- Materials and methods
- Signalment and disease presentation
- Treatment outcome
- Favorable treatment response indicators
- Changes in serum proteins
- Decrease in viral RNA levels in cells from ascitic fluid associated with treatment
- Table 2
- Side effects observed during and after treatment
- Table 3
- Necropsy findings
- Supplemental Material
- Supplemental Material
- Supplemental Material
- Supplemental Material
The aim of this study was to determine the safety and efficacy of the nucleoside analog GS-441524 for cats suffering from various forms of naturally acquired feline infectious peritonitis (FIP).
Cats ranged from 3.4–73 months of age (mean 13.6 months); 26 had effusive or dry-to-effusive FIP and five had non-effusive disease. Cats with severe neurological and ocular FIP were not recruited. The group was started on GS-441524 at a dosage of 2.0 mg/kg SC q24h for at least 12 weeks and increased when indicated to 4.0 mg/kg SC q24h.
Four of the 31 cats that presented with severe disease died or were euthanized within 2–5 days and a fifth cat after 26 days. The 26 remaining cats completed the planned 12 weeks or more of treatment. Eighteen of these 26 cats remain healthy at the time of publication (OnlineFirst, February 2019) after one round of treatment, while eight others suffered disease relapses within 3–84 days. Six of the relapses were non-neurological and two neurological. Three of the eight relapsing cats were treated again at the same dosage, while five cats had the dosage increased from 2.0 to 4.0 mg/kg q24h. The five cats treated a second time at the higher dosage, including one with neurological disease, responded well and also remain healthy at the time of publication. However, one of the three cats re-treated at the original lower dosage relapsed with neurological disease and was euthanized, while the two remaining cats responded favorably but relapsed a second time. These two cats were successfully treated a third time at the higher dosage, producing 25 long-time survivors. One of the 25 successfully treated cats was subsequently euthanized due to presumably unrelated heart disease, while 24 remain healthy.
Conclusions and relevance
GS-441524 was shown to be a safe and effective treatment for FIP. The optimum dosage was found to be 4.0 mg/kg SC q24h for at least 12 weeks.
Drugs that inhibit virus replication have become mainstays in the treatment of acute and chronic RNA and DNA virus infections of people.1 However, interest in antiviral drugs for infections of animals has been much slower to develop. This is especially true for cats, which suffer from several chronic viral infections resembling those in people. The infectious agents include feline leukemia and immunodeficiency viruses (FeLV and FIV, respectively),2 feline herpesvirus (FHV),3 virulent systemic calicivirus4,5 and a coronavirus causing feline infectious peritonitis (FIPV).6 FeLV and FIV infections have been controlled with testing, isolation and/or vaccination. FHV-associated disease was the first feline viral infection to incorporate an antiviral for treatment.3 Highly fatal systemic calicivirus affects only a small number of cats. FIPV infection is the best candidate for antiviral drug development as vaccines are ineffective, multi-cat environments make prevention extremely difficult and it kills 0.3–1.4% of cats around the world.7–9
The emergence of exotic diseases such as Ebola, Middle East respiratory syndrome and severe acute respiratory syndrome in people has prompted intensive research into drugs that will inhibit RNA virus replication. One of the most promising antiviral drugs against emerging RNA viruses is the adenosine nucleoside monophosphate prodrug GS-5734 (Remdesivir; Gilead Sciences). GS-5734 has been effective in preventing experimental Ebola in rhesus monkeys,10 and inhibiting both epidemic and zoonotic coronaviruses in tissue culture and in mouse infection models.11 These promising findings prompted initial research on GS-5734 and its parent nucleoside GS-441524 against FIPV infection of cats.12 GS-441524 and GS-5734 were found to have comparable EC50 (1.0 µM) and CC50 (>100 µM) values against FIPV in cat cells. Therefore, it was decided to concentrate on the less chemically complex GS-441524 for further testing with laboratory cats. A pharmacokinetic study in two laboratory cats demonstrated sustained and effective plasma levels of GS-441524 over 24 h following a single dose given subcutaneously (SC) or intravenously (IV). These results were then extended to 10 laboratory cats with experimentally induced abdominal effusive feline infectious peritonitis (FIP).12 This study showed GS-441524 to be highly effective against experimental FIP and opened the way for the present field trial.
The goal of this study was to demonstrate the safety and efficacy of GS-441524 in the treatment of cats with naturally occurring FIP. Small-molecule drugs such as GS-441524 are <900 daltons in weight and around 1 nm in size, and can easily enter cells and interact with key target molecules. Unlike published substances or drugs that inhibit FIPV by hampering cellular processes usurped by viruses for their replication,13,14 small molecules like GS-441524 interfere directly with replicative processes encoded by the virus.12,15
Materials and methods
GS-441524 was provided by Gilead Sciences as a pure and highly stable powder and diluted to a concentration of 10 or 15 mg/ml in 5% ethanol, 30% propylene glycol, 45% PEG 400, 20% water (pH 1.5 with HCI). The mixture was placed in sterile 50 ml glass injection bottles, agitated until in suspension, and then placed in a sonicated water bath for 5–20 mins until clear. The diluted drug was refrigerated and used within 3–4 weeks.
This study was conducted under protocols 19336 and 19863 approved by the Institutional Animal Care and Use Committee and the Clinical Trial Review Board of the Veterinary Medical Teaching Hospital (VMTH) Clinical Trials Committee, University of California (UC), Davis. Institutional rules precluded the use of diseased cats obtained directly from shelters or kitten foster/rescue groups, thus requiring that all cats be legally owned/adopted and treated under specific conditions and with owner consent (supplementary material). The study did not incorporate a control group because there is no effective treatment to compare it against. A placebo treatment group was not included, given that preparatory in vitro and in vivo studies indicated that GS-441524 would be safe and more effective than no treatment.12
Case selection and disease confirmation
Cats with FIP were recruited from owners or their veterinarians seeking current treatment options or access to an earlier antiviral drug trial.6 The initial diagnosis of FIP was based primarily on characteristic signalment, clinical histories and disease signs, routine laboratory test results, and examination of abdominal or thoracic effusions. A more definitive diagnosis based on RT-PCR or immunohistochemistry was desirable but not essential for inclusion. Cats with obvious ocular or neurological disease were discouraged to enter the trial because of concerns over the ability of antiviral drugs, including GS-441524, to penetrate the blood–brain or blood–eye barriers.12,15
Thirty-one cats and their owners were ultimately recruited (Table 1). Owners or representatives of 26 cats came to UC Davis for initial treatment, and five owners and their cats (CT59, CT73, CT76, CT78, CT80) were treated by their local veterinarian. Cats seen at UC Davis were re-evaluated and their FIP diagnosis reconfirmed based on signalment, clinical history, physical examination, prior laboratory test results and a repeat of complete blood count (CBC), serum protein and effusion analyses. Thoracic or abdominal effusions from cats with wet FIP were confirmed positive for FIPV 7b RNA by RT-PCR.16 Cats with signs of non-effusive FIP were further tested by abdominal and thoracic ultrasonography for primary lesions. Ocular disease was confirmed by the ophthalmology service of the VMTH, UC Davis. Neurological status in cases with possible central nervous system disease signs was evaluated by the VMTH neurology service.