Protease-mediated enzymatic hydrolysis and activation of aryl phosphoramidate derivatives of stavudine

[Remdesivir for COVID-19]

Remdesivir is a direct-acting antiviral agent that inhibits viral RNA synthesis developed by Gilead Sciences, Inc. in the United States. It has been shown to have antiviral activity against single-stranded RNA viruses, including coronaviruses, in cell culture systems and animal models, and has been developed as a therapeutic agent for Ebola virus infection since 2015. however, to date, it has not been approved in any country. A novel coronavirus infection (COVID-19) was identified in Wuhan, Hubei Province, China in Dec, 2019, and is a respiratory disease characterized by fever, cough, and dyspnea. In severe cases, it may cause serious pneumonia, multi-organ failure and death. Gilead Sciences, Inc. U.S. embarked on the development of COVID-19 as a therapeutic drug, using remdesivir, which has shown in vitro and in vivo antiviral activities against MERS-CoV and SARS-CoV, which are single-stranded RNA coronaviruses that cause Middle East respiratory syndrome (MERS) and severe acute respiratory syndrome (SARS). The in vitro antiviral activity of remdesivir against SARS-CoV-2, which causes COVID-19, was confirmed and clinical studies were initiated in February 2020. Based on the results of clinical studies conducted by the National Institute of Allergy and Infectious Diseases (NIAID) and Gilead Sciences, Inc. and experience of administration from a compassionate use, an exceptional approval system based on the "Pharmaceuticals and Medical Devices Act" was also approved in Japan as of May 7, 2020 for the indication of "infections caused by SARS-CoV-2." In this article, the background of the development and clinical results of remdesivir are described.

Elucidation of remdesivir cytotoxicity pathways through genome-wide CRISPR-Cas9 screening and transcriptomics

The adenosine analogue remdesivir has emerged as a front-line antiviral treatment for SARS-CoV-2, with preliminary evidence that it reduces the duration and severity of illness1.Prior clinical studies have identified adverse events1,2, and remdesivir has been shown to inhibit mitochondrial RNA polymerase in biochemical experiments7, yet little is known about the specific genetic pathways involved in cellular remdesivir metabolism and cytotoxicity. Through genome-wide CRISPR-Cas9 screening and RNA sequencing, we show that remdesivir treatment leads to a repression of mitochondrial respiratory activity, and we identify five genes whose loss significantly reduces remdesivir cytotoxicity. In particular, we show that loss of the mitochondrial nucleoside transporter SLC29A3 mitigates remdesivir toxicity without a commensurate decrease in SARS-CoV-2 antiviral potency and that the mitochondrial adenylate kinase AK2 is a remdesivir kinase required for remdesivir efficacy and toxicity. This work elucidates the cellular mechanisms of remdesivir metabolism and provides a candidate gene target to reduce remdesivir cytotoxicity.

Remdesivir: A Review of Its Discovery and Development Leading to Emergency Use Authorization for Treatment of COVID-19

The global pandemic of SARS-CoV-2, the causative viral pathogen of COVID-19, has driven the biomedical community to action-to uncover and develop antiviral interventions. One potential therapeutic approach currently being evaluated in numerous clinical trials is the agent remdesivir, which has endured a long and winding developmental path. Remdesivir is a nucleotide analogue prodrug that perturbs viral replication, originally evaluated in clinical trials to thwart the Ebola outbreak in 2014. Subsequent evaluation by numerous virology laboratories demonstrated the ability of remdesivir to inhibit coronavirus replication, including SARS-CoV-2. Here, we provide an overview of remdesivir's discovery, mechanism of action, and the current studies exploring its clinical effectiveness.

AZT and AZT-monophosphate prodrugs incorporating HIV-protease substrate fragment: synthesis and evaluation as specific drug delivery systems

With the view to deliver anti-HIV nucleoside and nucleoside-monophosphate (MP) analogues specifically into HIV-infected cells, we synthesized a series of ester and phosphoramidate peptide conjugates of zidovudine (AZT) and of AZT-MP, respectively, wherein the peptide sequences derive from a HIV-protease (PR) hydrolysable substrate. Their in vitro stability with respect to hydrolysis, anti-HIV activity and cytotoxicity, and ability to inhibit the HIV-PR activity were investigated. Concerning the ester AZT-peptide conjugates, their antiviral activity level in thymidine kinase-expressing (TK+) CEM-SS and MT-4 cells was in most cases closely correlated to their hydrolysis rate: the faster the hydrolysis, the closer the anti-HIV activity to that of AZT. None of them was a HIV-PR substrate, indicating that their antiviral activity was not related to their intracellular hydrolysis by this enzyme. None of them inhibited HIV in TK-deficient (TK-) CEM cells, demonstrating that they probably act as prodrugs of AZT. Most of the phosphoramidate peptide conjugates of AZT-MP were rapidly degraded in a physiological buffer into several metabolites including AZT. Their anti-HIV activity in TK+ CEM-SS and MT-4 cells was much lower than that of AZT, indicating that only low amounts of AZT or AZT-MP were released into cells during incubation. Antiviral activities measured on TK- CEM cells for some phosphoramidates suggest that low amounts of AZT-MP could be released intracellularly. However, this AZT-MP release was not initiated by a HIV-PR hydrolysis, as no evidence for peptide cleavage was obtained by HPLC analysis of one representative compound after incubation with HIV-PR.

Synthesis and metabolism of naphthyl substituted phosphoramidate derivatives of stavudine

The synthesis of naphthylphosphoramidate derivatives of stavudine was achieved using a four-step procedure. The derivatives were subjected to several different enzymes including lipase, esterase, Subtilisin Carlsberg, and Carica papaya, and their hydrolysis rates were determined. Based on the rates of hydrolysis, we were able to differentiate between the chiralities at the phosphorus center of the phosphoramidate compounds. In addition, lipase was found to distinguish between both alpha and beta forms of the compounds. The superior chiral selectivity shown by lipase toward the naphthyl substituted phosphoramidate derivatives is attributed to the restrictive binding pocket of the lipase.

Effect of change in nucleoside structure on the activation and antiviral activity of phosphoramidate derivatives

Changing the nucleoside group of a series of phosphoramidate derivatives affects the enzyme mediated hydrolysis rate of the compounds. d4T and AZT-substituted analogs were activated by enzymes such as lipases, esterases, and proteases. On the other hand, 3dT-substituted derivatives were comparatively less prone to hydrolysis under similar experimental conditions. From the experimental results, we propose that the most preferable nucleoside group for enzyme activation is d4T rather than AZT or 3dT. Additionally, we also observed that depending on the enzymes used the chiral selectivity of the enzymes for the phosphorus center of these phosphoramidate derivatives differed, demonstrating the importance of the nucleoside structure for this class of compounds.