Interaction of herpes simplex virus with cell surface glycosaminoglycans as a target for antiviral intervention
Sammanfattning: Herpes simplex virus (HSV) infections in humans are predominantly manifested as oral cold sores or genital ulcers. As HSV infects cells by interaction with cell surface heparan sulfate (HS) and/or chondroitin sulfate (CS), the aim of the research work presented in this thesis was to explore the possibility of antiviral intervention with compounds that mimic HS or CS. Three structurally distinct compounds were found to target this step of HSV-cell interaction thus preventing the HSV infection of cells. These include (i) the low molecular weight HS-mimetic PI-88, (ii) CS type E (CS-E) derived from squid cartilage, and (iii) the monosulfated cyclitol SC1. PI-88 is a mixture of highly sulfated mannose-containing di- to hexa-saccharides that was previously explored as an anti-cancer drug. In this thesis PI-88 was found to be a potent inhibitor of the cell-to-cell spread of HSV. This feature of the virus is essential for the development of both viral plaques in cell cultures and of oral or genital lesions in humans. One structural feature of PI-88, its low molecular weight, was found to be important for the antiviral properties as PI-88 but not the high molecular weight HS-mimetic heparin could inhibit the cell-to-cell spread of HSV. The antiviral activity of PI-88 is very likely due to its ability to access the narrow intercellular space where PI-88 was demonstrated to block the interaction of viral envelope glycoproteins gB, gC, and gD with cellular HS.Although cell surface CS is regarded as an auxiliary receptor for HSV and purified preparations of CS types A, B, and C are known to be poor inhibitors of HSV invasion of cells, in this thesis it was found that CS type E, from squid cartilage, was one of the most potent inhibitors of initial virus adherence to cultured cells. The concentrations of CS-E that inhibited the virus infectivity by 50% (IC50) were approximately 0.1 µg/ml in normal cells, and <1 ng/ml in mutant CS-expressing cells. In addition, because disaccharide analysis of CS forms found on the cell surface revealed the presence of E disaccharide units, CS-E may block HSV invasion of cells by interference with the virus binding to the E unit of the cell surface CS.By screening for the anti-HSV activity of a mini-library of 96 compounds, previously synthesized to search for inhibitors of protein-HS interaction, a monosulfated cyclitol molecule designated SC1 was discovered to completely inhibit HSV infectivity in cultured cells. SC1 was found to target and to inactivate the viral particle. Complete inactivation of HSV type 1 and type 2 particles occurred within 5 min at 37°C and 15 30 min at 37°C respectively. In addition SC1, in contrast to some other virus-inactivating agents, exhibited substantial selectivity in its antiviral action as the concentration of SC1 that was toxic for cells was at least fifty fold higher than the virus-inactivating doses. The anti-HSV activity of SC1 was found to be due to the inactivation of viral components other than those required for the virus attachment to cells.In conclusion three novel antivirals, discovered and described in this thesis, are proposed as candidate compounds for prevention and/or treatment of HSV infections in humans.
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