# Evaluating Immune Activation Feasibility in Pancreatic Ductal Adenocarcinoma via Oxygen Bubble-Induced Anti-Vascular Therapy

## TL;DR

This study explores using oxygen-filled bubbles to disrupt blood vessels in pancreatic tumors, aiming to boost immune responses, but found limited immune activation despite some tumor damage.

## Contribution

The study introduces oxygen-loaded nanobubbles for anti-vascular therapy and evaluates their impact on tumor hypoxia and immune activation.

## Key findings

- ONB treatment reduced tumor perfusion by 52 ± 5% and caused 57 ± 11% necrosis.
- Tumor hypoxia decreased by 29 ± 4%, but immune activation was not significantly enhanced.
- Distant tumor growth was not inhibited despite increased primary tumor necrosis.

## Abstract

Background/Objectives: Anti-vascular therapy presents a potential strategy for activating anti-tumor immunity. Disrupted vascular debris provides effective antigens that activate dendritic cells, leading to subsequent immune responses. However, the resulting tumor hypoxia following vascular disruption may contribute to immune suppression, thereby hindering effective immune activation. Ultrasound-stimulated microbubble cavitation can locally disrupt tumor vessels through mechanical effects to achieve physical anti-vascular therapy. Therefore, this study designed oxygen-loaded nanobubbles (ONBs) to combine anti-vascular effects with local oxygen release under ultrasound stimulation. The feasibility of enhancing anti-tumor immune activation by alleviating tumor hypoxia was evaluated. Methods: A murine pancreatic subcutaneous solid tumor model was used to evaluate the efficacy of anti-vascular therapy-associated immunotherapy. Results: After ONB treatment, tumor perfusion was reduced to 52 ± 5%, which resulted in a subsequent 57 ± 11% necrosis and a 29 ± 4% reduction in hypoxia, demonstrating the anti-vascular effect and reoxygenation, respectively. However, subsequent immune responses exhibited no significant activation in intratumoral cytokine expression or splenic immune cell composition. Primary tumors exhibited a 15.7 ± 5.0% increase in necrosis following ONB treatment, but distant tumor growth was not significantly inhibited. Conclusions: These results highlighted a crucial issue regarding the complex correlations between vessel disruption, antigen production, oxygen delivery, hypoxia, and immunity when combining anti-vascular therapy with immunotherapy.