Intracellular marriage of bicarbonate and Mn ions as “immune ion reactors” to regulate redox homeostasis and enhanced antitumor immune responses

Abstract

Abstract Background Different from Fe ions in Fenton reaction, Mn ions can function both as catalyst for chemodynamic therapy and immune adjuvant for antitumor immune responses. In Mn-mediated Fenton-like reaction, bicarbonate ($${\text{HCO}}_{3}^{ - }$$ HCO 3 - ), as the most important component to amplify therapeutic effects, must be present, however, intracellular $${\text{HCO}}_{3}^{ - }$$ HCO 3 - is strictly limited because of the tight control by live cells. Results Herein, Stimuli-responsive manganese carbonate-indocyanine green complexes (MnCO3-ICG) were designed for intracellular marriage of bicarbonate and Mn ions as “immune ion reactors” to regulate intracellular redox homeostasis and antitumor immune responses. Under the tumor acidic environment, the biodegradable complex can release “ion reactors” of Mn2+ and $${\text{HCO}}_{3}^{ - }$$ HCO 3 - , and ICG in the cytoplasm. The suddenly increased $${\text{HCO}}_{3}^{ - }$$ HCO 3 - in situ inside the cells regulate intracellular pH, and accelerate the generation of hydroxyl radicals for the oxidative stress damage of tumors cells because $${\text{HCO}}_{3}^{ - }$$ HCO 3 - play a critical role to catalyze Mn-mediated Fenton-like reaction. Investigations in vitro and in vivo prove that the both CDT and phototherapy combined with Mn2+-enhanced immunotherapy effectively suppress tumor growth and realize complete tumor elimination. Conclusions The combination therapy strategy with the help of novel immune adjuvants would produce an enhanced immune response, and be used for the treatment of deep tumors in situ.