Immunohistochemical analysis of P-glycoprotein expression correlated with chemotherapy resistance in locally advanced breast cancer

Cold Atmospheric Plasma Restores Paclitaxel Sensitivity to Paclitaxel-Resistant Breast Cancer Cells by Reversing Expression of Resistance-Related Genes

Paclitaxel (Tx) is a widely used therapeutic chemical for breast cancer treatment; however, cancer recurrence remains an obstacle for improved prognosis of cancer patients. In this study, cold atmospheric plasma (CAP) was tested for its potential to overcome the drug resistance. After developing Tx-resistant MCF-7 (MCF-7/TxR) breast cancer cells, CAP was applied to the cells, and its effect on the recovery of drug sensitivity was assessed in both cellular and molecular aspects. Sensitivity to Tx in the MCF-7/TxR cells was restored up to 73% by CAP. A comparison of genome-wide expression profiles between the TxR cells and the CAP-treated cells identified 49 genes that commonly appeared with significant changes. Notably, 20 genes, such as KIF13B, GOLM1, and TLE4, showed opposite expression profiles. The protein expression levels of selected genes, DAGLA and CEACAM1, were recovered to those of their parental cells by CAP. Taken together, CAP inhibited the growth of MCF-7/TxR cancer cells and recovered Tx sensitivity by resetting the expression of multiple drug resistance–related genes. These findings may contribute to extending the application of CAP to the treatment of TxR cancer.

P-Glycoprotein Expression in Indian Breast Cancer Patients with Reference to Molecular Subtypes and Response to Anthracycline-Based Chemotherapy-a Prospective Clinical Study from a Developing Country

Chemo-resistance is an important factor determining the response of tumor to neoadjuvant chemotherapy (NACT). Our study was aimed to determine the role of P-glycoprotein (P-glyp) expression as a predictor of response to NACT in locally advanced breast cancer (LABC) patients with special reference to molecular subtypes. Sixty cases of locally advanced breast cancer (LABC) were subjected to trucut biopsy and the tissue samples were evaluated immunohistochemically for P-glyp, ER, PR, and Her 2 neu status. Pre- and post-NACT P-glyp expression was correlated with clinical response (using WHO criteria after three cycles of CEF regimen) and molecular subtypes. The change in the P-glyp expression before (pre-) and after (post-) NACT was statistically significant with higher stage (p = 0.02), hormonal negative molecular subtypes (p = 0.01), and poor clinical response (p = 0.01). Pre-NACT-positive P-glyp expression is associated with higher stage and hormonal negative molecular subtypes and poor clinical response. The increased expression of P-glyp induced by NACT likely explains the concept of acquired chemo-resistance and may prove as an intermediate checkpoint in determining chemo-sensitivity for further treatment so that additional doses of ineffective chemotherapy may be avoided in non-responders translating into better patient safety.

PCNA/Cyclin and P-Glycoprotein as Prognostic Factors in Locally Advanced Breast Cancer. An Immunohistochemical, Retrospective Study

Aims and Background

The aim of the present study was to determine, retrospectively, whether the immunohistochemical expression of two biologic markers of aggressivity, P-glycoprotein (P-gp) and PCNA/cyclin (PCNA), could be related to response to chemotherapy and prognosis in locally advanced breast cancer.

Methods

PC 10 Mab was used to determine the proliferation index (PCNA) and C-219 Mab to determine P-gp in 25 locally advanced breast carcinomas subjected to preoperative chemotherapy with MDR-related drugs.

Results

P-gp and PCNA were expressed in 76 % and 100 % of the tumors, respectively. No case of high P-gp expression was associated with good chemosensitivity, and all P-gp-negative cases showed the best chemotherapeutic response. P-gp and PCNA were both highly expressed in patients who developed local-regional or distant metastases. No recurrence was associated with a negative or low P-gp score.

Conclusions

Statistical analysis showed that high P-gp expression was related to a poor response to chemotherapy and a short disease-free survival. A high PCNA score was not found to be significant for predicting chemosensitivity or survival.

Effectiveness of imatinib mesylate over etoposide in the treatment of sensitive and resistant chronic myeloid leukaemia cells in vitro

Chronic myeloid leukaemia (CML) is a form of leukaemia derived from the myeloid cell lineage. Imatinib mesylate, the breakpoint cluster region-abelson murine leukeamia kinase inhibitor, is a specific reagent used in the clinical treatment of CML. The DNA topoisomerase II inhibitor, etoposide, is also employed as a therapeutic, though it is used to a lesser extent. The present study aims to evaluate the effects of CML-targeted therapy, utilising imatinib mesylate and etoposide in the in vitro treatment of parental sensitive and adriamycin-resistant CML in the K562 and K562/ADM cell lines, respectively. Preliminary work involved the screening of multidrug resistant (MDR) gene expression, including MDR1, MRP1 and B-cell lymphoma 2 (BCL-2) at the mRNA levels. The sensitive and resistant CML cell lines expressed the MRP1 gene, though the sensitive K562 cells expressed low, almost undetectable levels of MDR1 and BCL-2 genes relative to the K562/ADM cells. Following treatment with imatinib mesylate or etoposide, the IC50 for imatinib mesylate did not differ between the sensitive and resistant cell lines (0.492±0.024 and 0.378±0.029, respectively), indicating that imatinib mesylate is effective in the treatment of CML regardless of cell chemosensitivity. However, the IC50 for etoposide in sensitive K562 cells was markedly lower than that of K562/ADM cells (50.6±16.5 and 194±8.46 µM, respectively), suggesting that the higher expression levels of MDR1 and/or BCL-2 mRNA in resistant cells may be partially responsible for this effect. This is supported by terminal deoxynucleotidyl transferase dUTP nick-end labeling data, whereby a higher percentage of apoptotic cells were found in the sensitive and resistant K562 cells treated with imatinib mesylate (29.3±0.2 and 31.9±16.7%, respectively), whereas etoposide caused significant apoptosis of sensitive K562 cells (18.3±8.35%) relative to K562/ADM cells (5.17±3.3%). In addition, the MDR genes in K562/ADM cells were knocked down by short interfering RNAs. The percentage knockdowns were 15.4% for MRP1, 17.8% for MDR and 30.7% for BCL-2, which resulted in a non-significant difference in the half maximal inhibitory concentration value of K562/ADM cells relative to K562 cells upon treatment with etoposide.

Drug transporters in breast cancer: response to anthracyclines and taxanes

Despite the advances that have taken place in the past decade, including the development of novel molecular targeted agents, cytotoxic chemotherapy remains the mainstay of cancer treatment. In breast cancer, anthracyclines and taxanes are the two main chemotherapeutic options used on a routine basis. Although effective, their usefulness is limited by the inevitable development of resistance, a lack of response to drug-induced cancer cell death. A large body of research has resulted in the characterization of a plethora of mechanisms involved in resistance; ATP-binding cassette transporter proteins, through their function in xenobiotic clearance, play an important role in resistance. We review here the current evidence for drug transporters as biomarkers and the benefit of adding drug transporter modulators to conventional chemotherapy.

Downregulated DYRK2 expression is associated with poor prognosis and Oxaliplatin resistance in hepatocellular carcinoma

We aimed to investigate the molecular mechanisms of DYRK2 and the HCC sensitivity to Oxaliplatin in DYRK2-depleted HCC cells. HCC tissue specimens were obtained from 86 HCC patients during hepatectomy. We used immunohistochemistry and western blot to analyze DYRK2 expression in HCC tissues and cell lines, and used siRNA transfection to decrease DYRK2 expression in HCC cells. Flow cytometry and CCK-8 assay were detected in cell cycle progression, cell proliferation and the efficacy of Oxaliplatin, DYRK2 was down-regulated in HCC tissues, compared with adjacent nontumor ones. The significant correlation between DYRK2 expression and clinicopathologic factors was apparently shown in the immunohistochemical and statistical analyses. The expression of DYRK2 was significantly associated with histological grade of HCC patients. Univariate and multivariate survival analyses revealed that DYRK2 was a significant predictor for overall survival of HCC patients. The depletion of DYRK2 promoted HCC cell proliferation, and increased resistance to Oxaliplatin. These data showed that the downregulated expression of DYRK2 in HCC tumor tissues could promote the proliferation of HCC cells. In addition, reducing DYRK2 expression was associated with poor prognosis and Oxaliplatin resistance in HCC.

A simplicial complex-based approach to unmixing tumor progression data

BACKGROUND

Tumorigenesis is an evolutionary process by which tumor cells acquire mutations through successive diversification and differentiation. There is much interest in reconstructing this process of evolution due to its relevance to identifying drivers of mutation and predicting future prognosis and drug response. Efforts are challenged by high tumor heterogeneity, though, both within and among patients. In prior work, we showed that this heterogeneity could be turned into an advantage by computationally reconstructing models of cell populations mixed to different degrees in distinct tumors. Such mixed membership model approaches, however, are still limited in their ability to dissect more than a few well-conserved cell populations across a tumor data set.

RESULTS

We present a method to improve on current mixed membership model approaches by better accounting for conserved progression pathways between subsets of cancers, which imply a structure to the data that has not previously been exploited. We extend our prior methods, which use an interpretation of the mixture problem as that of reconstructing simple geometric objects called simplices, to instead search for structured unions of simplices called simplicial complexes that one would expect to emerge from mixture processes describing branches along an evolutionary tree. We further improve on the prior work with a novel objective function to better identify mixtures corresponding to parsimonious evolutionary tree models. We demonstrate that this approach improves on our ability to accurately resolve mixtures on simulated data sets and demonstrate its practical applicability on a large RNASeq tumor data set.

CONCLUSIONS

Better exploiting the expected geometric structure for mixed membership models produced from common evolutionary trees allows us to quickly and accurately reconstruct models of cell populations sampled from those trees. In the process, we hope to develop a better understanding of tumor evolution as well as other biological problems that involve interpreting genomic data gathered from heterogeneous populations of cells.

Therapeutic melting pot of never in mitosis gene a related kinase 2 (Nek2): a perspective on Nek2 as an oncology target and recent advancements in Nek2 small molecule inhibition

The global incidence of cancer is on the rise, and within the next decade, the disease is expected to become the leading cause of death worldwide. Forthcoming strategies used to treat cancers focus on the design and implementation of multidrug therapies to target complementary cancer specific pathways. A more direct means by which this multitargeted approach can be achieved is by identifying and targeting interpathway regulatory factors. Recent advances in understanding Nek2 (NIMA related kinase 2) biology suggest that the kinase potentially represents a multifaceted therapeutic target. In this regard, pharmacologic modulation of Nek2 with a single agent may effect several mechanisms important for tumor growth, survival, progression, and metastasis. We herein review the development of Nek2 as an oncology target and provide a succinct chronology of drug discovery campaigns focused on targeting Nek2.

Taxane resistance in breast cancer: a closed HER2 circuit?

Microtubule inhibitors, such as the taxanes docetaxel and paclitaxel, are commonly used drugs for the treatment of breast cancer. Although highly active in a large fraction of individuals a considerable number of patients show poor response due to either intrinsic or acquired drug resistance. Extensive research in the past identified several taxane resistance-related mechanisms being activated by pathologically altered single gene function. To date, however, a clinically relevant predictive biomarker for taxanes has not been derived yet from this knowledge, most likely due to the manifold of resistance mechanisms that may combine in one tumor, thereby fostering escape from taxane cytotoxicity. Here, we aimed to comprehensively review the current literature on taxane resistance mechanisms in breast cancer. Interestingly, besides altered microtubule physiology we identified the HER2 signaling cascade as a major dominator influencing several routes of cytotoxicity escape, such as cell survival, apoptosis, drug efflux, and drug metabolism. Furthermore, the transcription factor YBX-1, activated by HER2, facilitates a sustaining HER2 signaling feedback loop contributing to the establishment of cellular survival detours. In conclusion, taxane resistance in breast cancer follows a multiplex establishment of drug cytotoxicity escape routes, which may be most efficiently therapeutically targeted by interference with their mutually governing signaling nodes.

A literature review of molecular markers predictive of clinical response to cytotoxic chemotherapy in patients with breast cancer

BACKGROUND

We aimed to identify, through a review of the literature, candidate genes for a prospective predictive chemosensitivity test in patients with breast cancer.

METHODS

Papers demonstrating an association between gene alterations in tumor tissue and clinical chemosensitivity in breast cancer patients were selected by Medline searches. We calculated odds ratios (ORs) and their 95% confidence intervals (CIs) of response rates for patients who had tumors with or without gene alteration. Combined ORs and CIs were estimated using the DerSimonian-Laird method.

RESULTS

A total of 18 genes were evaluated for association with clinical chemosensitivity in 6378 patients registered in 69 studies. The median (range) number of patients in each study was 73 (29-319). Overexpression of ABCB1 (P-glycoprotein) was associated with poor responses to first-line chemotherapy (combined OR [CI], 0.16 [0.05-0.59]; n = 322). Overexpression and amplification of TOP2A (topoisomerase II-alfa) were more frequently observed in patients who responded to first-line chemotherapy (combined OR [CI], 2.73 [1.02-7.27]; n = 323). Overexpression of ERBB2 (c-erbB2) was associated with favorable responses in patients treated with both first-line anthracycline-based chemotherapy and second-line taxane-based chemotherapy (combined ORs [CIs], 1.60 [1.19-2.17]; n = 1807 and 2.24 [1.06-4.74]; n = 259, respectively). BCL2 overexpression was associated with resistance to first-line chemotherapy (combined OR [CI], 0.44 [0.21-0.91]; n = 816).

CONCLUSION

ABCB1, TOP2A, ERBB2, and BCL2 were good candidates for future clinical trials of predictive chemosensitivity tests in patients with breast cancer.

Single nucleotide polymorphisms in the multidrug resistance gene 1 (ABCB1): effects on its expression and clinicopathological characteristics in breast cancer patients

OBJECTIVES

Resistance of tumor cells to multiple cytostatic agents is one of the major impediments of successful cancer chemotherapy. A large part of resistance of tumors to chemotherapy is caused by the ABC transporter P-glycoprotein encoded by the ABCB1 gene. The main aim of this study was to assess the prognostic value of ABCB1 genotype and phenotype in breast cancer.

METHODS

Six ABCB1 single nucleotide polymorphisms (SNPs) were determined in 90 Czech breast cancer patients by a novel method that allows simultaneous assessment of multiple polymorphisms on a single electronic microarray. Expression levels of ABCB1 were quantified in tumor and nontumor samples of breast cancer patients by real-time PCR. T-test, analysis of variance and Fisher's exact test were used to analyze the effect of ABCB1 polymorphisms on ABCB1 expression levels and for the analysis of associations between ABCB1 expression, genotype and clinical and pathological characteristics.

RESULTS

ABCB1 was expressed in 98.9% of the tumor and in 97.5% of the nontumor samples. ABCB1 was downregulated in 79.5% of tumors compared with the nontumor samples. No significant correlation was observed between ABCB1 mRNA expression levels and clinical and pathological characteristics. High frequencies of the variant alleles in ABCB1 exon 12 (1236C>T, 38.3%) and exon 26 (3435C>T, 54.0%) were observed. Individuals with variant alleles in exons 12 and 26 had significantly lower ABCB1 expression levels in their tumors. SNPs in exons 12 and 26 also correlated with estrogen receptor status of patients.

CONCLUSION

ABCB1 SNPs may affect function of P-glycoprotein by influencing the expression level and modify breast cancer prognosis.

Multidrug resistance in locally advanced breast cancer

BACKGROUND

Advanced breast cancer cases can still be encountered resulting in poor prognosis. The primary treatment for these patients is chemotherapy, and multidrug resistance (MDR) is a serious obstacle in the treatment. Detecting drug resistance before first-line chemotherapy may increase the patient's survival. In this study, the role of MDR is evaluated in locally advanced breast cancer patients.

METHODS

Reverse transcriptase polymerase chain reaction was used for the detection of MDR genes, ABCB1 and ABCC1. Immunohistochemistry was used for the detection of MDR proteins, P-glycoprotein (Pgp) and MDR-associated protein 1.

RESULTS

Breast tissues from 25 patients both before and after chemotherapy were examined. Five patients were unresponsive to chemotherapy. Four had ABCB1 gene expression induced by chemotherapy, and Pgp positivity was detected in 9 patients after chemotherapy. Both the induction of ABCB1 gene expression (p < 0.001) and Pgp positivity (p < 0.001) during chemotherapy were significantly related with clinical response. Although 80% of the clinically unresponsive patients had ABCC1 gene expression, the relation between ABCC1 expression and clinical drug response was not significant.

CONCLUSION

In locally advanced breast cancer, ABCB1 gene expression during chemotherapy contributes to clinical unresponsiveness. However, ABCC1 gene expression did not correlate strongly with the clinical response.

Role of p-glycoprotein expression in predicting response to neoadjuvant chemotherapy in breast cancer--a prospective clinical study

Background

Neoadjuvant chemotherapy (NACT) is an integral part of multi-modality approach in the management of locally advanced breast cancer. It is vital to predict response to chemotherapy in order to tailor the regime for a particular patient. The prediction would help in avoiding the toxicity induced by an ineffective chemotherapeutic regime in a non-responder and would also help in the planning of an alternate regime. Development of resistance to chemotherapeutic agents is a major problem and one of the mechanisms considered responsible is the expression of 170-k Da membrane glycoprotein (usually referred to as p-170 or p-glycoprotein), which is encoded by multidrug resistance (MDR1) gene. This glycoprotein acts as an energy dependent pump, which actively extrudes certain families of chemotherapeutic agents from the cells. The expression of p-glycoprotein at initial presentation has been found to be associated with refractoriness to chemotherapy and a poor outcome. Against this background a prospective study was conducted using C219 mouse monoclonal antibody specific for p-glycoprotein to ascertain whether pretreatment detection of p-glycoprotein expression could be utilized as a reliable predictor of response to neoadjuvant chemotherapy in patients with breast cancer.

Patients and methods

Fifty cases of locally advanced breast cancer were subjected to trucut^® biopsy and the tissue samples were evaluated immunohistochemically for p-glycoprotein expression and ER, PR status. The response to neoadjuvant chemotherapy was assessed clinically and by using ultrasound after three cycles of FAC regime (cyclophosphamide 600 mg/m², Adriamycin 50 mg/m², 5-fluorourail 600 mg/m² at an interval of three weeks). The clinical response was correlated with both the pre and post chemotherapy p-glycoprotein expression. Descriptive studies were performed with SPSS version 10. The significance of correlation between tumor response and p-glycoprotein expression was determined with chi square test.

Results

A significant relationship was found between the pretreatment p-glycoprotein expression and clinical response. The positive p-glycoprotein expression was associated with poor clinical response rates. When the clinical response was correlated with p-glycoprotein expression, a statistically significant negative correlation was observed between the clinical response and p- glycoprotein expression (p < 0.05). There was another significant observation in terms of development of post NACT p-glycoprotein positivity. Before initiation of NACT, 26 patients (52%) were p-glycoprotein positive and after three cycles of NACT, the positivity increased to 73.5% patients.

Conclusion

The study concluded that pretreatment p-glycoprotein expression predicts and indicates a poor clinical response to NACT. Patients with positive p-glycoprotein expression before initiation of NACT were found to be poor responders. Thus pretreatment detection of p-glycoprotein expression may be utilized, as a reliable predictor of response to NACT in patients with breast cancer The chemotherapy induced p-glycoprotein positivity observed in the study could possibly explain the phenomenon of acquired chemoresistance and may also serve as an intermediate end point in evaluating drug response particularly if the adjuvant therapy is planned with the same regime.

Inhibition of P-glycoprotein function by XR9576 in a solid tumour model can restore anticancer drug efficacy

Resistance to cancer chemotherapy involves both altered drug activity at the designated target and modified intra-tumour pharmacokinetic properties (e.g. uptake, metabolism). The membrane transporter P-glycoprotein (P-gp) plays a major role in pharmacokinetic resistance by preventing sufficient intracellular accumulation of several anticancer agents. Whilst inhibiting P-gp has great potential to restore chemotherapeutic effectiveness in blood-borne cancers, the situation in solid tumours is less clear. Therefore, the degree of resistance tumours pose to the cytotoxicity of vinblastine and doxorubicin was characterised using the multicellular tumour spheroid model. Tumour spheroids were generated from either drug-sensitive MCF7(WT) breast cancer cells or a resistant P-gp-expressing variant (NCI/ADR(Res)). Drug-induced cytotoxicity in tumour spheroids was measured using an outgrowth assay and compared with that observed in monolayer cultures. As anticipated, the 3-D organisation of MCF7(WT) in tumour spheroids was associated with a reduction in the potency of doxorubicin and vinblastine-i.e. the inherent multicellular resistance phenomenon. In contrast, tumour spheroids from NCI/ADR(Res) cells did not display multicellular resistance. However their constitutive expression of P-gp reduced the potency of both anticancer drugs. Moreover, the highly potent P-gp inhibitor, the anthranilic acid derivative, XR9576, was able to restore the cytotoxic efficacy of both drugs in tumour spheroids comprising NCI/ADR(Res) cells. The results suggest that inhibition of P-gp in solid tumours is achievable and that generation of potent inhibitors will provide a significant benefit towards restoration of chemotherapy in solid tissues.

The expression of P-glycoprotein does influence the distribution of novel fluorescent compounds in solid tumour models

Solid tumours display a complex drug resistance phenotype that involves inherent and acquired mechanisms. Multicellular resistance is an inherent feature of solid tumours and is known to present significant barriers to drug permeation in tumours. Given this barrier, do acquired resistance mechanisms such as P-glycoprotein (P-gp) contribute significantly to resistance? To address this question, the multicellular tumour spheroid (MCTS) model was used to examine the influence of P-gp on drug distribution in solid tissue. Tumour spheroids (TS) were generated from either drug-sensitive MCF7(WT) cells or a drug-resistant, P-gp-expressing derivative MCF7(Adr). Confocal microscopy was used to measure time courses and distribution patterns of three fluorescent compounds; calcein-AM, rhodamine123 and BODIPY-taxol. These compounds were chosen because they are all substrates for P-gp-mediated transport, exhibit high fluorescence and are chemically dissimilar. For example, BODIPY-taxol and rhodamine 123 showed high accumulation and distributed extensively throughout the TS(WT), whereas calcein-AM accumulation was restricted to the outermost layers. The presence of P-gp in TS(Adr) resulted in negligible accumulation, regardless of the compound. Moreover, the inhibition of P-gp by nicardipine restored intracellular accumulation and distribution patterns to levels observed in TS(WT). The results demonstrate the effectiveness of P-gp in modulating drug distribution in solid tumour models. However, the penetration of agents throughout the tissue is strongly determined by the physico-chemical properties of the individual compounds.

Expression of MRP1, LRP and Pgp in breast carcinoma patients treated with preoperative chemotherapy

Our purpose was to determine the expression of the drug resistance factors multidrug resistance protein (MRP1), lung resistance protein (LRP) and P-glycoprotein (Pgp) in breast carcinoma patients treated with preoperative chemotherapy. We have studied the expression of these proteins in breast carcinomas by immunohistochemistry both prior (n = 80) and after (n = 68) preoperative chemotherapy and compared their expression with response to preoperative chemotherapy. In paired samples prior and after chemotherapy expression of drug resistance factors was significantly lower in prechemotherapy samples as compared with postchemotherapy specimens. This was observed for MRP1 (62% vs. 88%, P < 0.001), LRP (65% vs. 97%, P < 0.001) and Pgp (55% vs. 100%, P < 0.001). Prechemotherapy expression of MRP1 was more frequently observed in patients with distant metastases than in those without (50% vs. 8%, P = 0.02). No associations were observed between LRP expression and clinical parameters. Pgp expression was more frequently detected in lobular carcinomas than in ductal carcinomas (93% vs. 46%, P = 0.001) and in patients with positive lymph nodes than in patients with negative lymph nodes (65% vs. 31%, P = 0.008) but was independent of other clinical parameters. No significant associations were found between the prechemotherapy or postchemotherapy expression of either of these three proteins and response to preoperative chemotherapy. However, prechemotherapy MRP1 expression was significantly associated with shorter progression-free survival of the patients (P = 0.02), whereas no such associations were observed for either LRP or Pgp. In conclusion, preoperative chemotherapy increases the expression of MRP1, LRP and Pgp. Response to chemotherapy is not associated with pre- or postchemotherapy expression levels of these drug resistance proteins but time to progression may be influenced by prechemotherapy MRP1 expression.

P-glycoprotein, metallothionein and NM23 protein expressions in breast carcinoma

Cellular drug resistance and increased metastatic potential are the major obstacles in the successful treatment of cancer with chemotherapy. The aim of this study was to investigate whether the immunohistochemical expression of two proteins implicated in drug resistance (P-glycoprotein and metallothionein) and the product of the suppressor gene nm23 could be related to prognosis in breast cancer. Seventy-two patients with palpable or occult breast carcinoma, not treated with chemotherapy or endocrine therapy, were examined. Immunohistochemical methods were used to determine the expression of P-glycoprotein (PG), metallothionein (MT), nm23, as well as the estrogen receptor (ER), the p53 status, and the Ki67 index. The results were correlated with clinical and morphological features. Cytoplasmic and membrane-specific immunostainings of PG were seen exclusively in tumor cells and identified in 14 of 72 cases (19.4%). Only a statistically significant association with metastases, (p = 0.06) and recurrences (p = 0.1) was observed. MT-positive reaction was identified in the cytoplasm of the tumor cells in 47 (65.3%) cases. Statistical significance was associated with metastases (p = 0.07), but not with death or recurrences. Specific immunostaining of nm23 protein was seen only in the cytoplasm of tumor cells. A positive reaction was observed in 55 of 72 (89.3%) cases. Although a significant association between nm23 protein expression and other morphologic and immunohistochemical variables did not exist, we observed a higher morbidity in patients with the MT-positive/nm23-negative tumor phenotype. Univariate analysis for survival selected the following variables: histologic grade (p = 0.001), ER (p = 0.002), mitotic index (p = 0.005), Ki 67 index (p = 0.068), MT (p = 0.046) and PG (p = 0.085). The Cox model provided the following independent variables: histologic grade (p = 0.021) and metallothionein (p = 0.03). These data confirm the prognosis observed in patients with PG or metallothionein expression as well as the independence of these two variables. It also suggests that nm23 is not necessarily involved in the development of an invasive phenotype.

Phase I dose-finding and pharmacokinetic study of paclitaxel and carboplatin with oral valspodar in patients with advanced solid tumors

PURPOSE

To evaluate the maximum-tolerated dose (MTD), dose-limiting toxicities (DLTs), and pharmacokinetic (PK) profile of paclitaxel and carboplatin when administered every 3 weeks with the oral semisynthetic cyclosporine analog valspodar (PSC 833), an inhibitor of P-glycoprotein function.

PATIENTS AND METHODS

Fifty-eight patients were treated with escalating doses of paclitaxel ranging from 54 to 94.5 mg/m(2) and carboplatin area under the plasma concentration versus time curve (AUC) ranging from 6 to 9 mg.min/mL, every 21 days. The dose of valspodar was fixed at 5 mg/kg every 6 hours for a total of 12 doses from day 0 to day 3. The MTD was determined for the following two groups: (1) previously treated patients, where paclitaxel and carboplatin doses were escalated; and (2) chemotherapy-naïve patients, where paclitaxel dose was escalated and carboplatin AUC was fixed at 6 mg.min/mL. PK studies of paclitaxel and carboplatin were performed on day 1 of course 1.

RESULTS

Fifty-eight patients were treated with 186 courses of paclitaxel, carboplatin, and valspodar. Neutropenia, thrombocytopenia, and hepatic transaminase elevations were DLTs. In previously treated patients, no DLTs occurred at the first dose level (paclitaxel 54 mg/m(2) and carboplatin AUC 6 mg.min/mL). However, one of 12, two of six, two of four, four of 11, and two of five patients experienced DLTs at doses of paclitaxel (mg/m(2))/carboplatin AUC (mg.min/mL) of 67.5/6, 81/6, 94.5/6, 67. 5/7.5, and 67.5/9, respectively. In chemotherapy-naïve patients, one of 17 developed DLT at paclitaxel 81 mg/m(2) and carboplatin AUC 6 mg/mL.min. There was prolongation of the terminal phase of paclitaxel elimination as evidenced by an increased time that plasma paclitaxel concentration was >/= 0.05 micromol/L, ranging from 16.6 +/- 6.7 hours to 41.5 +/- 9.8 hours for paclitaxel doses of 54.5 mg/m(2) to 94.5 mg/m(2), respectively.

CONCLUSION

The recommended phase II dose in chemotherapy-naïve patients is paclitaxel 81 mg/m(2), carboplatin AUC 6 mg.min/mL, and valspodar 5 mg/kg every 6 hours. In previously treated patients, the recommended phase II dose is paclitaxel 67.5 mg/m(2), carboplatin AUC 6 mg.min/mL, and valspodar 5 mg/kg every 6 hours. The acceptable toxicity profile supports the rationale for performing disease-directed evaluations of paclitaxel, carboplatin and valspodar on the schedule evaluated in this study.

c-erbB-2 (HER-2/neu) protein and drug resistance in breast cancer patients treated with induction chemotherapy

Expression of c-erbB-2 protein has been associated with poor prognosis and poor response to chemotherapy in breast cancer patients. In the present prospective study, we have analyzed whether c-erbB-2, p53 and P170 proteins may be determinants of tumor resistance in locally advanced breast cancer patients treated with induction chemotherapy. Biopsies (n = 60) were examined by immuno-histochemistry; in 62% of cases core or incisional biopsies were taken before drug administration, allowing comparison in paired biopsies of the cytological and molecular changes induced by treatment Sixty percent of the patients received relatively high doses of FAC or FEC (5-fluorouracil, doxorubicin or epirubicin and cyclophosphamide), and 40% received relatively high doses of doxorubicin or epirubicin alone. No significant changes were observed in the molecular markers studied following chemotherapy; in the few biopsies where changes appeared, the changes did not exhibit any significant or similar trend. For 30 of the patients who received FAC/FEC treatment, follow-up reached a median of 34 months. In these cases, neither the clinical (reduction in tumor size) nor the histological (evaluated after neoadjuvant chemotherapy) responses showed statistically significant differences between the patients who developed distant metastases and the disease-free patients. c-erbB-2 was over-expressed in 50% of patients who developed distant metastases vs. 7% of the disease-free patients. Disease free survival (DFS) curves between c-erbB-2-positive and c-erbB-2-negative patients were statistically significant. No correlation between p53 or P170 expression with DFS was found. Our results suggest that c-erbB-2 protein expression is associated with development of distant metastases in breast cancer patients treated with relatively high doses of anthracyclines in induction chemotherapy.

Phorbol ester-induced P-glycoprotein phosphorylation and functionality in the HTB-123 human breast cancer cell line

The discordance between P-glycoprotein (P-gp) expression and functionality [as measured by the efflux of doxorubicin (DOX)] was analyzed in a DOX-sensitive human breast cancer cell line (HTB-123) with high reactivity against four P-gp specific monoclonal antibodies (C219, MRK-16, UIC2, and 4E3). Reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting analyses confirmed the overexpression of MDR1 mRNA and P-gp in this cell line. However, incubation of cells with efflux blockers, verapamil (VPL) or dipyridamole (DPD), did not enhance cellular (DOX) accumulation or cytotoxicity. Upon incubation with 12-O-tetradecanoylphorbol-13-acetate (TPA), HTB-123 cells retained less DOX than control cells and were sensitive to the efflux blockers verapamil or dipyridamole. These observations suggest that 12-O-tetradecanoylphorbol-13-acetate-induced P-gp phosphorylation may be associated with induction of P-gp-mediated drug efflux in the HTB-123 cell line.

A multivariate analysis of tumour biological factors predicting response to cytotoxic treatment in advanced breast cancer

The study was designed to identify factors that could predict response to chemotherapy in breast cancer. A total of 173 patients with measurable or evaluable metastatic breast cancer were enrolled in a randomized trial between November 1987 and January 1991 to receive a monthly dose of 5-fluorouracil (500 mg m(-2)), epirubicin (60 mg m(-2)) and cyclophosphamide (500 mg m(-2)) either administered in four weekly doses or in an every-4-week dose as first-line cytotoxic treatment. In 103 evaluable patients we performed a multivariate analysis of the tumour biological factors, i.e. histological grade, oestrogen receptor (ER), progesterone receptor (PR), S-phase fraction (SPF), ploidy, p53, c-erbB-2, Bcl-2 and Bax expression, which showed significance in the univariate analysis according to treatment response, time to progression (TTP) or overall survival (OS). In the univariate analysis only SPF, grade and the proapoptotic protein Bax correlated with the response to cytotoxic treatment. In the multivariate analysis SPF had the strongest correlation, followed by grade and Bax. In the univariate analysis grade, PR, Bax and Bcl-2 correlated significantly with TTP, whereas in the multivariate analysis only PR showed a statistically significant correlation. In the univariate analysis PR and Bax correlated with OS and both retained its significance in the multivariate analysis. The factors that correlated significantly with the response to cytotoxic treatment in the univariate analysis, i.e. grade, SPF and Bax, seemed to predict independently the response to treatment in the multivariate analysis also. TTP and OS could be predicted partly by the same factors, although the association was quite weak. More studies and new tumour biological factors are needed to identify the group of breast cancer patients who get the most benefit from chemotherapy.

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.

In vivo model systems in P-glycoprotein-mediated multidrug resistance

In this article we review the in vivo model systems that have been developed for studying P-glycoprotein-mediated multidrug resistance (MDR) in the preclinical setting. Rodents have two mdr genes, both of which confer the MDR phenotype: mdr 1a and mdr 1b. At gene level they show strong homology to the human MDR1 gene and the tissue distribution of their gene product is very similar to P-glycoprotein expression in humans. In vivo studies have shown the physiological roles of P-glycoprotein, including protection of the organism from damage by xenobiotics. Tumors with intrinsic P-glycoprotein expression, induced MDR or transfected with an mdr gene, can be used as syngeneic or xenogenic tumor models. Ascites, leukemia, and solid MDR tumor models have been developed. Molecular engineering has resulted in transgenic mice that express the human MDR1 gene in their bone marrow and in knockout mice missing a murine mdr gene. The data on pharmacokinetics, efficacy, and toxicity of chemosensitizers of P-glycoprotein in vivo are described. Results from studies using monoclonal antibodies directed against P-glycoprotein and other miscellaneous approaches for modulation of MDR are mentioned. The importance of in vivo studies prior to clinical trials is being stressed and potential pitfalls due to differences between species are discussed.

No evidence of significant activity of the multidrug resistance gene product in primary human breast cancer

BACKGROUND

The discovery of the multidrug resistance (MDR1) gene product P-glycoprotein (P-gp) has been widely seen as an important milestone in our understanding of the mechanisms underlying the clinical phenomenon of the emergence of resistant cells. MDR1 expression has been shown for numerous solid tumors and for virtually all hematologic malignancies. Nevertheless, results regarding MDR1/P-gp expression in human breast cancer have been controversial and the results of clinical trials on modulation of P-gp activity have not been encouraging.

PATIENTS AND METHODS

MDR1/P-gp expression and the function of the P-gp pump were investigated in 61 tumor samples from patients with primary breast cancers by multiparameter analysis using MDR1-RT-PCR, immunohistochemistry with two MAbs (UIC2 and MRK16) and the rhodamine 123 (Rh123) efflux assay. The cellular composition of the tumor cell suspension was analyzed by using specific MAbs against the P-gp expressing lymphocyte subsets CD4, CD8 and CD56, as well as against the HER-2/neu gene product, which was used to identify breast carcinoma cells.

RESULTS

UIC2 and MRK16 revealed a staining positivity in 72% and 75% of samples, respectively. A positive MDR1-RT-PCR signal was detected in 62% of the samples. Nevertheless, no correlation between immunohistochemistry and RT-PCR could be established. Furthermore, there was no correlation between HER-2/neu expression and MDR1-RT-PCR or P-gp immunohistochemical assays. A contamination by CD8+ and CD4+ lymphocytes was established in 100% and 84% of tumor cell suspensions, respectively. As assessed by the Rh123 efflux assay CD8+ and the CD4+ lymphocytes exhibited marked P-glycoprotein activity, whereas such activity was not detectable in a single instance for the breast carcinoma cells. In MDR1-RT-PCR positive samples, contamination by CD8 lymphocytes averaged 4.3%, while the contamination of CDS cells in the MDR1 mRNA-negative samples was only 2.4% (P = 0.007). This signal vanished after elimination of the lymphocyte subpopulations by T-cell rosetting.

CONCLUSIONS

In primary breast cancer detection of MDR1 gene expression by means of RT-PCR or immunohistochemical assays is not indicative for the MDR phenotype, since there is no evidence of significant activity of the P-gp pump.

Multiple gene expression analysis reveals distinct differences between G2 and G3 stage breast cancers, and correlations of PKC eta with MDR1, MRP and LRP gene expression

A possible link between protein kinase C (PKC) and P-glycoprotein (P-gp)-mediated-multidrug resistance (MDR) was assumed from studies on MDR cell lines selected in vitro. The functional relevance of PKC for the MDR phenotype remains unclear, and the involvement of a particular PKC isozyme in clinically occurring drug resistance is not known. Recently, we have demonstrated significant correlations between the expression levels of the PKC eta isozyme and the MDR1 or MRP (multidrug resistance-associated protein) genes in blasts from patients with acute myelogenous leukaemia (AML) and in ascites cell aspirates from ovarian cancer patients. To extend these findings to further types of human tumours we analysed specimens from 64 patients with primary breast cancer for their individual expression levels of several MDR-associated genes (MDR1, MRP, LRP (lung cancer resistance-related protein), topoisomerase (Topo) II alpha/IIbeta, cyclin A and the PKC isozyme genes (alpha, beta1, beta2, eta, theta, and mu) by a cDNA-PCR approach. We found significantly enhanced mean values for MRP, LRP and PKC eta gene expression, but significantly decreased Topo II alpha and cyclin A gene expression levels in G2 tumours compared with G3. Remarkably, significant positive correlations between the MDR1, MRP or LRP gene expression levels and PKC eta were determined: MDR1/PKC eta (rs = +0.6451, P < 0.0001) n = 62; MRP/PKC eta (rs = +0.5454, P < 0.0001) n = 63; LRP/PKC eta (rs = +0.5436, P < 0.0001) n = 62; MRP/LRP (rs = +0.7703, P < 0.0001) and n = 62, MDR1/MRP (rs = +0.5042, P < 0.0001) n = 62. Our findings point to the occurrence of a multifactorial MDR in the clinics and to PKC eta as a possible key regulatory factor for up-regulation of a series of MDR-associated genes in different types of tumours.

Immunohistochemical Detection of P-glycoprotein in Breast Cancer and Its Significance as a Prognostic Factor

Overexpression of P-glycoprotein (Pgp) in tumors is one of the major mechanisms which mediates the multidrug resistance (MDR) phenotype. To evaluate the prognostic significance of Pgp in breast cancer, Pgp expression was examined in paraffin-embedded tissue sections of 94 breast cancer specimens by immunohistochemistry. Tissue specimens were obtained by mastectomy without preoperative chemotherapy. UIC2 monoclonal antibody which recognizes an extracellular epitope of human Pgp was employed. Of the 94 breast cancer specimens, 35(37.2%)were positive for Pgp expression. Pgp expression had no correlation with menopausal or hormone receptor status, axillary Iymph node involvement or tumor size. However, a significant correlation was observed between Pgp expression and disease relapse (p=0.0322). Pgp-positive patients showed a significantly shorter disease-free survival period than Pgp-negative patients by the Kaplan-Meier method (p=0.0433). These results suggest that immunohistochemical detection of Pgp in breast cancer tissue may have prognostic value after radical operation.

Cross-reactivity of C219 anti-p170(mdr-1) antibody with p185(c-erbB2) in breast cancer cells: cautions on evaluating p170(mdr-1)

BACKGROUND

Increased expression of the multidrug resistance gene (MDR-1)-encoded P-glycoprotein (p170[mdr-1]) is a major cause of tumor cell multidrug resistance. p170(mdr-1) functions as a drug-efflux pump to reduce the cellular accumulation of specific drugs. MDA-MB-435 human breast cancer cells that have been transfected with oncogene c-erbB2 complementary DNA (435.eb cells) express high levels of the transmembrane glycoprotein p185(c-erbB2) and exhibit increased resistance to the chemotherapeutic agent paclitaxel via p170(mdr-1)-independent mechanisms. We have recently discovered that the widely used monoclonal antibody C219, which is specific for p170(mdr-1), may cross-react with p185(c-erbB2) in 435.eb cells. In this study, we have investigated the nature of this cross-reactivity.

METHODS

Immunoprecipitation experiments involving the use of breast cancer cells that express different levels of p185(c-erbB2) were performed, and C219 was used for western blot analysis of immunoprecipitated proteins. Immunohistochemical analyses were performed on acetone-fixed slides of human breast cancer cells. Peptide sequence comparisons and enzyme-linked immunosorbent assays were performed to determine the molecular basis of C219 cross-reactivity with p185(c-erbB2).

RESULTS

The cross-reactivity of C219 with p185(c-erbB2) was demonstrated by both western blot and immunohistochemical analyses. Peptide sequence comparisons revealed that C219 recognizes an epitope in p170(mdr-1) (C219 epitope) that shares sequence homology with p185(c-erbB2). Enzyme-linked immunosorbent assays demonstrated that C219 recognizes synthetic peptides derived from both the C219 epitope in p170(mdr-1) and the C219 epitope-homologous region in p185(c-erbB2).

CONCLUSIONS

The anti-p170(mdr-1) monoclonal antibody C219 cross-reacts with p185(c-erbB2) through a peptide sequence in p185(c-erbB2) that is homologous to the C219 epitope in p170(mdr-1).

Immunocytochemical detection of P-glycoprotein in the management of malignant effusions

P-glycoprotein (P-gp), a cell membrane protein, has been found in multidrug-resistant cancer cells. A total of 104 smears from patients with breast-cancer-associated pleural effusions and ovarian-cancer-related peritoneal effusions were studied for P-gp with the antibody C-219 and the avidin-biotin-immunoperoxidase method. Samples were taken before and 3 and 7 days after intracavitary bleomycin therapy and reaccumulation of effusion was assessed at 30 days. Smears that were P-gp-negative by the 7th day were associated with a good 30-day response to bleomycin in the majority of cases, while P-gp-positive smears were associated with a significant reaccumulation of fluid at 30 days. P-gp status is a valuable prognostic indicator of response to intracavitary bleomycin treatment in effusions from breast or ovarian cancer.

mdr1 mRNA expression by RT-PCR in patients with primary breast cancer submitted to neoadjuvant therapy

mdr1 expression by reverse transcription and polymerase chain reaction (RT-PCR) has been compared to P-glycoprotein (Pgp) expression by immunohistochemistry (IHC) and correlated with clinical response to neoadjuvant therapy. RNA has been recovered from glass slide smears of fine-needle aspiration from 57 untreated primary breast cancers prior to neoadjuvant chemotherapy (33 cases), hormone therapy (23 cases), or both (1 case). Furthermore, mdr1 mRNA has been analyzed in 6 cases after 2 months of treatment. The neoadjuvant therapy consisted of 4 cycles of adriamycin and cyclophosphamide or tamoxifen. Of 57 tumor specimens, an interpretable result was obtained in 52 cases, indicating the feasibility of the analysis by RT-PCR with very small tumor specimens. The presence of mdr1 mRNA has been documented in 44/52 (84%) tumor samples with a spectrum of expression levels. The expression of mdr1 mRNA was compared with P-glycoprotein (Pgp) expression by IHC using JSB-1, 4E3, and C494 monoclonal antibodies in 48 of the 52 interpretable tumor samples. 12/48 (25%) expressed Pgp by IHC. All tumors expressing Pgp by IHC were also positive by RT-PCR. The results confirm the higher prevalence of mdr1 mRNA compared to the protein expression. However, mdr1 mRNA expression was found to correlate significantly with resistance to neoadjuvant hormone therapy only while Pgp expression detected by JSB-1 immunostaining only correlated with chemoresistance. The lack of convincing correlation with chemoresistance suggests that mRNA and Pgp may not be directly or solely responsible for clinical response to drugs. Further studies should focus on the post-translational modulation of P-glycoprotein and other mechanisms of drug resistance.

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.

A new mdr-1 encoded P-170 specific monoclonal antibody: (6/1C) on paraffin wax embedded tissue without pretreatment of sections

AIMS

The generation and characterisation of a monoclonal antibody that specifically recognises the mdr-1 encoded protein, P-glycoprotein (P-170), on routinely processed formalin fixed, paraffin wax embedded tissue sections.

METHODS

The monoclonal antibody, designated 6/1C, was produced following a combination of in vivo and in vitro immunisation regimens in Balb/c mice with a synthetic 12 amino acid peptide that corresponds to amino acids 21-32 (believed to be intracellularly located) of P-170 and has insignificant homology with the mdr-3 encoded P-170. Antibody 6/1C was characterised by western blotting and immunocytochemistry on cytospins of paired multidrug resistant or sensitive cell lines, including mdr-1 and mdr-3 transfected cells, and by immunohistochemistry on normal and malignant formalin fixed paraffin wax embedded tissue sections.

RESULTS

Antibody 6/1C showed a single band at 170 kDa on western blots of multidrug resistant cell lysates and mdr-1 transfected cell lysates that was absent on similar preparations of drug sensitive cells and mdr-3 transfected cells. Immunocytochemical studies on cytospins of multidrug resistant cells and mdr-1 transfected cells revealed strong inner plasma membrane/cytoplasmic staining. Staining was negligible on drug sensitive cells and cells transfected with the mdr-3 gene. Immunohistochemical studies on formalin fixed, paraffin wax embedded normal adult kidney, liver, and breast tissue and a range of fetal tissues exhibited staining patterns of a variety of secretory surfaces consistent with documented mdr-1 specific staining. Specific staining of malignant cells in similarly treated sections of breast tumours was seen also with antibody 6/1C. Staining on paraffin wax embedded tissue with this antibody did not require any pretreatment of tissue sections.

CONCLUSIONS

This new monoclonal antibody, chosen for its specificity with the mdr-1 encoded P-170 and its reactivity on routinely fixed paraffin wax embedded tissue samples without pretreatment, appears to be useful for the investigation of P-170 in archival material. It is especially useful for retrospective studies on pretreatment and post-treatment tissue sections, and could help establish when and how rapidly mdr-1 associated drug resistance develops during chemotherapeutic regimens. Immunohistochemical assessment of P-170 expression in many cancers has potential for diagnostic purposes and may influence the choice of chemotherapeutic drugs used in the treatment of refractory tumours.

P-glycoprotein mediated multidrug resistance and its implications for pathology

The discovery of P-glycoprotein has revealed a fundamental mechanism by which cancer cells evade chemotherapy and this principle has proven relevant to general cellular defence mechanisms in normal physiology. To date this knowledge has promised to improve current cancer chemotherapy through the manipulation of drug combinations according to the P-glycoprotein status of the tumor. Furthermore, the discovery of inhibitors of the protein may provide new therapeutic tools in the treatment of multidrug resistant neoplasia, provided the benefits are deemed greater than the potential detrimental side effects. When looking towards future therapies, however, we must also consider additional mechanisms which undoubtedly contribute to clinical drug resistance. Complete elucidation of this complex cellular defence network will hopefully translate into therapeutic opportunities to circumvent all mechanisms of multidrug resistance, thus positively impacting on patient survival.

P-glycoprotein: the intermediate end point of drug response to induction chemotherapy in locally advanced breast cancer

Expression and clinical relevance of p-glycoprotein (p-gp) were evaluated in 31 cases of locally advanced breast cancer and 9 cases involving inflammatory breast cancer after induction chemotherapy. The de novo p-gp expression rate was 26% and increased up to 58% (p = 0.03) with the FAC (5-fluorouracil, adriamycin, cyclophosphamide) regimen. Although more clinically complete responders were found in the secondary p-gp negative group (p = 0.02), this difference was not found in pathological tumor response. Moreover, as the grade of the secondary p-gp expression increased, the chemotherapeutic effect decreased, suggesting an inverse relationship between p-gp expression and drug effect (p = 0.04). When we subgrouped the patients into 4 groups using these two parameters, p-gp negative patients presenting with a high drug effect showed a low recurrence rate (p = 0.05) and marginal survival benefits (p = 0.09) as opposed to patients with a low drug effect. But in p-gp positive groups, the recurrence rate was the same between the two groups regardless of the drug effect. Thus, in the p-gp negative patient with a high drug effect, adjuvant chemotherapy with the same regimen as induction chemotherapy may induce more prognostically favorable results. Therefore, clinical application of the secondary p-gp detection can be used as an intermediate endpoint in evaluating drug response for an induction regimen.

Combination chemotherapy with cyclophosphamide, vincristine, adriamycin, and dexamethasone (CVAD) plus oral quinine and verapamil in patients with advanced breast cancer

We evaluated the question of whether the chemosensitizers verapamil and quinine given orally to breast cancer patients failing combination chemotherapy alone would result in additional clinical responses. In vitro studies reported here showed verapamil sensitization of Adriamycin resistance in 18.8% of fresh human breast cancer specimens tested. Patients (27) were first treated with cyclophosphamide, vincristine, Adriamycin and dexamethasone (CVAD) alone. Verapamil and quinine were added in patients with tumors failing to respond or progressing on CVAD alone. Following treatment with CVAD alone there were no complete remissions and 3 patients (11%) developed partial remissions lasting 5.5, 8, 10.5 months. With the addition of verapamil and quinine to the CVAD regimen, one patient (4%) developed a complete remission of 11.8 months duration and 4 additional patients (15%) developed partial remissions lasting 2.8, 17.3, 19 and > 40 months. Thus, the overall rate of CVAD sensitization by verapamil and quinine was 19%. Treatment with CVAD plus verapamil and quinine was generally well tolerated with observed toxicities including: myelosuppression, neuropathy, Cushingoid symptoms and tinnitus and/or dizziness due to quinine. We conclude that addition of the non-cytotoxic chemosensitizers verapamil and quinine to CVAD in patients failing CVAD alone results in additional clinical responses in a small percentage of patients, some with long term durations. The results of this study lend credence to the notion that non-cytotoxic chemosensitizers can enhance the clinical activity of combination chemotherapy and the search for more effective and less toxic chemosensitizers continues.

Primary breast cancer imaging with technetium-99m sestamibi and its relation with P-glycoprotein overexpression

The aim of this preliminary study was to evaluate retrospectively sestamibi scintigraphy in relation to the presence of the 170-kDa P-glycoprotein (Pgp), which represents an expression of multidrug resistance in patients with primary breast cancer. Fifteen women (age range 37-76 years) were referred for technetium-99m sestamibi scintigraphy because of suspicious breast lesions detected by mammography and ultrasonography, and subsequently assessed by fine-needle aspiration. Scintigraphy was performed 30 min following the injection of 500 MBq 99mTc-sestamibi. Three planar anterior and oblique images were obtained with the patient in the supine position. Excised tumours were assessed for cytosolic CA 15.3, oestrogen (OR) and progesterone (PR) receptors and c-erb B2 neu oncogene. Pathology revealed that only 13 of the 15 patients had malignant tumours. The two benign tumours were sestamibi-negative and Pgp-positive. Sestamibi scintigraphy was positive in 10 of the 13 malignant lesions (including nine of ten infiltrating ductal carcinomas). Two of the three lesions with false-negative scintigraphy were Pgp-negative; in one of these cases histology revealed an invasive lobular carcinoma and in the other, mucinous adenocarcinoma. The third false-negative lesion was a Pgp-positive infiltrating ductal carcinoma which was c-erb B2 neu-negative but CA 15.3-, OR- and PR-positive. This preliminary study confirms that the resistance to chemotherapy which may occur in patients with primary breast cancer can be a cause of negative sestamibi scintigraphy.

Sequential assessment of multidrug resistance phenotype and measurement of S-phase fraction as predictive markers of breast cancer response to neoadjuvant chemotherapy

BACKGROUND

The authors examined the relevance of S-phase fraction (SPF) and multidrug resistance (MDR) phenotype as predictive tests of breast cancer response in a series of patients treated by conventional doses of neoadjuvant chemotherapy with (FAC) or without (FTC) doxorubicin.

METHODS

Fine needle samplings of tumors were used to measure SPF by flow cytometry before treatment (Day 0), and to assess the MDR phenotype using semiquantified reverse transcriptase polymerase chain reaction and immunocytochemistry, before and after (Days 8 and 28) the first cycle of chemotherapy.

RESULTS

Measurement of SPF before treatment was significantly associated with clinical response, but sequential assessment of MDR phenotype identified three groups of tumors with distinct outcomes: (1) tumors with a positive and constant expression of MDR1, in which prediction of resistance was restricted to patients treated by FAC; (2) tumors without any detectable expression, in which resistance to FAC or FTC treatments was rarely observed; and (3) tumors with an early (Day 8) acquired or increased MDR1 gene expression, which were always resistant to therapy to both treatment regimens. These results were confirmed at the protein level.

CONCLUSIONS

Sequential assessment of MDR phenotype is a relevant tool for monitoring breast cancer response in neoadjuvant chemotherapy.

p-Glycoprotein expression as a predictor of breast cancer recurrence

BACKGROUND

Many new prognostic factors for breast cancer have been described, and yet the ability to predict patient outcomes remains poor. Overexpression of p-glycoprotein (p-gp), the multidrug resistance efflux pump, confers a worse prognosis to patients with certain leukemias and other tumors. The purpose of this study was to analyze the potential usefulness of p-gp expression as a prognostic factor in patients with breast cancer.

METHODS

Paraffin blocks were obtained from 55 previously untreated patients who underwent surgery between 1987 and 1988. To determine p-gp expression, tumor cell suspensions were incubated with the p-gp-specific C219 monoclonal antibody and analyzed using an indirect immunofluorescent flow cytometric assay.

RESULTS

Twenty-four (44%) of the tumors were p-gp positive and 31 (56%) were p-gp negative. Among the p-gp positive patients, 65% had recurrence of their disease, whereas only 13% of the p-gp negative patients experienced recurrence (p = 0.0001). The 5-year disease-free rate for p-gp positive patients was 39% compared with 83% for p-gp negative patients (p = 0.0001). In univariate analysis examining 10 different variables, significant predictors of recurrence were p-gp, stage, and tumor size. Multivariate analysis using Cox Proportional Hazards regression showed that only p-gp and stage were significant independent predictors of recurrence (p = 0.0002).

CONCLUSIONS

p-gp is frequently expressed in patients with untreated breast cancer, with p-gp-positive patients being at significantly greater risk for disease recurrence. p-gp appears to be a useful prognostic factor in breast cancer and could potentially help guide management.

Prognostic relevance of P-glycoprotein expression in breast cancer

BACKGROUND

P-glycoprotein (Pgp) expression has been reported to be associated with a poor prognosis in some malignancies such as neuroblastoma, soft tissue sarcoma and acute myeloid leukemia. The prognostic role of Pgp expression in breast cancer is still unclear. We investigated the expression of Pgp in primary and metastatic breast cancer tissues in relation to patient characteristics and treatment outcome.

PATIENTS AND METHODS

Pgp expression was evaluated in 92 primary and 12 metastatic breast cancers by the use of immunohisto/cytochemistry with three monoclonal antibodies (MAbs) (JSB-1, C219, MRK16), and an RNAse protection assay. Follow-up information was available for 77 primary breast cancer patients (median follow-up 42 months; range 2-63 months).

RESULTS

Concordance among the anti-Pgp MAbs varied, the highest being between JSB-1 and MRK16 (71%; p=0.002). Pgp expression was more frequent in metastatic disease (58%) than in primary breast cancer (29%) (JSB-1; p=0.055). Pgp expression as assessed with JSB-1 (univariate analysis; p<0.05) was associated with shorter overall survival (OS). Nineteen (21%) primary breast cancers had Pgp expression in fibroblasts in desmoplastic stroma and this did not correlate with Pgp expression in the tumor. The combination of Pgp-positive tumor cells and Pgp-expressing fibroblasts was the strongest prognostic factor for OS by multivariate analysis. Subgroup analysis suggested that Pgp expression was associated with a shorter OS in tamoxifen-treated patients, but not in those who received chemotherapy (most often CMF).

CONCLUSIONS

Pgp expression in tumor cells, and especially when accompanied by Pgp expression in fibroblasts in desmoplastic stroma, has prognostic value in primary breast cancer patients and is likely to be a marker of a more malignant phenotype. Pgp expression of tumor cells might play a role in tamoxifen resistance. These findings may have important implications for teh treatment of breast cancer patients, and warrant further prospective investigation in a larger patient population.