Patterns of drug resistance parameters in adult leukemia

Genetic variation at the catalytic subunit of glutamate cysteine ligase contributes to the susceptibility to sporadic colorectal cancer: a pilot study

BACKGROUND

Glutathione is a tripeptide detoxifying a variety of exogenous and endogenous free radicals and carcinogens, and a deficiency of glutathione is associated with an increased host susceptibility to oxidative stress, a pathological condition implicated in the development and progression of cancer. The catalytic subunit of glutamate-cysteine ligase (GCLC) is an enzyme responsible for the initial and rate-limiting step of glutathione biosynthesis.

METHODS AND RESULTS

The aim of this pilot study was to investigate whether genetic variation at the GCLC gene contributes to the risk of colorectal cancer (CRC). DNA samples from 681 unrelated Russian individuals (283 patients with CRC and 398 age- and sex-matched healthy controls) were genotyped for six common functional SNPs of the GCLC gene (SNPs) such as rs12524494, rs17883901, rs606548, rs636933, rs648595 and rs761142 of the GCLC gene using the MassARRAY-4 system. We found that genotype rs606548-C/T is significantly associated with increased risk of CRC regardless of sex and age (OR 2.24; 95% CI 1.24-4.03; P = 0.007, FDR = 0.04). Moreover, ten GCLC genotype combinations showed association with the risk of CRC (P < 0.05). Functional SNP annotation enabled establishing the CRC-associated polymorphisms are associated with a decreased GCLC expression that may be attributed to epigenetic effects of histone modifications operating in a colon-specific manner.

CONCLUSIONS

The present study was the first to show that genetic variation at the catalytic subunit of glutamate-cysteine ligase may contribute to the risk of colorectal cancer risk. However, further genetic association studies with a larger sample size are required to substantiate the role of GCLC gene polymorphisms in the development of sporadic colorectal cancer.

Redox manipulation of enzyme activity through physiologically active molecule

The effective utility of physiologically active molecules is crucial in numerous biological processes. However, the regulation of enzyme functions through active substances remains challenging at present. Here, glutathione (GSH), produced in cells, was used to modulate the catalytic activity of thrombin without external stimulus. It was found that high concentrations of GSH was more conducive to initiate the cleavage of compound AzoDiTAB in the range of concentration used to mimic the difference between cancer and normal cells, which has practical implications for targeting cancel cells since GSH is overexpressed in cancer cells. Importantly, GSH treatment caused the deformation of G4 structure by cleaving AzoDiTAB and thus triggered the transition of thrombin from being free to be inhibited in complex biological systems. This work would open up a new route for the specific manipulation of enzyme-catalyzed systems in cancer cells.

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The transition of telomere DNA structures based on redox switch

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Achieving redox manipulation of thrombin activity through active substance

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This switch can be specifically used for enzyme regulation in cancer cells

The Effect of Glutathione Peroxidase-1 Knockout on Anticancer Drug Sensitivities and Reactive Oxygen Species in Haploid HAP-1 Cells

The role of glutathione peroxidases (GPx) in cancer and their influence on tumor prognosis and the development of anticancer drug resistance has been extensively and controversially discussed. The aim of this study was to evaluate the influence of GPx1 expression on anticancer drug cytotoxicity. For this purpose, a GPx1 knockout of the near-haploid human cancer cell line HAP-1 was generated and compared to the native cell line with regards to morphology, growth and metabolic rates, and oxidative stress defenses. Furthermore, the IC₅₀ values of two peroxides and 16 widely used anticancer drugs were determined in both cell lines. Here we report that the knockout of GPx1 in HAP-1 cells has no significant effect on cell size, viability, growth and metabolic rates. Significant increases in the cytotoxic potency of hydrogen peroxide and tert-butylhydroperoxide, the anticancer drugs cisplatin and carboplatin as well as the alkylating agents lomustine and temozolomide were found. While a concentration dependent increases in intracellular reactive oxygen species (ROS) levels were observed for both HAP-1 cell lines treated with either cisplatin, lomustine or temozolamide, no significant enhancement in ROS levels was observed in the GPx1 knockout compared to the native cell line except at the highest concentration of temozolamide. On the other hand, a ca. 50% decrease in glutathione levels was noted in the GPx1 knockout relative to the native line, suggesting that factors other than ROS levels alone play a role in the increased cytotoxic activity of these drugs in the GPx1 knockout cells.

A simple assay for glutathione in whole blood

A method for detecting glutathione selectively in whole blood deposited on filter paper is described. GSH is fractionated from proteins, hemoglobin and other potentially interfering components and determined using a resorufin-acrylate fluorescent probe. The relative standard deviation is lower than 5% (n = 5). Recoveries of GSH from whole blood are between 94% and 108.6%.

Expression of xCT and activity of system xc(-) are regulated by NRF2 in human breast cancer cells in response to oxidative stress

Cancer cells adapt to high levels of oxidative stress in order to survive and proliferate by activating key transcription factors. One such master regulator, the redox sensitive transcription factor NF E2 Related Factor 2 (NRF2), controls the expression of cellular defense genes including those encoding intracellular redox-balancing proteins involved in glutathione (GSH) synthesis. Under basal conditions, Kelch-like ECH-associated protein 1 (KEAP1) targets NRF2 for ubiquitination. In response to oxidative stress, NRF2 dissociates from KEAP1, entering the nucleus and binding to the antioxidant response element (ARE) in the promoter of its target genes. Elevated reactive oxygen species (ROS) production may deplete GSH levels within cancer cells. System xc(-), an antiporter that exports glutamate while importing cystine to be converted into cysteine for GSH synthesis, is upregulated in cancer cells in response to oxidative stress. Here, we provided evidence that the expression of xCT, the light chain subunit of system xc(-), is regulated by NRF2 in representative human breast cancer cells. Hydrogen peroxide (H2O2) treatment increased nuclear translocation of NRF2, also increasing levels of xCT mRNA and protein and extracellular glutamate release. Overexpression of NRF2 up-regulated the activity of the xCT promoter, which contains a proximal ARE. In contrast, overexpression of KEAP1 repressed promoter activity and decreased xCT protein levels, while siRNA knockdown of KEAP1 up-regulated xCT protein levels and transporter activity. These results demonstrate the importance of the KEAP1/NRF2 pathway in balancing oxidative stress in breast cancer cells through system xc(-). We have previously shown that xCT is upregulated in various cancer cell lines under oxidative stress. In the current investigation, we focused on MCF-7 cells as a model for mechanistic studies.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

Polymer-coated echogenic lipid nanoparticles with dual release triggers

Although lipid nanoparticles are promising drug delivery vehicles, passive release of encapsulated contents at the target site is often slow. Herein, we report contents release from targeted, polymer-coated, echogenic lipid nanoparticles in the cell cytoplasm by redox trigger and simultaneously enhanced by diagnostic frequency ultrasound. The lipid nanoparticles were polymerized on the external leaflet using a disulfide cross-linker. In the presence of cytosolic concentrations of glutathione, the lipid nanoparticles released 76% of encapsulated contents. Plasma concentrations of glutathione failed to release the encapsulated contents. Application of 3 MHz ultrasound for 2 min simultaneously with the reducing agent enhanced the release to 96%. Folic acid conjugated, doxorubicin-loaded nanoparticles showed enhanced uptake and higher cytotoxicity in cancer cells overexpressing the folate receptor (compared to the control). With further developments, these lipid nanoparticles have the potential to be used as multimodal nanocarriers for simultaneous targeted drug delivery and ultrasound imaging.

Divergent effects of compounds on the hydrolysis and transpeptidation reactions of γ-glutamyl transpeptidase

A novel class of inhibitors of the enzyme γ-glutamyl transpeptidase (GGT) were evaluated. The analog OU749 was shown previously to be an uncompetitive inhibitor of the GGT transpeptidation reaction. The data in this study show that it is an equally potent uncompetitive inhibitor of the hydrolysis reaction, the primary reaction catalyzed by GGT in vivo. A series of structural analogs of OU749 were evaluated. For many of the analogs, the potency of the inhibition differed between the hydrolysis and transpeptidation reactions, providing insight into the malleability of the active site of the enzyme. Analogs with electron withdrawing groups on the benzosulfonamide ring, accelerated the hydrolysis reaction, but inhibited the transpeptidation reaction by competing with a dipeptide acceptor. Several of the OU749 analogs inhibited the transpeptidation reaction by slow onset kinetics, similar to acivicin. Further development of inhibitors of the GGT hydrolysis reaction is necessary to provide new therapeutic compounds.

The role of glutathione in cancer

Glutathione is an abundant natural tripeptide found within almost all cells. Glutathione is highly reactive and is often found conjugated to other molecules via its sulfhydryl moiety. It instils several vital roles within a cell including antioxidation, maintenance of the redox state, modulation of the immune response and detoxification of xenobiotics. With respect to cancer, glutathione metabolism is able to play both protective and pathogenic roles. It is crucial in the removal and detoxification of carcinogens, and alterations in this pathway, can have a profound effect on cell survival. However, by conferring resistance to a number of chemotherapeutic drugs, elevated levels of glutathione in tumour cells are able to protect such cells in bone marrow, breast, colon, larynx and lung cancers. Here we present a number of studies investigating the role of glutathione in promoting cancer, impeding chemotherapy, and the use of glutathione modulation to enhance anti-neoplastic therapy.

Multiple drug resistance parameter expression in ovarian cancer

OBJECTIVE

Drug resistance represents a complex problem for the treatment of ovarian cancer. This study was undertaken to assess several putative resistance parameters (DRP) in parallel in cancer tissue from newly diagnosed patients with ovarian cancer in order to establish possible correlations to known clinical factors and prognosis.

MATERIAL AND METHODS

Tumor and adjacent tumor free ovarian tissue samples from 39 consecutive, untreated female patients with ovarian cancer were obtained and as potential DRPs, the level of glutathione (GSH), the activities of glutathione S-transferase (GST), glutathione-peroxidase (GPx), O6-alkylguanine-DNA alkyltransferase (Atase), and topoisomerase II (TOPO) were assessed biochemically, and P-glycoprotein (Pgp) was assessed by Western blotting.

RESULTS

Interindividual variations were high and each patient exhibited an individual profile of resistance factor expression. Levels of GSH were increased with stage (linear trend: P < 0.002), and GST, GPx, and Atase showed a similar tendency. With few exceptions no correlation was found between the DRPs and other prognostic characteristics. All tested DRPs except Pgp showed significantly higher levels/activities in tumor tissues than in the surrounding tumor free tissues (P < 0.05). The tested DRPs were found not to influence response to treatment.

CONCLUSIONS

It is concluded that elevated DRPs reflect an intrinsic pattern of components of the detoxifying system in the tumor tissue. This pattern differs between patients and may partly explain the difficulty to assess the clinical importance of individual DRPs in order to translate them into recommendations for specific therapies.

Breast cancer: pretreatment drug resistance parameters (GSH-system, ATase, P-glycoprotein) in tumor tissue and their correlation with clinical and prognostic characteristics

BACKGROUND

The identification of new factors predicting relapse, outcome and response to systemic therapy in breast cancer is warranted. The measurement of biological markers such as drug resistance parameters (DRPs), which are part of the phenotype of malignant cells and contribute to resistance to anti-cancer drugs may be a possibility, which may ultimately lead to improvement of therapeutic results.

PATIENTS AND METHODS

The level of glutathione (GSH), activities of glutathione-S-transferase (GST), glutathione-peroxidase (GPx), 06-alkylguanine-DNA-alkyltransferase (ATase), and P-glycoprotein (PGP) were measured in tumor and adjacent tumor free tissue samples from 89 consecutive, untreated females with breast cancer and correlated with clinical and prognostic factors. Early breast cancer (EBC) was diagnosed in 56 patients, 22 patients had locally advanced (LABC) and 11 patients metastatic breast cancer.

RESULTS

All DRPs showed significantly higher expression in tumor than in tumor free tissues. GPx was positively correlated with GST (r = 0.3, P = 0.0048) and with GSH (r = 0.5, P = 0.0001) in tumor as well as in normal tissue. GST activity was significantly higher in EBC than in LABC or metastatic breast cancer (P = 0.02). GSH level was significantly higher in grade 1 than in grade 2 or grade 3 tumors (P = 0.01). When clinical characteristics were related to the level of DRP, 'high' GSH was associated with age > 60 years (P = 0.01) in EBC, and with grade 1-2 tumors (P = 0.05) in LABC. No differences in OS were apparent between groups of 'high' and 'low' DRP-expression. However, the four-year estimated disease-free survival of EBC tended to be higher in patients with 'high' GST (P = 0.10) and of LABC in patients with 'high' GPx levels (P = 0.06).

CONCLUSION

We conclude that 'high' levels of DRP in tumor tissue of breast cancer patients are part of the initial phenotype of the malignant cells. Due to its high prevalence (83% in EBC, 100% in primarily metastatic breast cancer), PGP did not add to prognostic information. High levels of GSH, GST and GPx were associated with favorable clinical characteristics and good prognosis, whereas low levels of GSH and GST activity were associated with more aggressive or more advanced disease.