Theranostic nanodrugs combining magnetic resonance imaging (MRI) and cancer therapy have attracted extensive interest in cancer diagnosis and treatment. Herein, a manganese (Mn)-doped mesoporous polydopamine (Mn-MPDA) nanodrug incorporating the nitric oxide (NO) prodrug BNN6 and immune agonist R848 was developed. The nanodrug responded to the H⁺ and glutathione being enriched in tumor microenvironment to release R848 and Mn²⁺. The abundant Mn²⁺ produced through a Fenton-like reaction enabled a highly sensitive T1-T2 dual-mode MRI for monitoring the tumor accumulation process of the nanodrug, based on which an MRI-guided laser irradiation was achieved to trigger the NO gas therapy. Meanwhile, R848 induced the re-polarization of tumor-promoting M2-like macrophage to a tumoricidal M1 phenotype. Consequently, a potent synergistic antitumor effect was realized in mice bearing subcutaneous 4T1 breast cancer, which manifested the great promise of this multifunctional nanoplatform in cancer treatment.

Although gas-filled microbubbles with high echogenicity are widely applied inclinical ultrasonography, the micron scale particle size impedes their use in the treatment of solid tumors, which are accessible to objects less than several hundred nanometers. We herein propose an unusual approach involving apH-induced core–shell micelle-to-vesicle transition to prepare ultrasound-sensitive polymeric nanospheres (polymersomes in structure) possessing multiple features, including nanosize, monodispersity, and incorporation of a phase-transitional imaging agent into the aqueous lumen. These features are not achievable via the conventional double-emulsion method for polymersome preparation. The nanospheres were constructed based on a novel triblock copolymer with dual pH sensitivity. The liquid-to-gas phase transition of the imaging agent induced by external low-frequency ultrasound may destroy the nanospheres for a rapid drug release, with simultaneous tissue-penetrating drug delivery inside a tumor. These effects may provide new opportunities for the development of an effective cancer therapy with few adverse effects.