Repurposing Efavirenz, the HIV Antiretroviral Drug for Chikungunya Virus Infection

Chikungunya virus (CHIKV) has frequently recurred in recent decades, causing outbreaks worldwide in tropical and subtropical regions. The re-emergence of CHIKV poses a substantial risk to human health, as no efficacious drugs are currently available to curb new outbreaks. Here, the anti-CHIKV activity of efavirenz was investigated by <i>in vitro</i> cell culture-based antiviral assays in different relevant cell lines. Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI) used for the treatment of acquired immunodeficiency syndrome (AIDS), and it has good oral bioavailability, long half-life, and affordable low cost. This study demonstrated dose-dependent robust anti-CHIKV activity of efavirenz at low micromolar concentration in two different cell lines with 50% effective concentration (EC₅₀) of 1.1 to 1.3 μM. Interestingly, efavirenz also inhibited the replication of Sindbis virus (SINV) at a low micromolar range indicating potential broad anti-alphavirus activity. Time of addition assay, direct transfection of virus replicon RNA, and minus-sense-specific reverse transcription polymerase chain reaction (RT-PCR) elucidated that efavirenz hinders the viral replication at an early stage after the virus entry by inhibiting the viral RNA synthesis. Further, the binding affinity of efavirenz toward purified capsid protein (CP) was observed, suggesting that CP could be one of the antiviral targets for efavirenz in addition to viral or host proteins involved in viral RNA replication. Finally, the <i>in vivo</i> efficacy of efavirenz was assessed in a murine model and a decrease in CHIKV viral load was observed. In summary, the present study underscores the potential of repurposing efavirenz for antiviral therapy against CHIKV to curb future viral outbreaks.