A Universal Protein Tag for Delivery of SiRNA-Aptamer Chimeras

Liu, Hong Yan; Gao, Xiaohu

In conclusion, to solve the endosome escape problem of the highly promising siRNA-aptamer chimera based therapy, we have designed a dual-block small protein by combining dsRBD and polyhistidine and identified the optimal length of polyhistidine. The resulted protein tag shares the simplicity feature of siRNA-aptamer chimera, yet offers exactly complementary functionalities. The dsRBD selectively binds to the siRNA block, leaving the targeting aptamer accessible. In terms of size, different from conventional cationic delivery vehicles, the dsRBD-His 18 tagged chimera remains discrete in solution rather than forming large aggregates. In terms of functionalities, chimera and dsRBD-His 18 are highly complementary to each other, and thus offer the complete set of features necessary for targeted siRNA delivery (e.g., targeting, therapeutic, siRNA protection, and endosomal escape). This platform is also universal, able to chaperone any chimera sequences for cell type-specific delivery. Largely based on natural proteins, dsRBD-His 18 is an excellent candidate for potential clinical translation because of its simple structure and biodegradability. Further development of this small protein tag with in vivo testing should raise exciting opportunities for siRNA clinical translation and personalized medicine.