Phase I/II study of pegylated arginine deiminase (ADI-PEG 20) in patients with advanced melanoma

Arginine metabolism and deprivation in cancer therapy

Certain cancer cells with nutrient auxotrophy and have a much higher nutrient demand compared with normal human cells. Arginine as a versatile amino acid, has multiple biological functions in metabolic and signaling pathways. Depletion of this amino acid by arginine depletor is generally well tolerated and has become a targeted therapy for arginine auxotrophic cancers. However, the modulatory eff ;ect of arginine on cancer cells is very complicated and still controversial. Therefore, this article focuses on arginine metabolism and depletion therapy in cancer treatment to provide systemical review on this issue.

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.

Arginine Deiminase: Current Understanding and Applications

BACKGROUND

Arginine deiminase (ADI), an arginine catabolizing enzyme, is considered as an anti-tumor agent for the treatment of arginine auxotrophic cancers. However, some obstacles limit its clinical applications.

OBJECTIVE

This review will summarize the clinical applications of ADI, from a brief history to its limitations, and will discuss the different ways to deal with the clinical limitations.

METHOD

The structure analysis, cloning, expression, protein engineering and applications of arginine deiminase enzyme have been explained in this review.

CONCLUSION

Recent patents on ADI are related to ADI engineering to increase its efficacy for clinical application. The intracellular delivery of ADI and combination therapy seem to be the future strategies in the treatment of arginine auxotrophic cancers. Applying ADIs with optimum features from different sources and or ADI engineering, are promising strategies to improve the clinical application of ADI.

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.

Metabolic therapy with PEG-arginase induces a sustained complete remission in immunotherapy-resistant melanoma

BACKGROUND

Metastatic melanoma is an aggressive skin cancer with a poor prognosis. Current treatment strategies for high-stage melanoma are based around the use of immunotherapy with immune checkpoint inhibitors such as anti-PDL1 or anti-CTLA4 antibodies to stimulate anti-cancer T cell responses, yet a number of patients will relapse and die of disease. Here, we report the first sustained complete remission in a patient with metastatic melanoma who failed two immunotherapy strategies, by targeting tumour arginine metabolism.

CASE PRESENTATION

A 65-year-old patient with metastatic melanoma who progressed through two immunotherapy strategies with immune checkpoint inhibitor antibodies was enrolled in a phase I study (NCT02285101) and treated with 2 mg/kg intravenously, weekly pegylated recombinant arginase (BCT-100). The patient experienced no toxicities > grade 2 and entered a complete remission which is sustained for over 30 months. RNA-sequencing identified a number of transcriptomic pathway alterations compared to control samples. The tumour had absent expression of the recycling enzymes argininosuccinate synthetase (ASS) and ornithine transcarbamylase (OTC) indicating a state of arginine auxotrophy, which was reconfirmed by immunohistochemistry, and validation in a larger cohort of melanoma tumour samples.

CONCLUSIONS

Targeting arginine metabolism with therapeutic arginase in arginine auxotrophic melanoma can be an effective salvage for the treatment of patients who fail immunotherapy.

Amino Acid Uptake Measured by [18F]AFETP Increases in Response to Arginine Starvation in ASS1-Deficient Sarcomas

Rational: In a subset of cancers, arginine auxotrophy occurs due to the loss of expression of argininosuccinate synthetase 1 (ASS1). This loss of ASS1 expression makes cancers sensitive to arginine starvation that is induced by PEGylated arginine deiminase (ADI-PEG20). Although ADI-PEG20 treatment is effective, it does have important limitations. Arginine starvation is only beneficial in patients with cancers that are ASS1-deficient. Also, these tumors may metabolically reprogram to express ASS1, transforming them from an auxotrophic phenotype to a prototrophic phenotype and thus rendering ADI-PEG20 ineffective. Due to these limitations of ADI-PEG20 treatment and the potential for developing resistance, non-invasive tools to monitor sensitivity to arginine starvation are needed.

Methods: Within this study, we assess the utility of a novel positron emission tomography (PET) tracer to determine sarcomas reliant on extracellular arginine for survival by measuring changes in amino acid transport in arginine auxotrophic sarcoma cells treated with ADI-PEG20. The uptake of the ¹⁸F-labeled histidine analogue, (S)-2-amino-3-[1-(2-[¹⁸F]fluoroethyl)-1H-[1,2,3]triazol-4-yl]propanoic acid (AFETP), was assessed in vitro and in vivo using human-derived sarcoma cell lines. In addition, we examined the expression and localization of cationic amino acid transporters in response to arginine starvation with ADI-PEG20.

Results: In vitro studies revealed that in response to ADI-PEG20 treatment, arginine auxotrophs increase the uptake of L-[³H]arginine and [¹⁸F]AFETP due to an increase in the expression and localization to the plasma membrane of the cationic amino acid transporter CAT-1. Furthermore, in vivo PET imaging studies in mice with arginine-dependent osteosarcoma xenografts showed increased [¹⁸F]AFETP uptake in tumors 4 days after ADI-PEG20 treatment compared to baseline.

Conclusion: CAT-1 transporters localizes to the plasma membrane as a result of arginine starvation with ADI-PEG20 in ASS1-deficient tumor cells and provides a mechanism for using cationic amino acid transport substrates such as [¹⁸F]AFETP for identifying tumors susceptible to ADI-PEG20 treatment though non-invasive PET imaging techniques. These findings indicate that [¹⁸F]AFETP-PET may be suitable for the early detection of tumor response to arginine depletion due to ADI-PEG20 treatment.

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).

Decreasing the immunogenicity of arginine deiminase enzyme via structure-based computational analysis

The clinical applications of therapeutic enzymes are often limited due to their immunogenicity. B-cell epitope removal is an effective approach to solve this obstacle. The identification of hot spot epitopic residues is a critical step in the removal of protein B-cell epitope. Hereof, computational approaches are a suitable alternative to costly and labor-intensive experimental approaches. Arginine deiminase, a Mycoplasma arginine-catabolizing enzyme, is in the clinical trial for treating arginine auxotrophic cancers, especially hepatocellular carcinomas and melanomas through depleting plasma arginine and causing cell starvation. In this study, arginine deiminase from Mycoplasma hominis (MhADI) was computationally analyzed for recognizing and locating its immune-reactive regions. The 3D structure of the bioactive form of MhADI was modeled. The B-cell epitope mapping of protein was performed using various servers with different algorithms. Six segments: 31-40, 48-55, 131-140, 196-206, 294-314, and 331-344 were predicted to be the consensus immunogenic regions. The modification of epitopic hot spot residue was performed to reduce immune-reactiveness. The hot spot residue was selected considering a high B-cell epitope score, convexity index, surface accessibility, flexibility, and hydrophilicity. The structure stability of native and mutant proteins was evaluated through molecular dynamics simulation. The E304L mutein was suggested as a lower antigenic and stable enzyme derivative.

Oncogene-Driven Metabolic Alterations in Cancer

Cancer is the leading cause of human deaths worldwide. Understanding the biology underlying the evolution of cancer is important for reducing the economic and social burden of cancer. In addition to genetic aberrations, recent studies demonstrate metabolic rewiring, such as aerobic glycolysis, glutamine dependency, accumulation of intermediates of glycolysis, and upregulation of lipid and amino acid synthesis, in several types of cancer to support their high demands on nutrients for building blocks and energy production. Moreover, oncogenic mutations are known to be associated with metabolic reprogramming in cancer, and these overall changes collectively influence tumor-microenvironment interactions and cancer progression. Accordingly, several agents targeting metabolic alterations in cancer have been extensively evaluated in preclinical and clinical settings. Additionally, metabolic reprogramming is considered a novel target to control cancers harboring un-targetable oncogenic alterations such as KRAS. Focusing on lung cancer, here, we highlight recent findings regarding metabolic rewiring in cancer, its association with oncogenic alterations, and therapeutic strategies to control deregulated metabolism in cancer.

Global metabolomic profiling of uterine leiomyomas

BACKGROUND

Uterine leiomyomas can be classified into molecularly distinct subtypes according to their genetic triggers: MED12 mutations, HMGA2 upregulation, or inactivation of FH. The aim of this study was to identify metabolites and metabolic pathways that are dysregulated in different subtypes of leiomyomas.

METHODS

We performed global metabolomic profiling of 25 uterine leiomyomas and 17 corresponding myometrium specimens using liquid chromatography-tandem mass spectroscopy.

RESULTS

A total of 641 metabolites were detected. All leiomyomas displayed reduced homocarnosine and haeme metabolite levels. We identified a clearly distinct metabolomic profile for leiomyomas of the FH subtype, characterised by metabolic alterations in the tricarboxylic acid cycle and pentose phosphate pathways, and increased levels of multiple lipids and amino acids. Several metabolites were uniquely elevated in leiomyomas of the FH subtype, including N6-succinyladenosine and argininosuccinate, serving as potential biomarkers for FH deficiency. In contrast, leiomyomas of the MED12 subtype displayed reduced levels of vitamin A, multiple membrane lipids and amino acids, and dysregulation of vitamin C metabolism, a finding which was also compatible with gene expression data.

CONCLUSIONS

The study reveals the metabolomic heterogeneity of leiomyomas and provides the requisite framework for strategies designed to target metabolic alterations promoting the growth of these prevalent tumours.

New molecular targets for functionalized nanosized drug delivery systems in personalized therapy for hepatocellular carcinoma

Hepatocellular carcinoma, the most frequent solid tumor of the liver, has a very poor prognosis, being the second most common cause of death from cancer worldwide. The incidence and mortality of this liver tumor are increasing in most areas of the world as a consequence of aging and the emerging of new risk factors such as the metabolic syndrome, beside the recognized role of hepatitis B and C viral infections and alcohol abuse. Despite the increasing knowledge on the molecular mechanisms underlying hepatic carcinogenesis, effective therapeutic strategies are still an unmet clinical need. Efforts have been made to develop selective drugs as well as effective targeted drug delivery systems. The development of novel drug carriers for therapeutic molecules can indeed offer a valuable strategy to ameliorate the efficacy of HCC treatment. In this review, we discuss recent drug delivery strategies for HCC treatment based on the exploitation of targeted nanoparticles (NPs). Indeed, a few of these platforms have achieved an advanced stage of preclinical development. Here, we review the most promising drug nanovehicles based on both synthetic and natural polymers, including polysaccharides that have emerged for their biocompatibility and biodegradability. To maximize site-selectivity and therapeutic efficacy, drug delivery systems should be functionalized with ligands which can specifically recognize and bind targets expressed by HCC, namely cell membrane associated antigens, receptors or biotransporters. Cell surface and intracellular molecular targets are exploited either to selectively deliver drug-loaded nanovehicles or to design novel selective therapeutics. In conclusion, the combination of novel and safe drug delivery strategies based on site-specific targeted drug nanovehicles with therapeutic molecular targets may significantly improve the pharmacological efficacy for the treatment of HCC.

Deciphering molecular mechanisms of arginine deiminase-based therapy - Comparative response analysis in paired human primary and recurrent glioblastomas

Arginine auxotrophy constitutes the Achilles' heel for several tumors, among them glioblastoma multiforme (GBM). Hence, arginine-depleting enzymes such as arginine deiminase (ADI) from Streptococcus pyogenes are promising for treatment of primary and maybe even refractory GBM. Based on our previous study in which ADI-susceptibility was shown on a panel of patient-derived GBM cell lines, we here aimed at deciphering underlying molecular mechanisms of ADI-mediated growth inhibition. We found that ADI (35 mU/mL) initially induces a cellular stress-response that is characterized by upregulation of genes primarily belonging to the heat-shock protein family. In addition to autophagocytosis, we show for the first time that senescence constitutes another cellular response mechanism upon ADI-treatment and that this bacterial enzyme is able to act as radiosensitizer (¼ cases). Long-term treatment schedules revealed no resistance development, with treated cells showing morphological signs of cell stress. Next, several combination strategies were employed to optimize ADI-based treatment. Simultaneous and sequential S. pyogenes ADI-based combinations included substances acting at different molecular pathways (curcumin, resveratrol, quinacrine, and sorafenib, 2 × 72 h treatment). Adding drugs to GBM cell lines (n = 4, including a matched pair of primary and recurrent GBM in one case) accelerated and potentiated ADI-mediated cytotoxicity. Autophagy was identified as the main cause of tumor growth inhibition. Of note, residual cells again showed classical signs of senescence in most combinations. Our results suggest an alternative treatment regimen for this fatal cancer type which circumvents many of the traditional barriers. Using the metabolic defect in GBM thus warrants further (pre-) clinical evaluation.

Targeting Metabolism for Cancer Therapy

Metabolic reprogramming contributes to tumor development and introduces metabolic liabilities that can be exploited to treat cancer. Chemotherapies targeting metabolism have been effective cancer treatments for decades, and the success of these therapies demonstrates that a therapeutic window exists to target malignant metabolism. New insights into the differential metabolic dependencies of tumors have provided novel therapeutic strategies to exploit altered metabolism, some of which are being evaluated in preclinical models or clinical trials. Here, we review our current understanding of cancer metabolism and discuss how this might guide treatments targeting the metabolic requirements of tumor cells.

A phase 1/1B trial of ADI-PEG 20 plus nab-paclitaxel and gemcitabine in patients with advanced pancreatic adenocarcinoma

BACKGROUND

ADI-PEG 20 is a pegylated form of the arginine-depleting enzyme arginine deiminase. Normal cells synthesize arginine with the enzyme argininosuccinate synthetase (ASS1); ADI-PEG 20 selectively targets malignant cells, which lack ASS1.

METHODS

A single-arm, nonrandomized, open-label, phase 1/1B, standard 3 + 3 dose escalation with an expansion cohort of 9 patients at the recommended phase 2 dose (RP2D) was conducted. Patients who had metastatic pancreatic cancer, up to 1 line of prior treatment (the dose-escalation cohort) or no prior treatment (the expansion cohort), and an Eastern Cooperative Oncology Group performance status of 0 to 1 were included. Patients received both gemcitabine (1000 mg/m² ) and nab-paclitaxel (125 mg/m² ) for 3 of 4 weeks and intramuscular ADI-PEG 20 at 18 mg/m² weekly (cohort 1) or at 36 mg/m² weekly (cohort 2 and the expansion cohort).The primary endpoint was to determine the maximum tolerated dose and RP2D of ADI-PEG 20 in combination with nab-paclitaxel and gemcitabine.

RESULTS

Eighteen patients were enrolled. No dose-limiting toxicities (DLTs) were observed in cohort 1; cohort 2 was expanded to 6 patients because of 1 DLT occurrence (a grade 3 elevation in bilirubin, aspartate aminotransferase, and alanine aminotransferase). The most frequent adverse events (AEs) of any grade were neutropenia, thrombocytopenia, leukopenia, anemia, peripheral neuropathy, and fatigue; all 18 patients experienced grade 3/4 AEs. The most frequent grade 3/4 toxicities, regardless of the relation with any drugs, included neutropenia (12 patients or 67%), leukopenia (10 patients or 56%), anemia (8 patients or 44%), and lymphopenia (6 patients or 33%). The RP2D for ADI-PEG 20 was 36 mg/m² weekly in combination with standard-dose gemcitabine and nab-paclitaxel. The overall response rate among patients treated at the RP2D in the first-line setting was 45.5% (5 of 11).The median progression-free survival time for these patients treated at the RP2D was 6.1 months (95% confidence interval, 5.3-11.2 months), and the median overall survival time was 11.3 months (95% confidence interval, 6.7 months to not reached).

CONCLUSIONS

ADI-PEG 20 was well tolerated in combination with gemcitabine and nab-paclitaxel. Activity was observed in previously treated and untreated patients with advanced pancreatic cancer and in patients with ASS1-deficient and -proficient tumors. Cancer 2017;123:4556-4565. © 2017 American Cancer Society.

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.

Phase 1 Dose-Escalation Study of Pegylated Arginine Deiminase, Cisplatin, and Pemetrexed in Patients With Argininosuccinate Synthetase 1-Deficient Thoracic Cancers

Purpose Pegylated arginine deiminase (ADI-PEG 20) depletes essential amino acid levels in argininosuccinate synthetase 1 (ASS1) -negative tumors by converting arginine to citrulline and ammonia. The main aim of this study was to determine the recommended dose, safety, and tolerability of ADI-PEG 20, cisplatin, and pemetrexed in patients with ASS1-deficient malignant pleural mesothelioma (MPM) or non-small-cell lung cancer (NSCLC). Patients and Methods Using a 3 + 3 + 3 dose-escalation study, nine chemotherapy-naïve patients (five MPM, four NSCLC) received weekly ADI-PEG 20 doses of 18 mg/m2, 27 mg/m2, or 36 mg/m2, together with pemetrexed 500 mg/m2 and cisplatin 75 mg/m2 which were given every three weeks (maximum of six cycles). Patients achieving stable disease or better could continue ADI-PEG 20 monotherapy until disease progression or withdrawal. Adverse events were assessed by Common Terminology Criteria for Adverse Events version 4.03, and pharmacodynamics and immunogenicity were also evaluated. Tumor response was assessed by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 for NSCLC and by modified RECIST criteria for MPM. Results No dose-limiting toxicities were reported; nine of 38 reported adverse events (all grade 1 or 2) were related to ADI-PEG 20. Circulating arginine concentrations declined rapidly, and citrulline levels increased; both changes persisted at 18 weeks. Partial responses were observed in seven of nine patients (78%), including three with either sarcomatoid or biphasic MPM. Conclusion Target engagement with depletion of arginine was maintained throughout treatment with no dose-limiting toxicities. In this biomarker-selected group of patients with ASS1-deficient cancers, clinical activity was observed in patients with poor-prognosis tumors. Therefore, we recommend a dose for future studies of weekly ADI-PEG 20 36 mg/m2 plus three-weekly cisplatin 75 mg/m2 and pemetrexed 500 mg/m2.

Stem cell, biomaterials and growth factors therapy for hepatocellular carcinoma

Hepatocellular carcinoma is an antecedent of liver illnesses, including viral hepatitis, alcohol abuse, or metabolic disease. Transforming growth factor-Beta (TGF-b) plays an important role in creating a favorable microenvironment for tumor cell growth via two major mechanisms: an intrinsic activity as an autocrine growth factor and an extrinsic activity by inducing microenvironment changes. Recently stem cell therapy as also been a promising and potential treatment for liver cancer and in addition signaling pathways like GF/GFR systems, SDF-1α/CXC4 ligand receptor interaction and PI3K/Akt signaling, and cytokines has been identified to regulate cell fate decisions, and can be utilized to positively influence cell therapy outcomes. Thus stem cell-based therapy, together with signaling pathways can become a practical option in regenerative processes for replacing dead hepatocytes cells. Targeted drug delivery systems (TDDS) via biomaterials are presently been explored for cancer therapeutics especially liver cancer as it allows the enhancement of drug concentration in the liver and decrease the dosage and side effects. This review is intended to give a comprehensive summary of available liver cancer therapy using stem cells, growth factor and biomaterials.

Arginine Deprivation Inhibits the Warburg Effect and Upregulates Glutamine Anaplerosis and Serine Biosynthesis in ASS1-Deficient Cancers

Targeting defects in metabolism is an underutilized strategy for the treatment of cancer. Arginine auxotrophy resulting from the silencing of argininosuccinate synthetase 1 (ASS1) is a common metabolic alteration reported in a broad range of aggressive cancers. To assess the metabolic effects that arise from acute and chronic arginine starvation in ASS1-deficient cell lines, we performed metabolite profiling. We found that pharmacologically induced arginine depletion causes increased serine biosynthesis, glutamine anaplerosis, oxidative phosphorylation, and decreased aerobic glycolysis, effectively inhibiting the Warburg effect. The reduction of glycolysis in cells otherwise dependent on aerobic glycolysis is correlated with reduced PKM2 expression and phosphorylation and upregulation of PHGDH. Concurrent arginine deprivation and glutaminase inhibition was found to be synthetic lethal across a spectrum of ASS1-deficient tumor cell lines and is sufficient to cause in vivo tumor regression in mice. These results identify two synthetic lethal therapeutic strategies exploiting metabolic vulnerabilities of ASS1-negative cancers.

Argininosuccinate lyase interacts with cyclin A2 in cytoplasm and modulates growth of liver tumor cells

Arginine is a critical amino acid in specific cancer types including hepatocellular carcinoma (HCC) and melanoma. Novel molecular mechanisms and therapeutic targets in arginine metabolism-mediated cancer formation await further identification. Our laboratory has previously demonstrated that arginine metabolic enzyme argininosuccinate lyase (ASL) promoted HCC formation in part via maintenance of cyclin A2 protein expression and arginine production for channeling to nitric oxide synthase. In this study, we investigated the mechanism by which ASL regulates cyclin A2 expression. We found that ASL interacted with cyclin A2 in HCC cells and the localization of their interaction was in the cytoplasm. Mutation of essential residues for enzymatic activity of ASL did not affect the binding of ASL to cyclin A2. Moreover, the mutant ASL retained the ability to restore the decreased tumorigenicity caused by ASL shRNA. Furthermore, overexpression of ASL conferred resistance to arginine deprivation therapy. Finally, the important pathways and potential therapeutic targets in ASL-regulated HCC were identified by bioinformatics analyses with Metacore database and Connectivity Map database. Our analyses suggested that bisoprolol, celecoxib, and ipratropium bromide, are potential therapeutics for ASL-regulated HCC formation. Thus, ASL interacts with cyclin A2 in cytoplasm, and may promote HCC formation through this non-enzymatic function. Overexpression of ASL may be a contributing factor in drug resistance for arginine deprivation therapy.

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

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

Targeting Cancer Metabolism: Dietary and Pharmacologic Interventions

Most tumors display oncogene-driven reprogramming of several metabolic pathways, which are crucial to sustain their growth and proliferation. In recent years, both dietary and pharmacologic approaches that target deregulated tumor metabolism are beginning to be considered for clinical applications. Dietary interventions exploit the ability of nutrient-restricted conditions to exert broad biological effects, protecting normal cells, organs, and systems, while sensitizing a wide variety of cancer cells to cytotoxic therapies. On the other hand, drugs targeting enzymes or metabolites of crucial metabolic pathways can be highly specific and effective, but must be matched with a responsive tumor, which might rapidly adapt. In this review, we illustrate how dietary and pharmacologic therapies differ in their effect on tumor growth, proliferation, and metabolism and discuss the available preclinical and clinical evidence in favor of or against each of them. We also indicate, when appropriate, how to optimize future investigations on metabolic therapies on the basis of tumor- and patient-related characteristics.

SIGNIFICANCE

To our knowledge, this is the first review article that comprehensively analyzes the preclinical and preliminary clinical experimental foundations of both dietary and pharmacologic metabolic interventions in cancer therapy. Among several promising therapies, we propose treatment personalization on the basis of tumor genetics, tumor metabolism, and patient systemic metabolism.Cancer Discov; 6(12); 1315-33. ©2016 AACR.

Arginine-Dual roles as an onconutrient and immunonutrient

Arginine is an important player in numerous biologic processes and studies have demonstrated its importance for cellular growth that becomes limiting in states of rapid turnover (e.g., malignancy). Thus, arginine deprivation therapy is being examined as an adjuvant cancer therapy, however, arginine is also necessary for immune destruction of malignant cells. Herein we review the data supporting arginine deprivation or supplementation in cancer treatment and the currently registered trials aimed at understanding these divergent strategies. J. Surg. Oncol. 2017;115:273-280. © 2016 Wiley Periodicals, Inc.

A metabolic synthetic lethal strategy with arginine deprivation and chloroquine leads to cell death in ASS1-deficient sarcomas

Sarcomas comprise a large heterogeneous group of mesenchymal cancers with limited therapeutic options. When treated with standard cytotoxic chemotherapies, many sarcomas fail to respond completely and rapidly become treatment resistant. A major problem in the investigation and treatment of sarcomas is the fact that no single gene mutation or alteration has been identified among the diverse histologic subtypes. We searched for therapeutically druggable targets that are common to a wide range of histologies and hence could provide alternatives to the conventional chemotherapy. Seven hundred samples comprising 45 separate histologies were examined. We found that almost 90% were arginine auxotrophs, as the expression of argininosuccinate synthetase 1 was lost or significantly reduced. Arginine auxotrophy confers sensitivity to arginine deprivation, leading temporarily to starvation and ultimately to cell survival or death under different circumstances. We showed that, in sarcoma, arginine deprivation therapy with pegylated arginine deiminase (ADI-PEG20) maintains a prolonged state of arginine starvation without causing cell death. However, when starvation was simultaneously prolonged by ADI-PEG20 while inhibited by the clinically available drug chloroquine, sarcoma cells died via necroptosis and apoptosis. These results have revealed a novel metabolic vulnerability in sarcomas and provided the basis for a well-tolerated alternative treatment strategy, potentially applicable to up to 90% of the tumors, regardless of histology.

Inhibition of the Polyamine Synthesis Pathway Is Synthetically Lethal with Loss of Argininosuccinate Synthase 1

Argininosuccinate synthase 1 (ASS1) is the rate-limiting enzyme for arginine biosynthesis. ASS1 expression is lost in a range of tumor types, including 50% of malignant pleural mesotheliomas. Starving ASS1-deficient cells of arginine with arginine blockers such as ADI-PEG20 can induce selective lethality and has shown great promise in the clinical setting. We have generated a model of ADI-PEG20 resistance in mesothelioma cells. This resistance is mediated through re-expression of ASS1 via demethylation of the ASS1 promoter. Through coordinated transcriptomic and metabolomic profiling, we have shown that ASS1-deficient cells have decreased levels of acetylated polyamine metabolites, together with a compensatory increase in the expression of polyamine biosynthetic enzymes. Upon arginine deprivation, polyamine metabolites are decreased in the ASS1-deficient cells and in plasma isolated from ASS1-deficient mesothelioma patients. We identify a synthetic lethal dependence between ASS1 deficiency and polyamine metabolism, which could potentially be exploited for the treatment of ASS1-negative cancers.

Novel drugs that target the metabolic reprogramming in renal cell cancer

Molecular profiling studies of tumor tissue from patients with clear cell renal cell cancer (ccRCC) have revealed extensive metabolic reprogramming in this disease. Associations were found between metabolic reprogramming, histopathologic Fuhrman grade, and overall survival of patients. Large-scale genomics, proteomics, and metabolomic analyses have been performed to identify the molecular players in this process. Genes involved in glycolysis, the pentose phosphate pathway, glutamine metabolism, and lipogenesis were found to be upregulated in renal cell cancer (RCC) specimens as compared to normal tissue. Preclinical research indicates that mutations in VHL, FBP1, and the PI3K-AKT-mTOR pathway drives aerobic glycolysis through transcriptional activation of the hypoxia-inducible factors (HIF). Mechanistic studies revealed glutamine as an important source for de novo fatty acid synthesis through reductive carboxylation. Amplification of MYC drives reductive carboxylation. In this review, we present a detailed overview of the metabolic changes in RCC in conjunction with potential novel therapeutics. We discuss preclinical studies that have investigated targeted agents that interfere with various aspects of tumor cell metabolism and emphasize their impact specifically on glycolysis, lipogenesis, and tumor growth. Furthermore, we describe a number of phase 1 and 2 clinical trials that have been conducted with these agents.

Oncogene-directed alterations in cancer cell metabolism

Oncogenes are key drivers of tumor growth. Although several cancer-driving mechanisms have been identified, the role of oncogenes in shaping metabolic patterns in cancer cells is only beginning to be appreciated. Recent studies show that oncogenes directly regulate critical metabolic enzymes and metabolic signaling pathways. Here, we present evidence for oncogene-directed cancer metabolic regulation and discuss the importance of identifying underlying mechanisms that can be targeted for developing precision cancer therapies.

Decreased miR122 in hepatocellular carcinoma leads to chemoresistance with increased arginine

Reduced expression of microRNA122 (miR122), a liver-specific microRNA, is frequent in hepatocellular carcinoma (HCC). However, its biological significances remain poorly understood. Because deregulated amino acid levels in cancers can affect their biological behavior, we determined the amino acid levels in miR122-silenced mouse liver tissues, in which intracellular arginine levels were significantly increased. The increased intracellular arginine levels were through upregulation of the solute carrier family 7 (SLC7A1), a transporter of arginine and a direct target of miR122. Arginine is the substrate for nitric oxide (NO) synthetase, and intracellular NO levels were increased in miR122-silenced HCC cells, with increased resistance to sorafenib, a multikinase inhibitor. Conversely, maintenance of the miR122-silenced HCC cells in arginine-depleted culture media, as well as overexpression of miR122 in miR122-low-expressing HCC cells, reversed these effects and rendered the cells more sensitive to sorafenib. Using a reporter knock-in construct, chemical compounds were screened, and Wee1 kinase inhibitor was identified as upregulators of miR122 transcription, which increased the sensitivity of the cells to sorafenib. These results provide an insight into sorafenib resistance in miR122-low HCC, and suggest that arginine depletion or a combination of sorafenib with the identified compound may provide promising approaches to managing this HCC subset.

Arginine dependence of tumor cells: targeting a chink in cancer's armor

Arginine, one among the 20 most common natural amino acids, has a pivotal role in cellular physiology as it is being involved in numerous cellular metabolic and signaling pathways. Dependence on arginine is diverse for both tumor and normal cells. Because of decreased expression of argininosuccinate synthetase and/or ornithine transcarbamoylase, several types of tumor are auxotrophic for arginine. Deprivation of arginine exploits a significant vulnerability of these tumor cells and leads to their rapid demise. Hence, enzyme-mediated arginine depletion is a potential strategy for the selective destruction of tumor cells. Arginase, arginine deiminase and arginine decarboxylase are potential enzymes that may be used for arginine deprivation therapy. These arginine catabolizing enzymes not only reduce tumor growth but also make them susceptible to concomitantly administered anti-cancer therapeutics. Most of these enzymes are currently under clinical investigations and if successful will potentially be advanced as anti-cancer modalities.

Use of response surface method for maximizing the production of arginine deiminase by Pseudomonas putida

•

First report on Arginine deiminase production from Pseudomonas putida using RSM.

•

Optimum conditions for ADI production were established in shake flasks.

•

ADI production was assessed in a 14 L bioreactor under the optimized conditions.

•

Repressor effect of aeration on ADI production was observed in 14 L bioreactor.

•

Substantial improvement of 4.5-folds in ADI titre was achieved.

Statistically designed experiments were used to optimize the production of arginine deiminase (ADI) by Pseudomonas putida KT2440 in batch culture. A Plackett-Burman design involving eleven factors showed that ADI production was most influenced by the initial pH and the initial concentrations of glucose and yeast extract. A central composite experimental design showed that the optimal values of these factors were 8.0, 10 g/L and 12.5 g/L, respectively. The other components of the optimal culture medium were bacto peptone 7.5 g/L, Triton X–100 0.30% (v/v), and arginine 3 g/L, for a culture temperature of 25 °C. Compared with the basal medium, the ADI activity in the optimized medium had nearly 4.5-fold increase (4.31 U/mL). The optimized medium was then used for a further study of ADI production in a 14 L stirred tank bioreactor. The agitation speed and the aeration rates were varied to determine suitable values of these variables.

Arginine starvation in colorectal carcinoma cells: Sensing, impact on translation control and cell cycle distribution

Tumor cells rely on a continued exogenous nutrient supply in order to maintain a high proliferative activity. Although a strong dependence of some tumor types on exogenous arginine sources has been reported, the mechanisms of arginine sensing by tumor cells and the impact of changes in arginine availability on translation and cell cycle regulation are not fully understood. The results presented herein state that human colorectal carcinoma cells rapidly exhaust the internal arginine sources in the absence of exogenous arginine and repress global translation by activation of the GCN2-mediated pathway and inhibition of mTOR signaling. Tumor suppressor protein p53 activation and G1/G0 cell cycle arrest support cell survival upon prolonged arginine starvation. Cells with the mutant or deleted TP53 fail to stop cell cycle progression at defined cell cycle checkpoints which appears to be associated with reduced recovery after durable metabolic stress triggered by arginine withdrawal.

Selective Intracellular Delivery of Recombinant Arginine Deiminase (ADI) Using pH-Sensitive Cell Penetrating Peptides To Overcome ADI Resistance in Hypoxic Breast Cancer Cells

Arginine depletion strategies, such as pegylated recombinant arginine deiminase (ADI-PEG20), offer a promising anticancer treatment. Many tumor cells have suppressed expression of a key enzyme, argininosuccinate synthetase 1 (ASS1), which converts citrulline to arginine. These tumor cells become arginine auxotrophic, as they can no longer synthesize endogenous arginine intracellularly from citrulline, and are therefore sensitive to arginine depletion therapy. However, since ADI-PEG20 only depletes extracellular arginine due to low internalization, ASS1-expressing cells are not susceptible to treatment since they can synthesize arginine intracellularly. Recent studies have found that several factors influence ASS1 expression. In this study, we evaluated the effect of hypoxia, frequently encountered in many solid tumors, on ASS1 expression and its relationship to ADI-resistance in human MDA-MB-231 breast cancer cells. It was found that MDA-MB-231 cells developed ADI resistance in hypoxic conditions with increased ASS1 expression. To restore ADI sensitivity as well as achieve tumor-selective delivery under hypoxia, we constructed a pH-sensitive cell penetrating peptide (CPP)-based delivery system to carry ADI inside cells to deplete both intra- and extracellular arginine. The delivery system was designed to activate the CPP-mediated internalization only at the mildly acidic pH (6.5-7) associated with the microenvironment of hypoxic tumors, thus achieving better selectivity toward tumor cells. The pH sensitivity of the CPP HBHAc was controlled by recombinant fusion to a histidine-glutamine (HE) oligopeptide, generating HBHAc-HE-ADI. The tumor distribution of HBHAc-HE-ADI was comparable to ADI-PEG20 in a mouse xenograft model of human breast cancer cells in vivo. In addition, HBHAc-HE-ADI showed increased in vitro cellular uptake in cells incubated in a mildly acidic pH (hypoxic conditions) compared to normal pH (normoxic conditions), which correlated with pH-sensitive in vitro cytotoxicity in hypoxic MDA-MB-231 and human prostate cancer PC3 cells. Together, we conclude that the HBHAc-HE-based peptide delivery offers a useful means to overcome hypoxia-induced resistance to ADI in breast cancer cells, and to target the mildly acidic tumor microenvironment.

Targeting amino acid metabolism in cancer growth and anti-tumor immune response

Recent advances in amino acid metabolism have revealed that targeting amino acid metabolic enzymes in cancer therapy is a promising strategy for the development of novel therapeutic agents. There are currently several drugs in clinical trials that specifically target amino acid metabolic pathways in tumor cells. In the context of the tumor microenvironment, however, tumor cells form metabolic relationships with immune cells, and they often compete for common nutrients. Many tumors evolved to escape immune surveillance by taking advantage of their metabolic flexibility and redirecting nutrients for their own advantage. This review outlines the most recent advances in targeting amino acid metabolic pathways in cancer therapy while giving consideration to the impact these pathways may have on the anti-tumor immune response.

Therapeutic interventions to disrupt the protein synthetic machinery in melanoma

Control of the protein synthetic machinery is deregulated in many cancers, including melanoma, to increase the protein production. Tumor suppressors and oncogenes play key roles in protein synthesis from the transcription of rRNA and ribosome biogenesis to mRNA translation initiation and protein synthesis. Major signaling pathways are altered in melanoma to modulate the protein synthetic machinery, thereby promoting tumor development. However, despite the importance of this process in melanoma development, involvement of the protein synthetic machinery in this cancer type is an underdeveloped area of study. Here, we review the coupling of melanoma development to deregulation of the protein synthetic machinery. We examine existing knowledge regarding RNA polymerase I inhibition and mRNA translation focusing on their inhibition for therapeutic applications in melanoma. Furthermore, the contribution of amino acid biosynthesis and involvement of ribosomal proteins are also reviewed as future therapeutic strategies to target deregulated protein production in melanoma.

Arginine deprivation using pegylated arginine deiminase has activity against primary acute myeloid leukemia cells in vivo

The strategy of enzymatic degradation of amino acids to deprive malignant cells of important nutrients is an established component of induction therapy of acute lymphoblastic leukemia. Here we show that acute myeloid leukemia (AML) cells from most patients with AML are deficient in a critical enzyme required for arginine synthesis, argininosuccinate synthetase-1 (ASS1). Thus, these ASS1-deficient AML cells are dependent on importing extracellular arginine. We therefore investigated the effect of plasma arginine deprivation using pegylated arginine deiminase (ADI-PEG 20) against primary AMLs in a xenograft model and in vitro. ADI-PEG 20 alone induced responses in 19 of 38 AMLs in vitro and 3 of 6 AMLs in vivo, leading to caspase activation in sensitive AMLs. ADI-PEG 20-resistant AMLs showed higher relative expression of ASS1 than sensitive AMLs. This suggests that the resistant AMLs survive by producing arginine through this metabolic pathway and ASS1 expression could be used as a biomarker for response. Sensitive AMLs showed more avid uptake of arginine from the extracellular environment consistent with their auxotrophy for arginine. The combination of ADI-PEG 20 and cytarabine chemotherapy was more effective than either treatment alone resulting in responses in 6 of 6 AMLs tested in vivo. Our data show that arginine deprivation is a reasonable strategy in AML that paves the way for clinical trials.

Arginine depletion by arginine deiminase does not affect whole protein metabolism or muscle fractional protein synthesis rate in mice

Due to the absolute need for arginine that certain cancer cells have, arginine depletion is a therapy in clinical trials to treat several types of cancers. Arginine is an amino acids utilized not only as a precursor for other important molecules, but also for protein synthesis. Because arginine depletion can potentially exacerbate the progressive loss of body weight, and especially lean body mass, in cancer patients we determined the effect of arginine depletion by pegylated arginine deiminase (ADI-PEG 20) on whole body protein synthesis and fractional protein synthesis rate in multiple tissues of mice. ADI-PEG 20 successfully depleted circulating arginine (<1 μmol/L), and increased citrulline concentration more than tenfold. Body weight and body composition, however, were not affected by ADI-PEG 20. Despite the depletion of arginine, whole body protein synthesis and breakdown were maintained in the ADI-PEG 20 treated mice. The fractional protein synthesis rate of muscle was also not affected by arginine depletion. Most tissues (liver, kidney, spleen, heart, lungs, stomach, small and large intestine, pancreas) were able to maintain their fractional protein synthesis rate; however, the fractional protein synthesis rate of brain, thymus and testicles was reduced due to the ADI-PEG 20 treatment. Furthermore, these results were confirmed by the incorporation of ureido [14C]citrulline, which indicate the local conversion into arginine, into protein. In conclusion, the intracellular recycling pathway of citrulline is able to provide enough arginine to maintain protein synthesis rate and prevent the loss of lean body mass and body weight.

Phase I Trial of Arginine Deprivation Therapy with ADI-PEG 20 Plus Docetaxel in Patients with Advanced Malignant Solid Tumors

PURPOSE

This phase I study examined the toxicity and tolerability of pegylated arginine deiminase (ADI-PEG 20) in combination with docetaxel in patients with advanced solid malignancies.

EXPERIMENTAL DESIGN

Eligible patients had histologically proven advanced solid malignancies, with any number of prior therapies, Zubrod performance status 0-2, and adequate organ function. Patients received ADI-PEG 20 weekly intramuscular injection ranging from 4.5 to 36 mg/m(2) and up to 10 doses of docetaxel (75 mg/m(2)) every 3 weeks. Primary endpoints were safety, toxicity, and a recommended phase II dose. Circulating arginine levels were measured before each cycle. Tumor response was measured as a secondary endpoint every 6 weeks on study.

RESULTS

Eighteen patients received a total of 116 cycles of therapy through four dose levels of ADI-PEG 20. A single dose-limiting toxicity (grade 3 urticarial rash) was observed at the 1st dose level, with no additional dose-limiting toxicities observed. Hematologic toxicities were common with 14 patients experiencing at least one grade 3 to 4 leukopenia. Fatigue was the most prevalent toxicity reported by 16 patients. Arginine was variably suppressed with 10 patients achieving at least a 50% reduction in baseline values. In 14 patients with evaluable disease, four partial responses (including 2 patients with PSA response) were documented, and 7 patients had stable disease.

CONCLUSIONS

ADI-PEG 20 demonstrated reasonable toxicity in combination with docetaxel. Promising clinical activity was noted, and expansion cohorts are now accruing for both castrate-resistant prostate cancer and non-small cell lung cancer at a recommended phase II dose of 36 mg/m(2).

Purification, immobilization, and biochemical characterization of l-arginine deiminase from thermophilic Aspergillus fumigatus KJ434941: anticancer activity in vitro

l-Arginine deiminase (ADI) has a powerful anticancer activity against various tumors, via arginine depletion, arresting the cell cycle at G1 phase. However, the current clinically tried bacterial ADI displayed a higher antigenicity and lower thermal stability. Thus, our objective was to purify and characterize this enzyme from thermophilic fungi, to explore its catalytic and antigenic properties for therapeutic uses. ADI was purified from thermophilic Aspergillus fumigatus KJ434941 to its electrophoretic homogeneity by 5.1-fold, with molecular subunit 50 kDa. The purified ADI was PEGylated and covalently immobilized on dextran to explore its catalytic properties. The specific activity of free ADI, PEG-ADI, and Dex-ADI was 26.7, 21.5, and 18.0 U/mg, respectively. At 50°C, PEG-ADI displays twofold resistance to thermal denaturation (t1/2 13.9 h), than free ADI (t1/2 6.9 h), while at 70°C, the thermal stability of PEG-ADI was increased by 1.7-fold, with similar stability to Dex-ADI with the free one. Kinetically, free ADI had the higher catalytic affinity to arginine, followed by PEG-ADI and Dex-ADI. Upon proteolysis for 30 min, the residual activity of native ADI, PEG-ADI, and Dex-AD was 8.0, 32.0, and 20.0% for proteinase K and 10.0, 52.0, and 90.0% for acid protease, respectively. The anticancer activity of the ADIs was assessed against HCT, HEP-G2, and MCF7, in vitro. The free and PEG-ADI exhibits a similar cytotoxic efficacy for the tested cells, lower than Dex-ADI. The free ADI had IC50 value 22.0, 16.6, and 13.9 U/mL, while Dex-ADI had 3.98, 5.18, and 4.43 U/mL for HCT, MCF7, and HEPG-2, respectively. The in vitro anticancer activity of ADI against HCT, MCF7, and HEPG-2 was increased by five-, three-, and threefold upon covalent modification by dextran. The biochemical and hematological parameters of the experimented animals were not affected by ADIs dosing, with no signs of anti-ADI immunoglobulins in vivo. The in vivo half-life time of free ADI, PEG-ADI, and Dex-ADI was 29.7, 91.1, 59.6 h, respectively. The present findings explored a novel thermostable, less antigenic ADI from thermophilic A. fumigatus, with further molecular and crystallographic analyses, this enzyme will be a powerful candidate for clinical trials.

Arginine deprivation in cancer therapy

PURPOSE OF REVIEW

There has been an increased and renewed interest in metabolic therapy for cancer, particularly Arg deprivation. The purpose of this review is to highlight recent studies that focus on Arg-dependent malignancies with Arginine (Arg)-degrading enzymes, including arginase and Arg deiminase.

RECENT FINDINGS

New developments in this area include understanding of the role of most significantly downregulated gene regulating amino acid metabolism, argininosuccinate synthetase and its expression and therapeutic relevance in different tumors. Recent studies have also shed light on the mechanism of tumor cell death with Arg deprivation, with arginase and pegylated Arg deiminase. Particularly important is understanding the mechanism of resistance that cancers develop after such drug exposure. Finally, recent clinical trials have been performed or are ongoing to use Arg deprivation as treatment for advanced malignancies.

SUMMARY

Arg deprivation is a promising approach for the treatment of various malignancies.

Investigational cancer drugs targeting cell metabolism in clinical development

Introduction: Malignant cell transformation and tumor progression are associated with alterations in glycolysis, fatty acid synthesis, amino acid delivery and production of reactive oxygen species. With increased understanding of the role of metabolism in tumors, there has been interest in developing agents that target tumor specific metabolic pathways. Numerous promising agents targeting altered metabolic pathways are currently in Phase I - III clinical trials. Areas covered: This paper reviews the early phase clinical trial development of these agents and provides perspective on the future direction of this emerging field. Specifically, the authors describe novel and repurposed therapies, focusing on the effects of each agent on tumor metabolism and results from relevant Phase I and II clinical trials. Expert opinion: Metabolism modulating agents, alone and in combinations with other classes of agents, have shown efficacy in the treatment of neoplasm, which, the authors believe, will bear positive results in future studies. Because of the significant crosstalk between metabolic pathways and oncogenic signaling pathways, the authors also believe that combining metabolic modifiers with targeted agents will be an important strategy. An increased understanding of cancer metabolism, in addition to the continued study of metabolic modulators, should lead to further advances in this nascent therapeutic field in the future.

Nanomedicine in cancer therapy: challenges, opportunities, and clinical applications

Cancer is a leading cause of death worldwide. Currently available therapies are inadequate and spur demand for improved technologies. Rapid growth in nanotechnology towards the development of nanomedicine products holds great promise to improve therapeutic strategies against cancer. Nanomedicine products represent an opportunity to achieve sophisticated targeting strategies and multi-functionality. They can improve the pharmacokinetic and pharmacodynamic profiles of conventional therapeutics and may thus optimize the efficacy of existing anti-cancer compounds. In this review, we discuss state-of-the-art nanoparticles and targeted systems that have been investigated in clinical studies. We emphasize the challenges faced in using nanomedicine products and translating them from a preclinical level to the clinical setting. Additionally, we cover aspects of nanocarrier engineering that may open up new opportunities for nanomedicine products in the clinic.

Blocking autophagy enhanced cytotoxicity induced by recombinant human arginase in triple-negative breast cancer cells

Depletion of arginine by recombinant human arginase (rhArg) has proven to be an effective cancer therapeutic approach for a variety of malignant tumors. Triple-negative breast cancers (TNBCs) lack of specific therapeutic targets, resulting in poor prognosis and limited therapeutic efficacy. To explore new therapeutic approaches for TNBC we studied the cytotoxicity of rhArg in five TNBC cells. We found that rhArg could inhibit cell growth in these five TNBC cells. Intriguingly, accumulation of autophagosomes and autophagic flux was observed in rhArg-treated MDA-MB-231 cells. Inhibition of autophagy by chloroquine (CQ), 3-methyladenine (3-MA) and siRNA targeting Beclin1 significantly enhanced rhArg-induced cytotoxic effect, indicating the cytoprotective role of autophagy in rhArg-induced cell death. In addition, N-acetyl-l-cysteine (NAC), a common antioxidant, blocked autophagy induced by rhArg, suggesting that reactive oxygen species (ROS) had an essential role in the cytotoxicity of rhArg. This study provides new insights into the molecular mechanism of autophagy involved in rhArg-induced cytotoxicity in TNBC cells. Meanwhile, our results revealed that rhArg, either alone or in combination with autophagic inhibitors, might be a potential novel therapy for the treatment of TNBC.

Down-regulation of argininosuccinate synthetase is associated with cisplatin resistance in hepatocellular carcinoma cell lines: implications for PEGylated arginine deiminase combination therapy

Background

Many advanced human tumors, including hepatocellular carcinomas (HCC) are auxotrophic for arginine due to down-regulation of argininosuccinate synthetase (ASS1), the rate-limiting enzyme in arginine synthesis. The arginine-lowering agent PEGylated arginine deiminase (ADI-PEG 20) has shown efficacy as a monotherapy in clinical trials for treating arginine-auxotrophic tumors and is currently being evaluated in combination with cisplatin in other cancer types. Epigenetic silencing via methylation of the ASS1 promoter has been previously demonstrated in other cancer types, and a reciprocal relationship between ASS1 expression and cisplatin resistance has also been observed in ovarian cancer. However, the mechanism of ASS1 down-regulation, as well as the correlation with cisplatin resistance has not been explored in HCC. The present study investigates ADI-PEG 20 and cisplatin sensitivities in relation to ASS1 expression in HCC. In addition, we show how this biomarker is regulated by cisplatin alone and in combination with ADI-PEG 20.

Methods

ASS1 protein expression in both untreated and drug treated human HCC cell lines was assessed by western blot. The correlation between ASS1 protein levels, ADI-PEG 20 sensitivity and cisplatin resistance in these cell lines was established using a luminescence-based cell viability assay. Epigenetic regulation of ASS1 was analyzed by bisulfite conversion and methylation-specific PCR.

Results

A good correlation between absence of ASS1 protein expression, ASS1 promoter methylation, sensitivity to ADI-PEG 20 and resistance to cisplatin in HCC cell lines was observed. In addition, cisplatin treatment down-regulated ASS1 protein expression in select HCC cell lines. While, at clinically relevant concentrations, the combination of ADI-PEG 20 and cisplatin restored ASS1 protein levels in most of the cell lines studied.

Conclusion

ASS1 silencing in HCC cell lines is associated with simultaneous cisplatin resistance and ADI-PEG 20 sensitivity which suggests a promising combination therapeutic strategy for the management of HCC.