Targeted photothermal ablation of murine melanomas with melanocyte-stimulating hormone analog - conjugated hollow gold nanospheres

Purpose: To develop melanoma-targeted hollow gold nanospheres (HAuNS) and evaluate their potential utility forselective photothermal ablation in melanoma. Experimental Design: A new class of photothermal coupling agents based on HAuNS was synthesized. HAuNS were stabilized with polyethylene glycol (PEG) coating and attached with α - melanocyte-stimulating hormone (MSH) analog, [Nle ⁴,D-Phe ⁷]α-MSH (NDP-MSH), which is a potent agonist of melanocortin type-1 receptor overexpressed in melanoma. The intracellular uptake of the NDP-MSH - conjugated PEGylated HAuNS (NDP-MSH-PEG-HAuNS) and the distribution of β-arrestin were examined in murine B16/F10 melanoma cells. The biodistribution of NDP-MSH-PEG-HAuNS was assessed at 4 hours post i.v. injection in tumor-bearing nude mice. Photothermal ablation effect of the nanoparticles was evaluated both histologically using excised tissue and functionally by [ ¹⁸F]fluorodeoxyglucose positron emission tomography. Results: NDP-MSH-PEG-HAuNS consist only of a thin gold wall with hollow interior (outer diameter, 43.5 ± 2.3 nm; shell thickness, 3-4 nm), which displays strong and tunable resonance absorption in near-IR region (peak, 808 nm). The nanoparticles were specifically taken up by melanoma cells, which initiated the recruitment of β-arrestins, the adapters to link the activated G-protein - coupled receptors to clathrin, indicating the involvement of receptor-mediated endocytosis. This resulted in enhanced extravasation of NDP-MSH-PEG-HAuNS from tumor blood vessels and theirdispersion into tumormatrix compared with nonspecific PEGylated HAuNS. Successful selective photothermal ablation of B16/F10 melanoma with targeted HAuNS was confirmed by histologic and [ ¹⁸F]fluorodeoxyglucose positron emission tomography evaluation at 24 hours post near IR - region laser irradiation at a low-dose energy of 30 J/cm ². Conclusion: NDP-MSH-PEG-HAuNS have the potentials to mediate targeted photothermal ablation of melanoma.