PET in vivo generators $^{134}$Ce and $^{140}$Nd on an internalizing monoclonal antibody probe

The in vivo-generator radionuclides $^{140}$Nd (t$_{1/2}$ = 3.4 d) and $^{134}$Ce (t$_{1/2}$ = 3.2 d) were used to trace a urokinase-type plasminogen activator (uPA)-targeting mouse monoclonal antibody, ATN-291, in U87 MG xenograft tumor-bearing mice. ATN-291 is known to internalize on the uPA/uPA-receptor pair, making it an appropriate targeting vector for investigating the fate of in vivo generator daughters on internalizing probes. Ante-mortem and post-mortem PET imaging at 120 h post-injection gave no indication of redistribution of the positron emitting daughter nuclides $^{134}$La and $^{140}$Pr from tumor tissue (p > 0.5). The lack of redistribution indicates that the parent radionuclides $^{134}$Ce and $^{140}$Nd could be considered as long-lived PET-diagnostic matches to therapeutic radionuclides like $^{177}$Lu, $^{161}$Tb and $^{225}$Ac when internalizing bioconjugates are employed.