In Vitro and In Vivo Evaluation of Melanin-Binding Decapeptide 4B4 Radiolabeled with super(177)Lu, super(166)Ho, and super(153)Sm Radiolanthanides for the Purpose of Targeted Radionuclide Therapy of Melanoma

• Published in: Cancer biotherapy & radiopharmaceuticals Vol. 26; no. 5; pp. 547 - 556
• Main Authors: Ballard, B, Jiang, Z, Soil, CE, Revskaya, E, Cutler, C S, Dadachova, E, Francesconi, L C
• Format: Journal Article
• Language: English
• Published: 01.10.2011
• ISSN: 1084-9785
• DOI: 10.1089/cbr.2011.0954

Melanoma is a malignancy with increasing incidence. Although primary tumors that are localized to the skin can be successfully treated by surgical removal, there is no satisfactory treatment for metastatic melanoma, a condition that has currently an estimated 5-year survival of just 6%. During the last decade, beta - or alpha -emitter-radiolabeled peptides that bind to different receptors on a variety of tumors have been investigated as potential therapeutic agents in both the preclinical and clinical settings with encouraging results. A recent study demonstrated that 188-Rhenium ( super(188)Re)-labeled, via HYNIC ligand, fungal melanin-binding decapeptide 4B4 was effective against experimental MNT1 human melanoma and was safe to normal melanized tissues. The availability of radiolanthanides with diverse nuclear emission schemes and half-lives provides an opportunity to expand the repertoire of peptides for radionuclide therapy of melanoma. The melanin-binding decapeptide 4B4 was radiolabeled with super(177)Lu, super(166)Ho, and super(153)Sm via a DO3A chelate. The stability studies of Ln*-DO3A-4B4 in phosphate-buffered saline, serum, and a hydroxyapatite assay demonstrated that super(177)Lu-labeled peptide was more stable than super(166)Ho- and super(153)Sm-labeled peptides, most likely because of the smallest ionic radius of the former allowing for better complexation with DO3A. Binding of Ln*-DO3A-4B4 to the lysed highly melanized MNT1 melanoma cells demonstrated the specificity of peptides binding to melanin. In vivo biodistribution data for super(177)Lu-DO3A-4B4 given by intraperitoneal administration to lightly pigmented human metastatic A2058 melanoma-bearing mice demonstrated very high uptake in the kidneys and low tumor uptake. Intravenous administration did not improve the tumor uptake. The plausible explanation of low tumor uptake of super(177)Lu-DO3A-4B4 could be its decreased ability to bind to melanin during in vitro binding studies in comparison with super(188)Re-HYNIC-4B4, exacerbated by the very fast clearance from the blood and the kidneys "sink" effect.