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

Introduction: Diagnosis of malignant melanoma is critical, since a patient's prognosis is poor. Previous studies have shown that ⁶⁴Cu- and ⁸⁶Y-DOTA-ReCCMSH(Arg¹¹) have the potential for early detection of malignant melanoma by exploiting the sensitivity and high resolution of positron emission tomography (PET). This encouraged us to investigate DOTA-ReCCMSH(Arg¹¹) labeled with another β⁺-emitting radionuclide, ⁶⁸Ga. Methods: DOTA-ReCCMSH(Arg¹¹) was successfully labeled with ⁶⁸Ga at pH 3.8-4 at 85°C. Acute biodistribution and small-animal PET imaging studies were performed in mice bearing B16/F1 melanoma tumor. Results: Biodistribution studies showed moderate receptor-mediated tumor uptake, fast nontarget organ clearance and high tumor to nontarget tissue ratios. Preadministration of d-lysine significantly reduced kidney uptake without affecting the uptake of the agent in the tumor. Small-animal PET images showed that the tumor could be clearly visualized at all time points examined (0.5-2 h) with the standardized uptake value analysis following a similar trend as the biodistribution data. Conclusions: The preliminary data obtained suggest that ⁶⁸Ga-DOTA-ReCCMSH(Arg¹¹) is a promising PET imaging agent for early detection of malignant melanoma.