key: cord-325432-geb4esu5
authors: Bukreyeva, Natalya; Mantlo, Emily K.; Sattler, Rachel A.; Huang, Cheng; Paessler, Slobodan; Zeldis, Jerry
title: The IMPDH inhibitor merimepodib suppresses SARS-CoV-2 replication in vitro
date: 2020-04-09
journal: bioRxiv
DOI: 10.1101/2020.04.07.028589
sha: 
doc_id: 325432
cord_uid: geb4esu5

The ongoing COVID-19 pandemic continues to pose a major public health burden around the world. The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected over one million people worldwide as of April, 2020, and has led to the deaths of nearly 300,000 people. No approved vaccines or treatments in the USA currently exist for COVID-19, so there is an urgent need to develop effective countermeasures. The IMPDH inhibitor merimepodib (MMPD) is an investigational antiviral drug that acts as a noncompetitive inhibitor of IMPDH. It has been demonstrated to suppress replication of a variety of emerging RNA viruses. We report here that MMPD suppresses SARS-CoV-2 replication in vitro. After overnight pretreatment of Vero cells with 10 μM of MMPD, viral titers were reduced by 4 logs of magnitude, while pretreatment for 4 hours resulted in a 3-log drop. The effect is dose-dependent, and concentrations as low as 3.3 μM significantly reduced viral titers when the cells were pretreated prior to infection. The results of this study provide evidence that MMPD may be a viable treatment option for COVID-19.

The ongoing COVID-19 pandemic continues to pose a major public health burden around the world. The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected over one million people worldwide as of April, 2020, and has led to the deaths of nearly 300,000 people. No approved vaccines or treatments in the USA currently exist for COVID-19, so there is an urgent need to develop effective countermeasures. The IMPDH inhibitor merimepodib (MMPD) is an investigational antiviral drug that acts as a noncompetitive inhibitor of IMPDH. It has been demonstrated to suppress replication of a variety of emerging RNA viruses. We report here that MMPD suppresses SARS-CoV-2 replication in vitro. After overnight pretreatment of Vero cells with 10 μM of MMPD, viral titers were reduced by 4 logs of magnitude, while pretreatment for 4 hours resulted in a 3-log drop.

The effect is dose-dependent, and concentrations as low as 3.3 μM significantly reduced viral titers when the cells were pretreated prior to infection. The results of this study provide evidence that MMPD may be a viable treatment option for COVID-19. Drugs with history of being tested in human patients or used for treatment of other conditions offer the most expedient option, and several such drugs are currently being tested for efficacy against SARS-CoV-2, including many broad-spectrum antivirals. One such antiviral, merimepodib (MMPD), has already being tested against hepatitis C in patients as well as against many emerging RNA viruses in cell culture, including Zika, Ebola, Lassa, Junin, and chikungunya viruses (1) . MMPD noncompetitively inhibits inosine-5'-monophosphate dehydrogenase (IMPDH), an enzyme responsible for de novo synthesis of guanosine nucleotides (2, 3) . In vitro, inhibition can be reversed by addition of exogenous guanosine (4).

Early work suggests that IMPDH may directly interact with SARS-CoV-2 nsp13, perhaps indicating that drugs targeting IMPDH such as MMPD might have an impact on viral replication (5) . This drug, while still investigational, is considered to be safe in humans. More than 300 patients have received the drug in Phase I and Phase II clinical trials. Many were treated for six months. In this study, we aimed to examine whether MMPD may be active in reducing SARS-CoV-2 replication.

Vero cells (CCL-81, ATCC) were maintained in Dulbecco's modified eagle medium (Hyclone) supplemented with 10% FBS (Gibco) and 1% penicillin and streptomycin solution (Hyclone). We also tested T-705, another broad-spectrum antiviral that acts as a nucleoside analog. Both overnight and 4-hour pretreatment with high doses (33-100 μM) of T-705 failed to inhibit SARS-CoV-2 replication. Overall, our results indicate that therapeutic concentrations of MMPD, but not T-705, is effective in reducing SARS-COV-2 coronavirus titers.

Our results show that MMPD can inhibit SARS-CoV-2 replication at low concentrations. This is likely due its inhibition of IMPDH, leading to a depletion of guanosine for use by the viral polymerase during replication. By contrast, T-705 has been reported to weakly inhibit IMPDH, instead acting as a nucleotide analogue and interacting more specifically with certain viral polymerases (7) . Further work is needed to characterize the full mechanism behind MMPD inhibition of SARS-CoV-2 as well as its efficacy in animal models of corona virus infections.

In COVID-19 infection it is essential to minimize the spread of the viral infection to the lower respiratory tract. We chose to test MMPD pretreated uninfected cells in order to see if viral spread can be limited. This approach potentially allows us to model the use of this drug for prophylaxis. This is important since a large proportion of exposed patients can experience rapid expansion of their viral burden while being asymptomatic. A drug that thwarts this viral expansion will allow the immune system to eliminate the nascent infection. Since MMPD is a host directed therapy and not a direct acting antiviral, the likelihood of emergence of resistant variants of the virus to MMPD is low. Potentially MMPD might be used in combination with direct antivirals or immunomodulators.

The concentrations tested in this study are easily clinically-achievable in human patients. 50 mg MMPD administered orally results in plasma concentrations of around 1154 ng/ml (2500 μM) shortly after administration (8) . MMPD may therefore be a viable treatment option for COVID-19 that can be quickly tested and deployed. 

Merimepodib, an IMPDH inhibitor, suppresses replication of Zika virus and other emerging viral pathogens

IMP Dehydrogenase: Structure, Mechanism, and Inhibition

The structure of inosine 5′-monophosphate dehydrogenase and the design of novel inhibitors

Broad-Spectrum Antiviral Activity of the IMP Dehydrogenase Inhibitor VX-497: a Comparison with Ribavirin and Demonstration of Antiviral Additivity with Alpha Interferon

A SARS-CoV-2-Human Protein-Protein Interaction Map Reveals Drug Targets and Potential Drug-Repurposing

Potent Antiviral Activities of Type I Interferons to SARS-CoV-2 Infection

Mechanism of Action of T-705 against Influenza Virus

Merimepodib, pegylated interferon, and ribavirin in genotype 1 chronic hepatitis C pegylated interferon and ribavirin nonresponders