The Development of Star Nanoparticles for siRNA Delivery in Pancreatic Cancer

Pancreatic cancer (PC) is a lethal disease due to chemoresistance and metastatic spread. We have shown that the microtubule protein βIII-tubulin is upregulated in PC cells, and that inhibition of βIII-tubulin (siRNA or shRNA) increased chemosensitivity in vitro and reduced tumour growth/metastases in vivo (McCarroll et al., Oncotarget, 6, pg.2235-49, 2015). Clinical translation of this work is limited by a lack of pharmacological inhibitors for βIII-tubulin. siRNA-based therapeutics are a potential solution, but require a delivery vehicle (e.g. nanoparticles). Novel star nanoparticles were designed to deliver siRNA to PC cells.The aims of this study were: 1) to design and optimise novel star-shaped nanoparticles that deliver functional siRNA to PC cells in vitro; 2) to examine the biodistribution and gene silencing activity of star-siRNA complexes in vivo using preclinical PC mouse models; and 3) to determine the potential of star-βIII-tubulin siRNA complexes to reduce tumour growth in preclinical PC mouse models. Results of this study demonstrated that star nanoparticles were able to complex and deliver βIII-tubulin siRNA to PC cells and potently silence βIII-tubulin expression. We modified our generation 1 nanoparticles by addition of PEGylation (Star-PEG) which enabled high gene silencing efficiency in PC cells in the presence of serum (an essential property for systemic administration in patients). All the star nanoparticles were non-toxic to PC cells and normal human pancreatic ductal cells. However, star-PEG nanoparticles displayed a superior toxicity profile compared to the non-PEGylated star nanoparticles. Star-PEG 4 (with 12.5% covalently attached PEG and longer cationic side-arms) was non-toxic in vivo and delivered siRNA to pancreatic tumours after systemic administration. Star-PEG 4-βIII-tubulin siRNA potently silenced βIII-tubulin in PC tumours and pilot studies indicated reduced tumour growth in both a subcutaneo