Basic and translational research has investigated the role of nm23 in the regulation of tumor metastasis. Five transfection studies have documented that overexpression of nm23 cDNA in either breast carcinoma or melanoma cell lines results in a 50-90% decrease in tumor metastatic potential in vivo. The biochemical mechanism whereby Nm23 suppresses metastatic potential is under investigation. We have transfected site directed mutants of nm23-H1 into breast carcinoma cell lines and examined their in vitro motility to correlate Nm23 structure and biological function. Two mutations abrogated the tumor cell motility suppressive capacity of Nm23:proline 96, the killer of prune mutation in the Drosophila nm23 homolog, which can cause aberrant differentiation; serine 120, a site of mutation in human Stage IV neuroblastomas, and phosphorylation. We have subsequently expressed and purified each Nm23 mutant protein, and tested them for biochemical activities in vitro. We found that the proline 96 and serine 120 mutant proteins were uniquely deficient in aspects of histidine-dependent protein phosphotransferase pathways, and have hypothesized that this biochemical pathway may be responsible for the biological suppressive effects of Nm23. Two translational projects are underway: We have identified the promoter for nm23-H1, and the portion which determines whether breast carcinoma cell lines of varying metastatic potentials express high or low Nm23 levels. No mutations were detected in this region. Talks are underway with a pharmaceutical company to use the nm23-H1 promoter to screen for drugs which will elevate cellular Nm23 expression. Using the COMPARE computer program in collaboration with DTP, we have used Nm23 as a marker to identify novel compounds with preferential in vitro inhibitory activity against the most aggressive human breast and melanoma cell lines. One of these compounds, NSC680718, has in vivo activity in the hollow fiber assay and has been referred by the BEC for xenograft testing.
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