RNAi has been successfully applied in genomic research, and it also holds considerable promise as a therapeutic approach to suppress disease-causing gene expression. Here, we show that attenuated S. typhimurium were capable of delivering shRNA-expressing vectors to mammalian cells and inducing RNAi in vitro and in vivo. Upon oral administration, S. typhimurium carrying shRNA-expressing vectors targeting bcl2 induced significant gene silencing in murine melanoma cells that led to a remarkably delayed tumor growth and prolonged survival in the mouse model. These results suggest that bacteria mediated RNAi may be a new potent approach to the treatment of cancers.

Colon cancer is one of the major causes of cancer mortality worldwide. However, the underlying mechanism and therapeutic targets of colon cancer have not yet been fully elucidated. In the present study, we demonstrate that citron rho-interacting, serine/threonine kinase 21 (CIT) promotes the growth of human colon cancer cells. CIT is overexpressed in human colon cancer tissues and cell lines. High expression of CIT predicts poor survival for patients with colon cancer. In colon cancer cells, CIT knockdown represses cellular proliferation and colony formation. Our in vivo xenograft experiments showed that CIT knockdown reduces the growth rate of colon cancer cells and the final tumor weight. We found that CIT knockdown induces cell cycle arrest and apoptosis in colon cancer cells. Further microarray and bioinformatics analyses indicated that CIT regulates the p53 signaling pathway, which may account for the effects of CIT on colon cancer cells. Taken together, our findings provide evidence that CIT may promote the development of colon cancer, at least in part, through the p53 signaling pathway. Therefore, CIT may be a potential therapeutic target for colon cancer treatment.

Attenuated Salmonella typhimurium possess the ability to stimulate innate immune responses and preferentially allocate within the solid tumor. These two main characteristics make attenuated Salmonella one of the most attractive vehicles for development of vaccine and also targeted cancer therapies. However, location of Salmonella prevents the process of antigen presentation. Salmonella Type III secretion system can be utilized to circumvent this problem because this system secretes the protein it encoded outside the cells. Heat shock protein 70 (Hsp70) is referred to as an "immunochaperone" for its capacity to elicit tumor-specific adaptive immune responses in the form of Hsp70-TAA (tumor associated antigen) complex. Hsp70 facilitates the cross-presentation of exogenous antigens through its receptor on antigen-presenting cells and therefore activates an antigen-specific cytotoxic T lymphocyte (CTL) response, which can directly contribute to potent anti-tumor immunity. Here, we designed a novel therapeutic vaccine utilizing the type III secretion system and Hsp70 to deliver and present the tumor-specific antigen. This live recombinant bacteria vaccine, when administrated orally, successfully broke the immune tolerance, induced a specific CTL response against tumor cells, and therefore revealed protective and therapeutic effects against generation and growth of B16F10 melanoma in C57BL/6J mice.

Therapeutic vaccines of cancer are attractive for their capacity of breaking the immune tolerance and invoking long-term immune response targeting cancer cells without autoimmunity. An efficient antigen delivery system is the key issue of developing an effective cancer vaccine. Attenuated Salmonella typhimurium as the carrier of cancer vaccine are able to transfer DNA from the prokaryote to the eukaryote and preferentially replicate within the tumor tissue. Heat shock protein 70 delivers the tumor-associated antigens to antigen presenting cells through its polypeptide-binding domain and breaks immune tolerance of the cancer cells. Here we described a novel low-copy-number DNA vaccine based on the Hsp70-TAA complex and carried by the attenuated S. typhimurium strain SL3261. Oral administration of this vaccine elicited specific CTL-mediated lysis of the melanoma tumor cells and marked activation of the T-cells. The therapeutic vaccine effectively protected 57.1% C57BL/6J mice from lethal challenge with B16F10 melanoma tumor cells in prophylactic settings and eraicated 62.5% tumor growth in therapeutic settings. This approach may provide a new strategy for the prevention and treatment of cancer.