RNA Therapeutics for Targeted Treatment of Colon Cancer

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 DESCRIPTION: There is an urgent need to develop novel strategies for treatment of advanced and metastatic colon cancers since they have limited responses to conventional chemotherapies. In this proposal, we will apply a new RNA-based strategy to deliver therapeutic miRNA and siRNA for targeted colon cancer therapy. We (Bin Guo's group) have recently found that miR-627 is induced by calcitriol and acts as a key mediator of calcitriol's suppression of colon cancer (Gastroenterology, 2013, 145(2):437-46). We have further demonstrated that miR-627 targets histone demethylase JMJD1A, an epigenetic regulator that has growth-promoting activity. Both miR-627 and JMJD1A-targeting siRNA can significantly inhibit colon cancer growth in vitro and in vivo (nude mice xenografts). We hypothesize that if we could employ targeted delivery of miR-627 or siRNA to directly inhibit JMJD1A, it would be possible to bypass the side effects associated with calcitriol and achieve tumor suppression. The co-investigator's (Peixuan Guo) group has discovered an unusually stable phi29 pRNA three-way junction (3WJ) motif that can be used as a scaffold to construct multivalent RNA nanoparticles with very high chemical and thermodynamic stability (Nature Nanotechnology, 2011, 6:658-67; Nano Today, 2012, 7:245- 257). The resulting RNA nanoparticles harbor different siRNA, miRNA, and cancer targeting module (such as RNA aptamer) that retain their folding and independent functionalities for gene silencing and cancer targeting both in vitro and in vivo. These RNA nanoparticles are resistant to denaturation in 8 M urea and do not dissociate at ultra-low concentrations in vitro and in vivo. Systemic injection into the tail-vein of mice has revealed that they remain intact and strongly bind to cancers without accumulating in the liver, lungs or other vital organs. This nanotechnology approach has enhanced the half-life of the RNA nanoparticles by 10-fold compared to the bare siRNA. The 3WJ-pRNA nanoparticles are non-toxic and display favorable pharmacological profiles that include biodistribution, pharmacokinetics (stability, half-life, and clearance rate), and undetectable immune responses (Molecular Therapy, 2011, 19:1312-22). The goal of this research project is to construct multivalent nanoparticles composed of RNA, to obtain enhanced or synergistic therapeutic effects for the treatment of colon cancer. We will conjugate (1) EpCAM aptamer for targeting tumor antigen EpCAM or A33 scFv for specific binding to colon cancer specific cell surface antigen A33 resulting in the internalization of RNA nanoparticles into the colon cancer cells; and (2) therapeutic modules, miR-627 and/or JMJD1A siRNA, to silence the expression of JMJD1A. Emphasis will be on specific tumor targeting and efficiency of gene silencing in vivo for treatment of primary tumor as well as suppression of metastasis. We will systematically evaluate the pharmacological profiles concerning biodistribution, pharmacokinetics, and immune responses (antibody induction, and interferon, toll-like and innate immunity, PKR effect, and cytokine induction) of this innovative RNA delivery platform. The combined effect of the multivalent RNA nanoparticles for enhancing chemotherapy will be evaluated. We are confident that our RNA-based approach will result in an innovative therapeutic for colon cancer.