphthyridin-4-one-based MET-targeting antitumor drug candidates.

Modulating microRNA Processing: Enoxacin, the Progenitor of a New Class of Drugs

The RNA interference (RNAi) process encompasses the cellular mechanisms by which short-noncoding RNAs posttranscriptionally modulate gene expression. First discovered in 1998, today RNAi represents the foundation underlying complex biological mechanisms that are dysregulated in many diseases. MicroRNAs are effector molecules of gene silencing in RNAi, and their modulation can lead to a wide response in cells. Enoxacin was reported as the first and unique small-molecule enhancer of microRNA (SMER) maturation. Herein, the biological activity of enoxacin as SMER is discussed to shed light on its innovative mode of action, its potential in treating different diseases, and the feasibility of using enoxacin as a chemical template for inspiring medicinal chemists. We debate its mechanism of action at the molecular level and the possible impact on future ligand and/or structure-guided chemical optimizations, as well as opportunities and drawbacks associated with the development of quinolones such as SMERs.

Advances toward Curing HIV-1 Infection in Tissue Reservoirs

A disease of more than 39.6 million people worldwide, HIV-1 infection has no curative therapy. To date, one man has achieved a sterile cure, with millions more hoping to avoid the potential pitfalls of lifelong antiretroviral therapy and other HIV-related disorders, including neurocognitive decline. Recent developments in immunotherapies and gene therapies provide renewed hope in advancing efforts toward a sterilizing or functional cure. On the horizon is research concentrated in multiple separate but potentially complementary domains: vaccine research, viral transcript editing, T-cell effector response targeting including checkpoint inhibitors, and gene editing. Here, we review the concept of targeting the HIV-1 tissue reservoirs, with an emphasis on the central nervous system, and describe relevant new work in functional cure research and strategies for HIV-1 eradication.

Current Strategies for Elimination of HIV-1 Latent Reservoirs Using Chemical Compounds Targeting Host and Viral Factors

Since the implementation of combination antiretroviral therapy (cART), rates of HIV type 1 (HIV-1) mortality, morbidity, and newly acquired infections have decreased dramatically. In fact, HIV-1-infected individuals under effective suppressive cART approach normal life span and quality of life. However, long-term therapy is required because the virus establish a reversible state of latency in memory CD4⁺ T cells. Two principle strategies, namely "shock and kill" approach and "block and lock" approach, are currently being investigated for the eradication of these HIV-1 latent reservoirs. Actually, both of these contrasting approaches are based on the use of small-molecule compounds to achieve the cure for HIV-1. In this review, we discuss the recent progress that has been made in designing and developing small-molecule compounds for both strategies.

Antiplasmodial and antimalarial activities of quinolone derivatives: An overview

Malaria remains one of the most deadly infectious diseases globally. Considering the growing spread of resistance, development of new and effective antimalarials remains an urgent priority. Quinolones, which are emerged as one of the most important class of antibiotics in the treatment of various bacterial infections, showed potential in vitro antiplasmodial and in vivo antimalarial activities, making them promising candidates for the chemoprophylaxis and treatment of malaria. This review presents the current progresses and applications of quinolone-based derivatives as potential antimalarials to pave the way for the development of new antimalarials.

Improving combination antiretroviral therapy by targeting HIV-1 gene transcription

INTRODUCTION

Combination Antiretroviral Therapy (cART) has not allowed the cure of HIV. The main obstacle to HIV eradication is the existence of quiescent reservoirs. Several other limitations of cART have been described, such as strict life-long treatment and high costs, restricting it to Western countries, as well as the development of multidrug resistance. Given these limitations and the impetus to find a cure, the development of new treatments is necessary. Areas covered: In this review, we discuss the current status of several efficient molecules able to suppress HIV gene transcription, including NF-kB and Tat inhibitors. We also assess the potential of new proteins belonging to the intriguing DING family, which have been reported to have potential anti-HIV-1 activity by inhibiting HIV gene transcription. Expert opinion: Targeting HIV-1 gene transcription is an alternative approach, which could overcome cART-related issues, such as the emergence of multidrug resistance. Improving cART will rely on the identification and characterization of new actors inhibiting HIV-1 transcription. Combining such efforts with the use of new technologies, the development of new models for preclinical studies, and improvement in drug delivery will considerably reduce drug toxicity and thus increase patient adherence.

Tumour cell population growth inhibition and cell death induction of functionalized 6-aminoquinolone derivatives

OBJECTIVES

A number of previous studies has provided evidence that the well-known anti-bacterial quinolones may have potential as anti-cancer drugs. The aim of this study was to evaluate potential anti-tumour activity and selectivity of a set of 6-aminoquinolones showing some chemical similarity to naphthyridone derivative CX-5461, recently described as innovative anti-cancer agent.

MATERIALS AND METHODS

In-house quinolones 1-8 and ad hoc synthesized derivatives 9-13 were tested on Michigan Cancer Foundation-7 (MCF-7) breast cancer cells and mesenchymal progenitor (MePR2B) cell lines, analysing their effects on the cell cycle and cell death using FACS methodology. Activation of p53 was evaluated by western blotting.

RESULTS

Benzyl esters 4, 5 and their amide counterparts 12, 13 drastically modulated MCF-7 cell cycles inducing DNA fragmentation and cell death, thus proving to be potential anti-tumour compounds. When assayed in non-tumour MePR2B cells, compounds 4 and 5 were cytotoxic while 12 and 13 had a certain degree of selectivity, with compound 12 emerging as the most promising. Western blot analysis revealed that severe p53-K382ac activation was promoted by benzylester 5. In contrast, amide 12 exerted only a moderate effect which was, however, comparable to that of suberoylanilide hydoxamic acid (SAHA).

CONCLUSIONS

Taken together, these results further reinforce evidence that quinolones have potential as anti-cancer agents. Future work will be focused on understanding compound 12 mechanisms of action, and to obtain more potent and selective compounds.

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.

Targeting HIV transcription: the quest for a functional cure

Antiretroviral therapy (ART) potently suppresses HIV-1 replication, but the virus persists in quiescent infected CD4(+)T cells as a latent integrated provirus, and patients must indefinitely remain on therapy. If ART is terminated, these integrated proviruses can reactivate, driving new rounds of infection. A functional cure for HIV requires eliminating low-level ongoing viral replication that persists in certain tissue sanctuaries and preventing viral reactivation. The HIV Tat protein plays an essential role in HIV transcription by recruiting the kinase activity of the P-TEFb complex to the viral mRNA's stem-bulge-loop structure, TAR, activating transcriptional elongation. Because the Tat-mediated transactivation cascade is critical for robust HIV replication, the Tat/TAR/P-TEFb complex is one of the most attractive targets for drug development. Importantly, compounds that interfere with transcription could impair viral reactivation, low-level ongoing replication, and replenishment of the latent reservoir, thereby reducing the size of the latent reservoir pool. Here, we discuss the potential importance of transcriptional inhibitors in the treatment of latent HIV-1 disease and review recent findings on targeting Tat, TAR, and P-TEFb individually or as part of a complex. Finally, we discuss the impact of extracellular Tat in HIV-associated neurocognitive disorders and cancers.

Modulation of HIV-1-induced activation of plasmacytoid dendritic cells by 6-desfluoroquinolones

Chronic activation of plasmacytoid dendritic cells (pDCs) is an important contributor to the immunopathogenesis of HIV infection. The quinolone derivative chloroquine (CQ) prevents endosomal acidification, required for toll-like receptor sensing of HIV by pDCs, and is currently under clinical trial as an immunotherapeutic approach. We tested three different 6-desfluoroquinolones (6-DFQs), structurally related to CQ and endowed with antiretroviral activity, for their ability to inhibit HIV-induced pDC activation and interferon (IFN)-α production in peripheral blood mononuclear cells (PBMCs) in vitro. PBMCs from six healthy donors were cultured overnight with aldrithiol-2 (AT-2)-inactivated HIV-1MN in the presence or absence of 6-DFQs or CQ. IFN-α production was measured by ELISA; pDC and monocyte activation was analyzed by flow cytometry. Incubation with HIV labeled with the fluorescent dye DyLight-488 (DL488) was used to test virus uptake by flow cytometry. We found that the 6-DFQs effectively inhibited HIV-induced IFN-α similar to CQ, but only 6-DFQs also inhibited the upregulation of the pDC activation marker CD83. Interestingly, HIV-induced expression of the costimulatory molecule CD80 and, to a lesser extent CD86, was further enhanced on pDCs by 6-DFQs, but not CQ. Conversely, 6-DFQs and CQ had similar inhibitory effects on HIV-induced monocyte activation, consistent with the primary mechanism being associated with IFN-α signaling. Finally, 6-DFQs interfered with HIV interaction with pDCs and monocytes, but not myeloid DCs. Our data indicate that 6-DFQs may interfere with pDC-mediated and IFN-α-dependent immunopathogenesis while supporting pDC differentiation into mature antigen-presenting cells by favoring expression of costimulatory molecules.

The versatile nature of the 6-aminoquinolone scaffold: identification of submicromolar hepatitis C virus NS5B inhibitors

We have previously reported that the 6-aminoquinolone chemotype is a privileged scaffold to obtain antibacterial and antiviral agents. Herein we describe the design, synthesis, and enzymatic and cellular characterization of new 6-aminoquinolone derivatives as potent inhibitors of NS5B polymerase, an attractive and viable therapeutic target to develop safe anti-HCV agents. The 6-amino-7-[4-(2-pyridinyl)-1-piperazinyl]quinolone derivative 8 proved to be the best compound of this series, exhibiting an IC50 value of 0.069 μM against NS5B polymerase and selective antiviral effect (EC50 = 3.03 μM) coupled with the absence of any cytostatic effect (CC50 > 163 μM; SI > 54) in Huh 9-13 cells carrying a HCV genotype 1b, as measured by MTS assay. These results indicate that the 6-aminoquinolone scaffold is worthy of further investigation in the context of NS5B-targeted HCV drug discovery programs.

Design, synthesis, and evaluation of WC5 analogues as inhibitors of human cytomegalovirus Immediate-Early 2 protein, a promising target for anti-HCMV treatment

Although human cytomegalovirus (HCMV) infection is mostly asymptomatic for immunocompetent individuals, it remains a serious threat for those who are immunocompromised, in whom it is associated with various clinical manifestations. The therapeutic utility of the few available anti-HCMV drugs is limited by several drawbacks, including cross-resistance due to their common mechanism of action, i.e., inhibition of viral DNA polymerase. Therefore, compounds that target other essential viral events could overcome this problem. One example of this is the 6-aminoquinolone WC5, which acts by directly blocking the transactivation of essential viral Early genes by the Immediate-Early 2 (IE2) protein. In this study, the quinolone scaffold of the lead compound WC5 was investigated in depth, defining more suitable substituents for each of the scaffold positions explored and identifying novel, potent and nontoxic compounds. Some compounds showed potent anti-HCMV activity by interfering with IE2-dependent viral E gene expression. Among them, naphthyridone 1 was also endowed with potent anti-HIV activity in latently infected cells. Their antiviral profile along with their innovative mechanism of action make these anti-HCMV quinolones a very promising class of compounds to be exploited for more effective antiviral therapeutic treatment.

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-hydrogen-8-methylquinolones active against replicating and non-replicating Mycobacterium tuberculosis

The screening of an in-house quinolones library against Mycobacterium tuberculosis (Mtb) H(37) Rv, followed by a first cycle of optimization, yielded 6-hydrogen-8-methyl derivatives endowed with good potency. The antitubercular activity also encompassed the bacteria in a non-replicating state (NRP-TB) with minimum inhibitory concentration values lower than those of the reference agent, moxifloxacin. Among the best compounds, 11w and 11ai, characterized by a properly substituted piperidine at the C-7 position, were active against single-drug-resistant (SDR-TB) Mtb strains, maintaining overall good potency also against ciprofloxacin-resistant Mtb. This study expands the body of SAR around antitubercular quinolones leading to reconsider the role played by the usual fluorine atom at the C-6 position. Further elaboration of the 6-hydrogen-8-methylquinolone scaffold, with a particular focus on the C-7 position, is expected to give even more potent congeners holding promise for shortening the current anti-TB regimen.

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.

A time-of-drug addition approach to target identification of antiviral compounds

Insight into the mode of action of newly discovered antiviral agents is now almost a prerequisite for clinical development. This protocol describes a method that provides information on the target of inhibitors of the human immunodeficiency virus (HIV); it can also be adapted to other viruses. The results from this experiment are available within 2 d. This time-based approach determines how long the addition of a compound can be postponed before losing its antiviral activity in cell culture. The target of an antiviral compound can be identified by comparing its relative position in the time scale to that of reference drugs. Therefore, it is more precise than, for example, in the case of HIV, a determination of pre- or postintegrational mode of action, and combines in one routine different assays for studying mechanisms of action.

Structural investigation of the naphthyridone scaffold: identification of a 1,6-naphthyridone derivative with potent and selective anti-HIV activity

Building upon a large, previously reported series of anti-HIV 6-desfluoroquinolones endowed with a peculiar mechanism of action, the inhibition of Tat-mediated transcription, replacement of the quinolone nucleus with a naphthyridone core was shown to be very productive. In this work, the naphthyridone scaffold was investigated in depth by synthesizing various analogues. This led to the identification of NM13 as the most selective derivative obtained in MT-4 cells. It is the result of the successful combination of the 1,6-naphthyridone nucleus and the C7 benzothiazolpiperazine group, which, for the first time, not only grants potent anti-HIV activity but displays very high selectivity. Further studies aimed at a more thorough investigation of the anti-HIV profile of this new derivative are in progress.

Studies of anti-HIV transcription inhibitor quinolones: identification of potent N1-vinyl derivatives

The 6-desfluoroquinolones (6-DFQs) are anti-HIV agents that target Tat-mediated transcription. This particular mechanism of action makes this class of compounds very attractive for further structural investigations. Identification of the pharmacophore required for inhibition will ultimately result in the design of more selective analogues for use in combination therapy for the treatment of HIV infections. We have focused on the pyridone ring of the quinolone nucleus present in these compounds, designing new modifications to broaden the structure-activity relationship knowledge base. Herein, we present novel and very potent anti-HIV quinolones, most notably those bearing an amino or vinyl group at the N1 position. Attempts were made to determine the structural parameters necessary to impart potent anti-HIV activity to the vinyl derivatives.

A 1,8-naphthyridone derivative targets the HIV-1 Tat-mediated transcription and potently inhibits the HIV-1 replication

The emergence of multidrug resistant HIV-1 strains and the inability of the HAART to eradicate HIV-1 virus from infected patients demand new drugs able to interfere with an alternative step of the replicative cycle. The naphthyridone 3 (HM13N), described in the present study, is a promising anti-HIV agent due to its ability to inhibit the HIV-1 Tat-mediated transcription and the potent antiviral activity observed in acutely, chronically, and latently infected cells. The absence of any tendency to select for resistance mutations in vitro adds to the potential clinical value of this type of compounds, especially as these compounds are drug-like and obey the Lipinski rules.

The 6-aminoquinolone WC5 inhibits human cytomegalovirus replication at an early stage by interfering with the transactivating activity of viral immediate-early 2 protein

WC5 is a 6-aminoquinolone that potently inhibits the replication of human cytomegalovirus (HCMV) but has no activity, or significantly less activity, against other herpesviruses. Here we investigated the nature of its specific anti-HCMV activity. Structure-activity relationship studies on a small series of analogues showed that WC5 possesses the most suitable pattern of substitutions around the quinolone scaffold to give potent and selective anti-HCMV activity. Studies performed to identify the possible target of WC5 indicated that it prevents viral DNA synthesis but does not significantly affect DNA polymerase activity. In yield reduction experiments with different multiplicities of infection, the anti-HCMV activity of WC5 appeared to be highly dependent on the viral inoculum, suggesting that WC5 may act at an initial stage of virus replication. Consistently, time-of-addition and time-of-removal studies demonstrated that WC5 affects a phase of the HCMV replicative cycle that precedes viral DNA synthesis. Experiments to monitor the effects of the compound on virus attachment and entry showed that it does not inhibit either process. Evaluation of viral mRNA and protein expression revealed that WC5 targets an event of the HCMV replicative cycle that follows the transcription and translation of immediate-early genes and precedes those of early and late genes. In cell-based assays to test the effects of WC5 on the transactivating activity of the HCMV immediate-early 2 (IE2) protein, WC5 markedly interfered with IE2-mediated transactivation of viral early promoters. Finally, WC5 combined with ganciclovir in checkerboard experiments exhibited highly synergistic activity. These findings suggest that WC5 deserves further investigation as a candidate anti-HCMV drug with a novel mechanism of action.

Studies on anti-HIV quinolones: new insights on the C-6 position

The 6-desfluoroquinolones which have been developed by our group represent a promising class of compounds for the treatment of HIV infection since they act on transcriptional regulation, a crucial step in the replication cycle that has not been clinically exploited, yet. Focussing attention on the N-1 and C-6 positions, a novel series of quinolones has been synthesized. New SAR insights have been obtained, in particular, the hydroxyl group emerged as a suitable C-6 substituent when coupled with the appropriate arylpiperazine at the neighboring C-7 position.

A 6-aminoquinolone compound, WC5, with potent and selective anti-human cytomegalovirus activity

We identified a 6-aminoquinolone compound, WC5, that inhibits human cytomegalovirus (HCMV) replication with a selectivity index of approximately 500. WC5 also showed activity against drug-resistant HCMV strains. In contrast, it did not significantly affect the replication of human herpesvirus 6 and 8 and was approximately 10-fold less active against murine cytomegalovirus. Thus, WC5 may represent a lead for the development of new, potent, and selective anti-HCMV compounds.

Structure-activity relationship study on anti-HIV 6-desfluoroquinolones

On the basis of our recent findings that 6-aminoquinolones inhibit the HIV Tat-mediated transactivation, we have designed a broad series of derivatives identifying novel potent agents such as the 6-desfluoroquinolones 24 (HM12) and 27 (HM13), which showed pronounced anti-HIV activity in acutely, chronically, and latently HIV-1 infected cell cultures. We demonstrate here that highly potent molecules can be obtained by optimizing the substituent in the various positions of the quinolone nucleus.

Novel in vivo model for the study of human immunodeficiency virus type 1 transcription inhibitors: evaluation of new 6-desfluoroquinolone derivatives

Two novel 6-desfluoroquinolone derivatives, HM-12 and HM-13, were evaluated for anti-human immunodeficiency virus (anti-HIV) activity in acutely, chronically, and latently HIV type 1 (HIV-1)-infected cell cultures and were found to behave as potent HIV-1 transcription inhibitors. In order to extend this result in vivo, we developed an artificial hu-SCID mouse model for HIV-1 latency based on SCID mice engrafted with latently HIV-1-infected promyelocytic OM-10.1 cells in which HIV-1 can be reactivated in vivo by the administration of human tumor necrosis factor alpha (hTNF-alpha). Treating these SCID mice with HM-12 or HM-13 prior to hTNF-alpha stimulation resulted in a pronounced suppressive effect on viral reactivation. Since both quinolone derivatives were able to inhibit the reactivation of HIV-1 from this artificial viral reservoir in vivo, we provide encouraging evidence for the use of quinolones in the control of HIV-1 infections.

Synthesis and Anti-BVDV Activity of Acridones As New Potential Antiviral Agents

In this study we report the design, synthesis, and activity against bovine viral diarrhea virus (BVDV) of a novel series of acridone derivatives. BVDV is responsible for major losses in cattle. The virus is also considered to be a valuable surrogate for the hepatitis C virus (HCV) in antiviral drug studies. Some of the synthesized acridones elicited selective anti-BVDV activity with EC(50) values ranging from 0.4 to 4 microg/mL and were not cytotoxic at concentrations that were 25- to 200-fold higher (CC(50) >100 microg/mL). It was proven that the most potent acridone derivative 10 was able to not only protect cells from virus-induced cytopathic effect but also reduce the production of infectious virus and extracellular viral RNA. Furthermore, compound 10, as well as a number of other analogues, inhibited HCV replication to some extent. However, there was no direct correlation between anti-BVDV and anti-HCV activity. Thus, the acridone scaffold, when appropriately functionalized, can yield compounds with selective activity against pestiviruses and related viruses such as the HCV.

Antiviral 6-amino-quinolones: Molecular basis for potency and selectivity

Structural modifications introduced in 6-amino-quinolones to increase antiviral activity can strongly affect cytotoxicity to host cells. By competition to Tat-TAR complex and binding experiments to viral and cellular DNA and RNA structures, we show that the nature of the substituent at position 7 modifies drug affinity and specificity for the nucleic acid. Interestingly, the basicity of the above substituent modulates chelation of the quinolone template to magnesium ions, which, in turn, critically affects the potency and target selectivity in the antiviral quinolone family.

Cell-dependent interference of a series of new 6-aminoquinolone derivatives with viral (HIV/CMV) transactivation

OBJECTIVES

Quinolone derivatives have been shown to inhibit human immunodeficiency virus (HIV) replication at the transcriptional level. Recently, a series of new 6-aminoquinolones that are endowed with more pronounced anti-HIV activities compared with the formerly reported quinolone derivatives have been published. These potent 6-aminoquinolones were further evaluated for their broad-spectrum antiviral properties.

METHODS

Latently HIV-1-infected cell lines as well as cytomegalovirus (CMV)-infected fibroblasts were used to evaluate the antiviral potency of the 6-aminoquinolone derivatives. Additionally green fluorescent protein (GFP) transactivation experiments using different promoters were conducted.

RESULTS

The compounds completely suppressed tumour necrosis factor alpha (TNF-alpha)- and phorbol 12-myristate 13-acetate (PMA)-induced HIV-1 expression in latently HIV-1-infected OM-10.1 and U1 cell lines at non-toxic concentrations. In addition, HIV-1 mRNA production was dramatically suppressed in both cell lines in a dose-dependent manner. In the same concentration range, the compounds inhibited TNF-alpha release from PMA-induced OM-10.1 cells but allowed TNF-alpha production from PMA-induced U1 cells at all concentrations tested. The 6-aminoquinolone derivatives were not only inhibitory to the Tat-mediated transactivation of the HIV-1 LTR promoter, but were also found to interfere in a cell-dependent way with the transactivation process mediated from the human CMV immediate early and the human EF-1alpha promoter. Additionally, the 6-aminoquinolone derivatives were also found to be inhibitory to CMV replication in fibroblast cells.

CONCLUSIONS

It thus appears that the antiviral spectrum of this class of compounds is not confined to the specific inhibition of HIV but encompasses CMV as well. This broad-spectrum activity window might provide an interesting platform for future applications for the 6-aminoquinolone derivatives.

A novel and efficient approach to discriminate between pre- and post-transcription HIV inhibitors

Established anti-human immunodeficiency virus (HIV) treatments are not always effective or well tolerated, highlighting the need for further refinement of antiviral drug design and development. Given the multitude of molecular targets with which the anti-HIV agents can interact, studies on the mechanism of action of newly discovered HIV inhibitors are quite elaborate. In this article, we describe the use of an efficient reporter system allowing rapid discrimination between a pre- or post-transcriptional mode of action of anti-HIV compounds based on infection by a replication competent HIV-1 molecular clone expressing the green fluorescent protein as part of the nef multiply spliced RNA. Using fluorescence microscopy and flow cytometry, this system enabled us to differentiate between compounds acting at a pre- or post-transciptional level of the virus life cycle. Antiviral activities were determined for four reference compounds as well as one putative novel HIV inhibitor. The results obtained were in agreement with the known characteristics of the reference compounds and revealed that the novel compound interfered with a target before or overlapping with HIV transcription. We showed that during a single replication cycle, compounds inhibiting a molecular target occurring before or coinciding with HIV transcription suppressed GFP expression, whereas compounds interfering at a later stage (such as protease inhibitors, which act after transcription) did not inhibit GFP expression. This GFP-based reporter system is adaptable for high-throughput screening.