308 Metabolic Isozyme Switching Offers a Targeted Treatment Strategy in Cushing's Disease

• Published in: Neurosurgery Vol. 65; no. CN_suppl_1; p. 125
• Main Authors: Boyle, Jacqueline, Floros, Konstantinos V, Lu, Jie, Chatain, Grégoire P, Maric, Dragan, Chaudhury, Abhik R, Chittiboina, Prashant
• Format: Journal Article
• Language: English
• Published: Philadelphia Oxford University Press 01-09-2018; Copyright by the Congress of Neurological Surgeons; Wolters Kluwer Health, Inc
• Subjects: Enzymes; Metabolism; Neurosurgery
• ISSN: 0148-396X; 1524-4040
• DOI: 10.1093/neuros/nyy303.308

Abstract
INTRODUCTION
We have previously found evidence of metabolic reprogramming in adrenocorticotrophic hormone secreting adenomas (corticotropinomas) causing Cushing's disease. We found activation of canonical EGFR signaling and anaerobic glycolysis in corticotropinomas (Warburg effect) in the absence of oncogenic mutations. We now investigated the role of isozyme switching in key glycolytic pathway enzymes [hexokinase (HK) and lactate dehydrogenase (LDH)] on corticotropinoma metabolism/survival.
METHODS
Fluorescent multiplex IHC (mIHC) was performed on human-derived corticotropinomas and adjacent normal gland (n = 12). Paired western-blot analysis of key glycolytic enzymes (HK-2, HK-1, LDH-A) in corticotropinomas versus adjacent normal gland and AtT20 cells versus normal murine pituitary cells was performed. Glycolysis and mitochondrial respiration was analyzed with Seahorse XF-96 system. Cell survival was tested with CellTiter-Glo® assay following treatment with bromopyruvic acid (3-BP), a specific HK-2 inhibitor.
RESULTS
mIHC revealed remarkable overexpression of HK-2 (n = 7/8) and LDH-A (n = 11/12) in a majority of corticotropinomas compared to the adjacent normal gland. HK-2 overexpression (but not HK-1) was detected in corticotropinomas (n = 4) compared to adjacent normal gland, suggesting isozyme switching. LDH-A was overexpressed in AtT20 compared to normal murine pituitary cells. Seahorse analysis suggested increased glycolytic potential in human corticotropinomas (n = 2) and AtT20 compared to matched normal counterparts. Treatment with 3-BP resulted in decreased glycolytic flux (60% decrease) only in corticotropinomas, suggesting selective metabolic dependence on HK-2. Treatment with 3-BP significantly increased cell death in corticotropinomas compared to matched normal counterparts (77% vs 41%) suggesting selective survival dependence on HK-2.
CONCLUSION
Our results suggest that isozyme switching in key glycolytic enzymes (HK and LDH) occurs in human corticotropinomas. Results of 3-BP treatment suggest that HK-2, the first irreversible step in glycolysis, contributes directly to increased glycolytic flux in corticotropinomas. Lastly, we found that HK-2 inhibition may offer a targeted strategy for anti-tumor therapy against corticotropinomas.