Imaging of melanoma using ⁶⁴Cu- and ⁸⁶Y-DOTA- ReCCMSH(Arg¹¹), a cyclized peptide analogue of α-MSH

Early detection of melanoma is essential, since a patient's prognosis with metastatic melanoma is poor. Previous studies showed that ¹¹¹In-DOTA- ReCCMSH(ATg¹¹), a cyclic analogue of α-melanocyte stimulating hormone (α-MSH), exhibited high tumor concentration and rapid clearance from nontarget tissue. The goal of this current study was to label DOTA-ReCCMSH(Arg¹¹) with β⁺-emitting radionuclides, to determine if the high sensitivity of positron emission tomography (PET) imaging would aid in the detection of malignant melanoma. DOTA-ReCCMSH(Arg ¹¹) was labeled with ⁶⁴Cu and ⁸⁶Y. Biodistribution and small animal PET imaging were carried out in mice implanted with B16/F1 murine melanoma tumor and compared with data obtained in the same animal model with [¹⁸F]FDG. In both cases a subset of animals were co-injected with 20 μg of DOTA-ReCCMSH(Arg¹¹) to determine if tumor concentration was receptor mediated. Tumor concentration for both the ⁸⁶Y- and ⁶⁴Cu-complexes reached a maximum at 30 min, while coadministering 20 μg of unlabeled complex reduced tumor uptake significantly. Nontarget organ concentration was considerably lower with ⁸⁶Y-DOTA-ReCCMSH(Arg¹¹) than its ⁶⁴Cu analogue, except in the kidneys, where the ⁶⁴Cu complex had lower accumulation at all time points. Small animal PET images for both complexes showed the tumor could be visualized after 30 min, with the standardized uptake value (SUV) analysis following a similar trend as the biodistribution data. The data obtained suggests that DOTA-ReCCMSH(Arg¹¹), when labeled with α⁺-emitting radionuclides, has the potential for early detection of malignant melanoma by exploiting the sensitivity and high resolution of PET.