Expression of P-glycoprotein in breast cancer tissue and in vitro resistance to doxorubicin and vincristine

Diethylhexyl Phthalate and Bisphenol A Promote Vincristine and Tamoxifen Resistance in Vitro

Environmental estrogen active compounds are strong determinants of estrogen receptor (ER)-positive breast cancers, and increased evidence indicates their contribution to chemotherapy resistance. In the current study, the efficacy of vincristine and tamoxifen, with the presence of diethylhexyl phthalate (DEHP) and bisphenol A (BPA) and the possible involvement of estrogen and estrogen receptor-related mechanisms, was evaluated in an ER+ mammary tumor cancer cell line, MCF-7. Chemotherapeutics tamoxifen as an estrogen receptor modulator and vincristine as an antimitotic compound were selected for evaluation against the presence of common endocrine disrupters. BPA and DEHP preincubation at their proliferative concentrations for 4 h was found to decrease the cytotoxicity of vincristine. mRNA and protein expression of ESR1 and ESR 2 were decreased by vincristine, while this decrease was reversed by DEHP and BPA. Both BPA and DEHP were able to interfere with the cytotoxic activity of vincristine against MCF-7 cells through ESR1 and ESR2. This study provides in vitro toxicological evidence for vincristine resistance and its relation to estrogen active environmental pollutants in ER+ breast cancer cells.

P-Glycoprotein and Breast Cancer Resistance Protein in Canine Inflammatory and Noninflammatory Grade III Mammary Carcinomas

P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) expression are frequently related to multidrug resistance (MDR) in neoplastic cells. Canine inflammatory and grade III noninflammatory mammary carcinomas (IMC and non-IMC) are aggressive tumors that could benefit from chemotherapy. This study describes the immunohistochemical detection of P-gp and BCRP in 20 IMCs and 18 non-IMCs from dogs that had not received chemotherapy. Our aim was to determine if P-gp and BCRP expression was related to the "inflammatory" phenotype, to establish a basis for future studies analyzing the response to chemotherapy in dogs with highly malignant mammary cancer. Immunolabeling was primarily membranous for P-gp with a more intense labeling in emboli, and immunolabeling was membranous and cytoplasmic for BCRP. P-gp was expressed in 17 of 20 (85%) IMCs compared to 7 of 18 (39%) non-IMCs (P = 0.006). BCRP was expressed within emboli in 15 of 19 (79%) emboli in IMC, 12 of 15 (80%) primary IMCs, and 12 of 18 (67%) non-IMCs, without statistically significant differences (P > .05). All IMCs and 67% of non-IMCs expressed at least 1 of the 2 transporters, and 63% (12/19) of IMCs and 39% (7/18) of non-IMCs expressed both P-gp and BCRP. P-gp and BCRP evaluation might help select patients for chemotherapy. P-gp, expressed in a significantly higher percentage of IMCs vs non-IMCs, might play a specific role in the chemoresistance of IMC.

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.

Sweat but no gain: inhibiting proliferation of multidrug resistant cancer cells with "ersatzdroges"

ATP-binding cassette (ABC) drug transporters consuming ATPs for drug efflux is a common mechanism by which clinical cancers develop multidrug resistance (MDR). We hypothesized that MDR phenotypes could be suppressed by administration of "ersatzdroges," nonchemotherapy drugs that are, nevertheless, ABC substrates. We reasoned that, through prolonged activation of the ABC pumps, ersatzdroges will force MDR cells to divert limited resources from proliferation and invasion thus delaying disease progression. We evaluated ABC substrates as ersatzdroge by comparing their effects on proliferation and survival of MDR cell lines (MCF-7/Dox and 8226/Dox40) with the effects on the drug-sensitive parental lines (MCF-7 and 8226/s, respectively) in glucose-limited condition. The changes in glucose and energy demands were also examined in vitro and in vivo. MCF-7/Dox showed higher ATP demand and susceptibility to glucose resource limitation. Ersatzdroges significantly decreased proliferation of MCF-7/Dox when the culture media contained physiological glucose concentrations (1.0 g/L) or less, but had no effect on MCF-7. Similar evidence was obtained from 8226/Dox40 and 8226/s comparison. In vivo 18F-FDG-PET imaging demonstrated that glucose uptake was increased by systemic administration of an ersatzdroge in tumors composed of MDR. These results suggest that administration of ersatzdroges, by increasing the metabolic cost of resistance, can suppress proliferation of drug-resistance phenotypes. This provides a novel and relatively simple application model of evolution-based strategy, which can exploit the cost of resistance to delay proliferation of drug-resistant cancer phenotypes. Furthermore, suggested is the potential of ersatzdroges to identify tumors or regions of tumors that express the MDR phenotype.

Deconstructing breast cancer cell biology and the mechanisms of multidrug resistance

Cancer complexity constantly challenges the way that clinicians manage breast cancer therapy. Tumor heterogeneity and intratumoral stroma characteristics allow cells with different phenotypes and deregulated apoptotic, proliferative and migration abilities to co-exist contributing to a disappointing therapeutic response. While new approaches are being associated with conventional chemotherapy, such as hormonal therapy or target monoclonal antibodies, recurrence and metastasization are still observed. Membrane transporters are the cell's first line of contact with anticancer drugs having a major role in multidrug resistance events. This structural-based activity enables the cell to be drug-resistant by decreasing drug intracellular concentration through an efflux-transport mechanism, mainly associated with overexpression of ATP-binding cassette (ABC) proteins. This review focuses on some of the important structural and biological properties of the malignant cell and tumor microenvironment, addressing the role of the membrane ABC transporters in therapeutic outcomes, and highlighting related molecular pathways that may represent meaningful target therapies.

Expression of multidrug resistance membrane transporter (Pgp) and p53 protein in canine mammary tumours

The aim of this study was to determine the expression rate of P-glycoprotein (Pgp), a multidrug resistance marker and the p53 tumour-suppressor protein in canine mammary tumours. A total of 30 tumours were examined in parallel to patient history. The tumours were allotted to four groups: tubulopapillar carcinomas, complex carcinomas, benign tumours, and other malignant tumours. A monoclonal mouse antibody (C494) was used for the immunohistochemical evaluation of Pgp and a polyclonal rabbit antibody for p53. We found that the intact ductal epithelium and connective tissue showed pronounced Pgp expression. The most intensive staining was detected in tubulopapillar carcinomas for both Pgp and p53. The expression rate of Pgp and p53 differed significantly between tubulopapillar carcinoma and complex carcinoma, and between tubulopapillar carcinoma and benign mammary tumour, respectively. The expressions of Pgp and p53 highly correlated statistically; therefore, both can determine malignancy in a similar manner. In the case of tubulopapillar carcinomas, more relapsed tumours occurred than in relation to complex carcinomas and other malignant tumours. Pgp expression rate was proportional to the probability of the tumour becoming recidivant postoperatively, as well. These results suggest that routine evaluation of Pgp expression in canine mammary tumours may be prognostically helpful.

Evolutionary approaches to prolong progression-free survival in breast cancer

Many cancers adapt to chemotherapeutic agents by upregulating membrane efflux pumps that export drugs from the cytoplasm, but this response comes at an energetic cost. In breast cancer patients, expression of these pumps is low in tumors before therapy but increases after treatment. While the evolution of therapeutic resistance is virtually inevitable, proliferation of resistant clones is not, suggesting strategies of adaptive therapy. Chemoresistant cells must consume excess resources to maintain resistance mechanisms, so adaptive therapy strategies explicitly aim to maintain a stable population of therapy-sensitive cells to suppress growth of resistant phenotypes through intratumoral competition. We used computational models parameterized by in vitro experiments to illustrate the efficacy of such approaches. Here, we show that low doses of verapamil and 2-deoxyglucose, to accentuate the cost of resistance and to decrease energy production, respectively, could suppress the proliferation of drug-resistant clones in vivo. Compared with standard high-dose-density treatment, the novel treatment we developed achieved a 2-fold to 10-fold increase in time to progression in tumor models. Our findings challenge the existing flawed paradigm of maximum dose treatment, a strategy that inevitably produces drug resistance that can be avoided by the adaptive therapy strategies we describe.

Taxane resistance in breast cancer: mechanisms, predictive biomarkers and circumvention strategies

BACKGROUND

Taxanes are established in the treatment of metastatic breast cancer (MBC) and early breast cancer (EBC) as potent chemotherapy agents. However, their therapeutic usefulness is limited by de-novo refractoriness or acquired resistance, which are common drawbacks to most anti-cancer cytotoxics. Considering that the taxanes will remain principle chemotherapeutic agents for the treatment of breast cancer, we reviewed known mechanisms of resistance in with an outlook of optimizing their clinical use.

METHODS

We searched the PubMed and MEDLINE databases for articles (from inception through to 9th January 2012; last search 10/01/2012) and journals known to publish information relevant to taxane chemotherapy. We imposed no language restrictions. Search terms included: cancer, breast cancer, response, resistance, taxane, paclitaxel, docetaxel, taxol. Due to the possibility of alternative mechanisms of resistance all combination chemotherapy treated data sets were removed from our overview.

RESULTS

Over-expression of the MDR-1 gene product Pgp was extensively studied in vitro in association with taxane resistance, but data are conflicting. Similarly, the target components microtubules, which are thought to mediate refractoriness through alterations of the expression pattern of tubulins or microtubule associated proteins and the expression of alternative tubulin isoforms, failed to confirm such associations. Little consensus has been generated for reported associations between taxane-sensitivity and mutated p53, or taxane-resistance and overexpression of Bcl-2, Bcl-xL or NFkB. In contrary sufficient in vitro data support an association of spindle assembly checkpoint (SAC) defects with resistance. Clinical data have been limited and inconsistent, which relate to the variety of methods used, lack of standardization of cut-offs for quantitation, differences in clinical endpoints measured and in methods of tissue collection preparation and storage, and study/patient heterogeneity. The most prominent finding is that pharmaceutical down-regulation of HER-2 appears to reverse the taxane resistance.

CONCLUSIONS

Currently no valid practical biomarkers exist that can predict resistance to the taxanes in breast cancer supporting the principle of individualized cancer therapy. The incorporation of several biomarker analyses into prospectively designed studies in this setting are needed.

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.

Two different docetaxel resistant MCF-7 sublines exhibited different gene expression pattern

The objective of the present study was to investigate gene expression pattern of two docetaxel resistant MCF-7 breast carcinoma sublines step wisely selected in 30 and 120 nM docetaxel. Cell proliferation assay was performed in order to demonstrate development of docetaxel resistance. cDNA microarray analysis was performed using Affymetrix(®) Human Genome U133 Plus 2.0 Arrays in duplicate experiments. Quantitative and semi-quantitative gene expression analysis was also performed to confirm gene expression analysis for selected genes. XTT results demonstrated that 30 (MCF-7/30nM DOC) and 120 nM (MCF-7/120nM DOC) docetaxel selected cells were 13- and 47-fold resistant, respectively. cDNA microarray analysis demonstrated that expression profiles of MCF-7 and MCF-7/30nM DOC were more similar to each other where expression profile of MCF-7/120nM DOC was different as examined by line graphs and scatter plots. 2,837 and 4,036 genes were significantly altered in 30 and 120 nM docetaxel resistant sublines, respectively. Among these, 849 genes were altered in common in two docetaxel resistant sublines. Antiapoptotic gene expression (e.g., Bcl-2 and APRIL) were noticeably altered in MCF-7/30nM DOC. However, docetaxel resistance in MCF-7/120nM DOC were more complicated with the involvement of ECM related gene expression, cytokine and growth factor signaling, ROS metabolism and EMT related gene expression together with higher level of MDR1 expression. Expression profiles in 30 and 120 nM docetaxel resistant sublines changed gradually with increasing resistance index. Drug resistance development seems to be step wise event in MCF-7 cells.

Consequences of cell-to-cell P-glycoprotein transfer on acquired multidrug resistance in breast cancer: a cell population dynamics model

BACKGROUND

Cancer is a proliferation disease affecting a genetically unstable cell population, in which molecular alterations can be somatically inherited by genetic, epigenetic or extragenetic transmission processes, leading to a cooperation of neoplastic cells within tumoural tissue. The efflux protein P-glycoprotein (P-gp) is overexpressed in many cancer cells and has known capacity to confer multidrug resistance to cytotoxic therapies. Recently, cell-to-cell P-gp transfers have been shown. Herein, we combine experimental evidence and a mathematical model to examine the consequences of an intercellular P-gp trafficking in the extragenetic transfer of multidrug resistance from resistant to sensitive cell subpopulations.

METHODOLOGY AND PRINCIPAL FINDINGS

We report cell-to-cell transfers of functional P-gp in co-cultures of a P-gp overexpressing human breast cancer MCF-7 cell variant, selected for its resistance towards doxorubicin, with the parental sensitive cell line. We found that P-gp as well as efflux activity distribution are progressively reorganized over time in co-cultures analyzed by flow cytometry. A mathematical model based on a Boltzmann type integro-partial differential equation structured by a continuum variable corresponding to P-gp activity describes the cell populations in co-culture. The mathematical model elucidates the population elements in the experimental data, specifically, the initial proportions, the proliferative growth rates, and the transfer rates of P-gp in the sensitive and resistant subpopulations.

CONCLUSIONS

We confirmed cell-to-cell transfer of functional P-gp. The transfer process depends on the gradient of P-gp expression in the donor-recipient cell interactions, as they evolve over time. Extragenetically acquired drug resistance is an additional aptitude of neoplastic cells which has implications in the diagnostic value of P-gp expression and in the design of chemotherapy regimens.

Pegylated phosphotidylethanolamine inhibiting P-glycoprotein expression and enhancing retention of doxorubicin in MCF7/ADR cells

The failure of the clinical treatment of cancer patients is often attributed to drug resistance of the tumor to chemotherapeutic agents. P-glycoprotein (P-gp) contributes to drug resistance via adenosine 5'-triphosphate (ATP)-dependent drug efflux pumps and is widely expressed in many human cancers. Up to date, a few of nanomaterials have shown the effects on P-gp function by different ways. To study the mechanism of the increased cytotoxicity of doxorubicin (DOX) by pegylated phosphotidylethanolamine (PEG-PE) in drug-resistant cancer cells, a series of in vitro cell assays were performed, including identification of P-gp function, quantitative studies on uptake and efflux of DOX, inhibitory effects of blank PEG-PE micelles on mRNA and protein levels of P-gp, and intracellular ATP content alteration. Finally, combining MDR-1 RNA interference (siRNA) with DOX encapsulated in PEG-PE micelles (M-DOX) to improve cytotoxicity of DOX was also studied. M-DOX showed fivefold lower the concentration that caused 50% killing tumor cell than that of free DOX in the P-gp-overexpressing MCF-7 breast cancer (MCF-7/ADR) cells. M-DOX enhanced the cellular uptake and retention of DOX in MCF-7/ADR cells. PEG-PE block molecules can inhibit P-gp expression through downregulating MDR-1 gene. Cytotoxicity of M-DOX was further improved by knocking down the MDR-1 gene using siRNA in the multidrug-resistant cells. We conclude that the increased cytotoxicity of DOX encapsulated in PEG-PE micelle is due to the reduced P-gp expression by PEG-PE block molecules, and accordingly enhancing the cellular accumulation of DOX. To overcome drug resistance of tumor cells, the combination of nanotechnology and biotechnology could be an effective strategy such as PEG-PE formed micelles and siRNA.

Drug resistant MCF-7 cells exhibit epithelial-mesenchymal transition gene expression pattern

PURPOSE

Multidrug resistance is resistance to structurally unrelated anticancer agents. Large-scale expression analysis by using high-density oligonucleotide microarrays may provide information about new candidate genes contributing to MDR. This study demonstrates alterations in expression levels of several genes related to epithelial-mesenchymal transition (EMT) in paclitaxel, docetaxel, and doxorubicin resistant MCF-7 cells.

METHODS

Resistant sublines were developed from sensitive cells by selective paclitaxel, docetaxel, and doxorubicin applications in dose increments. cDNA microarray analysis was performed for sensitive and resistant cells. Genes having statistically significantly altered expression levels more than two-folds compared to the sensitive MCF-7 cells were considered. Genes encoding the determinants of the EMT were evaluated. Immunostaining was performed for relevant protein expressions.

RESULTS

Key elements of EMT were transcriptionally activated in paclitaxel, docetaxel and doxorubicin resistant sublines. One of the upregulated genes was Slug, a transcription factor of E-cadherin, occludin repression, and N-cadherin, vimentin activation. Decreased estrogen receptor-α (ER) levels in cells might have stimulated Slug expression. Increased expression levels of TGF-beta receptor2 (TGFBR2) together with SMAD3 might have stimulated EMT in resistant cells. Immunocytochemistry results confirmed loss of ER and E-cadherin, together with high vimentin levels.

CONCLUSIONS

EMT was induced in multidrug resistant MCF-7 cells indicating a relationship of this process and drug resistance. However, the relationship of each specific component of EMT with drug resistance requires further analysis.

Development of radioresistance in drug resistant human MCF-7 breast cancer cells

Background and purpose: Radiotherapy is used for the treatment of malignant tumours, and may be used as the primary therapy. It is also common to combine radiotherapy with surgery, chemotherapy, hormone therapy or some combination of them. Even if the tumour is treated intensively, women diagnosed with breast cancer may develop a recurrence. Most recurrences may be in the form of distant metastases, development of multi-drug resistance phenotype or both together. This study demonstrated that some of the multi-drug resistant cancer cells may also become radioresistant.

Materials and Methods: Chemoresistance in paclitaxel (MCF-7/Pac), docetaxel (MCF-7/Doc), vincristine (MCF-7/Vinc), doxorubicin (MCF-7/Dox) and zoledronic acid (MCF-7/Zol) resistant MCF-7 cells were demonstrated by XTT assay. MDR1 gene expression was detected by real-time PCR in human MCF-7 breast cancer cells. Drug resistant and sensitive cells were exposed to γ-radiation and development of radioresistance was investigated.

Results: Results have indicated that paclitaxel, docetaxel, vincristine, doxorubicin and zoledronic acid–selected cells gained varying degrees of resistance to their selective drugs when compared with original MCF-7/S. MCF-7/Pac, MCF-7/Doc, MCF-7/Vinc and MCF-7/Dox cells have all acquired MDR1 expression. Among the resistant sub-lines, MCF-7/Pac and MCF-7/Doc cells were significantly cross-resistant to irradiation compared to the sensitive cells.

Conclusion: MCF-7/Pac and MCF-7/Doc cell lines were found radioresistant to γ-radiation. On the contrary, doxorubicin, vincristine and zoledronic acid resistant cancer cells were still sensitive to radiation.

Association of C3435T single-nucleotide polymorphism of MDR1 gene with breast cancer in an Iranian population

The human multidrug resistance gene 1 (MDR1) encodes a plasma membrane, P-glycoprotein (Pgp), which functions as the transmembrane efflux pump for various structurally unrelated anticancer agents and toxins. Polymorphisms in the MDR1 gene may have an impact on the expression and function of Pgp, thereby influencing the susceptibility to various diseases, including cancer. Recently, a silent C3435T polymorphism in exon 26 of MDR1 has been reported to be associated with decreased expression of Pgp in TT genotype carriers and thus it may alter the physiological protective role of Pgp and influence disease risk. To evaluate the association of this polymorphism with breast cancer, 106 patients with breast cancer and 77 healthy controls were enrolled in this study. They were visited at two centers during a 1-year period (2006-2007). Data about the risk factors of breast cancer were collected using questionnaires. DNA of the whole-blood sample was extracted, and the polymorphic fragment was amplified by polymerase chain reaction using specific primers. The C3435T polymorphism was detected by the restriction fragment length polymorphism method. There were no significant differences in genotype (p = 0.744) and allele (p = 0.590) frequencies between patients and control subjects. Moreover, distribution of the breast cancer patients' risk factors was not different among CC, CT, and TT genotypes. Our results suggest that C3435T MDR1 polymorphism was not associated with the susceptibility to breast cancer in the population studied.

Chemotherapy compared with biochemotherapy for the treatment of metastatic melanoma: a meta-analysis of 18 trials involving 2,621 patients

PURPOSE

To assess the effect of adding interferon-alpha (IFN) +/- interleukin-2 (IL-2) to chemotherapy in patients with metastatic melanoma. METHODS A published data meta-analysis of trials of biochemotherapy versus chemotherapy in patients with metastatic melanoma was undertaken. End points evaluated were rates of partial response (PR), complete response (CR) and overall (partial + complete) response (OR); response duration; progression-free survival; overall survival (OS); and toxicity. The only subgroup analysis performed was by type of immunotherapy, with trials divided according to whether IFN only or IFN and IL-2 were administered in the biochemotherapy arm.

RESULTS

Eighteen randomized trials were identified: 11 trials of chemotherapy +/- IFN and seven trials of chemotherapy +/- IFN and IL-2. More than 2,600 patients were entered onto the trials, with 555 responses and 2,039 deaths. There was a clear benefit for biochemotherapy for PR (odds ratio = 0.66; 95% CI, 0.53 to 0.82; P = .0001), CR (odds ratio = 0.50; 95% CI, 0.35 to 0.73; P = .0003) and OR (odds ratio = 0.59; 95% CI, 0.49 to 0.72; P < .00001). For OR, these benefits were significant for both the IFN (odds ratio = 0.60; 95% CI, 0.46 to 0.79; P = .0002) and IFN + IL-2 (odds ratio = 0.58; 95% CI, 0.44 to 0.77; P = .0001) subgroups. In contrast, there was no benefit overall in OS (odds ratio = 0.99; 95% CI, 0.91 to 1.08; P = .9), but there was evidence of heterogeneity of treatment effect between the individual trials (P = .006).

CONCLUSION

This meta-analysis provides a comprehensive summary of all the data currently available, and shows that although biochemotherapy clearly improves response rates, this does not appear to translate into a survival benefit.

Trabectedin (ET-743, Yondelis) is a substrate for P-glycoprotein, but only high expression of P-glycoprotein confers the multidrug resistance phenotype

Trabectedin (ET-743, Yondelis) is a novel anticancer drug currently undergoing phase II and III investigations. There are various and conflicting reports whether trabectedin is a substrate for P-glycoprotein (P-gp), an important factor in drug disposition and multi-drug resistance (MDR). We have now unambiguously shown that trabectedin is a P-gp substrate by investigating vectorial transport over monolayers of LLC-PK1 pig kidney and Madine-Darby Canine kidney (MDCK) cells and the mdr1a and/or MDR1 transfected subclones. We further characterized the cytotoxic effects and cellular accumulation of trabectedin in these cell lines as well as in a panel of other cell lines with high or moderate expression levels of P-gp. Trabectedin displayed the typical MDR phenotype only in highly P-gp expressing cell lines, but not in cell lines with expression levels more closely conforming to clinical samples, suggesting that P-gp will not confer resistance to trabectedin in cancer patients.

YB-1 is upregulated during prostate cancer tumor progression and increases P-glycoprotein activity

BACKGROUND

Currently, the main obstacle to curing advanced prostate cancer is development of androgen independence (AI), where malignant cells acquire the ability to survive in the absence of androgens. Our initial experimental approach used cDNA microarrays to characterize changes in gene expression in the LNCaP human prostate tumor model during progression to AI. The transcription factor Y-box binding protein (YB-1) was shown to be one of the genes upregulated. We focused on increased YB-1 expression during progression in clinical specimens, and further examined one of its downstream targets, P-glycoprotein (P-gp).

METHODS

Northern blot analysis was performed on LNCaP tumor series, as well as immunohistochemical analyses of human prostate cancer tissue samples. YB-1 was transiently transfected and transport analysis were performed to analyze P-gp efflux activity.

RESULTS

YB-1 expression is markedly increased during benign to malignant transformation and further following androgen ablation. In addition, increased YB-1 expression after castration in the LNCaP model is linked to upregulation of P-gp. We demonstrate that YB-1 upregulates P-gp activity resulting in a 40% intracellular decrease in the P-gp substrate vinblastine. We have also found that P-gp increases the efflux of the endogenous androgen, dihydrotestosterone (DHT), from prostate cells and leads to decreased androgen regulated gene expression.

CONCLUSIONS

We hypothesize that early in prostate cancer progression, increased expression of YB-1 may increase P-gp activity which may in turn lower androgen levels in the prostate tumor cells. Suppression of androgen levels may activate cell survival pathways and lead to an adaptive survival advantage of androgen independent prostate cancer cells following androgen ablation therapy.

Combined treatment of Bcl-2 antisense oligodeoxynucleotides (G3139), p-glycoprotein inhibitor (PSC833), and sterically stabilized liposomal doxorubicin suppresses growth of drug-resistant growth of drug-resistant breast cancer in severely combined immunodeficient mice

We studied the possibility of increasing sensitization of drug-resistant MDA435/LCC6 multidrug-resistant (MDR) human breast cancer cells to doxorubicin (DOX) by increasing cellular drug retention with P-glycoprotein (P-gp) inhibitor PSC833 in combination with induction of cell death through down-regulation of Bcl-2 protein using Bcl-2 antisense (G3139). In in vitro cytotoxicity assays, the combination of G3139 with DOX exhibited 40% increased cytotoxicity in both wild-type (WT) and MDR cells. PSC833 increased the cytotoxicity of DOX and Taxol with complete and partial reversal of the resistance of MDR cells to DOX and Taxol, respectively. The presence of G3139 did not increase the cytotoxicity of PSC833 combined with DOX or Taxol in both cell lines. In vivo studies with WT and MDR cell lines transplanted into severely combined immunodeficient mice demonstrated that G3139 (5 mg/kg) was able to suppress the growth of both WT and MDR tumors to an equivalent extent. PSC833 (100 mg/kg) partially restored the sensitivity of resistant tumors to DOX, and the combination of G3139 and PSC833 with liposomal DOX showed maximum growth suppression of MDR tumors compared with individual treatments. The improved efficacy of this treatment was attributed to Bcl-2 antisense-induced apoptosis, combined with cellular retention of DOX in tumor cells via P-gp blockade.

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.

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.

Chemosensitivity of advanced larynx carcinoma cells in vitro and significance of multidrug resistance markers in these tumors

Thirty cases of previously untreated advanced larynx carcinoma were checked for in vitro chemosensitivity and presence of the resistance markers viz. P-glycoprotein (P-gp) glutathione-S-transferase-pi (GST-pi) and protein kinase C (PKC) overexpression. The cytotoxicity testing was done using MTT assay and the resistance markers were checked by immunohistochemical methods using monoclonal antibodies. The drug combinations employed in MIT assay were 5FU* + MTX*, 5FU + cisPt*, 5FU + Mito*, cisPt + Mito and MTX + Mito (*5FU = 5Fluorouracil, MTX-methotrexate, cisPt-cisplatin and Mito = mitomycin C). No statistically significant correlation was observed between resistance to the above drug combinations and presence of the resistance markers under consideration. A statistically significant correlation was observed between node positivity and expression of resistance markers which indicates that presence of one or more of these markers in these tumors may be considered as a negative prognosis marker. CisPt-Mito was found to be the most effective drug combination in vitro, in the cases studied.

Phase II trial of dexverapamil and epirubicin in patients with non-responsive metastatic breast cancer

Agents capable of reversing P-glycoprotein-associated multidrug resistance have usually failed to enhance chemotherapy activity in patients with solid tumours. Based on its toxicity profile and experimental potency, dexverapamil, the R-enantiomer of verapamil, is considered to be promising for clinical use as a chemosensitizer. The purpose of this early phase II trial was to evaluate the effects of dexverapamil on epirubicin toxicity, activity and pharmacokinetics in patients with metastatic breast cancer. A two-stage design was applied. Patients first received epirubicin alone at 120 mg m(-2) i.v. over 15 min, repeated every 21 days. Patients with refractory disease continued to receive epirubicin at the same dose and schedule but supplemented with oral dexverapamil 300 mg every 6 h x 13 doses. The Gehan design was applied to the dexverapamil/epirubicin cohort of patients. Thirty-nine patients were entered on study, 25 proceeded to receive epirubicin plus dexverapamil. Dexverapamil did not increase epirubicin toxicity. The dose intensity of epirubicin was similar when used alone or with dexverapamil. In nine intrapatient comparisons, the area under the plasma concentration-time curve (AUC) of epirubicin was significantly reduced by dexverapamil (mean 2968 vs 1901 microg ml[-1] h[-1], P= 0.02). The mean trough plasma levels of dexverapamil and its major metabolite nor-dexverapamil were 1.2 and 1.5 microM respectively. The addition of dexverapamil to epirubicin induced partial responses in 4 of 23 patients evaluable for tumour response (17%, CI 5-39%, s.e.P 0.079). The remissions lasted 3, 8, 11 and 11+ months. These data suggest that the concept of enhancing chemotherapy activity by adding chemosensitizers may function not only in haematological malignancies but also in selected solid tumours. An increase in the AUC and toxicity of cytotoxic agents does not seem to be a prerequisite for chemosensitizers to enhance anti-tumour activity.

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.

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.

Development and characterisation of novel human multidrug resistant mammary carcinoma lines in vitro and in vivo

Clinical chemotherapy of breast carcinomas must be considered insufficient, mainly due to the appearance of drug resistance. The multidrug resistance (MDR) phenotype, either intrinsically occurring or acquired, e.g., against a panel of different antineoplastic drugs, is discussed in relation to several MDR-associated genes such as the MDR-gene mdr1 encoding the P-glycoprotein (PGP), the MRP gene (multidrug resistance protein) encoding an MDR-related protein or the LRP gene encoding the lung resistance protein. Numerous experimental and clinical approaches aiming at reversing resistance require well-characterised in vitro and in vivo models. The aim of our work was to develop multidrug resistant sublines from human xenotransplanted breast carcinomas, in addition to the broadly used line MCF-7 and its multidrug resistant subline MCF-7/AdrR. MDR was induced in vitro with increasing concentrations of Adriablastin (ADR) for several weeks, resulting in a 3.5- to 35-fold increase in IC50 values using the MTT-test. Cell lines were cross-resistant toward another MDR-related drug, vincristine, but remained sensitive to non-MDR-related compounds such as cisplatin and methotrexate. The resistance toward Adriamycin and vincristine was confirmed in vivo by a lack of tumour growth inhibition in the nude mouse system. Gene expression data for the mdr1/PGP, MRP/MRP and LRP/LRP on both the mRNA (RT-PCR) and the protein levels (immunoflow cytometry) demonstrated that induction of mdr1 gene expression was responsible for the acquired MDR phenotype. Rhodamine efflux data, indicated by PGP overexpression, underlined the development of this MDR mechanism in the newly established breast carcinoma lines MT-1/ADR, MT-3/ADR and MaTu/ADR.

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.

Nuclear localization and increased levels of transcription factor YB-1 in primary human breast cancers are associated with intrinsic MDR1 gene expression

Breast cancers are either primarily resistant to chemotherapy (intrinsic resistance), or respond to chemotherapy but later recur with a multidrug-resistant phenotype because of overexpression of the multidrug transporter P-glycoprotein. The MDR1 gene encoding P-glycoprotein may be transcriptionally regulated by a Y-box transcription factor. We now report that, in multidrug-resistant MCF-7 breast cancer cells, nuclear localization of YB-1 is associated with MDR-1 gene expression. In drug-sensitive MCF-7 cells, however, YB-1 was localized to the cytoplasm. Regulated overexpression of YB-1 in drug-sensitive diploid breast epithelial cells induced MDR-1 gene expression and multidrug resistance. In 27 out of 27 untreated primary breast cancers, YB-1 protein was expressed in the cytoplasm although it was undetectable in normal breast tissue of these patients. In a subgroup of tumors (9/27), however, YB-1 was also localized to the nucleus and, in these cases, high levels of P-glycoprotein were present. These results show that in a subset of untreated primary breast cancers, nuclear localization of YB-1 protein is associated with intrinsic multidrug resistance. Our data show that YB-1 has an important role in controlling MDR1 gene transcription and this finding provides a basis for the analysis of molecular mechanisms responsible for intrinsic multidrug resistance in human breast cancer.

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.

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.

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.

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.

MDA435/LCC6 and MDA435/LCC6MDR1: ascites models of human breast cancer

We have established a novel ascites tumour model (MDA435/LCC6) from the oestrogen receptor-negative, invasive and metastatic MDA-MB-435 human breast cancer cell line. MDA435/LCC6 cells grow as both malignant ascites and solid tumours in vivo in nude mice and nude rats, with a tumour incidence of approximately 100%. Untreated mice develop ascites following i.p. inoculation of 1 x 10(6) cells and have a reproducible life span of approximately 30 days, with all animals dying within a 48 h period. The in vivo response of MDA435/LCC6 ascites to several cytotoxic drugs, including doxorubicin, etoposide (VP-16), BCNU and mitomycin C, closely reflects the activity of these single agents in previously untreated breast cancer patients. MDA435/LCC6 cells also retain the anchorage-dependent and anchorage-independent in vitro growth properties of the parental MDA-MB-435 cells, and can be used in standard in vitro drug screening assays. The drug resistance pattern of the MDA435/LCC6 cells suggests that they may have few active endogenous drug resistance mechanisms. To generate a model for the screening of MDR1-reversing agents, MDA435/LCC6 were transduced with a retroviral vector directing the constitutive expression of the MDR1 cDNA, producing a cell line with a classical MDR1 resistance pattern (MDA435/LCC6MDR1). THese ascites models may be a viable alternative to the murine leukaemia ascites (L1210, P388) and, in conjunction with other breast cancer cell lines, facilitate the in vitro and in vivo screening of new cytotoxic drugs and drug combinations.

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.

Intrapatient comparison of single-agent epirubicin with or without lonidamine in metastatic breast cancer

The aim of this study was to determine if lonidamine (LND) supplementation to single-agent epirubicin (EPI) could reverse anthracycline resistance in patients with metastatic breast cancer. 45 patients with metastatic breast cancer were treated with EPI 120 mg/m2 by intravenous (i.v.) bolus every 3 weeks. Patients who progressed were given the same chemotherapy regimen on day 4 in combination with oral LND, 150 mg on day 1, 300 mg on day 2 and 450 mg on days 3-5. Among the 40 evaluable patients, 6 complete responses (CR) and 14 partial responses (PR) were achieved with EPI treatment alone for an overall response rate of 50%. The median duration of response was 6.5 months. Among the 25 patients treated with EPI+LND, 5 PR (21% of 24 evaluable patients) were observed with a median duration of response of 7 months. The median survival in patients receiving both treatments was 20 months. The survival for all patients was 18 months. The survival of patients receiving LND was not significantly longer than for the other patients. Myelotoxicity was the most common side-effect followed by alopecia, nausea and vomiting, and stomatitis. LND-related toxic effects were mild-to-moderate epigastralgia and myalgia. Anthracycline-related toxicity was the same in the two treatment groups. This study indicates that LND may circumvent clinical resistance to EPI without altering the pattern or severity of the toxicity of this anthracycline. Continued investigation of the clinical modulation of EPI resistance by LND in breast cancer is warranted, hopefully in patients with known multidrug resistance status.

A pilot study of amiodarone with infusional doxorubicin or vinblastine in refractory breast cancer

Increasing evidence suggests that P-glycoprotein (Pgp) expression can mediate drug resistance in refractory breast cancer. We studied 33 patients with refractory breast cancer enrolled in a pilot study of oral amiodarone as a Pgp antagonist given in combination with infusional doxorubicin or vinblastine. Whenever possible, tumors were biopsied and Pgp expression was assayed. Patients received either 60 mg/m2 doxorubicin over 96 h or 8.5 mg/m2 vinblastine over 120 h by continuous intravenous infusion. Beginning with the second cycle of chemotherapy, 600-800 mg amiodarone was given orally each day. Patients who experienced toxicity due to amiodarone but were responding to chemotherapy were placed on quinidine. Partial responses were observed in 9 of 33 patients on study and were sometimes observed after the first cycle of chemotherapy, before amiodarone was given, suggesting that some patients may have responded to treatment because of the infusional schedule. Toxicities were primarily the known side effects of the antineoplastic agents and of amiodarone. The major amiodarone toxicity was gastrointestinal, with nausea, vomiting, anorexia, or diarrhea being noted in 21 patients. Biopsy samples were obtained from 29 patients and in 21 cases, viable tumor tissue was present and the results were interpretable. Of the 21 samples, 9 had Pgp expression as determined by immunohistochemical staining; 12 were considered negative. The presence of Pgp expression was associated with an acceleration of the time to treatment failure. Whereas normal-tissue toxicities related to the combination of a Pgp antagonist with chemotherapy were not observed, amiodarone was associated with too many untoward effects to be utilized as a drug resistance-reversing agent.

Morphonuclear characterization of drug resistance by means of digital cell-image analysis: an in vitro assessment

The prediction of tumor resistance to antineoplastic drugs remains an important challenge in cancer chemotherapy. Several methods have been proposed in this connection, but they present a number of problems such as clinical relevance and applicability. In the present work we put forward an original methodology to assess the drug sensitivity of cancer cells. For this purpose we submitted chemosensitive and chemoresistant cell lines to different anticancer drugs and monitored the cell growth and the drug-induced morphonuclear effects by means of digital cell-image analysis of Feulgen-stained nuclei. The results showed that drug-induced effects at the morphonuclear level correlated statistically with the effects produced at the cell proliferation level. For example, the mean nuclear size value increased as a function of the drugs' efficiency recorded at the cell proliferation level. In the same way, the frequency of large dense chromatin clumps also increased in accordance with the drugs' efficiency. The present work thus demonstrates that digital cell-image analysis can be applied to monitor the efficiency of chemotherapeutic treatment carried out on cell lines in vitro. The present methodology could possibly be used on solid tumors, from which biological material can be obtained serially by means of fine-needle aspiration. As evidence of this, the present methodology can also be applied to hematological cancers.

Reversal of P-glycoprotein-mediated multidrug resistance by pure anti-oestrogens and novel tamoxifen derivatives

In this study the ability of five novel anti-oestrogens [4-iodotamoxifen, pyrrolidino-4-iodotamoxifen, ethyl bromide tamoxifen (EBTx), ICI 164,384 (ICI 164) and ICI 182,780] to alter drug toxicity to multidrug resistant cell lines have been compared. The effect of these compounds on ATP-dependent vinblastine (VBL) transport was also tested using inside-out vesicles (IOV) prepared from highly P-glycoprotein (Pgp)-expressing CCRF-CEM/VBL1000 cells. The pure anti-oestrogen ICI 164 was most effective, enhancing doxorubicin and VBL toxicity to MCF-7Adr cells 25- and 35-fold, respectively, and was also the best inhibitor of ATP-dependent [3H]VBL accumulation by IOV. Pure anti-oestrogens, tamoxifen and iodotamoxifens completely reversed VBL resistance in the mdr1 transfected lung cancer cell line, S1/1.1, where resistance relative to wild-type cells was mediated solely by Pgp. The membrane impermeant tamoxifen derivative EBTx did not modify drug resistance, yet was as effective an inhibitor of VBL accumulation by inside-out Pgp-positive vesicles as tamoxifen. This indicates an intracellular role for tamoxifen and its derivatives in the modulation of Pgp-mediated drug resistance.