Arginine deprivation in cancer therapy

The arginine metabolism and its deprivation in cancer therapy

Arginine deprivation has emerged as a promising therapeutic strategy in cancer treatment due to the auxotrophy of certain tumors. Many cancers, such as pancreatic, colorectal, and hepatocellular carcinoma, exhibit downregulated argininosuccinate synthetase, making them reliant on external arginine sources. This dependency allows targeted therapies that deplete arginine, inhibiting tumor growth while sparing normal cells. Arginine is crucial for various cellular processes, including protein synthesis and immune function. Its deprivation affects both tumor metabolism and immune responses, potentially enhancing cancer therapy. Studies have explored using enzymes like arginine deiminase and arginase, often modified for increased stability and reduced immunogenicity, to effectively lower arginine levels in the tumor microenvironment. These approaches show promise, particularly in tumors with low argininosuccinate synthetase expression. However, the impact on immune cells and the potential for resistance highlight the need for further research. Combining arginine deprivation with other treatments might improve outcomes, offering a novel approach to combat arginine-dependent cancers.

L-arginine dependence of breast cancer - molecular subtypes matter

L-arginine limits proliferation in highly proliferative tissues. It is a substrate for nitric oxide synthases, arginases; its methylation by protein-L-arginine methyltransferases (PRMTs) leads to asymmetric (ADMA) and symmetric dimethylarginine (SDMA). We measured L-arginine and its metabolites L-ornithine, L-citrulline, ADMA, and SDMA in a prospective cohort of 243 women with primary breast cancer (BC) and their associations with mortality and disease recurrence during 88 (IQR, 82-93) months of follow-up. We quantified these metabolites and expression of genes involved in L-arginine metabolic pathways in MCF-7, BT-474, SK-BR-3, MDA-MB-231, and MDA-MB-468 cells representing ER-positive, HER2-positive, and triple-negative BC compared to MCF-12 A cells. Plasma L-arginine and ADMA concentrations were elevated in 47 patients with recurrent disease and in 34 non-survivors. ADMA was significantly associated with mortality and recurrent disease in Luminal A patients; low L-citrulline was significantly associated with survival in triple-negative BC. In all BC cells except MCF-7, DDAH1 and DDAH2 expression was higher than in MCF-12 A (DDAH1: 32-44 fold, DDAH2: 1.7-4.2 fold; p < 0.05). By contrast, MCF-7 cells showed low DDAH1 and DDAH2, but high PRMT4 and PRMT6 expression and high L-arginine content. BT-474 and MDA-MB-468 cells showed high ARG2 expression and high L-ornithine concentrations, and MDA-MB-468 cells had the highest L-citrulline/L-arginine ratio. In conclusion, regulation of L-arginine metabolic pathways shows a complex and differential pattern between BC subtypes. ADMA is a prognostic biomarker in Luminal A patients; its metabolizing enzyme, DDAH, is highly overexpressed in BC cells. Thus, fingerprinting of L-arginine metabolism may offer novel personalized treatment options within BC subtypes.

Endoplasmic Reticulum Stress and Its Role in Metabolic Reprogramming of Cancer

Background/Objectives: Endoplasmic reticulum (ER) stress occurs when ER homeostasis is disrupted, leading to the accumulation of misfolded or unfolded proteins. This condition activates the unfolded protein response (UPR), which aims to restore balance or trigger cell death if homeostasis cannot be achieved. In cancer, ER stress plays a key role due to the heightened metabolic demands of tumor cells. This review explores how metabolomics can provide insights into ER stress-related metabolic alterations and their implications for cancer therapy. Methods: A comprehensive literature review was conducted to analyze recent findings on ER stress, metabolomics, and cancer metabolism. Studies examining metabolic profiling of cancer cells under ER stress conditions were selected, with a focus on identifying potential biomarkers and therapeutic targets. Results: Metabolomic studies highlight significant shifts in lipid metabolism, protein synthesis, and oxidative stress management in response to ER stress. These metabolic alterations are crucial for tumor adaptation and survival. Additionally, targeting ER stress-related metabolic pathways has shown potential in preclinical models, suggesting new therapeutic strategies. Conclusions: Understanding the metabolic impact of ER stress in cancer provides valuable opportunities for drug development. Metabolomics-based approaches may help identify novel biomarkers and therapeutic targets, enhancing the effectiveness of antitumor therapies.

Efficient extraction via titanium organic frameworks facilitates in-depth profiling of urinary exosome metabolite fingerprints

Urinary exosome metabolite analysis has demonstrated notable advantages in uncovering disease status, yet its potential in decoding the intricacies of clear cell renal cell carcinoma (ccRCC) remains untapped. To address this, a core-shell magnetic titanium organic framework was designed to capture urinary exosomes and assist laser desorption/ionization mass spectrometry (LDI MS) to decipher the exosomal metabolic profile of ccRCC, with high sensitivity, throughput, and speed. A total of 492 urinary exosome metabolite fingerprints (UEMFs) from 176 samples were extracted for exploring the differences between ccRCC and healthy individuals. Leveraging machine learning algorithms, the exosomal metabolic profile was disclosed, achieving accurate differentiation and prediction of ccRCC patients versus healthy individuals, with an accuracy exceeding 97.3%. Furthermore, an optimized algorithm panel comprising five key features demonstrated consistent and high diagnosing accuracy rates of over 94.0% both in the training and blind test sets for ccRCC, underscoring the remarkable effectiveness and superiority of this strategy in ccRCC detection. This study not only refines the LDI MS method for metabolite analysis in urinary exosomes but also introduces a promising technical approach for unraveling the mysteries of ccRCC.

Targeting Metabolic Vulnerabilities to Combat Drug Resistance in Cancer Therapy

Drug resistance remains a significant barrier to effective cancer therapy. Cancer cells evade treatment by reprogramming their metabolism, switching from glycolysis to oxidative phosphorylation (OXPHOS), and relying on alternative carbon sources such as glutamine. These adaptations not only enable tumor survival but also contribute to immune evasion through mechanisms such as reactive oxygen species (ROS) generation and the upregulation of immune checkpoint molecules like PD-L1. This review explores the potential of targeting metabolic weaknesses in drug-resistant cancers to enhance therapeutic efficacy. Key metabolic pathways involved in resistance, including glycolysis, glutamine metabolism, and the kynurenine pathway, are discussed. The combination of metabolic inhibitors with immune checkpoint inhibitors (ICIs), particularly anti-PD-1/PD-L1 therapies, represents a promising approach to overcoming both metabolic and immune evasion mechanisms. Clinical trials combining metabolic and immune therapies have shown early promise, but further research is needed to optimize treatment combinations and identify biomarkers for patient selection. In conclusion, targeting cancer metabolism in combination with immune checkpoint blockade offers a novel approach to overcoming drug resistance, providing a potential pathway to improved outcomes in cancer therapy. Future directions include personalized treatments based on tumor metabolic profiles and expanding research to other tumor types.

Overcoming resistance to arginine deprivation therapy using GC7 in pleural mesothelioma

Pleural mesothelioma is a highly chemotherapy-resistant cancer. Approximately 50% of mesotheliomas do not express argininosuccinate synthetase 1 (ASS1), the rate-limiting enzyme in arginine biosynthesis, making arginine depletion with pegylated arginine deiminase (ADI-PEG20) an attractive therapeutic strategy. We investigated whether combinatory treatment composed of ADI-PEG20 and polyamine inhibitors constitutes a promising novel therapeutic strategy to overcome ADI-PEG20 resistance in mesothelioma patients. Treatment of ADI-PEG20-resistant cell lines with a range of different polyamine inhibitors demonstrated that ADI-PEG20-resistant cell lines were highly sensitive to the spermidine-analog GC7. We observed a synergistic effect of GC7 and ADI-PEG20 in both ADI-PEG20-sensitive and ADI-PEG20-resistant cell lines. Metabolomic analysis revealed that sensitivity to GC7 is due to inhibition of the Tricarboxylic (TCA) cycle. Significantly, combination of GC7 and ADI-PEG20 prevented the emergence of resistant cells in vitro. Taken together, we have identified the therapeutic potential of combinatorial treatment of ADI-PEG20 with GC7 for mesothelioma management.

Classification of colorectal cancer patients based on serum micronutrients: An exploratory investigation

BACKGROUND

Colorectal cancer (CRC) is a growing global health challenge with a multifactorial etiology encompassing genetic susceptibility, nutrition, and inflammation in the bowel.

OBJECTIVE

To examine micronutrient status in CRC patients undergoing CRC resection.

DESIGN

We performed a case-control study including 13 consecutive CRC patients and 10 healthy controls (CTRL) comparing the serum levels of 29 micronutrients, namely Copper, Zinc, Selenium, Chromium, Manganese, Carnitine, Choline, Inositol, Methylmalonic acid (MMA), Vitamin (Vit) B1, Vit B2, Vit B3, Vit B5, Vit B6, Vit C, Vit A, Vit D3, Vit E, Vit K1, Vit K2 and the amino acids Serine, Valine, Leucine, Isoleucine, Asparagine, Glutamine, Arginine, Citrulline and Cysteine.

RESULTS

After considering the effect of age and sex, copper, arginine, and cysteine were increased, while zinc, selenium, chromium, Vit B1, Vit K1, and Vit A were decreased in CRC patients in comparison with CTRL. Zinc levels perfectly predicted the diagnosis of CRC, and were associated with lymph nodes (pN), of the pTNM staging. Copper levels in serum were strongly associated with the pathological pTNM staging of CRC.

CONCLUSION

Though this is a preliminary study that needs confirmation with a larger longitudinal cohort, our results show that serum micronutrients are linked to tumor growth, likely caused by increased demand from tumor tissue associated with an aberrant cell proliferation and changes in the antioxidant function.

Participation of protein metabolism in cancer progression and its potential targeting for the management of cancer

Cancer malignancies may broadly be described as heterogeneous disorders manifested by uncontrolled cellular growth/division and proliferation. Tumor cells utilize metabolic reprogramming to accomplish the upregulated nutritional requirements for sustaining their uncontrolled growth, proliferation, and survival. Metabolic reprogramming also called altered or dysregulated metabolism undergoes modification in normal metabolic pathways for anabolic precursor's generation that serves to continue biomass formation that sustains the growth, proliferation, and survival of carcinogenic cells under a nutrition-deprived microenvironment. A wide range of dysregulated/altered metabolic pathways encompassing different metabolic regulators have been described; however, the current review is focused to explain deeply the metabolic pathways modifications inducing upregulation of proteins/amino acids metabolism. The essential modification of various metabolic cycles with their consequent outcomes meanwhile explored promising therapeutic targets playing a pivotal role in metabolic regulation and is successfully employed for effective target-specific cancer treatment. The current review is aimed to understand the metabolic reprogramming of different proteins/amino acids involved in tumor progression along with potential therapeutic perspective elucidating targeted cancer therapy via these targets.

Development and internal validation of nomograms based on plasma metabolites to predict non-small cell lung cancer risk in smoking and nonsmoking populations

BACKGROUND

Lung cancer has significantly higher incidence and mortality rates worldwide. In this study, we analyzed the metabolic profiles of non-small cell lung cancer (NSCLC) patients and constructed prediction models for smokers and nonsmokers with internal validation.

METHODS

Plasma was collected from all patients enrolled for metabolic profiling by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The total population was divided into two groups according to smoking or not. Statistical analysis of metabolites was performed separately for each group and prediction models were constructed.

RESULTS

A total of 1723 patients (1109 NSCLC patients and 614 healthy controls) were enrolled from the affiliated hospital during 2018 to 2021. After grouping by smoking history, each group was statistically analyzed and prediction models were constructed, which resulted in eight indicators (propionylcarnitine, arginine, citrulline, etc.) significantly associated with lung cancer risk for smokers and eight indicators (dodecanoylcarnitine, hydroxybutyrylcarnitine, asparagine, etc.) for nonsmokers (p < 0.05). The smoker model indicated an AUC of 0.860 in the training set and 0.850 in the validation set. The nonsmoker model showed an AUC of 0.783 in the training set and 0.762 in the validation set. Further calibration tests for both models indicated excellent goodness-of-fit results.

CONCLUSIONS

In this study, we found a series of metabolites significantly associated with lung cancer incidence and constructed respectively prediction models for NSCLC risk in smokers and nonsmokers, with internal validation to confirm the efficiency to discriminate lung cancer risk in both smoking and nonsmoking states.

Downregulation of argininosuccinate synthase 1 (ASS1) is associated with hypoxia in placental development

Argininosuccinate synthase (ASS1) is involved in nitric oxide production, which has a key role in placental development improving pregnancy outcomes. Syncytiotrophoblast and extravillous trophoblast differentiations are milestones of placental development and their impairment can cause pathologies, such as preeclampsia (PE) and fetal growth restriction (FGR). Immunohistochemistry and Western blotting were used to localize and quantify ASS1 in first trimester (8.2 ± 1.8 weeks), third trimester (38.6 ± 1.1 weeks), and PE (36.3 ± 1.5 weeks) placentas. In addition, cell cultures were used to evaluate ASS1 expression under hypoxic conditions and the syncytialization process. Our data showed that ASS1 is localized in the villous cytotrophoblast of first trimester, third trimester, and PE placentas, while the villous cytotrophoblast adjacent to the extravillous trophoblast of cell columns as well as the extravillous trophoblast were negative for ASS1 in first trimester placentas. In addition, ASS1 was decreased in third trimester compared to the first trimester placentas (p = 0.003) and no differences were detected between third trimester and PE placentas. Moreover, ASS1 expression was decreased in hypoxic conditions and syncytialized cells compared to those not syncytialized. In conclusion, we suggest that the expression of ASS1 in villous cytotrophoblast is related to maintaining proliferative phenotype, while ASS1 absence may be involved in promoting the differentiation of villous cytotrophoblast in extravillous cytotrophoblast of cell columns in first trimester placentas.

Arginine transportation mechanism through cationic amino acid transporter 1: insights from molecular dynamics studies

Metabolic and signaling mechanisms in mammalian cells are facilitated by the transportation of L-arginine (Arg) across the plasma membrane through cationic amino acid transporter (CAT) proteins. Due to a lack of argininosuccinate synthase (ASS) activity in various tumor cells such as acute myeloid leukemia, acute lymphocytic leukemia, and chronic lymphocytic leukemia, these tumor entities are arginine-auxotrophic and therefore depend on the uptake of the amino acid arginine. Cationic amino acid transporter-1 (CAT-1) is the leading arginine importer expressed in the aforementioned tumor entities. Hence, in the present study, to investigate the transportation mechanism of arginine in CAT-1, we performed molecular dynamics (MD) simulation methods on the modeled human CAT-1. The MM-PBSA approach was conducted to determine the critical residues interacting with arginine within the corresponding binding site of CAT-1. In addition, we found out that the water molecules have the leading role in forming the transportation channel within CAT-1. The conductive structure of CAT-1 was formed only when the water molecules were continuously distributed across the channel. Steered molecular dynamics (SMD) simulation approach showed various energy barriers against arginine transportation through CAT-1, especially while crossing the bottlenecks of the related channel. These findings at the molecular level might shed light on identifying the crucial amino acids in the binding of arginine to eukaryotic CATs and also provide fundamental insights into the arginine transportation mechanisms through CAT-1. Understanding the transportation mechanism of arginine is essential to developing CAT-1 blockers, which can be potential medications for some types of cancers.Communicated by Ramaswamy H. Sarma.

Gain-of-function genetic screens in human cells identify SLC transporters overcoming environmental nutrient restrictions

Solute carrier (SLC) transporters control fluxes of nutrients and metabolites across membranes and thereby represent a critical interface between the microenvironment and cellular and subcellular metabolism. Because of substantial functional overlap, the interplay and relative contributions of SLCs in response to environmental stresses remain poorly elucidated. To infer functional relationships between SLCs and metabolites, we developed a strategy to identify SLCs able to sustain cell viability and proliferation under growth-limiting concentrations of essential nutrients. One-by-one depletion of 13 amino acids required for cell proliferation enabled gain-of-function genetic screens using a SLC-focused CRISPR/Cas9-based transcriptional activation approach to uncover transporters relieving cells from growth-limiting metabolic bottlenecks. Among the transporters identified, we characterized the cationic amino acid transporter SLC7A3 as a gene that, when up-regulated, overcame low availability of arginine and lysine by increasing their uptake, whereas SLC7A5 was able to sustain cellular fitness upon deprivation of several neutral amino acids. Moreover, we identified metabolic compensation mediated by the glutamate/aspartate transporters SLC1A2 and SLC1A3 under glutamine-limiting conditions. Overall, this gain-of-function approach using human cells uncovered functional transporter-nutrient relationships and revealed that transport activity up-regulation may be sufficient to overcome environmental metabolic restrictions.

Metabolic Pathways, Enzymes, and Metabolites: Opportunities in Cancer Therapy

Metabolic reprogramming enables cancer cells to proliferate and produce tumor biomass under a nutrient-deficient microenvironment and the stress of metabolic waste. A cancer cell adeptly undergoes a variety of adaptations in metabolic pathways and differential expression of metabolic enzyme genes. Metabolic adaptation is mainly determined by the physiological demands of the cancer cell of origin and the host tissue. Numerous metabolic regulators that assist cancer cell proliferation include uncontrolled anabolism/catabolism of glucose metabolism, fatty acids, amino acids metabolism, nucleotide metabolism, tumor suppressor genes, microRNAs, and many regulatory enzymes and genes. Using this paradigm, we review the current understanding of metabolic reprogramming in tumors and discuss the new strategies of cancer metabolomics that can be tapped into for cancer therapeutics.

Targeted Arginine Metabolism Therapy: A Dilemma in Glioma Treatment

Efforts in the treatment of glioma which is the most common primary malignant tumor of the central nervous system, have not shown satisfactory results despite a comprehensive treatment model that combines various treatment methods, including immunotherapy. Cellular metabolism is a determinant of the viability and function of cancer cells as well as immune cells, and the interplay of immune regulation and metabolic reprogramming in tumors has become an active area of research in recent years. From the perspective of metabolism and immunity in the glioma microenvironment, we elaborated on arginine metabolic reprogramming in glioma cells, which leads to a decrease in arginine levels in the tumor microenvironment. Reduced arginine availability significantly inhibits the proliferation, activation, and function of T cells, thereby promoting the establishment of an immunosuppressive microenvironment. Therefore, replenishment of arginine levels to enhance the anti-tumor activity of T cells is a promising strategy for the treatment of glioma. However, due to the lack of expression of argininosuccinate synthase, gliomas are unable to synthesize arginine; thus, they are highly dependent on the availability of arginine in the extracellular environment. This metabolic weakness of glioma has been utilized by researchers to develop arginine deprivation therapy, which ‘starves’ tumor cells by consuming large amounts of arginine in circulation. Although it has shown good results, this treatment modality that targets arginine metabolism in glioma is controversial. Exploiting a suitable strategy that can not only enhance the antitumor immune response, but also “starve” tumor cells by regulating arginine metabolism to cure glioma will be promising.

Arginase: Mechanisms and Clinical Application in Hematologic Malignancy

Compared to normal tissues and cells, the metabolic patterns of tumor illnesses are more complex, and there are hallmarks of metabolic reprogramming in energy metabolism, lipid metabolism, and amino acid metabolism. When tumor cells are in a state of fast growth, they are susceptible to food shortage, resulting in growth suppression. Using this metabolic sensitivity of tumor cells to construct amino acid consumption therapy does not harm the function of normal cells, which is the focus of metabolic therapy research at the moment. As a non-essential amino acid, arginine is involved in numerous crucial biological processes, including the signaling system, cell proliferation, and material metabolism. Rapidly dividing tumor cells are more likely to be deficient in arginine; hence, utilizing arginase to consume arginine can suppress tumor growth. Due to the absence of arginine succinate synthase, arginine succinate lyase, and ornithine carbamoyl transferase in some blood tumors, arginases may be employed to treat blood tumors. By investigating the mechanism of arginase treatment and the mechanism of drug resistance in greater depth, arginase treatment becomes more successful in hematological cancers and a new anti-cancer agent in clinical practice.

A metabolomics strategy to identify potential biomarkers associated with human laryngeal cancer based on dried blood spot mass spectrometry approach

ABSTRACT

Laryngeal cancer (LC) as one of common malignant tumors in the head and neck region accounted for 1% to 5% of new cancer cases and was ranked as the third otolaryngology cancer. However, some patients with LC were diagnosed at the advanced stage, which can cause delayed diagnosis and treatment. It is an urgent task to seek effective biomarkers for the early diagnosis of LC aimed at alleviating suffering.A combination of dried blood spot sampling and direct infusion mass spectrometry technology was applied to 39 patients with LC and 53 healthy individuals. Multiple algorithms towards 93 metabolites including amino acids and carnitine/acylcarnitines were run for selecting differential metabolites. Furthermore, leave-one-out cross-validation method was used to evaluate diagnostic performance of selected metabolite biomarkers.A biomarker panel consisting of arginine, proline, hexacosanoic carnitine, ornithine /citrulline, and 3-hydroxy-octadecenoylcarnitine exhibited potential to distinguish patients with LC from healthy individuals, with a sensitivity of 0.8974 and a specificity of 0.8302 in leave-one-out cross-validation model.The metabolomic analysis of LC patients is beneficial to screen disease-associated biomarkers and develop new diagnostic approaches.

Preclinical investigation of Pegylated arginase 1 as a treatment for retina and brain injury

Arginase 1 (A1) is the enzyme that hydrolyzes the amino acid, L-arginine, to ornithine and urea. We have previously shown that A1 deletion worsens retinal ischemic injury, suggesting a protective role of A1. In this translational study, we aimed to study the utility of systemic pegylated A1 (PEG-A1, recombinant human arginase linked to polyethylene glycol) treatment in mouse models of acute retinal and brain injury. Cohorts of WT mice were subjected to retinal ischemia-reperfusion (IR) injury, traumatic optic neuropathy (TON) or brain cerebral ischemia via middle cerebral artery occlusion (MCAO) and treated with intraperitoneal injections of PEG-A1 or vehicle (PEG only). Drug penetration into retina and brain tissues was measured by western blotting and immunolabeling for PEG. Neuroprotection was measured in a blinded fashion by quantitation of NeuN (neuronal marker) immunolabeling of retina flat-mounts and brain infarct area using triphenyl tetrazolium chloride (TTC) staining. Furthermore, ex vivo retina explants and in vitro retina neuron cultures were subjected to oxygen-glucose deprivation (OGD) followed by reoxygenation (R) and treated with PEG-A1. PEG-A1 given systemically did not cross the intact blood-retina/brain barriers in sham controls but reached the retina and brain after injury. PEG-A1 provided neuroprotection after retinal IR injury, TON and cerebral ischemia. PEG-A1 treatment was also neuroprotective in retina explants subjected to OGD/R but did not improve survival in retinal neuronal cultures exposed to OGD/R. In summary, systemic PEG-A1 administration is neuroprotective and provides an excellent route to deliver the drug to the retina and the brain after acute injury.

Human Recombinant Arginase I [HuArgI(Co)-PEG5000]-Induced Arginine Depletion Inhibits Pancreatic Cancer Cell Migration and Invasion Through Autophagy

OBJECTIVES

Pancreatic cancer is one of the most aggressive solid cancers and the fourth leading cause of cancer death in men and women. We previously showed that arginine depletion, using arginase I [HuArgI(Co)-PEG5000], selectively triggers cell death by autophagy in PANC-1 pancreatic cancer cells. The mechanism of action of [HuArgI(Co)-PEG5000], however, has remained poorly understood. In this study, we investigated the effects of arginine depletion on PANC-1 cell migration, adhesion, and invasion and determined the main molecular targets, which mediate PANC-1 cell response to treatment with HuArgI(Co)-PEG5000.

METHODS

This was done through examining 2-dimensional (2D) cell motility assays (wound healing and time lapse), cell adhesion, and cell invasion assays, as well as immunostaining for focal adhesions and invadopodia in cells without or with the treatment with arginase.

RESULTS

We demonstrate that arginine depletion decreases PANC-1 2D cell migration, adhesion, and 3D invasion. Moreover, our data suggest that these effects are mediated by autophagy and subsequent decrease in the activation of members of Ras homolog gene family (Rho) GTPase family.

CONCLUSIONS

Altogether, these findings uncover the mechanism of action of [HuArgI(Co)-PEG5000] and highlight the promising and selective anticancer potential for arginine depletion in the treatment of pancreatic cancer cells.

Extracellular Vesicles in Cancer Metabolism: Implications for Cancer Diagnosis and Treatment

Metabolic reprogramming is one of the most common characteristics of cancer cells. The metabolic alterations of glucose, amino acids and lipids can support the aggressive phenotype of cancer cells. Exosomes, a kind of extracellular vesicles, participate in the intercellular communication through transferring bioactive molecules. Increasing evidence has demonstrated that enzymes, metabolites and non-coding RNAs in exosomes are responsible for the metabolic alteration of cancer cells. In this review, we summarize the past and recent findings of exosomes in altering cancer metabolism and elaborate on the role of the specific enzymes, metabolites and non-coding RNAs transferred by exosomes. Moreover, we give evidence of the role of exosomes in cancer diagnosis and treatment. Finally, we discuss the existing problems in the study and application of exosomes in cancer diagnosis and treatment.

Cisplatin Resistance and Redox-Metabolic Vulnerability: A Second Alteration

The development of drug resistance in tumors is a major obstacle to effective cancer chemotherapy and represents one of the most significant complications to improving long-term patient outcomes. Despite early positive responsiveness to platinum-based chemotherapy, the majority of lung cancer patients develop resistance. The development of a new combination therapy targeting cisplatin-resistant (CR) tumors may mark a major improvement as salvage therapy in these patients. The recent resurgence in research into cellular metabolism has again confirmed that cancer cells utilize aerobic glycolysis ("the Warburg effect") to produce energy. Hence, this observation still remains a characteristic hallmark of altered metabolism in certain cancer cells. However, recent evidence promotes another concept wherein some tumors that acquire resistance to cisplatin undergo further metabolic alterations that increase tumor reliance on oxidative metabolism (OXMET) instead of glycolysis. Our review focuses on molecular changes that occur in tumors due to the relationship between metabolic demands and the importance of NAD+ in redox (ROS) metabolism and the crosstalk between PARP-1 (Poly (ADP ribose) polymerase-1) and SIRTs (sirtuins) in CR tumors. Finally, we discuss a role for the tumor metabolites of the kynurenine pathway (tryptophan catabolism) as effectors of immune cells in the tumor microenvironment during acquisition of resistance in CR cells. Understanding these concepts will form the basis for future targeting of CR cells by exploiting redox-metabolic changes and their consequences on immune cells in the tumor microenvironment as a new approach to improve overall therapeutic outcomes and survival in patients who fail cisplatin.

Arginine starvation elicits chromatin leakage and cGAS-STING activation via epigenetic silencing of metabolic and DNA-repair genes

Rationale: One of the most common metabolic defects in cancers is the deficiency in arginine synthesis, which has been exploited therapeutically. Yet, challenges remain, and the mechanisms of arginine-starvation induced killing are largely unclear. Here, we sought to demonstrate the underlying mechanisms by which arginine starvation-induced cell death and to develop a dietary arginine-restriction xenograft model to study the in vivo effects. Methods: Multiple castration-resistant prostate cancer cell lines were treated with arginine starvation followed by comprehensive analysis of microarray, RNA-seq and ChIP-seq were to identify the molecular and epigenetic pathways affected by arginine starvation. Metabolomics and Seahorse Flux analyses were used to determine the metabolic profiles. A dietary arginine-restriction xenograft mouse model was developed to assess the effects of arginine starvation on tumor growth and inflammatory responses. Results: We showed that arginine starvation coordinately and epigenetically suppressed gene expressions, including those involved in oxidative phosphorylation and DNA repair, resulting in DNA damage, chromatin-leakage and cGAS-STING activation, accompanied by the upregulation of type I interferon response. We further demonstrated that arginine starvation-caused depletion of α-ketoglutarate and inactivation of histone demethylases are the underlying causes of epigenetic silencing. Significantly, our dietary arginine-restriction model showed that arginine starvation suppressed prostate cancer growth in vivo, with evidence of enhanced interferon responses and recruitment of immune cells. Conclusions: Arginine-starvation induces tumor cell killing by metabolite depletion and epigenetic silencing of metabolic genes, leading to DNA damage and chromatin leakage. The resulting cGAS-STING activation may further enhance these killing effects.

Role of LncRNAs in regulating cancer amino acid metabolism

The metabolic change of tumor cells is an extremely complicated process that involves the intersection and integration of various signal pathways. Compared with normal tissues, cancer cells show distinguished metabolic characteristics called metabolic reprogramming, which has been considered as a sign of cancer occurrence. With the deepening of tumor research in recent years, people gradually found that amino acid metabolism played crucial roles in cancer progression. Long non-coding RNAs (lncRNAs), which are implicated in many important biological processes, were firstly discovered dysregulating in cancer tissues and participating in extensive regulation of tumorigenesis. This review focuses on the reprogramming of amino acid metabolism in cancers and how lncRNAs participate in the regulatory network by interacting with other macromolecular substances. Understanding the functions of lncRNA in amino acid reprogramming in tumors might provide a new vision on the mechanisms of tumorigenesis and the development of new approaches for cancer therapy.

Untargeted metabolomics of prostate cancer zwitterionic and positively charged compounds in urine

Prostate cancer, a leading cause of cancer-related deaths worldwide, principally occurs in over 50-year-old men. Nowadays there is urgency to discover biomarkers alternative to prostate-specific antigen, as it cannot discriminate patients with benign prostatic hyperplasia from clinically significant forms of prostatic cancer. In the present paper, 32 benign prostatic hyperplasia and 41 prostatic cancer urine samples were collected and analyzed. Polar and positively charged metabolites were therein investigated using an analytical platform comprising an up to 40-fold analyte enrichment step by graphitized carbon black solid-phase extraction, HILIC separation, and untargeted high-resolution mass spectrometry analysis. These classes of compounds are often neglected in common metabolomics experiments even though previous studies reported their significance in cancer biomarker discovery. The complex metabolomics big datasets, generated by the UHPLC-HRMS, were analyzed with the ROIMCR procedure, based on the selection of the MS regions of interest data and their analysis by the Multivariate Curve-Resolution Alternating Least Squares chemometrics method. This approach allowed the resolution and tentative identification of the metabolites differentially expressed by the two data sets. Among these, amino acids and carnitine derivatives were tentatively identified highlighting the importance of the proposed methodology for cancer biomarker research.

Metabolomic characterisation of progression and spontaneous regression of melanoma in the melanoma-bearing Libechov minipig model

Melanoma-bearing Libechov minipig (MeLiM) represents a large animal model for melanoma research. This model shows a high incidence of complete spontaneous regression of melanoma - a phenomenon uncommon in humans. Here, we present the first metabolomic characterisation of the MeLiM model comparing animals with progressing and spontaneously regressing melanomas. Plasma samples of 19 minipigs with progression and 27 minipigs with evidence of regression were analysed by a targeted metabolomic assay based on mass spectrometry detection. Differences in plasma metabolomics patterns were investigated by univariate and multivariate statistical analyses. Overall, 185 metabolites were quantified in each plasma sample. Significantly altered metabolomic profile was found, and 42 features were differentially regulated in plasma. Besides, the machine learning approach was used to create a predictive model utilising Arg/Orn and Arg/ADMA ratios to discriminate minipigs with progressive disease development from minipigs with regression evidence. Our results suggest that progression of melanoma in the MeLiM model is associated with alteration of arginine, glycerophospholipid and acylcarnitines metabolism. Moreover, this study provides targeted metabolomics characterisation of an animal model of melanoma with progression and spontaneous regression of tumours.

Human recombinant arginase I [HuArgI (Co)-PEG5000]-induced arginine depletion inhibits ovarian cancer cell adhesion and migration through autophagy-mediated inhibition of RhoA

Ovarian carcinoma is the second most common malignancy of the female reproductive system and the leading cause of death from female reproductive system malignancies. Cancer cells have increased proliferation rate and thus require high amounts of amino acids, including arginine. L-arginine is a non-essential amino acid synthesized from L-citrulline by the Arginosuccinate synthetase (ASS1) enzyme. We have previously shown that the ovarian cancer cells, SKOV3, are auxotrophic to arginine, and that arginine deprivation by treatment with the genetically engineered human arginase I (HuArgI (Co)-PEG5000) triggers the death of SKOV3 cells by autophagy. In this study we examine the effect of HuArgI (Co)-PEG5000 on ovarian cancer cell migration and we dissect the mechanism involved. Wound healing assays, 2D random cell migration assays and cell adhesion analysis indicate that arginine deprivation decreases SKOV3 cell migration and adhesion. This effect was mimicked when autophagy was induced through rapamycin and reversed with the autophagy inhibitor chloroquine when autophagy was inhibited. This proved that arginine deprivation leads to the inhibition of cancer cell migration through autophagy, in addition to cell death. In addition, we were able to establish through pull-down assays and reversal experiments, that arginine deprivation-mediated autophagy inhibits cell migration through a direct inhibition of RhoA, member of the Rho family of GTPases. In conclusion, here we identify, for the first time, an autophagy-mediated inhibition of RhoA that plays an important role in regulating ovarian cancer cells motility and adhesion in response to arginine depletion.

Targeting Metabolic Pathways in Kidney Cancer: Rationale and Therapeutic Opportunities

Alterations in cellular sugar, amino acid and nucleic acid, and lipid metabolism, as well as in mitochondrial function, are a hallmark of renal cell carcinoma (RCC). The activation of oncogenes such as hypoxia-inducible factor and loss of the von Hippel-Lindau function and other tumor suppressors frequently occur early on during tumorigenesis and are the drivers for these changes, collectively known as "metabolic reprogramming," which promotes cellular growth, proliferation, and stress resilience. However, tumor cells can become addicted to reprogrammed metabolism. Here, we review the current knowledge of metabolic addictions in clear cell RCC, the most common form of RCC, and to what extent this has created therapeutic opportunities to interfere with such altered metabolic pathways to selectively target tumor cells. We highlight preclinical and emerging clinical data on novel therapeutics targeting metabolic traits in clear cell RCC to provide a comprehensive overview on current strategies to exploit metabolic reprogramming clinically.

Arginine deprivation: a potential therapeutic for cancer cell metastasis? A review

Arginine is a semi essential amino acid that is used in protein biosynthesis. It can be obtained from daily food intake or synthesized in the body through the urea cycle using l-citrulline as a substrate. Arginine has a versatile role in the body because it helps in cell division, wound healing, ammonia disposal, immune system, and hormone biosynthesis. It is noteworthy that l-arginine is the precursor for the biosynthesis of nitric oxide (NO) and polyamines. In the case of cancer cells, arginine de novo synthesis is not enough to compensate for their high nutritional needs, forcing them to rely on extracellular supply of arginine. In this review, we will go through the importance of arginine deprivation as a novel targeting therapy by discussing the different arginine deprivation agents and their mechanism of action. We will also focus on the factors that affect cell migration and on the influence of arginine on metastases through polyamine and NO.

Integrated Non-targeted and Targeted Metabolomics Uncovers Amino Acid Markers of Oral Squamous Cell Carcinoma

Purpose: It is very important to develop potential molecular associated with oral squamous cell carcinoma (OSCC) malignant transformation and progression. Thus, the aim of our study was to determine the amino acid metabolic characteristics of OSCC patients and test their diagnostic value.

Experimental Design: Eight pairs of matched tumor and normal samples were collected for gas chromatography–mass spectrometry (GC-MS) high-throughput untargeted analysis. Another 20 cases (each case including tumor and normal tissues) were also enrolled for ultrahigh-performance liquid chromatography–tandem mass spectrometer (UHPLC-MS/MS) amino acid quantitative analysis. T-test and receiver operating characteristic (ROC) curve analysis were used to determine candidate markers. Principal component analysis, partial least squares discriminant analysis, and heat map analysis were used to verify the ability of candidate markers to distinguish tumors from normal tissues.

Results: A total of 10 amino acids biomarker were selected as OSCC candidate diagnostic biomarkers by GC-MS high-throughput untargeted metabolomics analyses [area under the curve (AUC) >0.80]. We further measured the specific concentration of these candidate amino acids biomarkers in another batch of 20 cases by UHPLC-MS/MS quantitative analysis. The result validated that nine amino acids had been detected, which had statistically significant difference (t-test, p < 0.05). Moreover, three of nine amino acid markers (glutamate, aspartic acid, and proline) displayed high sensitivity and specificity (AUC >0.90) by ROC curve analysis and obtained optimal sensitivity and specificity by binary logistic regression in the Glmnet package (AUC = 0.942).

Conclusions: In conclusion, a panel including three amino acids (glutamate, aspartic acid, and proline) was identified as potential diagnostic biomarkers of OSCC by a combination of non-targeted and targeted metabolomics methods.

Modulation of dysregulated cancer metabolism by plant secondary metabolites: A mechanistic review

Several signaling pathways and basic metabolites are responsible for the control of metabolism in both normal and cancer cells. As emerging hallmarks of cancer metabolism, the abnormal activities of these pathways are of the most noticeable events in cancer. This altered metabolism expedites the survival and proliferation of cancer cells, which have attracted a substantial amount of interest in cancer metabolism. Nowadays, targeting metabolism and cross-linked signaling pathways in cancer has been a hot topic to investigate novel drugs against cancer. Despite the efficiency of conventional drugs in cancer therapy, their associated toxicity, resistance, and high-cost cause limitations in their application. Besides, considering the numerous signaling pathways cross-linked with cancer metabolism, discovery, and development of multi-targeted and safe natural compounds has been a high priority. Natural secondary metabolites have exhibited promising anticancer effects by targeting dysregulated signaling pathways linked to cancer metabolism. The present review reveals the metabolism and cross-linked dysregulated signaling pathways in cancer. The promising therapeutic targets in cancer, as well as the critical role of natural secondary metabolites for significant anticancer enhancements, have also been highlighted to find novel/potential therapeutic agents for cancer treatment.

Role of tumor and host autophagy in cancer metabolism

Macroautophagy (referred to here as autophagy) degrades and recycles cytoplasmic constituents to sustain cellular and mammalian metabolism and survival during starvation. Deregulation of autophagy is involved in numerous diseases, such as cancer. Cancers up-regulate autophagy and depend on it for survival, growth, and malignancy in a tumor cell-autonomous fashion. Recently, it has become apparent that autophagy in host tissues as well as the tumor cells themselves contribute to tumor growth. Understanding how autophagy regulates metabolism and tumor growth has revealed new essential tumor nutrients, where they come from, and how they are supplied and used, which can now be targeted for cancer therapy.

A reliable LC-MS/MS method for the quantification of natural amino acids in mouse plasma: Method validation and application to a study on amino acid dynamics during hepatocellular carcinoma progression

A simple and fast LC-MS/MS method was developed and validated for simultaneous quantification of 20 proteinogenic l-amino acids (AAs) in a small volume (5 μL) of mouse plasma. Chromatographic separation was achieved on an Intrada Amino Acid column within 13 min via gradient elution with an aqueous solution containing 100 mM ammonium formate and an organic mobile phase containing acetonitrile, water and formic acid (v:v:v = 95:5:0.3), at the flow rate of 0.6 mL/min. Individual AAs and corresponding stable-isotope-labeled AAs internal standards were analyzed by multiple reaction monitoring (MRM) in positive ion mode under optimized conditions. Method validation consisted of linearity, sensitivity, accuracy and precision, recovery, matrix effect, and stability, and the results demonstrated this LC-MS/MS method as a specific, accurate, and reliable assay. This LC-MS/MS method was thus utilized to compare the dynamics of individual plasma AAs between healthy and orthotopic hepatocellular carcinoma (HCC) xenograft mice housed under identical conditions. Our results revealed that, 5 weeks after HCC tumor progression, plasma l-arginine concentrations were significantly decreased in HCC mice while l-alanine and l-threonine levels were sharply increased. These findings support the utilities of this LC-MS/MS method and the promise of specific AAs as possible biomarkers for HCC.

Metabolism within the tumor microenvironment and its implication on cancer progression: An ongoing therapeutic target

Since reprogramming energy metabolism is considered a new hallmark of cancer, tumor metabolism is again in the spotlight of cancer research. Many studies have been carried out and many possible therapies have been developed in the last years. However, tumor cells are not alone. A series of extracellular components and stromal cells, such as endothelial cells, cancer-associated fibroblasts, tumor-associated macrophages, and tumor-infiltrating T cells, surround tumor cells in the so-called tumor microenvironment (TME). Metabolic features of these cells are being studied in deep in order to find relationships between metabolism within the TME and tumor progression. Moreover, it cannot be forgotten that tumor growth is able to modulate host metabolism and homeostasis, so that TME is not the whole story. Importantly, the metabolic switch in cancer is just a consequence of the flexibility and adaptability of metabolism and should not be surprising. Treatments of cancer patients with combined therapies including antitumor agents with those targeting stromal cell metabolism, antiangiogenic drugs, and/or immunotherapy are being developed as promising therapeutics.

TRAIL stabilization and cancer cell sensitization to its pro-apoptotic activity achieved through genetic fusion with arginine deiminase

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) binds to death receptors and induces apoptosis in various cancer cell lines while sparing normal cells. Recombinant TRAIL has shown good safety and efficacy profiles in preclinical cancer models. However, clinical success has been limited due to poor PK and development of resistance to death receptor-induced apoptosis. We have addressed these issues by creating a fusion protein of TRAIL and arginine deiminase (ADI). The fusion protein benefits from structural and functional synergies between its two components and has an extended half-life in vivo. ADI downregulates survivin, upregulates DR5 receptor and sensitizes cancer cells to TRAIL induced apoptosis. ADI-TRAIL fusion protein was efficacious in a number of cell lines and synergized with some standard of care drugs. In an HCT116 xenograft model ADI-TRAIL localized to the tumor and induced dose-dependent tumor regression, the fusion protein was superior to rhTRAIL administered at the same molar amounts.

Arginase 1 promotes retinal neurovascular protection from ischemia through suppression of macrophage inflammatory responses

The lack of effective therapies to limit neurovascular injury in ischemic retinopathy is a major clinical problem. This study aimed to examine the role of ureohydrolase enzyme, arginase 1 (A1), in retinal ischemia-reperfusion (IR) injury. A1 competes with nitric oxide synthase (NOS) for their common substrate l-arginine. A1-mediated l-arginine depletion reduces nitric oxide (NO) formation by NOS leading to vascular dysfunction when endothelial NOS is involved but prevents inflammatory injury when inducible NOS is involved. Studies were performed using wild-type (WT) mice, global A1^+/− knockout (KO), endothelial-specific A1 KO, and myeloid-specific A1 KO mice subjected to retinal IR injury. Global as well as myeloid-specific A1 KO mice showed worsened IR-induced neuronal loss and retinal thinning. Deletion of A1 in endothelial cells had no effect, while treatment with PEGylated (PEG) A1 improved neuronal survival in WT mice. In addition, A1^+/− KO mice showed worsened vascular injury manifested by increased acellular capillaries. Western blotting analysis of retinal tissue showed increased inflammatory and necroptotic markers with A1 deletion. In vitro experiments showed that macrophages lacking A1 exhibit increased inflammatory response upon LPS stimulation. PEG-A1 treatment dampened this inflammatory response and decreased the LPS-induced metabolic reprogramming. Moreover, intravitreal injection of A1 KO macrophages or systemic macrophage depletion with clodronate liposomes increased neuronal loss after IR injury. These results demonstrate that A1 reduces IR injury-induced retinal neurovascular degeneration via dampening macrophage inflammatory responses. Increasing A1 offers a novel strategy for limiting neurovascular injury and promoting macrophage-mediated repair.

Cisplatin-induced synthetic lethality to arginine-starvation therapy by transcriptional suppression of ASS1 is regulated by DEC1, HIF-1α, and c-Myc transcription network and is independent of ASS1 promoter DNA methylation

Many human tumors require extracellular arginine (Arg) for growth because the key enzyme for de novo biosynthesis of Arg, argininosuccinate synthetase 1 (ASS1), is silenced. These tumors are sensitive to Arg-starvation therapy using pegylated arginine deiminase (ADI-PEG20) which digests extracellular Arg. Many previous studies reported that ASS1 silencing is due to epigenetic inactivation of ASS1 expression by DNA methylation, and that the demethylation agent 5-aza-deoxycytidine (Aza-dC) can induce ASS1 expression. Moreover, it was reported that cisplatin suppresses ASS1 expression through ASS1 promoter methylation, leading to synthetic lethality to ADI-PEG20 treatment. We report here that cisplatin supppresses ASS1 expression is due to upregulation of HIF-1α and downregulation of c-Myc, which function as negative and positive regulators of ASS1 expression, respectively, by reciprocal bindings to the ASS1 promoter. In contrast, we found that Aza-dC induces ASS1 expression by downregulation of HIF-1α but upregulation of c-Myc. We further demonstrated that the clock protein DEC1 is the master regulator of HIF-1α and c-Myc that regulate ASS1. cDDP upregulates DEC1, whereas Aza-dC suppresses its expression. Using two proteasomal inhibitors bortezomib and carfilzomib which induce HIF-1α accumulation, we further demonstrated that HIF-1α is involved in ASS1 silencing for the maintenance of Arg auxotrophy for targeted Arg-starvation therapy.

Metabolomic profiling identifies distinct phenotypes for ASS1 positive and negative GBM

Background

Tumour cells have a high demand for arginine. However, a subset of glioblastomas has a defect in the arginine biosynthetic pathway due to epigenetic silencing of the rate limiting enzyme argininosuccinate synthetase (ASS1). These tumours are auxotrophic for arginine and susceptible to the arginine degrading enzyme, pegylated arginine deiminase (ADI-PEG20). Moreover, ASS1 deficient GBM have a worse prognosis compared to ASS1 positive tumours. Since altered tumour metabolism is one of the hallmarks of cancer we were interested to determine if these two subtypes exhibited different metabolic profiles that could allow for their non-invasive detection as well as unveil additional novel therapeutic opportunities.

Methods

We looked for basal metabolic differences using one and two-dimensional gas chromatography-time-of-flight mass spectrometry (1D/2D GC-TOFMS) followed by targeted analysis of 29 amino acids using liquid chromatography-time-of-flight mass spectrometry (LC-TOFMS). We also looked for differences upon arginine deprivation in a single ASS1 negative and positive cell line (SNB19 and U87 respectively). The acquired data was evaluated by chemometric based bioinformatic methods.

Results

Orthogonal partial least squares-discriminant analysis (OPLS-DA) of both the 1D and 2D GC-TOFMS data revealed significant systematic difference in metabolites between the two subgroups with ASS1 positive cells generally exhibiting an overall elevation of identified metabolites, including those involved in the arginine biosynthetic pathway. Pathway and network analysis of the metabolite profile show that ASS1 negative cells have altered arginine and citrulline metabolism as well as altered amino acid metabolism. As expected, we observed significant metabolite perturbations in ASS negative cells in response to ADI-PEG20 treatment.

Conclusions

This study has highlighted significant differences in the metabolome of ASS1 negative and positive GBM which warrants further study to determine their diagnostic and therapeutic potential for the treatment of this devastating disease.

Chromatin remodeling system p300-HDAC2-Sin3A is involved in Arginine Starvation-Induced HIF-1α Degradation at the ASS1 promoter for ASS1 Derepression

Argininosuccinate synthetase 1 (ASS1) is the key enzyme that controls biosynthesis of arginine (Arg). ASS1 is silenced in many human malignancies therefore, these tumors require extracellular Arg for growth. The Arg-degrading recombinant protein, pegylated arginine deiminase (ADI-PEG20), has been in clinical trials for targeting Arg auxotrophic tumors by Arg starvation therapy. Resistance to Arg starvation is often developed through reactivation of ASS1 expression. We previously demonstrated that ASS1 silencing is controlled by HIF-1α and Arg starvation-reactivated ASS1 is associated with HIF-1α downregulation. However, mechanisms underlying ASS1 repression and HIF-1α turnover are not known. Here, we demonstrate that interplay of p300-HDAC2-Sin3A in the chromatin remodeling system is involved in HIF-1α degradation at the ASS1 promoter. The histone acetyltransferase p300 is normally associated with the ASS1 promoter to maintain acetylated H3K14ac and H3K27ac for ASS1 silencing. Arg starvation induces p300 dissociation, allowing histone HDAC2 and cofactor Sin3A to deacetylate these histones at the ASS1 promoter, thereby facilitating HIF-1α-proteasomal complex, driven by PHD2, to degrade HIF-1α in situ. Arg starvation induces PHD2 and HDAC2 interaction which is sensitive to antioxidants. This is the first report describing epigenetic regulation of chromosomal HIF-1α turnover in gene activation that bears important implication in cancer therapy.

PEGylated arginine deiminase can modulate tumor immune microenvironment by affecting immune checkpoint expression, decreasing regulatory T cell accumulation and inducing tumor T cell infiltration

PEGylated arginine deiminase (ADI-PEG 20) is being investigated in clinical studies in arginine auxotrophic cancers and is well-tolerated. The anti-tumor properties of ADI-PEG 20 have been extensively investigated - ADI-PEG 20 inhibits the growth of auxotrophic cancers in vitro and in vivo - however, its impact on immune cells is largely unknown. Here we report the potential impact of ADI-PEG 20 on the tumor immune microenvironment. ADI-PEG 20 induced immunosuppressive programmed death-ligand 1 expression on some cancer cells in vitro, but the magnitude of the increase was cell line dependent and in most relatively small. Using healthy donor human peripheral blood mononuclear cells (PBMCs) we discovered that when present during initiation of T cell activation (but not later on) ADI-PEG 20 can inhibit their differentiation after early activation stage manifested by the expression of CD69 marker.

In vivo, ADI-PEG 20 induced tumor T-cell infiltration in a poorly immunogenic syngeneic mouse melanoma B16-F10 model and reduced its growth as a single agent or when combined with anti-PD-1 mAb. It was also effective by itself or in combination with anti-PD-L1 mAb in CT26 colon carcinoma syngeneic model.

The Combination of Arginine Deprivation and 5-Fluorouracil Improves Therapeutic Efficacy in Argininosuccinate Synthetase Negative Hepatocellular Carcinoma

Argininosuccinate synthetase (ASS), a key enzyme to synthesize arginine is down regulated in many tumors including hepatocellular carcinoma (HCC). Similar to previous reports, we have found the decrease in ASS expression in poorly differentiated HCC. These ASS(-) tumors are auxotrophic for arginine. Pegylated arginine deiminase (ADI-PEG20), which degrades arginine, has shown activity in these tumors, but the antitumor effect is not robust and hence combination treatment is needed. Herein, we have elucidated the effectiveness of ADI-PEG20 combined with 5-Fluorouracil (5-FU) in ASS(-)HCC by targeting urea cycle and pyrimidine metabolism using four HCC cell lines as model. SNU398 and SNU387 express very low levels of ASS or ASS(-) while Huh-1, and HepG2 express high ASS similar to normal cells. Our results showed that the augmented cytotoxic effect of combination treatment only occurs in SNU398 and SNU387, and not in HepG2 and Huh-1 (ASS(+)) cells, and is partly due to reduced anti-apoptotic proteins X-linked inhibitor of apoptosis protein (XIAP), myeloid leukemia cell differentiation protein (Mcl-1) and B-cell lymphoma-2 (Bcl-2). Importantly, lack of ASS also influences essential enzymes in pyrimidine synthesis (carbamoyl-phosphate synthetase2, aspartate transcarbamylase and dihydrooratase (CAD) and thymidylate synthase (TS)) and malate dehydrogenase-1 (MDH-1) in TCA cycle. ADI-PEG20 treatment decreased these enzymes and made them more vulnerable to 5-FU. Transfection of ASS restored these enzymes and abolished the sensitivity to ADI-PEG20 and combination treatment. Overall, our data suggest that ASS influences multiple enzymes involved in 5-FU sensitivity. Combining ADI-PEG20 and 5-FU may be effective to treat ASS(-)hepatoma and warrants further clinical investigation.

Proliferation and motility of hepatocellular, pancreatic and gastric cancer cells grown in a medium without glucose and arginine, but with galactose and ornithine

Human primary hepatocytes are able to survive in a medium without glucose and arginine, but supplemented with galactose and ornithine (hepatocyte selection medium; HSM). To address the possibility of the application of HSM in cancer therapy, hepatocellular carcinoma cells, pancreatic cancer cells and gastric cancer cells were cultured in HSM. Cell proliferation was analyzed using an MTS assay. Morphological changes were analyzed using hematoxylin and eosin staining. Apoptosis was analyzed using a TUNEL assay and cell motility was assessed with a scratch assay. Cell proliferation was significantly suppressed in cell lines grown in HSM (P<0.01 in all the cell lines). Hematoxylin and eosin staining revealed pyknotic nuclei, suggesting that these cells had undergone apoptosis. The number of TUNEL-positive cells was significantly increased in HSM. In the scratch assay, the distance between the growing edge and the scratched edge was significantly lower (P<0.01 in all the cell lines) in cells cultured in HSM, compared with those grown in Dulbecco's modified Eagle's medium or RPMI-1640. Therefore, the proliferation and motility of hepatocellular carcinoma cells, pancreatic cancer cells and gastric cancer cells was suppressed, and these cells subsequently underwent apoptosis in a medium without glucose and arginine, but containing galactose and ornithine.

Arginine Metabolism Revisited

Mammalian arginine metabolism is complex due to the expression of multiple enzymes that utilize arginine as substrate and to interactions or competition between specific enzymes involved in arginine metabolism. Moreover, cells may contain multiple intracellular arginine pools that are not equally accessible to all arginine metabolic enzymes, thus presenting additional challenges to more fully understanding arginine metabolism. At the whole-body level, arginine metabolism ultimately results in the production of a biochemically diverse range of products, including nitric oxide, urea, creatine, polyamines, proline, glutamate, agmatine, and homoarginine. Included in this group of compounds are the methylated arginines (e.g., asymmetric dimethylarginine), which are released upon degradation of proteins containing methylated arginine residues. Changes in arginine concentration also can regulate cellular metabolism and function via a variety of arginine sensors. Although much is known about arginine metabolism, elucidation of the physiologic or pathophysiologic roles for all of the pathways and their metabolites remains an active area of investigation, as exemplified by current findings highlighted in this review.

Argininosuccinate synthetase 1 (ASS1) is a common metabolic marker of chemosensitivity for targeted arginine- and glutamine-starvation therapy

Argininosuccinate synthetase 1 (ASS1) is the rate-limiting enzyme that catalyzes the biosynthesis of arginine (Arg). Many malignant human tumors are auxotrophic for Arg because ASS1 is silenced. ASS1 has been established as a sensor of Arg auxotrophic response and a chemosensitivity marker for Arg starvation therapy. Here, we report that ASS1 is also a sensor for glutamine (Gln)-deprivation response, and that upregulation of ASS1 expression is associated with resistance to Gln-starvation treatments. Knockdown of ASS1 expression resulted in increased sensitivity to both Arg- and Gln-starvation, whereas increased ASS1 expression by ectopic transfection is associated with resistance to both Arg- and Gln-starvation. The addition of permeable fumarate, a metabolite that bridges the tricarboxylic acid and urea cycles, resulted in downregulation of ASS1 expression and increased sensitivity to both Arg- and Gln-deprivation treatments. Mechanistically, the Gln-deprivation response, like the arginine-auxotrophic response, downregulates HIF-1α resulting in de-silencing of ASS1. Our results demonstrate that ASS1 is a common biosensor for Arg and Gln deprivation response and a shared target for Arg- and Gln-starvation therapies which have been in several current clinical trials.