Bifunctional short hairpin RNA (bi-shRNA): design and pathway to clinical application

The discovery of RNA interference (RNAi) engendered great excitement and raised expectations regarding its potential applications in biomedical research and clinical usage. Over the ensuing years, expanded understanding of RNAi and preliminary results from early clinical trials tempered enthusiasm with realistic appraisal resulting in cautious optimism and a better understanding of necessary research and clinical directions. As a result, data from more recent trials are beginning to show encouraging positive clinical outcomes. The capability of delivering a pharmacologically effective dose to the target site while avoiding adverse host reactions still remains a challenge although the delivery technology continues to improve. We have developed a novel vector-driven bifunctional short hairpin RNA (bi-shRNA) technology that harnesses both cleavage-dependent and cleavage-independent RISC loading pathways to enhance knockdown potency. Consequent advantages provided by the bi-shRNA include a lower effective systemic dose than comparator siRNA/shRNA to minimize the potential for off-target side effects, due to its ability to induce both a rapid (inhibition of protein translation) and delayed (mRNA cleavage and degradation) targeting effect depending on protein and mRNA kinetics, and a longer duration of effectiveness for clinical applications. Here, we provide an overview of key molecular methods for the design, construction, quality control, and application of bi-shRNA that we believe will be useful for others interested in utilizing this technology.