Biokinetics and Dosimetry of 177Lu-Pentixather

The chemokine receptor 4 (CXCR4), which is overexpressed in many solid and hematologic malignancies, can be targeted for radiopeptide therapy via the antagonist pentixather. The biokinetics and dosimetry of Lu-177-pentixather and Y-90-pentixather were analyzed in this study. Methods: This retrospective study was a standardized reevaluation of data collected for treatment planning. Nineteen patients with complete sets of planar whole-body scans over at least 4 d and a single SPECT/CT scan after administration of 200 MBq of Lu-177-pentixather were included. Kinetics were measured in the whole body, in tissues with activity retention, and in 10 individuals in the blood. Time-integrated activity coefficients and tissue-absorbed doses were derived. Results: Increased uptake of pentixather was observed in the kidneys, liver, spleen, and bone marrow, inducing respective median absorbed doses of 0.91 Gy (range, 0.38-3.47 Gy), 0.71 Gy (range, 0.39-1.17 Gy), 0.58 Gy (range, 0.34-2.26 Gy), and 0.47 Gy (range, 0.14-2.33 Gy) per GBq of Lu-177-pen-tixather and 3.75 Gy (range, 1.48-12.2 Gy), 1.61 Gy (range, 1.14-2.97 Gy), 1.66 Gy (range, 0.97-6.69 Gy), and 1.06 Gy (range, 0.27-4.45 Gy) per GBq of 90Y-pentixather. In most tissues, activity increased during the first day after the administration of Lu-177-pentixather and afterward decayed with mean effective half-lives of 41 +/- 10 h (range, 24-64 h) in the kidneys and median half-lives of 109, 86, and 92 h in the liver, spleen, and bone marrow, respectively. Maximum uptake per kidney was 2.2% +/- 1.0% (range, 0.6%-5.1%). In organs showing no specific uptake, absorbed doses exceeding 0.3 Gy/GBq of 90Y-pentixather were esti-mated for the urinary bladder and for tissues adjacent to accumulating organs such as the adrenal glands, bone surface, and gallbladder. Dose estimates for tumors and extramedullary lesions ranged from 1.5 to 18.2 Gy/GBq of Y-90-pentixather. Conclusion: In patients with hematologic neoplasms, absorbed doses calculated for bone marrow and extrame-dullary lesions are sufficient to be effective as an adjunct to high-dose chemotherapies before stem cell transplantation.