Herpes simplex virus type 1 variants arising after selection with an antiviral carrageenan: Lack of correlation between drug susceptibility and syn phenotype

Abstract

Natural carrageenans of diverse structural types isolated from the red seaweed Gigartina skottsbergii have been recently identified as potent and selective inhibitors of herpes simplex virus (HSV) types 1 and 2. The m/n carrageenan 1C3 was tested in vitro for its ability to select resistant variants. After serial passages of HSV-1 strain F in Vero cells in the presence of increasing concentrations of 1C3, there emerged viruses which were approximately 2-10 fold more resistant to 1C3 inhibition than parental virus and formed large plaques with an altered syncytial phenotype (1C3-syn). Plaque-purified syncytial variants isolated from passages 13 and 14 have shown variable levels of resistance to 1C3 as well as to the other antiviral carrageenans isolated from G. skottsbergii, and to other sulfated polysaccharides with known antiviral activity, such as heparin and dextran sulfate 8000, but all the clones were susceptible to acyclovir. The syn phenotype was not related to polysaccharide-resistance. All the 1C3-syn variants formed large syncytia in Vero and CV-1 cells, but did not induce fusion in other cell types. The growth efficiency in Vero cells as well as the virulence for mice by intracerebral or intraperitoneal inoculation of 1C3-syn variants showed no significative alterations in comparison to the parental virus. The syncytial properties were not affected by cyclosporin A or melittin, suggesting that an alteration on glycoprotein gB could be responsible of the syn phenotype induced by 1C3.