Many forms of cancer are characterized by the inappropriate growth and division of cells. To counteract the inappropriate proliferation of cancer cells, the overall goal of this project is to develop a novel cancer therapy that is targeted against a cellular protein that has a central role in controlling cell division and that has recently emerged as a prognostic indicator for some forms of cancer including prostate. This protein, known as Pin1, is also of interest because it is related to the protein targets of immunosuppressive drugs such as cyclophilin that have been effectively used for treatment of transplant patients. To develop strategies to target Pin1 for therapy, we will determine the three-dimensional structure of Pin1 together with novel inhibitors that we have recently developed. Information from these studies will tell us how inhibitors work to block the functions of Pin1 so that we can design better inhibitors of Pin1 and then test them for effects on the growth and division of breast and prostate cancer cells.