2.  Antiviral activity of CQ/HCQ against human coronavirus in vitro and in vivo
The antiviral activity of CQ against MERS-CoV and HCoV-229E was assessed in the human hepatoma cell line (Huh-7) and found that the 50% effective concentrations (EC50) were 3.0(±1.1) μM and 3.3(±1.2) μM, the 50% cytotoxic concentrations (CC50) were 58.1(±1.1) μM and >50, and the selectivity indexes (SI; calculated as CC50/EC50) were 19.4 and >15, respectively [10]. CQ could inhibit an early step in the MERS-CoV replication cycle. Addition of CQ to VeroE6 cells 1 h after MERS-CoV infection did not affect virus production. However, when CQ was added 1 h before MERS-CoV infection, 16 μm and 32 μM concentrations of CQ could reduce the virus production of 1-log and 2-log, respectively [10].
In VeroE6 cells, the antiviral activity of CQ/HCQ against SARS-CoV had an EC50 of 4.1 (±1.0) μM and 34(±5) μM, CC50 of >128 μM and CC50 > 100 and SI of >31 and SI>3, respectively [10,11]. SARS-CoV replication was inhibited by 99% at 16 μM CQ 3 days post-infection [12]. The data indicates that CQ has stronger anti-SARS-CoV activity than HCQ. In addition, CQ has both a prophylactic and a therapeutic advantage. Vincent et al. tested various concentrations of CQ (0.1–10 µM) added 20–24 h prior to SARS-CoV infection and found that 0.1, 1, and 10 µM CQ reduced infectivity by 28%, 53%, and 100%, respectively; when CQ was added immediately after virus adsorption, 0.1–1 µM and 33–100 µM reduced the infection by 50% up to 90–94%; addition of CQ 3 and 5 h after virus adsorption was still significantly effective, yet to achieve equivalent antiviral effect, a higher concentration of CQ was needed [13]. In HRT-18 cells, the antiviral activity of CQ against HCoV-OC43 had an EC50 of 0.306 (±0.091) μM, CC50 of 419.0 (±192.5) μM, and SI of 1.369 [14].
An in vivo study found that CQ could exert anti-HCoV-OC43 activity transplacentally or via maternal milk. The data from mouse models showed that 98.6% of the pups survived when pregnant mice were treated with 15 mg/kg of CQ, and survival rates decreased in a dose-dependent manner, with 88% and 13% survival when treated with 5 mg/kg and 1 mg/kg CQ, respectively [14]. The survival rate of newborn mice via maternal milk was 69.0% with 15 mg/kg of CQ [14]. In another mouse study, CQ strongly attenuated HCoV-OC43 replication in the brain and prevented the infection from spreading to the spinal cord [15]. The above studies confirmed that CQ/HCQ have a broad-spectrum anti-HCoV activity in vitro and in vivo.