Abstract
RNA interference (RNAi) technology has not only become a powerful tool for functional genomics, but also allows rapid drug target discovery and in vitro validation of these targets in cell culture. Furthermore, RNAi represents a promising novel therapeutic option for treating human diseases, in particular cancer. Selective gene silencing by RNAi can be achieved essentially by two nucleic acid based methods: i) cytoplasmic delivery of short double-stranded (ds) interfering RNA oligonucleotides (siRNA), where the gene silencing effect is only transient in nature, and possibly not suitable for all applications; or ii) nuclear delivery of gene expression cassettes that express short hairpin RNA (shRNA), which are processed like endogenous interfering RNA and lead to stable gene down-regulation. Both processes involve the use of nucleic acid based drugs, which are highly charged and do not cross cell membranes by free diffusion. Therefore, in vivo delivery of RNAi therapeutics must use technology that enables the RNAi therapeutic to traverse biological membrane barriers in vivo. Viruses and the vectors derived from them carry out precisely this task and have become a major delivery system for shRNA. Here, we summarize and compare different currently used viral delivery systems, give examples of in vivo applications, and indicate trends for new developments, such as replicating viruses for shRNA delivery to cancer cells.
Highlights
The human genome project unraveled the human genetic code, but spin-off technical improvements inspired genome sequencing of a multitude of other organisms
Knowledge about the in vivo phenotype after knocking out gene products is a prerequisite to assess the therapeutic potential of inhibitors against specific targets, so in drug development knock-out animal models have become very important
Adenovirus vectors Adenoviruses (AdV) belong to the family of Adenoviridae, and adenoviral vectors are frequently used for experimental gene therapy and 25% of clinical gene therapy trials currently underway are using adenovirus [51]
Summary
The human genome project unraveled the human genetic code, but spin-off technical improvements inspired genome sequencing of a multitude of other organisms. These single-stranded (ss)RNA viruses belong to the family of Retroviridae and replicate through a doublestranded DNA intermediate They integrate their genomes stably into the host cell DNA allowing long-term expression of inserted therapeutic genes. In an upcoming clinical trial one application of RNAi will involve ex vivo lentiviral vector delivery of an shRNA expression cassette into hematopoietic stem cells collected from patients infected with HIV. A strategy based on exploiting an HIV-based lentiviral vector carrying an antisense sequence targeting HIV to treat HIV infection has entered clinical trials This trial is evaluating a conditionally replicating HIV-1-derived vector pseudotyped with VSV-G expressing an 937-base antisense gene against the HIV envelope [120]. Our results show that replicating MLVs are excellent tools for efficient delivery and expression of shRNAs, have great potential for functional genomics, and might be suitable for in vivo cancer gene therapy, if combined with efficient entry targeting. We are currently focusing on in vivo studies using these viruses and look forward to promising results
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
