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

The aim of this work was to explore ¹³²La as a PET imaging surrogate for ²²⁵Ac using a DOTA-based, tumor-targeting alkylphosphocholine (NM600). Methods:¹³²La was produced on a biomedical cyclotron. For in vivo experiments, mice bearing 4T1 tumors were administered ¹³²La-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 ²²⁵Ac-NM600. Results: PET/CT images showed elevated, persistent ¹³²La-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 ¹³²La-NM600 and ²²⁵Ac-NM600 tissue distributions revealed a similar biodistribution for the 2 radiotracers. Conclusion: These findings suggest that ¹³²La is a suitable imaging surrogate to probe the in vivo biodistribution of ²²⁵Ac radiotherapeutics.