How a Single Kinase Hijacks Cell Metabolism to Drive Lung Cancer Growth
PLK1 phosphorylates PDHA1 at T57, blocking glucose entry into the TCA cycle and forcing cells into the Warburg glycolytic state — and blocking both enzymes synergistically kills tumors.
Summary
Lung cancer cells exploit a metabolic switch called the Warburg effect, burning glucose via glycolysis rather than efficient mitochondrial respiration. This study reveals the molecular trigger: the kinase PLK1 phosphorylates a single site (T57) on the enzyme PDHA1, preventing pyruvate from entering the energy-producing TCA cycle. Using stable-isotope metabolomics in human cells and a novel knock-in mouse model, the researchers traced exactly how carbon flow is redirected. Cells compensate by burning glutamate and aspartate instead. Critically, combining the PLK1 inhibitor Onvansertib with dichloroacetic acid (DCA), which blocks the kinase that normally suppresses PDHA1, synergistically killed lung tumor cells by boosting mitochondrial ROS, cutting glycolysis, and triggering apoptosis — providing preclinical rationale for a clinical trial.
Detailed Summary
Lung cancer is one of the most genetically diverse cancers, with TP53, KRAS, EGFR, and PIK3CA mutations varying widely across subtypes. This diversity limits the effectiveness of mutation-targeted therapies and highlights the appeal of targeting universal cancer hallmarks. One such hallmark is the Warburg effect — the shift from mitochondrial oxidative phosphorylation (OXPHOS) to aerobic glycolysis — present across virtually all lung cancer subtypes regardless of genetic background.
This study identifies a previously unclear molecular mechanism driving that shift: PLK1, a serine/threonine kinase overexpressed 9.7-fold in lung adenocarcinoma and 20.8-fold in lung squamous cell carcinoma compared to normal adjacent tissue, directly phosphorylates PDHA1 at threonine 57 (T57). PDHA1 is the catalytic subunit of the pyruvate dehydrogenase (PDH) complex, the gatekeeper enzyme that converts pyruvate into acetyl-CoA for entry into the TCA cycle. A companion paper established that this phosphorylation triggers PDHA1 protein degradation via mitophagy; the current study maps the downstream metabolic consequences using stable-isotope resolved metabolomics (SIRM).
Using uniformly labeled ¹³C-glucose ([U-¹³C]-glucose) in Cr(VI)-transformed BEAS-2B human bronchial epithelial cells expressing either a phospho-null (T57A) or phospho-mimetic (T57D) PDHA1 mutant, the researchers tracked carbon flow through glycolysis, the TCA cycle, and amino acid metabolism via NMR and IC-FTMS. Although glucose uptake was unchanged between the two cell lines, ¹³C-labeled pyruvate accumulated markedly in T57D cells — both in cell extracts and culture media — confirming a metabolic block at the PDH step. Upstream glycolytic intermediates (G6P, F6P, PEP) were consumed faster in T57D cells, while ¹³C-enriched TCA metabolites (citrate, cis-aconitate, isocitrate) were substantially reduced. The citrate m+2 / pyruvate m+3 ratio (a surrogate for PDH activity) was significantly depressed in T57D cells, and pyruvate carboxylase (PC) activity was also reduced by approximately half. Notably, more than 40% of TCA intermediates in T57D cells derived from unlabeled (non-glucose) carbon sources, with aspartate and glutamate levels both elevated — indicating a compensatory reliance on the aspartate-malate shuttle.
To validate these findings in vivo, the team generated a conditional knock-in mouse expressing PDHA1-T57D. Mouse embryonic fibroblasts (MEFs) from these mice, after Cre-mediated T57D induction, showed a 50% increase in proton efflux rate (PER) from glycolysis and reduced maximal respiratory capacity and ATP production compared to controls. Whole-body metabolic measurements in tamoxifen-treated transgenic mice confirmed reduced oxygen consumption and altered respiratory exchange ratio consistent with a glycolytic shift, validating the in vivo relevance of the PLK1-PDHA1 axis.
Translationally, the study tested dual blockade of PLK1 (Onvansertib) and pyruvate dehydrogenase kinase (DCA, which normally suppresses PDH) in lung cancer cell lines and xenograft models. The combination synergistically inhibited tumor growth, enhanced mitochondrial ROS production, suppressed glycolytic flux, and induced apoptosis. This is mechanistically logical: PLK1 inhibition preserves PDHA1 protein, while DCA prevents PDK from phosphorylating and inactivating the restored PDH complex — two complementary nodes that both push cancer cells back toward OXPHOS, where elevated ROS becomes lethal. These findings provide direct preclinical support for a clinical trial combining Onvansertib (already in Phase II trials for NSCLC and SCLC, NCT05450965) with DCA.
Key Findings
- PLK1 is overexpressed ~9.7-fold in lung adenocarcinoma and ~20.8-fold in lung squamous cell carcinoma versus normal adjacent tissue, correlating with worse overall survival.
- PDHA1-T57D (phospho-mimetic) cells accumulated 3× more total pyruvate (labeled + unlabeled) compared to PDHA1-T57A (phospho-null) cells, confirming metabolic blockade at the PDH step.
- ¹³C-labeled TCA precursor metabolites (citrate, cis-aconitate, isocitrate) were significantly reduced in T57D cells, with >40% of downstream TCA intermediates (α-KG, succinate, fumarate, malate) derived from non-glucose sources.
- Pyruvate carboxylase (PC) activity surrogate was reduced by ~50% in PDHA1-T57D cells versus T57A cells, despite PC being a separate enzymatic pathway.
- Mouse embryonic fibroblasts with Cre-induced PDHA1-T57D showed a 50% increase in glycolytic proton efflux rate (PER) versus controls, confirming in vivo metabolic reprogramming.
- Onvansertib (PLK1 inhibitor) combined with DCA (PDK inhibitor) synergistically inhibited lung tumor growth by enhancing mitochondrial ROS, suppressing glycolysis, and inducing apoptosis in preclinical models.
- Aspartate and glutamate levels were both significantly elevated in PDHA1-T57D cells versus T57A cells, indicating compensatory upregulation of the aspartate-malate shuttle when pyruvate-TCA entry is blocked.
Methodology
The study used stable-isotope resolved metabolomics (SIRM) with [U-¹³C]-glucose tracer and readout by NMR and IC-FTMS in Cr(VI)-transformed BEAS-2B human bronchial epithelial cells expressing PDHA1-T57A or T57D mutants. In vivo validation employed a novel conditional knock-in mouse model expressing PDHA1-T57D (tamoxifen-inducible via Cre-ERT2), with MEFs and whole-animal respiratory measurements. Therapeutic efficacy was assessed using Onvansertib and DCA in lung cancer cell lines and xenograft models. Statistical methods included isotopologue distribution analysis and metabolic flux ratio calculations (e.g., citrate m+2/pyruvate m+3 for PDH activity).
Study Limitations
The primary in vitro model (Cr(VI)-transformed BEAS-2B cells) represents a specific heavy-metal carcinogenesis context that may not fully generalize to all lung cancer subtypes with diverse mutational origins. The knock-in mouse model demonstrates in vivo metabolic effects of T57D but stops short of a full oncogenesis model, leaving the causal link between this phosphorylation event and frank tumor formation partially inferential. No conflicts of interest were declared by the authors, though the study is limited by the lack of patient-derived organoid or clinical tissue validation of the SIRM findings.
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