Preclinical research has shown that endogenous hydrogen sulfide (H2S) can act as a tumor suppressor against glioblastoma. Directly giving patients H2S is risky, so researchers at the Cleveland Clinic are exploring whether the body's natural production of H2S can be increased by reducing thyroid hormone levels. In addition to continued preclinical work, Dr. Hine and Dr. Peereboom will run a small Phase 2 trial to evaluate the safety and efficacy of using oral methimazole (drug approved to treat hyperthyroidism) in patients with progressive GBM. They'll also look at other potential ways to enhance H2S signaling in patients, aside from using thyroid hormone inhibitors.