Solid-phase synthesis, characterization and RNAi activity of branch and hyperbranch siRNAs

Linear, branch and hyperbranch siRNAs were effectively prepared for down-regulating GRP78 expression and inducing cell death in HepG2 liver cancer cells. Branch and hyperbranch GRP78 siRNAs were synthesized by automated solid-phase synthesis in good yields (44-78%) and isolated in excellent purities (>99%) following HPLC purification. Moreover, siRNAs adopted stable intramolecular hybrids as discerned by native PAGE and thermal denaturation studies. These sequences also exhibited the pre-requisite A-type helical trajectory for triggering RNAi activity as determined by CD spectroscopy. Biological studies confirmed potent suppression of GRP78 expression (50-60%) while compromising cancer cell viability by ∼20%. Thus, branch and hyperbranch siRNAs may serve as potent siRNA candidates in cancer gene therapy applications.