siRNA Lipid Nanoparticle Potently Silences Clusterin and Delays Progression When Combined with Androgen Receptor Cotargeting in Enzalutamide-Resistant Prostate Cancer

Purpose: Lipid nanoparticle (LNP) formulations facilitate tumor uptake and intracellular processing through an enhanced permeation and retention effect (EPR), and currently multiple products are undergoing clinical evaluation. Clusterin (CLU) is a cytoprotective chaperone induced by androgen receptor (AR) pathway inhibition to facilitate adaptive survival pathway signalling and treatment resistance. In our study, we investigated the efficacy of siRNA tumor delivery using LNP systems in an enzalutamide-resistant (ENZ-R) castration-resistant prostate cancer (CRPC) model. Experimental Design: Gene silencing of a luciferase reporter gene in the PC3-M-luc stable cell line was first assessed in subcutaneous and metastatic PC-3 xenograft tumors. Upon validation, the effect of LNP siRNA targeting CLU in combination with AR antisense oligonucleotides (ASO) was assessed in ENZ-R CRPC LNCaP in vitro and in vivo models. Results: LNP LUC-siRNA silenced luciferase expression in PC-3M-luc subcutaneous xenograft and metastatic models. LNP CLU-siRNA potently suppressed CLU and AR ASO induced CLU and AKT and ERK phosphorylation in ENZ-R LNCaP cells in vitro, more potently inhibiting ENZ-R cell growth rates and increased apoptosis when compared to AR-ASO monotherapy. In subcutaneous ENZ-R LNCaP xenografts, combinatory treatment of LNP CLU-siRNA plus AR-ASO significantly suppressed tumor growth and serum PSA levels compared to LNP Luc-siRNA (control) and AR-ASO. Conclusions: LNP siRNA can silence target genes in vivo and enable inhibition of traditionally non-druggable genes like CLU and other promising co-targeting approaches in ENZ-R CRPC therapeutics.