PHGDH at the crossroads: metabolic plasticity, metastatic paradoxes, and therapeutic reconnaissance in cancer.

Phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme of the serine biosynthesis pathway (SSP), is a central metabolic hub and multifunctional oncoprotein that drives tumorigenesis through both canonical and non-canonical mechanisms. This review outlines the multi-level regulation of PHGDH, covering epigenetic remodeling (DNA hypomethylation, H3K4me3/H3K36me3 dynamics), transcriptional control (ATF4, MYC, EWS-FLI1), post-transcriptional fine-tuning (mA/mC modifications, RNA-binding proteins), and post-translational modifications (ubiquitination, methylation, phosphorylation). Together, these regulatory layers allow cancer cells to adapt metabolically to microenvironmental stress. Beyond its fundamental role in supplying nucleotides, maintaining redox homeostasis, and supporting one-carbon metabolism, PHGDH also performs moonlighting function. For example, its translocation to the nucleus inhibits PARP1 to sustain oncogenic transcription, while its presence in mitochondria helps remodel electron transport chains to promote metastasis. Critically, PHGDH exhibits a therapeutic paradox wherein its inhibition can synergize with chemotherapy, radiotherapy, and immunotherapy across diverse malignancies, yet tumors develop resistance via metabolic plasticity, or by selection of PHGDH-low metastatic clones. The clinical translation of PHGDH inhibitors is further challenged by inherent neurotoxicity risks, as neurons rely on de novo serine synthesis. To address these challenges, we propose a precision roadmap that integrates spatial multi-omics, AI-driven allosteric inhibitor design, dynamic biosensing (e.g., F-metabolite PET), and biomarker-stratified clinical trials. By reconciling the dual nature of PHGDH biology, we can transform this metabolic linchpin from a confounding paradox into a clinically actionable vulnerability.