Simplified Preparation via Streptavidin of Antisense Oligomers/Carriers Nanoparticles Showing Improved Cellular Delivery in Culture

Objective: Carriers are increasingly now viewed as helpful or even essential to improve cellular uptake in connection with antisense tumor targeting and other applications requiring transmembrane delivery of oligomers. Evaluation of many of the large number of available and potentially useful carriers is limited only by the complexities of preparing the oligomer/carriers by covalent conjugation. However, using streptavidin as a linker between biotinylated carriers and biotinylated antisense oligomers would require only simple mixing for preparation. The goal of this study was to evaluate the preparation and cell accumulation in culture of carrier/streptavidin nanoparticle of an antisense phosphorodiamide morpholino (MORF) oligomer. Methods: The model carriers were cholesterol, a 10 mer HIV-tat peptide, and a 10 mer polyarginine, each having been reported elsewhere to improve cellular delivery of oligomers. The model antisense oligomer was the 25 mer MORF targeting the survivin mRNA. The accumulations of the antisense MORF/carrier nanoparticle were compared to the sense MORF/carrier, to the carrier-free nanoparticles, and to the naked antisense MORF in the survivin-expressing MCF-7 cells. The MORFs and peptides were purchased biotinylated, while the cholesterol was biotinylated in-house. In all cases, the 99mTc radiolabel was placed on the oligomers. Cell studies were performed at low nM concentration as required for antisense imaging applications and at 37 degrees C primarily in 1% FBS. Results: Each radiolabeled oligomer/streptavidin/carrier nanoparticle was successfully prepared by careful mixing at a 1:1 molar ratio. As evidence of carrier participation, the radiolabeled MORF showed increased accumulation in cells when incubated as the nanoparticle compared to the carrier-free nanoparticle and by as much as a factor of 11. Accumulation of the antisense MORF/streptavidin/tat nanoparticle was significantly higher than the sense MORF/streptavidin/tat nanoparticle as evidence of specific antisense targeting. Conclusions: The preparation of oligomer/carrier nanoparticles was greatly simplified over covalent conjugations by using streptavidin as a linker. Furthermore, our results suggest that the addition of streptavidin did not interfere with the cellular delivery function of the tat, polyarginine, or cholesterol carriers nor with the specific antisense mRNA binding function of the MORF oligomer.