The coronavirus disease 2019 (COVID-19) pandemic has had overwhelming impacts on healthcare systems and has claimed over 4.9 million lives globally. The emerging novel variants of the severe acute respiratory syndrome coronavirus-2 (SARS‑CoV‑2) harbor vaccine escape capacities; besides, some individuals may still face vaccine access inequity. Hence, repurposing of clinically approved, safe, accessible, and active drugs against SARS-CoV-2 is anticipated.
Study: Antiviral Potential of the Antimicrobial Drug Atovaquone against SARS-CoV-2 and Emerging Variants of Concern. Image Credit: Susan Schmitz/ Shutterstock
The FDA-approved molecule atovaquone/malarone may represent an effective therapeutic strategy in treating COVID-19, specifically for preventing infection among frontline workers and/or high-risk populations.
Atovaquone (the active compound of malarone) has proven efficacy against Pneumocystis jirovecii pneumonia and as a fixed-dose combination with proguanil in preventing and treating malaria. This agent is a ubiquinol analog that affects parasitic mitochondrial functions without inhibiting the mammalian mitochondrial bc1 complex.
This drug has an excellent safety profile and has been approved by the US Food and Drug Administration (FDA) to treat malaria. Recently, its potential broad-spectrum antiviral role has been described against arboviruses, including Zika, chikungunya, and dengue viruses. The antiviral action of atovaquone is expressed through the inhibition of the pyrimidine biosynthesis pathway involved in viral RNA replication and the impedance of viral entry into host cells. Furthermore, its efficacy in limiting the infectivity of the Middle East respiratory syndrome-related coronavirus (MERS-CoV) has been demonstrated in vitro.
A new study published in the journal ACS Infectious Diseases aimed to examine the antiviral potential of atovaquone against the original SARS-CoV-2 strain and other variants of concern.
Here, the antiviral potential of atovaquone was assessed following infection with SARS-CoV-2-spike-pseudotyped vesicular stomatitis virus (VSV) and wild-type (wtVSV), both expressing green fluorescent protein (GFP). In this study, VeroE6 cells were treated with various atovaquone concentrations; after that, the cells were infected with wtVSV-spike or wtVSV and were imaged for GFP as a proxy for infection rate. Additionally, cellular viability was evaluated 48 hours post-infection.
The results showed a dose-dependent block in the infectivity of both wtVSV and VSV-spike. It was noted that wtVSV was more toxic than VSV-spike, and there was a slight increase in cellular viability with atovaquone. Quantitative polymerase chain reaction (qPCR) of the SARS-CoV-2 genome established that a concentration of 10 μM atovaquone was the most efficient in inhibiting viral replication. All concentrations of the drug prove to be non-toxic.
Additionally, a 105 −106 log-fold reduction in the production of viral progeny was observed in atovaquone-treated cells. Immunofluorescence staining showed an almost complete absence of the intracellular SARS-CoV-2 spike protein after atovaquone treatment. The antiviral effect of the drug was retained in the human lung epithelial cell line Calu-3, with more than a 100-fold reduction in viral genome expression. The suppressed SARS-CoV-2 infectivity in the presence of atovaquone led to reduced virus-induced cytotoxicity of the infected Calu-3 cells.
After establishing atovaquone as a promising antiviral agent against the original SARS-CoV-2 strain, the antiviral capabilities of this agent were investigated against different variants of concern (VOCs)—including the cluster 5 variant (mink variant), alpha variant, beta variant, and delta variant.
The results showed that treatment of VeroE6 hTMPRSS2 efficiently inhibited SARS-CoV-2 viral gene expression with the original viral strain and the mink variant. Meanwhile, the antiviral capacity of atovaquone was expressed on alpha and beta variants. Despite this effect being slightly low on the SARS-CoV-2 delta variant, atovaquone could drastically interfere with the variant’s gene expression. Furthermore, an almost complete reduction of the intracellular SARS-CoV-2 spike protein for the different variants could be achieved with atovaquone treatment.
To investigate whether atovaquone had a broad antiviral activity, the same experiments were performed on two mild human coronaviruses OC43 and 229E. It was observed that when Huh-7 and Caco-2 cells were treated with atovaquone, they exhibited reduced viral gene expressions. The antiviral activity of atovaquone was more pronounced against OC43 than 229E. Thus, the potent and broad-spectrum antiviral action of this agent could be confirmed against SARS-CoV-2 VOCs.
Furthermore, atovaquone pretreatment of Calu-3 cells impeded the virus-induced inflammatory response—which is known to render the “cytokine storm.” It was found that pretreatment for two hours inhibited RIG-I-induced antiviral gene levels, but not inflammatory gene levels.
The results indicated that atovaquone is a promising antiviral agent that benefits against SARS-CoV-2 infection by inhibiting viral replication and virus-induced inflammation at non-toxic concentrations in VeroE6 hTMPRSS2 cells and lung epithelial Calu-3 cells. Atovaquone interferes with the viral entry into the host cells and appears to affect the intracellular phase of viral replication.
This study revealed that this drug works both pre-and post-infection on SARS-CoV-2; and, therefore, can be used prophylactically and following exposure to the virus. Future studies should be directed towards investigating if the atovaquone-induced antiviral activity could result from cleavage of ACE2 through the TMPRSS2-mediated proteolytic activity and whether this drug could be used alone or as a combination treatment for COVID-19.