3.1 Triterpenoid saponins from Codonopsis lanceolatainhibit the infection of SARS-CoV-2
We first tested whether CL has an inhibitory activity against SARS-CoV-2 infection using a pseudovirus that expresses S protein on HIV-based lentiviral particles (pSARS-CoV-2), which has been used as a model system for analyzing SARS-CoV-2 infection(Crawford et al., 2020; Kim et al., 2021). pSARS-CoV-2 entry assay showed that the 70% EtOH extracts of the roots and aerial parts of CL prevented pSARS-CoV-2 from entering the ACE2-overexpressing H1299 human lung carcinoma cells (ACE2+ H1299) in a dose-dependent manner with half-maximal inhibitory concentrations (IC50) of 251 μg/ml and 540 μg/ml, respectively, without obvious cell toxicity (Figure. 1a and 1b). These results indicate that CL extracts contain substances with inhibitory activity against SARS-CoV-2 infection, which are higher in the roots than the aerial parts. In order to identify bioactive compounds in the CL, eight main compounds we previously isolated from the roots of CL (Du et al., 2018) were subjected to the examinations for their inhibitory effects against two SARS-CoV-2 entry pathways, that is, endosomal pathway in ACE2+ H1299 cells and TMPRSS2-mediated membrane fusion in ACE2 and TMPRSS2 double-positive cells (ACE2/TMPRSS2+ H1299) (Figure 1c). Our results revealed that both SARS-CoV-2 entry pathways were effectively blocked by pentacyclic triterpenoid saponins such as lancemaside A (LA) and lancemaside B (LB), but not others including lancemaside D (LD) (Figure 1d), indicating that LA and LB are biologically active compounds responsible for the blockade of SARS-CoV-2 infection in CL extracts.