Background: Glioblastoma (GBM) is an aggressive and often fatal cancer with limited treatment options. However, immunotherapy, such as programmed cell death protein 1 (PD-1) inhibitors, in combination with emerging treatments like biomedical-engineered Escherichia coli (E. coli), has shown promise in preclinical studies. Nonetheless, dynamically assessing the efficacy of this combination therapy in the brain remains a challenge. High-field 7.0 T animal magnetic resonance imaging (MRI), with its exceptional spatial and temporal resolution, provides detailed anatomical information on tumor growth and blood-brain barrier disruption, quantifies changes in tumor perfusion and vascular permeability, and offers an effective tool for monitoring the dynamic effects of glioma treatment. Goals: This study aims to employ MRI technology to dynamically monitor the evolution of the tumor microenvironment and changes in tumor volume following PD-1 inhibitor and E. coli combination therapy in a mouse GBM model. The accuracy of MRI imaging results in assessing the therapeutic efficacy is verified through techniques such as immunofluorescence and immunohistochemistry. Our research seeks to investigate the efficacy of PD-1 inhibitors and E. coli combination therapy in a mouse GBM model, as well as the efficiency of high-field animal MRI technology in evaluating changes in the tumor microenvironment and treatment outcomes post combination therapy. Approach: We established a mouse glioblastoma model by implanting GL261 cells into the brains of C57BL/6 mice, dividing the mice into four groups: control, E. coli treatment, PD-1 inhibitor treatment, and E. coli and PD-1 inhibitor combination treatment groups. The experimental groups received treatment with PD-1 inhibitors and E. coli, while the control group received PBS treatment. On the first day before treatment and the fourth and seventh days after treatment, various MRI sequences, including dynamic contrast-enhanced MRI (DCE-MRI), enhanced T1-weighted imaging (T1WI), blood oxygen level-dependent functional MRI (BOLD-fMRI), diffusion tensor imaging (DTI), and perfusion-weighted imaging (PWI), were utilized. Analysis of diffusion tensor imaging along the vasculature space (DTI-AIPS) was performed to regularly monitor changes in tumor volume, tumor oxygen levels, tumor perfusion, vascular permeability, and brain lymphatic flow, among other biomarkers. Additionally, we conducted various observations and analyses, including immunohistochemistry and immunofluorescence, to study the infiltration of immune cells within the tumor. Results: The results demonstrate that combination therapy with biomedical-engineered E. coli and PD-1 inhibitors can improve mouse survival and enhance the tumor's response to combination treatment when compared to single treatments. MRI results show a significant reduction in tumor volume, increased tumor perfusion, blood oxygen levels, and vascular permeability in the combination therapy group, along with an increase in DTI-AIPS index compared to the control group. Furthermore, ELISA data analysis of brain tissue samples, immunohistochemistry, and immunofluorescence analysis confirm the MRI findings. The results indicate that, relative to the control group, the combination therapy group exhibits an increase in the number of natural immune factors within the tumor, increased infiltration of CD3+ T cells, CD4+ T cells, and CD8+ T cells, and a suppression of regulatory T cells (Tregs) within the tumor. These findings suggest that the combination of PD-1 inhibitors and biomedical-engineered E. coli enhances the anti-tumor immune response, while high-field MRI technology allows for dynamic monitoring of the combination therapy, confirming improved treatment outcomes.

Acknowledgements

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References

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