This proposal seeks continuation of support for a project to develop new approaches to the chelation therapy of human iron overload that is a consequence of beta-thalassemia (Cooley's anemia). The project will continue to focus on three goals: 1) The development of new ligands for Fee+. 2) The thermodynamic evaluation of new ligands. 3) The biological evaluation of new ligands. For goal #1, the failure of 3-hydroxy-l, 2- dimethyl-4(1H) -pyridinone (L1) in clinical trials has again emphasized the need for a new chelating agent for human iron overload. The research in our laboratories and the early promise of L1 continue to point toward hydroxypyridonate (HOPO) ligands as promising. However the limited thermodynamic stability of a simple bidentate ligand such as L1 makes such ligands poor candidates relative to analogous hexadentate ligands. We now have synthetic procedures to introduce either 3,4-HOPO or 3,2-HOPO ligand groups into hexadentate ligands with a geometry optimal for octahedral coordination to Fe3+. This has not been true of other hexadentate ligands reported to date. Several new - synthetic routes to 3,2- and 3,4-HOPO ligands have been found and are being explored. We have also found that the incorporation of one catechol group into a multidentate ligand such as desferrioxamine B (the trihydroxamate ligand in current clinical use) increases the rate of iron removal from the human iron transport protein transferrin by two orders of magnitude. It is proposed that this feature be exploited by combining catechol groups into mixed function ligands. The thermodynamic stability of new ligands with Fe3+ and competing physiological metal ions will be examined. An initial biological screen will be the rate of iron removal from transferrin. The kinetics and mechanisms of iron exchange with mammalian iron storage and transport proteins will be studied. Preliminary toxicity studies will be carried out in collaboration with Dr. P. Durbin. Screening for iron removal will be carried out for the most promising compounds in collaboration with Dr. R. Bergeron.
