2007 Annual Meeting

(121c) Development of Asymmetric Liposomal Nanoparticles for Targeted Delivery of siRNA to Silence Gene Expression

Authors

Jeremiah Whittenton - Presenter, University of Houston
Sivaram Harendra - Presenter, University of Houston
Ramanan Pitchumani - Presenter, University of Houston
Kishore Mohanty - Presenter, University of Houston
Sundararajah Thevananther - Presenter, Baylor College of Medicine & Texas Children's Liver Center


It is estimated that hepatocellular carcinoma (HCC) is the fifth most common type of cancer and is the fourth leading cause of cancer-related deaths worldwide. Advances in the molecular understanding of HCC have raised the possibility of targeting cellular pathways involved in the formation and progression of HCC. Silencing cyclin D1 gene expression, which is over-expressed in HCC, by cyclin D1 specific siRNAs may provide an improved therapy over less effective and toxic systemic therapies. Yet the delivery of siRNA to HCC is challenging. Conventional techniques using liposomes and cationic polymers have low encapsulation efficiencies and/or high toxicity. The goal of this study is to develop asymmetric liposomal nanoparticles to overcome these deficiencies.

Inverse emulsion particles have been developed with a single lipid leaflet of cationic and neutral lipids covering an aqueous core containing a fluorescently labeled 21-mer DNA oligo (a cheaper substitute for siRNAs). The particles are accelerated through an oil-water interface containing a second lipid leaflet containing neutral lipids to form oligo encapsulated unilamellar liposome nanoparticles. The placement of cationic lipids in the inner leaflet may increase encapsulation efficiency by forming electrostatic attractions with the negatively charged oligo. Yet the placement of neutral lipids in the outer leaflet provides an uncharged exterior for decreased toxicity.

The results so far provide several conclusions: (1) Inverse emulsion particles can be consistently produced to encapsulate an aqueous environment containing negatively charged oligo; (2) A second lipid leaflet can be formed around the particles to form encapsulated liposomes, but with a much lower efficiency than expected; and (3) The liposomes are relatively stable over a four day period. Future work includes targeting of these liposomes to HCC cells and in vitro siRNA delivery to cells.