Eukaryotic protein translation iniation factor 5A (eIF-5A) contains one residue of hypusine and appears to be the only cellular protein with this unique amino acid. Hypusine is produced post-translationally by transfer of the butylamine portion of the polyamine spermidine to a lysine residue in the eIF-5A precursor to form deoxyhypusine followed by hydroxylation to form hypusine. These findings reveal a novel cellular metabolic pathway. Hypusine is essential for the biological activity of eIF-5A in an in vitro translation initiation assay and hypusine and eIF-5A appear to be vital elements for growth of eukaryotic cells. Thus, the hypusine biosynthetic steps, deoxyhypusine synthesis and deoxyhypusine hydroxylation present special potential targets for intervention in cellular proliferation. Several inhibitors of the enzymes deoxyhypusine synthase, and deoxyhypusine hydroxylase were developed and their cellular effects have been examined. The most potent inhibitor of deoxyhypusine synthase monoguanyl-1,7-diaminoheptane, (Ki=0.01 micromoles compared to the Km of spermidine of 4micromoles) in vitro is the most effective inhibitor of hypusine formation and growth in CHO cells (IC 50 for growth inhibition 0.3micromoles). The compound is taken up actively by the polyamine transport system. Mutant CHO cells defective in polyamine transport are resistant to growth inhibition by monoguanyl-1,7- diaminoheptane indicating that it exerts antiproliferative activity intracellularly by inhibition of hypusine synthesis. The guanylated diamines represent a new class of antiproliferative agents, the action of which is targeted toward a single specific cellular process, hypusine biosynthesis.
