Inhibition of Glycogen Metabolism Induces Reactive Oxygen Species-Dependent Apoptosis in Anaplastic Thyroid Cancer

Anaplastic thyroid cancer (ATC) is one of the most lethal solid tumors, yet there are no effective, long-lasting treatments for ATC patients. Most tumors, including tumors of the endocrine system, exhibit an increased consumption of glucose to fuel cancer progression, and some cancers meet this high glucose requirement by metabolizing glycogen. Our goal was to determine if ATC cells metabolize glycogen and if this could be exploited for treatment. We detected glycogen synthase and glycogen phosphorylase (PYG) isoforms in normal thyroid and thyroid cancer cell lines and patient-derived biopsy samples. Inhibition of PYG using CP-91,149 induced apoptosis in ATC cells but not normal thyroid cells. CP-91,149 decreased NADPH levels and induced reactive oxygen species accumulation. CP-91,149 severely blunted ATC tumor growth in vivo. Our work establishes glycogen metabolism as a novel metabolic process in thyroid cells that presents a unique, oncogenic target that could offer an improved clinical outcome. SignificanceGlycogen metabolism plays an important role in combating reactive oxygen species and apoptosis in anaplastic thyroid cancer. Glycogen phosphorylase was inhibited with small molecule inhibitors that limited cell proliferation in vitro and blunted tumor growth in a nude mouse xenograft. This study demonstrates that glycogen metabolism is a viable target in one of the most lethal solid tumors.