Modulation of cisplatin cytotoxicity by sulphasalazine

Molecular Hybridization as a Strategy for Developing Artemisinin-Derived Anticancer Candidates

Artemisinin is a natural compound extracted from Artemisia species belonging to the Asteraceae family. Currently, artemisinin and its derivatives are considered among the most significant small-molecule antimalarial drugs. Artemisinin and its derivatives have also been shown to possess selective anticancer properties, however, there are several limitations and gaps in knowledge that retard their repurposing as effective anticancer agents. Hybridization resulting from a covalent combination of artemisinin with one or more active pharmacophores has emerged as a promising approach to overcome several issues. The variety of hybridization partners allows improvement in artemisinin activity by tuning the ability of conjugated artemisinin to interact with various molecule targets involved in multiple biological pathways. This review highlights the current scenario of artemisinin-derived hybrids with potential anticancer activity. The synthetic approaches to achieve the corresponding hybrids and the structure-activity relationships are discussed to facilitate further rational design of more effective candidates.

Chemical hybridization of sulfasalazine and dihydroartemisinin promotes brain tumor cell death

Gliomas are primary brain tumors with still poor prognosis for the patients despite a combination of cytoreduction via surgery followed by a radio-chemotherapy. One strategy to find effective treatment is to combine two different compounds in one hybrid molecule via linker to add to or at best potentiate their impact on malignant cells. Here, we report on the effects of a newly synthesized hybrid of sulfasalazine (SAS) and dihydroartemisinin (DHA), called AC254. In previous studies, both SAS and DHA have already proved to have anti-tumor properties themselves and to have sensitizing respectively potentiating effects on other treatments against malignant tumors. We investigated the impact of individual drugs SAS and DHA, their 1:1 combination and a novel SAS-DHA hybrid compound (AC254) on rodent and human glioma cells. In our study SAS alone showed no or only a mild effect on glioma, whereas DHA led to a significant reduction of cell viability in a dose-dependent manner. Next we compared the efficacy of the hybrid AC254 to the combinational treatment of its parent compounds SAS and DHA. The hybrid was highly efficient in combating glioma cells compared to single treatment strategies regarding cell viability and cell death. Interestingly, AC254 showed a remarkable advantage over the combinational treatment with both parent compounds in most used concentrations. In addition to its reduction of tumor cell viability and induction of cell death, the hybrid AC254 displayed changes in cell cycle and reduction of cell migration. Taken together, these results demonstrate that clinically established compounds such as SAS and DHA can be potentiated in their anti-cancer effects by chemical hybridization. Thus, this concept provides the opportunity to devise new effective chemotherapeutic agents.

Haploinsufficiency Interactions between RALBP1 and p53 in ERBB2 and PyVT Models of Mouse Mammary Carcinogenesis

Simple Summary

Rlip knockout has been reported to prevent cancer in highly cancer-susceptible mice lacking p53, and Rlip knockdown kills many types of cancer cells. In humans, breast cancer shows diverse characteristics, including HER2-driven subtypes and viral-driven subtypes. HER2 can be targeted; however, escape of the cancer from targeted therapies remains a problem. In this work we evaluated the capacity of Rlip knockout to prevent breast cancer in genetically engineered mouse models of HER2-driven breast cancer (Erbb2 model) and polyomavirus-driven breast cancer (PyVT model). We found that in Erbb2 mice, Rlip knockout significantly delayed oncogenesis and reduced the expression of genes associated with poor prognosis in patients. In PyVT mice, Rlip knockout did not delay oncogenesis or tumor growth, but Rlip knockdown reduced tumor metastasis to the lung. We conclude that Rlip inhibitors may significantly improve survival in HER2-positive patients, but are unlikely to offer benefits to patients with polyomavirus-associated tumors.

Abstract

We recently reported that loss of one or both alleles of Ralbp1, which encodes the stress-protective protein RLIP76 (Rlip), exerts a strong dominant negative effect on both the inherent cancer susceptibility and the chemically inducible cancer susceptibility of mice lacking one or both alleles of the tumor suppressor p53. In this paper, we examined whether congenital Rlip deficiency could prevent genetically-driven breast cancer in two transgenic mouse models: the MMTV-PyVT model, which expresses the polyomavirus middle T antigen (PyVT) under control of the mouse mammary tumor virus promoter (MMTV) and the MMTV-Erbb2 model which expresses MMTV-driven erythroblastic leukemia viral oncogene homolog 2 (Erbb2, HER2/Neu) and frequently acquires p53 mutations. We found that loss of either one or two Rlip alleles had a suppressive effect on carcinogenesis in Erbb2 over-expressing mice. Interestingly, Rlip deficiency did not affect tumor growth but significantly reduced the lung metastatic burden of breast cancer in the viral PyVT model, which does not depend on either Ras or loss of p53. Furthermore, spontaneous tumors of MMTV-PyVT/Rlip+/+ mice showed no regression following Rlip knockdown. Finally, mice lacking one or both Rlip alleles differentially expressed markers for apoptotic signaling, proliferation, angiogenesis, and cell cycling in PyVT and Erbb2 breast tumors. Our results support the efficacy of Rlip depletion in suppressing p53 inactivated cancers, and our findings may yield novel methods for prevention or treatment of cancer in patients with HER2 mutations or tumor HER2 expression.

Restoring microenvironmental redox and pH homeostasis inhibits neoplastic cell growth and migration: therapeutic efficacy of esomeprazole plus sulfasalazine on 3-MCA-induced sarcoma

Neoplastic cells live in a stressful context and survive thanks to their ability to overcome stress. Thus, tumor cell responses to stress are potential therapeutic targets. We selected two such responses in melanoma and sarcoma cells: the xc- antioxidant system, that opposes oxidative stress, and surface v-ATPases that counteract the low pHi by extruding protons, and targeted them with the xc- blocker sulfasalazine and the proton pump inhibitor esomeprazole. Sulfasalazine inhibited the cystine/cysteine redox cycle and esomeprazole decreased pHi while increasing pHe in tumor cell lines. Although the single treatment with either drug slightly inhibited cell proliferation and motility, the association of sulfasalazine and esomeprazole powerfully decreased sarcoma and melanoma growth and migration. In the 3-methylcholanthrene (3-MCA)-induced sarcoma model, the combined therapy strongly reduced the tumor burden and increased the survival time: notably, 22 % of double-treated mice recovered and survived off therapy. Tumor-associated macrophages (TAM) displaying M2 markers, that abundantly infiltrate sarcoma and melanoma, overexpress xc- and membrane v-ATPases and were drastically decreased in tumors from mice undergone the combined therapy. Thus, the double targeting of tumor cells and macrophages by sulfasalazine and esomeprazole has a double therapeutic effect, as decreasing TAM infiltration deprives tumor cells of a crucial allied. Sulfasalazine and esomeprazole may therefore display unexpected therapeutic values, especially in case of hard-to-treat cancers.

xCT expression modulates cisplatin resistance in Tca8113 tongue carcinoma cells

Tongue squamous cell carcinoma (TSCC), which is a subtype of head and neck cancer, is the most common type of oral cancer. Due to its high recurrence rate and chemoresistance, the average survival rate for patients with TSCC remains unsatisfactory. At present, cisplatin (CDDP) is utilized as the first-line treatment for numerous solid neoplasms, including TSCC. CDDP resistance develops in the majority of patients; however, the mechanism of such resistance remains unknown. Therefore, the present study aimed to clarify the mechanism of CDDP resistance and attempted to reduce chemoresistance. The results indicated that CDDP significantly increased expression of xCT, which is the light chain and functional subunit of the glutamate/cysteine transporter system x_c^-, and a subsequent increase in glutathione (GSH) levels was observed. The present study demonstrated that the upregulation of xCT expression and intercellular GSH levels contributed to CDDP resistance in TSCC cells. Furthermore, xCT suppression, induced by small interfering RNA or pharmacological inhibitors, sensitized TSCC cells to CDDP treatment. In conclusion, the present study revealed that CDDP-induced xCT expression promotes CDDP chemoresistance, and xCT inhibition sensitizes TSCC cells to CDDP treatment. These results provide a novel insight into the molecular mechanisms involved in TSCC cell chemoresistance.

MRP1 and GSTp1 expression in non-small cell lung cancer does not correlate with clinicopathological parameters: A Slovakian population study

We detected MRP1 (multidrug resistance-associated protein 1) and GSTp1 (glutathione-S-transferase p1) protein expression in samples of non-small cell lung cancer (NSCLC) and our results were compared to basic clinicopathological parameters. The indirect immunohistochemical method was used for localization of monitored proteins. A total of 135 tissue samples of NSCLC were characterized according to histopathological type of tumor. Next, we compared our results with basic clinicopathological parameters (histopathological type of tumor, tumor grade and TNM stage of disease). In MRP1 and GSTp1 positive tumor cells, strong brown cytoplasmic immunostaining was visible. In our set of samples 71% showed MRP1 positivity, while according to histopathological type the squamous cell carcinoma reached the highest level of positivity (76%). Our GSTp1 results showed that similarly to MRP1, 70% of samples were GSTp1 positive. According to histopathological type the adenocarcinoma samples showed the highest GSTp1 expression (77%). For precise statistical evaluation the Kruskal-Wallis, Chi-square and Mann-Whitney tests were used. We did not find any statistically significant correlations between MRP1 and clinicopathological parameters. In the group of GSTp1, by Mann-Whitney test we found a statistically significant correlation between GSTp1 and histological grade (p=0.025) in adenocarcinoma samples. As this was only one group of statistically significant correlation we wanted to confirm this finding. For this we applied also Chi-square test which revealed no statistically significant dependence (p=0.077). No statistically significant relation was seen in the coexpression of both proteins (p=0.753). Despite this, the majority of samples simultaneously expressed MRP1 and GSTp1 proteins. In conclusion, our results show that MRP1 and GSTp1 proteins represent independent prognostic features in NSCLC. Nevertheless, the clinical outcome in individual patients is often difficult to predict. Identification of the factors that characterize the resistant cases would permit immediate treatment of the patients with alternative therapeutic approaches.

Cytotoxicity of cyclometalated platinum complexes based on tridentate NCN and CNN-coordinating ligands: remarkable coordination dependence

A series of cyclometalated platinum complexes with diverse coordination patterns and geometries were screened for their anticancer activity. It was discovered that the N^C^N-coordinated platinum complex based on 1,3-di(pyridyl)benzene displayed much higher cytotoxicity against human lung cancer cells NCI-H522, HCC827, and NCI-H1299, and human prostate cancer cell RV1 than cisplatin. In a sharp contrast, the C^N^N-coordinated platinum complex based on 6-phenyl-2,2'-bipyridine was ineffective on these cancer cells. This remarkable difference in cytotoxicity displayed by N^C^N- and C^N^N-coordinated platinum complexes was related to the trans effect of the carbon donor in the cyclometalated platinum complexes, which played a crucial role in facilitating the dissociation of the chloride ligand to create an active binding site. The DNA binding was studied for the N^C^N-coordinated platinum complex using electrophoresis and emission titration. The cellular uptake observed by fluorescent microscope showed that the complex is largely concentrated in the cytoplasm. The possible pathways for the cell apoptosis were studied by western blot analysis and the activation of PARP via caspase 7 was observed.

miR-513a-3p sensitizes human lung adenocarcinoma cells to chemotherapy by targeting GSTP1

Cisplatin is a classic chemotherapy agent used for treating human non-small cell lung cancer (NSCLC). However, cisplatin resistance is a challenge against successful clinical use. Glutathione S-transferase P1 (GSTP1) has been reported to contribute to cisplatin resistance in many studies. MicroRNAs (miRNAs) are short non-coding RNAs that are 21-25 nucleotides in length. They play a role in post-transcriptional gene regulation by inducing repression and/or mRNA degradation. Recent studies have shown that miRNAs are responsible for cisplatin resistance. This study aims to determine whether deregulated miRNAs can sensitize human lung adenocarcinoma cells to cisplatin by targeting GSTP1. Real-time RT-PCR revealed that GSTP1 mRNA expression was 2.7 ± 0.38 folds (p=0.039) upregulated in A549/CDDP cells, compared with the parental A549 cells, while miR-513a-3p expression was 0.34 ± 0.03 folds (p=0.023) downregulated. Luciferase activity assay proved that GSTP1 was a target gene of miR-513a-3p, which was confirmed by Western blot analysis. Furthermore, CCK-8 assay showed that overexpression of miR-513a-3p could enhance cisplatin-induced apoptosis in human lung adenocarcinoma cell lines, A549/CDDP and SPC-A-1. In conclusion, our data demonstrated that miR-513a-3p can sensitize human lung adenocarcinoma cells to cisplatin by targeting GSTP1.

Spectroscopic, thermal and antitumor investigations of sulfasalazine drug in situ complexation with alkaline earth metal ions

The complexes of sulfasalazine (H(3)Suz) with some of alkaline metals Mg(II), Ca(II), Sr(II) and Ba(II) have been investigated. Sulfasalazine complexes were synthesized and characterized by spectroscopic tools; infrared spectra, electronic and mass spectra. The IR spectra of the prepared complexes were suggested that the H(3)Suz behaves as a bi-dentate ligand through the carboxylic and phenolic groups. The molar conductance measurements gave an idea about the non-electrolytic behavior of the H(3)Suz complexes. The thermal decomposition processes for metal(II) complexes of H(3)Suz viz: [M(HSuz)(H(2)O)(4)] (where M = Mg(II), Ca(II), Sr(II) or Ba(II)) have been accomplished on the basis of TG/DTG and DTA studies, and the formula conforms to the stoichiometry of the complexes based on elemental analysis. The kinetic analyses of the thermal decomposition were studied using the Coats-Redfern and Horowitz-Metzger equations. The antitumor and antimicrobial activities of the H(3)Suz and their alkaline metal(II) complexes were evaluated.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

Autocrine production of interleukin-6 confers cisplatin and paclitaxel resistance in ovarian cancer cells

It has been shown that IL-6 is elevated in the serum and ascites of ovarian cancer patients, and increased IL-6 concentration correlates with poor prognosis and chemoresistance. However, the role of IL-6 expression in the acquisition of the chemoresistance phenotype and the underlining mechanisms of drug resistance in ovarian cancer cells remain unclear. Here we demonstrate that both exogenous (a relatively short period of treatment with recombination IL-6) and endogenous IL-6 (by transfecting with plasmid encoding for sense IL-6) induce cisplatin and paclitaxel resistance in non-IL-6-expressing A2780 cells, while deleting of endogenous IL-6 expression in IL-6-overexpressing SKOV3 cells (by transfecting with plasmid encoding for antisense IL-6) promotes the sensitivity of these cells to anticancer drugs. IL-6-mediated resistance of ovarian cancer cells exhibits decreased proteolytic activation of caspase-3. Meanwhile, the further study demonstrates that the chemoresistance caused by IL-6 is associated with increased expression of both multidrug resistance-related genes (MDR1 and GSTpi) and apoptosis inhibitory proteins (Bcl-2, Bcl-xL and XIAP), as well as activation of Ras/MEK/ERK and PI3K/Akt signaling. Therefore, modulation of IL-6 expression or its related signaling pathway may be a promising strategy of treatment for drug-resistant ovarian cancer.

The x(c)- cystine/glutamate antiporter: a potential target for therapy of cancer and other diseases

The x(c) (-) cystine/glutamate antiporter is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. Its main functions in the body are mediation of cellular cystine uptake for synthesis of glutathione essential for cellular protection from oxidative stress and maintenance of a cystine:cysteine redox balance in the extracellular compartment. In the past decade it has become evident that the x(c) (-) transporter plays an important role in various aspects of cancer, including: (i) growth and progression of cancers that have a critical growth requirement for extracellular cystine/cysteine, (ii) glutathione-based drug resistance, (iii) excitotoxicity due to excessive release of glutamate, and (iv) uptake of herpesvirus 8, a causative agent of Kaposi's sarcoma. The x(c) (-) transporter also plays a role in certain CNS and eye diseases. This review focuses on the expression and function of the x(c) (-) transporter in cells and tissues with particular emphasis on its role in disease pathogenesis. The potential use of x(c) (-) inhibitors (e.g., sulfasalazine) for arresting tumor growth and/or sensitizing cancers is discussed.

Sulfasalazine suppresses drug resistance and invasiveness of lung adenocarcinoma cells expressing AXL

Metastasis and drug resistance are the major causes of mortality in patients with non-small cell lung cancer (NSCLC). Several receptor tyrosine kinases (RTKs), including AXL, are involved in the progression of NSCLC. The AXL/MER/SKY subfamily is involved in cell adhesion, motility, angiogenesis, and signal transduction and may play a significant role in the invasiveness of cancer cells. Notably, no specific inhibitors of AXL have been described. A series of CL1 sublines with progressive invasiveness established from a patient with NSCLC has been identified that positively correlates with AXL expression and resistance to chemotherapeutic drugs. The ectopic overexpression of AXL results in elevated cell invasiveness and drug resistance. Nuclear factor-kappaB (NF-kappaB) signaling activity is associated with AXL expression and may play an important role in the enhancement of invasiveness and doxorubicin resistance, as shown by using the NF-kappaB inhibitor, sulfasalazine, and IkappaB dominant-negative transfectants. In the current study, sulfasalazine exerted a synergistic anticancer effect with doxorubicin and suppressed cancer cell invasiveness in parallel in CL1 sublines and various AXL-expressing cancer cell lines. Phosphorylation of AXL and other RTKs (ErbB2 and epidermal growth factor receptor) was abolished by sulfasalazine within 15 min, suggesting that the inhibition of NF-kappaB and the kinase activity of RTKs are involved in the pharmacologic effects of sulfasalazine. Our study suggests that AXL is involved in NSCLC metastasis and drug resistance and may therefore provide a molecular basis for RTK-targeted therapy using sulfasalazine to enhance the efficacy of chemotherapy in NSCLC.

Sulfasalazine-induced reduction of glutathione levels in breast cancer cells: enhancement of growth-inhibitory activity of Doxorubicin

BACKGROUND

We previously showed that the anti-inflammatory drug, sulfasalazine (salicylazosulfapyridine, SASP), can arrest proliferation of MCF-7 and MDA-MB-231 mammary cancer cells by inhibiting uptake of cystine via the x(c-) cystine/glutamate antiporter. Here we examined SASP with regard to reduction of cellular glutathione (GSH) levels and drug efficacy-enhancing ability.

METHODS

GSH levels were measured spectrophotometrically. Cellular drug retention was determined with 3H-labeled methotrexate, and drug efficacy with a colony formation assay.

RESULTS

Incubation of the mammary cancer cells with SASP (0.3-0.5 mM) led to reduction of their GSH content in a time- and concentration-dependent manner. Similar to MK-571, a multidrug resistance-associated protein inhibitor, SASP increased intracellular accumulation of methotrexate. Preincubation of cells with SASP (0.3 mM) significantly enhanced the potency of the anticancer agent doxorubicin (2.5 nM).

CONCLUSIONS

SASP-induced reduction of cellular GSH levels can lead to growth arrest of mammary cancer cells and enhancement of anticancer drug efficacy.

Therapeutic resistance in lung cancer

Despite considerable progress over the last 25 years in the systemic therapy of lung cancer, intrinsic and acquired resistance to chemotherapeutic agents and radiation remains a vexing problem. The number of mechanisms of therapeutic resistance in lung cancer has expanded considerably over the past three decades, and the crucial role of stress resistance pathways is increasingly recognised as a cause of intrinsic and acquired chemo- and radiotherapy resistance. This paper reviews recent evidence for stress defence proteins, particularly RALBP1/RLIP76, in mediating intrinsic and acquired chemotherapy and radiation resistance in human lung cancer.

Can NF-κB be a target for novel and efficient anti-cancer agents?

Since the discovery of the NF-kappaB transcription factor in 1986 and the cloning of the genes coding for NF-kappaB and IkappaB proteins, many studies demonstrated that this transcription factor can, in most cases, protect transformed cells from apoptosis and therefore participate in the onset or progression of many human cancers. Molecular studies demonstrated that ancient widely used drugs, known for their chemopreventive or therapeutic activities against human cancers, inhibit NF-kappaB, usually among other biological effects. It is therefore considered that the anti-cancer activities of NSAIDs (non-steroidal anti-inflammatory drugs) or glucocorticoids are probably partially related to the inhibition of NF-kappaB and new clinical trials are being initiated with old compounds such as sulfasalazine. In parallel, many companies have developed novel agents acting on the NF-kappaB pathway: some of these agents are supposed to be NF-kappaB specific (i.e. IKK inhibitors) while others have wide-range biological activities (i.e. proteasome inhibitors). Today, the most significant clinical data have been obtained with bortezomib, a proteasome inhibitor, for the treatment of multiple myeloma. This review discusses the preclinical and clinical data obtained with these various drugs and their putative future developments.

Glutathione S-transferases as antioxidant enzymes: Small cell lung cancer (H69) cells transfected with hGSTA1 resist doxorubicin-induced apoptosis

It has been suggested that the alpha-class glutathione S-transferases (GSTs) protect various cell types from oxidative stress and lipid peroxidation (LPO). In order to examine the protective role of alpha-class GST isozyme hGSTA1-1 against doxorubicin (DOX)-induced lipid peroxidation, cytotoxicity, and apoptosis, human small cell lung cancer (SCLC) H69 cells were stably transfected with hGSTA1. Immunological and biochemical characterization of hGSTA1-transfected cells revealed the expression of functionally active hGSTA1-1 localized near the cellular plasma membranes. hGSTA1-transfected cells acquired significantly increased resistance to the DOX-induced cytotoxicity by suppressing lipid peroxidation levels in these cells. Overexpression of hGSTA1-1 in cells inhibited DOX-mediated depletion of GSH and higher GSH levels were found in DOX-treated hGSTA1-transfected cells as compared with empty vector-transfected controls. hGSTA1-1 overexpression also provided protection to cells from DOX-induced apoptosis by inhibiting phosphorylation of c-Jun-N-terminal kinases (JNK), caspase-3 activation, and by preserving the levels of anti-apoptotic protein Bcl-2. These results are consistent with the idea that the alpha-class GSTs provide protection against oxidative stress by attenuating lipid peroxidation and these enzymes can modulate signaling for apoptosis.

Molecular Modeling, Synthesis, and Preliminary Biological Evaluation of Glutathione-S-Transferase Inhibitors as Potential Therapeutic Agents

Changes in the GSH/GST system have been found to correlate with resistance to anticancer alkylating agents, presumably through accelerated detoxification of these drugs since some GSTs have been shown to catalyze the conjugation of GSH to specific antineoplastic agents. GSH-alkyl derivatives were designed by molecular modeling, synthesized, and tested as inhibitors of human GST-Pi.

Depletion of RLIP76 sensitizes lung cancer cells to doxorubicin

Ral-interacting protein (RLIP76) (RALBP1) is an anti-apoptotic non-ABC glutathione (GSH)-conjugate transporter involved in receptor-ligand endocytosis, as well as in multispecific drug transport and resistance. Partial inhibition of RLIP76 using antibodies in the absence of chemotherapy drug causes apoptosis in multiple small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cell lines and in the presence of doxorubicin (DOX), marked synergy is observed. These findings indicated that RLIP76 should be a good target for cancer cell killing; its down-regulation would promote apoptosis through both drug-dependent and drug-independent effects. To examine the effect of complete and specific RLIP76 depletion on apoptosis, we tested the effects of RLIP76 siRNA in a number of lung cancer cell lines. Growth inhibition and apoptosis was observed in all cases upon RLIP76 depletion. Consistent with these findings, augmenting cellular RLIP76 through transfection or liposomal protein delivery conferred resistance to apoptosis mediated by either DOX or 4-hydroxynonenal (4-HNE). Taken together, our results show that RLIP76 is rational and promising new target for lung cancer therapy.

Differential roles of 3H-1,2-dithiole-3-thione-induced glutathione, glutathione S-transferase and aldose reductase in protecting against 4-hydroxy-2-nonenal toxicity in cultured cardiomyocytes

4-hydroxy-2-nonenal (HNE) plays an important role in the pathogenesis of cardiac disorders. While conjugation with glutathione (GSH) catalyzed by GSH S-transferase (GST) has been suggested to be a major detoxification mechanism for HNE in target cells, whether chemically upregulated cellular GSH and GST afford protection against HNE toxicity in cardiac cells has not been investigated. In addition, the differential roles of chemically induced GSH and GST as well as other cellular factors in detoxifying HNE in cardiomyocytes are unclear. In this study, we have characterized the induction of GSH and GST by 3H-1,2-dithiole-3-thione (D3T) and the protective effects of the D3T-elevated cellular defenses on HNE-mediated toxicity in rat H9C2 cardiomyocytes. Treatment of cardiomyocytes with D3T resulted in a significant induction of both GSH and GST as well as the mRNA expression of gamma-glutamylcysteine ligase catalytic subunit and GSTA. Both GSH and GST remained elevated for at least 72 h after removal of D3T from the culture media. Treatment of cells with HNE led to a significant decrease in cell viability and an increased formation of HNE-protein adducts. Pretreatment of cells with D3T dramatically protected against HNE-mediated cytotoxicity and protein-adduct formation. HNE treatment caused a significant decrease in cellular GSH level, which preceded the loss of cell viability. Either depletion of cellular GSH by buthionine sulfoximine (BSO) or inhibition of GST by sulfasalazine markedly sensitized the cells to HNE toxicity. Co-treatment of cardiomyocytes with BSO was found to completely block the D3T-mediated GSH elevation, which however failed to reverse the cytoprotective effects of D3T, suggesting that other cellular factor(s) might be involved in D3T cytotprotection. In this regard, D3T was shown to induce cellular aldose reductase (AR). Surprisingly, inhibition of AR by sorbinil failed to potentiate HNE toxicity in cardiomyocytes. In contrast, sorbinil dramatically augmented HNE cytotoxicity in cells with GSH depletion induced by BSO. Similarly, in BSO-treated cells, D3T cytoprotection was also largely reversed by sorbinil, indicating that AR played a significant role in detoxifying HNE only under the condition of GSH depletion in cardiomyocytes. Taken together, this study demonstrates that D3T can induce GSH, GST, and AR in cardiomyocytes, and that the above cellular factors appear to play differential roles in detoxification of HNE in cardiomyocytes.

Reversal of multidrug resistance by small interfering double-stranded RNAs in ovarian cancer cells

OBJECTIVE

Cisplatin (DDP) resistance is a major barrier to overcome before chemotherapy can become curative for most patients presenting with ovarian cancer. In this study, we investigated the effect of siRNAs on expression of p-gp, GST-pi mRNA and protein in cisplatin-resistant human ovarian cancer cells in order to restore sensitivity to DDP.

METHODS

Small interfering double-stranded RNAs (siRNA) were designed to target p-glycoprotein (p-gp) and glutathione S-transferases (GST) mRNA as a strategy to inhibit both resistant gene expression at the mRNA level. Using Real-Time PCR and western blotting assay the changes of the RNA and protein levels of both drug resistant genes were studied.

RESULTS

Transfection of MDR-1 and GST siRNAs into human multi-drug resistance (MDR) ovarian cancer cell lines, COC1/DDP and SKOV3/DDP, resulted in a time-dependent inhibition of both gene expressions with the decline of the IC(50) values but had no effect on the expression of a-Tubulin. Inhibition of P-gp and GST expression by siRNA enhanced the intracellular accumulation of and restored sensitivity to DDP.

CONCLUSIONS

These studies suggest that p-gp and GST siRNAs are effective inhibitors of MDR gene expression and reverse the resistance of ovarian carcinomas. Our studies may provide a new insight to develop siRNAs as a novel therapeutic tool for the treatment of ovarian carcinomas.

Polymorphisms of the glutathione S-transferase P1 gene and head and neck cancer susceptibility

BACKGROUND

Factors determining the individual susceptibility to head and neck squamous cell carcinoma (HNSCC) are still largely unknown. An imbalance between enzymes involved in the toxification and detoxification of (pre)-carcinogens closely related to HNSCC, which may appear during smoking and alcohol consumption, may play a role. Genetic polymorphisms in glutathione S-transferases (GSTs) often result in altered detoxification, which may contribute to individual susceptibility to HNSCC.

METHODS

We studied the frequencies of polymorphic variants in the GSTP1 gene in 235 patients with HNSCC and 285 healthy controls. In addition, data on exposure to alcohol and tobacco consumption were recorded. DNA was extracted from whole blood, and polymerase chain reaction-based methods were used to detect genetic polymorphisms.

RESULTS

In patients with HNSCC and control groups, the homozygous GSTP1 BB genotype was observed in 12.3% and 13.6%, respectively. No statistical differences were found for the GSTP1 AA and GSTP1 AB/GSTP1BB genotypes.

CONCLUSIONS

Our study showed that genetic polymorphisms of GSTP1 are not associated with altered susceptibility to HNSCC.

Modulation of cisplatin cytotoxicity and cisplatin-induced DNA cross-links in HepG2 cells by regulation of glutathione-related mechanisms

Glutathione (GSH), glutathione S-transferase (GST), and glutathione conjugate export pump (GS-X pump) have been shown to participate collectively in the detoxification of many anticancer drugs, including cisplatin. Identification and regulation of the rate-limiting step in the overall system for cisplatin detoxification is of crucial importance for sensitization of human tumor cells to cisplatin. In this study, the GSH content, GST activity, and GS-X pump activity were regulated separately to examine effects of the regulation on cisplatin cytotoxicity and cisplatin-induced DNA interstrand cross-links (ICL) in HepG2 cells. Seventy-percent depletion of GSH by buthionine sulfoximine (BSO) and 50% increase of GSH by monoethyl GSH ester (GSHe) potentiated and decreased cisplatin cytotoxicity, respectively. This was reflected by a significant decrease and increase of their respective IC(50) values by 62 and 107%. Cisplatin-induced ICL was also potentiated by depletion of GSH by BSO and decreased by enrichment of GSH by GSHe, as shown by a 125% increase and a 34% decrease of cross-linked DNA compared with control samples exposed to cisplatin alone (p = 0.008 and 0.03, respectively). On the other hand, inhibition of GST and GS-X pump by ethacrynic acid, quercetin, tannic acid, and indomethacin at concentrations that inhibited activities of GST and GS-X pump by more than 50% had no significant effects on cisplatin cytotoxicity and cisplatin-induced DNA ICL in these cells. The results showed that of the parameters measured, intracellular GSH seems to be the rate-limiting factor, and its regulation would provide a more promising strategy for sensitization of human liver tumor cells to cisplatin.

Glutathione S-transferase-pi gene expression and platinum drug exposure in human lung cancer

We examined the association between the gene expression levels of glutathione S-transferase-pi (GST-pi) and platinum drug exposure in human lung cancer. First we monitored GST-pi gene expression levels in two lung cancer cell lines and in peripheral mononuclear cells of ten previously untreated lung cancer patients after platinum drug exposure. Next we examined GST-pi gene expression levels in 40 lung cancer autopsy specimens. The GST-pi gene expression levels were assessed by the quantitative reverse transcription-polymerase chain reaction or Northern blot analysis. The GST-pi gene expression was not induced by platinum drugs either in vitro and in vivo within 24 h of exposure. In contrast, GST-pi gene expression levels in lung cancer tissues of patients who had been exposed to platinum drugs at least 1 month before death were significantly higher than that in those of patients who had not been exposed. These results suggest that GST-pi gene expression is associated with chronic exposure to platinum drugs in lung cancer and/or the stress response to xenobiotics.

The ligandin (non-substrate) binding site of human Pi class glutathione transferase is located in the electrophile binding site (H-site)

Glutathione S -transferases (GSTs) play a pivotal role in the detoxification of foreign chemicals and toxic metabolites. They were originally termed ligandins because of their ability to bind large molecules (molecular masses >400 Da), possibly for storage and transport roles. The location of the ligandin site in mammalian GSTs is still uncertain despite numerous studies in recent years. Here we show by X-ray crystallography that the ligandin binding site in human pi class GST P1-1 occupies part of one of the substrate binding sites. This work has been extended to the determination of a number of enzyme complex crystal structures which show that very large ligands are readily accommodated into this substrate binding site and in all, but one case, causes no significant movement of protein side-chains. Some of these molecules make use of a hitherto undescribed binding site located in a surface pocket of the enzyme. This site is conserved in most, but not all, classes of GSTs suggesting it may play an important functional role.

Characterization of a chlorambucil-resistant human ovarian carcinoma cell line overexpressing glutathione S-transferase mu

Ovarian carcinoma cells 10-fold resistant to the alkylating agent chlorambucil (CBL) were isolated after repeated exposure of the parent cells to gradually escalating concentrations of the drug. The resistant variant, A2780(100), was highly cross-resistant (9-fold) to melphalan and showed lower-level resistance to other cross-linking agents. The resistant A2780(100) cells had almost 5-fold higher glutathione S-transferase (GST) activity than the parental A2780 cells with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. The pi-class GST(s) was the major isoform(s) in both cell lines. However, the resistant A2780(100) cells had at least 11-fold higher GST mu as compared with the parental cells, in which this isoform was barely detectable. A significant induction of GST mu was observed in A2780 cells, but not in the resistant cells, 18 hr after a single exposure to 100 microM CBL. The induction of GST mu by CBL was both time- and concentration-dependent. Assays of the conjugation of CBL with GSH showed that the human mu-class GST had 3.6- and 5.2-fold higher catalytic efficiency relative to the pi- and alpha-class GSTs, respectively. This difference was reflected in the relatively higher (about 6-fold) efficiency of CBL conjugation in A2780(100) cells as compared with the parental cells. These results have demonstrated for the first time a near-linear correlation between CBL resistance and overexpression of mu-class GSTs and suggest that this overexpression maybe responsible, at least in part, for the acquired resistance of ovarian carcinoma cells to CBL, and possibly the other bifunctional alkylating agents. Consistent with this hypothesis, we found evidence for decreased formation of DNA lesions in A2780(100) compared with the drug-sensitive A2780 cells after exposure to CBL.

The role of glutathione S-transferases as a defense against reactive electrophiles in the blood vessel wall

The glutathione transferases (GSTs) are a family of ubiquitous enzymes that catalyze the conjugation of reduced glutathione (GSH) with reactive electrophiles. Rat vascular tissue contains GST isoforms that represent a major cellular defense mechanism against atherogenic alpha,beta-unsaturated aldehydes (Misra et al., Toxicol. Appl. Pharmacol. 133, 27-33, 1995). In this study we examined the role of GSTs in providing protection to cultured neonatal vascular smooth muscle cells (VSMCs) from the alpha,beta-unsaturated carbonyl cardiovascular toxins, allylamine and its metabolite, acrolein. Confluent cultured cells were exposed to 2 to 10 microM allylamine (a cardiovascular toxin that is metabolized in vivo and in vitro by VSMCs to the reactive aldehyde, acrolein) or to acrolein (2-10 microM) for 48 h; dose-cytotoxicity curves were generated utilizing a tetrazolium-dependent cytotoxicity assay. Concommittant treatment with sulfasalazine, an established inhibitor of GST, was found to markedly increase allylamine- or acrolein-induced cytotoxicity, decreasing the LC50 by two- to threefold at 50 to 100 microM sulfasalazine. A clonogenic survival assay in VSMCs exposed to these compounds for 4 h confirmed lethal toxicity and enhanced toxicity following cotreatment with sulfasalazine. Isobologram analysis (which statistically defines the limits of additivity of two independent treatments) showed that the sulfasalazine effect on both allylamine and acrolein cytotoxicity was supraadditive, or synergistic. Sulfasalazine was not cytotoxic to VSMCs in the range of concentrations that augmented acrolein or allylamine cytoxicity; total GST activity was inhibited, however, in a dose-dependent manner in that range. GST purified by GSH-affinity chromatography from pelleted untreated cells gave specific activities and kinetic constants consistent with those previously reported for rat aorta total GSTs. The catalytic efficiency (Kcat/Vm) was found to be much greater for 4-hydroxy-2-nonenal than for 1-chloro-2,4-dinitrobenzene (0.058 vs 0.4 s-1 mM-1). Western blot of purified total GSTs using antibodies against rec-mGSTA4-4 revealed a single band at 25 kDa, confirming the presence of a GST isozyme immunologically similar to rat GST8-8, which is known to utilize alpha,beta-unsaturated carbonyls as preferred substrates. Our data indicate that GSTs are an important defense in the vascular media, protecting blood vessels against alpha,beta-unsaturated carbonyl cardiovascular toxins that are involved in initiating atherosclerotic lesions.

Inhibitors of glutathione S-transferases as therapeutic agents

Glutathione S-transferases (GST) are a family of phase II detoxification enzymes with broad substrate specificities. They catalyze the conjugation of glutathione with many different types of xenobiotics, rendering the compound more water soluble and thus more easily eliminated. Resistance to cancer chemotherapeutic drugs, such as the alkylating agents, has been directly correlated with the overexpression of GSTs. Subsequently, a rationale has been established to utilize agents that inhibit GST in combination with alkylating agents to circumvent this resistance. Two such agents, ethacrynic acid (EA) and Terrapin 199 (TER 199), have been examined for this purpose. EA, an inhibitor of all classes of GST isozymes, has been used clinically in combination with thiotepa. More recently, TER 199, a glutathione analog-based GST inhibitor, has been modeled specifically to inhibit GST pi, an enzyme which is commonly found at high levels in human tumor biopsies. Furthermore, a therapeutic strategy has been designed to take advantage of GST pi activation of a prodrug, TER 286. Recent studies have investigated the molecular mechanisms involved in the cellular response to GST inhibitors and have employed techniques such as differential display to examine altered gene expression as well as to identify novel genes induced by these agents. Overall, this strategy may provide further insight into the action of these agents in the cell as well as prove useful in endeavors to modulate anticancer drug resistance.

Purification and characterization of class alpha and Mu glutathione S-transferases from porcine liver

Six cytosolic GSTs from porcine liver were purified by a combination of glutathione affinity chromatography and ion-exchange HPLC. The isoenzymes were characterized by SDS-PAGE, gel filtration, isoelectric focusing, immunoblotting analysis and determination of substrate specificities and inhibition characteristics. The purified GSTs belong to the alpha and mu classes, respectively. No class pi isoenzyme was isolated or detected. The class alpha GST pA1-1* exists as a homodimer (M(r) = 25.3 kDa), whereas GST pA2-3* consists of two subunits with different M(r) values (27.0 and 25.3 kDa). The estimated pI values were 9.5 and 8.8, respectively. Furthermore, four class mu porcine GSTs, pM1-1*, pM1-2*, pM3-?* and pM4-?*, were isolated. The isoenzyme pM1-1* possesses a relative molecular mass of 27.2 kDa and a pI value of 6.2. Additional pM1 isoenzymes hybridize with the subunit pM2* (M(r) = 25.2) to furnish a heterodimer, which shows a pI value of 5.8. The other class mu isoenzymes are heterodimers with pI values of 5.45 and 5.05. Substrate specificities and inhibition characteristics correlate very well with those of the corresponding human isoenzymes. The results are discussed with regard to the usefulness of porcine GSTs as an in vitro testing model.

Lentinan enhances sensitivity of mouse colon 26 tumor to cis-diamminedichloroplatinum (II) and decreases glutathione transferase expression

We investigated the influence of a combination of lentinan, a biological response modifier, and cis-diamminedichloroplatinum(II) (CDDP) on the growth and glutathione S-transferase (GST) content of colon 26 tumor to examine whether lentinan represses GST expression and enhances the therapeutic effects of CDDP. Female CDF1 mice inoculated subcutaneously with transplantable colon 26 adenocarcinoma cells (1 X 10(6)/mouse) received intraperitoneal administrations of lentinan, CDDP, or the two drugs in combination, on days 10, 14, 17 and 21 after the inoculation. On day 24, tumor weights (estimated from their length and width) were significantly lower in the CDDP+ lentinan group (2.7+/-1.3 g) than in the CDDP alone group (4.3+/-0.7 g, P<0.05), both values being less than in the nontreated control group (7.2+/-1.5 g). The major GST form of colon 26 tumor was identified as GST-II, the Pi class form, and a minor form as GST-III belonging to the Mu class. Both GST-II and GST-III values on day 24 were significantly decreased in the lentinan alone (0.90+/-0.29 and 0.26 +/-0.11 microg/mg protein, respectively) and lentinan + CDDP groups (0.98+/-0.22 and 0.29+/-0.07 microg/mg protein), as compared with the control levels (1.39+/-0.20 and 0.52+/-0.11 microg/mg protein). However, these values were not different between the CDDP alone and lentinan + CDDP groups. Neither tissue interleukin (IL)-6, glutathione nor platinum values were different between the two groups. IL-6 values were elevated in about half of the samples treated with lentinan or CDDP and exhibited a modest inverse correlation with GST-II levels (r= -0.46). A GST inhibitor, ethacrynic acid, enhanced the sensitivity of cultured colon 26 cells to CDDP, suggesting the possible involvement of GST in modulating the cytotoxicity of CDDP to this cell line. These results indicated that lentinan administration decreases tissue GST-II and GST-III contents and enhances the sensitivity of colon 26 tumor to CDDP.