The unique amino acid hypusine occurs only in one cellular protein, eukaryotic protein translation initiation factor 5A (eIF-5A), and only at a single site. Because hypusine is formed posttranslationally and since both eIF-5A and its hypusine modification are essential for cell growth, we have aimed our attention toward inhibition of hypusine formation as a means of controlling eukaryotic cell proliferation. The two enzymatic steps in hypusine production, deoxyhypusine synthesis and deoxyhypusine hydroxylation, offer prime targets for intervention and inhibitors for the enzymes that catalyze these steps are being designed, synthesized and tested for their cellular effects. Guanyl diamines modeled after quazatine, a quanylated polyamine with broad spectrum activity against seed-borne fungi and citrus mold which displayed some inhibition against the enzyme deoxyhypusine synthase, proved to be potent inhibitors of both this enzyme and cell proliferation and provided the basis for a recent U.S. patent entitled """"""""Compositions and methods for inhibiting deoxyhypusine synthase and the growth of cells"""""""". That these inhibitors prevent growth of cells through intercellular inhibition of hypusine biosynthesis places them in a novel class of antiproliferative agents. Knowledge of the structural requirements for inhibitors of this enzyme has allowed design of agents for labeling of specific sites in its active center and has provided a degree of understanding of its mechanism of catalysis. Certain metal chelating agents prevent hypusine formation through inhibition of deoxyhypusine hydroxylase. Suppression of hypusine formation by inhibition of this enzyme correlates with arrest of cell proliferation resulting in accumulation of cells in the late G1 phase of the cell cycle. Since certain of these agents also cause inhibition of prolyl 4-hydroxylase, arrest of proline-to-hydroxyproline conversion and consequently suppression of collagen secretion, they were tested for combined antiproliferative/fibrosuppressive effects on smooth muscle cells of human atherosclerotic coronary arteries. The positive combined effects have important implications for control of fibrosis in general and, in particular, for understanding the pathophysiology of restenosis, the recurrent closing of vessels of the heart following surgical reconstruction.
