Pegylated arginine deiminase: a novel anticancer enzyme agent

Characterization, modeling, and anticancer activity of L.arginase production from marine Bacillus licheniformis OF2

BACKGROUND

L-arginase, is a powerful anticancer that hydrolyzes L-arginine to L-ornithine and urea. This enzyme is widely distributed and expressed in organisms like plants, fungi, however very scarce from bacteria. Our study is based on isolating, purifying, and screening the marine bacteria that can produce arginase.

RESULTS

The highest arginase producing bacteria will be identified by using microbiological and molecular biology methods as Bacillus licheniformis OF2. Characterization of arginase is the objective of this study. The activity of enzyme was screened, and estimated beside partial sequencing of arginase gene was analyzed. In silico homology modeling was applied to generate the protein's 3D structure, and COACH and COFACTOR were applied to determine the protein's binding sites and biological annotations based on the I-TASSER structure prediction. The purified enzyme was undergone an in vitro anticancer test.

CONCLUSIONS

L-arginase demonstrated more strong anti-cancer cells with an IC50 of 21.4 ug/ml in a dose-dependent manner. L-arginase underwent another investigation for its impact on the caspase 7 and BCL2 family of proteins (BCL2, Bax, and Bax/Bcl2). Through cell arrest in the G1/S phase, L-arginase signals the apoptotic cascade, which is supported by a flow cytometry analysis of cell cycle phases.

A metabolic perspective on nitric oxide function in melanoma

Nitric oxide (NO) generated from nitric oxide synthase (NOS) exerts a dichotomous effect in melanoma, suppressing or promoting tumor progression. This dichotomy is thought to depend on the intracellular NO concentration and the cell type in which it is generated. Due to its central role in the metabolism of multiple critical constituents involved in signaling and stress, it is crucial to explore NO's contribution to the metabolic dysfunction of melanoma. This review will discuss many known metabolites linked to NO production in melanoma. We discuss the synthesis of these metabolites, their role in biochemical pathways, and how they alter the biological processes observed in the melanoma tumor microenvironment. The metabolic pathways altered by NO and the corresponding metabolites reinforce its dual role in melanoma and support investigating this effect for potential avenues of therapeutic intervention.

PEGylated therapeutics in the clinic

The covalent attachment of polyethylene glycol (PEG) to therapeutic agents, termed PEGylation, is a well-established and clinically proven drug delivery approach to improve the pharmacokinetics and pharmacodynamics of drugs. Specifically, PEGylation can improve the parent drug's solubility, extend its circulation time, and reduce its immunogenicity, with minimal undesirable properties. PEGylation technology has been applied to various therapeutic modalities including small molecules, aptamers, peptides, and proteins, leading to over 30 PEGylated drugs currently used in the clinic and many investigational PEGylated agents under clinical trials. Here, we summarize the diverse types of PEGylation strategies, the key advantages of PEGylated therapeutics over their parent drugs, and the broad applications and impacts of PEGylation in clinical settings. A particular focus has been given to the size, topology, and functionalities of PEG molecules utilized in clinically used PEGylated drugs, as well as those under clinical trials. An additional section has been dedicated to analyzing some representative PEGylated drugs that were discontinued at different stages of clinical studies. Finally, we critically discuss the current challenges faced in the development and clinical translation of PEGylated agents.

Recent advances in glucose oxidase-based nanocarriers for tumor targeting therapy

Glucose oxidase (GOx) can specifically catalyze the conversion of β-d-glucose into gluconic acid and hydrogen peroxide (H2O2) in the presence of oxygen, making it promising for tumor starvation therapy and oxidative therapy. However, GOx's immunogenicity, poor in vivo stability, short half-life, and potential systemic toxicity, limit its application in cancer therapy. Nanocarriers are capable of improving the pharmacological properties of therapeutic drugs (e.g. stability, circulating half-life, and tumor accumulation) and lower toxicity, hence resolving GOx issues and enhancing its efficacy. Although the application of targeted nanocarriers based on GOx has recently flourished, this field has not yet been reviewed and evaluated. Herein, we initially examined the mechanism of GOx-based nanocarriers for enhanced tumor therapy. Also, we present a comprehensive and up-to-date review that highlights GOx-based nanocarriers for tumor targeting therapy. This review expands on GOx-based nano-targeted combination therapies from both passive and active targeting perspectives, meanwhile, active targeting is further classified into ligand-mediated targeting and physical-mediated targeting. Furthermore, this review also emphasizes the present challenges and promising advancements.

Arginine deprivation as a treatment approach targeting cancer cell metabolism and survival: A review of the literature

Amino acid requirement of metabolically active cells is a key element in cellular survival. Of note, cancer cells were shown to have an abnormal metabolism and high-energy requirements including the high amino acid requirement needed for growth factor synthesis. Thus, amino acid deprivation is considered a novel approach to inhibit cancer cell proliferation and offer potential treatment prospects. Accordingly, arginine was proven to play a significant role in cancer cell metabolism and therapy. Arginine depletion induced cell death in various types of cancer cells. Also, the various mechanisms of arginine deprivation, e.g., apoptosis and autophagy were summarized. Finally, the adaptive mechanisms of arginine were also investigated. Several malignant tumors had high amino acid metabolic requirements to accommodate their rapid growth. Antimetabolites that prevent the production of amino acids were also developed as anticancer therapies and are currently under clinical investigation. The aim of this review is to provide a concise literature on arginine metabolism and deprivation, its effects in different tumors, its different modes of action, as well as the related cancerous escape mechanisms.

Human arginase I: a potential broad-spectrum anti-cancer agent

With high rates of morbidity and mortality, cancer continues to pose a serious threat to public health on a global scale. Considering the discrepancies in metabolism between cancer and normal cells, metabolism-based anti-cancer biopharmaceuticals are gaining importance. Normal cells can synthesize arginine, but they can also take up extracellular arginine, making it a semi-essential amino acid. Arginine auxotrophy occurs when a cancer cell has abnormalities in the enzymes involved in arginine metabolism and relies primarily on extracellular arginine to support its biological functions. Taking advantage of arginine auxotrophy in cancer cells, arginine deprivation, which can be induced by introducing recombinant human arginase I (rhArg I), is being developed as a broad-spectrum anti-cancer therapy. This has led to the development of various rhArg I variants, which have shown remarkable anti-cancer activity. This article discusses the importance of arginine auxotrophy in cancer and different arginine-hydrolyzing enzymes that are in various stages of clinical development and reviews the need for a novel rhArg I that mitigates the limitations of the existing therapies. Further, we have also analyzed the necessity as well as the significance of using rhArg I to treat various arginine-auxotrophic cancers while considering the importance of their genetic profiles, particularly urea cycle enzymes.

A role for macrophages under cytokine control in mediating resistance to ADI-PEG20 (pegargiminase) in ASS1-deficient mesothelioma

BACKGROUND

Pegylated arginine deiminase (ADI-PEG20; pegargiminase) depletes arginine and improves survival outcomes for patients with argininosuccinate synthetase 1 (ASS1)-deficient malignant pleural mesothelioma (MPM). Optimisation of ADI-PEG20-based therapy will require a deeper understanding of resistance mechanisms, including those mediated by the tumor microenvironment. Here, we sought to reverse translate increased tumoral macrophage infiltration in patients with ASS1-deficient MPM relapsing on pegargiminase therapy.

METHODS

Macrophage-MPM tumor cell line (2591, MSTO, JU77) co-cultures treated with ADI-PEG20 were analyzed by flow cytometry. Microarray experiments of gene expression profiling were performed in ADI-PEG20-treated MPM tumor cells, and macrophage-relevant genetic "hits" were validated by qPCR, ELISA, and LC/MS. Cytokine and argininosuccinate analyses were performed using plasma from pegargiminase-treated patients with MPM.

RESULTS

We identified that ASS1-expressing macrophages promoted viability of ADI-PEG20-treated ASS1-negative MPM cell lines. Microarray gene expression data revealed a dominant CXCR2-dependent chemotactic signature and co-expression of VEGF-A and IL-1α in ADI-PEG20-treated MPM cell lines. We confirmed that ASS1 in macrophages was IL-1α-inducible and that the argininosuccinate concentration doubled in the cell supernatant sufficient to restore MPM cell viability under co-culture conditions with ADI-PEG20. For further validation, we detected elevated plasma VEGF-A and CXCR2-dependent cytokines, and increased argininosuccinate in patients with MPM progressing on ADI-PEG20. Finally, liposomal clodronate depleted ADI-PEG20-driven macrophage infiltration and suppressed growth significantly in the MSTO xenograft murine model.

CONCLUSIONS

Collectively, our data indicate that ADI-PEG20-inducible cytokines orchestrate argininosuccinate fuelling of ASS1-deficient mesothelioma by macrophages. This novel stromal-mediated resistance pathway may be leveraged to optimize arginine deprivation therapy for mesothelioma and related arginine-dependent cancers.

Microbial cancer therapeutics: A promising approach

The success of conventional cancer therapeutics is hindered by associated dreadful side-effects of antibiotic resistance and the dearth of antitumor drugs' selectivity and specificity. Hence, the conceptual evolution of anti-cancerous therapeutic agents that selectively target cancer cells without impacting the healthy cells or tissues, has led to a new wave of scientific interest in microbial-derived bioactive molecules. Such strategic solutions may pave the way to surmount the shortcomings of conventional therapies and raise the potential and hope for the cure of wide range of cancer in a selective manner. This review aims to provide a comprehensive summary of anti-carcinogenic properties and underlying mechanisms of bioactive molecules of microbial origin, and discuss the current challenges and effective therapeutic application of combinatorial strategies to attain minimal systemic side-effects.

Sustained Drug Release from Smart Nanoparticles in Cancer Therapy: A Comprehensive Review

Although nanomedicine has been highly investigated for cancer treatment over the past decades, only a few nanomedicines are currently approved and in the market; making this field poorly represented in clinical applications. Key research gaps that require optimization to successfully translate the use of nanomedicines have been identified, but not addressed; among these, the lack of control of the release pattern of therapeutics is the most important. To solve these issues with currently used nanomedicines (e.g., burst release, systemic release), different strategies for the design and manufacturing of nanomedicines allowing for better control over the therapeutic release, are currently being investigated. The inclusion of stimuli-responsive properties and prolonged drug release have been identified as effective approaches to include in nanomedicine, and are discussed in this paper. Recently, smart sustained release nanoparticles have been successfully designed to safely and efficiently deliver therapeutics with different kinetic profiles, making them promising for many drug delivery applications and in specific for cancer treatment. In this review, the state-of-the-art of smart sustained release nanoparticles is discussed, focusing on the design strategies and performances of polymeric nanotechnologies. A complete list of nanomedicines currently tested in clinical trials and approved nanomedicines for cancer treatment is presented, critically discussing advantages and limitations with respect to the newly developed nanotechnologies and manufacturing methods. By the presented discussion and the highlight of nanomedicine design criteria and current limitations, this review paper could be of high interest to identify key features for the design of release-controlled nanomedicine for cancer treatment.

Metabolic reprogramming in cholangiocarcinoma

Metabolic reprogramming is a hallmark of cancer and allows tumour cells to meet the increased energy demands required for rapid proliferation, invasion, and metastasis. Indeed, many tumour cells acquire distinctive metabolic and bioenergetic features that enable them to survive in resource-limited conditions, mainly by harnessing alternative nutrients. Several recent studies have explored the metabolic plasticity of cancer cells with the aim of identifying new druggable targets, while therapeutic strategies to limit the access to nutrients have been successfully applied to the treatment of some tumours. Cholangiocarcinoma (CCA), a highly heterogeneous tumour, is the second most common form of primary liver cancer. It is characterised by resistance to chemotherapy and poor prognosis, with 5-year survival rates of below 20%. Deregulation of metabolic pathways have been described during the onset and progression of CCA. Increased aerobic glycolysis and glutamine anaplerosis provide CCA cells with the ability to generate biosynthetic intermediates. Other metabolic alterations involving carbohydrates, amino acids and lipids have been shown to sustain cancer cell growth and dissemination. In this review, we discuss the complex metabolic rewiring that occurs during CCA development and leads to unique nutrient addiction. The possible role of therapeutic interventions based on metabolic changes is also thoroughly discussed.

Insight into the interplay between mitochondria-regulated cell death and energetic metabolism in osteosarcoma

Osteosarcoma (OS) is a pediatric malignant bone tumor that predominantly affects adolescent and young adults. It has high risk for relapse and over the last four decades no improvement of prognosis was achieved. It is therefore crucial to identify new drug candidates for OS treatment to combat drug resistance, limit relapse, and stop metastatic spread. Two acquired hallmarks of cancer cells, mitochondria-related regulated cell death (RCD) and metabolism are intimately connected. Both have been shown to be dysregulated in OS, making them attractive targets for novel treatment. Promising OS treatment strategies focus on promoting RCD by targeting key molecular actors in metabolic reprogramming. The exact interplay in OS, however, has not been systematically analyzed. We therefore review these aspects by synthesizing current knowledge in apoptosis, ferroptosis, necroptosis, pyroptosis, and autophagy in OS. Additionally, we outline an overview of mitochondrial function and metabolic profiles in different preclinical OS models. Finally, we discuss the mechanism of action of two novel molecule combinations currently investigated in active clinical trials: metformin and the combination of ADI-PEG20, Docetaxel and Gemcitabine.

Characterisation of Expression the Arginine Pathway Enzymes in Childhood Brain Tumours to Determine Susceptibility to Therapeutic Arginine Depletion

Despite significant improvements in treatment and survival in paediatric cancers, outcomes for children with brain tumours remain poor. Novel therapeutic approaches are needed to improve survival and quality of survival. Extracellular arginine dependency (auxotrophy) has been recognised in several tumours as a potential therapeutic target. This dependency is due to the inability of cancer cells to recycle or synthesise intracellular arginine through the urea cycle pathway compared to normal cells. Whilst adult glioblastoma exhibits this dependency, the expression of the arginine pathway enzymes has not been delineated in paediatric brain tumours. We used immunohistochemical (IHC) methods to stain for arginine pathway enzymes in paediatric high-grade glioma (pHGG), low-grade glioma (pLGG), ependymoma (EPN), and medulloblastoma (MB) tumour tissue microarrays (TMAs). The antibodies detected protein expression of the metaboliser arginase (Arg1 and Arg2); recycling enzymes ornithine transcarbamoylase (OTC), argininosuccinate synthetase (ASS1), and argininosuccinate lyase (ASL); and the transporter SLC7A1. Deficiency of OTC, ASS1, and ASL was seen in 87.5%, 94%, and 79% of pHGG samples, respectively, consistent with an auxotrophic signature. Similar result was obtained in pLGG with 96%, 93%, and 91% of tumours being deficient in ASL, ASS1, and OTC, respectively. 79%, 88%, and 85% of MB cases were ASL, ASS1, and OTC deficient whilst ASL and OTC were deficient in 57% and 91% of EPN samples. All tumour types highly expressed SLC7A1 and Arginase, with Arg2 being the main isoform, demonstrating that they could transport and utilise arginine. Our results show that pHGG, pLGG, EPN, and MB demonstrate arginine auxotrophy based on protein expression and are likely to be susceptible to arginine depletion. Pegylated arginase (BCT-100) is currently in phase I/II trials in relapsed pHGG. Our results suggest that therapeutic arginine depletion may also be useful in other tumour types and IHC analysis of patient tumour samples could help identify patients likely to benefit from this treatment.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Pegylated arginine deiminase drives arginine turnover and systemic autophagy to dictate energy metabolism

Obesity is a multi-systemic disorder of energy balance. Despite intense investigation, the determinants of energy homeostasis remain incompletely understood, and efficacious treatments against obesity and its complications are lacking. Here, we demonstrate that conferred arginine iminohydrolysis by the bacterial virulence factor and arginine deiminase, arcA, promotes mammalian energy expenditure and insulin sensitivity and reverses dyslipidemia, hepatic steatosis, and inflammation in obese mice. Extending this, pharmacological arginine catabolism via pegylated arginine deiminase (ADI-PEG 20) recapitulates these metabolic effects in dietary and genetically obese models. These effects require hepatic and whole-body expression of the autophagy complex protein BECN1 and hepatocyte-specific FGF21 secretion. Single-cell ATAC sequencing further reveals BECN1-dependent hepatocyte chromatin accessibility changes in response to ADI-PEG 20. The data thus reveal an unexpected therapeutic utility for arginine catabolism in modulating energy metabolism by activating systemic autophagy, which is now exploitable through readily available pharmacotherapy.

The "Dark Side" of autophagy on the maintenance of genome stability: Does it really exist during excessive activation?

Dysregulation of DNA damage response/repair and genomic instability promote tumorigenesis and the development of various neurological diseases. Autophagy is a dynamic catabolic process used for removing unnecessary or dysfunctional proteins and organelles in cells. Despite the consensus in the field that upregulation of autophagy promotes the initiation of the DNA damage response and assists the process of homologous recombination upon genotoxic stress, a few studies showed that upregulation of autophagy (or excessive autophagy), under certain circumstances, triggers caspase/apoptosis-independent DNA damage and promotes genomic instability in cells. As the cytoprotective and the DNA repairing roles of autophagy have been discussed extensively in different reviews, here, we mainly focus on describing the latest studies which reported the "opposite" roles of autophagy (or excessive autophagy). We will discuss whether the "dark side" (i.e., the opposite/unconventional effect) of autophagy on the maintenance of DNA integrity and genomic stability really does exist in cells and if it does, will it be one of the yet-to-be-identified causes of cancer, in this review.

Enhancing the Effect of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Signaling and Arginine Deprivation in Melanoma

Melanoma as a very aggressive type of cancer is still in urgent need of improved treatment. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and arginine deiminase (ADI-PEG20) are two of many suggested drugs for treating melanoma. Both have shown anti-tumor activities without harming normal cells. However, resistance to both drugs has also been noted. Studies on the mechanism of action of and resistance to these drugs provide multiple targets that can be utilized to increase the efficacy and overcome the resistance. As a result, combination strategies have been proposed for these drug candidates with various other agents, and achieved enhanced or synergistic anti-tumor effect. The combination of TRAIL and ADI-PEG20 as one example can greatly enhance the cytotoxicity to melanoma cells including those resistant to the single component of this combination. It is found that combination treatment generally can alter the expression of the components of cell signaling in melanoma cells to favor cell death. In this paper, the signaling of TRAIL and ADI-PEG20-induced arginine deprivation including the main mechanism of resistance to these drugs and exemplary combination strategies is discussed. Finally, factors hampering the clinical application of both drugs, current and future development to overcome these hurdles are briefly discussed.

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-dependent immune responses

A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.

Metabolic alterations and vulnerabilities in hepatocellular carcinoma

Liver cancer is a serious disease. It is ranked as the cancer with the second highest number of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC), which arises from transformed hepatocytes, is the major subtype of liver cancer. It accounts for 85% of total liver-cancer cases. An important aspect of HCC that has been actively studied is its metabolism. With the liver as the primary site of numerous metabolic processes in the body, it has been shown that the metabolism of HCC cells is highly dysregulated compared to that of normal hepatocytes. It is therefore crucial to understand the metabolic alterations caused by HCC and the underlying mechanisms for these alterations. This deeper understanding will allow diagnostic and therapeutic advancements in the treatment of HCC. In this review, we will summarize the current literature in HCC metabolic alterations, induced vulnerabilities, and potential therapeutic interventions.

The Janus-like role of proline metabolism in cancer

The metabolism of the non-essential amino acid L-proline is emerging as a key pathway in the metabolic rewiring that sustains cancer cells proliferation, survival and metastatic spread. Pyrroline-5-carboxylate reductase (PYCR) and proline dehydrogenase (PRODH) enzymes, which catalyze the last step in proline biosynthesis and the first step of its catabolism, respectively, have been extensively associated with the progression of several malignancies, and have been exposed as potential targets for anticancer drug development. As investigations into the links between proline metabolism and cancer accumulate, the complexity, and sometimes contradictory nature of this interaction emerge. It is clear that the role of proline metabolism enzymes in cancer depends on tumor type, with different cancers and cancer-related phenotypes displaying different dependencies on these enzymes. Unexpectedly, the outcome of rewiring proline metabolism also differs between conditions of nutrient and oxygen limitation. Here, we provide a comprehensive review of proline metabolism in cancer; we collate the experimental evidence that links proline metabolism with the different aspects of cancer progression and critically discuss the potential mechanisms involved.

Phase II Study of Arginine Deprivation Therapy With Pegargiminase in Patients With Relapsed Sensitive or Refractory Small-cell Lung Cancer

BACKGROUND

Pre-clinical studies indicated that arginine-deprivation therapy using pegylated arginine deiminase (pegargiminase, ADI-PEG 20) may be effective in patients with argininosuccinate synthetase 1 (ASS1)-deficient small-cell lung cancer (SCLC).

PATIENTS AND METHODS

Patients were enrolled into either a 'sensitive' disease cohort (≥ 90 days response to first-line chemotherapy) or a 'refractory' disease cohort (progression while on chemotherapy or < 90 days afterwards or ≥ third-line treatment). Patients received weekly intramuscular pegargiminase, 320 IU/m² (36.8 mg/m²), until unacceptable toxicity or disease progression. The primary endpoint was tumor response assessed by Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 with secondary endpoints including tolerability, pharmacodynamics, and immunogenicity.

RESULTS

Between January 2011 and January 2014, 22 patients were enrolled: 9 in the sensitive disease cohort and 13 in the refractory disease cohort. At a pre-planned interim analysis, the best overall response observed was stable disease in 2 patients in each cohort (18.2%). Owing to the lack of response and slow accrual in the sensitive disease cohort, the study was terminated early. Pegargiminase treatment was well-tolerated with no unexpected adverse events or discontinuations.

CONCLUSION

Although pegargiminase monotherapy in SCLC failed to meet its primary endpoint of RECIST-confirmed responses, more recent molecular stratification, including MYC status, may provide new opportunities moving forward.

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.

Amino Acids Sequence-based Analysis of Arginine Deiminase from Different Prokaryotic Organisms: An In Silico Approach

BACKGROUND

Arginine deiminase is a bacterial enzyme, which degrades L-arginine. Some human cancers such as hepatocellular carcinoma (HCC) and melanoma are auxotrophic for arginine. Therefore, PEGylated arginine deiminase (ADI-PEG20) is a good anticancer candidate with antitumor effects. It causes local depletion of L-arginine and growth inhibition in arginineauxotrophic tumor cells. The FDA and EMA have granted orphan status to this drug. Some recently published patents have dealt with this enzyme or its PEGylated form.

OBJECTIVE

Due to increasing attention to it, we aimed to evaluate and compare 30 arginine deiminase proteins from different bacterial species through in silico analysis.

METHODS

The exploited analyses included the investigation of physicochemical properties, multiple sequence alignment (MSA), motif, superfamily, phylogenetic and 3D comparative analyses of arginine deiminase proteins thorough various bioinformatics tools.

RESULTS

The most abundant amino acid in the arginine deiminase proteins is leucine (10.13%) while the least amino acid ratio is cysteine (0.98%). Multiple sequence alignment showed 47 conserved patterns between 30 arginine deiminase amino acid sequences. The results of sequence homology among 30 different groups of arginine deiminase enzymes revealed that all the studied sequences located in amidinotransferase superfamily. Based on the phylogenetic analysis, two major clusters were identified. Considering the results of various in silico studies; we selected the five best candidates for further investigations. The 3D structures of the best five arginine deiminase proteins were generated by the I-TASSER server and PyMOL. The RAMPAGE analysis revealed that 81.4%-91.4%, of the selected sequences, were located in the favored region of arginine deiminase proteins.

CONCLUSION

The results of this study shed light on the basic physicochemical properties of thirty major arginine deiminase sequences. The obtained data could be employed for further in vivo and clinical studies and also for developing the related therapeutic enzymes.

Harnessing cancer immunotherapy during the unexploited immediate perioperative period

The immediate perioperative period (days before and after surgery) is hypothesized to be crucial in determining long-term cancer outcomes: during this short period, numerous factors, including excess stress and inflammatory responses, tumour-cell shedding and pro-angiogenic and/or growth factors, might facilitate the progression of pre-existing micrometastases and the initiation of new metastases, while simultaneously jeopardizing immune control over residual malignant cells. Thus, application of anticancer immunotherapy during this critical time frame could potentially improve patient outcomes. Nevertheless, this strategy has rarely been implemented to date. In this Perspective, we discuss apparent contraindications for the perioperative use of cancer immunotherapy, suggest safe immunotherapeutic and other anti-metastatic approaches during this important time frame and specify desired characteristics of such interventions. These characteristics include a rapid onset of immune activation, avoidance of tumour-promoting effects, no or minimal increase in surgical risk, resilience to stress-related factors and minimal induction of stress responses. Pharmacological control of excess perioperative stress-inflammatory responses has been shown to be clinically feasible and could potentially be combined with immune stimulation to overcome the direct pro-metastatic effects of surgery, prevent immune suppression and enhance immunostimulatory responses. Accordingly, we believe that certain types of immunotherapy, together with interventions to abrogate stress-inflammatory responses, should be evaluated in conjunction with surgery and, for maximal effectiveness, could be initiated before administration of adjuvant therapies. Such strategies might improve the overall success of cancer treatment.

Metabolic rearrangements in primary liver cancers: cause and consequences

Primary liver cancer (PLC) is the fourth most frequent cause of cancer-related death. The high mortality rates arise from late diagnosis and the limited accuracy of diagnostic and prognostic biomarkers. The liver is a major regulator, orchestrating the clearance of toxins, balancing glucose, lipid and amino acid uptake, managing whole-body metabolism and maintaining metabolic homeostasis. Tumour onset and progression is frequently accompanied by rearrangements of metabolic pathways, leading to dysregulation of metabolism. The limitation of current therapies targeting PLCs, such as hepatocellular carcinoma and cholangiocarcinoma, points towards the importance of deciphering this metabolic complexity. In this Review, we discuss the role of metabolic liver disruptions and the implications of these processes in PLCs, emphasizing their clinical relevance and value in early diagnosis and prognosis and as putative therapeutic targets. We also describe system biology approaches able to reconstruct the metabolic complexity of liver diseases. We also discuss whether metabolic rearrangements are a cause or consequence of PLCs, emphasizing the opportunity to clinically exploit the rewired metabolism. In line with this idea, we discuss circulating metabolites as promising biomarkers for PLCs.

Multilevel algorithms and evolutionary hybrid tools for enhanced production of arginine deiminase from Pseudomonas furukawaii RS3

In the present study a high arginine deiminase (ADI) yielding bacterium was isolated from soil samples of Haryana, India and identified as Pseudomonas furukawaii. The specific enzyme activity was optimized to 1.420 IU/ml by OFAT and further enhanced to 2.708 IU/ml (an increase of 90.7%) with the help of statistical parametric optimization approaches using GA-ANN and GA-ANFIS. The obtained value of the coefficient of correlation (R = 0.88) for ANN and epoch error (0.12) for ANFIS, indicates the prediction accuracy and strength of these data training models. ADI production was improved significantly in simple super broth media supplemented with 1.5% fructose and 1.75% arginine at pH 7 at 37 °C using multilevel algorithms and evolutionary hybrid tools. The native enzyme was partially purified (ten-fold) up to a specific enzyme activity of 29.559 IU/mg.

Amino acid metabolism in hematologic malignancies and the era of targeted therapy

Tumor cells rewire metabolic pathways to adapt to their increased nutritional demands for energy, reducing equivalents, and cellular biosynthesis. Alternations in amino acid metabolism are 1 modality for satisfying those demands. Amino acids are not only components of proteins but also intermediate metabolites fueling multiple biosynthetic pathways. Amino acid-depletion therapies target amino acid uptake and catabolism using heterologous enzymes or recombinant or engineered human enzymes. Notably, such therapies have minimal effect on normal cells due to their lower demand for amino acids compared with tumor cells and their ability to synthesize the targeted amino acids under conditions of nutrient stress. Here, we review novel aspects of amino acid metabolism in hematologic malignancies and deprivation strategies, focusing on 4 key amino acids: arginine, asparagine, glutamine, and cysteine. We also present the roles of amino acid metabolism in the immunosuppressive tumor microenvironment and in drug resistance. This summary also offers an argument for the reclassification of amino acid-depleting enzymes as targeted therapeutic agents.

Isolation and screening of extracellular anticancer enzymes from halophilic and halotolerant bacteria from different saline environments in Iran

It was confirmed that several enzymes have anti-cancer activity. The enzymes L-asparaginase, L-glutaminase, and L-arginase were chosen according to amino acids starvation in cancer cells and screened in halophilic and halotolerant bacteria, given probably less immunological reactions of halophilic or halotolerant enzymes in patients. Out of 110 halophilic and halotolerant strains, isolated from different saline environments in Iran and screened, some could produce a variety of anticancer enzymes. A total of 29, 4, and 2 strains produced L-asparaginase, L-glutaminase, and L-arginase, respectively. According to the phenotypic characteristics and partial 16S rRNA gene sequence analysis, the positive strains-strains with the ability to produce these anticancer enzymes-were identified as the members of the genera: Bacillus, Dietzia, Halobacillus, Rhodococcus, Paenibacillus and Planococcus as Gram-positive bacteria and Pseudomonas, Marinobacter, Halomonas, Idiomarina, Vibrio and Stappia as Gram-negative bacteria. The production of anticancer enzymes was mostly observed in the rod-shaped Gram-negative isolates, particularly in the members of the genera Halomonas and Marinobacter. Most of the enzymes were produced in the stationary phase of growth and the maximum enzyme activity was experienced in strain GBPx3 (Vibrio sp.) for L-asparaginase at 1.0 IU/ml, strain R₂S₂₅ (Rhodococcus sp.) for L-glutaminase at 0.6 IU/ml and strain GAAy3 (Planococcus sp.) for L-arginase at 3.1 IU/ml. The optimum temperature and pH for L-asparaginase and L-glutaminase activities in selected strains were similar to the physiological conditions of human body and the enzymes could tolerate NaCl up to 7.5% concentration.

Endogenous arginase 2 as a potential biomarker for PEGylated arginase 1 treatment in xenograft models of squamous cell lung carcinoma

Depletion of arginine induced by PEGylated arginase 1 (ARG1) (BCT-100) has shown anticancer effects in arginine auxotrophic cancers that lack argininosuccinate synthetase (ASS1) and ornithine transcarbamylase (OTC). High levels of endogenous arginase 2 (ARG2) have been previously reported in human lung cancers. Although a high-ARG2 level neither causes immunosuppression nor affects disease progression, it may theoretically affect the efficacy of PEGylated ARG1 treatment. ARG2 was shown to be highly expressed in H520 squamous cell lung carcinoma (lung SCC) xenografts but undetectable in SK-MES-1 and SW900 lung SCC xenografts. We propose that high-endogenous expression of ARG2 could impede the anti-tumor effect of PEGylated ARG1 in lung SCC. The in vivo effect of PEGylated ARG1 was investigated using three xenograft models of lung SCC. PEGylated ARG1 (60 mg/kg) suppressed tumor growth in SK-MES-1 and SW900 but not H520 xenografts. ASS1 was expressed in SK-MES-1 and SW900 xenografts while OTC expression remained low in all xenografts. A high-endogenous ARG2 level was detected only in H520 xenografts. Serum arginine level was decreased significantly by PEGylated ARG1 in all xenografts. Nonetheless intratumoral arginine level was decreased by PEGylated ARG1 in SK-MES-1 and SW900, not H520 xenografts. In SK-MES-1 xenografts, PEGylated ARG1 treatment induced G1 arrest, downregulation of Ki67 and Mcl-1 and activation of apoptosis. In SW900 xenografts, upregulation of Bim and activation of apoptosis were observed upon PEGylated ARG1 treatment. Silencing of ARG2 re-sensitized the H520 xenografts to PEGylated ARG1 treatment, partially mediated through arginine depletion via G1 arrest and apoptosis. PEGylated ARG1 treatment (BCT-100) was effective in lung SCC xenografts with low-endogenous levels of ASS1/OTC and ARG2. High-endogenous ARG2 expression may cause resistance to PEGylated ARG1 treatment in lung SCC xenografts. ARG2 may serve as a third predictive biomarker in PEGylated ARG1 treatment in lung SCC.

A Phase I Study of Pegylated Arginine Deiminase (Pegargiminase), Cisplatin, and Pemetrexed in Argininosuccinate Synthetase 1-Deficient Recurrent High-grade Glioma

PURPOSE

Patients with recurrent high-grade gliomas (HGG) are usually managed with alkylating chemotherapy ± bevacizumab. However, prognosis remains very poor. Preclinically, we showed that HGGs are a target for arginine depletion with pegargiminase (ADI-PEG20) due to epimutations of argininosuccinate synthetase (ASS1) and/or argininosuccinate lyase (ASL). Moreover, ADI-PEG20 disrupts pyrimidine pools in ASS1-deficient HGGs, thereby impacting sensitivity to the antifolate, pemetrexed.

PATIENTS AND METHODS

We expanded a phase I trial of ADI-PEG20 with pemetrexed and cisplatin (ADIPEMCIS) to patients with ASS1-deficient recurrent HGGs (NCT02029690). Patients were enrolled (01/16-06/17) to receive weekly ADI-PEG20 36 mg/m² intramuscularly plus pemetrexed 500 mg/m² and cisplatin 75 mg/m² intravenously once every 3 weeks for up to 6 cycles. Patients with disease control were allowed ADI-PEG20 maintenance. The primary endpoints were safety, tolerability, and preliminary estimates of efficacy.

RESULTS

Ten ASS1-deficient heavily pretreated patients were treated with ADIPEMCIS therapy. Treatment was well tolerated with the majority of adverse events being Common Terminology Criteria for Adverse Events v4.03 grade 1-2. The best overall response was stable disease in 8 patients (80%). Plasma arginine was suppressed significantly below baseline with a reciprocal increase in citrulline during the sampling period. The anti-ADI-PEG20 antibody titer rose during the first 4 weeks of treatment before reaching a plateau. Median progression-free survival (PFS) was 5.2 months (95% confidence interval (CI), 2.5-20.8) and overall survival was 6.3 months (95% CI, 1.8-9.7).

CONCLUSIONS

In this recurrent HGG study, ADIPEMCIS was well tolerated and compares favorably to historical controls. Additional trials of ADI-PEG20 in HGG are planned.

Recombinant human arginase induces apoptosis through oxidative stress and cell cycle arrest in small cell lung cancer

Small cell lung cancer (SCLC) accounts for approximately 13% of all lung cancer cases. Small cell lung cancer is characterized by frequent relapse, and current treatments lack tumor specificity. Arginine is a non‐essential amino acid for human normal cells but critical to some tumor cells that cannot synthesize arginine. Therefore, arginine deprivation has become a potential therapeutic option for selected tumors. BCT‐100 is a pegylated arginase that has documented anticancer activity in arginine auxotrophic tumors, such as melanoma, hepatocellular carcinoma, and acute myeloid leukemia. One of the resistance mechanisms to arginase treatment is overexpression of argininosuccinate synthetase (ASS1) and ornithine transcarbamylase (OTC), two important enzymes in the urea cycle. We selected 9 SCLC and 1 non‐small cell lung carcinoma cell lines to determine the growth inhibition effects of BCT‐100 and established that cell lines with low expression of ASS1 and OTC are relatively sensitive to BCT‐100 treatment. Knocking down OTC in a H841 cell line could potentiate its sensitivity to BCT‐100 treatment. Arginine concentration was sharply decreased, accompanied by apoptosis through oxidative stress as well as G₁ cell cycle arrest. In addition, BCT‐100 showed an anticancer effect on H446 and H510A xenograft models by lowering arginine levels and inducing apoptosis.

Sensitivity of Colorectal Cancer to Arginine Deprivation Therapy is Shaped by Differential Expression of Urea Cycle Enzymes

Tumors deficient in the urea cycle enzymes argininosuccinate synthase-1 (ASS1) and ornithine transcarbamylase (OTC) are unable to synthesize arginine and can be targeted using arginine-deprivation therapy. Here, we show that colorectal cancers (CRCs) display negligible expression of OTC and, in subset of cases, ASS1 proteins. CRC cells fail to grow in arginine-free medium and dietary arginine deprivation slows growth of cancer cells implanted into immunocompromised mice. Moreover, we report that clinically-formulated arginine-degrading enzymes are effective anticancer drugs in CRC. Pegylated arginine deiminase (ADI-PEG20), which degrades arginine to citrulline and ammonia, affects growth of ASS1-negative cells, whereas recombinant human arginase-1 (rhArg1peg5000), which degrades arginine into urea and ornithine, is effective against a broad spectrum of OTC-negative CRC cell lines. This reflects the inability of CRC cells to recycle citrulline and ornithine into the urea cycle. Finally, we show that arginase antagonizes chemotherapeutic drugs oxaliplatin and 5-fluorouracil (5-FU), whereas ADI-PEG20 synergizes with oxaliplatin in ASS1-negative cell lines and appears to interact with 5-fluorouracil independently of ASS1 status. Overall, we conclude that CRC is amenable to arginine-deprivation therapy, but we warrant caution when combining arginine deprivation with standard chemotherapy.

Inhibition of ornithine decarboxylase 1 facilitates pegylated arginase treatment in lung adenocarcinoma xenograft models

Arginine depletion has shown anticancer effects among arginine auxotrophic cancers. An anti-proliferative effect of pegylated arginase (BCT-100) has been shown in acute myeloid leukaemia, hepatocellular carcinoma and mesothelioma. The aim of the present study was to evaluate the effect of BCT-100 in lung adenocarcinoma. A panel of lung adenocarcinoma cell lines and xenograft models were used to investigate the effect of BCT-100. Protein expression, arginine level, putrescine level, spermidine level and apoptosis were analyzed by western blotting, ELISA, high performance liquid chromatography, dot blot and TUNEL assay, respectively. BCT-100 converts arginine to ornithine. BCT-100 reduced in vitro cell viability across different lung adenocarcinoma cell lines and suppressed tumour growth in an HCC4006 ×enograft, while paradoxical growth stimulation was observed in H358, HCC827, H1650 and H1975 ×enografts. Upon BCT-100 treatment, ornithine decarboxylase 1 (ODC1) was induced in two solid tumour xenografts (H1650 and H1975). It was postulated that the accumulated ornithine could be channeled via ODC1 to produce polyamines that promoted tumour growth. The action of an ODC1 inhibitor (α-difluoromethylornithine, DFMO) was studied in the restoration of the anticancer effects of BCT-100 in lung adenocarcinoma. In both H1650 and H1975 ×enografts, a combination of DFMO and BCT-100 significantly suppressed tumour growth, resulting in doubled median survival compared with the control. Putrescine was decreased in almost all treatment arms in the H1650, H1975 and HCC4006 ×enografts. Nonetheless spermidine was reduced only following DFMO/BCT-100 treatment in the H1650 and H1975 ×enografts. Apoptosis was enhanced in the combined treatment arm in both H1650 and H1975 ×enografts. In the HCC4006 ×enograft, addition of DFMO did not alter the tumour suppressive effect of BCT-100. In conclusion, inhibition of ODC1 by DFMO was crucial in facilitating BCT-100 treatment in lung adenocarcinoma that was partially mediated by depleting arginine and polyamines with consequent apoptosis.

p53 and metabolism: from mechanism to therapeutics

The tumor cell changes itself and its microenvironment to adapt to different situations, including action of drugs and other agents targeting tumor control. Therefore, metabolism plays an important role in the activation of survival mechanisms to keep the cell proliferative potential. The Warburg effect directs the cellular metabolism towards an aerobic glycolytic pathway, despite the fact that it generates less adenosine triphosphate than oxidative phosphorylation; because it creates the building blocks necessary for cell proliferation. The transcription factor p53 is the master tumor suppressor; it binds to more than 4,000 sites in the genome and regulates the expression of more than 500 genes. Among these genes are important regulators of metabolism, affecting glucose, lipids and amino acids metabolism, oxidative phosphorylation, reactive oxygen species (ROS) generation and growth factors signaling. Wild-type and mutant p53 may have opposing effects in the expression of these metabolic genes. Therefore, depending on the p53 status of the cell, drugs that target metabolism may have different outcomes and metabolism may modulate drug resistance. Conversely, induction of p53 expression may regulate differently the tumor cell metabolism, inducing senescence, autophagy and apoptosis, which are dependent on the regulation of the PI3K/AKT/mTOR pathway and/or ROS induction. The interplay between p53 and metabolism is essential in the decision of cell fate and for cancer therapeutics.

Reduced argininosuccinate synthetase expression in refractory sarcomas: Impacts on therapeutic potential and drug resistance

Background

Treating drug-resistant sarcomas remains a major challenge. The present study aimed to identify a novel therapy for drug-resistant sarcomas based on metabolic errors involving argininosuccinate synthetase1 (ASS1).

Results

ASS1 expression was reduced in Dox-resistant sarcoma cells. Immunohistochemistry and real-time PCR showed an inverse correlation between ASS1 and P-gp expressions. The inhibition of cellular proliferation with G1-arrest was shown to lead to autophagy with arginine deprivation. In addition, the combination of an autophagy inhibitor plus arginine deprivation was more effective than arginine deprivation alone. In cells with suppressed ASS1 expression, P-gp expression was upregulated as compared to that in negative controls.

Discussion

These results indicate that the reduced ASS1 expression in Dox-resistant sarcomas may contribute to drug resistance in association with the expression of P-gp. ASS1 deficiency is a potential target for novel drug therapies. The combination of arginine-deprivation therapy and an autophagy inhibitor may have anti-tumor effects in refractory sarcomas.

Methods

We assessed the expressions of ASS1 and P-glycoprotein (P-gp) in clinical specimens and cell lines of osteosarcoma (KHOS), doxorubicin (Dox)-resistant osteosarcoma (KHOS_R2), epithelioid sarcomas (ES-X and VAESBJ) and alveolar soft part sarcoma (ASPS-KY). Each cell line was cultured in arginine-containing and arginine-free media. Cell growth was assessed using an XTT assay and flow cytometry. We analyzed the induction of autophagy in arginine-free medium. Moreover, we assessed the expression of P-gp after suppressing ASS1 in Dox-sensitive cells (MCF-7 and KHOS) and after transfecting ASS1 into Dox-resistant cells (ES-X, VAESBJ, ASPS-KY and KHOS_R2).

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.

Drug-induced amino acid deprivation as strategy for cancer therapy

Cancer is caused by uncontrollable growth of neoplastic cells, leading to invasion of adjacent and distant tissues resulting in death. Cancer cells have specific nutrient(s) auxotrophy and have a much higher nutrient demand compared to normal tissues. Therefore, different metabolic inhibitors or nutrient-depleting enzymes have been tested for their anti-cancer activities. We review recent available laboratory and clinical data on using various specific amino acid metabolic pathways inhibitors in treating cancers. Our focus is on glutamine, asparagine, and arginine starvation. These three amino acids are chosen due to their better scientific evidence compared to other related approaches in cancer treatment. Amino acid-specific depleting enzymes have been adopted in different standard chemotherapy protocols. Glutamine starvation by glutaminase inhibitior, transporter inhibitor, or glutamine depletion has shown to have significant anti-cancer effect in pre-clinical studies. Currently, glutaminase inhibitor is under clinical trial for testing anti-cancer efficacy. Clinical data suggests that asparagine depletion is effective in treating hematologic malignancies even as a single agent. On the other hand, arginine depletion has lower toxicity profile and can effectively reduce the level of pro-cancer biochemicals in patients as shown by ours and others’ data. This supports the clinical use of arginine depletion as anti-cancer therapy but its exact efficacy in various cancers requires further investigation. However, clinical application of these enzymes is usually hindered by common problems including allergy to these foreign proteins, off-target cytotoxicity, short half-life and rapidly emerging chemoresistance. There have been efforts to overcome these problems by modifying the drugs in different ways to circumvent these hindrance such as (1) isolate human native enzymes to reduce allergy, (2) isolate enzyme isoforms with higher specificities and efficiencies, (3) pegylate the enzymes to reduce allergy and prolong the half-lives, and (4) design drug combinations protocols to enhance the efficacy of chemotherapy by drug synergy and minimizing resistance. These improvements can potentially lead to the development of more effective anti-cancer treatment with less adverse effects and higher therapeutic efficacy.

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.

Growth suppressive effect of pegylated arginase in malignant pleural mesothelioma xenografts

Background

Malignant pleural mesothelioma (MPM) is a difficult-to-treat global disease. Pegylated arginase (BCT-100) has recently shown anti-tumor effects in hepatocellular carcinoma, acute myeloid leukemia and melanoma. This study aims to investigate the effects of PEG-BCT-100 in MPM.

Methods

A panel of 5 mesothelioma cell lines (H28, 211H, H226, H2052 and H2452) was used to study the in vitro effects of BCT-100 by crystal violet staining. The in vivo effects of BCT-100 were studied using 211H and H226 nude mice xenografts. Protein expression (argininosuccinate synthetase, ornithine transcarbamylase, cleaved PARP, cleaved caspase 3, cyclins (A2, D3, E1 and H), CDK4 and Ki67) and arginine concentration were evaluated by Western blot and ELISA respectively. Cellular localization of BCT-100 was detected by immunohistochemistry and immunoflorescence. TUNEL assay was used to identify cellular apoptotic events.

Results

Argininosuccinate synthetase was expressed in H28, H226, and H2452 cells as well as 211H and H266 xenografts. Ornithine transcarbamylase was undetectable in all cell lines and xenograft models. BCT-100 reduced in vitro cell viability (IC₅₀ values at 13–24 mU/ml, 72 h) across different cell lines and suppressed tumor growth in both 211H and H226 xenograft models. BCT-100 (60 mg/kg) significantly suppressed tumor growth (p < 0.01) with prolonged median survival (p < 0.01) in both xenograft models. Combining BCT-100 with pemetrexed or cisplatin conferred no additional benefits over single agents. Serum and intratumoral arginine levels were effectively decreased by BCT-100, associated with cytosolic accumulation of BCT-100 within tumor cells. Apoptosis (PARP cleavage in 211H xenografts; Bcl-2 downregulation, and cleavage of PARP and caspase 3 in H226 xenografts; positive TUNEL staining in both) and G1 arrest (downregulation of cyclin A2, D3, E1 and CDK4 in 211H xenografts; suppression of cyclin A2, E1, H and CDK4 in H226 xenografts) were evident with BCT-100 treatment. Furthermore, proliferative factor Ki67 was downregulated in BCT-100 treatments arms.

Conclusions

BCT-100 suppressed tumor growth with prolonged median survival partially mediated by intratumoral arginine depletion resulting in apoptosis and G1 arrest in mesothelioma xenograft models. The findings provide scientific evidence to support further clinical development of BCT-100 in treatment of MPM.

BRAF inhibitor resistance enhances vulnerability to arginine deprivation in melanoma

BRAF inhibitor (BRAFi) has been used for treatment of melanomas harboring V600E mutation. Despite a high initial response rate, resistance to BRAFi is inevitable. Here, we demonstrate that BRAFi-resistant (BR) melanomas are susceptible to arginine deprivation due to inability to initiate re-expression of argininosuccinate synthetase (ASS1, a key enzyme for arginine synthesis) as well as ineffective autophagy. Autophagy and ASS1 re-expression are known to protect melanoma cells from cell death upon arginine deprivation. When melanoma cells become BR cells by long-term in vitro incubation with BRAFi, c-Myc-mediated ASS1 re-expression and the levels of autophagy-associated proteins (AMPK-α1 and Atg5) are attenuated. Furthermore, our study uncovers that downregulation of deubiquitinase USP28 which results in more active c-Myc degradation via ubiquitin-proteasome machinery is the primary mechanism for inability to re-express ASS1 upon arginine deprivation in BR cells. Overexpression of USP28 in BR cells enhances c-Myc expression and hence increases ASS1 transcription upon arginine deprivation, and consequently leads to cell survival. On the other hand, overexpression of Atg5 or AMPK-α1 in BR cells can redirect arginine deprivation-induced apoptosis toward autophagy. The xenograft models also confirm that BR tumors possess lower expression of ASS1 and are hypersensitive to arginine deprivation. These biochemical changes in BRAFi resistance which make them vulnerable to arginine deprivation can be exploited for the future treatment of BR melanoma patients.