title: Metabolomics identifies pyrimidine starvation as the mechanism of 5-aminoimidazole-4-carboxamide-1-β-riboside-induced apoptosis in multiple myeloma cells.
abstract: To investigate the mechanism by which 5-aminoimidazole-4-carboxamide-1-β-riboside (AICAr) induces apoptosis in multiple myeloma cells, we conducted an unbiased metabolomics screen. AICAr had selective effects on nucleotide metabolism, resulting in an increase in purine metabolites and a decrease in pyrimidine metabolites. The most striking abnormality was a 26-fold increase in orotate associated with a decrease in uridine monophosphate (UMP) levels, indicating an inhibition of UMP synthetase (UMPS), the last enzyme in the de novo pyrimidine biosynthetic pathway, which produces UMP from orotate and 5-phosphoribosyl-α-pyrophosphate (PRPP). As all pyrimidine nucleotides can be synthesized from UMP, this suggested that the decrease in UMP would lead to pyrimidine starvation as a possible cause of AICAr-induced apoptosis. Exogenous pyrimidines uridine, cytidine, and thymidine, but not purines adenosine or guanosine, rescued multiple myeloma cells from AICAr-induced apoptosis, supporting this notion. In contrast, exogenous uridine had no protective effect on apoptosis resulting from bortezomib, melphalan, or metformin. Rescue resulting from thymidine add-back indicated apoptosis was induced by limiting DNA synthesis rather than RNA synthesis. DNA replicative stress was identified by associated H2A.X phosphorylation in AICAr-treated cells, which was also prevented by uridine add-back. Although phosphorylation of AICAr by adenosine kinase was required to induce multiple myeloma cell death, apoptosis was not associated with AMP-activated kinase activation or mTORC1 inhibition. A possible explanation for inhibition of UMP synthase activity by AICAr was a depression in cellular levels of PRPP, a substrate of UMP synthase. These data identify pyrimidine biosynthesis as a potential molecular target for future therapeutics in multiple myeloma cells.
authors.affiliation: Division of Hematology-Oncology, Greater Los Angeles VA Healthcare Center, 111H, VA West LA Med Ctr., 11301 Wilshire BLVD, Los Angeles, CA 90073, USA.
authors.forename: Carolyne
authors.initials: C
authors.lastname: Bardeleben
authors.forename: Sanjai
authors.initials: S
authors.lastname: Sharma
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Reeve
authors.forename: Sara
authors.initials: S
authors.lastname: Bassilian
authors.forename: Patrick
authors.initials: P
authors.lastname: Frost
authors.forename: Bao
authors.initials: B
authors.lastname: Hoang
authors.forename: Yijiang
authors.initials: Y
authors.lastname: Shi
authors.forename: Alan
authors.initials: A
authors.lastname: Lichtenstein
mesh_terms: D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D006801:Humans; D055432:Metabolomics / Q000379:methods; D009101:Multiple Myeloma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011743:Pyrimidines / Q000096:biosynthesis / Q000378:metabolism*; D012263:Ribonucleosides / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D011743:Pyrimidines; D012263:Ribonucleosides; D000620:Aminoimidazole Carboxamide