Background
MDL-001 is a first-in-category oral direct-acting non-nucleoside inhibitor that binds a previously underexploited allosteric pocket in the Thumb-1 domain of viral polymerase. We assessed inhibition of hepatitis C virus (HCV) and hepatitis B virus (HBV) in mono- and co-infection in vitro, established HCV and HBV proof-of-concept (POC) in vivo, and summarized nonclinical pharmacokinetic (PK) and safety data supporting clinical translation.
Methods
HCV activity was measured in genotype 1b Con1 (Huh-luc/neo-ET) and genotype 2a JFH1 (Huh7.5.1) subgenomic replicons. HBV (AD38 ayw) activity was measured in HepAD38 cells, and HCV JFH1/HBV AD38 ayw co-infection was assessed in Huh7.5.1 cells. In vivo efficacy was evaluated in humanized MUP-uPA-SCID/Beige mice infected with HCV (JFH1/J6) or HBV (AD38). Resistance was selected by 8 weeks of serial passaging in an HCV replicon and characterized by genomic profiling. PK and safety data were compiled from completed nonclinical studies.
Results
MDL-001 inhibited HCV mono-infection in vitro with EC50/90 values of 164/460 nM and 72/300 nM in the Con1 and JFH1 replicons, respectively, and inhibited HBV mono-infection with an EC50/90 of 52/88 nM. MDL-001 suppressed an in vitro HCV and HBV co-infection model at similar potencies. In vivo, oral MDL-001 reduced plasma HCV RNA by 3.27 ± 0.12 log10 on day 28 compared to the vehicle, achieving an efficacy equivalent to that of sofosbuvir, with both treatments achieving viral load levels within the assay’s limit of detection. In vivo, oral MDL-001 reduced plasma HBV rcDNA by 1.8 log10 on day 28. Pharmacokinetic studies demonstrated Cmax and C24 drug liver tissue concentrations far in excess of EC90s. An 8-week HCV resistance-mutation study yielded three MDL-001-resistant colonies with a convergent P495S mutation in the NS5B Thumb-1 domain. Safety data from more than 400 animals dosed in vivo at up to 16-fold the minimum efficacious dose (1.0 log10 plasma viral load reduction in HCV) in a single-dose study and 6-fold the minimum efficacious dose at 28 days reported no observed adverse events.
Conclusions
MDL-001 targets a Thumb-1 cryptic allosteric site present across RNA-dependent viral polymerases and delivers dual preclinical efficacy against HCV and HBV, including co-infection, with a PK/safety profile consistent with oral dosing. These data support completion of IND-enabling studies and clinical evaluation in chronic hepatitis B and C, including coinfected cohorts.
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