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

Mechanisms of sunitinib resistance in renal cell carcinoma and associated opportunities for therapeutics

Sunitinib is the first-line drug for renal cell carcinoma (RCC) treatment. However, patients who received sunitinib treatment will ultimately develop drug resistance after 6-15 months, creating a huge obstacle to the current treatment of renal cell carcinoma. Therefore, it is urgent to clarify the mechanisms of sunitinib resistance and develop new strategies to overcome it. In this review, the mechanisms of sunitinib resistance in renal cell carcinoma have been summarized based on five topics: activation of bypass or alternative pathway, inadequate drug accumulation, tumour microenvironment, metabolic reprogramming and epigenetic regulation. Furthermore, present and potential biomarkers, as well as potential treatment strategies for overcoming sunitinib resistance in renal cell carcinoma, are also covered.

Multi-Omics Analysis Revealed a Significant Alteration of Critical Metabolic Pathways Due to Sorafenib-Resistance in Hep3B Cell Lines

Hepatocellular carcinoma (HCC) is the second prominent cause of cancer-associated death worldwide. Usually, HCC is diagnosed in advanced stages, wherein sorafenib, a multiple target tyrosine kinase inhibitor, is used as the first line of treatment. Unfortunately, resistance to sorafenib is usually encountered within six months of treatment. Therefore, there is a critical need to identify the underlying reasons for drug resistance. In the present study, we investigated the proteomic and metabolomics alterations accompanying sorafenib resistance in hepatocellular carcinoma Hep3B cells by employing ultra-high-performance liquid chromatography quadrupole time of flight mass spectrometry (UHPLC-QTOF-MS). The Bruker Human Metabolome Database (HMDB) library was used to identify the differentially abundant metabolites through MetaboScape 4.0 software (Bruker). For protein annotation and identification, the Uniprot proteome for Homo sapiens (Human) database was utilized through MaxQuant. The results revealed that 27 metabolites and 18 proteins were significantly dysregulated due to sorafenib resistance in Hep3B cells compared to the parental phenotype. D-alanine, L-proline, o-tyrosine, succinic acid and phosphatidylcholine (PC, 16:0/16:0) were among the significantly altered metabolites. Ubiquitin carboxyl-terminal hydrolase isozyme L1, mitochondrial superoxide dismutase, UDP-glucose-6-dehydrogenase, sorbitol dehydrogenase and calpain small subunit 1 were among the significantly altered proteins. The findings revealed that resistant Hep3B cells demonstrated significant alterations in amino acid and nucleotide metabolic pathways, energy production pathways and other pathways related to cancer aggressiveness, such as migration, proliferation and drug-resistance. Joint pathway enrichment analysis unveiled unique pathways, including the antifolate resistance pathway and other important pathways that maintain cancer cells' survival, growth, and proliferation. Collectively, the results identified potential biomarkers for sorafenib-resistant HCC and gave insights into their role in chemotherapeutic drug resistance, cancer initiation, progression and aggressiveness, which may contribute to better prognosis and chemotherapeutic outcomes.

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.

Targeting purine synthesis in ASS1-expressing tumors enhances the response to immune checkpoint inhibitors

Argininosuccinate synthase (ASS1) downregulation in different tumors has been shown to support cell proliferation and yet, in several common cancer subsets ASS1 expression associates with poor patient prognosis. Here we demonstrate that ASS1 expression under glucose deprivation is induced by c-MYC, providing survival benefit by increasing nitric oxide synthesis and activating the gluconeogenic enzymes pyruvate carboxylase and phosphoenolpyruvate carboxykinase by S-nitrosylation. The resulting increased flux through gluconeogenesis enhances serine, glycine and subsequently purine synthesis. Notably, high ASS1-expressing breast cancer mice do not respond to immune checkpoint inhibitors and patients with breast cancer with high ASS1 have more metastases. We further find that inhibiting purine synthesis increases pyrimidine to purine ratio, elevates expression of the immunoproteasome and significantly enhances the response of autologous primary CD8⁺ T cells to anti-PD-1. These results suggest that treating patients with high-ASS1 cancers with purine synthesis inhibition is beneficial and may also sensitize them to immune checkpoint inhibition therapy.

Metabolic pathways of L-arginine and therapeutic consequences in tumors

Difference in the metabolism of normal and cancer cells inspires to search for new, more specific and less toxic therapies than those currently used. The development of tumors is conditioned by genetic changes in cancer-transformed cells, immunological tolerance and immunosuppression. At the initial stages of carcinogenesis, the immune system shows anti-tumor activity, however later, cancer disrupts the function of Th1/Th17/Th2 lymphocytes by regulatory T (Treg) cells, tumor-associated macrophages (TAMs), and myeloid-derived suppressor cells (MDSCs) and finally causes immunosuppression. Recently, much attention has been devoted to the influence of l-arginine metabolism disorders on both carcinogenesis and the immune system. l-Arginine is essential for the maturation of the T cell receptor zeta (TCRζ), and its absence deprives T-cells of the ability to interact with tumor antigens. MDSCs deplete l-arginine due to a high expression of arginase 1 (ARG1) and their number increases 4-10 times depending on the type of the cancer. L-Arginine has been shown to be essential for the survival and progression of arginine auxotrophic tumors. However, the progression of arginine non-auxotrophic tumors is independent of exogenous l-arginine, because these tumors have arginine-succinate synthetase (ASS1) activity and are available to produce l-arginine from citrulline. Clinical studies have confirmed the high efficacy of arginine auxotrophic tumors therapy based on the elimination of l-arginine. However, l-arginine supplementation may improve the results of treatment of patients with arginine non-auxotrophic cancer. This review is an attempt to explain the seemingly contradictory results of oncological therapies based on the deprivation or supplementation of l-arginine.

Low-Dose Radiation Enhanced Inhibition of Breast Tumor Xenograft and Reduced Myocardial Injury Induced by Doxorubicin

We reported that low-dose radiation (LDR) alleviated cardiotoxicity of doxorubicin (DOX) via inhibiting myocardial cell apoptosis and oxidative stress in vivo. Here, we tested whether LDR could enhance chemotherapeutic effect of DOX and alleviate myocardial injury induced by DOX by observing cell proliferation, apoptosis, and metastasis of heterotopic tumor in vivo. Mice implanted with 4T1 breast carcinoma cells were given 7.5 mg/kg DOX or 0.9% NaCl solution 72 hours after LDR (0 or 75 mGy). The histology of tumor tissue was observed by hematoxylin and eosin staining, the apoptosis was determined by terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling, and the expression of Ki67, Bcl-2, Bax, cleaved caspase3, matrix metalloproteinase 2 (MMP2), MMP9, and CD34 was detected by Western blot. Expression of Ki67 and CD34 was also detected by immunohistochemistry. Results showed that cell proliferation of the breast tumor and protein expression of the metastasis-related molecules were significantly reduced and the apoptosis of tumor cells was significantly increased in the LDR + DOX-treated tumor-bearing mice. Pretreatment with LDR significantly prevented DOX-induced cardiotoxicity likely through preventing DOX-induced mitochondrial Bcl2/Bax dyshomeostasis-induced caspase-3 cleavage-dependent apoptosis. These results suggested that LDR not only enhances DOX antitumor effect but also reduces DOX cardiotoxicity, which may potentially overcome the limitation for DOX clinical usage.

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.

Arginine and the metabolic regulation of nitric oxide synthesis in cancer

Nitric oxide (NO) is a signaling molecule that plays important roles in diverse biological processes and thus its dysregulation is involved in the pathogenesis of various disorders. In cancer, NO has broad and sometimes dichotomous roles; it is involved in cancer initiation and progression, but also restricts cancer proliferation and invasion, and contributes to the anti-tumor immune response. The importance of NO in a range of cellular processes is exemplified by its tight spatial and dosage control at multiple levels, including via its transcriptional, post-translational and metabolic regulation. In this Review, we focus on the regulation of NO via the synthesis and availability of its precursor, arginine, and discuss the implications of this metabolic regulation for cancer biology and therapy. Despite the established contribution of NO to cancer pathogenesis, the implementation of NO-related cancer therapeutics remains limited, likely due to the challenge of targeting and inducing its protective functions in a cell- and dosage-specific manner. A better understanding of how arginine regulates the production of NO in cancer might thus support the development of anti-cancer drugs that target this key metabolic pathway, and other metabolic pathways involved in NO production.

Cabozantinib and dastinib exert anti-tumor activity in alveolar soft part sarcoma

Background

Alveolar soft part sarcoma (ASPS) is an extremely rare metastatic soft tissue tumor with a poor prognosis for which no effective systemic therapies have yet been established. Therefore, the development of novel effective treatment approaches is required. Tyrosine kinases (TKs) are being increasingly used as therapeutic targets in a variety of cancers. The purpose of this study was to identify novel therapeutic target TKs and to clarify the efficacy of TK inhibitors (TKIs) in the treatment of ASPS.

Experimental design

To identify novel therapeutic target TKs in ASPS, we evaluated the antitumor effects and kinase activity of three TKIs (pazopanib, dasatinib, and cabozantinib) against ASPS cells using an in vitro assay. Based on these results, we then investigated the phosphorylation activities of the identified targets using western blotting, in addition to examining antitumor activity through in vivo assays of several TKIs to determine both the efficacy of these substances and accurate targets.

Results

In cell proliferation and invasion assays using pazopanib, cabozantinib, and dasatinib, all three TKIs inhibited the cell growth in ASPS cells. Statistical analyses of the cell proliferation and invasion assays revealed that dasatinib had a significant inhibitory effect in cell proliferation assays, and cabozantinib exhibited marked inhibitory effects on cellular functions in both assays. Through western blotting, we also confirmed that cabozantinib inhibited c-MET phosphorylation and dasatinib inhibited SRC phosphorylation in dose-dependent fashion. Mice that received cabozantinib and dasatinib had significantly smaller tumor volumes than control animals, demonstrating the in vivo antitumor activity of, these substances.

Conclusions

Our findings suggest that cabozantinib and dasatinib may be more effective than pazopanib against ASPS cells. These in vitro and in vivo data suggest that c-MET may be a potential therapeutic target in ASPS, and cabozantinib may be a particularly useful therapeutic option for patients with ASPS, including those with pazopanib-resistant ASPS.

Arginine auxotrophic gene signature in paediatric sarcomas and brain tumours provides a viable target for arginine depletion therapies

Paediatric sarcomas and brain tumours, remain cancers of significant unmet need, with a poor prognosis for patients with high risk disease or those who relapse, and significant morbidities from treatment for those that survive using standard treatment approaches. Novel treatment strategies, based on the underlying tumour biology, are needed to improve outcomes. Arginine is a semi-essential amino acid that is imported from the extracellular microenvironment or recycled from intracellular precursors through the combined expression of the enzymes ornithine transcarbamylase (OTC), argininosuccinate synthase (ASS) and argininosuccinate lyase (ASL) enzymes. The failure to express at least one of these recycling enzymes makes cells reliant on extracellular arginine - a state known as arginine auxotrophism. Here we show in large in silico patient cohorts that paediatric sarcomas and brain tumours express predominately the arginine transporter SLC7A1 and the arginine metabolising enzyme Arginase 2 (ARG2), but have low-absent expression of OTC. The arginine metabolic pathway correlated with the expression of genes associated with tumour pathogenesis, and overall survival in paediatric sarcomas. This gene signature of arginine auxotrophism indicates paediatric sarcomas and brain tumours are a viable target for therapeutic arginase drugs under current clinical trial development.