Gene Targeting to Endogenous Stem Cells for Segmental Bone Fracture Healing
Segmental bone fractures are a complex medical condition. These injuries cause great suffering to patients, long-term hospitalization, repeated surgeries, loss of working days, and considerable costs to the health system. It is well known that bone grafts taken from the patient (autografts) are considered the gold-standard therapy for these bone defects. Yet these grafts are not always available, and their harvest often leads to prolonged pain. Allografts, are "dead" bone grafts, which are readily available from tissue banks, but have very low potential to induce bone repair. We have previously shown that stem cells from human bone marrow, engineered with a bone-forming gene, can lead to complete repair of segmental fractures. However, such an approach requires several steps, which could complicate and prolong the pathway to clinical use. An alternative approach would be to gene-modify stem cells that already reside in the fracture site. We were the first to show, in a rodent model, that a segmental bone defect can be completely repaired by recruitment stem cells to the defect site followed by direct gene delivery. In the proposed project we aim to further promote this approach to clinical studies. The project will include the development of a direct gene delivery technology, based on ultrasound. We will test the efficiency of the method in repairing large bone defects and its safety. If successful, we will be able to proceed to FDA approval towards first-in-human trials.
Segmental bone defects are a complex medical problem that often requires bone grafting. Autografts are considered the gold standard for these defects, but their usage is limited by availability and donor-site morbidity and supply. Allografts are more available but often fail to integrate with the host bone. Thus there is an unmet need in the field of orthopedic medicine for novel therapies for segmental bone fractures. We propose to develop a novel approach for the treatment of such fractures without the need for a bone graft. Specifically, we will utilize ultrasound to deliver a bone-forming gene to stem cells that will be recruited to the defect site. As we have already shown, the gene would trigger the cells to regenerate the bone that had been lost due to trauma or cancer. If successful, this project could lead to the development of a simple treatment for massive bone loss. Such a treatment will benefit the citizens of California by reducing loss of workdays, duration of hospital stays, and operative costs, and by improving quality of life for Californians with complex segmental bone fractures.
Segmental bone fractures constitute a complex medical condition with no effective treatment. These injuries cause great suffering to patients, long-term hospitalization, repeated surgeries, loss of working days, and considerable costs to the health system. It is well known that autologous bone grafts (autografts) that are harvested from the patient, are considered the gold-standard therapy for these bone defects. Yet these grafts are not always available, and their harvest often leads to prolonged postoperative pain and comorbidity at the donor site. Bone allografts obtained from tissue banks are readily available, but lead to poor graft-host integration resulting in numerous failures. We have previously shown that mesenchymal stem cells (MSCs) engineered with a specific bone-forming gene can be used to achieve complete regeneration of segmental fractures in long bones. However, such an approach requires several steps—cell isolation, expansion, and engineering—which could complicate and prolong the regulatory pathway to clinical use. An alternative approach would be to gene-modify endogenous stem cells that reside within in the body. We were the first to show, in a rodent model, that a segmental bone defect can be completely repaired by recruitment of endogenous stem cells to the fracture site followed by direct gene delivery. In this research project we aimed to further promote this therapeutic approach to clinical studies. During the first year of the project we investigated the use of an ultrasound system to deliver genes to feature sites. Our results showed that we were able to deliver the genes to 40-50% of the cells residing in the fracture site. Moreover, 70-90% of the cells that received the genes were identified as stem cells, which are the target of the therapeutic approach. Our next goal would be to deliver bone-forming genes to stem cells in the fracture site in order to induce complete defect repair.
Our goal was to develop a novel therapy for complex bone fractures that do not spontaneously heal and require bone grafting. Bone grafts can be harvested from the patient or obtained from tissue banks. Both approaches entail hazardous disadvantages such as prolonged pain, infection and graft failure. We proposed to recruit the body's own stem cells to the fracture site and then to activate them to rapidly form bone by delivering a bone-inducing molecule using ultrasound. In the 1st year of the project we established the model and therapeutic protocol. During the 2nd year we tested the protocol in a bone fracture model that mimics the clinical scenario in trauma patients. Our results so far have been very encouraging indicating that we were able to repair all fractures after one treatment. Our results are based on x-ray imaging and biomechanical testing analyses performed 6 weeks post treatment.