In vitro photodynamic therapy of methylene blue-loaded acetyl resistant starch nanoparticles

Background Combination therapies comprising multiple methods, such as photodynamic therapy have been applied to be complements chemotherapy as they increase the therapeutic efficiency by enabling the intelligent drug delivery to target sites by exposing the photosensitizer to light and activating it in the tumor tissue. This study evaluated in vitro photodynamic therapy of methylene blue (MB)-loaded acetyl resistant starch (ARS) nanoparticles (NPs). Methods ARS was synthesized by the reaction between resistant starch (RS) and acetic anhydride. MB-loaded ARS NPs and ARS NPs were prepared by a single emulsion method. Synthesized ARS was measured by NMR. Prepared ARS NPs and MB-loaded ARS NPs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction, UV/Vis, and circular dichroism (CD). MB-loaded ARS NPs were treated in mouse colon cancer cells (CT-26) and they were treated under near-infrared (NIR) laser irradiation. Results Synthesis of ARS was confirmed by NMR and the degree of substitutions in the ARS was 7.1. The morphologies of ARS NPs observed by TEM were spherical shapes and the particle sizes of ARS NPs were 173.4 nm with a surface charge of - 17.24 mV. The d-spacing of ARS NPs was smaller than those of RS and the conformational changes of RS occurred by the formation of self-assembled polymeric NPs with induction of CD of the MB by chiral ARS NPs. The phototoxicity of CT-26 cells treated by MB-loaded ARS NPs dramatically decreased in a dose-dependent manner under NIR laser irradiation compared to free MB. Conclusion This study demonstrated the ordered nanosized structures in the ARS NPs and conformational change from random coil structure of RS to alpha-helices one of ARS occurred and CD of the achiral MB was induced. The MB-loaded ARS NPs showed a higher generation of reactive oxygen species (ROS) in the CT-26 cells than free MB with the NIR laser irradiation and resulting in phototoxicity under irradiation.