Targeted Gene-and-host Progenitor Cell Therapy for Nonunion Bone Fracture Repair

Abstract

Nonunion fractures present a challenge to orthopedics with no optimal solution. In-vivo DNA electroporation is a gene-delivery technique that can potentially accelerate regenerative processes. We hypothesized that in vivo electroporation of an osteogenic gene in a nonunion radius bone defect site would induce fracture repair. Nonunion fracture was created in the radii of C3H/HeN mice, into which a collagen sponge was placed. To allow for recruitment of host progenitor cells (HPCs) into the implanted sponge, the mice were housed for 10 days before electroporation. Mice were electroporated with either bone morphogenetic protein 9 (BMP-9) plasmid, Luciferase plasmid or injected with BMP-9 plasmid but not electroporated. In vivo bioluminescent imaging indicated that gene expression was localized to the defect site. Microcomputed tomography (µCT) and histological analysis of murine radii electroporated with BMP-9 demonstrated bone formation bridging the bone gap, whereas in the control groups the defect remained unbridged. Population of the implanted collagen sponge by HPCs transfected with the injected plasmid following electroporation was noted. Our data indicate that regeneration of nonunion bone defect can be attained by performing in vivo electroporation with an osteogenic gene combined with recruitment of HPCs. This gene therapy approach may pave the way for regeneration of other skeletal tissues.

Gene Therapy Applications for Fracture Repair

“…However, expression of transgene from the plasmid vector continues for only 3-7 days, a time frame achieved with adenoviral vectors. With respect to bone repair, electroporation of a BMP-9 expression plasmid into a collagen sponge implant healed a murine radial segmental defect (Kimelman-Bleich et al, 2010). This result is quite promising for the future of non-viral gene therapy in the clinic, although few such studies have been performed to date.…”

Realizing the potential of gene-based molecular therapies in bone repair

“…(53) A similar system was also effective for intraosseous application, where electroporation with 50 µg of BMP-9 plasmid induced bone formation in a critical-size defect in a mouse radius. (54) No bone formation was evident without electroporation. The use of only 50 µg pDNA to heal a defect with electroporation represents $10-fold decrease in the pDNA dose needed for naked pDNA delivery (from above studies).…”

The Pharmacology of Regenerative Medicine

“…Simply improving the delivery of BMPs might have significant benefit, as leakage of excess cytokine can result from overloading of collagen sponges. Genetically modified cells represent one possible system to provide BMP locally (Kimelman-Bleich et al, 2011). Osteoconductive materials, permissive for bone development, might synergize with BMPs and potentially reduce side effects.…”