More than 2 million bone-grafting procedures are performed each year using autografts or allografts. However, both options carry disadvantages, and there remains a clear medical need for the development of new therapies for massive bone loss and fracture nonunions. We hypothesized that localized ultrasound-mediated, microbubble-enhanced therapeutic gene delivery to endogenous stem cells would induce efficient bone regeneration and fracture repair. To test this hypothesis, we surgically created a critical-sized bone fracture in the tibiae of Yucatan mini-pigs, a clinically relevant large animal model. A collagen scaffold was implanted in the fracture to facilitate recruitment of endogenous mesenchymal stem/progenitor cells (MSCs) into the fracture site. Two weeks later, transcutaneous ultrasound-mediated reporter gene delivery successfully transfected 40% of cells at the fracture site, and flow cytometry showed that 80% of the transfected cells expressed MSC markers. Human bone morphogenetic protein-6 (BMP-6) plasmid DNA was delivered using ultrasound in the same animal model, leading to transient expression and secretion of BMP-6 localized to the fracture area. Micro-computed tomography and biomechanical analyses showed that ultrasound-mediated BMP-6 gene delivery led to complete radiographic and functional fracture healing in all animals 6 weeks after treatment, whereas nonunion was evident in control animals. Collectively, these findings demonstrate that ultrasound-mediated gene delivery to endogenous mesenchymal progenitor cells can effectively treat nonhealing bone fractures in large animals, thereby addressing a major orthopedic unmet need and offering new possibilities for clinical translation.
Bez, Maxim Sheyn, Dmitriy Tawackoli, Wafa Avalos, Pablo Shapiro, Galina Giaconi, Joseph C Da, Xiaoyu David, Shiran Ben Gavrity, Jayne Awad, Hani A Bae, Hyun W Ley, Eric J Kremen, Thomas J Gazit, Zulma Ferrara, Katherine W Pelled, Gadi Gazit, Dan eng P30 AR069655/AR/NIAMS NIH HHS/ P50 AR054041/AR/NIAMS NIH HHS/ R01 CA112356/CA/NCI NIH HHS/ Sci Transl Med. 2017 May 17;9(390). pii: eaal3128. doi: 10.1126/scitranslmed.aal3128.