Proliferating cells require a steady supply of nucleotides to support DNA replication. Most mechanistic studies of nucleotide metabolism have used standard culture media that do not reproduce the circulating metabolite composition of mammals, leaving open how physiological nutrient availability shapes nucleotide acquisition strategies. This study investigated those questions using a mouse model of B-cell acute lymphoblastic leukemia (B-ALL) and a tailored in vitro medium that mimics plasma metabolite levels.
To assess how environmental nutrients impact nucleotide metabolism, the authors formulated a mouse plasma-like medium (MPM) that reproduces the circulating metabolite composition measured in mice bearing B-ALL. This plasma-like medium was used to culture leukemia cells and compare nucleotide acquisition and growth behavior with that observed in standard cell culture conditions where nucleotide metabolism has historically been studied.
When leukemia cells were cultured in MPM, their pattern of nucleotide acquisition shifted relative to standard culture conditions. The study reports that in plasma-like nutrient conditions, cells relied more heavily on nucleotide salvage pathways to obtain the nucleotides needed for DNA synthesis. This contrasts with the conventional view derived from standard media, where de novo nucleotide synthesis is often emphasized.
The authors found that select nucleotide salvage pathways are required for proliferation of B-ALL cells cultured in MPM. Disruption of these salvage pathways in plasma-like conditions impaired cell proliferation. Thus, access to salvage pathways becomes more relevant for supporting tumor cell proliferation under physiological nutrient availability than might be predicted from standard in vitro models.
Importantly, the dependence on nucleotide salvage in MPM was not explained by a shortage of precursor metabolites for de novo nucleotide synthesis. Instead, the investigators identified physiological folate levels as a limiting factor: circulating folate concentrations reproduced in MPM were insufficient to support adequate deoxynucleotide triphosphate (dNTP) synthesis required for DNA replication. This insufficiency led to DNA replication stress and impaired proliferation when nucleotide salvage pathways were disrupted, linking folate availability directly to the capacity for dNTP production and genomic replication fidelity under physiological conditions.
Extending the in vitro observations, the study reports that dietary folate restriction in mice exacerbated the impaired leukemia progression phenotype observed in nucleotide salvage–deficient B-ALL cells. This in vivo result is consistent with the interpretation that limited folate access constrains de novo dNTP synthesis and increases reliance on salvage pathways for tumor progression in a physiological setting.
Taken together, these findings demonstrate that micronutrient abundance—here, folate availability—can alter metabolic dependencies of cancer cells. Under plasma-like nutrient conditions, folate levels can serve as an endogenous limitation on nucleotide synthesis, elevating the importance of nucleotide salvage pathways for maintaining dNTP pools and supporting DNA replication in leukemia. The work underscores that metabolic vulnerabilities identified in standard culture may change when cells are examined in environments that better reflect physiological metabolite levels.
The authors declare funding from multiple sources, including the Howard Hughes Medical Institute, the U.S. National Science Foundation, the National Institutes of Health, the Damon Runyon Cancer Research Foundation, the Koch Institute Cancer Center Support Grant, the Ludwig Cancer Center, and the National Heart, Lung, and Blood Institute Division of Intramural Research. A competing interest statement notes that M.G.V.H. discloses scientific advisory roles with several biotechnology companies; all other authors declared no competing interests.
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