AIC246, also known as letermovir, is a novel anti-CMV compound with IC50 value of 5.1 ± 1.2 nM. It targets the pUL56 (amino acid 230-370) subunit of the viral terminase complex [1].The subunit pUL56 is a component of the terminase complex which is responsible for packaging unit length DNA into assembling virions.AIC246 has a novel mode of action targets the enzyme UL56 terminase and keep active to other drug-resistant virus. The anti-HCMV activity of AIC246 was evaluated in vitro by using different HCMV laboratory strains, GCV-resistant viruses. The result showed that the inhibitory potentcy of AIC246 surpasses the current gold standard GCV by more than 400-fold with respect to EC50s (mean, ∼4.5 nM versus ∼2 μM) and by more than 2,000-fold with respect to EC90 values (mean, ∼6.1 nM versus ∼14.5 μM). In the CPE-RA strains, the EC50 values of AIC 246 ranged from 1.8 nM to 6.1 nM [2]. In mouse model with HCMV subcutaneous xenograft, oral administration of AIC246 caused significant a dose-dependent reduction of the HCMV titer. 30 mg/kg/d AIC246 for 9 days induced PFU reduction with maximum efficiency, compared with the gold standard GCV at the ED50 and ED90 level [2].References: [1].Verghese PS, Schleiss MR. Letermovir Treatment of Human Cytomegalovirus Infection Anti-infective Agent. Drugs Future. 2013, 38(5):291-298.[2]. Lischka P1, Hewlett G, Wunberg T, et al.In vitro and in vivo activities of the novel anticytomegalovirus compound AIC246.Antimicrob Agents Chemother. 2010, 54(3):1290-1297.