Lipid nanoparticle delivery of small interfering RNA targeting androgen receptor variants for prostate cancer

Expression of constitutively active splice variants of the androgen receptor (AR) currently poses treatment challenges for advanced stages of prostate cancer. Conventional hormone therapies for prostate cancer target the AR ligand-binding domain, which is completely absent in most AR splice variants. Utilizing small interfering RNA (siRNA) as a genetic drug can provide an approach to target such cancer-promoting variants, but requires a vehicle to prevent premature degradation and promote delivery to the cytosol of diseased cells. This thesis investigates the efficacy of a lipid nanoparticle (LNP) carrier of siRNA that specifically targets all AR variant forms (siARv). Two human prostate cancer models were utilized throughout the studies described here: the 22Rv1 cell line exhibits high expression levels of AR splice variants and growth dependency on the like; LNCaP cell growth is dependent on full-length AR and expresses extremely low levels of splice variant forms. A screen in 22Rv1 cells identified siARv from a panel of siRNAs designed against exon 1 of AR mRNA, a target that enables knockdown of full-length and variant ARs. The ability of a clinical-grade LNP formulation containing siARv to facilitate silencing of ARs was demonstrated in 22Rv1 and LNCaP cells, and it was shown that this knockdown of ARs also affected AR transcriptional activity, as exhibited by reduction of prostate-specific antigen levels in both models upon treatment. It was demonstrated that treatment with siARv-LNP reduced the viability of 22Rv1 cells more effectively than LNP carrying siARfl (siRNA targeting full-length AR mRNA only), whereas the effect on LNCaP cell viability of siARv-LNP and siARfl-LNP was not differentiable. The biodistribution of siARv-LNP formulated for optimal in vivo activity was measured in mice bearing 22Rv1 xenografts, demonstrating a measurable accumulation of LNP at distal tumors. The antitumor activity of the siARv-LNP system was subsequently tested on 22Rv1 xenografts upon repeat dosing, exhibiting slowed tumor progression, as well as enhanced survival, compared to animals treated with siARfl-LNP. These results provide an alternative means to target AR variants by way of LNP-mediated gene therapy, and comment on the relative utility of this approach in treating an AR variant-dependent prostate cancer model.Medicine, Faculty ofBiochemistry and Molecular Biology, Department ofGraduat