PBT434 inhibits alpha- synuclein in the brain., page-21

This may help. [The affinity of PBT434 for iron is greater than that of alpha-synuclein but lower than that of endogenous iron trafficking proteins, e.g., ferritin.]
https://www.mdsabstracts.org/abstract/pbt434-prevents-the-accumulation-of-glial-cell-inclusions-and-insoluble-alpha-synuclein-in-a-mouse-model-of-multiple-system-atrophy/
So tightly bound stores of iron are not touched by PBT434. Only free and lightly attached iron is effected by PBT434. By that MOA PBT434 is able to remove the problem iron with no chance of causing undesirable effects of clawing iron from tightly held iron stores like ferritin.