Cyclotron-Produced 132La as a PET Imaging Surrogate for Therapeutic 225Ac

The aim of this work was to explore La-132 as a PET imaging surrogate for Ac-225 using a DOTA-based, tumor-targeting alkylphosphocholine (NM600). Methods: La-132 was produced on a biomedical cyclotron. For in vivo experiments, mice bearing 4T1 tumors were administered La-132-NM600, and PET/CT scans were acquired up to 24 h after injection. After the last time point, the ex vivo tissue distribution was measured to corroborate the in vivo PET data. The ex vivo tissue distribution in mice was determined at 4 and 24 h after injection of Ac-225-NM600. Results: PET/CT images showed elevated, persistent La-132-NM600 uptake in the tumor. Low bone accumulation confirmed the in vivo stability of the conjugate. Ex vivo biodistribution studies validated the image-derived quantitative data, and the comparison of the La-132-NM600 and Ac-225-NM600 tissue distributions revealed a similar biodistribution for the 2 radiotracers. Conclusion: These findings suggest that La-132 is a suitable imaging surrogate to probe the in vivo biodistribution of Ac-225 radiotherapeutics.