During the process of glycolysis, pyruvate molecules are converted into lactate through the action of cytoplasmic lactate dehydrogenase (LDH), rather than directly entering the tricarboxylic acid (TCA) cycle (1). In 1923, Otto Heinrich Warburg made the observation that cancer cells exhibit a proclivity for producing significant amounts of lactate via glycolysis, irrespective of the presence of oxygen ( Figure 1 ). This observation came to be known as the Warburg effect (2). Subsequent investigations have revealed that lactate serves as a signaling molecule, exerting notable influences on immune cell function, immune response modulation, cell metabolism regulation, and immune surveillance (3–5). The tumor microenvironment (TME) constitutes a multifaceted network comprising tumor cells, stromal cells, blood vessels, endothelial cells, growth factors, nutrients, and cell metabolites (6). Expanding upon the postulated Warburg effect hypothesis, researchers have observed that the release of lactate from tumor cells contributes to the acidification of the TME. This acidic microenvironment promotes tumor angiogenesis, triggers metastasis development, induces drug resistance, and facilitates immune evasion (7). Recent studies have additionally indicated that cancer cells can utilize lactate as an energy source (8, 9). Consequently, therapeutic strategies targeting metabolic processes, including lactate synthesis, have emerged as potential innovative approaches for the treatment of cancer patients (10).

Lactylation, alternatively known as lysine lactylation (Kla), is a post-translational modification (PTM) that involves the covalent attachment of lactic acid moieties to protein lysine residues, thereby exerting influence on gene expression regulations. The elucidation of lactylation has significantly broadened our comprehension of lactate’s role in biological systems. Consequently, the presence of lactylated histone and non-histone proteins holds paramount importance in the modulation of gene transcription (11). As a prevalent PTM, lactate-induced protein lactylation not only contributes to normal physiological processes (12), such as the regulation of immune homeostasis during cardiac repair (13), but also plays a significant role in the etiology and progression of various diseases, particularly cancer (14, 15). Evidence suggests that lactylation of tumor cells, tumor stem cells, and tumor-infiltrating immune cells in the TME can actively contribute to cancer progression through downstream modulation of gene expression, thus emerging as a promising therapeutic target in cancer treatment (16). However, our understanding of the intricate regulatory mechanisms involving lactate-induced lactylation in malignant tumors and the clinical potential of therapeutic interventions targeting this pathway remains incomplete.

Here, we have summarized recent literature in this area to gain a more encompassing understanding on the current research landscape, delineate potential avenues for future investigation, overcome the constraints of current cancer treatments, and present novel avenues for therapeutic strategies targeting lactate-induced lactylation.

The ability of cancer cells to undergo metabolic reprogramming and avoid detection by the immune system is regarded as an emerging hallmark of cancer (17). As previously mentioned, the Warburg effect is a pivotal aspect of energy metabolism in cancer cells, where they preferentially rely on glycolysis to sustain biosynthetic processes (18). This results in the production of high levels of lactate, actively maintaining an acidic TME that suppresses anti-tumor immune responses (19). Consequently, lactate plays a crucial role in bridging metabolic reprogramming with immune evasion mechanisms (20). Remarkably, lactate has intricate effects on both tumor cells and immune cells that infiltrate the tumor within the TME ( Figure 1 and Table 1 ).

Excessive lactate within the TME can hinder the effectiveness of anti-tumor immunity by interfering with the function of various immune cells that infiltrate the tumor (50). Watson MJ, et al., and Angelin, Alessia et al. (21, 51) have confirmed that the activation of effector CD8+ and CD4+ T cells is commonly suppressed when the pH of the TME falls within the range of 6.0 to 6.5, resulting in diminished cytotoxicity and cytokine production. Lactic acid plays a crucial role in enhancing the growth and performance of tumor-infiltrating regulatory T cells (Tregs). Kouidhi S, et al. (52) and Wu H, et al. (53) have demonstrated that the reversal of the acidic TME through the application of proton pump inhibitors can restore the inhibition of anti-tumor immunity and enhance immunotherapy, thereby corroborating these findings. Moreover, a number of studies have indicated that a high concentration of lactate can impede the activity of natural killer (NK) cells and induce apoptosis in these cells (54–56). Mechanistically, Brand A, et al. (22) revealed that lactic acid impedes the activation of nuclear factor-activated T cells (NFAT) in NK cells, resulting in reduced production of IFN-γ. Husain Z, et al. (23) discovered that lactate not only directly impairs the functionality of NK cells, but also indirectly suppresses these cells by increasing the population of myeloid-derived suppressor cells (MDSCs) ( Figure 1 ).

In a recent study by Colegio OR et al. (24), it was discovered that lactic acid derived from tumors plays a crucial role in inducing the transformation of tumor-associated macrophages (TAMs) into an M2-like phenotype. This process is facilitated by the activation of hypoxia-inducing factor 1α (HIF1α), which subsequently promotes tumor growth within the context of the TME ( Figure 1 ). Significantly, the regulation of extracellular signals also plays a crucial role in several intracellular signaling pathways, a mechanism that holds particular importance within TME (57). Consistent with this, Chen P. et al. (25, 58) demonstrated that lactate induces the polarization of M2 macrophages through the upregulation of vascular endothelial growth factor (VEGF) and arginase-1 (ARG1) via the extracellular signal-regulated kinase/transcription 3 (ERK/STAT3) signaling pathway.

As a ubiquitous biological process, lactylation has been proven to be associated with the growth of numerous cancers. Recent investigations have not just delved into its crucial role in ocular melanoma, colorectal cancer, gastric cancer, acute myeloid leukemia, and bladder cancer (details below), but also investigated its implications in non-small cell lung cancer (26), hepatocellular carcinoma (27), glioma (28), clear cell renal cell carcinoma (29), prostate cancer (30), and pancreatic ductal adenocarcinoma (31) ( Table 1 ). In a recent investigation involving 82 cases of ocular melanoma and 28 cases of normal tissues, researchers observed elevated levels of lactylation in tumor tissues compared to normal tissues, particularly at the histone H3K18 site. This process was found to hinder the proliferation and migration of tumor cells (32). Mechanistically, lactylation of H3K18 affects the development of ocular melanoma by regulating the reader protein YTHDF2, which is responsible for RNA m6A modifications. Notably, increased expression of YTHDF2 is associated with a negative prognosis for patients (59). Additional research has unveiled that histone lactylation increases the expression of ALKBH3 in ocular melanoma patients at high risk. This modification influences the formation of the tumor suppressor protein PML condensate by reducing N1-methyladenosine (m1A) methylation on SP100A, thereby accelerating tumor progression (33). Thus, strategies targeting ALKBH3 may offer substantial potential for melanoma treatment.

Chemotherapeutics, including platinum drugs and targeted agents such as bevacizumab, play essential roles in the management of advanced and metastatic colorectal cancer (CRC) (60, 61). Nevertheless, the widespread issue of drug resistance cannot be overlooked (62–64). Notably, CRC patients who are resistant to bevacizumab therapy exhibit significantly elevated glycolytic signaling and histone H3K18la (histone H3 lysine-18 lactylation) levels. These observations may provide insight into a potential underlying cause for patient resistance to this agent (34). In a separate study, investigators explored organoid models and xenotransplantation models (PDXs) of CRC patients, revealing that the Warburg effect can enhance homologous recombination (HR) and therefore contribute to chemotherapy resistance in cancer cells. Additionally, they observed that the inhibition of HR and reversal of drug resistance can be achieved by using cell-penetrating peptides that block the lactylation of MRE11, which encodes a nuclear protein involved in HR and DNA double-strand break (DSB) repair. Consequently, this approach increases the sensitivity of cancer cells to cisplatin and polyADP ribose polymerase inhibitors (PARPi) (35). This finding exposes the critical regulatory role of MRE11 lactylation in HR and offers a novel perspective on the relationship between tumor cell metabolism and DSB. Furthermore, it suggests a potential therapeutic strategy for overcoming chemotherapy resistance in CRC patients (65).

Elevated lactate and copper concentrations have been observed in gastric cancer (GC) (36). The researchers discovered that the m6A modification on ferredoxin 1 (FDX1) mRNA, mediated by an atypical methyltransferase called METTL16, plays a crucial role in copper-induced apoptosis. To further clarify, FDX1 encodes a reductase responsible for reducing Cu²⁺ to its more toxic form, Cu¹⁺. They found that under conditions of copper stress, the lactylation of METTL16 at the K229 site is enhanced but inhibited by SIRT2 (37). Interestingly, the elevated levels of lactylation induced by METTL16 can enhance the therapeutic effectiveness of the copper ionophore elesclomol (66). When elesclomol is combined with the SIRT2 inhibitor AGK2, it induces copper-induced apoptosis in gastric tumors both in vitro and in vivo (36). This combination therapy offers a promising treatment strategy for GC.

In acute myeloid leukemia (AML), the upregulation of glycolysis by STAT5 results in the accumulation of lactate (38). This, in turn, promotes the translocation of E3 binding protein (E3BP) and histone lactylation to the nucleus, ultimately enhancing the transcription of PD-L1 in leukemia cells. The inhibition of PD-1/PD-L1 using immune checkpoint inhibitors (ICIs) can restore the activity of CD8+ T cells when co-cultured with AML cells that express high levels of STAT5. This suggests that PD-1/PD-L1 based immunotherapy may be beneficial for AML patients with STAT5-induced glycolysis and lactate accumulation (45, 67, 68).

A comprehensive investigation has been conducted to gain a deeper understanding of the underlying mechanism by which circXRN2 regulates tumor growth in bladder cancer (39). The findings revealed that circXRN2 has the capacity to bind with LATS1 protein, thus protecting it from undergoing speckle-type POZ protein-mediated ubiquitination and subsequent degradation. This interplay triggers activation of the Hippo signaling pathway, consequently restraining H3K18 lactylation and ultimately impeding the progression of bladder cancer. Importantly, these groundbreaking observations shed light on a potentially robust target for therapeutic intervention in the clinical management of bladder cancer.

When confronted with environmental changes, tumor cells undergo metabolic reprogramming to adapt to the new environment (96). Lactate, as a byproduct of glycolysis, can lactylate both histone and non-histone proteins under the influence of specific enzymes (11). Although lactate was once regarded as a mere “metabolic waste” of glycolysis, numerous studies have gradually unraveled the Warburg effect, confirming its integral role in the TME. It is involved in tumor angiogenesis and mediates immune suppression among other processes (7), making it a potential target for cancer therapy. Further exploration of lactate’s potential role in tumorigenesis and the immune microenvironment is expected to yield fascinating discoveries.

Based on these findings, targeting lactate-lactylation and its associated metabolic pathways has emerged as a novel research avenue for cancer therapy. One strategy involves interfering with tumor cell metabolism by inhibiting lactate production and transport to reduce lactate accumulation and immunosuppression within the TME. Another strategy focuses on developing targeted drugs that affect lactate-lactylation to interfere with its effects on tumors and immune cells. Currently, notable progress has been achieved in studies targeting MCT4 (43, 44) and LDH (45, 49), but inhibitors targeting glycolysis are still at the preclinical stage involving animal model experiments without sufficient clinical translation. Despite the potential of targeting Lactate-Lactylation, there exist several challenges and limitations that hinder its clinical translation. For instance, shared enzymes exist between lactylation and acetylation, posing the risk of complications during treatment. Moreover, the risk lies in the expression of MCT1 in normal tissues, particularly the retina and heart. There have been reports of reversible vision loss and elevations in cardiac troponin levels in patients undergoing MCT1-targeted therapies, which are indicators of retinal effects and myocardial injury, respectively (40). It is imperative to carefully consider the balance between potential benefits and risks when pursuing targeted lactate therapy and explore strategies to mitigate these side effects. Still, inhibitors with more specificity targeting MCT and LDH remains limited. On top of that, current strategies and clinical trials do not prioritize the consideration of pH value, an aspect that could significantly impact therapeutic outcomes.

Although current research has gradually illuminated the role of lactate-lactylation in the TME, there are still intriguing avenues to explore. Firstly, certain studies have indicated that the immunoprotective effect of lactate may be underestimated. In contrast to lactic acid, lactate might exert an immunoprotective role against tumor immunity, primarily due to the confounding influence of proton-induced immunosuppression within the acidic TME. This discovery offers a novel perspective for further investigation (47). Additionally, investigations into the impact of lactic acid and lactate on tumor cells and immune infiltrates within TME can sometimes be influenced by experimental conditions both in vitro and in vivo (48). Consequently, comprehending the effects of lactic acid and lactate on TME and tumor immunotherapy is likely intricate; thus necessitating additional reliable experimental studies to clarify their potential implications on TME while reassessing specific roles played by lactic acid and lactate.

Currently, the bulk of investigations on lactylation focus on its downstream. To fully understand the complex conditions that lead to lactylation, more researches are needed. Besides, the specific reader of lactylation remains unclear, and the study concerning inhibitors for lactylation epigenetic tools are limited. Notably, lactylation and acetylation share certain enzymes, indicating a potential competitive relationship. Thus, it becomes imperative to discern its complex interplay with other PTMs such as acetylation, methylation, ubiquitination, SUMOylation etc., within organisms; thereby further investigating whether lactylation exerts broader impacts on physiological and pathological processes within organisms.

To summarize, Lactate-Lactylation plays a pivotal role in tumor metabolic reprogramming as well as tumor immunity. Enhancing our understanding of the intricate involvement of lactate-lactylation in TME will facilitate better understanding of tumorigenesis and development biological processes. Consequently, this will pave the way for the exploration of novel therapeutic targets aimed at improving the prognosis of cancer patients.

JZ: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. JZ: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. JL: Data curation, Formal analysis, Resources, Visualization, Software, Writing – original draft, Writing – review & editing. GZ: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. MH: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. WG: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. JY: Methodology, Conceptualization, Formal analysis, Project administration, Validation, Investigation, Visualization, Writing – original draft, Writing – review & editing. GF: Data curation, Methodology, Supervision, Conceptualization, Project administration, Validation, Funding acquisition, Resources, Visualization, Software, Writing – original draft, Writing – review & editing.