The roles of KRAS in cancer metabolism, tumor microenvironment and clinical therapy

KRAS and the Warburg effect

The Warburg effect, proposed by Otto Warburg, is a process where cancer cells preferentially produce energy through increased glycolysis, followed by lactic acid fermentation and lactate secretion. This process, also known as aerobic glycolysis, produces less ATP per glucose molecule compared to oxidative phosphorylation but operates much faster, enabling cancer cells to rapidly generate energy to support the accelerated growth and proliferation [18]. The role of the KRAS in metabolic reprogramming was initially uncovered by its ability to enhance glycolysis. This unique function allows tumor cells to more efficiently metabolize glucose, providing both energy and the molecular precursors for biomass synthesis (Table 1). Consequently, tumor cells gain the capacity for uncontrolled proliferation and growth [33].

There are two distinct isoforms of KRAS (KRAS4A and KRAS4B), which differ in their C-terminal regions [58]. Amendola and colleagues reported that KRAS4A promotes glycolytic flux via interacting with hexokinase 1 (HK1), a key glycolytic enzyme located on the outer mitochondrial membrane (Fig. 1A) [34]. Ying found that withdrawal of KRAS G12D results in a significant reduction in glycolytic intermediates, including glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), and fructose-1,6-bisphosphate (FBP). Moreover, KRAS G12D extinction also downregulates several rate-limiting glycolytic enzymes like HK1, hexokinase 2 (HK2), PFKl and lactate dehydrogenase A (LDHA), while decreasing the glucose uptake and lactate production in pancreatic cancer. In addition, they demonstrated that KRAS G12D modulates glycolytic reprogramming via MAPK and MYC pathways, stimulating glucose uptake and driving glucose intermediates into the hexosamine biosynthesis and nonoxidative pentose phosphate pathways (PPP) (Fig. 2A, B) [36]. Liu et al., explored this metabolic reprogramming in a KRAS^LSLG12D/Tp53^fl/fl (KP) engineered mouse model with ARID1A loss (KPA). They observed that ARID1A loss in KPA mice accelerate lung tumor growth, and promote glycolysis activity, enhance the transcription of glycolytic intermediates such as PGAM1, PKM2, and PGK1 [59].

The Warburg effect plays a critical role in immune evasion [60, 61]. Cong performed a study using a CRE-inducible KRAS^LSLG12D mouse model, which revealed a significant reduction in NK cell population and an increase in glycolysis during various stages of KRAS-driven lung cancer. The study further identified that FBP1, an enzyme for glyconeogenesis, is upregulated in NK cells within lung tumors. Highly expressed FBP1 results in repressed glycolytic capacity, whereas inhibition of FBP1 with MB05032 sufficiently restores glycolysis and promotes tumor growth (Fig. 1B) [61, 47]. Additionally, KRAS mutation enhances the expression of Type I cytokine receptor IL4rα in pancreatic ductal adenocarcinoma (PDAC). IL4rα is required to maintain PDAC progression in vivo through a JAK-STAT-MYC modulated glycolytic activity. (Fig. 2C). Immunohistochemical (IHC) staining reveals that a substantial presence of T effector 1 (Th2) cells in tumor samples. Treatment with anti-CD4 Th2 neutralizing antibody leads to a significant reduction in tumor formation [38] .

Nutrition plays a significant role in cancer prevention, treatment, and recovery [62]. Wiel et al., reported that supplementation with the antioxidants N-acetylcysteine and vitamin E promotes the progression and metastasis of KRAS G12D-driven lung cancer. Mechanistically, these antioxidants stabilize HK2 and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, enhance glucose uptake, increase glycolytic rates and stimulate lactate secretion, thereby facilitating glycolysis-responsive lung cancer development [63]. In contrast, vitamin C, another member of vitamin family, inhibits KRAS G12D-driven colorectal cancer. Specifically, vitamin C represses glycolysis and inactivates GAPDH, a key rate-limiting glycolytic enzymes. This inhibitory effect can be counteracted by either inhibiting PARP or supplementing with nicotinamide mononucleotide (Fig. 2D) [53].

KRAS and lipid metabolism

Lipid metabolism is a complex and tightly regulated processes which is crucial for energy storage, membrane structure, and cellular signaling [64]. Cancer cells often reprogram their lipid metabolism to support rapid proliferation and energy production. This reprogramming involves lipid synthesis, alterations in fatty acid oxidation, lipid droplet formation, and modulation of lipid signaling pathways [22]. The study of lipid metabolism has gained significant attention, particularly regarding its interplay with KRAS mutations in cancer (Table 2) [65]. Hereby, we outline key points on how KRAS mutations influence lipid metabolism.

Sphingolipid synthesis is essential for cancer proliferation [81]. Soula recently showed that sphingolipid deficiency enhances pro-apoptotic effect of NK cells and CD8 + T cells via the activation of interferon-γ (IFNγ) signalling. The loss of sphingolipid synthesis sensitizes cancer cells to IFNγ treatment. Clinically, combining eliglustat, a glycosphingolipids inhibitor, with checkpoint blockade therapies such as anti-CTAL4 or anti-PD-1, has been shown to suppress KRAS-driven lung adenocarcinoma (LUAD) [80]. In addition, Liu and colleagues reported that KRAS G12V enhance the synthesis of glycosphingolipids. They also found that glycosphingolipid synthesis is required for KRAS functions, indicating KRAS and glycosphingolipid synthesis form a reciprocal axis in cancer (Fig. 3A) [37].

Rozeveld et al., reported that excess lipid promotes PDAC invasion and migration through lipolysis. KRAS G12D enhances this utilization and storage of lipid droplets by downregulating hormone-sensitive lipase (HSL). In addition, enforced HSL expression converts metabolism from glycolysis to oxidative phosphorylation in KRAS G12D-driven PDAC (Fig. 3B, Top) [82, 83]. KRAS G12V promotes steatosis and prevents hyperplasia in hepatocellular carcinoma (HCC). However, Wnt/MYC signalling can attenuate the extensive hepatic steatosis and senescence triggered by KRAS expression. MK8245, an inhibitor of stearoyl-CoA desaturase (SCD), strikingly inhibits hepatomegaly in Tg (Wnt&KRAS) and Tg (MYC & KRAS) mouse models, implying fatty acid desaturation is an important therapeutic target for antagonizing the combined effects of Wnt and RAS signaling pathways in HCC [84]. Fuentes et al., demonstrated that dietary supplemented with fish oil containing long-chain n-3 polyunsaturated fatty acids (n-3 PUFA), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), reduces CRC in an inducible genetic model. This effect is attributed to the reshaping of cholesterol-dependent and -independent nanoclusters and downregulation of ERK signaling (Fig. 3C) [76]. KRAS can enhance fatty acid uptake, fatty acid oxidation (FAO), and lipogenesis in pancreas via GLI1-induced SLC25A1, an important citrate transporter which plays a key role in FAO and fatty acid synthesis in PDAC. A high-fat diet (HFD) further stimulates the KRAS G12D-GLI1-SLC25A1 axis, leading to increased citrate and fatty acids. Pharmacological targeting GLI1 or SLC25A1 could suppress KRAS G12D-driven PDAC in the context of a HFD (Fig. 3B, Bottom) [69]. Acetyl-CoA carboxylase (ACC) control fatty acid synthesis [85]. Svensson reported that chronic treatment with ND-646 (ACC inhibitor) remarkedly dampens KRAS-driven lung cancer [72].

KRAS and amino acid metabolism

Amino acid metabolism is vital for protein synthesis, energy production, and the synthesis of various bioactive molecules [86]. This process is tightly regulated to meet the physiological demands of the body, and its dysregulation is associated with various diseases, including metabolic disorders and cancer [87, 88]. KRAS also regulates these metabolic pathways (Table 3). Targeting the metabolic vulnerabilities offers a promising approach to developing effective therapies against KRAS-driven cancers.

Najumudeen observed that KRAS rewires the amino acid metabolism in colorectal cancer (CRC) tumorigenesis through its dependency on SLC7A5, a glutamine antiporter. Mechanistically, SLC7A5 maintains intracellular amino acid levels, and its loss suppresses mTOR signaling. The abrogation of SLC7A5, in conjunction with mTORC1 inhibition, represses KRAS-driven CRC development (Fig. 4A, Left) [103]. In addition, SLC25A22 drives asparagine uptake, which binds and activates SRC phosphorylation. SRC subsequently recruits ERK, facilitating the transcription of CXCL1 (Fig. 4A, Right). Targeting SLC25A22 in combination with anti-PD1 therapy synergizes with immunological surveillance to suppress KRAS-mutant CRC growth in vivo [95]. SLC7A11, another glutamate antiporter, is required for KRAS-mutant driven lung cancer. Inhibition of SLC7A11 by HG106 decreases cystine uptake, enhances cytotoxicity, and promotes oxidative stress- and ER stress-mediated cell apoptosis (Fig. 4B, Left) [100]. Dietary restriction with low methionine has been shown to inhibit KRAS-driven CRC and increase sensitize to radiation therapy [104]. Lee demonstrated that PDAC exerts a distinct dependence on de novo ornithine synthesis from glutamine. KRAS mutant drive uptake of arginine-derived ornithine, induce expression of ornithine aminotransferase (OAT), and eventually promote PDAC development (Fig. 4C) [89].

Several studies have highlighted the essential role of asparagine synthetase (ASNS) in tumorigenesis [105–107]. For example, Lin showed that knockout of autophagy gene ATG5 impairs KRAS G12V-driven tumor growth. Metabolite profiling revealed a deficiency in the nonessential amino acid asparagine alongside overexpressed ASNS. Inhibition of ATG5 and ASNS represses cell proliferation, migration, and invasion [108]. KRAS can enhance asparagine biosynthesis via ATF4 in NSCLC. ATF4 activates ASNS, thus repressing apoptosis, facilitating protein biosynthesis, and activating mTORC1 pathway (Fig. 4B, Right [98]) .

KRAS and glutamine metabolism

Glutamine, the most abundant amino acid in the bloodstream, serves as an important metabolic fuel for rapidly proliferating cells. It supports the increased demand for ATP, biosynthetic precursors, and reducing agents [24]. In cancer cells, glutamine is transported into cell through the amino acid transporter ASCT2/SLC1A5. It then undergoes a catabolized process called glutaminolysis, where it is converted into glutamate and alpha-ketoglutarate (α-KG), an intermediate of the tricarboxylic acid (TCA) cycle which is essential for energy production and biosynthesis [109].

KRAS also alters glutaminolysis [110]. Wong and colleagues observed increased glutamine uptake and a reduced α-KG composition in KRAS-mutant CRC. They also found a reduced DNA demethylation and hypermethylation at CpG sites of WNT signalling genes. Furthermore, SLC25A22 is essential for the KRAS mediated DNA methylation, while silencing SLC25A22 activates H3K4me3 demethylation in promoter regions of stemness-associated genes, and suppresses LGR5 expression in CRC [111]. 6-diazo-5-oxo-L-norleucine (DON), a glutamine (Gln) antagonist, can lead to a metabolic crisis. Similarly, sirpiglenastat (DRP-104), a pro-drug version of DON, reduces tumor growth in KRAS driven-PDAC [112]. Hu employed a genetic model harboring KRAS G12D activation and SIRT5 inhibition, finding that SIRT5 loss enhances glutamine and glutathione metabolism via glutamate–oxaloacetate transaminase 1 (GOT1), and eventually promoting pancreatic tumorigenesis [113]. In addition, mitochondrial uncoupling protein 2 (UCP2) can also trigger glutamine metabolism. Silencing UCP2 in KRAS mutant cells decreases glutaminolysis, cell proliferation, and tumor growth in PDAC [114].

In summary, cancer metabolism involves a complex and dynamic reprogramming of cellular metabolic pathways, allowing cancer cells to thrive in challenging environments. These metabolic adaptations provide potential targets for therapeutic intervention, offering new strategies to disrupt the metabolic dependencies of tumors.

KRAS and immune cells

The TME is a complex and dynamic environment composed of cancer cells, stromal cells, blood vessels, immune cells, and signaling molecules. Immune cells within the TME can either help eliminate cancer cells or, conversely, contribute to tumor growth and immune evasion [122]. Mutational alterations in oncogenes like KRAS influence the inflammatory status of tumors and affect immune elimination, even during immunotherapy or vaccination strategies [123]. Liu reported that pancreatic intraepithelial neoplasia lesions (PanINs) frequently harbor KRAS mutations but rarely progress to PDAC. However, activation of the peroxisome proliferator-activated receptor-delta (PPARδ) ligand by High fat diets (HFD) or its agonist GW501516 enhances IL6/STAT3 signalling and rewires PDAC tumor microenvironment. This alteration is mediated through the induction of CCL2 secretion, which recruits immunosuppressive macrophages and myeloid-derived suppressor cells into the pancreas via the CCL2/CCR2 axis. This recruitment orchestrates an immunosuppressive tumor microenvironment and drives the progression of PanINs to PDAC (Fig. 5A, Top) [121]. Moreover, tumor-associated neutrophils (TANs) affect cell fate and tumor microenvironment of lung cancer. Koyama et al., deciphered that genetic silencing of STK11/LKB1 in KRAS-driven NSCLC results in the accumulation of neutrophils and T-cell exhaustion [124]. In the KRAS-driven lung squamous cancer, enforced expression of SOX2 and/or loss of NKX2-1 leads to an increased TANs and promotes lung cancer tumorigenesis. The authors performed a ChIP-seq and observed that increased TANs are required for SOX2-induced transcription of chemokine CXCL5, a well-known neutrophil chemoattractant gene [125]. Ottaiano and colleagues observed that CD3⁺/CD8⁺ lymphocytes derived from oligometastatic CRC patients exhibit distinct cytotoxic activity against human colon cancer cells harboring KRAS mutations [126]. In addition, they demonstrated that the loss of KRAS mutations in lung-specific oligometastatic CRC further suggests a unique evolutionary trajectory, potentially linked to reduced aggressiveness or changes in the tumor microenvironment [127]. Hosein generated a generated Ptf1a-Cre;LSL-KRAS G12D;Rnf43flox/flox (KRC) and Ptf1a-Cre; LSL-KRAS G12D (KC) mice and found that KPC mice with lack RNF43, exert poor survival, an increase in T and B lymphocytes, as well as a decrease macrophages. They further found that CXCL5 is decreased in KPC mice, compared to KC mice, which may responsible for the tumor formation in PDAC [128].

KRAS and chemokines

Chemokines are a family of small signaling proteins that play a crucial role in the immune system by directing the migration, activation, and positioning of immune cells. They are essential for immune surveillance, inflammation, tissue repair, and cancer progression [129, 130]. Hou et al., identified HDAC5 is a potential downstream target of KRAS via an iKPC mice model. Enforced HDAC5 represses Socs3, thus upregulating CCL2 expression and promoting CCL2-recruited macrophages. These tumor-associated macrophages (TAMs) provide cancer cells with trophic support, including TGFβ/SMAD4, enabling KRAS mutation to bypass inhibitory mechanisms in PDAC development (Fig. 5A, Middle) [131]. KRAS G12D mutant also affect immune landscape in NSCLC by repressing CD8⁺ tumor-infiltrating lymphocytes (TILs) through inhibition of chemokines CXCL10/CXCL11 in NSCLC. Mechanistically, KRAS G12D actives P70S6K/PI3K/AKT signalling and reduces CXCL10/CXCL11/HMGA2 level. In comparison to PD-L1 inhibitor monotherapy, chemo-immunotherapy of PD-L1 blockade with paclitaxel significantly suppressed tumor growth in a mouse model of KRAS G12D-mutant lung adenocarcinoma (Fig. 5B, Top) [132]. Liao demonstrated that the KRAS-IRF2-CXCL3-CXCR2 axis is a potential target for therapeutic strategies in CRC, particularly in tumors resistant to current ICB therapies. Specifically, oncogenic KRAS represses IRF2 expression, leading to elevated CXCL3 expression, a chemokine that recruits myeloid-derived suppressor cells (MDSCs) into the TME. Increased MDSC infiltration suppresses cytotoxic T cell responses, creating an immune-suppressive environment. Restoring IRF2 expression or inhibiting CXCR2, a CXCL3 receptor, reduces MDSC infiltration and enhances T cell-mediated anti-tumor responses in colorectal cancer [133].

KRAS and cytokines

Cytokines are small proteins secreted by cells, especially immune cells, that act as signaling molecules to regulate and coordinate immune responses. They play a crucial role in inflammation, immunity, and tissue repair [134, 135]. Dey and colleagues identified that IL4R is among the top 50 most overexpressed genes in KRAS-driven PDAC tumors. IL4R can promote PDAC in vitro and in vivo via activating of JAK-STAT-MYC signalling, which enhances glycolysis by increasing HK2 expression and extracellular acidification rate (ECAR) (Fig. 5A, Bottom). Utilizing the Pdx-Cre;KRAS^LSLG12D model, the authors detected enriched IL4, STAT6 and MYC level in these tumor lesion, which are dramatically infiltrated by CD4 + T cells, potentially contributing to pancreatic cancer initiation and progression [38]. Jang et al., reported that Leukotriene B4 receptor-2 (BLT2) plays a pivotal role in KRAS-driven lung tumor progression by promoting IL-6-mediated inflammation. High BLT2 expression is observed in human lung adenocarcinomas with KRAS mutations, whereas BLT2 inhibition, either pharmacologically or through genetic knockout, decreases lung tumor formation, IL-6 production, and airway inflammation in KRAS-mutant mouse models [136]. Oncogenic KRAS G12D in PDAC cells upregulates IL-33, a cytokine that recruits and activates type 2 immune cells like T_H2 and ILC2. These immune cells secrete cytokines like IL-4 and IL-13, which drive tumor progression through immune suppression and metabolic reprogramming of cancer cells [137].Interestingly, Donahue and colleagues demonstrated that stromal IL-33 production by cancer-associated fibroblasts (CAFs) is driven by signals from epithelial cells harboring the KRAS G12D mutation. This process supports a pro-tumorigenic environment by promoting immunosuppressive changes and reducing tumor-infiltrating CD8 + T cells. Targeted deletion of IL33 in stromal cells using compartment-specific knockout mouse models results in increased CD8 + T-cell infiltration and activation, reprogramming of the tumor microenvironment-including CAFs and myeloid cells-toward a less immunosuppressive state, and a reduction in tumor growth [138]. Hu depicted that KRAS mutation impairs the macrophage phagocytosis sensitivity by increasing CD47 expression in lung cancer. Mutant KRAS enhances PI3K/STAT3 signalling, which in turn, represses microRNA-34a, leading to increased CD47 expression. Therapeutical targeting KRAS, STAT3 or re-overexpressed microRNA-34a can restore the inmate immune surveillance and favor a beneficial therapy (Fig. 5B, Bottom) [139].

KRAS and tumor heterogeneity

Cancers exhibit substantial heterogeneity, meaning that individual cancer cells within the same tumor mass can have distinct metabolic and genetic phenotypes [140]. Even tumors of similar molecular profiles can vary significantly between patients in terms of genetic mutations, molecular signatures, and treatment responses. This variability contributes to differences in clinical outcomes and therapeutic effectiveness. For instance, KRAS G12D activation and p53 deletion foster both NSCLC and PDAC development. However, these tumors exert distinct patterns of amino acid metabolism. NSCLC is characterized by increased uptake of branched-chain amino acids (BCAAs) and elevated activity of BCAA catabolic enzymes, whereas PDAC tends to inhibit BCAAs uptake. The removal of Bcat1 and Bcat2, the enzymes responsible for BCAA catabolism, renders NSCLC formation, but do not affect PDAC tumorigenesis [141]. These findings underscore the heterogeneity of cell of origin and tissue microenvironment in influencing genetic events and metabolic reprograms.

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Competing interests

The authors declare no competing interests.