Glutathione S-transferase (placental) as a marker of transformation in the human cervix uteri: an immunohistochemical study

Recent Progress in Triple Negative Breast Cancer Research

Triple-negative breast cancer (TNBC) is defined as a type of breast carcinoma that is negative for expression of oestrogene and progesterone hormone receptors (ER, PR) and HER2. This form of breast cancer is marked by its aggressiveness, low survival rate and lack of specific therapies. Recently, important molecular characteristics of TNBC have been highlighted and led to the identification of some biomarkers that could be used in diagnosis, as therapeutic targets or to assess the prognosis. In this review, we summarize recent progress in TNBC research focusing on the genetic and epigenetic alterations of TNBC and the potential use of these biomarkers in the targeted therapy for better management of TNBC.

Can serum Glutathione-S-transferase levels in carcinoma cervix be a predictor of radiation response?

We conducted a pilot study wherein serum Glutathione-S-transferase levels were measured before and after radiotherapy in carcinoma cervix patients and correlated with response to treatment during a two-year follow-up period. Out of 17 patients who received radiotherapy, 9 showed a significant decrease (p<0.005) while 8 showed significant increase (p<0.004) in post radiotherapy glutathione-S-transferase values as compared to pre treatment values respectively. These patients were followed up for two years and we observed that 71% who had significant increase in post radiotherapy values had relapse of cancer within 2 years where as 66% of those who had significant decrease in post radiotherapy values had no evidence of relapse. This shows that alterations in serum Glutathione-S-transferase levels may help us to predict radiation response.

GSTPi-positive tumour microenvironment-associated fibroblasts are significantly associated with GSTPi-negative cancer cells in paired cases of primary invasive breast cancer and axillary lymph node metastases

Background:

Glutathione S-transferase Pi (GSTPi) expression is one of the factors, which is known to be associated with development of resistance to chemotherapeutics in cancer patients, including those with breast cancer. Yet, its expression has been reported to be undetectable in cancer cells in high percent of patients with primary breast cancer. However, GSTPi expression in stromal cells in breast tumour microenvironment, namely cancer-associated fibroblast (CAF), which is recognised to have major roles in cancer progression, remains poorly reported.

Methods:

The aim of the study was to determine the expression of GSTPi; vimetin, a fibroblast-associated cytoskeleton protein; and α-smooth muscle actin (α-SMA), a known marker of CAF in breast cancer tissue, by immunohistochemical staining method in consecutive histologic sections of formalin-fixed and paraffin-embedded tissue biopsy specimens from a cohort of 39 paired cases of patients with invasive breast cancer and the corresponding axillary lymph nodes metastases.

Results:

Ductal and acinar luminal epithelial cells, myoepithelial cells and surrounding fibroblasts exhibited a homogeneous cytoplasmic reactivity with anti-GSTPi antibody in 11 of 11 cases of benign breast tissue biopsies. The vimentin-positive fibroblasts were unreactive with anti-α-SMA antibody. Loss of GSTPi expression was observed in breast cancer cells, at both the primary and metastatic sites, in 31 of 39 paired cases, as compared with benign breast epithelial cells (Fisher's exact test P<0.001). A significant association was observed between GSTPi-positive, vimentin-positive and α-SMA-positive fibroblast in tumour microenvironment at both sites.

Conclusion:

This is an original report of demonstration of a significance association between tumour microenvironment-associated GSTPi-positive CAF (vimentin/α-SMA-positive) and the GSTPi-negative cancer cells in paired cases of primary invasive breast cancer and the corresponding axillary lymph nodes metastases.

Glutathione S-transferase: differential expression of alpha, mu, and pi isoenzymes in benign prostate, prostatic intraepithelial neoplasia, and prostatic adenocarcinoma

Glutathione S-transferases (GST) comprise a family of enzymes which are critical for inactivation of toxins and carcinogens. We examined the cellular expression of multiple subclasses of GST immunohistochemically in 25 radical prostatectomy specimens with clinically localized prostate cancer. Gleason scores ranged from 5 to 9, and pathologic stages varied from pT2a to pT3b (all N0M0). Antibodies were directed against GST Ya, Yc, and Yk (alpha subclass), Yb1 (micro subclass), and YPr (pi subclass). The percentage of positive cells and intensity of staining was assessed for benign epithelium, high-grade prostatic intraepithelial neoplasia (PIN), and adenocarcinoma. GSTalpha (Ya) was detected in 30% of cells (mean) in benign acini, 4.9% of cells in high-grade PIN, and 4.5% of cells in adenocarcinoma. The corresponding results for alpha (Yk), micro (Yb1), and pi (Yp) were 12.7%, 10.9%, and 3.5%; 8.7%, 5.2%, and 0.6%; and 66.7,% 0%, and 0%, respectively. GST Yc (alpha subclass) displayed the lowest level of expression, with diffuse weak staining in scattered benign secretory cells and only single cells (<1%) in high-grade PIN and carcinoma. These results demonstrate consistent reduction or loss of expression of all subclasses of GST with progression of prostatic neoplasia from benign epithelium to high-grade PIN and carcinoma. We hypothesize that carcinogenesis in the prostate results from impaired cellular handling of mutagenic agents owing to reduction or loss of expression of multiple GST and other detoxifying and antimutagenesis agents.

Glutathione S-transferase pi (GSTP1) hypermethylation in prostate cancer: review 2007

Prostatic carcinoma is characterised by the silencing of the pi-class glutathione S-transferase gene (GSTP1), which encodes a detoxifying enzyme. The silencing of GSTP1 results from aberrant methylation at the CpG island in the promoter-5' and occurs in the vast majority of cases of high-grade prostatic intraepithelial neoplasia (PIN) and prostate cancers. We review the potential novel role of GSTP1 and its related expression in prostate cancer. The loss of expression (silencing) of the GSTP1 gene is the most common (>90%) genetic alteration reported to date in prostate cancer. Quantitative methylation-specific PCR assays allow detection of GSTP1 methylation in prostate biopsies and may improve the sensitivity of cancer detection. Advances in the epigenetic characterisation of prostate cancer have enabled the development of DNA methylation assays that may soon be used in diagnostic testing of serum and tissue for prostate cancer. Inhibition of aberrant promoter methylation could theoretically prevent carcinogenesis.

Nuclear localisation of glutathione S-transferase pi is an evaluation factor for drug resistance in gynaecological cancers

AIMS

Nuclear glutathione S-transferase pi (GST7pi) has been reported to protect cancer cells against anticancer drugs. The aim of the present study was to evaluate the clinical significance of nuclear GSTpi in gynaecological cancer.

MATERIALS AND METHODS

We carried out an immunohistochemical analysis of GSTpi, and examined the correlation between nuclear GSTpi: expression and prognosis in 43 epithelial ovarian cancers. We compared expression levels before and after chemotherapy in uterine cervical cancers and endometrial cancers.

RESULTS

The 5-year progression-free survival rate of the nuclear GSTpi-positive group was lower than that of the cytoplasmic GSTpi-positive group, and was significantly lower than that of the negative group (14.3% vs 34.8% vs 66.7%; P = 0.041). The expression of nuclear GSTpi was compared before and after chemotherapy in uterine cervical and endometrial cancers. In eight out of 12 cases (66.7%), the expression turned positive after the chemotherapy.

CONCLUSIONS

We suggest that nuclear localisation of GSTpi is associated with drug resistance. The nuclear localisation of GSTpi in tumour cells is a useful prognosticator, and may contribute to the selection of anticancer drugs for gynaecological cancers.

Immunohistochemistry of omega class glutathione S-transferase in human tissues

Omega class glutathione transferase (GSTO) has been recently described in a number of mammalian species. We used immunohistochemistry to determine the cellular and tissue distribution of GSTO1-1 in humans. Expression of GSTO1-1 was abundant in a wide range of normal tissues, particularly liver, macrophages, glial cells, and endocrine cells. We also found nuclear staining in several types of cells, including glial cells, myoepithelial cells of the breast, neuroendocrine cells of colon, fetal myocytes, hepatocytes, biliary epithelium, ductal epithelium of the pancreas, Hoffbauer cells of the placenta, and follicular and C-cells of the thyroid. These observations and the known activity of GSTO1-1 suggest biological functions that are not shared with other GSTs.

Expression of pi-class glutathione S-transferase: two populations of high grade prostatic intraepithelial neoplasia with different relations to carcinoma

BACKGROUND/AIMS

Patients with high grade prostatic intraepithelial neoplasia of the transition zone appear to be at increased risk of developing prostatic carcinoma, although not to the same degree as patients with high grade prostatic intraepithelial neoplasia of the peripheral/central zone. Previous investigations have shown loss of expression of pi-class glutathione S-transferase (GST-pi; an enzyme that protects against electrophilic carcinogens) in prostatic carcinoma and in high grade prostatic intraepithelial neoplasia. The aim of this study was to compare the expression of GST-pi in high grade prostatic intraepithelial neoplasia of the transition zone with that in high grade prostatic intraepithelial neoplasia of the peripheral/central zone (that is, non-transition zone).

METHODS

Immunostaining with the anti-GST-pi antibody was performed on 20 high grade prostatic intraepithelial neoplasia samples of the transition zone, either isolated or associated with prostatic carcinoma (groups 1 and 2, respectively; 10 cases each) and on 20 high grade prostatic intraepithelial neoplasia samples of the non-transition zone, either isolated or associated with prostatic carcinoma (groups 3 and 4, respectively; 10 cases each). This study also included six samples of high grade prostatic intraepithelial neoplasia simultaneously present in the transition and non-transition zones and not associated with prostatic carcinoma (group 5). The presence of immunostaining, staining intensity, and the distribution of immunostaining were evaluated in the high grade prostatic intraepithelial neoplasia lesions and in the normal tissue and cancer areas.

RESULTS

The GST-pi antibody stained the cytoplasm of the cells lining the ducts and acini of normal prostate tissue. Staining was stronger and more diffuse in the basal cell layer than in the luminal (or secretory) cell layer. Immunohistochemical staining with anti-GST-pi antibodies failed to detect the enzyme in all prostatic carcinoma foci but one. Two patterns were detected in high grade prostatic intraepithelial neoplasia. One was represented by GST-pi staining similar to that of the normal tissue (pattern A). The other deviated from it and was characterised by absence of GST-pi expression in the secretory cells and abundant expression in scattered basal cells (pattern B). Pattern A staining was seen more frequently in the transition than in the non-transition zone. Pattern B staining was seen mainly in high grade prostatic intraepithelial neoplasia of non-transition zone associated with cancer.

CONCLUSIONS

The differential expression of GST-pi in the transition and non-transition zones indicates the existence of two populations with the morphological appearance of high grade prostatic intraepithelial neoplasia that might have different associations with carcinoma.

Immunohistochemical expression of pi class glutathione S-transferase in the basal cell layer of benign prostate tissue following chronic treatment with finasteride

BACKGROUND

Glutathione S-transferases (GST) may prevent carcinogenesis through inactivation of reactive electrophiles by conjugation to reduced glutathione. Treatment directed at the induction or preservation of GST-pi expression in normal epithelium could have a profound impact on the prevention of prostate neoplasia. Finasteride, a 5-alpha-reductase inhibitor, is used as a chemopreventive agent because it blocks the conversion of testosterone to its byproduct which promotes prostate tumour growth.

OBJECTIVE

To investigate GST-pi expression immunohistochemically in benign prostate tissue from untreated patients and from patients chronically treated with finasteride.

MATERIALS

Immunostaining with anti-GST-pi antibody was performed on 10 (cysto-) prostatectomy, eight simple prostatectomy, and three transurethral prostatectomy specimens. The first set of 10 prostates was from untreated patients operated on for bladder cancer. The other cases were from patients with benign prostatic hyperplasia and chronically treated with finasteride. None of the specimens in either group showed prostatic cancer, prostatic intraepithelial neoplasia, urothelial carcinoma, or chronic prostatitis. Specimens were evaluated for the presence, intensity, and distribution of immunostaining.

RESULTS

Diffuse cytoplasmic immunostaining was observed in the basal cell layer of the untreated specimens. Some variability in the expression of GST-pi was seen within each zone and also between the prostate zones. Only a minority of the secretory cells was stained weakly, mainly in the subnuclear region of the cells facing an uninterrupted basal cell layer. Staining was more homogeneously diffuse in the cytoplasm of the luminal cells facing the basement membrane directly. In the benign epithelium of the finasteride treated specimens the circumferential staining of the basal cells appeared to be more continuous than in the untreated cases, the gaps in the stained basal cell layer being fewer, shorter, or even absent in some ducts and acini. There was no variability in the intensity of staining of the basal cell layer, all the cells being intensely stained in a uniform way. The intensity of staining of the secretory cells was not influenced by finasteride treatment.

CONCLUSIONS

Following chronic treatment with finasteride the immunohistochemical expression of pi class glutathione S-transferase in the benign prostate ducts and acini is upregulated in relation to an expanded basal cell layer. This could indicate that finasteride acts as a GST-pi inducer.

Immunohistochemical expression of pi-class glutathione S-transferase is down-regulated in adenocarcinoma of the prostate

BACKGROUND

Glutathione S-transferase is often up-regulated in neoplastic tissues. A single previous study found a loss of expression associated with carcinogenesis of the prostate.

METHODS

To extend these results, the authors performed immunohistochemical staining for the pi-class of glutathione S-transferase (GSTpi) on 74 archival sequential prostate specimens. The antibody used was derived from rabbits immunized against purified human GSTpi. Paraffin blocks containing both benign tissue and adenocarcinoma were studied.

RESULTS

Heterogeneous expression of GSTpi in benign acini was found in 96% of cases, but GSTpi was not expressed in 95% of invasive adenocarcinomas of the prostate, nor was it expressed in any of the foci of high grade prostatic intraepithelial neoplasia. Basal cells of benign acini showed strong, diffuse staining for GSTpi, whereas the secretory luminal epithelium expressed GSTpi weakly and focally.

CONCLUSIONS

This study confirms the down-regulation of GSTpi in adenocarcinoma of the prostate and shows that the loss of GSTpi expression is a phenotype associated with malignant transformation.

The relationship between tumour glutathione concentration, glutathione S-transferase isoenzyme expression and response to single agent carboplatin in epithelial ovarian cancer patients

There is evidence to suggest that glutathione (GSH) and glutathione-S-transferases (GST) are important factors in determining sensitivity to cytotoxic drugs in vitro and in preclinical in vivo model systems. To define the relationship between tumour GSH concentration, GST isoenzyme expression and response to carboplatin in epithelial ovarian cancer (EOC), tumour samples from 39 patients with assessable disease after primary surgery were analyzed for GSH content and GST expression. Response was assessed after completing six courses of single agent carboplatin therapy. GSH was measured by high performance liquid chromatography (HPLC) in fresh tumour samples taken at primary laparatomy. GST isoenzyme expression was assessed by immunohistochemistry of fixed tumour material using antibodies specific for pi, alpha and mu classes. GST isoenzyme expression was defined as positive if the staining intensity was strong and more than 10% of tumour cells were involved. The mean GSH concentrations were: 8351 +/- 4496, 7211 +/- 5026, 6559 +/- 4573 and 3758 +/- 1885 (nmol g-1 tissue dry weight mean +/- s.d.) for tumours from patients who subsequently achieved a complete response (CR, n = 18), partial response (PR, n = 10) or who had static disease (SD, n = 7) or progressive disease (PD, n = 4) respectively. There was no relationship between GSH concentration and response (ANOVA, P = 0.32). There were also no relationship between GST isoenzyme expression and response (P Fisher's exact test 0.51-0.55 and chi-squared test 0.98-0.99). In conclusion, there was no association between the concentration of GSH or expression of GST isoenzymes and response to single agent carboplatin in primary previously untreated EOC.

The expression of placental-type glutathione S-transferase (GST-pi) in human cutaneous squamous cell carcinoma and normal human skin

The expression of human placental-type glutathione S-transferase (GST-pi) was investigated in human cutaneous squamous cell carcinoma (SCC) and normal skin using Northern blot and immunohistochemical analysis. In Northern blot examination, the expression of GST-pi transcript was recognized in all instances, and SCC showed a significantly higher expression of GST-pi than normal skin. In immunohistochemical examination, GST-pi was stained well in the cytoplasm of all cells of the stratum granulosum, many cells of the stratum spinosum and a few cells of the stratum basale in normal skin. Some cells of the stratum spinosum and almost all cells of the stratum basale showed only a weakly positive or almost negative reaction for GST-pi. No nuclear staining of GST-pi was obvious in normal epidermal cells. In SCC, many cells showed strong positivity for GST-pi in the cytoplasm, and some were obviously accompanied by nuclear staining of GST-pi. These findings suggest that GST-pi exists mainly in many cells in the upper layers of the normal epidermis and that GST-pi is involved in the process of carcinogenesis.

Glutathione S-transferase in bone marrow metastases of disseminated neuroblastoma

Antisera to each of the three main cytosolic forms of glutathione S-transferase (GST; alpha, mu, and pi) has been used to characterise GST expression by metastatic neuroblastoma in bone marrow trephine biopsies taken from 15 patients at presentation and from five of this group at relapse. There was no correlation between expression of extra-nuclear alpha or mu GST and outcome, and no consistent pattern at relapse. Seven of eight expressing nuclear pi GST at presentation died of resistant disease. Three of five cases with no detectable nuclear pi class GST remain alive and disease free. The results provide no encouragement for further investigation of alpha or mu GST in this disease but larger studies of uniformly treated patients may show whether nuclear pi GST expression at presentation indicates likely relapse.

Expression of glutathione S-transferases in normal and malignant pancreas: an immunohistochemical study

The glutathione S-transferases (GSTs) are a family of detoxification and metabolising enzymes, which have been linked with the susceptibility of tissues to environmental carcinogens and resistance of tumours to chemotherapy. Environmental carcinogens have been implicated in the pathogenesis of pancreatic carcinoma, which is also a tumour characterised by marked chemotherapeutic drug resistance. In this study 26 pancreatic adenocarcinoma and 12 normal pancreatic samples were examined immunohistochemically for expression of pi (acidic), alpha (basic), and mu (neutral) GST. Fourteen (54%) of the tumours expressed pi GST alone, two (8%) expressed both pi and alpha GST, and two (8%) showed immunoreactivity with alpha GST alone. In the normal pancreas the intralobular ducts and centroacinar cells expressed pi GST alone whereas the large ducts expressed both pi and alpha GST. The acinar cells showed immunoreactivity only with anti-alpha GST. Mu GST was not expressed by normal or malignant pancreas. Expression of pi GST by pancreatic carcinoma may be a marker of the malignant phenotype and be induced during neoplastic transformation. Alternatively it could possibly reflect cell of origin, suggesting that the tumour arises from the centroacinar cells or intralobular ducts, or both rather than the large ducts.

Glutathione-S-transferase pi expression in transitional cell carcinoma of the bladder

Glutathione-S-transferase pi (GST pi) is a multifunctional protein that acts as an enzyme, involved in the detoxification of drugs and carcinogens. It has been implicated both in drug resistance and malignant transformation of epithelium. Using an indirect immunohistochemical technique, we have evaluated cytoplasmic and nuclear staining in normal urothelium, 23 superficial bladder tumours and 26 invasive tumours. All 26 invasive tumours had been treated with platinum-based chemotherapy. Cytoplasmic staining was seen in normal urothelium and all bladder tumours. Nuclear staining was seen in 1 superficial tumour and in 13 invasive tumours. There was no association between nuclear staining and response to chemotherapy. Nuclear staining was seen in 1 area of dysplasia and in 2 of 3 areas of carcinoma in situ. GST pi expression is not a predictor of response to chemotherapy. Increased intra-nuclear expression of GST pi may be associated with progression of transitional cell carcinoma of the bladder.

Expression of glutathione S-transferase-pi in human squamous cell carcinomas of the pharynx and larynx. Loss after radiation therapy

BACKGROUND AND METHODS

The expression of the placental form of glutathione S-transferase (GST-pi) in human squamous cell carcinomas of the pharynx and larynx was investigated immunohistochemically before and after radiation therapy.

RESULTS

Before the treatment, 47 of 71 carcinoma specimens (66.2%) demonstrated positive reactions, GST-pi being diffusely stained throughout the tumor lesions. Positive rates for moderately and well differentiated carcinomas were 69.7% and 88.0%, respectively, with both of these values being significantly higher than that for poorly differentiated carcinomas (15.4%, P < 0.01). Thus, GST-pi expression seems to be related to the degree of differentiation. Although several tumors exhibiting GST-pi staining did not respond to radiation therapy, most cases responded positively and no relation was apparent in the 41 cases of squamous cell carcinoma studied between response to radiation therapy and previous GST-pi staining. After irradiation of 1000 to 7000 cGy, however, most carcinoma specimens exhibited negative GST-pi staining, regardless of response to radiation therapy.

CONCLUSIONS

The results suggest that although GST-pi expression is not directly involved in determining sensitivity to radiation, GST-pi expression can be influenced by exogenous agents. The loss or decrease of GST-pi after irradiation is in clear contrast to the enhanced expression observed in many cancer cell lines resistant to chemotherapy.

Glutathione S-transferase activity and isoenzyme distribution in ovarian tumour biopsies taken before or after cytotoxic chemotherapy

A study involving the measurement of glutathione S-transferase activities and isoenzyme distributions in human ovarian tumours has been carried out. These tumours have been obtained either at initial debulking surgery, prior to cytotoxic chemotherapy, or at second look laparotomy following chemotherapy. The response rates of these two groups to chemotherapy differ markedly, with patients who have relapsed following initial chemotherapy showing a reduction in response rates to subsequent chemotherapy. Analysis of these data show no statistically significant differences between the glutathione S-transferase activity or isoenzyme distribution in these two groups of patients. Significant differences were observed in the glutathione-S-transferase activities (GST) between tumours and normal ovaries. GST activities in pre-chemotherapy tumours (n = 33, P = 0.01) and post-chemotherapy tumours (n = 20, P = 0.001) where significantly higher than the GST activity in normal ovaries (n = 15). One feature was the expression of the basic isoenzyme which is expressed more in normal ovaries than in tumours. No differences in these parameters were observed in normal peritoneal tissue taken from patients before or after chemotherapy. These data do not support the hypothesis that changes in glutathione S-transferase enzyme activity or isoenzyme expression are major determinants of response to chemotherapy in ovarian tumours.

Glutathione S-transferases in neonatal liver disease

AIMS

To investigate the distribution of alpha and pi class glutathione S-transferases (GST) in normal fetal, neonatal, and adult liver; and to examine changes in GST expression in neonatal liver disease.

METHODS

alpha and pi class GST were immunolocalised in sections of formalin fixed liver tissue obtained from human fetuses (n = 21), neonates (n = 8), young children (n = 9) and adults (n = 10), and from neonates with extrahepatic biliary atresia (n = 15) and neonatal hepatitis (n = 12). Monospecific rabbit polyclonal antibodies were used with a peroxidase-antiperoxidase method.

RESULTS

Expression of pi GST was localised predominantly within biliary epithelial cells of developing and mature bile ducts of all sizes from 16 weeks' gestation until term and in neonatal and adult liver. Coexpression of pi and alpha GST was seen in hepatocytes of developing fetal liver between 16 and 34 weeks' gestation. Although pi GST was seen in occasional hepatocytes up to six months of life, this isoenzyme was not expressed by hepatocytes in adult liver. By contrast, alpha GST continued to be expressed by hepatocytes in adult liver; this isoenzyme was also seen in some epithelial cells of large bile ducts in adult liver. No change was observed in the distribution of alpha GST in either neonatal hepatitis or extrahepatic biliary atresia. However, aberrant expression of pi GST was identified in hepatocytes of all but one case of extrahepatic biliary atresia but in only two cases of neonatal hepatitis.

CONCLUSIONS

The phenotypic alterations noted in extrahepatic biliary atresia may result from the effect of cholate stasis. Evaluation of the pattern of pi and alpha GST distribution by immunohistochemical staining may provide valuable information in distinguishing between these two forms of neonatal liver disease.

Activity of glutathione-S-transferase in rat liver and kidneys after administration of lead or cadmium

The influence of an acute dose of lead nitrate or cadmium chloride on the activity of glutathione-S-transferase (GST) was investigated in rats. CdCl2 (10 mumol/kg) did not influence the enzyme activity in either organ. In contrast Pb(NO3)2 (100 mumol/kg) caused a significant increase of GST activity in both organs. SDS polyacrylamide gel electrophoresis (SDS-PAGE) showed that in liver the activity enhancement is due mainly to the induction of the isoenzyme GST 7-7, while in the kidneys the activity of all the isoenzymes is increased.

Glutathione transferases and cancer

The glutathione transferases, a family of multifunctional proteins, catalyze the glutathione conjugation reaction with electrophilic compounds biotransformed from xenobiotics, including carcinogens. In preneoplastic cells as well as neoplastic cells, specific molecular forms of glutathione transferase are known to be expressed and have been known to participate in the mechanisms of their resistance to drugs. In this article, following a brief description of recently identified molecular forms, we review new findings regarding the respective molecular forms involved in carcinogenesis and anticancer drug resistance, with particular emphasis on Pi class forms in preneoplastic tissues. The rat Pi class form, GST-P (GST 7-7), is strongly expressed not only in hepatic foci and hepatomas, but also in initiated cells that occur at the very early stages of chemical hepatocarcinogenesis, and is regarded as one of the most reliable markers for preneoplastic lesions in the rat liver. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-responsive element-like sequences have been identified in upstream regions of the GST-P gene, and oncogene products c-jun and c-fos are suggested to activate the gene. The Pi-class forms possess unique enzymatic properties, including broad substrate specificity, glutathione peroxidase activity toward lipid hydroperoxides, low sensitivity to organic anion inhibitors, and high sensitivity to active oxygen species. The possible functions of Pi class glutathione transferases in neoplastic tissues and drug-resistant cells are discussed.

Immunohistochemical demonstration of glutathioneS-transferases in primary human breast carcinomas

The expression of cytosolic glutathione S-transferase (GST) isoenzymes has been assessed in a series of 74 primary human breast carcinomas using an immunohistochemical method. GST pi was detected in sections from all 74 tumours; it was expressed by non-epithelial (stromal and inflammatory) cells in 62 tumours (84 per cent), but by tumour epithelium in only 35 (47 per cent). Non-neoplastic mammary epithelium was uniformly positive for GST pi. Expression of GST alpha and mu was observed in 19 and 42 per cent of the tumours, respectively, and was largely confined to the neoplastic component. Lack of staining of tumour epithelium for GST pi was significantly associated with poorer tumour differentiation (higher grade). There was no association between expression of any of the three isoenzymes and either menopausal status or expression of c-erbB-2 oncogene protein product. Immunohistochemistry is a useful method for the investigation of expression and cellular localization of GSTs within tumours; such data are needed to improve our understanding of the role of these enzymes in neoplasia and in resistance to cytotoxic drug therapy.