Poster abstracts

Poster number 68 submitted by Tabatha Simmons

Minicircle plasmid DMD vectors for gene transfer studies in mdx

Tabatha Simmons (MCDB, Center for Gene Therapy, The Research Institute at Nationwide Childrens Hospital), Adeline Vulin-Chaffion (Center for Gene Therapy, The Research Institute at Nationwide Childrens Hospital), Nicolas Wein (Center for Gene Therapy, The Research Institute at Nationwide Childrens Hospital), Louise Rodino-Klapac (Center for Gene Therapy, The Research Institute at Nationwide Childrens Hospital), Kevin Flanigan (Center for Gene Therapy, The Research Institute at Nationwide Childrens Hospital)

Abstract:
Duchenne Muscular Dystrophy (DMD) is a lethal X-linked disorder that is the result of mutations in the DMD gene that lead to an absence of the dystrophin protein. DMD mutations causing the allelic Becker Muscular Dystrophy (BMD) preserve an open mRNA reading frame, typically by an internal in-frame deletion of dystrophin exons, resulting in the expression of some residual dystrophin. Adeno-associated viruses have emerged as the front-runner for clinical gene transfer in DMD, but because AAV vectors are limited in the size of transgenes, only internally truncated BMD-like genes (mini- or microdystrophin) may be encapsulated by the virus. While these have shown benefit in studies in the mdx mouse model of DMD, the ultimate clinical effect in humans may be less pronounced. Transfer of the full-length human dystrophin (hDYS) gene would be predicted to be of the greatest clinical benefit, but hDYS gene transfer using lentiviral or adenoviral techniques increases the risk for a greater degree of toxicity and lacks the muscle tropism of AAV. Also, IM injection of naked hDYS DNA plasmid in humans showed minimal expression in a sole clinical trial. Alternatively, biopolymer-mediated delivery has also been extensively studied in pre-clinical models for a variety of disorders1,2,3. It has the theoretical potential of transferring hDYS, unlike AAV. Additionally, by using minicircle (MC) DNA plasmid technology, expression duration should be increased according to previous studies showing sustained transgene expression in quiescent cells and tissues when using the MC plasmids4,5. While it is currently the most advanced technology in the field to deliver microdystrophin to skeletal muscle using AAV, it still has limitations. Utilization of a liposome for transgene delivery and the MC system allows for not only the potential delivery of large transgenes, including the hDYS, but also increased expression and duration of transgenes following IM injection into skeletal muscle.

References:
1.) Nishikawa M et al. Nonviral vectors in the new millennium: delivery barriers in gene transfer. Hum Gene Ther. 2001 May 20;12(8):861-70.
2.) Nemunaitis G et al. Hereditary inclusion body myopathy: single patient response to intravenous dosing of GNE gene lipoplex. Hum Gene Ther. 2011 Nov;22(11):1331-41.
3.) Phadke AP et al. Safety and in vivo expression of a GNE-transgene: a novel treatment approach for hereditary inclusion body myopathy-2. Gene Regul Syst Bio. 2009 May 8;3:89-101.
4.) Kay MAet al. A robust system for production of minicircle DNA vectors. Nat Biotechnol. 2010 Dec;28(12):1287-9. Epub 2010 Nov 21. PubMed PMID: 21102455.
5.) Huang M et al. Novel minicircle vector for gene therapy in murine myocardial infarction. Circulation. 2009 Sep 15;120(11 Suppl):S230-7.

Keywords: Minicircle, Duchenne, Therapy