Research progress of lactate and lactylation modification in tumour immunotherapy

Introduction

Tumour immunotherapy has emerged as a groundbreaking and highly effective treatment modality, now firmly established as the fourth pillar in cancer treatment, alongside surgery, radiotherapy and chemotherapy. Its essence lies in the ability to overcome tumour immune evasion by activating or restoring the function of malfunctioning immune cells, setting it apart from traditional therapeutic approaches. The clinical triumph of immunotherapy, especially through immune checkpoint inhibitors (ICIs), has been nothing short of remarkable—offering long-term remission for certain tumours that remain resistant to other conventional therapies. This has led to a paradigm shift in cancer treatment, from simply suppressing the malignant proliferation and invasiveness of tumour cells to delving into the intricate and dynamic interplay between tumours and their surrounding microenvironment. However, the reality is far from simple. Due to both primary and acquired resistance, only a small subset of patients truly benefit from ICI therapy.1 Studies indicate that nearly 85% of cancer patients experience either inherent or developed resistance to ICIs,2 likely driven by the complexity of the tumour microenvironment (TME) and immune signalling pathways. This poses a substantial challenge, curbing the broader clinical applicability of immunotherapy. And yet, within this complexity lies a potential key to unlocking new therapeutic avenues—post-translational modifications (PTMs). These molecular modifications can, in diverse and profound ways, influence the efficacy of immunotherapy. By modulating immune checkpoints or reshaping the tumour immune microenvironment, PTMs hold the promise of amplifying the therapeutic impact of immunotherapy, providing a new layer of hope in the fight against cancer.

PTMs refer to the enzymatic processes that modify proteins after translation, altering their physicochemical properties to regulate protein activity, localisation, folding and interactions with other biomolecules. These modifications are at the core of many cellular signalling events. PTMs are ubiquitous, with a single protein potentially carrying multiple PTM sites. As a result, the combination of different PTMs on the same protein gives rise to a diverse array of protein forms.3 Over the years, significant efforts have been made to map the human cellular epigenome. Recent advancements in mass spectrometry techniques have unveiled a variety of novel epigenetic marks derived from cellular metabolites, leading to the creation of rich protein PTM maps, including lactylation.4 In 2019, Professor Zhao Yingming’s team at the University of Chicago made a groundbreaking discovery in Nature, reporting histone lactylation for the first time. This finding provided a new mechanism for how glycolysis-derived lactate exerts its effects. Subsequent studies confirmed that histone lactylation regulates macrophage polarisation (M1/M2), somatic reprogramming and tumourigenesis. Consequently, lactate in the TME may influence immune evasion by tumour cells through lactylation.5 However, research into lactylation is still in its early stages, and the precise regulatory mechanisms in various diseases and biological processes remain to be fully explored.

Lactate

Lactate, arguably the most famous metabolic byproduct, plays a surprisingly multifaceted role in mammalian metabolism. Lactate is not merely a byproduct but also a crucial player in cellular signalling and metabolism, participating in various essential processes, including glucose metabolism, fatty acid synthesis, redox balance and PTMs.6 Emerging research highlights lactate as one of the key metabolites in the TME. Lactate has the ability to regulate immune cell metabolism and inhibit their activation, proliferation and infiltration. As a signalling molecule, it exerts a pivotal influence on immune responses within tumour cells, directly impacting immune surveillance and evasion behaviours, which are central to the progression of cancer.7–9

Lactylation

Lactylation (Kla), an emerging lactate-driven PTM, has gained increasing attention in recent years. It occurs primarily on lysine residues of both histone and non-histone proteins.5 In histones, lactylation regulates gene expression by modulating chromatin structure and function. For instance, H3K56 lactylation in hepatocellular carcinoma (HCC) promotes the expression of stemness-related genes such as octamer-binding transcription factor 4, enhancing the properties of liver cancer stem cells.10 In non-histone proteins, lactylation significantly influences protein function and tumour progression. For instance, lactylation of adenylate kinase 2 enhances HCC proliferation and metastasis,10 while lactylation regulates carcinoembryonic antigen-related cell adhesion molecule 6 protein stability in colorectal cancer.11

The regulatory mechanism of lactylation involves three key steps under enzyme-dependent conditions: writing (Writers), reading (Readers) and erasing (Erasers). The ‘Writers’ belong to the histone acetyltransferase family, including p300, general control non-derepressible 5, lysine acetyltransferase (KAT)8 and KAT7.5 12–14 The ‘Erasers’ include histone deacetylase (HDAC)1–3, HDAC8 and Sirtuins 1–3, which remove lactylation marks.15 Recently, Brahma-related gene 1 was identified as a ‘Reader’ that specifically recognises H3K18la, leading to its accumulation at promoters of mesenchymal-epithelial transition (MET)-related genes.16

In addition to its effects on histones, lactylation also plays a role in DNA end resection and homologous recombination (HR), facilitating DNA damage repair and chemoresistance. This modification enhances the sensitivity of tumour cells to chemotherapy in patient-derived xenograft and organ models.17 18 Interestingly, lactate also has a previously unrecognised function in post-myocardial infarction fibrosis, where it promotes endothelial-to-mesenchymal transition, increasing cardiac fibrosis and exacerbating heart failure. In the TME, lactate acts as a natural inhibitor of p53. Aminoacyl-tRNA synthetase 1, a lactate sensor and lactyltransferase within cells, mediates the lactylation of p53 on lysine residues. This lactylation reduces p53’s ability to bind DNA, thus contributing to tumourigenesis.19 Subsequent research has confirmed that Kla is a key pathway through which lactate exerts its functions, impacting immune microenvironment regulation,20 tumour proliferation21 and metabolic regulation. Moreover, lactylation plays a crucial role in the efficacy of immunotherapy.22

The role of lactic acid and lactic acid modification in gynaecological tumours

In recent years, lactic acid and lactylation modifications have received increasing attention in the field of gynaecological oncology research. As a core product of tumour metabolic reprogramming, lactic acid not only promotes immune suppression and tumour progression in the microenvironment but its derived lactylation modifications have also been confirmed to directly regulate gene expression and cell functions. In gynaecological malignancies such as ovarian cancer and endometrial cancer, the level of lactylation modification is closely related to disease progression, chemotherapy resistance and immune evasion, gradually becoming a potential biomarker and therapeutic target.

In clinical studies of gynaecological tumours, drugs targeting lactic acid metabolism have shown potential efficacy. Research has indicated that lactic acid produced by ovarian cancer cells remodels tumour-associated macrophages (TAMs) into the M2 phenotype via the lactic acid sensing receptor G protein-coupled receptor 132. M2-type TAMs release C-C motif chemokine ligand (CCL)18, which in turn promotes tumour growth and metastasis. Additionally, lactic acid regulates the expression of CCL18 through H3K18 lactylation modifications, thus driving ovarian cancer progression.23 For example, the clinical trial NCT01791595 focuses on evaluating the efficacy of therapies targeting lactic acid metabolism in patients with ovarian cancer (http://clinicaltrials.gov/show/NCT01791595). In ovarian cancer, the concentration of lactic acid is closely related to tumour immune infiltration and chemotherapy resistance; lactic acid can inhibit the anti-tumour response of CD8+ T cells by upregulating endothelial cell-specific molecule 1, thereby promoting tumour growth and drug resistance.24 Lactate-derived histone H3K9 lactylation activates transcription of HR repair genes such as RAD51 recombinase and breast cancer type 2 susceptibility protein, thereby enhancing HR-mediated DNA repair and promoting platinum resistance in ovarian cancer.25 Accumulated lactate induces histone H4K12 lactylation, which activates a myelocytomatosis oncogene-dependent super-enhancer that upregulates RAD23 nucleotide excision repair protein a, enhancing DNA damage repair and driving niraparib resistance in ovarian cancer cells.26 Lactate promotes chemoresistance by directly binding X-ray repair cross-complementing protein 4 (XRCC4) and strengthening XRCC4–DNA ligase IV complex assembly, thereby enhancing non-homologous end joining DNA repair in ovarian cancer cells.27

In the PTM process of cervical cancer, L-lactic acid acts as a signalling molecule, promoting the transcriptional expression of discoidin, CUB and LCCL domain containing 1 (DCBLD1) by activating hypoxia-inducible factor (HIF)-1α. Furthermore, L-lactic acid directly enhances the lactylation modification of DCBLD1, especially the lactylation at lysine-172, a process that inhibits the ubiquitination of DCBLD1, stabilising its expression and promoting the development of cervical cancer.28 Tumour cell-derived lactate promotes histone lactylation (H3K18la) in TAMs, activating ARG1 expression and driving M2 polarisation to create an immunosuppressive TME.29 Additionally, in endometrial cancer, histone lactylation modifications regulate the expression of USP39, which activates the PI3K/AKT/HIF-1α signalling pathway through interaction with PGK1. This activation stimulates glycolysis, leading to increased lactic acid production, further enhancing histone lactylation modifications.30 The predictive value of lactylation modification biomarkers in the immunotherapy of endometrial cancer has also been validated. A risk scoring model for endometrial cancer constructed using lactylation-related genes (IGSF1, ZFHX4, SCGB2A1) can effectively predict the overall survival of patients, with the key gene IGSF1 regarded as a potential therapeutic target, its expression being associated with immune suppression and poor prognosis, demonstrating its potential in personalised treatment.31 This indicates that lactylation modifications not only affect the TME but may also serve as new biomarkers to guide clinical treatment (figure 1).

Lactate and lactylation modulate the tumour immune microenvironment

Lactate plays an indispensable role in the TME, and with the progressive unveiling of the lactylation modification mechanism, its functions within the TME are gaining increasing attention. Numerous studies have begun to explore the relationship between lactate, lactylation modifications and the TME.32 The Warburg effect, a hallmark of many solid tumours, leads to the accumulation of lactate, which has become a distinguishing feature of tumour metabolism. In this context, Tat-interactive protein 60 (TIP60), a lysine lactyltransferase, has been shown to promote lactylation of NBS1 at the K388 site. Research indicates that when ataxia-telangiectasia mutated (ATM) is depleted, the lactylation level of NBS1 at K388 decreases, suggesting that ATM plays a role in the lactylation process of NBS1. TIP60-mediated lactylation of Nijmegen breakage syndrome (NBS1) K388 is crucial for the assembly of the MRE11-RAD50-NBS1 (MRN) complex and efficient DNA repair. Thus, lactate, as a metabolic byproduct, helps to maintain genomic integrity and grants cancer cells the ability to survive in the face of genotoxic agents.33

Additionally, histone lactylation can influence gene expression in both tumour and immune cells, further regulating tumour progression and immune suppression. For instance, the glucose metabolism driven by protein kinase RNA-like endoplasmic reticulum kinase (PERK) and lactate produced by monocyte-derived macrophages (MDM) promotes histone lactylation, which in turn drives the expression of interleukin (IL)−10.34 This suppresses T cell activity and enhances the immunosuppressive functions of MDMs. More specifically, lactate-induced histone H3K18 lactylation upregulates the levels of CD39 and CD73 and increases the expression of chemokine receptors (CCR8) and their ligands CCL1 and CCL18, thus disturbing the balance between regulatory T cells (Tregs) and T helper 17 (Th17) cells, ultimately creating an immunosuppressive TME.35 Similarly, elevated lactate levels in the TME lead to increased lactylation of H3K18, which reduces IL-17A production by Th17 cells. Through reactive oxygen species (ROS)-mediated IL-2 secretion, this modification upregulates the expression of forkhead box P3, suppressing the pathogenicity of Th17 cells.36

The accumulation of lactate in the TME plays a critical role in maintaining its persistent immunosuppressive function, with the Kla-METTL3-m6A-JAK/STAT3 pathway paving the way for this effect. Specifically, histone lactylation induces the upregulation of myeloid erythroid factor 3 (METTL3), and the Kla of METTL3 enhances its ability to capture m6A-modified RNA, which is a key mechanism behind lactate-driven immune modulation.37 Moreover, lactate has been shown to inhibit vacuolar ATPase-mediated HIF2α stabilisation. Through the promotion of histone lactylation-induced epigenetic reprogramming, lactate further drives the polarisation of TAMs towards an M2/MHC-II low expression phenotype. This process is pivotal in immune evasion, as the shift in TAM polarisation supports an immunosuppressive TME, thereby facilitating tumour progression and resistance to immune surveillance.29 38

Conversely, some studies have suggested that Kla also plays a role in promoting immunity within the TME. For instance, high copper levels in gastric cancer (GC) tumours were shown to elevate glycolytic lactate production in the TME, which subsequently led to lactylation of METTL16 at K229. This lactylation of METTL16 enhances its ability to upregulate the mRNA and protein levels of ferredoxin 1 (FDX1) via m6A modification. The upregulated FDX1 then induces the lipolytic activity of dihydrolipoamide S-acetyltransferase in GC, and under high copper conditions in tumour cells, this mechanism leads to copper-induced apoptosis. This suggests that lactate, through the METTL16-Kla pathway, might play an important role in regulating cellular responses to metal-induced stress and apoptosis in tumours.39 On the other hand, liver kinase B1 (LKB1) induces lactate production and suppresses histone lactylation at H4K8 and H4K16, which further affects the transcriptional activity of specific protein 1. This alteration influences the expression of telomerase reverse transcriptase in non-small cell lung cancer cells, thereby promoting cellular senescence and telomerase regulation.40 Therefore, to fully understand the potential tumour-suppressive mechanisms of Kla, more extensive and thorough studies are required. Such investigations are crucial for evaluating Kla’s potential in cancer therapy and laying the groundwork for its future clinical applications. These findings collectively highlight the diverse functions of lactate and lactylation across different tumour types.

Research progress of lactic acid targeting inhibitors

The accumulation of lactic acid in the TME can lead to acidification and immune suppression. Inhibitors targeting lactic acid metabolic pathways, such as the selective lactate dehydrogenase (LDH)-A inhibitor FX11, can enhance anti-tumour immunity by inhibiting lactic acid production and specifically stabilising cyclic GMP-AMP synthase protein in a lung adenocarcinoma model.41 Monocarboxylate transporter (MCT) inhibitors target the lactic acid transporter MCT to block the efflux of intracellular lactic acid, interfere with tumour metabolism and help improve the pH of the microenvironment and immune suppression state, thereby creating a more favourable condition for anti-tumour immune responses. Notably, key members like MCT1 and MCT4 inhibitors, such as AZD3965, are also research hotspots.42 Preclinical trials show that the MCT1 inhibitor AZD3965 combined with anti-PD-1 therapy can reduce the secretion of lactic acid into the TME and decrease the infiltration of exhausted PD-1+Tim-3+ T cells in solid tumours, thereby improving anti-tumour immunity.43 Given this, specific knockout of MCT1 on Tregs, combined with anti-PD-1 therapy, helps suppress tumour growth; this suggests that pharmacologically inhibiting MCT1 may play a dual role in suppressing lactic acid secretion.44 Clinical trials indicate that the MCT inhibitor AZD3965 shows potential efficacy in solid tumour patients, especially when used in combination with ICIs (such as PD-1 inhibitors). Such combination strategies significantly improve the objective response rate in patients. The mechanism of synergy involves altering tumour metabolic characteristics to enhance the immune system’s recognition, while lactic acid depletion not only alleviates immune suppression in the microenvironment but may also promote immune cell infiltration, thereby strengthening the overall anti-tumour immune response.42

Interestingly, nanomaterials have attracted attention for their targeting properties, biocompatibility and functionality, showing great potential in diagnosis and treatment, overcoming deficiencies such as low delivery efficiency and poor tumour permeability associated with traditional tumour immunotherapies.45 46 Notably, some studies indicate that FX-11 encapsulated in PEG-Ce6 nanoparticles (FX-11@PEG-Ce6) can alleviate the acidity of the TME, aiding in the elimination of tumour cells. Meanwhile, FX-11@PEG-Ce6 also significantly enhances the efficacy of α-PD-1 and demonstrates good biocompatibility.47 Additionally, using biocompatible mesoporous dopamine (mPDA) as a carrier, a Syr-loaded nanoparticle delivery system (Syr@mPDA@CP) has been constructed. When targeting tumour tissue, the released Syr can significantly inhibit lactic acid efflux, leading to intracellular lactic acid accumulation. It can significantly reduce the expression of MCT4 in tumour cells, blocking lactic acid efflux and causing intracellular lactic acid accumulation and extracellular lactic acid reduction.48 Moreover, studies have used microfluidic technology to prepare AZD3965 loaded inside the ultra-pH-sensitive (AZD-UPS) nanoparticles with ultra-high pH sensitivity, capable of targeted delivery of the MCT1 inhibitor AZD3965, and rapidly releasing the drug in the acidic TME to achieve precise inhibition of lactic acid transport. This nanoparticle, when combined with anti-PD-1 therapy, results in increased T cell infiltration and decreased T cell exhaustion, successfully reversing lactic acid-mediated immune suppression.49

Progress in combination therapy of immune checkpoint inhibitors and targeting the lactate-lactylation pathway

Abnormal lactate levels affect the differentiation, metabolism and function of tumour-infiltrating immune cells through multiple pathways. A deeper understanding of lactate and its lactylation effects, particularly in immune modulation, has spurred the development of new therapeutic targets aimed at improving cancer immunotherapy. The exploration of how lactate and lactylation modulate immune responses is opening novel avenues for enhancing the efficacy of immune therapies. Given the distinct mechanisms of action of various ICIs combining multiple ICIs has become a key focus of research. These inhibitors act in different ‘spaces’ and ‘times’, complementing each other to enhance therapeutic effects and reduce resistance. Therefore, understanding how the suppression of lactate and lactate production will interact with a range of immunotherapy strategies will be crucial.

Signal transducer and activator of transcription 5 (STAT5) enhances glycolysis, driving the accumulation of lactate, which in turn increases histone lactylation at the PD-L1 promoter. This modification leads to the transcriptional activation of PD-L1, further impairing the activation of CD8+ T cells. Interestingly, inhibiting the interaction between PD-1 and PD-L1 can re-activate CD8+ T cells in acute myeloid leukaemia (AML) with high STAT5 expression. In this context, lactate induced by STAT5 may serve as a novel biomarker for immune therapy in AML. This underscores the potential of lactate as a regulator of immune escape in cancer, offering a new angle for improving immunotherapeutic strategies.50

The inhibition of PERK has been shown to alter ATP and lactate production in glioma cells, while concurrently activating transcription factor 4 in CD4+ T cells to enhance glycolysis. These findings highlight the pivotal role of PERK-driven Kla in modulating the function of MDMs, suggesting that targeting the immune-suppressive behaviour of MDMs could provide a therapeutic strategy in cancer treatment.20 By influencing MDMs, this pathway presents new opportunities for immunotherapy in glioma and potentially other malignancies, shifting the balance toward immune activation. Additionally, oxalate has emerged as a potential inhibitor of lactate production, suppressing histone H3K18 lactylation, and downregulating the activity of gene promoters such as CD39, CD73 and CCR8. This modulation alters the immune-suppressive TME, promoting immune activation and offering a promising strategy for overcoming tumour immune evasion. In particular, oxalate may serve as a potential enhancer of chimeric antigen receptor T cell function in glioblastoma therapy.21 Lactic acid reshapes the tumour immune environment by promoting the polarisation of biphasic macrophages, while also promoting the proliferation of Tregs through the transforming growth factor-β (TGF-β)/IL-10 pathway and activating the cytotoxic T-lymphocyte-associated protein 4 immune checkpoint, thereby consolidating the immunosuppressive microenvironment.51

Elevated levels of LDH in both blood and the TME have been linked to poor prognosis in cancer patients, serving as a useful biomarker for tumour staging, particularly in melanoma.52 High LDH levels in melanoma patients are associated with a poor response to anti-PD-1 immunotherapy.53 54 In a mouse melanoma model, blocking LDH-A using ICIs enhanced antitumour immunity by increasing the production of interferon-γ and granzyme B (GZMB) in natural killer (NK) cells and CD8+ T cells.55 Another study revealed that lactate can catalyse the lactylation of the lysine residue at position K72 in moesin (MOESIN), a membrane-associated protein. This modification enhances MOESIN’s interaction with TGF-β receptor I and the downstream SMAD3 signalling pathway, thus regulating the generation of regulatory T cells. The combination of LDH inhibitors with anti-PD-1 antibodies further potentiates antitumour immune responses, highlighting lactate’s role in immune modulation within the TME and its potential as a therapeutic target.44

Conclusion

Lactate and lactylation have recently emerged as critical links connecting tumour metabolic reprogramming with immune regulation. Increasing evidence demonstrates that lactate is not merely a metabolic byproduct but also a key signalling molecule capable of reshaping the tumour immune microenvironment through metabolic, epigenetic and transcriptional mechanisms. Through these processes, lactate influences the differentiation, activation and function of various immune cells, including macrophages, regulatory T cells and CD8+ T cells, thereby promoting immune evasion and tumour progression.

As a newly identified PTM, lactylation further expands the biological influence of lactate. By regulating gene transcription, protein stability and intracellular signalling pathways, lactylation participates in multiple aspects of tumour development, including proliferation, metastasis, drug resistance and immune suppression. Importantly, accumulating studies indicate that the lactate-lactylation axis plays a crucial role in determining the responsiveness of tumours to ICIs and other immunotherapeutic strategies.

Taken together, current research highlights the lactate-lactylation pathway as a central regulatory hub linking tumour metabolism, epigenetic modification, and immune modulation. A deeper understanding of this metabolic-epigenetic network will provide important insights into the mechanisms underlying tumour immune escape and therapeutic resistance. Moreover, targeting lactate metabolism and lactylation-related processes may represent a promising strategy for improving the efficacy of cancer immunotherapy and expanding the clinical benefits of immunotherapeutic approaches.

Prospects

Future cancer immunotherapy is expected to benefit substantially from strategies targeting lactate metabolism and lactylation. Inhibitors of lactic acid production, lactate transporters and lactylation-related enzymes hold great promise in reversing immune suppression and improving the efficacy of ICIs. Combination therapies integrating metabolic intervention with immunotherapy may overcome inherent and acquired resistance, expanding the applicability of ICIs to a broader patient population. Moreover, nanomedicine-based delivery systems offer new opportunities for precise metabolic modulation within the TME.

Despite these advances, several key issues remain to be addressed, including the cell-type specificity of lactylation, its temporal dynamics, and its interactions with other epigenetic modifications. Future research should aim to establish lactylation-based biomarkers to guide treatment selection and to develop more potent, clinically safe agents that modulate lactate signalling. With deeper mechanistic understanding and technological innovation, targeting the lactate–lactylation axis is expected to become a valuable component of next-generation cancer immunotherapy.