Robert W. Buckheit

Inhibitors of HIV nucleocapsid protein zinc fingers as candidates for the treatment of AIDS.

Strategies for the treatment of human immunodeficiency virus-type 1 (HIV-1) infection must contend with the obstacle of drug resistance. HIV-1 nucleocapsid protein zinc fingers are prime antiviral targets because they are mutationally intolerant and are required both for acute infection and virion assembly. Nontoxic disulfide-substituted benzamides were identified that attack the zinc fingers, inactivate cell-free virions, inhibit acute and chronic infections, and exhibit broad antiretroviral activity. The compounds were highly synergistic with other antiviral agents, and resistant mutants have not been detected. Zinc finger-reactive compounds may offer an anti-HIV strategy that restricts drug-resistance development.

Shikonin, a Component of Chinese Herbal Medicine, Inhibits Chemokine Receptor Function and Suppresses Human Immunodeficiency Virus Type 1

ABSTRACT Shikonin is a major component of zicao (purple gromwell, the dried root of Lithospermum erythrorhizon), a Chinese herbal medicine with various biological activities, including inhibition of human immunodeficiency virus (HIV) type 1 (HIV-1). G protein-coupled chemokine receptors are used by HIV-1 as coreceptors to enter the host cells. In this study, we assessed the effects of shikonin on chemokine receptor function and HIV-1 replication. The results showed that, at nanomolar concentrations, shikonin inhibited monocyte chemotaxis and calcium flux in response to a variety of CC chemokines (CCL2 [monocyte chemoattractant protein 1], CCL3 [macrophage inflammatory protein 1α], and CCL5 [regulated upon activation, normal T-cell expressed and secreted protein]), the CXC chemokine (CXCL12 [stromal cell-derived factor 1α]), and classic chemoattractants (formylmethionyl-leucine-phenylalanine and complement fraction C5a). Shikonin down-regulated surface expression of CCR5, a primary HIV-1 coreceptor, on macrophages to a greater degree than the other receptors (CCR1, CCR2, CXCR4, and the formyl peptide receptor) did. CCR5 mRNA expression was also down-regulated by the compound. Additionally, shikonin inhibited the replication of a multidrug-resistant strain and pediatric clinical isolates of HIV in human peripheral blood mononuclear cells, with 50% inhibitory concentrations (IC50s) ranging from 96 to 366 nM. Shikonin also effectively inhibited the replication of the HIV Ba-L isolate in monocytes/macrophages, with an IC50 of 470 nM. Our results suggest that the anti-HIV and anti-inflammatory activities of shikonin may be related to its interference with chemokine receptor expression and function. Therefore, shikonin, as a naturally occurring, low-molecular-weight pan-chemokine receptor inhibitor, constitutes a basis for the development of novel anti-HIV therapeutic agents.

Diarylsulfones, a new chemical class of nonnucleoside antiviral inhibitors of human immunodeficiency virus type 1 reverse transcriptase.

A series of variously substituted diarylsulfones and related derivatives were found to prevent human immunodeficiency virus type 1 (HIV-1) replication and HIV-1-induced cell killing in vitro. One of the more potent derivatives, 2-nitrophenyl phenyl sulfone (NPPS), completely protected human CEM-SS lymphoblastoid cells from the cytopathic effects of HIV-1 in cell culture at 1 to 5 microM concentrations. HIV-1 replication, as assessed by the production of infectious virions, viral p24 antigen, and virion reverse transcriptase (RT), was inhibited by NPPS at similar concentrations. There was no evidence of direct cytotoxicity of the drug at concentrations below 100 microM. A variety of other CD4+ T-cell lines as well as cultures of peripheral blood leukocytes and monocytes were protected from HIV-1-induced cytopathicity and/or viral replication. NPPS also inhibited several distinctly different strains of HIV-1 but was ineffective against three strains of HIV-2. Biochemical studies revealed that NPPS inhibited HIV-1 RT but not HIV-2 RT. NPPS had no direct effect on HIV-1 virions, nor did it block the initial binding of HIV-1 to target cells. Time-limited treatments of cells with NPPS found that NPPS had to be present continuously in culture to provide maximum antiviral protection. In addition, HIV-1 replication in cells in which infection was already fully established or in chronically infected cells was also unaffected by NPPS. We conclude that NPPS acts in a reversible manner as a nonnucleoside HIV-1-specific RT inhibitor. Although markedly different in structure from a larger, structurally diverse group of known HIV-1-specific nonnucleoside RT inhibitors, NPPS shares several of the biological properties that characterize this emerging new pharmacologic class.

Antiviral activity of hop constituents against a series of DNA and RNA viruses

We investigated whether crude hop extracts and purified hop components representing every major chemical class of hop compound have antiviral activity. These hop constituents were tested for antiviral activity against bovine viral diarrhea virus (BVDV) as a surrogate model of hepatitis C virus (HCV), human immunodeficiency virus (HIV), influenza A virus (FLU-A), influenza B virus (FLU-B), rhinovirus (Rhino), respiratory syncytial virus (RSV), yellow fever virus (YFV), cytomegalovirus (CMV), hepatitis B virus (HBV), and herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). The extracts all failed to prevent the replication of HIV, FLU-A, FLU-B, RSV and YFV. A xanthohumol-enriched hop extract displayed a weak to moderate antiviral activity against BVDV (therapeutic index (TI)=6.0), HSV-2 (TI=>5.3), Rhino (TI=4.0) and HSV-1 (TI=>1.9) with IC(50) values in the low microg/ml range. Pure iso-alpha-acids demonstrated low to moderate antiviral activity against both BVDV (TI=9.1) and CMV (TI=4.2) with IC(50) values in the low microg/ml range. No antiviral activity was detected using beta-acids or a hop oil extract. Ultra-pure preparations (>99% pure) were used to show that xanthohumol accounted for the antiviral activity observed in the xanthohumol-enriched hop extract against BVDV, HSV-1 and HSV-2. Xanthohumol was found to be a more potent antiviral agent against these viruses than the isomer iso-xanthohumol. With Rhino, the opposite trend was observed with iso-xanthohumol showing superior antiviral activity to that observed with xanthohumol. Xanthohumol also showed antiviral activity against CMV, suggesting that it might have a generalized anti-herpesvirus antiviral activity. Again, superior antiviral activity was observed with the xanthohumol isomer against CMV. In summary, iso-alpha-acids and xanthohumol were shown to have a low-to-moderate antiviral activity against several viruses. These hop constituents might serve as interesting lead compounds from which more active anti-HCV, anti-Rhino and anti-herpesvirus antiviral agents could be synthesized.

A TIBO derivative, R82913, is a potent inhibitor of HIV-1 reverse transcriptase with heteropolymer templates.

R82913, (+)-S-4,5,6,7-tetrahydro-9-chloro-5-methyl-6-(3-methyl-2-butenyl)- imidazo[4,5,1-jk][1,4]-benzodiazepin-2(1H)-thione (a TIBO derivative), inhibited the replication of thirteen different strains of HIV-1 in CEM cells with a median IC50 of 0.15 microM. The concentration of compound that killed 50% of the cells was much higher (46 microM), indicating that R82913 has a high selectivity index. R82913 was 20-fold more potent than AZT-TP in the inhibition of HIV-1 reverse transcriptase in an assay using a naturally occurring template (ribosomal RNA) that more accurately resembles native viral RNA than a synthetic homopolymer. With this template, R82913 inhibited HIV-1 reverse transcriptase with an ID50 (0.01 microM) that is equal to, or lower than, the IC50 for this compound in all of our cell culture assays (0.01-0.65 microM). R82913 has no effect on the replication of HIV-2 in CEM cells and does not inhibit the reverse transcriptase from this virus.

Michellamine B, a novel plant alkaloid, inhibits human immunodeficiency virus-induced cell killing by at least two distinct mechanisms.

Studies of the mechanism of action of michellamine B, a novel anti-human immunodeficiency virus (HIV) alkaloid from the tropical plant Ancistrocladus korupensis, have revealed that the compound acts at two distinct stages of the HIV life cycle. The compound had no direct effect on HIV virions and did not block the initial binding of HIV to target cells. Postinfection time course studies revealed that the agent partially inhibited HIV-induced cell killing and syncytium formation when added up to 48 h following acute infection; however, viral reproduction was fully inhibited only when the compound was added immediately after infection. Time-limited treatments of HIV-infected cells revealed that michellamine B had to be present continuously to provide maximum antiviral protection. HIV replication in cells in which infection was already fully established or in chronically infected cells was unaffected by michellamine B. Biochemical studies showed that michellamine B inhibited the enzymatic activities of reverse transcriptases (RTs) from both HIV type 1 and HIV type 2 as well as two different nonnucleoside drug-resistant RTs with specific amino acid substitutions. In addition, human DNA polymerases alpha and beta were inhibited by the alkaloid. Michellamine B exerted a potent dose-dependent inhibition of cell fusion in two independent cell-based fusion assays. Thus, michellamine B acts both at an early stage of the HIV life cycle by inhibiting RT as well as at later stages by inhibiting cellular fusion and syncytium formation.

Antireplicative and anticytopathic activities of prostratin, a non-tumor-promoting phorbol ester, against human immunodeficiency virus (HIV).

Prostratin, a non-tumor-promoting phorbol ester, inhibited human immunodeficiency virus (HIV)-induced cell killing and viral replication in a variety of acutely-infected cell systems. The potency and degree of cytoprotection was dependent on both viral strain and host cell type. Prostratin activated viral expression in two latently-infected cell lines, but had little or no effect on chronically-infected cell lines. Prostratin caused a dose-dependent, but reversible, decrease in CD4 expression in the CEM-SS and MT-2 cell lines. This down-regulation of CD4 was inhibited in a dose-dependent manner by the protein kinase C (PKC) antagonist, staurosporine. In addition, the cytoprotective and cytostatic effects of prostratin in CEM-SS cells acutely infected with HIV-1RF were reversed by bryostatin-1, a PKC agonist. Prostratin had no effect on reverse transcriptase or HIV-1 protease, nor did it inhibit the binding of gp120 to CD4. We conclude that prostratin inhibits HIV cytopathicity and replication through mechanism(s) involving PKC enzyme(s).

Identification of Novel Human Immunodeficiency Virus Type 1-Inhibitory Peptides Based on the Antimicrobial Peptide Database

ABSTRACT To identify novel anti-HIV-1 peptides based on the antimicrobial peptide database (APD; http://aps.unmc.edu/AP/main.php ), we have screened 30 candidates and found 11 peptides with 50% effective concentrations (EC50) of <10 μM and therapeutic indices (TI) of up to 17. Furthermore, among the eight peptides (with identical amino acid compositions but different sequences) generated by shuffling the sequence of an aurein 1.2 analog, two had a TI twice that of the original sequence. Because antiviral peptides in the database have an arginine/lysine (R/K) ratio of >1, increases in the Arg contents of amphibian maximin H5 and dermaseptin S9 peptides and the database-derived GLK-19 peptide improved the TIs. These examples demonstrate that the APD is a rich resource and a useful tool for developing novel HIV-1-inhibitory peptides.

Vaginal Microbicide Gel for Delivery of IQP-0528, a Pyrimidinedione Analog with a Dual Mechanism of Action against HIV-1

ABSTRACT Pyrimidinediones, a novel class of compounds, have previously been shown to possess antiviral activity at nanomolar concentrations. One member of this class of compounds, IQP-0528, was selected as the lead molecule for formulation development owing to its stability at physiologically relevant conditions, wide therapeutic window, and antiviral activity in the nanomolar range. Here, we report the development of two vaginal gels—3.0% hydroxyethyl cellulose (HEC) formulation and a 0.65% Carbopol formulation—for the sustained delivery of IQP-0528. Stability studies under accelerated conditions confirmed the chemical stability of IQP-0528 and mechanical stability of the gel formulation for 3 months. In vitro release studies revealed that diffusion-controlled release of IQP-0528 occurred over 6 h, with an initial lag time of approximately 1 h. Based on the drug release profile, the 3.0% HEC gel was selected as the lead formulation for safety and activity evaluations. The in vitro and ex vivo safety evaluations showed no significant loss in cell viability or significant inflammatory response after treatment with a 3.0% HEC gel containing 0.25% IQP-0528. In an in vitro HIV-1 entry inhibition assay, the lead formulation showed an 50% effective concentration of 0.14 μg/ml for gel in culture media, which corresponds to ∼0.001 μM IQP-0528. The antiviral activity was further confirmed by using polarized cervical explants, in which the formulation showed complete protection against HIV infection. In summary, these results are encouraging and warrant further evaluation of IQP-0528 gel formulations in in vivo models, as well as the development of alternative formulations for the delivery of IQP-0528 as a microbicide.

In vitro preclinical testing of nonoxynol-9 as potential anti-human immunodeficiency virus microbicide: a retrospective analysis of results from five laboratories.

ABSTRACT The first product to be clinically evaluated as a microbicide contained the nonionic surfactant nonoxynol-9 (nonylphenoxypolyethoxyethanol; N-9). Many laboratories have used N-9 as a control compound for microbicide assays. However, no published comparisons of the results among laboratories or attempts to establish standardized protocols for preclinical testing of microbicides have been performed. In this study, we compared results from 127 N-9 toxicity and 72 efficacy assays that were generated in five different laboratories over the last six years and were performed with 14 different cell lines or tissues. Intra-assay reproducibility was measured at two-, three-, and fivefold differences using standard deviations. Interassay reproducibility was assessed using general linear models, and interaction between variables was studied using step-wise regression. The intra-assay reproducibility within the same N-9 concentration, cell type, assay duration, and laboratory was consistent at the twofold level of standard deviations. For interassay reproducibility, cell line, duration of assay, and N-9 concentration were all significant sources of variability (P < 0.01). Half-maximal toxicity concentrations for N-9 were similar between laboratories for assays of similar exposure durations, but these similarities decreased with lower test concentrations of N-9. Results for both long (>24 h) and short (<2 h) exposures of cells to N-9 showed variability, while assays with 4 to 8 h of N-9 exposure gave results that were not significantly different. This is the first analysis to compare preclinical N-9 toxicity levels that were obtained by different laboratories using various protocols. This comparative work can be used to develop standardized microbicide testing protocols that will help advance potential microbicides to clinical trials.