A chelator bundle is a packed multi-arm linker carrying multiple chelator groups, such as 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 2,2′,2”-(1,4,7-triazacyclononane-1,4,7-triyl)triacetic acid (NOTA), and diethylenetriaminepentaacetic acid (DTPA). These chelator groups can bind to a range of cations, such as those of yttrium (Y), indium (In), gallium (Ga), zirconium (Zr), lutetium (Lu), etc. These elements exist in various radioactive nuclei, some of which have particle emissions and half-lives of decay at applicable ranges. The chelator bundles can be conjugated with a targeting moiety, such as an antibody or a receptor-binding peptide, and the resulting conjugates may be used for diagnostic (imaging) and/or therapeutic purposes. Typically, a maleimide group is installed at the end of coupling arm. A cluster of acidic amino acid residues may also be installed adjacent to the maleimide group. The cluster of negative charges of the chelators and of the acidic amino acid residues potentiate the maleimide group as an electrophile.
Here is an example of a chelator bundle.