Biodistribution and dosimetry of 177Lu-DOTA-IBA for therapy of bone metastases.

Background: We designed and synthesized a novel bisphosphonate radiopharmaceutical (⁶⁸ Ga- or ¹⁷⁷Lu-labeled DOTA-ibandronate [⁶⁸ Ga/¹⁷⁷Lu-DOTA-IBA]) for the targeted diagnosis and treatment of bone metastases. The biodistribution and internal dosimetry of a single therapeutic dose of ¹⁷⁷Lu-DOTA-IBA were evaluated using a series of single-photon emission computerized tomography (SPECT) images and blood samples. Five patients with multiple bone metastases were included in this prospective study. After receiving 1110 MBq ¹⁷⁷Lu-DOTA-IBA, patients underwent whole-body planar, SPECT/CT imaging and venous blood sampling over 7 days. Dosimetric evaluation was performed for the main organs and tumor lesions. Safety was assessed using blood biomarkers.

Results: ¹⁷⁷Lu-DOTA-IBA showed fast uptake, high retention in bone lesions, and rapid clearance from the bloodstream in all patients. In this cohort, the average absorbed doses (ADs) in the bone tumor lesions, kidneys, liver, spleen, red marrow, bladder-wall, and osteogenic cells were 5.740, 0.114, 0.095, 0.121, 0.095, and 0.333 Gy/GBq, respectively. Although no patient reached the predetermined dose thresholds, the red marrow will be the dose-limiting organ. There were no adverse reactions recorded after the administration of 1110 MBq ¹⁷⁷Lu-DOTA-IBA.

Conclusion: Dosimetric results show that the ADs for critical organs and total body are within the safety limit and with high bone retention. It is a promising radiopharmaceutical alternative for the targeted treatment of bone metastases, controlling its progression, and improving the survival and quality of life of patients with advanced bone metastasis.