Discovery of an Indirubin Derivative as a Novel c-Met Kinase Inhibitor with In Vitro Anti-Tumor Effects

The c-Met protein is a receptor tyrosine kinase involved in cell growth, proliferation, survival, and angiogenesis of several human tumors. Overexpression of c-Met has been found in gastric cancers and correlated with a poor prognosis. Indirubin is the active component of Danggui Longhui Wan, which is a traditional Chinese antileukemic recipe. In the present study, we tested the anti-cancer effects of an indirubin derivative, LDD-1937, on human gastric cancer cells SNU-638. When we performed the in vitro kinase assay against the c-Met activity, LDD-1937 inhibited the activity of c-Met. This result was confirmed by immunoblot and immunofluorescence of phosphorylated c-Met. Immunoblot analysis showed that LDD-1937 decreased the expression of the Erk1/2, STAT3, STAT5, and Akt, downstream proteins of c-Met. In addition, LDD-1937 reduced the cell viability and suppressed colony formation and migration of SNU-638 cells. Furthermore, LDD-1937 induced G2/M phase arrest in the SNU-638 cells by decreasing the expression levels of cyclin B1 and CDC2. Cleaved-PARP, an apoptosis-related protein, was up-regulated in cells treated with LDD-1937. Overall, this study suggests that LDD-1937 may be a novel small-molecule with therapeutic potential for selectively inhibiting c-Met and c-Met downstream pathways in human gastric cancers overexpressing c-Met.

Characterization of the Indirubin Derivative LDD970 as a Small Molecule Aurora Kinase A Inhibitor in Human Colorectal Cancer Cells

Aurora kinase A plays an essential role in mitosis including chromosome separation and cytokinesis. Aberrant expression and activity of Aurora kinase A is associated with numerous malignancies including colorectal cancer followed by poor prognosis. The aim of this study is to determine the inhibitory effects of LDD970, an indirubin derivative, on Aurora kinase A in HT29 colorectal cancer cells. In vitro kinase assay revealed that, LDD970 inhibited levels of activated Aurora kinase A (IC₅₀=0.37 mM). The inhibitory effects of LDD970 on Aurora kinase A, autophosphorylation and phosphorylation of histone H3 (Ser10), were confirmed by immunoblot analysis. Moreover, LDD970 inhibited migration of HT29 cells and upregulated apoptosis-related protein cleaved PARP. In cell viability assay, LDD970 was observed to suppress HT29 cell growth (GI₅₀=4.22 µM). Although further studies are required, results of the present study suggest that LDD970 provide a valuable insight into small molecule indirubin derivative for therapeutic potential in human colorectal cancer.