| Summary: | The androgen receptor (AR) plays a critical role in the progression of prostate cancer. This thesis is focused on investigating the ability of lipid nanoparticle (LNP) formulations of small-interfering RNA (siRNA) to silence AR (LNP AR-siRNA) in human prostate tumor cells in vitro and in LNCaP xenograft tumors following intravenous (i.v.) injection.
The first part of this thesis characterized the properties of LNP AR-siRNA systems that contained the ionizable cationic lipid DLin-KC2-DMA. Inclusion of DLin-KC2-DMA was found to exhibit the most potent AR silencing effects in LNCaP cells. This is attributed to an optimized ability of DLin-KC2-DMA-containing LNP to be taken up into cells and to release the siRNA into the cell cytoplasm following endocytotic uptake. Importantly, it is demonstrated that LNP AR-siRNA systems containing DLin-KC2-DMA can silence AR gene expression in distal LNCaP xenograft tumors and reduce serum prostate specific antigen (PSA) following i.v. injection at a dose level of 10 mg siRNA/kg body weight.
The latter part of this thesis describes optimization of LNP AR-siRNA by stabilizing the AR-siRNA sequence through introduction of a phosphorothioate backbone and methylations of nucleotides at the 2’O position and also employing an optimized cationic lipid 3-(dimethylamino)propyl(12Z,15Z)-3-[(9Z,12Z)-octadeca-9,12-dien-1-yl]henicosa-12,15-dienoate (DMAP-BLP). In addition, specific targeting to the prostate specific membrane antigen (PSMA) on LNCaP cells was made possible via chemical conjugation of a small molecule 2-[3-(1,3-dicarboxypropyl)-ureido]pentanedioic acid (DUPA) to the PEG-lipid formulated into LNP AR-siRNA. With the incorporation of the DUPA-targeting moiety, a 5-fold increase in cellular uptake was observed in LNCaP cells in vitro, as well as a dramatic improvement in AR knockdown. The PEG-lipid employed in formulating the LNP was also optimized to produce longer circulation lifetimes that result in improved accumulation at the distal tumor site. It is shown that as a result of these improvements the doses of siRNA employed in LNP-siRNA systems could be reduced by a factor of two as compared to previous systems. In addition improved reductions in serum PSA, cellular proliferation, and AR levels were also observed. These results support the potential clinical utility of LNP-siRNA systems to silence the AR for treatment of advanced prostate cancer. === Medicine, Faculty of === Biochemistry and Molecular Biology, Department of === Graduate
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