Ellagic acid-Fe@BSA nanoparticles for endogenous H2S accelerated Fe(III)/Fe(II) conversion and photothermal synergistically enhanced chemodynamic therapy

Rationale: Chemodynamic therapy (CDT) based on the Fe(II)-mediated Fenton reaction is an emerging tumor treatment strategy. However, the catalytic efficiency in tumors is crucially limited by Fe(II). Herein, an endogenous hydrogen sulfide (H2S) accelerated Fe(III)/Fe(II) transformation and photothermal synergistically enhanced CDT strategy based on ellagic acid-Fe-bovine serum albumin (EA-Fe@BSA) nanoparticles (NPs) was developed for colon tumor inhibition. On the one hand, the Fe(III) with low catalytic activity in the EA-Fe@BSA NPs could be rapidly reduced to the highly active Fe(II) by the abundant H2S in colon cancer tissues. Thus, a rapid Fe(III)/Fe(II) conversion system was established, wherein highly active Fe(II) ions were continuously regenerated to improve the CDT efficiency. On the other hand, the photothermal effect of EA-Fe@BSA NPs also accelerated the production of hydroxyl radicals (center dot OH), thereby synergistically enhancing the CDT performance and improving the therapeutic efficacy. Methods: The endogenous H2S accelerated Fe(III)/Fe(II) conversion and PTT enhanced CDT were investigated by characterization of the Fe valence state and detection of center dot OH. T1-weighted magnetic resonance imaging (MRI) was tested both in vitro and in vivo. The biocompatibility of NPs were examined via MTT assay, hemolysis analysis and routine blood measurements. The enhanced CDT was investigated in HCT116 colon cancer cells by Calcein-AM/PI staining and MTT assay, and tumor inhibition was demonstrated in HCT116 tumor bearing mice. Results: In this work, EA-Fe@BSA NPs were constructed as a CDT theranostic reagent. The H2S accelerated Fe(III)/Fe(II) conversion was confirmed, more degradation of MB and generation of center dot OH demonstrated the enhanced CDT in vitro. EA-Fe@BSA NPs exhibited good T1-weighted MRI performance. More importantly, it displayed strong near-infrared (NIR) absorption and excellent photothermal efficiency, further promotes the production of center dot OH. Hence, the efficacy of CDT was enhanced, and the tumor growth was inhibited efficiently. Conclusion: All results demonstrate that this strategy based on endogenous H2S promoted Fe(III)/Fe(II) transformation together with PTT acceleration permits efficient Fenton-reaction-mediated CDT both in vitro and in vivo, which holds great potential for effective colon cancer theranostics.