Abstract P96: Oxygen Nanobubbles as Theranostic Agents: In Vivo Evaluation of Contrast Properties and Oxygen Delivery

Abstract

Hypoxia is a common feature of the tumor microenvironment and can significantly impair the efficacy of standard cancer therapies. Both microbubbles and nanobubbles, containing perfluorocarbon and/or air, are already widely used as effective contrast agents in ultrasound imaging. They help to visualize vasculature and tissue structure, as well as determine tissue perfusion parameters. Replacing the gas content with oxygen opens up a promising therapeutic strategy due to their ability to locally release oxygen when exposed to ultrasound-induced cavitation. To explore their potential for combined therapeutic and diagnostic (theranostic) applications, experiments were carried out using tissue-mimicking phantoms and a 4T1 breast cancer model implanted in the mammary fat pad of female Balb/c mice. The aim of this study was to characterize the contrast performance of oxygen nanobubbles, assess their ultrasound responsiveness, and evaluate their capacity to elevate oxygen partial pressure in biological tissues. After selecting the most optimal gas mixture for the core, the stability and physicochemical properties of the oxygen nanobubbles were evaluated using contrast-enhanced ultrasound imaging and dynamic light scattering (DLS). The theranostic properties of the bubbles were then assessed in vivo. Their contrast-enhancing abilities were verified through contrast-mode ultrasound imaging, while electron paramagnetic resonance (EPR) spectroscopy enabled quantification of the oxygen delivered by the bubbles into the tumor tissue. The experiments confirmed that the nanobubbles maintained the expected size, not exceeding 400 nm, and remained stable for at least 30 minutes post-administration. A significant enhancement in ultrasound contrast was observed, improving tumor visualization. Oxygen measurements demonstrated a marked increase in oxygen levels within the tumor microenvironment. These findings highlight the potential of oxygen nanobubbles as a component of multimodal anticancer therapy and provide a solid foundation for future studies on their toxicity, effects on metastasis, and interactions with the immune system. The work was financed by the OPUS Project, 2022/45/B/NZ4/01215, National Science Center.