Synthesis and Preclinical Evaluation of a Ga-Labeled Pyridine-Based Benzamide Dimer for Malignant Melanoma Imaging.

Benzamide (BZA), a small molecule that can freely cross cell membranes and bind to melanin, has served as an effective targeting group for melanoma theranostics. In this study, a novel pyridine-based BZA dimer (denoted as H-2) was labeled with Ga ([Ga]Ga-H-2) for positron emission tomography (PET) imaging of malignant melanomas. [Ga]Ga-H-2 was obtained with high radiochemical yield (98.0 ± 2.0%) and satisfactory radiochemical purity (>95.0%). The specificity and affinity of [Ga]Ga-H-2 were confirmed in melanoma B16F10 cells and PET imaging of multiple tumor models (B16F10 tumors, A375 melanoma, and lung metastases). Monomeric [Ga]Ga-H-1 was prepared as a control radiotracer to verify the effects of the molecular structure on pharmacokinetics. The values of the lipid-water partition coefficient of [Ga]Ga-H-2 and [Ga]Ga-H-1 demonstrated hydrophilicity with log = -2.37 ± 0.07 and -2.02 ± 0.09, respectively. PET imaging and biodistribution showed a higher uptake of [Ga]Ga-H-2 in B16F10 primary and metastatic melanomas than that in A375 melanomas. However, the relatively low uptake of monomeric [Ga]Ga-H-1 in B16F10 tumors and high accumulation in nontarget organs resulted in poor PET imaging quality. This study demonstrates the synthesis and preclinical evaluation of the novel pyridine-based BZA dimer [Ga]Ga-H-2 and indicates that the dimer tracer has promising applications in malignant melanoma-specific PET imaging because of its high uptake and long-time retention in malignant melanoma.