Dicoumarol Shows Promise as a Potential Antiviral Agent against Omicron Variant in Airway Epithelial Cells

The COVID-19 pandemic has brought about the emergence of highly transmissible variants of the SARS-CoV-2 virus, such as the Omicron variant identified in South Africa in November 2021.

This variant is characterized by its high transmissibility and a short incubation period, making it spread faster than previous variants even in highly vaccinated populations. As a result, scientists worldwide are actively researching drugs to inhibit the replication of SARS-CoV-2.

While there are existing therapeutic agents available, their limited availability, high cost, and logistical challenges have hindered their widespread use. Repurposing existing drugs, such as dicoumarol (DCM), presents a potential solution due to their established safety profiles and mechanisms of action.

DCM, a derivative of natural origin, has long been prescribed as a safe oral anticoagulant in clinical settings. Previous studies have demonstrated its broad antiviral activity against Hepatitis B virus (HBV) and human immunodeficiency virus (HIV).

A pharmacological review of dicoumarol: An old natural anticoagulant agent

The legend of dicoumarol (3,3’-methylenebis(4-hydroxycoumarin), Fig. 1A), a coumarin-like compound, is started in 1940 when Karl Link extracted it from spoilage by fungi in sweet clover of Melilotus officinalis (L.) Pall (Fig. 1) [1]. Melilotus officinalis (L.) Pall is one of the species in the genus of Fabaceae widely distributed in Asia and Europe.

In China, it has been used as a traditional Chinese herb with functions of heat-clearing and detoxifying. The medical usage of Melilotus officinalis (L.) Pall had also been recorded by the National Health Commission of the People’s Republic of China and the European Medicines Agency in the pharmacopeias [2].

Dicoumarol also distributed in numerous plants besides Melilotus officinalis (L.) Pall. Its chemical structure is consisting of double benzene rings fused to lactone rings respectively [3]. The physical and chemical properties of dicoumarol are as follow:

Previously, dicoumarol was used as a natural anticoagulant due to its chemical structure similarity to vitamin K (Fig. 1B). Besides, dicoumarol competes with NAD(P)H for binding to NAD(P)H: quinine oxidoreductase 1 (NQO1), resulting in inhibition of NQO1 enzymatic activity. Here, we summarized the biological activities, side effects, and pharmacokinetics of dicoumarol.

DCM inhibits the NAD(P)H: quinone oxidoreductase 1 (NQO1) enzyme, which reduces reactive oxygen species production, and antagonizes the blood clotting process by inhibiting the vitamin K epoxide reductase complex subunit 1 (VKORC1). Reduced vitamin K levels have been associated with poor prognosis in COVID-19 patients.

DCM has been identified in virtual screening studies as a potential drug for the treatment of COVID-19, but its inhibitory effects and mechanisms of action against SARS-CoV-2, particularly the Omicron variant, remain unknown.

Airway epithelium serves as the primary defense against pathogen infection through mucociliary clearance and the production of defense proteins.

Dysfunction of mucociliary clearance can lead to mucus accumulation and tissue damage, contributing to the development of respiratory diseases. SARS-CoV-2 targets ciliated and club cells in the airway epithelium by binding to the angiotensin-converting enzyme 2 (ACE2) receptor.

Omicron variants have been found to accelerate spread via the ciliary transport/microvilli reprogramming pathway, leading to increased attack rates compared to previous variants. Inhibiting viral replication and reducing viral load in airway epithelial cells (AECs) infected with the Omicron variant could prevent disease progression and limit infectivity.

Study Objectives

The objective of this study was to investigate the potential of DCM in regulating the anti-Omicron function of primary human AECs cultured at an air-liquid interface (ALI) condition. The researchers aimed to assess the inhibitory effects of DCM on SARS-CoV-2 replication in AECs, explore the relationship between DCM targets (NQO1 and VKORC1) and SARS-CoV-2 infection, and unravel the underlying mechanism of DCM’s anti-Omicron replication activity.

Methods and Results

Using time-of-addition and drug withdrawal assays, the researchers demonstrated that DCM, when added shortly after infection, suppresses SARS-CoV-2 replication in primary AECs. They also performed single-cell sequencing analysis to assess the expression of NQO1 and VKORC1 in AECs infected with SARS-CoV-2.

The results showed a significant positive correlation between NQO1 expression levels and the severity of COVID-19 in patients as well as viral copies in cultured AECs. DCM treatment was found to attenuate NQO1 expression. Transcriptome sequencing was conducted to investigate the mechanism of DCM’s anti-Omicron replication activity.

The analysis revealed that DCM treatment significantly downregulated genes associated with viral replication and upregulated genes related to host defense and immune response pathways in AECs infected with the Omicron variant.

To further elucidate the molecular mechanism of DCM’s antiviral activity, the researchers conducted protein-protein interaction network analysis. They identified key proteins that interacted with NQO1 and VKORC1, including several viral proteins involved in SARS-CoV-2 replication and host cellular processes. This analysis suggested that DCM may disrupt viral replication by modulating the interactions between these proteins and their respective signaling pathways.

To validate the findings from the in vitro experiments, the researchers conducted in vivo studies using a hamster model infected with the Omicron variant. The hamsters were treated with DCM orally, and viral load, lung pathology, and pro-inflammatory cytokine levels were assessed.

The results showed that DCM treatment significantly reduced viral load in the lungs, mitigated lung tissue damage, and suppressed the release of pro-inflammatory cytokines compared to the control group.

Discussion and Conclusion

This study provides compelling evidence that dicoumarol (DCM) exhibits potent antiviral activity against the Omicron variant in airway epithelial cells (AECs). The findings suggest that DCM’s inhibitory effects on SARS-CoV-2 replication may be mediated through its interactions with NQO1 and VKORC1, as well as modulation of host defense and immune response pathways.

Furthermore, the in vivo results in the hamster model support the potential therapeutic value of DCM in reducing viral replication, lung pathology, and inflammation associated with Omicron variant infection.

The repurposing of DCM as an antiviral agent against the Omicron variant holds promise due to its established safety profile and oral administration route. However, further research is necessary to investigate the optimal dosage, treatment duration, and potential drug interactions of DCM in COVID-19 patients. Additionally, clinical trials are warranted to evaluate the efficacy and safety of DCM in humans, including its potential combination with other therapeutic agents.

Overall, this study highlights the potential of DCM as a novel antiviral agent against the Omicron variant and provides valuable insights into its mechanisms of action. The findings contribute to the ongoing efforts in developing effective treatments for COVID-19 and combating the challenges posed by emerging variants of SARS-CoV-2.

reference link :https://www.nature.com/articles/s41392-023-01511-7#Sec8

https://www.sciencedirect.com/science/article/abs/pii/S1043661820315012