A phase 1 dose-escalating study of pegylated recombinant human arginase 1 (Peg-rhArg1) in patients with advanced hepatocellular carcinoma

Opportunities and Challenges of Arginase Inhibitors in Cancer: A Medicinal Chemistry Perspective

The overexpression of two arginase (ARG) isoforms, ARG1 and ARG2, contributes to the onset of numerous disorders, including cardiovascular and immune-mediated diseases, as well as tumors. To elucidate the specific roles of ARG1 and ARG2 without interfering with their physiological functions, it is crucial to develop effective ARG inhibitors that target only one isoform, while maintaining low toxicity and an adequate pharmacokinetic profile. In this context, we present a comprehensive overview of the different generations of ARG inhibitors. Given the general lack of selectivity in most existing inhibitors, we analyzed the structural features and plasticity of the ARG1 and ARG2 binding sites to explore the potential for designing inhibitors with novel binding patterns. We also review ongoing preclinical and clinical studies on selected inhibitors, highlighting both progress and challenges in developing potent, selective ARG inhibitors. Furthermore, we discuss medicinal chemistry strategies that may accelerate the discovery of selective ARG inhibitors.

Reprogramming of urea cycle in cancer: Mechanism, regulation and prospective therapeutic scopes

Hepatic urea cycle, previously known as ornithine cycle, is the chief biochemical pathway that deals with the disposal of excessive nitrogen in form of urea, resulted from protein breakdown and concomitant condensation of ammonia. Enzymes involved in urea cycle are expressed differentially outside hepatic tissue and are mostly involved in production of arginine from citrulline in arginine-depleted condition. Inline, cancer cells frequently adapt metabolic rewiring to support sufficient biomass production in order to sustain tumor cell survival, multiplication and subsequent growth. For the accomplishment of this aim, metabolic reprogramming in cancer cells is set in way so that cellular nitrogen and carbon repertoire can be utilized and channelized maximally towards anabolic reactions. A strategy to meet such outcome is to cut down unnecessary catabolic reactions and nitrogen elimination. Thus, transfigured urea cycle is a hallmark of neoplasia. During oncogenesis, altered expression and regulation of enzymes involved in urea cycle is a revolutionary approach meet to maximum incorporation of nitrogen for sustaining tumor specific biogenesis. Currently, we have reviewed neoplasm-specific deregulations of urea cycle-enzymes in different types and stages of cancers suggesting its context-oriented dynamic nature. Considering such insight to be valuable in terms of prospective cancer diagnosis and therapeutics adaptive evolution of deregulated urea cycle has been enlightened.

Metabolic reprogramming and immune evasion: the interplay in the tumor microenvironment

Tumor cells possess complex immune evasion mechanisms to evade immune system attacks, primarily through metabolic reprogramming, which significantly alters the tumor microenvironment (TME) to modulate immune cell functions. When a tumor is sufficiently immunogenic, it can activate cytotoxic T-cells to target and destroy it. However, tumors adapt by manipulating their metabolic pathways, particularly glucose, amino acid, and lipid metabolism, to create an immunosuppressive TME that promotes immune escape. These metabolic alterations impact the function and differentiation of non-tumor cells within the TME, such as inhibiting effector T-cell activity while expanding regulatory T-cells and myeloid-derived suppressor cells. Additionally, these changes lead to an imbalance in cytokine and chemokine secretion, further enhancing the immunosuppressive landscape. Emerging research is increasingly focusing on the regulatory roles of non-tumor cells within the TME, evaluating how their reprogrammed glucose, amino acid, and lipid metabolism influence their functional changes and ultimately aid in tumor immune evasion. Despite our incomplete understanding of the intricate metabolic interactions between tumor and non-tumor cells, the connection between these elements presents significant challenges for cancer immunotherapy. This review highlights the impact of altered glucose, amino acid, and lipid metabolism in the TME on the metabolism and function of non-tumor cells, providing new insights that could facilitate the development of novel cancer immunotherapies.

Arginine reprograms metabolism in liver cancer via RBM39

Metabolic reprogramming is a hallmark of cancer. However, mechanisms underlying metabolic reprogramming and how altered metabolism in turn enhances tumorigenicity are poorly understood. Here, we report that arginine levels are elevated in murine and patient hepatocellular carcinoma (HCC), despite reduced expression of arginine synthesis genes. Tumor cells accumulate high levels of arginine due to increased uptake and reduced arginine-to-polyamine conversion. Importantly, the high levels of arginine promote tumor formation via further metabolic reprogramming, including changes in glucose, amino acid, nucleotide, and fatty acid metabolism. Mechanistically, arginine binds RNA-binding motif protein 39 (RBM39) to control expression of metabolic genes. RBM39-mediated upregulation of asparagine synthesis leads to enhanced arginine uptake, creating a positive feedback loop to sustain high arginine levels and oncogenic metabolism. Thus, arginine is a second messenger-like molecule that reprograms metabolism to promote tumor growth.

Arginine dependency is a therapeutically exploitable vulnerability in chronic myeloid leukaemic stem cells

To fuel accelerated proliferation, leukaemic cells undergo metabolic deregulation, which can result in specific nutrient dependencies. Here, we perform an amino acid drop-out screen and apply pre-clinical models of chronic phase chronic myeloid leukaemia (CML) to identify arginine as a nutrient essential for primary human CML cells. Analysis of the Microarray Innovations in Leukaemia (MILE) dataset uncovers reduced ASS1 levels in CML compared to most other leukaemia types. Stable isotope tracing reveals repressed activity of all urea cycle enzymes in patient-derived CML CD34+ cells, rendering them arginine auxotrophic. Thus, arginine deprivation completely blocks proliferation of CML CD34+ cells and induces significantly higher levels of apoptosis when compared to arginine-deprived cell lines. Similarly, primary CML cells, but not normal CD34+ samples, are particularly sensitive to treatment with the arginine-depleting enzyme, BCT-100, which induces apoptosis and reduces clonogenicity. Moreover, BCT-100 is highly efficacious in a patient-derived xenograft model, causing > 90% reduction in the number of human leukaemic stem cells (LSCs). These findings indicate arginine depletion to be a promising and novel strategy to eradicate therapy resistant LSCs.

Arginine Is a Novel Drug Target for Arginine Decarboxylase in Human Colorectal Cancer Cells

Colorectal cancer (CRC) has been proven to be highly reliant on arginine availability. Limiting arginine-rich foods or treating patients with arginine-depleting enzymes arginine deiminase (ADI) or arginase can suppress colon cancer. However, arginase and ADI are not the best drug candidates for CRC. Ornithine, the product of arginase, can enhance the supply of polyamine, which favors CRC cell growth, while citrulline, the product of ADI, faces the problem of arginine recycling due to the overexpression of argininosuccinate synthetase (ASS). Biosynthetic arginine decarboxylase (ADC), an enzyme that catalyzes the conversion of arginine to agmatine and carbon dioxide, may be a better choice as it combines both arginine depletion and suppression of intracellular polyamine synthesis via its product agmatine. ADC has anti-tumor potential yet has received much less attention than the other two arginine-depleting enzymes. In order to gain a better understanding of ADC, the preparation and the anti-cancer properties of this enzyme were explored in this study. When tested in vitro, ADC inhibited the proliferation of three colorectal cancer cell lines regardless of their ASS cellular expression. In contrast, ADC had a lesser cytotoxic effect on the human foreskin fibroblasts and rat primary hepatocytes. Further in vitro studies revealed that ADC induced S and G2/M phase cell-cycle arrest and apoptosis in HCT116 and LoVo cells. ADC-induced apoptosis in HCT116 cells followed the mitochondrial apoptotic pathway and was caspase-3-dependent. With all results obtained, we suggest that arginine is a potential target for treating colorectal cancer with ADC, and the anti-cancer properties of ADC should be more deeply investigated in the future.

Unlocking the Potential of Arginine Deprivation Therapy: Recent Breakthroughs and Promising Future for Cancer Treatment

Arginine is a semi-essential amino acid that supports protein synthesis to maintain cellular functions. Recent studies suggest that arginine also promotes wound healing, cell division, ammonia metabolism, immune system regulation, and hormone biosynthesis-all of which are critical for tumor growth. These discoveries, coupled with the understanding of cancer cell metabolic reprogramming, have led to renewed interest in arginine deprivation as a new anticancer therapy. Several arginine deprivation strategies have been developed and entered clinical trials. The main principle behind these therapies is that arginine auxotrophic tumors rely on external arginine sources for growth because they carry reduced key arginine-synthesizing enzymes such as argininosuccinate synthase 1 (ASS1) in the intracellular arginine cycle. To obtain anticancer effects, modified arginine-degrading enzymes, such as PEGylated recombinant human arginase 1 (rhArg1-PEG) and arginine deiminase (ADI-PEG 20), have been developed and shown to be safe and effective in clinical trials. They have been tried as a monotherapy or in combination with other existing therapies. This review discusses recent advances in arginine deprivation therapy, including the molecular basis of extracellular arginine degradation leading to tumor cell death, and how this approach could be a valuable addition to the current anticancer arsenal.

Dietary Manipulation of Amino Acids for Cancer Therapy

Cancer cells cannot proliferate and survive unless they obtain sufficient levels of the 20 proteinogenic amino acids (AAs). Unlike normal cells, cancer cells have genetic and metabolic alterations that may limit their capacity to obtain adequate levels of the 20 AAs in challenging metabolic environments. However, since normal diets provide all AAs at relatively constant levels and ratios, these potentially lethal genetic and metabolic defects are eventually harmless to cancer cells. If we temporarily replace the normal diet of cancer patients with artificial diets in which the levels of specific AAs are manipulated, cancer cells may be unable to proliferate and survive. This article reviews in vivo studies that have evaluated the antitumor activity of diets restricted in or supplemented with the 20 proteinogenic AAs, individually and in combination. It also reviews our recent studies that show that manipulating the levels of several AAs simultaneously can lead to marked survival improvements in mice with metastatic cancers.

Regulated Arginine Metabolism in Immunopathogenesis of a Wide Range of Diseases: Is There a Way to Pass between Scylla and Charybdis?

More than a century has passed since arginine was discovered, but the metabolism of the amino acid never ceases to amaze researchers. Being a conditionally essential amino acid, arginine performs many important homeostatic functions in the body; it is involved in the regulation of the cardiovascular system and regeneration processes. In recent years, more and more facts have been accumulating that demonstrate a close relationship between arginine metabolic pathways and immune responses. This opens new opportunities for the development of original ways to treat diseases associated with suppressed or increased activity of the immune system. In this review, we analyze the literature describing the role of arginine metabolism in the immunopathogenesis of a wide range of diseases, and discuss arginine-dependent processes as a possible target for therapeutic approaches.

The addition of arginine deiminase potentiates Mithramycin A-induced cell death in patient-derived glioblastoma cells via ATF4 and cytochrome C

BACKGROUND

Arginine auxotrophy constitutes a shortcoming for ~ 30% of glioblastoma multiforme (GBM). Indeed, arginine-depleting therapy using arginine deiminase from Streptococcus pyogenes (SpyADI) has proven activity against GBM in preclinical studies. The good safety profile of SpyADI renders this agent an ideal combination partner for cytostatic therapy.

METHODS

In this study, we combined the antineoplastic antibiotic Mithramycin A (MitA) with SpyADI to boost single-agent activity and analyzed underlying response mechanisms in-depth.

RESULTS

MitA monotherapy induced a time- and dose-dependent cytotoxicity in eight patient-derived GBM cell lines and had a radiosensitizing effect in all but one cell line. Combination treatment boosted the effects of the monotherapy in 2D- and 3D models. The simultaneous approach was superior to the sequential application and significantly impaired colony formation after repetitive treatment. MitA monotherapy significantly inhibited GBM invasiveness. However, this effect was not enhanced in the combination. Functional analysis identified SpyADI-triggered senescence induction accompanied by increased mitochondrial membrane polarization upon mono- and combination therapy. In HROG63, induction of lysosomes was seen after both monotherapies, indicative of autophagy. These cells seemed swollen and had a more pronounced cortically formed cytoskeleton. Also, cytochrome C and endoplasmatic reticulum-stress-associated proteins ATF4 and Calnexin were enhanced in the combination, contributing to apoptosis. Notably, no significant increases in glioma-stemness marker were seen.

CONCLUSIONS

Therapeutic utilization of a metabolic defect in GBM along with cytostatic therapy provides a novel combination approach. Whether this SpyADI/MitA regimen will provide a safe alternative to combat GBM, will have to be addressed in subsequent (pre-)clinical trials.

The exploitation of enzyme-based cancer immunotherapy

Cancer immunotherapy utilizes the immune system and its wide-ranging components to deliver anti-tumor responses. In immune escape mechanisms, tumor microenvironment-associated soluble factors and cell surface-bound molecules are mainly accountable for the dysfunctional activity of tumor-specific CD8⁺ T cells, natural killer (NK) cells, tumor associated macrophages (TAMs) and stromal cells. The myeloid-derived suppressor cells (MDSCs) and Foxp3⁺ regulatory T cells (Tregs), are also key tumor-promoting immune cells. These potent immunosuppressive networks avert tumor rejection at various stages, affecting immunotherapies' outcomes. Numerous clinical trials have elucidated that disruption of immunosuppression could be achieved via checkpoint inhibitors. Another approach utilizes enzymes that can restore the body's potential to counter cancer by triggering the immune system inhibited by the tumor microenvironment. These immunotherapeutic enzymes can catalyze an immunostimulatory signal and modulate the tumor microenvironment via effector molecules. Herein, we have discussed the immuno-metabolic roles of various enzymes like ATP-dephosphorylating ectoenzymes, inducible Nitric Oxide Synthase, phenylamine, tryptophan, and arginine catabolizing enzymes in cancer immunotherapy. Understanding the detailed molecular mechanisms of the enzymes involved in modulating the tumor microenvironment may help find new opportunities for cancer therapeutics.

Plasma arginase-1 as a predictive marker for early transarterial chemoembolization refractoriness in unresectable hepatocellular carcinoma

Objective

To explore the relationship between plasma arginase-1 (ARG1) and early transarterial chemoembolization (TACE) refractoriness in patients with hepatocellular carcinoma (HCC) and develop nomograms for predicting early TACE refractoriness.

Methods

A total of 200 patients with HCC, treated with TACE, were included in the study, including 120 in the training set and 80 in the validation set. Pre-treatment enzyme-linked immunosorbent assay was used to detected the plasma ARG1 levels of the patient, and independent predictors of early TACE refractoriness were determined using a multivariate logistic regression model, based on which a predictive model was developed using a nomogram.

Results

Risk of early TACE refractoriness was negatively correlated with plasma ARG1 levels, and multivariate logistic analysis showed tumour size (OR = 1.138, 95% CI = 1.006-1.288, P = 0.041), multiple tumors (OR=4.374, 95% CI = 1.189-16.089, P = 0.026), platelet count (OR = 0.990, 95% CI = 0.980-0.999, P = 0.036), and plasma ARG1 levels (OR = 0.209, 95% CI = 0.079-0.551, P = 0.002) to be independent prognostic factors for early TACE refractoriness.The AUC value for the nomogram of the training cohort was 0.786 (95% CI = 0.702–0.870), and the validation set AUC value was 0.833 (95% CI = 0.791-0.875).The decision curve analysis suggested that the nomogram had good clinical utility.

Conclusion

High plasma ARG1 expression was associated with a lower incidence of early TACE refractoriness. The nomogram constructed based on four independent prognostic factors could facilitate an individualised prediction of the incidence of early TACE refractoriness.

Systemic Administration of Pegylated Arginase-1 Attenuates the Progression of Diabetic Retinopathy

Diabetic retinopathy (DR) is a serious complication of diabetes that results from sustained hyperglycemia, hyperlipidemia, and oxidative stress. Under these conditions, inducible nitric oxide synthase (iNOS) expression is upregulated in the macrophages (MΦ) and microglia, resulting in increased production of reactive oxygen species (ROS) and inflammatory cytokines, which contribute to disease progression. Arginase 1 (Arg1) is a ureohydrolase that competes with iNOS for their common substrate, L-arginine. We hypothesized that the administration of a stable form of Arg1 would deplete L-arginine’s availability for iNOS, thus decreasing inflammation and oxidative stress in the retina. Using an obese Type 2 diabetic (T2DM) db/db mouse, this study characterized DR in this model and determined if systemic treatment with pegylated Arg1 (PEG-Arg1) altered the progression of DR. PEG-Arg1 treatment of db/db mice thrice weekly for two weeks improved visual function compared with untreated db/db controls. Retinal expression of inflammatory factors (iNOS, IL-1β, TNF-α, IL-6) was significantly increased in the untreated db/db mice compared with the lean littermate controls. The increased retinal inflammatory and oxidative stress markers in db/db mice were suppressed with PEG-Arg1 treatment. Additionally, PEG-Arg1 treatment restored the blood–retinal barrier (BRB) function, as evidenced by the decreased tissue albumin extravasation and an improved endothelial ZO-1 tight junction integrity compared with untreated db/db mice.

A phase 1 study of pegylated recombinant arginase (PEG-BCT-100) in combination with systemic chemotherapy (capecitabine and oxaliplatin)[PACOX] in advanced hepatocellular carcinoma patients

INTRODUCTION

We investigated the safety and efficacy of a pegylated arginase (PEG-BCT-100) in combination with chemotherapy (oxaliplatin and capecitabine) [PACOX] in advanced HCC patients.

METHODS

This was a single centre phase 1 trial to assess the safety and tolerability of PACOX. All the enrolled subjects received treatment in 3-weekly cycles: intravenous PEG-BCT-100 2.7 mg/kg on days 1, 8 and 15 of each cycle; oral capecitabine 1000 mg/m2 twice daily on day 1-14 of each cycle and intravenous oxaliplatin on day 1. Three dose levels of oxaliplatin (85 mg/m2, 100 mg/m2 or 130 mg/m2) were studied to define the maximum tolerated dose (MTD). Adverse events (AEs), efficacy by RECIST v1.1, time to progression (TTP), progression-free survival (PFS) and overall survival (OS) were studied.

RESULTS

Seventeen patients were enrolled at 3 dose levels of oxaliplatin: 85 mg/m2 (8 patients), 100 mg/m2 (3 patients), and 130 mg/m2 (6 patients). The median age was 55 years; all had had locoregional chemotherapy or targeted therapy such as sorafenib, but no systemic chemotherapy. The most common AEs were nausea (82%), injection site reaction (76%), palmar-plantar erythrodysesthesia (59%), oral mucositis (53%) and vomiting (53%). There was no dose-limiting toxicity (DLT). Median duration on study was 8 weeks overall. In 14 evaluable cases, one achieved partial response (PR), 4 had stable disease (SD); disease control rate was 36%; most responses were observed in the 130 mg/m2 cohort with 1 PR and 2 SDs. Median TTP and PFS were both 7.0 weeks. Overall median OS was 10.7 months; the median OS was not reached at 19.4 months of follow-up in the 130 mg/m2 cohort.

CONCLUSION

The PACOX regimen demonstrated good anti-cancer activity and survival advantage in advanced pre-treated HCC with favourable safety profile. It warrants further phase II/III studies.

Arginine and Arginases Modulate Metabolism, Tumor Microenvironment and Prostate Cancer Progression

Arginine availability and activation of arginine-related pathways at cancer sites have profound effects on the tumor microenvironment, far beyond their well-known role in the hepatic urea cycle. Arginine metabolism impacts not only malignant cells but also the surrounding immune cells behavior, modulating growth, survival, and immunosurveillance mechanisms, either through an arginase-mediated effect on polyamines and proline synthesis, or by the arginine/nitric oxide pathway in tumor cells, antitumor T-cells, myeloid-derived suppressor cells, and macrophages. This review presents evidence concerning the impact of arginine metabolism and arginase activity in the prostate cancer microenvironment, highlighting the recent advances in immunotherapy, which might be relevant for prostate cancer. Even though further research is required, arginine deprivation may represent a novel antimetabolite strategy for the treatment of arginine-dependent prostate cancer.

Review of arginase as a promising biocatalyst: characteristics, preparation, applications and future challenges

As a committed step in the urea cycle, arginase cleaves l-arginine to form l-ornithine and urea. l-Ornithine is essential to: cell proliferation, collagen formation and other physiological functions, while the urea cycle itself converts highly toxic ammonia to urea for excretion. Recently, arginase was exploited as an efficient catalyst for the environmentally friendly synthesis of l-ornithine, an abundant nonprotein amino acid that is widely employed as a food supplement and nutrition product. It was also proposed as an arginine-reducing agent in order to treat arginase deficiency and to be a means of depleting arginine to treat arginine auxotrophic tumors. Targeting arginase inhibitors of the arginase/ornithine pathway offers great promise as a therapy for: cardiovascular, central nervous system diseases and cancers with high arginase expression. In this review, recent advances in the characteristics, structure, catalytic mechanism and preparation of arginase were summarized, with a focus being placed on the biotechnical and medical applications of arginase. In particular, perspectives have been presented on the challenges and opportunities for the environmentally friendly utilization of arginase during l-ornithine production and in therapies.

Arginine depriving enzymes: applications as emerging therapeutics in cancer treatment

Cancer is the second leading cause of death globally. Chemotherapy and radiation therapy and other medications are employed to treat various types of cancer. However, each treatment has its own set of side effects, owing to its low specificity. As a result, there is an urgent need for newer therapeutics that do not disrupt healthy cells' normal functioning. Depriving nutrient or non/semi-essential amino acids to which cancerous cells are auxotrophic remains one such promising anticancer strategy. L-Arginine (Arg) is a semi-essential vital amino acid involved in versatile metabolic processes, signaling pathways, and cancer cell proliferation. Hence, the administration of Arg depriving enzymes (ADE) such as arginase, arginine decarboxylase (ADC), and arginine deiminase (ADI) could be effective in cancer therapy. The Arg auxotrophic cancerous cells like hepatocellular carcinoma, human colon cancer, leukemia, and breast cancer cells are sensitive to ADE treatment due to low expression of crucial enzymes argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and ornithine transcarbamylase (OCT). These therapeutic enzyme treatments induce cell death through inducing autophagy, apoptosis, generation of oxidative species, i.e., oxidative stress, and arresting the progression and expansion of cancerous cells at certain cell cycle checkpoints. The enzymes are undergoing clinical trials and could be successfully exploited as potential anticancer agents in the future.

Safety, PK/PD and preliminary anti-tumor activities of pegylated recombinant human arginase 1 (BCT-100) in patients with advanced arginine auxotrophic tumors

Background The study determined the safety, pharmacokinetics/pharmacodynamics (PK/PD), and recommended Phase II dose of BCT-100 for arginine auxotrophic tumours in a non-Chinese population. Methods This is a Phase I, 3 + 3 dose-escalation, open-label, multi-centre study in two arginine auxotrophic cancers-Malignant Melanoma (MM) and Castration Resistant Prostate Cancer (CRPC). Patients were enrolled to receive weekly intravenous BCT-100. The dose cohorts were respectively 0.5 mg/kg, 1.0 mg/kg, 1.7 mg/kg and 2.7 mg/kg. Results There were 14 MM and 9 CRPC patients, 16 males and 7 females with a median age of 71. No dose-limiting toxicities were reported. Among all the AEs, 18 were drug-related (mostly were Grade 1). Although there were individual variations in PKs amongst the patients in each cohort, the median arginine level was maintained at 2.5 µM (lower limit of quantification) in all 4 cohorts of patients after the second BCT-100 injection. Therapeutic Arginine Depletion was found in the 1.7 and 2.7 mg/kg/week cohorts when anti-tumor activities were observed. The two cohorts had a similar AUC (20,947 and 19,614 h*µg/ml respectively). Since the 2.7 mg/kg/week cohort had a more sustained arginine depletion for 2 weeks, the 2.7 mg/kg/week dose is chosen as the future phase II dose. There were two complete remissions (1 MM & 1 CRPC), 1PR (MM) and 2 stable diseases with a disease control rate (CR + PR + SD) of 5/23 (22%). Conclusions BCT-100 is safe in a non-Chinese population and has anti-tumor activities in both MM and CRPC. Weekly BCT-100 at 2.7 mg/kg is defined as the optimal biological dose for future clinical phase II studies.

Arginine Signaling and Cancer Metabolism

Arginine is an amino acid critically involved in multiple cellular processes including the syntheses of nitric oxide and polyamines, and is a direct activator of mTOR, a nutrient-sensing kinase strongly implicated in carcinogenesis. Yet, it is also considered as a non- or semi-essential amino acid, due to normal cells' intrinsic ability to synthesize arginine from citrulline and aspartate via ASS1 (argininosuccinate synthase 1) and ASL (argininosuccinate lyase). As such, arginine can be used as a dietary supplement and its depletion as a therapeutic strategy. Strikingly, in over 70% of tumors, ASS1 transcription is suppressed, rendering the cells addicted to external arginine, forming the basis of arginine-deprivation therapy. In this review, we will discuss arginine as a signaling metabolite, arginine's role in cancer metabolism, arginine as an epigenetic regulator, arginine as an immunomodulator, and arginine as a therapeutic target. We will also provide a comprehensive summary of ADI (arginine deiminase)-based arginine-deprivation preclinical studies and an update of clinical trials for ADI and arginase. The different cell killing mechanisms associated with various cancer types will also be described.

Amino Acid Metabolic Vulnerabilities in Acute and Chronic Myeloid Leukemias

Amino acid (AA) metabolism plays an important role in many cellular processes including energy production, immune function, and purine and pyrimidine synthesis. Cancer cells therefore require increased AA uptake and undergo metabolic reprogramming to satisfy the energy demand associated with their rapid proliferation. Like many other cancers, myeloid leukemias are vulnerable to specific therapeutic strategies targeting metabolic dependencies. Herein, our review provides a comprehensive overview and TCGA data analysis of biosynthetic enzymes required for non-essential AA synthesis and their dysregulation in myeloid leukemias. Furthermore, we discuss the role of the general control nonderepressible 2 (GCN2) and-mammalian target of rapamycin (mTOR) pathways of AA sensing on metabolic vulnerability and drug resistance.

A phase II clinical study on the efficacy and predictive biomarker of pegylated recombinant arginase on hepatocellular carcinoma

Background: Pegylated recombinant human arginase (PEG-BCT-100) is an arginine depleting drug. Preclinical studies showed that HCC is reliant on exogenous arginine for growth due to the under-expression of the arginine regenerating enzymes argininosuccinate synthetase (ASS) and ornithine transcarbamylase (OTC). Methods: This is a single arm open-label Phase II trial to assess the potential clinical efficacy of PEG-BCT-100 in chemo naïve sorafenib-failure HCC patients. Pre-treatment tumour biopsy was mandated for ASS and OTC expression by immunohistochemistry (IHC). Weekly intravenous PEG-BCT-100 at 2.7 mg/kg was given. Primary endpoint was time to progression (TTP); secondary endpoints included radiological response as per RECIST1.1, progression free survival (PFS) and overall survival (OS). Treatment outcomes were correlated with tumour immunohistochemical expressions of ASS and OTC. Results: In total 27 patients were recruited. The median TTP and PFS were both 6 weeks (95% CI, 5.9–6.0 weeks). The disease control rate (DCR) was 21.7% (5 stable disease). The drug was well tolerated. Post hoc analysis showed that duration of arginine depletion correlated with OS. For patients with available IHC results, 10 patients with ASS-negative tumour had OS of 35 weeks (95% CI: 8.3–78.0 weeks) vs. 15.14 weeks (95% CI: 13.4–15.1 weeks) in 3 with ASS-positive tumour; expression of OTC did not correlate with treatment outcomes. Conclusions: PEG-BCT-100 in chemo naïve post-sorafenib HCC is well tolerated with moderate DCR. ASS-negative confers OS advantage over ASS-positive HCC. ASS-negativity is a potential biomarker for OS in HCC and possibly for other ASS-negative arginine auxotrophic cancers. Trial registration number: NCT01092091. Date of registration: March 23, 2010.

Impact of Lifestyle Behaviors on Cancer Risk and Prevention

Cancer incidences are rising globally. Therefore, in order to prevent and treat cancer, understanding cancer pathology is crucial. Tumors reprogram their metabolic phenotype to meet their needs for bioenergy, biosynthesis, and redox control. Alteration of the metabolic pathway has been proposed as the hallmark of cancer and explains the distinction between normal and cancer cells concerning nutrient utilization. Changes in the metabolism of nutrients such as glucose, amino acid, and fatty acid are associated with cancer risk. Luckily, this can be controlled with lifestyle modifications. Improvements in lifestyle behaviors to reduce cancer risks include a healthy diet, calorie restriction, and regular physical activity. This review begins with the understandings of metabolic reprogramming in cancer. Then, there will be evidence on the correlation between lifestyle factors and altered nutrient metabolism suggesting an application of lifestyle intervention for cancer risk reduction.

Optimal biological dose: a systematic review in cancer phase I clinical trials

BACKGROUND

Classical phase 1 dose-finding designs based on a single toxicity endpoint to assess the maximum tolerated dose were initially developed in the context of cytotoxic drugs. With the emergence of molecular targeted agents and immunotherapies, the concept of optimal biological dose (OBD) was subsequently introduced to account for efficacy in addition to toxicity. The objective was therefore to provide an overview of published phase 1 cancer clinical trials relying on the concept of OBD.

METHODS

We performed a systematic review through a computerized search of the MEDLINE database to identify early phase cancer clinical trials that relied on OBD. Relevant publications were selected based on a two-step process by two independent readers. Relevant information (phase, type of therapeutic agents, objectives, endpoints and dose-finding design) were collected.

RESULTS

We retrieved 37 articles. OBD was clearly mentioned as a trial objective (primary or secondary) for 22 articles and was traditionally defined as the smallest dose maximizing an efficacy criterion such as biological target: biological response, immune cells count for immunotherapies, or biological cell count for targeted therapies. Most trials considered a binary toxicity endpoint defined in terms of the proportion of patients who experienced a dose-limiting toxicity. Only two articles relied on an adaptive dose escalation design.

CONCLUSIONS

In practice, OBD should be a primary objective for the assessment of the recommended phase 2 dose (RP2D) for a targeted therapy or immunotherapy phase I cancer trial. Dose escalation designs have to be adapted accordingly to account for both efficacy and toxicity.

Amino Acid Degrading Enzymes and Autophagy in Cancer Therapy

Recently, there has been renewed interest in metabolic therapy for cancer, particularly in amino acid deprivation by enzymes. L-asparaginase was approved for the treatment of acute lymphoblastic leukemia by the U.S. Food and Drug Administration. Arginine deiminase and recombinant human arginase have been developed into clinical trials as potential cancer therapeutic agents for the treatment of arginine-auxotrophic tumors. Moreover, other novel amino acid degrading enzymes, such as glutaminase, methionase, lysine oxidase, phenylalanine ammonia lyase, have been developed for the treatment of malignant cancers. One of the greatest obstacles faced by anticancer drugs is the development of drug resistance, which is reported to be associated with autophagy. Autophagy is an evolutionarily conserved catabolic process that is responsible for the degradation of dysfunctional proteins and organelles. There is a growing body of literature revealing that, in response to metabolism stress, autophagy could be induced by amino acid deprivation. The manipulation of autophagy in combination with amino acid degrading enzymes is actively being investigated as a potential therapeutic approach in preclinical studies. Importantly, shedding light on how autophagy fuels tumor metabolism during amino acid deprivation will enable more potential combinational therapeutic strategies. This study summarizes recent advances, discussing several potential anticancer enzymes, and highlighting the promising combined therapeutic strategy of amino acid degrading enzymes and autophagy modulators in tumors

Arginine deprivation as a strategy for cancer therapy: An insight into drug design and drug combination

Extensive studies have shown that cancer cells have specific nutrient auxotrophy and thus have much a higher demand for certain nutrients than normal cells. Amino acid deprivation has attracted much attention in cancer therapy with positive outcomes from clinical trials. Arginine, as one of the conditionally essential amino acids, plays a pivotal role in cellular division and metabolism. Since many types of cancer cells exhibit decreased expression of argininosuccinate synthetase and/or ornithine transcarbamylase, they are auxotrophic for arginine, which makes arginine deprivation an accessible choice for cancer treatment. Arginine deiminase (ADI) and human arginase (hArg) are the two major protein drugs used for arginine deprivation and are undergoing many clinical trials. However, the clinical application of ADI and hArg is facing some common problems, including their short half-lives, immunogenicity and inconsistent production, which underlines the importance of improving these drugs using protein engineering techniques. Thus, we systematically review the latest studies of protein engineering and anti-cancer studies based on in vitro, in vivo and clinical models of ADI and hArg, and we include the latest studies on drug combinations consisting of ADI/hArg with chemotherapeutic drugs.

Fine-Tuning the Tumour Microenvironment: Current Perspectives on the Mechanisms of Tumour Immunosuppression

Immunotherapy has revolutionised the treatment of cancers by harnessing the power of the immune system to eradicate malignant tissue. However, it is well recognised that some cancers are highly resistant to these therapies, which is in part attributed to the immunosuppressive landscape of the tumour microenvironment (TME). The contexture of the TME is highly heterogeneous and contains a complex architecture of immune, stromal, vascular and tumour cells in addition to acellular components such as the extracellular matrix. While understanding the dynamics of the TME has been instrumental in predicting durable responses to immunotherapy and developing new treatment strategies, recent evidence challenges the fundamental paradigms of how tumours can effectively subvert immunosurveillance. Here, we discuss the various immunosuppressive features of the TME and how fine-tuning these mechanisms, rather than ablating them completely, may result in a more comprehensive and balanced anti-tumour response.

Cancer cell metabolism: Rewiring the mitochondrial hub

To adapt to tumoral environment conditions or even to escape chemotherapy, cells rapidly reprogram their metabolism to handle adversities and survive. Given the rapid rise of studies uncovering novel insights and therapeutic opportunities based on the role of mitochondria in tumor metabolic programing and therapeutics, this review summarizes most significant developments in the field. Taking in mind the key role of mitochondria on carcinogenesis and tumor progression due to their involvement on tumor plasticity, metabolic remodeling, and signaling re-wiring, those organelles are also potential therapeutic targets. Among other topics, we address the recent data intersecting mitochondria as of prognostic value and staging in cancer, by mitochondrial DNA (mtDNA) determination, and current inhibitors developments targeting mtDNA, OXPHOS machinery and metabolic pathways. We contribute for a holistic view of the role of mitochondria metabolism and directed therapeutics to understand tumor metabolism, to circumvent therapy resistance, and to control tumor development.

Metabolic interaction between amino acid deprivation and cisplatin synergistically reduces phosphoribosyl-pyrophosphate and augments cisplatin cytotoxicity

Cisplatin is a mainstay of cancer chemotherapy. It forms DNA adducts, thereby activating poly(ADP-ribose) polymerases (PARPs) to initiate DNA repair. The PARP substrate NAD⁺ is synthesized from 5-phosphoribose-1-pyrophosphate (PRPP), and we found that treating cells for 6 h with cisplatin reduced intracellular PRPP availability. The decrease in PRPP was likely from (1) increased PRPP consumption, because cisplatin increased protein PARylation and PARP1 shRNA knock-down returned PRPP towards normal, and (2) decreased intracellular phosphate, which down-regulated PRPP synthetase activity. Depriving cells of a single essential amino acid decreased PRPP synthetase activity with a half-life of ~ 8 h, and combining cisplatin and amino acid deprivation synergistically reduced intracellular PRPP. PRPP is a rate-limiting substrate for purine nucleotide synthesis, and cisplatin inhibited de novo purine synthesis and DNA synthesis, with amino acid deprivation augmenting cisplatin’s effects. Amino acid deprivation enhanced cisplatin’s cytotoxicity, increasing cellular apoptosis and DNA strand breaks in vitro, and intermittent deprivation of lysine combined with a sub-therapeutic dose of cisplatin inhibited growth of ectopic hepatomas in mice. Augmentation of cisplatin’s biochemical and cytotoxic effects by amino acid deprivation suggest that intermittent deprivation of an essential amino acid could allow dose reduction of cisplatin; this could reduce the drug’s side effects, and allow its use in cisplatin-resistant tumors.

Arginine metabolism: a potential target in pancreatic cancer therapy

ABSTRACT

Pancreatic ductal adenocarcinoma (PDAC) is an extremely malignant disease, which has an extremely low survival rate of <9% in the United States. As a new hallmark of cancer, metabolism reprogramming exerts crucial impacts on PDAC development and progression. Notably, arginine metabolism is altered in PDAC cells and participates in vital signaling pathways. In addition, arginine and its metabolites including polyamine, creatine, agmatine, and nitric oxide regulate the proliferation, growth, autophagy, apoptosis, and metastasis of cancer cells. Due to the loss of argininosuccinate synthetase 1 (ASS1) expression, the key enzyme in arginine biosynthesis, arginine deprivation is regarded as a potential strategy for PDAC therapy. However, drug resistance develops during arginine depletion treatment, along with the re-expression of ASS1, metabolic dysfunction, and the appearance of anti-drug antibody. Additionally, arginase 1 exerts crucial roles in myeloid-derived suppressor cells, indicating its potential targeting by cancer immunotherapy. In this review, we introduce arginine metabolism and its impacts on PDAC cells. Also, we discuss the role of arginine metabolism in arginine deprivation therapy and immunotherapy for cancer.

Rational design, engineer, and characterization of a novel pegylated single isomer human arginase for arginine depriving anti-cancer treatment

AIMS

Arginine depleting enzymes are found effective to treat arginine-auxotrophic cancers and therapy-resistant malignancies, alone or in combination with cytotoxic agents or immune checkpoint inhibitors. We aim to select and validate a long-lasting, safe and effective PEGylated and cobalt-chelated arginase conjugated at the selective cysteine residue as a therapeutic agent against cancers.

MAIN METHODS

Exploring pharmacokinetic and pharmacodynamic properties of the three arginase conjugates with different PEG modality (20 kDa linear as A20L, 20 kDa branched as A20Y, and 40 kDa branched as A40Y) by cell-based and animal studies.

KEY FINDINGS

Arginase conjugates showed comparable systemic half-lives, about 20 h in rats and mice. The extended half-life of PEGylated arginase was concurrent with the integrity of conjugates of which PEG and protein moieties remain attached in bloodstream for 72 h after drug administration. Arginase modified with a linear 20 kDa PEG (A20L) was chosen as the lead candidate (PT01). In vitro assays confirmed the very potent cytotoxicity of PT01 against cancer cell lines of breast, prostate, and pancreas origin. In MIA PaCa-2 pancreatic and PC-3 prostate tumor xenograft models, weekly infusion of the PT01 at 5 and 10 mg/kg induced significant tumor growth inhibition of 44-67%. All mice experienced dose-dependent but rapidly reversible weight loss following each weekly dose, suggesting tolerable toxicity.

SIGNIFICANCE

These non-clinical data support PT01 as the lead candidate for clinical development that may benefit cancer patients by providing an alternative cytotoxic mechanism.

Novel molecular targets in hepatocellular carcinoma

Globally, hepatocellular carcinoma (HCC) is a leading cause of cancer and cancer-related deaths. The therapeutic efficacy of locoregional and systemic treatment in patients with advanced HCC remains low, which results in a poor prognosis. The development of sorafenib for the treatment of HCC has resulted in a new era of molecular targeted therapy for this disease. However, the median overall survival was reported to be barely higher in the sorafenib treatment group than in the control group. Hence, in this review we describe the importance of developing more effective targeted therapies for the management of advanced HCC. Recent investigations of molecular signaling pathways in several cancers have provided some insights into developing molecular therapies that target critical members of these signaling pathways. Proteins involved in the Hedgehog and Notch signaling pathways, Polo-like kinase 1, arginine, histone deacetylases and Glypican-3 can be potential targets in the treatment of HCC. Monotherapy has limited therapeutic efficacy due to the development of inhibitory feedback mechanisms and induction of chemoresistance. Thus, emphasis is now on the development of personalized and combination molecular targeted therapies that can serve as ideal therapeutic strategies for improved management of HCC.

Myeloid Cell-Derived Arginase in Cancer Immune Response

Amino acid metabolism is a critical regulator of the immune response, and its modulating becomes a promising approach in various forms of immunotherapy. Insufficient concentrations of essential amino acids restrict T-cells activation and proliferation. However, only arginases, that degrade L-arginine, as well as enzymes that hydrolyze L-tryptophan are substantially increased in cancer. Two arginase isoforms, ARG1 and ARG2, have been found to be present in tumors and their increased activity usually correlates with more advanced disease and worse clinical prognosis. Nearly all types of myeloid cells were reported to produce arginases and the increased numbers of various populations of myeloid-derived suppressor cells and macrophages correlate with inferior clinical outcomes of cancer patients. Here, we describe the role of arginases produced by myeloid cells in regulating various populations of immune cells, discuss molecular mechanisms of immunoregulatory processes involving L-arginine metabolism and outline therapeutic approaches to mitigate the negative effects of arginases on antitumor immune response. Development of potent arginase inhibitors, with improved pharmacokinetic properties, may lead to the elaboration of novel therapeutic strategies based on targeting immunoregulatory pathways controlled by L-arginine degradation.

A modified arginine-depleting enzyme NEI-01 inhibits growth of pancreatic cancer cells

Arginine deprivation cancer therapy targets certain types of malignancies with positive result in many studies and clinical trials. NEI-01 was designed as a novel arginine-depleting enzyme comprising an albumin binding domain capable of binding to human serum albumin to lengthen its half-life. In the present work, NEI-01 is shown to bind to serum albumin from various species, including mice, rat and human. Single intraperitoneal administration of NEI-01 to mice reduced plasma arginine to undetectable level for at least 9 days. Treatment of NEI-01 specifically inhibited cell viability of MIA PaCa-2 and PANC-1 cancer cell lines, which were ASS1 negative. Using a human pancreatic mouse xenograft model, NEI-01 treatment significantly reduced tumor volume and weight. Our data provides proof of principle for a cancer treatment strategy using NEI-01.

Arginase Pathway in Acute Retina and Brain Injury: Therapeutic Opportunities and Unexplored Avenues

Ischemic retinopathies represent a major cause of visual impairment and blindness. They include diabetic retinopathy (DR), acute glaucoma, retinopathy of prematurity (ROP), and central (or branch) retinal artery occlusion (CRAO). These conditions share in common a period of ischemia or reduced blood supply to the retinal tissue that eventually leads to neuronal degeneration. Similarly, acute brain injury from ischemia or trauma leads to neurodegeneration and can have devastating consequences in patients with stroke or traumatic brain injury (TBI). In all of these conditions, current treatment strategies are limited by their lack of effectiveness, adverse effects or short time window for administration. Therefore, there is a great need to identify new therapies for acute central nervous system (CNS) injury. In this brief review article, we focus on the pathway of the arginase enzyme as a novel therapeutic target for acute CNS injury. We review the recent work on the role of arginase enzyme and its downstream components in neuroprotection in both retina and brain acute injury models. Delineating the similarities and differences between the role of arginase in the retina and brain neurodegeneration will allow for better understanding of the role of arginase in CNS disorders. This will also facilitate repurposing the arginase pathway as a new therapeutic target in both retina and brain diseases.

Indospicine combined with arginine deprivation triggers cancer cell death via caspase-dependent apoptosis

Arginine-deprivation therapy is a rapidly developing metabolic anticancer approach. To overcome the resistance of some cancer cells to this monotherapy, rationally designed combination modalities are needed. In this report, we evaluated for the first time indospicine, an arginine analogue of Indigofera plant genus origin, as potential enhancer compound for the metabolic therapy that utilizes recombinant human arginase I. We demonstrate that indospicine at low micromolar concentrations is selectively toxic for human colorectal cancer cells only in the absence of arginine. In arginine-deprived cancer cells indospicine deregulates some prosurvival pathways (PI3K-Akt and MAPK) and activates mammalian target of rapamycin, exacerbates endoplasmic reticulum stress and triggers caspase-dependent apoptosis, which is reversed by the exposure to translation inhibitors. Simultaneously, indospicine is not degraded by recombinant human arginase I and does not inhibit this arginine-degrading enzyme at its effective dose. The obtained results emphasize the potential of arginine structural analogues as efficient components for combinatorial metabolic targeting of malignant cells.

Preclinical safety and antitumor activity of the arginine-degrading therapeutic enzyme pegzilarginase, a PEGylated, cobalt-substituted recombinant human arginase 1

Metabolic remodeling contributes to the development and progression of some cancers and exposes them to vulnerabilities, including specific nutrient dependencies that can be targeted therapeutically. Arginine is a semiessential amino acid, and several cancers are unable to endogenously synthesize sufficient levels of arginine for survival and proliferation, most commonly due to reduced expression of argininosuccinate synthase (ASS1). Such cancers are dependent on arginine and they can be targeted via enzyme-mediated depletion of systemic arginine. We report the preclinical safety, antitumor efficacy, and immune-potentiating effects of pegzilarginase, a highly potent human arginine-degrading enzyme. Toxicology studies showed that pegzilarginase-mediated arginine depletion is well tolerated at therapeutic levels that elicit an antitumor growth effect. To determine which tumor types are best suited for clinical development, we profiled clinical tumor samples for ASS1 expression, which correlated with pegzilarginase sensitivity in vivo in patient-derived xenograft (PDx) models. Among the histologies tested, malignant melanoma, small cell lung cancer and Merkel cell carcinoma had the highest prevalence of low ASS1 expression, the highest proportion of PDx models responding to pegzilarginase, and the strongest correlation between low or no ASS1 expression and sensitivity to pegzilarginase. In an immune-competent syngeneic mouse model, pegzilarginase slowed tumor growth and promoted the recruitment of CD8⁺ tumor infiltrating lymphocytes. This is consistent with the known autophagy-inducing effects of arginine depletion, and the link between autophagy and major histocompatibility complex antigen presentation to T cells. Our work supports the ongoing clinical investigations of pegzilarginase in solid tumors and clinical combination of pegzilarginase with immune checkpoint inhibitors.

Microbial enzymes for deprivation of amino acid metabolism in malignant cells: biological strategy for cancer treatment

Amino acid deprivation therapy (AADT) is emerging as a promising strategy for the development of novel therapeutics against cancer. This biological therapy relies upon the differences in the metabolism of cancer and normal cells. The rapid growth of tumors results in decreased expression of certain enzymes leading to auxotrophy for some specific amino acids. These auxotrophic tumors are targeted by amino acid-depleting enzymes. The depletion of amino acid selectively inhibits tumor growth as the normal cells can synthesize amino acids by their usual machinery. The enzymes used in AADT are mostly obtained from microbes for their easy availability. Microbial L-asparaginase is already approved by FDA for the treatment of acute lymphoblastic leukemia. Arginine deiminase and methionase are under clinical trials and the therapeutic potential of lysine oxidase, glutaminase and phenylalanine ammonia lyase is also being explored. The present review provides an overview of microbial amino acid depriving enzymes. Various attributes of these enzymes like structure, mode of action, production, formulations, and targeted cancers are discussed. The challenges faced and the combat strategies to establish AADT in standard cancer armamentarium are also reviewed.Key Points • Amino acid deprivation therapy is a potential therapy for auxotrophic tumors. • Microbial enzymes are used due to their ease of manipulation and high productivity. • Enzyme properties are improved by PEGylation, encapsulation, and genetic engineering. • AADT can be employed as combinational therapy for better containment of cancer.

The Metabolic Remodelling in Lung Cancer and Its Putative Consequence in Therapy Response

Lung cancer is the leading cause of cancer-related deaths worldwide in both men and women. Conventional chemotherapy has failed to provide long-term benefits for many patients and in the past decade, important advances were made to understand the underlying molecular/genetic mechanisms of lung cancer, allowing the unfolding of several other pathological entities. Considering these molecular subtypes, and the appearance of promising targeted therapies, an effective personalized control of the disease has emerged, nonetheless benefiting a small proportion of patients. Although immunotherapy has also appeared as a new hope, it is still not accessible to the majority of patients with lung cancer.The metabolism of energy and biomass is the basis of cellular survival. This is true for normal cells under physiological conditions and it is also true for pathophysiologically altered cells, such as cancer cells. Thus, knowledge of the metabolic remodelling that occurs in cancer cells in the sense of, on one hand, surviving in the microenvironment of the organ in which the tumour develops and, on the other hand, escaping from drugs conditioned microenvironment, is essential to understand the disease and to develop new therapeutic approaches.

NO and hepatocellular cancer

NO has broad and sometimes dichotomous roles in cancer. The effects of NO in tumours depend on the type and localization of NOS isoforms, concentration and duration of NO exposure, and cellular sensitivity to NO. Hepatocellular carcinoma (HCC) is a common and lethal disease for which no effective therapy other than surgical resection exists. Over two decades of research has yielded evidence that NO generated by the inducible NOS (iNOS or NOS2) contributes to HCC progression in at least a subset of patients with HCC. The co-expression of iNOS with COX-2 may portend a particularly aggressive cancer phenotype in HCC and at the same time reveal an opportunity for pharmacological intervention. In this review, we focus on what is known about the influence of NO in HCC neoplastic transformation, proliferation and apoptosis, angiogenesis, invasion, and metastasis, cancer stem cells, and the host immune response against the tumour. We discuss the implications of recent findings for targeting the NO pathways in HCC.

Cationic Amino Acid Transporter-1-Mediated Arginine Uptake Is Essential for Chronic Lymphocytic Leukemia Cell Proliferation and Viability

Interfering with tumor metabolism by specifically restricting the availability of extracellular nutrients is a rapidly emerging field of cancer research. A variety of tumor entities depend on the uptake of the amino acid arginine since they have lost the ability to synthesize it endogenously, that is they do not express the rate limiting enzyme for arginine synthesis, argininosuccinate synthase (ASS). Arginine transport through the plasma membrane of mammalian cells is mediated by eight different transporters that belong to two solute carrier (SLC) families. In the present study we found that the proliferation of primary as well as immortalized chronic lymphocytic leukemia (CLL) cells depends on the availability of extracellular arginine and that primary CLL cells do not express ASS and are therefore arginine-auxotrophic. The cationic amino acid transporter-1 (CAT-1) was the only arginine importer expressed in CLL cells. Lentiviral-mediated downregulation of the CAT-1 transporter in HG3 CLL cells significantly reduced arginine uptake, abolished cell proliferation and impaired cell viability. In a murine CLL xenograft model, tumor growth was significantly suppressed upon induced downregulation of CAT-1 in the CLL cells. Our results suggest that inhibition of CAT-1 is a promising new therapeutic approach for CLL.

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.

Amino Acid Degrading Enzymes and their Application in Cancer Therapy

BACKGROUND

Amino acids are essential components in various biochemical pathways. The deprivation of certain amino acids is an antimetabolite strategy for the treatment of amino acid-dependent cancers which exploits the compromised metabolism of malignant cells. Several studies have focused on the development and preclinical and clinical evaluation of amino acid degrading enzymes, namely L-asparaginase, L-methionine γ-lyase, L-arginine deiminase, L-lysine α-oxidase. Further research into cancer cell metabolism may therefore define possible targets for controlling tumor growth.

OBJECTIVE

The purpose of this review was to summarize recent progress in the relationship between amino acids metabolism and cancer therapy, with a particular focus on Lasparagine, L-methionine, L-arginine and L-lysine degrading enzymes and their formulations, which have been successfully used in the treatment of several types of cancer.

METHODS

We carried out a structured search among literature regarding to amino acid degrading enzymes. The main aspects of search were in vitro and in vivo studies, clinical trials concerning application of these enzymes in oncology.

RESULTS

Most published research are on the subject of L-asparaginase properties and it's use for cancer treatment. L-arginine deiminase has shown promising results in a phase II trial in advanced melanoma and hepatocellular carcinoma. Other enzymes, in particular Lmethionine γ-lyase and L-lysine α-oxidase, were effective in vitro and in vivo.

CONCLUSION

The findings of this review revealed that therapy based on amino acid depletion may have the potential application for cancer treatment but further clinical investigations are required to provide the efficacy and safety of these agents.

The Diverse Functions of Non-Essential Amino Acids in Cancer

Far beyond simply being 11 of the 20 amino acids needed for protein synthesis, non-essential amino acids play numerous important roles in tumor metabolism. These diverse functions include providing precursors for the biosynthesis of macromolecules, controlling redox status and antioxidant systems, and serving as substrates for post-translational and epigenetic modifications. This functional diversity has sparked great interest in targeting non-essential amino acid metabolism for cancer therapy and has motivated the development of several therapies that are either already used in the clinic or are currently in clinical trials. In this review, we will discuss the important roles that each of the 11 non-essential amino acids play in cancer, how their metabolic pathways are linked, and how researchers are working to overcome the unique challenges of targeting non-essential amino acid metabolism for cancer therapy.

Recombinant human arginase I elicited immunosuppression in activated macrophages through inhibiting autophagy

Arginase I has been documented to impair T cell function and attenuate cellular immunity, however, there is little evidence to reveal the effect of arginase I on macrophage function. Recently, recombinant human arginase I (rhArg) has been developed for cancer therapy and is in clinical trial for hepatocellular carcinoma, whereas the potential immunosuppression induced by rhArg limited its therapeutic efficacy. To improve the clinical outcome of rhArg, addressing the immune suppression appears to be particularly important. In this study, we found that rhArg attenuated macrophage functions, including inhibiting macrophage cell proliferation, nitric oxide (NO) and reactive oxygen species (ROS) production, cytokine secretion, MHC-II surface expression, and phagocytosis, thereby inducing immunosuppression in lipopolysaccharides (LPS)/interferon-γ (IFN-γ)-activated macrophages. Notably, we observed that rhArg downregulated autophagy in activated macrophages. Moreover, application of trehalose (an autophagy inducer) significantly restored the impaired immune function in activated macrophages, suggesting the essential role of autophagy in rhArg-induced immunosuppression. To further illustrate the effect of autophagy in immunosuppression, we then observed the effect of 3-MA (an autophagy inhibitor) on the immune function of macrophages. As expected, inhibiting autophagy by 3-MA attenuated immune functions in activated macrophages. Collectively, this study elucidated that rhArg induced immunosuppression in activated macrophages via inhibiting autophagy, providing potential strategy to ameliorate the immune suppression which is of great significance to cancer therapy and facilitating the development of rhArg as a potential therapy for malignant carcinomas.

Macrophage-Derived IL1β and TNFα Regulate Arginine Metabolism in Neuroblastoma

Neuroblastoma is the most common childhood solid tumor, yet the prognosis for high-risk disease remains poor. We demonstrate here that arginase 2 (ARG2) drives neuroblastoma cell proliferation via regulation of arginine metabolism. Targeting arginine metabolism, either by blocking cationic amino acid transporter 1 (CAT-1)-dependent arginine uptake in vitro or therapeutic depletion of arginine by pegylated recombinant arginase BCT-100, significantly delayed tumor development and prolonged murine survival. Tumor cells polarized infiltrating monocytes to an M1-macrophage phenotype, which released IL1β and TNFα in a RAC-alpha serine/threonine-protein kinase (AKT)-dependent manner. IL1β and TNFα established a feedback loop to upregulate ARG2 expression via p38 and extracellular regulated kinases 1/2 (ERK1/2) signaling in neuroblastoma and neural crest-derived cells. Proteomic analysis revealed that enrichment of IL1β and TNFα in stage IV human tumor microenvironments was associated with a worse prognosis. These data thus describe an immune-metabolic regulatory loop between tumor cells and infiltrating myeloid cells regulating ARG2, which can be clinically exploited. SIGNIFICANCE: These findings illustrate that cross-talk between myeloid cells and tumor cells creates a metabolic regulatory loop that promotes neuroblastoma progression.

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.

Autophagy maintains tumour growth through circulating arginine

Autophagy captures intracellular components and delivers them to lysosomes, where they are degraded and recycled to sustain metabolism and to enable survival during starvation^1-5. Acute, whole-body deletion of the essential autophagy gene Atg7 in adult mice causes a systemic metabolic defect that manifests as starvation intolerance and gradual loss of white adipose tissue, liver glycogen and muscle mass¹. Cancer cells also benefit from autophagy. Deletion of essential autophagy genes impairs the metabolism, proliferation, survival and malignancy of spontaneous tumours in models of autochthonous cancer^6,7. Acute, systemic deletion of Atg7 or acute, systemic expression of a dominant-negative ATG4b in mice induces greater regression of KRAS-driven cancers than does tumour-specific autophagy deletion, which suggests that host autophagy promotes tumour growth^1,8. Here we show that host-specific deletion of Atg7 impairs the growth of multiple allografted tumours, although not all tumour lines were sensitive to host autophagy status. Loss of autophagy in the host was associated with a reduction in circulating arginine, and the sensitive tumour cell lines were arginine auxotrophs owing to the lack of expression of the enzyme argininosuccinate synthase 1. Serum proteomic analysis identified the arginine-degrading enzyme arginase I (ARG1) in the circulation of Atg7-deficient hosts, and in vivo arginine metabolic tracing demonstrated that serum arginine was degraded to ornithine. ARG1 is predominantly expressed in the liver and can be released from hepatocytes into the circulation. Liver-specific deletion of Atg7 produced circulating ARG1, and reduced both serum arginine and tumour growth. Deletion of Atg5 in the host similarly regulated [corrected] circulating arginine and suppressed tumorigenesis, which demonstrates that this phenotype is specific to autophagy function rather than to deletion of Atg7. Dietary supplementation of Atg7-deficient hosts with arginine partially restored levels of circulating arginine and tumour growth. Thus, defective autophagy in the host leads to the release of ARG1 from the liver and the degradation of circulating arginine, which is essential for tumour growth; this identifies a metabolic vulnerability of cancer.

Combined use of arginase and dichloroacetate exhibits anti-proliferative effects in triple negative breast cancer cells

Objectives

Drug combination in cancer therapy aims to achieve synergistic therapeutic effect, reduced drug dosage, reduced drug toxicity and minimizes or delays the induction of drug resistance. In the present study, we investigated the anticancer effects of the combination of two metabolic modulators, dichloroacetate (DCA) and bacillus caldovelox arginase (BCA) (or pegyated human arginase (HA)).

Methods

The combination treatments were evaluated in MCF-7 and MDA-MB 231 cells as well as in MDA-MB 231 breast cancer xenograft model.

Key findings

Dichloroacetate and BCA combination exhibited anti-proliferative effects on MCF-7 cells, which were found to be synergistic. Analysis of the gene expression upon drug treatments revealed that the synergistic anti-proliferative effect on MCF-7 cells was possibly in part due to the activation of the p53 pathway. A similar synergistic anti-proliferative effect was observed in the combined use of DCA and HA on MCF-7 and MDA-MB231 cells, which was due to induction of cell cycle arrest at G2/M phase. Moreover, the combination enhanced anti-tumour activity in a MDA-MB 231 xenograft mouse model.

Conclusions

Our results suggested that dichloroacetate and arginase combination exhibited enhanced anti-cancer effects in preclinical breast cancer models which may offer an additional treatment option for breast cancer.

Rewiring urea cycle metabolism in cancer to support anabolism

Cancer cells reprogramme metabolism to maximize the use of nitrogen and carbon for the anabolic synthesis of macromolecules that are required during tumour proliferation and growth. To achieve this aim, one strategy is to reduce catabolism and nitrogen disposal. The urea cycle (UC) in the liver is the main metabolic pathway to convert excess nitrogen into disposable urea. Outside the liver, UC enzymes are differentially expressed, enabling the use of nitrogen for the synthesis of UC intermediates that are required to accommodate cellular needs. Interestingly, the expression of UC enzymes is altered in cancer, revealing a revolutionary mechanism to maximize nitrogen incorporation into biomass. In this Review, we discuss the metabolic benefits underlying UC deregulation in cancer and the relevance of these alterations for cancer diagnosis and therapy.