CMR 2005: 12.05: Use of in vivo imaging to follow siRNA‐mediated reporter gene inhibition in a transgenic mouse skin model

Abstract

Rationale and Objectives: A number of diseases of the skin could be treated with nucleic acid-based therapies and, owing to its accessibility, the skin represents an attractive tissue target for these approaches. RNA interference offers the potential for a novel therapeutic approach for treating skin disorders, and the ability to deliver high concentrations of these inhibitors locally to skin cells, without the side-effects associated with systemic delivery, should facilitate new treatment options for a variety of skin disorders including psoriasis, scleroderma, pachyonychia congenita and epidermolysis bullosa. Toward optimizing delivery of nucleic acids to skin, we employed a reporter gene construct (pL2G) expressing a hybrid fLuc/eGFP mRNA in a murine model and used imaging to assess expression levels. Methods: DNA was introduced by intradermal injection into footpads (AEelectroporation) and expression analyzed over time. Peak luciferase expression occurred between 24 and 48 h following injection and expression remained high for at least 7 days. Electroporation resulted in an $10-fold increase in delivery of reporter genes and had little or no effect on expression kinetics. In order to evaluate the ability of RNAi to inhibit skin gene expression, the pL2G reporter was co-injected with specific siRNAs targeting the eGFP region of the dual-function mRNA and the in vivo effects were relative to non-specific controls were measured. Results: The results revealed that specific eGFP siRNAs (but not nonspecific matched controls) strongly inhibited reporter gene expression in mice (>70% inhibition of fLuc activity). In parallel tissue culture experiments using human 293FT cells cotransfected with pL2G and a plasmid expressing secreted alkaline phosphatase (pSEAP, added to control for transfection efficiency), the eGFP inhibitors robustly inhibited eGFP expression (as determined by fluorescence microscopy) and fLuc expression (luciferase assay), with little or no effect on SEAP expression. Alternatively, transgenic mice constitutively expressing the L2G reporter were treated with multiple injections of the inhibitors and the in vivo effects were measured by following the fLuc and eGFP signal. The results revealed that specific unmodified and modified siRNAs (but not nonspecific matched controls) strongly inhibit reporter gene expression in mice. These results also indicated that siRNAs, delivered locally as RNAi or expressed from viral or nonviral vectors (shRNA), may be effective agents for treating skin disorders. The unmodified and modified siRNAs used in this study were kindly provided by Dharmacon. (1) were conjugated with biotinylated ultra-small (50 nm) superparamagnetic iron oxide particles (bUSPIO). Injections were performed stereotactically into the right lateral ventricles of rat brain. Spin-and gradient-echo MRI were performed at 4.7 T. Time points of 2 h (0) and 1, 3, 6 and 14 days after injection in vivo were studied (n ¼ 4).Results: bUSPIO conjugation with Baavi was demonstrated by atomic force microscopy...