(UroToday.com) The 2025 European Society of Medical Oncology (ESMO) Annual Congress held in Berlin, Germany, was host to the Poster presentation session. Dr. Aaron Holmes presented the poster Multi Cycle Dosimetry of the Albumin Binding PSMA Ligand [¹⁷⁷Lu]Ludotadipep in Metastatic Castration Resistant Prostate Cancer: Phase II Trial Results.
Dr. Hyun O began the presentation by introducing [¹⁷⁷Lu]Ludotadipep, a novel PSMA-targeted, albumin-binding radiopharmaceutical (as outlined below) designed to enhance tumor uptake and prolong therapeutic exposure. They presented a multi-cycle phase II study (NCT05579184) evaluating organ-absorbed radiation doses and safety outcomes in patients with metastatic castration-resistant prostate cancer (mCRPC).
A total of 24 patients with mCRPC received a total of 68 cycles of [¹⁷⁷Lu]Ludotadipep, with dosimetry evaluable in 67 cycles. Organ-absorbed doses were estimated using serial planar imaging (2–168 hours post-injection) and venous blood sampling (up to 72 hours). Red marrow activity was derived from a hematocrit-adjusted red marrow-to-blood activity ratio tailored for albumin-bound agents and validated by quantitative SPECT/CT in selected metastasis-free regions.
The hematocrit-adjusted red marrow-to-blood activity ratio (0.28 ± 0.01) was consistent with SPECT/CT-derived values, reinforcing the accuracy of this dosimetric model for albumin-bound radiopharmaceuticals.
The investigators reported that the salivary glands and kidneys exhibited the highest absorbed-dose coefficients during the first treatment cycle (1.22 ± 0.53 Gy·GBq⁻¹ and 0.67 ± 0.33 Gy·GBq⁻¹, respectively), while red marrow exposure remained low (0.053 ± 0.012 Gy·GBq⁻¹). With subsequent cycles, salivary gland doses significantly decreased (p < 0.001), likely reflecting radiation-induced changes within glandular tissue. Importantly, cumulative organ doses over six treatment cycles stayed within accepted safety limits 8.13 Gy for kidneys and 1.28 Gy for red marrow as illustrated below.
Dr. Hyun O concluded that up to six cycles of [¹⁷⁷Lu]Ludotadipep can be administered safely, with organ-absorbed doses comparable to those seen with [¹⁷⁷Lu]Lu-PSMA-617. He further noted that incorporating hematocrit- or SPECT/CT-adjusted red marrow-to-blood activity ratios may enhance dosimetric accuracy and enable more individualized treatment planning for albumin-conjugated PSMA radiopharmaceuticals.
Presented by: Joo Hyun O, MD, Associate Professor at The Catholic University of Korea, Nuclear Medicine Radiopharmaceutical therapy. Seoul, Republic of Korea.
Written by: Julian Chavarriaga, MD – Urologic Oncologist at Cancer Treatment and Research Center (CTIC) via Society of Urologic Oncology (SUO) Fellow at The University of Toronto. @chavarriagaj on Twitter during the 2025 European Society for Medical Oncology (ESMO) Annual Congress, Berlin, Germany, October 17–21, 2025