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Temozolomide-Derived AIC Is Incorporated into Purine Synthesis in Glioblastoma
Mark L Sowers1,2,3, Tuvshintugs Baljinnyam1,3, Jason L Herring1,3
1University of Texas Medical Branch, Galveston, Texas 77555, United States.
Abstract:
Glioblastoma (GBM) is a lethal brain tumor with limited therapeutic options. Temozolomide (TMZ), a standard-of-care chemotherapeutic agent, exerts its cytotoxicity by alkylating DNA, which triggers a DNA damage response and depletes ATP and NAD+. However, TMZ also releases the byproduct 4-amino-5-imidazole carboxamide (AIC), which is believed to be a benign metabolite. We considered the possibility that AIC from TMZ could enter the de novo purine synthesis pathway, contributing to AMP and NAD+ synthesis and thus potentially antagonizing the anticancer activity of TMZ. The purpose of this article is to determine if AIC from TMZ can be incorporated into cellular purines. Using mass spectrometry with isotope-labeled TMZ, we demonstrate that the AIC derived from TMZ is incorporated into AMP and NAD+ in glioblastoma cell lines. Further, we performed an analysis of publicly available transcriptomic data from the Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases. Our analyses demonstrate that de novo purine synthesis is upregulated in GBM relative to the normal brain. Collectively, our findings demonstrate that a drug metabolite of TMZ, AIC, can be incorporated into de novo purine synthesis, which is upregulated in GBM.
Insights
Temozolomide (TMZ) releases a metabolite, AIC, that glioblastoma cells incorporate into purines. This AIC incorporation may counteract TMZ
Area of Science:
- Oncology
- Biochemistry
- Molecular Biology
Background:
- Glioblastoma (GBM) is an aggressive brain tumor with poor prognosis.
- Temozolomide (TMZ) is a standard chemotherapy, but its efficacy is limited.
- TMZ's mechanism involves DNA alkylation, ATP/NAD+ depletion, and AIC byproduct release.
Purpose of the Study:
- To investigate if the TMZ byproduct 4-amino-5-imidazole carboxamide (AIC) can be incorporated into cellular purines.
- To determine if AIC contributes to purine synthesis pathways in glioblastoma.
- To assess the potential for AIC to antagonize TMZ's anticancer effects.
Main Methods:
- Utilized isotope-labeled TMZ and mass spectrometry to trace AIC metabolism.
- Analyzed AIC incorporation into AMP and NAD+ in glioblastoma cell lines.
- Examined transcriptomic data from TCGA and GTEx databases for purine synthesis pathway activity.
Main Results:
- Demonstrated that AIC derived from TMZ is incorporated into AMP and NAD+ in glioblastoma cells.
- Confirmed AIC's entry into the de novo purine synthesis pathway.
- Found that de novo purine synthesis is upregulated in GBM compared to normal brain tissue.
Conclusions:
- The drug metabolite AIC from TMZ can be incorporated into cellular purines via the de novo synthesis pathway.
- Upregulated de novo purine synthesis in GBM may provide a salvage pathway for AIC, potentially reducing TMZ efficacy.
- These findings highlight a novel mechanism of drug resistance and suggest therapeutic strategies targeting purine metabolism in GBM.
