Objective  To investigate the potential antitumor effects of cholesterol-conjugated let-7a mimics (let-7a mimics) on hepatocellular carcinoma (HCC) by down-regulating all 3 human Ras, with the aim to explore alternative therapeutic strategy for HCC.

  Methods  Effects of let-7a mimics on HCC cells in vitro were detected using MTT-based cell proliferation assays in combination with propidium iodide staining and annexin-V/FITC double staining. The antitumor effects in vivo of let-7a mimics on HCC growth were analyzed in subcutaneous xenograft nude mice with intra-tumoral injections. Expressions of let-7a and its target human Ras were examined with real-time PCR and Western blot.

  Results  let-7a mimics-transfected HCC cells showed increased let-7a levels and slower proliferation compared with the negative controls (both P < 0.05). let-7a mimics induced more cell-cycle arrest at the G0-G1 phase and promoted apoptosis of HCC cells (both P < 0.05). In addition, significant reductions in tumor size, local invasion and metastasis to liver were observed in let-7a mimics-treated nude mice compared to negative controls. The tumor size after let-7a treatment was 54.97% that of negative controls (P=0.039). Furthermore, the up-regulation of let-7a coincided with the reduction of K-Ras, H-Rras, and N-Ras mRNA and protein expressions in HCC cells and xenograft tumor (all P < 0.05).

  Conclusions  let-7a mimics could affect cell cycle, inhibit cell proliferation and promote cell apoptosis by downregulation of mRNA and protein expressions of all the 3 human Ras. Local injections of cholesterol-conjugated let-7a mimics could effectively suppress the growth, invasion and metastasis of xenograft tumor. These findings suggest that Ras-targeting let-7 mimics could be a potential therapeutic option for HCC.