Effect of total flavonoids in Scutellaria barbata in mediating autophagy in tumor cells via PI3K/AKT/mTOR pathway

Abstract

To investigate the effect of the total flavonoids in Scutellaria barbata(TF-SB) against autophagy in tumor cells in vivo, and further determine whether the mechanism is correlated with the PI3K/AKT/mTOR pathway, which lead to autophagy-induced tumor cell death. Melanoma-bearing mice were prepared and divided into control group, rapamycin group (Rap 1.5 mg•kg⁻¹), and high, middle and low-dose TF-SB (200, 100, 50 mg•kg⁻¹) groups. The groups were given drugs once a day for successively 11 days. The inhibitory effect of TF-SB on the growth of melanoma was determined by measuring tumor volume and tumor inhibition rate. TUNEL method was used to detect the apoptosis of tumor cells to further verify the antitumor activity of TF-SB. The protein expressions of LC3-Ⅰ and LC3-Ⅱ were detected by Western blot, and the relative expression of LC3-Ⅱ was calculated based on LC3-Ⅱ/LC3-Ⅰ. In addition, the effect of TF-SB on autophagy of tumor cells, the underlying molecular mechanism of TF-SB in inducing autophagy and PI3K/AKT/mTOR pathway marker protein phosphorylation were also studied. According to the results, TF-SB effectively inhibited melanoma growth in mice, reduced tumor volume, increased the tumor inhibition rate, and significantly increased tumor cell apoptosis index and the ratio of LC3-Ⅱ/LC3-I (P<0.05, P<0.01 or P<0.001). The protein expressions of p-PI3K, p-AKT and p-mTOR were also suppressed dramatically compared with those in control group (P<0.05, P<0.01 or P<0.001). In conclusion, the total flavonoids in S. barbata could inhibit the growth of melanoma in vivo by inducing autophagy and apoptosis of tumor cells, which may be correlated with suppression of PI3K/AKT/mTOR pathway.