Salinomycin and Sulforaphane Exerted Synergistic Antiproliferative and Proapoptotic Effects on Colorectal Cancer Cells by Inhibiting the PI3K/Akt Signaling Pathway in vitro and in vivo

BACKGROUND: Both salinomycin (SAL) and sulforaphane (SFN) exert their antitumorigenic effects in various types of cancer We investigated whether combining salinomycin (SAL, an antibiotic ionophore) with sulforaphane (SFN, a phytochemical) exerted synergistic antiproliferative and proapoptotic activities in colorectal cancer (CRC) cells in vitro and in vivo by evaluating the proliferative and apoptotic responses of two CRC cell lines. MATERIALS AND METHODS: The combination index (CI) was calculated using the Chou-Talalay method, and the effects of the synergistic combination (CI<1) of lower doses of SAL and SFN were selected for further studies. Anti-tumor effect of the combination of SAL and SFN was tested both in vitro and in vivo. RESULTS: Cotreatment effectively inhibited proliferation, migration and invasion and enhanced apoptosis. The xenograft model also showed similar results. Furthermore, we evaluated the molecular mechanism behind SAL- and SFN-mediated CRC cell apoptosis. The combination treatment induced apoptosis in Caco-2 and CX-1 cells by inhibiting the PI3K/Akt pathway, which increased the expression of the tumor suppressor protein p53. The treatment also decreased the expression of the survival protein Bcl-2 and increased the expression of the proapoptotic protein Bax, which increased the Bax/Bcl-2 ratio, as well as enhanced poly ADP-ribose polymerase (PARP) cleavage. Upon inhibiting the PI3K/Akt pathway with LY294002 prior to cotreatment, we detected enhanced PARP cleavage compared to that in the cotreatment only group. CONCLUSION: We investigated whether the combination of SAL and SFN had antiproliferative and proapoptotic effects in CRC cells both in vitro and in vivo. Cotreatment also significantly decreased migration and invasion compared to that of the control and SAL or SFN monotherapies. This novel combination of SAL and SFN might provide a potential strategy to treat CRC.