We have isolated and sequenced a novel 11-kDa virucidal protein, named cyanovirin-N (CV-N), from cultures of the cyanobacterium (blue-green alga) Nostoc ellipsosporum. We also have produced CV-N recombinantly by expression of a corresponding DNA sequence in Escherichia coli. Low nanomolar concentrations of either natural or recombinant CV-N irreversibly inactivate diverse laboratory strains and primary isolates of human immunodeficiency virus (HIV) type 1 as well as strains of HIV type 2 and simian immunodeficiency virus. In addition, CV-N aborts cell-to-cell fusion and transmission of HIV-1 infection. Continuous, 2-day exposures of uninfected CEM-SS cells or peripheral blood lymphocytes to high concentrations (e.g., 9,000 nM) of CV-N were not lethal to these representative host cell types. The antiviral activity of CV-N is due, at least in part, to unique, high-affinity interactions of CV-N with the viral surface envelope glycoprotein gp120. The biological activity of CV-N is highly resistant to physicochemical denaturation, further enhancing its potential as an anti-HIV microbicide.

Eight new coumarin compounds (1-8) were isolated by anti-HIV bioassay-guided fractionation of an extract of Calophyllum lanigerum. The structures of calanolide A (1), 12-acetoxycalanolide A (2), 12-methoxycalanolide A (3), calanolide B (4), 12-methoxycalanolide B (5), calanolide C (6) and related derivatives 7 and 8 were solved by extensive spectroscopic analyses, particularly HMQC, HMBC, and difference NOE NMR experiments. The absolute stereochemistry of calanolide A (1) and calanolide B (4) was established by a modified Mosher's method. Calanolides A (1) and B (4) were completely protective against HIV-1 replication and cytopathicity (EC50 values of 0.1 microM and 0.4 microM, respectively), but were inactive against HIV-2. Some of the related compounds also showed evidence of anti-HIV-1 activity. Studies with purified bacterial recombinant reverse transcriptases (RT) revealed that the calanolides are HIV-1 specific RT inhibitors. Moreover, calanolide A was active not only against the AZT-resistant G-9106 strain of HIV-1 but also against the pyridinone-resistant A17 strain. This was of particular interest since the A17 virus is highly resistant to previously known HIV-1 specific, non-nucleoside RT inhibitors (e.g., TIBO; BI-RG-587; L693,593) which comprise a structurally diverse but apparently common pharmacologic class. The calanolides represent a substantial departure from the known class and therefore provide a novel new anti-HIV chemotype for drug development.

Celite and rinsed with 1.0 mL of dichloromethane, 1.0 mL of ethyl acetate, 12 mL of dichloromethane with 2% acetic acid, and 10 mL of ethyl acetate with 1% acetic acid. The filtrate was concentrated in vacuo to give a brown solid. The residue was chromatographed over 0.6 g of silica gel (eluted with ethyl acetate-hexane, 1:5 progressing to 1:1, and then with ethyl acetate-hexane-acetic acid, 66:31:2) to give 2.9 mg (32%) of pleurotin (1) as a pale yellow solid:

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The solution structure of cyanovirin-N, a potent 11,000 Mr HIV-inactivating protein that binds with high affinity and specificity to the HIV surface envelope protein gp120, has been solved by nuclear magnetic resonance spectroscopy, including extensive use of dipolar couplings which provide a priori long range structural information. Cyanovirin-N is an elongated, largely beta-sheet protein that displays internal two-fold pseudosymmetry. The two sequence repeats (residues 1-50 and 51-101) share 32% sequence identity and superimpose with a backbone atomic root-mean-square difference of 1.3 A. The two repeats, however, do not form separate domains since the overall fold is dependent on numerous contacts between them. Rather, two symmetrically related domains are formed by strand exchange between the two repeats. Analysis of surface hydrophobic clusters suggests the location of potential binding sites for protein-protein interactions.

An extract from Phyllanthus engleri was identified in a bioinformatic analysis of NCI 60-cell natural product extract screening data, that selectively inhibited the growth of renal cancer cell lines. Bioassay guided fractionation yielded two new guaiane sesquiterpenes, englerins A (1) and B (2). Englerin A showed 1000-fold selectivity against 6 of 8 renal cancer cell lines with GI50 values ranging from 1-87 nM. The structures of 1 and 2 and their relative stereochemistry were established by spectroscopic methods.

The cyanobacterial protein cyanovirin-N (CV-N) potently inactivates diverse strains of HIV-1 and other lentiviruses due to irreversible binding of CV-N to the viral envelope glycoprotein gp120. In this study, we show that recombinant CV-N effectively blocks HIV-1(Ba-L) infection of human ectocervical explants. Furthermore, we demonstrate the in vivo efficacy of CV-N gel in a vaginal challenge model by exposing CV-N-treated female macaques (Macaca fascicularis) to a pathogenic chimeric SIV/HIV-1 virus, SHIV89.6P. All of the placebo-treated and untreated control macaques (8 of 8) became infected. In contrast, 15 of 18 CV-N-treated macaques showed no evidence of SHIV infection. Further, CV-N produced no cytotoxic or clinical adverse effects in either the in vitro or in vivo model systems. Together these studies suggest that CV-N is a good candidate for testing in humans as an anti-HIV topical microbicide.