Melanoma is a highly malignant
skin cancer that frequently metastasizes to the lung, bone, and brain at an early phase. Therefore, noninvasive detection of metastasized
melanoma could be beneficial to determine suitable therapeutic strategies. We previously reported a biocompatible ternary anionic complex composed of plasmid
DNA (pDNA),
polyethyleneimine (PEI), and γ-
polyglutamic acid (γ-
PGA) based on an electrostatic interaction, which was highly taken up by
melanoma cells (B16-F10), even if it was negatively charged. Here, we developed a radiolabeled γ-
PGA complex by using
indium-111 (111In)-labeled
polyamidoamine dendrimer (4th generation; G4) instead of pDNA and
iodine-125 (125I)-labeled PEI instead of native PEI, and evaluated its effectiveness as a
melanoma-targeted imaging probe. This ternary complex was synthesized at a theoretical charge ratio; carboxyl groups of 111In-diethylenetriaminepentaacetic
acid (
DTPA)-G4 : amino groups of 125I-PEI : carboxyl groups of γ-
PGA was 1 : 8 : 16, and the size and zeta potential were approximately 29 nm and -33 mV, respectively. This complex was taken up by B16-F10 cells with time. Furthermore, a biodistribution study, using normal mice, demonstrated its accumulation in the liver, spleen, and lung, where macrophage cells are abundant. Almost the same level of radioactivity derived from both 111In and 125I was observed in these organs at an early phase after probe injection. Compared with the normal mice, significantly higher lung-to-blood ratios of radioactivity were observed in the B16-F10-lung metastatic
cancer model. In conclusion, the radiolabeled γ-
PGA complex would hold potentialities for nuclear medical imaging of lung metastatic
melanoma.