Prophylactic Antiheparanase Activity by PG545 Is Antiviral In Vitro and Protects against Ross River Virus Disease in Mice

Recently we reported on the efficacy of pentosan polysulfate(PPS), a heparan sulfate mimetic, to reduce the recruitment of inflammatory infiltrates and protect the cartilage matrix from degradation in Ross River virus(RRV) infected PPS--treated mice. Herein, we describe both prophylactic and therapeutic treatment with PG545, a low molecular weight heparan sulfate mimetic, for arthritogenic alphaviral infection. We first assessed anti-viral activity, through a 50% plaque reduction (IC) assay. Increasing concentrations of PG545, inhibited plaque formation prior to viral adsorption in viral strains; RRV T48, Barmah forest virus2193 (BFV 2193), chikungunyaEast/Central/South African virus (CHIKV ESCA) and CHIKV Asian strain, suggesting a strong anti-viral mode of action. The viral particle--compound dissociation constant (K) was then evaluated through isothermal titration calorimetry(ITC). Furthermore, prophylactic RRV-infected PG545-treated mice had reduced viral titres in target organs corresponding to lower clinical scores of limb weakness and immune infiltrate recruitment. At peak disease, PG545-treated RRV-infected mice had lower concentrations of the matrix degrading enzyme heparanase(HPSE) in conjunction with a protective effect on tissue morphology as seen in the histopathology of skeletal muscle. ELISA quantification of cartilage oligomeric matrix protein(COMP) and crosslinked C-telopeptidesof type II collagen(CTX-II) and knee histopathology showed increased matrix protein degradation and cartilage erosion in RRV-infected PBS-treated mice in comparison to their PG545-treated RRV infected counterparts. Taken together these findings suggest that PG545 may have a both a direct anti-viral effect on arthritogenic alphaviral infection, as well curtailing RRV-induced inflammatory disease when administered as a prophylaxis.