Mechanism and application of lactylation in cancers

Abstract

Lactate is a crucial product of cancer metabolism, creating an acidic environment that supports cancer growth and acts as a substrate for lactylation. Lactylation, a newly discovered epigenetic modification, plays a vital role in cancer cell signaling, metabolic reprogramming, immune response, and other functions. This review explores the regulation of lactylation, summarizes recent research on its role in cancers, and highlights its application in cancer drug resistance and immunotherapy. These insights aim to provide new avenues for targeting lactylation in cancer therapy.

Introduction

Cancer cells produce large amounts of lactate through glycolysis even when oxygen is sufficient, known as the Warburg effect [1]. The accumulation of lactate in the cancer microenvironment provides a favorable environment for angiogenesis, invasion and immune escape [2]. For a long time, lactate was considered a metabolic ‘waste product’ until the lactate shuttle hypothesis was proposed. Lactate shuttle refers to the fact that lactate can be transferred between glycolysis and gluconeogenesis and function as a signaling molecule in cells [3, 4]. This proves lactate is not only a metabolic ‘waste’, but also an important metabolic intermediate and signaling molecule.

In 2019, Professor Zhao Yingming’s team discovered a new post-translational modification method through mass spectrometry, lysine lactylation (Kla), in which lactate is involved in regulating cancer progression as a substrate. Lactylation refers to the process of attaching the lactyl group provided by lactyl CoA to the ε-amino group of the protein lysine residue. Recent evidence suggests that alanyl-tRNA synthetase 1 (AARS1) uses lactic acid directly as a substrate instead of lactyl CoA [5]. In this work, researchers proposed that lactate-driven histone lactylation induces target gene transcription [6] (Fig. 1A). In addition, recent studies have also shown that histone lactylation can regulate chromatin remodeling [7], stimulate neovascularization [8], promote repair gene transcription [9], regulate macrophages [10, 11], and control muscle structure and function [12] (Fig. 1B–F). Those new modifications become an important part of lactate function linking histone lactylation with cell metabolism and gene regulation, and provide a new way to explore epigenetic modification. As research progresses, it has been discovered that not only histones but also non-histone proteins can undergo and be regulated by lactylation [13]. Non-histone lactylation mainly regulates protein stability, protein interaction and downstream target gene expression [14]. As one of the human non-histone proteins widely involved in post-translational modification (PTM), Kla is a universal modification existing in the outside of histone proteins and applying in their transcriptional regulation.

Fig. 1.

Application of lactylation in cancer. A: Lactylation induces transcription of target genes. B: Lactylation regulates chromatin remodeling. C: Lactylation stimulates neoangiogenesis. D: Lactylation promotes repair genes transcription. E: Lactylation modulates macrophages. F: Lactylation controls muscle structure and function

An expanding body of experimental evidence indicates that lactylation contributes to tumorigenesis. This phenomenon opens up a novel domain for the investigation of protein PTMs and signals a fresh direction for lactic acid research within the realms of cancer and immunity. Nevertheless, the role of lactylation in tumorigenesis and development remains inadequately understood. Here, based on current studies on the progression of lactylation in cancers, we summarize the potential cancer treatment targets of lactylation, explore the potential avenues for targeting lactylation in cancer treatment, and propose that the combined application of regulation of intracellular lactylation and immunotherapy is promising to become a more effective cancer treatment strategy.

Regulation of lactylation

Influencing lactylation by regulating lactate production

Lactate is the product of glycolysis. Regulation of glycolysis can affect lactate production and then lactylation [15]. Current studies have shown that regulation of the expression of important enzymes during glycolysis can mediate lactate generation and affect lactylation, including glucose transporter 3 (GLUT3), lactate dehydrogenase A (LDHA) and LDHB, and aldolase A (ALDOA). Yang et al. found through experiments that the high expression of GLUT3 in gastric cancer cells can increase the uptake of glucose, resulting in intracellular lactate accumulation to promote lactylation [16]. Moreover, lactylation of glycolytic enzymes can change the expression of the enzyme and regulate the production of lactate to affect the lactylation of cells [8]. In addition, studies have shown that ALDOA K147 exhibits A high abundance of lactylation that can reduce the activity of its own enzyme. Basis on this, the researchers also proposed a negative feedback loop: when the glycolytic pathway was over-activated and too much lactate was produced, the activity of the upstream enzyme ALDOA would be inhibited by lactylation, resulting in the inhibition of the glycolytic process and the reduction of lactate level to maintain cell homeostasis [13]. This view was also confirmed by Jiang et al. that excessive lactate production in non-small cell lung cancer (NSCLC) lead to decreased glycolysis levels and thus reduced histone lactylation [17]. Furthermore, non-coding RNA can also participate in the regulation of histone lactylation. CircXRN2 affects the glycolysis process by regulating the Hippo signaling pathway, and then inhibits the production of lactate and exerts the anticancer function of histone H3 K18 lactylation [18]. The above studies indicate that the lactylation is regulated by the glycolysis process (Fig. 2A).

Fig. 2.

Regulation of lactylation. A: GLUT3 overexpression significantly decreased levels of LDHA, L-lactic acid, H3 K9, H3 K18, and H3 K56. When the glycolysis pathway is over-activated and too much lactic acid is produced, the activity of the upstream enzyme ALDOA will be inhibited by lactylation, inhibiting glycolysis. NUSAP1 up-regulated LDHA promoted lactylation and inhibited the protein degradation of NUSAP1. HIF-1α lactate modifies HIF-1α protein, while HIF-1α promotes glucose uptake and glycolysis. B: EP300 inhibited histone lactylation and down-regulated YTHDF2 expression. CBP inhibits lactylation at MRE11 K673. p300/CBP promotes the lactylation of HMGB1. Histone deacetylase SIRT2 inhibits the lactylation of METTL16. SIRT3 inhibits the lactylation of cyclin CCNE2. SIRT6 acts as a cancer suppressor by regulating lactate production

Influencing lactylation by regulating lactylation enzymes

Based on the present study,"Writer"and"Eraser"enzymes are involved in lactylation [19]. The role of the"writer"enzyme is to transfer the lactoacyl group to the lysine protein residue to form a lactylation. The"Eraser"enzyme removes lactoacyl groups from protein lysine residues to prevent the lasting reactions of the lactylation and maintain the microenvironment balance [20]. It has been reported that histone acetyltransferases (HATs) can act as"reader"enzymes to regulate the lactylation process, and the identified lysine lactyltransferases include P300/CBP, lactate Coenzyme A transferase (ALCTs), alanyl-tRNA synthetase 1(AARS1), mitochondrial alanyl-tRNA synthetase (AARS2), etc. [21–24]. YU et al. found that the degree of EP300 aggregation near histones can affect the level of histone lactylation [25]. Since the lactylation of HMGB1 is dependent on p300/CBP [19], CBP also regulates the lactylation in the MRE11 K673 site of homologous recombinant protein (HR) [26]. In addition to these enzymes, acyltransferases such as KAT5/TIP60 are also found to be involved in the regulation of lactylation [27]. Current studies have shown that the"Eraser"enzymes involved in lactylation are deacetylases Sirtuin family and histone deacetylases (HDACs) [28, 29]. SIRT2 has been shown to inhibit the lactylation of METTL16 in gastric cancer cells, and other studies have confirmed that SIRT2 also acts as acyltransferases to remove histone lactylation [26, 30]. SIRT3, another member of the SIRT family, can inhibit cell apoptosis induced by lactylation of cyclin CCNE2 [31]. HDAC2 acts as an eraser of histone lactonization in pancreatic ductal adenocarcinoma (PDAC) [32]. This suggests that more enzymes have not been reported and need further study (Fig. 2B).

Other modulations of lactylation

Conversely, it has been observed that certain lactylation events are not subject to enzymatic regulation. Gaffney et al. reported on a non-enzymatic lactylation process, wherein the lactoyl transfer of lactoylglutathione (LGSH) lactide to protein lysine residues resulting in the formation of a ‘lactoyl’ modification [33]. This discovery enhances our understanding of lactylation and opens up a new avenue for studying lactylation.

Lactylation and cancer progression

At present, many studies have found that lactylation plays an indispensable role in tumor. Histone lactylation can regulate the expression of downstream target genes to promote or suppress cancer. The lactylation on non-histone proteins affects its role in cancer mainly by changing the stability of the lactylation’s protein. Based on previous reports, it is suggested that there are many unexplained mechanisms of the role of lactylation in cancer development.

Lactylation regulates the expression of target genes

Histones include core histones (H2 A, H2B, H3 and H4) and junction histones (H1 and H5). Histone lactylation refers to the covalent modifications by which different acyl groups can be atta ched to amino acid residues on histones. Due to the various covalent modification forces, the acyl groups have an effect on how tightly histones and DNA are bound, resulting in transcriptional activation or gene silencing [20]. In 2021, Yu et al. found that lactylation on histone H3 can promote the expression of downstream target gene YTHDF2 and thus promote the development of melanoma [25]. This study is the first time to demonstrate that lactylation can promote oncogene expression and participate in cancer development. Histone H3 is the most extensively studied histone in lactylation, particularly at lysine residue 18 (H3 K18). As significantly enriched in the gene promoter region, The lactylation of histone H3 lysine residue 18 (H3 K18) can promote the expression of oncogenes in cancer cells to participate in the occurrence and development of cancers [34]. Studies have demonstrated that histone lactylation can facilitate downstream gene expression in colorectal cancer cells and breast cancer cells. For instance, GPR37 can activate the Hippo pathway to enhance glycolysis and induce histone H3 K18 lactylation, thereby promoting the expression of downstream target genes CXCL1 and CXCL5, leading to liver metastasis in colorectal cancer [35]. Furthermore, Madhura et al. discovered that H3 K18 lactylation promotes c-Myc-induced proliferation of breast cancer cells [36]. Yang et al. also provided evidence that histone lactylation drives the progression of renal clear cell carcinoma (ccRCC) by activating transcription of platelet-derived growth factor receptor β (PDGFRβ), while PDGFRβ signaling has been shown to stimulate histone lactylation as to forming a positive feedback loop in ccRCC [37]. Additionally, it has been observed that histone H3 lactylation increases the expression of non-coding RNA LINC01127 in glioblastoma (GBM), inducing cellular self-renewal [38]. Nevertheless, lactylation of histone H3 has also been demonstrated to inhibit the expression of target genes. Zheng et al. confirmed through CHIP-QPCR that lactylation on H3 K14 and H3 K18 could enrich and repress transcription in the SLC25 A29 promoter region, thereby impacting the proliferation, migration, and apoptosis of lung adenocarcinoma endothelial cells [39]. The translation initiation factor BZW2 promotes the malignant progression of LUAD by facilitating glycolysis-mediated production of histone H3 K18 lactylation, providing a theoretical basis for targeted treatment of LUAD focusing on glycolysis and Kla [40]. Moreover, besides histone H3, lactylation on other histones can also regulate downstream target gene expression. For instance, lactic modification on histone H4 can enhance the expression of glycolytic-related genes HK-1 and IDH3G to promote NSCLC proliferation and migration [41]. Lactylation at H4 K12 can activate multiple genes essential for thyroid undifferentiated carcinoma (ATC) proliferation [42], also it can activate CCNB1 transcription while accelerating DNA replication and cell cycle progression [43]. Furthermore, increased lactylation at histone H4 K8 can upregulate non-coding RNA LINC00152 transcription to facilitate colorectal cancer invasion and migration [44]. In conclusion, lactylation histones can regulate downstream target gene expression and influence cancer malignancy (Fig. 3). In addition, the researchers also discovered that lactylation can effectively regulate proprioceptive transcription. Lactylation of CENPA K124 significantly enhances its transcriptional activation in hepatocellular carcinoma (HCC) cells and promotes the progression of HCC by primarily attributed to an augmented chromatin binding [45].

Fig. 3.

Histone lactylation and cancer progression. A: Lactylation of H3 K18 promotes the expression of oncogene YTHDF2 in cancer cells. B: GPR37 enhances glycolysis and histone H3 K18 lactylation through the Hippo pathway, promoting liver metastasis of colorectal cancer. C: H3 K18 lactylation promotes c-Myc expression to promote the proliferation of breast cancer cells. D: DML can inhibit the lactylation of H3 K9 and K56 sites and thus inhibit liver cancer. RJA inhibits the development of HCC by interfering with lactylation and inhibiting lactylation at H3 K9 and H3 K14 sites. E: FGS inhibits non-small cell lung cancer by targeting H3 histone lactylation. F: Lactylation on H3 K14 and H3 K18 inhibited SLC25 A29 transcription and affected the proliferation, migration and apoptosis of lung adenocarcinoma endothelial cells. G: Histone H4 lactylation can promote the expression of glycolytic-related genes and promote the proliferation and migration of NSCLC. H: Lactylation of H4 K12 activates the expression of multiple genes necessary for the proliferation of undifferentiated thyroid carcinoma (ATC), and the blocking of cellular lactylation mechanisms in combination with BRAFV600E inhibitors can synergistically inhibit the malignant progression of thyroid cancer. I: The AKR1B10 promotes glycolysis and stimulates H4 K12 la to activate CCNB1 transcription. While silencing AKR1B10 increases the sensitivity of the drug PEM in vitro and in vivo. J: Histone lactylation promotes the progression of ccRCC by activating the transcription of platelet-derived growth factor receptor β (PDGFRβ), while PDGFRβ signal transduction stimulates histone lactylation. K: The combination of histone lactylation and PDGFRβ significantly enhanced the therapeutic effect. CircXRN2 affects the glycolysis process by regulating the Hippo signaling pathway, inhibits lactate production and affects the lactylation of histone H3 K18. L: Increased lactylation of histone H4 K8 upregulates transcription of LINC00152 and promotes invasion and migration of colorectal cancer. M: Lactylation of histone H3 can increase the expression of LINC01127, leading to the promotion of GBM cell self-renewal

Lactylation regulates protein expression

With further research, non-histone lactylation can regulate the expression of modified proteins and impact the malignant progression of cancers. Lactylation on non-histone proteins regulates protein function through steric hindrance, conformational changes, and charge neutralization caused by modifications, ultimately influencing protein function by affecting molecular interactions, stability, subcellular localization, and enzyme activity.

Yang et al. conducted proteomic and lactylation omics analysis to sequence HCC and nearby liver tissue, resulting in the identification of 9,256 non-histone lactylation sites [46]. This finding suggests a significant role of non-histone lactylation in the progression of HCC. The reduction in c-myc lactylation was found to decrease its protein stability and expression, consequently reducing the viability and dryness of hypoxic HCC cells [47]. These results further emphasize the crucial involvement of non-histone proteins in hepatocellular carcinoma progression. Similarly, Feng et al., through website analysis, screened potential target genes for non-histone lactylation and proposed that lactylation holds high prognostic value in cutaneous melanoma (CM), based on prognostic analysis [48]. In addition, non-histone lactylation has also been found in prostate cancer, colorectal cancer, glioblastoma, etc., and is involved in the regulation of tumor evil biological behavior. For example, Luo et al. found that lactylation of hypoxia-inducing factor HIF-1α in prostate cancer cells stabilizes its protein HIF-1α itself, which in turn affects downstream gene transcription [49]. In colorectal cancer, ALDOB mediates the formation of lactate and increases the lacylation of CEA cell adhesion moleculin-6 (CEACAM6) to enhance the stability of CEACAM6 protein and to promote the malignant progression of colorectal cancer [50]. Moreover, LDHA can bind to and enhance the lactylation of vascular endothelial growth factor receptor 2 (VEGFR2) and VE-cadherin (VE-Cadherin), leading to a increased protein expression level. These two molecules serve as markers of angiogenesis simulation (VM) and promote the proliferation, migration, and invasion of GBM cells [51]. Then nucleolar and spindle-associated protein 1(NUSAP1) promotes its own lactylation by upregulating LDHA-mediated glycolysis in PDAC, thereby inhibiting protein degradation and accelerating malignant progression [52]. Through multi-omics analysis combined with in vitro and in vivo validation, Chen et al. demonstrated that lactylation at K70 site of APO protein APOC2 enhanced its stability, extracellular lipolysis to generate free fatty acids, cancer metastasis, and immunotherapy resistance [53]. These studies provide evidence that non-histone lactylation can alter protein stability to exert its function (Fig. 4).

Fig. 4.

Non-histone lactylation and cancer progression. A: The lactylation of CENP at lysine 124 (K124) promotes the activation of CENPA and promotes the proliferation of HCC cells and cancer growth. B: GPC3 knockdown decreased c-myc lactylation, further reducing the protein stability of c-myc and cell viability and dryness of HCC cells. C: Lactylation of hypoxia-inducing factor HIF-1α in prostate cancer cells can stabilize the protein HIF-1α itself, thereby promoting the transcription of downstream genes. D: Lactylation of CALML5 is associated with cutaneous melanoma. E: The translation initiation factor BZW2 promotes the malignant progression of LUAD by promoting glycosylation-mediated lactate production and lactylation of IDH3G. F: Aldob-mediated lactic acid production enhances the stability of CEACAM6 protein by increasing CEACAM6 Kla and promotes the malignant progression of colorectal cancer. G: LDHA binds and promotes the lactylation of VEGFR2 and VE-cadherin, and increases their protein expression. These two molecules act as markers of angiogenesis simulation VM to promote the proliferation, migration, and invasion of GBM cells

Interactions between lactylation and other post-translational modifications in cancer progression

Current research has confirmed that various post-translational modifications (PTMs), including acetylation, ubiquitination, butyrylation, and crotonylation, can interact with lactylation and collectively contribute to tumor initiation and progression. These modifications may not only exert synergistic effects but also antagonize each other in certain regulatory mechanisms [54, 55]. For instance, Sirtuin 3 (SIRT3), a deacetylase, downregulation leads to increased acetylation of the pyruvate dehydrogenase E1 component subunit α (PDHA1), resulting in its inactivation and subsequent lactate accumulation. Additionally, lactate can induce acute kidney injury by promoting the lactylation of mitochondrial fission protein 1 (Fis1) at lysine 20 (Fis1 K20 la) [56]. Similarly, lactylation can regulate the acetylation of high mobility group protein B1 (HMGB1), highlighting the potential role of lactylation in epigenetic regulation [57]. Notably, a potential link exists between lactylation and butyrylation Studies have shown that butyrate enhances overall protein lactylation levels in HeLa cells and may prevent the removal of lactylation by inhibiting multiple histone deacetylases (HDACs). Furthermore, as both occurring on lysine residues, lactylation and ubiquitination may compete for modification at the same site. For example, lactylation at lysine 91 (K91) of TFEB inhibits its interaction with the E3 ubiquitin ligase WWP2, thereby reducing TFEB ubiquitination and preventing its degradation [58]. Similarly, Meng et al. found that lactylation of DCBLD1 stabilized its protein levels by suppressing its ubiquitination [55]. Moreover, enzymes involved in lactylation not only regulate this modification but also influence acetylation to further support the hypothesis where lactylation and acetylation may compete for the same amino acid residues [55]. For instance, Rho et al. reported that lactylation and acetylation of H3 K18 exhibited competitive modification during liver fibrosis, collectively regulating the pathological process [59]. Although current studies have revealed interactions between lactylation and various PTMs, whether lactylation coordinates with broader modification networks to regulate tumor initiation and progression remains to be elucidated. Moreover, lactylation may enhance its role in epigenetics by influencing RNA modifications. In gastric cancer research, elevated copper ion levels were found to promote the lactylation of the non-histone protein METTL2-K16, thereby regulating the m6 A modification of its downstream target genes and accelerating gastric cancer malignancy [60]. Additionally, N1-methyladenosine (m1 A) RNA modification plays a crucial role in RNA metabolism. Research by Gu et al. demonstrated that increased histone lactylation in melanoma cells enhanced ALKBH3 expression, facilitating the removal of m1 A methylation from the target gene SP100 A [41].

Challenges in lactylation research

As an emerging post-translational modification (PTM), lactylation still faces several challenges in elucidating its biological functions. These challenges mainly include the following aspects.

First, due to the high activity of anaerobic glycolysis in cancer cells, a large amount of lactate accumulates within the cells. The supplementation of exogenous lactate can further increase intracellular lactate and pyruvate levels, thereby altering the redox state and leading to an imbalance of NAD +/NADH ratio. Additionally, excessive lactate accumulation disrupts the acid–base balance of the immune microenvironment, promoting immune evasion. However, the precise role of lactylation in immune regulation remains unclear. In experimental studies, exogenous lactate treatment is commonly used to assess the function of lactylation; nevertheless, the lactate concentration applied in these experiments often far exceeds the physiological levels found in cancer cells, potentially exaggerating the effects of lactylation and limiting the physiological relevance of the findings.

Second, the specific regulatory mechanisms of lactylation remain incompletely understood. Some deacetylases as HDAC and SIRT1, have been implicated in lactylation, no specific enzyme responsible for catalyzing lactylation has been identified. Moreover, changes in the expression of lactate dehydrogenases LDHA and LDHB not only affect lactate levels but also mediate other critical biological processes, including redox homeostasis [4], lipid metabolism [61], mitochondrial respiration [62], cell signaling [63], and tumor immune suppression [64]. For instance, LDHA inhibition can alter the NAD +/NADH ratio, thereby modulating the redox state and reducing reactive oxygen species (ROS) accumulation. Studies have shown that LDHA activation facilitates immune evasion in hepatitis B virus (HBV) infection [65], while increased LDHA levels can lower lactate concentrations to attenuate the anti-tumor immune response in colorectal cancer [66].

Additionally, compared to directly targeting LDHA, metabolic interventions that inhibit upstream glycolytic regulators may have broader and less predictable biological effects. For example, inhibiting glyceraldehyde-3-phosphate dehydrogenase (GAPDH) can modulate immune responses [67], whereas reducing 2-hydroxyglutarate (2-HG) levels can suppress immune dysregulation [68]. Therefore, precisely controlling the impact of lactylation on cellular biological functions remains a major challenge in this field. To overcome these difficulties, future research should focus on optimizing detection technologies for lactylation on enhancing specificity and sensitivity. Additionally, a comprehensive understanding of the intricate role of lactylation in cancer metabolism is required to elucidate its broad influence on various biological processes, ultimately providing more precise strategies for lactylation-targeted interventions.

Lactylation cancer therapy

Increasingly, researchers are investigating the mechanisms of lactylation in cancers and exploring drug therapies that target lactylation sites. By focusing on these specific sites, they aim to develop new strategies for cancer treatment. This approach holds promise for improving therapeutic outcomes by potentially overcoming drug resistance and modulating the tumor microenvironment [69, 70]. It was found that methylated silanaldehyde (DML) can inhibit the lactylation of H3 K9 and H3 K56 sites and thus achieve the purpose of anti-liver cancer [71]. In addition, Royal Jelly Acid (RJA) inhibits the development of HCC by interfering with lactate production and inhibiting lactylation at H3 K9 and H3 K14 sites [72]. Fargesin (FGS) has shown anticancer effects in non-small cell lung cancer by targeting the H3 histone lactylation signaling pathway [73]. These lactylation-associated gene signature could serve as a cancer prognostic marker and potential therapeutic target.

Lactylation and drug resistance

Drug therapy stands as a crucial treatment for cancer patients; however, the development of resistance over time poses a significant challenge. Most existing drugs face the issue of resistance, where cancer cells adapt to the treatment to diminish its effectiveness [74]. Therapy resistance remains a formidable challenge in cancer treatment, often resulting in rapid recurrence, disease progression, and ultimately, mortality [75]. The production of Kla has been linked to a poor prognosis in patients with breast cancer (BC) and is pivotal in shaping the BC cancer microenvironment and fostering drug resistance [76] while the association of histone lactylation with cisplatin resistance has also been verified in bladder cancer [24]. Lactylation findings may be a potential independent prognostic biomarker in colorectal cancer, gastric cancer, glioblastoma in clinical applications. Studies have revealed elevated levels of histone lactylation in bevacizumab-resistant colorectal cancer patients, promoting cancer cell proliferation and survival under hypoxic conditions. Notably, the combination of histone lactylation inhibition with the bevacizumab monoclonal antibody demonstrates improved efficacy in the treatment of colorectal cancer [77]. For instance, SMC4 has been identified as a promoter of glycolytic enzyme expression, leading to increased lactate production. Simultaneously, the induction of histone lactylation enhances the expression of ABC transporter proteins, contributing to chemoresistance and insensitivity to chemotherapy in colorectal cancer cells [78]. In addition, NBS1 lactonylation is essential in gastric cancer for the formation of the MRE11-RAD50-NBS1 (MRN) complex and the accumulation of homologous recombinant repair proteins at DNA double-strand break sites. The use of stiripentol (clinically for anti-epileptic treatment) inhibits NBS1 lactylation, reduces DNA repair efficacy and overcomes resistance to chemotherapy [79]. Moreover, stiripentol crosses the blood–brain barrier and inhibits LDHA/B activity to inhibit lactylation, making glioblasts more sensitive to Temozolomide (TMZ) in vitro and in vivo [80]. Furthermore, lactic acid-induced lactylation has been implicated in resistance observed in prostate cancer and lung adenocarcinoma [81]. This could potentially serve as a crucial factor in treating cancer cells by modulating lactylation of cancer cell plasticity as a therapeutic target. These findings contribute to a deeper understanding of drug resistance mechanisms and may lay the groundwork for future theoretical bases in therapeutic strategies.

Lactylation and immunotherapy

The excessive accumulation of lactate produced by cancer cells can result in extracellular acidification, a crucial and indispensable element in shaping the immune microenvironment. Lactate serves as a substrate in the trichloroacetic acid (TCA) cycle to provide energy to cancer cells. Moreover, it modulates cellular immune metabolism and hinders the activation and proliferation of immune cells. Lactylation can facilitate the modification of immune-related molecules by regulating the expression of target genes. In order to understand the role of lactylation played in cancertumor immunity, Gu et al. found that the cancer metabolite lactate promoted hepatocellular carcinogenesis by modulating MOESIN lactylation and enhancing TGF-β signaling in regulatory T cells [82]. Elevated levels of H3 lysine 18 lactylation (H3 K18 la) in non-small cell lung cancer induce PD-L1 expression to enhance immune escape [83]. Studies have shown that inhibition of lactylation can be involved in tumorigenesis and development through immune pathways and lactylation is more beneficial in combination with immunotherapy. Professor Qingqing Wang’s team discovered that lactate produced by cancer cells fostered the malignant progression of colon cancer. This occurs through the promotion of Mettl3 expression in tumor-infiltrating myeloid cells (TIMs) via histone lysine lactylation (Kla). Moreover, lactate directly mediates the lactylation of Mettl3, consequently promoting m6 A-mediated immunosuppression [84]. Collectively, these processes contribute to the advancement of cancer progression. Research indicates that the inhibition of lactylation can play a role in tumorigenesis through the immune pathway and that it is more advantageous for cancer treatment when combined with immunotherapy. For instance, in prostate cancer (PCa), Wuchererine inhibits histone lactylation, HIF1 A, and PD-L1 expression, thereby suppressing cell proliferation. This positions Wuchererine as a promising agent for immunotherapy [85]. (a jump) Increased intracellular lactate in glioblastoma cells promotes histone H3 K18 lactylation and upregulates CD39, CD73, and CCR8 expression, whereas CAR-T therapy downregulates this effect, and the combination of lactate dehydrogenase A (LDHA) inhibition and CAR-T therapy has better efficacy against GBM [86]. Furthermore, the combination of anti-PD-1 and lactate dehydrogenase inhibitors exhibits a more potent anticancer effect compared to anti-PD-1 agents alone [82]. Immunometabolic strategies aimed at reversing lactate- and PD-1-mediated immunosuppression of tumor-associated macrophages (TAM), in conjunction with androgen deprivation therapy (ADT), prove beneficial in treating patients with Phosphatase and tensin homolog (PTEN)-deficient castration resistant prostate cancer (mCRPC) [87]. Leo et al. also demonstrated in melanoma cells that the combination of histone lactylation elimination and immunotherapy blocked cancer cell progression [88]. When combined with immunotherapy, the inhibition of lactic acidification can achieve a synergistic effect (Fig. 5).

Fig. 5.

Lactylation and immunotherapy. A: Lactic acid promotes the expression of Mettl3 through Kla, thus promoting the malignant progression of colon cancer, and lactic acid can directly mediate the lactylation of Mettl3 to promote immunosuppression. B: Lactic acid promotes hepatocellular carcinoma by modulating MOESIN lactylation and enhancing TGF-β signaling. C: Evodiine can inhibit the expression of histone lactylation, HIF1 A and PD-L1, thereby inhibiting the proliferation of prostate cancer cells. D: Increased lactate promotes the lactylation of histone H3 K18 and upregulates the expression of CD39, CD73 and CCR8. Inhibition of lactate LDHA combined with CAR-T therapy has better efficacy against GBM

Conclusion

We provide a comprehensive summary of the currently identified mechanisms governing lactylation, the implications of lactylation in tumorigenesis and development, and the potential applications of lactylation in cancer therapy. Both acetyl coenzyme A and lactyl coenzyme A generated through glycolysis, serve as substrates for acetylation and lactylation, respectively, in epigenetic modifications. Interestingly, it has been discovered that the enzymes governing acetylation can also influence lactylation. Given that both modifications target lysine residues, it becomes imperative to explore whether lactylation and acetylation engage in competitive interactions.

During our summarization, we found that different histone lactylation could play the same role in the same disease, e.g., H4 K12 la promotes disease progression by increasing glycolysis in Alzheimer’s disease [89] while H3 K18 la promotes Alzheimer’s disease progression by stimulating the NFκB signaling pathway [90]. The findings of Wan et al. supported the hypothesis that lactylation is mediated through its different receptors (e.g., NCL) rather than histones alone to control gene transcription [13]. This also suggests that lactylation on our multiproteins collaborate with each other in the cell to co-regulate downstream gene expression. The current study confirms that lactylation can be involved in cancer progression with other metabolic pathways. Lactylation mediates m6 A modification, apoptosis, cellular pyroptosis [91], cellular senescence [90], autophagy [27] and other processes by promoting the expression of target genes. Lactylation was found to promote mitochondrial fission and induced ATP depletion, mitochondrial reactive oxygen species (mtROS) overproduction, and mitochondrial apoptosis [56]. It has now been demonstrated that evodiamine inhibits prostate cancer cell proliferation by inducing iron death through decreasing the expression of glutathione peroxidase 4 (GPX4) [85]. This suggests that lactylation may affect ferroptosis by modulating ROS and thus regulating cancer development.

As a lactate substrate, Lactate regulates lactylation and participates in cancer development; therefore, lactate-related genes may become new cancer markers or therapeutic targets, and these findings also provide new ideas for cancer diagnosis and treatment. Some researchers have found that lactylation-associated models exhibit robust predictive efficiency in hepatocellular carcinoma [92]. Accumulation of lactate and adenosine in TME are two major factors of immunosuppression, and lactylation scores are closely associated with cancer mutational load, genomic instability, ICI treatment response, immune cell infiltration, and immune escape [93, 94]. Cai et al. found that lactylation-modifying enzymes EP300 and HDAC1-3 dysregulation was associated with the proportion of immune cell infiltration in hepatocellular carcinoma, especially in B cells [62]. When in colorectal cancer cells, Protein convertase subtilisin/kexin type9 (PCSK9) promotes M2 macrophage polarization, while inhibiting M1 macrophage polarization by promoting proteolactic acidification [95]. Meanwhile, the Cox model predicts the role of differentially expressed Kla-specific genes (DEKlaGs) in the immune microenvironment, immunotherapy and drug resistance is also gaining attention [96].

Traditional methods for lactylation site detection involve the enrichment of lactylated proteins and the identification of lactylation sites through mass spectrometry. Cheng et al. utilized mass spectrometry to identify lactylated proteins and sites in FHC cells and SW480 colon cancer cells [97]. Several servers for analyzing lactylation sites are presently accessible, including Auto-Kla [98], FSL-Kla [99], and Kla sites, facilitated by computer simulation. In addition, an H4 K16 la-based fluorescent probe, p-H4 K16 laNBD, has been constructed that can be used to directly detect the delactylation process [100]. When the relevant enzyme erases the lactoyl group, the exposed amino group initiates an attack on the O-NBD portion, leading to its conversion into the N-NBD moiety, thereby generating strong and easily detectable fluorescence. Utilizing the fluorescence produced, we can compare the delactylation activities of different enzymes and calculate the delactylation reaction constants. An alkyne-functionalized bioorthogonal chemical reporter gene, YnLac, is also reported as an alkyne-functionalized L-lactic acid analog that can be metabolically doped into L-lactylated proteins in living cells, enabling fluorescence detection and proteomic characterization of novel L-lactylated proteins [101]. The refinement of the lactylation assay method not only enables a more in-depth exploration of the molecular mechanism underlying lactylation but also establishes the theoretical foundation for the application of targeted lactylation in cancer research.

Given the emerging post-translational modification of protein lactylation, there are still challenges in exploring its biological functions, including the following aspects. First, due to the anaerobic glycolysis in cancer cells, a large amount of lactate is produced, and the accumulation of lactate causes changes in the pH of the immune microenvironment, inducing immune resistance. The relationship between lactylation and immune-related functions remains unclear. Moreover, in lactylation studies, exogenous lactate is usually added to emphasize the effect of lactylation, which makes the lactate concentration much higher than that in cancer cells in vivo, amplifying the effect of lactylation. Secondly, the enzymes that can regulate lactylation, such as HDAC and SIRT1, reported so far are mainly deacetylases, while the specific enzymes for lactylation have not been discovered. Additionally, knocking down LDHA/LDHB not only increases the lactate concentration but may also affect the changes of other related products of glycolysis. Therefore, there are certain challenges in precisely controlling the impact of lactylation changes on cell biological functions. For this reason, researchers need to develop more precise detection methods and comprehensively consider the broader impact of lactylation in cancer metabolism.

Abbreviations

Kla

Lysine lactylation

PTM

Post-translational modification

HATs

Histone acetyltransferases

HDACs

Histone deacetylases

ALCTs

Lactate CoA-transferases

AARS1

Alanyl-tRNA synthetase 1

AARS2

Alanyl-tRNA synthetase 2

SIRT

Sirtuin

LGSH

Lactoylglutathione

GLUT3

Glucose transporter 3

LDHA

Lactate dehydrogenase A

ALDOA

Aldolase A

NSCLC

Non-small cell lung cancer

NUSAP1

Nucleolar and spindle associated protein1

Kbu

Butyrylation

PDAC

Pancreatic ductal adenocarcinoma

HR

Recombinant protein

SCC

Squamous cell carcinoma

H3 K18

Histone 3 lysine 18

DML

Demethylzeylasteral

RJA

Royal Jelly Acid

FGS

Fargesin

ATC

Anaplastic thyroid cancer

AKR1B10

Aldo–keto reductase 1B10

PEM

Pemetrexed

ccRCC

Clear cell renal cell carcinoma

PDGFRβ

Platelet-derived growth factor receptor β

GBM

Glioblastoma

CENP

Centromeric protein

GPC3

Glypican-3

CM

Cutaneous melanoma

LUAD

Lung adenocarcinoma

ALDOB

Aldolase B

CEACAM6

Carcinoembryonic antigen cell adhesion molecule 6

VEGFR2

Vascular endothelial growth factor receptor 2

VM

Vasculogenic mimicry

PDHA1

Pyruvate dehydrogenase E1 component subunit alpha

Fis1

Fission 1 protein

BC

Breast cancer

TCA

Trichloroacetic acid

TIMs

Tumor-infiltrating myeloid cells

PCa

Prostate cancer

TAM

Tumor-associated macrophages

ADT

Androgen deprivation therapy

PTEN

Phosphatase and tensin homolog

mCRPC

Castration resistant prostate cancer

mtROS

Mitochondrial reactive oxygen species

GPX4

Glutathione peroxidase 4

PCSK9

Protein convertase subtilisin/kexin type9

DEKlaGs

Differentially expressed Kla-specific genes

Author contributions

WJ, PM and OY reviewed the literature and made original draft preparation; SM, LS, JX, RZ, PQ, XX, TS, XL, YW, LH, WN, TY and LJ reviewed the literature; LQ, HY and ZY designed the outline and revised the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported in part by grants from the following sources: the National Natural Science Foundation of China (82302987, 82303534, 82203233, 82202966, 82173142), the Natural Science Foundation of Hunan Province (2023 JJ60469, 2023 JJ40413, 2023 JJ40417, 2023 JJ30372, 2023 JJ30375), Science and Technology Innovation Program of Hunan Province (2023ZJ1122, 2023RC3199, 2023SK4034, 2023RC1073), the Research Project of Health Commission of Hunan Province (202203034978, 202202055318), and by Hunan Cancer Hospital Climb Plan (ZX2020001-3, YF2020002, 2023 NSFC-A001, 2023 NSFC-A002, 2023 NSFC-A004).

Availability of data and materials

Not applicable.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

Not applicable.