A Phase 2 and Pharmacodynamic Study of Sitagliptin in Patients With Progressive Grade 4 Gliomas

The purpose of this study is to evaluate whether treating glioblastoma patients with sitagliptin can improve immune response against the tumor by targeting specific immune cells called myeloid-derived suppressor cells (MDSCs) that suppress your body\'s natural immune response against cancer. Sitagliptin is an investigational drug for this condition that works by inhibiting an enzyme called dipeptidyl peptidase 4 (DPP-4), which MDSCs rely on to enter the brain and function. While sitagliptin is FDA-approved for diabetes treatment, its use in glioblastoma is investigational (experimental).