Secondary metabolite mapping identifies Scutellaria inhibitors of human lung cancer cells

Scutellaria baicalensis root is widely used in China as an adjuvant to orthodox chemotherapy of lung cancer. However, functional biomarkers of this plant for anti-lung cancer activity have not yet been reported. We therefore determined the growth inhibition activity by MTT assay of eight solvent extracts of S. baicalensis in the human lung cancer cell line SK-MES-1. This activity was then mapped onto the secondary metabolite profile of crude extracts by principal components analysis (PCA) of proton NMR and HPLC-UV data. NMR- and HPLC-PCA maps revealed highest inhibitory activity for the non-aqueous extracts. The first two components of both maps discriminated extract activity mainly based on the differential content of three compounds, which were then tested individually. The IC₅₀ values for baicalin (IC₅₀: 64 ± 5 μM), baicalein (IC₅₀: 80 ± 6 μM) and wogonin (IC₅₀: 39 ± 10 μM) were comparable to that of the antineoplastic cisplatin (IC₅₀: 79 ± 16 μM). A partial least squares regression (PLS)-NMR model highly correlated with the corresponding PLS-HPLC model for prediction of inhibition. Secondary metabolite mapping of lung cancer growth inhibitors in crude extracts may be an important first step to qualify Chinese herbal prescriptions required for meaningful clinical trials of such integrated therapies.