Direct Transfection of Fatty Acid Conjugated siRNAs and Knockdown of the Glucose-Regulated Chaperones in Prostate Cancer Cells

The emerging field of RNAi nanotechnology has led to rapid advances in the applications of siRNAs in chemical biology, medicinal chemistry, and biotechnology. In our RNAi approach, bioconjugation of linear, V-, and Y-shaped RNA templates were designed using a series of saturated and unsaturated fatty acids to improve cell uptake and knockdown efficacy of the oncogenic glucose regulated proteins (GRPs) in prostate (PC-3) cancer cells. An optimized HCTU-coupling procedure was developed for tagging variable saturated and unsaturated fatty acids onto the 5′-ends of linear and V-shaped RNA templates that were constructed by semiautomated solid phase RNA synthesis. Hybridization and self-assembly of complementary strands yielded linear, V-, and Y-shaped fatty acid-conjugated siRNAs which were characterized by native PAGE. CD spectroscopy confirmed their A-type helix conformations. RP IP HPLC provided trends in amphiphilic properties, whereas DLS and TEM confirmed multicomponent self-assembled structures that were prone to aggregation. Subsequently, the fatty acid conjugated siRNA bioconjugates were tested for their RNAi activity by direct transfection within PC-3 cells known to overexpress oncogenic GRP activity. The siRNA bioconjugates with sense strand modifiers provided more potent GRP knockdown relative to the antisense modified siRNAs, but to a lesser extent when compared to the unconjugated siRNA controls that were transfected with the commercial Trans-IT X2 dynamic delivery system. Flow cytometry revealed that the latter may be at least in part attributed to limited cell uptake of the fatty acid conjugated siRNAs. Nonetheless, these new constructs represent an entry point in modifying higher-order siRNA constructs that may lead to the generation of more efficient siRNA bioconjugates for screening important oncogene targets and for cancer gene therapy applications