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Since its discovery in 1998 RNA interference (RNAi), a potent and highly selective gene silencing mechanism, has revolutionized the field of biological science. The ability of RNAi to specifically down-regulate the expression of any cellular protein has had a profound impact on the study of gene function in vitro. This property of RNAi also holds great promise for in vivo functional genomics and interventions against a wide spectrum of diseases, especially those with "undruggable" therapeutic targets. Despite the enormous potential of RNAi for medicine, development of in vivo applications has met with significant problems, particularly in terms of delivery. For effective gene silencing to occur, silencing RNA must reach the cytoplasm of the target cell. Consequently, various strategies using chemically modified siRNA, liposomes, nanoparticles and viral vectors are being developed to deliver silencing RNA. These approaches, however, can be expensive and in many cases they lack target cell specificity or clinical compatibility. Recently, we have shown that RNAi can be activated in vitro and in vivo by non-pathogenic bacteria engineered to manufacture and deliver silencing shRNA to target cells. This new approach, termed TransKingdom RNAi (tkRNAi), has several key advantages. First, tkRNAi may provide a viable means to accomplish therapeutic RNAi since non-pathogenic bacteria have a proven safety record in clinical applications. Second, tkRNAi eliminates the cost of siRNA manufacture since silencing shRNA are produced inside bacteria. Moreover, the intracellular mechanism of shRNA release inherent to tkRNAi may circumvent, or mitigate, the activation of host immune responses. Finally, tkRNAi may facilitate high-throughput in vivo functional genomics screening since bacteria-based RNAi libraries can be easily constructed, stored, reproduced and amplified, thereby allowing for the creation of a stable gene silencing system.

Over the last few years, RNA Interference (RNAi), a naturally occurring mechanism of gene regulation conserved in plant and mammalian cells, has opened numerous novel opportunities for basic research across the field of biology. While RNAi has helped accelerate discovery and understanding of gene functions, it also has great potential as a therapeutic and potentially prophylactic modality. Challenging diseases failing conventional therapeutics could become treatable by specific silencing of key pathogenic genes. More specifically, therapeutic targets previously deemed "undruggable" by small molecules, are now coming within reach of RNAi based therapy. For RNAi to be effective and elicit gene silencing response, the double-stranded RNA molecules must be delivered to the target cell. Unfortunately, delivery of these RNA duplexes has been challenging, halting rapid development of RNAi-based therapies. In this review we present current advancements in the field of siRNA delivery methods, including the pros and cons of each method.

The etiology and significance of genomic instability (GIN), a hallmark of human cancers, remains controversial. The paradigm that inactivation of tumor suppressors [e.g. p53 or adenomatous polyposis coli (APC) genes] leads to GIN is largely based on experiments in vitro and in animal models. It remains unclear whether GIN is a cause or a result of cancer, particularly in patients. Precancerous Barrett's esophagus (BE) provides a clinical model to investigate GIN in cancer progression. We analyzed specimens from endoscopic biopsies or esophagectomies in patients with BE (ten cases, including five cases with multilayered epithelium (ME)), BE-associated esophageal adenocarcinoma (ten cases), or with normal gastro-esophageal junction (five cases). Chromosomal enumeration probe Cep 7, 11, 12, 17 and 18 were detected by fluorescence in situ hybridization (FISH). Expression of p53 and APC were determined by immunohistochemistry. Increased p53 expression, a measurement of p53 mutations, was observed in BE with high grade dysplasia (HGD) and in BE-associated esophageal cancer (EC). The expression of wild type APC was decreased in BE with HGD and in advanced EC. Chromosomal abnormalities were found in all EC samples. Numeric changes of chromosome 7, 11 and 12 were observed in BE in 14%, 64% and 43% of cases, respectively. Aneusomy of chromosome 11 and 12 were found in ME and in BE without dysplasia, in the presence of normal expression pattern of p53 and APC. Our results suggest that GIN is an early event that occurs at precancerous stages prior to changes in tumor suppressor genes (p53 and APC) in BE-associated tumorigenesis in patients, suggesting that GIN may serve as a causative link between chronic inflammation and cancer.