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Vaginal microbicides that reduce or eliminate the risk of HIV-1 sexual transmission must do so safely without adversely affecting the integrity of the cervicovaginal epithelium. The present studies were performed to assess the safety of the biguanide-based antiviral compound NB325 in a formulation suitable for topical application. Experiments were performed using a mouse model of cervicovaginal microbicide application, which was previously shown to be predictive of topical agent toxicity revealed in microbicide clinical trials. Mice were exposed vaginally to unformulated NB325 or NB325 formulated in the hydroxyethyl cellulose “universal placebo.” Following exposures to formulated 1% NB325 for 10 min to 24 h, the vaginal and cervical epithelia were generally intact, although some areas of minimal vaginal epithelial damage were noted. Although formulated NB325 appeared generally safe for application in these studies, the low but observable level of toxicity suggests the need for improvements in the compound and/or formulation.

Polyhexamethylene biguanide (PHMB) is a polybiguanide (PBG) oligomer with antimicrobial activity that is used extensively and safely as a disinfectant. The reported mechanism of PHMB antimicrobial activity, which involves interactions with cell membrane components, suggested that PHMB or other PBG-based compounds might also have antiviral or virucidal activity against the human immunodeficiency virus type 1 (HIV-1). PHMB had modest in vitro activity against both cell-free and cell-associated HIV-1, as well as the ability to interfere with viral binding and entry. However, PHMB was comparable in cytotoxicity to the spermicidal agent nonoxynol-9 (N-9), a compound that has been characterized in previous studies as generally cytotoxic and detrimental to cervicovaginal epithelial integrity. To identify structural variants of PHMB with greater anti-HIV-1 activity and/or less cytotoxicity, modified versions of PHMB incorporating length changes in the hydrocarbon linker units were synthesized and evaluated for in vitro cytotoxicity and inhibition of HIV-1 infectivity. These experiments demonstrated that the PHMB variant polyethylene hexamethylene biguanide (PEHMB) was just as active against HIV-1 as PHMB, yet was much less cytotoxic than either N-9 or PHMB, resulting in an in vitro therapeutic index (TI) approximately 114-fold greater than the TI of N-9. PEHMB, which has been identified in these studies as a promising microbicidal candidate in this family of compounds, will be the focus of further in vitro and in vivo evaluations of anti-HIV-1 activity, toxicity, and mechanisms of action.

Previously, we have described inhibition of HIV-1 infection by T30177, 5'-(GTGGTGGGTGGGTGGGT)-3', an oligonucleotide that is a potent inhibitor of HIV-1 integrase in vitro (Mazumder et al. (1996) Biochemistry 35, 13762). Here a family of oligonucleotides, analogs of T30177, has been studied. On the basis of thermal denaturation, we show that a folded structure of T30177 is much more stable than that of the thrombin binding aptamer, which only differs with T30177 in the loop sequence. Sequence changes reveal that loop interactions are solely responsible for this observed stability difference. In the presence of K+ ion, the fold of T30695, a designed 16mer derivative, is indeed more stable than T30177. Loop folding within T30695 is very ion selective. Quantitative analysis of thermal denaturation suggests that the loops of T30695, 5'-(GGGTGGGTGGGTGGGT)-3', and T30177 confer the ability to coordinate three equivalents of K+ ion (one bound to the core octet and two bound to the loops); however, the thrombin binding aptamer is shown to bind only one K+ equivalent. Folding kinetics and CD titration demonstrate that K+-induced folding of T30695 and T30177 is a two-step process, consistent with a sequential model in which a first equivalent of K+ binds to the octet core, followed by slow K+-induced rearrangement of the loop domains. Comparing structural stability with the capacity of the folded oligomers to inhibit the HIV-1 integrase enzyme in vitro or HIV-1 infection in cell culture, we have found that the folding and activity data are highly correlated, suggesting that formation of an orderly, ion-coordinated loop structure similar to that in T30177 or T30695 may be a prerequisite for both integrase inhibition and anti-HIV-1 activity.

Antisense oligonucleotides directed against HSV- 1 immediate early gene mRNA were synthesized with replacement of the internal pyrimidine nucleotides by the corresponding 5-(l-hexynyl) analogues and with end-capping by phosphorothioates. These compounds were found to have improved binding affinity, increased stability towards nucleases and enhanced antiviral activity in a cell culture assay.

An alternating copolymer of styrene and maleic acid (alt-PSMA) differs from other polyanionic antiviral agents in that the negative charges of alt-PSMA are provided by carboxylic acid groups instead of sulfate or sulfonate moieties. We hypothesized that alt-PSMA would have activity against human immunodeficiency virus type 1 (HIV-1) comparable to other polyanions, such as the related compound, poly(sodium 4-styrene sulfonate) (PSS). In assays using cell lines and primary immune cells, alt-PSMA was characterized by low cytotoxicity and effective inhibition of infection by HIV-1 BaL and IIIB as well as clinical isolates of subtypes A, B, and C. In mechanism of action assays, in which each compound was added to cells and subsequently removed prior to HIV-1 infection (“washout” assay), alt-PSMA caused no enhancement of infection, while PSS washout increased infection 70% above control levels. These studies demonstrate that alt-PSMA is an effective HIV-1 inhibitor with properties that warrant further investigation.

Microbicides, which are products capable of reducing or eliminating the risk of HIV-1 sexual transmission, are urgently needed to combat the global spread of HIV-1. Our efforts in this area are focused on the preclinical development of the polybiguanide, PEHMB (polyethylene hexamethylene biguanide). PEHMB has been shown to have low cytotoxicity both in vitro and in vivo, as well as in vitro activity against both cell-free and cell-associated forms of HIV-1. Flow cytometric analyses have shown that PEHMB exposure results in epitope-specific alterations in the detection of viral co-receptors CXCR4 and CCR5, suggesting that PEHMB acts by interfering with events critical to viral binding and entry. Changes in co-receptor detection have also been observed up to 24 hr after removal of PEHMB. Consistent with the latter result was the demonstration of persistent protection from infection in experiments in which cells were challenged with HIV-1 after removal of PEHMB. Cumulatively, these results suggest that HIV-1 co-receptors may play roles in PEHMB-mediated protection from HIV-1 infection, and that products containing PEHMB may provide both shortand longterm protection against HIV-1 transmission. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005

Topical microbicides that reduce or eliminate the risk of human immunodeficiency virus type 1 (HIV-1) sexual transmission must function effectively within the cervicovaginal environment where multiple factors may impact the efficacy of the active agent. Factors relevant to potential changes in microbicide efficacy include the presence of mucins within the cervical mucus. We hypothesize that polycationic PEHMB molecules will interact with the anionic mucin molecules to form a lattice-like network that serves as a physical barrier to the movement of infectious virus and HIV-1-infected cells to the cervical and vaginal epithelia. In vitro experiments demonstrated that the anti-HIV-1 activity of PEHMB was increased almost two logs in the presence of mucin. In contrast, the activity of anionic dextran sulfate was unaffected. These results suggest that electrostatic interactions between PEHMB and mucin molecules may augment the inherent antiHIV-1 activity of PEHMB by facilitating the formation of a physical barrier between HIV-1 and susceptible cells. This property would be expected to increase the in vivo efficacy of PEHMB. from 2005 International Meeting of The Institute of Human Virology Baltimore, USA, 29 August – 2 September 2005

The 1-[(Z)-2-penten-1-yl] and 1-(3-methyl-2-buten-1-yl) derivatives of cytosine, 5-bromocytosine, 5-fluorocytosine, and 5-iodocytosine were prepared by a reaction of the sodium salt of the requisite cytosine with (Z)-1-bromo-2-pentene and 4-bromo-2-methyl-2-butene, respectively. The eight alkenylcytosines 5a-5h were evaluated in cell culture for their anti-HCMV activity. Only the derivatives of 5-bromocytosine, 5c and 5d, showed slight activity in this assay.

The gene of the human cytomegalovirus (HCMV) major envelope glycoprotein, gB, was cloned from the Towne strain and inserted into adenovirus type 5 downstream of the E3 promoter. The recombinant virus, Ad-gB, expressed antigenically related proteins of 58, 30, 25, and 23 kDa in A549 and MRC-5 cells; the 58-kDa protein had the same mobility as the native gB from HCMV-infected MRC-5 cells and virions. All four proteins were detected by a monospecific polyclonal antiserum and by a monoclonal antibody in immunoblot and immunofluorescence assays. Hamsters infected intranasally with live Ad-gB developed protein-specific and HCMV-neutralizing antibody. This study confirms the importance of gB in the generation of the neutralizing immune response to HCMV and demonstrates the potential of live adenoviruses as vaccine vectors.