Cell experiment:

ALS-8112 and its prodrug ALS-8176 are stored at 4℃ in dimethyl sulfoxide (DMSO), and diluted in water. HEp-2 cells per well are plated in a 96-well plate. Each compound is serially diluted (1:3) up to 9 distinct concentrations. Cells are pre-incubated with compounds for 24 hours at 37℃ in a 5% CO2 atmosphere. After 24 hours of pre-incubation with compounds, RSV A2, Long, or B1 at a multiplicity of infection (MOI) of 0.5 is added to the cells, except for the background controls. The plate is then incubated for additional 4 days in the same conditions and at the end of the incubation 50 μL the supernatant from each well of the plate is collected[4].

ALS-8112 is a potent and selective respiratory syncytial virus (RSV) polymerase inhibitor. The 5'-triphosphate form of ALS-8112 inhibits RSV polymerase with an IC50 of 0.02 μM.

The 5'-triphosphate form of ALS-8112 (ALS-8112-TP) is the active form of the drug and selectively inhibits RSV polymerase through chain termination of RNA synthesis[2]. ALS-008112 enters various types of epithelial cells in the respiratory tract and is subsequently phosphorylated to form an intracellular nucleoside triphosphate with a half-life of approximately 29 hours. The nucleoside triphosphate analogue inhibits RSV replication by means of chain termination[3]. ALS-8112 is a pan-strain inhibitor of RSV replication in vitro. The RNA transcription activity of the RSV-RNP complex is dose-proportionally inhibited by ALS-8112-TP with an IC50 of 0.020 ± 0.008 μM[4].

[1]. Wang G, et al. Discovery of 4'-chloromethyl-2'-deoxy-3',5'-di-O-isobutyryl-2'-fluorocytidine (ALS-8176), a first-in-class RSV polymerase inhibitor for treatment of human respiratory syncytial virus infection. J Med Chem. 2015 Feb 26;58(4):1862-78. [2]. Jordan PC, et al. Activation Pathway of a Nucleoside Analog Inhibiting Respiratory Syncytial Virus Polymerase. ACS Chem Biol. 2017 Jan 20;12(1):83-91. [3]. DeVincenzo JP, et al. Activity of Oral ALS-008176 in a Respiratory Syncytial Virus Challenge Study. N Engl J Med. 2015 Nov 19;373(21):2048-58. [4]. Deval J, et al. Molecular Basis for the Selective Inhibition of Respiratory Syncytial Virus RNA Polymerase by 2'-Fluoro-4'-Chloromethyl-Cytidine Triphosphate. PLoS Pathog. 2015 Jun 22;11(6):e1004995.