IDO1 and neoplasm: Biodegradable hydrogels embedded with IDO1 inhibitors (Zhuang et al., 2023), kynureninase (Wang et al., 2022a), Wnt or GSK-3β antagonists (Wang et al., 2022b), glycolytic inhibitors (LDHA, PDK1) (Meng et al., 2022), and glutaminolysis inhibitors (GLS) (Guo et al., 2025) could provide sustained drug release which gradually alters the tumor microenvironment and preventing metabolic adaptation over time.