Glutathione depletion increases the cytotoxicity of melphalan to PC-3, an androgen-insensitive prostate cancer cell line

Design Strategies and Applications of ROS-Responsive Phenylborate Ester-Based Nanomedicine

Reactive oxygen species (ROS)-responsive nanomedicine has been extensively developed to improve the therapeutic effects while reducing the systemic toxicity. ROS, as important biological metabolites and signaling molecules, are known to overexpress in most of tumors and inflammations. Among various ROS-sensitive moieties, phenylborate ester (PBAE) with easy modifiable structure and excellent biocompatibility, represents one of the most ROS-sensitive structures. To harness it as a switch, the past several years had witnessed a booming of ROS-sensitive PBAE-based nanomedicine for various medical purposes. Much of the efforts were devoted to exploiting the potential in the management of antitumor and anti-inflammation. This review first summarizes the design strategies of PBAE in the construction of nanomedicine, with PBAE acting as not only the ROS-responsive unit, but also the roles of hydrophobic backbone or bridging segment in the macromolecular structures. The ROS-responsive mechanisms are then briefly discussed. Afterward, we focus on the introduction of the state-of-the-art research on ROS-responsive PBAE-based nanomedicine for antitumor and anti-inflammation applications. The conclusion and future perspectives of ROS-responsive nanomedicine are also provided.

Modulation of cell death in human colorectal and breast cancer cells through a manganese chelate by involving GSH with intracellular p53 status

Chemotherapy is central to current treatment modality especially for advanced and metastatic colorectal and breast cancers. Targeting the key molecular events of the neoplastic cells may open a possibility to treat cancer. Although some improvements in understanding of colorectal and breast cancer treatment have been recorded, the involvement of glutathione (GSH) and dependency of p53 status on the modulation of GSH-mediated treatment efficacy have been largely overlooked. Herein, we tried to decipher the underlying mechanism of the action of Mn-N-(2-hydroxyacetophenone) glycinate (MnNG) against differential p53 status bearing Hct116, MCF-7, and MDA-MB-468 cells on the backdrop of intracellular GSH level and reveal the role of p53 status in modulating GSH-dependant abrogation of MnNG-induced apoptosis in these cancer cells. Present study discloses that MnNG targets specifically wild-type-p53 expressing Hct116 and MCF-7 cells by significantly depleting both cytosolic, mitochondrial GSH, and modulating nuclear GSH through Glutathione reductase and Glutamate-cysteine ligase depletion that may in turn induce p53-mediated intrinsic apoptosis in them. Thus GSH addition abrogates p53-mediated apoptosis in wild-type-p53 expressing cells. GSH addition also overrides MnNG-induced modulation of phase II detoxifying parameters in them. However, GSH addition partially replenishes the down-regulated or modulated GSH pool in cytosol, mitochondria, and nucleus, and relatively abrogates MnNG-induced intrinsic apoptosis in p53-mutated MDA-MB-468 cells. On the contrary, although MnNG induces significant cell death in p53-null Hct116 cells, GSH addition fails to negate MnNG-induced cell death. Thus p53 status with intracellular GSH is critical for the modulation of MnNG-induced apoptosis.

Erythropoietin stimulates growth and STAT5 phosphorylation in human prostate epithelial and prostate cancer cells

BACKGROUND

Erythropoietin (Epo), the principal regulator of erythroid progenitor survival, growth, and differentiation, initiates its action by binding to its cognate cell surface receptor (EpoR). EpoR have been identified on a variety of non-hematopoietic cells, both normal and malignant, however, little is known about the function of EpoR on malignant cells.

METHODS

RT-PCR, Western blotting, and immunohistochemistry were used to demonstrate that prostate cancer cells express EpoR at both the gene and protein level. Cell proliferation assays and STAT5 phosphorylation were used to demonstrate Epo's mitogenic action and intracellular signaling, respectively.

RESULTS

We have demonstrated that transformed prostate epithelial and prostate cancer cell lines, as well as primary prostate tissue, express the EpoR. Importantly, the EpoR on prostate cells are functional, as demonstrated by the observation that each of the cell lines exhibited a dose-dependent proliferative response to Epo, and that Epo triggered STAT5b phosphorylation in the cells.

CONCLUSION

Human prostatic epithelial cells and prostate cancer cells express functional EpoR, and Epo serves as a growth factor for these cells. These results have implications for our understanding of normal prostatic growth and development and of the pathobiology of human prostate cancer.

The ceramide analog, B13, induces apoptosis in prostate cancer cell lines and inhibits tumor growth in prostate cancer xenografts

BACKGROUND

Apoptosis is a therapeutic target for the elimination of cancer cells. As elevations in ceramide levels induce apoptosis, there is much excitement about the use of agents that elevate ceramide levels as novel chemotherapeutic agents. Ceramidases are enzymes involved in degradation of ceramide and inhibition of ceramidase has been proposed as a mechanism to increase ceramide levels. This study provides the first insight into the effect of B13, an inhibitor of acid ceramidase, on human prostate cancer cell lines and xenografts.

METHODS

Cell death was evaluated by the trypan blue assay; apoptosis by the Apo2.7 apoptosis assay; and glutathione levels by HPLC. Tumors were irradiated with a dose of 5 Gy of X-rays (250 kVp, 15 mA, 2 Gy/min) and tumor volume was measured during the course of the experiment. At the conclusion of the experiment, tumor weight was determined and the tumors were evaluated histologically.

RESULTS

B13 is an inducer of cell death, by apoptosis, in cultured prostate cancer cells. LNCaP and PC3 cells have different responsiveness to the enantiomers of B13. In LNCaP cells, the R enantiomer of B13 (10 microM) was significantly more effective than the S enantiomer at inducing cell death as determined by the trypan blue assay, culminating in approximately 90% cell death at 48 hr. In contrast, the same concentration of B13S induced <20% cell death at 48 hr. In PC3 cells, the S enantiomer was a more effective inducer of cell death, culminating in approximately 30% cell death, relative to 14% for B13R in this model. Evaluation of induction of apoptosis by the Apo2.7 mitochondrial assay confirmed that this induction of cell death was by apoptosis. Concurrent with induction of apoptosis, glutathione levels drop in response to B13. Specifically, B13R caused a significant drop in glutathione levels in LNCaP cells, culminating in a reduction to 40% control values at 48 hr. In PC3 cells, in contrast, the drop in glutathione levels was more dramatic, culminating in a drop to 12% control values in response to B13S at 48 hr. The effects of B13R, however, were not significantly different from control values. In in vivo studies using a model of xenografted androgen-insensitive prostate cancer, B13 sensitized the tumors to the effects of radiation, resulting in a significant reduction in tumor volume and weight after treatment with the combination of B13 and radiation. Microscopic evaluation of the tumors indicated that apoptosis was the primary mechanism of this effect.

CONCLUSIONS

Targeting ceramide pathways may be a novel treatment strategy for hormone refractory prostate cancer.

Changes in endogenous tissue glutathione level in relation to murine ascites tumor growth and the anticancer activity of cisplatin

Changes in glutathione levels were determined in tissues of 11- to 12-week-old Swiss albino mice at different stages of Dalton's lymphoma tumor growth and following cisplatin (8 mg/kg body weight, ip) treatment for 24-96 h, keeping 4-5 animals in each experimental group. Glutathione levels increased in spleen of tumor-bearing compared to normal mice (9.95 +/- 0.14 vs 7.86 +/- 1.64 micromol/g wet weight, P<or=0.05) but decreased in blood (0.64 +/- 0.10 vs 0.85 +/- 0.09 mg/ml) and testes (9.28 +/- 0.15 vs 10.16 +/- 0.28 micromol/g wet weight, P<or=0.05). Dalton's lymphoma cells showed an increase in glutathione concentration (4.43 +/- 0.26 micromol/g wet weight) as compared to splenocytes, their normal counterpart (3.62 +/- 0.41 micromol/g wet weight). With the progression of tumor in mice, glutathione levels decreased significantly in testes (approximately 10%) and bone marrow cells (approximately 13%) while they increased in Dalton's lymphoma cells (28-46%) and spleen (15-27%). Glutathione levels in kidney, Dalton's lymphoma cells and bone marrow cells (8.50 +/- 1.22, 4.43 +/- 0.26 and 3.28 +/- 0.17 micromol/g wet weight, respectively) decreased significantly (6.04 +/- 0.42, 3.51 +/- 0.32 and 2.17 +/- 0.14 micro mol/g wet weight, P<or=0.05) after in vivo cisplatin treatment for 24 h. Along with a decrease in glutathione level, the glutathione-S-transferase (GST) activity also decreased by 60% in tumor cells after cisplatin treatment. The elevated drug uptake by the tumor cells under the conditions of reduced glutathione concentration and GST activity after treatment could be an important contributory factor to cisplatin's anticancer activity leading to tumor regression. Furthermore, lower doses of cisplatin in combination with buthionine sulfoximine (an inhibitor of glutathione synthesis) may be useful in cancer chemotherapy with decreased toxicity in the host.

Priming prostate carcinoma cells for increased apoptosis is associated with up-regulation of the caspases

BACKGROUND

The potential to prime prostatic carcinoma cell lines for apoptosis represents an exciting strategy for the treatment of patients with this disease. The ability and the underlying molecular mechanisms involved in sensitizing both androgen-sensitive and androgen-insensitive cell types to a range of apoptotic-inducing agents are investigated by the authors.

METHODS

Primary and secondary cell lines were pretreated with diethyl-maleate (DEM) prior to the induction of apoptosis by Fas antibody (1 microg/mL), cycloheximide (1 microg/mL), etoposide (62.5 microM), and radiation (5 grays). It was demonstrated previously that DEM (50 microM) increases the sensitivity to apoptosis induced by these agents. The effects of DEM on both protein and RNA expression was determined by Western blot analysis and a ribonuclease protection assay, respectively. The effects of DEM on intracellular glutathione (GSH) levels and its intracellular distribution also were assessed.

RESULTS

DEM did not affect the expression of the caspases at the transcriptional level but was associated with increased procaspase-3 and caspase-8 protein levels. DEM preincubation restored sensitivity to Fas antibody and radiation-induced apoptosis in cells from the LNCaP-bcl-2 transfectant cell line that, normally, are resistant to these apoptotic stimuli. It is that DEM chemically depletes intracellular thiol levels. Although no depletion in total intracellular thiol GSH was observed at these concentrations of DEM, trafficking of GSH from the nucleus to the cytosol was demonstrated.

CONCLUSIONS

Identification of the caspases as a potential target for chemical manipulation may serve as an effective, adjuvant-based approach in the treatment of patients with prostate carcinoma and, in particular, for immunotherapy and radiation-based strategies that rely on the activation of these death-effector proteases.

Thiol-mediated apoptosis in prostate carcinoma cells

BACKGROUND

Glutathione (GSH) maintains an optimum cellular redox potential. Chemical depletion, physical efflux from the cell, or intracellular redistribution of this thiol antioxidant is associated with the onset of apoptosis. The aim of this study was to determine the effects of a thiol-depleting agent, diethylmaleate (DEM), on androgen sensitive and insensitive prostate carcinoma cells.

METHODS

LNCaP and PC-3 cell lines were induced to undergo apoptosis by DEM and diamide. Apoptosis was quantified by annexin V binding and propidium iodide incorporation using flow cytometry and was confirmed by DNA gel electrophoresis. Intracellular GSH was quantified using a thiol quantitation kit and the generation of reactive oxygen intermediates was measured using dihydrorhodamine 123. Western blot assessed caspase-3, caspase-8, Bcl-2, and Bcl-XL protein expression. Mitochondrial permeability was measured using DiOC6 and stabilized using bongkrekic acid.

RESULTS

DEM and diamide induced apoptosis in both androgen sensitive and insensitive cells. Apoptosis was also induced in an LNCaP transfectant cell line overexpressing Bcl-2. Apoptosis was caspase-3 dependent and caspase-8 independent. Bongkrekic acid partially prevented the effects of DEM on mitochondrial permeability but was unable to prevent the induction of apoptosis. Decreased Bcl-2 and Bci-XL protein expression was observed at the time of initial caspase-3 activation.

CONCLUSIONS

This study demonstrates that thiol depletion can be used as an effective means of activating caspase-3 in both androgen sensitive and insensitive prostate carcinoma cells. Direct activation of this effector caspase may serve as a useful strategy for inducing apoptosis in prostate carcinoma cells.

Gamma-glutamyl transpeptidase immunoreactivity in benign and malignant breast tissue

GGT 129, a polyclonal antibody directed against gamma-glutamyl transpeptidase (GGT), was used to study GGT expression in formalin-fixed paraffin-embedded tissues from normal breast, 24 benign lesions, 27 in situ carcinomas or atypical hyperplasias, and 79 infiltrating mammary carcinomas. Epithelium of the ducts and ductules in normal breast tissue showed immunoreactivity along the apical surface. There was a strong correlation (P < 0.01) between the histologic classification of the tissue and GGT expression. All of the benign breast lesions stained positive for GGT. Among in situ carcinomas and atypical hyperplasias, 5/27 (19%) were negative for GGT while 22/27 were immunopositive. Infiltrating carcinomas showed the greatest deviation from normal tissue with 23/79 (29%) negative for GGT. GGT expression in benign and malignant breast tissue was not correlated with the age of the patient, suggesting that menopausal status does not influence expression of GGT. Correlation of GGT immunoreactivity with tubule formation, nuclear pleomorphism, mitoses, grade, size of tumor, lymph node status, and ER/PR status was performed for 69 cases of infiltrating ductal adenocarcinoma. There were no statistically significant relationships between the level of GGT immunoreactivity and any of the parameters. The loss of GGT in some of the cases is evidence that this enzyme is not required for mammary tumor development or maintenance. However, as GGT is a component of the pathways that metabolize glutathione and glutathione-conjugates, the difference in levels of the enzyme in invasive breast cancers may be one explanation for the variation in chemotherapy response that has been observed in patients treated for advanced mammary cancer.

Nitric oxide enhancement of melphalan-induced cytotoxicity

The effects of the diatomic radical, nitric oxide (NO), on melphalan-induced cytotoxicity in Chinese hamster V79 and human MCF-7 breast cancer cells were studied using clonogenic assays. NO delivered by the NO-releasing agent (C2H5)2N[N(O)NO]- Na+ (DEA/NO; 1 mM) resulted in enhancement of melphalan-mediated toxicity in Chinese hamster V79 lung fibroblasts and human breast cancer (MCF-7) cells by 3.6- and 4.3-fold, respectively, at the IC50 level. Nitrite/nitrate and diethylamine, the ultimate end products of DEA/NO decomposition, had little effect on melphalan cytotoxicity, which suggests that NO was responsible for the sensitization. Whereas maximal sensitization of melphalan cytotoxicity by DEA/NO was observed for simultaneous exposure of DEA/NO and melphalan, cells pretreated with DEA/NO were sensitized to melphalan for several hours after NO exposure. Reversing the order of treatment also resulted in a time-dependent enhancement in melphalan cytotoxicity. To explore possible mechanisms of NO enhancement of melphalan cytotoxicity, the effects of DEA/NO on three factors that might influence melphalan toxicity were examined, namely NO-mediated cell cycle perturbations, intracellular glutathione (GSH) levels and melphalan uptake. NO pretreatment resulted in a delayed entry into S phase and a G2/M block for both V79 and MCF-7 cells; however, cell cycle redistribution for V79 cells occurred after the cells returned to a level of cell survival, consistent with treatment with melphalan alone. After 15 min exposure of V79 cells to DEA/NO (1 mM), GSH levels were reduced to 40% of control values; however, GSH levels recovered fully after 1 h and were elevated 2 h after DEA/NO incubation. In contrast, DEA/NO (1 mM) incubation did not reduce GSH levels significantly in MCF-7 cells (approximately 10%). Melphalan uptake was increased by 33% after DEA/NO exposure in V79 cells. From these results enhancement of melphalan cytotoxicity mediated by NO appears to be complex and may involve several pathways, including possibly alteration of the repair of melphalan-induced lesions. Our observations may give insights for improving tumour kill with melphalan using either exogenous or possibly endogenous sources of NO.

Glutathione and glutathione S-transferase in benign and malignant prostate cell lines and prostate tissues

Metastatic prostate adenocarcinoma is unresponsive to alkylator chemotherapy with virtually no prolonged remissions. Glutathione (GSH) and glutathione S-transferase (GST) have been reported to play a role in tumor resistance to alkylator therapy; however, there are no baseline studies that have investigated and compared GSH and GST in human prostate cell lines and tissues. Thus, we determined the GSH content and GST activity in benign prostate, in primary and metastatic prostate adenocarcinoma tissues, in immortal adenocarcinoma cell lines, and in primary cell cultures derived from both benign prostate and primary prostatic carcinoma tissue. The GSH content was higher in the immortal cell lines than in the fresh tissues and primary cultures. Conversely, the GST activity was significantly higher in the tissues and primary cultures than in the cell lines. The GSH content and GST activity of the primary cultured prostatic cells were similar to those of the prostate tissues. The differences between the immortal prostate cancer cell lines and prostate tissue are of sufficient magnitude to suggest that in vitro results with cell lines may not extrapolate to prostate cancer in vivo. The GSH content and GST activity in a prostate specific antigen-secreting human prostate tumor xenograft, LuCaP23, maintained in nude mice were similar to those of human prostate tissue and primary cultures. Both the xenograft and primary cultures from patients with prostate cancer may be more appropriate models than established cell lines for investigating techniques to increase the effectiveness of alkylators in prostate cancer.

Glutathione concentration in oral cancer tissues

Glutathione (GSH) concentrations in human epidermoid carcinoma tissues were measured by high performance liquid chromatography. The mean glutathione content of 26 epidermoid carcinoma intratumor tissue specimens was 24.36 nmol/mg protein, which was significantly higher than that in adjacent non-tumor tissue parts (3.04 nmol/mg protein). The mean concentration found in normal oral mucosa was 4.80 nmol/mg protein. Tissue GSH levels were not correlated with the age of the patients or tumor size. Additionally, cellular GSH levels in nine different cell lines were found to spread over a wide range from 0.97 to 50.97 nmol/mg protein. Elevated GSH levels in cancer tissues were probably due to their abnormal proliferative activities. These results indicate that the glutathione level of oral tissues may be a useful marker for oral cancer, which is in agreement with findings from lung squamous cell carcinoma, cervical squamous cell carcinoma and other squamous cell carcinomas.