Necroptosis-inducing nanobubbles for effective oxygen delivery and enhanced sonodynamic immunotherapy of breast cancer via UTND

Abstract

Purpose

Breast cancer (BC) is a global threat to female health. Sonodynamic therapy (SDT) has been shown to induce apoptosis in tumor cells and trigger immunogenic cell death, leading to the activation of antitumor immunity. However, the immunogenicity of this process may be compromised by oxidative stress and proteolysis. Necroptosis caused by ultrasound-targeted nanobubble destruction (UTND) could boost immunity. Therefore, we tested if necroptosis-inducible nanobubbles (NB) could enhance sonodynamic immunotherapy for BC. We also assessed whether O₂-filled NB could address tumor hypoxia and enhance SDT efficacy.

Methods

A novel multifunctional nano-system, comprising NB for UTND encapsulating chlorin e6 (Ce6) for SDT and O₂ for hypoxia alleviation was established. Ce6-O₂NB cytocompatibility and intracellular uptake was studied in vitro, as well as whether Ce6-O₂NB could generated reactive oxygen species when exposed to ultrasound irradiation in order to induce apoptosis in tumor cells. In vivo pharmacokinetics, therapeutic efficacy, and immune activation after Ce6-O₂NB treatment were studied in 4T1 tumor-bearing mice.

Results

Ce6-O₂NB had a well-designed core–shell structure and desirable biocompatibility and safe therapeutic effects. Ce6-O₂NB was able to load both ce6 and oxygen to increase ce6 and oxygen accumulation in tumors. After triggering by ultrasound, Ce6-O₂NB generated reactive oxygen species (ROS) and acted as sonosensitizers for SDT, promoting tumor cell death through apoptotic and/or necrotic mechanisms. Furthermore, antitumor immunity was activated by stimulation of spleen lymphocyte proliferation and cytotoxicity, and increasing cytotoxic T lymphocyte numbers. Combination of oxygen with SDT ultimately strengthened its antitumor effects. In addition, Ce6-O₂NB alleviated tumor hypoxia, induced increased ROS generation, and improved immune responses and therapeutic efficacy of SDT. Ce6-O₂NB also facilitated fluorescence and contrast-enhanced ultrasound imaging.

Conclusions

Ce6-O₂NB can mitigate tumor hypoxia, enhance SDT, and activate antitumor immunity by inducing simultaneous immunogenic apoptosis and necroptosis, ultimately activating antitumor immunity and inhibiting breast tumor growth in mice.