# Hyperpolarized Carbon-13 Metabolic Imaging Differentiates Distinctive Molecular Phenotypes in Diffuse Midline Gliomas

## TL;DR

Hyperpolarized carbon-13 metabolic imaging can distinguish molecular differences in brain tumors with similar appearances.

## Contribution

This study demonstrates the use of hyperpolarized 13C MR imaging to noninvasively detect molecular features like hypoxia and LDH-A activity in gliomas.

## Key findings

- SF8628 tumors showed significantly higher lactate to pyruvate ratios compared to SF7761 tumors.
- Elevated lactate levels in SF8628 correlated with increased LDH-A and carbonic anhydrase-IX staining.
- 13C metabolic imaging revealed distinct metabolic profiles despite similar histological appearances.

## Abstract

Despite a specific histone mutation defining the unique genetic makeup, diffuse midline gliomas are heterogeneous tumors with a wide range of morphologic and molecular spectrum. We investigated the feasibility of using hyperpolarized carbon-13(13C) MR metabolic imaging to differentiate distinctive molecular features from two H3K27M-mutant, biopsy-originated diffuse midline glioma xenografts. 13C MR metabolic imaging data were acquired on a 3T scanner from 12 rats that had been implanted with SF8628 or SF7761 diffuse midline glioma cells in brainstem, following injection of hyperpolarized [1-13C]pyruvate. Despite the two tumors’ similar appearance of T2-hyperintensity throughout the cerebellum and pons without contrast enhancement, 13C metabolic imaging data revealed that SF8627 had significantly higher ratios of lactate to pyruvate, lactate to total carbon, and normalized lactate than SF7761. Elevated lactate levels in SF8628 were associated with large amounts of lactate dehydrogenase (LDH)-A and carbonic anhydrase-IX staining in SF8628 compared to SF7761, which implied that the highly hypoxic condition in SF8628 appeared to contribute to the high level of LDH-A enzyme activity, which, in turn, induced the large conversion from hyperpolarized pyruvate to lactate. Our findings suggest that this advanced metabolic imaging technique may be used for the noninvasive characterization of molecular hypoxia and lactate dehydrogenase-A activity in these pediatric brainstem gliomas.