Inhibition of gene expression at the mRNA levels can be accomplished by several methods, including ribozymes, DNAzymes, and small interfering RNAs (siRNAs) (1 –3 ). This is now driven predominantly by siRNAs, as they are not technically demanding as traditional antisense and ribozyme technologies (4 ,5 ). The success of siRNAs as therapeutics, however, is largely dependent on the development of a delivery vehicle that can efficiently deliver them in vivo.