Synergetic Inhibition of Human Colorectal Cancer Cells by Combining Polyyne-Enriched Fraction from Oplopanax elatus and Irinotecan

Although irinotecan is an important anticancer drug for treating colorectal cancer, its dose-dependent side effects limited its clinical application. Thus, it's important to develop low-toxic candidates to enhance the efficacy of irinotecan. Polyynes from genus Oplopanax were reported to possess potential anticancer effects on colorectal cancer. Hereby, we evaluated the synergetic inhibition of human colorectal cancer cells by combining polyyne-enriched fraction from Oplopanax elatus (the dichloromethane fraction of Oplopanax elatus, OED) and irinotecan. The results showed that 5 mu g/ml of OED combined with 40 mu M of irinotecan possessed significant synergetic inhibition on SW-480 cells with a combination index (CI) of 0.56. Besides, the percentage of apoptotic cells was significantly increased from 69.57% (40 mu M of irinotecan) or 72.7% (5 mu g/ml of OED) to 95.6% after treatment of OED combined with irinotecan (OCI), suggesting OED and irinotecan possess the synergistic apoptotic effect (P < 0.01). Furthermore, Caspase-3 was significantly activated in OCI group (P < 0.05). Besides, the percentage of apoptotic cells of OED or/and irinotecan significantly decreased after inhibition of caspase-3. These data indicated that OED could enhance antiproliferative effects of irinotecan on colorectal cancer cells, which was related with induction of apoptosis and regulations of activity of caspase-3.