There is mounting evidence that vitamin D receptor (VDR) agonists can inhibit the growth of prostate cancer cell lines, primary prostate cancer cells, and tumors in animal models. Although 1,25-dihydroxyvitamin D3 (1,25D) is hypercalcemic at levels required to inhibit tumor growth, we and others have shown that less calcemic analogs such as EB1089 can inhibit tumor growth in animal models without causing hypercalcemia, the major clinical side effect of elevated 1,25D levels. Although 1,25D can cause a variety of changes including cell cycle accumulation and can induce apoptosis, the primary targets of 1,25D action that lead to growth inhibition, for the most part, have not been identified. Moreover, we do not know whether the same changes would occur in human tumors. One of the biggest difficulties in translating work from cell culture and animal models is in determining whether the same changes will occur in human tumors. In many cases, there is insufficient data to justify a clinical trial. Clinical trials are very expensive and difficult to set up. Moreover, comparisons are usually made between treated and untreated patients. It is rarely possible to use a patient as his/her own control. We will use a novel prostate disc organ culture model developed by our collaborator, Dr. David Rowley, to determine whether the changes we detect in prostate cancer cell lines will also occur in human tumors. Fresh tumor samples taken immediately after removal of the prostate during radical prostatectomy will be cultured with or without the VDR agonist EB1089 for 3 days. The samples will then be prepared for various immunohistochemical analyses and RNA studies. We will also prepare RNA from two independent prostate cancer cell lines treated or not with EB1089, and using microarray analysis to survey a large number of genes, we will determine which genes are regulated by EB1089. We will determine by microarray analysis of a small number of tumor samples whether the same sets of genes are regulated. We will also measure the contribution of several of these genes to the actions of EB1089 in LNCaP cells using a variety of molecular biological techniques and endpoints, including cell growth. We have already identified several changes induced by VDR agonists that are likely to be important for inhibition of tumor growth, including down-regulation of c-myc and Bcl-2 and induction of two other proteins, AS3 and IGFBP-3. We will also determine whether the expression of these proteins and the newly identified proteins are regulated in the tumors. We may find that a subset of tumors respond similarly to the cell lines. This will allow us to determine the likelihood of responsiveness of tumors to treatment, whether most tumors will respond, and possibly, characteristics of those likely to respond to treatment. These studies will not only provide important information regarding the usefulness of compounds such as EB1089, but will help to verify the utility of this novel model for testing other forms of treatment. If we are successful, the information will provide support for trials in the near future with VDR agonists and will help to identify the patients likely to respond to treatment. Moreover, a better understanding of the actions of VDR agonists will aid in determining how best to use VDR agonists in combination with other treatments.