Article

ASCT2-Mediated Glutamine Metabolism as a Central Axis Linking Tumor Metabolism to Malignancy, Metastasis, and Drug Resistance

Seo Lyn Choi^1,12,4, Chang-Whan Yoon^1,2,4, Jaehyeon Kim³, Seo Young Kim⁴, Eo Jin Kim^1,5,#, Sei Young Lee^4,#, Sang-Hyuk Lee^1,2,#

Abstract

Background/Objectives: Metabolic reprogramming is a hallmark of cancer that supports tumor growth and survival under hostile microenvironmental conditions. Glutamine addiction is a characteristic of many aggressive cancers, and alanine, serine, cysteine-preferring transporter 2 (ASCT2, SLC1A5) is the primary transporter responsible for glutamine uptake. This review summarizes the molecular and clinical roles of ASCT2 in cancer progression and evaluates its therapeutic potential.

Methods: Recent experimental and clinical studies investigating ASCT2-mediated glutamine metabolism were reviewed. Evidence was integrated to examine the role of ASCT2 in metabolic regulation, oncogenic signaling, epithelial–mesenchymal transition (EMT), cancer stem cell (CSC) maintenance, metastasis, therapeutic resistance, and clinical applications across multiple cancer types, particularly head and neck squamous cell carcinoma (HNSCC).

Results: ASCT2-mediated glutamine uptake promotes anabolic metabolism, maintains redox homeostasis, and activates oncogenic signaling pathways, including the mTORC1–MYC axis, thereby enhancing tumor growth and survival. ASCT2 also promotes EMT, CSC maintenance, metastatic dissemination, and metabolic adaptation under therapeutic stress, leading to treatment resistance. Preclinical studies consistently demonstrate that pharmacological or genetic inhibition of ASCT2 suppresses tumor progression and enhances sensitivity to anticancer therapies.

Conclusions: ASCT2 is a central regulator linking glutamine metabolism with tumor progression, stemness, metastasis, and therapeutic resistance. Targeting ASCT2-mediated glutamine metabolism represents a promising therapeutic strategy, and ASCT2 may serve as a useful biomarker for patient stratification and precision treatment in metabolically active cancers.

Keywords

ASCT2, HNSCC, CANCER STEMNESS, EMT, METABOLISM

Introduction

Tumor progression is driven not only by genetic alterations but also by profound metabolic rewiring that enables cancer cells to survive and proliferate under nutrient-limited and hypoxic conditions. While glucose metabolism has long been emphasized, glutamine metabolism has emerged as an equally critical pathway supporting tumor growth.

Glutamine functions as a versatile metabolic substrate, providing carbon and nitrogen for biosynthesis, fueling the tricarboxylic acid (TCA) cycle, and maintaining redox balance through glutathione production. To sustain these demands, cancer cells upregulate glutamine transport systems, among which ASCT2 (SLC1A5) serves as the dominant transporter.

ASCT2 operates as a sodium-dependent antiporter, facilitating glutamine influx in exchange for intracellular neutral amino acids. Importantly, its role extends beyond nutrient transport, acting as a central regulator of oncogenic signaling networks.

Recent evidence suggests that ASCT2 functions as a molecular hub that integrates metabolic reprogramming with malignant signaling pathways. This review adopts a unified framework in which ASCT2-mediated glutamine metabolism drives a sequential cascade.

ASCT2 as a Metabolic Gatekeeper in Cancer

ASCT2-mediated glutamine uptake represents a critical initiating step in cancer metabolic reprogramming. Once transported into the cell, glutamine is converted into glutamate and subsequently into α-ketoglutarate (α-KG), which replenishes tricarboxylic acid (TCA) cycle intermediates and sustains mitochondrial ATP production. This anaplerotic function is essential for maintaining energy homeostasis, particularly in rapidly proliferating cancer cells that divert glycolytic intermediates toward biosynthetic pathways [1, 2].

Beyond its role in energy metabolism, glutamine serves as a key substrate for anabolic processes that support tumor growth. Carbon and nitrogen derived from glutamine are utilized for nucleotide biosynthesis, enabling DNA replication and cell division, while α-KG can be redirected toward citrate production for lipid synthesis, facilitating membrane biogenesis. These processes collectively support biomass accumulation and uncontrolled proliferation in cancer cells [3, 4].

Importantly, ASCT2-driven glutamine metabolism plays a pivotal role in maintaining redox homeostasis. Glutamate derived from glutamine acts as a precursor for glutathione (GSH) synthesis, which protects cancer cells from reactive oxygen species (ROS)-induced oxidative stress and apoptosis. This antioxidant capacity enables tumor cells to survive under hypoxic and metabolically stressful conditions, including exposure to therapeutic agents [5, 6].

In addition to its metabolic functions, ASCT2 influences oncogenic signaling pathways. Intracellular glutamine promotes mTORC1 activation through amino acid exchange mechanisms, while also stabilizing MYC, forming a feed-forward loop that enhances SLC1A5 expression and metabolic flux. Through these integrated roles in metabolism, redox regulation, and signaling, ASCT2 functions as a central metabolic gatekeeper that supports tumor growth and provides a foundation for malignant progression and therapeutic resistance [7, 8].

ASCT2-Driven Malignancy Through mTOR–MYC Axis

The metabolic advantages conferred by ASCT2-mediated glutamine uptake are directly translated into malignant phenotypes through activation of key oncogenic signaling pathways. A central mechanism involves the activation of mechanistic target of rapamycin complex 1 (mTORC1), a master regulator of cell growth and protein synthesis. Intracellular glutamine promotes amino acid exchange via LAT1 (SLC7A5), facilitating leucine influx and subsequent lysosomal localization and activation of mTORC1. This signaling cascade enhances translational capacity, biomass accumulation, and sustained proliferation of cancer cells [7, 9].

In parallel, ASCT2 is functionally linked to the oncogene MYC through a reciprocal regulatory loop. MYC directly binds to the promoter region of SLC1A5, driving ASCT2 transcription and increasing glutamine uptake. Conversely, glutamine metabolism supports MYC stability and activity by maintaining cellular metabolic homeostasis and supporting nucleotide biosynthesis. This feed-forward loop amplifies oncogenic signaling, enabling persistent proliferative signaling and metabolic reprogramming that are characteristic of aggressive tumors [8, 10].

Beyond growth signaling, ASCT2 also contributes to tumor cell survival by regulating redox balance. Enhanced glutamine flux increases glutathione (GSH) synthesis, allowing cancer cells to neutralize reactive oxygen species (ROS) and avoid oxidative stress–induced apoptosis. This antioxidant defense mechanism is particularly important in the tumor microenvironment, where hypoxia and metabolic stress would otherwise limit tumor viability [2, 5].

Collectively, the integration of mTORC1 activation, MYC-driven transcriptional amplification, and redox homeostasis establishes ASCT2 as a central driver of tumor malignancy. Through these coordinated mechanisms, ASCT2 not only supports tumor growth but also reinforces the molecular foundation for subsequent progression, including EMT, metastasis, and therapeutic resistance.

ASCT2 as a Driver of EMT and Metastatic Dissemination

Beyond its role in tumor growth, ASCT2 plays a pivotal role in metastatic progression by functionally linking metabolic reprogramming to epithelial–mesenchymal transition (EMT). Elevated glutamine uptake mediated by ASCT2 enhances oncogenic signaling pathways, particularly mTORC1 and MYC, which are known to regulate EMT-associated transcriptional programs. Activation of these pathways induces key EMT transcription factors, including Snail, Twist, and Vimentin, resulting in the suppression of epithelial markers such as E-cadherin and the acquisition of mesenchymal phenotypes that promote cell motility and invasiveness [8, 11].

In addition to transcriptional reprogramming, ASCT2-driven metabolism contributes to the structural changes required for metastatic dissemination. Enhanced glutamine flux supports cytoskeletal remodeling and extracellular matrix (ECM) interaction through integrin-mediated signaling and actin reorganization. These changes enable tumor cells to detach from the primary tumor mass, invade surrounding tissues, and intravasate into the vasculature, facilitating systemic dissemination [2, 9].

Importantly, ASCT2 is also closely associated with the maintenance of cancer stem cell (CSC) properties, which are critical for metastasis and tumor recurrence. Glutamine-dependent metabolic adaptation supports stemness-associated signaling pathways and epigenetic regulation, allowing CSC populations to survive under nutrient-deprived and hypoxic conditions. These cells exhibit enhanced plasticity and resistance to environmental stress, enabling successful colonization at distant metastatic sites [12, 13].

Collectively, these findings establish ASCT2 as a critical molecular bridge connecting metabolic reprogramming to EMT, stemness, and metastatic dissemination. Through coordinated regulation of signaling pathways, cytoskeletal dynamics, and cellular plasticity, ASCT2 facilitates the progression from localized tumor growth to systemic metastasis.

ASCT2 as a Driver of EMT and Metastatic Dissemination

Therapeutic resistance remains a major challenge in cancer treatment, and accumulating evidence indicates that ASCT2 plays a central role in this process by enabling metabolic adaptation under therapeutic stress. A key mechanism involves the regulation of cellular redox balance. ASCT2-mediated glutamine uptake enhances the production of glutathione (GSH), a major intracellular antioxidant that neutralizes reactive oxygen species (ROS) generated by chemotherapy. This redox buffering capacity protects cancer cells from oxidative damage and prevents apoptosis, thereby diminishing the cytotoxic efficacy of anticancer agents [2, 5].

In addition to redox regulation, ASCT2 contributes to metabolic flexibility, allowing cancer cells to dynamically reprogram their metabolic pathways in response to treatment-induced stress. Increased glutamine flux supports continued TCA cycle activity, nucleotide biosynthesis, and energy production, even under conditions of metabolic inhibition. This adaptability is particularly important in resistance to platinum-based chemotherapies such as cisplatin, where cancer cells rely on enhanced antioxidant defenses and metabolic rewiring to survive cytotoxic stress [4, 11].

Furthermore, ASCT2 plays a critical role in maintaining cancer stem cell (CSC) populations, which are intrinsically resistant to conventional therapies. Glutamine-dependent metabolic pathways support stemness-associated signaling and epigenetic regulation, enabling CSCs to persist following treatment and drive tumor recurrence. These cells exhibit enhanced survival capacity, plasticity, and resistance to apoptosis, contributing to long-term therapeutic failure [1, 12].

Collectively, these mechanisms establish ASCT2 as a central mediator of drug resistance, integrating redox homeostasis, metabolic reprogramming, and stemness maintenance. Targeting ASCT2-mediated glutamine metabolism may therefore represent an effective strategy to overcome therapeutic resistance and improve clinical outcomes in cancer patients.

Translational Implications: ASCT2 as a Therapeutic Target

Given its central role in coordinating metabolic reprogramming, oncogenic signaling, and therapeutic resistance, ASCT2 has emerged as an attractive target for cancer therapy. Pharmacological inhibition of ASCT2 disrupts glutamine uptake, leading to impaired TCA cycle activity, reduced biosynthetic capacity, and increased oxidative stress. The small molecule inhibitor V-9302 has demonstrated significant anti-tumor activity in preclinical models by selectively blocking glutamine transport, resulting in decreased tumor growth and enhanced sensitivity to cytotoxic agents [14, 15].

Importantly, targeting ASCT2 may be particularly effective in combination with existing therapeutic strategies. Inhibition of glutamine metabolism can sensitize cancer cells to chemotherapy by reducing antioxidant capacity and increasing susceptibility to ROS-induced apoptosis. Moreover, emerging evidence suggests that metabolic targeting may enhance the efficacy of immune checkpoint inhibitors by modulating the tumor microenvironment and alleviating metabolic competition between tumor cells and immune cells. Combination approaches integrating ASCT2 inhibitors with chemotherapy, radiotherapy, or immunotherapy therefore represent a promising strategy to overcome treatment resistance [2, 16].

In addition to its therapeutic relevance, ASCT2 expression holds potential as a predictive biomarker for patient stratification. High ASCT2 expression is frequently associated with aggressive tumor phenotypes, increased metabolic dependency, and poor clinical outcomes across multiple cancer types. In metabolically active tumors such as head and neck squamous cell carcinoma (HNSCC), ASCT2 expression may identify patient subsets that are particularly responsive to metabolic-targeted therapies, thereby supporting precision oncology approaches [9, 11].

Collectively, these findings highlight the translational significance of ASCT2 as both a therapeutic target and a biomarker. Future clinical development of ASCT2-targeted therapies, particularly in combination regimens and biomarker-guided settings, may provide new opportunities to improve treatment outcomes in patients with metabolically driven cancers.

Discussion

The emerging role of ASCT2 highlights a paradigm shift in cancer biology, where metabolic regulation actively drives tumor progression rather than merely supporting it. ASCT2-mediated glutamine uptake functions as a central upstream event that fuels metabolic reprogramming, sustains biosynthetic demand, and maintains redox homeostasis. These metabolic processes are tightly coupled to oncogenic signaling pathways, particularly the mTOR–MYC axis, thereby linking nutrient availability directly to sustained proliferation and malignant transformation. This integrated framework positions ASCT2 as a key molecular hub that connects metabolism with core hallmarks of cancer.

Beyond tumor growth, ASCT2 plays a critical role in coordinating EMT, metastatic dissemination, and therapeutic resistance. By activating EMT-associated transcriptional programs and supporting cytoskeletal remodeling, ASCT2 enables tumor cells to acquire invasive and migratory properties. Simultaneously, glutamine-dependent metabolic adaptation promotes cancer stem cell (CSC) maintenance, contributing to tumor plasticity, immune evasion, and resistance to therapy. Enhanced glutathione production and metabolic flexibility further allow cancer cells to withstand treatment-induced stress, ultimately driving recurrence and poor clinical outcomes, particularly in metabolically active cancers such as HNSCC.

From a translational perspective, targeting ASCT2 offers a promising strategy to disrupt multiple tumor-promoting processes simultaneously. Pharmacological inhibition of glutamine transport, especially in combination with chemotherapy, immunotherapy, or metabolic inhibitors, may enhance therapeutic efficacy and overcome resistance. Furthermore, integrating ASCT2-based metabolic profiling with emerging approaches such as spatial transcriptomics and organoid models may enable improved patient stratification and precision oncology strategies, underscoring the clinical significance of ASCT2 as both a therapeutic target and biomarker.

Conclusion

ASCT2 functions as a central molecular hub that links glutamine metabolism to tumor progression, metastasis, and therapeutic resistance. By integrating metabolic reprogramming with oncogenic signaling and cellular plasticity, ASCT2 drives key processes underlying cancer aggressiveness.

Targeting ASCT2-mediated glutamine metabolism therefore represents a promising strategy for improving treatment outcomes, particularly in metabolically active and therapy-resistant cancers, and may serve as a foundation for future precision oncology approaches.

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