Angiogenesis is obligatory for the genesis and progression of solid cancers and is a logical target for cancer chemoprevention. This grant application will test the hypothesis that methylselenol or related monomethylselenium metabolites inhibit vascular endothelial angiogenic responses by multiple processes: a) inhibiting mitogenic signaling leading to G1 cell cycle arrest; b) inducing apoptosis through caspase-driven execution; c) inhibiting the expression of matrix metalloproteinase (MMP)-2 that is required for degrading tissue matrix. We will 1) investigate the mediator role of a methylselenium-inhibition of the phosphatidylinositol 3- kinase (PI3K) signaling cascade in vascular cell G1 arrest using biochemical, kinase pharmacologic inhibitor and active kinase mutant transfection approaches; 2) define the pathways through which methy-seLenium induces vascular endothelial cell apoptosis, especially what caspases are activated and any role of the mitochondria and cytochrome C in their activation as well as whether PI3K and/or mitogenic activated protein kinase (MAPKJERK1/2) inhibition mediate apoptosis signaling; 3) define what stage(s) of MMP-2 expression is targeted by methylselenium and elucidate the biochemical/molecular mechanisms involved. In particular, we will test whether methylselenol disrupts disulfide bonds in MMP-2 and model protein/peptide molecules. Human umbilical vein endothelial cells and their telomerized immortal clones will be used in cell culture models to accomplish these aims. By accomplishing the first 2 aims, we expect to validate a mediator role of PI3K and/or MAPK1/2 pathways for methylselenium inhibition of endothelial cell cycling as well as for apoptosis signaling leading to caspase-driven execution. This can lay the foundation for future work to investigate how methylselenium reacts/interacts with these target proteins to bring about the biochemical and cellular effects. In addition, elucidating the mechanisms of MMP-2 expression regulation in Aim 3 and especially disulfide disruption as a potential cause of its degradation may have broader mechanistic implications for inhibiting autocrine/paracrine-mediated tumor angiogenesis, growth, survival and invasiveness by selenium. [unreadable] [unreadable]