A cell-permeable pyridoxyl-ornithine compound that acts as an effective analog of the transition state coenzyme-substrate adduct during orthithine decarboxylase- (ODC) catalyzed conversion of L-orthithine to Pultrescine. POB is typically 5- to 10-fold more potent than DFMO (Cat. No. 288500) in inhibiting intracellular ODC activity and tumor cell growth in cultures, while exhibiting little effect against the growth of nontumorigenic human aortic smooth muscle cells.