Abstract 3046: In situ analysis of microenvironmental glycogen in Ewing's sarcoma patient samples by mass spectrometry imaging

Abstract Ewing's sarcoma (ES) is a rare pediatric cancer of the bone and soft tissues affecting adolescents and young adults, with peak incidence from ages 10 to 15 years. A clinical feature of ES is the accumulation of Periodic acid-Schiff positive (PAS+) aggregates. PAS+ staining in ES histopathology analysis has been speculated to be glycogen accumulation, however, this has not been confirmed. To interrogate these aggregates, we developed a novel workflow for the high-sensitive detection of in situ glycogen via enzymatic release of glycogen substrates coupled to matrix assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) from formalin-fixed patient tissues. We utilized this method to study the nature of PAS+ staining in a cohort of ES patient samples surgically removed from tibia, rib, chest, shoulder, abdomen and testicle tissues. Using this innovative technique, we discovered profound intra-tumoral glycogen accumulation compared to adjacent stroma, normal, muscle and/or necrotic tissue. Further, intra-tumoral glycogen also has an increased phosphate content and distinct chain length profile compared to normal glycogen found in adjacent and patient-matched tissue. Notably, genetic manipulation and pharmacological inhibition of glycogen synthesis, or removal of glycogen phosphates, blunted ES tumor growth in xenografted mouse models. These findings suggest an important role of ES glycogen aggregates in tumor growth. Together, application of this novel MALDI-IMS technique, and the insights provided by formalin-fixed ES patient samples, reveals a distinct role of ES glycogen aggregates and uncovers a new therapeutic opportunity for this rare pediatric cancer. Citation Format: Lyndsay E. Young, Lindsey R. Conroy, Harrison A. Clarke, Derek B. Allison, Richard R. Drake, Matthew S. Gentry, Ramon C. Sun. In situ analysis of microenvironmental glycogen in Ewing's sarcoma patient samples by mass spectrometry imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3046.