W21-007 An Optimized Bioassay for Screening Combined Anticoronaviral Compounds for Efficacy against Feline Infectious Peritonitis Virus with Pharmacokinetic Analyses of GS-441524, Remdesivir, and Molnupiravir in Cats (An EveryCat-funded research project)

Principal Investigators: Sarah Cook, DVM, MS, DACVP; Brian Murphy, DVM, PhD, DACVP; University of California, Davis. Viruses. 2022;14(11):2429. https://doi.org/10.3390/v14112429  PMID: 36366527 

The EveryCat Health Foundation has made a strong commitment to furthering research on treatments for Feline Infectious Peritonitis (FIP), a once thought incurable disease. This EveryCat-funded research study, published in the journal Viruses in 2022, set out to determine the antiviral efficacies of 6 different compounds as well as determine the pharmacokinetic properties of several of these after administration to cats to establish target doses.

The Following Compounds Tested Were:

1. GC376: a previously studied antiviral agent that has shown effectiveness in treatment of cats with experimental and naturally acquired FIP.
2. GS-441524: another extensively studied compound that had proven success in treatment of cats infected in FIV.
3. Remdesivir (RDV): a prodrug of GS-441524 that has demonstrated efficacy in blocking the replication of multiple families of RNA viruses, including Coronaviridae. This medication is currently utilized in adults and children over the age of 12 for SARS-Co-V-2 treatment.
4. Nirmatrelvir: a compound similar to GC376 that has been used in oral combination with Ritonavir (marketed as Paxlovid (Pfizer)) to treat COVID-19 in adults and children over 12 years old.
5. Molnupiravir (MPV): an anti-coronaviral compound that has shown activity against FIPV and SARS-Co V-2 with only anecdotal reports of its use in cats.
6. Beta-D-N4-hydroxycytidine (NHC): the active prodrug of MPV that has shown anti-viral activity against multiple coronaviruses including FIPV in vitro.

The premise of this portion of the study was to compare these antiviral agents used as monotherapies as well as combined anticoronaviral therapies (CACT) in vitro against FIPV I and FIPV II strains. Bioassays of the individual compounds were performed as well the following CACT combinations:

1. RDV & GC376
2. RDV & Nirmatrelvir
3. MPV & Nirmatrelvir
4. These combinations were selected as they included compounds with different mechanisms (a nucleoside analog coupled with a viral protease inhibitor).

Important Findings That Were Obtained From This Study Included:

• All the antiviral compounds as monotherapies effectively blocked the replication of FIPV I and II serotypes in vitro.
• NHC showed direct compound-associated cell injury (cytotoxicity) at greater concentrations. This information warrants additional evaluation both in vitro and in vivo (such as monitoring repeat dosing and biochemical parameters) in cats to assess the cytotoxicity of this agent.
• Compound synergy was identified in all 3 CACT combinations.

The second part of the study determined the pharmacokinetic properties of orally administered MPV, GS-441524, and RDV as well as the intravenous administration of RDV to healthy, specific pathogen free (SPF) cats (n= 3 for each). Doses were administered to each cat, multiple blood samples were collected at various time points over the first 24 hours post-dose for drug concentration, and biochemical parameters were evaluated to identify any acute changes. The following information was obtained about each compound:

MPV (oral):

1. No evidence of acute organ toxicity based on pre- and post-treatment CBC and serum chemistry panels was noted.
2. All treated cats demonstrated various signs of nausea (such as hypersalivation and/or vomiting) after oral administration within the first few hours.
3. MPV was not detected at the 12-h time point, consistent with rapid conversion to the prodrug NHC.

GS-441524 (oral):

1. No clinical abnormalities were detected after oral administration.
2. High plasma levels were achieved which is similar to what has been previously described in the literature.

RDV (oral and IV):

1. Mild nausea, hypersalivation, and lethargy were observed in 2/3 after oral treatment, but cats were clinically normal by 12 hours later.
2. Plasma levels of GS-441524 (the main circulating metabolite of RDV) were high in both oral and IV RDV groups.

For each of the compounds, targeted mg/kg doses were identified.

What can be gained from these findings?

In human medicine, combination therapies for various viral diseases such as HIV and hepatitis C are employed for improved clinical outcomes. The information gained in this study builds upon prior research by utilizing a bioassay to assess CACT. Additionally, there is little to no pharmacokinetic data on some of the antiviral agents presented in this research. Due to the differing forms and clinical presentations of FIP (such as CNS and ocular forms), adding to the armamentarium of antiviral compounds is imperative.  ~BJP