Target the human Alanine/Serine/Cysteine Transporter 2(ASCT2): Achievement and Future for Novel Cancer Therapy

Disulfidptosis decoded: a journey through cell death mysteries, regulatory networks, disease paradigms and future directions

Cell death is an important part of the life cycle, serving as a foundation for both the orderly development and the maintenance of physiological equilibrium within organisms. This process is fundamental, as it eliminates senescent, impaired, or aberrant cells while also promoting tissue regeneration and immunological responses. A novel paradigm of programmed cell death, known as disulfidptosis, has recently emerged in the scientific circle. Disulfidptosis is defined as the accumulation of cystine by cancer cells with high expression of the solute carrier family 7 member 11 (SLC7A11) during glucose starvation. This accumulation causes extensive disulfide linkages between F-actins, resulting in their contraction and subsequent detachment from the cellular membrane, triggering cellular death. The RAC1-WRC axis is involved in this phenomenon. Disulfidptosis sparked growing interest due to its potential applications in a variety of pathologies, particularly oncology, neurodegenerative disorders, and metabolic anomalies. Nonetheless, the complexities of its regulatory pathways remain elusive, and its precise molecular targets have yet to be definitively identified. This manuscript aims to meticulously dissect the historical evolution, molecular underpinnings, regulatory frameworks, and potential implications of disulfidptosis in various disease contexts, illuminating its promise as a groundbreaking therapeutic pathway and target.

Exploiting the Achilles' heel of cancer: disrupting glutamine metabolism for effective cancer treatment

Cancer cells have adapted to rapid tumor growth and evade immune attack by reprogramming their metabolic pathways. Glutamine is an important nitrogen resource for synthesizing amino acids and nucleotides and an important carbon source in the tricarboxylic acid (TCA) cycle and lipid biosynthesis pathway. In this review, we summarize the significant role of glutamine metabolism in tumor development and highlight the vulnerabilities of targeting glutamine metabolism for effective therapy. In particular, we review the reported drugs targeting glutaminase and glutamine uptake for efficient cancer treatment. Moreover, we discuss the current clinical test about targeting glutamine metabolism and the prospective direction of drug development.

Design strategies and recent development of bioactive modulators for glutamine transporters

Glutamine transporters are integral to the metabolism of glutamine in both healthy tissues and cancerous cells, playing a pivotal role in maintaining amino acid balance, synthesizing biomolecules, and regulating redox equilibrium. Their critical functions in cellular metabolism make them promising targets for oncological therapies. Recent years have witnessed substantial progress in the field of glutamine transporters, marked by breakthroughs in understanding of their protein structures and the discovery of novel inhibitors, prodrugs, and radiotracers. This review provides a comprehensive update on the latest advancements in modulators targeting the glutamine transporter, with special attention given to LAT1 and ASCT2. It also discusses innovative approaches in drug design aimed at these transporters.

Loss of RACK1 promotes glutamine addiction via activating AKT/mTOR/ASCT2 axis to facilitate tumor growth in gastric cancer

BACKGROUND

Metabolic reprogramming is closely related to the development of gastric cancer (GC), which remains as the fourth leading cause of cancer-related death worldwide. As a tumor suppressor for GC, whether receptor for activated C-kinase 1 (RACK1) play a modulatory role in metabolic reprogramming remains largely unclear.

METHODS

GC cell lines and cell-derived xenograft mouse model were used to identify the biological function of RACK1. Flow cytometry and Seahorse assays were applied to examine cell cycle and oxygen consumption rate (OCR), respectively. Western blot, real-time PCR and autophagy double fluorescent assays were utilized to explore the signaling. Immunohistochemistry was performed to detect the expression of RACK1 and other indicators in tissue sections.

RESULTS

Loss of RACK1 facilitated the viability, colony formation, cell cycle progression and OCR of GC cells in a glutamine-dependent manner. Further investigation revealed that RACK1 knockdown inhibited the lysosomal degradation of Alanine-serine-cysteine amino acid transporter 2 (ASCT2). Mechanistically, depletion of RACK1 remarkably decreased PTEN expression through up-regulating miR-146b-5p, leading to the activation of AKT/mTOR signaling pathway which dampened autophagy flux subsequently. Moreover, knockdown of ASCT2 could reverse the promotive effect of RACK1 depletion on GC tumor growth both in vitro and in vivo. Tissue microarray confirmed that RACK1 was negatively correlated with the expression of ASCT2 and p62, as well as the phosphorylation of mTOR.

CONCLUSION

Together, our results demonstrate that the suppressive function of RACK1 in GC is associated with ASCT2-mediated glutamine metabolism, and imply that targeting RACK1/ASCT2 axis provides potential strategies for GC treatment.

Glutamine addiction and therapeutic strategies in pancreatic cancer

Pancreatic cancer remains one of the most lethal diseases worldwide owing to its late diagnosis, early metastasis, and poor prognosis. Because current therapeutic options are limited, there is an urgent need to investigate novel targeted treatment strategies. Pancreatic cancer faces significant metabolic challenges, principally hypoxia and nutrient deprivation, due to specific microenvironmental constraints, including an extensive desmoplastic stromal reaction. Pancreatic cancer cells have been shown to rewire their metabolism and energy production networks to support rapid survival and proliferation. Increased glucose uptake and glycolytic pathway activity during this process have been extensively described. However, growing evidence suggests that pancreatic cancer cells are glutamine addicted. As a nitrogen source, glutamine directly (or indirectly via glutamate conversion) contributes to many anabolic processes in pancreatic cancer, including amino acids, nucleobases, and hexosamine biosynthesis. It also plays an important role in redox homeostasis, and when converted to α-ketoglutarate, glutamine serves as an energy and anaplerotic carbon source, replenishing the tricarboxylic acid cycle intermediates. The present study aims to provide a comprehensive overview of glutamine metabolic reprogramming in pancreatic cancer, focusing on potential therapeutic approaches targeting glutamine metabolism in pancreatic cancer.

Multiplex Bioanalytical Methods for Comprehensive Characterization and Quantification of the Unique Complementarity-Determining-Region Deamidation of MEDI7247, an Anti-ASCT2 Pyrrolobenzodiazepine Antibody-Drug Conjugate

Deamidation, a common post-translational modification, may impact multiple physiochemical properties of a therapeutic protein. MEDI7247, a pyrrolobenzodiazepine (PBD) antibody-drug conjugate (ADC), contains a unique deamidation site, N102, located within the complementarity-determining region (CDR), impacting the affinity of MEDI7247 to its target. Therefore, it was necessary to monitor MEDI7247 deamidation status in vivo. Due to the low dose, a sensitive absolute quantification method using immunocapture coupled with liquid chromatography-tandem mass spectrometry (LBA-LC-MS/MS) was developed and qualified. We characterized the isomerization via Electron-Activated Dissociation (EAD), revealing that deamidation resulted in iso-aspartic acid. The absolute quantification of deamidation requires careful assay optimization in order not to perturb the balance of the deamidated and nondeamidated forms. Moreover, the selection of capture reagents essential for the correct quantitative assessment of deamidation was evaluated. The final assay was qualified with 50 ng/mL LLOQ for ADC for total and nondeamidated antibody quantification, with qualitative monitoring of the deamidated antibody. The impact of deamidation on the pharmacokinetic characteristics of MEDI7247 from clinical trial NCT03106428 was analyzed, revealing a gradual reduction in the nondeamidated form of MEDI7247 in vivo. Careful quantitative biotransformation analyses of complex biotherapeutic conjugates help us understand changes in product PTMs after administration, thus providing a more complete view of in vivo pharmacology.

ASCT2-mediated glutamine uptake promotes Th1 differentiation via ROS-EGR1-PAC1 pathway in oral lichen planus

Oral lichen planus (OLP) is a T cell-mediated autoimmune disease of oral mucosa concerning with the redox imbalance. Although glutamine uptake mediated by alanine-serine-cysteine transporter 2 (ASCT2) is critical to T cell differentiation, the exact mechanism remains ambiguous. Here, we elucidate a novel regulatory mechanism of ASCT2-mediated uptake in the differentiation and proliferation of T cells through maintaining redox balance in OLP. The results of immunohistochemistry (IHC) showed that both ASCT2 and glutaminase (GLS) were obviously upregulated compared to controls in OLP. Moreover, correlation analyses indicated that ASCT2 expression was significantly related to GLS level. Interestingly, the upregulation of glutamine metabolism in epithelial layer was consistent with that in lamina propria. Functional assays in vitro revealed the positive association between glutamine metabolism and lymphocytes infiltration. Additionally, multiplex immunohistochemistry (mIHC) uncovered a stronger colocalization among ASCT2 and CD4 and IFN-γ, which was further demonstrated by human Th1 differentiation assay in vitro. Mechanistically, targeting glutamine uptake through interference with ASCT2 using L-γ-Glutamyl-p-nitroanilide (GPNA) decreased the glutamine uptake of T cells and leaded to the accumulation of intracellular reactive oxygen species (ROS), which promoted dual specificity phosphatase 2 (DUSP2/PAC1) expression through activation of early growth response 1 (EGR1) to induce dephosphorylation of signal transducer and activator of transcription 3 (STAT3) and inhibit Th1 differentiation in turn. These results demonstrated that glutamine uptake mediated by ASCT2 induced Th1 differentiation by ROS-EGR1-PAC1 pathway, and restoring the redox dynamic balance through targeting ASCT2 may be a potential treatment for T cell-mediated autoimmune diseases.

Comprehensive bioinformatics analysis of the solute carrier family and preliminary exploration of SLC25A29 in lung adenocarcinoma

According to the latest epidemiological investigation, lung adenocarcinoma (LUAD) is one of the most fatal cancer among both men and women. Despite continuous advancements in treatment approaches in recent years, the prognosis for LUAD remains relatively poor. Given the crucial role of the solute carrier (SLC) family in maintaining cellular energy metabolism stability, we conducted a comprehensive analysis of the association between SLC genes and LUAD prognosis. In the present study, we identified 71 genes among the SLC family members, of which 32 were downregulated and 39 were upregulated in LUAD samples. Based on these differentially expressed genes, a prognostic risk scoring model was established that was composed of five genes (SLC16A7, SLC16A4, SLC16A3, SLC12A8, and SLC25A15) and clinical characteristics; this model could effectively predict the survival and prognosis of patients in the cohort. Notably, SLC2A1, SLC25A29, and SLC27A4 were identified as key genes associated with survival and tumor stage. Further analysis revealed that SLC25A29 was underexpressed in LUAD tissue and regulated the phenotype of endothelial cells. Endothelial cell proliferation and migration increased and apoptosis decreased with a decrease in SLC25A29 expression. Investigation of the upstream regulatory mechanisms of SLC25A29 revealed that SLC25A29 expression gradually decreased as the lactate concentration increased. This phenomenon suggested that the expression of SLC25A29 may be related to lactylation modification. ChIP-qPCR experiments confirmed the critical regulatory role played by H3K14la and H3K18la modifications in the promoter region of SLC25A29. In conclusion, this study confirmed the role of SLC family genes in LUAD prognosis and revealed the role of SLC25A29 in regulating endothelial cell phenotypes. These study results provided important clues to further understand LUAD pathogenesis and develop appropriate therapeutic strategies.

Serine Metabolic Reprogramming in Tumorigenesis, Tumor Immunity, and Clinical Treatment

Serine has been recently identified as an essential metabolite for oncogenesis, progression, and adaptive immunity. Influenced by many physiologic or tumor environmental factors, the metabolic pathways of serine synthesis, uptake, and usage are heterogeneously reprogrammed and frequently amplified in tumor or tumor-associated cells. The hyperactivation of serine metabolism promotes abnormal cellular nucleotide/protein/lipid synthesis, mitochondrial function, and epigenetic modifications, which drive malignant transformation, unlimited proliferation, metastasis, immunosuppression, and drug resistance of tumor cells. Dietary restriction of serine or phosphoglycerate dehydrogenase depletion mitigates tumor growth and extends the survival of tumor patients. Correspondingly, these findings triggered a boom in the development of novel therapeutic agents targeting serine metabolism. In this study, recent discoveries in the underlying mechanism and cellular function of serine metabolic reprogramming are summarized. The vital role of serine metabolism in oncogenesis, tumor stemness, tumor immunity, and therapeutic resistance is outlined. Finally, some potential tumor therapeutic concepts, strategies, and limitations of targeting the serine metabolic pathway are described in detail. Taken together, this review underscores the importance of serine metabolic reprogramming in tumorigenesis and progression and highlights new opportunities for dietary restriction or selective pharmacologic intervention.

Identification and validation of ferroptosis-related prognostic risk model and immune landscape in hepatocellular carcinoma

BACKGROUND

Ferroptosis has been paid much more attention on account of the correlation withtumorigenesis and development. However, the molecular characteristics and immune landscape of ferroptosis regulators in hepatocellular carcinoma (HCC) have not been fully elucidated.

METHODS

RNA-sequencing data and matched clinical data were collected from The Cancer Genome Atlas (TCGA) database, then underwent gene expression, genetic variations, prognostic risk model, and immune characterization analyses. An independent cohort from Gene Expression Omnibus (GEO) database was utilized to validate ferroptosis-related prognostic risk model.

RESULTS

We first identified the differentially expressed ferroptosis regulators between the tumor tissues and normal controls in HCC. Furthermore, the prognostic risk model based on ferroptosis regulators was constructed, of which the high risk group presented poor clinical outcomes compared to the low risk group. Importantly, the ferroptosis-related prognostic risk model consistently presented excellent prediction ability in recognizing the high and low risk patients according to the validation from an independent cohort. Subsequently, immune landscape analysis uncovered that most of ferroptosis regulatory genes were significantly associated with the infiltration of multiple immune cells and the expression of immune checkpoints in HCC. Moreover, the correlations of risk score with immune cells infiltration and immune checkpoints were determined in HCC.

CONCLUSION

Our study developed a prognostic risk model based on ferroptosis regulatory genes, which could accurately predict the patients' prognosis. Immune characteristics analysisrevealed that ferroptosis regulatory genes were associated with immune cells infiltration and immune checkpoints in HCC.

2D MoS2 Nanosheets Induce Ferroptosis by Promoting NCOA4-Dependent Ferritinophagy and Inhibiting Ferroportin

The exposure of MoS₂ nanosheets can cause cytotoxicity, which causes health risks and affects its medical applications. However, knowledge of the underlying molecular mechanisms remains limited. This study reports that MoS₂ nanosheets induces ferroptosis in vivo and in vitro, which is caused by the nanosheet themselves rather than by the dissolved ions. MoS₂ nanosheets induce ferroptosis in epithelial (BEAS-2B) and macrophage (RAW264.7) cells due to nuclear receptor coactivator 4 (NCOA4)-dependent excusive ferritinophagy and the inhibition of ferroportin-1 (FPN). In this process, most of the MoS₂ nanosheets enter the cells via macropinocytosis and are localized to the lysosome, contributing to an increase in the lysosomal membrane permeability. At the same time, NCOA4-dependent ferritinophagy is activated, and ferritin is degraded in the lysosome, which generates Fe²⁺ .Fe²⁺ leaks into the cytoplasm, leading to ferroptosis. Furthermore, the inhibition of FPN further aggravates the overload of Fe²⁺ in the cell. It has also been observed that ferroptosis is increased in lung tissue in mouse models exposed to MoS₂ nanosheets. This work highlights a novel mechanism by which MoS₂ nanosheets induce ferroptosis by promoting NCOA4-dependent ferritinophagy and inhibiting FPN, which could be of importance to elucidate the toxicity and identify the medical applications of 2D nanoparticles.

Serine signaling governs metabolic homeostasis and health

Serine has functions that are involved in metabolic homeostasis and health in pathological or stressful situations. Notably, the de novo serine synthesis pathway (SSP) plays a vital role in targeted regulation of immune responses, cell proliferation, and lipid/protein metabolism. The presentation of serine residues derived from SSP may be a signal of stress and provide novel insights into the relationship between metabolic homeostasis and diseases. Here, we summarize the current trends in understanding the regulatory mechanisms of serine metabolism, discuss how serine signaling governs metabolic and antistress processes, including oxidative stress, immunity, energy and lipid metabolism, intestinal microbiota, and the neurological system. We present a possible framework by which serine metabolism maintains metabolic homeostasis and treats human diseases.

Metabolic Rewiring and Stemness: A Critical Attribute of Pancreatic Cancer Progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive diseases with a poor 5-year survival rate. PDAC cells rely on various metabolic pathways to fuel their unlimited proliferation and metastasis. Reprogramming glucose, fatty acid, amino acid, and nucleic acid metabolisms contributes to PDAC cell growth. Cancer stem cells are the primary cell types that play a critical role in the progression and aggressiveness of PDAC. Emerging studies indicate that the cancer stem cells in PDAC tumors are heterogeneous and show specific metabolic dependencies. In addition, understanding specific metabolic signatures and factors that regulate these metabolic alterations in the cancer stem cells of PDAC paves the way for developing novel therapeutic strategies targeting CSCs. In this review, we discuss the current understanding of PDAC metabolism by specifically exploring the metabolic dependencies of cancer stem cells. We also review the current knowledge of targeting these metabolic factors that regulate CSC maintenance and PDAC progression.

lncRNA SYTL5-OT4 promotes vessel co-option by inhibiting the autophagic degradation of ASCT2

AIMS

Vessel co-option is responsible for tumor resistance to antiangiogenic therapies (AATs) in patients with colorectal cancer liver metastasis (CRCLM). However, the mechanisms underlying vessel co-option remain largely unknown. Herein, we investigated the roles of a novel lncRNA SYTL5-OT4 and Alanine-Serine-Cysteine Transporter 2 (ASCT2) in vessel co-option-mediated AAT resistance.

METHODS

SYTL5-OT4 was identified by RNA-sequencing and verified by RT-qPCR and RNA fluorescence in situ hybridization assays. The effects of SYTL5-OT4 and ASCT2 on tumor cells were investigated by gain- and loss-of-function experiments, and those of SYTL5-OT4 on ASCT2 expression were analyzed by RNA immunoprecipitation and co-immunoprecipitation assays. The roles of SYTL5-OT4 and ASCT2 in vessel co-option were detected by histological, immunohistochemical, and immunofluorescence analyses.

RESULTS

The expression of SYTL5-OT4 and ASCT2 was higher in patients with AAT-resistant CRCLM. SYTL5-OT4 enhanced the expression of ASCT2 by inhibiting its autophagic degradation. SYTL5-OT4 and ASCT2 promoted vessel co-option by increasing the proliferation and epithelial-mesenchymal transition of tumor cells. Combination therapy of ASCT2 inhibitor and antiangiogenic agents overcame vessel co-option-mediated AAT resistance in CRCLM.

CONCLUSION

This study highlights the crucial roles of lncRNA and glutamine metabolism in vessel co-option and provides a potential therapeutic strategy for patients with AAT-resistant CRCLM.

ASCT2-mediated glutamine uptake of epithelial cells facilitates CCL5-induced T cell infiltration via ROS-STAT3 pathway in oral lichen planus

BACKGROUND

Oral lichen planus (OLP) is a chronic inflammatory disease characterized by T cell infiltration at lesion sites. T cell migration is greatly facilitated by chemokines produced by epithelial cells. Studies have noted the potential role of glutamine uptake in OLP and other inflammatory diseases. Here, we investigated the effect of altered glutamine uptake of epithelial cells on T cell infiltration and its underlying mechanisms in OLP.

METHODS

Immunohistochemistry was used to identify the expressions of glutamine transporter alanine-serine-cysteine transporter 2 (ASCT2) and C-C motif chemokine ligand 5 (CCL5) in oral tissues of OLP and healthy controls. Human gingival epithelial cells (HGECs) were treated with glutamine deprivation and ASCT2 inhibiter GPNA respectively to detect the expressions of CCL5 and its related signaling molecules. Additionally, we had determined the impact of epithelial cell-derived CCL5 on T-cell migration using a co-culture system in vitro.

RESULTS

ASCT2 and CCL5 expressions in OLP were significantly higher than healthy controls and positively correlated with the density of inflammatory infiltrations. Glutamine supplement significantly increased CCL5 production in HGECs, which was effectively inhibited by GPNA. Besides, glutamine could inhibit reactive oxygen species (ROS) production to activate the signal transducer and activator of transcription 3 (STAT3) causing higher expression level of CCL5 in HGECs. Simultaneously, T cell migration could be blocked by anti-CCL5 neutralizing antibody and STAT3 inhibitor stattic in the co-culture system.

CONCLUSION

The upregulated ASCT2-mediated glutamine uptake in epithelial cells promotes CCL5 production via ROS-STAT3 signaling, which boosts the T-cell infiltration in OLP lesion.

Focusing on discoidin domain receptors in premalignant and malignant liver diseases

Discoidin domain receptors (DDRs) are receptor tyrosine kinases on the membrane surface that bind to extracellular collagens, but they are rarely expressed in normal liver tissues. Recent studies have demonstrated that DDRs participate in and influence the processes underlying premalignant and malignant liver diseases. A brief overview of the potential roles of DDR1 and DDR2 in premalignant and malignant liver diseases is presented. DDR1 has proinflammatory and profibrotic benefits and promotes the invasion, migration and liver metastasis of tumour cells. However, DDR2 may play a pathogenic role in early-stage liver injury (prefibrotic stage) and a different role in chronic liver fibrosis and in metastatic liver cancer. These views are critically significant and first described in detail in this review. The main purpose of this review was to describe how DDRs act in premalignant and malignant liver diseases and their potential mechanisms through an in-depth summary of preclinical in vitro and in vivo studies. Our work aims to provide new ideas for cancer treatment and accelerate translation from bench to bedside.

Recent progress of amino acid transporters as a novel antitumor target

Glutamine transporters transport different amino acids for cell growth and metabolism. In tumor cells, glutamine transporters are often highly expressed and play a crucial role in their growth. By inhibiting the amino acid transport of these transporters, the growth of cancer cells can be inhibited. In recent years, more and more attention has been paid to the study of glutamine transporter. In this article, the differences between the ASC system amino acid transporter 2 (ASCT2), L-type amino acid transporter 1 (LAT1), and the cystine–glutamate exchange (xCT) transporters research progress on the mechanism of action and corresponding small molecule inhibitors are summarized. This article introduces 62 related small molecule inhibitors of different transporters of ASCT2, LAT1, and xCT. These novel chemical structures provide ideas for the research and design of targeted inhibitors of glutamine transporters, as well as important references and clues for the design of new anti-tumor drugs.

Glutamine metabolism in cancers: Targeting the oxidative homeostasis

Glutamine is the most abundant amino acid in blood and tissues, and the most important nutrient except for glucose in cancer cells. Over the past years, most studies have focused on the role of Gln metabolism in supporting energy metabolism rather than maintaining oxidative homeostasis. In fact, Gln is an important factor in maintaining oxidative homeostasis of cancer cells, especially in “Glutamine addicted” cancer cells. Here, this paper will review the recent scientific literature about the link between Gln metabolism and oxidative homeostasis, with an emphasis on the potential role of Gln metabolism in different cancers. Given that oxidative homeostasis is of critical importance in cancer, understanding the impacts of a Gln metabolism on oxidative homeostasis, gaining great insights into underlying molecular mechanisms, and developing effective therapeutic strategies are of great importance.

Targeting metabolic reprogramming in chronic lymphocytic leukemia

Metabolic reprogramming, fundamentally pivotal in carcinogenesis and progression of cancer, is considered as a promising therapeutic target against tumors. In chronic lymphocytic leukemia (CLL) cells, metabolic abnormalities mediate alternations in proliferation and survival compared with normal B cells. However, the role of metabolic reprogramming is still under investigation in CLL. In this review, the critical metabolic processes of CLL were summarized, particularly glycolysis, lipid metabolism and oxidative phosphorylation. The effects of T cells and stromal cells in the microenvironment on metabolism of CLL were also elucidated. Besides, the metabolic alternation is regulated by some oncogenes and tumor suppressor regulators, especially TP53, MYC and ATM. Thus, the agents targeting metabolic enzymes or signal pathways may impede the progression of CLL. Both the inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) statins and the lipoprotein lipase inhibitor orlistat induce the apoptosis of CLL cells. In addition, a series of oxidative phosphorylation inhibitors play important roles in decreasing the proliferation of CLL cells. We epitomized recent advancements in metabolic reprogramming in CLL and discussed their clinical potentiality for innovative therapy options. Metabolic reprogramming plays a vital role in the initiation and progression of CLL. Therapeutic approaches targeting metabolism have their advantages in improving the survival of CLL patients. This review may shed novel light on the metabolism of CLL, leading to the development of targeted agents based on the reshaping metabolism of CLL cells.

Characterizing unexpected interactions of a glutamine transporter inhibitor with members of the SLC1A transporter family

The solute carrier 1A family comprises a group of membrane proteins that act as dual-function amino acid transporters and chloride (Cl⁻) channels and includes the alanine serine cysteine transporters (ASCTs) as well as the excitatory amino acid transporters. ASCT2 is regarded as a promising target for cancer therapy, as it can transport glutamine and other neutral amino acids into cells and is upregulated in a range of solid tumors. The compound L-γ-glutamyl-p-nitroanilide (GPNA) is widely used in studies probing the role of ASCT2 in cancer biology; however, the mechanism by which GPNA inhibits ASCT2 is not entirely clear. Here, we used electrophysiology and radiolabelled flux assays to demonstrate that GPNA activates the Cl⁻ conductance of ASCT2 to the same extent as a transported substrate, whilst not undergoing the full transport cycle. This is a previously unreported phenomenon for inhibitors of the solute carrier 1A family but corroborates a body of literature suggesting that the structural requirements for transport are distinct from those for Cl⁻ channel formation. We also show that in addition to its currently known targets, GPNA inhibits several of the excitatory amino acid transporters. Together, these findings raise questions about the true mechanisms of its anticancer effects.

Neddylation inhibition induces glutamine uptake and metabolism by targeting CRL3SPOP E3 ligase in cancer cells

Abnormal neddylation activation is frequently observed in human cancers and neddylation inhibition has been proposed as a therapy for cancer. Here, we report that MLN4924, a small-molecule inhibitor of neddylation activating enzyme, increases glutamine uptake in breast cancer cells by causing accumulation of glutamine transporter ASCT2/SLC1A5, via inactivation of CRL3-SPOP E3 ligase. We show the E3 ligase SPOP promotes ASCT2 ubiquitylation, whereas SPOP itself is auto-ubiquitylated upon glutamine deprivation. Thus, SPOP and ASCT2 inversely regulate glutamine uptake and metabolism. SPOP knockdown increases ASCT2 levels to promote growth which is rescued by ASCT2 knockdown. Adding ASCT2 inhibitor V-9302 enhances MLN4924 suppression of tumor growth. In human breast cancer specimens, SPOP and ASCT2 levels are inversely correlated, whereas lower SPOP with higher ASCT2 predicts a worse patient survival. Collectively, our study links neddylation to glutamine metabolism via the SPOP-ASCT2 axis and provides a rational drug combination for enhanced cancer therapy.

Neddylation inhibition has been reported as a therapy for cancer. Here, the authors show that neddylation inhibition increases glutamine metabolism by stabilizing glutamine transporter ASCT2, therefore targeting ASCT2 improves the anti-cancer effect of neddylation inhibitors.

Glutamine Metabolism Is Required for Alveolar Regeneration during Lung Injury

(1) Background: Abnormal repair after alveolar epithelial injury drives the progression of idiopathic pulmonary fibrosis (IPF). The maintenance of epithelial integrity is based on the self-renewal and differentiation of alveolar type 2 (AT2) cells, which require sufficient energy. However, the role of glutamine metabolism in the maintenance of the alveolar epithelium remains unclear. In this study, we investigated the role of glutamine metabolism in AT2 cells of patients with IPF and in mice with bleomycin-induced fibrosis. (2) Methods: Single-cell RNA sequencing (scRNA-seq), transcriptome, and metabolomics analyses were conducted to investigate the changes in the glutamine metabolic pathway during pulmonary fibrosis. Metabolic inhibitors were used to stimulate AT2 cells to block glutamine metabolism. Regeneration of AT2 cells was detected using bleomycin-induced mouse lung fibrosis and organoid models. (3) Results: Single-cell analysis showed that the expression levels of catalytic enzymes responsible for glutamine catabolism were downregulated (p < 0.001) in AT2 cells of patients with IPF, suggesting the accumulation of unusable glutamine. Combined analysis of the transcriptome (p < 0.05) and metabolome (p < 0.001) revealed similar changes in glutamine metabolism in bleomycin-induced pulmonary fibrosis in mice. Mechanistically, inhibition of the key enzymes involved in glucose metabolism, glutaminase-1 (GLS1) and glutamic-pyruvate transaminase-2 (GPT2) leads to reduced proliferation (p < 0.01) and differentiation (p < 0.01) of AT2 cells. (4) Conclusions: Glutamine metabolism is required for alveolar epithelial regeneration during lung injury.

Ferroptosis-related local immune cytolytic activity in tumor microenvironment of basal cell and squamous cell carcinoma

BACKGROUND

Ferroptosis, a recently discovered form of cell death, whose role in basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) has not been well disclosed. To improve our understanding of the differences in tumor progression and therapeutic effects between BCC and SCC, and to find potential therapeutic targets, this study systematically analyzed ferroptosis-related genes (FRGs) and their associated local immune cytolytic activity (LICA) and tumor microenvironment (TME) metabolic function differences.

METHODS

Two bulk RNA-seq datasets, GSE7553 and GSE125285, from the Gene Expression Omnibus database were compared within and between groups to screen for common differentially expressed genes (DEGs) for enrichment analysis. The currently recognized FRGs in DEGs gene set were selected as the targets to analyze their correlation and difference in LICA and TME metabolic functions. And validated using immune cell populations from another single-cell RNA-seq (scRNA-seq) dataset (GSE123813) to accurately understand the difference in LICA. All of the gene sets for functional enrichment analysis comes from published results and MSigDB database.

RESULTS

Ten FRGs were used to further analyze the differences in LICA and TME metabolic functions between BCC and SCC. In the SCC samples, LICA (e.g. Treg, CCR, Cytolytic activity, etc.) and TME metabolic functions (e.g. lipid and energy, etc.) were significantly related to ferroptosis genes (e.g. SLC1A5, CD44, NQO1, HMOX1 and STEAP3), and the ferroptosis potential index were also significantly higher than that in the BCC samples. Finally, based on these ten FRGs and related enrichment results, we postulated a model of NQO1 homeostasis regulated by FRGs during induction of ferroptosis in SCC.

CONCLUSIONS

The results showed that three FRGs, SLC1A5, CD44 and NQO1, have significant potential in targeted therapies for SCC chemotherapy resistance. And two FRGs, STEAP3 and HMOX1, formed a synergistic effect on the occurrence of ferroptosis in tumor cells. Our findings can be used as the main research materials for metastasis and chemotherapy resistance in SCC patients.

SLC1A5 Prefers to Play as an Accomplice Rather Than an Opponent in Pancreatic Adenocarcinoma

Background: SLC1A5, a ferroptosis regulator gene, plays a dual role in cancer regulation. However, the roles of SLC1A5 in pancreatic adenocarcinoma (PAAD) remain elusive.

Methods: SLC1A5’s expression and somatic mutation information were determined by TCGA, GEO, Oncomine, and cBioPortal databases. Its prognostic value was assessed in TCGA cohort and was validated in three independent cohorts. The effects of SLC1A5 on the tumor immune microenvironment were analyzed by the CIBERSORT algorithm, ssGSEA method, and TISIDB and TIMER databases. The “oncoPredict” R package, TIDE algorithm, ImmuCellAI online tool, and GSE35141 and GSE59357 datasets were used to ascertain its therapeutic correlations. GSEA and Western blot were applied to reveal the effects of SLC1A5 on the mTORC1 signaling pathway and ferroptosis process. The biofunctions of SLC1A5 were assessed by MTT, wound-healing, Transwell, and xenograft assays.

Results: SLC1A5 was significantly upregulated in the PAAD samples but was not commonly accompanied with somatic mutation (2.3%). Overexpression of SLC1A5 led to a poor prognosis and was identified as an independent prognostic factor. Moreover, high SLC1A5 expression suppressed the antitumor immune process by changing the infiltrating levels of immune cells. As for therapeutic correlations, SLC1A5 was related to the efficacy of dasatinib, sunitinib, sorafenib, and imatinib but may not predict that of radiotherapy, chemotherapeutic drugs, and immune checkpoints inhibitors (ICIs). Notably, the overexpression of SLC1A5 could activate the mTORC1 signaling pathway and may increase the cellular sensitivity to ferroptosis. Finally, the overexpression of SLC1A5 markedly promoted proliferation, migration, and invasion of pancreatic cancer cells. At the in vivo level, SLC1A5 deletion inhibited tumor growth in a mice xenograft model.

Conclusions: SLC1A5 prefers to play as an accomplice rather than an opponent in PAAD. Our findings provide novel insights into PAAD treatment.

Targeting ASCT2-mediated glutamine metabolism inhibits proliferation and promotes apoptosis of pancreatic cancer cells

Some tumor cells have a high rate of glutamine uptake and exhibit glutamine addiction. Alanine-serine cysteine-preferring transporter 2 (ASCT2) is a major mediator of glutamine supply in many tumor cells, but the underlying effects and mechanisms of ASCT2 in pancreatic cancer (PC) are largely unknown. Our results show that ASCT2 expression is significantly higher in PC than in normal pancreatic duct cells and pancreas. Utilizing the Kaplan-Meier Plotter database, a high expression of SLC1A5 mRNA was significantly associated with poor overall survival (OS) in patients with PC. shRNA-mediated inhibition of ASCT2 function in vitro can significantly decrease glutamine consumption, α-ketoglutarate (α-KG) production and ATP generation and increase the reactive oxygen species (ROS) level. Moreover, the antioxidant N-acetylcysteine partially attenuated the increase in the ROS levels and reduced ATP generation. These data suggest that ASCT2 mediates glutamine metabolism and maintains redox homeostasis in PC. To further investigate whether ASCT2 is involved in PC cell growth, we blocked ASCT2 activity with the ASCT2 inhibitor l-γ-glutamyl-p-nitroanilide (GPNA) and silenced the expression of ASCT2 with specific shRNAs. We found that the growth of PC cells was significantly inhibited. Additionally, knockdown of ASCT2 induced apoptosis through the Akt/mTOR signaling pathway. Furthermore, the loss of ASCT2 in BxPC-3 cell xenografts significantly inhibited tumor growth in vivo, and this effect was associated with an increase in cleaved caspase-3 expression and a decrease in Ki67 staining. Taken together, our results show that ASCT2 may be utilized as a putative therapeutic target for PC.

Ameliorative Potential of L-Alanyl L-Glutamine Dipeptide in Colon Cancer Patients Receiving Modified FOLFOX-6 Regarding the Incidence of Diarrhea, the Treatment Response, and Patients’ Survival: A Randomized Controlled Trial

Background and Objectives: Diarrhea induced by chemotherapy may represent a life-threatening adverse effect in cancer patients receiving chemotherapy. FOLFOX, an effective treatment for colon cancer, has been associated with diarrhea with high severity, particularly with higher doses. Management of diarrhea is crucial to increase the survival of cancer patients and to improve the quality of life. Glutamine is an abundant protein peptide found in blood and has a crucial role in boosting immunity, increasing protein anabolism, and decreasing the inflammatory effects of chemotherapy on the mucosal membranes, including diarrhea. This study aimed to provide evidence that parenteral L-alanyl L-glutamine dipeptide may have a positive influence on the incidence of diarrhea, treatment response, and the overall survival in colon cancer patients treated with modified FOLFOX-6 (mFOLFOX-6). Materials and Methods: Forty-four stage II and III colon cancer patients were included in this study where they were treated with the standard colon cancer chemotherapy mFOLFOX-6 and were randomly allocated into glutamine group and placebo group, each of 22 patients. Results: L-alanyl L-glutamine dipeptide was found to be significantly effective in decreasing the frequency and severity of diarrhea when compared to the placebo group, particularly after four and six cycles of mFOLFOX-6. There was no significant difference between the studied groups regarding to the overall survival. Conclusion: L-alanyl L-glutamine dipeptide can be considered as an add-on with chemotherapy to improve the quality of life and the overall survival of colon cancer patients.

Curcumin suppresses tumorigenesis by ferroptosis in breast cancer

Breast cancer (BC) is one of the most common malignant tumors found in females. Previous studies have demonstrated that curcumin, which is a type of polyphenol compound extracted from Curcuma longa underground rhizome, is able to inhibit the survival of cancer cells. However, the functional role and mechanism of curcumin in BC are still unclear. The Cell Counting Kit-8 assay was performed to examine the effects of curcumin on cell viability in the BC cell lines MDA-MB-453 and MCF-7. The levels of lipid reactive oxygen species (ROS), malondialdehyde (MDA) production, and intracellular Fe2+ were determined to assess the effects of curcumin on cell ferroptosis. Western blot analysis was also carried out to detect the protein levels. Finally, the antitumorigenic effect of curcumin on BC was identified in a xenograft tumor model. In the present study, the results indicated that curcumin could dose-dependently suppress the viability of both MDA-MB-453 and MCF-7 cells. Further studies revealed that curcumin facilitated solute carrier family 1 member 5 (SLC1A5)-mediated ferroptosis in both MDA-MB-453 and MCF-7 cells by enhancing lipid ROS levels, lipid peroxidation end-product MDA accumulation, and intracellular Fe2+ levels. In vivo experiments demonstrated that curcumin could significantly hamper tumor growth. Collectively, the results demonstrated that curcumin exhibited antitumorigenic activity in BC by promoting SLC1A5-mediated ferroptosis, which suggests its use as a potential therapeutic agent for the treatment of BC.

Discoidin domain receptor 1 promotes hepatocellular carcinoma progression through modulation of SLC1A5 and the mTORC1 signaling pathway

PURPOSE

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world with a high mortality rate. Receptor tyrosine kinases play important roles in the occurrence and development of various cancers. Discoid protein domain receptor 1 (DDR1) is a special type of transmembrane receptor tyrosine kinase. Here, we show that the expression of DDR1 is significantly increased in HCC and is related to a poor clinical prognosis.

METHODS

The expression of DDR1 in HCC cell lines and primary HCC specimens was evaluated using Western blotting and immunohistochemistry. A correlation between DDR1 and SLC1A5 expression was also investigated in primary HCC specimens. Cell proliferation was evaluated using in vitro CCK8 and colony formation assays. Gene knock-down and overexpression assays, CHX, NH₄CL and Mg132 interference tests and immunoprecipitation, as well as nude mouse xenograft models were used to assess the mechanism by which DDR1 promotes tumorigenesis in vitro and in vivo.

RESULTS

We found that DDR1 promotes the proliferation of HCC cells and accelerates the growth of HCC tumor xenografts, while DDR1 downregulation had the opposite effect. We also found that loss or gain of DDR1 expression affected HCC cell cycle progression. Mechanistically, we found that DDR1 interacts with SLC1A5, which belongs to the solute carrier (SLC) family of transporters, and regulates its stability, thereby affecting the mTORC1 signaling pathway. In addition, we found that SLC1A5 regulation by DDR1 can be restored by lysosome inhibitors. We also found that DDR1 is highly expressed in HCC tissues and that increased DDR1 expression predicts a shorter overall survival (OS) time. We additionally found that the expression of SLC1A5 was positively correlated with that of DDR1. Together, our data indicate that DDR1 acts as a tumor-promoting factor that can control HCC cell proliferation and cell cycle progression by stabilizing SLC1A5 in a lysosome-dependent way.

CONCLUSIONS

Our study reveals a new mechanism by which DDR1 plays a liver cancer-promoting role. We also found that DDR1 expression serves as an independent prognostic marker, and that DDR1 and SLC1A5 expression levels are positively correlated in clinical samples. Our findings provide a new perspective for understanding HCC development and offers new targets for the treatment and management of HCC.

Extracellular Vesicles Derived-LAT1 mRNA as a Powerful Inducer of Colorectal Cancer Aggressive Phenotype

Colorectal cancer (CRC) is the third most common cancer in the world and represents the third most deadly tumor worldwide. About 15–25% of patients present metastasis in the moment of diagnosis, the liver being the most common site of metastization. Therefore, the development of new therapeutic agents is needed, to improve the patients’ prognosis. Amino acids transporters, LAT1 and ASCT2, are described as upregulated in CRC, being associated with a poor prognosis. Extracellular vesicles have emerged as key players in cell-to-cell communication due to their ability to transfer biomolecules between cells, with a phenotypic impact on the recipient cells. Thus, this study analyzes the presence of LAT1 and ASCT2 mRNAs in CRC-EVs and evaluates their role in phenotype modulation in a panel of four recipient cell lines (HCA-7, HEPG-2, SK-HEP-1, HKC-8). We found that HCT 116-EVs carry LAT1, ASCT2 and other oncogenic mRNAs being taken up by recipient cells. Moreover, the HCT 116-EVs’ internalization was associated with the increase of LAT1 mRNA in SK-HEP-1 cells. We also observed that HCT 116-EVs induce a higher cell migration capacity and proliferation of SK-HEP-1 and HKC-8 cells. The present study supports the LAT1-EVs’ mRNA involvement in cell phenotype modulation, conferring advantages in cell migration and proliferation.

A structural view onto disease-linked mutations in the human neutral amino acid exchanger ASCT1

The ASCT1 transporter of the SLC1 family is largely involved in equilibration of neutral amino acids' pools across the plasma membrane and plays a prominent role in the transport of both L- and D-isomers of serine, essential for the normal functioning of the central nervous system in mammals. A number of mutations in ASCT1 (E256K, G381R, R457W) have been linked to severe neurodevelopmental disorders, however in the absence of ASCT1 structure it is hard to understand their impact on substrate transport. To ameliorate that we have determined a cryo-EM structure of human ASCT1 at 4.2 Å resolution and performed functional transport assays and molecular dynamics simulations, which revealed that given mutations lead to the diminished transport capability of ASCT1 caused by instability of transporter and impeded transport cycle.

V-9302 inhibits proliferation and migration of VSMCs, and reduces neointima formation in mice after carotid artery ligation

Rapidly proliferating cells such as vascular smooth muscle cells (VSMCs) require metabolic programs to support increased energy and biomass production. Thus, targeting glutamine metabolism by inhibiting glutamine transport could be a promising strategy for vascular disorders such as atherosclerosis, stenosis, and restenosis. V-9302, a competitive antagonist targeting the glutamine transporter, has been investigated in the context of cancer; however, its role in VSMCs is unclear. Here, we examined the effects of blocking glutamine transport in fetal bovine serum (FBS)- or platelet-derived growth factor (PDGF)-stimulated VSMCs using V-9302. We found that V-9302 inhibited mTORC1 activity and mitochondrial respiration, thereby suppressing FBS- or PDGF-stimulated proliferation and migration of VSMCs. Moreover, V-9302 attenuated carotid artery ligation-induced neointima in mice. Collectively, the data suggest that targeting glutamine transport using V-9302 is a promising therapeutic strategy to ameliorate occlusive vascular disease.

Comprehensive molecular and clinical characterization of SLC1A5 in human cancers

Although SLC1A5 has been reported to be closely associated with some cancer types, a comprehensive and systematic assessment of SLC1A5 across human cancers is lacking. Thus, Pan-cancer analysis of SLC1A5 was performed across 30 types of human cancers in this study. We examined mRNA expression, protein expression, copy number variation (CNV), DNA methylation, clinical relevance, cell functions, drug response and total immune infiltrates of SLC1A5 in more than 9000 patients across 30 human cancer types from The Cancer Genome Atlas (TCGA) dataset. Additionally, nine independent Gene Expression Omnibus datasets, more than 800 cancer cell lines from the Cancer Cell Line Encyclopedia dataset and the Project Achilles dataset were used to validate our findings in the TCGA dataset. Landscapes of SLC1A5 were established across multiple cancers. We showed that SLC1A5 is upregulated in multiple cancers, particularly in digestive and respiratory system cancers. SLC1A5 upregulation may be driven by CNV gain and DNA hypomethylation in human cancers. Furthermore, SLC1A5 overexpression is associated with tumor progression and poor survival in multiple cancers. Moreover, we systematically explored the potential effects of SLC1A5 expression on cell functions and drug response in human cancers. SLC1A5 knockdown showed significant proliferation-inhibiting effects in most human cancer types, especially in the digestive system and KRAS-mutant cancers. SLC1A5 expression is associated with proliferation activities of KRAS-mutant cancer cell lines and drug response of many anti-cancer drugs. Finally, we demonstrated that SLC1A5-realted tumor immune microenvironment characteristics showed strong heterogeneity in human cancers. Taken together, our findings highlight the important roles of SLC1A5 in tumorigenesis, progression, prognosis and therapy.

Glutamate - A multifaceted molecule: Endogenous neurotransmitter, controversial food additive, design compound for anti-cancer drugs. A critical appraisal

One of the most widely used flavour enhancers in the food industry is monosodium glutamate (MSG). MSG consumption has been on an upward trend, worrying in terms of potential toxic effects. This review is focused on the long-term toxicity of MSG and the experimental evidence that supports it. The article's primary purpose was to survey recently published data regarding the consumption of MSG within safe limits. The administered doses in animal models are very varied and have given rise to controversy. Also, the paper comprises pathways to lower MSG toxicity and highlight other underexploited biological effects, as anti-cancer potential. The administration of MSG, combined with various compounds, has been shown benefit against toxic effects. Several recent studies have identified a possible mechanism that recommends MSG and some derivatives as potential anti-cancer agents. New anti-cancer compounds based on the glutamic acid structure must be studied and further exploited. International regulations require harmonization of safe doses of MSG based on current scientific studies. Replacing MSG with other umami flavour enhancers may be a safer alternative for human health in the future. The biological consequences of MSG consumption or therapeutical administration have not been fully deciphered yet.

First-in-Human PET Imaging and Estimated Radiation Dosimetry of l-[5-11C]-Glutamine in Patients with Metastatic Colorectal Cancer

Altered metabolism is a hallmark of cancer. In addition to glucose, glutamine is an important nutrient for cellular growth and proliferation. Noninvasive imaging via PET may help facilitate precision treatment of cancer through patient selection and monitoring of treatment response. l-[5-¹¹C]-glutamine (¹¹C-glutamine) is a PET tracer designed to study glutamine uptake and metabolism. The aim of this first-in-human study was to evaluate the radiologic safety and biodistribution of ¹¹C-glutamine for oncologic PET imaging. Methods: Nine patients with confirmed metastatic colorectal cancer underwent PET/CT imaging. Patients received 337.97 ± 44.08 MBq of ¹¹C-glutamine. Dynamic PET acquisitions that were centered over the abdomen or thorax were initiated simultaneously with intravenous tracer administration. After the dynamic acquisition, a whole-body PET/CT scan was acquired. Volume-of-interest analyses were performed to obtain estimates of organ-based absorbed doses of radiation. Results: ¹¹C-glutamine was well tolerated in all patients, with no observed safety concerns. The organs with the highest radiation exposure included the bladder, pancreas, and liver. The estimated effective dose was 4.46E-03 ± 7.67E-04 mSv/MBq. Accumulation of ¹¹C-glutamine was elevated and visualized in lung, brain, bone, and liver metastases, suggesting utility for cancer imaging. Conclusion: PET using ¹¹C-glutamine appears safe for human use and allows noninvasive visualization of metastatic colon cancer lesions in multiple organs. Further studies are needed to elucidate its potential for other cancers and for monitoring response to treatment.

Anticancer Properties of Lobetyolin, an Essential Component of Radix Codonopsis (Dangshen)

Lobetyolin (LBT) is a polyacetylene glycoside found in diverse medicinal plants but mainly isolated from the roots of Codonopsis pilosula, known as Radix Codonopsis or Dangshen. Twelve traditional Chinese medicinal preparations containing Radix Codonopsis were identified; they are generally used to tonify spleen and lung Qi and occasionally to treat cancer. Here we have reviewed the anticancer properties of Codonopsis extracts, LBT and structural analogs. Lobetyolin and lobetyolinin are the mono- and bis-glucosylated forms of the polyacetylenic compound lobetyol. Lobetyol and LBT have shown activities against several types of cancer (notably gastric cancer) and we examined the molecular basis of their activity. A down-regulation of glutamine metabolism by LBT has been evidenced, contributing to drug-induced apoptosis and tumor growth inhibition. LBT markedly reduces both mRNA and protein expression of the amino acid transporter Alanine-Serine-Cysteine Transporter 2 (ASCT2). Other potential targets are proposed here, based on the structural analogy with other anticancer compounds. LBT and related polyacetylene glycosides should be further considered as potential anticancer agents, but more work is needed to evaluate their efficacy, toxicity, and risk-benefit ratio.

Amino Acid Metabolism in Lupus

T cell metabolism is central to cell proliferation, survival, differentiation, and aberrations have been linked to the pathophysiology of systemic autoimmune diseases. Besides glycolysis and fatty acid oxidation/synthesis, amino acid metabolism is also crucial in T cell metabolism. It appears that each T cell subset favors a unique metabolic process and that metabolic reprogramming changes cell fate. Here, we review the mechanisms whereby amino acid transport and metabolism affects T cell activation, differentiation and function in T cells in the prototype systemic autoimmune disease systemic lupus erythematosus. New insights in amino acid handling by T cells should guide approaches to correct T cell abnormalities and disease pathology.

LAT1 and ASCT2 Related microRNAs as Potential New Therapeutic Agents against Colorectal Cancer Progression

The development and progression of colorectal cancer (CRC) have been associated with genetic and epigenetic alterations and more recently with changes in cell metabolism. Amino acid transporters are key players in tumor development, and it is described that tumor cells upregulate some AA transporters in order to support the increased amino acid (AA) intake to sustain the tumor additional needs for tumor growth and proliferation through the activation of several signaling pathways. LAT1 and ASCT2 are two AA transporters involved in the regulation of the mTOR pathway that has been reported as upregulated in CRC. Some attempts have been made in order to develop therapeutic approaches to target these AA transporters, however none have reached the clinical setting so far. MiRNA-based therapies have been gaining increasing attention from pharmaceutical companies and now several miRNA-based drugs are currently in clinical trials with promising results. In this review we combine a bioinformatic approach with a literature review in order to identify a miRNA profile with the potential to target both LAT1 and ASCT2 with potential to be used as a therapeutic approach against CRC.

ASCT2 and LAT1 Contribution to the Hallmarks of Cancer: From a Molecular Perspective to Clinical Translation

The role of the amino acid transporters ASCT2 and LAT1 in cancer has been explored throughout the years. In this review, we report their impact on the hallmarks of cancer, as well as their clinical significance. Overall, both proteins have been associated with cell death resistance through dysregulation of caspases and sustainment of proliferative signaling through mTOR activation. Furthermore, ASCT2 appears to play an important role in cellular energetics regulation, whereas LAT1 expression is associated with angiogenesis and invasion and metastasis activation. The molecular impact of these proteins on the hallmarks of cancer translates into various clinical applications and both transporters have been identified as prognostic factors in many types of cancer. Concerning their role as therapeutic targets, efforts have been undertaken to synthesize competitive or irreversible ASCT2 and LAT1 inhibitors. However, JHP203, a selective inhibitor of the latter, is, to the best of our knowledge, the only compound included in a Phase 1 clinical trial. In conclusion, considering the usefulness of ASCT2 and LAT1 in a variety of cancer-related pathways and cancer therapy/diagnosis, the development and testing of novel inhibitors for these transporters that could be evaluated in clinical trials represents a promising approach to cancer prognosis improvement.

Inhibition of Glutamine Uptake Improves the Efficacy of Cetuximab on Gastric Cancer

Treatment for advanced gastric cancer is challenging. Epidermal growth factor receptor (EGFR) contributes to the proliferation and development of gastric cancer (GC), and its overexpression is associated with unfavorable prognosis in GC. Cetuximab, a monoclonal antibody targeting EGFR, failed to improve the overall survival of gastric cancer patients indicated in phase III randomized trials. Glutamine is a vital nutrient for tumor growth and its metabolism contributes to therapeutic resistance, making glutamine uptake an attractive target for cancer treatment. The aim of the present study was to investigate whether intervention of glutamine uptake could improve the effect of cetuximab on GC. The results of MTT assay showed that by glutamine deprivation or inhibition of glutamine uptake, the viability of gastric carcinoma cells was inhibited more severely than that of human immortal gastric mucosa epithelial cells (GES-1). The expression of the key glutamine transporter alanine-serine-cysteine (ASC) transporter 2 (ASCT2; SLC1A5) was significantly higher in gastric carcinoma tissues and various gastric carcinoma cell lines than in normal gastric tissues and cells, as shown by immunohistochemistry and western blotting, while silencing ASCT2 significantly inhibited the viability and proliferation of gastric carcinoma cells. Consistent with previous studies, it was shown herein by MTT and EdU assays that cetuximab had a weak inhibitory effect on the cell viability of gastric carcinoma cells. However, inhibiting glutamine uptake by blockade of ASCT2 with l-γ-glutamyl-p-nitroanilide (GPNA) significantly enhanced the inhibitory effect of cetuximab on suppressing the proliferation of gastric cancer both in vitro and in vivo. Moreover, combining cetuximab and GPNA induced cell apoptosis considerably in gastric carcinoma cells, as shown by flow cytometry, and had a higher depressing effect on gastric cancer proliferation both in vitro and in vivo, as compared to either treatment alone. The present study suggested that inhibition of glutamine uptake may be a promising strategy for improving the inhibitory efficacy of cetuximab on advanced gastric cancer.

Interplay of Carbonic Anhydrase IX With Amino Acid and Acid/Base Transporters in the Hypoxic Tumor Microenvironment

Solid tumors are challenged with a hypoxic and nutrient-deprived microenvironment. Hence, hypoxic tumor cells coordinatively increase the expression of nutrient transporters and pH regulators to adapt and meet their bioenergetic and biosynthetic demands. Carbonic Anhydrase IX (CAIX) is a membrane-bound enzyme that plays a vital role in pH regulation in the tumor microenvironment (TME). Numerous studies have established the importance of CAIX in mediating tumor progression and metastasis. To understand the mechanism of CAIX in mediating tumor progression, we performed an unbiased proteomic screen to identify the potential interactors of CAIX in the TME using the proximity-dependent biotin identification (BioID) technique. In this review, we focus on the interactors from this BioID screen that are crucial for nutrient and metabolite transport in the TME. We discuss the role of transport metabolon comprising CAIX and bicarbonate transporters in regulating intra- and extracellular pH of the tumor. We also discuss the role of amino acid transporters that are high confidence interactors of CAIX, in optimizing favorable metabolic state for tumor progression, and give our perspective on the coordinative interplay of CAIX with the amino acid transporters in the hypoxic TME.

Membrane Transporters for Amino Acids as Players of Cancer Metabolic Rewiring

Cancer cells perform a metabolic rewiring to sustain an increased growth rate and compensate for the redox stress caused by augmented energy metabolism. The metabolic changes are not the same in all cancers. Some features, however, are considered hallmarks of this disease. As an example, all cancer cells rewire the amino acid metabolism for fulfilling both the energy demand and the changed signaling routes. In these altered conditions, some amino acids are more frequently used than others. In any case, the prerequisite for amino acid utilization is the presence of specific transporters in the cell membrane that can guarantee the absorption and the traffic of amino acids among tissues. Tumor cells preferentially use some of these transporters for satisfying their needs. The evidence for this phenomenon is the over-expression of selected transporters, associated with specific cancer types. The knowledge of the link between the over-expression and the metabolic rewiring is crucial for understanding the molecular mechanism of reprogramming in cancer cells. The continuous growth of information on structure-function relationships and the regulation of transporters will open novel perspectives in the fight against human cancers.

Glutaminases regulate glutathione and oxidative stress in cancer

Targeted therapies against cancer have improved both survival and quality of life of patients. However, metabolic rewiring evokes cellular mechanisms that reduce therapeutic mightiness. Resistant cells generate more glutathione, elicit nuclear factor erythroid 2-related factor 2 (NRF2) activation, and overexpress many anti-oxidative genes such as superoxide dismutase, catalase, glutathione peroxidase, and thioredoxin reductase, providing stronger antioxidant capacity to survive in a more oxidative environment due to the sharp rise in oxidative metabolism and reactive oxygen species generation. These changes dramatically alter tumour microenvironment and cellular metabolism itself. A rational design of therapeutic combination strategies is needed to flatten cellular homeostasis and accomplish a drop in cancer development. Context-dependent glutaminase isoenzymes show oncogenic and tumour suppressor properties, being mainly associated to MYC and p53, respectively. Glutaminases catalyze glutaminolysis in mitochondria, regulating oxidative phosphorylation, redox status and cell metabolism for tumour growth. In addition, the substrate and product of glutaminase reaction, glutamine and glutamate, respectively, can work as signalling molecules moderating redox and bioenergetic pathways in cancer. Novel synergistic approaches combining glutaminase inhibition and redox-dependent modulation are described in this review. Pharmacological or genetic glutaminase regulation along with oxidative chemotherapy can help to improve the design of combination strategies that escalate the rate of therapeutic success in cancer patients.