Gamma-glutamyltransferase-dependent resistance to arsenic trioxide in melanoma cells and cellular sensitization by ascorbic acid

High-dose intravenous vitamin C, a promising multi-targeting agent in the treatment of cancer

Mounting evidence indicates that vitamin C has the potential to be a potent anti-cancer agent when administered intravenously and in high doses (high-dose IVC). Early phase clinical trials have confirmed safety and indicated efficacy of IVC in eradicating tumour cells of various cancer types. In recent years, the multi-targeting effects of vitamin C were unravelled, demonstrating a role as cancer-specific, pro-oxidative cytotoxic agent, anti-cancer epigenetic regulator and immune modulator, reversing epithelial-to-mesenchymal transition, inhibiting hypoxia and oncogenic kinase signalling and boosting immune response. Moreover, high-dose IVC is powerful as an adjuvant treatment for cancer, acting synergistically with many standard (chemo-) therapies, as well as a method for mitigating the toxic side-effects of chemotherapy. Despite the rationale and ample evidence, strong clinical data and phase III studies are lacking. Therefore, there is a need for more extensive awareness of the use of this highly promising, non-toxic cancer treatment in the clinical setting. In this review, we provide an elaborate overview of pre-clinical and clinical studies using high-dose IVC as anti-cancer agent, as well as a detailed evaluation of the main known molecular mechanisms involved. A special focus is put on global molecular profiling studies in this respect. In addition, an outlook on future implications of high-dose vitamin C in cancer treatment is presented and recommendations for further research are discussed.

Analysis of gamma-glutamyltransferase in acute promyelocytic leukemia patients undergoing arsenic trioxide treatment

OBJECTIVES

The remarkable effect of arsenic trioxide (ATO) was verified, but elevated gamma-glutamyltransferase (GGT), aminotransferases (ALT and AST) are generally observed in acute promyelocytic leukemia (APL) patients undergoing ATO treatment. However, utilization of hepatoprotective agents or discontinuation of ATO may inhibit ATO efficacy. In order to maintain ATO effect from hepatoprotective agents' influence so we investigate relationships between single elevation in GGT and hepatocellular injury in this study.

METHODS

Correlation of GGT variation and leukocyte counts were analyzed in all 81 APL patients, correlations among liver enzymes (ALT, AST and GGT) were also analyzed in patients without prophylactic hepatoprotective agents. In following study, we take the clinical observation of changes in aminotransferases in patients with single elevation in GGT without hepatoprotective agents.

RESULTS

The average elevated GGT in the WBC abnormal group was more than the normal group (53.86U/L vs. 31.03U/L, P = 0.008), a positive Pearson's correlation of GGT variation and changed leukocyte counts in patients without prophylactic hepatoprotective agents. There are no significant correlation between aminotransferases (ALT and AST) and GGT but correlation between ALT and AST was statistically significant (R = 0.649, P = 0.000). For APL patients with single elevation in GGT, ALT and AST levels were normal throughout the ATO treatment without hepatoprotective agents.

CONCLUSION

Single elevation in GGT without elevated aminotransferases can't be identified as hepatotoxicity, and the elevated levels of GGT are associated with increasing leukocyte counts. Continue single-agent ATO without prophylactic hepatoprotective agents is recommended in APL patients with single elevation in GGT, in order to maintain ATO effect.

The dark side of gamma-glutamyltransferase (GGT): Pathogenic effects of an 'antioxidant' enzyme

Having long been regarded as just a member in the cellular antioxidant systems, as well as a clinical biomarker of hepatobiliary diseases and alcohol abuse, gamma-glutamyltransferase (GGT) enzyme activity has been highlighted by more recent research as a critical factor in modulation of redox equilibria within the cell and in its surroundings. Moreover, due to the prooxidant reactions which can originate during its metabolic function in selected conditions, experimental and clinical studies are increasingly involving GGT in the pathogenesis of several important disease conditions, such as atherosclerosis, cardiovascular diseases, cancer, lung inflammation, neuroinflammation and bone disorders. The present article is an overview of the laboratory findings that have prompted an evolution in interpretation of the significance of GGT in human pathophysiology.

Antitumoral effects of pharmacological ascorbate on gastric cancer cells: GLUT1 expression may not tell the whole story

The recently reported results of Lu et al. (Theranostics. 2018; 8: 1312-26) - highlighting GLUT1 expression as a marker for sensitivity of gastric cancer cells to therapeutic doses of ascorbate - are discussed in the light of additional factors potentially affecting the underlying processes, such as the concomitant expression of membrane gamma-glutamyltransferase activity, the resistance of cancer cells to oxidative injury and other known biomarkers.

Biochemical clinical factors associated with missed abortion independent of maternal age: A retrospective study of 795 cases with missed abortion and 694 cases with normal pregnancy

The incidence of fertile women with missed abortion dramatically increased in recent years, while very few serum indices have been identified for the diagnosis of missed abortion. The aim of this study was to identify related factors for missed abortion through a retrospective study of serum indices.A total of 795 cases of women with missed abortion and 694 cases of women with normal pregnancy between March 2014 and March 2017 were included in the present study. The diagnosis of missed abortion was based on clinical history, clinical examination, and transvaginal ultrasound findings. The final diagnosis of missed abortion was based on assessment of pregnancy structures (i.e., a gestational sac without fetal heart rate) via transvaginal ultrasound. We evaluated the clinical values of 4 serum indices and their relationship to missed abortion: gamma-glutamyltransferase (GGT), lactate dehydrogenase (LDH), adenosine deaminase (ADA), and fibrinogen (FIB).The serum levels of GGT, ADA, and FIB showed statistically significant differences comparing women who experienced missed abortion with women who had normal pregnancies (controls). Among women with missed abortion, the levels of GGT and ADA were dramatically increased (GGT: P < .0001; ADA: P = .0459), while FIB levels were slightly lower (P = .0084) compared to controls. The LDH levels exhibited a non-significant trend toward lower levels in the missed abortion group (P = .3951). Interestingly, the observed significant increase in serum GTT levels among women with missed abortion was not affected by maternal age.This study found that GTT may be a useful marker which was associated with missed abortion, indicating its potential clinical roles in missed abortion.

Environmental arsenic exposure: From genetic susceptibility to pathogenesis

More than 200 million people in 70 countries are exposed to arsenic through drinking water. Chronic exposure to this metalloid has been associated with the onset of many diseases, including cancer. Epidemiological evidence supports its carcinogenic potential, however, detailed molecular mechanisms remain to be elucidated. Despite the global magnitude of this problem, not all individuals face the same risk. Susceptibility to the toxic effects of arsenic is influenced by alterations in genes involved in arsenic metabolism, as well as biological factors, such as age, gender and nutrition. Moreover, chronic arsenic exposure results in several genotoxic and epigenetic alterations tightly associated with the arsenic biotransformation process, resulting in an increased cancer risk. In this review, we: 1) review the roles of inter-individual DNA-level variations influencing the susceptibility to arsenic-induced carcinogenesis; 2) discuss the contribution of arsenic biotransformation to cancer initiation; 3) provide insights into emerging research areas and the challenges in the field; and 4) compile a resource of publicly available arsenic-related DNA-level variations, transcriptome and methylation data. Understanding the molecular mechanisms of arsenic exposure and its subsequent health effects will support efforts to reduce the worldwide health burden and encourage the development of strategies for managing arsenic-related diseases in the era of personalized medicine.

Multifactorial Modes of Action of Arsenic Trioxide in Cancer Cells as Analyzed by Classical and Network Pharmacology

Arsenic trioxide is a traditional remedy in Chinese Medicine since ages. Nowadays, it is clinically used to treat acute promyelocytic leukemia (APL) by targeting PML/RARA. However, the drug's activity is broader and the mechanisms of action in other tumor types remain unclear. In this study, we investigated molecular modes of action by classical and network pharmacological approaches. CEM/ADR5000 resistance leukemic cells were similar sensitive to As2O3 as their wild-type counterpart CCRF-CEM (resistance ratio: 1.88). Drug-resistant U87.MG ΔEGFR glioblastoma cells harboring mutated epidermal growth factor receptor were even more sensitive (collateral sensitive) than wild-type U87.MG cells (resistance ratio: 0.33). HCT-116 colon carcinoma p53-/- knockout cells were 7.16-fold resistant toward As2O3 compared to wild-type cells. Forty genes determining cellular responsiveness to As2O3 were identified by microarray and COMPARE analyses in 58 cell lines of the NCI panel. Hierarchical cluster analysis-based heat mapping revealed significant differences between As2O3 sensitive cell lines and resistant cell lines with p-value: 1.86 × 10-5. The genes were subjected to Galaxy Cistrome gene promoter transcription factor analysis to predict the binding of transcription factors. We have exemplarily chosen NF-kB and AP-1, and indeed As2O3 dose-dependently inhibited the promoter activity of these two transcription factors in reporter cell lines. Furthermore, the genes identified here and those published in the literature were assembled and subjected to Ingenuity Pathway Analysis for comprehensive network pharmacological approaches that included all known factors of resistance of tumor cells to As2O3. In addition to pathways related to the anticancer effects of As2O3, several neurological pathways were identified. As arsenic is well-known to exert neurotoxicity, these pathways might account for neurological side effects. In conclusion, the activity of As2O3 is not restricted to acute promyelocytic leukemia. In addition to PML/RARA, numerous other genes belonging to diverse functional classes may also contribute to its cytotoxicity. Network pharmacology is suited to unravel the multifactorial modes of action of As2O3.

Gamma-glutamyl transpeptidase level is a novel adverse prognostic indicator in human metastatic colorectal cancer

AIM

Biomarkers have been utilized for prognosis in colorectal cancer; however, relatively few have been identified. We compared the prognostic value of serum alkaline phosphatase (ALP), lactate dehydrogenase (LDH) and gamma-glutamyl transpeptidase (GGT) with carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA19-9) in patients with metastatic colorectal cancer (mCRC).

METHOD

Blood samples were collected from 239 patients with mCRC presenting between 2005 and 2010 in the Sun Yat-sen University Cancer Center.

RESULTS

CEA (P < 0.001), CA19-9 (P < 0.001), GGT (P < 0.001), ALP (P < 0.001) and LDH (P = 0.001) were statistically significant prognostic factors of overall survival (OS). CEA (P = 0.002) and GGT (P = 0.021) were validated as independent predictors. On univariate analysis, CEA (P = 0.003), CA19-9 (P = 0.006), GGT (P < 0.001) and ALP (P = 0.001) were statistically significant predictive factors of progression-free survival (PFS) in patients having first-line chemotherapy. CEA (P = 0.011) and GGT (P = 0.027) were independent predictors. GGT (P = 0.001), ALP (P = 0.016) and LDH (P = 0.039) levels were correlated with the tumour response rate assessed by CT, whilst CEA (P = 0.724) and CA19-9 (P = 0.822) were not. There was a statistically significant difference in OS (P < 0.001) and PFS (P < 0.001) among patients who had elevations of both CEA and GGT compared with those in whom only one or neither was elevated.

CONCLUSION

Among GGT, LDH and ALP, only GGT plays an independent role with CEA in predicting OS and PFS in mCRC. When coupled with CEA, GGT may lead to improved prognostic predictors.

Factors determining sensitivity and resistance of tumor cells to arsenic trioxide

Previously, arsenic trioxide showed impressive regression rates of acute promyelocytic leukemia. Here, we investigated molecular determinants of sensitivity and resistance of cell lines of different tumor types towards arsenic trioxide. Arsenic trioxide was the most cytotoxic compound among 8 arsenicals investigated in the NCI cell line panel. We correlated transcriptome-wide microarray-based mRNA expression to the IC(50) values for arsenic trioxide by bioinformatic approaches (COMPARE and hierarchical cluster analyses, Ingenuity signaling pathway analysis). Among the identified pathways were signaling routes for p53, integrin-linked kinase, and actin cytoskeleton. Genes from these pathways significantly predicted cellular response to arsenic trioxide. Then, we analyzed whether classical drug resistance factors may also play a role for arsenic trioxide. Cell lines transfected with cDNAs for catalase, thioredoxin, or the anti-apoptotic bcl-2 gene were more resistant to arsenic trioxide than mock vector transfected cells. Multidrug-resistant cells overexpressing the MDR1, MRP1 or BCRP genes were not cross-resistant to arsenic trioxide. Our approach revealed that response of tumor cells towards arsenic trioxide is multi-factorial.

The cystine/cysteine cycle and GSH are independent and crucial antioxidant systems in malignant melanoma cells and represent druggable targets

AIMS

Cancer chemoresistance is often due to upregulation of antioxidant systems. Therapeutic targeting of these systems is however hampered by their redundancy. Here, we have performed a functional dissection of the antioxidant systems in different melanoma cases aimed at the identification of the most effective redox active drug.

RESULTS

We have identified two crucial antioxidant mechanisms: glutathione (GSH), the major intracellular redox buffer, and the cystine/cysteine cycle, which switches the extracellular redox state from an oxidized to a reduced state. The two mechanisms are independent in melanoma cells and may be substitutes for each other, but targeting both of them is lethal. Exposure to the pro-oxidant compound As(2)O(3) induces an antioxidant response. However, while in these cells the intracellular redox balance remains almost unaffected, a reduced environment is generated extracellularly. GSH depletion by buthioninesulfoximine (BSO), or cystine/cysteine cycle inhibition by (S)-4-carboxyphenylglycine (sCPG), enhanced the sensitivity to As(2)O(3). Remarkably, sCPG also prevented the remodeling of the microenvironment redox state.

INNOVATION

We propose that the definition of the prevalent antioxidant system(s) in tumors is crucial for the design of tailored therapies involving redox-directed drugs in association with pro-oxidant drugs.

CONCLUSION

In melanoma cells, BSO is the best enhancer of As(2)O(3) sensitivity. However, since the strong remodeling of the microenvironmental redox state caused by As(2)O(3) may promote tumor progression, the concomitant use of cystine/cysteine cycle blockers is recommended.

Anticancer activity of metal complexes: involvement of redox processes

Cells require tight regulation of the intracellular redox balance and consequently of reactive oxygen species for proper redox signaling and maintenance of metal (e.g., of iron and copper) homeostasis. In several diseases, including cancer, this balance is disturbed. Therefore, anticancer drugs targeting the redox systems, for example, glutathione and thioredoxin, have entered focus of interest. Anticancer metal complexes (platinum, gold, arsenic, ruthenium, rhodium, copper, vanadium, cobalt, manganese, gadolinium, and molybdenum) have been shown to strongly interact with or even disturb cellular redox homeostasis. In this context, especially the hypothesis of "activation by reduction" as well as the "hard and soft acids and bases" theory with respect to coordination of metal ions to cellular ligands represent important concepts to understand the molecular modes of action of anticancer metal drugs. The aim of this review is to highlight specific interactions of metal-based anticancer drugs with the cellular redox homeostasis and to explain this behavior by considering chemical properties of the respective anticancer metal complexes currently either in (pre)clinical development or in daily clinical routine in oncology.

Modulation of cell sensitivity to antitumor agents by targeting survival pathways

The advent of drugs targeting tumor-associated prosurvival alterations of cancer cells has changed the interest of antitumor drug development from cytotoxic drugs to target-specific agents. Although single-agent therapy with molecularly targeted agents has shown limited success in tumor growth control, a promising strategy is represented by the development of rational combinations of target-specific agents and conventional antitumor drugs. Activation of survival/antiapoptotic pathways is a common feature of cancer cells that converge in the development of cellular resistance to cytotoxic agents. The survival pathways implicated in cellular response to drug treatment are primarily PI3K/Akt and Ras/MAPK, which also mediate the signalling activated by growth factors and play a role in the regulation of critical processes including cell proliferation, metabolism, apoptosis and angiogenesis. Inhibitors of PI3K, Akt and mTOR have been shown to sensitize selected tumor cells to cytotoxic drugs through multiple downstream effects. Moreover, the MAPK pathway, also implicated in the regulation of gene expression in response to stress stimuli, can interfere with the chemotherapy-induced proapoptotic signals. Targeting Hsp90, which acts as a molecular chaperone for survival factors including Akt, may have the potential advantage to simultaneously block multiple oncogenic pathways. Overall, the available evidence supports the interest of rationally designed approaches to enhance the efficacy of conventional antitumor treatments through the inhibition of survival pathways and the notion that the concomitant targeting of multiple pathways may be a successful strategy to deal with tumor heterogeneity and to overcome drug resistance of tumor cells.

Gallic acid ester derivatives induce apoptosis and cell adhesion inhibition in melanoma cells: The relationship between free radical generation, glutathione depletion and cell death

Malignant melanoma is a lethal disease, and the incidence and mortality associated with it are increasing worldwide. It has a significant tendency to develop both metastasis and resistance to chemotherapy. The tumor cells show abnormal redox regulation, and although the molecular mechanisms involved are not well characterized, they seem to be related to oxidative stress. In a previous study, we showed the antitumoral properties of gallic acid ester derivatives in leukemia cells. Here, we show the effect of octyl, decyl, dodecyl and tetradecyl gallates on B16F10 cells, a melanoma cell line. All compounds induced cytotoxic effects, and the IC(50) values obtained were between 7microM and 17microM after 48h of incubation. Cell death occurred through apoptosis, as demonstrated by the genomic DNA fragmentation pattern. The gallates were able to induce significant production of free radicals, deplete both glutathione and ATP, activate NF-kappaB and promote the inhibition of cell adhesion under the experimental conditions. The glutathione depletion induced by these compounds was related to the inhibition of gamma-glutamylcysteine synthase activity. These results suggest that gallates induce tumoral cell death through apoptosis as a consequence of oxidative stress, though they use different mechanisms to do so. These findings are important since melanoma cells are resistant to death because of their high level of antioxidant defense, adhesion capability and propensity to metastasize.