Hematopoietic stem cell transplantation (HSCT) has increased the survival of children and adults afflicted with malignant and non-malignant hematological diseases. Prior to transplant, patients receive a conditioning regimen of cytotoxic drugs (e.g. cyclophosphamide/busulfan) and/or total body irradiation in order to suppress the immune system and, in the case of malignancies, eradicate remaining cancer cells. Unfortunately, conditioning drugs and radiation are not specific for the hematopoietic system or cancer cells but also damage normal tissues (e.g. liver, lungs and kidneys, oral mucositis), suggesting that developing conditioning agents that specifically target hematopoietic cells (normal and malignant) may have clinical benefit. Using a cell-based readout system, we have identified a small molecule (SM27) that selectively kills cells of hematopoietic origin, including a panel of human leukemia cell lines, normal human blood cells and mouse bone marrow cells. Our preliminary screening provides proof-of-principle evidence that specific targeting of the hematopoietic system is feasible. However, the maximum activity of SM27 is at 5M concentrations and the molecule is structurally unstable (e.g. contains an ester linkage). Therefore, the goals of this proposal are 1) to structurally optimize SM27 using synthetic chemistry to modify portions of the molecule that may be responsible for instability, 2) to identify additional hematopoietic-specific agents through the screening of novel chemical libraries (250,000+ compounds) and 3) to characterize hits against a wide panel of human cancer cell lines of hematopoietic and non-hematopoietic origina as well as normal human tissue cells (lung, kidney, liver, oral, bone marrow) known to be targeted or damaged by standard conditioning regimens in order to identify potential lead compounds that are highly hematopoietic-specific. The significance of this project lies in its potential for developing a less toxic conditioning regimen for HSCT for treatment of hematological diseases. The results of this proposal have major implications for all patients requiring HSCT for the treatment of malignant and non-malignant hematological diseases. PUBLIC HEALTH RELEVANCE: Hematopoietic stem cell transplantation (HSCT) has improved the survival rates of high-risk and relapsed patients suffering from malignant and non-malignant hematological diseases. However, conditioning regimens used to prepare patients for HSCT are not specific to cells of hematopoietic origin and thus can cause damage to liver, lung, kidneys and other tissues leading to short-term and long-term complications that can be potentially fatal. The development of hematopoietic-specific conditioning agents should provide a less toxic alternative to current regimens and, thus, has major implications for patients receiving HSCT for the treatment of hematological diseases.