The evaluation of the interaction of baicalein (5,6,7-trihydroxyflavone) with human IgG and a glioblastoma multiforme (GBM) cell line

Abstract

Baicalein, a nutritional phenolic bioactive small molecule present in the roots of Scutellaria baicalensis and Scutellaria lateriflora, shows promising therapeutic effects against a wide range of cancer cells. However, its potential binding with blood carrier proteins and its anticancer mechanisms have not been well investigated. In this study, the interaction between baicalein and immunoglobulin G (IgG) was analyzed by analyzing intrinsic fluorescence, ellipticity changes, as well as molecular docking. The anticancer effects of baicalein against a glioblastoma multiforme (GBM) cell line, U87MG, and one normal immortalized human astrocytes were assessed by MTT, real-time PCR, caspase assay, and western blot. It was shown that the fluorescence quenching mechanism of human IgG by baicalein was based on a static quenching, where one binding site was responsible for the formation of baicalein-IgG complex derived by the formation of hydrogen bonds and van der Waals forces. A molecular docking study indicated that tyrosine residues (Tyr 91 and Tyr 98) were mostly involved in the binding site of baicalein to IgG. The cellular assay demonstrated that baicalein induced U87MG cell line death with an IC₅₀ concentration of 73.19 µM, whereas normal astrocytes depicted over 82.94% portion of viability at 100 µM baicalein. The Bax mRNA overexpression, Bcl-2 mRNA downexpression, as well as the elevation of caspase-9 and caspase-3 activities confirmed that baicalein could effectively trigger the apoptosis of U87MG cells. Moreover, it was explored that baicalein downregulated the expression of the Axl/STAT3 signaling pathway in the U87MG cells, which is responsible for cellular proliferation and growth. In conclusion, these data may provide useful information regarding the pharmaceutical application of baicalein.