Polyamines (PA) are small cationic molecules required for entry and progression through the cell cycle. To address their increased need for PA, cells with short cycling times up-regulate both PA biosynthesis and PA transport. PA autoregulate when high intracellular PA concentrations induce a full-length active protein, antizyme (Az), via a translational +1 frameshift. Az inhibits both the first and rate-limiting enzyme of PA biosynthesis, ornithine decarboxylase (ODC), and PA transport. This 2 pronged mechanism effectively limits the ability of the cell to acquire PA. The kidney is exceptional in demonstrating high intracellular agmatine (Agm) levels (-400 uM) and high constitutive activity of the enzyme that converts arginine to Agm, arginine decarboxylase (ADC). The kidney appears an important source of systemic Agm. We have recently shown that Agm can induce Az. Agm induction of Az depletes intracellular PA levels in transformed cell lines and markedly inhibits their proliferation. Agm is the only known molecule, exclusive of the canonical PA, with the capacity to induce Az. Further investigation of this kidney derived anti-proliferative molecule is warranted. This proposal demonstrates Agm uptake is via PA transporters. These transporters are undetectable in quiescent cells, and up regulated in rapidly proliferating cells. We hypothesize that Agm selectively targets rapidly proliferating cells. In SA #1 we characterize Agm transport and its dependence on PA transporters. In SA#2 we evaluate targeting via the relative uptake vs. effects of Agm in cell lines representing increasing stages of tumorigenesis. In SA #3 we address the mechanisms of Agm mediated inhibition of proliferation. We hypothesize that this active cell mediated mechanism may be analogous to that noted for senescence. Attaining a K01 award would allow the PI to formally establish his independence for future R01 applications, and to pursue an appointment in the Academic Research series at the University of California San Diego. UCSD has established itself as a leading academic institution and thus provides an excellent environment for the exchange of ideas and techniques essential for the growth of the PI's career.