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Systemic delivery of HK Raf-1 siRNA polyplexes inhibits MDA-MB-435 xenografts

Cancer Gene Therapy volume 15, pages 485–495 (2008)Cite this article

Abstract

Our past research has focused on identifying an effective carrier composed of histidine and lysine for delivery of nucleic acid into cells. For this purpose, we developed histidine-lysine-rich (HK) polymers with specific sequences and branching. We have found that branched HK polymers in complex with Raf-1 siRNA markedly decreased Raf-1 mRNA and induced apoptosis in cell lines in vitro. The primary focus of the present study was to determine an effective carrier to deliver siRNA systemically to tumor xenografts. After comparing HK:Raf-1 polyplexes for their in-vivo efficacy, we investigated in greater detail whether one of these polymers, H3K(+H)4b, in complex with Raf-1 siRNA, inhibited the growth of MDA-MB-435 xenografts. H3K(+H)4b is a four-branched HK peptide whose predominant repeating sequence within the terminal arm is -HHHK-. After the first tail-vein injection in a mouse model, there was a statistically significant reduction in tumor size between the H3K(+H)4b:Raf-1 siRNA-treated and the control groups (P<0.01). By the third injection, there was nearly a 50% reduction in the Raf-1 siRNA-treated group compared to the control siRNA-treated or -untreated group. Consistent with a significant effect of the HK:Raf-1 polyplex on the tumor, there were marked histological changes, increased apoptosis and fewer vessels in the Raf-1 siRNA-treated group. Raf-1 protein within the tumor was significantly decreased after treatment with the HK:Raf-1 siRNA polyplex compared to the control treatment groups. Despite the striking effect on the tumor by the HK Raf-1 siRNA, there was little evidence of toxicity in normal tissues with this therapy. By harnessing the ability to modify the amino-acid sequence and branching of HK polymers, we expect continued development of HK polymers as in-vivo carriers of siRNA.

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Acknowledgements

We are grateful to Dr Pamela Talalay for her careful reading and useful comments concerning the article. We thank Dr Nicholas Ambulos and Dr Pat Campbell of the Maryland Biopolymer laboratory for synthesizing the peptides in this study. This study was supported by the National Cancer Institute CA70394.

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Author notes

  1. P Scaria & M C Woodle

    Present address: 4Current Address: Aparna Biosciences, Rockville, MD 20852, USA.,

Authors and Affiliations

  1. Department of Pathology, University of Maryland, Baltimore, MD, USA

    Q Leng & A J Mixson

  2. Intradigm Corporation, Palo Alto, CA, USA

    P Scaria & M C Woodle

  3. Sirnaomics Inc., Gaithersburg, MD, USA

    P Lu

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  1. Q Leng
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  2. P Scaria
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Correspondence to A J Mixson.

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Leng, Q., Scaria, P., Lu, P. et al. Systemic delivery of HK Raf-1 siRNA polyplexes inhibits MDA-MB-435 xenografts. Cancer Gene Ther 15, 485–495 (2008). https://doi.org/10.1038/cgt.2008.29

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