Detoxifying enzymes in human ovarian tissues: comparison of normal and tumor tissues and effects of chemotherapy

Degradable redox-responsive disulfide-based nanogel drug carriers via dithiol oxidation polymerization

Stimuli-responsive nanogels are important drug and gene carriers that mediate the controlled release of therapeutic molecules. Herein, we report the synthesis of fully degradable disulfide cross-linked nanogel drug carriers formed by oxidative radical polymerization of 2,2'-(ethylenedioxy)diethanethiol (EDDET) as a monomer with different cross-linkers, including pentaerythritol tetramercaptoacetate (PETMA). Because the poly(EDDET) backbone repeat structure and cross-linking junctions are composed entirely of disulfide bonds, these nanogels specifically degrade to small molecule dithiols intracellularly in response to the reducing agent glutathione present inside of cells. Cross-linked nanogels were synthesized using controlled microfluidic mixing in the presence of a nonionic Pluronic surfactant PLU-127 to increase the nanogel stability. Adjusting the monomer to cross-linker ratio from 5 : 1 to 100 : 1 (mol/mol) tuned the cross-linking density, resulting in swelling ratios from 1.65 to >3. Increasing the amount of stabilizing Pluronic surfactant resulted in a decrease of nanogel diameter, as expected due to increased surface area of the resulting nanogels. The monomer to cross-linker ratio in the feed had no effect on the formed nanogel diameter, providing a way to control cross-linking density with constant nanogel size but tunable drug release kinetics. Nanogels exhibited an entrapment efficiency of up to 75% for loading of Rhodamine B dye. In vitro studies showed low cytotoxicity, quick uptake, and fast degradation kinetics. Due to the ease of synthesis, rapid gelation times, and tunable functionality, these non-toxic and fully degradable nanogels offer potential for use in a variety of drug delivery applications.

pH- and redox-responsive poly(ethylene glycol) and cholesterol-conjugated poly(amido amine)s based micelles for controlled drug delivery

An optimized condition is identified to prepare linear poly(amido amine)s via Michael Addition polymerization of trifunctional amine, 4-(aminomethyl)piperidine (AMPD), with an equimolar diacrylamide, N,N-cystaminebis(acrylamide) (BAC). Poly(ethylene glycol) (PEG) and cholesterol (CE) are conjugated to linear poly(BAC-AMPD) through the reactions with the secondary amino groups in the backbone, respectively, to form poly(BAC-AMPD)-g-PEG-g-CE. The chemical structures of poly(BAC-AMPD) and poly(BAC-AMPD)-g-PEG-g-CE are characterized using NMR and gel permeation chromatography (GPC). Transmission electron microscopy (TEM), dynamic light scattering (DLS) and (1)H NMR results show that micelles with PEG shells and hydrophobic cores composed of poly(BAC-AMPD) and CE are formed via self-assembly of poly(BAC-AMPD)-g-PEG-g-CE in aqueous solution, and the micelles of poly(BAC-AMPD)-g-PEG-g-CE can be degraded by the presence of L-dithiothreitol and show a limited cytotoxicity in vitro. The anti-cancer drug, doxorubicin (DOX), can be loaded into the micelles. The DOX loaded micelles of poly(BAC-AMPD)-g-PEG-g-CE show pH- and redox-responsive drug release and redox-induced formation of aggregates, and it is shown that the DOX loaded micelles can deliver DOX into cells and show a higher efficacy in killing cancer cells than free drug.

Glutathione levels in human tumors

This review summarizes clinical studies in which glutathione was measured in tumor tissue from patients with brain, breast, gastrointestinal, gynecological, head and neck and lung cancer. Glutathione tends to be elevated in breast, ovarian, head and neck, and lung cancer and lower in brain and liver tumors compared to disease-free tissue. Cervical, colorectal, gastric, and esophageal cancers show both higher and lower levels of tumor glutathione. Some studies show an inverse relationship between patient survival and tumor glutathione. Based on this survey, we recommend approaches that may improve the clinical value of glutathione as a biomarker.

Significance of the O6-methylguanine-DNA methyltransferase and glutathione S-transferase activity in the sera of patients with malignant and benign ovarian tumors

OBJECTIVE

To demonstrate O6-methylguanine-DNA methyltransferase (MGMT) and glutathione S-transferase (GST) activities by analyzing the sera separately obtained from patients with malignant ovarian tumors, benign ovarian tumors, and healthy individuals.

STUDY DESIGN

Fourty-nine patients with ovarian cancer, nine patients with benign tumors, and 22 healthy women were included in this study. Blood samples were obtained from all the subjects in the malignant-tumor, benign-tumor, and control groups. Patients with malignant tumors underwent second and third phlebotomies one week following the surgery and after the chemotherapy regimen, respectively. MGMT, GST, and protein levels were measured for each serum sample. GST activity of the samples was measured by the method of Habig et al. using l-chloro-2-4 dinitrobenzene (CDNB) as substrate. MGMT activity was measured by the transfer of radio labelled methyl groups from a prepared MG-DNA substrate to the enzyme fraction of serum. Protein concentration was measured by biuret method.

RESULTS

Our work demonstrated that untreated patients with malignant ovarian tumors revealed significantly greater MGMT and GST activities in their sera than did both healthy individuals and patients with benign ovarian tumors, while no significant difference was found between the healthy group and the patients with benign ovarian tumors with respect to their sera MGMT and GST activities. GST activity following chemotherapy was significantly lower than the postoperative values preceding chemotherapy. A relationship between sera MGMT and GST activities, tumor histology and pathology was not found in this study.

CONCLUSION

Our work suggests the fact that detection of sera MGMT and GST activities is important in diagnostic and therapeutic approaches during the course of ovarian cancer.

Levels and subcellular distributions of detoxifying enzymes in the ovarian corpus luteum of the pregnant and non-pregnant pig

The levels and subcellular distribution of enzymes involved in defenses against reactive oxygen superoxide dismutase (SOD; E.C.1.15.1.1), glutathione peroxidase (GPX; E.C.1.11.1.9), catalase (CAT; E.C.1.11.1.6), and DT-diaphorase (DT; E.C.1.6.99.2) and of the conjugating enzymes glutathione transferase (GST; E.C.2.5.1.18) and p-sulphotransferase (p-ST; E.C.2.8.2.1) in the corpus luteum of ovaries from pregnant and non-pregnant pigs were investigated. In addition, non-protein thiols and glutathione reductase (GRD; E.C.1.6.4.2) were examined in the same manner. The total cytosolic activities of CAT, DT, GRD, and p-ST were significantly increased, whereas total GST activity was decreased in the pregnant corpus luteum compared to the corresponding activities in non-pregnant corpus luteum. In the case of the mitochondrial fraction from pregnant corpus luteum, GPX and GRD displayed significant increases in specific activity. Upon subfractionation of the mitochondrial fraction (i.e. mitoplast preparation), SOD activity was distributed equally between the mitoplasts and the supernatant. CAT and GPX activities were mainly recovered in the supernatant, while the major GRD activity pelleted with the mitoplasts. Microsomes from pregnant corpus luteum demonstrated increased specific GPX activity and decreased SOD activity compared to the non-pregnant corpus luteum. No differences in the non-protein thiol levels in the cytosolic, mitochondrial, or microsomal fractions from the corpus luteum were observed between non-pregnant and pregnant sows.

The role of the glutathione-dependent system in tumor sensitivity to cisplatin: a study of human tumor xenografts

BACKGROUND

Glutathione, the most important intracellular thiol, has been implicated in modulating tumor cell sensitivity to alkylating agents and cisplatin. However, the role of the glutathione-dependent detoxification system in mediating cisplatin resistance of human tumors remains unclear.

DESIGN

Glutathione content and related enzyme activities were assessed in a series of human tumor xenografts representative of responsive (i.e., small-cell lung cancer and ovarian carcinoma) and resistant tumor types (i.e., non-small-cell lung cancer and colorectal carcinoma), in an attempt to establish a correlation with response to cisplatin treatment.

RESULTS

The pattern of tumor response to cisplatin treatment for tumors selected in the two panels corresponded to the one expected from the clinical experience, since drug-induced tumor growth inhibition ranged from 70% to 100% in the group of sensitive tumors and from 20% to 60% in the group of resistant tumors. No correlation was observed between glutathione level and cisplatin response in the resistant tumor panel. An inverse correlation was found for glutathione-S-transferase activity level and tumor response only in the panel of chemoresponsive tumors. In the latter panel, the only unresponsive tumor (POCS) showed the highest glutathione level in the entire series investigated. No significant correlation was found between other enzymes investigated and tumor response to cisplatin treatment. In addition, a very low activity of gamma-glutamyltranspeptidase was found to be associated with sensitive tumors.

CONCLUSIONS

Although glutathione may have a role in modulating cisplatin cell sensitivity, it is unlikely that alteration in glutathione level and metabolism is a primary mechanism of cisplatin resistance in human tumors, since: a) no significant correlations were found between glutathione level and response to cisplatin treatment in a series of chemosensitive and chemoresistant human tumor xenografts; b) a marked increase in glutathione level might be responsible for cisplatin resistance but, in contrast to findings on cell systems selected in vitro for resistance, it is not a frequent event in human tumors.

Detoxification ability and toxicity of quinones in mouse and human tumor cell lines used for anticancer drug screening

The in vitro testing of antitumor drugs involves the use of mouse and human tumor cells. In particular, there is interest in developing agents active against human solid tumors. We examined several biochemical parameters that may contribute to the differential sensitivity of the cell lines used in our laboratory to the toxic effects of antitumor compounds. The tumor cell lines examined were of mouse (colon 38, L1210 leukemia, and C1498 leukemia) and human origin (CEM leukemia, CX1 colon, H116 colon, HCT8 colon and H125 lung). Quinone reductase activity was markedly different between leukemia and solid-tumor cell lines of either mouse or human origin, with increased activity being observed in the solid-tumor cell lines relative to the leukemia lines. GSH transferase activity also was generally increased in solid-tumor relative to leukemia cell lines. Superoxide dismutase activity and thiol levels were similar in leukemia and solid-tumor cell lines, except that thiol levels were very low in colon 38. Mouse cell lines from in vitro passage had somewhat higher activity of superoxide dismutase and thiol levels than did cells maintained in vivo, indicating relatively increased antioxidant defenses. The toxicity of 2,3-dimethoxy-1,4-naphthoquinone, a model quinone that exerts its toxic effects via production of reactive oxygen species, was significantly lower in mouse lines maintained in vitro than in those tested in vivo, whereas the toxicity of another quinone, menadione, was just slightly lower. Quinone reductase activity, GSH transferase activity, and thiol levels were significantly higher in the human lines than in the mouse lines. Accordingly, the toxicity of both quinones tended to be lower in the human lines than in the mouse lines.

Toxicity, single-strand breaks, and 5-hydroxymethyl-2'-deoxyuridine formation in human breast epithelial cells treated with hydrogen peroxide

DNA damage induced by oxidants includes formation of DNA strand breaks as well as oxidative damage to DNA bases. We quantified both forms of DNA damage concurrently in two model human breast epithelial cell lines treated with hydrogen peroxide to compare the dose-dependent induction of each form of DNA damage with growth inhibition. Antioxidant defenses also were quantified. MCF-7 breast cancer cells had relatively higher levels of non-protein thiols, oxidized glutathione (GSSG) reductase, catalase, and superoxide dismutase than did the MCF-10A line of immortalized, but not transformed, human breast epithelial cells. The levels of antioxidant defenses were not predictive of endogenous oxidative DNA damage levels nor of toxicity and DNA damage induced by hydrogen peroxide. The endogenous levels of 5-hydroxymethyl-2'-deoxyuridine were higher in MCF-7 than MCF-10A cells. The cells were treated with 10-200 microM hydrogen peroxide for 15 min at 37 degrees C in complete media. Low concentrations of hydrogen peroxide were growth stimulatory to both cell lines. At higher concentrations, growth inhibition by hydrogen peroxide was greater in MCF-7 than in MCF-10A cells. Accordingly, induction of both single-strand DNA breaks and 5-hydroxymethyl-2'-deoxyuridine in DNA was greater in MCF-7 than MCF-10A cells. In both cell lines, the dose-dependent induction of single-strand breaks paralleled growth inhibition more closely than did formation of 5-hydroxymethyl-2'-deoxyuridine.

Advanced ovarian cancer. Drug resistance, supportive care and dose intensity

BACKGROUND

Both intrinsic and acquired drug resistance occur in ovarian cancer. Much work on in vivo or in vitro, obtained drug resistance has been done and this knowledge is presently being converted into clinical studies.

MATERIALS AND METHODS

The review focuses on the detoxifying system, MDR (multidrug resistance), and supportive care in relation to dose intensity.

RESULTS

In vitro models suggest that the amount of glutathione, glutathione S-transferase activity or metallothioneins could play a role in the outcome of chemotherapy treatment. The results of human tumour samples studies however do not support this idea. Expression of the cell membrane P-glycoprotein in tumour cells appears in vitro to be an important adverse prognostic factor concerning the effect of natural products. Again the results in human tumour samples vary. The supportive agent sodium thiosulphate protects against cisplatin induced nephrotoxicity, but the exact role of sulphur compounds in ameliorating the neurotoxicity is not yet established. The neuropeptide Org 2766 may be a possible neuroprotector. Hemopoietic growth factors such as GM-CSF, G-CSF and interleukin-3, protect the bone marrow to varying degrees. Autologous bone marrow transplantation induces high, but often short lasting response rates in chemotherapy resistant patients.

CONCLUSIONS

More clinical studies on intervention of drug resistance and on high dose chemotherapy are needed to define the role of these strategies in ovarian cancer.

Glutathione S-transferase activity and isoenzyme composition in benign ovarian tumours, untreated malignant ovarian tumours, and malignant ovarian tumours after platinum/cyclophosphamide chemotherapy

Glutathione S-transferase (GST) isoenzyme composition, isoenzyme quantities and enzymatic activity were investigated in benign (n = 4) ovarian tumours and malignant ovarian tumours, before (n = 20) and after (n = 16) chemotherapy. Enzymatic activity of GST in cytosols was measured by determining 1-chloro-2,4-dinitrobenzene conjugation with glutathione, cytosolic GST subunits were determined by wide pore reversed phase HPLC, using a S-hexylglutathione-agarose affinity column, and isoelectric focussing. Both GST activity and GST pi amount were not related to histopathologic type, differentiation grade, or tumour volume index in untreated malignant tumours. GST isoenzyme patterns were identical in benign tumours and malignant tumours before and after platinum/cyclophosphamide chemotherapy, while GST pi was the predominant transferase. Mean GST activity and GST pi amount were decreased (P < 0.05) in malignant ovarian tumours after platinum/cyclophosphamide chemotherapy compared to untreated ovarian malignant tumours. No relation was found in untreated ovarian tumours between GST pi amount and response to platinum/cyclophosphamide chemotherapy. Thus, within the limitations of the current study no arguments were found for a role of GST in in vivo drug resistance of malignant ovarian tumours to platinum/cyclophosphamide chemotherapy.