Adenosine triphosphate-dependent transport of leukotriene C4 by membrane vesicles prepared from cisplatin-resistant human epidermoid carcinoma tumor cells

Beyond Single-Cell Analysis of Metallodrugs by ICP-MS: Targeting Cellular Substructures

Platinum compounds such as cisplatin (cisPt) embody the backbone of combination chemotherapy protocols against advanced lung cancer. However, their efficacy is primarily limited by inherent or acquired platinum resistance, the origin of which has not been fully elucidated yet, although of paramount interest. Using single cell inductively coupled plasma mass spectrometry (SC-ICP-MS), this study quantifies cisPt in single cancer cells and for the first time in isolated nuclei. A comparison of cisPt uptake was performed between a wild type (wt) cancer cell line and related resistant sublines. In both, resistant cells, wt cells, and their nuclei, cisPt uptake was measured at different incubation times. A lower amount of cisPt was found in resistant cell lines and their nuclei compared to wt cells. Moreover, the abundance of internalized cisPt decreased with increasing resistance. Interestingly, concentrations of cisPt found within the nuclei were higher than compared to cellular concentrations. Here, we show, that SC-ICP-MS allows precise and accurate quantification of metallodrugs in both single cells and cell organelles such as nuclei. These findings pave the way for future applications investigating the potency and efficacy of novel metallodrugs developed for cancer treatment.

Characterization of a novel HDAC/RXR/HtrA1 signaling axis as a novel target to overcome cisplatin resistance in human non-small cell lung cancer

BACKGROUND

Cisplatin is a first-line drug for the treatment of human non-small cell lung cancer (NSCLC); however, the majority of patients will develop drug resistance after treatment. In order to overcome cisplatin resistance, it is important to understand the mechanisms underlying the resistance.

METHODS

A gene microarray was used to screen for genes related to cisplatin resistance in NSCLC cell lines. Subsequently, the correlation between the HDAC, RXR and HtrA1 genes, in NSCLC, were verified using gene manipulation. Immunohistochemical staining was used to detect HDAC, RXR and HtrA1 expression in NSCLC specimens. Proliferation, migration and invasion assays were performed in vitro and in vivo to determine the role of the HDAC/RXR/HtrA1 signaling axis in cisplatin resistance, and luciferase reporter analysis and ChIP assays were performed to ascertain the mechanisms by which HDAC and RXR regulate the expression of HtrA1. Furthermore, in vitro and in vivo experiments were conducted in NSCLC cisplatin-resistant NSCLC to elucidate the effect of the low molecular weight compound, DW22, which targets the NSCLC cisplatin resistance HDAC/RXR/HtrA1 signaling pathway.

RESULTS

HtrA1 was identified as a cisplatin resistance-related gene in NSCLC cells. The regulation of HtrA1 by HDAC and RXR significantly decreased the efficacy of cisplatin in NSCLC cells resistant to cisplatin. Immunohistochemistry results showed a negative relationship between HDAC1 and HtrA1, and a positive relationship between RXRα and HtrA1 in NSCLC patients' tissues. Notably, the expression of HDAC1 and HtrA1 can be considered as biomarkers for the efficacy of platinum-based drugs and prognosis in NSCLC patients. Mechanistically, the heterodimers of the nuclear receptor RXR, in combination with the enzyme, HDAC, regulate the transcription of HtrA1 in NSCLC cells. The rescue of HtrA1 expression by dual targeting of HDAC and RXR with the compound, DW22, significantly inhibited the proliferation, migration and invasion of NSCLC cells resistant to cisplatin, and induced NSCLC cell apoptosis.

CONCLUSION

Our results indicate that HtrA1, a cisplatin resistance-related gene, is synergistically regulated by HDAC and RXR in NSCLC. Targeting the HDAC/RXR/HtrA1 signaling axis can rescue HtrA1 expression and reverse cisplatin resistance in NSCLC.

Methyl-Cantharidimide (MCA) Has Anticancer Efficacy in ABCB1- and ABCG2-Overexpressing and Cisplatin Resistant Cancer Cells

In this study, we investigated the efficacy of methyl-cantharidimide (MCA), a cantharidin (CTD) analog, as an anticancer drug, in cancer cells overexpressing either ABCB1 or ABCG2 transporters and in cisplatin-resistant cancer cells. The results indicated that: (i) MCA was efficacious in the ABCB1-overexpressing cell line, KB-C2, and the ABCB1-gene-transfected cell line, HEK293/ABCB1 (IC50 from 6.37 to 8.44 mM); (ii) MCA was also efficacious in the ABCG2-overexpressing cell line, NCI-H460/MX20, and the ABCG2-gene-transfected cell lines, HEK293/ABCG2-482-R2, HEK293/ABCG2-482-G2, and the HEK293/ABCG2-482-T7 cell lines (IC50 from 6.37 to 9.70 mM); (iii) MCA was efficacious in the cisplatin resistant cancer cell lines, KCP-4 and BEL-7404/CP20 (IC50 values from 7.05 to 8.16 mM); (iv) MCA (up to 16 mM) induced apoptosis in both BEL-7404 and BEL-7404/CP20 cancer cells; (v) MCA arrested both BEL-7404 and BEL-7404/CP20 cancer cells in the G0/G1 phase of the cell cycle; (vi) MCA (8 mM) upregulated the expression level of the protein, unc-5 netrin receptor B (UNC5B) in HepG2 and BEL-7404 cancer cells. Overall, our results indicated that MCA's efficacy in ABCB1- and ABCG2-overexpressing and cisplatin resistant cancer cells is due to the induction of apoptosis and cell cycle arrest in the G0/G1 phase.

Generation of Stable cisPt Resistant Lung Adenocarcinoma Cells

Platinum compounds represent the backbone of combined chemotherapy protocols for advanced lung cancer. The mechanisms responsible for its frequent primary or acquired resistance to cisplatin (cisPt)-based chemotherapy remains enigmatic. The availability of two cell lines of the same origin, one resistant and the other sensitive, will facilitate research to reveal the mechanism of resistance formation. Lung adenocarcinoma cells, A240286S (A24), were cultivated in increasing cisPt concentrations over a prolonged time. After a significant increase in IC₅₀ was measured, cultivation of the cells was continued in absence of cisPt and IC₅₀s determined over a long period (>7 months). As a result, a cell line with lasting, high-level cisPt resistance, designated (D-)A24cisPt8.0, was obtained. The cells were cross-resistant to oxaliplatin and to pemetrexed at a low level. Previous publications have claimed that Leucine-rich repeat-containing protein 8 (LRRC8A and LRRC8D) of the volume-regulated anion channels (VRACs) affect cellular resistance to cisPt. Even though cisPt decreased LRRC8D expression levels, we showed by knockdown and overexpression experiments with LRRC8A and D that these proteins do not govern the observed cisPt resistance. The tumor cell sublines described here provide a powerful model to study the mechanisms of resistance to cisPt in lung cancer cells and beyond.

The role of oxidative stress in the development of cisplatin resistance in epithelial ovarian cancer

OBJECTIVE

To investigate the role of oxidative stress in the development of cisplatin resistance in epithelial ovarian cancer (EOC).

METHODS

Two parent EOC cell lines (MDAH-2774 and SKOV-3) and their chemoresistant counterparts (cisplatin, 50 µmol/L) were used. Total RNA was extracted and subjected to real-time reverse transcriptase polymerase chain reaction to evaluate the expression of glutathione reductase (GSR) and inducible nitric oxide synthase (iNOS), as well as nitrate/nitrite levels. Analysis of variance was used for main effects and Tukey for post hoc analysis at P < .05 for statistical significance.

RESULTS

Both cisplatin resistant cell lines displayed a significant decrease in GSR messenger RNA (mRNA) levels and activity (P < .01). As compared to sensitive controls, nitrate/nitrite levels were significantly higher in SKOV-3 cisplatin resistant cells while iNOS mRNA levels were significantly higher in MDAH-2774 cisplatin resistant cells (P < .05).

CONCLUSION

Our data suggest that the development of cisplatin resistance tilts the balance toward a pro-oxidant state in EOC.

Molecular markers predict outcome in squamous cell carcinoma of the head and neck after concomitant cisplatin-based chemoradiation

Not all patients with squamous cell carcinomas of the head and neck (HNSCC) benefit from concurrent cisplatin-based chemoradiation, but reliable predictive markers for outcome after chemoradiation are scarce. We have investigated potential prognostic biomarkers for outcome in a large group of patients. Ninety-one tumor biopsies taken from consecutive HNSCC patients were evaluated for protein expression on a tissue microarray. Using immunohistochemistry, 18 biomarkers, involved in various cellular pathways were investigated. Univariable and multivariable proportional hazard analyses were performed to investigate associations between each individual marker and outcome. In addition, the global test was used to test all variables simultaneously and selected combinations of markers for an overall association with local control. Univariable analysis showed statistically significant increased relative risks of RB, P16 and MRP2 for local control and MDR1 and HIF-1alpha for overall survival. MRP2, MDR1 and P16 levels were positively associated with outcome whereas RB and HIF-1alpha had a negative relationship. Using Goeman's global testing no combination of markers was identified that was associated with local control. Grouping the markers according to their function revealed an association between a combination of 3 markers (P16, P21 and P27) and outcome (p = 0.05) was found. In the multivariable analysis, MRP2 and RB remained significant independent predictive markers for local control. This study describes the prognostic value of biomarkers for the outcome in patients uniformly treated with concurrent chemoradiation. MRP2 and RB were found to be associated with outcome in patients treated with concurrent chemoradiation.

Alterations in the glycoform of cisplatin-resistant human carcinoma cells are caused by defects in the endoplasmic reticulum-associated degradation system

Cisplatin, cis-diamineplatinum-(II) dichloride (CDDP), is one of the most common and valuable chemotherapeutic reagents for various cancers. However, it is well known that tumor cells gain acquired or intrinsic resistance to treatment by this anti-cancer reagent. In spite of extensive efforts using genetic and proteomic approaches, the mechanism underlying CDDP resistance remains unclear. In the present study, we report drastic structural changes in the N-glycans of glycoproteins in CDDP-resistant tumor cells (the KCP-4 cell line obtained from KB-3-1 human carcinoma cells). It was suggested that the CDDP-resistant cells exhibited an increase in one of the high-mannose-type glycans, particularly M8.1. This N-glycan is well known as a tag for the transport of unfolded protein from the endoplasmic reticulum to the lysosome, a process known as endoplasmic reticulum-associated degradation (ERAD) system. The revertant cells (KCP-4R) obtained from the KCP-4 cell line showed almost the same glycoform profile as that of the parental cells, suggesting that N-glycan biosynthesis in tumor cells clearly corresponds to the alteration in the sensitivity against CDDP. Gene expression analysis using a cDNA microarray showed a decrease in the expression of major histocompatibility complex (MHC) proteins in the resistant cells. MHC proteins form a complex with lysosome-degradated proteins and are presented on the cell surface. These results suggest that CDDP tolerance in KCP-4 cells is caused by a defect in the ERAD system.

The role of cellular accumulation in determining sensitivity to platinum-based chemotherapy

The platinum (Pt) drugs cisplatin and carboplatin are heavily employed in chemotherapy regimens; however, similar to other classes of drugs, a number of intrinsic and acquired resistance mechanisms hamper their effectiveness. The method by which Pt drugs enter cells has traditionally been attributed to simple passive diffusion. However, recent evidence suggests a number of active uptake and efflux mechanisms are at play, and altered regulation of these transporters is responsible for the reduced accumulation of drug in resistant cells. This review suggests a model that helps reconcile the disparate literature by describing multiple pathways for Pt-containing drugs into and out of the cell.

p73 and MDM2 confer the resistance of epidermoid carcinoma to cisplatin by blocking p53

p73 responds to DNA damage and exerts its pro-apoptotic function. However, p73 might contribute to the development of drug-resistance in certain tumor cells. In this study, we found that p73 and MDM2 correlate with cisplatin-resistant phenotype of human epidermoid carcinoma-derived cells. p73 and MDM2 were kept at low levels in the cisplatin-sensitive KB-3-1 cells, whereas p53 was induced to be phosphorylated at Ser-15 in response to cisplatin. In contrast, p73 and MDM2 were expressed at higher levels, and cisplatin-mediated p53 phosphorylation was undetectable in the cisplatin-resistant KCP-4 cells. Enforced expression of p73 in KB-3-1 cells caused an accumulation of unphosphorylated form of p53 and MDM2, and conferred the cisplatin resistance. Collectively, our results suggest that a loss of the cisplatin sensitivity is at least in part due to a lack of cisplatin-induced p53 phosphorylation, and p73 might cooperate with MDM2 to be involved in this process.

Role of the Glutathione Metabolic Pathway in Lung Cancer Treatment and Prognosis: A Review

Inherent and acquired drug resistance is a cause of chemotherapy failure, and pharmacogenomic studies have begun to define gene variations responsible for varied drug metabolism, which influences drug efficacy. Platinum-based compounds are the most commonly used chemotherapeutic agents in the treatment of advanced stage lung cancer patients, and the glutathione metabolic pathway is directly involved in the detoxification or inactivation of platinum drugs. Consequently, genotypes corresponding to higher drug inactivation enzyme activity may predict poor treatment outcome. Available evidence is consistent with this hypothesis, although a definitive role for glutathione system genes in lung cancer prognosis needs to be elucidated. We present evidence supporting a role of the glutathione system in acquired and inherited drug resistance and/or adverse effects through the impact of either drug detoxification or drug inactivation, thus adversely effecting lung cancer treatment outcome. The potential application of glutathione system polymorphic genetic markers in identifying patients who may respond favorably, selecting effective antitumor drugs, and balancing drug efficacy and toxicity are discussed.

Nucleotide excision repair pathways involved in Cisplatin resistance in non-small-cell lung cancer

BACKGROUND

In spite of the growing list of genetic abnormalities identified as being involved in DNA repair pathways that alter chemosensitivity in non-small-cell lung cancer (NSCLC) patients, translational assays have not yet been developed for use in individualized chemotherapy.

METHODS

In metastatic NSCLC, no single cisplatin-based chemotherapy regimen has been shown to be superior to any other. Although these studies show a small survival tail at 3 years, the majority of patients had a median survival of 8 to 10 months. We review the principal mechanisms of cisplatin resistance, particularly those involved in the nucleotide excision repair (NER) pathways (transcription-coupled repair and global genomic repair).

RESULTS

ERCC1 is a single-stranded DNA endonuclease that forms a tight heterodimer with xeroderma pigmentosum complementation group F. It incises DNA on the 5' side of a lesion such as cisplatin-DNA adduct. Therefore, overexpression of ERCC1 and other NER enzymes during ovarian cancer chemotherapy with cisplatin appears to be implicated in the formation of cellular and clinical drug resistance. Recently, baseline ERCC1 mRNA overexpression has been related to poor response and survival in cisplatin-treated NSCLC patients.

CONCLUSIONS

The level of evidence for many assays is limited, and only ERCC1 mRNA levels have been analyzed extensively. The impact of ERCC1 should be fully validated in prospective clinical trials.

Glutathione content is correlated with the sensitivity of lines of PC12 cells to cisplatin without a corresponding change in the accumulation of platinum

A study of the involvement of glutathione (GSH) in cellular resistance to cisplatin was performed using methylmercury-resistant sublines (PC12/TM series) of the PC12 line of rat pheochromocytoma cells. The seven clonal sublines of PC12 cells (PC12/TM, PC12/TM2, PC12/TM5, PC12/TM11, PC12/TM15, PC12/TM23, PC12/TM26) used in the study had intracellular levels of GSH that ranged from 8.7-39.9 nmol/mg protein. The intracellular level of GSH was significantly correlated (p < 0.01, r = 0.87) with the sensitivity to cisplatin of PC12 cells and the seven sublines. Among the seven sublines, PC12/TM cells contained the highest concentration of GSH and were the most resistant to cisplatin. Treatment of PC12/TM cells with L-buthionine-SR-sulfoximine, which reduced the level of GSH to that in the parental PC12 cells, significantly reduced the resistance of the cells to cisplatin. The amount of platinum accumulated by resistant PC12/TM cells after treatment with cisplatin was higher than that by sensitive PC12 cells. These results suggest that the intracellular level of GSH might be directly involved in the resistance to cisplatin of these cell lines. However, a high intracellular concentration of GSH does not appear to contribute to a decrease in the accumulation of cisplatin in these cells.

Mechanisms of resistance to cisplatin

The use of cisplatin in cancer chemotherapy is limited by acquired or intrinsic resistance of cells to the drug. Cisplatin enters the cells and its chloride ligands are replaced by water, forming aquated species that react with nucleophilic sites in cellular macromolecules. The presence of the cisplatin adducts in DNA is thought to trigger cell cycle arrest and apoptosis. Knowledge of the mechanism of action of cisplatin has improved our understanding of resistance. Decreased intracellular concentration due to decreased drug uptake, increased reflux or increased inactivation by sulfhydryl molecules such as glutathione can cause resistance to cisplatin. Increased excision of the adducts from DNA by repair pathways or increased lesion bypass can also result in resistance. Finally, altered expression of regulatory proteins involved in signal transduction pathways that control the apoptotic pathway can also affect sensitivity to the drug. An improved understanding of the mechanisms of resistance operative in vivo has identified targets for intervention and may increase the utility of cisplatin for the treatment of cancer.

Increased expression of the MRP5 gene is associated with exposure to platinum drugs in lung cancer

To investigate the role of the multidrug resistance-associated protein (MRP1) homologue MRP5 in relation to platinum drug resistance, we examined the steady-state levels of the mRNAs for MRP5 in both lung cancer cell lines and peripheral mononuclear cells (PMN) after exposure to platinum drug and in normal lung and lung cancer tissue specimens. Firstly, we examined MRP5 gene expression levels in 80 autopsy samples (40 primary tumors and 40 corresponding normal lung tissues) from 40 patients who had died from lung cancer. Next, we monitored MRP5 gene expression levels within 24 hr in both lung cancer cell lines incubated with cisplatin and in PMN from 10 previously untreated lung cancer patients after carboplatin administration alone. The MRP5 gene expression levels were assessed by quantitative reverse transcription polymerase chain reaction or RNase protection assay. The MRP5 expression levels in normal lung tissues and in tumors from patients exposed to platinum drugs during their lifetime were significantly higher than those in tissues from non-exposed patients. On the other hand, the MRP5 expression levels were not rapidly induced by platinum drugs either in lung cancer cell lines or in PMN within 24 hr. Our results suggest that increased expression levels of the MRP5 gene are associated with exposure to platinum drugs in lung cancer in vivo and/or the chronic stress response to xenobiotics.

Current Clinical Practice: Application of Resistance Reversal Agents in Hematologic Malignancies

The clinical application of resistance reversal drugs for patients with hematologic malignancies is reviewed. The phenomenon of multidrug resistance versus other mechanisms are discussed. The pump-like mechanisms of P-glycoprotein, multidrug resistance associated protein, lung resistance protein and of other ATP binding cassette transporter proteins are reviewed briefly, as well as the important substrate drugs and pump-blocking compounds. The problems associated with resistance protein assays in clinical samples and the concept of prognostic versus therapeutic clinical relevance are described, within the context of selected hematologic malignancies. Toxicities and treatment outcomes of phase II and III trials of reversal agents in lymphoma, multiple myeloma, myelodysplastic syndromes, acute myeloid leukemia and blast phase of chronic myeloid leukemia are reviewed. Finally, current options for on-study management of relapsed or refractory hematologic malignancy patients are discussed.

An enhanced active efflux of CPT-11 and SN-38 in cisplatin-resistant human KB carcinoma cells

Cisplatin-resistant KCP-4 cells were 12.4- and 31.6-fold more resistant to CPT-11 and SN-38 than parental KB-3-1 cells, respectively. We studied the mechanism of cross-resistance to CPT-11 and SN-38. Our previous study showed that multidrug resistance protein (MRP), canalicular multispecific organic anion transporter (cMOAT) and P-glycoprotein (P-gp) were not expressed in KCP-4 cells (Chen, Z.-S. et al., Exp. Cell Res., 240 (1998) 312-320, and Chuman, Y. et al., Biochem. Biophys. Res. Commun., 226 (1996) 158-165). The accumulation of both CPT-11 and SN-38 in KCP-4 cells was lower than that in KB-3-1 cells. The ATP-dependent efflux of CPT-11 and SN-38 from KCP-4 cells was enhanced compared with that from KB-3-1 cells. DNA topoisomerase (topo) I expression, topo I activity, topo I-mediated cleavable complex, and the sensitivity to SN-38 of DNA topo I in KCP-4 were similar to those in KB-3-1 cells. Furthermore, the conversion of CPT-11 to SN-38 in the two cell lines was also similar. The transport of LTC4 in KCP-4 membrane vesicles was competitively inhibited by bis-(glutathionato)-platinum (II) (GS-Pt), CPT-11 and SN-38. These findings suggested that an unknown transporter distinct from P-gp, MRP or cMOAT is expressed in KCP-4 cells and transports CPT-11 and SN-38.

Induction of gamma-glutamylcysteine synthetase gene expression by platinum drugs in peripheral mononuclear cells of lung cancer patients

BACKGROUND

To investigate in vivo the roles of gamma-glutamylcysteine synthetase (gamma-GCS), multidrug resistance-associated protein (MRP), human canalicular multispecific organic anion transporter (cMOAT) and DNA topoisomerase I (topo I) in relation to platinum drug resistance, we monitored the changes of the steady-state levels of the mRNAs for these factors in peripheral mononuclear cells (PMN) after completing platinum drug administration.

PATIENTS AND METHODS

PMN from 46 subjects were studied. We obtained PMN from 14 previously untreated lung cancer patients and 14 normal volunteers to measure the baseline gene expression levels. We then obtained PMN from 18 patients with previously untreated advanced lung cancer before and after they received platinum drug treatment. We analyzed the gene expression levels by using the quantitative reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

There were no differences in the baseline expression levels between normal volunteers and lung cancer patients in any of the genes. After platinum drug administration, the heavy subunit of gamma-GCS (gamma-GCSh) expression level increased 2.5-fold within 24 hours and the increase persisted for a month, whereas the light subunit of gamma-GCS (gamma-GCSl) expression level did not show an early response but had increased after a month. By contrast, the MRP, cMOAT and topo I expression levels were similar before, during and after chemotherapy.

CONCLUSIONS

These results suggest that the gene expression levels of both subunits of gamma-GCS play an important in vivo role in platinum drug resistance.

Differences in substrate specificity among glutathione conjugates (GS-X) pump family members: comparison between multidrug resistance-associated protein and a novel transporter expressed on a cisplatin-resistant cell line (KCP-4)

The substrate specificity of primary active transporters expressed on two kinds of human epidermoid KB-3-1 derived cell lines, C-A500 and KCP-4, was examined; the former expresses multidrug resistance-associated protein (MRP1), whereas the latter is resistant to cis-diamminedichloroplatinum (II) (cisplatin). Northern blot analysis indicated that neither P-glycoprotein, MRP1, MRP2 (canalicular multispecific organic anion transporter; cMOAT) nor MRP3 was overexpressed on KCP-4. Membrane vesicles isolated from C-A500 and KCP-4, but not from KB-3-1, exhibited the ATP-dependent uptake of glutathione conjugates (GS-X) such as leukotriene C4 and 2,4-dinitrophenyl-S-glutathione (DNP-SG), indicating the presence of GS-X pumps on these cells. The uptake of these GS-X by membrane vesicles from C-A500 was approximately twice that in the case of KCP-4. Kinetic analysis indicated that the Km and Vmax values for DNP-SG uptake were 2.56 and 1.43 microM, and 570 and 160 pmol/min/mg protein for C-A500 and KCP-4, respectively. In marked contrast, significant ATP-dependent uptake of glutathione-platinum complex was observed only in membrane vesicles from KCP-4, but not those from KB-3-1 and C-A500. The transport properties of estradiol-17beta-D-glucuronide (E(2)17betaG) were also different between the two cell lines. This was reflected in the findings that the ATP-dependent uptake of this conjugated metabolite in membrane vesicles from C-A500 (Km=2.33 microM, Vmax=34 pmol/min/mg protein) was much more extensive than that in the case of KCP-4 (Km=5.5 microM, Vmax=35 pmol/min/mg protein), and that comparable uptake was observed between KCP-4 and KB-3-1. Overall, a clear difference in substrate specificity among GS-X pump family members expressed on resistant tumor cells was demonstrated.

Drug resistance in lung cancer

The major problem in lung cancer chemotherapy is the emergence of inherent and acquired drug resistance of the cancer cells. Establishment of drug-resistant sublines and comparative investigations of such cell lines with their parental cells to determine their molecular, biologic, and biochemical properties are important research strategies. Genetic changes in tumor cells may induce changes in their biochemical properties and chemosensitivity. Many mechanisms that render tumor cells resistant have been identified, and they have provided new molecular targets for surrogate markers to predict chemosensitivity. The new categories of anticancer drugs, such as topoisomerase I inhibitors and taxanes, and non-cytotoxic new drugs, have been introduced clinically. It is important to define the molecular determinants of resistance to these drugs. The development of an appropriate model for overcoming drug resistance is one of the important issues that should be solved before carrying out further clinical trials.

Isolation of a novel human canalicular multispecific organic anion transporter, cMOAT2/MRP3, and its expression in cisplatin-resistant cancer cells with decreased ATP-dependent drug transport

The human multidrug resistance protein (MRP) gene encodes a membrane protein involved in the ATP-dependent transport of hydrophobic compounds. We previously isolated a canalicular multispecific organic anion transporter, cMOAT1/MRP2, that belongs to the ATP binding cassette (ABC) superfamily, which is specifically expressed in liver, and cMOAT1/MRP2 is responsible for the defects in hyperbilirubinemia II/Dubin-Johnson syndrome. In this study, we isolated a new cDNA of the ABC superfamily designated cMOAT2/MRP3 that is homologous to human MRP1 and cMOAT1/MRP2: cMOAT2/MRP3 is 56% identical to MRP1 and 45% identical to cMOAT1/MRP2, respectively. Fluorescence in situ hybridization demonstrated the chromosomal locus of this gene on chromosome 17q22. The human cMOAT2 cDNA hybridized to a 6.5-kb mRNA that was mainly expressed in liver and to a lesser extent in colon, small intestine, and prostate. The cMOAT2/MRP3 gene was not overexpressed in cisplatin-resistant cell lines with increased ATP-dependent transport of cisplatin over their parental counterparts derived from human head and neck cancer and human prostatic cancer cell lines. The human cMOAT2/MRP3, a novel member of the ABC superfamily, may function as a membrane transporter in liver, colon, and prostate.

Lack of a role for MRP1 in platinum drug resistance in human ovarian cancer cell lines

The level of expression of the multidrug resistance-associated protein (MRP1) in a panel of human ovarian carcinoma cell lines and their variants with acquired cisplatin resistance was determined using Western blotting. No overexpression of MRP1 was detected in any of the cell lines. In addition, we have transfected the MRP1 gene into an intrinsically cisplatin-resistant cell line SKOV3, previously shown to have elevated levels of glutathione (GSH). The MRP1-transfected line SKOV3-S2 was shown to be cross-resistant to doxorubicin, vincristine and etoposide but not to paclitaxel, vinblastine and platinum agents, such as cisplatin, JM216 [bis-acetato-ammine-dichloro-cyclohexylamine platinum (IV)] and AMD473 [cis-ammine dichloro (2-methyl-pyridine) platinum (II)]. No cross-resistance to any of the platinum agents was observed in a MRP1-overexpressing human lung cancer cell line with acquired doxorubicin resistance. Reduction of GSH levels (80-90%) by buthionine sulphoximine (BSO) produced significant potentiation in cisplatin sensitivity in the parental SKOV3, the vector-alone control SKOV3-puro and the MRP1-transfected line SKOV3-S2. The degree of sensitization was similar in all cell lines (1.6-fold). However, selective sensitization by BSO to vincristine was observed in the MRP1-transfected line (4.1-fold) but not in the vector control. No significant differences were observed in cisplatin accumulation in the SKOV3-puro and the SKOV3-S2 cells, although both these transfected lines accumulated significantly more than the parental line. Our results suggest that MRP1 does not play a significant role in platinum resistance in the human tumour cell lines investigated in this study.

An active efflux system for heavy metals in cisplatin-resistant human KB carcinoma cells

The mechanism for cisplatin resistance in cisplatin-resistant KCP-4 cells was studied. Although multidrug resistance-associated protein (MRP) was not detected in KCP-4 cells, the cells were more resistant to heavy metals than multidrug-resistant C-A120 cells that overexpressed MRP. KCP-4 cells expressed metallothionein, but it was scarcely involved in cisplatin resistance in these cells. KCP-4 cells did not express canalicular multispecific organic anion transporter (cMOAT). The glutathione (GSH) level was 4.7-fold higher in KCP-4 cells than in KB-3-1 cells. When the GSH level in KCP-4 cells was decreased by treating the cells with buthionine sulfoximine and nitrofurantoin, the accumulation of and sensitivity to cisplatin in the cells were increased. C-A120 cells were only 3.0-fold more resistant to cisplatin than KB-3-1 cells and this resistance was not affected by the increased glutathione level. The accumulation of platinum in C-A120 and KCP-4 cells was 68.5 and 20.4% of that in KB-3-1 cells, respectively, while the intracellular levels of antimony potassium tartrate in C-A120 and KCP-4 cells were 13.2 and 9.9% of that in KB-3-1 cells, respectively. The ATP-dependent efflux of antimony was enhanced in both C-A120 and KCP-4 cells. These results, taken together, suggest an efflux pump for heavy metals different from MRP and cMOAT is involved in cisplatin resistance in KCP-4 cells.

Expression of gamma-glutamylcysteine synthetase (gamma-GCS) and multidrug resistance-associated protein (MRP), but not human canalicular multispecific organic anion transporter (cMOAT), genes correlates with exposure of human lung cancers to platinum drugs

We examined the steady-state levels of mRNA for gamma-glutamylcysteine synthetase (gamma-GCS), multidrug resistance-associated protein (MRP) and human canalicular multispecific organic anion transporter (cMOAT) in human lung cancer specimens to elucidate their roles in relation to platinum drug resistance in vivo. Seventy-six autopsy samples (38 primary tumours and their corresponding normal lung tissues) obtained from 38 patients were analysed using the quantitative reverse transcription polymerase chain reaction (RT-PCR) method. Both subunits (heavy and light subunits) of gamma-GCS expression levels of normal lung and tumour tissues exposed to platinum drugs during life were significantly higher than those of non-exposed tissues, whereas only the MRP expression levels of tumours were elevated in association with ante-mortem platinum drug exposure. The gamma-GCS and MRP expression levels correlated significantly. The cMOAT expression levels did not correlate with ante-mortem platinum drug exposure. Next, we monitored gamma-GCS heavy subunit expression levels in peripheral mononuclear cells of eight previously untreated lung cancer patients after platinum drug administration, which revealed that these drugs induced gamma-GCS expression in vivo. These results suggest that gamma-GCS expression is induced by platinum drugs in vivo and/or the physiological stress response to xenobiotics.

Human canalicular multispecific organic anion transporter (cMOAT) is expressed in human lung, gastric, and colorectal cancer cells

Human canalicular multispecific organic anion transporter (cMOAT), a glutathione conjugate membrane transporter, has been isolated from cisplatin-resistant cancer cells and is distributed mainly in normal liver. We analyzed the expression of human cMOAT in 14 lung, 11 gastric, and 9 colorectal non-drug-selected human cancer cells, two multidrug-resistant cells, and one cisplatin-resistant cells, using quantitative RT-PCR and newly developed anti-human cMOAT antibody. All cell lines analyzed here expressed human cMOAT at the level of mRNA and protein, and some of them expressed higher levels of human cMOAT than the cisplatin-resistant cells. The two multidrug-resistant cell lines co-expressed human cMOAT gene and both or either of MRP and MDR1 genes. Immunostaining showed that human cMOAT was predominantly localized to the cytoplasm of these single cells. Our results indicate that human cMOAT is expressed in various human cancer cells including drug-resistant cells.

Reduction of cellular cisplatin resistance by hyperthermia--a review

Resistance to cisplatin (cDDP) is a major limitation to its clinical effectiveness. Review of literature data indicates that cDDP resistance is a multifactorial phenomenon. This provides an explanation why attempts to reverse or circumvent resistance using cDDP-analogues or combination therapy with modulators of specific resistance mechanisms have had limited success so far. It therefore provides a rationale to use hyperthermia, an agent with pleiotropic effects on cells, in trying to modulate cDDP resistance. In this review the effects of hyperthermia on cDDP cytotoxicity and resistance as well as underlying mechanisms are discussed. Hyperthermia is found to be a powerful modulator of cDDP cytotoxicity, both in sensitive and resistant cells. Relatively high heat doses (60 min 43 degrees C) seem to specifically interfere with cDDP resistance. The mechanism of interaction has not been fully elucidated so far, but seems to consist of multiple (simultaneous) effects on drug accumulation, adduct-formation and -repair. This may explain why hyperthermia seems to be so effective in increasing cDDP cytotoxicity, irrespective of the presence of resistance mechanisms. Therefore, the combination of hyperthermia and cDDP deserves further attention.

Multidrug resistance-associated protein: a protein distinct from P-glycoprotein involved in cytotoxic drug expulsion

1. Multidrug resistance (MDR) is a phenomenon originally seen in cultured tumor cells that, following selection for resistance to a single anticancer agent, become resistant to a range of chemically diverse anticancer agents. These MDR cells show a decrease in intracellular drug accumulation due to active efflux by transporter proteins. The transporter best characterized is P-glycoprotein (Pgp). This protein has been identified in many cancers and has been the target for agents able to inhibit its action, thereby reversing resistance. 2. More recently, another transporter, multidrug resistance-associated protein (MRP) has been identified in a number of MDR human tumor cell lines that do not apparently express Pgp. The presence of MRP at the cell surface of these cells is associated with alterations in drug accumulation and distribution. 3. The gene-encoding MRP has been cloned and sequenced and shown by transfection studies to be able to confer resistance and changes in drug accumulation in sensitive tumor cells. The profile of anticancer drugs expelled in the presence of MRP is similar, but not identical, to that of Pgp. 4. MRP has been identified in a number of different types of cancers, but it is not yet clear to what extent it is involved with clinical resistance. Furthermore, resistance modulators useful against Pgp are less effective in reversing MRP-mediated resistance. 5. It is not fully understood how MRP brings about drug efflux, but it is clear that the underlying mechanisms are different from those responsible for Pgp-mediated drug efflux. In particular, glutathione (GSH) is required for the effective expulsion of the anticancer agents. 6. Unlike Pgp, MRP is able to transport metallic oxyanions and glutathione and other conjugates, including peptidyl leukotrienes. Agents that inhibit organic anion transport, such as probenecid, can block MRP activity. 7. Like Pgp, MRP is expressed not only in resistant tumor cells, but also in normal human tissues. These include the epithelial cells lining the airways and the gastrointestinal tract. In cells in normal tissues, MRP appears to be located within the cytoplasm, which may mean that it functions here in a manner slightly different to that in malignant cells. It is now also recognized in cells and tissues from other species, such as the rat and mouse.

Effect of glutathione depletion on cisplatin resistance in cancer cells transfected with the gamma-glutamylcysteine synthetase gene

Overexpression of the human gamma-glutamylcysteine (gamma-GCS) gene resulted in cisplatin resistance with an increased glutathione (GSH) content, increased ATP-dependent glutathione S-conjugate export pump (GS-X pump) activity and decreased platinum accumulation in human lung cancer cells transfected with a gamma-GCS cDNA expression vector, as we previously reported. In this study, we examined the effects of buthionine sulfoximine (BSO), a specific inhibitor of gamma-GCS, to determine whether GSH depletion alters cisplatin resistance in a gamma-GCS-transfected cell line, SBC-3/GCS. In the presence of 10 microM BSO for 4 days, SBC-3/GCS still showed resistance to cisplatin, although it was partially reversed. Under these conditions, GS-X pump activity remained up-regulated in spite of low GSH content, and the platinum content was decreased. These data suggest that the GS-X pump itself influences cisplatin resistance, as well as cellular GSH content.

DNA repair in cisplatin-sensitive and resistant human cell lines measured in specific genes by quantitative polymerase chain reaction

More than 80% of patients with testicular germ cell tumours (TGCT) are cured using cisplatin-based combination chemotherapy, and resistance to cisplatin is the final barrier to the cure of nearly all patients with this disease. In this study, we used quantitative polymerase chain reaction (Q-PCR) to investigate the role of DNA repair in cisplatin resistance in two genes, one transcribed and one not transcribed. Three pairs of cisplatin-sensitive and resistant cell lines were used, two derived from TGCT and one from a bladder cancer. In these pairs of sublines, we observed no major differences between the repair of cisplatin-induced damage in the transcribed and nontranscribed genes, nor did there appear to be any relationship between DNA repair capacity and the development of cisplatin resistance. Despite the strong indication that the sensitivity of testis tumour cells to cisplatin is related to their reduced ability to repair cisplatin-damaged DNA, these cells apparently do not become resistant to cisplatin by acquiring DNA repair capacity.

The human multidrug resistance-associated protein functionally complements the yeast cadmium resistance factor 1

A Saccharomyces cerevisiae strain with a disrupted yeast cadmium resistance factor (YCF1) gene (DTY168) is hypersensitive to cadmium. YCF1 resembles the human multidrug resistance-associated protein MRP (63% amino acid similarity), which confers resistance to various cytotoxic drugs by lowering the intracellular drug concentration. Whereas the mechanism of action of YCF1 is not known, MRP was recently found to transport glutathione S-conjugates across membranes. Here we show that expression of the human MRP cDNA in yeast mutant DTY168 cells restores cadmium resistance to the wild-type level. Transport of S-(2,4-dinitrobenzene)-glutathione into isolated yeast microsomal vesicles is strongly reduced in the DTY168 mutant and this transport is restored to wild-type level in mutant cells expressing MRP cDNA. We find in cell fractionation experiments that YCF1 is mainly localized in the vacuolar membrane in yeast, whereas MRP is associated both with the vacuolar membrane and with other internal membranes in the transformed yeast cells. Our results indicate that yeast YCF1 is a glutathione S-conjugate pump, like MRP, and they raise the possibility that the cadmium resistance in yeast involves cotransport of cadmium with glutathione derivatives.

Coordinated induction of MRP/GS-X pump and gamma-glutamylcysteine synthetase by heavy metals in human leukemia cells

We recently reported that GS-X pump activity, as assessed by ATP-dependent transport of the glutathione-platinum complex and leukotriene C4, and intracellular glutathione (GSH) levels were remarkably enhanced in cis-diamminedichloroplatinum(II) (cisplatin)-resistant human leukemia HL-60 cells (Ishikawa, T., Wright, C. D., and Ishizuka, H. (1994) J. Biol. Chem. 269, 29085-29093). Now, using Northern hybridization and RNase protection assay, we provide evidence that the multidrug resistance-associated protein (MRP) gene, which encodes a human GS-X pump, is expressed at higher levels in cisplatin-resistant (HL-60/R-CP) cells than in sensitive cells, whereas amplification of the MRP gene is not detected by Southern hybridization. Culturing HL-60/R-CP cells in cisplatin-free medium resulted in reduced MRP mRNA levels, but these levels could be induced to rise within 30 h by cisplatin and heavy metals such as arsenite, cadmium, and zinc. The increased levels of MRP mRNA were closely related with enhanced activities of ATP-dependent transport of leukotriene C4 (LTC4) in plasma membrane vesicles. The glutathione-platinum (GS-Pt) complex, but not cisplatin, inhibited ATP-dependent LTC4 transport, suggesting that the MRP/GS-X pump transports both LTC4 and the GS-Pt complex. Expression of gamma-glutamylcysteine synthetase in the cisplatin-resistant cells was also co-induced within 24 h in response to cisplatin exposure, resulting in a significant increase in cellular GSH level. The resistant cells exposed to cisplatin were cross-resistant to melphalan, chlorambucil, arsenite, and cadmium. These observations suggest that elevated expression of the MRP/GS-X pump and increased GSH biosynthesis together may be important factors in the cellular metabolism and disposition of cisplatin, alkylating agents, and heavy metals.

Mechanisms of resistance of human small cell lung cancer lines selected in VP-16 and cisplatin

BACKGROUND

The combination of VP-16 and cisplatin is one of the most active regimens available for the treatment of small cell lung cancer (SCLC), however, most tumors eventually become resistant to these drugs.

METHODS

To investigate the problem of resistance to VP-16 and cisplatin in patients with SCLC, we established two resistant sublines from the drug sensitive human SCLC line, NCI-H209, by in vitro selection in VP-16 and cisplatin.

RESULTS

The VP-16-selected cell line, H209/VP, was more than 100-fold resistant to VP-16, and displayed cross-resistance to VM-26 and other topoisomerase II interactive drugs, but not to vinca alkaloids. There was no difference in accumulation of VP-16 in H209/VP compared with its parent cell line. The level of topoisomerase II-alpha was reduced to 8% of that in the parent cell line, and there was an altered form of this enzyme with a molecular weight of 160 kilodaltons (kDa), in addition to the normal 170 kDa protein. The cisplatin-selected cell line, H209/CP, was 11.5-fold resistant to cisplatin, with only a low level of cross-resistance to other platinum compounds including carboplatin, tetraplatin, iproplatin, and lobaplatin. This line was highly cross-resistant to vinca alkaloids, but not to anthracyclines or epipodophyllotoxins. The H209/CP cell line was not resistant to cadium chloride, suggesting that alterations in metallothionein are unlikely to be a cause of resistance. Although glutathione (GSH) levels were increased nearly 2-fold in H209/CP, there was no difference in levels of the GSH-related enzymes glutathione-S-transferase, glutathione peroxidase, and glutathione reductase, compared with the parent line. The H209/CP line had a 1.4-fold elevation of topoisomerase II-alpha. The accumulation of cisplatin was reduced in this cell line, and there were fewer DNA-interstrand cross links formed in the presence of cisplatin in H209/CP, compared with the parent line. Neither H209/VP nor H209/CP expressed MDR1, the gene for P-glycoprotein. The MRP gene was expressed at a slightly higher level in the H209/VP cell line, but there was no significant increase in expression of this gene in the H209/CP cell line.

CONCLUSIONS

The resistance of the H209/VP cell line is associated with an alteration of topoisomerase II-alpha, whereas the resistance in the H209/CP line is associated with reduced drug accumulation.

Positive correlation between cellular glutathione and acquired cisplatin resistance in human ovarian cancer cells

While multiple changes are frequently found to be associated with cisplatin resistance in a variety of tumor cell lines, a cause-effect relationship of these alterations with the resistant phenotype has not been established. In order to identify the resistance-relevant determinants, a series of cisplatin-resistant sublines with different degrees of resistance to cisplatin was developed in a human ovarian carcinoma cell line (O-129). Three derived resistant cell lines displayed 2.1-fold (O-129/DDP4, low), 4.1-fold (O-129/DDP8, moderate) and 6.3-fold (O-129/DDP16, high) resistance, respectively, to cisplatin, compared with the sensitive parental line O-129. While the activity of poly(ADP-ribose) polymerase, an enzyme proposed to be involved in DNA repair, was elevated in all three resistant lines, a significant karyotypic change was observed only in the high-resistance line with the karyotype alteration from near diploidy to heteroploidy. The moderate (4.1-fold) and high (6.3-fold) DDP resistance was associated with a slow proliferation rate in drug-free medium, but cellular glutathione level was highly correlated with DDP sensitivity in all four cell lines. Taken together, the present studies establish that while many changes at cellular level can occur with development of cisplatin resistance, only elevation of intracellular glutathione concentration appears to be related to the resistance phenotype in these human ovarian cancer cells.

Role of glutathione in the export of compounds from cells by the multidrug-resistance-associated protein

Multidrug-resistance-associated protein (MRP) is a plasma membrane glycoprotein that can confer multidrug resistance (MDR) by lowering intracellular drug concentration. Here we demonstrate that depletion of intracellular glutathione by DL-buthionine (S,R)-sulfoximine results in a complete reversal of resistance to doxorubicin, daunorubicin, vincristine, and VP-16 in lung carcinoma cells transfected with a MRP cDNA expression vector. Glutathione depletion had less effect on MDR in cells transfected with MDR1 cDNA encoding P-glycoprotein and did not increase the passive uptake of daunorubicin by cells, indicating that the decrease of MRP-mediated MDR was not due to nonspecific membrane damage. Glutathione depletion resulted in a decreased efflux of daunorubicin from MRP-transfected cells, but not from MDR1-transfected cells, suggesting that glutathione is specifically required for the export of drugs from cells by MRP. We also show that MRP increases the export of glutathione from the cell and this increased export is further elevated in the presence of arsenite. Our results support the hypothesis that MRP functions as a glutathione S-conjugate carrier.