DESCRIPTION: (Applicant's Description) The long-term goal of these studies is to develop the use of peptide taraeting for the novel neuroendocrine neurokinin (NK) receptor system, which is constitutively overexpressed in breast cancer. Unlabeled substance P (SP), or analogues that selectively bind either NK-1 or NK-2 will be evaluated in vitro and in vivo. Auger-emitting radionuclides (e.g., IN-111) will be chelates to NK-Receptor targeting agents. Upon cell internalization of the carrier, In-111 is expected to have substantial radiotoxic effects, which are expected to translate into tumor growth controt effects in vivo. The studies have been subdivided into four hypothesis-driven aims. To achieve our stated goal, we will: (1) Use cultured breast cancer lines to establish an appropriate carrier of therapeutic agents to the NK-receptor system. The in vitro cytotoxicity of unconjugated SP agonist and antagonists (amino terminal fragment 6-11, CP-96,345) will be evaluated. Results will be compared with carriers containing radioindium. Binding affinity, internalization rate, and cell retention of the radionuclide will be established. (2) Determine whether the number of NK-1 and NK-2 binding sites is affected by exposure to cytokines (e.g., IFNa, IL-1, IL-6) or chemotherapy (e.g., taxol, doxorubicin). (3) Establish the biodistribution of NK-directed carriers in vivo in breast tumor xenografts. Uptake will be determined using whole tissue counting, whole animal imaging and microautoradiography of tissue sections. (4) Evaluate the therapeutic efficacy of SP-based carriers in a subcutaneous breast tumor model and a micrometastatic (intracardiac MDA-231) breast model. Potential GI and marrow toxicity will be assessed by monitoring body weight changes and white blood cell and platelet counts. Mice will also be monitored for possible neurotoxicity.