Biosynthetic Melanin/Ce6-Based Photothermal and Sonodynamic Therapies Significantly Improved the Anti-Tumor Efficacy.

Photothermal therapy (PTT) and sonodynamic therapy (SDT) are becoming promising therapeutic modalities against various tumors in recent years. However, the single therapeutic modality with SDT or PTT makes it difficult to achieve a satisfactory anti-tumor outcome due to their own inherent limitations, such as poor tissue penetration for the near-infrared (NIR) laser and the limited cytotoxic reactive oxygen species (ROS) generated from conventional sonosensitizers irradiated by ultrasound (US). Here, we successfully biosynthesized melanin with a controllable particle size with genetically engineered bacteria harboring a heat-inducible gene circuit. The biosynthetic melanin with 8 nm size and chlorin e6 (Ce6) was further encapsulated into liposomes and obtained SDT/PTT dual-functional liposomes (designated as MC@Lip). The resulting MC@Lip had an approximately 100 nm particle size, with 74.71% ± 0.54% of encapsulation efficiency for melanin and 94.52% ± 0.78% for Ce6. MC@Lip exhibited efficient O production and photothermal conversion capability upon receiving irradiation by US and NIR laser, producing significantly enhanced anti-tumor efficacy in vitro and in vivo. Especially, US and NIR laser irradiation of tumors received with MC@Lip lead to complete tumor regression in all tested tumor-bearing mice, indicating the great advantage of the combined use of SDT and PTT. More importantly, MC@Lip possessed good photoacoustic (PA) and fluorescence dual-modal imaging performance, making it possible to treat tumors under imaging guidance. Our study provides a novel approach to synthesize a melanin nanoparticle with controllable size and develops a promising combined SDT/PTT strategy to treat tumors.