Sulfated K5 Escherichia coli polysaccharide derivatives as wide range inhibitors of genital types of human papillomavirus

Department of Clinical and Biological Sciences, University of Turin, S. Luigi Gonzaga Hospital, 10043, Orbassano, Turin, Italy; Department of Biomedical Sciences and Biotechnology, University of Brescia, 25123 Brescia, Italy; Department of Medicine and Experimental Oncology, University of Turin, 10125 Turin, and Center for Experimental Research and Medical Studies (CERMS), San Giovanni Battista Hospital, 10126-Turin, Italy; Glycores 2000 S.r.l. 20155 Milan, Italy; Department of Public Health and Microbiology, University of Turin, 1026 Turin, Italy

^* To whom correspondence should be addressed. Email: david.lembo{at}unito.it.

	Abstract

Genital human papillomaviruses (HPV) represent the most common sexually transmitted agents and are classified into low or high risk by their propensity to cause genital warts or cervical cancer respectively. Topical microbicides against HPV may be a useful adjunct to the newly licensed HPV vaccine. A main objective in the development of novel microbicides is to block HPV entry into epithelial cells through cell-surface heparan sulfate proteoglycans. In this study, selective chemical modification of the Escherichia coli K5 capsular polysaccharide was integrated with innovative biochemical and biological assays, to prepare a collection of sulfated K5 derivatives with a backbone structure resembling the heparin/heparan biosynthetic precursor and to test them for their anti-HPV activity. Surface plasmon resonance assay revealed that O-sulfated K5 with high sulfation degree (K5-OS(H)) and N,O-sulfated K5 with high (K5-N,OS(H)) or low (K5-N,OS(L)) sulfation degree, but not unmodified K5, N-sulfated K5 and O-sulfated K5 with low sulfation degree, prevented the interaction between HPV-16 pseudovirions and immobilized heparin. In cell-based assays, K5-OS(H), K5-N,OS(H) and K5-N,OS(L) inhibited HPV-16, HPV-18 and HPV-6 pseudovirions infection. Their 50% inhibitory concentration was between 0.1 and 0.9 µg/ml, without evidence of cytotoxicity. These findings provide insights into the design of novel, safe and broad-spectrum microbicides against genital HPV infections.