The goal of the parent grant is to investigate the role of Notch signaling in inflammatory osteoporosis. We found that persistent activation of Notch in mesenchymal stem/progenitor cells limits their osteoblast (OB) differentiation potential and causes bone loss, which can be prevented by Notch inhibitors, DAPT and Thapsigarin [1]. Our findings suggest that Notch inhibitors could be used as bone anabolic agents. However, Notch inhibitors have severe adverse effects due to systemic distribution [2], limiting their use in common diseases such as osteoporosis. Thus, making bone targeted Notch inhibitors to reduce their systemic side effects will be a very attractive approach. In this revision, we will form a ne interdisciplinary team including a Bone Biologist (Dr. Xing, the PI of the parent grant) and Chemists (Dr. Boeckman, a co-PI of the revision; Dr. Ebetino, consultant of the revision) to design and synthesize bone targeted Bortezomib by conjugating it to a bisphosphonate using a novel carbamate linker that will release Bortezomib from the Bortezomib- bisphosphonate. Two special aims are proposed.
In aim 1, we will design and synthesize bone-targeted Bortezomib conjugates and in aim 2, we will examine the bioactivity of bone-targeted Bortezomib conjugates in OB cultures and in mouse fracture healing. If we are successful, we will use a similar approach to synthesize bone targeted Notch inhibitors to reduce their toxic effects in the treatment of inflammatory osteoporosis, a main goal of the parent grant, and perhaps in other bone loss related to inflammation. The application will also lead to new directions for both Drs. Xing and Boeckman's lab: understanding the role of the ubiquitin- proteasome system in bone fracture repair in the aged population with a focus on mesenchymal stem/progenitor cells (Xing's lab); and using a novel chemical linker in other drugs and compounds, which will open a new strategy of bone targeting chemistry (Boeckman's lab).
Bone fractures affect 5 million Americans each year. Promoting fracture healing could reduce pain, complications and medical cost. We found that a drug called Velcade, used in the treatment of patients with multiple myeloma, can promote the healing of bone fractures in mice. However, Velcade has toxic side effects when it enters the bloodstream, which prevents its broader use. We propose making a new form of Velcade that will only act on bone, thereby reducing side effects. We will test this new Velcade in mice with bone fractures. If successful, our study will provide a new drug for patients with fractures and other bone-related diseases such as multiple myeloma and tumor metastasized to bone.
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