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Genkwadaphnin (GD-1) is isolated from the flower buds of Daphne genkwa Siebold et Zuccarini (Thymelaeaceae), and it has been used as a traditional Korean and Chinese medicine. In this study, the authors observe that GD-1 inhibits the growth of the colon cancer cell line, SW620, through the up-regulation of p21 expression in a PRDM1-dependent manner. After treatment with GD-1, the transcriptional repressor PRDM1 is prominently induced in SW620 cells. Furthermore, GD-1 induce the phosphorylation of PKD1 and MEK and subsequently provide PRDM1 enhancement, resulting in the suppression of c-Myc expression and the up-regulation of p21. PKD1 knockdown using siRNA abrogates PRDM1 expression by GD-1 and subsequently disrupts the regulation of c-Myc and p21 expression. Treating SW620 cells with GD-1 inhibits cell-cycle progression and is characterized by the down-regulation of c-Myc followed by the up-regulation of p21 expression. The up-regulation of p21 by GD-1 induces the growth arrest of the SW620 colon cancer cell line. Based on these data, the authors propose that GD-1 has tumor-suppressor activity that may contribute to the anti-tumor effects of PRDM1 in colon cancer.

Bioactivity-guided fractionation of the leaves of aleurites fordii leads to the isolation of the new phorbol ester (I) together with four known phorbol esters.