Human immunodeficiency virus gene regulation as a target for antiviral chemotherapy

Bioavailable inhibitors of HIV-1 RNA biogenesis identified through a Rev-based screen

New antiretroviral agents with alternative mechanisms are needed to complement the combination therapies used to treat HIV-1 infections. Here we report the identification of bioavailable molecules that interfere with the gene expression processes of HIV-1. The compounds were detected by screening a small library of FDA-approved drugs with an assay based on measuring the displacement of Rev, and essential virus-encoded protein, from its high-affinity RNA binding site. The antiretroviral activity of two hits was based on interference with post-integration steps of the HIV-1 cycle. Both hits inhibited RRE-Rev complex formation in vitro, and blocked LTR-dependent gene expression and viral transcription in cellular assays. The best compound altered the splicing pattern of HIV-1 transcripts in a manner consistent with Rev inhibition. This mechanism of action is different from those used by current antiretroviral agents. The screening hits recognized the Rev binding site in the viral RNA, and the best compound did so with substantial selectivity, allowing the identification of a new RNA-binding scaffold. These results may be used for developing novel antiretroviral drugs.

Achieving a cure for HIV infection: do we have reasons to be optimistic?

The introduction of highly active antiretroviral therapy (HAART) in 1996 has transformed a lethal disease to a chronic pathology with a dramatic decrease in mortality and morbidity of AIDS-related symptoms in infected patients. However, HAART has not allowed the cure of HIV infection, the main obstacle to HIV eradication being the existence of quiescent reservoirs. Several other problems have been encountered with HAART (such as side effects, adherence to medication, emergence of resistance and cost of treatment), and these motivate the search for new ways to treat these patients. Recent advances hold promise for the ultimate cure of HIV infection, which is the topic of this review. Besides these new strategies aiming to eliminate the virus, efforts must be made to improve current HAART. We believe that the cure of HIV infection will not be attained in the short term and that a strategy based on purging the reservoirs has to be associated with an aggressive HAART strategy.

Human-Phosphate-Binding-Protein inhibits HIV-1 gene transcription and replication

The Human Phosphate-Binding protein (HPBP) is a serendipitously discovered lipoprotein that binds phosphate with high affinity. HPBP belongs to the DING protein family, involved in various biological processes like cell cycle regulation. We report that HPBP inhibits HIV-1 gene transcription and replication in T cell line, primary peripherical blood lymphocytes and primary macrophages. We show that HPBP is efficient in naïve and HIV-1 AZT-resistant strains. Our results revealed HPBP as a new and potent anti HIV molecule that inhibits transcription of the virus, which has not yet been targeted by HAART and therefore opens new strategies in the treatment of HIV infection.

Measuring cooperative Rev protein-protein interactions on Rev responsive RNA by fluorescence resonance energy transfer

The export of viral RNA from the nucleus to the cytoplasm of the cellular host is a crucial step in the life cycle of HIV-1 that is mediated by the viral Rev protein. One aspect of the Rev function, its multimerization, is still unexplored as a target for antiviral therapy. This is partly due to the lack of a fast and solid system to measure Rev multimerization. We have developed a high throughput in vitro Rev multimerization assay based on fluorescence resonance energy transfer (FRET) in which real-time Rev-Rev interactions can be measured both in the absence and the presence of Rev specific RRE RNA. Well-characterized Rev multimerization deficient mutants showed reduced FRET as well as unlabeled Rev molecules were able to inhibit the FRET signal demonstrating the specificity of the assay. Upon multimerization along RRE RNA the FRET signal significantly increased but dropped again at equimolar Rev/RRE ratios suggesting that in this condition most Rev molecules are bound as monomers to the RRE. Furthermore, using this assay, we demonstrate that a previously selected llama heavy-chain only antibody was shown to not only prevent the development of Rev multimers but also disassemble the already formed complexes confirming the dynamic nature of the Rev-Rev interactions. The in vitro FRET based multimerization assay facilitates the further study of the basic mechanism of cooperative Rev multimerization along the RRE and is also widely applicable to study the assembly of other functional complexes involving protein homo-multimerization or cooperative protein-protein interactions on RNA or DNA.

HIV-1 regulation of latency in the monocyte-macrophage lineage and in CD4+ T lymphocytes

The introduction in 1996 of the HAART raised hopes for the eradication of HIV-1. Unfortunately, the discovery of latent HIV-1 reservoirs in CD4+ T cells and in the monocyte-macrophage lineage proved the optimism to be premature. The long-lived HIV-1 reservoirs constitute a major obstacle to the eradication of HIV-1. In this review, we focus on the establishment and maintenance of HIV-1 latency in the two major targets for HIV-1: the CD4+ T cells and the monocyte-macrophage lineage. Understanding the cell-type molecular mechanisms of establishment, maintenance, and reactivation of HIV-1 latency in these reservoirs is crucial for efficient therapeutic intervention. A complete viral eradication, the holy graal for clinicians, might be achieved by strategic interventions targeting latently and productively infected cells. We suggest that new approaches, such as the combination of different kinds of proviral activators, may help to reduce dramatically the size of latent HIV-1 reservoirs in patients on HAART.

Novel piperidinylpyrimidine derivatives as inhibitors of HIV-1 LTR activation

Piperidinylpyrimidine derivatives, previously prepared as inhibitors of TNF-alpha production, were evaluated for their inhibitory activity against HIV-1 LTR activation. Some of these derivatives inhibited activation of HIV-1 LTR-directed CAT gene expression induced by PMA in Jurkat cells. In this report, we describe SAR in this series of compounds and show that the 3,4-methylenedioxybenzoyl (piperonyloyl) group on the nitrogen of piperidine and lipophilic substitution at the C(6)-position of pyrimidine are important for this inhibitory activity. Some of the synthesized compounds also inhibited HIV-1 LTR transactivation induced by viral protein Tat. These results suggest that piperidinylpyrimidines are useful as potent AIDS therapeutics that directly inhibit HIV-1 LTR activation and indirectly suppress TNF-alpha production.

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.

Pyridine N-oxide derivatives inhibit viral transactivation by interfering with NF-κB binding

Pyridine N-oxide derivatives represent a new class of anti-HIV compounds for which some members exclusively inhibit HIV-1 RT, whereas other members act, additionally or alternatively, at a post-integrational event in the replicative cycle of HIV. A prototype pyridine N-oxide derivative, JPL-32, inhibited tumor necrosis factor alpha (TNF-alpha)-induced HIV-1 expression in latently HIV-1-infected OM-10.1 and U1 cells, which could be reversed by the addition of N-acetyl-L-cysteine (NAC). The reversal of the antiviral activity of JPL-32 by NAC suggested the possible role of a redox-sensitive factor as target of inhibition. Indeed, when nuclear extracts of TNF-alpha-stimulated OM-10.1 and U1 cells cultured in the presence of JPL-32 were analyzed by an electrophoretic mobility shift assay (EMSA), a dose-dependent inhibition of DNA binding of nuclear NF-kappaB was observed, which could be reversed by the addition of NAC. JPL-32 did not inhibit the release and subsequent degradation of IkappaBalpha, nor did JPL-32 affect the nuclear translocation of NF-kappaB. EMSA revealed that the inhibition of the NF-kappaB DNA binding activity by JPL-32 could be reversed by the addition of reducing agents such as dithiothreitol or beta-mercaptoethanol. Moreover, JPL-32 was able to directly oxidize the thiol groups on the purified p50 subunit of recombinant NF-kappaB. The oxidative modification of the thiol groups on NF-kappaB by JPL-32 could be ascribed to the intracellular pro-oxidant effect of JPL-32. Consequently, JPL-32 was able to increase the intracellular glutathione (GSH) levels and to induce apoptosis in a dose-dependent way.

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

We have recently discovered that 6-aminoquinolone derivatives could be valid leads for the development of new anti-HIV agents because of their new and diversified mode of action. In fact, studies carried out on the lead WM5 showed that this derivative is able to inhibit the Tat-mediated long terminal repeat driven transcription, an essential step in the HIV-1 replication cycle. Thus, starting from lead WM5, we performed the design and synthesis of an enlarged series of 6-aminoquinolones, which permitted some very potent anti-HIV 6-amino derivatives to be obtained and the structure-activity relationship to be delineated. Some derivatives, 26c, 26e, 26i, and 26j, proved to be highly effective in inhibiting HIV replication at 50% inhibitory concentration in the range of 0.0087-0.7 microg/mL in MT-4, PBMCs and CEM cell lines coupled with positive selectivity indexes that reach values higher than 1000 on CEM cell lines for compounds 26e and 26i. Time-of-addition experiments clearly confirm that the new, potent 6-aminoquinolones interact at a postintegration step in the replication cycle of HIV.

Novel human immunodeficiency virus (HIV) inhibitors that have a dual mode of anti-HIV action

We have found that novel pyridine oxide derivatives are inhibitors of a wide range of human immunodeficiency virus (HIV) type 1 (HIV-1) and HIV-2 strains in CEM cell cultures. Some of the compounds showed inhibitory activities against recombinant HIV-1 reverse transcriptase (RT), whereas others were totally inactive against this viral protein in vitro. Partial retention of anti-HIV-1 activity against virus strains that contain a variety of mutations characteristic of those for resistance to nonnucleoside RT inhibitors and a lack of inhibitory activity against recombinant HIV-2 RT suggested that these pyridine oxide derivatives possess a mode of antiviral action independent from HIV RT inhibition. Time-of-addition experiments revealed that these pyridine oxide derivatives interact at a postintegration step in the replication cycle of HIV. Furthermore, it was shown that these compounds are active not only in acutely HIV-1-infected cells but also in chronically HIV-infected cells. A dose-dependent inhibition of virus particle release and viral protein expression was observed upon exposure to the pyridine oxide derivatives. Finally, inhibition of HIV-1 long terminal repeat-mediated green fluorescence protein expression in quantitative transactivation bioassays indicated that the additional target of action of the pyridine oxide derivatives may be located at the level of HIV gene expression.

Plant substances as anti-HIV agents selected according to their putative mechanism of action

Despite the continuous advances made in antiretroviral combination therapy, AIDS has become the leading cause of death in Africa and the fourth worldwide. Today, many research groups are exploring the biodiversity of the plant kingdom to find new and better anti-HIV drugs with novel mechanisms of action. In this review, plant substances showing a promising anti-HIV activity are discussed according to the viral targets with which they interact. Most of these compounds, however, interfere with early steps in the HIV replication, such as the virus entry steps and the viral enzymes reverse transcriptase and integrase, whereas until now almost no plant compounds have been found to interact with the many other viral targets. Since some plant substances are known to modulate several cellular factors, such as NF-kappa B and TNF-alpha, which are also involved in the replication of HIV, their role as potential anti-HIV products is also discussed. In conclusion, several plant-derived antiviral agents are good candidates to be further studied for their potential in the systemic therapy and/or prophylaxis of HIV infections, most probably in combination with other anti-HIV drugs.

Regulation of HIV-1 gene transcription: from lymphocytes to microglial cells

Transcription is a crucial step for human immunodeficiency virus type 1 (HIV-1) expression in all infected host cells, from T lymphocytes, thymocytes, monocytes, macrophages, and dendritic cells in the immune system up to microglial cells in the central nervous system. To maximize its replication, HIV-1 adapts transcription of its integrated proviral genome by ideally exploiting the specific cellular environment and by forcing cellular stimulatory events and impairing transcriptional inhibition. Multiple cell type-specific interplays between cellular and viral factors perform the challenge for the virus to leave latency and actively replicate in a great diversity of cells, despite the variability of its long terminal repeat region in different HIV strains. Knowledge about the molecular mechanisms underlying transcriptional regulatory events helps in the search for therapeutic agents that target the step of transcription in anti-HIV strategies.

New anti-HIV agents and targets

Virtually all the compounds that are currently used or are subject of advanced clinical trials for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside reverse transcriptase inhibitors (NRTIs): i.e., zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir, emtricitabine and nucleotide reverse transcriptase inhibitors (NtRTIs) (i.e., tenofovir disoproxil fumarate); (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e., nevirapine, delavirdine, efavirenz, emivirine; and (iii) protease inhibitors (PIs): i.e., saquinavir, ritonavir, indinavir, nelfinavir, amprenavir, and lopinavir. In addition to the reverse transcriptase and protease reaction, various other events in the HIV replicative cycle can be considered as potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulfates, polysulfonates, polycarboxylates, polyoxometalates, polynucleotides, and negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 (i.e., bicyclam (AMD3100) derivatives) and CCR5 (i.e., TAK-779 derivatives); (iii) virus-cell fusion, through binding to the viral envelope glycoprotein gp41 (T-20, T-1249); (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as 4-aryl-2,4-dioxobutanoic acid derivatives; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (flavopiridol, fluoroquinolones). Also, various new NRTIs, NNRTIs, and PIs have been developed that possess, respectively: (i) improved metabolic characteristics (i.e., phosphoramidate and cyclosaligenyl pronucleotides by-passing the first phosphorylation step of the NRTIs), (ii) increased activity ["second" or "third" generation NNRTIs ( i.e., TMC-125, DPC-083)] against those HIV strains that are resistant to the "first" generation NNRTIs, or (iii), as in the case of PIs, a different, modified peptidic (i.e., azapeptidic (atazanavir)) or non-peptidic scaffold (i.e., cyclic urea (mozenavir), 4-hydroxy-2-pyrone (tipranavir)). Non-peptidic PIs may be expected to inhibit HIV mutant strains that have become resistant to peptidomimetic PIs.

The immunosuppressant rapamycin represses human immunodeficiency virus type 1 replication

The immunosuppressive macrolide rapamycin is used in humans to prevent graft rejection. This drug acts by selectively repressing the translation of proteins that are encoded by an mRNA bearing a 5'-polypyrimidine tract (e.g., ribosomal proteins, elongation factors). The human immunodeficiency virus type 1 (HIV-1) carries a polypyrimidine motif that is located within the tat exon 2. Treatment of human T lymphoid cells with rapamycin resulted in a marked diminution of HIV-1 transcription when infection was performed with luciferase reporter T-tropic and macrophage-tropic viruses. Replication of fully infectious HIV-1 particles was abolished by rapamycin treatment. The rapamycin-mediated inhibitory effect on HIV-1 production was reversed by FK506. The anti-HIV-1 effect of rapamycin was also seen in primary human cells (i.e., peripheral blood lymphocytes) from different healthy donors. Rapamycin was shown to diminish basal HIV-1 long terminal repeat gene expression, and the observed effect of rapamycin on HIV-1 replication seems to be independent of the virus-specific transactivating Tat protein. A constitutive beta-actin promoter-based reporter gene vector was unaffected by rapamycin treatment. Kinetic virus infection studies and exposure to reporter viruses pseudotyped with heterologous envelope proteins (i.e., amphotropic murine leukemia virus and vesicular stomatitis virus G) suggested that rapamycin is primarily affecting the life cycle of HIV-1 at a transcriptional level. Northern blot analysis confirmed that this compound is selectively targeting HIV-1 mRNA synthesis.

Long-term culture of HIV-1-infected cells with the transcription inhibitor K-37

We have previously reported that the fluoroquinoline derivative K-37 is a potent and selective inhibitor of HIV-1 replication in both acutely and chronically infected cells. K-37 blocks the HIV-1 transcription process through the inhibition of still unknown cellular factor(s). To gain further insight into the target of K-37 for HIV-1 replication, we have conducted long-term culture of acutely infected cells in the presence of K-37. When MOLT-4 and U937 cells were infected with HIV-1 and cultured in the absence of K-37, the p24 antigen levels in the culture supernatants reached a plateau within 12 days. In the presence of K-37 (0.25 and 0.5 microM), the elevation of p24 antigen levels was delayed but reached a similar plateau level on day 16 or later. At a concentration of 1 microM, K-37 markedly suppressed HIV-1 replication. However, viral breakthrough was observed after 1 month of the culture period in both MOLT-4 and U937 cells. We established MOLT-4 cell lines chronically infected with the breakthrough viruses (M(1) and U(1)) or the corresponding wild-type strains (M(0) and U(0), respectively), and K-37 was examined for its inhibitory effects on HIV-1 replication in these cell lines. No substantial difference in anti-HIV-1 activity was observed between the two cell lines. However, acute infection experiments revealed that the infectivity of M(1) and U(1) was much lower than that of M(0) and U(0), respectively. Furthermore, both M(1) and U(1) had a G to T nucleotide mutation at position -215 in the second nuclear factor of activated T-cells-binding domain (-215 to -203) of the HIV-1 long terminal repeat.

New developments in anti-HIV chemotherapy

Virtually all the compounds that are currently used, or are subject of advanced clinical trials, for the treatment of human immunodeficiency virus (HIV) infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs): i.e. zidovudine (AZT), didanosine (ddI), zalcitabine (ddC), stavudine (d4T), lamivudine (3TC), abacavir (ABC), emtricitabine [(-)FTC], tenofovir disoproxil fumarate; (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e. nevirapine, delavirdine, efavirenz, emivirine; and (iii) protease inhibitors (PIs): i.e. saquinavir, ritonavir, indinavir, nelfinavir, amprenavir and lopinavir. In addition to the reverse transcriptase (RT) and protease reaction, various other events in the HIV replicative cycle can be considered as potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulfates, polysulfonates, polycarboxylates, polyoxometalates, polynucleotides, and negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 [bicyclam (AMD3100) derivatives] and CCR5 (TAK-779 derivatives); (iii) virus-cell fusion, through binding to the viral envelope glycoprotein gp41 (T-20, T-1249); (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as 4-aryl-2,4-dioxobutanoic acid derivatives; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (flavopiridol, fluoroquinolones). Also, various new NRTIs, NNRTIs and PIs have been developed that possess, respectively: (i) improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides by-passing the first phosphorylation step of the NRTIs), (ii) increased activity ["second" or "third" generation NNRTIs (i.e. TMC-125, DPC-083)] against those HIV strains that are resistant to the "first" generation NNRTIs, or (iii) as in the case of PIs, a different, nonpeptidic scaffold [i.e. cyclic urea (mozenavir), 4-hydroxy-2-pyrone (tipranavir)]. Nonpeptidic PIs may be expected to inhibit HIV mutant strains that have become resistant to peptidomimetic PIs. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating the mode of action of these agents from cell-free enzymatic assays to intact cells. Two examples in point are L-chicoric acid and the nonapeptoid CGP64222, which were initially described as an integrase inhibitor or Tat antagonist, respectively, but later shown to primarily act as virus adsorption/entry inhibitors, the latter through blockade of CXCR4.

Strategies in the design of antiviral drugs

A decade ago, just five drugs were licensed for the treatment of viral infections. Since then, greater understanding of viral life cycles, prompted in particular by the need to combat human immunodeficiency virus, has resulted in the discovery and validation of several targets for therapeutic intervention. Consequently, the current antiviral repertoire now includes more than 30 drugs. But we still lack effective therapies for several viral infections, and established treatments are not always effective or well tolerated, highlighting the need for further refinement of antiviral drug design and development. Here, I describe the rationale behind current and future drug-based strategies for combating viral infections.

New developments in anti-HIV chemotherapy

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs): i.e. zidovudine, didanosine, zalcitabine, stavudine, lamivudine, abacavir, emtricitabine, tenofovir (PMPA) disoproxil fumarate; (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs): i.e. nevirapine, delavirdine, efavirenz, emivirine; and (iii) protease inhibitors (PIs): i.e. saquinavir, ritonavir, indinavir, nelfinavir and amprenavir. In addition, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120; (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5; (iii) virus-cell fusion; (iv) viral assembly and disassembly; (v) proviral DNA integration; (vi) viral mRNA transcription. Also, new NRTIs, NNRTIs and PIs have been developed that possess respectively improved metabolic characteristics, or increased activity against NNRTI-resistant HIV strains or, as in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells.

1H-13C nuclear magnetic resonance assignment and structural characterization of HIV-1 Tat protein

Tat is a viral protein essential for activation of the HIV genes and plays an important role in the HIV-induced immunodeficiency. We chemically synthesized a Tat protein (86 residues) with its six glycines C alpha labelled with 13C. This synthetic protein has the full Tat activity. Heteronuclear nuclear magnetic resonance (NMR) spectra and NOE back-calculation made possible the sequential assignment of the 86 spin systems. Consequently, 915 NMR restraints were identified and 272 of them turned out to be long range ([i-j] > 4), providing structural information on the whole Tat protein. The poor spectral dispersion of Tat NMR spectra does not allow an accurate structure to be determined as for other proteins studied by 2D NMR. Nevertheless, we were able to determine the folding for Tat protein at a 1-mM protein concentration in a 100 mM, pH 4.5 phosphate buffer. The two main Tat functional regions, the basic region and the cysteine-rich region, are well exposed to solvent while a part of the N-terminal region and the C-terminal region constitute the core of Tat Bru. The basic region adopts an extended structure while the cysteine-rich region is made up of two loops. Resolution of this structure was determinant to develop a drug design approach against Tat. The chemical synthesis of the drugs allowed the specific binding and the inhibition of Tat to be verified.

Novel compounds in preclinical/early clinical development for the treatment of HIV infections

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs) and (iii) protease inhibitors (PIs). In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulphates, polysulphonates, polyoxometalates, zintevir, negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (AMD3100), polyphemusins (T22), TAK-779]; (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), siamycins, betulinic acid derivatives]; (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (peptoid CGP64222, fluoroquinolone K-12, Streptomyces product EM2487). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess, respectively, improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains, or, in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand; and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.

Inhibition of human papillomavirus type 16 gene expression by nordihydroguaiaretic acid plant lignan derivatives

Several methylated derivatives of a plant lignan, nordihydroguaiaretic acid (NDGA) were found to be potent anti-viral agents by suppressing Sp1 regulated transcription within the sexually transmitted viruses human immunodeficiency virus (HIV) and herpes simplex virus (HSV). A prominent Sp1 DNA binding site within many human papillomavirus (HPV) promoters has been noted to play an active role in HPV gene expression. In this report it is shown that the three NDGA derivatives, Mal.4, M(4)N, and tetra-acetyl NDGA can also inhibit gene expression from the early promoter P(97) of HPV16. The drug activity on gene expression was measured after DNA transfection of recombinant vector constructs linking the viral promoter and enhancer elements to the luciferase reporter gene. Using the specific luciferase activity as the indicator of gene expression, Mal.4 and M(4)N were found to be active in a dose dependent manner that is in the same range of concentrations reported for the promoters of HIV, HSV, and simian virus 40 (SV40) while tetra-acetyl NDGA was much more active in suppression of the HPV P(97) promoter activity than Mal.4 and M(4)N. The drugs showed limited to no effect on gene expression driven by the adenovirus major late promoter and the cytomegalovirus (CMV) promoter. Hence, such drug derivatives may be significant in the therapy of papillomavirus infections and their associated induced human cancers.