# Metabolic Shift Mirrors GBM Immunity to Anti-PD-L1 Immunotherapy: A Deuterium MRS Study

## TL;DR

This study shows that brain tumors in previously irradiated areas have a different metabolism linked to poor response to immunotherapy.

## Contribution

The study links metabolic changes in irradiated brains to immunotherapy resistance in glioblastoma using deuterium MRS.

## Key findings

- Tumors in irradiated brains showed reduced glycolysis and increased TCA cycle activity.
- Metabolic shifts correlated with immune dysfunction and resistance to anti-PD-L1 therapy.

## Abstract

Immune checkpoint blockade (ICB) therapy has been ineffective in glioblastoma (GBM) that recurs following standard-of-care resection and chemoradiation of the primary tumor. Herein, we investigate whether the delayed effect of intracranial radiation alters the tumor lesion metabolic profile.

Naïve (non-irradiated) GL261 tumor cells were implanted into the brains of C57BL/6 mice. Brains of one cohort were hemispherically irradiated six weeks prior to implantation, ultimately resulting in ICB refractory GBM. Brains of the control cohort were not irradiated. Following subcutaneous infusion of [6,6-2H2] glucose (Glc), single voxel deuterium metabolic imaging (DMI) monitored Glc uptake and the production of semi-heavy water (HOD), 2H2-lactate (Lac) and the 50/50 mix of [2H2-glutamate + 2H2-glutamine] (Glx).

GL261 tumors growing in previously irradiated brain showed reduced Warburg effect (aerobic glycolysis; glucose → lactate) and greater TCA cycle activity (respiration, oxidative phosphorylation) relative to tumors growing in non-irradiated brain as evidenced by cohort differences in the ratios Glx/Lac (p < 0.01), Glx/Glc (p < 0.02), and Lac/Glc (p < 0.01).

A metabolic program skewed toward oxidative phosphorylation and away from glycolysis has been associated with immune dysfunction. This study documents such a skewed metabolic state in ICB refractory GL261 GBM growing in irradiated brain (tumors were not irradiated) compared to control brain.