Suppression of Slit3 induces tumor proliferation and chemoresistance in hepatocellular carcinoma through activation of GSK3ß/ß-catenin pathway.

BACKGROUND: It is essential to understand the mechanisms responsible for hepatocellular carcinoma (HCC) progression and chemoresistance in order to identify prognostic biomarkers as well as potential therapeutic avenues. Recent findings have shown that SLIT3 appears to function as a novel tumor suppressor gene in various types of cancers, yet its clinical correlation and role in HCC has not been understood clearly. METHODS: We determined the transcript levels of Slit3 in tumor and adjacent normal tissues within two cohorts (N = 40 and 25) of HCC patients, and correlated the gene expression with the clinicopathological data. Subsequently, the functional effects and underlying molecular mechanisms of Slit3 overexpression and/or repression were studied using cell-line and mouse models. RESULTS: Our results demonstrated a repression in Slit3 expression in nearly 50% of the HCC patients, while the overall expression of Slit3 inversely correlated with the size of the tumor in both cohorts of patients. Stable down-regulation of Slit3 in HCC cell-lines induced cell proliferation in vitro and tumor growth in vivo, while stable Slit3 overexpression repressed these effects. Molecular investigations showed that the stable Slit3 repression-induced cell proliferation was associated with a higher expression of ß-catenin and a repressed GSK3ß activity. Moreover, Slit3-repression induced chemoresistance to sorafenib, oxaliplatin and 5-FU through impairment of ß-catenin degradation and induction of cyclin D3 and survivin levels. The effects induced by stable Slit3-repression were diminished by transient repression of ß-catenin by siRNA approach. CONCLUSION: This study suggests that Slit3 acts as a tumor suppressor in HCC by repressing the tumor growth and thus tumor progression. Low Slit3 level indicates a poor response of HCC cells to chemotherapy. Restoration or overexpression of Slit3 is a potential therapeutic approach to repress the tumor growth and enhance the efficacy of chemotherapeutic agents.

Preclinical analysis of the anti-tumor and anti-metastatic effects of Raf265 on colon cancer cells and CD26(+) cancer stem cells in colorectal carcinoma.

BACKGROUND: In colorectal carcinoma (CRC), activation of the Raf/MEK/ERK signaling pathway is commonly observed. In addition, the commonly used 5FU-based chemotherapy in patients with metastatic CRC was found to enrich a subpopulation of CD26(+) cancer stem cells (CSCs). As activation of the Raf/MEK/ERK signaling pathway was also found in the CD26(+) CSCs and therefore, we hypothesized that an ATP-competitive pan-Raf inhibitor, Raf265, is effective in eliminating the cancer cells and the CD26(+) CSCs in CRC patients. METHODS: HT29 and HCT116 cells were treated with various concentrations of Raf265 to study the anti-proliferative and apoptotic effects of Raf265. Anti-tumor effect was also demonstrated using a xenograft model. Cells were also treated with Raf265 in combination with 5FU to demonstrate the anti-migratory and invasive effects by targeting on the CD26(+) CSCs and the anti-metastatic effect of the combined treatment was shown in an orthotopic CRC model. RESULTS: Raf265 was found to be highly effective in inhibiting cell proliferation and tumor growth through the inhibition of the RAF/MEK/ERK signaling pathway. In addition, anti-migratory and invasive effect was found with Raf265 treatment in combination with 5FU by targeting on the CD26(+) cells. Finally, the anti-tumor and anti-metastatic effect of Raf265 in combination with 5FU was also demonstrated. CONCLUSIONS: This preclinical study demonstrates the anti-tumor and anti-metastatic activity of Raf265 in CRC, providing the basis for exploiting its potential use and combination therapy with 5FU in the clinical treatment of CRC.