A delivery system targeting bone formation surfaces to facilitate RNAi-based anabolic therapy

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Abstract

Metabolic skeletal disorders associated with impaired bone formation are a major clinical challenge. One approach to treat these defects is to silence bone-formation–inhibitory genes by small interference RNAs (siRNAs) in osteogenic-lineage cells that occupy the niche surrounding the bone-formation surfaces. We developed a targeting system involving dioleoyl trimethylammonium propane (DOTAP)-based cationic liposomes attached to six repetitive sequences of aspartate, serine, serine ((AspSerSer)6) for delivering siRNAs specifically to bone-formation surfaces. Using this system, we encapsulated an osteogenic siRNA that targets casein kinase-2 interacting protein-1 (encoded by Plekho1, also known as Plekho1). In vivo systemic delivery of Plekho1 siRNA in rats using our system resulted in the selective enrichment of the siRNAs in osteogenic cells and the subsequent depletion of Plekho1. A bioimaging analysis further showed that this approach markedly promoted bone formation, enhanced the bone micro-architecture and increased the bone mass in both healthy and osteoporotic rats. These results indicate (AspSerSer)6-liposome as a promising targeted delivery system for RNA interference–based bone anabolic therapy.

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Figure 1: Differential occupancy characteristics of (AspSerSer)6 compared to Asp8 at bone-formation or bone-resorption surfaces in nondecalcified bone sections using a confocal laser scanning microscope.
Figure 2: Organ-selective delivery and gene knockdown in vivo.
Figure 3: Cell-selective delivery and knockdown efficiency in vivo.
Figure 4: In vivo microCT examinations of the three-dimensional trabecular architecture and an ex vivo bone formation evaluation in nondecalcified bone sections in healthy rats.
Figure 5: In vivo microCT examination of the three-dimensional trabecular architecture in OVX-treated rats.

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Acknowledgements

We thank X.-H. Yang for technical support with the confocal imaging, H. Yang for technical support with the flow cytometry and F.C. Chun-Wan for assistance with the bone histomorphometry. This study was supported by the Chinese National Basic Research Programs (2011CB910602), the Hong Kong Competitive Earmarked Research Grant (CUHK479111 and 473011), the Direct Grant of Faculty of Medicine of the Chinese University of Hong Kong (2041478 and 2041525), the Faculty Research Grant of Hong Kong Baptist University (30-08-089), the Chinese National Natural Science Foundation Project (30830029) and the National Key Technologies Research and Development Program for New Drugs (2009ZX09503-002).

Author information

All the authors were involved in conducting, drafting or revising the manuscript. All the authors approved the final version of the manuscript for submission. L.Q. had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and supervision: G.Z., L.Q., L. Zhang, F.H. Design and preparation of delivery system: G.Z., H.W., Z.Y., H.C., Y.L., K.T. Design, synthesis and screening of siRNA sequences: T.T., G.Z., L. Zheng, Z.H., N.D. Analysis and interpretation of data from cell biology and molecular biology: B.G., T.T., B.-T.Z., G.Z., D.L., X.W., L.Q. Analysis and interpretation of data from immunohistochemistry: B.-T.Z., B.G., G.Z., K. Lee, L.Q. Analysis and interpretation of data from biophotonic imaging: B.G., G.Z., G.L., L.Q. Analysis and interpretation of data from microCT and bone histomorphometry: B.G., G.Z., Y.H., Y.W., L.Q. Analysis and interpretation of data for clinical relevance: G.Z., L.Q., X.P., L.H., K. Leung.

Correspondence to Ge Zhang or Lingqiang Zhang or Ling Qin.

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The authors declare no competing financial interests.

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Supplementary Figures 1–4, Supplementary Tables 1–4, Supplementary Methods, Supplementary Discussion and Supplementary Results (PDF 3361 kb)

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