Prediction of doxorubicin resistance in vitro in myeloma, lymphoma, and breast cancer by P-glycoprotein staining

Synthesis and Characterization of a pH- and Temperature-Sensitive Fe3O4-SiO2-Poly(NVCL-co-MAA) Nanocomposite for Controlled Delivery of Doxorubicin Anticancer Drug

This work reports the synthesis, characterization, and in vitro release studies of pH- and temperature-sensitive Fe₃O₄-SiO₂-poly(NVCL-co-MAA) nanocomposite. Fe₃O₄ nanoparticles were prepared by chemical coprecipitation, coated with SiO₂ by the Stöber method, and functionalized with vinyl groups. The copolymer poly(N-vinylcaprolactam-co-methacrylic acid) (poly(NVCL-co-MAA)) was grafted onto the functionalized Fe₃O₄-SiO₂ nanoparticles by free radical polymerization. XRD, FTIR, TGA, VSM, and TEM techniques were performed to characterize the nanocomposite. The release behavior of Doxorubicin (DOX) loaded in the nanocomposite at pH 5.8 and 7.4, and two temperatures, 25 and 37 °C, was studied. According to the release studies, approximately 55% of DOX is released in 72 h at pH 7.4, regardless of temperature. At pH 5.8, 78% of DOX was released in 48 h at 25 °C, and when increasing the temperature to 37 °C, more than 95 % of DOX was released in 24 h. The DOX release data treated with Zero-order, first-order, Higuchi, and Korsmeyer-Peppas models showed that Higuchi's model best fits the data, indicating that the DOX is released by diffusion. The findings suggest that the synthesized nanocomposite may be useful as a DOX carrier in biomedical applications.

Thermoresponsive Iron Oxide Nanocubes for an Effective Clinical Translation of Magnetic Hyperthermia and Heat-Mediated Chemotherapy

The use of magnetic nanoparticles in oncothermia has been investigated for decades, but an effective combination of magnetic nanoparticles and localized chemotherapy under clinical magnetic hyperthermia (MH) conditions calls for novel platforms. In this study, we have engineered magnetic thermoresponsive iron oxide nanocubes (TR-cubes) to merge MH treatment with heat-mediated drug delivery, having in mind the clinical translation of the nanoplatform. We have chosen iron oxide based nanoparticles with a cubic shape because of their outstanding heat performance under MH clinical conditions, which makes them benchmark agents for MH. Accomplishing a surface-initiated polymerization of strongly interactive nanoparticles such as our iron oxide nanocubes, however, remains the main challenge to overcome. Here, we demonstrate that it is possible to accelerate the growth of a polymer shell on each nanocube by simple irradiation of a copper-mediated polymerization with a ultraviolet light (UV) light, which both speeds up the polymerization and prevents nanocube aggregation. Moreover, we demonstrate herein that these TR-cubes can carry chemotherapeutic doxorubicin (DOXO-loaded-TR-cubes) without compromising their thermoresponsiveness both in vitro and in vivo. In vivo efficacy studies showed complete tumor suppression and the highest survival rate for animals that had been treated with DOXO-loaded-TR-cubes, only when they were exposed to MH. The biodistribution of intravenously injected TR-cubes showed signs of renal clearance within 1 week and complete clearance after 5 months. This biomedical platform works under clinical MH conditions and at a low iron dosage, which will enable the translation of dual MH/heat-mediated chemotherapy, thus overcoming the clinical limitation of MH: i.e., being able to monitor tumor progression post-MH-treatment by magnetic resonance imaging (MRI).

Paclitaxel Activity in Anthracycline Refractory Breast Cancer Patients

Aims and background

We investigated the efficacy and tolerability of two doses of paclitaxel, 175 mg/m2 and 135 mg/m2, over a 3-hr infusion, without prophylactic G-CSF, in heavily pretreated patients with anthracycline-resistant breast cancer. Although paclitaxel may share with anthracyclines a common mechanism of drug resistance, there is evidence that the two drugs are not completely cross resistant.

Methods

From July 1994 to January 1996, 42 patients were treated every 3 weeks, for a maximum of 6 cycles; paclitaxel dose was established according to pretreatment extension.

Results

In 41 assessable patients we observed 9 partial responses, for an overall response rate of 22% (95% CI, 10–34%). There was no difference in response rate between the two dose levels. Median duration of response was 9 months, median time to progression 5 months, and median survival 9 months. The dose-limiting toxicity was neutropenia, which was grade 3–4 in 40% (135 mg/m2) and 62% (175 mg/m2) of the patients (P = 0.28); neutropenic fever occurred in 24% of the patients, without significant differences between the two dose levels. Other toxicity was mild to moderate.

Conclusions

Paclitaxel at doses of 175 mg/m2 or 135 mg/m2 is active and well tolerated in advanced breast cancer patients resistant to anthracyclines. The prophylactic use of colony-stimulating factors seems appropriate in heavily pretreated patients given the higher dose level.

Exostosin 1 regulates cancer cell stemness in doxorubicin-resistant breast cancer cells

Cancer stem cells (CSCs) are associated with cancer recurrence following radio/chemotherapy owing to their high resistance to therapeutic intervention. In this study, we investigated the role of exostoxin 1 (EXT1), an endoplasmic reticulum (ER)-residing type II transmembrane glycoprotein, in cancer cell stemness. DNA microarray analysis revealed that doxorubicin-resistant MCF7/ADR cells have high levels of EXT1 expression compared to its parental cell line, MCF7. These cells showed significantly higher populations of CSCs and larger populations of aldehyde dehydrogenase (ALDH⁺) and CD44⁺/CD24^-cells, as compared to MCF7 cells. siRNA-mediated knockdown of EXT1 in MCF7/ADR cells significantly reduced cancer stem cell markers, populations of ALDH⁺and CD44⁺/CD24^- cells, mRNA and protein expression for CD44, and mammosphere number. Furthermore, epithelial mesenchymal transition (EMT) markers and migratory behavior were also repressed with reduced EXT1. In an in vitro soft agar colony formation assay, EXT1 knockdown by short hairpin RNA (shRNA) reduced the colony formation ability of these cells. Based on these results, we suggest that EXT1 could be a promising novel target to overcome cancer cell stemness in anthracycline-based therapeutic resistance.

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.

Predictive Modeling of Drug Response in Non-Hodgkin's Lymphoma

We combine mathematical modeling with experiments in living mice to quantify the relative roles of intrinsic cellular vs. tissue-scale physiological contributors to chemotherapy drug resistance, which are difficult to understand solely through experimentation. Experiments in cell culture and in mice with drug-sensitive (Eµ-myc/Arf-/-) and drug-resistant (Eµ-myc/p53-/-) lymphoma cell lines were conducted to calibrate and validate a mechanistic mathematical model. Inputs to inform the model include tumor drug transport characteristics, such as blood volume fraction, average geometric mean blood vessel radius, drug diffusion penetration distance, and drug response in cell culture. Model results show that the drug response in mice, represented by the fraction of dead tumor volume, can be reliably predicted from these inputs. Hence, a proof-of-principle for predictive quantification of lymphoma drug therapy was established based on both cellular and tissue-scale physiological contributions. We further demonstrate that, if the in vitro cytotoxic response of a specific cancer cell line under chemotherapy is known, the model is then able to predict the treatment efficacy in vivo. Lastly, tissue blood volume fraction was determined to be the most sensitive model parameter and a primary contributor to drug resistance.

The role of P-glycoprotein in drug resistance in multiple myeloma

Multiple myeloma (MM) is a malignant neoplastic cancer of the plasma cells that involves the bone marrow. The majority of patients with MM initially respond to chemotherapy, but they eventually become resistant to later drug therapy. One of the reasons for drug resistance in patients with MM is efflux transporters. P-glycoprotein (P-gp) is the most studied of the multidrug resistance proteins, and is up-regulated in response to many chemotherapeutic drugs. This up-regulation of P-gp causes a decrease in the intracellular accumulation of these drugs, limiting their therapeutic efficacy. In this review, we focus on the role of P-gp in drugs used for patients with MM. P-gp has been found to be an important factor with regard to drug resistance in many of the drug classes used in the treatment of MM (proteasome inhibitors, anthracyclines, alkylating agents and immunomodulators are examples). Thus, our further understanding of its mechanism and inhibitory effects will help us decrease drug resistance in patients with MM.

DualChip®microarray as a new tool in cancer research

Over the last 5 years, the emergence of gene expression profiling using high-density DNA microarrays led to a better understanding of tumor development and identified new prognostic markers. However, high-density microarrays failed to leap from the researcher's bench to the clinical practice due to their cost, data management and lack of standardization. DualChip low-density DNA microarrays were developed as a new flexible tool that is able to reliably quantify the expression of a limited number of genes of clinical relevance. This review will illustrate how DualChip technology can be applied to tumor diagnosis and tumor-acquired drug resistance.

P-Glycoprotein (P-170) expression in acute leukemias

Multidrug resistance (MDR) is still a major obstacle to chemotherapy success in acute myeloid leukemia (AML) and to a less extent acute lymphoblastic leukemia (ALL). Recent studies have shown that the expression of certain gene products mediate the development of resistance to chemotherapeutic agents. The most well characterized of these genes is the multidrug resistance gene MDR-1. This study was planned to study the expression of P-glycoprotein/170 in patients with acute leukemia and the effect of Cyclosporin A (CSA) as a modulator of P-glycoprotein functional activity. The study was carried out on 20 patients with acute leukemia (14 AML cases and 6 ALL cases). In addition, 6 normal individuals served as a reference group. Flow cytometric analysis of P-gp/170 surface expression was performed using UIC-2 MoAb together with the functional assay using Rhodamine 123 (Rh 123) and Cyclosporin A as a modulator.P-gp/170 was expressed on the leukemic cells of 37.5% of relapsed patients (40.0% of AML and 33.3% of ALL cases), whereas 27.2% of de novo patients expressed P-gp/170 (33.3% of AML cases and 0% of ALL cases). The functional activity of MDR-1 gp was 71.4% in AML and 33.3% in ALL patients compared with16.6% in normal lymphocytes. From this study, it is clear that P-gp/170 is expressed to a higher degree in leukemic cells and this is greater in relapsed compared to de novo cases and more in AML than ALL blasts. Functional activity is a more sensitive predictor of chemoresistance than P-gp/170 surface expression.

Identification of an ABCB1 (P-glycoprotein)-positive carfilzomib-resistant myeloma subpopulation by the pluripotent stem cell fluorescent dye CDy1

Multiple myeloma (MM) is characterized by the malignant expansion of differentiated plasma cells. Although many chemotherapeutic agents display cytotoxic activity toward MM cells, patients inevitably succumb to their disease because the tumor cells become resistant to the anticancer drugs. The cancer stem cell hypothesis postulates that a small subpopulation of chemotherapy-resistant cancer cells is responsible for propagation of the tumor. Herein we report that efflux of the pluripotent stem cell dye CDy1 identifies a subpopulation in MM cell lines characterized by increased expression of P-glycoprotein, a member of the ABC (ATP-binding cassette) superfamily of transporters encoded by ABCB1. We also demonstrate that ABCB1-overexpressing MM cells are resistant to the second-generation proteasome inhibitor carfilzomib that recently received accelerated approval for the treatment of therapy-refractive MM by the U.S. Food and Drug Administration. Moreover, increased resistance to carfilzomib in sensitive MM cells following drug selection was associated with upregulation of ABCB1 cell-surface expression which correlated with increased transporter activity as measured by CDy1 efflux. We further show that chemosensitization of MM cells to carfilzomib could be achieved in vitro by cotreatment with vismodegib, a hedgehog pathway antagonist which is currently in MM clinical trials. CDy1 efflux may therefore be a useful assay to determine whether high expression of ABCB1 is predictive of poor clinical responses in MM patients treated with carfilzomib. Our data also suggest that inclusion of vismodegib might be a potential strategy to reverse ABCB1-mediated drug resistance should it occur.

Mechanisms of multidrug resistance in cancer treatment

Advanced breast cancer responds to a range of cytotoxic agents, but resistance always develops. Understanding the mechanisms of resistance may provide new therapeutic options. There are several major groups of resistance mechanisms. 1) The multidrug resistant phenotype. This is due to a membrane pump that can extrude a wide range of anticancer drugs--the P-glycoprotein. It is inhibited by a range of clinically used calcium channel blockers such as nifedipine and verapamil. Several other membrane proteins of 180 KD, 170 KD, 300 KD and 85 KD have been reported and are associated with MDR. 2) Glutathione transferences and detoxification mechanisms. These are a multigene family of enzymes that conjugate glutathione to chemically reactive groups. There are 3 major groups of enzymes--acidic, basic and neutral. They have been implicated in resistance to doxorubicin, melphalan cisplatinum chlorambucil and other alkylating agents. Other protecting systems include metallothionein and selenium dependent glutathione peroxidase. HSP27 confers doxorubicin resistance. 3) Topoisomerase II. DNA topoisomerases are involved in several aspects of DNA metabolism in particular genetic recombination, DNA transcription, chromosome segregation. They are a target for doxorubicin, mitoxantrone, VP16. Low levels of expression are associated with resistance. However, it is oestrogen inducible and this may be of therapeutic value. A novel topo IIb which is more drug resistant has been reported. 4) DNA repair. A score or more of genes are involved in the repair of DNA damage by drugs and radiation. Defective DNA repair may predispose to cancer of the breast and be responsible for adverse radiation reactions. Enhanced repair has been shown to be a mechanism of cisplatinum resistance. Several genes are inducible by DNA damage and may confer resistance e.g. A45. 5) Drug activation. Mitomycin C as well as cyclophosphamide and VP16 require activation for their effects. Low levels of cytochrome p450 reductase are associated with MMC resistance.

Correlation of MDR1 /P-170 expression with daunorubicin uptake and sensitivity of leukemic progenitors in acute myeloid leukemia

Prior studies have shown that multidrug resistance gene products may be detected in acute myeloid leukemia (AML) cells, and are associated with poor response to therapy. We studied whether P-170 expression was associated with in vitro daunorubicin (DNR) accumulation and sensitivity of leukemic clonogenic cells (CFU-L) to DNR in 16 newly diagnosed AML samples. P-170 expression was assessed by indirect immunofluorescence using the monoclonal antibody MRK16. DNR cellular content was measured by flow cytometry after short incubation with increasing concentrations of DNR, and was not correlated with P-170 expression, although there was a trend for higher values in P-170-negative samples. The sensitivity of CFU-L was studied in a semisolid culture assay by calculating the dose of DNR inhibiting the growth of 90% of CFU-L (D90). The D90 was significantly higher in P-170-positive than in P-170-negative samples (mean = 1.68 +/- 0.42 microgram/ml versus 0.97 +/- 0.35 micrograms/ml respectively, p less than 0.005). Eight of 9 cases achieving complete remission (CR) after intensive chemotherapy were P-170-negative, whereas 7 of 7 nonresponders were P-170-positive (p less than 10(-5)). D90 was significantly lower for patients achieving CR than for those who did not achieve CR (1.12 +/- 0.55 micrograms/ml versus 1.59 +/- 0.37 micrograms/ml, p = 0.04). It is concluded that P-170 expression is correlated with in vitro resistance of clonogenic cells to DNR and may be one mechanism of resistance to chemotherapy.

Emerging Data on the Use of Anthracyclines in Combination with Bortezomib in Multiple Myeloma

Since the inception of infusional vincristine/doxorubicin/pulsed dexamethasone (VAD) for the treatment of multiple myeloma, anthracyclines have remained an important class of antimyeloma agents. More recently, the introduction of pegylated liposomal doxorubicin with improved pharmacokinetic characteristics has led to the development of newer anthracycline-containing regimens with improved toxicity profiles. Bortezomib, a first in class reversible inhibitor of the proteasome, has also emerged as an important novel agent for the treatment of multiple myeloma and is currently approved for patients with relapsed/refractory disease progressing after 1 previous therapy. Although both classes of agents have potent proapoptotic activity, they also induce activation of an antiapoptotic prosurvival program that limits their own efficacy, a process known as inducible chemotherapy resistance. Importantly, in preclinical studies, each of these drugs has been shown to attenuate chemotherapy resistance induced by the other, and combinations of the 2 have demonstrated striking synergistic activity. Furthermore, early phase I/II clinical trials have shown impressive activity of pegylated liposomal doxorubicin and conventional doxorubicin in combination with bortezomib in patients with newly diagnosed and relapsed/refractory myeloma. Phase II/III clinical trials evaluating these regimens in patients with newly diagnosed and relapsed/refractory disease have recently completed accrual and will better define the role of these combinations in myeloma therapy. Herein, we review the preclinical data supporting the use of bortezomib with anthracyclines and the promising clinical data with these combinations.

Gene expression profiling of ATP-binding cassette (ABC) transporters as a predictor of the pathologic response to neoadjuvant chemotherapy in breast cancer patients

Drug resistance is a major obstacle to the successful chemotherapy. Several ATP-binding cassette (ABC) transporters including ABCB1, ABCC1 and ABCG2 have been known to be important mediators of chemoresistance. Using oligonucleotide microarrays (HG-U133 Plus 2.0; Affymetrix), we analyzed the ABC transporter gene expression profiles in breast cancer patients who underwent sequential weekly paclitaxel/FEC (5-fluorouracil, epirubicin and cyclophosphamide) neoadjuvant chemotherapy. We compared the ABC transporter expression profile between two classes of pretreatment tumor samples divided by the patients' pathological response to neoadjuvant chemotherapy (residual disease [RD] versus pathologic complete response [pCR]) ABCB3, ABCC7 and ABCF2 showed significantly high expression in the pCR. Several ABC transporters including ABCC5, ABCA12, ABCA1 ABCC13, ABCB6 and ABCC11 showed significantly increased expression in the RD (p<0.05). We evaluated the feasibility of developing a multigene predictor model of pathologic response to neoadjuvant chemotherapy using gene expression profiles of ABC transporters. The prediction error was evaluated by leave-one-out cross-validation (LOOCV). A multigene predictor model with the ABC transporters differentially expressed between the two classes (p<or=0.003) showed an average 92.8% of predictive accuracy (95% CI, 88.0-97.4%) with a 93.2% (95% CI, 85.2-100%) positive predictive value for pCR, a 93.6% (95% CI, 87.8-99.4%) negative predictive value, a sensitivity of 88.1%(95% CI, 76.8-99.4%), and a specificity of 95.9% (91.1% CI, 87.8-100%). Our results suggest that several ABC transporters in human breast cancer cells may affect the clinical response to neoadjuvant chemotherapy, and transcriptional profiling of these genes may be useful to predict the pathologic response to sequential weekly paclitaxel/FEC in breast cancer patients.

Multifocal Primary Breast Lymphoma

Primary breast lymphoma (PBL) is a rare condition, accounting for only 0.04 to 0.5% of breast malignancies and less than 2% of extranodal lymphomas. Clinical presentation and imaging may suggest a benign condition. Reports of treatment vary widely. Surgical therapy has been reported to include only biopsy or extend to partial mastectomy, total mastectomy, or even radical mastectomy. Chemotherapy with various agents is often used. Radiotherapy has been used in the adjuvant setting or as primary local therapy. Immunotherapy and radioimmunotherapy have shown some promise in other lymphomas and may be useful here as well. There is no standard or consensus of treatment for PBL. This report describes a case of multifocal PBL in a 45-year-old female and discusses the physical findings, diagnosis, and treatment options for this condition.

IIVP Salvage Regimen Induces High Response Rates in Patients With Relapsed Lymphoma Before Autologous Stem Cell Transplantation

Patients with relapsed lymphoma can be cured with high-dose chemotherapy and autologous hematopoietic stem cell transplantation (HSCT). New therapeutic approaches with better cytoreductive capacity are needed for relapsed patients to keep their chance for cure with transplantation. We report 30 patients with relapsed lymphoma, median age 43 years, treated with IIVP salvage regimen consisting of ifosfamide, mesna, idarubicin, and etoposide for 2 or 3 cycles. Seventeen patients had non-Hodgkin lymphoma (NHL) and 13 patients had Hodgkin disease (HD). Fourteen (47%) patients were at their first relapse. Overall response rate was 86.6% (n = 26) with 19 patients (63.3%) achieving complete response. Overall response rate was 92% in patients with HD and 82% in NHL. The most frequent side effects observed were grade III-IV neutropenia (87%) and thrombocytopenia (73%). IIVP regimen is a highly effective salvage therapy for patients with relapsed HD or NHL who are candidates for autologous HSCT. Close follow up is necessary because of the high incidence of grade III-IV hematologic toxicity.

Expression of MDR1/P-glycoprotein, the multidrug resistance protein MRP, and the lung-resistance protein LRP in multiple myeloma

The purpose of this study was to determine the incidence of three genes associated with multidrug resistance (MDR) in multiple myeloma in relation to treatment status. MDR1/Pgp (P-glycoprotein) expression was detected in 41% of 93 myeloma samples. Generally, the incidence of MDR1/Pgp expression was higher in pretreated samples, and treatments with doxorubicin and/or vincristine were more effective in MDR1/Pgp expression than with alkylating agents. A significant association was observed between MDR1 /Pgp-positiveness and the ability of verapmil to increase doxorubicin sensitivity, suggesting functional relevance of MDR1/Pgp expression. MRP (multidrug resistance protein) expression was detected in 20.5% of 88 myeloma samples, in 26% at the mRNA level analyzed by quantitative reverse transriptase-polymerase chain reaction, and in only 3 of 79 samples by immunohistochemistry. LRP (lung-resistance protein) protein expression was observed in 12.5% of 72 myeloma samples. MRP and LRP expression was similar in samples with and without prior therapy. Approximately 80% of the myeloma samples with detectable mRNA expression of MDRI and MRP exhibited low expression levels corresponding to < 10% of the Pgp- and MRP-overexpressing multidrug-resistant human myeloma cell lines 8226/Dox6 and 8226/DOXint40c, respectively. Some normal bone marrow samples showed higher levels of MRP mRNA as compared to myeloma specimens, whereas MDRI mRNA expression in normal bone marrow was much lower (< or = 5%) than that in 8226/Dox6. These findings indicate a requirement to develop single-cell assays for MRP detection in multiple myeloma that are more sensitive than immunohistochemistry and might be useful to evaluate the incidence of genes associated with MDR.

Expression and localization of P-glycoprotein in human heart: effects of cardiomyopathy

ABC-type transport proteins, such as P-glycoprotein (P-gp), modify intracellular concentrations of many substrate compounds. They serve as functional barriers against entry of xenobiotics (e.g., in the gut or the blood-brain barrier) or contribute to drug excretion. Expression of transport proteins in the heart could be an important factor modifying cardiac concentrations of drugs known to be transported by P-gp (e.g., beta-blockers, cardiac glycosides, doxorubicin). We therefore investigated the expression and localization of P-gp in human heart. Samples from 15 human hearts (left ventricle; five non-failing, five dilated cardiomyopathy, and five ischemic cardiomyopathy) were analyzed for expression of P-gp using real-time RT-PCR, immunohistochemistry, and in situ hybridization. Immunohistochemistry revealed expression of P-gp in endothelium of both arterioles and capillaries of all heart samples. Although P-gp mRNA was detected in all samples, its expression level was significantly reduced in patients with dilated cardiomyopathy. We describe variable expression of P-gp in human heart and its localization in the endothelial wall. Thus, intracardiac concentrations of various compounds may be modified, depending on the individual P-gp level.

Resistant mechanisms of anthracyclines--pirarubicin might partly break through the P-glycoprotein-mediated drug-resistance of human breast cancer tissues

Juliano and Ling initially reported the expression of a 170 kDa glycoprotein in the membrane of Chinese hamster ovarian cells in 1976, and named this glycoprotein P-glycoprotein (P-gp) based on its predicted role of causing "permeability" of the cell membrane. After much research on anthracycline-resistance, this P-gp was finally characterized as a multidrug-resistant protein coded by the mdr1 gene. Multidrug resistance associated protein (MRP) was initially cloned from H69AR, a human small cell-lung carcinoma cell line which is resistant to doxorubicin (DXR) but does not express P-gp. MRP also excretes substrates through the cell membrane using energy from ATP catabolism. The substrate of MRP is conjugated with glutathione before active efflux from cell membrane. Recently, membrane transporter proteins were re-categorized as members of "ATP-Binding Cassette transporter"(ABC-transporter) superfamily, as shown at http://www.med.rug.nl/mdl/humanabc.htm and http://www.gene.ucl.ac.uk/nomenclature/genefamily/abc.html. A total of ABC transporters have been defined, and MDR1 and multidrug resistance associated protein 1 (MRP1) were reclassified as ABCB1 and ABCC1, respectively. Their associated superfamilies include 11 and 13 other protein, in addition to ABCB and ABCC, respectively. Lung resistance-related protein (LRP) is not a member of the superfamily of ABC transporter proteins, because it shows nuclear membrane expression and transports substrate between nucleus and cytoplasm. LRP was initially cloned from a non-small cell lung carcinoma cell line, SW1573/2R120 which is resistant to DXR, vincristine, etoposide and gramicidin D and does not express P-gp. The mechanisms of resistance remains unclear, and why some resistant cell lines express P-gp and others express MRP and/or LRP is likewise unclear.

Multidrug resistance gene 1 expression in salivary gland adenocarcinomas and oral squamous-cell carcinomas

In combined chemotherapy for head-and-neck cancer (HNC), salivary gland-cell adenocarcinoma (SGA) shows insufficient clinical outcome, and it has been suggested that the sensitivity and/or the mechanism of resistance to anti-cancer drugs are different between SGA and oral squamous-cell carcinoma (SCC). The aim of our study was to clarify whether P-glycoprotein (P-gp) expression is associated with multidrug resistance (MDR) in HNC and the difference in the process of its development between SGA and SCC. In immunohistochemical analysis, P-gp expression was found in the ductal cells of salivary glands but not in oral mucosal epithelium. In cancer tissues, a few SCC cells in 12 of 37 and most cells in all SGAs expressed P-gp. The intensive P-gp expression was significantly found in SGA compared with SCC. In an in vivo chemotherapeutic model using tumor-bearing nude mice, P-gp expression in counterparts was observed in only a few cells of the HSY line, while no P-gp expression was observed in Hepd cells. However, P-gp expression was developed in both HSY and Hepd cell lines after vincristine (VCR) treatment. RT-PCR showed that the mean ratios of mdr1 mRNA expression levels in HSY clones were 3.7-fold higher than those in Hepd clones after VCR treatment, while each cell line exhibited both induction and activated production of P-gp. These results suggest that P-gp-related MDR in SGA is an inherent phenotype caused by both high levels of P-gp induction and activated P-gp production during VCR treatment, while that in SCC is an acquired phenotype chiefly caused by induction of P-gp.

Enhancement of mdr1 gene expression in normal tissue adjacent to advanced breast cancer

In the present study, mdr1 gene expression was investigated by a sensitive reverse transcriptase-PCR assay in advanced breast cancer and in corresponding adjacent normal tissues obtained before and after treatment with primary chemotherapy. Comparatively to normal tissues, a significant induction of mdr1 expression was observed in untreated tumors (p = 0.0222). Similarly, a significant induction of mdr1 expression was revealed when treated samples were compared to untreated counterparts (p = 0.0222), but no differences were detected between tumor and normal samples (p = 0.3199). Noteworthy, a significant induction of mdr1 gene expression occurred in treated normal samples comparatively to untreated ones (p = 0.0037), and this induction was even more important in normal than in tumoral tissue (p = 0.0627). However, neither the basal expression nor the induction of mdr1 were correlated with subsequent response to chemotherapy or with survival. Thus, in agreement with previous reports, our data show that chemotherapy induce mdr1 gene expression in breast cancer cells, but they also indicate that a similar phenomenon occurs in adjacent normal tissues. Therefore, our results strongly suggest that mdr1 gene overexpression is not a characteristic of breast malignant cells, but rather constitutes a general phenomenon occurring both in normal and tumor cells which could explain at least in part the absence of relationship between mdr1 expression and the clinical outcome of breast cancer patients.

Competitive reverse transcription-polymerase chain reaction assay for quantification of human multidrug resistance 1 (MDR1) gene expression in fresh leukemic cells

We have analyzed MDR1 gene expression in 69 clinical samples obtained from 64 patients with leukemic hematologic malignancies by using a competitive reverse transcription-polymerase chain reaction assay with a heterologous competitor RNA. To exclude a false-positive result caused by concomitant normal lymphocytes that physiologically express MDR1, in samples we determined a cut-off value of 8 amol MDR1 transcript per microgram of RNA by simultaneous measurement of rhodamine 123 dye efflux either in lymphocyte or gated leukemic cell populations. Consequently, 23 of 69 samples were concluded to be MDR1-positive in leukemic cells per se. The MDR1 expression rate was significantly correlated with factors such as a history of preceding chemotherapy, elder age of the patient, and certain disease types (eg, leukemia progressed from myelodysplastic syndrome). Moreover, the complete response rate after chemotherapy was significantly higher in MDR1-negative patients than in MDR1-positive patients (52% vs 17%, respectively; P = .01). The assay established will enable the quantification of MDR1 gene expression in blood samples from patients with leukemic hematologic malignancies and will be applicable to clinical laboratories as a routine test.

Multidrug resistance phenotype in high grade soft tissue sarcoma: correlation of P-glycoprotein immunohistochemistry with pathologic response to chemotherapy

BACKGROUND

P-glycoprotein-mediated drug efflux has been implicated as an important mechanism of multidrug resistance (MDR) in cancer. Its role in chemotherapy resistance in soft tissue sarcoma is unclear.

METHODS

Tumor specimens prior to and following neoadjuvant chemotherapy from 29 cases of high grade soft tissue sarcoma were analyzed with 2 monoclonal antibodies (C494 and JSB-1) that recognize different epitopes of P-glycoprotein. Staining intensity was graded 0 = negative, 1 = equivocal, 2 = moderate, 3 = strong. Only cases with Grade 2 or 3 staining intensity with both antibodies were considered MDR positive. The resection specimens were evaluated for tumor necrosis postchemotherapy. Pathologic response was graded as good for <15%, moderate for 15-50%, or poor for >50% posttreatment tumor viability.

RESULTS

Of the 29 pretreatment specimens, 10 (34%) were MDR positive and 19 (66%) were MDR negative. Pathologic response to treatment was characterized as good in 6, moderate in 7, and poor in 16 patients. Of the MDR positive biopsies, 9 (90%) had poor response, compared with 7 (36%) in the MDR negative biopsy group (P = 0.0078). None of the cases with MDR positive biopsies had a good response, compared with 6 cases in which biopsies were MDR negative (32%) (P = 0.057). Only one MDR negative case became MDR positive posttreatment.

CONCLUSIONS

Expression of MDR phenotype is found in approximately one-third of high grade soft tissue sarcomas. These preliminary data show a significant correlation between MDR phenotype and poor pathologic response to chemotherapy, and suggest that MDR induction by chemotherapy in soft tissue sarcoma is an uncommon event.

Retroviral transfer of human MDR1 gene to hematopoietic cells: effects of drug selection and of transcript splicing on expression of encoded P-glycoprotein

Protection of hematopoietic cells of patients undergoing anticancer chemotherapy by MDR1 gene transfer is currently being studied in clinical trials. From animal studies, it has been suggested that aberrant splicing due to cryptic donor and acceptor sites in the MDR1 cDNA could be a major reason for failure to obtain high-level expression of P-glycoprotein in bone marrow. We investigated effects of drug selection on protein expression levels and on splicing of MDR1 transcripts in murine bone marrow cells (BMCs) in vitro. To this end, retroviruses were generated through an identical plasmid, pHaMDR1/A, introduced into different packaging cells. GP + E86- but not PA317-derived producer cells were found to express truncated in addition to full-length message. In BMCs transduced with GP + E86-derived viruses, both messages were increased after treatment with colchicine or daunomycin. Similar results were obtained with NIH 3T3 fibroblasts. However, transduced and drug-selected BMCs displayed the spliced transcript even if the respective PA317-derived producer cells contained no truncated RNA as detected in transduced NIH 3T3 fibroblasts. Short-term drug selection in BMCs transduced with either ecotropic or amphotropic retroviruses resulted in a striking increase in P-glycoprotein expression. Thus, aberrant splicing failed to abrogate P-glycoprotein expression in BMCs. We also studied a vector in which MDR1 was coexpressed with glucocerebrosidase, using an internal ribosomal entry site. Although chemoprotection was less efficient than with pHaMDR1/A, augmentation of protein expression was observed at low selecting drug concentrations. Our study shows that drug selection can partially compensate for inefficient transduction of hematopoietic cells, and may help to develop strategies by which unstable expression of transduced genes can be overcome.

Antitumor spectra of anthracyclines against gastric cancer tissues obtained from surgical specimens with reference to P-glycoprotein expression

BACKGROUND AND OBJECTIVES

Although the mechanism of P-glycoprotein (Pgp)-related resistance of doxorubicin is known, it has not been clarified for other anthracycline derivatives. We have examined the chemosensitivity of gastric cancer tissues to three anthracyclines in relation to Pgp expression.

METHODS

Sixty-six surgical specimens obtained from patients with gastric cancer were subjected to histoculture drug response assay using doxorubicin (DXR), epirubicin (EPI), and 4'-O-tetrahydropyranyldoxorubicin (pirarubicin; THP). The cutoff concentrations used were 15 microg/ml for DXR and EPI and 17 microg/ml for THP.

RESULTS

A 50% or more inhibition index (I.I.) was regarded as sensitive, at which the correlation rates were 95.8% (23/24) and 74.2% (49/66) for DXR-EPI and DXR-THP, respectively. Twenty-six specimens were immunohistochemically stained with monoclonal antibody to Pgp, with a positive rate of 53.8% (14/26). In Pgp-positive specimens, all cases were resistant to DXR and 28.6% (4/14) of cases were sensitive to THP, while the antitumor activity of EPI was essentially identical to that of DXR.

CONCLUSIONS

The expression of Pgp might affect resistance to DXR and EPI, although THP may partially impair this resistance, suggesting the clinical usefulness of THP in treatment of DXR-refractory gastric carcinoma.

Monoclonal antibodies to P-glycoprotein: preparation and applications to basic and clinical research

P-Glycoprotein, a member of the ABC transporter group, plays an important role in anticancer drug resistance. Many monoclonal antibodies to P-glycoprotein have been developed and used to study the molecular and cellular functions of P-glycoprotein. These monoclonal antibodies were used for gene cloning, purification and reconstitution of P-glycoprotein, analysis of transport functions of P-glycoprotein, immunological detection and selective killing of tumors that express P-glycoprotein for diagnostic, and therapeutic purposes.

P-170 Glycoprotein (MDR) and p53 Expression in Breast Cancer

An immunohistochemical comparative analysis of P-170 glycoprotein and p53 was performed in 37 breast cancer patients who underwent curative resection without preoperative chemotherapy. The antibodies utilized were C-219 and JSB-1 for P-gp and DO-7 for p53. Positive cytoplasmic and membrance positivity for P-gp was found in 22 (59.45%) of the 37 tumor specimens. In comparing tissue immunoreactivity by the specific antibodies, 15 (40.54%) samples showed immunostaining for C-219, 12 (32.43%) for JSB-1, and 5 (23%) for both. P-gp expression was not statistically related with the clinicopathological variables analyzed, that is, age, TNM stage, histologic type, lymph node involvement, tumor diameter, and hormone receptor status. p53 overexpression was observed in 22 (59.45%) of the 37 tumor samples analyzed. There was a significant correlation between p53 overexpression and P-gp positive immunostaining (p = .007). p53 was also significantly correlated with TNM stage (p < .05) and lymph node involvement (p < .02). Our results demonstrated that the three distinct patterns of reactivity with the two antibodies result from the combined expression of each of the three P-gp isoforms. An immunohistochemical analysis with different antibodies may be used to determine and correlate the expression pattern of P-gp isoforms with response to 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.

Reactivity of monoclonal antibody FC-2.15 against drug resistant breast cancer cells. Additive cytotoxicity of adriamycin and taxol with FC-2.15

Monoclonal antibody (MAb) FC-2.15 recognizes Lewis x antigen (Le(x)-Ag) expressed on the cell surface of most human breast cancer cells. FC-2.15 displays important human complement (C')-mediated cytotoxicity (CMC) against its target cells. In this study the reactivity of FC-2.15 against drug resistant-breast cancer cells was investigated, as well as the possibility to combine the antitumor activities of this MAb with adriamycin (Adr) or taxol. Since resistant clones with altered expression of tumor-associated antigens usually emerge after chemotherapy, the expression of Le(x)-Ag was analyzed in Adr(R) MCF-7 breast cancer cells (Adr resistant subline) and in tumor samples from nine patients with locally advanced breast carcinoma who were treated with FEC chemotherapy. A flow cytometry assay showed that most of Adr(R) MCF-7 cells, as well as wild type (WT) cells, expressed Le(x)-Ag; however, the Le(x) epitope is probably bound to different backbones in these cells. When the cytotoxic ability of FC-2.15 against WT and Adr(R) MCF-7 cells was compared, it was found that a 90 min treatment with FC-2.15 plus C' induced similar CMC against both cell lines. An important cytolysis was obtained at 5 microg/ml FC-2.15, reaching a plateau at 25 microg/ml, at which cell population was diminished to 21.1% for WT and 27.9 for Adr(R) MCF-7 cells. Regarding human tumors, Le(x)-Ag expression was evaluated in samples obtained before and in most cases after chemotherapy, and it could be observed that: 1) before treatment, tumor samples from all patients analyzed (responders and non-responders to chemotherapy) were FC-2.15-positive; 2) the presence of Le(x)-Ag was not modified after treatment. The combined action of Adr or taxol with FC-2.15 was then evaluated. WT and Adr(R) MCF-7 cells were cultured with Adr or taxol followed by an incubation with different FC-2.15 concentrations plus C'. When the effect of Adr alone was determined, ID50 were 1 x 10(-7) M for WT and 4.2 x 10(-5) M for Adr(R) MCF-7 cells. The cytotoxic ability of taxol alone was also tested, and ID50 were 6.4 x 10(-9) M for WT and 3.1 x 10(-6) M for Adr(R) MCF-7 cells. When FC-2.15 was added to Adr or taxol, the cytotoxicity of the drug-FC-2.15 combined treatment was always higher than the isolated effects, showing additive cytotoxicity at the different concentrations tested and with both cell lines. Our results suggest that FC-2.15 may be a useful agent against breast tumor cells which survive chemotherapy with Adr or taxol.

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.

Studies on the relationship between estrogen receptor content, glutathione S-transferase pi expression, and induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin and drug resistance in human breast cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces both phase I and phase II drug-metabolizing enzymes in rodent liver and hepatoma cell lines and this induction is mediated by the aryl hydrocarbon (Ah) receptor. Induction of CYP1A1 by TCDD in human breast cancer cells has been reported and results of several studies suggest that the estrogen receptor (ER) may be required for Ah responsiveness. This study investigates the induction of GST pi by TCDD in human breast cancer cells and the role of the ER in mediating this response. TCDD did not induce chloramphenicol acetyl transferase (CAT) activity in ER positive (ER+) MCF-7 and ER- MDA-MB-468 and MDA-MB-231 human breast cancer cell lines transiently transfected with GST pi (human) or GSTP (rat) promoter-reporter constructs containing the -291/+36 and -2.9/+59 region, respectively, of the GST pi and GSTP gene promoters. Furthermore, TCDD did not induce GST pi or GSTP in MDA-MB-468 and MDA-MB-231 human breast cancer cells stably transfected with the ER. RT-PCR confirmed that GST pi mRNA levels were low in ER+ MCF-7 cells and high in ER- MDA-MB-468 and MDA-MB-231 cells; however, in MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER GST pi mRNA levels remained elevated and were not inducible. MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER exhibited increased GST activity and decreased GSH content compared to wild-type cells; however, in MDA-MB-468 cells stably transfected with ER, the susceptibility to doxorubicin, ellipticine, chlorambucil, malphalan, or cisplatin was similar to that observed in wild-type cells. Adriamycin accumulation was similar in wild-type and ER stably transfected cells and verapamil did not affect this response, suggesting that ER expression did not influence p-glycoprotein activity. Taken together these data suggest that not all GST isoforms are responsive to TCDD and stable transfection of ER- cells with ER is not sufficient to restore the ER+ phenotype in some breast cancer cell lines.

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.

Expression of drug resistance proteins in breast cancer, in relation to chemotherapy

Drug resistance plays an important role in chemotherapy failure in breast cancer. We studied the expression of MDR1, MRP, LRP, DNA topoisomerases, p53 and Ki-67 in different groups of breast cancer patients in relation to chemotherapy. Tissues from 6 normal breasts and 20 primary operable, 40 locally advanced and 10 anthracycline-resistant metastatic breast cancers were assessed. Sequential samples of the same patient were available from 17 patients with locally advanced breast cancer undergoing neo-adjuvant chemotherapy and in 7 metastatic patients undergoing paclitaxel treatment. Protein expression was investigated by immunohistochemistry. Significantly higher protein expression was observed for Pgp, Ki-67 and p53 in the locally advanced breast cancers than in primary operable breast cancers. No other significant differences in protein expression were found among the 3 breast cancer groups. Expression of none of the markers that could be assessed (Pgp, MRP, LRP, p53 and Ki-67) in locally advanced breast cancer had predictive value for pathological response. Interestingly, after chemotherapy a significant decrease in percentage of Ki-67 positive tumor cells was observed, whereas the other markers did not vary substantially. Furthermore, considering all breast cancer samples, a cumulative dose of doxorubicin >400 mg/m2 inversely correlated with Ki-67 positivity. However, 2 patients with a pathological complete remission had only 5-10% Ki67-positive tumor cells before chemotherapy, indicating that Ki67 negativity itself is not responsible for chemoresistance. In conclusion, none of the known proteins related to multidrug resistance predicted response to chemotherapy in breast cancer, and resistant clones left behind generally had a low proliferation rate.

In vivo drug-selectable genes: a new concept in gene therapy

Chemoresistance genes, initially considered to be a major impediment to the successful treatment of cancer, may become useful tools for gene therapy of cancer and of genetically determined disorders. Various target cells are rendered resistant to anticancer drugs by transfer of chemoresistance genes encoding P-glycoprotein, the multidrug resistance-associated protein-transporter, dihydrofolate reductase, glutathione-S-transferase, O6-alkylguanine DNA alkyltransferase, or aldehyde reductase. These genes can be used for selection in vivo because of the pharmacology and pharmacokinetics of their substrates. In contrast, several other selectable marker genes conferring resistance to substrates like neomycin or hygromycin can only be utilized in tissue culture. Possible applications for chemoresistance genes include protection of bone marrow and other organs from adverse effects caused by the toxicity of chemotherapy. Strategies have also been developed to introduce and overexpress nonselectable genes in target cells by cotransduction with chemoresistance genes. Thereby expression of both transgenes can be increased following selection with drugs. Moreover, treatment with chemotherapeutic agents should restore transgene expression when or if expression levels decrease after several weeks or months. This approach may improve the efficacy of somatic gene therapy of hematopoietic disorders which is hampered by low or unstable gene expression in progenitor cells. In this article we review preclinical studies in tissue culture and animal models, and ongoing clinical trials on transfer of chemoresistance genes to hematopoietic precursor cells of cancer patients.

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.

Hydroxyurea Did Not Enhance the Clinical Response to Vinblastine in Patients with Anthracycline-Resistant Metastatic Breast Cancer

Background

Vinblastine is commonly used in metastatic breast cancer after anthracycline failure. The response rate to vinblastine is approximately 20%, with short duration of response. In vitro studies have shown that the addition of hydroxyurea resulted in increased accumulation of vinblastine in tumor cells and in loss of double minutes. We evaluated the combination of vinblastine and hydroxyurea in patients with anthracycline-resistant metastatic breast cancer.

Patients and Methods

Fourteen assessable patients with metastatic breast cancer were entered in the study. All patients had progressed on anthracyclines or progressed within 8 months of stopping anthracyclines. Patients received hydroxyurea (500 mg orally) every Monday, Wednesday and Friday starting one week before the first course of chemotherapy and continuing throughout treatment until disease progression. Vinblastine (6 mg/m2) was given intravenously every 21 days.

Results

The median number of courses for vinblastine was 3.5 (range, 1-6). Three patients had partial responses in soft tissue metastases (21%). Four patients had stable disease. Four patients had > grade 2 neutropenia, and 1 patient had grade 4 thrombocytopenia. There were 2 cases of grade 3 constipation, 2 of grade 3 nausea, and 1 each of grade 2 neuropathy and myalgia. There was no treatment-related mortality.

Conclusions

Low-dose hydroxyurea in combination with vinblastine has a 21% response rate in metastatic breast cancer after anthracycline failure. Toxicity was mild and generally reversible. At the adopted dose schedule of hydroxyurea, the antitumor activity of vinblastine in anthracycline-resistant metastatic breast cancer did not appear to be enhanced.

Failure to induce resistance to cytotoxic drugs in normal lymphocytes

Lymphocytes from patients who had received chemotherapy for lung cancer were examined for evidence of drug resistance using an in vitro assay for sensitivity to the effects of chlorambucil and etoposide. There was no evidence of induced resistance to the effects of chlorambucil or etoposide in the patients' lymphocytes when compared to the sensitivity of the normal control subjects' lymphocytes. In four patients, in whose lymphocytes sensitivity to chlorambucil was measured before and after a course of treatment, there was no significant change in the in vitro drug sensitivity. These findings are in contrast to those made previously using the lymphocytes of patients with chronic lymphocytic leukaemia and indicate that acquired drug resistance is a property of malignant cells and is not inducible in normal lymphocytes.

p53 and P-glycoprotein are often co-expressed and are associated with poor prognosis in breast cancer

Expression of both P-glycoprotein (P-gp) and mutant p53 have recently been reported to be associated with poor prognosis of breast cancer. The expression of P-gp is associated in vitro and in vivo with cross-resistance to several anti-cancer drugs. p53 plays a regulatory role in apoptosis, and mutant p53 has been suggested to be involved in drug resistance. Interestingly, in vitro experiments have shown that mutant p53 can activate the promoter of the MDR1 gene, which encodes P-gp. We investigated whether p53 and P-gp are simultaneously expressed in primary breast cancer cells and analysed the impact of the co-expression on patients prognosis. Immunohistochemistry was used to investigate P-gp expression (JSB-1, C219) and nuclear p53 accumulation (DO-7) in 20 operable chemotherapy untreated and 30 locally advanced breast cancers undergoing neoadjuvant chemotherapy with doxorubicin and cyclophosphamide. Double immunostaining showed that P-gp expression and nuclear p53 accumulation often occur concomitantly in the same tumour cells. A correlation between p53 and P-gp expression was found in all 50 breast cancers (P = 0.003; Fisher's exact test). P-gp expression, nuclear p53 accumulation, and co-expression of p53 and P-gp were more frequently observed in locally advanced breast cancers than in operable breast cancers (P = 0.0004, P = 0.048; P = 0.002 respectively. Fisher's exact test). Co-expression of p53 and P-gp was the strongest prognostic factor for shorter survival by multivariate analysis (P = 0.004) in the group of locally advanced breast cancers (univariate analysis: P = 0.0007). Only 3 out of 13 samples sequentially taken before and after chemotherapy displayed a change in P-gp or p53 staining. In conclusion, nuclear p53 accumulation is often associated with P-gp expression in primary breast cancer, and simultaneous expression of p53 and P-gp is associated with shorter survival in locally advanced breast cancer patients. Co-expression of P-gp and mutant p53 belong to a series of molecular events resulting in a more aggressive phenotype, drug resistance and poor prognosis.

The effects of cyclosporin A, tamoxifen, and medroxyprogesterone acetate on the enhancement of adriamycin cytotoxicity in primary cultures of human breast epithelial cells

Adriamycin (Adr), the single most active agent used in the treatment of breast cancer, may become ineffective as treatment progresses due to the development of multidrug resistant (MDR) tumors. A major mechanism associated with MDR is increased P-glycoprotein (Pgp) expression. This study examined the abilities of the anti-estrogen tamoxifen (TAM) and the progestin medroxyprogesterone acetate (MPA) as well as cyclosporin A (CsA), a known resistance modifier, to enhance the cytotoxic effects of Adr on human breast epithelial cells (HBEC) in primary culture. Pgp and estrogen receptor (ER) expression were determined in each of the cultures by immunocytochemical assays using the monoclonal antibodies C219 and H222 Sp gamma, respectively. The Adr-sensitive, Pgp-, ER+ MCF-7 cell line and the Adr-resistant, Pgp+, ER- MCF7-AdrR cell line were used as controls. Primary cultures were categorized as HBEC from tissues with or without previous chemotherapy. Pgp was detected in 1 of the 15 cell cultures from tissues without previous chemotherapy and in 5 of the 6 cell cultures from tissues previously exposed to chemotherapy. Incubation with either CsA or MPA plus Adr enhanced Adr toxicity in Pgp+ but not Pgp- cell cultures, whereas TAM had no effect on the sensitivity of any of the cultures. Of the 21 primary cultures of HBEC, 3 were ER+. There was no correlation between the enhancement of Adr cytotoxicity and ER status. The data suggest that MPA as well as CsA may be useful as modifying agents in overcoming Pgp-associated multidrug resistance.

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-mediated multidrug resistance: experimental and clinical strategies for its reversal

The study of the cellular, biochemical, and molecular biology and pharmacology of MDR has provided one of the most active and exciting areas within cancer research and one that holds great promise for translation into clinical benefit. While convincing evidence for the functional role of P-gp in mediating clinical drug resistance in humans remains elusive, studies of the clinical expression of P-gp and trials of chemosensitizers with cancer chemotherapy suggest "resistance modification" strategies may be effective in some tumors with intrinsic or acquired drug resistance. However, even if P-gp-associated MDR proves to be a relevant and reversible cause of clinical drug resistance, numerous problems remain to be solved before effective clinical chemosensitization may be achieved. Such factors as absorption, distribution, and metabolism; the effect of chemosensitizers on chemotherapeutic drug clearance; toxicity to normal tissues expressing P-gp; and the most efficacious modulator regimens all remain to be defined in vivo. Clearly, the identification of more specific, potent, and less clinically toxic chemosensitizers for clinical use remains critical to the possible success of this approach. Nonetheless, the finding that a number of pharmacological agents can antagonize a well-characterized form of experimental drug resistance provides promise for potential clinical applications. Further study of chemosensitizers in humans and the rational design of novel chemosensitizers with improved activity should define the importance of MDR in clinically resistant cancer.