Discovery of specific inhibitors for intestinal E. coli ß-glucuronidase through in silico virtual screening.

Glucuronidation is a major metabolism process of detoxification for carcinogens, 4-(methylnitrosamino)-1-(3-pyridy)-1-butanone (NNK) and 1,2-dimethylhydrazine (DMH), of reactive oxygen species (ROS). However, intestinal E. coli ß-glucuronidase (eßG) has been considered pivotal to colorectal carcinogenesis. Specific inhibition of eßG may prevent reactivating the glucuronide-carcinogen and protect the intestine from ROS-mediated carcinogenesis. In order to develop specific eßG inhibitors, we found that 59 candidate compounds obtained from the initial virtual screening had high inhibition specificity against eßG but not human ßG. In particular, we found that compounds 7145 and 4041 with naphthalenylidene-benzenesulfonamide (NYBS) are highly effective and selective to inhibit eßG activity. Compound 4041 (IC50 = 2.8 µM) shows a higher inhibiting ability than compound 7145 (IC50 = 31.6 µM) against eßG. Furthermore, the molecular docking analysis indicates that compound 4041 has two hydrophobic contacts to residues L361 and I363 in the bacterial loop, but 7145 has one contact to L361. Only compound 4041 can bind to key residue (E413) at active site of eßG via hydrogen-bonding interactions. These novel NYBS-based eßG specific inhibitors may provide as novel candidate compounds, which specifically inhibit eßG to reduce eßG-based carcinogenesis and intestinal injury.

Furano-1,2-Naphthoquinone Inhibits Src and PI3K/Akt Signaling Pathways in Ca9-22 Human Oral Squamous Carcinoma Cells.

Furano-1,2-naphthoquinone (FNQ), a biologically active component ofAvicennia marina, has been demonstrated to display anticancer activity. FNQ exerted cytotoxicity with the G2/M cell cycle arrest and apoptosis in Ca9-22 cells. FNQ-induced G2/M arrest was correlated with a marked decrease in the expression levels of cyclin A and cyclin B, and their activating partner cyclin-dependent kinases (CDK) 1 and 2 with concomitant induction of p27. FNQ-induced apoptosis was accompanied by Bax and Bad upregulation, and the downregulation of Bcl-2, Bcl-XL, Mcl-1, and X-linked inhibitor of apoptosis (XIAP), resulting in cytochrome C release and sequential activation of caspase-9 and caspase-3. Mechanistic studies showed that FNQ suppressed Src phosphorylation, PI3K, and Akt activation in Ca9-22 cells. Moreover, the Src inhibitor PP2 reduced the phosphorylation of Src and activation of PI3K/Akt, which was comparable with FNQ treatment. The combined treatment of FNQ with PP2 enhanced the cell cycle arrest and apoptosis and also led to the downregulation of Bcl-XL, Mcl-1, XIAP, cyclin A, cyclin B, CDK1, and CDK2 and upregulation of p27, Bax, and Bad. These findings suggest that FNQ-mediated cytotoxicity of Ca9-22 cells is related with the G2/M cell cycle arrest and apoptosis via inactivation of Src and PI3K/Akt-mediated signaling pathways.

Brazilein suppresses migration and invasion of MDA-MB-231 breast cancer cells.

Brazilein, a bioactive compound isolated from Caesalpinia sappan L., has long been used in oriental folk medicines. Cancer metastasis is a primary cause of cancer death. However, the anti-metastatic effects of brazilein remain elusive. In this study, we found that brazilein inhibited human breast cancer MDA-MB-231 cell migration and invasion using wound-healing assay and Boyden chamber assay. The results of Western blot, gelatin zymography and reversed transcription-PCR analysis showed that brazilein suppressed matrix metalloproteinase-2 (MMP-2) expression in a concentration-dependent manner. Brazilein also decreased the nuclear protein level of nuclear factor kappaB (NF-κB). Brazilein potently suppressed the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), phosphatidylinositide-3-kinase (PI3K) and Akt, but did not affect phosphorylation of extracellular signal regulating kinase (ERK)1/2 and c-Jun N-terminal kinase (JNK). Additionally, treatment of SB203580 (p38 MAPK inhibitor) or wortmannin (PI3K inhibitor) resulted in a reduced activity and expression of MMP-2 as well as inhibition on cell migration and invasion in MDA-MB-231 cells. Taken together, these results suggest that brazilein inhibition of MDA-MB-231 cells may be mediated through inactivation of both PI3K/Akt and p38 MAPK signaling pathways, leading to inhibitory effect on NF-κB activation. Consequently, brazilein suppresses MMP-2 expression, and thus confers anti-migration and anti-invasion of MDA-MB-231 cells.