[Inhibitory effects of small interfering RNA targeting c-myc in combination with 5-fluorouracil on the growth in vitro and in vivo].

OBJECTIVE: To observe the effects of small interfere RNA (siRNA) targeting the c-myc in combination with 5-fluorouracil (5-Fu) on the growth of Hep-2 cells in vitro and in vivo.

METHODS: Hep-2 cells transfected with or without c-myc siRNA were treated with 5-Fu for 48 h. C-myc protein levels in Hep-2 cells were detected using the Western blot. The cell cycle was analyzed by flow cytometry. Hep-2 cells were subcutaneously inoculated into the back of BALB/c nude mice to establish the implanted laryngeal squamous carcinoma model. PBS, c-myc siRNA, and 5-Fu, alone or in combinations were administered i.p. The mice were sacrificed after the treatments and the tumor masses were removed to determine the tumor volume and weight. The inhibitory rate was calculated. Expression of c-myc in tumor tissue was detected by immunocytochemistry and cell apoptosis was analyzed by terminal transferase dUTP nick end labeling (TUNEL).

RESULTS: The protein levels of c-myc decreased after transfected with c-myc siRNA. C-myc siRNA-transfected cells showed an increase in the percentage of cells in the GO-G1 phase and a decrease in the percentage of cells in the S phase. When combined with 5-Fu, the results were improved. The tumor growth was faster in the control group and was significantly slower in the c-myc siRNA plus 5-Fu group than that in the c-myc siRNA group or 5-Fu group (P < 0.05). The tumor weight in the c-myc siRNA plus 5-Fu group was significantly smaller than that in the c-myc siRNA or 5-Fu group (P < 0.05). Immunohistochemistry showed that c-myc siRNA inhibited the expression of c-myc in tumor tissues in the c-myc siRNA group and c-myc siRNA plus 5-Fu group (P < 0.05). The number of apoptotic cells in the c-myc siRNA plus 5-Fu group was higher than those in the c-myc siRNA groups (P < 0.05).

CONCLUSIONS: C-myc siRNA inhibits the expression of c-myc in Hep-2 cells and in the tumor tissues of nude mice. C-myc siRNA combined with 5-Fu inhibits the growth of implanted laryngeal squamous carcinoma and promotes cell apoptosis. C-myc could become a novel target for the treatment of laryngeal squamous carcinoma.