To further probe this, both DU145-PSMA+ and DU145 cells were treated with solutions of "free"/"unchelated" [ 201 Tl]Tl(I)Cl for 1 h. Tl activity measured 6.1 ± 0.9% AR in DU145-PSMA+ and 6. can behave as a K(I) "mimic". We hypothesize that after dissociating from K222-PSMA, There are many endogenous biomolecules that are likely to compete with ligands such as K222 derivatives for binding to K(I)-mimics such as Tl(I). For example, potassium ion channels transport K(I) across cell membranes. These channels possess high affinity for K(I) to compensate for the energetic cost of dehydration/desolvation of K(I), which is required to enable transport. It is entirely plausible that in addition to transporting