Expression of a multidrug resistance gene in human cancers

[Expression of multidrug resistance (MDR)-associated proteins in solid tumors]

The causes of drug resistance in tumor cells vary widely. The present study aims to provide an update of multidrug resistance in tumor cells and, in particular, of multidrug resistance-associated proteins.

Structure-activity relationship of natural and synthetic coumarins inhibiting the multidrug transporter P-glycoprotein

A set of 32 natural and synthetic coumarins were tested in order to evaluate their activity on human leukemic cells (K562/R7) overexpressing P-glycoprotein (P-gp). Their ability to reduce the P-gp-mediated drug efflux of daunorubicin out of cells was evaluated at 10 microM. Four natural compounds, previously isolated from Calophyllum dispar (Clusiaceae) and substituted by a common alpha-(hydroxyisopropyl)dihydrofuran moiety, exhibited a significant inhibitory effect on P-gp when compared to the positive control cyclosporin A. A 3D-quantitative structure-activity relationship (3D-QSAR) analysis of the coumarins was performed using the biological results obtained by comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) of P-gp. Results showed a favorable electrostatic and steric volume, like the alpha-(hydroxyisopropyl)dihydrofuran moiety, beside C(5)-C(6) or C(7)-C(8) positions. In addition, the analysis revealed an important hydrophobic, neutral charge group, like phenyl, in position C(4) on the coumarinic ring.

Multidrug resistance in AIDS-related lymphoma

PURPOSE OF REVIEW

AIDS-related lymphoma has a decreased response rate and poorer prognosis to standard chemotherapy when compared with lymphoma in the non-HIV population. In addition to the known HIV-related and lymphoma-related poor prognostic factors, this review discusses another factor, MDR-1 expression and its impact on response to therapy in patients with AIDS-related lymphoma.

RECENT FINDINGS

There is an increased incidence of de-novo MDR-1 expression in AIDS-related lymphoma compared with lymphoma in the non-HIV settings. MDR-1 expression in AIDS-related lymphoma is associated with poor response to conventional combination chemotherapy. Liposomal encapsulation of doxorubicin when substituted for doxorubicin in the CHOP regimen (cyclophosphamide, doxorubicin, vincristine, prednisone) seems to overcome P-glycoprotein-mediated drug resistance in AIDS-related lymphoma.

SUMMARY

The overexpression of MDR-1 gene product P-glycoprotein is an adverse prognostic factor in AIDS-related lymphoma. Treatment with liposomal encapsulated doxorubicin seems to overcome the P-glycoprotein-related drug resistance. This and other strategies to modulate MDR-1 should be further explored in order to improve success rates in the treatment of AIDS-related lymphoma.

In vivo antitumor effect of the mTOR inhibitor CCI-779 and gemcitabine in xenograft models of human pancreatic cancer

Mammalian target of rapamycin (mTOR) is considered to be a major effector of cell growth and proliferation that controls protein synthesis through a large number of downstream targets. We investigated the expression of the phosphatidylinositol 3'-kinase (PI3K)/mTOR signaling pathway in human pancreatic cancer cells and tissues, and the in vivo antitumor effects of the mTOR inhibitor CCI-779 with/without gemcitabine in xenograft models of human pancreatic cancer. We found that the Akt, mTOR and p70 S6 kinase (S6K1) from the PI3K/mTOR signaling pathway were activated in all of the pancreatic cancer cell lines examined. When surgically resected tissue specimens of pancreatic ductal adenocarcinoma were examined, phosphorylation of Akt, mTOR and S6K1 was detected in 50, 55 and 65% of the specimens, respectively. Although CCI-779 had no additive or synergistic antiproliferative effect when combined with gemcitabine in vitro, it showed significant antitumor activity in the AsPC-1 subcutaneous xenograft model as both a single agent and in combination with gemictabine. Furthermore, in the Suit-2 peritoneal dissemination xenograft model, the combination of these 2 drugs achieved significantly better survival when compared with CCI-779 or gemcitabine alone. These results demonstrate promising activity of the mTOR inhibitor CCI-779 against human pancreatic cancer, and suggest that the inhibition of mTOR signaling can be exploited as a potentially tumor-selective therapeutic strategy.

The effects of cannabinoids on P-glycoprotein transport and expression in multidrug resistant cells

Cannabis is the most widely used illicit drug in the world. Cannabinoids are used therapeutically by some patients as they have analgesic, anti-emetic and appetite stimulant properties which palliate adverse symptoms. Use of these agents in an oncology setting raises the question of whether they act to modulate the effectiveness of concurrently administered anti-cancer drugs. The transporter, P-glycoprotein (P-gp) confers multiple drug resistance (MDR) by effluxing a diverse array of anti-cancer agents. This study was undertaken to examine the effect of cannabinoids on P-gp. Unlike the known P-gp inhibitor, PSC833, short 1h exposure to three plant-derived cannabinoids, cannabinol (CBN), cannabidiol (CBD) and Delta(9)-tetrahydrocannabinol (THC) and the synthetic cannabinoid receptor agonist, WIN55, 212-2 (WIN) did not inhibit the efflux of the P-gp substrate Rhodamine 123 (Rh123) in either a drug-selected human T lymphoblastoid leukaemia cell line (CEM/VLB(100)) or in a mouse fibroblast MDR1 transfected cell line (77.1). However, in CEM/VLB(100) cells, prolonged 72 h exposure to the cannabinoids, THC and CBD, decreased P-gp expression to a similar extent as the flavonoid, curcumin (turmeric). This correlated with an increase in intracellular accumulation of Rh123 and enhanced sensitivity of the cells to the cytotoxic actions of the P-gp substrate, vinblastine. Taken together, these results provide preliminary evidence that cannabinoids do not exacerbate P-gp mediated MDR. Further, plant-derived cannabinoids are moderately effective in reversing MDR in CEM/VLB(100) cells by decreasing P-gp expression.

Induction of Apoptosis in Renal Cell Carcinoma by Reactive Oxygen Species: Involvement of Extracellular Signal-Regulated Kinase 1/2, p38δ/γ, Cyclooxygenase-2 Down-Regulation, and Translocation of Apoptosis-Inducing Factor

Renal cell carcinoma (RCC) is the most common malignancy of the kidney. Unfortunately, RCCs are highly refractory to conventional chemotherapy, radiation therapy, and even immunotherapy. Thus, novel therapeutic targets need to be sought for the successful treatment of RCCs. We now report that 6-anilino-5,8-quinolinequinone (LY83583), an inhibitor of cyclic GMP production, induced growth arrest and apoptosis of the RCC cell line 786-0. It did not prove deleterious to normal renal epithelial cells, an important aspect of chemotherapy. To address the cellular mechanism(s), we used both genetic and pharmacological approaches. LY83583 induced a time- and dose-dependent increase in RCC apoptosis through dephosphorylation of mitogen-activated protein kinase kinase 1/2 and its downstream extracellular signal-regulated kinases (ERK) 1 and -2. In addition, we observed a decrease in Elk-1 phosphorylation and cyclooxygenase-2 (COX-2) down-regulation. We were surprised that we failed to observe an increase in either c-Jun NH(2)-terminal kinase or p38alpha and -beta mitogen-activated protein kinase activation. In contradiction, reintroduction of p38delta by stable transfection or overexpression of p38gamma dominant negative abrogated the apoptotic effect. Cell death was associated with a decrease and increase in Bcl-x(L) and Bax expression, respectively, as well as release of cytochrome c and translocation of apoptosis-inducing factor. These events were associated with an increase in reactive oxygen species formation. The antioxidant N-acetyl l-cysteine, however, opposed LY83583-mediated mitochondrial dysfunction, ERK1/2 inactivation, COX-2 down-regulation, and apoptosis. In conclusion, our results suggest that LY83583 may represent a novel therapeutic agent for the treatment of RCC, which remains highly refractory to antineoplastic agents. Our data provide a molecular basis for the anticancer activity of LY83583.

Deciphering cellular states of innate tumor drug responses

BACKGROUND

The molecular mechanisms underlying innate tumor drug resistance, a major obstacle to successful cancer therapy, remain poorly understood. In colorectal cancer (CRC), molecular studies have focused on drug-selected tumor cell lines or individual candidate genes using samples derived from patients already treated with drugs, so that very little data are available prior to drug treatment.

RESULTS

Transcriptional profiles of clinical samples collected from CRC patients prior to their exposure to a combined chemotherapy of folinic acid, 5-fluorouracil and irinotecan were established using microarrays. Vigilant experimental design, power simulations and robust statistics were used to restrain the rates of false negative and false positive hybridizations, allowing successful discrimination between drug resistance and sensitivity states with restricted sampling. A list of 679 genes was established that intrinsically differentiates, for the first time prior to drug exposure, subsequently diagnosed chemo-sensitive and resistant patients. Independent biological validation performed through quantitative PCR confirmed the expression pattern on two additional patients. Careful annotation of interconnected functional networks provided a unique representation of the cellular states underlying drug responses.

CONCLUSION

Molecular interaction networks are described that provide a solid foundation on which to anchor working hypotheses about mechanisms underlying in vivo innate tumor drug responses. These broad-spectrum cellular signatures represent a starting point from which by-pass chemotherapy schemes, targeting simultaneously several of the molecular mechanisms involved, may be developed for critical therapeutic intervention in CRC patients. The demonstrated power of this research strategy makes it generally applicable to other physiological and pathological situations.

A selective retinoid X receptor agonist bexarotene (LGD1069, Targretin) prevents and overcomes multidrug resistance in advanced prostate cancer

BACKGROUND

We previously reported that a retinoid X receptor agonist bexarotene prevented and overcame acquired drug resistance in advanced breast cancer and non-small cell lung cancer. The present study was to evaluate the effect of bexarotene on the development of multidrug resistance in advanced prostate cancer.

METHODS

Human prostate cancer cells PC3 were repeatedly treated in culture with paclitaxel, doxorubicin, or cisplatin with or without bexarotene for 3 months. Thereafter, cells were isolated and characterized for their drug sensitivity.

RESULTS

Compared to parental cells, cells treated with a single therapeutic agent was resistant to the therapeutic agent, whereas cells treated with the combination remained chemosensitive. Cells with acquired drug resistance showed increased sensitivity to the cytotoxic agent when treated with the combination. Fluctuation analysis demonstrated that treatment with bexarotene decreased the rate of spontaneous development of drug resistance. These in vitro findings were further confirmed in the PC3 xenograft model.

CONCLUSION

Our results suggest a role of bexarotene in combination with chemotherapeutic agents in prevention and overcoming acquired drug resistance in advanced prostate cancer.

Relationship between therapeutic efficacy of arterial infusion chemotherapy and expression of P-glycoprotein and p53 protein in advanced hepatocellular carcinoma

AIM: To investigate the relationship between the chemotherapeutic drug efficacy and the expression of P-glycoprotein (PGP) and p53 protein in advanced hepatocellular carcinoma (HCC).

METHODS: The study was conducted on 41 patients with advanced HCC who were treated by repeated arterial infusion chemotherapy. Biopsy specimens from the tumor were collected before the start of treatment in all the patients, and the specimens were stored frozen until immunohistochemical staining, which was performed after the start of treatment, to detect PGP and p53 protein expressions. Twenty of the forty-one patients were treated with an anthracycline drug (epirubicin hydrochloride; anthracycline group), and the remaining 21 were treated with a non-anthracycline drug (mitoxantrone hydrochloride in 11 patients and carboplatin in 10 patients; non-anthracycline group). The relationship between the chemotherapeutic efficacy and the results of immunostaining were compared between the two groups.

RESULTS: Before the start of the treatment, PGP-positive rate was 90.2% (strongly-positive, 36.6%) and p53 protein-positive rate was 34.1% (strongly-positive, 19.5%). In the anthracycline group, the response rate was 40.0%. The number of patients showing poor response to the treatment was significantly larger in the patients with strongly positive PGP expression (P = 0.005), and their prognoses were poor (P = 0.001). In the non-anthracycline group, the response rate was 42.9%, and there was no significant relationship between the chemotherapeutic drug efficacy and the PGP or p53 protein expression. When only the data from the 11 patients treated with anthraquinone drug, mitoxantrone, were analyzed, however, the number of patients who showed poor response to treatment was significantly higher among the p53-positive patients (P = 0.012), irrespective of the survival outcome.

CONCLUSION: The chemotherapeutic efficacy with an anthracycline drug for advanced HCC can be predicted by immunohistochemical analysis of PGP expression. Similarly, immunostaining to evaluate p53 protein may be useful to predict the response in patients treated with an anthraquinone drug.

Microtubule targeting agents: basic mechanisms of multidrug resistance (MDR)

Multidrug resistance (MDR) results in the loss of activity of anticancer agents against cells possessing the MDR phenotype. In some cases, tumor cells are intrinsically resistant to chemotherapeutic drugs (intrinsic resistance), while in other instances cells become resistant after exposure to cytotoxic agents (acquired resistance). MDR has a significant impact on the management of patients with solid tumors, including those with breast cancer, where it has been previously correlated with a decreased response to treatment and a poor prognosis. Taxanes are among the most important components of chemotherapy regimens to treat recurrent breast cancer. In taxane-refractory cells, the two mechanisms most commonly associated with the development of MDR are the overexpression of members of the ATP-binding cassette family of transporters, of which P-glycoprotein is the best known, and alterations of tubulin, which is the cellular target of the taxanes. In vitro and in vivo models have been developed to study the development of MDR and to assess the potential clinical application of MDR modulators. However, despite promising advances using MDR modulators in preclinical models, clinical applications have met with limited success. Novel strategies are needed to circumvent the development of drug resistance. New cytotoxic agents capable of evading MDR offer hope for patients with breast cancer.

The molecular basis of multidrug resistance in cancer: the early years of P-glycoprotein research

The discovery and characterization of P-glycoprotein, an energy-dependent multidrug efflux pump, as a mechanism of multidrug resistance in cancer is generally accepted as a significant contribution to the ongoing effort to end death and suffering from this disease. The historical reflections of Victor Ling and Michael Gottesman concerning the early years of this research highlight the important contributions of the multidisciplinary teams involved in these studies, and illustrate how technological developments in biochemistry and molecular and cell biology enabled this discovery.

Characterization of a new antibody raised against the NH2 terminus of P-glycoprotein

PURPOSE

Cancers exposed to chemotherapy develop multidrug resistance, a major cause for chemotherapy failure. One mechanism of multidrug resistance development is due to overexpression of P-glycoprotein (Pgp) in these cancer cells. Thus, a prechemotherapy evaluation of Pgp in cancer cells aids in the design of alternative regimens that can circumvent such failure. As few Pgp-specific antibodies are available in detecting low levels of Pgp, there is a need for preparing an antibody that allows the detection of Pgp by various immunologic methods.

EXPERIMENTAL DESIGN

We selected the amino acid stretch 11 to 34 in the cytoplasmically located NH2 terminus of Pgp as antigen, which was chemically synthesized and used to raise an antibody in a rabbit, termed NH2 11 antibody. We compared the properties of NH2 11 antibody with that of the well-characterized Pgp-specific antibody, C219, by Western blotting, immunoprecipitation, immunocytochemistry, and immunohistochemistry.

RESULTS

Immunoblotting analysis suggested that NH2 11 antibody efficiently interacts with both recombinant and constitutively expressed Pgp in cancerous and noncancerous human cells. Immunoprecipitation reactions indicated that the NH2 11 antibody selectively immunoprecipitates Pgp. Immunocytochemical analyses indicated that the NH2 11 antibody detects Pgp in drug-resistant breast cancer cells as well as in human prostate and breast adenocarcinoma tissue sections.

CONCLUSION

As the NH2 11 antibody detects Pgp present in cells and tissues, we conclude that the amino acid sequence to which this antibody was raised is highly antigenic and the antibody is useful in the detection of Pgp by a variety of immunologic methods.

Interpreting epithelial cancer biology in the context of stem cells: tumor properties and therapeutic implications

Over 90% of all human neoplasia is derived from epithelia. Significant progress has been made in the identification of stem cells of many epithelia. In general, epithelial stem cells lack differentiation markers, have superior in vivo and in vitro proliferative potential, form clusters in association with a specialized mesenchymal environment (the 'niche'), are located in well-protected and nourished sites, and are slow-cycling and thus can be experimentally identified as 'label-retaining cells'. Stem cells may divide symmetrically giving rise to two identical stem cell progeny. Any stem cells in the niche, which defines the size of the stem cell pool, may be randomly expelled from the niche due to population pressure (the stochastic model). Alternatively, a stem cell may divide asymmetrically yielding one stem cell and one non-stem cell that is destined to exit from the stem cell niche (asymmetric division model). Stem cells separated from their niche lose their stemness, although such a loss may be reversible, becoming 'transit-amplifying cells' that are rapidly proliferating but have a more limited proliferative potential, and can give rise to terminally differentiated cells. The identification of the stem cell subpopulation in a normal epithelium leads to a better understanding of many previously enigmatic properties of an epithelium including the preferential sites of carcinoma formation, as exemplified by the almost exclusive association of corneal epithelial carcinoma with the limbus, the corneal epithelial stem cell zone. Being long-term residents in an epithelium, stem cells are uniquely susceptible to the accumulation of multiple, oncogenic changes giving rise to tumors. The application of the stem cell concept can explain many important carcinoma features including the clonal origin and heterogeneity of tumors, the occasional formation of tumors from the transit amplifying cells or progenitor cells, the formation of precancerous 'patches' and 'fields', the mesenchymal influence on carcinoma formation and behavior, and the plasticity of tumor cells. While the concept of cancer stem cells is extremely useful and it is generally assumed that such cells are derived from normal stem cells, more work is needed to identify and characterize epithelial cancer stem cells, to address their precise relationship with normal stem cells, to study their markers and their proliferative and differentiation properties and to design new therapies that can overcome their unusual resistance to chemotherapy and other conventional tumor modalities.

Neoplastic growth: the consequence of evolutionary malignant resistance to chronic damage for survival of cells (review of a new theory of the origin of cancer)

In the present review, a new theory that the mechanisms of general evolutionary persistent resistance to damaging factors are closely related to the development of tumour cells is introduced. Evolutionary resistance and its variability have an immense power to drive and control the process of carcinogenesis and the success of microbial and antitumour chemotherapy. First, this phenomenon of adaptation is characteristic of microbial cells whose resistance to antibiotics and other chemotherapeutic drugs is manifested through ATP-dependent transmembrane transporters. The structure and function of some multidrug transporters of resistance are conserved from microorganisms to mammals. When somatic cells are exposed to carcinogens and develop into tumour cells, they also acquire resistance to the toxic effects of carcinogens through these same transmembrane transporters (P-glycoprotein, glutathione S-transferases and other products of evolutionary resistance-related genes arisen for detoxification and exportation of cytotoxic xenobiotics and drugs). Cancerous cells acquire a persistent evolutionary resistance to chemotherapy drugs or irradiation through the same ATP-dependent transporters encountered in prokaryotic and eukaryotic cells. The mechanism of acquired resistance of cells to damaging factors, which becomes manifested during tumorigenic process formation, is a general biological law of primary significance in carcinogenesis. This resistance can be called malignant as, once formed, it does not disappear, as does also a clone of malignant cells. In tumorous cells, the mutagenic processes, morphological and functional modifications are a mechanism of secondary significance in carcinogenesis, contributing to formation of damage-resistant cells. This mechanism characterizes the processes of simplification arising in damage-resistant cells. Such cells acquire parasitic features. To survive under unfavourable conditions, they get adapted as if returning down the evolutionary stairs back to a more primitive stage of atavistic regression, which is characteristic of primitive forms of existence. Therefore they cease obeying the growth-regulating mechanisms in the organism and acquire the potential of unlimited division and accelerated growth (metastases) as do unicellular organisms or their forms resistant to damaging factors in the environment and in the host organism. Thus, cancer is a natural self-protective response of the damaged cells to the biological, physical and chemical damage and oxidative stress. This response has been developed in the process of evolution under the impact of the general biological Darwinian law of nature--to survive through variability and adaptation to the changed environmental conditions. Thus, malignization is the consequence of an evolutionary variety of the general biological resistance of cells to damage and stress in order to survive.

Combined effect of epirubicin and lymphokine-activated killer cells on the resistant human breast cancer cells

Accumulating evidence suggests the concept that epirubicin and lymphokine-activated killer (LAK) cells cytotoxicity may be mediated by free radicals generation and P-glycoprotein-positive (Pg-p+) cancer cells are more sensitive for LAK cells than their drug-sensitive parental lines. We tested this hypothesis further by exposing drug-sensitive (WT) and epirubicin-resistant MCF-7 human breast tumor cells to epirubicin and LAK cells. Subsequently, we monitored cell proliferation as a measure of cytotoxicity. The cytotoxicity of epirubicin, LAK, and LAK + epirubicin (1/10 of IC50) was evaluated in 400-fold epirubicin resistant MCF-7 EPI(R) (P-glycoprotein overexpressing) and drug-sensitive MCF-7 WT cells. IC50 values were measured using the MTT cytotoxicity test. The MCF-7 EPI(R) cells exhibited an increased susceptibility to LAK cells than did the MCF-7 WT cells. P-gp+ MCF-7 EPI(R) cells were lysed by human LAK cells to a greater extend than were their drug-sensitive counterparts. LAK + epirubicin combined treatment increased susceptibility of MCF-7 WT and MCF-7 EPI(R) cells to LAK cells cytotoxicity. For both cell lines, cytotoxicity was dependent upon the concentration of the epirubicin and effector cell/target cell (E/T) ratio. The resistance of MCF-7 EPI(R) cells to epirubicin appears to be associated with a developed tolerance to superoxide, most likely because of a tree-fold increase in superoxide dismutase (SOD) activity and 13-fold augmented selenium dependent glutathione peroxidase (GSH-Px) activity. Acting in concert, these two enzymes would decrease the formation of hydroxyl radical from reduced molecular oxygen intermediates. The addition of SOD decreased cytotoxicity of epirubicin and LAK cells. Taken together, these observations support the role of oxygen radicals in the cytotoxicity mechanism of epirubicin and suggest further that the development of resistance to this drug by the MCF-7 EPI(R) tumor cells may have a component linked to oxygen free radicals. It is proposed that production of reactive oxygen species by the treatment of epirubicin and LAK cells can cause cytotoxicity of MCF-7 WT and MCF-7 EPI(R) cells. SOD, catalase, GSH-Px, GST (glutathione S-transferase), and GSH (reduced glutathione) must be considered as part of the intracellular antioxidant defense mechanism of MCF-7 WT and MCF-7 EPI(R) cells against reactive oxygen species.

A phase I trial of liposomal doxorubicin, paclitaxel and valspodar (PSC-833), an inhibitor of multidrug resistance

PURPOSE

The aim of this study was to determine (i) the maximum tolerated dose (MTD) of liposomal doxorubicin (L-DOX) and paclitaxel (DP), (ii) the MTD of DP plus valspodar (DPV) and (iii) pharmacokinetic (PK) interactions of valspodar with L-DOX and paclitaxel.

METHODS

Twenty-three patients with metastatic cancers received DP, followed 4 weeks later by DPV. Dose levels of DP were (mg/m2 for L-DOX/paclitaxel): 30/135 (n = 7), 30/150 (n = 4), 35/150 (n = 8) and 40/150 (n = 4). Dose levels of DPV were 15/70 (n = 10) and 15/60 (n = 10). Serial, paired PK studies were performed.

RESULTS

The MTD of DP was 40/150. For DPV at 15/70, five of 10 patients experienced grade 4 neutropenia. In the next cohort, a reduced dose of 15/60 was well tolerated. Valspodar produced reversible grade 3 ataxia in seven patients, requiring dose reduction from 5 to 4 mg/kg. Paired PK studies indicated no interaction between L-DOX and valspodar, and a 49% increase in the median half-life of paclitaxel. Two partial and one minor remissions were noted.

CONCLUSIONS

The use of valspodar necessitated dose reductions of DP, with neutropenia being dose limiting. Valspodar PK interactions were observed with paclitaxel but not L-DOX.

The chemoresistance gene ABCG2 (MXR/BCRP1/ABCP1) is not expressed in melanomas but in single neuroendocrine carcinomas of the skin

BACKGROUND

As the molecular mechanisms in melanoma chemoresistance remain unknown to date, we hypothesized these tumors to express the ATP-binding cassette (ABC) transporter G2 (ABCG2/MXR/BCRP1/ABCP1), a recently detected membrane transporter and putative stem-cell marker. Besides melanoma, we addressed the neuroendocrine carcinoma of the skin (Merkel cell carcinoma), another cutaneous cancer supposed to originate from neuroectoderm and usually chemoresistant.

METHODS AND RESULTS

Upon semiquantitative reverse transcription polymerase chain reaction, ABCG2 mRNA expression was not upregulated in 18 melanoma resection specimens when compared with 19 acquired melanocytic nevi from which melanomas are known to often arise (Mantel-Haenszel test, p=0.3). At protein level, immunohistochemistry was negative in all 66 investigated melanoma resection specimens (50 primary melanomas and 16 cutaneous/subcutaneous metastases) and in 19 acquired melanocytic nevi. Among 29 neuroendocrine carcinomas of the skin, ABCG2 protein was detected in single clusters of cells in three tumors. As a positive control, three dermatofibrosarcomas were also stained and showed ABCG2 protein expression of the endothelial cells of the blood vessels.

CONCLUSION

Altogether, chemoresistance of melanomas and neuroendocrine carcinomas of the skin cannot be explained by expression of the ABCG2-chemoresistance gene. Most of these tumors do not exhibit this potential stem-cell feature.

Prediction of doxorubicin sensitivity in breast tumors based on gene expression profiles of drug-resistant cell lines correlates with patient survival

Up to date clinical tests for predicting cancer chemotherapy response are not available and individual markers have shown little predictive value. We hypothesized that gene expression patterns attributable to chemotherapy-resistant cells can predict response and cancer prognosis. We contrasted the expression profiles of 13 different human tumor cell lines of gastric (EPG85-257), pancreatic (EPP85-181), colon (HT29) and breast (MCF7 and MDA-MB-231) origin and their counterparts resistant to the topoisomerase inhibitors daunorubicin, doxorubicin or mitoxantrone. We interrogated cDNA arrays with 43 000 cDNA clones ( approximately 30 000 unique genes) to study the expression pattern of these cell lines. We divided gene expression profiles into two sets: we compared the expression patterns of the daunorubicin/doxorubicin-resistant cell lines and the mitoxantrone-resistant cell lines independently to the parental cell lines. For identifying predictive genes, the Prediction Analysis for Mircorarrays algorithm was used. The analysis revealed 79 genes best correlated with doxorubicin resistance and 70 genes with mitoxantrone resistance. In an independent classification experiment, we applied our model of resistance for predicting the sensitivity of 44 previously characterized breast cancer samples. The patient group characterized by the gene expression profile similar to those of doxorubicin-sensitive cell lines exhibited longer survival (49.7+/-26.1 months, n=21, P=0.034) than the resistant group (32.9+/-18.7 months, n=23). The application of gene expression signatures derived from doxorubicin-resistant and -sensitive cell lines allowed to predict effectively clinical survival after doxorubicin monotherapy. Our approach demonstrates the significance of in vitro experiments in the development of new strategies for cancer response prediction.

ABCB5-mediated doxorubicin transport and chemoresistance in human malignant melanoma

Enhanced drug efflux mediated by ABCB1 P-glycoprotein and related ATP-binding cassette transporters is one of several mechanisms of multidrug resistance thought to impair chemotherapeutic success in human cancers. In malignant melanoma, its potential contribution to chemoresistance is uncertain. Here, we show that ABCB5, which functions as a determinant of membrane potential and regulator of cell fusion in physiologic skin progenitor cells, is expressed in clinical malignant melanoma tumors and preferentially marks a subset of hyperpolarized, CD133+ stem cell phenotype-expressing tumor cells in malignant melanoma cultures and clinical melanomas. We found that ABCB5 blockade significantly reversed resistance of G3361 melanoma cells to doxorubicin, an agent to which clinical melanomas have been found refractory, resulting in a 43% reduction in the LD50 from 4 to 2.3 micromol/L doxorubicin (P < 0.05). Our results identified ABCB5-mediated doxorubicin efflux transport as the underlying mechanism of resistance, because ABCB5 blockade significantly enhanced intracellular drug accumulation. Consistent with this novel ABCB5 function and mechanism in doxorubicin resistance, gene expression levels of the transporter across a panel of human cancer cell lines used by the National Cancer Institute for drug screening correlated significantly with tumor resistance to doxorubicin (r = 0.44; P = 0.016). Our results identify ABCB5 as a novel drug transporter and chemoresistance mediator in human malignant melanoma. Moreover, our findings show that ABCB5 is a novel molecular marker for a distinct subset of chemoresistant, stem cell phenotype-expressing tumor cells among melanoma bulk populations and indicate that these chemoresistant cells can be specifically targeted via ABCB5 to enhance cytotoxic efficacy.

Expression of copper-transporting P-type adenosine triphosphatase (ATP7B) as a prognostic factor in human endometrial carcinoma

OBJECTIVE

Copper-transporting P-type adenosine triphosphate (ATP7B) has been reported to be associated with cisplatin resistance in vitro. However, the clinical significance of this transporter has not previously been addressed in endometrial carcinoma. Our goal was to investigate if ATP7B is expressed in endometrial carcinoma and whether its expression correlates with prognosis.

METHODS

We performed immunohistochemical analysis of ATP7B using a monoclonal antibody against ATP7B in 51 endometrial endometrioid adenocarcinomas. 27 of 51 patients were treated with cisplatin-based chemotherapy after surgery.

RESULTS

Cytoplasmic staining of tumor cells was observed in 37.3% (19/51 cases) of the analyzed carcinomas and no staining was observed in adjacent non-neoplastic cells. ATP7B positivity in the degree of differentiation of G2 and G3 carcinoma was significantly higher than that of G1 carcinoma (P = 0.019). The patients with ATP7B-positive tumors had a worse prognosis than that with ATP7B-negative tumors in overall survival and disease-free survival, respectively (P < 0.01).

CONCLUSIONS

These findings suggest that overexpression of ATP7B expression in endometrial carcinoma is correlated with unfavorable clinical outcome in patients treated with cisplatin-based chemotherapy. ATP7B expression could be considered as a prognostic factor in patients with endometrial carcinoma.

The selective retinoid X receptor agonist bexarotene (LGD1069, Targretin) prevents and overcomes multidrug resistance in advanced breast carcinoma

Acquired drug resistance represents a major challenge in the therapeutic management of breast cancer patients. We reported previously that the retinoid X receptor-selective agonist bexarotene (LGD1069, Targretin) was efficacious in treating animal models of tamoxifen-resistant breast cancer. The goal of this study was to evaluate the effect of bexarotene on development of acquired drug resistance and its role in overcoming acquired drug resistance in advanced breast cancer. Paclitaxel, doxorubicin, and cisplatin were chosen as model compounds to determine the effect of bexarotene on the development of acquired drug resistance. Human breast cancer cells MDA-MB-231 were repeatedly treated in culture with a given therapeutic agent with or without bexarotene for 3 months. Thereafter, cells were isolated and characterized for their drug sensitivity. Compared with parental cells, cells treated with a single therapeutic agent became resistant to the therapeutic agent, whereas cells treated with the bexarotene combination remained chemosensitive. Cells with acquired drug resistance, when treated with the combination, showed increased sensitivity to the cytotoxic agent. Furthermore, cells treated with the combination regimen had reduced invasiveness and angiogenic potential than their resistant counterparts. These in vitro findings were further confirmed in an in vivo MDA-MB-231 xenograft model. Our results suggest a role for bexarotene in combination with chemotherapeutic agents in prevention and overcoming acquired drug resistance in advanced breast carcinoma.

The effect of apoptotic activity, survivin, Ki-67, and P-glycoprotein expression on prognosis in pancreatic carcinoma

OBJECTIVES

The pathogenetic mechanisms that regulate the aggressive behavior of pancreatic cancer still remain to be clarified. Alterations in the apoptotic pathway and proliferative activity of tumor cells as well as mechanisms contributing to the intrinsic drug resistance of pancreatic tumors have been investigated. Survivin is a recently described antiapoptotic protein, which, when overexpressed, is associated with worse prognosis in a majority of tumors. P-glycoprotein, a product of multidrug resistance gene-1 (MDR-1) was reported to be expressed in drug-resistant tumors. The purpose of this study was to investigate whether apoptosis, its regulation by survivin, tumor cell proliferation, and P-glycoprotein expression have a significant role on the biologic behavior of pancreatic adenocarcinoma.

METHODS

Tumors of 45 patients with pancreatic adenocarcinoma were studied for the detection of survivin, P-glycoprotein, and Ki-67 expression by immunohistochemical method and apoptotic index by TUNEL method. Immunohistochemical staining was scored and Ki-67 and apoptotic indices were expressed as percentage of stained cells.

RESULTS

Immunohistochemistry for survivin and P-glycoprotein revealed positive staining in 7 (15.4%) and 36 (79.5%) of the 45 tumors, respectively. The mean Ki-67 proliferative index was 43.75 +/- 25.30%. The mean apoptotic index evaluated with the TUNEL method was 37.12 +/- 34.55% for the whole group. We found no significant association between apoptotic index, expressions of survivin and P-glycoprotein, and clinicopathologic variables and survival.

CONCLUSIONS

Apoptotic activity, survivin, and P-glycoprotein expression failed to predict the disease extent and biologic behavior in pancreatic adenocarcinoma in our cases.

Establishment and characterization of new cellular lymphoma model expressing transgenic human MDR1

Multidrug resistance (MDR) due to the expression of the MDR1 gene and its P-glycoprotein (Pgp) product is a major factor in the prognosis and clinical outcome of patients with refractory lymphomas and other malignancies. The aim of our study was to establish a lymphoma, cellular system where a de novo acquisition of multidrug resistance is specifically related to overexpression of a transgenic, human MDR1. A multidrug sensitive lymphoma cell line (LM1) was established from a sporadic T-cell lymphoma of BALB/c mouse and was transduced by a retroviral vector containing the human MDR1 cDNA. The resultant cell variant (LM1/MDR) was characterized in comparison to the parental LM1 cells. The LM1/MDR cell variant is cross-resistant to DOX, COL, ACT D and VBL. This cell variant expresses the human MDR1 and exhibits de novo functional Pgp activity that can be blocked by the Pgp-modulators VRP and KT-5720. The acquired MDR of LM1/MDR is not accompanied with gene amplification, alternative splicing or up-regulation of the murine endogenous mdr1a, mdr1b, mrp1, mrp2 and mrp3 transporter-genes. Therefore, the acquired MDR is, specifically, human MDR1-dependent as it has been found in malignant cells of most lymphoma patients. Moreover, this system can be used as a model to study MDR and the efficacy of drugs and modulators on malignant cells where human Pgp is a major factor of multidrug resistance.

Plasma glutathione S-Transferase P1-1 as a prognostic factor in patients with advanced non-Hodgkin's lymphoma (stages III and IV)

PURPOSE

This study aims to investigate whether the plasma level of glutathione S-transferase P1-1 (GSTP1-1), which is a phase II detoxifying enzyme known to be a resistance factor for anticancer drugs, could be a prognostic factor of de novo non-Hodgkin lymphoma (NHL) in clinical stages (CSs) III and IV.

EXPERIMENTAL DESIGN

Study population consisted of 80 NHL patients with no prior treatment: 12 patients were at CS I, 14 at CS II, 25 at CS III, and 29 at CS IV. All 54 patients at CS III or CS IV were treated with cyclophosphamide, doxorubicin, vincristine, and prednisolone (CHOP). Plasma GSTP1-1 concentration was measured by ELISA. We stained lymph node tissues for GSTP1-1 using anti-GSTP1-1 monoclonal antibody 5F and quantitatively assessed the intensity of immunostaining by using the KS-400 image analyzing system.

RESULTS

There was a significant stepwise increment of plasma GSTP1-1 concentration from CS I to CS IV (P < 0.05). Of the 54 patients with CS III or IV treated with CHOP, 28 (52%) had elevated plasma GSTP1-1 levels. Plasma GSTP1-1 concentration tended to correlate with the intensity of GSTP1-1 expression in lymphoma tissues as assessed by immunostaining (P = 0.07). The CR rates in patients at CS III and CS IV treated by CHOP, 55.2% (14 of 26) and 16.0% (5 of 28) for the low and high plasma GSTP1-1 groups, respectively, were significantly different (P < 0.01). For these two groups, the median survival times were 64 and 25 months, respectively (P < 0.01), and the median times to progression were 58 and 12 months, respectively (P < 0.01). There was no significant correlation between plasma GSTP1-1 concentrations and other NHL prognostic indicators in these patients as determined by univariate and multivariate analyses.

CONCLUSION

These results showed that plasma GSTP1-1 is a useful prognostic factor for CS III and IV advanced NHL. Thus, it may be a promising strategy to treat NHL concomitantly with anticancer drugs and GSTP1-1-specific inhibitors.

The effects of S-phase kinase-associated protein 2 (SKP2) on cell cycle status, viability, and chemoresistance in A549 lung adenocarcinoma cells

S-phase kinase-associated protein 2 (SKP2), a member of the F-box family of ubiquitin-protein ligase complexes, controls the stability of cell cycle-related proteins including p27Kip1. The authors examined how the expression level of SKP2 affects the expression level of cell cycle-related proteins, cell cycle status, viability, and chemoresistance in A549 lung adenocarcinoma cells. Overexpression of SKP2 reduced the expression of p27Kip1, cyclin E, and p21Cip1, increased S-phase cells, rescued A549 cells from apoptosis due to adenoviral infection, and also increased chemoresistance against camptothecin, cisplatin, and AG1478. Down-regulation of SKP2 did not affect cell cycle status, and reduced cell viability.

P-glycoprotein expression is induced in human pancreatic cancer xenografts during treatment with a cell cycle regulator, mimosine

Application of several cell cycle checkpoint regulators seem to be promising in various experimental models including pancreatic cancer, and they are being evaluated in Phase I-II clinical trials. Among these compounds, mimosine, a plant-derived amino acid has shown an antineoplastic effect on human lung or pancreatic cancer xenografts in addition to cell cycle arrest in the late G1 phase. In the present study, immunosuppressed CBA mice bearing subcutaneously growing human ductal pancreatic adenocarcinomas were treated with 30 mg/kg L-mimosine for 34 days. The treatment resulted in retardation of tumor growth, accompanied by a significantly diminished proliferative activity (22.6%+/-1.7% Ki-67 positivity vs. 29.9%+/-1.1% in controls, mean+/-SEM, P<0.007) and an increased apoptotic rate (14.5+/-1.1 apoptotic cells/mm2 vs. 3.8+/-0.4/mm2 in the controls, P<0.0001). The immunohistochemical expression of the multidrug resistance gene (MDR1)-encoded P glycoprotein (p 170) was studied. The parental and the untreated tumors did not express p 170 protein, but in the mimosine-treated samples 30 to 60% of the carcinoma cells displayed a linear, membrane bound positivity. The results indicate that P-glycoprotein is inducible by a cell cycle regulator, creating an acquired resistant phenotype.

Molecular characterisation of two human cancer cell lines selected in vitro for their chemotherapeutic drug resistance to ET-743

ET-743 (Yondelis(TM), Trabectedin) isolated from the tunicate Ecteinascidia turbinata, is being tested in phase II clinical trials in Europe and the United States of America (USA). Studies with different solid tumours have shown antitumour activity in advanced, pre-treated sarcomas as well as in drug-resistant breast and ovarian cancer. The primary mechanism of action for ET-743 has not been fully elucidated and different models have been suggested to explain its molecular mechanism of action. ET-743 binds tightly to the minor groove of DNA and previous data have suggested that ET-743 acts by interfering with RNA transcription. To further investigate the mechanism of in vitro drug resistance, we evaluated the gene expression profile in ovarian and chondrosarcoma cell lines selected for resistance to ET-743. We found 70 genes whose expression was modulated in both drug-resistant cell lines when compared with their respective parental drug-sensitive cell lines. This pattern of gene expression seems to be selective for ET-743-resistant cells, since ovarian cancer cells resistant to paclitaxel did not share the same gene expression changes. Data presented in this study reveal different molecular pathways that could be involved in the cellular mechanism of ET-743 resistance.

A Phase I trial of a potent P-glycoprotein inhibitor, zosuquidar trihydrochloride (LY335979), administered intravenously in combination with doxorubicin in patients with advanced malignancy

PURPOSE

Our intention was to (a) to investigate the safety and tolerability of a potent P-glycoprotein modulator, zosuquidar trihydrochloride (LY335979), when administered i.v. alone or in combination with doxorubicin, (b) to determine the pharmacokinetics of zosuquidar and correlate exposure to inhibition of P-glycoprotein function in a surrogate assay, and (c) to compare the pharmacokinetics of doxorubicin in the presence and absence of zosuquidar.

PATIENTS AND METHODS

Patients with advanced malignancies who provided written informed consent received zosuquidar and doxorubicin administered separately during the first cycle of therapy and then concurrently in subsequent cycles. Zosuquidar was given i.v. over 48 h in a cohort-dose escalation manner until the occurrence of dose-limiting toxicity or protocol specified maximum exposure. Doxorubicin doses of 45, 60, 75 mg/m(2) were administered during the course of the trial.

RESULTS

Dose escalation proceeded through 9 cohorts with a total of 40 patients. The maximal doses administered were 640 mg/m(2) of zosuquidar and 75 mg/m(2) of doxorubicin. No dose-limiting toxicity of zosuquidar was observed. Pharmacokinetic analysis revealed that, in the presence of zosuquidar at doses that exceeded 500 mg, there was a modest decrease in clearance (17-22%) and modest increase in area under the curve (15-25%) of doxorubicin. This change was associated with an enhanced leukopenia and thrombocytopenia but was without demonstrable clinical significance. The higher doses of zosuquidar were associated with maximal P-glycoprotein inhibition in natural killer cells.

CONCLUSION

Zosuquidar can be safely coadministered with doxorubicin using a 48 h i.v. dosing schedule.

Genotype and Allele Frequencies of C3435T Polymorphism of the MDR1 Gene in Various Jewish Populations of Israel

The human multidrug-resistant gene (MDR1) encodes for P-glycoprotein (P-gp), which is a membrane-bound efflux-transporter conferring resistance to a number of natural cytotoxic drugs and potentially toxic xenobiotics. The wobble C3435T polymorphism at exon 26 was associated with different expression levels of the MDR1 gene and substrate uptake. Differences in allele frequencies of the C3435T polymorphism have previously been demonstrated between racial groups. In this study, 500 individuals from 5 Jewish populations of Israel (Ashkenazi, Yemenite, North African, Mediterranean, Near-Eastern) were examined for C3435T polymorphism using a PCR-RFLP-based technique to calculate genotype and allele frequencies. Frequencies of the C allele were quite similar among the Ashkenazi (0.65), Yemenite (0.645), and North-African (0.615) Jewish populations. However, the frequency of this allele was slightly lower among Mediterranean Jews (0.58) and significantly lower among Near-Eastern Jews (0.445). The frequency of the C allele among Near-Eastern Jews is, therefore, significantly different from those of all other tested Jewish populations. In comparison to previously studied non-Jewish populations, the frequency of this allele among Near-Eastern Jews is different from that in West Africans (0.91) but is similar to that in whites (0.497). However, the C allele frequencies among the other 4 Jewish populations are significantly lower than that found among West Africans and significantly higher than among non-Jewish whites. These data may have important therapeutic and prognostic implication for P-gp-related drug dosage recommendation in Jewish populations.

Pharmacogenomics of MDR1/ABCB1 gene: the influence on risk and clinical outcome of haematological malignancies

Pharmacogenomics is a rapidly developing field of biomedical research, which investigates phenotypic and pharmacodynamic consequences of the genetic variations among individuals. The multi-drug resistance-1, MDR1 (ABCB1) gene belongs to ATP-binding cassette (ABC) family and encodes for membrane transporter P-glycoprotein (P-gp). A wide array of P-gp substrates comprises toxic xenobiotics and numerous commonly used medications including anti-cancer drugs. Under physiological conditions P-gp protects cells against toxins, whereas in malignant cells P-gp confers multi-drug resistance phenotype. Moreover, characteristic tissue localisation enables P-gp to influence the uptake, tissue distribution and elimination of P-gp transported drugs. A number of recent studies identified variety of single nucleotide polymorphisms (SNPs) in the MDR1 gene and demonstrated significant ethnic differences in their allelic frequency distribution. Furthermore, it was shown that some of these SNPs, especially silent C3435T polymorphism in exon 26, may alter P-gp expression and transport activity. Consequently, it is likely that specific functional MDR1 haplotypes may result with altered exposure to toxins and drugs, thus influencing predisposition to certain diseases as well as efficacy or toxicity of pharmacotherapy. In this paper, we focus on the available data concerning the impact of MDR1 polymorphism on the risk and clinical outcome of haematological malignancies. The structure and function of P-gp as well as results of studies addressing the relevance of MDR1 polymorphism in non-haematological disorders are also briefly discussed.

99mTc tetrofosmin scintigraphy in acute leukaemia: the relationship between marrow uptake of tetrofosmin and P-glycoprotein and chemotherapy response

BACKGROUND

The non-invasive detection of P-glycoprotein (Pgp) and multidrug resistance related proteins in vivo, will represent the greatest challenge in overcoming multidrug resistance. Although 99mTc tetrofosmin has been used previously as a myocardial perfusion agent, it is now also being used in the imaging of various tumours. In the current study, Tc tetrofosmin was used in the investigation of acute leukaemia.

AIM

To show the uptake pattern of 99mTc tetrofosmin in the bone marrow of patients with acute leukaemia, and to ascertain the relationship between 99mTc tetrofosmin uptake and the level of Pgp expression and their relation to the response to chemotherapy. In addition, CD95, which is an indicator of apoptosis (programmed cell death), has also been assessed.

MATERIALS AND METHODS

Pgp and CD95 were detected by using flow cytometry. Of the 27 acute leukaemia patients assessed, nine had previously received chemotherapy, and 18 had had an initial diagnosis. All patients had undergone 99mTc tetrofosmin scintigraphy, and their Pgp and CD95 levels had been determined. The same parameters were studied again for 14 patients. The responses to chemotherapy were assessed by patients' clinicians. A control group of 37 patients without bone marrow pathology was also studied in order to provide comparisons for the scintigraphy results. The control images were assessed only qualitatively.

RESULTS

In leukaemia patients the uptake of 99mTc tetrofosmin into bone marrow was found to be considerably higher than in control patients (P=0.000). An analysis of the relationship between Pgp, CD95, and the qualitative and quantitative tetrofosmin uptake ratios (URs) showed that there was an inverse correlation only between Pgp and the quantitative uptake ratio (P=0.016, r=-0.461). When the patients were grouped as 'good' and 'poor', as related to the chemotherapy response, there were no meaningful differences between these two groups regarding Pgp, CD95 and tetrofosmin URs (P>0.05). By evaluating the scintigraphic findings of the 'repeated' 14 patients, we showed that if the 99mTc tetrofosmin UR in the second imaging test was reduced by >0.08, the response to chemotherapy tended to be good. This method, based on follow-up scanning with tetrofosmin, showed a sensitivity of 83% and a specificity of 62% in the prediction of a 'good' response, if a decrease of 0.08 was taken into consideration.

CONCLUSION

In this study, patients with acute leukaemia showed significant uptake of tetrofosmin into the bone marrow. The addition of basal and repeated 99mTc tetrofosmin scintigraphy to the management protocol for leukaemia could lead to the preferential determination of responses to chemotherapy, by evaluating whole bone marrow non-invasively. This method seems promising, but it needs further support from various similar investigations comprising more patients in order to confirm our results.

Inhibition of glucosylceramide synthase does not reverse drug resistance in cancer cells

The multidrug-resistant cancer cell lines NCI/AdR(RES) and MES-SA/DX-5 have higher glycolipid levels and higher P-glycoprotein expression than the chemosensitive cell lines MCF7-wt and MES-SA. Inhibiting glycolipid biosynthesis by blocking glucosylceramide synthase has been proposed to reverse drug resistance in MDR cells by causing an increased accumulation of proapoptotic ceramide during treatment of cells with cytotoxic drugs. We treated both multidrug-resistant cell lines with the glucosylceramide synthase inhibitors PDMP (d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol), C9DGJ (N-nonyl-deoxygalactonojirimycin) or C4DGJ (N-butyl-deoxygalactonojirimycin). PDMP achieved a significant reversal of drug resistance in agreement with previous reports. However, the N-alkylated iminosugars C9DGJ and C4DGJ, which are more selective glucosylceramide synthase inhibitors than PDMP, failed to cause any reversal of drug resistance despite depleting glycolipids to the same extent as PDMP. Our results suggest that (a) inhibition of glucosylceramide synthase does not reverse multidrug resistance and (b) the chemosensitization achieved by PDMP cannot be caused by inhibition of glucosylceramide synthase alone.

Daphnetin induced differentiation of human renal carcinoma cells and its mediation by p38 mitogen-activated protein kinase

Daphnetin has been shown to be a potent in vitro anti-proliferative agent to the human renal cell carcinoma (RCC) cell line, A-498. In the present study, we investigated its effects on mitogen-activated protein kinase (MAPK) signalling along with cell cycle events and cellular differentiation. Daphnetin-activated p38, however, higher concentrations were required to inhibit ERK1/ERK2. In addition, it did not activate SAPK or induce apoptosis, but instead inhibited S phase cell cycle transition of A-498 cells at low concentrations and time of exposure. In addition, a late G(1), early S phase inhibition was observed at higher concentrations and time of exposure, indicating that the mechanism of daphnetin-induced differentiation was concentration dependent. Increased expression of the epithelial differentiation markers cytokeratins 8 and 18, correlated with increasing concentrations of daphnetin, while pre-treatment with a specific p38-inhibitor, served to limit this effect. There was no evidence that P-glycoprotein (P-gp) mediated multi-drug resistance (MDR) played a role in the anti-proliferative activity of daphnetin. Consequently, we concluded that p38 MAP kinase is intrinsically involved in mediating the effect of daphnetin in A-498 cells, suggesting that this drug may act by promotion of cellular maturation, and consequently may represent a novel low toxic approach for the treatment of poorly differentiated RCCs.

Glutathione S-transferase P1 has protective effects on cell viability against camptothecin

Glutathione S-transferase P1 (GSTP1) is one of the important xenobiotic-metabolizing enzymes. It was reported that GSTP1 was overexpressed in malignant tissues, and its expression level was associated with resistance to chemotherapeutics. We carried out transfection of GSTP1 sense and antisense vectors to examine effects of GSTP1 on cell cycle arrest and apoptosis induced by camptothecin in HeLa cells. Transfection of GSTP1 antisense vector induced apoptosis. Camptothecin-induced S- or G2/M arrest was intensified by transfection of GSTP1 antisense vector, and subsequent apoptosis was attenuated by transfection of GSTP1 sense vector. These results suggest that GSTP1 has protective effects against camptothecin-induced cytotoxicity.

Investigation of intracellular signalling events mediating the mechanism of action of 7-hydroxycoumarin and 6-nitro-7-hdroxycoumarin in human renal cells

Previously, 7-hydroxycoumarin (7-OHC) and 6-nitro-7-hydroxycoumarin (6-NO2-7-OHC) have been shown to be potent and selective anti-proliferative agents to the human renal cell carcinoma (RCC) cell line, A-498. Their effect on mitogen-activated protein kinases (MAPK's) was investigated. 6-NO2-7-OHC was shown to alter the phosphorylation status of ERK1/ERK2, p38 and SAPK, while 7-OHC activated ERK1/ERK2 but had no effect on p38 and SAPK. Also, 7-OHC inhibited topoisomerase II mediated relaxation of DNA, while neither compound was a substrate for P-glycoprotein (P-gp) mediated multi-drug resistance (MDR). Therefore, 6-NO2-7-OHC, rather than 7-OHC, modulated signalling events associated with cellular differentiation and apoptosis, suggesting its mechanism of action may be the promotion of cellular maturation and/or death. Consequently, 6-NO2-7-OHC may represent a novel therapeutic agent for the treatment of RCC's.

P-glycoprotein: from genomics to mechanism

Resistance to chemically different natural product anti-cancer drugs (multidrug resistance, or MDR) results from decreased drug accumulation, resulting from expression of one or more ATP-dependent efflux pumps. The first of these to be identified was P-glycoprotein (P-gp), the product of the human MDR1 gene, localized to chromosome 7q21. P-gp is a member of the large ATP-binding cassette (ABC) family of proteins. Although its crystallographic 3-D structure is yet to be determined, sequence analysis and comparison to other ABC family members suggest a structure consisting of two transmembrane (TM) domains, each with six TM segments, and two nucleotide-binding domains. In the epithelial cells of the gastrointestinal tract, liver, and kidney, and capillaries of the brain, testes, and ovaries, P-gp acts as a barrier to the uptake of xenobiotics, and promotes their excretion in the bile and urine. Polymorphisms in the MDR1 gene may affect the pharmacokinetics of many commonly used drugs, including anticancer drugs. Substrate recognition of many different drugs occurs within the TM domains in multiple-overlapping binding sites. We have proposed a model for how ATP energizes transfer of substrates from these binding sites on P-gp to the outside of the cell, which accounts for the apparent stoichiometry of two ATPs hydrolysed per molecule of drug transported. Understanding of the biology, genetics, and biochemistry of P-gp promises to improve the treatment of cancer and explain the pharmacokinetics of many commonly used drugs.

Saquinavir induces stable and functional expression of the multidrug transporter P-glycoprotein in human CD4 T-lymphoblastoid CEMrev cells

BACKGROUND

The multidrug transporter P-glycoprotein (P-gp) is expressed in HIV-1 target cells, in a range of pharmacological barriers and in AIDS-associated tumours. P-gp substrates include HIV-1 protease inhibitors (PIs) and anticancer drugs, which are efficiently effluxed from multidrug-resistant (MDR) cells.

OBJECTIVES

The aim of this study was to investigate the effect on human CD4 T-lymphoblastoid CEMrev cells of saquinavir and other PIs in terms of P-gp expression and to characterize the functional and biochemical patterns of PI-induced P-gp molecules.

METHODS

CEMrev cells no longer expressing detectable amounts of P-gp were cultured for a prolonged period in the presence of 10 microg/mL saquinavir (CEMsaq10) and tested for P-gp expression and function. Subsequently, CEMsaq10 cells were transferred into medium containing 15 microg/mL saquinavir (CEMsaq15) and cultured for several months. These cell lines were continuously monitored for P-gp expression, function and immunochemical patterns. A similar strategy was adopted to determine whether other PIs, such as ritonavir and indinavir, were able to induce P-gp expression in CEMrev cells.

RESULTS

Compared with the drug-diluent control, the exposure of CEMrev cells to 10 microg/mL saquinavir induced, in a consistent fraction of cells (45-50%), de novo expression of functioning P-gp molecules. The transfer of CEMsaq10 cells to 15 microg/mL saquinavir was associated with a dramatic increase in P-gp expression and function (85-90% of CEMsaq15 cells expressed P-gp and effluxed P-gp dye substrates). These saquinavir-induced P-gp molecules included 75-kDa molecules as well as the classical 170-kDa form of P-gp, suggesting induction of a particular isoform of P-gp termed mini-P-glycoprotein. Conversely, ritonavir and indinavir induced transient P-gp expression in a small percentage of the CEMrev cells.

CONCLUSIONS

Treatment of human CD4 T-lymphoblastoid CEMrev cells with saquinavir caused over-expression of functioning P-gp molecules. This de novo acquired MDR phenotype, which differed from that induced by other PIs, was stable, as expression and activity of P-gp were observed in CEMsaq10 and CEMsaq15 cells during prolonged in vitro culturing, even in drug-free conditions.

Pyrazolotriazolopyrimidine derivatives sensitize melanoma cells to the chemotherapic drugs: taxol and vindesine

In this study, we have evaluated the "in vitro" modulatory activity of a series of pyrazolotriazolopyrimidine derivatives (PTP-d) in sensitizing malignant melanoma cells to the chemotherapic drugs: taxol and vindesine. To that end, we have described the impact of chemotherapeutic agents on the cell cycle and on the induction of apoptosis when used alone or in combination with PTP-d. We have demonstrated that four PTP-d reduced chemotherapic drugs EC(50) doses of the G(2)/M accumulation with an average of 1.7-fold for taxol and 9.5-fold for vindesine when challenged on A375 human melanoma cell line. This sensitization activity was also confirmed by analyzing the apoptosis degree induced by the chemotherapic drugs. Interestingly, PTP-d had no effects on the response to cytotoxic agents by skin-derived human keratinocyte cells, NCTC 2544. Therefore, we have investigated the signaling pathway sustaining the sensitizing effect of PTP-d, providing functional evidence that active compounds are able to inhibit multidrug resistance-associated ATP-binding cassette drug transporter. These results suggested that PTP-d hold great promise for the treatment of multidrug resistance in cancers, leading to potential new therapies for melanoma.

Repetitive doxorubicin treatment of glioblastoma enhances the PGP expression--a special role for endothelial cells

The glioblastoma is the highest dedifferentiated form of astrocytic brain tumors, which is refractory to chemotherapy in most cases. The lack of chemotherapeutic success is correlated with overexpression of the product P-glycoprotein (PGP) coded by the multidrug resistance 1 (MDR1) gene and a subsequent release of drugs from the tumor cells. For the chemotherapeutical treatment of glioblastomas, the endothel cell is of special importance since due to its manifold metabolic and protective tasks within the blood-brain barrier, it already has a relatively high PGP expression under physiological conditions. The aim of the present study was to analyze the uptake of the antimitotic drug Doxorubicin (DOX) and the expression of PGP in human and rat glioblastoma cell lines and in a human endothelial cell line at different time points. In the following in vivo approach DOX enriched glioblastoma cells were transplanted into rats and the developed tumor was investigated histologically. The results showed an increased uptake and an enhanced expression of PGP at certain time points in every cell line. In the tissue a DOX release was mainly observed in perivascular surroundings. It was concluded that DOX enhanced the constitutive PGP expression which led to a subsequent exclusion of DOX in tumor cells but also in the endothelial cells of the tumor vasculature. Since the vascularization is a prerequisite for tumor growth, the inhibition of the PGP expression in tumor endothelial cells might be a clinical approach to make the DOX treatment more effective.

Role of NF-kappaB and Akt/PI3K in the resistance of pancreatic carcinoma cell lines against gemcitabine-induced cell death

Pancreatic cancer is resistant to almost all cytotoxic drugs. Currently, gemcitabine appears to be the only clinically active drug but, because of pre-existing or acquired chemoresistance of most of the tumor cells, it failed to significantly improve the outcome of pancreatic carcinoma patients. The current study examined the relevance of nuclear factor kappaB (NF-kappaB) and PI3K/Akt in the resistance of five pancreatic carcinoma cell lines towards gemcitabine. Treatment for 24 h with gemcitabine (0.04-20 micro M) led to a strong induction of apoptosis in PT45-P1 and T3M4 cells but not in BxPc-3, Capan-1 and PancTu-1 cells. These resistant cell lines exhibited a high basal NF-kappaB activity in contrast to the sensitive cell lines. Furthermore, gemcitabine showed a dose-dependent induction of NF-kappaB. At a dose of 0.04 micro M, gemcitabine still induced apoptosis in the sensitive cell lines, but did not induce NF-kappaB. In addition, NF-kappaB inhibition by MG132, sulfasalazine or the IkappaBalpha super-repressor strongly diminished the resistance against gemcitabine (0.04-20 micro M). In contrast to this obvious correlation between basal NF-kappaB activity and gemcitabine resistance, PI3K/Akt seems not to be involved in gemcitabine resistance of these cell lines. Neither did the basal Akt activity correlate with the sensitivity towards gemcitabine treatment, nor did the inhibition of PI3K/Akt by LY294002 alter gemcitabine-induced apoptosis. These results indicate that constitutive NF-kappaB activity confers resistance against gemcitabine and that modulation of this activity by pharmacological or genetic approaches may have therapeutical potential when combined with gemcitabine in the treatment of pancreatic carcinoma.

Activity of docetaxel with or without estramustine phosphate versus mitoxantrone in androgen dependent and independent human prostate cancer xenografts

PURPOSE

Prostate cancer is known to be refractory to chemotherapy with only mitoxantrone showing some benefit. Recent clinical data indicate the antitumoral efficacy of taxanes alone or combined with estramustine phosphate. We compared the response to these treatments of hormone dependent and independent human prostate cancer xenografts.

MATERIALS AND METHODS

PAC120, an androgen dependent human prostate cancer xenograft, and several HIDs, which are androgen independent variants, were established in nude mice. Human gene expression was determined by semiquantitative reverse transcriptase-polymerase chain reaction. Androgen deprivation was achieved by surgical castration. Tumor bearing mice received 20 mg./kg. docetaxel on day 2, 1 mg./kg. hydrocortisone on days 1 to 3, 4 mg./kg. estramustine phosphate on days 1 to 4 or 1 mg./kg. mitoxantrone on day 1 by the intraperitoneal route for 3-week cycles. Relative tumor volume and growth delay were evaluated. Histological examination of tumors was done before and after treatment.

RESULTS

Mitoxantrone transiently decreased the growth rate of HID xenografts but did not affect that of PAC120. Estramustine phosphate alone inhibited the growth of PAC120 but not that of HID variants. Docetaxel inhibited the growth of all prostate cancer xenografts (PAC120 and HIDs) and increased survival. PAC120 showed distinct response patterns during prolonged treatment. Efficacy was significantly decreased by splitting docetaxel into 2 doses given at a 7-day interval (p = 0.01). The docetaxel effect was potentiated by estramustine phosphate in 1 of the 2 HID variants tested. In castrated mice docetaxel induced a greater growth delay than in intact male mice (p = 0.01). High Her2/neu and beta2-tubulin transcripts were detected in all samples. Prostate specific antigen, androgen receptor and multidrug related protein-1 mRNA did not correlate with the drug response, while CYP3A4 mRNA inversely correlated with the response. Docetaxel treated tumors had an increased number of mitotic cells with centrosome alterations and multinuclei, an increased number of Ki67 labeled cells and a strong decrease in beta-tubulin without evidence of apoptosis.

CONCLUSIONS

Docetaxel showed a significant antitumoral effect on hormone dependent and tumors, which was largely superior to that of mitoxantrone. Estramustine phosphate alone had a modest effect. The drug response was associated with high Her2/neu expression, low CYP3A4 expression and the induction of numerous mitotic abnormalities.

Genetic alterations in ovarian cancer cells that might account for sensitivity to chemotherapy in patients

The cellular response to anticancer agent treatments is determined by many factors that could be altered in tumor cells. The induction of apoptosis of cancer cells is thought to be important for the overall response of these cells. Despite the introduction of new and potent anticancer agents, the survival rate for patients with ovarian cancer remains poor. In general ovarian cancer cells present a poor propensity to undergo apoptosis, which could be one of the reasons for this relatively poor response observed in the clinic. Induction of apoptosis is the result of activation and repression of pro- and antiapoptotic genes, which are regulated by complex mechanisms. Many cancer cells activate a "survival" program to escape disruption and allow propagation. In this review we have analyzed the role of genetic alterations observed in ovarian cancer cells in determining cellular response to drug treatment.

Prognostic factors of renal cell carcinoma

PURPOSE

Determination of prognostic factors is essential for the management of renal cell carcinoma. Stage, histological grade and type, and performance status are now well known and commonly used. During the last decade numerous predictors of patient outcome were tested. This review summarizes the most important studies, explores and compares the results, and tries to respond to the question, "Today, what do we expect of clinical, molecular and genetic factors concerning survival of patients with renal cell carcinoma?"

MATERIALS AND METHODS

Based on MEDLINE literature searches we comprehensively reviewed the literature on the prognostic factors associated with the tumor, the patient and the treatment.

RESULTS

During the last decades numerous factors have been studied but few of them maintained independent significance in terms of overall survival as assessed by multivariate analysis. Results are more often controversial from one series to another. No known molecular or cytogenetic tumor marker has been identified to help diagnose, manage or confirm renal cell carcinoma remission, progression or relapse.

CONCLUSIONS

The classical prognostic factors remain histological grade, histological type, performance status, patient age, number and location(s) of metastatic sites, time to appearance of metastases and prior nephrectomy. The only striking advancement during the last few years has been the proven contribution of radical nephrectomy for metastatic disease in patients with good performance status.

Nuclear expression of YB-1 protein correlates with P-glycoprotein expression in human breast carcinoma

Drug resistance is a common clinical problem in cancer treatment. The overexpression of P-glycoprotein appears to be closely associated with multi-drug resistance to anticancer agents. YB-1 binds to the Y-box in the promoter region of MDR1, which encodes P-glycoprotein. We evaluated the correlation between nuclear YB-1 and P-glycoprotein expression and other molecules, such as hormonal receptors, angiogenic factors, immune factors, and methalloprotease in 63 human breast cancers. Nuclear YB-1 expression had a significant correlation with P-glycoprotein and PgR expression, and also with CD68 grade, concerning accumulation of tumor associated macrophages. This series did not demonstrate P-glycoprotein and nuclear YB-1 expression might be one of the useful prognostic marker of breast cancer.

Improvement of oral drug treatment by temporary inhibition of drug transporters and/or cytochrome P450 in the gastrointestinal tract and liver: an overview

The oral bioavailability of many cytotoxic drugs is low and/or highly variable. This can be caused by high affinity for drug transporters and activity of metabolic enzymes in the gastrointestinal tract and liver. In this review, we will describe the main involved drug transporters and metabolic enzymes and discuss novel methods to improve oral treatment of affected substrate drugs. Results of preclinical and clinical phase I and II studies will be discussed in which affected substrate drugs, such as paclitaxel, docetaxel, and topotecan, are given orally in combination with an inhibitor of drug transport or drug metabolism. Future randomized studies will, hopefully, confirm that this strategy for oral treatment is at least as equally effective and safe as standard intravenous administration of these drugs.

Frequency distribution of C3435T mutation in exon 26 of the MDR1 gene in a Spanish population

P-glycoprotein (PGP) is a transmembrane efflux transporter with an important role in drug therapy. The level of PGP expression leads to relevant consequences in terms of efficacy and toxicity by modulating drug disposition. A single nucleotide polymorphism (SNP) in exon 26 of the gene C3435T was recently associated to PGP levels and substrate uptake. Persons who were homozygous for the T-allele had significantly decreased PGP expression compared with C/C persons. Due to this fact and bearing in mind the important differences among populations regarding the frequencies of persons carrying mutations affecting drug disposition, the authors wanted to study the prevalence of this genetic trait in their population. DNA samples from 408 persons were assayed by a PCR-RFLP method. The results showed that the distributions of the C/C, T/T, and C/T genotypes in the Spanish population were 26%, 22%, and 52%, respectively. With regard the C-allele frequency, which has been studied in several populations, the result in their population was 52%, significantly lower (P < 0.0001) than that found in African populations and similar to several Asian and Caucasian (UK) populations (P > 0.05). By contrast, the C-allele frequency in southwest Asian, German, and Portuguese populations was significantly lower than in the Spanish population (P < 0.001, P < 0.01, and P < 0.05, respectively). The great differences found between their population and others, such as the African and southwest Asian populations, could have important therapeutic implications when drugs that are a substrate of PGP are used.

Expression of copper-transporting P-type adenosine triphosphatase (ATP7B) as a chemoresistance marker in human oral squamous cell carcinoma treated with cisplatin

An important clinical problem in the treatment of oral squamous cell carcinoma is the intrinsic/acquired resistance to cisplatin-based chemotherapy. Copper-transporting P-type adenosine triphosphate (ATP7B) has been reported to be associated with cisplatin resistance in vitro (Komatsu et al., Cancer Res 60, 1312-1316,2000). However, the clinical significance of this transporter has not previously been addressed. Our aim of this study was to investigate if ATP7B is expressed in oral squamous cell carcinoma and whether its expression correlates with prognosis and reduced responsiveness to cisplatin treatment. Biopsy tissues were obtained from the tumors of 70 patients with oral SCC, and 51 patients received cisplatin-based preoperative chemotherapy. We performed immunohistochemical analysis of ATP7B using monoclonal antibody against ATP7B in 51 oral SCC and adjacent neoplastic tissues. The significance of ATP7B in the prognosis of patients with oral SCC was also examined in the survival analysis of mortality follow-up data covering the period 1991 through 2000. We retrospectively examined the expression of ATP7B in primary oral SCC carcinoma and its association with chemotherapeutic effect. A variable degree of cytoplasmic staining of tumor cells was observed in 54.9% (28/51 cases) of the analyzed carcinomas. Patients with ATP7B-positive tumors had a significantly inferior response to chemotherapy compared with the patients with ATP7B-negative tumors (P = 0.03). The patients who received cisplatin-based chemotherapy with ATP7B-positive carcinomas had a significantly poorer overall survival than those with ATP7B-negative tumors (P = 0.015). These findings suggest that high levels of ATP7B expression in oral SCC are associated with unfavorable clinical outcome in patients with oral SCCs treated with cisplatin-based chemotherapy. ATP7B expression may be a preoperative indicator for a choice of cisplatin in some patients.