Advisory Committee Chair
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Glioblastoma (GBM) is the most common primary malignant brain tumor in adults with a median survival of 15 months. Poor patient survival is, in part, caused by a stem-like and therapy-resistant population of brain tumor initiating cells (BTICs). BTICs are plastic, with the capacity to overcome oxidative damage. Guanosine triphosphate cyclohydrolase I (GCH1), a rate limiting enzyme in the de novo synthesis of the redox cofactor, tetrahydrobiopterin (BH4), was previously identified as a significant regulator of oxidative stress in BTICs. Reducing oxidative damage in the form of lipid peroxidation is imperative for GBM growth: lipid metabolism is required for the synthesis of new membranes, signaling molecules, and alternative fuel sources, where increased lipid peroxidation is associated with cell death in the form of ferroptosis. As recent studies demonstrate the GCH1 pathway as a potent suppressor of ferroptosis, we hypothesize that BTICs elevate GCH1 to protect lipid synthesis and, therefore, support the highly proliferative nature since in BTICs. Transcriptomic and metabolomic analysis of BTICs with altered GCH1 levels support alterations in cellular metabolism, especially lipid-associated pathways. Among some of the most significantly altered metabolites are related to polyunsaturated fatty acids (PUFAs). PUFAs are fatty acids that are susceptible to oxidative damage and can undergo lipid peroxidation (LPO). Changes observed in lipid metabolism and their metabolites upon GCH1 knockdown (KD) suggest reduction in BH4 induced changes. We sought to pharmacologically inhibit the GCH1/BH4 pathway with dual treatment of pyrimethamine (PYR) and sulfasalazine (SAZ). PYR is a methotrexate derivative that inhibits dihydrofolate reductase (DHFR), the enzyme that regenerates BH4 from BH2. SAZ inhibits sepiapterin reductase (SPR), the final step in BH4 de novo synthesis. Together, treatment with PYR and SAZ increased cell death and reduced BTIC viability in both GCH1 OE and EV BTICs, where the greatest effect was observed in GCH1 OE. Finally, LPO was measured after inhibitor treatment where LPO was successfully induced in GCH1 OE cells when compared to the EV. Together, this study demonstrated an association between GCH1/BH4 with lipid metabolism, while pharmacological inhibition of this pathway induces redox distress in BTICs.
Tuy, Kaysaw C., "Role of GTP Cyclohydrolase I in Glioblastoma" (2023). All ETDs from UAB. 3536.
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