Background: The mammary glands of adult female animals are remarkably sensitive to KGF. KGF acts at the KGFR to produce a rapid and profound stimulation of breast cancer cell proliferation and motility. Further, KGF-induced motility in breast cancer cells is mediated via the Erk1/2 signaling pathway. Thus, enhancement of KGF/KGFR signal transduction may be an early step in the metastatic progression of breast cancer. Receptor modeling of KGFR was used to identify a library of selective KGFR TKI molecules with high receptor affinity. Forty of the KGFR TKI have been synthesized and are available to study the involvement of KGFR signaling in breast cancer metastasis. Hypothesis: KGFR is an important therapeutic target in breast cancer; and thus, selective inhibition of KGFR-mediated signaling will reduce or eliminate breast cancer cell proliferation, motility and metastasis. Specific Aims: The First Specific Aim will measure the relative activity and specificity of the 40 KGFR TKI on KGF-mediated KGFR signal transduction in human breast cancer cells. The Second Specific Aim will examine the ability of these 40 inhibitors to reduce KGF-induced breast cancer cell proliferation and motility in vitro. The Third Specific Aim will determine the inhibitory effect of the most selective and potent KGFR TKI (as determined in vitro in Specific Aims #1 and 2) on KGF-mediated growth and metastasis of human breast cancer cells in a mouse xenograft model. Methods: In Specific Aim #1, MCF-7 breast cancer cells will receive either a motility stimulating dose of KGF (50 ng/ml) or KGFR TKI at doses ranging from 10 to 200 [unreadable]M or KGF (50 ng/ml) + KGFR TKI at each inhibitor dose or Iressa (epidermal growth factor receptor selective TK inhibitor; used as a negative control) over the same dosage range or KGF + Iressa (at the same doses) or vehicle control. At various times, from 1 to 48 hrs following KGF administration, the cells will be harvested to determine the protein expression of KGFR, phospho-KGFR, Erk1/2, phospho-Erk1/2 and [unreadable]-actin by Western blotting. In Specific Aim #2 proliferation and migration of MCF-7 cells will be evaluated with both time-lapse videomicroscopy and a culture wounding assay over a period of 1 to 3 days using the same experimental groups and doses described in the first specific aim. In Specific Aim #3 the influence of KGFR inhibition on the growth and metastasis of tumor xenografts will be determined. The xenograft studies will be conducted by implanting MCF-7 cells into mammary fat pads of nude mice. At the end of the experiment, tumor, lung and liver will be removed and frozen sections examined by fluorescent microscopy to quantify tumor growth and development of lung and liver micro-metastasis. Significance: The establishment of KGFR as an important therapeutic target, together with the identification of specific and potent KGFR TKI, should result in the rapid development of a new class of highly selective therapeutic agents to prevent the metastatic progression of cancer. The establishment of KGFR as an important therapeutic target, together with the identification of specific and potent KGFR TKI, should result in the rapid development of a new class of highly selective therapeutic agents designed to prevent the metastatic progression of cancer. This project addresses several focus areas of the National Cancer Institute; namely, the biology of cancer metastasis and the development of highly selective and molecularly targeted therapeutic agents. [unreadable] [unreadable] [unreadable]