Intracellular trafficking of Bisphosphonates in bone mesenchymal Stem Cells

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DESCRIPTION (provided by applicant): Nitrogen-containing bisphosphonates (n-BP) effectively control dysregulated bone turnover, osteolytic lesions of cancer metastasis and have anti-tumor activities. Unfortunately, osteonecrosis of the jaw (ONJ) is a major complication of n-BP therapy. Reasons for jaw-specific location of n-BP related osteonecrosis are unclear making it challenging to design targeted therapies. n-BPs act on osteoclasts and cancer cells by blocking the farnesyl pyrophosphate (FPP) synthase in the mevalonate signaling pathway; the outcome is loss of prenylation of small GTPase signaling proteins and dysregulation of cell survival and differentiation. We have shown that orofacial bone marrow stromal cells or bone mesenchymal stem cells (BMSCs) from neural crest-derived maxilla/mandible (OFMSCs) are highly proliferative with long population doublings relative to those of mesoderm-derived iliac bone (ICMSCs) and long bones (LBMSCs). Therefore, they may readily succumb to n-BP similar to rapidly proliferative cancer cells. Our preliminary studies showed that OFMSCs are indeed more sensitive to n-BP than ICMSCs based on enhanced n-BP uptake, slow elimination from the cytosol, decreased survival and decreased osteogenic differentiation. We hypothesize that sensitivity of OFMSCs to n-BP contributes in part to initiation of ONJ based on site-dependent n-BP uptake, intracellular processing, inhibition of FPP synthase in the mevalonate pathway and consequent loss of prenylation of small GTPase signaling proteins. In aim 1 we will determine how uptake and intracellular trafficking of n-BP in OFMSCs modulates survival and aim 2 will explore BMSC-based therapy to prevent ONJ in a small animal model. The goal is to formulate preventive measures for ONJ.