Preparation and In vitro Evaluation of Polydopamine-coated Immunoadjuvant Nanoparticles

[Objectives]The paper was to prepare immunoadjuvant nanoparticles with good photothermal conversion efficiency and to achieve the synergistic antitumor effect of phototherapy and immunotherapy.[Methods]Poly(lactic-co-glycolic acid)(PLGA)nanoparticles of imiquimod(R837)were prepared by emulsified solvent evaporation method.Dopamine was oxidized and self-polymerized to form polydopamine(PDA)under alkaline conditions,which then adhered to the surface of R837-PNPs(PDA-R837-PNPs).Particle size,Zeta potential and photothermal conversion capacity were used as indicators to select the best polymerization conditions.The photothermal conversion properties and photothermal stability of nanoparticles were investigated by near-infrared light(NIR)irradiation;the encapsulation efficiency and drug loading capacity of R837 were determined by HPLC;the cytotoxicity and cellular uptake of PDA-R837-PNPs were preliminarily investigated using 4T1 cells.[Results]PDA-R837-PNPs were prepared successfully.The optimal polymerization conditions were 0.5 mg/mL dopamine,3 h reaction time and 1.8 mg/mL R837-PNPs.The particle size of PDA-R837-PNPs was(186.7±4.81)nm;the PDI was 0.17±0.02;the Zeta potential was(-21.6±0.56)mV;the encapsulation efficiency was(58.02±0.04)%;and the drug loading capacity was(1.42±0.05)%.PDA-R837-PNPs had good photothermal conversion and photothermal stability in vitro.Cell experiments showed that PDA coating could significantly improve the celluar uptake of PNPs without obvious cytotoxicity,and PDA-R837-PNPs could produce heat to effectively kill 4T1 cells after NIR irradiation.[Conclusions]PDA-R837-PNPs have the characteristics of uniform particle size,good photothermal conversion effect and high cellular uptake rate,thus is expected to achieve efficient antitumor photoimmunotherapic effect.