Restitution of tumor suppressor microRNAs using a systemic nanovector inhibits pancreatic cancer growth in mice

Misexpression of microRNAs (miRNAs) is widespread in human cancers, including in pancreatic cancer. Aberrations of miRNA include overexpression of oncogenic miRs ("Onco-miRs"), or downregulation of so-called tumor suppressor "TSG-miRs". Restitution of TSG-miRs in cancer cells through systemic delivery is a promising avenue for pancreatic cancer therapy. We have synthesized a lipid-based nanoparticle for systemic delivery of miRNA expression vectors to cancer cells ("nanovector"). The plasmid DNA-complexed nanovector is ~100nM in diameter, and demonstrates no apparent histopathological or biochemical evidence of toxicity upon intravenous injection. Two miRNA candidates known to be downregulated in the majority of pancreatic cancers were selected for nanovector delivery: miR-34a, which is a component of the p53 transcriptional network and regulates "cancer stem cell" (CSC) survival, and the miR-143/145 cluster, which together repress the expression of KRAS2, and its downstream effector Ras-responsive element binding protein-1 (RREB1). Systemic intravenous delivery with either miR-34a or miR-143/145 nanovectors inhibited the growth of MiaPaCa-2 subcutaneous xenografts (P<0.01 for miR-34a, P<0.05 for miR-143/145); the effects were even more pronounced in the orthotopic (intra-pancreatic) setting (P<0.0005 for either nanovector), when compared to vehicle or "mock" nanovector delivering an empty plasmid. Tumor growth inhibition was accompanied by increased apoptosis and decreased proliferation. MiRNA restitution was confirmed in treated xenografts by significant upregulation of the corresponding miRNA, and significant decreases in specific miRNA targets (SIRT1, CD44 and aldehyde dehydrogenase for miR34a, and KRAS2 and RREB1 for miR-143/145). The nanovector is a platform with potential broad applicability in systemic miRNA delivery to cancer cells.