Metallic elements and their molecular roles in gastric cancer: Pathogenic mechanisms and therapeutic implications

Abstract

Gastric cancer (GC) remains among the leading causes of cancer-related mortality globally. Increasing evidence indicates that metallic elements such as iron, copper (Cu²⁺), zinc, and calcium (Ca²⁺) play crucial roles in GC pathogenesis, diagnosis, and treatment through diverse molecular mechanisms. This review systematically summarizes recent advances in the application of metallomics in GC. Relevant studies published up to 2024 were retrieved from PubMed, Web of Science, and Scopus using keywords including “gastric cancer”, “metal ions”, “metallomics”, and “metal-based therapy”. After screening and evaluation, representative studies elucidating the roles of metallic elements in GC were analyzed and synthesized. The findings revealed that iron overload induces oxidative stress and immune suppression via the Fenton reaction. Further analysis indicated that Cu²⁺ imbalance triggers mitochondrial dysfunction and cuproptosis, zinc deficiency disrupts transcriptional regulation through zinc finger proteins and metalloproteinases, and Ca²⁺ dysregulation activates Ca²⁺/calmodulin-dependent protein kinase kinase- AMP-activated protein kinase signaling to promote proliferation and chemoresistance. Advances in analytical techniques such as laser ablation inductively coupled plasma mass spectrometry have enabled spatial mapping of metal distributions in tumors, providing novel diagnostic and prognostic insights. Moreover, metal-based anti-cancer drugs and combination regimens involving traditional Chinese medicines exhibit promising therapeutic potential. Understanding the molecular crosstalk of metal metabolism offers new perspectives for precision diagnosis and targeted treatment in GC.

Key Words: Gastric cancer; Metallomics; Trace element; Exposure; Metal-based therapies

Core Tip: Metallomics, a study of metallic elements in biological systems, is critical for understanding gastric cancer (GC). It helps identify biomarkers for early diagnosis and offers insights into treatment strategies. Novel biomarkers like matrix metalloproteinases, ferritin, and zinc (Zn²⁺) finger proteins can improve the sensitivity and accuracy of GC diagnosis compared to conventional tumor markers. Role of metals in GC: (1) Iron: Altered iron metabolism is linked to GC progression and can serve as a prognostic marker; (2) Copper: Copper imbalances contribute to GC development, and supplementation may enhance therapeutic effects; (3) Zn²⁺: Zn²⁺ stability is essential for cell function, and imbalances may indicate GC risk; and (4) Calcium: Abnormal calcium signal transduction may promote the occurrence, migration, invasion and other aspects of GC and affect prognosis. Metallomics faces challenges in identifying and quantifying metal-related biomarkers, dealing with low concentrations of elements, and overcoming issues with drug resistance. Advancements in analytical techniques and combining metal-based drugs with traditional therapies could improve GC diagnosis and treatment outcomes.

INTRODUCTION

Metallomics is a comprehensive interdisciplinary discipline that studies the distribution, content, and function of metallic elements in cellular compartments, cells, or organisms. Following genomics, proteomics, and metabolomics, one study[1] first proposed the concept of “metallomics” in 2002, and the definition later expanded to represent all metallic elements present in cells or tissues. Metallomics is a rapidly evolving field of biometal science that integrates technologies and perspectives from other “omics” sciences (e.g., genomics, proteomics, metabolomics), and it has received widespread attention in the field of oncology[2,3].

Gastric cancer (GC) is the fifth leading cause of cancer and fourth leading cause of cancer-related deaths globally, accounting for nearly 800000 deaths annually[4,5]. Asia has the highest incidence and mortality of GC globally, accounting for 820000 new cases and 576000 deaths in 2020[6]. Because of the atypical clinical symptoms of GC, its onset is relatively insidious, and tumor marker levels display no significant alteration during disease screening. Consequently, most patients with GC are diagnosed at advanced stages, precluding surgical treatment. Thus, GC treatment relies on chemotherapy, targeted therapy, or combination chemotherapy based on metal-based anti-cancer drugs. Although progress has been made in the past 40 years, these methods cannot completely cure GC because of several issues such as drug resistance, recurrence, and metastasis[7-9]. Therefore, it is particularly important to understand the research progress and mechanism of metallomics in GC to facilitate early diagnosis and treatment.

METHODOLOGY

Web of Science, PubMed, Wanfang Data, CNKI, Google Scholar, and the Chinese Biomedical Database (2005-2024) were searched to identify relevant literature without language restrictions. We searched for articles using the following keywords: (1) Metallic element or metal-based anti-cancer drugs; (2) Gastric carcinoma; and (3) GC. In total, 411 articles, including 42 articles, 31 articles, 21 articles, 192 articles, 125 articles, and 16 articles identified in Web of Science, PubMed, Wanfang Data, CNKI, Google Scholar, and the Chinese Biomedical Database, respectively, were screened by title and abstract.

The criteria for article selection were as follows: (1) Evaluated the role of metal element metabolism in gastric carcinogenesis; (2) Evaluated the efficacy and prognostic significance of metal-based anti-cancer drugs in the treatment of GC; and (3) Described the prognostic significance of matrix metalloproteinase (MMP) expression at the invasive front in GC. Meanwhile, studies that used overlapping databases and those that were not published as full articles (e.g., abstracts) were excluded. Fifty-two articles meeting our inclusion criteria were further reviewed.

RESEARCH STATUS

The role of metallomics in the early diagnosis of GC

Tumor markers are substances secreted into body fluids or tissues by cancer cells or produced by the body when fighting cancer. These substances might only appear in the embryonic stage or remain unexpressed prior to the development of cancer, and clinicians can preliminarily diagnose tumors and the degree of malignancy of tumors based on changes in the expression of tumor markers. Common tumor markers, including carcinoembryonic antigen (CEA), associated antigen (CA) 19-9, CA12-5, and CA72-4, have displayed low sensitivity and specificity for the diagnosis of GC and exhibited little value for the early diagnosis of GC[10-12]. Therefore, the identification of novel biomarkers for GC has become a focus of GC research.

MMPs comprise a group of proteolytic enzymes containing active Zn²⁺ that target many extracellular proteins, such as proteases, growth factors, cell surface receptors, and adhesion molecules. MMPs are considered important factors in normal tissue remodeling during embryonic development, wound repair, cancer invasion, angiogenesis, oncogenesis, and cell apoptosis[13,14]. MMPs, comprising a superfamily of zinc (Zn²⁺)-dependent endopeptidases, have a core biological function of precisely degrading key components of the basement membrane and extracellular matrix, including structural macromolecules such as collagen, laminin, and fibronectin[15]. This process is not merely “tissue degradation”; instead, by disrupting the structural homeostasis of the cellular microenvironment, it facilitates abnormal cell proliferation and invasion. Therefore, MMPs are widely recognized as key regulatory factors in tumor progression, and their activity and expression are directly associated with the tumor growth rate, invasive ability, and potential for distant metastasis[16].

Furthermore, in the tumor tissues, adjacent non-tumor tissues, and peripheral blood of patients with GC, the levels of MMP subtypes such as MMP-2, MMP-3, MMP-7, and MMP-9 are significantly higher than those in healthy individuals and patients with precancerous lesions. Moreover, their high expression characteristics are closely related to the clinicopathological parameters of GC[17]. Through precise molecular regulation, the MMP family serves as a key driver of GC invasion and metastasis, with each subtype exhibiting distinct specificity and synergy in its mechanism of action. Zn²⁺ acts as the core regulatory factor throughout the activation and functional implementation of MMPs. The synergistic effect of MMP-2 and MMP-9, from activation to substrate degradation, relies on the regulation of Zn²⁺. Initially, both MMPs exist in their inactive zymogen forms. After the propeptide domain is hydrolyzed and removed by plasmin or other proteases, the active-site Zn²⁺ in their catalytic domains is exposed and stabilized. Collagen IV, the main structural component of the vascular basement membrane, forms a three-dimensional network that acts as a natural barrier against tumor cell invasion. After activation, MMP-2 and MMP-9 form coordinate bonds with oxygen atoms in the peptide segments of collagen IV via the active-site Zn²⁺, enabling precise substrate localization and initiating the hydrolysis reaction[18]. Specifically, Zn²⁺ first polarizes the carbonyl carbon in the peptide bond to reduce its electron cloud density and then assists water molecules in attacking this site, ultimately breaking the peptide bond and causing disintegration of the basement membrane structure. This process creates space for the migration and proliferation of vascular endothelial cells and promotes the formation of new blood vessels mediated by vascular endothelial growth factor (VEGF), both providing energy for GC cells and establishing a “channel for hematogenous metastasis”[19].

MMP-7 is highly expressed specifically in GC tissues[20], and its degradation of intercellular adhesion molecules (e.g., E-cadherin) also depends on Zn²⁺. Within the catalytic domain of MMP-7, Zn²⁺ both maintains the spatial conformation of the enzyme protein to ensure its accurate recognition of the extracellular domain of E-cadherin and plays a central catalytic role in the hydrolysis process. By regulating the stability of reaction intermediates, Zn²⁺ accelerates the cleavage of E-cadherin peptide bonds, disrupts intercellular adhesion, and causes GC cells to detach from the primary tumor site. Meanwhile, the degradation products activate downstream signaling pathways to enhance the motility of cancer cells.

As a signal amplifier, MMP-3 also requires Zn²⁺ for the activation and regulation of pro-MMP-9. After pro-MMP-3 is activated, the active-site Zn²⁺ endows it with hydrolytic activity, allowing the enzyme to specifically recognize the regulatory region of pro-MMP-9. During the hydrolysis of pro-MMP-9, Zn²⁺ ensures the efficient conversion of pro-MMP-9 into its active form by regulating substrate binding affinity, thereby amplifying the enzymatic cascade reaction and accelerating the infiltration and metastasis of GC[21].

The redox environment is another key factor regulating MMP activity. In the tumor microenvironment, the rapid proliferation and abnormal metabolism of tumor cells are often accompanied by elevated levels of reactive oxygen species (ROS). ROS can affect the activity of MMPs through multiple pathways. During the activation of MMPs, ROS can oxidize the cysteine residues in the propeptide of MMPs, disrupting their binding to Zn²⁺. This relieves the inhibition of the catalytic site and promotes the activation of MMPs. Studies have found that ROS such as hydrogen peroxide (H₂O₂) can act directly on the precursor of MMP-9, enabling its activation even at low protease concentrations and enhancing the invasive ability of tumor cells. Additionally, ROS can increase the gene expression of MMPs by activating intracellular signaling pathways, such as the mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways, further promoting the invasion and metastasis of tumor cells. When antioxidants or antioxidant enzymes [e.g., superoxide dismutase (SOD), glutathione peroxidase (GPX)] are present in cells, they can neutralize ROS and reduce oxidative stress, thereby inhibiting the activation and expression of MMPs. After treating tumor cells with antioxidants, the activity of MMPs decreases, and the invasive and metastatic capabilities of tumor cells are significantly suppressed. This indicates that the activity of MMPs can be effectively regulated by modulating the redox environment, providing a new strategy for GC treatment[22-25]. In conclusion, MMP activity is associated with cancer progression, and MMP is a tumor marker of GC invasion, metastasis, and prognosis and a potential therapeutic target for GC therapy.

Serum ferritin is involved in the regulation of hematopoiesis and the immune system, and its levels can reflect the body’s iron (Fe²⁺) storage and nutritional status[26]. Recent studies indicated that changes in serum ferritin levels are associated with disease progression, and serum ferritin can serve as a prognostic marker for patients with GC[27]. Under normal circumstances, serum ferritin coordinates with transferrin to regulate the release and utilization of Fe²⁺, thereby maintaining Fe²⁺ homeostasis. However, during the progression of GC, tumor cells overexpress Fe²⁺ metabolism-related proteins such as hepcidin, inhibiting Fe²⁺ efflux, while accelerating Fe²⁺ uptake by enhancing the expression of Fe²⁺ transporters (e.g., divalent metal transporter 1)[28]. This imbalance leads to abnormally elevated serum ferritin levels. On the one hand, increased Fe²⁺ reserves in tumor cells provide fuel for their rapid division; on the other hand, elevated serum ferritin can promote tumor angiogenesis through paracrine signaling. Fe²⁺ released by this process can activate the VEGF signaling pathway, thereby enhancing the migration and proliferation capabilities of vascular endothelial cells and providing nutritional support for tumor invasion and metastasis. In addition, serum ferritin plays a crucial role in regulating oxidative stress and remodeling the immune microenvironment. First, the free Fe²⁺ released by serum ferritin can generate large amounts of ROS, such as hydroxyl radicals (∙OH), through the Fenton reaction. Low concentrations of ROS can activate pro-tumor signaling pathways such as NF-κB and MAPK pathways in GC cells, promoting cell survival and invasion. Although high concentrations of ROS can induce cell apoptosis, GC cells can tolerate the toxic effects of ROS by increasing the expression of antioxidant enzymes such as GPX and instead use ROS-mediated DNA damage to accelerate gene mutations and the development of tumor heterogeneity. Furthermore, ROS can degrade collagen and laminin in the extracellular matrix, synergizing with MMPs to enhance tumor invasiveness and further promote disease progression.

Second, serum ferritin can induce the polarization of macrophages toward the M2 phenotype by binding to toll-like receptor 4 on the surface of immune cells. These pro-tumor macrophages secrete anti-inflammatory factors such as interleukin (IL)-10 and transforming growth factor beta, inhibiting the killing activity of CD8⁺ T cells and natural killer cells and creating an “immune escape” microenvironment for tumor cells. Conversely, serum ferritin can also reduce the antigen-presenting ability of dendritic cells, reducing the presentation of tumor antigens to T cells and further impairing the adaptive immune response. In summary, serum ferritin promotes GC progression by regulating Fe²⁺ metabolism, enhancing oxidative stress, and inhibiting immune function. Changes in Fe²⁺ levels can both reflect disease severity and serve as a convenient and non-invasive indicator for assessing the prognosis of patients with GC, providing important references for the clinical development of individualized treatment plans.

Zinc finger proteins (ZFPs) comprise a class of proteins that can fold themselves to form a “finger” structure by stably binding to Zn²⁺ and regulate the expression of genes at the transcriptional and translation levels by binding to DNA, RNA, and DNA-RNA, as well as binding to itself or other ZFPs. The core feature of ZFPs, one of the largest families of transcriptional regulatory proteins in humans, is the formation of coordinate bonds with two or more Zn²⁺ ions to stabilize a “finger-like” spatial structure, which is folded from amino acid sequences rich in cysteine and histidine, enabling precise recognition and binding to specific sequences of target molecules. Because of this characteristic, ZFPs can interfere with gene expression at multiple stages, such as transcription initiation, mRNA processing, and translational regulation, through interactions with DNA, RNA, or other proteins[29]. In recent years, a growing number of studies have confirmed that some ZFPs are abnormally overexpressed in GC tissues, and they can act as driver genes in the occurrence and development of GC through multi-dimensional regulatory mechanisms. Their expression is closely related to tumor stage, lymph node metastasis, and survival time in patients with GC, making them important markers of poor prognosis[30].

The unlimited proliferation of GC cells relies on the continuous activation of oncogenes, and some ZFPs can directly act as transcriptional activators to bind to the promoter or enhancer regions of oncogenes and increase their expression. For example, the positive rate of ZFP217 in GC tissues is as high as 68.3%. The zinc finger domain of ZFP217 can specifically recognize and bind to the promoter region of the cyclin D1 gene (the core binding sequence is 5′-GGGGCGG-3′), promoting the transcription and expression of cyclin D1. As a key regulatory factor for G1/S phase transition, the increased expression of cyclin D1 can accelerate the entry of GC cells from G1 into S phase, shorten the cell cycle, and achieve malignant proliferation. In addition, the ZFP X-linked has also been confirmed to enhance the transcriptional activity of MYC proto-oncogene, bHLH transcription factor (c-Myc) by binding to the enhancer region of the c-Myc gene. As a classic oncogene, c-Myc can both promote metabolic reprogramming of GC cells (such as enhancing the glycolysis rate) and inhibit the expression of apoptosis-related genes (such as Bax), dually promoting malignant cell transformation.

In addition to activating oncogenes, some ZFPs can also inhibit the expression of tumor suppressor genes by directly binding to their regulatory regions or forming complexes with other transcriptional repressors, thereby disrupting the “proliferation constraint mechanism” of cells. For example, the ZFP snail family transcriptional repressor 1 (SNAI1, also known as Snail) often has increased activity in GC because of enhanced Zn²⁺ binding capacity. SNAI1 can bind to the promoter region of E-cadherin (a tumor suppressor gene product) through its Zn²⁺ finger structure, recruit histone deacetylase, reduce histone acetylation in this region, and thus inhibit the transcription of E-cadherin. In addition, SNAI1 can bind to p53 protein, thereby interfering with the activation of tumor suppressor genes such as p21. The downregulation of E-cadherin disrupts intercellular adhesion and promotes the detachment and invasion of GC cells, whereas impaired p53 function leads to the failure of cell cycle checkpoints, making it impossible to eliminate abnormal cells with DNA damage.

ZFPs can also enhance the invasiveness and metastatic potential of GC cells by interfering with the activity of key signaling pathways. Among them, regulation of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway by the ZFP ZNF322A is the most typical example. Specifically, the Zn²⁺ finger structure of ZNF322A can bind to the 3′-untranslated region of the PI3K catalytic subunit p110α, inhibiting its degradation and leading to an increase in p110α protein expression. As a core molecule for PI3K pathway activation, p110α upregulation further activates Akt and mTOR. On the one hand, p110α promotes the expression and secretion of MMPs (MMP-2, MMP-9), accelerating the degradation of the extracellular matrix; on the other hand, it enhances epithelial - mesenchymal transition in GC cells by increasing the expression of N-cadherin and vimentin, endowing cells with mesenchymal characteristics and enhancing their migratory capacity. In addition, ZFP64 can promote the release of inflammatory factors such as IL-6 and tumor necrosis factor alpha by activating the NF-κB pathway. These factors can both activate invasion-related genes in GC cells themselves and induce the transformation of surrounding fibroblasts into cancer-associated fibroblasts, creating a favorable microenvironment for tumor metastasis.

In summary, ZFPs are deeply involved in the occurrence, proliferation, invasion, and metastasis of GC through a multi-dimensional mechanism of activating oncogenes-inhibiting tumor suppressor genes-regulating signaling pathways. Abnormal ZFP expression is a molecular marker for the malignant transformation of GC cells, and ZFPs are directly related to the poor prognosis of patients, providing new targets and ideas for targeted therapy (such as designing ZFP inhibitors and interfering with Zn²⁺ binding activity) and prognosis assessment in GC[31-33]. The sensitivity of tumor markers used to screen for GC in clinical practice is insufficient, and some research found through endoscopy that the expression of CEA, CA19-9, CA12-5, and CA72-4 in some patients with intermediate or advanced GC or those with metastatic GC is normal or slightly higher than normal[34,35]. Novel tumor markers such as MMPs, ferritin, and ZFP have high sensitivity, which is conducive to the early diagnosis of GC and selection of therapeutic targets for clinicians.

The role of metal-based anti-cancer drugs in GC treatment

Cisplatin was developed as the first metal-based anti-cancer drug. Until the mid-1960s, cancer chemotherapy was based on pure organic compounds. The unexpected discovery of the anti-cancer properties of platinum-based inorganic coordination compounds permitted the development of inorganic anti-cancer treatments. In 1965, Rosenberg discovered that the platinum complex produced by the platinum electrode during electrolysis inhibits the binary fission of Escherichia coli, and it has subsequently been used to treat cancer[27].

In 1978, the United States Food and Drug Administration approved cisplatin for cancer chemotherapy[36]. Subsequently, China has permitted the use of oxaliplatin (OXA) as a chemotherapy drug for cancer.

For patients with intermediate and advanced GC, chemotherapy is the most commonly used treatment modality in clinical practice. Park et al[37] reported that OXA intraperitoneal hyperthermic perfusion significantly improved the functional status of patients with GC, reduce the levels of serum tumor markers, and promote disease recovery. In patients with radical D2 resection, adjuvant OXA treatment with S-1 prolonged the 3-year survival rate of patients with stage II/III node-positive GC from 64.8% to 74.3% compared with S-1 monotherapy (P = 0.042)[38], illustrating the survival benefit of OXA for patients with intermediate and advanced GC. With the widespread use of OXA, drug resistance has emerged, and the importance of combination treatments has become increasingly prominent. Boku et al[38] found that nivolumab combined with OXA was well tolerated, achieving an objective response rate of 57.1% in patients with unresectable advanced or recurrent human epidermal growth factor receptor 2-negative GC. Huang et al[39] reported that P21 protein-activated protein kinase 6 (PAK6-P21) enters the nucleus to activate ataxia telangiectasia Rad3-related protein (ATR), which further activates the downstream repair protein cell cycle checkpoint kinase 1 and recruits RAD51 from the cytoplasm to sites of DNA damage to repair broken DNA. ATR activation is a necessary step in PAK6-mediated homologous recombination to protect cells from OXA-induced apoptosis, whereas ATR inhibitors (e.g., AZD6738) can block PAK6-mediated homologous recombination, thereby reversing resistance to OXA and even promoting susceptibility to OXA.

In this process, the intracellular concentration of OXA is a key factor affecting its efficacy and drug resistance, and copper (Cu²⁺) transporters [copper transporter 1 (CTR1), ATPase copper transporting alpha/beta (ATP7α/β)] play a crucial regulatory role in these effects. As the main Cu²⁺ uptake protein, CTR1 can mediate the entry of OXA into GC cells, and a decrease in CTR1 expression will directly reduce the influx of OXA, leading to insufficient intracellular drug concentrations and the subsequent development of drug resistance. By contrast, ATP7α/β, as Cu²⁺ efflux proteins, can transport intracellular OXA to the extracellular space; when these proteins are highly expressed, they accelerate the efflux of OXA, which also results in drug resistance. In addition, intracellular metallothioneins and glutathione affect the efficacy of OXA through detoxification. Metallothioneins can form stable complexes with OXA, thereby reducing its free drug concentration and impairing its DNA-damaging effect. Conversely, glutathione promotes the metabolic inactivation of OXA through a thiolation reaction, further exacerbating drug resistance.

Wang et al[40] demonstrated that NORAD, activated by oxidative stress, can positively regulate autotropism-related gene 3 and enhance autophagic flux through the sponge miR-5-12p. Non-coding RNAs activated by DNA damage could be potential biomarkers for predicting OXA resistance and mediating oxidative stress, and they represent therapeutic targets for reversing OXA resistance. For both monotherapy and combination therapy with other drugs, the survival and quality of life benefits of platinum drugs for patients with GC should not be underestimated.

Based on the aforementioned effects of metal handling systems on the efficacy of OXA, manipulating these systems has become a crucial strategy to reverse OXA resistance in GC cells. For instance, the intracellular uptake of OXA can be increased by increasing the expression of CTR1 or inhibiting its degradation. Downregulating ATP7α/β or blocking their transport function can reduce drug efflux, thereby maintaining effective intracellular drug concentrations. Meanwhile, inhibiting the synthesis of metallothioneins or using glutathione-depleting agents (such as buthionine sulfoximine) can impair the ability of cells to detoxify OXA and restore the cytotoxic effect of the drug on GC cells.

In the late 1980s, researchers studied organotin complexes and identified strong toxicity and side effects and a narrow anti-cancer spectrum, precluding their clinical application. Nath et al[41] discovered the excellent anti-cancer activity of the organotin dipeptide derivative triphenyltin. Ruthenium-based anti-cancer drugs (e.g., NAMIA, KP1019, KP1339) have been widely studied because of their strong inhibition of cancer cell proliferation, and although they have displayed great therapeutic prospects in clinical trials, they were not approved by the United States Food and Drug Administration to enter clinical trials until 2020[42-44]. At present, there are few broad-spectrum metal-based anti-cancer drugs used in clinical practice, mainly because the pathogenesis of cancer and mechanism of action of metal-based anti-cancer drugs in the treatment of GC remain unclear. Therefore, understanding the mechanisms of metal-based anti-cancer drugs is of great significance for GC treatment.

The role of metallic elements in GC treatment

Although the incidence of GC is declining in Western countries, it is rising in Asia and Central and South America[45]. Lifestyle and genetic changes (e.g. mutations, epigenetics, gene-environment interactions) contribute to cancer development and progression. Among the environmental factors, metallic elements occupy an important place. Almost all metallic elements can be found in food, water, and air; therefore, any change in the environment might affect the distribution of metallic elements, thus causing adverse effects on human health. In recent years, metallic elements in human tissues have attracted extensive attention because of their important roles in biochemical and physiological processes. Metallic elements influence the development of many diseases in the human body through DNA damage, enzymatic reactions, ROS production, and oxidative stress, thereby altering the permeability of cell membranes. Recent studies revealed that changes of metallic element levels in the body might be related to the formation and development of GC[46,47].

Fe²⁺ is abundantly stored in the mitochondria of metabolically active organs such as the heart, liver, and kidneys. When mitochondrial Fe²⁺ metabolism is disturbed, cellular metabolic balance is disrupted. In particular, mitochondrial Fe²⁺ overload leads to excessive levels of free Fe²⁺, which reacts with H₂O₂via the Fenton reaction (Fe²⁺ + H₂O₂ to Fe³⁺ + ∙OH + ∙OH⁻)[48,49], generating highly reactive ∙OH. These ROS promote GC development through two major mechanisms.

First, ∙OH directly damages nuclear and mitochondrial DNA (mtDNA) in gastric mucosal cells, causing double-strand breaks and base oxidation (e.g., converting guanine to 8-hydroxydeoxyguanosine) and leading to increasing gene mutation. Mutation of the tumor suppressor gene p53 abolishes its apoptotic and anti-proliferative functions, significantly increasing malignant transformation risk. Concurrently, ROS-mediated oxidation of mtDNA impairs the respiratory chain, aggravating mitochondrial dysfunction and creating a self-reinforcing cycle of Fe²⁺ overload from elevated ROS to mtDNA damage.

Second, ROS act as critical signaling molecules that activate multiple oncogenic pathways. By phosphorylating inhibitor of kappa B, the inhibitor of NF-κB, ROS induce the release of NF-κB, permitting its translocation to the nucleus, where it binds to promoters of cyclin D1 and B-cell lymphoma-2. Upregulated cyclin D1 accelerates the cell cycle, whereas B-cell lymphoma-2 inhibits apoptosis, thereby promoting GC cell proliferation and survival. ROS-induced membrane damage also aberrantly activates extracellular Wnt ligands, preventing β-catenin degradation. Stabilized β-catenin translocates into the nucleus, forms complexes with T-cell factor/Lymphoid enhancer factor transcription factors, and drives expression of c-Myc and cyclin E, enhancing metabolic activity and G1/S transition. Furthermore, under hypoxic tumor conditions, ROS stabilize hypoxia inducible factor-1 alpha (HIF-1α), which coordinates Fe²⁺ uptake and angiogenesis.

Fe²⁺ dysregulation also alters global cellular metabolism. Iron regulatory proteins (IRP1/2), which maintain intracellular Fe²⁺ homeostasis by binding Fe²⁺-responsive elements on target mRNAs, are aberrantly regulated in GC. Normally, Fe²⁺ deficiency activates IRPs to upregulate transferrin receptor 1 (TfR1) to increase Fe²⁺ uptake and suppress ferritin synthesis to limit its storage. In GC, HIF-1α inhibits ubiquitin-mediated IRP2 degradation, leading to sustained IRP2 activation. This results in TfR1 overexpression and ferritin suppression, elevating labile Fe²⁺ levels. The excess Fe²⁺ fuels cancer cell proliferation and amplifies ROS generation, thereby reinforcing NF-κB and Wnt/β-catenin signaling. Meanwhile, HIF-1α, co-activated by Fe²⁺ and hypoxia, induces VEGF expression, promoting neovascularization, which nourishes tumors and facilitates metastasis. Additionally, IRP2-driven Fe²⁺ overload enhances mitochondrial respiration, supporting oncogene-driven metabolism (e.g., c-Myc) and forming a malignant feedback loop of IRP2 activation (Fe²⁺ accumulation; signaling activation; and cancer proliferation).

Feng et al[46] found that the Fe²⁺ concentration was higher in 65 GC tissue samples than in their adjacent tissue samples, and the rDNA copy number variation between individuals was correlated with the concentration of elemental Fe²⁺. Sawayama et al[50] evaluated Fe²⁺ content and total iron-binding capacity (TIBC) in 298 patients undergoing radical gastrectomy without preoperative chemotherapy. Multiple regression analysis revealed that low Fe²⁺ levels (< 60 μg/dL) were associated with longer cancer-specific survival in patients with stage III GC (P = 0.0333). Cox proportional hazards model analysis illustrated that low TIBC was significantly associated with shorter disease-free survival (P = 0.0086) and overall survival (P = 0.0173). In conclusion, preoperative serum TIBC in patients with GC undergoing radical gastrectomy emerged as a novel prognostic marker in univariate and multivariate analyses[51], confirming the important role of Fe²⁺ in GC progression and its potential as a prognostic marker.

Ferroptosis is an Fe²⁺-dependent form of regulated cell death characterized by the accumulation of lipid peroxides and ROS. In GC, dysregulated Fe²⁺ metabolism, particularly elevated intracellular Fe²⁺ levels mediated by TfR1 and divalent metal transporter 1, facilitates excessive ROS production through the Fenton reaction. This leads to oxidative damage of polyunsaturated fatty acids in cellular membranes, triggering ferroptotic death[52]. Mechanistically, inhibition of GPX4 and cystine/glutamate antiporter (solute carrier family 7a member 11) sensitizes GC cells to ferroptosis, providing a promising therapeutic strategy to overcome chemoresistance[52]. Several studies have revealed that ferroptosis inducers, such as erastin and RAS-selective lethal 3, can enhance the cytotoxicity of conventional chemotherapeutic agents (e.g., cisplatin, OXA) and suppress tumor growth in GC models[53]. Moreover, ferroptosis-related gene signatures (including acyl-CoA synthetase long chain family member 4, GPX4, and solute carrier family 7a member 11) have been proposed as potential biomarkers for GC prognosis, with higher ferroptosis sensitivity correlating with improved survival outcomes[54].

Cuproptosis is a newly identified form of Cu²⁺-induced regulated cell death that occurs when excess intracellular Cu²⁺ binds to lipoylated enzymes of the tricarboxylic acid (TCA) cycle. In normal cells, Cu²⁺ homeostasis is tightly controlled; however, abnormal Cu²⁺ influx (e.g., CTR1 upregulation) or efflux (e.g., ATP7α/β dysfunction) results in excessive free Cu²⁺ accumulation[55,56]. The metal preferentially binds to the sulfhydryl groups of lipoic acid residues on dihydrolipoamide S-acetyltransferase, a key component of the pyruvate dehydrogenase complex[57]. This interaction disrupts dihydrolipoamide S-acetyltransferase’s conformation, promotes aggregation of lipoylated proteins, and leads to TCA cycle arrest and energy depletion. The resulting protein aggregates cause severe proteotoxic stress that overwhelms chaperone systems such as heat shock proteins 70 and 90, impairing mitochondrial integrity and redox balance[58]. Unlike apoptosis or ferroptosis, cuproptosis is characterized by mitochondrial swelling, loss of membrane potential, and release of pro-inflammatory damage-activated molecular patterns. Because this process selectively targets cells with high TCA cycle activity, it represents a potential therapeutic vulnerability in metabolically active tumors such as GC[59].

Magnesium (Mg²⁺), an essential nutrient-related metal ion, has emerged as a potential regulator of GC progression. Clinical studies revealed that preoperative serum Mg²⁺ levels in patients with early-stage GC are approximately 12%-15% higher than those in healthy controls, and Mg²⁺ levels are positively correlated with tumor invasion depth, with approximately one-third of patients exhibiting hypermagnesemia[60]. Elevated Mg²⁺ levels promote tumor growth mainly through two mechanisms (Figure 1): Serving as a cofactor for kinase activation, particularly AMP-activated protein kinase (AMPK) α2, which stimulates ribosomal S6 phosphorylation, enhances mitochondrial complex I activity, increases adenosine triphosphate synthesis, and accelerates protein translation[61]; and disturbing intestinal barrier integrity and microbiota balance, inducing chronic inflammation characterized by elevated expression of IL-6 and tumor necrosis factor alpha, which amplify tumor-promoting signaling[62]. Clinically, preoperative Mg²⁺ levels exceeding 0.95 mmol/L are associated with an approximately 18% reduction in 3-year recurrence-free survival. Overall, Mg²⁺ dysregulation drives GC proliferation and survival through activation of the AMPKα2-mTOR-cyclin D1 axis and inflammation-mediated oxidative stress[63].

Figure 1 The core mechanism and correlation diagram of metal elements in gastric cancer. It is divided into three modules: (1) Interference between metal pools; (2) Metal steady-state imbalance; and (3) Activation of oncogenic pathways. The models present the pathways and potential associations of individual metals. The image was created using BioRender.com. Akt: Protein kinase B; ATP7α: ATPase copper transporting alpha; ATP7β: ATPase copper transporting beta; CaM: Calmodulin; CaMKII: Ca²⁺/calmodulin-dependent protein kinase II; CTR1: Copper transporter 1; Cys: Cysteine; DMT1: Divalent metal transporter 1; MAPK: Mitogen-activated protein kinase; MMPs: Matrix metalloproteinases; NF-κB: Nuclear factor-kappa B; ∙OH: Hydroxyl radical; PI3K: Phosphoinositide 3-kinase; ROS: Reactive oxygen species; ZFPs: Zinc finger proteins; ZIP4: Zrt-and Irt-like protein 4.

Within the metal crosstalk network, Mg²⁺ interacts with Fe²⁺ and calcium (Ca²⁺). Mg²⁺ deficiency suppresses hepatic hepcidin synthesis, enhancing intestinal Fe²⁺ absorption and aggravating Fe²⁺ accumulation in GC cells[62]. Meanwhile, reduced Mg²⁺ levels relieve voltage-gated calcium channel inhibition, causing Ca²⁺ influx, whereas excess Mg²⁺ levels activate calcineurin - NFAT signaling. Both processes enhance calmodulin (CaM)/Ca²⁺/CaM-dependent protein kinase - PI3K/Akt activity and strengthen pro-oncogenic pathways. Collectively, maintaining Mg²⁺ homeostasis might improve GC management, serving as both a prognostic biomarker and a therapeutic target for optimizing chemotherapy tolerance and clinical outcomes[63].

Recently, 54 Cu²⁺-binding proteins were collectively identified as the human Cu²⁺ proteome, and changes in their RNA expression have been observed in many tumors[64]. Many Cu²⁺-binding proteins are differentially expressed in tumor tissues, and they exert regulatory effects on cancer progression[65,66]. Bo et al[65] found that Cu²⁺ supplementation could enhance the anti-cancer effects of lactoferrin hydrolysate on GC cell lines, including growth inhibition, cell cycle arrest, mitochondrial membrane potential disruption, and apoptosis induction. Concerning the mechanism, Cu²⁺ supplementation can induce apoptosis by activating apoptosis-related proteins, leading to autophagy inhibition by activating autophagy-related proteins. Zn²⁺ is widely involved in the anabolism and catabolism of important life substances such as sugars, lipids, proteins, and nucleic acids in the body, and it is an important metallic element for maintaining the stability of enzyme systems and cells. In addition, Zn²⁺ plays an important role in the growth and development of the human body. Wei et al[67] measured the levels of Cu²⁺ and Zn²⁺ in the sera and gastric juice of 35 patients with cancer before and after surgery, and the results revealed that the serum Cu²⁺ level and Cu²⁺/Zn²⁺ ratio were higher in patients with cancer than in controls. Conversely, the serum Zn²⁺ level was lower in patients with cancer.

In addition, serum Cu²⁺ levels in patients gradually increase with cancer progression. After tumor resection, serum Cu²⁺ levels and the Cu²⁺/Zn²⁺ ratio decreased, and serum Zn²⁺ levels increased. Qi et al[68] identified mucolipin 1 as a drug target for oncogenic autophagy in GC. Mucolipin 1 regulates autophagy by mediating the release of Zn²⁺ from lysosomes to the cytoplasm. In addition, the influx of Zn²⁺ from outside the cell also prevents autophagy, confirming the essential function of Zn²⁺ as a membrane trafficking participant. Lin et al[69] conducted a case-control study of 214 patients with GC and 120 healthy people to assess the relationship between serum Cu²⁺/Zn²⁺ SOD expression and cancer risk. The results suggest that serum Cu²⁺/Zn²⁺ SOD expression is significantly elevated in patients with GC compared with that in healthy controls, and this upregulation might be associated with an increased risk of cancer. In short, the changes in Zn²⁺ and Cu²⁺ levels and the Cu²⁺/Zn²⁺ ratio in patients’ tissues and body fluids are signals of disease or even carcinogenesis in the body, thereby providing a reference for clinical diagnosis.

Ca²⁺ is an important component of human bones and teeth, and the balance of Ca²⁺ metabolism plays an important role in maintaining the physiological functions of various systems[70]. Aberrant Ca²⁺ signaling promotes tumor progression by regulating cell proliferation, migration, invasion, apoptosis, and autophagy. CaM is a key protein that triggers various signaling pathways in response to increased Ca²⁺[71,72]. Under physiological conditions, the intracellular Ca²⁺ concentration is maintained at 100-200 nM. However, GC cells disrupt this balance by upregulating membrane Ca²⁺ channels such as transient receptor potential cation channel, subfamily C, member 6 and voltage-gated calcium channels, leading to excessive extracellular Ca²⁺ influx, and by aberrantly activating inositol 1,4,5-trisphosphate receptors on the endoplasmic reticulum, releasing stored Ca²⁺[73]. These alterations increase cytoplasmic Ca²⁺ levels by as much as 5-fold, activating CaM. Activated CaM triggers the CaM-dependent protein kinase kinase (CaMKK)-AMPK signaling cascade, in which CaMKKβ phosphorylates AMPK at Thr172. Low-level AMPK activation enhances mitochondrial respiration and adenosine triphosphate synthesis, supporting rapid GC cell proliferation, whereas GC cells simultaneously downregulate tumor suppressors (p53, p21), converting AMPK into a “pro-oncogenic metabolic switch”. Additionally, the CaM-CaMKK-AMPK axis promotes MMP-9 secretion and multiple drug resistance 1 expression, facilitating extracellular matrix degradation, metastasis, and resistance to chemotherapeutic agents such as OXA and 5-fluorouracil[74].

Xie et al[70] found that Ca²⁺-sensing receptor expression was enhanced in patients with GC and positively correlated with serum Ca²⁺ concentrations, tumor progression, and poor survival rates. Both Ca²⁺-sensing receptor and transient receptor potential cation channel subfamily V member 4 are involved in the Ca²⁺-induced proliferation, migration, and invasion of cancer cells through Ca²⁺/Akt/β-catenin, potentially promoting carcinogenesis. Li et al[75], through clinical case analysis, revealed that Ca²⁺ channel blockers in Helicobacter pylori-eradicated patients reduced the occurrence of GC. Najar et al[76] identified CaMKK2 as a serine- threonine kinase that is highly expressed in GC, and it promotes the progression of GC by stimulating cell migration, invasion, and colony-forming activity, further confirming the important role of Ca²⁺ in the development of GC.

Based on these findings, our summary of ‘GC as a rewired state of metal homeostasis’ is presented in Table 1[48,49,51,77-94].

Table 1 Mechanisms of action of various metals in gastric cancer.

Metal element	Category of core mechanism	Specific molecular mechanism	Ref.
Fe2+	Oxidative damage mediated by the Fenton reaction	Excess free Fe2+ (elevated serum ferritin, high expression of divalent metal transporter 1) generates ∙OH via the Fenton reaction. ∙OH attacks DNA, causing base damage (e.g., 8-hydroxydeoxyguanosine) and double-strand breaks and thereby inducing gene mutations; meanwhile, ∙OH oxidizes cell membrane lipids and disrupts cell structure integrity	Dizdaroglu and Jaruga[48], Kabat and Rohan[49]
	Activation of pro-tumor pathways and metabolic reprogramming	Low concentrations of reactive oxygen species activate pro-tumor pathways such as NF-κB and mitogen-activated protein kinase, promoting GC cell proliferation and anti-apoptosis. Fe2+ upregulates mitochondrial respiratory chain proteins (e.g., cytochrome C oxidase) to enhance oxidative phosphorylation for energy supply. Fe2+ induces high expression of hepcidin, inhibiting Fe2+ efflux and exacerbating Fe2+ accumulation to form an “Fe2+-dependent” cycle	Seĭlanov et al[77], Morgan and Liu[78], Tomeckova et al[79]
	Inhibition of anti-tumor immunity	Excess Fe2+ induces polarization of macrophages to the M2 phenotype, leading to IL-10 and transforming growth factor beta secretion. Fe2+ suppresses the antigen-presenting ability of dendritic cells and inhibits the activity of CD8+ T cells and natural killer cells, facilitating GC immune evasion	Yu et al[80], Chen et al[81], Agoro et al[82]
Cu2+	Excess Cu2+ triggers cuproptosis	Free Cu2+ beyond homeostasis (dysfunction of ATPase copper transporting alpha/beta, high expression of copper transporter 1) binds to the thiol groups of lipoic acid residues in TCA cycle lipoylated proteins (dihydrolipoamide acetyltransferase, dihydrolipoamide dehydrogenase), disrupting protein structure and promoting cross-linking to form aggregates. This leads to TCA cycle arrest and proteotoxic stress, ultimately inducing GC cell death characterized by mitochondrial swelling, serving as a potential therapeutic target	Tsvetkov et al[51], Tang et al[83], Concilli et al[84], Clifford et al[85]
	Regulation of pro-tumor pathways by physiological concentrations	Cu2+ acts as a cofactor for enzymes (e.g., tyrosinase, superoxide dismutase), activating pathways such as phosphoinositide 3-kinase/protein kinase B and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase to promote GC cell proliferation and migration. Cu2+ enhances the activity of MMPs, accelerating extracellular matrix degradation and facilitating invasion and metastasis	Guo et al[86]
Zn2+	Gene regulation mediated by ZFPs	Zn2+ stabilizes the “finger-like” structure of ZFPs: Pro-tumor ZFPs (ZFP217, ZFP X-linked) bind to the promoters/enhancers of cyclin D1 and MYC proto-oncogene, bHLH transcription factor, accelerating cell cycle progression and metabolic reprogramming; snail family transcriptional repressor 1 inhibits E-cadherin and p53, disrupting cell adhesion and weakening proliferation constraints	Fang et al[87], Ecco et al[88]
	Maintenance of MMP activity	Zn2+ is a key ion in the catalytic center of MMPs (MMP2/9/7), helping them polarize substrate peptide bonds and hydrolyze vascular basement membrane collagen IV and intercellular adhesion molecules to promote angiogenesis and invasion. MMP-3 activates pro-MMP-9 via Zn2+, amplifying extracellular matrix destruction	Agrawal et al[89], Khrenova et al[90]
Ca2+	Intracellular Ca2+ elevation activates pro-tumor signals	GC cells upregulate Ca2+ channels (transient receptor potential canonical, voltage-gated calcium channel) or release endoplasmic reticulum Ca2+, increasing intracellular Ca2+. This activates CaM/Ca2+/CaM-dependent protein kinase II, which further activates pathways such as NF-κB and Wnt/β-catenin to promote proliferation, migration, and anti-apoptosis; this also enhances phospholipase C activity, accelerating inositol 1,4,5-trisphosphate production and forming a positive feedback loop of Ca2+ signaling	Liu et al[91]
	Homeostasis imbalance induces apoptosis	Under extreme conditions (e.g., chemotherapy), excessive intracellular Ca2+ disrupts the mitochondrial membrane, promoting cytochrome C release and activating the caspase cascade. Ca2+ also activates Ca2+-dependent nucleases, accelerating DNA fragmentation and enhancing the apoptotic effect	Yu et al[92], Colbran[93]
	Regulation of the tumor microenvironment	Extracellular Ca2+ promotes GC-associated fibroblasts to secrete IL-6 and vascular endothelial growth factor. Ca2+ enhances the migration and proliferation of vascular endothelial cells, facilitating tumor angiogenesis	Sadras et al[94]

Ca²⁺: Calcium; CaM: Calmodulin; Cu²⁺: Copper; Fe²⁺: Iron; GC: Gastric cancer; IL: Interleukin; MMP: Matrix metalloproteinase; NF-κB: Nuclear factor-kappa B; ∙OH, hydroxyl radical; TCA: Tricarboxylic acid; ZFPs: Zinc finger proteins; Zn²⁺: Zinc.

PERSPECTIVES

GC is a serious public health problem with high mortality and morbidity rates and an increasing prevalence globally. Metal-based anticancer drugs prolong the survival and improve the quality of life of patients. Changes in the levels of metallic elements such as Fe²⁺, Zn²⁺, Ca²⁺, and Cu²⁺ can be used as markers to measure the occurrence and development of GC. Exploring the changes and mechanisms of metallomics and metallic elements in GC occurrence and development (Figure 1), could provide a theoretical basis for the prevention and clinical treatment of GC.

However, metallomics research faces many challenges in GC. First, many of the metallic elements attached to biomolecules have relatively low content, and metal adsorption or ligand exchange often occurs during the separation process. Second, metalloproteins decompose during the separation process, resulting in significant errors in quantitative determination. Third, the structures of many metal biomolecules are unknown, and there is a lack of corresponding standard substances and reference materials for structural identification and quantitative analysis. Finally, the long-term use of a single metal-targeted drug might lead to drug resistance, toxin accumulation, reduced efficacy, and immunosuppression.

In the future, improvements in instrument sensitivity and chromatographic combination technology will provide more accurate analytical tools for metallomics research in the field of GC. The unique advantages of traditional Chinese medicine in regulating the tumor immune microenvironment permit combination treatment with metal-based anti-cancer drugs as an important direction for GC treatment, and the core mechanism of their synergistic effect is reflected in precise regulation at the molecular level.

The efficacy of metal drugs represented by OXA is often limited by lower intracellular drug concentrations and resistance mechanisms[95]. Chinese herbal ingredients can achieve synergistic effects by targeting key links in metal metabolism. Some active ingredients in Chinese herbal medicines (such as baicalin and curcumin) have specific metal chelation ability, allowing them to bind to free Cu²⁺, Fe²⁺, and other metals, reduce their competitive binding to OXA, and maintain OXA in its free state to enhance DNA damage effects. Meanwhile, these components can regulate the expression of metal transporters, such as suppressing the membrane localization of ATP7α/β, inhibiting the efflux of OXA, or increasing the expression of CTR1, thereby promoting the entry of OXA into GC cells and consequently increasing its intracellular concentration[96].

Meanwhile, traditional Chinese medicines can inhibit the metal detoxification mechanism related to OXA resistance. For example, demethoxyapigenin in Hedyotis diffusa can inhibit the synthesis of metallothionein and reduce its binding-mediated inactivation of OXA. Lycium barbarum polysaccharides deplete glutathione, thereby preventing thiolation-mediated OXA detoxification and restoring the drug’s killing effect on GC cells. In addition, traditional Chinese medicines can enhance the efficacy of OXA by regulating the immune microenvironment. For instance, Huangqi polysaccharides promote the polarization of M1 macrophages, enhancing CD8⁺ T cell infiltration[97] and synergistically clearing tumor cells in combination with OXA.

Emerging technologies such as laser ablation-inductively coupled plasma-mass spectrometry provide spatial research tools for analyzing the correlation between metal distribution in the tumor microenvironment and disease progression[98]. This technology uses precise laser ablation of small areas of tumor tissue (micrometer resolution) combined with high sensitivity detection of metal elements by mass spectrometry to visually present the spatial distribution characteristics of metals such as Fe²⁺, Cu²⁺, and Zn²⁺ in GC tissue[99]. For example, in the invasive tumor front, local enrichment of Fe²⁺ can often be detected, and this enrichment is closely related to the high generation of ROS and active degradation of extracellular matrix in this area. The high concentration of Cu²⁺ in the tumor core area might be related to enhanced mitochondrial metabolism and differences in sensitivity Cu²⁺-induced toxicity[100]. By overlaying metal distribution data with single-cell sequencing and immunohistochemistry results, the association between specific cell types and metal accumulation can also be revealed, such as the increased concentration of Zn²⁺ around cancer-associated fibroblasts, which might be related to their secretion of Zn²⁺-dependent MMPs, which promote tumor invasion. This spatial resolution ability can fuel the discovery of new mechanisms linking metal accumulation with cellular function and disease staging, such as clarifying the association between specific metal hotspot regions and GC metastasis potential, providing a basis for precise target selection in combination therapy[101-103].

CONCLUSION

In summary, the combination of metal-based drugs and traditional Chinese medicine achieves synergistic effects through molecular-level regulation of metal metabolism, whereas technologies such as laser ablation-inductively coupled plasma-mass spectrometry provide a new perspective for the study of metal mechanisms. These two activities will jointly facilitate the development of more precise and efficient GC therapy.