Viruses are obligate intracellular parasites that make use of the host metabolic machineries to meet their biosynthetic needs. Thus, identifying the host pathways essential for the virus replication may lead to potential targets for therapeutic intervention. The mechanisms and pathways explored by SARS-CoV-2 to support its replication within host cells are not fully known. Lipid droplets (LD) are organelles with major functions in lipid metabolism, energy homeostasis and intracellular transport, and have multiple roles in infections and inflammation. Here we described that monocytes from COVID-19 patients have an increased LD accumulation compared to SARS-CoV-2 negative donors. In vitro, SARS-CoV-2 infection were seen to modulate pathways of lipid synthesis and uptake as monitored by testing for CD36, SREBP-1, PPARγ, and DGAT-1 expression in monocytes and triggered LD formation in different human cell lines. LDs were found in close apposition with SARS-CoV-2 proteins and double-stranded (ds)-RNA in infected Vero cells. Electron microscopy (EM) analysis of SARS-CoV-2 infected Vero cells show viral particles colocalizing with LDs, suggestive that LDs might serve as an assembly platform. Pharmacological modulation of LD formation by inhibition of DGAT-1 with A922500 significantly inhibited SARS-CoV-2 replication as well as reduced production of mediators pro-inflammatory response. Taken together, we demonstrate the essential role of lipid metabolic reprograming and LD formation in SARS-CoV-2 replication and pathogenesis, opening new opportunities for therapeutic strategies to COVID-19.

Zika virus (ZIKV) is a member of the Flaviviridae family, along with other agents of clinical significance such as dengue (DENV) and hepatitis C (HCV) viruses. Since ZIKV causes neurological disorders during fetal development and in adulthood, antiviral drugs are necessary. Sofosbuvir is clinically approved for use against HCV and targets the protein that is most conserved among the members of the Flaviviridae family, the viral RNA polymerase. Indeed, we found that sofosbuvir inhibits ZIKV RNA polymerase, targeting conserved amino acid residues. Sofosbuvir inhibited ZIKV replication in different cellular systems, such as hepatoma (Huh-7) cells, neuroblastoma (SH-Sy5y) cells, neural stem cells (NSC) and brain organoids. In addition to the direct inhibition of the viral RNA polymerase, we observed that sofosbuvir also induced an increase in A-to-G mutations in the viral genome. Together, our data highlight a potential secondary use of sofosbuvir, an anti-HCV drug, against ZIKV.

Yellow fever virus (YFV) is a member of the Flaviviridae family. In Brazil, yellow fever (YF) cases have increased dramatically in sylvatic areas neighboring urban zones in the last few years. Because of the high lethality rates associated with infection and absence of any antiviral treatments, it is essential to identify therapeutic options to respond to YFV outbreaks. Repurposing of clinically approved drugs represents the fastest alternative to discover antivirals for public health emergencies. Other Flaviviruses, such as Zika (ZIKV) and dengue (DENV) viruses, are susceptible to sofosbuvir, a clinically approved drug against hepatitis C virus (HCV). Our data showed that sofosbuvir docks onto YFV RNA polymerase using conserved amino acid residues for nucleotide binding. This drug inhibited the replication of both vaccine and wild-type strains of YFV on human hepatoma cells, with EC₅₀ values around 5 μM. Sofosbuvir protected YFV-infected neonatal Swiss mice and adult type I interferon receptor knockout mice (A129^-/-) from mortality and weight loss. Because of its safety profile in humans and significant antiviral effects in vitro and in mice, Sofosbuvir may represent a novel therapeutic option for the treatment of YF. Key-words: Yellow fever virus; Yellow fever, antiviral; sofosbuvir Yellow fever virus is transmitted by mosquitoes and its infection may be asymptomatic or lead to a wide clinical spectrum ranging from a mild febrile illness to a potentially lethal viral hemorrhagic fever characterized by liver damage. Although a yellow fever vaccine is available, low coverage allows 80,000–200,000 cases and 30,000–60,000 deaths annually worldwide. There are no specific therapy and treatment relies on supportive care, reinforcing an urgent need for antiviral repourposing. Here, we showed that sofosbuvir, clinically approved against hepatitis C, inhibits yellow fever virus replication in liver cell lines and animal models. In vitro, sofosbuvir inhibits viral RNA replication, decreases the number of infected cells and the production of infectious virus particles. These data is particularly relevante since the liver is the main target of yellow fever infection. Sofosbuvir also protected infected animals from mortality, weight loss and liver injury, especially prophylatically. Our pre-clinical results supports a second use of sofosbuvir against yellow fever.

Chikungunya virus (CHIKV) causes a febrile disease associated with chronic arthralgia, which may progress to neurological impairment. Chikungunya fever (CF) is an ongoing public health problem in tropical and subtropical regions of the world, where control of the CHIKV vector, Aedes mosquitos, has failed.