Increased expression of argininosuccinate synthetase protein predicts poor prognosis in human gastric cancer

PSMD2 contributes to the progression of esophageal squamous cell carcinoma by repressing autophagy

BACKGROUND

The ubiquitin-proteasome and autophagy-lysosomal systems collaborate in regulating the levels of intracellular proteins. Dysregulation of protein homeostasis is a central feature of malignancy. The gene encoding 26S proteasome non-ATPase regulatory subunit 2 (PSMD2) of the ubiquitin-proteasome system is an oncogene in various types of cancer. However, the detailed role of PSMD2 in autophagy and its relationship to tumorigenesis in esophageal squamous cell carcinoma (ESCC) remain unknown. In the present study, we have investigated the tumor-promoting roles of PSMD2 in the context of autophagy in ESCC.

METHODS

Molecular approaches including DAPgreen staining, 5-Ethynyl-2'-deoxyuridine (EdU), cell counting kit 8 (CCK8), colony formation, transwell assays, and cell transfection, xenograft model, immunoblotting and Immunohistochemical analysis were used to investigate the roles of PSMD2 in ESCC cells. Data-independent acquisition (DIA) quantification proteomics analysis and rescue experiments were used to study the roles of PSMD2 in ESCC cells.

RESULTS

We demonstrate that the overexpression of PSMD2 promotes ESCC cell growth by inhibiting autophagy and is correlated with tumor progression and poor prognosis of ESCC patients. DIA quantification proteomics analysis shows a significant positive correlation between argininosuccinate synthase 1 (ASS1) and PSMD2 levels in ESCC tumors. Further studies indicate that PSMD2 activates the mTOR pathway by upregulating ASS1 to inhibit autophagy.

CONCLUSIONS

PSMD2 plays an important role in repressing autophagy in ESCC, and represents a promising biomarker to predict prognosis and a therapeutic target of ESCC patients.

Targeting IGF1R signaling enhances the sensitivity of cisplatin by inhibiting proline and arginine metabolism in oesophageal squamous cell carcinoma under hypoxia

BACKGROUND

Cisplatin (DDP)-based chemotherapy is commonly adopted as the first-line treatment for patients with oesophageal squamous cell carcinoma (OSCC), but the high rate of drug resistance limits its clinical application and the underlying mechanisms at play remain unclear. The aims of this study were to elucidate the role of abnormal signal transmission and metabolism in the chemoresistance of OSCC under hypoxia and to identify targeted drugs that enhance the sensitivity of DDP chemotherapy.

METHODS

Upregulated genes in OSCC were determined by RNA sequencing (RNA-seq), the Cancer Genome Atlas (TCGA) database, immunohistochemistry (IHC), real-time quantitative PCR (RT-qPCR), and western blotting (WB). The clinicopathological significance of insulin-like growth factor-I receptor (IGF1R), argininosuccinate synthetase 1 (ASS1), and pyrroline-5-carboxylate reductase 1 (PYCR1) in OSCC was analysed using tissue micriarray (TMA). Metabolic abnormalities were determined by untargeted metabolomics analysis. The DDP-resistance role of IGF1R, ASS1, and PYCR1 in OSCC was investigated in vitro and in vivo.

RESULTS

Generally, tumour cells exist in a hypoxic microenvironment. By genomic profiling, we determined that IGF1R, as a receptor tyrosine kinase (RTK), was upregulated in OSCC under low-oxygen conditions. Clinically, enhanced IGF1R expression was associated with higher tumour stages and a poorer prognosis in OSCC patients, and its inhibitor, linsitinib, showed synergistic effects with DDP therapy in vivo and in vitro. Since oxygen-deprivation frequently lead to metabolic reprogramming, we further learned via metabolomics analysis that abnormal IGF1R pathways promoted the expression of metabolic enzymes ASS1 and PYCR1 by the transcriptional activity of c-MYC. In detail, enhanced expression of ASS1 promotes arginine metabolism for biological anabolism, whereas PYCR1 activates proline metabolism for redox balance, which maintains the proliferation ability of OSCC cells during DDP treatment under hypoxic conditions.

CONCLUSION

Enhanced expression of ASS1 and PYCR1 via IGF1R pathways rewired arginine and proline metabolism, promoting DDP resistance in OSCC under hypoxia. Linsitinib targeting IGF1R signaling may lead to promising combination therapy options for OSCC patients with DDP resistance.

Targeted Arginine Metabolism Therapy: A Dilemma in Glioma Treatment

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

Snail enhances arginine synthesis by inhibiting ubiquitination-mediated degradation of ASS1

Snail is a dedicated transcriptional repressor and acts as a master inducer of EMT and metastasis, yet the underlying signaling cascades triggered by Snail still remain elusive. Here, we report that Snail promotes colorectal cancer (CRC) migration by preventing non-coding RNA LOC113230-mediated degradation of argininosuccinate synthase 1 (ASS1). LOC113230 is a novel Snail target gene, and Snail binds to the functional E-boxes within its proximal promoter to repress its expression in response to TGF-β induction. Ectopic expression of LOC113230 potently suppresses CRC cell growth, migration, and lung metastasis in xenograft experiments. Mechanistically, LOC113230 acts as a scaffold to facilitate recruiting LRPPRC and the TRAF2 E3 ubiquitin ligase to ASS1, resulting in enhanced ubiquitination and degradation of ASS1 and decreased arginine synthesis. Moreover, elevated ASS1 expression is essential for CRC growth and migration. Collectively, these findings suggest that TGF-β and Snail promote arginine synthesis via inhibiting LOC113230-mediated LRPPRC/TRAF2/ASS1 complex assembly and this complex can serve as potential target for the development of new therapeutic approaches to treat CRC.

Chromatin accessibility governs the differential response of cancer and T cells to arginine starvation

Depleting the microenvironment of important nutrients such as arginine is a key strategy for immune evasion by cancer cells. Many tumors overexpress arginase, but it is unclear how these cancers, but not T cells, tolerate arginine depletion. In this study, we show that tumor cells synthesize arginine from citrulline by upregulating argininosuccinate synthetase 1 (ASS1). Under arginine starvation, ASS1 transcription is induced by ATF4 and CEBPβ binding to an enhancer within ASS1. T cells cannot induce ASS1, despite the presence of active ATF4 and CEBPβ, as the gene is repressed. Arginine starvation drives global chromatin compaction and repressive histone methylation, which disrupts ATF4/CEBPβ binding and target gene transcription. We find that T cell activation is impaired in arginine-depleted conditions, with significant metabolic perturbation linked to incomplete chromatin remodeling and misregulation of key genes. Our results highlight a T cell behavior mediated by nutritional stress, exploited by cancer cells to enable pathological immune evasion.

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.

Argininosuccinate synthase 1 suppresses cancer cell invasion by inhibiting STAT3 pathway in hepatocellular carcinoma

Metastasis is the main reason for high recurrence and poor survival of hepatocellular carcinoma (HCC). The molecular mechanism underlying HCC metastasis remains unclear. In this study, we found that argininosuccinate synthase 1 (ASS1) expression was significantly decreased and down-regulation of ASS1 was closely correlated with poor prognosis in HCC patients. DNA methylation led to the down-regulation of ASS1 in HCC. Stable silencing of ASS1 promoted migration and invasion of HCC cells, whereas overexpression of ASS1-inhibited metastasis of HCC cells in vivo and in vitro. We also revealed that ASS1-knockdown increased the phosphorylation level of S727STAT3, which contributed to HCC metastasis by up-regulation of inhibitor of differentiation 1 (ID1). These findings indicate that ASS1 inhibits HCC metastasis and may serve as a target for HCC diagnosis and treatment.

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.

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.

Comparison of tumor related signaling pathways with known compounds to determine potential agents for lung adenocarcinoma

Background

This study compared tumor‐related signaling pathways with known compounds to determine potential agents for lung adenocarcinoma (LUAD) treatment.

Methods

Kyoto Encyclopedia of Genes and Genomes signaling pathway analyses were performed based on LUAD differentially expressed genes from The Cancer Genome Atlas (TCGA) project and genotype‐tissue expression controls. These results were compared to various known compounds using the Connectivity Mapping dataset. The clinical significance of the hub genes identified by overlapping pathway enrichment analysis was further investigated using data mining from multiple sources. A drug‐pathway network for LUAD was constructed, and molecular docking was carried out.

Results

After the integration of 57 LUAD‐related pathways and 35 pathways affected by small molecules, five overlapping pathways were revealed. Among these five pathways, the p53 signaling pathway was the most significant, with CCNB1, CCNB2, CDK1, CDKN2A, and CHEK1 being identified as hub genes. The p53 signaling pathway is implicated as a risk factor for LUAD tumorigenesis and survival. A total of 88 molecules significantly inhibiting the five LUAD‐related oncogenic pathways were involved in the LUAD drug‐pathway network. Daunorubicin, mycophenolic acid, and pyrvinium could potentially target the hub gene CHEK1 directly.

Conclusion

Our study highlights the critical pathways that should be targeted in the search for potential LUAD treatments, most importantly, the p53 signaling pathway. Some compounds, such as ciclopirox and AG‐028671, may have potential roles for LUAD treatment but require further experimental verification.

Opposite Effects of Two Human ATG10 Isoforms on Replication of a HCV Sub-genomic Replicon Are Mediated via Regulating Autophagy Flux in Zebrafish

Autophagy is a host mechanism for cellular homeostatic control. Intracellular stresses are symptoms of, and responses to, dysregulation of the physiological environment of the cell. Alternative gene transcription splicing is a mechanism potentially used by a host to respond to physiological or pathological challenges. Here, we aimed to confirm opposite effects of two isoforms of the human autophagy-related protein ATG10 on an HCV subgenomic replicon in zebrafish. A liver-specific HCV subreplicon model was established and exhibited several changes in gene expression typically induced by HCV infection, including overexpression of several HCV-dependent genes (argsyn, leugpcr, rasgbd, and scaf-2), as well as overexpression of several ER stress related genes (atf4, chop, atf6, and bip). Autophagy flux was blocked in the HCV model. Our results indicated that the replication of the HCV subreplicon was suppressed via a decrease in autophagosome formation caused by the autophagy inhibitor 3MA, but enhanced via dysfunction in the lysosomal degradation caused by another autophagy inhibitor CQ. Human ATG10, a canonical isoform in autophagy, facilitated the amplification of the HCV-subgenomic replicon via promoting autophagosome formation. ATG10S, a non-canonical short isoform of the ATG10 protein, promoted autophagy flux, leading to lysosomal degradation of the HCV-subgenomic replicon. Human ATG10S may therefore inhibit HCV replication, and may be an appropriate target for future antiviral drug screening.

Argininosuccinate synthetase 1 contributes to gastric cancer invasion and progression by modulating autophagy

Argininosuccinate synthetase 1 (ASS1) is a rate-limited enzyme in arginine biosynthesis. The oncogenic potential of ASS1 in terms of prognosis and cancer metastasis in arginine prototrophic gastric cancer (GC) remains unclear at present. We identify differentially expressed proteins in microdissected GC tumor cells relative to adjacent nontumor epithelia by isobaric mass tag for relative and absolute quantitation proteomics analysis. GC cells with stable expression or depletion of ASS1 were further analyzed to identify downstream molecules. We investigated their effects on chemoresistance and cell invasion in the presence or absence of arginine. ASS1 was highly expressed in GC and positively correlated with GC aggressiveness and poor outcome. Depletion of ASS1 led to inhibition of tumor growth and decreased cell invasion via induction of autophagy-lysosome machinery, resulting in degradation of active β-catenin, Snail, and Twist. Ectopic expression of ASS1 in GC cells reversed these effects and protected cancer cells from chemotherapy drug-induced apoptosis via activation of the AKT-mammalian target of rapamycin signaling pathway. ASS1 contributes to GC progression by enhancing aggressive potential resulting from active β-catenin, Snail, and Twist accumulation. Our results propose that ASS1 might contribute to GC metastasis and support its utility as a prognostic predictor of GC.-Tsai, C.-Y., Chi, H.-C., Chi, L.-M., Yang, H.-Y., Tsai, M.-M., Lee, K.-F., Huang, H.-W., Chou, L.-F., Cheng, A.-J., Yang, C.-W., Wang, C.-S., Lin, K.-H. Argininosuccinate synthetase 1 contributes to gastric cancer invasion and progression by modulating autophagy.

Cyclin D1 overexpression correlates with poor tumor differentiation and prognosis in gastric cancer

Overexpression of cyclin D is associated with the molecular tumorigenesis of gastric cancer. The purpose of the present study was to investigate the expression of cyclin D in human gastric cancer and to determine the potential correlations between cyclin D expression and clinicopathological characteristics of specific histological types, as well as its prognostic significance. In the present study, the expression of the cyclin D1 (CCND1), cyclin D2 (CCND2) and cyclin D3 (CCND3) genes in gastric cancer patients was explored using the Oncomine database, and their correlation with overall survival (OS) and progression-free survival (PFS) was evaluated using Kaplan-Meier analysis. The prognostic significance of CCND1 protein expression was evaluated by western blot analysis of 32 matched specimens of gastric adenocarcinomas and normal tissues obtained from patients treated at the National Cheng Kung University Hospital (Tainan, Taiwan). Analysis of the Oncomine cancer microarray database revealed that CCND1 gene expression was significantly increased in gastric intestinal-type adenocarcinoma, while CCND2 was significantly increased in diffuse gastric adenocarcinoma, gastric intestinal-type adenocarcinoma and gastric mixed adenocarcinoma. Kaplan-Meier analysis indicated that overexpression of CCND1 was associated with reduced OS and PFS. In addition, overexpression of CCND1 and downregulation of CCND2 were significantly correlated with receptor tyrosine-protein kinase erb-2-negative tumors and poor differentiation. The ratio of relative CCND1 expression (expressed as the CCND1/β-actin ratio) in tumor tissues compared with that in normal tissues was correlated with poor differentiation (P=0.0018). In summary, CCND1 overexpression is associated with shorter survival in patients with gastric cancer and with poorly differentiated tumors.

Mucin 2 silencing promotes colon cancer metastasis through interleukin-6 signaling

Downregulation of Mucin 2 (MUC2) expression is associated with early carcinogenesis events in colon cancer. MUC2 plays a role in the progression of colon cancer, and reduced MUC2 protein expression correlates with increased interleukin-6 (IL-6) expression. However, the interaction between MUC2 and IL-6 in colorectal cancer metastasis remains unclear. We systematically analyzed MUC2 and IL-6 expression and determined the survival of cancer patients with high or low MUC2 and IL-6 expression using the Oncomine and PrognoScan databases, respectively. This analysis identified downregulation of MUC2 and overexpression of IL-6 in colon cancer but not in normal colon tissue, and this expression pattern was correlated with poor survival of colon cancer patients. We examined the effects of MUC2 on colon cancer metastasis and used vector-mediated application of short hairpin RNA (shRNA) to suppress MUC2 expression. MUC2 suppressed the migration of colon cancer cells in vitro and dramatically diminished liver metastases in vivo. Treatment with IL-6 increased signal transducer and activator of transcription 3 (STAT3) phosphorylation, promoted checkpoint kinase 2 (Chk2) activation, attenuated cAMP response element-binding protein (CREB) phosphorylation, and suppressed E-cadherin protein expression in MUC2-silenced HT-29 cancer cells. Most importantly, MUC2 is a potential prognostic indicator for colon cancer.

Argininosuccinate Synthase 1 is a Metabolic Regulator of Colorectal Cancer Pathogenicity

Like many cancer types, colorectal cancers have dysregulated metabolism that promotes their pathogenic features. In this study, we used the activity-based protein profiling chemoproteomic platform to profile cysteine-reactive metabolic enzymes that are upregulated in primary human colorectal tumors. We identified argininosuccinate synthase 1 (ASS1) as an upregulated target in primary human colorectal tumors and show that pharmacological inhibition or genetic ablation of ASS1 impairs colorectal cancer pathogenicity. Using metabolomic profiling, we show that ASS1 inhibition leads to reductions in the levels of oncogenic metabolite fumarate, leading to impairments in glycolytic metabolism that supports colorectal cancer cell pathogenicity. We show here that ASS1 inhibitors may represent a novel therapeutic approach for attenuating colorectal cancer through compromising critical metabolic and metabolite signaling pathways and demonstrate the utility of coupling chemoproteomic and metabolomic strategies to map novel metabolic regulators of cancer.

Nonessential amino acid metabolism in breast cancer

Interest in studying cancer metabolism has risen in recent years, as it has become evident that the relationship between cancer and metabolic pathways could reveal novel biomarkers and therapeutic targets. Metabolic starvation therapy is particularly promising due to its low toxicity. Nonessential amino acids are promising metabolites for such therapy because they become essential in many tumor cells, including breast cancer cells. This review will focus on four nonessential amino acid metabolism pathways: glutamine-glutamate, serine-glycine, cysteine, and arginine-proline metabolism. Recent studies of these amino acids have revealed metabolic enzymes that have the potential to be effective as cancer therapy targets or biomarkers for response to metabolic starvation therapy. The review will also discuss features of nonessential amino acid metabolism that merit further investigation to determine their relevancy to breast cancer treatment.

Molecular basis and current strategies of therapeutic arginine depletion for cancer

Renewed interest in the use of therapeutic enzymes combined with an improved knowledge of cancer cell metabolism, has led to the translation of several arginine depletion strategies into early phase clinical trials. Arginine auxotrophic tumors are reliant on extracellular arginine, due to the downregulation of arginosuccinate synthetase or ornithine transcarbamylase-key enzymes for intracellular arginine recycling. Engineered arginine catabolic enzymes such as recombinant human arginase (rh-Arg1-PEG) and arginine deiminase (ADI-PEG) have demonstrated cytotoxicity against arginine auxotrophic tumors. In this review, we discuss the molecular events triggered by extracellular arginine depletion that contribute to tumor cell death.

The high expressed serum soluble neural cell adhesion molecule, a high risk factor indicating hepatic encephalopathy in hepatocelular carcinoma patients

OBJECTIVE

To investigate whether the expression of serum soluble neural cell adhesion molecule (sNCAM) is associated with hepatic encephalopathy (HE) in hepatocelular carcinoma (HCC) patients.

MATERIALS AND METHODS

The Oncomine Cancer Microarray database was used to determine the clinical relevance of NCAM expression in different kinds of human cancers. Sera from 75 HCC cases enrolled in this study were assessed for expression of sNCAM by enzyme linked immunosorbent assay (ELISA).

RESULTS

Dependent on the Oncomine Cancer Microarray database analysis, NCAM was down regulated in 10 different kinds of cancer, like bladder cancer, brain and central nervous system cancer, while up-regulated in lung cancer, uterine corpus leiomyoma and sarcoma, compared to normal groups. Puzzlingly, NCAM expression demonstrated no significant difference between normal and HCC groups. However, we found by quantitative ELISA that the level of sNCAM in sera from HCC patients with HE (347.4±151.9 ng/ml) was significantly more up-regulated than that in HCC patients without HE (260.3±104.2 ng/ml), the p-value being 0.008. sNCAM may be an important risk factor of HE in HCC patients, the correlation coefficients was 0.278 (P< 0.05) on rank correlation analysis.

CONCLUSIONS

This study highlights that up-regulated level of serum sNCAM is associated with HE in HCC patients and suggests that the high expression can be used as an indicator.

Enhanced anticancer effect of ABT-737 in combination with naringenin on gastric cancer cells

Gastric cancer is the second leading cause of cancer-associated mortality and is a frequently occurring cancer worldwide. Multiple drug resistance of gastric cancer cells leads to the poor prognosis. In addition, overexpression of anti-apoptotic protein B-cell lymphoma (Bcl)-2 have been demonstrated in various cancer cells and is closely associated with drug resistance and poor prognosis. Naringenin is a flavonoid that has antimutagenic and anticarcinogenic activities in numerous cancer types. In the present study, naringenin and a Bcl-2 inhibitor, ABT-737, were used to investigate their combinative anticancer effect in the SGC7901 gastric cancer cell line. The results revealed that naringenin and ABT-737 were able to inhibit SGC7901 cell growth and colony formation, alone or in combination. Furthermore, the combination of these drugs was found to further increase the cleavage of caspase-3 and poly ADP-ribose polymerase. Naringenin and ABT-737 also decreased Akt activation and increased p53 expression, suggesting the involvement of these pathways in the inhibition of gastric cell growth.

Argininosuccinate synthetase 1 suppression and arginine restriction inhibit cell migration in gastric cancer cell lines

Gastric cancer metastasis remains a major cause of cancer-related deaths. There is an urgent need to develop new therapeutic approaches targeting metastatic gastric cancer. Argininosuccinate synthetase 1 (ASS1) expression is increased in gastric cancer. We detected the protein expression of ASS1 in human gastric cancer cell lines (AGS, NCI-N87, and MKN45) and in murine gastric cancer cell lines (3I and 3IB2). We used vector-mediated short hairpin RNA (shRNA) expression to silence ASS1 expression in the MKN45 and 3IB2 cell lines, and analyzed the effects of this protein on cell migration and metastasis. We demonstrated that ASS1 silencing suppressed cell migration in the MKN45 and 3IB2 cell lines. ASS1 knockdown significantly reduced liver metastasis in mice after the intrasplenic implantation of 3IB2 cancer cell clones. To determine whether arginine restriction may represent a therapeutic approach to treat gastric cancer, the sensitivity of tumor cells to arginine depletion was determined in gastric cancer cells. Arginine depletion significantly inhibited cell migration in the gastric cancer cell line. The silencing of ASS1 expression in MKN45 and 3IB2 gastric cancer cells markedly decreased STAT3 protein expression. In conclusion, our results indicate that the ASS1 protein is required for cell migration in gastric cancer cell lines.