Letermovir (AIC246) (AIC246) is a novel anti-CMV compound (EC50: about 5 nM in fibroblast cells). It targets the pUL56 subunit of the viral terminase complex.

HCMV:~5 nM (in fibroblast cells)

Letermovir的抑制效力在EC50s方面超过了ganciclovir (GCV) 400倍以上（平均约4.5 nM对比约2 μM），在EC90值方面超过了2000倍以上（平均约6.1 nM对比约14.5 μM）。在抗病毒测试期间，当Letermovir浓度<33 μM时，NHDF单层细胞未显示出在显微镜下可见的细胞毒性效应[1]。Letermovir对人类巨细胞病毒具有显著的特异性，因为在测试的其他所有疱疹病毒中均未注意到显著活性[2]。

Letermovir治疗导致移植细胞内HCMV滴度与安慰剂对照组相比呈剂量依赖性降低，使用的是小鼠异种移植模型。统计分析显示，Letermovir的10-, 30-, 和100-mg/kg/日治疗组以及100-mg/kg/日VGCV对照组均显著抗病毒效果[1]。与安慰剂相比，letermovir的预防失败率为60 mg/日剂量时为48%，120 mg剂量时为32%，240 mg剂量时为29%。Kaplan-Meier预防失败的起始时间曲线对于每日240 mg剂量的letermovir与安慰剂的比较显示出显著差异[3]。

Briefly, 96-well microtiter plates were seeded with 1.5 × 10^4 cells/well and incubated overnight. Drugs were added to the wells in 3-fold serial dilutions starting from 0.33 mM (the DMSO concentration was kept constant at 0.66% throughout the whole plate). After a 7-day incubation period, alamarBlue solution was added to each well and the fluorescence signal was measured using a SpectraFluor Plus fluorescence reader. The relative fluorescence units of treated wells were expressed as percentages of untreated cell control wells and plotted against the logarithm of drug concentrations. Drug concentrations reducing cell viability by 50% (CC50s) were determined from dose-response curves. The assays were performed at least three times with duplicate samples. CC50 values were used to calculate the selectivity index (SI = CC50/EC50) for individual substances [1].

Briefly, Gelfoam hemostyptic gelatin devices were cut aseptically into 1-cm2 pieces. These implants were soaked in NHDF cell culture growth medium (GM), and sponges were brought to 37°C in a CO2 incubator. NHDF cells were infected with cell-free HCMV strain Davis at an MOI of 0.03. After 4 h, cells were collected by trypsinization followed by centrifugation at room temperature for 10 min at 800 × g. Cells were resuspended in GM and counted using a hemocytometer. Each Gelfoam implant was seeded with a suspension of 1 × 10^6 infected cells by pipetting the cells onto the sponges. Human cells were allowed to adhere to the collagen sponges for at least 3 to 4 h at 37°C. To enhance vascularization of the implant, 250 ng recombinant human basic fibroblast growth factor was pipetted onto each implant 1 h prior to transplantation. Mice (18 to 25 g body weight) were anesthetized, and the Gelfoam sponges were implanted subcutaneously in the dorsoscapular area. After transplantation, mice were randomized and grouped in ～10 animals per treatment group. Starting 4 h after transplantation, mice were treated once daily with the indicated compounds for nine consecutive days. Drugs were applied per os by oral gavage. Total administration volume was 10 ml/kg. Mice were sacrificed after 9 days of treatment, and the Gelfoam implants were removed and digested with collagenase at 37°C. After 2 to 3 h, human cells were recovered by centrifugation and resuspended in GM. Subsequently, the isolated cell suspensions were serially diluted and mixed with uninfected NHDF indicator cells and PFU were determined by plaque assays. Virus titers determined from isolated cells are given as PFU/ml [1].