6-Hydroxy-3-O-methyl-kaempferol 6-O-glucopyranoside potentiates the anti-proliferative effect of interferon alpha/beta by promoting activation of the JAK/STAT signaling by inhibiting SOCS3 in hepatocellular carcinoma cells

Suppressor of cytokine signaling 3 (SOCS3) is a key negative regulator of type I interferon (IFN alpha/beta) signaling. Inhibition of SOCS3 by small molecules may be a new strategy to enhance the efficacy of type I IFN and reduce its side effects. We established a cell-based screening assay using human hepatoma HepG2 cells stably transfected with a plasmid wherein the luciferase reporter activity was propelled by interferon alpha-stimulated response element (ISRE), which is a motif specifically recognized by type I IFN-induced activation of Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. After screening our chemical library, 6-hydroxy-3-O-methyl-kaempferol 6-O-glucopyranoside (K6G) was identified to be a potent activator of type I IFN with EC50 value of 3.33 +/- 0.04 mu M. K6G enhanced the phosphorylation of JAK1, Tyk2, and STAT1/2 but decreased the phosphorylation of STAT3. K6G also promoted endogenous IFN-alpha-regulated genes expression. More interestingly, K6G significantly decreased the expression of SOCS3 without affecting the expression of SOCS1. Furthermore, K6G enhanced the anti-proliferative effect of IFN-alpha on hepatocellular carcinoma (HCC) cells. These results suggested that K6G potentiated the inhibitory effect of IFN-alpha on HCC cell proliferation through activation of the JAK/STAT signaling pathway by inhibiting SOCS3 expression. K6G warrants further investigation as a novel therapeutic method to enhance the efficacy of IFN-alpha/beta

Dietary quercetin potentiates the antiproliferative effect of interferon-alpha in hepatocellular carcinoma cells through activation of JAK/STAT pathway signaling by inhibition of SHP2 phosphatase

Type I interferons (IFN-alpha/beta) have broad and potent immunoregulatory and antiproliferative activities, which are negatively regulated by Src homology domain 2 containing tyrosine phosphatase-2 (SHP-2). Inhibition of SHP2 by small molecules may be a new strategy to enhance the effcacy of type I IFNs. Using an in vitro screening assay for new inhibitors of SHP2 phosphatase, we found that quercetin was a potent inhibitor of SHP2. Computational modeling showed that quercetin exhibited an orientation favorable to nucleophilic attack in the phosphatase domain of SHP2. Quercetin enhanced the phosphorylation of signal transducer and activator of transcription proteins 1 (STAT1) and promoted endogenous IFN-alpha-regulated gene expression. Furthermore, quercetin also sensitized the antiproliferative effect of IFN-alpha on hepatocellular carcinoma HepG2 and Huh7 cells. The overexpression of SHP2 attenuated the effect of quercetin on IFN-alpha-stimulated STAT1 phosphorylation and antiproliferative effect, whereas the inhibition of SHP2 promoted the effect of quercetin on IFN-alpha-induced STAT1 phosphorylation and antiproliferative effect. The results suggested that quercetin potentiated the inhibitory effect of IFN-alpha on cancer cell proliferation through activation of JAK/STAT pathway signaling by inhibiting SHP2. Quercetin warrants further investigation as a novel therapeutic method to enhance the efficacy of IFN-alpha/beta