Metabolomic Profiling of Human Schwannoma Before and After Radiation

Introduction: Vestibular Schwannomas are treated with surgical resection and radiation, but when those approaches fail no further treatment options exist. Metabolomic profiling allows for relative quantification of metabolites present in tissue samples and has been used to identify novel therapeutic pathways in various neoplasms, but not schwannomas. Analyzing the metabolome may reveal novel pathways that can be targeted therapeutically for treatment-failed schwannoma patients.

Methods: Schwannomas were obtained from patients and implanted into nude mice. Four weeks post-implantation, mice were randomized to receive 0, 10, or 20 Gray (Gy) of ionizing radiation. 72 hours post-treatment the tumors were harvested. Part of each xenograft tumor was preserved and sectioned for immunohistochemistry to ensure accurate tissue sampling. Additionally, the Click-iT EdU Proliferation Assay was used to measure tumor cell proliferation rates to compare to observed metabolomic changes. The remaining sample was metabolically profiled using Gas Chromatography-Mass Spectrometry (GC-MS), and data was analyzed with MetaboAnalyst.

Results: Immunohistochemistry confirmed schwannoma xenografting, with significant signal difference between the antibody-positive and negative control sections of each tissue slide. 5-ethynyl-2′-deoxyuridine (EdU) cell proliferation data demonstrated a consistent trend where increasing radiation decreased proliferation rates. The average schwannoma proliferation rate for the sham radiation group was 3.66±1.92 (mean ± standard deviation), 2.47±1.69 for 10 Gy, and 1.62±1.62 for 20 Gy. Initial experiments utilized only the 0 Gy and 20 Gy treatment groups, and preliminary metabolomics data showed that seven metabolites demonstrated significant between-group differentiation: Ornithine, Succinate, Fumarate, Glycine, Glutamine, Cytosine, and Gamma-Aminobutyric Acid (GABA).

Conclusion : Preliminary data indicates several possible pathways that may be altered after radiation, including Ornithine-mediated polyamine synthesis, reactive oxygen species response involving Glutamate and Glutamine, and other DNA repair pathways involving Cytosine, GABA, and Glutamine. Increased sample size and future stable isotope tracing experiments will provide greater insight regarding the mechanism of these changes.