Engineering of small molecular organic nanoparticles for mitochondria-targeted mild photothermal therapy of malignant breast cancers

Conventional photothermal therapy (PTT) often causes unwanted hyperthermia damage to the surrounding healthy tissues, and fails in the ablation of infiltrating and malignant tumors, which even leads to tumor recurrence. The main reasons for the suboptimal therapeutic efficacy of PTT include: (i) the heterogenous distribution of PTT agents in cancer cells, (ii) the limited penetration depth of irradiation light, and (iii) importantly, the difficulty in controlling the photothermal process which often leads to overheated hyperthermia and severe side effects, including inflammation, immune escape, metastasis and damage to normal tissues surrounding the tumor. It is envisioned that organelle targeted mild PTT would be a good strategy to overcome these shortcomings and significantly improve the therapeutic efficacy, decrease the therapeutic threshold for both the drug dosage and hyperthermia temperature, and diminish damage to the neighboring healthy tissues. Although small biocompatible organic photothermal agents are promising candidates for organelle targeted mild PTT, related research together with their therapeutic mechanism study has rarely been reported so far. In this contribution, we fabricate efficient small organic molecules (TD1) via donor-acceptor molecular engineering, and further package TD1 molecules into a lipid carrier to construct mitochondria-targeted nanoparticles (M-TD1 NPs) for mild PTT. The highly desirable photothermal performance of M-TD1 NPs dramatically improves the efficacy of photothermal cancer cell ablation. Benefiting from the excellent PTT effects of M-TD1 NPs, favorable antitumor efficacy and metastasis inhibition are achieved in vitro and in vivo. Mechanistically, the improved mitochondria-based mild thermal treatment triggers the apoptosis-dependent cell death and influences the autophagy of cancer cells, resulting in enhanced cancer elimination and suppressed cancer cell migration. This work demonstrates that sub-cellular targeted mild PTT is promising to control cell apoptosis and autophagy and has potential for future metastatic cancer therapy.