Combined photothermal-immunotherapy via poly-tannic acid coated PLGA nanoparticles for cancer treatment

Photothermal therapy (PTT) is able to ablate tumors via hyperthermia, while immunotherapy could prevent tumor recurrence and metastasis by activating the host immune responses. Therefore, the combination of PTT and immunotherapy offers great advantages for the treatment of cancer. To achieve this goal, poly tannic acid (pTA) coated PLGA nanoparticles (PLGA-pTA NPs) were synthesized for combined photothermal-immunotherapy. pTA was a coordination complex formed by TA and Fe³⁺ and it could be easily coated on PLGA NPs within seconds with a coating rate of 5.89%. As a photothermal agent, PLGA-pTA revealed high photothermal conversion efficiency and excellent photo-stability upon 808 nm laser irradiation. It also exhibited strong photothermal cytotoxicity against 4T1 cells. Moreover, PLGA-pTA based PTT could effectively trigger DC maturation since it could induce the release of DAMPs. The result of animal experiments showed that PLGA-pTA plus laser irradiation raised the tumor temperature up to ca. 60 °C and effectively suppressed the growth of primary tumors. What's more, the progression of distant tumors as well as lung metastasis was also significantly inhibited due to the activation of anti-tumor responses by PLGA-pTA mediated PTT. When further combined with anti-PD-L1 antibody (a-PD-L1), the tumor growth and metastasis were almost completely inhibited. Our study provided a versatile platform to achieve combined photothermal-immunotherapy with enhanced therapeutic efficacy.