Developing the 134 Ce and 134 La pair as companion positron emission tomography diagnostic isotopes for 225 Ac and 227 Th radiotherapeutics.

Developing targeted α-therapies has the potential to transform how diseases are treated. In these interventions, targeting vectors are labelled with α-emitting radioisotopes that deliver destructive radiation discretely to diseased cells while simultaneously sparing the surrounding healthy tissue. Widespread implementation requires advances in non-invasive imaging technologies that rapidly assay therapeutics. Towards this end, positron emission tomography (PET) imaging has emerged as one of the most informative diagnostic techniques. Unfortunately, many promising α-emitting isotopes such as ²²⁵ Ac and ²²⁷ Th are incompatible with PET imaging. Here we overcame this obstacle by developing large-scale (Ci-scale) production and purification methods for ¹³⁴ Ce. Subsequent radiolabelling and in vivo PET imaging experiments in a small animal model demonstrated that ¹³⁴ Ce (and its ¹³⁴ La daughter) could be used as a PET imaging candidate for ²²⁵ Ac ^III (with reduced ¹³⁴ Ce ^III ) or ²²⁷ Th ^IV (with oxidized ¹³⁴ Ce ^IV ). Evaluating these data alongside X-ray absorption spectroscopy results demonstrated how success relied on rigorously controlling the Ce ^III /Ce ^IV redox couple.