Fattiviracins, Antiviral Antibiotics Produced by an Actinomycete

Most of the successes in the development of antivirals active against herpes viruses have been achieved with synthetic nucleoside analogues. It is well known that a synthetic chemotherapeutic agent, acyclovir, studied by Elion et al.1, 2), (awarded the Nobel Prize in the field of Physiology or Medicine, 1988), is the best medicine for herpes virus infections. Acyclovir has virus-specific activation in virus-infected cells and its activated form inhibits viral DNA replication through obligate chain termination. The remarkable characteristic of acyclovir is its lack of effect on uninfected cells. This lack of cytotoxicity has subsequently translated into an outstanding safety profile in the clinic. Over the past 20 years acyclovir has become the drug of choice for the treatment and suppression of herpes infections. Why could microorganisms including actinomycetes not produce the valuable antiviral antibiotics? Recently, new antiviral agents produced by actinomycetes, which are effective for herpes virus or human immunodeficiency virus, have been found: cycloviracins B1 and B2, and fattiviracins having the macrocyclic dilactones formed by the binding of two trihydroxy fatty acids and two D-glucose residues in the molecules. The author will introduce the antiviral antibiotics, mainly fattiviracins, that were isolated and studied in our laboratories. Cycloviracins3-5) The cycloviracin-producing strain, Kibdelosporangium albatum No. R761-7 (ATCC 55061), was isolated from a soil sample collected in Mindanao Island, the Philippines. A complex of new antibiotics was extracted from the fermentation broth with 1-butanol, and purified by column chromatographies on silica gel, reversed phase C18, preparative HPLC and Sephadex LH-20. Two major components, cycloviracins B1 and B2, have been isolated from the complex. They were soluble in methanol, pyridine and dimethyl sulfoxide, slightly soluble in ethyl acetate and acetone, but practically insoluble in n-hexane, chloroform and water. Their structures have been determined by chemical and spectroscopic methods including 2D NMR correlation spectroscopy. The antibiotics are unique macrocyclic diesters consisting of two D-glucoses, three 2-O-methyl-D-glucoses and two (C24 and C26) hydroxy fatty acids (Fig. 1). Antiviral activity of cycloviracins B1 and B2 was evaluated by the dye uptake6) and the plaque reduction assay7) using herpes simplex virus type 1 (HSV-1) (KOS strain) infection in Vero cells (a cell line of kidney from African green monkey). In the dye uptake assay, 200 μl of the Vero cell suspension containing 1.6 × 104 cells was poured into each well of 96-well microplates, and then 50 μl of a medium containing a test compound at various concentrations was added to each well. The viral suspension (50 μl) containing approximately 30 × TCID50 was inoculated at 37 °C for 72 hr under a 5% CO2 in humidified air environ-