GS-9191 is a potent inhibitor of DNA polymerase alpha and ß , a prodrug of the novel nucleoside analogue 9-(2-phosphonomethoxyethyl)guanine (PMEG) , which penetrates the skin and is metabolized in the epithelium to an active nucleoside triphosphate analogue.GS-9191 has antiproliferative activity and reduces the size of papillomas in a dose-related manner.GS-9191 may be useful in the treatment of HPV-induced lesions.

GS-9191 was markedly more potent than PMEG or cPrPMEDAP in a series of human papillomavirus (HPV)-positive cell lines, with effective concentrations to inhibit 50% cell growth (EC(50)) as low as 0.03, 207, and 284 nM, respectively. In contrast, GS-9191 was generally less potent in non-HPV-infected cells and primary cells (EC(50)s between 1 and 15 nM). DNA synthesis was inhibited by GS-9191 within 24 h of treatment; cells were observed to be arrested in S phase by 48 h and to subsequently undergo apoptosis (between 3 and 7 days).[2]
In an animal model (cottontail rabbit papillomavirus), topical GS-9191 was shown to decrease the size of papillomas in a dose-related manner. At the highest dose (0.1%), cures were evident at the end of 5 weeks, and lesions did not recur in a 30-day follow-up period. These data suggest that GS-9191 may have utility in the treatment of HPV-induced lesions.[2]