Influence of glutathione S-transferases on cellular glutathione determination by flow cytometry using monochlorobimane

Intracellular glutathione (GSH) levels for seven mammalian cell lines (four human tumors, two rodent, one monkey) were determined by flow cytometry following staining with monochlorobimane (MBCl), and the results were compared with GSH levels measured by the Tietze assay. The mean fluorescence intensity for all but the two rodent lines did not correlate with GSH levels determined biochemically. Good agreement between the two assays was observed for the rodent lines following depletion of GSH by buthionine sulfoximine, but the level of GSH depletion achieved in the human and monkey lines was always underestimated by MBCl/flow cytometry. These discrepancies were not resolved by increasing stain concentration or staining time. Total glutathione S-transferase (GST) activity and GST isozyme profiles were determined for each of the cell lines. Western analysis with antibodies raised against rat Ya, Yb1, and Yc and human pi isozymes revealed that the rodent cell lines expressed abundant alpha (Ya, Yc subunits) and mu (Yb1 subunits) class isozymes. In contrast, GST-pi was the predominant isozyme detected in the human tumor cell lines and Cos-7 monkey cells. Michaelis-Menten analysis with purified GSTs from rat liver as well as purified human placental (pi) GST revealed that the conjugation of MBCl and GSH catalyzed by the alpha (1-1 and 2-2) and mu (3-3 and 3-4) class GST isozymes was approximately 10 and 80 times more efficient than was conjugation by the GST pi form, respectively. These data indicate that the GST-catalyzed conjugation of GSH and MBCl is isozyme dependent and that MBCl is a relatively poor substrate for the pi isozyme. As a consequence of this isozyme rate differential, the MBCl/flow cytometry technique for GSH quantitation must be applied cautiously, particularly with human tumor cells, many of which have been shown to have high GST-pi activity. Application to other cell types should also be made after careful characterization of GSH levels and GST isozyme composition and only after comparison with other independent assays of GSH concentration.     

Low levels of urokinase plasminogen activator components in basal cell carcinoma of the skin

Basal cell carcinoma of the skin (BCC) is the most common cancer worldwide. Unlike most other human malignancies, BCCs rarely metastasise. In this investigation, we show that the serine protease urokinase plasminogen activator (u-PA), which is causally involved in metastasis, is expressed at lower levels in BCCs compared to other skin cancers, such as squamous-cell carcinomas (SCCs) or malignant melanomas. Similarly, the u-PA receptor as well as the inhibitor PAI-1 were present at lower levels in BCCs relative to both SCCs and melanomas. In contrast to u-PA, tissue-plasminogen activator, which is not thought to be involved in metastasis, was present at similar levels in the different types of skin lesion investigated. We conclude that the failure of BCCs to metastasise may at least be partially related to low expression of components of the u-PA system.     

Glutathione S-transferase polymorphisms: cancer incidence and therapy

The super family of glutathione S-transferases (GSTs) is composed of multiple isozymes with significant evidence of functional polymorphic variation. Over the last three decades, data from cancer studies have linked aberrant expression of GST isozymes with the development and expression of resistance to a variety of chemicals, including cancer drugs. This review addresses how differences in the human GST isozyme expression patterns influence cancer susceptibility, prognosis and treatment. In addition to the well-characterized catalytic activity, recent evidence has shown that certain GST isozymes can regulate mitogen-activated protein kinases or can facilitate the addition of glutathione to cysteine residues in target proteins (S-glutathionylation). These multiple functionalities have contributed to the recent efforts to target GSTs with novel small molecule therapeutics. Presently, at least two drugs are in late-stage clinical testing. The evolving functions of GST and their divergent expression patterns in individuals make them an attractive target for drug discovery.     

Prevalence of human papillomavirus in skin tumors from repair deficient xeroderma pigmentosum patients

The predisposition to skin cancers in childhood is the hallmark of xeroderma pigmentosum (XP), a rare autosomal recessive disorder, deficient in DNA repair and hypersensitive to ultraviolet irradiation. Human papillomavirus (HPVs), are common infections of the skin which are often found associated to benign lesions and non-melanoma skin cancers (NMSC), mainly squamous cell carcinomas (SCC) and basal cell carcinomas (BCC). Our study is the first to analyse 40 SCCs, 27 BCCs and nine normal skin biopsies from XP patients for HPV DNA which are found more frequently in SCCs (20/40) than in BCCs (4/27) or normal skin (2/9). The HPV spectrum includes 22 different epidermodysplasia verruciformis (EV) HPV types, which predominate in SCCs (48%) compared to BCCs (15%) and normal skin (22%). Our data, showing an association between EV HPV and SCCs from young XP patients is comparable to that found for NMSC from adult immunosuppressed organ transplant patients and raises the question of the importance of HPV infection in skin carcinogenesis.     

Reduction in IkappaB kinase alpha expression promotes the development of skin papillomas and carcinomas

We reported recently a marked reduction in IkappaB kinase alpha (IKKalpha) expression in a large proportion of human poorly differentiated squamous cell carcinomas (SCC) and the occurrence of Ikkalpha mutations in human SCCs. In addition, overexpression of IKKalpha in the epidermis inhibited the development of skin carcinomas and metastases in mice. However, whether a reduction in IKKalpha expression promotes skin tumor development is currently unknown. Here, we assessed the susceptibility of Ikkalpha hemizygotes to chemical carcinogen-induced skin carcinogenesis. Ikkalpha+/- mice developed 2 times more papillomas and 11 times more carcinomas than did Ikkalpha+/+ mice. The tumors were larger in Ikkalpha+/- than in Ikkalpha+/+ mice, but tumor latency was shorter in Ikkalpha+/- than in Ikkalpha+/+ mice. Some of the Ikkalpha+/- papillomas and most Ikkalpha+/- carcinomas lost the remaining Ikkalpha wild-type allele. Somatic Ikkalpha mutations were detected in carcinomas and papillomas. The chemical carcinogen-induced H-Ras mutations were detected in all the tumors. The phorbol ester tumor promoter induced higher mitogenic and angiogenic activities in Ikkalpha+/- than in Ikkalpha+/+ skin. These elevated activities were intrinsic to keratinocytes, suggesting that a reduction in IKKalpha expression provided a selective growth advantage, which cooperated with H-Ras mutations to promote papilloma formation. Furthermore, excessive extracellular signal-regulated kinase and IKK kinase activities were observed in carcinomas compared with those in papillomas. Thus, the combined mitogenic, angiogenic, and IKK activities might contribute to malignant conversion. Our findings provide evidence that a reduction in IKKalpha expression promotes the development of papillomas and carcinomas and that the integrity of the Ikkalpha gene is required for suppressing skin carcinogenesis.     

Skin cancer in Egypt: a word in your ear

BACKGROUND AND OBJECTIVES: In Egypt, the clinicopathologic features of skin cancer are still unknown. MATERIALS AND METHODS: To define these features, registries of the Pathology Departments, Assiut and South Valley University Hospitals were reviewed. The lesions included 21 melanomas, 39 squamous cell carcinomas (SCCs), and 202 basal cell carcinomas (BCCs). RESULTS: Skin cancer represented 5% of the malignant tumors of the entire body. BCC (77%) was the most common skin cancer followed by SCC (15%) and melanomas (8%). The mean age was 54 +/- 3 (melanomas), 66 +/- 10 (BCC), and 60 +/- 5.18 (SCC). The most common sites were the face (BCCs), face and extremities (SCCs), and face and lower limbs (melanomas). The average size (mm) was 21 +/- 0.3 (melanomas), 28 +/- 0.3 (BCC) and 30 +/- 1.1 (SCC). Melanomas, BCCs and SCCs were of nodular, keratotic invasive and nodular infiltrative types, respectively. CONCLUSIONS: In Egypt, skin cancer is uncommon malignancy. As compared to Western societies, the incidence rate of melanoma is very low and its topographic distribution is different. Alternatively, the rates for SCCs/BCCs are comparably high and their topographic distribution is similar. This is the first investigation that reports the clinicopathologic features of skin cancer in Egypt and compares it to other parts of Africa and Western societies.     

Expression of glutathione S-transferases in normal gastric mucosa and in gastric tumors

Glutathione S-transferases from both normal gastric mucosa and its matched gastric tumors from 10 different patients were investigated. The transferases were purified and subsequently the isoenzyme composition was studied. Glutathione S-transferase (GST)-pi was present in all specimens in large amounts. Class alpha GSTs were present in 9 out of 10 normal specimens and in six tumors. In malignant tissue, expression of GST-pi was increased at the expense of class alpha GST. In six patients, the ratio GST-pi/GST-alpha was higher in tumorous versus normal tissue. On a Western blot, using a monoclonal antibody, GST-mu was shown to be present in both normal and malignant tissue from four patients, the other six patients completely missed the enzyme in their gastric tissue. When present, GST-mu amounts to only a few per cent of total GST protein. GST-pi was quantified by densitometric analysis of Western blots, treated with a monoclonal antibody against GST-pi. Both total GST enzyme activity as well as the absolute amounts of GST-pi protein were significantly higher in the tumors, as compared to its matched normal mucosa. The importance of this overexpression of GST-pi was previously unknown. However, the frequent occurrence of this phenomenon in many refractory tumors, and as shown now also in gastric cancers, suggests a role for GST-pi in the mechanism of anti-cancer drug resistance.     

Biological amplification factor for sunlight-induced nonmelanoma skin cancer at high latitudes

Data for the incidence of basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of the skin, registered for six regions of Norway during 10 years (1976-1985), were used to evaluate the biological amplification factor Ab for induction of these cancers by sunlight. Ab is the ratio of the increment in skin cancer production to the increment in causative sunlight exposure. Two different approximations were used for the action spectrum for carcinogenesis: an erythema action spectrum; and an action spectrum for mutagenesis of cells in the basal layer of the skin. These two fundamentally different approaches yielded Ab values that were similar to within about 10%: 2.1-2.3 for BCCs; and 1.6-1.8 for SCCs. Using a radiation amplification factor for ozone depletion of 0.8-1.1, we find that the total amplification factor for BCCs is within the range 1.6-2.1 and that that for SCCs is within the range 1.3-1.7 at northern latitudes of 60-70 degrees. Thus, an ozone depletion of 1% will result in an increase in the incidence of BCCs by 1.6-2.1% and of SCCs by 1.3-1.7%. There were no significant differences between the values for men and women. Neither was there any significant difference between Ab values found for skin commonly exposed to sunlight (face) and for skin sites normally covered by clothes and therefore receiving much lower exposures, in spite of the fact that the tumor density per unit skin area was a factor of 20 or more larger at the former sites. This observation, as well as the curves relating cancer incidence with annual exposure to carcinogenic sunlight, supports a power law relationship between cancer incidence and annual sun exposure. Sunlight appears to be the main cause of BCCs and SCCs even at the high latitudes of Northern Norway. All over, BCCs were found to be about 6 times more frequent than SCCs. The ratio of the incidence of BCCs to that of SCCs seemed to be independent of the latitude. Finally, BCCs were found to be equally frequent among men and women, while SCCs were found to be about twice as frequent among men as among women.     

Differential patterns of stromelysin-2 (MMP-10) and MT1-MMP (MMP-14) expression in epithelial skin cancers

Co-expression of several members of the matrix metalloproteinase (MMP) family is characteristic of human malignant tumours. To investigate the role of stromelysin-2 (MMP-10) in growth and invasion of skin tumours, we studied cutaneous carcinomas with high metastatic capacity (squamous cell carcinomas, SCCs), only locally destructive tumours (basal cell carcinomas, BCCs) and pre-malignant lesions (Bowen's disease and actinic keratosis) using in situ hybridization. Expression of MMP-10 was compared with that of stromelysin-1 (MMP-3) and of MT1-MMP, the expression of which has been shown to correlate with tumour invasiveness. MMP-10 was expressed in 13/21 SSCs and 11/19 BCCs only in epithelial laminin-5 positive cancer cells, while premalignant lesions were entirely negative. MT1-MMP mRNA was detected in 19/21 SCCs both in epithelial cancer cells and stromal fibroblasts and in 14/18 BCCs only in fibroblasts. The level of MMP-10 was upregulated in a cutaneous SCC cell line (UT-SCC-7) by transforming growth factor-alpha and keratinocyte growth factor, and by interferon-gamma in combination with transforming growth factor-beta1 and tumour necrosis factor-alpha both in UT-SCC-7 and HaCaT cells. Our results show that MMP-10 expression does not correlate with the invasive behaviour of tumours as assessed by their histology and MT1-MMP expression, but may be induced by the wound healing and inflammatory matrix remodelling events associated with skin tumours.     

Immunohistochemical localization of glutathione S-transferases alpha, mu, and pi in normal tissue and carcinomas from human colon.

Analysis of the heterogeneity of glutathione S-transferase (GST) isozyme expression was carried out by immunohistochemical evaluation of human colon biopsy tissue from 30 patients. Using polyclonal antibodies specific for the GST alpha, mu and pi families of isozymes, an increased expression of pi was found in 21/30 carcinoma specimens compared to their pair-matched controls. This isozyme was the most prevalent in all colon samples. GST mu was expressed at reduced levels in 20/30 carcinoma specimens when compared to normal. GST alpha showed no consistent change. Analysis of the immunostaining in different cell types showed that the highest intensity stain for all isozymes was in the columnar epithelial cells. These cells were primarily responsible for the proportional changes in GST pi and mu between carcinoma and normal tissues. In addition, goblet (crypt), endothelial and muscle cells stained positively. In the lamina propria, lymphocytes and phagocytes stained positively, while fibroblasts, plasma cells and leukocytes were negative. Endocrine cells were also negative. The differential expression of GST pi and mu, confirming biochemical data, supports the potential utility of GST pi as a carcinoma marker.     

Numerical abnormalities of the Cyclin D1 gene locus on chromosome 11q13 in non-melanoma skin cancer

Deregulation of the cell-cycle G1-restriction point control via abnormalities of Rb-pathway components is a frequent event in the formation of cancer. The aim of this study was to evaluate numerical aberrations of the Cyclin D1 (CCND1, PRAD1, bcl-1) gene locus at chromosome 11q13 in basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of the skin and to compare it with the Cyclin D1 protein expression. Fluorescence in situ hybridization with DNA-probes specific for the Cyclin D1 gene locus and the centromere of chromosome 11 as well as immunostaining for Cyclin D1 protein was applied on 5 microm serial paraffin sections. Six of the 30 (20%) SCCs showed additional Cyclin D1 gene copies and 2/30 (6.6%) cases had a loss of the Cyclin D1 gene locus in relation to the centromere 11 number. In contrast, only one of the 14 BCCs (7%) showed one additional Cyclin D1 gene copy in relation to the centromere 11 number. None of the BCCs demonstrated aneusomy for chromosome 11 in contrast to SCCs, where it was found in 21/30 (70%) cases. Twenty-six of the 30 (86.6%) cutaneous SCCs and 13/14 (93%) BCCs expressed Cyclin D1 protein. All SCCs and the BCC with additional Cyclin D1 gene copies showed positivity for Cyclin D1 protein. Both SCCs with less Cyclin D1 gene copies than centromere 11 signals showed a weak protein expression. Our findings suggest that numerical abnormalities of the Cyclin D1 gene locus could result in an altered gene-dose effect, possibly leading to an aberrant expression in affected tumor cells. This might result in deregulation of cell cycle control, eventually leading to uncontrolled cell cycle progression.     

Glutathione transferase activity and isoenzyme composition in primary human breast cancers

The human glutathione transferases (GSTs) are a multigene family of detoxication enzymes with patterns of expression that are both tissue specific and genetically determined. Changes in the levels of one or more GST isoenzymes have been associated with the development of anticancer drug resistance in cultured cell lines. In this study, total GST activity and GST isoenzyme composition have been determined for 45 primary human breast carcinomas using a 1-chloro-2,4-dinitrobenzene substrate assay and Western blotting, respectively. The GST activity ranged from 5-208 mU/mg protein with a mean of 67 mU/mg protein (+/- 44 SD). GST-pi) isoenzyme protein was detectable on Western blots in 44 of 45 samples. Mu Class GST protein was detected in 18 of 38 samples and undetectable in 20 of the 38 samples tested. By polymerase chain reaction analysis of genomic DNA, the absence of mu class GST in breast tumors was determined to be due to the deletion of the gene for GST-mu in the DNA of those tumors. None of the 43 primary human breast cancer samples tested contained detectable alpha class GST protein. Neither the total GST activity of tumor samples, the quantity of GST-pi protein, nor the presence or absence of mu class GST correlated with other factors known to be of prognostic significance including tumor size, nodal status, estrogen receptor protein positivity, or progesterone receptor protein positivity. Substantial differences exist among primary breast carcinomas in both the amount of GST activity and GST isoenzyme composition. However, these are not tightly linked either to tumor stage or to hormone receptor status. Whether the levels of these enzymes are independent predictors of either risk of recurrence or response to anticancer therapy has yet to be tested directly.     

Targeted expression of c-Src in epidermal basal cells leads to enhanced skin tumor promotion,malignant progression,and metastasis

In this study, we generated transgenic mice that overexpressed either a constitutively active human c-src mutant (src(530)) or a wild-type human c-src (src(wt)) in epidermal basal cells driven by human keratin 14 (HK14) or bovine keratin 5 (BK5) promoters, respectively. HK14.src(530) transgenic mice developed severe epidermal hyperplasia and hyperkeratosis, and did not survive beyond 3 weeks of age. Four transgenic founders were obtained after injection of a BK5.src(wt) construct with variable phenotypes, and three lines (lines A-C) were established. BK5.src(wt) founder D exhibited a severe skin phenotype similar to HK14.src(530) transgenic mice and died 5 days after birth. Line C transgenic mice also exhibited significant epidermal hyperplasia and hyperkeratosis, and developed spontaneous squamous cell carcinomas (SCCs) of the skin beginning at approximately 3 months of age (70% incidence at 1 year). Mice from lines A and B did not show a marked phenotype; however, elevated human src(wt) protein in the epidermis of line B mice was clearly evident. Additional analyses of line B transgenic mice showed an enhanced responsiveness to 12-O-tetradecanoylphorbol-13-acetate-induced epidermal hyperplasia and cell proliferation. Analysis of the susceptibility of line B mice to two-stage skin carcinogenesis revealed that papillomas and SCCs arose earlier and in greater numbers compared with nontransgenic littermates. In addition, malignant conversion occurred more rapidly, and the SCCs that developed in line B transgenic mice had a greater propensity to metastasize to peripheral lymph nodes and other organs. These observations support the hypothesis that c-src plays an important role in skin tumor promotion. In addition, the data show that elevated c-src activity enhances malignant progression and metastasis in this model system.     

Specificity of murine glutathione S-transferase isozymes in the glutathione conjugation of (-)-anti- and (+)-syn-stereoisomers of benzo[g]chrysene 11,12-diol 13,14-epoxide.

Specificities of murine glutathione (GSH) S-transferase (GST) isozymes mGSTA1-1, mGSTA2-2, mGSTA3-3 and mGSTA4-4 (alpha class), mGSTP1-1 (pi class) and mGSTM1-1 (mu class) for GSH conjugation of (-)-anti- and (+)-syn-stereoisomers of benzo[g]chrysene 11, 12-diol 13,14-epoxide (B[g]CDE), the activated metabolites of the environmental pollutant benzo[g]chrysene (B[g]C), have been determined. When GST activity was determined as a function of varying (-)-anti- or (+)-syn-B[g]CDE concentration (10-320 microM) at a fixed saturating concentration of GSH (2 mM), each isozyme obeyed Michaelis-Menten kinetics. mGSTA1-1 was significantly more efficient than other murine GSTs in the GSH conjugation of not only (-)-anti-stereoisomer but also (+)-syn-B[g]CDE. For example, the catalytic efficiency (k(cat)/K(m)) of mGSTA1-1 towards (-)-anti-B[g]CDE was approximately 2.3- to 16.6-fold higher compared with other murine GSTs. Likewise, mGSTA1-1 was approximately 2.7-, 6.7-, 4.4- and 12.4-fold more efficient than mGSTA2-2, mGSTA3-3, mGSTP1-1 and mGSTM1-1, respectively, in catalyzing the GSH conjugation of (+)-syn-B[g]CDE. Interestingly, mGSTA4-4, which also belongs to class alpha, was virtually inactive towards both stereoisomers of B[g]CDE. The results of the present study indicate that murine GSTs, especially alpha class isozymes, significantly differ in their ability to detoxify B[g]CDE stereoisomers and that mGSTA1-1 plays a major role in the detoxification of both (-)-anti- and (+)-syn-B[g]CDE, which among four B[g]CDE stereoisomers are formed from the carcinogen B[g]C as major DNA binding metabolites.     

Glycoalkaloids from Solanum sodomaeum are effective in the treatment of skin cancers in man

A cream formulation containing glycoalkaloids purified from the plant species Solanum sodomaeum L. is effective in the treatment of the malignant human skin tumours; basal cell carcinomas (BCCs), squamous cell carcinomas (SCCs) and the benign tumours; keratoses and keratoacanthomas. Histological analyses of biopsies taken before, during and after treatment give compelling evidence of the efficacy of the formulation. The treated lesions did not recur for at least 3 years after cessation of therapy. The observed complete regressions were; 20/24 for the BCCs; 5/6 for the SCCs; 23/23 for the keratoses; and, 9/9 for the keratoacanthomas. Biochemical, haematological and urinanalytical studies demonstrated that there were no adverse effects on the liver, kidneys or haematopoietic system during treatment. Normal skin treated with the formulation likewise was free from adverse histological or clinical effects. The data indicate that glycoalkaloids of this type are therefore potentially useful in the treatment of several types of human skin cancers.     

Advances in the chemoprevention of non-melanoma skin cancer in high-risk organ transplant recipients

Patients with a history of more than four basal cell carcinomas (BCCs) or squamous cell carcinomas (SCCs) are at high risk for developing further skin cancers. Immunosuppressed patients, especially solid organ transplantation patients, harbor a higher risk of developing SCC. Systemic retinoids have been demonstrated to possess chemoprophylactic properties in the treatment of non-melanoma skin cancer. This article reviews the efficacies of the available oral retinoid agents in the chemoprophylaxis of SCCs in high-risk solid organ transplant recipients.     

Topical treatment of malignant and premalignant skin lesions by very low concentrations of a standard mixture (BEC) of solasodine glycosides

A cream formulation containing high concentrations (10%) of a standard mixture of solasodine glycosides (BEC) has been shown to be effective in the treatment of malignant and benign human skin tumours. We now report that a preparation (Curaderm) which contains very low concentrations of BEC (0.005%) is effective in the treatment of keratoses, basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs) of the skin of humans. In an open study, clinical and histological observations indicated that all lesions (56 keratoses, 39 BCCs and 29 SCCs) treated with Curaderm had regressed. A placebo formulation had no effect on a smaller number of treated lesions. Curaderm had no adverse effect on the liver, kidneys or haematopoietic system.     

Suppression of GST-P by treatment with glutathione-doxorubicin conjugate induces potent apoptosis in rat hepatoma cells.

A conjugate of doxorubicin and glutathione via glutaraldehyde (GSH-DXR) inhibited glutathione S-transferase (GST) activity of rat hepatoma AH66 cells, and treatment of the cells with GSH-DXR induced caspase-3 activation and DNA fragmentation. After treatment of AH66 cells with 0.1 microM GSH-DXR, GST-P (placental type of rat GST isozymes) mRNA and its protein increased transiently and then decreased thereafter compared with the levels in nontreated cells. Caspase-3 activation and DNA fragmentation were induced following the suppression of GST-P expression by treatment with GSH-DXR. When the cells were treated with 100 microM ethacrynic acid (ECA), an inhibitor of GST, DNA fragmentation and caspase-3 activation were observed. In contrast, treatment of AH66 cells with a low concentration of ECA (1 microM) that showed little inhibition of GST activity induced slight, but significantly enhanced expression and activity of GST-P, and consequent prevention of DXR- and GSH-DXR-induced DNA fragmentation. Overexpression of GST-pi (placental type of human GST isozymes) by transfection of GST-pi sense cDNA into AH66 cells decreased sensitivities to DXR and GSH-DXR, and the suppression of GST-P by transfection of the antisense cDNA into the cells increased drug sensitivity. On the other hand, there was little change in drug sensitivity caused by overexpression of site-directedly mutated GST-P in which the active-site residue Tyr39 was replaced with His (W39H) or the substrate-binding site residue Cys48 was replaced with Ser (C48S) by transfection of those cDNAs into AH66 cells. These results suggested that the suppression of GST-P in AH66 cells treated with GSH-DXR must play an important role in the induction of apoptosis.