Down-regulation of Notch1 signaling inhibits tumor growth in human hepatocellular carcinoma

In some human cancers, the Notch1 receptor and signaling pathway is upregulated, which increases the oncogenic potential of the cell through prevention of differentiation and inhibition of apoptosis. We sought to evaluate the role of Notch1 in hepatocellular cancer (HCC), and evaluate the therapeutic efficacy of curcumin, a known Notch1 inhibitor. Human liver tumors were compared to normal liver to evaluate for Notch1 and Notch1 Intracellular Domain (NICD). Three human HCC cell lines were exposed to curcumin and evaluated for downstream effectors by Western blot. In addition, standard MTT assays were performed to assess the effect of curcumin in vitro. Finally, a nude mouse xenograft model was utilized to assess the response to curcumin in vivo. High levels of NICD were present in the majority of human HCC samples and all three HCC cell lines. Treatment with curcumin led to a dose-dependent decrease in the expression of NICD associated with the induction of cleaved poly ADP-ribose polymerase (PARP), the degradation of cyclin D1 and increase in cyclin-dependent kinase p21. Curcumin inhibited HCC cell proliferation in vitro. Importantly, transfection of Notch1 small-interfering RNA (siRNA) into HCC cells resulted in cell growth inhibition and apoptosis, recapitulating the effects of curcumin. Finally, treatment with curcumin resulted in a 40% decrease in tumor growth in vivo. These results suggest for the first time that down-regulation of Notch1 signaling with curcumin is an attractive new therapeutic strategy for the treatment of patients with HCC.