A gene therapy approach to accelerating bone healing - Evaluation of gene expression in a New Zealand white rabbit model

It has been demonstrated that BMPs, IGFs, and TGF beta s improve the proces s of bone healing in vivo. We have suggested the use of gene therapy as a p ossible way to deliver growth factors to fracture sites in order to improve repair. The aim of this study was to develop a minimally invasive gene the rapy approach to treat bone injuries locally without damaging the local blo od circulation. A segmental defect of 1.3 cm was created in the diaphysis o f the femur in mature NZW rabbits. Internal fixation with 7-hole DCP plates and 2.7 mm screws was used to stabilize the bone. After building a chamber by tightly closing the muscles around the segmental defect, 0.5 mi of eith er saline solution or a collagen gel containing 1 x 10(10) particles of ade novirus carrying cDNA encoding either the bacterial beta-galactosidase gene (LacZ), or the firefly luciferase gene were injected into the gap. The con trol side received 0.5 ml of saline solution without virus particles. Bone marrow, cortical and trabecular bone and surrounding muscle were harvested from the injected femur and were analyzed for local gene expression through X-gal staining or measurement of local luciferase activity. To determine w hether distant sites were transduced, tissue from the spleen. liver, and lu ng were harvested as well as bone, bone marrow and muscle from the contrala teral diaphysis of the femur. The delivery of the adenoviral vector suspend ed in saline solution led to local transduction of the bone, bone marrow an d the muscle surrounding the gap. No luciferase activity was found in the c ontralateral femur, lung, or spleen, and only transient luciferase activity was seen in the liver. While marker gene expression persisted within the s urrounding soft tissues for at least 2 weeks, the expression in bone lasted up to 6 weeks. This study has shown that it is possible to use adenoviral vectors to transfer and express genes locally within a segmental defect. Ge ne expression persisted for several weeks, which may be already sufficient to accelerate repair.