The delivery of
nucleic acids, particularly of small
RNA molecules like siRNAs for the induction of RNA interference (RNAi), still represents a major hurdle with regard to their application in vivo. Possible therapeutic applications thus rely on the development of efficient non-viral gene delivery vectors. While low molecular weight
polyethylenimines (PEIs) have been successfully explored, the introduction of chemical modifications offers an avenue towards the development of more efficient vectors. In this paper, we describe the synthesis of a novel
tyrosine-modified low-molecular weight
polyethylenimine (P10Y) for efficient
siRNA complexation and delivery. The comparison with the respective parent PEI reveals that knockdown efficacies are considerably enhanced by the
tyrosine modification, as determined in different reporter cell lines, without appreciable cytotoxicity. We furthermore identify optimal conditions for complex preparation as well as for storing or lyophilization of the complexes without loss of biological activity. Beyond reporter cell lines, P10Y/
siRNA complexes mediate the efficient knockdown of endogenous target genes and, upon knockdown of the anti-apoptotic oncogene
survivin,
tumor cell inhibitory effects in different
carcinoma cell lines. Pushing the system further towards its therapeutic in vivo application, we demonstrate in mice the delivery of intact siRNAs and distinct biodistribution profiles upon systemic (intravenous or
intraperitoneal) injection. No adverse effects (hepatotoxicity, immunostimulation/alterations in immunophenotype,
weight loss) are observed. More importantly, profound
tumor-inhibitory effects in a
melanoma xenograft mouse model are observed upon systemic application of P10Y/
siRNA complexes for
survivin knockdown, indicating the therapeutic efficacy of P10Y/
siRNA complexes. Taken together, we (i) establish
tyrosine-modified PEI (P10Y) as efficient platform for
siRNA delivery in vitro and in vivo, (ii) identify optimal preparation and storage conditions as well as (iii) physicochemical and biological properties of P10Y complexes, and (iv) demonstrate their applicability as
siRNA therapeutic in vivo (v) in the absence of adverse effects.