Mechanism Study Of Active Compounds In Radix Actinidia On Inhibiting Colon Cancer Cells Survival

The epidermal growth factor receptor (EGFR) and Mitogen-activated protein kinase (MAPK) cascades are key signaling pathways involved in the regulation of colon caner cells proliferation, survival, differentiation and angiogenesis. Thus, the EGFR-Ras-Raf-MEK-ERK signaling network has been the subject of intense research and pharmaceutical scrutiny to identify novel target-based approaches for cancer treatment. Many traditional Chinese medicinal herbs, such as Radix actinidia, are commonly used in colorectal cancer treatment in China, but the mechanism is not yet fully understood. Ursolic acid and oleanolic acid are two active compounds present in the herb. Previous studies reported that they exhibits a broad range of pharmacological properties such as anti-inflammatory, antiviral, antioxidant, hepatoprotective, cytotoxic, anti-tumor, anti-angiogenesis, anti-metastasis activities. In this study, we investigate the effects of ursolic acid on the proliferation and apoptosis of human colon cancer cells through EGFR/MAPK signal pathway, and combined ursolic acid with chemotherapy drug oxaliplatin in vitro and in vivo. The MTT assay revealed that ursolic acid had the lowest IC50 values against four pairs of drug-sensitive and drug-resistant tumor cells in vitro, and among which ursolic acid displayed the strongest cytotoxic effect compared with oleanolic acid. We further examined ursolic acid inhibited cell proliferation and induced cell apoptosis in EGFR positive Cells, or KRAS mutation cells, or BRAF and PIK3CA mutation cells of human colon adenocarcinoma. Treated with ursolic acid demonstrated a dose-and time-dependent manner of cell growth and apoptosis. MEK1/2, ERK1/2 and IKKa were constitutively activated at transcriptional and protein level in K-RAS colon cancer cells, of which down-regulated of phosphorylation ERK1/2 level had a key role to ursolic acid treatment, whereas ERK1/2, AKT and IKKa were constitutively activated in BRAF and PIK3CA colon cancer cells at transcriptional and protein level, but showed relative resistant to ursolic acid. The mechanism partly belongs to PIK3CA mutant status which active the AKT signaling. Besides, ursolic acid also down-regulated the expression of Bcl-2, Bcl-xL, survivin and activated caspase-3,-8,-9. Finally, combined with ursolic acid and oxaliplatin at a suboptional dosage reached a synergistical effect in vitro. We further established a xenograft model in BALB/c-nu/nu mice inoculated with human SW620 colon cancer cells. We found that combined with ursolic acid and oxaliplatin significantly inhibited the growth of SW620 xenograft in comparison to controls and single drug alone. The immuhistochemistry assay and western blot assay found that combined with ursolic acid and oxalipaltin significantly decreased level of phosphyration ERK1/2 and CD34 in xenograft. To conclusion, we demonstrated that the naturally-occurring ursolic acid inhibited colon cancer cells proliferation and induced apoptosis, and more sensitive to K-RAS mutant colon cancer cells cpmparison to BRAF and PIK3CA mutant colon cancer cells. Ursolic acid combined with oxaliplatin at a suboptional dosage reached a synergistical effect in vitro, and antiangiogenesis effect in vivo. These results support Radix actindia used in clinical colon cancer treatment, and ursolic acid as potential applications in colon cancer therapy.