Novel bone specific pharmacological treatment for osteogenesis imperfecta

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Project Summary There is no cure for osteogenesis imperfecta (OI or brittle bone disease), the most common of the heritable disorders of bone affecting 1:15,000 births. The most evident clinical hallmarks of OI is bone fragility and skeletal deformities. OI is caused primarily by defects in collagen type I, leading to collagen molecules folding improperly, disrupting fibril alignment and structure, and providing an abnormal template for mineralization in bone. For this reason, OI has been traditionally considered a bone extracellular matrix disorder, and current treatments for OI rely on the use of pharmacological drugs, mainly bisphosphonates, a class of drugs that inhibit bone resorption and is used in the management of osteoporosis. Despite the initial success, the actual efficacy of these treatments to reduce the fracture risk are controversial and additional risks may arise from the long-term use of this drug in developing bones of children with OI. Recent research has demonstrated a cellular component to the OI disease: the endoplasmic reticulum (ER) stress in the osteoblasts of OI bone. We also recently found that pharmacological action toward ER stress using the 4-phenyl butyrate (4PBA) is able to reduce the OI phenotype severity, increasing bone formation and reducing skeletal deformities. This drug treatment needs two improvements: 1) increase its stability and 2) make it able to effectively reach the bone. Furthermore, unknown is the effect of the treatment on bone quality and mechanics. The rationale of the proposed experiments is to synthesize a 4PBA derivative, the N-benzyl glycine (N-BG), that is more stable and to determine its effect on OI ER cells stress and on OI bone material properties. In a second experiment, we will test the efficacy of a carrier ((GfO)8) to deliver N-BG to bone cells and the effect on OI bone quality. We will use primary isolated osteoblasts from Brtl mouse model of OI for the in vitro testing of ER and apoptotic stress with N-BG. Zebrafish models of recessive (p3h1-/-) and dominant (Chihuahua) type of OI, and healthy zebrafishes will be injected with either placebo or N-BG drug or (GfO)8-N-BG drug+carrier. Morphology and tissue porosity of precaudal vertebrae will be analyzed in the treated zebrafishes and the c hanges with drug therapy to the collagen fiber organization, bone tissue composition and mechanical properties will be examined using an array of high resolution experiments. The knowledge gained from this study will inform on the efficacy of new 4PBA derivatives therapies and on the use of carriers to treat bone fragility in OI. This work will also provide the first and standardized pipeline to evaluate drug effect on Zebrafish skeletal disease models.