Prostate cancer cells expressing prostate-specific membrane antigen (PSMA) have been targeted with RNA aptamer–small interfering (si)RNA chimeras, but therapeutic efficacy in vivo was demonstrated only with intratumoral injection. Clinical translation of this approach will require chimeras that are effective when administered systemically and are amenable to chemical synthesis. To these ends, we enhanced the silencing activity and specificity of aptamer-siRNA chimeras by incorporating modifications that enable more efficient processing of the siRNA by the cellular machinery. These included adding 2-nucleotide 3′-overhangs and optimizing the thermodynamic profile and structure of the duplex to favor processing of the siRNA guide strand. We also truncated the aptamer portion of the chimeras to facilitate large-scale chemical synthesis. The optimized chimeras resulted in pronounced regression of PSMA-expressing tumors in athymic mice after systemic administration. Anti-tumor activity was further enhanced by appending a polyethylene glycol moiety, which increased the chimeras' circulating half-life.
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We thank M. Henry (Department of Molecular Physiology and Biophysics, University of Iowa) for supplying PC-3 and 22Rv1(1.7) luciferase-positive cells, A. Klingelhutz (Department of Microbiology, University of Iowa) for providing immortalized human fibroblasts, J. Houtman (Department of Immunology, University of Iowa) for help with flow cytometry, and R. Sousa (Department of Biochemistry, University of Texas Health Science Center) for providing a plasmid encoding a mutant T7 RNA polymerase. We are also thankful to M. Behlke for help with the manuscript. J.P.D. is supported by an National Institutes of Health (NIH) graduate student training grant to the Molecular and Cellular Biology Program (University of Iowa), K.W.T. is supported by a Ladies Auxiliary to the Veterans of Foreign Wars postdoctoral fellowship, J.O.M. and A.P.M. are supported by the NIH. This research was supported by an American Cancer Society Institutional Research Grant and a Lymphoma SPORE Developmental Research Award to P.H.G.
Duke University (P.H.G. and J.O.M.) and the University of Iowa (P.H.G., J.O.M. and A.P.M.) have applied for patents based on this technology.
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Dassie, J., Liu, Xy., Thomas, G. et al. Systemic administration of optimized aptamer-siRNA chimeras promotes regression of PSMA-expressing tumors. Nat Biotechnol 27, 839–846 (2009). https://doi.org/10.1038/nbt.1560
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