TPEN (N,N,N′,N′-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine) is an intracellular membrane-permeable ion chelator. TPEN has a high affinity for many transition metals and should not be considered specific or selective for a particular ion. Chelators can be used in chelation therapy to remove toxic metals in the body. TPEN is a chelator that has a high affinity for zinc. For example, one study showed that TPEN is a stronger chelator compared to other chelators like pentetic acid (DTPA) when high levels of zinc are present (15 µM). When low levels of zinc were present however (0, 3, 6, 9 and 12 µM zinc), there was no significant difference. TPEN is a hexadentate ligand which also forms complexes with other soft metal ions such as Cd2+.