A tumor-associated bacteria-responsive magnetic exosome as a clearable T1 contrast agent for targeted imaging of tumors

Bacteria can colonize and grow in tumors due to the hypoxic and immunosuppressive tumor microenvironment. Indeed, recent studies have revealed that bacteria are intrinsic and integral components of the tumors. Herein, a tumor-associated bacteria-responsive magnetic exosome (Exo@ESIONs) with switchable magnetic resonance imaging (MRI) property is developed for sensitive tumor imaging. The magnetic exosomes loaded with extremely small iron oxide nanoparticles (ESIONs) possess the excellent properties of long circulation in blood, high accumulation in tumor tissues and rapid response in the tumor microenvironment. Stimulated by the pore-forming toxins (PFTs) secreted from the bacteria in the tumors, the Exo@ESIONs can be disintegrated and the ESIONs are rapidly released, enabling dynamic switchable T2/T1 MRI of the tumors. As a result, the T1 contrast effect of the magnetic nanomaterials can be selectively enhanced in the tumor tissues, even the tumor size is as small as 10 mm3. Moreover, the ESIONs can be rapidly elimination from the body via renal clearance after the MRI to avoid the potential toxicity.