P-1169. Obeldesivir and GS-441524 Antiviral Activity against L Protein Mutants in Respiratory Syncytial Virus (RSV) Minigenome and Recombinant Infectious Virus Systems

TL;DR

This study evaluates how well two antiviral drugs, Obeldesivir and GS-441524, work against mutations in the RSV virus's L protein, suggesting they are effective with a high resistance barrier.

Contribution

The study introduces a new optimized RSV minigenome system to assess drug susceptibility against L polymerase mutations.

Findings

Most L polymerase mutations showed similar susceptibility to GS-441524 and Obeldesivir as the wild-type virus.

The I777L mutation caused low-level resistance to both drugs in both minigenome and infectious virus systems.

The optimized minigenome system accurately predicted drug susceptibility in infectious virus systems.

Abstract

Obeldesivir (ODV), an orally bioavailable prodrug of the GS-441524 nucleoside analog, is under evaluation for treatment of RSV in nonhospitalized patients. Here, we report the antiviral activity of GS-441524 and ODV against RSV L polymerase substitutions that emerged during in vitro resistance selections in the presence of ODV, GS-441524, or ALS-8112 (parent nucleoside of lumicitabine) using an optimized RSV minigenome phenotypic assay and a recombinant infectious virus system.

In the optimized minigenome assay, plasmids encoding L, N, P, and M2-1 proteins were reverse-transfected with a firefly luciferase reporter into HEK293T cells, with luciferase activity measured at 48 hours. Phenotypic testing in an infectious virus system used HEp-2 cells with a cellomics-based immunofluorescent readout measured at 72 hours. The L polymerase substitutions C319R, I777L, and L1453W identified during in vitro resistance selection with GS-441524 or ODV and the QUAD substitutions (M628L + A789V + L795I + I796V), both alone and in combination, that emerged during in vitro selection with ALS-8112 were tested in both systems. GS-441524 and ODV half-maximal effective concentration (EC50) values were determined using variable slope non-linear regression.

L polymerase substitutions C319R, A789V, L795I, I796V, L1453W, and QUAD had similar susceptibility to GS-441524 and ODV as the wild type reference in the minigenome system (< 1.09- and < 1.20-fold change in EC50, respectively) and the infectious virus system (< 1.79- and < 2.00-fold change in EC50, respectively). The I777L substitution was associated with low-level reduced susceptibility to GS-441524 and ODV in both the minigenome system (2.06- and 2.07-fold change in EC50, respectively) and the infectious virus system (3.31- and 3.83-fold change in EC50, respectively). The M628L mutant could not be tested due to poor replication. Overall, GS-441524 and ODV EC50 fold changes were concordant in both phenotypic systems.

These data support the use of the optimized RSV minigenome system to evaluate the susceptibility of RSV L polymerase substitutions against GS-441524 and ODV and indicate that these drugs have a high barrier to resistance development.

Jasmine Moshiri, PhD, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) J. Lizbeth Reyes Zamora, PhD, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Dong Han, MS, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Josolyn Chan, MS, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Nadine Peinovich, MPH, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Christopher Richards, PhD, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Stacey Eng, BS, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) John P. Bilello, PhD, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company) Charlotte Hedskog, PhD, Gilead Sciences, Inc.: Employee|Gilead Sciences, Inc.: Stocks/Bonds (Public Company)