The combination of levodopa with levodopa-metabolizing enzyme inhibitors prevents severe fever with thrombocytopenia syndrome virus infection in vitro more effectively than single levodopa

Severe fever with thrombocytopenia syndrome is a hemorrhagic fever caused by a tick-borne infection. The causative agent, Dabie bandavirus, is also called the severe fever with thrombocytopenia syndrome virus (SFTSV). Ogawa et al. (2022) reported that levodopa, an antiparkinsonian drug with an o-dihydroxybenzene backbone, which is important for anti-SFTSV activity, inhibited SFTSV infection. Levodopa is metabolized by dopa decarboxylase (DDC) and catechol-O-methyltransferase (COMT) in vivo. We evaluated the anti-SFTSV efficacy of two DDC inhibitors, benserazide hydrochloride and carbidopa, and two COMT inhibitors, entacapone and nitecapone, which also have an o-dihydroxybenzene backbone. Only DDC inhibitors inhibited SFTSV infection with pretreatment of the virus (half-maximal inhibitory concentration [IC₅₀]: 9.0–23.6 μM), whereas all the drugs inhibited SFTSV infection when infected cells were treated (IC₅₀: 21.3–94.2 μM). Levodopa combined with carbidopa and/or entacapone inhibited SFTSV infection in both conditions: pretreatment of the virus (IC₅₀: 2.9–5.8 μM) and treatment of infected cells (IC₅₀: 10.7–15.4 μM). The IC₅₀ of levodopa in the above-mentioned study for pretreatment of the virus and treatment of infected cells were 4.5 and 21.4 μM, respectively. This suggests that a synergistic effect was observed, especially for treatment of infected cells, although the effect is unclear for pretreatment of the virus. This study demonstrates the anti-SFTSV efficacy of levodopa-metabolizing enzyme inhibitors in vitro. These drugs may increase the time for which the levodopa concentration is maintained in vivo. The combination of levodopa and levodopa-metabolizing enzyme inhibitors might be a candidate for drug repurposing.