Appearance and detection of multiple copies of the mdr-1 gene in clinical samples of mammary carcinoma

Molecular mechanisms of chemo- and radiotherapy resistance and the potential implications for cancer treatment

Cancer is a leading cause of death worldwide. Surgery is the primary treatment approach for cancer, but the survival rate is very low due to the rapid progression of the disease and presence of local and distant metastasis at diagnosis. Adjuvant chemotherapy and radiotherapy are important components of the multidisciplinary approaches for cancer treatment. However, resistance to radiotherapy and chemotherapy may result in treatment failure or even cancer recurrence. Radioresistance in cancer is often caused by the repair response to radiation-induced DNA damage, cell cycle dysregulation, cancer stem cells (CSCs) resilience, and epithelial-mesenchymal transition (EMT). Understanding the molecular alterations that lead to radioresistance may provide new diagnostic markers and therapeutic targets to improve radiotherapy efficacy. Patients who develop resistance to chemotherapy drugs cannot benefit from the cytotoxicity induced by the prescribed drug and will likely have a poor outcome with these treatments. Chemotherapy often shows a low response rate due to various drug resistance mechanisms. This review focuses on the molecular mechanisms of radioresistance and chemoresistance in cancer and discusses recent developments in therapeutic strategies targeting chemoradiotherapy resistance to improve treatment outcomes.

MRP3: a molecular target for human glioblastoma multiforme immunotherapy

Background

Glioblastoma multiforme (GBM) is refractory to conventional therapies. To overcome the problem of heterogeneity, more brain tumor markers are required for prognosis and targeted therapy. We have identified and validated a promising molecular therapeutic target that is expressed by GBM: human multidrug-resistance protein 3 (MRP3).

Methods

We investigated MRP3 by genetic and immunohistochemical (IHC) analysis of human gliomas to determine the incidence, distribution, and localization of MRP3 antigens in GBM and their potential correlation with survival. To determine MRP3 mRNA transcript and protein expression levels, we performed quantitative RT-PCR, raising MRP3-specific antibodies, and IHC analysis with biopsies of newly diagnosed GBM patients. We used univariate and multivariate analyses to assess the correlation of RNA expression and IHC of MRP3 with patient survival, with and without adjustment for age, extent of resection, and KPS.

Results

Real-time PCR results from 67 GBM biopsies indicated that 59/67 (88%) samples highly expressed MRP3 mRNA transcripts, in contrast with minimal expression in normal brain samples. Rabbit polyvalent and murine monoclonal antibodies generated against an extracellular span of MRP3 protein demonstrated reactivity with defined MRP3-expressing cell lines and GBM patient biopsies by Western blotting and FACS analyses, the latter establishing cell surface MRP3 protein expression. IHC evaluation of 46 GBM biopsy samples with anti-MRP3 IgG revealed MRP3 in a primarily membranous and cytoplasmic pattern in 42 (91%) of the 46 samples. Relative RNA expression was a strong predictor of survival for newly diagnosed GBM patients. Hazard of death for GBM patients with high levels of MRP3 RNA expression was 2.71 (95% CI: 1.54-4.80) times that of patients with low/moderate levels (p = 0.002).

Conclusions

Human GBMs overexpress MRP3 at both mRNA and protein levels, and elevated MRP3 mRNA levels in GBM biopsy samples correlated with a higher risk of death. These data suggest that the tumor-associated antigen MRP3 has potential use for prognosis and as a target for malignant glioma immunotherapy.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Quantitative study of ductal breast cancer--patient targeted prognosis: an exploration of case base reasoning

Current analytic methodologies allow the extraction, even from small tumor masses, of extensive information on the biologic characteristics of malignant lesions, such as tumor aggressivity, metastatic potential, drug resistance, and host interactions. Clinical practice now offers a wide range of therapeutic strategies. Information technological advances offer the opportunity to refer to very large data bases of patient anamnestic data, response to treatment and clinical outcome. There is a need to formulate therapy and prognosis for each individual case. Case based reasoning is a knowledge based methodology where the outcome for complex situations can be predicted by referring to a large data base of cases of known outcomes. The preliminary data obtained from this study suggest that case based reasoning may offer a promising approach to individual targeted prognosis.

Multidrug resistance in breast cancer: a meta-analysis of MDR1/gp170 expression and its possible functional significance

BACKGROUND

P-glycoprotein (gp170; encoded by the MDR1 gene [also known as PGY1]) is a membrane protein capable of exporting a variety of anticancer drugs from cells. MDR1/gp170 expression has been studied in breast cancer, but the prevalence of this expression and its role in breast tumor drug resistance are unclear.

PURPOSE

We conducted a critical review and meta-analysis of studies examining MDR1/gp170 expression in breast cancer to estimate the likely prevalence and clinical relevance of this expression. We also explored reasons for differences in the findings from individual studies.

METHODS

Published papers on MDR1/gp170 expression in breast cancer were identified by searching several literature databases and reviewing the bibliographies of identified papers. Variability across the studies in the proportion of tumors expressing MDR1/gp170 was assessed by use of chi-squared tests of homogeneity, weighted means, and weighted linear regression. Pooled relative risks (RRs) for the association between the induction of MDR1/gp170 expression and prior chemotherapy and associations between MDR1/gp170 expression and several clinical outcomes were estimated by use of Mantel-Haenszel methods. Heterogeneity among the pooled RRs was explored by use of chi-squared tests. Reported P values are two-sided.

RESULTS

Thirty-one studies were identified and evaluated. The proportion of breast tumors expressing MDR1/gp170 in all of the studies was 41.2%, but there was substantial heterogeneity in the values across individual studies (P<.0001). Regression analyses demonstrated that a considerable portion of the observed heterogeneity was a consequence of the change, over time, from RNA hybridization-based assays to immunohistochemistry-based assays of MDR1/gp170 expression. Measuring MDR1/gp170 expression before versus after chemotherapy and use of cytotoxic drugs that are not substrates for gp170 also contributed to the heterogeneity. Treatment with chemotherapeutic drugs or hormonal agents was associated with an increase in the proportion of tumors expressing MDR1/gp170 (RR = 1.77; 95% confidence interval [CI] = 1.46-2.15). Patients with tumors expressing MDR1/gp170 were three times more likely to fail to respond to chemotherapy than patients whose tumors were MDR1/gp170 negative (RR = 3.21; 95% CI = 2.28-4.51); this RR increased to 4.19 (95% CI = 2.71-6.47) when considering only patients whose tumor expression of MDR1/gp170 was measured after chemotherapy. MDR1/gp170 expression was not associated with lymph node metastases, estrogen receptor status, tumor size, tumor grade, or tumor histology.

CONCLUSIONS AND IMPLICATIONS

MDR1/gp170 expression in breast tumors is associated with treatment and with a poor response to chemotherapy. The data are consistent with a contributory role for MDR1/gp170 in the multidrug resistance in some breast tumors.

C-erb-b2/int-2 amplification appears faster in breast-cancer patients receiving second-line endocrine treatment

We have examined the appearance of c-erb-b2 and int-2 amplification in 2 different groups of breast-cancer patients. The groups differed with regard to their clinical status in that one group was receiving first-line endocrine treatment (tamoxifen) whereas the second was receiving second-line endocrine treatment (after failing on tamoxifen). The latter group of patients showed clinicallya a more advanced disease (higher frequency of stage-IV as compared to stage-III disease). Consecutive tumor samples were obtained using fine-needle biopsies from individual tumor lesions of each patient every second or third month. Median time from diagnosis to the last biopsy for patients receiving tamoxifen was 25 months and, for patients receiving second-line treatment, 55 months. The presence of amplification was determined using semi-quantificative PCR. We found that both genes developed amplification during tumor progression. The appearance of amplification was more pronounced in the clinically more advanced patients receiving second-line treatment (p = 0.018).

Prognostic significance of c-erb-B2 amplification in fine-needle biopsies of breast cancer patients not operated at diagnosis

Prognostication of breast cancer patients, not operated at diagnosis, poses a clinically difficult problem. To use gene amplification we examined cytological samples and determined c-erb-B2 gene copy number with semi-quantitative PCR. Control experiments showed the same gene-copy number in aliquots that were either air-dried (and MGG-stained), fixed in methanol (and air-dried), or snap-frozen in liquid nitrogen. Therefore we examined the prognostic value of c-erb-B2 amplification in 95 breast cancer patients that had not been operated at diagnosis (up to 12 years previously). Tumor cells were obtained from routine archival cytological smears. 15 patients (16%) had developed amplification. Univariate and multivariate analysis showed that c-erb-B2 amplification is a significant prognostic factor (p < 0.0001). Hence routine cytological MGG smears can be used for prognostic determination.

Higher frequency of gene amplification in breast cancer patients who received adjuvant chemotherapy

BACKGROUND

Amplification of certain genes is involved in resistance to chemotherapy. The development of such amplification in patients by drug treatment has not yet been established. We have assessed the appearance of gene amplification in breast cancer patients with recurrent disease. One group of patients had previously received adjuvant chemotherapy (cyclophosphamide, methotrexate, 5-fluorouracil [CMF]) after surgery. The second group had not. All of these patients had developed recurrent disease and were receiving first-line endocrine treatment (tamoxifen).

METHODS

Tumor cells were obtained from the recurrent carcinoma using fine-needle biopsies. Gene copy number was determined for dihydrofolate reductase and thymidylate synthase with semiquantitative polymerase chain reaction. Dihydrofolate reductase is involved in resistance to methotrexate (M) and thymidylate synthetase in resistance to 5-fluoropyrimidines (F), two targets for the CMF regime.

RESULTS

We found that amplification of the examined genes develops in higher frequency among patients who previously received chemotherapy (p = 0.002).

CONCLUSIONS

These findings provide strong evidence for gene amplification induced by drug treatment.

High rate of MDR-1 and heterogeneous pattern of MRP expression without gene amplification in endometrial cancer

The present study was undertaken to determine the pattern of expression of 2 molecular markers of multidrug resistance, the MDR-1 and MRP genes, in endometrial carcinomas from 50 untreated patients using a PCR semi-quantitative assay. In addition, PCR analysis of MDR-1 and MRP gene amplification was obtained in each case. High rate of MDR-1 expression without gene amplification was detected in all endometrial-carcinoma samples, as well as in 10 adenomatous hyperplasias and 50 samples of normal endometrium. On the other hand, MRP appeared to be expressed at moderate levels in normal endometrial tissue, while relatively high levels of MRP expression without gene amplification were occasionally observed in endometrial-carcinoma samples.

Anthracycline resistance in breast cancer: clinical applications of current knowledge

Anthracyclines are highly effective antineoplastic agents for the treatment of breast cancer. Nevertheless, essentially all breast cancer patients have tumours which are intrinsically resistant or which develop resistance during the course of therapy. Clinical trials provide indirect information on the nature of anthracycline resistance and work in the basic sciences has demonstrated molecular mechanisms which play a role. Initial clinical attempts to exploit and translate these mechanisms to predict, and interfere with, anthracycline resistance have met with mixed success, and have not yet led to accepted clinical applications.

Prognostic value of erb-B2 and myc amplification in breast cancer imprints

BACKGROUND

Amplification of erb-B2 and myc shows prognostic value in patients with operable breast cancer. Amplification is usually detected in tumor samples remaining after pathologic work-up, preventing the examination of small tumors.

METHODS

Tumor imprints that contained low numbers of contaminating normal cells were obtained from small tumors. The prognostic value of erb-B2 and myc amplification in imprint breast preparations was examined, using the polymerase chain reaction (PCR) to determine gene copy number. Tumor material was obtained from 162 patients with breast cancer operated 1975-1976.

RESULTS

Amplification of erb-B2 existed in 21% and myc in 16% of the patients. Both erb-B2 and myc amplification showed prognostic significance in univariate analysis for survival and relapse free survival. In multivariate analysis, erb-B2 was a significant factor. In small tumors less than 13 mm in greatest dimension, erb-B2 showed prognostic significance for survival but not for relapse free survival.

CONCLUSIONS

The use of imprints/PCR allows the detection of gene amplification in breast cancer. The procedure is suitable for the analysis of small tumors and can be used to examine very small tumors, such as those detected mammographically.

Effect of unmodified triple helix-forming oligodeoxyribonucleotide targeted to human multidrug-resistance gene mdr1 in MDR cancer cells

The human mdr1 gene encodes a transmembrane glycoprotein the over-expression of which is associated with development of multidrug resistance in human tumor cells. A negative modulation of human mdr1 has been attempted via a 27-mer unmodified triple helix-forming oligonucleotide, named 1D, targeted to a homopurine sequence in the coding region of the gene. By administering 10 microM of 1D we could find a significant reduction in MDR1 mRNA levels in the human drug-resistant cell line CEM-VLB100. This effect appears to be specific and due to a transient block of RNA polymerase mediated by triple helix formation.

High expression of the multidrug resistance-associated protein (MRP) in chronic and prolymphocytic leukaemia

The expression of the multidrug resistance-associated protein (MRP), a new glycoprotein involved in drug resistance, was investigated in tumour samples from 80 patients with chronic B-cell malignancies by a quantitative RNase protection assay. In B-cell chronic lymphocytic leukaemia (B-CLL) (n = 32), either treated (n = 18) or untreated (n = 14), a high percentage of patients (20/32: 63%) had relatively high expression levels of the MRP gene (25U or more). In addition, hyperexpression of the MRP gene was demonstrated in 4/10 (40%) untreated patients with B-cell prolymphocytic leukaemia (B-PLL). In contrast, low MRP mRNA expression levels were detected in hairy cell leukaemia (n = 7), non-Hodgkin's lymphoma (n = 13) and multiple myeloma (n = 18). Statistical analysis of MRP expression in untreated CLL (mean +/- SD 29.2 +/- 18.5 U) versus treated CLL (mean +/- SD 26.7 +/- 13.7 U) did not show significant differences in MRP expression between the two groups. Southern blot analysis did not reveal amplification of the MRP gene in the leukaemia samples with elevated MRP mRNA levels. We conclude that B-PLL and B-CLL frequently display high MRP expression and that this hyperexpression is probably due to transcriptional activation and/or increased mRNA stability.

Intratumoral heterogeneity for amplified genes in human breast carcinoma

Intratumoral heterogeneity was studied in human breast cancer by examining separate tumor lesions of individual patients. Tumor samples were obtained from each patient by fine-needle biopsies from 2 to 4 separate tumor lesions. We used a semi-quantitative PCR to distinguish between samples with gene amplification and single gene copy samples. Five genes were analyzed in each biopsy: MDR-1, dihydrofolate reductase, thymidylate synthase, c-erb-B2 and int-2. Three groups of patients were examined: those awaiting initiation of treatment; those receiving first-line endocrine therapy; and those receiving second-line endocrine treatment. A pattern of intratumoral heterogeneity for gene amplification was clearly apparent. The frequency of amplification was lowest before initiating therapy and highest in patients receiving second-line treatment (p = 0.023).

Breast cancer: prognostic significance of c-erb-B2 and int-2 amplification compared with DNA ploidy, S-phase fraction, and conventional clinicopathological features

The prognostic value of oncogene amplification and conventional clinicopathological features was determined in consecutive breast cancers detected during 5 months in 1975-1976 in 4 Swedish counties. Material was collected from 162 of the 179 patients and tumor size, nodal status, FSH, estrogen/progesterone receptor status, DNA ploidy and S-phase fraction determined. Tissues remaining from 80 patients were stored frozen until 1991, when amplification of the oncogenes c-erb-B2 and int-2 was determined. We show that c-erb-B2 amplification (but not int-2 amplification) and positive axillary nodal status show prognostic significance for both survival and relapse-free survival in univariate and multivariate analysis. The other examined factors showed no significance.

Gene amplification detected in carcinoma cells from human urinary bladder washings by the polymerase chain reaction method

BACKGROUND

Urinary bladder carcinoma often is diagnosed from malignant cells in bladder washings obtained at cystoscopic examination. In some cases, there are difficulties distinguishing between cytologic Grades 1 and 2. Detection of genetic alterations in combination with morphologic analysis may facilitate the diagnosis.

METHODS

The presence of amplified c-erb-B2 and epidermal growth factor receptor (EGF-R) was examined in tumor cells present in bladder washings. The gene copy number was determined with the polymerase chain reaction (PCR).

RESULTS

The authors detected amplified c-erb-B2 and EGF-R in cancer cells of cytologic Grade 2 and 3 tumors. They did not detect amplification in cytologic Grade 1 tumor cells or in cells from bladders, without known malignant neoplasms.

CONCLUSIONS

Examination of genetic alterations, in combination with morphologic analysis, facilitates the diagnosis of carcinoma.

Appearance of amplified thymidylate synthase or dihydrofolate reductase genes in stage-IV breast-cancer patients receiving endocrine treatment

We have examined the appearance of amplification of 2 genes involved in resistance to chemotherapy (thymidylate synthase, dihydrofolate reductase) in patients receiving endocrine treatment. Chronological tumor samples were obtained from breast-cancer patients with clinical stage-IV disease, using fine-needle biopsies. The presence of amplification of thymidylate synthase and dihydrofolate reductase was determined using PCR in 185 fine-needle biopsies from 37 patients. None of the initial samples of each patient showed amplification. However, in 7 of the 37 patients (19%) we detected development of gene amplification: in 2 cases of thymidylate synthase and in 5 cases of dihydrofolate reductase. Five of the 7 patients with amplification were receiving second-line endocrine treatment after failing to respond to tamoxifen.

Reduced occurrence of mdr-1 amplification in stage-IV breast-cancer patients treated with tamoxifen compared with other endocrine treatments

Amplification of mdr-1 occurs in breast cancer patients receiving endocrine treatment. We have compared a group of patients receiving tamoxifen and a group receiving second-line endocrine treatment after failure of tamoxifen treatment. Chronological tumor samples were obtained by fine-needle biopsies from the same tumor lesion of each patient and PCR was used to detect the appearance of gene amplification. Three of 20 patients receiving tamoxifen developed amplified mdr-1 whereas 7 of 17 patients receiving second-line endocrine treatment developed mdr-1 amplification.

Molecular cytogenetics of multiple drug resistance

The refractory nature of many human cancers to multi-agent chemotherapy is termed multidrug resistance (MDR). In the past several decades, a major focus of clinical and basic research has been to characterize the genetic and biochemical mechanisms mediating this phenomenon. To provide model systems in which to study mechanisms of multidrug resistance, in vitro studies have established MDR cultured cell lines expressing resistance to a broad spectrum of unrelated drugs. In many of these cell lines, the expression of high levels of multidrug resistance developed in parallel to the appearance of cytogenetically-detectable chromosomal anomalies resulting from gene amplification. This review describes cytogenetic and molecular-based studies that have characterized DNA amplification structures in MDR cell lines and describes the important role gene amplification played in the cloning and characterization of the mammalian multidrug resistance genes (mdr). In addition, this review discusses the genetic selection generally used to establish the MDR cell lines, and how drug selections performed in transformed cell lines generally favor the genetic process of gene amplification, which is still exploited to identify drug resistance genes that may play an important role in clinical MDR.

The use of reverse transcriptase-polymerase chain reaction (RT-PCR) to investigate specific gene expression in multidrug-resistant cells

Expression of specific genes at the level of mRNA can be studied using techniques such as Northern blot, slot/dot blot, RNase protection assay, in situ hybridisation and RT-PCR. In this article these methods of analysis are compared; RT-PCR offers higher levels of specificity and sensitivity than traditional methods of RNA analysis and as such has become the method of choice for the study of gene expression. The RT-PCR technique is described in detail with sections dealing with RNA extraction, choice of primers (including the use of cDNA sequence data bases), PCR and RT-PCR protocols in addition to the limitations of the method. The study of one particular mRNA transcript (MDR1) using RT-PCR is discussed in detail. Recently described methods for quantitation of PCR products are discussed. Quantitative PCR would appear to offer a method of studying gene expression in a more extensive way than has been possible to date.