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A Gallium-Labeled DOTA--Melanocyte- Stimulating Hormone Analog for PET Imaging of Melanoma Metastases

¹ Laboratory of Endocrinology, Department of Research, University Hospital and University Children’s Hospital, Basel, Switzerland
² Department of Diagnostic and Therapeutic Radiology, German Cancer Research Center, Heidelberg, Germany

View larger version (30K): [in a new window]   FIGURE 1. Structure of -MSH, MSHoct, NAPamide, and corresponding DOTA conjugates.

View larger version (26K): [in a new window]   FIGURE 2. Tumor versus kidney uptake. Radiolabeled DOTA--MSH analogs (, 111In-DOTA-MSHoct; , 111In-DOTA-NAPamide; , 67Ga-DOTA-NAPamide) were injected into melanoma-bearing mice and radioactivity accumulated in tumor and kidney was measured 4, 24, and 48 h after injection. Results are expressed as tumor AUC (left), kidney AUC (middle), and tumor-to-kidney ratios of AUC (right) (n = 8).

View larger version (47K): [in a new window]   FIGURE 3. Effect of quantity of peptide on tissue distribution. Melanoma-bearing mice were injected with 185 kBq 67Ga-DOTA-NAPamide (9.25 GBq/µmol) supplemented with various amounts of nonradioactive Ga-DOTA-NAPamide to obtain total peptide quantity per mouse of 20 pmol (), 170 pmol (), or 420 pmol (). Radioactivity accumulated in main tissues was measured 4 h after injection and results are expressed as percentage of uptake (%ID/g) observed after injection of 20 pmol (mean ± SEM, n = 3 or 4). *P < 0.05, P < 0.001 vs. 20 pmol. SI = small intestine.

View larger version (34K): [in a new window]   FIGURE 4. Autoradiographs of tissue sections from primary and metastatic melanoma. (A) Lung with melanotic melanoma metastases. (B) Lung with melanotic or amelanotic melanoma metastases. (C and D) Liver with melanotic melanoma metastases. (E) Primary melanoma with surrounding skin tissue. 67Ga-DOTA-NAPamide was injected into tumor-bearing mice. Primary skin melanoma and tissues showing macroscopic metastases were collected 4 h later and immediately fixed. After sectioning, tissues were exposed to Molecular Dynamics Storage Phosphor Plate (left) and later were exposed to scanner (right). Arrows indicate amelanotic (dotted arrow) or melanotic (solid arrows) metastatic nodules.

View larger version (40K): [in a new window]   FIGURE 5. PET imaging of melanoma-bearing mice with 68Ga-DOTA-NAPamide. (A and B) Scatter- and attenuation-corrected PET images of melanoma-bearing mice. 68Ga-DOTA-NAPamide (50.1 GBq/µmol; 40 pmol) was injected into mice implanted in right flank with B16F1 melanoma and imaged at 0.5, 1, 2, and 3 h after injection (n = 2): coronal image (A) and transaxial image (B) of mice 0.5 h (tumor weight, 300 mg) and 1 h (tumor weight, 344 mg) after injection. Only melanoma, kidneys, bladder, and, to a lesser extent, heart are detectable. No further background reduction could be observed at later time points. (C) Kinetics of tumor and kidney uptake. Melanoma-bearing mice were injected with either 40 pmol (50.1 GBq/µmol) or 290 pmol (16.5 GBq/µmol) 68Ga-DOTA-NAPamide. Melanoma and kidneys were collected 0.5, 1, 2, and 3 h after injection and radioactivity was measured in -counter. Results are expressed as %ID/g tissue (mean ± SEM; n = 2–4). P < 0.001 vs. 290 pmol.