Preclinical assessment of ¹⁷⁷Lu-DOTA-Pip-Nle-CycMSH_hex: In vivo evaluation and human dosimetry estimation

This study presents a preclinical assessment of ¹⁷⁷Lu-DOTA-Pip-Nle-CycMSHhex (¹⁷⁷Lu-CCZ01048), a previously reported radiolabeled α-MSH analogue targeting melanoma, with a focus on additional in vivo evaluation and human dosimetry extrapolation. ¹⁷⁷Lu-CCZ01048 was radiolabeled with a radiochemical purity exceeding 99% and demonstrated high stability in phosphate-buffered saline (PBS) and human serum, consistent with previous reports. Receptor binding assays confirmed a high affinity for the melanocortin-1 receptor (MC1R), with a dissociation constant (K_d) of 0.51 ± 0.09 nM, while internalization studies showed more than 50% cellular uptake in B16F10 melanoma cells within 6 h. Cytotoxicity evaluation using the MTT assay revealed a significant reduction in cell viability, with a 31% decrease observed at a concentration of 1000 nM. Biodistribution studies in tumor-bearing mice demonstrated high tumor uptake, rapid blood clearance, and minimal accumulation in non-target organs, accompanied by predominant renal metabolism and excretion. SPECT imaging confirmed selective tumor targeting. Absorbed dose estimates based on tumor-bearing mice biodistribution data identified the kidneys as the dose-limiting organ, while overall dosimetry values were within the range reported for clinically used and FDA-approved ¹⁷⁷Lu-labeled radiopharmaceuticals, including ¹⁷⁷Lu-DOTATATE and ¹⁷⁷Lu-PSMA-617. These findings support further preclinical and translational evaluation of ¹⁷⁷Lu-CCZ01048 for melanoma-targeted radionuclide therapy.