Dual‐Modality Imaging‐Guided Manganese‐Based Nanotransformer for Enhanced Gas‐Photothermal Therapy Combined Immunotherapeutic Strategy Against Triple‐Negative Breast Cancer

Abstract Activating the stimulator of the interferon gene (STING) is a promising immunotherapeutic strategy for converting “cold” tumor microenvironment into “hot” one to achieve better immunotherapy for malignant tumors. Herein, a manganese‐based nanotransformer is presented, consisting of manganese carbonyl and cyanine dye, for MRI/NIR‐II dual‐modality imaging‐guided multifunctional carbon monoxide (CO) gas treatment and photothermal therapy, along with triggering cGAS‐STING immune pathway against triple‐negative breast cancer. This nanosystem is able to transfer its amorphous morphology into a crystallographic‐like formation in response to the tumor microenvironment, achieved by breaking metal‐carbon bonds and forming coordination bonds, which enhances the sensitivity of magnetic resonance imaging. Moreover, the generated CO and photothermal effect under irradiation of this nanotransformer induce immunogenic death of tumor cells and release damage‐associated molecular patterns. Simultaneously, the Mn acts as an immunoactivator, potentially stimulating the cGAS‐STING pathway to augment adaptive immunity, resulting in promoting the secretion of type I interferon, the proliferation of cytotoxic T lymphocytes and M2‐macrophages repolarization. This nanosystem‐based gas‐photothermal treatment and immunoactivating therapy synergistic effect exhibit excellent antitumor efficacy both in vitro and in vivo, reducing the risk of triple‐negative breast cancer recurrence and metastasis; thus, this strategy presents great potential as multifunctional immunotherapeutic agents for cancer treatment.