Korean J Radiol.  2024 Feb;25(2):179-188. 10.3348/kjr.2023.0656.

Dosimetric Analysis of a Phase I Study of PSMA-Targeting Radiopharmaceutical Therapy With [ ¹⁷⁷ Lu]Ludotadipep in Patients With Metastatic Castration-Resistant Prostate Cancer

• Ha S
• O JH
• Park C
• Boo SH
• Yoo IR
• Moon HW
• Chi DY
• Lee JY

• KMID: 2552383
• DOI: http://doi.org/10.3348/kjr.2023.0656

Abstract

Objective
¹⁷⁷ Lutetium [Lu] Ludotadipep is a novel prostate-specific membrane antigen targeting therapeutic agent with an albumin motif added to increase uptake in the tumors. We assessed the biodistribution and dosimetry of [ ¹⁷⁷ Lu]Ludotadipep in patients with metastatic castration-resistant prostate cancer (mCRPC).
Materials and Methods
Data from 25 patients (median age, 73 years; range, 60–90) with mCRPC from a phase I study with activity escalation design of single administration of [ ¹⁷⁷ Lu]Ludotadipep (1.85, 2.78, 3.70, 4.63, and 5.55 GBq) were assessed. Activity in the salivary glands, lungs, liver, kidneys, and spleen was estimated from whole-body scan and abdominal SPECT/CT images acquired at 2, 24, 48, 72, and 168 h after administration of [ ¹⁷⁷ Lu]Ludotadipep. Red marrow activity was calculated from blood samples obtained at 3, 10, 30, 60, and 180 min, and at 24, 48, and 72 h after administration. Organand tumor-based absorbed dose calculations were performed using IDAC-Dose 2.1.
Results
Absorbed dose coefficient (mean ± standard deviation) of normal organs was 1.17 ± 0.81 Gy/GBq for salivary glands, 0.05 ± 0.02 Gy/GBq for lungs, 0.14 ± 0.06 Gy/GBq for liver, 0.77 ± 0.28 Gy/GBq for kidneys, 0.12 ± 0.06 Gy/GBq for spleen, and 0.07 ± 0.02 Gy/GBq for red marrow. The absorbed dose coefficient of the tumors was 10.43 ± 7.77 Gy/GBq.
Conclusion
[ ¹⁷⁷ Lu]Ludotadipep is expected to be safe at the dose of 3.7 GBq times 6 cycles planned for a phase II clinical trial with kidneys and bone marrow being the critical organs, and shows a high tumor absorbed dose.

Keyword

PSMA; mCRPC; Radiopharmaceutical therapy; Dosimetry; Albumin