Temozolomide-Derived AIC Is Incorporated into Purine Synthesis in Glioblastoma

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.