Antineoplastic drug resistance and breast cancer

Unexpected Lower Expression of Oncoprotein Gankyrin in Drug Resistant ABCG2 Overexpressing Breast Cancer Cell Lines

Background: Development of a multidrug resistance (MDR) phenotype to chemotherapy remains a major barrier in the treatment of cancer. Gankyrin (p28, p28GANK or PSMD10) is an oncoprotein overexpressed in different carcinoma cell lines. The aim of this study was to compare Gankyrin expression level in MDR cells (MCF-7/ADR and MCF-7/ MX) and non-MDR counterparts (MCF-7). Methods: Gankyrin, MDR1 (also known as ABCB1; the ATP-binding cassette sub-family B member 1) and ABCG2 (also known as BCRP; the human breast cancer resistance protein) mRNA levels were analyzed by real-time RT-PCR. Western blot analysis was used to detect the protein expression levels of Gankyrin. Results: The PCR results showed that the expression of Gankyrin was significantly lower in the ABCG2 overexpressing cell line MCF-7/MX than in non-resistanct MCF-7 cells. In contrast, there were no significant differences in mRNA expression of Gankyrin in the MDR1 overexpressing cell line MCF-7/ADR in comparison with MCF-7 cells. Similarly, Western blot analysis confirmed lower expression of Gankyrin protein in the MCF-7/MX cell line (26% compared to controls) but not in MCF-7/ADR cells. Conclusion: These findings showed that there may be a relation between down-regulation of Gankyrin and overexpression of ABCG2 but without any clear relationship with MDR1 expression in breast cancer cell lines.

Expression of HIF-2α/EPAS1 in hepatocellular carcinoma

AIM: To investigate the expression of hypoxia-inducible factor (HIF)-2α/endothelial PAS domain protein1 (EPAS1) in hepatocellular carcinoma (HCC).

METHODS: Expression of HIF-2α/EPAS1 was investigated immunohistochemically on paraffin-embedded sections from 97 patients with HCC. To further confirm that HIF-2α/EPAS1 in HCC tissues also correlated with angiogenesis, a parallel immunohistchemistry study of vascular endothelial growth factor (VEGF) was performed on these 97 cases.

RESULTS: HIF-2α/EPAS1 could be detected in 50 of 97 cases (51.6%), including 19 weakly positive (19.8%), and 31 strongly positive (31.1%), the other 47 cases were negative (48.4%). The expression of HIF-2α/EPAS1was significantly correlated with tumor size, capsule infiltration, portal vein invasion, and necrosis. A parallel immunohistochemical analysis of VEGF demonstrated its positive correlation with capsule infiltration, portal vein invasion, and HIF-2α/EPAS1 overexpression, which supported the correlation of HIF-2α/ EPAS1up-regulation with tumor angiogenesis. No apparent correlation was observed between HIF-2α/EPAS1 and capsular formation, presence of cirrhosis, and histological grade.

CONCLUSION: HIF-2α/EPAS1 is expressed in most of HCC with capsular infiltration and portal vein invasion, which indicates a possible role of HIF-2α/EPAS1 in HCC metastasis.

Glutathione conjugates and their synthetic derivatives as inhibitors of glutathione-dependent enzymes involved in cancer and drug resistance

Alterations in levels of glutathione (GSH) and glutathione-dependent enzymes have been implicated in cancer and multidrug resistance of tumor cells. The activity of a number of these, the multidrug resistance-associated protein 1, glutathione S-transferase, DNA-dependent protein kinase, glyoxalase I, and gamma-glutamyl transpeptidase, can be inhibited by GSH-conjugates and synthetic analogs thereof. In this review we focus on the function of these enzymes and carriers in cancer and anti-cancer drug resistance, in relation to their inhibition by GSH-conjugate analogs.

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

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

Glutathione S-transferases in wild-type and doxorubicin-resistant MCF-7 human breast cancer cell lines

1. Overexpression of glutathione S-transferases (GST) in breast cancer cells is hypothesized to be a component of the multifactorial doxorubicin-resistant phenotype. 2. We have characterized the expression of GST enzymes at the catalytic activity, protein and mRNA levels in wild-type MCF-7 (MCF-7/WT) human breast cancer cells and a line selected for resistance to doxorubicin (MCF-7/ADR), with the goal of modulating GST activity to overcome resistance. 3. The MCF-7/ADR cells were 30-65-fold more resistant to doxorubicin than the MCF-7/WT cells. 4. Total cytosolic GST catalytic activity was elevated 23-fold in the MCF-7/ADR cells as compared with the MCF-7/WT cells, and the MCF-7/ADR cells also showed 3-fold increases in catalytic activity toward GST mu and alpha class-selective substrates. Neither cell line showed detectable catalytic activity with a GST mu class-selective substrate. 5. MCF-7/ADR cells showed pronounced overexpression of GST mu protein and GST P1 mRNA in comparison with the wild-type cell line. Neither cell line displayed detectable GST alpha or mu at the protein level. 6. A glutathione analogue that functions as a selective GST alpha inhibitor was more potent at inhibiting total cytosolic GST catalytic activity in the MCF-7/ADR cell line than GST alpha and mu class-selective inhibitory glutathione analogues and the non-selective GST inhibitor ethacrynic acid. 7. The multidrug resistance-associated protein, which can function as a glutathione-conjugate transporter, appeared weakly overexpressed in the MCF-7/ADR cells in comparison with the MCF-7/WT cells.

Multimodal treatment strategy for locally advanced breast cancer

Between 1990 and 1995, 87 patients with locally advanced breast cancer were treated with initial chemotherapy consisting of 3-4 cycles of epirubicin and then with surgery, radiotherapy and chemotherapy. All patients with positive or unknown estrogen receptor status were administered tamoxifen. A complete response was observed in 9 patients and a partial response in 64. At a mean follow-up of 29.22 months, 25 patients had died of metastatic disease, and 48 patients are disease-free. 54% patients are alive at 5 years. Statistical analysis confirmed that neither age, menopausal status, size of the primary tumor nor histology seemed to influence the Disease Free and Overall Survival. Improved survival was observed in patients with negative lymph nodes and positive receptor status. The presence of a positive receptor status may be correlated with conserved integrity of hormone sensitivity and with a good response to the hormone therapy.

Comparative evaluation by semiquantitative reverse transcriptase polymerase chain reaction of MDR1, MRP and GSTp gene expression in breast carcinomas

Identification and quantitative evaluation of drug resistance markers are essential to assess the impact of multidrug resistance (MDR) in clinical oncology. The MDR1 gene confers pleiotropic drug resistance in tumour cells, but other molecular mechanisms are also involved in drug resistance. In particular, the clinical pattern of expression of the other MDR-related genes is unclear and their interrelationships are still unknown. Here, we report standardization of the procedures used to determine a reliable method of semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) using a standard series of drug-sensitive and increasingly resistant cell lines to evaluate the expression of three MDR-related genes, i.e. MDR1 (multidrug resistance gene 1), MRP (multidrug resistance related protein) and GSTp (glutathione-S-transferase p), reported to be endogenous standard genes for normalization of mRNAs. A total of 74 breast cancer surgical biopsies, obtained before any treatment, were evaluated by this method. When compared with classical clinical and laboratory findings, GSTp mRNA level was higher in diploid tumours. However, the main finding of our study suggests a clear relationship between two of these MDR-related gene expressions, namely GSTp and MRP. This finding provides new insight into human breast tumours, which may possibly be linked to the glutathione conjugate carrier function of MRP. Well defined semiquantitative RT-PCR procedures can therefore constitute a powerful tool to investigate MDR phenotype at mRNA levels of different related genes in small and precious tumour biopsy specimens.

Expression of glutathione S-transferase activity and glutathione content in squamous cell carcinoma of bladder associated with schistosomiasis in a population in Egypt

The present study was designed to describe the expression of the glutathione S-transferase/glutathione system in squamous cell carcinoma of the bladder in a population in Egypt. The glutathione-S transferase activity was significantly higher in bladder cancer specimens (n = 40) in comparison with schistosomiasis cystitis tissue (n = 42) (4-fold, p = 1 x 10(-12)) and with healthy control samples (n = 9) (10-fold, p = 1 x 10(-6)). The glutathione content was also significantly higher in bladder cancer than in cystitis tissue (2-fold, p = 8 x 10(-6)) and in control samples (6-fold, 8 x 10(-6)). When control mucosa and cystitis samples were compared, 2-fold increased values were obtained for glutathione-S transferase (p = 4 x 10(-3)) and glutathione (p = 1 x 10(-3)) in schistosomiasis bladder tissue. Results describe an over-expression of glutathione-S transferase and glutathione levels in squamous cell carcinoma of the bladder, and indicate a possible role in chemoresistance to pharmacological therapy.

Plasminogen activator inhibitor-1 (PAI-1) is not related to response to neoadjuvant chemotherapy in breast cancer

There is no information available on the relation between response to chemotherapy and the high-risk phenotype assessed by uPA and/or PAI-1. The clinical situation of neoadjuvant chemotherapy provides a means of rapidly assessing the sensitivity of the primary tumour to cytotoxic drug regimens. The goal of the study was to assess prospectively the predictive value of PAI-1 for response to first-line chemotherapy. PAI-1 concentration was measured on hypertonic cytosolic extracts (0.4 M potassium chloride) by ELISA before chemotherapy on a drill biopsy sample of the tumour in 69 T2 and T3 breast cancer patients (median age 46 years). Oestrogen receptor (ER) (51% ER+), progesterone receptor (PR) (58% PR+), S-phase (median 4.0%) and ploidy were also assessed in the majority of cases. The clinical response to treatment was evaluated after four cycles of FAC or FEC regimen (5-fluorouracil, epidoxorubicin or doxorubicin and cyclophosphamide) (one cycle every 4th week). PAI-1 could be assayed in 29 post-chemotherapy surgical samples. The objective response rate (complete response plus partial response) was 59% (41 out of 69). PAI-1 expressed as gram of tissue (range 19-2370 ng g(-1) tissue) was highly correlated (r = 0.98) to PAI-1 expressed as mg protein (range 0.5-68 ng mg(-1) protein). No correlation between PAI-1 level and response could be observed, with any cut-off. The post- and pre-chemotherapy PAI-1 levels were correlated (r = 0.66). Of all biological parameters, only high S-phase (cut-off 5%) was slightly correlated (chi2 = 3.91, P = 0.05) to response. These data suggest that PAI-1 is not a predictive marker of response to chemotherapy in breast cancer and that its level is not altered by neoadjuvant chemotherapy.

Nuclear medicine at the crossroads

Many nuclear medicine procedures, originally developed more than 20 years ago, are now performed with new radiopharmaceuticals or instruments; it is therefore apposite to reappraise what we are doing and why we are doing it. The clinical utility of nuclear medicine is discussed with reference, by way of example, to gated blood pools scans and myocardial perfusion imaging; the importance of the referred population for the outcome of studies is stressed. Attention is drawn to the likelihood that the detection of ischemia would be enhanced by the administration of nitroglycerin prior to rest thallium injection. Emphasis is also placed on the increasing acceptance of dual-tracer studies. The significance of expression of p-glycoprotein by some tumors for sestamibi imaging is discussed, and advances in respect of fluorodeoxyglucose imaging are reviewed. The final section covers issues relating to the development of new procedures, such as the value of nuclear medicine in the detection and characterization of tissue oxygen levels and the possible future role of nuclear medicine in the management of sleeping and eating disorders.

Clinical reversal of multidrug resistance

Reversal of drug resistance offers the hope of increasing the efficacy of conventional chemotherapy. We tested dexverapamil as a P-glycoprotein antagonist in combination with EPOCH chemotherapy in refractory non-Hodgkin's lymphoma. In a cross-over design, dexverapamil was added to EPOCH after disease stabilization or progression occurred. Objective responses were observed in 10 of 41 assessable patients. Biopsies for mdr-1 were obtained before EPOCH treatment and at the time of cross-over to dexverapamil. Levels of mdr-1 were low before EPOCH, but increased four-fold or more in 42% of patients in whom serial samples were obtained. Pharmacokinetic analysis revealed median peak concentrations of dexverapamil and its metabolite, nor-dexverapamil, of 1.66 mumol/l and 1.58 mumol/l, respectively. Since both are comparable antagonists, a median peak total reversing concentration of 3.24 mumol/l was achieved. Pharmacokinetic analysis of doxorubicin and etoposide levels confirmed a delay in the clearance of doxorubicin ranging from 5% to 24%; no change in the pharmacokinetics of etoposide was observed. This study provides sufficient rationale for testing dexverapamil in a randomized clinical trial.

Breast tumour response to primary chemotherapy predicts local and distant control as well as survival

The purpose of the present paper was to evaluate correlations between clinical response to chemotherapy and outcome in a subgroup analysis of premenopausal patients with tumours considered too large for breast conserving surgery, treated with primary chemotherapy (n = 200) from a previously published trial (Scholl S.M., Fourquet A., Asselain B, et al. Eur J Cancer 1994, 30A, 645-652). Objective response rates amounted to 65% following four courses. In a multivariate Cox regression analysis, comparing seven parameters, the following variables were associated with poor survival: clinically involved nodes [N1b:RR: 2.7 (95% CI 1.3-5.3)], the failure to respond to chemotherapy [D:RR: 2.62 (95% CI 1.3-5)] and a raised S phase fraction [SPF > 5%: RR: 2.4 (95% CI 1.2-5)]. Parameters associated with increased metastatic recurrence rates, by order of entry in the model, were: young age [< 35: RR: 2.46 (95% CI 1.2-5)], large clinical tumour size [T3: RR: 2.02 (95% CI 1.2-3.4)], poor histological grade (SBR III: RR: 1.93 (95% CI 1.1-3.3)] and the failure to respond to chemotherapy [D: RR: 1.91 (95% CI 1-3.4)]. The assessment of both tumour cell proliferation rates as well as possibly drug resistance markers (although not available in the present study) should be helpful in selecting patients likely to benefit from intensified chemotherapy regimens. The most accurate predictor of response in the present study appeared to be the response to chemotherapy treatment itself.