Enanta Pharmaceuticals, Inc. announced new data supporting the potential of EDP-235 for the treatment of COVID-19, which are being presented at the 36th International Conference on Antiviral Research (ICAR) being held March 13-17, 2023 at the Centre de Congrès de Lyon in Lyon, France. The company will have one oral presentation and three poster presentations, showcasing the potential of EDP-235 and Enanta's leadership in the development of small molecules for the treatment of viral respiratory infections. Phase 1 data presented continue to highlight EDP-235's promising overall safety, tolerability and pharmacokinetic (PK) profile, and preclinical data demonstrate EDP-235's ability to suppress viral replication and transmission in an animal model.

Additional preclinical data show EDP-235's targeted tissue penetration and potential to mitigate rebound in COVID-19 patients. A fourth presentation focuses on a high-throughput screen to identify non-nucleoside inhibitors of the RNA-dependent RNA polymerase. EDP-235 is currently being evaluated in SPRINT, a Phase 2 study of non-hospitalized, symptomatic adults with mild or moderate COVID-19, and has a data readout targeted for May 2023.

EDP-235's antiviral activity was evaluated in a ferret model of acute SARS-CoV-2 infection and transmission. Therapeutic treatment of infected animals with EDP-235 beginning 12 hours post-infection with SARS-CoV-2 resulted in a rapid and sustained reduction in both live virus titer and viral RNA in nasal lavage samples. Only vehicle-treated animals had detectable live virus in nasal turbinates four days post-infection, demonstrating complete inhibition of viral replication by both EDP-235 dosing regimens.

Further, EDP-235 exposures in ferrets were comparable to previously announced Phase 1 clinical EDP-235 plasma exposures, representing strong multiples over EC90. To evaluate the impact of EDP-235 treatment on SARS-CoV-2 transmission, infected source animals were co-housed with uninfected contact animals 60 hours post-infection. Live virus was recoverable from the nasal lavages of contact animals housed with vehicle-treated source animals from 12 hours onwards after co-housing.

In contrast, viral RNA and live virus were undetectable in nasal lavage and terminal nasal turbinate samples from contact ferrets co-housed with EDP-235-treated infected animals. Collectively, these data support the potential for EDP-235 to reduce household transmission. EDP-235 was evaluated in a Phase 1, randomized, double-blind, placebo (PBO)-controlled study to assess its safety and PK profile during single ascending dose (SAD), multiple ascending dose (MAD) and food effect cohorts in healthy subjects.

A total of 72 subjects were randomized. Forty subjects were enrolled into five SAD cohorts and thirty-two subjects were enrolled into four MAD cohorts dosed for seven days. EDP-235 was generally safe and well-tolerated in healthy subjects.

Three MAD dosing discontinuations resulted from one moderate headache in the 400 mg fasted cohort, one severe headache in the 800 mg fed cohort, and one grade 3 ALT/grade 2 AST elevation in the 800 mg fed cohort. There were no serious treatment emergent adverse events. Linear PK supported once daily dosing, with strong multiples over the EC90 without the need for ritonavir boosting.

In the SAD phase, EDP-235 exposure increased in an approximately dose-proportional manner, up to 800 mg. Plasma PK from the 200 mg fed cohort indicated a 4-fold food effect. Geometric mean t1/2 was 13-18 hours across dose range, supporting once daily dosing.

In the MAD phase, EDP-235 exposure increased with ascending multiple doses in an approximately dose-proportional manner, up to 400 mg. Steady state was reached 48 hours after the first dose and geometric mean t1/2 ranging from 13-22 hours. EDP-235 administered once daily for seven days resulted in steady state C24 concentrations up to 13-fold over the protein adjusted EC90 determined in Vero E6 cells infected with the Omicron lineage.

These data support the further evaluation of EDP-235 which is currently being studied in a Phase 2 clinical trial in non-hospitalized adults with mild or moderate COVID-19. EDP-235's penetration into target tissues was compared to nirmatrelvir in human cells and preclinical species infected with SARS-CoV-2. Intracellular uptake of EDP-235 was tested side-by-side with nirmatrelvir in human cells. The ratios of intracellular to extracellular concentrations of EDP-235 were 8.7 in human lungs, 9.9 in cardiac myocytes, 11.3 in salivary glands, 18.0 in kidneys, and 33.6 in adipocytes.

In contrast, nirmatrelvir had ratios of 0.6 to 1.2 in these human cells. EDP-235 showed favorable rat plasma exposure of 19.0 µg-hr/mL, whereas nirmatrelvir had a significantly lower rat plasma exposure of 4.9 µg-hr/mL. Consistent with in vitro observations, EDP-235 displayed excellent target tissue exposure in rats with tissue to plasma ratios of 4.1 in lungs, 4.7 in heart, 6.5 in salivary glands, 6.3 in kidneys, and 23.0 in adipose tissues, whereas nirmatrelvir had corresponding ratios of 0.8, 0.9, 0.8, 1.2 and 0.6 in those tissues.

These data demonstrate a more targeted tissue distribution and penetration, enabling EDP-235 to reach sites of potential viral reservoirs, which may help minimize viral rebound in COVID-19 patients. Approaches for developing small molecule antivirals include targeting non-structural proteins such as the proteases 3CL pro and PLpro, nsp13, nsp14, nsp16, and the RNA-dependent RNA polymerase (RdRp). Remdesivir, a nucleoside analog targeting the SARS-CoV-2 RdRp, has been successfully used for the treatment of hospitalized or high-risk patients with COVID-19, but its utility is limited by the intravenous delivery route.

A high throughput screen was conducted to identify non-nucleoside RdRp inhibitors, which could be useful additions to the SARS-CoV-2 treatment arsenal. A biochemical assay was developed where purified recombinant RdRp consisting of nsp12, nsp7, and nsp8 elongates a primer in an annealed primer/template pair and incorporates a fluorescent UTP analog, releasing the fluorophore. After counter-screens to remove RNA intercalators, redox cyclers, and compounds with undesirable medicinal chemistry properties, 15 compounds from 11 structural families with half-maximal inhibitory concentrations (IC50s) <10 µM were selected for mechanism of inhibition studies.

None of the compounds were RNA or NTP competitive inhibitors. Biochemical assays and analytical size-exclusion chromatography showed 11 compounds disrupted nsp12-nsp8 protein-protein interactions. Nano differential scanning fluorimetry analysis suggested five compounds target nsp12 directly.

This high throughput screen identified multiple, structurally diverse, non-nucleoside SARS-CoV-2 RdRp inhibitors as potential starting points for hit optimization.