Melanin-PEG nanoparticles as a photothermal agent for tumor therapy

To increase availability for biomedical applications of melanin, especially as a photothermal agent, poly(ethylene glycol) (PEG) was conjugated to melanin in this study. Melanin-PEG conjugate formed self-assembled nanoparticles with mean diameter of 109.3 ± 2.4 nm. Melanin-PEG nanoparticles showed no precipitation in aqueous solution for 7 days. Due to intrinsic photothermal properties of melanin, these melanin-PEG nanoparticles showed good photothermal conversion efficiencies both in vitro and in vivo. When melanin-PEG nanoparticles were injected into tail vein of 4T1-bearing mouse followed by exposure to 808 nm NIR laser at a power density of 1.5 W/cm2, temperature of the tumor region was increased to 48℃ and tumor growth was less than 50 % compared to that of the control group. As a result, tumor growth was suppressed effectively under NIR laser irradiation after intravenous injection of melanin-PEG nanoparticles. PEG conjugation to melanin can broaden the range of biomedical applications of melanin. Resultant melanin-PEG nanoparticles have great potential as photothermal agents for cancer therapy.