Targeting beta-catenin signaling in colorectal cancer: anti-cancer bioactivities of 20(S)-25-OCH3-PPD, a natural product from Panax notoginseng Free

A141

It is well known that the Wnt-β-catenin pathway plays a critical role in colorectal carcinogenesis, thus, agents targeting this pathway could be effective in prevention or therapy . This study was designed to evaluate a novel natural product, dammarane-type triterpene sapogenin, 20(S)-25-OCH3-PPD (PPD25), from the leaves of P.notoginseng. The anti-cancer biological activities of PPD25 were evaluated on 5 human colorectal cancer cell lines, which were LS174, HCT116, HT29, SW480 and SW620. We found that PPD25 significantly inhibited cell viability and cell proliferation in all cell lines. We then chose LS174 and SW620 for further studies. We found that PPD25 was also effective in the induction of apoptosis in both cell lines, though it did not affect the cell cycle. To elucidate the underlying mechanisms, we treated the LS174 cells with PPD25 in the concentrations of 5 and 25 μM for 48 hours, to determine the alterations of gene expression. We found that the expression of β-catenin, a key regulator in the Wnt pathway, was significantly reduced, and that the downstream elements of β-catenin, cyclin D1 and cdk4 were also repressed. To determine whether PPD25 has effects on β-catenin/TCF transcriptional activity, we transfected LS174 cells with β-catenin/TCF luciferase reporter construct TOPFlash which contains multiple optimal TCF/LEF binding sites that induce transcription of a luciferase reporter gene when activated by β-catenin. Indeed, the β-catenin/TCF transcriptional activity was significantly suppressed by PPD25. But, the expression of E-cadherin, a component of the β-catenin complex, was not changed by the PPD25. Taken together, our data demonstrated that 20(S)-25-OCH3-PPD has anti-colorectal cancer bioactivities through targeting beta-catenin signaling, suggesting that 20(S)-25-OCH3-PPD merits further investigation as a potential agent for chemoprevention and chemotherapy in colorectal cancer.