Cilia and Cellular Phenotypes
High-throughput RNAi (HT-RNAi) screening provides a means to discover new therapeutic targets. Pedro Aza-Blanc, Ph.D., director of functional genomics resources at the Sanford-Burnham Medical Research Institute, heads a core facility that performs siRNA screens.
“HT-RNAi screening allows forward-genetic approaches in tissue culture cells by providing rapid genetic screens for cellular phenotypes. This can be applied to multiple fields including cancer, virology, stem cell biology, and metabolism. You can address any cellular phenotype as long as you have a high-throughput amenable method to detect it. To perform a screen, individual siRNAs are transfected into cells in individual wells in a high-throughput manner. The effect is measured in an assay system such as a high-throughput microscope or a plate reader.”
According to Dr. Aza-Blanc, there are two major applications for HT-RNAi screening. “The most common application is target discovery toward the treatment of diseases that can be associated with cellular phenotypes. An emerging application is to profile compound activity in the same way that genetic screens in yeast have been used in the past.
“Although it is unclear how widely applicable it will be, one can envision this technology being used to classify compounds such as those directed against the same molecular target but displaying different activities in live cells. This will help in the drug discovery pipeline as you can get an early snapshot of the compound’s mechanism of action.”
Dr. Aza-Blanc described work performed in collaboration with Joon Kim and Joseph Gleeson to understand the dynamics of primary cilia. “In recent years, we’ve seen the importance of these organelles in regulating intracellular signals involved in diverse processes from embryonic development to cancer. The disruption of their structure or function can have profound phenotypic consequences.
“We have used siRNA-screening techniques to identify modulators of cilia formation. This work exemplifies the use of siRNA libraries. Such screening can cover the entire genome as long as you have an assay to measure an effect. Other types of screens may employ library subsets of the genome such as proteases or kinases.”
HT-RNAi screening will continue to emerge as a major player in therapeutics on several fronts, Dr. Aza-Blanc said. “HT-RNAi screening can identify genetic networks involved in disease, as well as help identify an agent’s target and detect unexpected off-target activities. Overall, this approach allows one to make better informed decisions early on in the drug discovery process.”
RNAi therapeutics possess enormous potential. Researchers are just beginning to scratch the surface of this young and vibrant field. Many challenges remain, but progress continues to encourage further development.