Conformation-dependent binding and tumor-targeted delivery of siRNA by a designed TRBP2: Affibody fusion protein.

Efficiency of systemically delivered siRNA in gene silencing is compromised due to lack of target-specific delivery and rapid clearance of siRNA by in vivo elimination pathways. We designed a fusion protein consisting of a dsRNA binding domain of transactivation response RNA binding protein (TRBP2) fused to ErbB2 binding affibody (AF) for target specific delivery of siRNA. Designated as TRAF, the fusion protein is stable and binds efficiently and specifically to siRNA, forming homogenous non-aggregated and nuclease-resistant particles that efficiently and selectively transport siRNA into HER-2 overexpressing cancer cells and tissues. Administration of siRNA by TRAF into cells resulted in significant silencing of chosen genes involved in cell proliferation viz. AURKB and ErbB2. Noticeably, intravenous administration of TRAF:siRNA against these genes resulted in remarkable tumor suppression in the SK-OV-3 xenograft mouse model. Our results establish the potential of engineered proteins for specific and systemic delivery of siRNA for cancer therapy. FROM THE CLINICAL EDITOR: The use of siRNA in one of many novel treatments in cancer therapy. However, a major challenge for using siRNA is the lack of specificity and rapid RNA clearance. In this article, the authors designed a tumor targeting fusion protein, which can deliver siRNA specifically. In the experimental xenograft model, it was shown that intravenous administration of this resulted in significant tumor suppression. The results seem to hold promise in future clinical studies.