Intradigm (Rockville, MD) makes use of RNA interference (RNAi) technology in which small interfering RNA (siRNA) oligos are used as gene inhibitors via the RNA-induced silencing complex (RISC) to degrade homologous mRNA with high specificity and potency. Intradigm focuses on an angiogenesis pathway shown to be important in cancer, inflammation, autoimmune, and other diseases.
The ability to perform in vivo target validation with efficacious, clinically viable siRNA delivery provides high value information to understand the role of a particular gene or protein in the disease process, multiple genes of the same pathway, as well as the role of the pathway in the disease.
This information is not only critical to the drug discovery process but also important for potential therapeutic siRNA development.
Patrick Lu, Ph.D., executive vp, Intradigm, who presented the company's technology approach at the "IBC Drug Discovery and Development Asia Pacific" meeting, pointed out that the use of siRNA in vivo to down-regulate the expression of a specific gene requires knowledge of target sequence accessibility, target tissue deliverability, and siRNA stability in both extracellular and intracellular environments.
It has been recognized that in vivo drug target validation performed in animal disease models is superior to in vitro validation performed in cell culture assays. Earlier studies that used cell culture assays to validate targets had a low success rate when the studies were taken to the animal models.
Dr. Lu emphasized that they have the capability to provide both systemic and local delivery of siRNA depending upon the disease of interest. The dual targeted ligand-directed nanoparticle allows them to deliver siRNA systemically with tissue-specific and gene-specific targeting. This process results in the release RNAi in the cytoplasm of the cells by taking advantage of receptor-mediated endocytosis.
More potent tumor inhibition can be achieved by using up to three different siRNA in the same transfection cocktail. This is unique to RNAi as it is difficult to use mixtures of antibodies to the target protein in vivo, said Dr. Lu. Cocktails of siRNA will provide better understanding of the entire pathway involved in disease progression, he added.
Immusol (San Diego) recently launched a proprietary technology that allows fast and efficient in vivo target validation for efficacy and safety in multiple disease models using siRNA vectors.
According to Henry Li, Ph.D., director of oncology, Immusol, who presented his company's research at the "IBC USA Early Efficacy Assessment" meeting, this technology represents a major breakthrough in disease target validation in vivo, providing critical information prior to the lengthy and expensive high throughput compound screening and lead development, and can potentially save millions of dollars and years in drug discovery cost.
Immusol has inducible RNAi vectors that can be stably introduced into cultured tumor cells or cell lines. Induction results in the expression of RNAi then can be used for target validation. The inducible vector can also be studied in a mouse xenograft tumor model.
In this case, human tumor cells that have been transduced with the inducible vector are grafted on nude mice, creating stably silenced cells in vitro and establishment of tumor in vivo in the absence of an inducer. Upon induction, tumor response to gene inactivation in vivo can be measured, thus allowing target validation and also rapid advance through the discovery process.
Simply by varying the timing of induction, the expression of the target can be modulated at any stage of tumor progression. This model can also be used for the study of two targets at the same time. Dr. Li added that the Immusol vector does not necessitate single cell cloning, which makes it faster and more efficient to obtain cells containing the vector.
There seems to be agreement among researchers that target validation in vivo with siRNA with efficacious, clinically viable siRNA provides a lot of information that helps understand the role of a particular gene in a disease, multiple genes in the pathway, as well as the role of the pathway in the disease.
Dr. Li announced that Immusol is in the process of generating transgenic mice with RNAi.