Lactate-induced epithelial-mesenchymal transition: a metabolic nexus in pancreatic cancer metastasis

Abstract

Lactate-driven epithelial-mesenchymal transition (EMT) constitutes a pivotal metabolic hub in pancreatic ductal adenocarcinoma (PDAC). PDAC is a highly lethal malignancy characterized by early metastasis, pronounced chemotherapy resistance, and poor prognosis, in which epithelial-mesenchymal plasticity (EMP) acts as the core mechanism driving malignant progression. Metabolic reprogramming represented by the Warburg effect leads to massive lactate accumulation in PDAC. Lactate is no longer regarded as an inert metabolic end product, but serves as a critical energy substrate, signaling molecule, and epigenetic modifier that mediates histone lactylation. This review systematically elaborates the unique characteristics of lactate metabolism in PDAC, including efficient lactate production driven by oncogenic mutations and hypoxic microenvironment, transmembrane transport via monocarboxylate transporters (MCTs), intracellular metabolic fate, and protein lactylation modification. It further summarizes the core mechanisms by which lactate metabolism regulates EMP, including direct regulation through lactate itself and lactylation modification, activation of signaling pathways such as TGF-β, GSK-3β, and YAP/TAZ-Hedgehog, as well as remodeling of tumor microenvironment (TME) involving cancer-associated fibroblasts (CAFs) and immune cells. Finally, therapeutic strategies targeting the lactate metabolism-EMP axis are discussed, covering inhibition of lactate production and transport, precise intervention of lactylation modification, and neutralization of TME acidification, aiming to provide novel theoretical basis and intervention targets for overcoming metastasis and chemotherapy resistance in PDAC.

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal malignant tumors of the digestive system (1). Its global incidence is increasing annually and is expected to reach 18.6 per 100,000 by 2050, with an average annual rise of 1.1%, thereby presenting a substantial public health challenge (2). The prognosis for PDAC is exceedingly grim; in Europe, disability-adjusted life years (DALYs) associated with the disease have surged by 30% over the past decade (1), and it is anticipated to become the second leading cause of cancer-related mortality in the United States (3). This disease encounters numerous obstacles, with low rates of early-stage diagnosis being the foremost issue. The initial manifestations of PDAC are frequently understated, and there is presently an absence of efficacious preventive strategies and screening techniques; consequently, around 80% of patients are identified when the malignancy has progressed to an incurable advanced stage (3). Furthermore, among the limited cohort of patients suitable for surgical intervention, up to 80% will experience local or distant metastases. Moreover, current chemotherapy protocols exhibit limited effectiveness and are susceptible to resistance development, complicating the treatment conundrum (1).

Epithelial-mesenchymal transition (EMT) is recognized as a fundamental mechanism that drives the malignant characteristics of PDAC. It not only facilitates tumor invasion and metastasis but also significantly contributes to the emergence of chemotherapy resistance (4). Research reveals that aberrant activation of EMT-regulating pathways accounts for drug resistance in PDAC cells (5), and a preclinical study shows that EMT suppression significantly increases tumor cell sensitivity to gemcitabine (6).

EMT plasticity is not a unidirectional transformation of tumor cells from an epithelial phenotype to a mesenchymal phenotype, but rather a dynamic, reversible process between the two. The fundamental principle is epithelial-mesenchymal plasticity (EMP), which encompasses complete EMT, partial EMT (characterized by a mixed epithelial-mesenchymal phenotype), and mesenchymal-epithelial transition (MET), representing three distinct stages (7). Notably, certain tumor cells exhibiting an EMT phenotype possess both epithelial and mesenchymal traits; these cells function as “seed cells” for PDAC invasion and distant metastasis, and are intricately linked to the preservation of cancer stem cell (CSC) attributes, chemoresistance, and immune evasion. Moreover, PDAC invasion and metastasis are not merely unidirectional EMT processes. Tumor cells must initially undergo EMT in situ to gain migratory and invasive capabilities; upon arriving at distant target organs and establishing colonization, they must undergo MET to restore their epithelial phenotype. These two biological phenomena together constitute the core essence of the EMT (8). It is evident that the dynamic balance between EMT and MET is not only a prerequisite for completing the full metastasis cycle but also places extremely high demands on the metabolic flexibility of tumor cells—they must meet the need for rapid energy supply during migration while adapting to the entirely new metabolic environment within the metastatic site. Consequently, clarifying the regulatory mechanisms of EMT plasticity and pinpointing critical targets that control this dynamic equilibrium constitute a fundamental approach for reversing the malignant phenotype of PDAC.

Simultaneously, metabolic reprogramming is widely acknowledged as a characteristic of cancer. Even under aerobic settings, tumor cells tend to create energy through glycolysis—a process known as “aerobic glycolysis” or the “Warburg effect” (9). For a long time, lactate was regarded as an inert end product of glycolysis. However, recent investigations have demonstrated that lactate plays numerous roles in tumor biology: it acts not only as an energy substrate and carbon source, but also as an essential signaling molecule and a donor for epigenetic modifications (10). It is worth noting that there is a close connection between lactate metabolism and the epithelial-mesenchymal plasticity (EMP). On the one hand, the EMT process itself is accompanied by a shift in metabolic patterns; on the other hand, lactate and its metabolites can directly or indirectly influence the expression of EMP-related genes and cellular phenotypes through various mechanisms (11). This article aims to systematically review the role of lactate metabolism in regulating EMP in pancreatic cancer and to outline recent research progress on the lactate-EMP regulatory network from multiple perspectives, including metabolic reprogramming, signal transduction, epigenetic modifications, lactate transport, and the tumor microenvironment (TME).

Specific characteristics of lactate metabolism in PDAC

For a long time, lactate was regarded as a useless end product of glycolysis. However, recent research has completely overturned this view: lactate is not only a key energy substrate and biosynthetic precursor, but also acts as an important signaling molecule that profoundly influences gene expression, cell fate, and the remodeling of the TME through the newly discovered process of lactylation (12,13). This chapter provides a systematic overview of the unique characteristics of lactate metabolism in PDAC, covering lactate production, transmembrane transport, intracellular fate, and lactate-mediated modifications as a signaling molecule. It seeks to provide the framework for forthcoming chapters that will study in depth the function of lactate in PDAC progression and treatment resistance.

High-efficiency production of lactate

PDAC cells exhibit a highly activated glycolytic phenotype, preferentially converting glucose to lactate even under aerobic conditions; this phenomenon is known as the “Warburg effect” (14,15). This metabolic reprogramming is not a random event, but rather the result of the combined effects of intrinsic genetic mutations and external microenvironmental stresses (Figure 1).

Figure 1.

Core drivers and metabolic network of efficient lactate production in PDAC (by Figdraw). Efficient lactate production is synergistically driven by oncogenic mutations, tumor suppressor gene inactivation, and the hypoxic microenvironment. Mutant KRAS activates MYC/AP-1 via the RAF-MEK-ERK and PI3K-AKT-mTORC1 pathways, upregulating key glycolytic enzymes (GLUT1, HK2, LDHA). p53 inactivation promotes glucose uptake via PON2 upregulation, while NFIA inactivation relieves its transcriptional inhibition on PKM, further enhancing glycolytic flux. The hypoxic microenvironment stabilizes HIF-1α, which induces transcription of GLUT1, HK2, LDHA, PDK1, and MCT4. Additionally, glutamine undergoes reductive carboxylation to produce malate and then pyruvate, which is ultimately converted to lactate by LDHA, providing an alternative carbon source for glycolysis. These mechanisms collectively sculpt PDAC cells into efficient “lactate production factories”. α-KG, α-ketoglutarate; Gln, glutamine; GLS, glutaminase; Glu, glutamate; LDHA, lactate dehydrogenase A; PDAC, pancreatic ductal adenocarcinoma; PKM, pyruvate kinase M.

Oncogene-driven glycolytic reprogramming

In PDAC, approximately 90% of patients carry activating mutations in the KRAS gene, which is the principal driver of lactate production (16-18). Mutant KRAS reshapes glucose metabolism through several downstream signaling pathways. KRAS activates the RAF-MEK-ERK cascade, phosphorylating and activating numerous transcription factors (such as MYC and AP-1). These transcription factors directly bind to the promoter regions of genes encoding key rate-limiting enzymes in glycolysis [lactate dehydrogenase A (LDHA); HK1/2; phosphofructokinase, liver type (PFKL); and glucose transporters GLUT1/SLC2A1], strongly promoting their transcription (19-21) and ultimately enhancing glucose uptake and glycolytic flux. KRAS simultaneously activates the PI3K-AKT signaling pathway, which, on one hand, promotes the translocation of GLUT1 to the cell membrane, increasing glucose uptake; on the other hand, by activating mTORC1, it enhances the translational efficiency of key enzymes such as HK2 and LDHA (22,23).

In PDAC, oncogenic KRAS signaling activates a MYC-centered transcriptional program (19). MYC is considered a global transcriptional amplifier that drives the expression of glycolytic genes, including LDHA (a direct target of MYC) and a broader range of glycolytic enzymes such as HK2 and ENO1, thereby maximizing glycolytic flux (24-26).

In addition to KRAS, tumor suppressor gene inactivation further exacerbates this process. For example, p53 inactivation leads to the upregulation of PON2; the overexpression of PON2 promotes glucose uptake by binding to the glucose transporter GLUT1 and blocking its interaction with the inhibitory protein STOM, thereby supporting the growth and metastasis of PDAC (27). Furthermore, in pancreatic cancer, downregulation (inactivation) of the key tumor suppressor NFIA lifts the transcriptional repression of the glycolytic enzyme pyruvate kinase M (PKM), thereby directly promoting glucose uptake and lactate production (28). Knocking out ENO1, a key enzyme in glycolysis, significantly reduces glucose uptake and lactate secretion in pancreatic cancer cells and inhibits tumor development (29). Although ENO1 itself is not classified as a traditional tumor suppressor gene, this study provides strong evidence that inhibiting the glycolytic pathway can reverse the malignant phenotype of pancreatic cancer. Conversely, if tumor suppressor gene inactivation leads to the overexpression of enzymes such as ENO1, it will exacerbate glycolysis.

The hypoxic microenvironment and the amplifying effect of HIF-1α

PDAC is characterized by a dense fibrotic stroma, which compresses blood vessels within the tumor, impairs perfusion, and creates areas of severe hypoxia (30,31). This hypoxic microenvironment stabilizes HIF-1α, which serves not only as a central transcription factor for cellular adaptation to hypoxia but also as a potent amplifier of glycolysis. Activated HIF-1α directly activates a variety of glycolysis-related genes, including those encoding GLUT1 (32), HK2 (33), LDHA (34), PDK1 (35), MCT4 (36). Consequently, genetic mutations and the hypoxic microenvironment exert a synergistic effect, jointly transforming PDAC cells into highly efficient “lactate production factories”. A study has shown that lactate concentrations in PDAC tumors can reach as high as 8–18 µmol/g of wet tissue, which is 5–11 times higher than in the normal pancreas (37). Lactate levels in PDAC tissue are substantially greater than in matched peritumoral tissue and are linked with poor prognosis (38).

Supplementation of glutamine metabolism

In addition to glucose, glutamine is another key source of lactate in PDAC cells. In the metabolic reprogramming driven by KRAS mutations, dependence on glutamine by PDAC cells constitutes a non-canonical pathway for lactate production (39). It is further converted into α-ketoglutarate, an intermediate in the tricarboxylic acid (TCA) cycle, via glutamate dehydrogenase (GLUD) or transaminases. In PDAC cells, because KRAS signaling suppresses the traditional oxidative phosphorylation (OXPHOS) pathway, α-ketoglutarate is transformed to malate through reductive carboxylation and subsequent metabolic processes. After malate is transported into the cytoplasm, it is ultimately converted to lactate by LDHA (40). Under conditions of hypoxia or impaired mitochondrial function, carbon derived from glutamine can be converted to pyruvate by malic enzyme (ME1) and ultimately to lactate by lactate dehydrogenase (LDH; LDHA). This pathway provides an important supplementary carbon source for glycolysis (41,42). A study has shown that KRAS supports the rapid proliferation of PDAC by upregulating glutamic-oxaloacetic transaminase (GOT1) and downregulating glutamate dehydrogenase (GLUD1), thereby forcing the glutamine carbon flux into this non-canonical pathway (39). The three major core drivers of efficient lactate production in PDAC (KRAS mutation, tumor suppressor gene inactivation, and hypoxic microenvironment) and their synergistic mechanisms are summarized in Figure 1.

Transmembrane transport of lactic acid and intracellular homeostasis

The lactate produced continuously at high rates within cells must be efficiently transported to prevent intracellular acidosis and maintain glycolytic flux. This process is primarily mediated by monocarboxylate transporters (MCTs) (43). Among the MCT family, the MCT1 and MCT4 subtypes have been most extensively studied in cancer and are highly expressed in various types of malignancies.

In PDAC, both MCT1 and MCT4 are significantly expressed and are linked with poor patient prognosis (44,45). In the metabolic reprogramming of pancreatic cancer, the MCT family demonstrates significant functional differentiation. MCT4 is characterized by low affinity and high transport capacity for lactate. Primarily induced by HIF-1α, it is located on the membranes of highly glycolytic tumor cells and is responsible for effluxing excess intracellular lactate into the extracellular space (46). Studies have confirmed that high MCT4 expression defines the glycolytic metabolic subtype of pancreatic cancer and is closely associated with poor patient prognosis. In contrast, MCT1 exhibits high affinity for lactate and is expressed in aerobic tumor cell subpopulations or stromal cells [such as cancer-associated fibroblasts (CAFs)]; it can both efflux lactate and take up lactate as an energy source in response to concentration gradients (36,47). In CAFs of pancreatic cancer, MCT4 is highly expressed while MCT1 is barely expressed; this expression pattern confers a highly glycolytic phenotype on CAFs and leads to lactate secretion (36); meanwhile, tumor cells utilize MCT1 to take up lactate from CAFs, transporting it into mitochondria for OXPHOS, thereby forming what is known as “metabolic symbiosis” or the “reverse Warburg effect”, which collectively supports the malignant progression of pancreatic cancer (47).

This differential MCT expression pattern allows the phenomena of “lactate shuttle” or “metabolic symbiosis” in the PDAC microenvironment (48,49). Specifically, lactate produced by tumor cells in hypoxic regions is effluxed via MCT4 and subsequently taken up by tumor cells or CAFs in well-oxygenated regions that highly express MCT1, serving as fuel for mitochondrial OXPHOS and thereby enabling the efficient recycling of energy (44,50). This not only conserves glucose but also shapes a dynamic metabolic environment.

In addition, lactate is co-transported with H⁺, and its large outflow immediately contributes to acidification of the tumor extracellular microenvironment (pH 6.0–6.5) (51). More crucially, lactate accumulating outside the cells works as a signaling molecule, activating its unique G protein-coupled receptor (GPCR), GPR81. GPR81 is highly expressed on the surface of PDAC cells. Upon binding to GPR81, lactate inhibits adenylate cyclase activity, hence lowering intracellular cyclic adenosine monophosphate (cAMP) levels and activating downstream pro-survival and pro-proliferation signaling pathways (52,53). The regulatory mechanisms of lactate transmembrane transport in PDAC, functional differentiation of MCT1/MCT4, lactate shuttling, and histone lactylation modifications are summarized in Figure 2.

Figure 2.

Transmembrane transport, lactate shuttle, and histone lactylation regulation in PDAC (by Figdraw). In hypoxic regions, tumor cells export excess intracellular lactate via MCT4 (low affinity, high capacity), leading to microenvironmental acidification (pH 6.0–6.5). Exported lactate activates the membrane receptor GPR81, inhibiting adenylyl cyclase and reducing cAMP levels to promote pro-proliferative signaling. Concurrently, lactate can be taken up by tumor cells in oxygen-rich regions or CAFs via MCT1, converted to pyruvate by LDHB, and channeled into mitochondria for OXPHOS, establishing a “lactate shuttle” or metabolic symbiosis. Furthermore, accumulated lactate induces histone H3K18la modification, which activates ACAT2 transcription and promotes cholesterol biosynthesis, forming a metabolic-epigenetic regulatory axis. CAF, cancer-associated fibroblast; cAMP, cyclic adenosine monophosphate; LDHB, lactate dehydrogenase B; OXPHOS, oxidative phosphorylation; PDAC, pancreatic ductal adenocarcinoma; TCA, tricarboxylic acid.

Intracellular metabolic fates of lactate: a multifunctional substrate

Lactate taken up by or retained in cells is not an inert molecule; rather, it actively participates in multiple metabolic processes. In cells expressing LDHB, lactate can be oxidized by LDH back into pyruvate, which enters the mitochondria to participate in the TCA cycle, thereby providing energy for the cell (54,55). A study has shown that in human lung tumors, lactate contributes even more to TCA cycle intermediates than glucose (56). When glucose is scarce, lactate serves as an effective precursor for gluconeogenesis, generating glucose-6-phosphate (G6P) through pathways such as the malate-aspartate shuttle, thereby maintaining the stability of intracellular energy levels and biosynthetic precursors (54). In the PDAC TME, lactate accumulation induces the H3K18la. H3K18la functions as a “molecular switch” to activate the transcription of ACAT2, and the activated ACAT2 directly promotes cholesterol biosynthesis (57).

Lactylation: enzymatic and non-enzymatic pathways

Lactate can serve as a direct substrate for lysine lactylation, a process that occurs via two distinct mechanisms: enzymatic L-lactylation and non-enzymatic D-lactylation (58,59). Enzymatic L-lactylation strictly relies on activated lactyl-CoA (60). The synthesis of lactyl-CoA is catalyzed by specific synthetases, primarily including acyl-CoA synthetase short-chain family member 2 (ACSS2) (61) and GTP-specific succinyl-CoA synthetase (GTPSCS) (62). Notably, ACSS2 not only drives lactyl-CoA production but also forms a functional complex with KAT2A, effectively coupling with it to enable its function as a lactyltransferase. Meanwhile, nuclear GTPSCS acts as a lactyl-CoA synthetase within the nucleus, providing an essential substrate pool for histone lactylation. Following its synthesis, the lactyl group is transferred to target lysine residues by lactyltransferases (“writers”). To date, several classical lysine acetyltransferases have been identified as possessing lactyltransferase activity, including p300 (38,63), CBP (64), GCN5 (65), KAT2A (66), members of the MYST family [such as MOF/KAT8 and HBO1/KAT7 (67)], and TIP60/KAT5 (68). Interestingly, a recent study has revealed that the alanyl-tRNA synthetases AARS1 and AARS2 (69) can directly utilize lactate and ATP to generate a lactyl-AMP intermediate. This highlights a novel, lactyl-CoA-independent mechanism for lactylation, thereby expanding the traditional paradigm that exclusively views enzymes like p300 as canonical writers.

Conversely, non-enzymatic D-lactylation primarily originates from the methylglyoxal (MG) pathway (70). Under the catalysis of GLO1, MG is converted into S-D-lactoylglutathione (SLG), which subsequently undergoes an intramolecular S-to-N acyl transfer to form D-lactyl-lysine modifications. Unlike L-lactylation, which predominantly activates gene transcription, D-lactylation has been shown to dampen inflammatory immune responses in macrophages (partially driven by the glyoxalase II substrate SLG), exerting a distinct anti-inflammatory effect. This suggests that the two stereoisomeric forms of lactylation likely govern divergent functional landscapes.

The dynamic homeostasis of lactylation is tightly maintained by delactylases (“erasers”), which primarily comprise class I histone deacetylases (HDAC1–3) (71) and SIRT family delactylases (SIRT1–3) (72). Together with lactyltransferases, these erasers orchestrate intracellular lactylation levels. Importantly, HDAC1–3 exhibit dual enzymatic activities, catalyzing both deacetylation and delactylation. Due to the potential crosstalk and competitive relationship between these enzymatic activities, administering HDAC inhibitors to block deacetylation may inadvertently suppress delactylation as well, paradoxically leading to elevated global lactylation levels. This potential risk and mechanistic complexity must be carefully evaluated in the context of clinical translation.

Core mechanisms of lactate metabolism in regulating EMT

Lactylation-directed mechanisms underlying EMT in pancreatic cancer

Lactate generated through glycolysis functions not merely as a metabolic end product, but directly orchestrates EMT transcriptional programs via histone and non-histone lactylation. This metabolic-epigenetic coupling constitutes a principal driving force for malignant progression in pancreatic cancer (73,74), operating through multiple self-sustaining positive feedback loops.

Histone lactylation directly Activates EMT transcriptional programs

Hyperactive glycolysis in pancreatic cancer cells generates substantial lactate, which undergoes lysine lactylation on histone and non-histone substrates catalyzed by lactyltransferases (writers), including p300 (38), ASF1A (75), and related enzymes. This epigenetic modification reshapes chromatin architecture, opens chromatin regions associated with EMT-related genes, and initiates aberrant target gene transcription.

Multiple upstream signaling pathways enhance histone lactylation by augmenting glycolytic output. In pancreatic cancer, elevated CCNB2 expression upregulates LDHA and LDHB through the PI3K/AKT pathway, accelerating glycolytic flux and increasing lactate production, thereby elevating global H3K18 lactylation levels (76). The calcium signaling pathway upregulates SIRT4 expression, thereby mediating the deacetylation of K358 in ENO1, enhancing its glycolytic enzyme activity, leading to massive lactate accumulation and genome-wide enrichment of H3K9la and H3K18la at promoter regions (77), markedly activating stemness pathways including WNT and NOTCH to promote malignant progression. LDHA-mediated lactate accumulation promotes H3K18la enrichment at the MESP1 promoter, activating MESP1 transcription and facilitating EMT, proliferation, and invasion (78). PSMD14 drives H3K18la enrichment at the ACLY gene enhancer region through deubiquitination-mediated stabilization of LDHA, thereby promoting lipid synthesis and indirectly supporting the metabolic reprogramming required for EMT (79). Elevated LDHA expression in pancreatic cancer results in significant lactate accumulation, which serves as a substrate for inducing H4K12 lactylation. This epigenetic modification activates the promoters of immunosuppressive genes including BNIPL and VSTM2A, upregulating inhibitory ligands such as nectin-2 and galectin-9, thereby establishing a locally immunosuppressive microenvironment that creates favorable conditions for tumor cell immune evasion and subsequent metastasis (80).

Distinct histone lactylation sites coordinately activate the EMT program by targeting various core transcription factors and upstream/downstream pathways. H3K18la serves as a central epigenetic switch that activates transcriptional regulatory programs mediating EMT and PDAC invasive capacity; analysis of 21 clinical sample pairs revealed significantly elevated H3K18la levels in tumor tissues (81). As the most extensively characterized lactylation site, H3K18la exerts multi-layered regulatory control over EMT. In atherosclerosis models, H3K18la is abundantly enriched at the promoters and enhancers of EMT-related genes, directly activating canonical EMT master transcription factors including SNAI1 and ZEB1 through chromatin remodeling; This process consequently downregulates epithelial markers such as E-cadherin while upregulating mesenchymal markers including N-cadherin and vimentin to drive phenotypic transformation (82). Simultaneously, in PDAC,H3K18la can target cell cycle regulatory genes including TTK/BUB1B (38,76), and through reinforcing p300 expression, in turn enhances its own modification levels, thereby establishing a lactate-H3K18la-EMT positive feedback loop that continuously amplifies signaling effects. Furthermore, integrated genome-wide cleavage under targets and tagmentation (CUT&Tag) and RNA sequencing (RNA-seq) analyses revealed that H3K18la co-enriches with H3K9la at WNT and NOTCH pathway genes, synchronously activating tumor stemness characteristics to form a dual driving force with EMT effects, collectively promoting tumor invasion and metastasis (77). H4K12la exhibits unique immune-metastasis coupled regulatory features in pancreatic cancer (80): beyond the aforementioned immunosuppressive functions, this modification is significantly upregulated in liver metastases, amplifying EMT phenotypes and immune evasion effects through metabolic-epigenetic coupling analogous to patterns observed in hepatocellular carcinoma. Conversely, H4K12la binds to and activates glycolytic genes including LDHA and PKM2, continuously reinforcing the high-lactate and high-histone lactylation state, ultimately forming a positive feedback loop integrating metabolism, epigenetics, and immune regulation.

Collectively, histone lactylation represents not a singular epigenetic event, but a critical nexus linking glycolytic metabolism, EMT, and immune regulation. The differential functions and cooperative effects of multi-site lactylation provide a comprehensive molecular framework for understanding invasive metastasis in pancreatic cancer and establish a theoretical foundation for exploring targeted intervention strategies.

Non-histone lactylation relieves EMT suppression and enhances transcription factor activity

Substantial lactate accumulation in the pancreatic adenocarcinoma microenvironment mediates lysine lactylation on diverse non-histone proteins, relieving constraints on malignant phenotypes while enhancing transcription factor function, thereby synergistically driving EMT through multiple pathways to facilitate tumor invasion, metastasis, and perineural infiltration.

Lactate can modify tumor suppressor-associated proteins, alleviating classical tumor suppressive constraints on malignant phenotypes: lactate accumulation induces lactylation of the tumor suppressor PRKCG (PKCγ) at K28/K34/K37, causing conformational changes and loss of activity, rendering it incapable of activating the p53 signaling pathway. This results in downregulation of p53 downstream targets including p21 and FAS, leading to dysregulated cell proliferation and apoptosis control, significantly enhanced invasive capacity, and establishment of permissive conditions for EMT initiation (83). Concurrently, lactylation targets RNA-binding proteins and metabolism-associated proteins, facilitating EMT progression through post-transcriptional regulation and metabolic reprogramming: lactate induces lactylation of heterogeneous nuclear ribonucleoprotein C (HNRNPC) at K176, enhancing HNRNPC binding to PAK6 pre-messenger RNA (pre-mRNA) and promoting upregulation of the oncogenic isoform PAK6S, ultimately driving tumor growth and metastasis (84). Lactate-mediated EP300-catalyzed NMNAT1 lactylation enhances nuclear transport efficiency and enzymatic activity, maintaining nuclear NAD⁺ metabolic homeostasis. Through modulating the p38-MAPK pathway, glutamine catabolism, and mitochondrial metabolism, this enables cancer cells to adapt to nutrient-deprived microenvironments and sustain proliferation, ensuring EMT phenotypic stability (63). Additionally, lactate-induced lactylation of RNA methyltransferase NSUN2 blocks its ubiquitination-mediated degradation and enhances protein stability, which, through 5-methylcytosine (m⁵C) methylation, upregulates CDCP1 and STC1 expression, strengthening cell migration, invasion capacity, and perineural infiltration, further amplifying EMT-mediated malignant phenotypes (85).

NUSAP1 is highly expressed in PDAC tissues and drives EMT, promoting cancer cell proliferation, migration, and invasion (86). Lactylation stabilizes NUSAP1 protein, which cooperates with c-Myc/HIF-1α to activate LDHA transcription, driving glycolytic output and expanding the lactate pool. Lactate subsequently functions as a signaling molecule activating EMT programs while reciprocally reinforcing NUSAP1 lactylation, forming a “lactate-NUSAP1 lactylation-LDHA-EMT” self-reinforcing loop (87). This loop tightly couples metabolic reprogramming with phenotypic transformation, offering dual intervention targets for therapeutic development.

Simultaneously, lactylation directly activates core EMT transcription factors to amplify mesenchymal transformation signals. In pancreatic cancer, RHOF upregulates PKM2 expression through the c-Myc pathway, intensifying glycolysis and lactate generation. Accumulated lactate further induces lactylation of the key EMT transcription factor Snail1, promoting Snail1 nuclear translocation and enhancing its transcriptional activity, consequently downregulating the epithelial marker E-cadherin while upregulating mesenchymal markers N-cadherin and vimentin, directly initiating EMT programs (88). The lactate-mediated “lactate-NUSAP1 lactylation-LDHA-EMT” positive feedback self-reinforcing loop is summarized in Figure 3.

Figure 3.

NUSAP1 lactylation-mediated “lactate-NUSAP1-LDHA-EMT” positive feedback loop (by Figdraw). In PDAC cells, high LDHA expression drives glycolysis and produces abundant lactate. Lactate induces NUSAP1 lactylation, enhancing its protein stability and transcriptional co-activator activity. Lactylated NUSAP1 synergizes with c-Myc/HIF-1α to further upregulate LDHA expression, amplifying glycolytic flux and lactate accumulation, thereby forming a self-reinforcing positive feedback loop. This loop concurrently drives EMT, characterized by downregulation of E-cadherin and upregulation of mesenchymal markers such as N-cadherin, vimentin, and Snail, tightly coupling metabolic reprogramming with malignant phenotypic conversion. EMT, epithelial-mesenchymal transition; LDHA, lactate dehydrogenase A; PDAC, pancreatic ductal adenocarcinoma.

In summary, non-histone lactylation comprehensively relieves EMT suppression and strengthens transcription factor activity through multiple mechanisms, including tumor suppressor inactivation, metabolic and RNA regulatory network remodeling, and direct activation of core EMT transcription factors, representing a critical epigenetic regulatory modality driving malignant progression in pancreatic adenocarcinoma.

Regulation of EMT by lactate and the acidic TME in pancreatic cancer

In PDAC, the Warburg effect drives substantial lactate efflux through MCT1/4, with lactate anions and extracellular protons collectively establishing an acidic TME. Notably, although lactate and acidic conditions (low pH) frequently co-exist, their regulatory mechanisms on tumor cells are fundamentally distinct: lactate functions as a signaling molecule and substrate for protein lactylation, directly driving EMT gene expression programs, whereas the acidic environment primarily selects for and shapes more aggressive tumor cell subpopulations through sustained selective pressure and metabolic reprogramming.

Beyond its established role as a lactylation substrate, the biological functions of lactate are predominantly mediated through its membrane receptor GPR81. As a GPCR, GPR81 activation by lactate suppresses adenylyl cyclase activity, reduces intracellular cAMP levels, and triggers downstream signaling cascades (52). A seminal study in PDAC first demonstrated that lactate upregulates the adhesion molecule AMIGO2 through its receptor GPR81, subsequently activating the TGFβ2-pSMAD2/3-ZEB1 signaling cascade to drive EMT and tumor progression, with this process occurring independently of protein lactylation (89). This mechanism has been corroborated in melanoma models, where lactate binding to GPR81 reduces intracellular cAMP and inhibits protein kinase A (PKA) activity, thereby blocking PKA-mediated HIF-1α ubiquitination and degradation. Stabilized HIF-1α transcriptionally upregulates Rab27a to promote tumor-derived extracellular vesicle release, ultimately accelerating pulmonary metastasis (90).

Acid-sensing ion channels (ASICs) serve as core molecular sensors of the acidic microenvironment. Zhu et al. (91) demonstrated in PDAC that ASIC1 and ASIC3 function as proton-gated cation channels, opening under acidic conditions to mediate Na⁺/Ca²⁺ influx, elevate intracellular Ca²⁺ concentrations, and activate the Ca²⁺/RhoA/ROCK signaling pathway. This drives actin cytoskeleton remodeling and alterations in cell adhesion, ultimately inducing EMT phenotypes. The study further confirmed that knockdown of ASIC1 or ASIC3 significantly reverses acidic environment-induced changes in EMT marker expression. At the transcriptional regulation level, the acidic microenvironment indirectly modulates EMT through microRNA (miRNA) networks. It has been shown that under acidic conditions, miR-652 expression is downregulated in PDAC cells, attenuating its inhibitory effect on the target gene ZEB1, resulting in elevated ZEB1 protein levels and promotion of EMT (92). This mechanism complements the lactate-GPR81 pathway, with both converging on ZEB1 as a critical EMT transcriptional regulatory node.

Long-term acid adaptation represents an important feature of PDAC malignant progression. Audero et al. (93) reported that acidic culture conditions selectively promote the expansion of PDAC cell subpopulations with EMT phenotypes, which exhibit enhanced invasive capacity and chemoresistance. Wu et al. (94) further elucidated that PDAC cells exhibit a “slow adaptation” mode to prolonged acidic environments, involving coordinated metabolic reprogramming and epigenetic modifications, with EMT phenotypes demonstrating reversibility. These findings indicate that the acidic microenvironment serves as a key factor dynamically regulating EMT plasticity. From a tumor ecology perspective, Pedersen et al. (95) proposed that alternating pH landscapes shape PDAC heterogeneity through selective pressure, promoting the clonal expansion of invasive subpopulations with EMT characteristics. More recently, it has been discovered that the acidic microenvironment can promote PDAC progression through the lncRNA-LOC100507424/E2F1/FOXM1 axis, further enriching the molecular network by which acidic TME regulates EMT (96). Schwab et al. (97) systematically reviewed pH-dependent ionic signaling in PDAC, emphasizing that ASICs and proton-sensing GPCRs (OGR1/GPR68, TDAG8/GPR65) collectively constitute a multi-layered sensing system for the acidic microenvironment in pancreatic cancer. The molecular mechanisms by which the lactate-GPR81 signaling pathway and the acidic microenvironment-ASIC channel pathway collaboratively regulate EMT are summarized in Figure 4.

Figure 4.

Synergistic regulation of EMT by lactate-GPR81 signaling and acidic microenvironment-ASIC channels in PDAC (by Figdraw). Lactate and H⁺ cooperatively activate the EMT program via their respective receptors/channels. In the lactate direct signaling pathway, lactate binding to GPR81 stabilizes HIF-1α by inhibiting the cAMP/PKA axis, upregulating Rab27a to promote pro-tumorigenic extracellular vesicle release; concurrently, it activates ZEB1 via the AMIGO2/TGFβ2/pSMAD2/3 axis. In the acidic microenvironment pathway, H⁺ activates ASIC1/3 channels, mediating Na⁺/Ca²⁺ influx, elevating intracellular Ca²⁺ concentration, and subsequently activating RhoA/ROCK signaling, which induces cytoskeletal remodeling and altered adhesion. Long-term acidic adaptation further induces metabolic reprogramming and enhances chemoresistance. Both pathways converge on the transcription factor ZEB1, jointly driving EMT, thereby promoting PDAC invasion, migration, and chemoresistance. ASIC, acid-sensing ion channel; cAMP, cyclic adenosine monophosphate; EMT, epithelial-mesenchymal transition; PDAC, pancreatic ductal adenocarcinoma; PKA, protein kinase A.

Immune microenvironment and EMP interplay

Lactylation not only directly acts on cancer cells but also reshapes the tumor immune microenvironment, creating a permissive “soil” for EMT and metastasis: in pancreatic tumor cells, lactate induces ENSA-K63la, triggering the STAT3/CCL2 signaling pathway. Elevated CCL2 secretion by tumor cells promotes recruitment of tumor-associated macrophages (TAMs) to the TME. High lactate levels further drive transcriptional reprogramming in TAMs through ENSA-STAT3 signaling, fostering an immunosuppressive environment that reduces immune surveillance pressure on EMT-transformed cancer cells, indirectly supporting tumor plasticity and progression (98). GPR132 functions as a lactate sensor highly expressed in macrophages within the acidic TME; in pancreatic cancer, elevated lactate promotes macrophage polarization toward the M2d subtype (99). Additionally, lactate transported into macrophages via MCTs stabilizes HIF-1α through the NF-κB/p65 pathway and promotes M2 polarization (100).

Polarized M2-type macrophages secrete leukemia inhibitory factor (LIF) to activate the JAK-STAT pathway, promoting EMT in pancreatic cancer cells (101). Furthermore, β-catenin signaling is specifically activated in TAMs, driving their polarization toward a hybrid phenotype with both M1/M2 characteristics, and enhancing EMT and metastasis through the OSM/STAT3/LOXL2 axis (102).

The bidirectional regulation between EMT and macrophage polarization has been established: in metastatic PDAC tissues, elevated expression of the EMT marker Snail significantly correlates with M1-to-M2 polarization, while decreased E-cadherin expression further reinforces this process, suggesting that EMT may represent a mechanism through which TME alterations induce macrophage polarization and promote PDAC metastasis (103). Multi-punch tissue microarray (TMA) samples from 120 PDAC patients demonstrated that transcription factors including ZEB1/ZEB2 are overexpressed in tumor budding regions, concurrently accompanied by reduced M1-type and increased M2-type macrophages (104).

Therapeutic strategies targeting the lactate-EMP axis

The tight coupling between lactate metabolism and EMP offers a multi-pronged framework for combating chemoresistance and metastasis in PDAC. From metabolic enzyme blockade to epigenetic modulation, therapies directed against the lactate-EMP axis are transitioning from bench to bedside.

Inhibition of lactate production and transport

Attacking the Warburg effect at its source is the foundational strategy for suppressing lactate-driven EMP. LDHA inhibitors have dominated pancreatic cancer metabolic therapy; however, first-generation compounds such as FX-11 (105-107), oxamate (108,109), and NHI-2 (110) were limited by potency, selectivity, or pharmacokinetic shortcomings. Subsequent structure-guided optimization yielded more promising agents. Sharma et al. reported compounds 6 (111) and 21 (112) with nanomolar potency and favorable bioavailability, while Du et al. developed ML-05 (113) and Sun et al. pioneered the LDHA proteolysis-targeting chimera (PROTAC) degrader MS6105 (114), representing two fundamentally distinct strategies: immune activation through LDHA inhibition versus direct elimination of the target through the proteasome. A summary of representative LDHA inhibitors and other metabolism-targeting agents, including their mechanisms and key features, is presented in Table 1.

Table 1. Key inhibitors targeting LDHA and other metabolic enzymes.

Inhibitor name	Mechanism of action (detailed)	Evidence type	References
Compound 6 (methyl esters)	An allosteric inhibitor targeting LDHA. By forming stable hydrogen bonds with key residues in the LDHA active site (Asn137, Arg168, His192), it competitively blocks the binding of the substrate (pyruvate) to the cofactor (NADH), thereby inhibiting its catalytic activity and reducing lactate production	Preclinical	(111)
Compound 21	A small-molecule inhibitor targeting the allosteric site of the LDHA tetramer. It binds to a unique allosteric pocket located between the two subunits of LDHA (chains A and D) and inhibits enzyme activity by inducing a conformational change, exhibiting greater selectivity than LDHB. Its carboxylic acid group is not essential for activity, and ester derivatives also retain high activity	Preclinical	(112)
FX-11	A competitive NADH inhibitor of LDHA. As a derivative of 2,3-dihydroxy-6-methyl-7-(phenylmethyl)-4-propylnaphthalene-1-carboxylic acid, it inhibits the conversion of pyruvate to lactate by LDHA by competing for the NADH binding site, thereby inducing oxidative stress and inhibiting tumor growth	PDAC-specific	(105-107)
NHI-2	An N-hydroxyindole-based selective inhibitor of LDHA. It simultaneously binds to the substrate (pyruvate) and cofactor (NADH) binding sites, exhibiting greater selectivity for LDHA inhibition than for LDHB	Preclinical	(110)
ML-05	A novel, potent LDHA inhibitor. Molecular docking studies reveal that its naphthalene ring forms a cation-π interaction with Arg105, while the amide carbonyl group forms dual hydrogen bonds with Tyr238 and Arg105. This mechanism enables highly effective inhibition of LDHA and activates antitumor immune responses (Th1 and GMZB+CD8+ T cells) within the TME	PDAC-specific	(113)
MS6105 (compound 22)	Developed the first LDHA PROTAC. By conjugating an LDHA inhibitor to a VHL E3 ubiquitin ligase ligand via a linker, this approach induces the ubiquitination and proteasome-dependent degradation of LDHA and LDHB (DC50: 38–74 nM), functionally eliminating the target proteins and overcoming the limitations of the space-occupying mechanism inherent in traditional inhibitors	PDAC-specific	(114)
Galloflavin	A novel broad-spectrum LDH inhibitor. By directly binding to and inhibiting the activity of LDHA/B, it reduces lactate production in a co-culture system of tumor cells and pancreatic stellate cells, thereby neutralizing the acidic microenvironment	Preclinical	(115)
NHI-Glc-2	A glucose-conjugated LDHA inhibitor. Designed to actively enter cells via GLUT-1, which is overexpressed in tumor cells, thereby enhancing bioavailability and tumor specificity while targeting LDHA	Preclinical	(116)
Oxamate	A classic competitive inhibitor of the pyruvate analog LDHA. By mimicking the structure of pyruvate, it competitively binds to the substrate-binding site of LDHA, reversibly inhibiting enzyme activity, though with relatively low potency (Ki >100 µM)	Preclinical	(108,109)
EGCG	Natural products downregulate LDHA expression through post-transcriptional regulation. As a major bioactive component of green tea, its mechanism of action does not involve direct inhibition of enzyme activity, but rather significantly downregulates LDHA at the protein expression level, thereby reducing lactate production and glycolytic flux	Preclinical	(108)
Scopoletin	Natural coumarin compounds reduce COX-2 and LDH levels. By decreasing the expression of COX-2 and LDH, they exert anti-inflammatory and anti-angiogenic effects, thereby inhibiting the progression of pancreatic cancer	Preclinical	(117)
Ag-NPs (fenugreek extract)	Biosynthetic silver nanoparticles inhibit COX-2 and LDH enzyme activity/expression. Silver nanoparticles synthesized via reduction using fenugreek extract significantly reduce serum concentrations of COX-2 and LDH, demonstrating antitumor and anti-angiogenic activity	Preclinical	(117)
NO2-NAT	A NO donor that induces apoptosis via an NO-mediated mitochondrial pathway. As a nitrated derivative of the antidiabetic drug nateglinide, it releases NO upon hydrolysis in solution and induces apoptosis in pancreatic cancer cells in a time- and concentration-dependent manner by activating caspase-3/7	Preclinical	(118)
CPI-613 (devimistat)	TCA cycle inhibitors. As an alpha-lipoic acid analog, it selectively inhibits PDH and α-KGDH in mitochondria, disrupting energy metabolism and biosynthesis in tumor cells and inducing the production of ROS	Clinical-stage	(119,120)
BLX-3030	A highly selective CDK9 inhibitor. By competitively binding to the ATP-binding site of CDK9 (IC50 <5 nM), it blocks its kinase activity, thereby downregulating the expression of the oncogenes N-MYC and C-MYC and inducing cell cycle arrest and apoptosis	Clinical-stage	(121)
Pimicotinib (ABSK021)	An orally administered, highly selective, and potent CSF-1R inhibitor. By inhibiting the kinase activity of the CSF-1R, it blocks the survival and proliferation of TAMs, thereby reshaping the tumor immune microenvironment and transforming “cold tumors” into “hot tumors”	Clinical-stage	(122)

α-KGDH, α-ketoglutarate dehydrogenase; Ag-NPs, silver nanoparticles; COX-2, cyclooxygenase-2; EGCG, epigallocatechin gallate; IC₅₀, half-maximal inhibitory concentration; LDH, lactate dehydrogenase; LDHA, lactate dehydrogenase A; LDHB, lactate dehydrogenase B; NADH, nicotinamide adenine dinucleotide; NO, nitric oxide; NO₂-NAT, nitrated nateglinide; PDAC, pancreatic ductal adenocarcinoma; PDH, pyruvate dehydrogenase; PROTAC, proteolysis-targeting chimera; ROS, reactive oxygen species; TAMs, tumor-associated macrophages; TCA, tricarboxylic acid; TME, tumor microenvironment.

Beyond LDHA, the pan-LDH inhibitor galloflavin reduces lactate production in pancreatic cancer cell-pancreatic stellate cell co-culture systems (115), whereas the glucose-conjugated NHI-Glc-2 exploits GLUT-1 overexpression to enhance tumor-specific delivery (116). NO donors such as nitrated nateglinide (NO₂-NAT) induce pancreatic cancer cell apoptosis through nitric oxide (NO) release (118), and the pyruvate dehydrogenase kinase (PDK) inhibitor dichloroacetic acid (DCA) redirects pyruvate into the TCA cycle by activating pyruvate dehydrogenase (PDH), indirectly attenuating global lactylation (123). Given the metabolic plasticity of PDAC, combination strategies have gained considerable attention: FX-11 plus the OXPHOS inhibitor phenformin (124), CPI-613-loaded biomimetic lipid droplets combined with anti-PD-1 antibody (125), and natural products including epigallocatechin gallate (EGCG) (108), scopoletin, and silver nanoparticles (117) all demonstrate synergistic efficacy.

An alternative approach targets the lactate transporter MCT1. However, autoregulatory mechanisms in cellular metabolism limit the utility of single-agent MCT inhibitors such as AZD3965 (126), syrosingopine (127), and AR-C155858 (128), as cells compensate by enhancing transmembrane driving forces (129). The pan-MCT inhibitor CHC blocks lactate shuttling by competitively inhibiting MCT1, MCT2, and MCT4 (120), which partially explains the disappointing clinical performance of some MCT inhibitors. Notably, the microencapsulated 3-bromopyruvate formulation ME3BP-7 (130) exploits MCT1 as a Trojan horse to bypass metabolic autoregulation and deliver its cytotoxic payload directly into MCT1-high cancer cells.

The metabolic complexity of PDAC has driven interest in multi-node blockade. Mito-(PEG)ⁿ-ATO, through PEGylation and TPP⁺ targeting, potently inhibits mitochondrial complexes I and III (131), while CPI-613 disrupts mitochondrial metabolism by inhibiting the TCA-cycle dehydrogenases PDH and α-ketoglutarate dehydrogenase (α-KGDH) (119,120). Combining these OXPHOS inhibitors with AZD3965 (131) or glutamine metabolism inhibitors (V9302, CB839) (132) yields robust synergistic antiproliferative effects: V9302 and CB839 disrupt redox homeostasis by blocking glutamine uptake or catabolism, and cancer cells attempt to compensate by upregulating MCT1 and importing lactate. Simultaneous OXPHOS suppression plus glutaminolysis or MCT blockade therefore deprives cells of energy while foreclosing compensatory pathways (131). A summary of key MCT and mitochondrial metabolism inhibitors is provided in Table 2.

Table 2. Key inhibitors targeting lactate transport and mitochondrial metabolism.

Inhibitor name	Mechanism of action (detailed)	Evidence type	References
ME3BP-7	An MCT1-targeted cytotoxic agent. This is a novel microencapsulated (cyclodextrin) formulation of 3BP that enters cells via MCT1 transport and acts as an alkylating agent to alkylate various intracellular proteins, leading to rapid cell death in cells with high MCT1 expression. This formulation significantly improves the serum stability of 3BP	PDAC-specific	(130)
Mito-(PEG)n-ATO	A mitochondria-targeted inhibitor of OXPHOS. It targets mitochondria via TPP+, and the length of its PEG-modified side chain (n=2–9) influences its potency. By inhibiting the activity of complexes I and III of the mitochondrial respiratory chain, it blocks OXPHOS, thereby inhibiting tumor cell proliferation	Preclinical	(131)
AZD3965	Selective MCT1 inhibitor. By targeting and inhibiting MCT1, it blocks the uptake of lactate from the microenvironment, thereby inhibiting lactate-dependent oxidative metabolism, leading to intracellular lactate accumulation and metabolic stress	Clinical-stage	(126)
V9302	ASCT2 glutamine transporter inhibitor. By targeting ASCT2, it competitively blocks glutamine uptake, leading to oxidative stress and growth inhibition in cancer cells due to glutamine deprivation	Preclinical	(132)
CB839 (telaglenastat)	GLS1 inhibitor. By inhibiting GLS1 activity, it blocks the conversion of glutamine to glutamate, thereby limiting its entry into the TCA cycle for anaplerosis and reducing GSH synthesis, leading to oxidative stress and cell death	Clinical-stage	(132,133)
CHC	A non-specific inhibitor of MCTs. It blocks the transmembrane transport of lactate by competitively inhibiting MCT1, MCT2, and MCT4. Its antitumor effects are partly attributed to the activation of the p38 signaling pathway	Preclinical	(120)
Syrosingopine	A dual inhibitor of MCT1 and MCT4. By simultaneously inhibiting MCT1 and MCT4, it blocks the efflux and uptake of lactate, leading to intracellular lactate accumulation and acidosis	Preclinical	(127)
3BP	An MCT1-dependent alkylating agent. As a pyruvate analog, it enters cells via MCT1 transport and alkylates various intracellular proteins, including glycolytic enzymes, thereby inhibiting energy metabolism and inducing cell death. Free 3BP has poor serum stability	Preclinical	(130)
AR-C155858	Selective MCT1/MCT2 inhibitor. By binding with high affinity and inhibiting the activity of MCT1 and MCT2, it blocks the transmembrane transport of monocarboxylic acids such as lactate	Preclinical	(128)

3BP, 3-bromo-2-propanone; CHC, α-cyano-4-hydroxycinnamate; GSH, glutathione; MCT, monocarboxylate transporter; OXPHOS, oxidative phosphorylation; PDAC, pancreatic ductal adenocarcinoma; PEG, polyethylene glycol; TCA, tricarboxylic acid; TPP⁺, triphenylphosphonium.

Precision targeting of lactylation

Direct modulation of the lactylation machinery has advanced considerably. The blocking peptide K63-pe-3 (134) competitively inhibits ENSA K63-lactylation, relieving PP2A suppression and attenuating the SRC/STAT3/CCL2 axis, thereby remodeling the immunosuppressive microenvironment and indirectly suppressing EMT. The p300 inhibitor C646 (135,136) and the CTCF inhibitor curaxin (137) target the lactylation “writer” and its upstream transcriptional regulator, respectively, reducing H3K18la levels and silencing downstream oncogenic programs. An indirect approach is provided by 2-deoxy-D-glucose (2-DG), a glucose analogue that halts glycolysis at the HK2-catalyzed step, blocking lactate supply (138).

Strategies targeting the lactylation-driven immunosuppressive microenvironment also show translational promise. PF-4136309 inhibits CCL2-CCR2 signaling to block M2 TAM recruitment (139), while STM2457 targets the N⁶-methyladenosine (m⁶A) methyltransferase METTL3, suppressing M2d macrophage polarization and restoring CD8⁺ T-cell function (140). Collectively, these findings position lactylation as more than an intracellular oncogenic event; it is a critical node linking metabolic reprogramming to immune evasion. Combinations such as KRAS inhibitors plus ENSA-K63la blocking peptides, or LDHA degraders plus CCR2 antagonists, may simultaneously attack upstream drivers and downstream effectors of lactylation to overcome immunotherapy resistance in PDAC (98). A summary of these lactylation-targeting strategies and their associated pathways is provided in Table 3.

Table 3. Intervention strategies targeting lactation and related pathways in pancreatic cancer.

Name	Mechanism of action/targets (detailed)	Evidence type	Full title of the cited paper
MRTX1133	Selective KRAS-G12D mutant inhibitor: a non-covalent inhibitor targeting the KRAS-G12D mutant that suppresses the transcription of key genes involved in glycolysis (SLC2A1, HK2, PFK, ENO1, LDHA, SLC16A3), reducing lactate production and thereby downregulating overall protein lactylation levels within tumor cells	Clinical-stage	(98)
K63-pe-3	ENSA-K63la-specific blocking peptide: a cell-penetrating peptide (with an N-terminal HLYVSPWGG transmembrane sequence) that specifically blocks K63-lactylation of ENSA by competitively binding to the region surrounding the K63 site on the ENSA protein. Inhibition of this modification releases ENSA’s inhibition of PP2A, thereby inhibiting SRC-S12 phosphorylation and STAT3-Y705 phosphorylation, downregulating CCL2 expression and secretion, and reshaping the tumor immune microenvironment	Preclinical	(98,134)
PF-4136309	CCR2-selective antagonist: specifically targets the chemokine receptor CCR2 and blocks the CCL2-CCR2 signaling axis. This signaling axis mediates the recruitment of monocytes/macrophages following the secretion of CCL2, which is induced by tumor-derived lactate via the ENSA-K63la/STAT3 pathway. CCR2 antagonism inhibits the infiltration of M2-type TAMs into tumor sites, thereby blocking their indirect induction of EMT in tumor cells	Clinical-stage	(139)
2-DG	Glycolysis inhibitors: acting as competitive analogs of glucose, these compounds are phosphorylated by hexokinase (HK2) to form 2-deoxy-D-glucose-6-phosphate. Since this compound cannot be further metabolized by G6P isomerase, it causes a metabolic block at the first step of glycolysis, thereby inhibiting the entire glycolytic pathway and reducing lactate production, which in turn indirectly lowers the overall level of protein lactation within the cell	Preclinical	(138)
C646	p300/CBP inhibitors: these selectively target the active site of the histone acetyltransferase p300/CBP and competitively inhibit the binding of acetyl-CoA to p300. p300 has been identified as a key “writer” of histone and non-histone acetylation; its inhibition reduces the acetylation levels of histones such as H3K18la and decreases acetylation modifications of non-histones such as ENSA	PDAC-specific	(135,136)
Curaxin	CTCF inhibitors: these target the zinc-finger domains of the transcription factor CTCF (specifically the DBR + SR2 domain), disrupting the interaction between CTCF and HNRNPU, thereby preventing the formation of the CTCF/HNRNPU/FLG-AS1 complex. Disruption of this complex inhibits the recruitment of EP300 to the IGF2BP2 promoter region, reduces H3K18la histone acetylation levels, downregulates IGF2BP2 expression, and ultimately suppresses M2 macrophage polarization and tumor progression	Preclinical	(137)
STM2457	METTL3 selective inhibitor: targets METTL3, the catalytic subunit of the m6A methyltransferase complex, competitively inhibits its binding to SAM, and blocks the establishment of m6A modification. This inhibition downregulates the m6A methylation level and expression of OAS3 mRNA, thereby suppressing M2d-type macrophage polarization and restoring CD8+ T cell function	Clinical-stage	(140)
DCA	PDK inhibitors: these agents target PDK (primarily acting on PDK1/2/3), inhibit PDK-mediated phosphorylation of the E1α subunit of PDH, activate PDH activity, promote the entry of pyruvate into the TCA cycle for oxidative metabolism, reduce lactate production, and thereby indirectly lower lactate levels	Clinical-stage	(123)

2-DG, 2-deoxy-D-glucose; DCA, dichloroacetic acid; EMT, epithelial-mesenchymal transition; G6P, glucose-6-phosphate; m⁶A, N⁶-methyladenosine; mRNA, messenger RNA; PDAC, pancreatic ductal adenocarcinoma; PDH, pyruvate dehydrogenase; PDK, pyruvate dehydrogenase kinase; SAM, S-adenosylmethionine; TCA, tricarboxylic acid; TAM, tumor-associated macrophage.

Neutralization of the acidic TME

Neutralizing TME acidity not only suppresses EMP but also enhances immunotherapy efficacy. Direct alkalinization with sodium bicarbonate (NaHCO₃) or calcium carbonate (CaCO₃) nanoparticles (141) reverses acid-driven immune suppression and chemoresistance: NaHCO₃ alleviates pH-mediated inhibition of T cells and NK cells while curtailing invasion and metastasis, and CaCO₃ nanoparticles maintain peritumoral pH within the physiological range, suppressing proliferation and migration (11).

PDAC harbors a uniquely acidic microenvironment (extracellular pH 6.5–6.8; endosomal/lysosomal pH 4.5–5.5 after uptake) (142,143), a gradient that provides the precise trigger for pH-responsive nanocarriers. pH-sensitive liposomes built on dioleoylphosphatidylethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) scaffolds remain stable at physiological pH 7.4 and undergo structural destabilization and membrane fusion upon endosomal acidification, enabling cytoplasmic drug release that bypasses efflux pumps (144); polyethylene glycol (PEG)-detachable (145), hyaluronic acid (HA)-modified (146), and amino-terminal fragment (ATF) peptide-modified liposomes (147) further optimize circulation half-life and active targeting (to CD44 and uPAR, respectively) to overcome the dense stromal barrier of PDAC. pH-responsive polymeric micelles such as PEG-b-PDPA (148) and PEG-b-polycarbonates (149) achieve ultra-selective drug release through protonation-driven micelle disassembly, with some formulations enabling co-delivery of ERK inhibitors and gemcitabine (150). Additional platforms-gradient TME-penetrating micelles (151), pH-switchable nanobombs (152), RG3-chitosan prodrug nanoparticles (153), and hybrid exosomes (154)-employ acid-labile linkages, hypoxia-responsive moieties, or carrier fusion to achieve charge reversal, sequential drug release, deep tumor penetration, and rapid payload deployment, significantly enriching cisplatin, paclitaxel, and gemcitabine concentrations within pancreatic tumors while minimizing systemic toxicity. A summary of acid-neutralizing and pH-responsive delivery strategies is provided in Table 4.

Table 4. Strategies for acid neutralization of the microenvironment in pancreatic cancer and related tumors.

Name/policy	Mechanism of action	Evidence type	Full title of the reference
NaHCO3	As an alkaline salt, it neutralizes lactate and other acidic metabolic byproducts in the TME through systemic or local administration, thereby raising the local pH level. This alleviates the inhibitory effects of acidity on immune cells (such as T cells and NK cells) and suppresses tumor cell invasion and metastasis	Preclinical	(141)
Acid-neutralizing CaCO3 nanoparticles	By leveraging the alkaline properties of CaCO3 nanoparticles, the acidic microenvironment at the tumor site is neutralized, maintaining the pH within the normal physiological range, thereby inhibiting the proliferation and migration of tumor cells	PDAC-specific	(141)
PSL/pPSL	Composed of DOPE and CHEMS, it remains stable at physiological pH (7.4) but undergoes structural destabilization in the acidic endosomal/lysosomal environment (pH 5.0–5.5), promoting membrane fusion and enabling “endosomal escape”, thereby efficiently releasing the drug into the cytoplasm and bypassing drug efflux pumps	Preclinical	(144)
CL-pPSL	PEG is attached to the surface of liposomes via an acid-cleavable hydrazone bond. Under acidic conditions, the hydrazone bond cleaves, causing the PEG to detach, thereby restoring the liposomes’ pH sensitivity and ability to escape endosomes while retaining their long circulation properties	Preclinical	(145)
HA-pSL	By covalently attaching HA to the surface of pSLs, active targeting is achieved through the high affinity between HA and the CD44 receptor. In the acidic endosomal environment, the liposomes become destabilized, enabling drug escape from the endosomes and release into the cytoplasm	Preclinical	(146)
ATF@Pt Lps	Using DOPE/CHEMS as the scaffold, the surface is modified with the uPAR-targeting peptide ATF and encapsulated with cisplatin (Pt). In an acidic TME (pH 6.5), the liposome structure disintegrates, enabling targeted drug release while simultaneously exerting antitumor and matrix-modulating effects	Preclinical	(147)
UPSM	PEG-b-polycarbonate block copolymer micelles with tertiary amine-modified side chains that undergo a sharp micelle-to-unimer phase transition within an extremely narrow pH range (<0.3 pH units). In acidic lysosomes (pH 4.5–5.5), rapid micelle dissociation triggers burst drug release; simultaneously, protonation of tertiary amines buffers lysosomal acidification, blocking lysosomal degradation and synergistically enhancing efficacy against KRAS mutant pancreatic cancer	Preclinical	(148)
PEG-DB/PEG-PY	PEG-b-polycarbonate block copolymers with side chains modified by tertiary amines having different pKa values (such as N,N'-dibutylethylenediamine with a pKa of 4.0 and 2-pyrrolidin-1-ylethylamine with a pKa of 5.4) undergo protonation at acidic pH, causing micelle dissociation and enabling pH-selective drug release	Preclinical	(149)
pH NPS	Composed of a PEG-b-polycarbonate block copolymer with side chains modified with N,N'-dibutyldiethylenediamine (pKa 4.0), this system co-delivers the ERK inhibitor (SCH772984) and GEM. In the acidic endosomal environment (pH 4.5), the micelles dissociate, enabling the synergistic release of the two drugs	Preclinical	(150)
T-Ni-PLP-P	Surface-modified Ni acts as a hypoxia-responsive group; in a hypoxic/acidic TME, it is reduced to aminoimidazole and protonated, causing a reversal of surface charge and enhancing penetration into deep tumor layers; simultaneously, PTX is released in a GSH-responsive manner via disulfide bonds	Preclinical	(151)
PDGL-GEM@CAP/CQ	The CAP shell dissolves in an acidic TME (pH 6.5), releasing CQ and PDGL-GEM, with PDGL-GEM subsequently penetrating deeper into the tumor. The CAP shell protects the core at physiological pH, enabling sequential release	Preclinical	(152)
pH-sensitive RG3-chitosan prodrug nanoparticles	Oxidized RG3 is conjugated to mPEG-CSO via a Schiff base bond; in the acidic TME (pH 5.5–6.8), the Schiff base bond hydrolyzes, releasing RG3, while the physically encapsulated Cel is also released as the nanoparticle disintegrates	Preclinical	(153)
pH-responsive hybrid exosomes (dasatinib-loaded hybrid exosomes)	Exosomes derived from pancreatic cancer cells were fused with PEGylated liposomes using a repeated freeze-thaw method to form hybrid exosomes. Under acidic pH conditions, the membrane fluidity of the hybrid exosomes increased, accelerating the drug release rate and enabling release responsive to the tumor’s acidic microenvironment	Preclinical	(154)

ATF, amino-terminal fragment; ATF@Pt Lps, ATF-peptide-modified pH-sensitive liposomes; CaCO₃, calcium carbonate; CAP, calcium-phosphate; Cel, celastrol; CHEMS, cholesteryl hemisuccinate; CL-pPSL, PEG-cleavable pH-sensitive liposomes; DOPE, dioleoylphosphatidylethanolamine; GEM, gemcitabine; GSH, glutathione; HA, hyaluronic acid; HA-pSL, HA-modified pH-sensitive liposomes; mPEG-CSO, methoxy polyethylene glycol-modified chitosan oligosaccharide; NaHCO₃, sodium bicarbonate; Ni, nitroimidazole; NK, natural killer; PDAC, pancreatic ductal adenocarcinoma; PDGL-GEM@CAP/CQ, pH-responsive size-switchable nanobombs; PEG, polyethylene glycol; PEG-DB/PEG-PY, pH-sensitive polymer micelles; pH NPs, pH-responsive nanoparticles; pPSL, PEGylated pH-sensitive liposomes; PSL, pH-sensitive liposomes; PTX, paclitaxel; T-Ni-PLP-P, gradient TME-promoted penetrating micelles; TME, tumor microenvironment; UPSM, ultra-pH-sensitive micelles.

Beyond direct acid neutralization, agents targeting other nodes in the TME show complementary potential. BLX-3030, a selective CDK9 inhibitor, induces cell-cycle arrest and apoptosis by downregulating N-MYC and C-MYC (121), whereas pimicotinib (ABSK021), an oral and highly selective CSF-1R inhibitor, remodels the immune microenvironment by blocking TAM survival and proliferation, converting “cold” tumors into “hot” tumors (122). Direct neutralization and intelligent pH-responsive delivery are mechanistically complementary: the former restores immune surveillance by reshaping TME acid-base balance, while the latter achieves efficient drug delivery through precise triggering. Their combined application may represent a key strategy for breaking through the therapeutic bottleneck in PDAC.

Clinical prediction and monitoring applications

Dysregulated lactate metabolism pervades the entire trajectory of PDAC initiation and progression, yielding a multi-dimensional clinical assessment framework that spans from serum enzymology to epigenetics, and from static staging to dynamic monitoring.

Serum LDH: a readily accessible window for prognostic assessment

Serum LDH is the most clinically accessible biomarker of the Warburg effect. Meta-analyses demonstrate that elevated pretreatment LDH is significantly associated with shortened overall survival in PDAC patients (155). A retrospective study of 96 Spanish patients with advanced or metastatic PDAC further established that the combined use of gamma-glutamyl transferase (GGT), LDH, and monocyte count serves as an independent positive prognostic factor in this disease (156). Yu et al. (157) demonstrated in 364 advanced PDAC patients receiving gemcitabine-based chemotherapy that LDH positively correlates with systemic inflammatory indices including neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR), indicating that LDH simultaneously reflects both metabolic tumor burden and the inflammatory microenvironment.

Lactate metabolism gene signatures: predictive models for treatment response

Transcriptomics-based lactate metabolism-related genes (LMRGs) signatures are transitioning from bioinformatics tools to clinical decision-support instruments. Huang et al. (158) constructed a seven-gene signature that predicts 1- to 5-year overall survival with area under the curve (AUC) values of 0.786–0.837; high-risk patients exhibited both reduced gemcitabine sensitivity and diminished immune effector cell infiltration, conferring dual predictive value for chemotherapy and immunotherapy response. The hypoxia-lactate metabolism-related genes (HLRGs) signature (SLC7A7, PYGL, HS3ST1, DDIT4, CYP27A1, ANKZF1, COL5A1) further revealed that high-risk patients harbor elevated tumor mutational burden and superior anti-PD-L1 therapeutic responses (159). These multi-gene models provide a molecular basis for individualized treatment selection beyond conventional tumor-node-metastasis (TNM) staging.

Histone lactylation: an epigenetic dimension for precision stratification

H3K18 lactylation (H3K18la) serves as a direct readout of metabolic–epigenetic coupling and is emerging as a core biomarker for PDAC precision stratification. A study has confirmed that tumor tissue H3K18la is significantly elevated compared with adjacent normal tissue and that its expression positively correlates with serum lactate, carbohydrate antigen 19-9 (CA19-9), and carcinoembryonic antigen (CEA) levels, yielding a diagnostic AUC of 0.848 for pancreatic cancer (81). A scoring model based on five lactylation-related genes constitutes an independent prognostic factor [hazard ratio (HR) =2.297] capable of predicting PDAC survival (136), with high-risk PDAC tumors displaying an immunosuppressive phenotype.

MCT4: from prognostic factor to companion diagnostic

MCT4/SLC16A3, the primary lactate efflux channel in glycolytic tumor cells, is significantly upregulated in PDAC and closely associated with tumor aggressiveness, lymph node metastasis, and shortened patient survival. A pan-cancer meta-analysis has further confirmed that high MCT4 expression correlates with unfavorable prognosis (160). Mechanistically, MCT4 promotes immune evasion through the HIF-1α-IL-8 axis (161), providing direct evidence for its utility as a companion diagnostic: the MCT4-high subgroup may derive preferential benefit from combined MCT1 inhibitors and immune checkpoint blockade.

Outlook

Although the central role of the lactate-EMP axis in PDAC has been well established, translating mechanistic insights into clinical applications continues to face several key challenges. Future research should prioritize the following directions.

1. Deciphering the complete landscape of lactylation modifications. Current studies have predominantly focused on H3K18la and a limited number of non-histone substrates. A systematic identification of global protein lactylation sites, along with their cognate writers, erasers, and readers across distinct stages of EMP, is urgently needed. The functional differences between L-lactylation and D-lactylation with respect to tissue specificity, signal transduction, and spatiotemporal dynamics warrant further elucidation using high-resolution mass spectrometry, precision gene editing, and site-specific mutagenesis. Such efforts will enable a paradigm shift from broad-spectrum inhibition of lactylation toward site-specific, target-restricted intervention.

2. Defining the metabolic switches governing EMP reversibility. The bidirectional transition between EMT and MET is critical for successful distant colonization by PDAC cells. However, the metabolic signals, lactate concentration thresholds, and lactylation levels that determine the direction of EMP plasticity remain largely undefined. Identifying the core nodal switches that operate at distinct phases—metastasis initiation, circulation, colonization, and post-colonization outgrowth—holds promise for achieving multi-point precision blockade of the metastatic cascade, rather than merely suppressing unidirectional EMT.

3. Overcoming metabolic plasticity and therapy resistance. The robust metabolic compensatory capacity of PDAC cells, mediated by the activation of alternative pathways such as glutaminolysis, fatty acid oxidation, and mitochondrial respiration, represents a major obstacle to single-agent metabolic therapy. Future strategies should pursue multi-node synergistic blockade, leveraging emerging technologies such as PROTACs, molecular glues, and dual-target inhibitors to enhance on-target efficacy and selectivity. Concurrently, integration of multi-omics data is required to establish predictive biomarkers of resistance that can guide adaptive therapeutic regimens.

4. Disrupting metabolic symbiosis and immunosuppression. The lactate-driven metabolic symbiosis network involving tumor cells, CAFs, neural cells, and immune cells constitutes a fundamental basis for drug resistance and immune evasion in PDAC. Key questions for future investigation include how to block lactate utilization by tumors without compromising normal tissue metabolism, and how to convert PDAC from a “cold” to a “hot” tumor through neutralization of the acidic TME, repolarization of TAMs, and restoration of CD8⁺ T cell function—thereby achieving synergistic efficacy between metabolic intervention and immunotherapy.

5. Advancing clinical translation and smart delivery systems. Current metabolic inhibitors are limited by insufficient target specificity, systemic toxicity, and poor tumor penetration. The development of intelligent nanocarriers featuring pH responsiveness, stroma-penetrating capability, and MCT-mediated active delivery may substantially enhance drug accumulation and deep penetration within tumor tissues. Concurrently, prospective clinical trials are needed to validate the utility of lactate-related biomarkers (serum lactate, MCT4, H3K18la) for prognostic stratification and treatment monitoring, thereby accelerating the integration of metabolism-targeted therapies into clinical guidelines.

Conclusions

In summary, lactate metabolism lies at the convergence of the most challenging biological features of PDAC—metastasis, drug resistance, and immune evasion. An increasingly refined understanding of the deeply coupled relationship between lactate metabolism and EMP not only redefines the molecular basis of tumor progression but also gives rise to an original class of therapeutic strategies that target the metabolic-epigenetic-phenotypic axis. As mechanistic dissection and technological innovation continue to synergize, targeting the lactate-EMP axis holds transformative potential to break the therapeutic deadlock in pancreatic cancer and improve long-term outcomes, while also providing a conceptual paradigm for other highly metastatic solid tumors.

Supplementary

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Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.