⁶⁴Cu-Labeled Alpha-Melanocyte-Stimulating Hormone Analog for MicroPET Imaging of Melanocortin 1 Receptor Expression

Abstract

The alpha-melanocyte-stimulating hormone (α-MSH) receptor (melanocortin type 1 receptor, or MC1R) plays an important role in the development and growth of melanoma cells. It was found that MC1R was overexpressed on most murine and human melanoma, making it a promising molecular target for melanoma imaging and therapy. Radiolabeled α-MSH peptide and its analogs that can specifically bind with MC1R have been extensively explored for developing novel agents for melanoma detection and radionuclide therapy. The goal of this study was to evaluate a 64 Culabeled α-MSH analog, Ac-Nle-Asp-His-D-Phe-Arg-Trp-Gly-Lys(DOTA)-NH 2 (DOTANAPamide), as a potential molecular probe for microPET imaging of melanoma and MC1R expression in melanoma xenografted mouse models. 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) conjugated NAPamide was synthesized and radiolabeled with 64 Cu (t 1/2 =12 h) in NH 4 OAc (0.1 M; pH 5.5) buffered solution for 60 min at 50 °C. Cell culture studies reveal rapid and high uptake and internalization of 64 Cu-DOTA-NAPamide in B16F10 cells. Over 90% of receptor-bound tracer is internalized at 3 h incubation. A cellular retention study demonstrates that the receptor-bound 64 Cu-DOTA-NAPamide is slowly released from the B16F10 cells into the medium; 66% of the radioactivity is still associated with the cells even after 3 h incubation. The biodistribution of 64 Cu-DOTA-NAPamide was then investigated in C57BL/6 mice bearing subcutaneous murine B16F10 melanoma tumors with high capacity of MC1R and Fox Chase Scid mice bearing human A375M melanoma with a relatively low number of MC1R receptors. Tumor uptake values of 64 Cu-DOTA-NAPamide are found to be 4.63 ± 0.45% and 2.49 ± 0.31% ID/g in B16F10 and A375M xenografted melanoma at 2 h postinjection (pi), respectively. The B16F10 tumor uptake at 2 h pi is further inhibited to 2.29 ± 0.24% ID/g, while A375M tumor uptake at 2 h pi remains 2.20 ± 0.41% ID/g with a coinjection of excess α-MSH peptide. MicroPET imaging of 64 Cu-DOTA-NAPamide in B16F10 tumor mice clearly shows good tumor localization. However, low A375M tumor uptake and poor tumor to normal tissue

Small-Animal PET of Melanocortin 1 Receptor Expression Using a 18F-Labeled -Melanocyte-Stimulating Hormone Analog

“…4). We recently synthesized a 64 Cu-labeled α-MSH peptide, 64 Cu-DOTA-NAPamide, and successfully demonstrated its use for microPET imaging of melanoma and MC1R expression (21,22). In this research, we further develop 18 F-labeled NAPamide as a molecular imaging probe for MC1R microPET imaging.…”

“…The MC1R is overexpressed in most murine and human melanoma metastases (7,8), thus making it a promising molecular target for imaging and therapy of melanomas. Various α-MSH peptides radiolabeled with 18 F (9), 99m Tc (10,11), 111 In (12)(13)(14)(15)(16)(17), 125 I (18), 67 Ga (19), 86 Y (20), and 64 Cu (20)(21)(22) that can recognize the MC1R in vitro or in vivo have been prepared and evaluated for melanoma detection. Moreover, an α-MSH peptide, ReCCMSH (Arg 11 ), radiolabeled with a therapeutic radionuclide-either 188 Re or 212 Pb-has shown promising therapeutic efficacy in mice bearing either B16F1 murine or TXM13 human xenografted melanoma (23,24).…”

“…An α-MSH analog, Ac-Nle-Asp-His-D-Phe-Arg-Trp-Gly-Lys-NH 2 (NAPamide), can target the MC1R with excellent pharmacokinetic properties in tumor mice models (19). We prepared and evaluated a 64 Cu-labeled 1,4,7,10-tetraazacy-clododecane-N,N′,N″,N‴-tetraacetic acid (DOTA)-NAPamide (21,22) for imaging MC1R expression using small-animal PET. Our results indicate that 64 Cu-DOTA-NAPamide is able to image MC1R expression imaging in living mice.…”

Gallium-68-labeled DOTA-rhenium-cyclized α-melanocyte-stimulating hormone analog for imaging of malignant melanoma

“…The tumor to muscle ratio of 68 Ga-DOTA-ReCCMSH(Arg 11 ) (43.2 ± 15.3) is similar to that of 64 Cu-CBTE2A-ReCCMSH(Arg 11 ) (44.6 ± 9.76, p = NS) and is significantly higher compared to 64 Cu-DOTAReCCMSH(Arg 11 ) (18.5 ± 3.17, p < 0.01). The 86 Y-DOTA-ReCCMSH(Arg 11 ) data [40] is superior to that seen for both 64 Cu DOTA-and 64 Cu-CBTE2A-ReCCMSH(Arg 11 ) analogs [40,46] as well as that seen for 67/68 Ga-DOTA-NAPamide [34], 64 Cu-DOTA-NAPamide [32], 18 F-FB-NAPamide [33], 18 F-FDG [40] and 68 Ga-DOTA-ReCCMSH(Arg 11 ). Overall differences in tumor accumulation can be attributed to the amount of peptide mass administered to the animals, differences in tumor types and volumes, and the status of the tumor cells maintained within each laboratory so care must be taken in the comparison of the current studies with those previously reported [32][33][34]40].…”

“…There have been a number of reports on α-MSH peptide-based agents that have demonstrated the ability to image the MCR1 receptor in vivo [31][32][33][34][35][36][37][38][39]. We previously described an α-MSHtargeting peptide system, DOTA-ReCCMSH(Arg 11 ), that was labeled with β + -emitting radiometals, as potential agents for the detection of malignant melanoma via PET imaging [40].…”