NIR-Mediated drug release and tumor theranostics using melanin-loaded liposomes

Heat generation in a drug delivery carrier by exposure to near-infrared (NIR) light with excellent tissue transmittance is an effective strategy for drug release and tumor therapy. Because liposomes have amphiphilic properties, they are useful as drug carriers. Liposomes are also very suitable for drug delivery strategies using heat generation by NIR laser because lipid bilayers are easily broken by heat. Thermally generated bubbles from liposomes not only induce drug release, but also enable ultrasound imaging.

Melanin, perfluorohexane (PFH), and 5-fluorouracil (5-FU)-loaded liposomes (melanin@PFH@5-FU-liposomes) that can generate heat and bubble by NIR laser irradiation were prepared by a thin film method. Conversion of light to heat and bubble generation of melanin@PFH@5-FU-liposomes were evaluated using an infrared (IR) thermal imaging camera and an ultrasound imaging system both in vitro and in vivo. To investigate tumor therapeutic effect, NIR laser of 808 nm was used to irradiate tumor site for 10 min after injecting melanin@PFH@5-FU-liposome into tail veins of CT26-bearing mice.

Melanin@PFH@5-FU-liposomes showed a spherical shape with a size of 209.6 ± 4.3 nm. Upon NIR laser irradiation, melanin@PFH@5-FU-liposomes exhibited effective temperature increase both in vitro and in vivo. In this regard, temperature increase caused a phase transition of PFH to induce bubble generation dramatically, resulting in effective drug release behavior and ultrasound imaging. The temperature of the tumor site was increased to 52 t and contrast was greatly enhanced during ultrasound imaging due to the generation of bubble. More importantly, tumor growth was effectively inhibited by injection of melanin@PFH@5-FU-liposomes with laser irradiation.

Based on intrinsic photothermal properties of melanin and phase transition properties of PFH, melanin@PFH@5-FU-liposomes exhibited effective heat and bubble generation upon NIR laser irradiation. The elevated temperature induced bubble generation, resulting in contrast enhancement of ultrasound imaging. Melanin@PFH@5-FU-liposomes under NIR laser irradiation induced the death of cancer cells, thereby effectively inhibiting tumor growth. These results suggest that melanin@PFH@5-FU-liposomes can be utilized as a promising agent for photothermal tumor therapy and ultrasound imaging.