Potent Inhibition of Herpes Simplex Virus by MDL 101028,a Novel Biphenyl Disulfonic Acid Urea Co-Polymer

A novel low-molecular-weight sulfonic acid polymer, MDL 101028, was investigated for antiviral activity against herpes simplex virus (HSV) type 1 and type 2 in human embryonic diploid fibroblasts (MRC-5) and in a line of monkey kidney cells (Vero). Potent antiviral activities were obtained when treatment was restricted to the adsorption phase of virus propagation as measured by plaque reduction assay, and this was confirmed by experiments at high multiplicity of infection. Inhibition of virus binding to host cells by MDL 101028 was compared to that of heparin, a known antagonist of virus attachment. Both compounds showed dose-dependent inhibition, with IC₅₀ values of 1.1 and 0.43 μg ml⁻¹, respectively. The effect on cell-to-cell fusion was investigated using a syncytial-positive (syn⁺) phenotypic mutant of HSV-1 (strain 17i). MDL 101028 (3-1 μm) dramatically halted the spread of syncytial lesions; this effect was accompanied by the destruction of the syncytium and regrowth into the lesion by uninfected Vero cells. In contrast, heparin (10 μg ml⁻¹) only partially reduced the spread of syncytia. Protection was also observed with MDL 29797 (100 μg ml⁻¹), an antagonist of glycoprotein maturation. Unexpectedly, only a marginal effect was observed with acyclovir (10 μg ml⁻¹), a potent inhibitor of viral DNA synthesis and HSV growth. As an extension to the current therapy for herpes simplex infection, acyclovir, the potent anti-fusion activity of MDL 101028 may have a clinical use in tissues or organs in which cell-to-cell fusion contributes to the pathology.