MRP1 Gene Research Articles

Inflammatory cytokines, but not bile acids, regulate expression of murine hepatic anion transporters in endotoxemia.

Endotoxin-mediated cholestasis stems from impaired hepatobiliary transport of bile acids and organic anions due to altered expression and activity of transporters, including Oatp, Mrp, Ntcp, and Bsep. However, the mechanisms by which the Oatp and Mrp genes are down-regulated are largely unknown. Using in vivo and in vitro murine models of inflammation, we examined the role of cytokines and bile acids in regulating Oatp and Mrp. Endotoxin (lipopolysaccharide, LPS), interleukin (IL)-6, IL-1beta, tumor necrosis factor (TNF)-alpha, cholic acid, taurocholate, or taurodeoxycholate was administered in vivo to mice or in vitro to Hepa 1-6 mouse hepatoma cells. Mrp, Oatp, and Bsep mRNA levels were measured by reverse transcription-polymerase chain reaction. Mrp efflux activity was measured using 5-carboxyfluorescein. In vivo, LPS treatment profoundly suppressed hepatic mRNA levels of Mrp2, Mrp3, Oatp1, Oatp2, and Bsep to 15, 60, 44, 30, and 32% of controls, respectively (p < 0.05), but did not significantly alter Mrp1 expression. IL-6 or IL-1beta administration suppressed Mrp2, Oatp1, Oatp2, and Bsep mRNA levels to 20 to 60% controls (p < 0.05). TNF-alpha administration affected mRNA levels of Mrp2, Mrp3, and Oatp2 but not Oatp1 or Bsep. Bile acid treatment increased the in vivo expression of Bsep but not Mrp or Oatp. Likewise, significantly lower mRNA levels of Mrp2 with a corresponding decrease in cellular efflux of 5-carboxyfluorescein was seen in vitro in IL-6- and IL-1beta-treated Hepa 1-6 cells, whereas bile acids did not have significant effects. In conclusion, cytokines are key mediators in regulating hepatic expression of anion transporters in inflammatory cholestasis, whereas bile acids likely play a minor role.

Copper-transporting P-type adenosine triphosphatase (ATP7B) as a cisplatin based chemoresistance marker in ovarian carcinoma: comparative analysis with expression of MDR1, MRP1, MRP2, LRP and BCRP.

Intrinsic or acquired resistance to chemotherapy is the major obstacle to overcome in the treatment of patients with solid carcinoma. Cisplatin is one of the most effective chemotherapeutic agents for treating ovarian carcinoma. Recently, copper-transporting P-type adenosine triphosphatase (ATP7B) has been demonstrated as one of the genes responsible for cisplatin resistance in vitro. We hypothesized that the expression of ATP7B gene increases resistance to cisplatin in ovarian carcinoma and a priori knowledge of its expression is important for the choice of therapy. The aim of our study was to assess the role of ATP7B gene in ovarian carcinoma and compare its expression with those of multidrug resistance-related transporters such as MDR1, MRP1, MRP2, LRP and BCRP genes. The transporters' gene expression profiles from 82 patients treated with cisplatin-based chemotherapy after surgery were assessed by RT-PCR. We did not observe any significant correlation between ATP7B gene expression and those of MDR1, MRP1, MRP2, LRP or BCRP. The expression level of ATP7B gene was significantly increased (p < 0.05) in patients with moderately-/poorly-differentiated ovarian carcinomas treated with cisplatin-based chemotherapy, thus ATP7B may serve as an independent prognostic factor in these patients. In contrast, the expression level of MDR1, MRP1, MRP2, LRP and BCRP genes were not prognostic indicators of disease. These findings suggest that ATP7B gene may be considered as a novel chemoresistance marker and that inhibitor(s) of ATP7B might be useful, in patients with ovarian carcinoma treated with cisplatin-based chemotherapy.

Chronic Arsenic-Exposed Human Prostate Epithelial Cells Exhibit Stable Arsenic Tolerance: Mechanistic Implications of Altered Cellular Glutathione and Glutathione S-transferase

Acquisition of stable arsenic tolerance in human cells following chronic arsenic exposure has not been previously reported. In the present work, we describe acquisition of stable arsenic tolerance in the human prostate epithelial cell line RWPE-1 following chronic arsenic exposure in vitro. RWPE-1 cells continuously exposed to 5 μM sodium arsenite for ≥18 weeks exhibited dramatic resistance to acute arsenite toxicity. The LC50 for acute arsenite exposure in these chronic arsenic-exposed prostate epithelial (CAsE-PE) cells was 43.8 μM versus 17.6 μM in control cells. Similar results were obtained using the antineoplastic agent arsenic trioxide. This tolerance was stable, as CAsE-PE cells grown in arsenic-free medium for 5 weeks retained their resistant phenotype. Compared to control cells, CAsE-PE cells showed a 90% reduction in arsenic accumulation over 24 h coupled with a 2.6-fold increase in the rate of arsenic efflux. CAsE-PE cells had increased basal GSH levels (4.9-fold) and increased GST activity (2.4-fold) and both GSH depletion and inhibition of GST activity abolished arsenic tolerance. Arsenic tolerance was also abolished by treatment with inhibitors of the Mdr1 and Mrp1 transporters, although no increases in mdr1 or mrp1 gene expression were observed. Our results indicate that this tolerance in human cells involves increases in GSH levels and GST activity that allow for more efficient arsenic efflux by MRP1 and MDR1. This study represents the first report of stable acquired arsenic tolerance in human cells, which could have important implications for both the toxicology and the pharmacology of arsenic.

Chronic Arsenic-Exposed Human Prostate Epithelial Cells Exhibit Stable Arsenic Tolerance: Mechanistic Implications of Altered Cellular Glutathione and Glutathione S-transferase

Acquisition of stable arsenic tolerance in human cells following chronic arsenic exposure has not been previously reported. In the present work, we describe acquisition of stable arsenic tolerance in the human prostate epithelial cell line RWPE-1 following chronic arsenic exposure in vitro. RWPE-1 cells continuously exposed to 5 μM sodium arsenite for ≥18 weeks exhibited dramatic resistance to acute arsenite toxicity. The LC50 for acute arsenite exposure in these chronic arsenic-exposed prostate epithelial (CAsE-PE) cells was 43.8 μM versus 17.6 μM in control cells. Similar results were obtained using the antineoplastic agent arsenic trioxide. This tolerance was stable, as CAsE-PE cells grown in arsenic-free medium for 5 weeks retained their resistant phenotype. Compared to control cells, CAsE-PE cells showed a 90% reduction in arsenic accumulation over 24 h coupled with a 2.6-fold increase in the rate of arsenic efflux. CAsE-PE cells had increased basal GSH levels (4.9-fold) and increased GST activity (2.4-fold) and both GSH depletion and inhibition of GST activity abolished arsenic tolerance. Arsenic tolerance was also abolished by treatment with inhibitors of the Mdr1 and Mrp1 transporters, although no increases in mdr1 or mrp1 gene expression were observed. Our results indicate that this tolerance in human cells involves increases in GSH levels and GST activity that allow for more efficient arsenic efflux by MRP1 and MDR1. This study represents the first report of stable acquired arsenic tolerance in human cells, which could have important implications for both the toxicology and the pharmacology of arsenic.

Multidrug resistance gene-1 is a useful predictor of Paclitaxel-based chemotherapy for patients with ovarian cancer.

The objective of this study was to determine the relationship between multidrug resistance and sensitivity to paclitaxel (PTX) in ovarian cancer. We used human ovarian adenocarcinoma cell lines, KF, a PTX-resistant cell line (KFTx), SK-OV-3, and KOC7c. Additionally, 27 patients with ovarian cancer who had residual disease were examined. All patients underwent postoperative chemotherapy consisting of 175 mg/m(2) PTX and area under curve (AUC) 5 carboplatin. The sensitivity of the cells to PTX or cisplatin (CDDP) was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. mRNA expression of multidrug resistance gene-1 (MDR-1) and multidrug resistance-associated protein-1 (MRP-1) and MRP-2 was determined by reverse transcription-polymerase chain reaction. beta-Tubulin polymerization and Bcl-2 phosphorylation were examined by Western blot analysis. Compared with KF, the IC(50) to PTX was 5.5-fold higher for KFTx, 0.3-fold for SK-OV-3, and 52.1-fold for KOC7c. The IC(50) to CDDP was 0.7-, 4.2-, and 5.8-fold, respectively. Expression of the MDR-1 gene was clearly observed in KFTx and KOC7c. Expression of MRP-1 was observed in SK-OV-3 and KOC7c. Expression of MRP-2 was detected only in KOC7c. CDDP enhanced beta-tubulin polymerization induced by PTX in CDDP-sensitive cells. Bcl-2 phosphorylation appeared after exposure to IC(50) PTX in all cells. Twenty-one patients responded to chemotherapy and six did not. Expression of the MDR-1 gene for nonresponders was significantly higher than that for responders (260.0 +/- 191.6 vs 9.3 +/- 21.8). With the cutoff value of MDR-1 expression at 100, the predictive value for chemoresponse was 96%. Expression of the MRP-1 and MRP-2 genes did not differ between nonresponders and responders. MDR-1 gene expression may be a useful predictor for PTX-based chemotherapy.

Sensitivity to anticancer agents and resistance mechanisms in clear cell carcinoma of the ovary.

We conducted the present study to determine the chemoresistance mechanisms in clear cell carcinoma of the ovary (CCC). Five human CCC cell lines (HAC‐2, RMG‐I, RMG‐II, KK, and KOC‐7c) were used in this study. The sensitivity of the cells to the anticancer agents was determined by 3–(4,5–dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay and we assessed drug sensitivity by calculating assay area under the curve (AUC) for each agent. The expression of multi‐drug resistance genes (MDR‐1, MRP‐1, MRP‐2) was detected by reverse transcription‐polymerase chain reaction (RT‐PCR). Glutathione (GSH) concentration was measured by an enzymatic assay. Topoisomerase (topo) I activity was assayed in terms of relaxation of supercoiled plasmid substrate DNA. The IC50 to anticancer agents ranged widely. The assay AUC indicated that 3 of 5 cell lines (RMG‐I, RMG‐II, and KK) were sensitive to paclitaxel (PTX), 3 (HAC‐2, RMG‐I, and RMG‐II) were sensitive to 7–ethyl‐10‐hydroxycamptothecin (SN‐38), which is an active metabolite of camptothecin (CPT‐11), and only one (HAC‐2) was sensitive to cisplatin (CDDP). All cell lines were resistant to mitomycin‐C (MMC) and etoposide (VP‐16). The MRP‐1 gene was detected in all cell lines. Only one cell line showed both MRP‐2 and MDR‐1 gene expression. Except for HAC‐2 cells, expression of MRP genes was related to CDDP resistance, and MDR‐1 gene expression was associated with PTX resistance. GSH concentrations increased after exposure to CDDP or MMC in all cell lines. There was a significant correlation between topo‐I enzymatic activity and the response to SN‐38. The present study revealed several resistance mechanisms in CCC and the results suggested that PTX and CPT‐11 might be effective agents to treat CCC.

MRP genes in the hepatic transport of a new MRI contrast agent

MRP genes in the hepatic transport of a new MRI contrast agent

Increased renal expression of bilirubin glucuronide transporters in a rat model of obstructive jaundice.

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

Molecular and functional MDR1-Pgp and MRPs expression in human glioblastoma multiforme cell lines.

The aim of our study was to investigate the functional expression of P-glycoprotein (Pgp) and multidrug resistance-associated proteins (MRPs) in 2 distinct glioma cells (GL15 and 8MG) from patients with glioblastoma multiforme. MDR1 gene and Pgp expression was not detected in either cell line by RT-PCR and Western blotting, respectively. In contrast, MRP1 was detected at both mRNA and protein level in both cell lines, with a higher expression in the 8MG cells that occur predominantly at the cell membrane. Three other MRPs (MRP3, MRP4 and MRP5) were detected by RT-PCR in both cell lines, whereas MRP2 was not expressed. In addition, MRP3 protein was also detected by immunocytochemistry in both GL15 and 8MG cell lines. Indomethacin and probenecid, 2 modulators of MRPs activity, increased the accumulation of vincristine and etoposide, 2 substrates of MRPs, by both cell lines. These modulators also decreased the efflux of vincristine from both cell lines with a more pronounced effect in 8MG cells. In conclusion, our results show functional expression of MRPs leading to a decrease in the intracellular vincristine and etoposide concentrations in human glioblastoma cell lines. Furthermore, our results that exhibit protein expression of MRP1 and MRP3 and gene expression of MRP4 and MRP5 in these 2 glioblastoma cell lines suggest new mechanisms that could lead to a MDR phenotype of tumour cells in patients with glioblastoma multiforme.

Transcriptional Regulation of the Rat Mrp3 Promoter in Intestine Cells

The promoter of rat multidrug resistance protein 3 (Mrp3) has been cloned and analyzed in the rat intestinal cell line (IEC-18 cells). A series of 5′ deletion mutants of the Mrp3 promoter region were constructed and placed into the pGL3-Basic vector (luciferase reporter gene). Deletion analysis of the Mrp3 promoter identified a basal transcription element at −123/−106, two negative response regions at −2723/−1128 and −530/−443, respectively, and two positive response regions at −1063/−943 and −302/−157. Further site-directed mutagenesis analysis and gel mobility shift assays provided evidence for Sp1 and Sp3 binding within −123/−105 regions. These studies indicate that Sp1 and Sp3 may be involved in the regulation of the rat Mrp3 gene.

Existence of two emm-like "mrp" and "emm" genes in the mga regulon of the Streptococcus pyogenes strain ST4547.

Streptococcus pyogenes ST4547 is an opacity factor negative strain, which has been recently reported as a new emm type from Malaysia. Nucleotide sequencing of the mga regulon of this strain showed the existence of two emm-like genes. The emm gene located upstream of the scpA gene comprises 1305 nucleotides encoding the putative precursor M protein of 435 amino acids in length with an M(r) of 49 kDa. or a predicted mature protein of 394 amino acids with an M(r) of 44.8 kDa. Another gene mrpST4547 was located upstream of the emm gene and downstream of the mga gene. The sequence of this mrp gene comprises 1167 nucleotides encoding a predicted protein of 388 amino acids in length with an M(r) of 42.2 kDa. or a predicted mature protein of 347 amino acids with an M(r) of 37.9 kDa. The mga regulon of strain ST4547 has a mosaic structure comprising segments, which originated from different OF positive and OF negative strains. The sequences flanking the hyper-variable and C repeats of the emmST4547 gene showed high similarity to corresponding regions in the mga regulon of OF positive strains notably M15, M4, M22 and M50. In contrast, the sequence within the hyper-variable and C repeat regions of the emmST4547 gene revealed high similarity to equivalent regions in the OF negative strains. These data indicates that horizontal transfer of emm-like gene could have occurred between OF positive and OF negative strains resulting in architectural divergence in the mga regulon.

Increased expression of multidrug resistance-associated proteins in bladder cancer during clinical course and drug resistance to doxorubicin.

Overexpression of the P-glycoprotein/multidrug resistance 1 (MDR1) and multidrug resistance protein 1 (MRP1) gene is closely associated with the clinical outcome of various malignancies, and it is involved in responses to some anticancer chemotherapeutic agents including doxorubicin. Six human MRP subfamily members (MRP2-7) with structural similarities to MRP1 have been identified. Recently, the relationships between MRP2 and MRP3 expression levels of some cancer cells and drug sensitivity to doxorubicin have been reported, but the relationship between the clinical samples and drug sensitivity remains unclear. We determined the expressions of the MDR1, MRP1, MRP2 and MRP3 gene in bladder cancer during the clinical course and sought to learn whether the expression was correlated with drug responses to doxorubicin. Doxorubicin, used in chemotherapeutic treatment including intravesical and systemic chemotherapy, is an important anticancer agent for the treatment of bladder cancer. We used quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for our study, and the sensitivity to doxorubicin in bladder cancer was determined using the in vitro succinate dehydrogenase inhibition test. Using 47 clinical samples of bladder cancer, we confirmed the significant correlation of MDR1, MRP1 and MRP3 mRNA levels with resistance to doxorubicin. We showed that the expression of MDR1, MRP1, MRP2 and MRP3 in recurrent tumors and residual tumors after chemotherapeutic treatment was higher than that in untreated primary tumors. In particular, the MDR1 expression in residual tumors was 5.7-fold higher than that in untreated primary tumors.

Expression of the Multidrug Resistance-associated Protein (mrp ) Gene in Chronic Lymphocytic Leukemia

In order to define more accurately the role of multidrug resistance (MDR)-related protein (mrp ) gene in chronic lymphocytic leukemia (CLL), we addressed the question of its expression pattern in isolated peripheral blood B lymphocytes in seven healthy donors and 28 patients with CLL, with respect to some laboratory and clinical parameters of the disease. For this purpose, we used a semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR), based on the coamplification of an internal standard not homologous to the DNA target to quantify the mrp transcription level in each studied sample. We report that the level of constitutive mrp gene's expression in peripheral blood lymphocytes is higher in CLL patients than in healthy controls. We found increased mrp gene expression levels in patients with higher white blood cells (WBC) and lymphocytes' counts as well as in more advanced disease stages according to Rai or Binet scale. Finally, mrp gene's expression was higher in patients with progressive CLL, especially in cases refractory to chemotherapy salvage. The results of the present study suggest that expression of mrp gene might be relevant in the pathogenesis of the MDR phenotype in CLL.

Effects of polymorphisms of MDR1, MRP1, and MRP2 genes on their mRNA expression levels in duodenal enterocytes of healthy Japanese subjects.

In the present study, we examined whether polymorphisms in the ATP-binding cassette (ABC) transporter genes, MDR1, MRP1 and MRP2, were associated with their respective mRNA expression levels in duodenal enterocytes of 13 healthy Japanese volunteers. MDR1 genotypes of T-129C, G2677(A,T) and C3435T, MRP1 genotypes of G128C, C218T, G2168A and G3173A, and MRP2 genotypes of C-24T, G1249A, C2302T, C2366T and G4348A were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) or direct sequencing. Mutations T-129C, G2677(A,T) and C3435T of MDRI gene were found at allele frequencies of 2/26, 16/26 and 12/26, respectively. Mutations G2168A of the MRPI gene and C-24T of the MRP2 gene were also found at allele frequencies of 1/26 and 6/26, respectively, whereas other mutations were not detected in MRP1 and MRP2 genes. The relative concentrations (mean +/- S.E.) of MDR1 mRNA to villin mRNA were 0.38 +/- 0.15, 0.56 +/- 0.14 and 1.13 +/- 0.42 in the subjects with C/C3435, C/T(3435) and T/T(3435), respectively, which supported the lower serum concentrations of digoxin after single oral administration in the subjects with the mutant T-allele at position 3435. Genetic collaboration between positions 3435 and 2677 was suggested, and those in G/G2677, G/(A,T)(2677) and T/(A,T)(2677) were 0.16 +/- 0.05, 1.10 +/- 0.40, and 0.63 +/- 0.16, respectively (p = 0.107). However, there was no remarkable effect of the G2168A of the MRP1 gene or of C-24T of the MRP2 gene on the relative MRP1 or MRP2 mRNA concentrations, respectively.

Subcellular daunorubicin distribution and its relation to multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R.

To investigate the correlation between subcellular daunorubicin distribution and the multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R. The multidrug resistant cell line SMMC-7721/R, a human hepatocellular carcinoma cell line, was established. Antisense oligonucleotides (AS-ODN) were used to obtain different multidrug resistance phenotypes by inhibiting the expression of mdr1 gene and/or multidrug resistance-related protein gene(mrp) using Lipofectamine as delivery agent. Expression of mdr1 and mrp genes was evaluated by RT-PCR and Western blotting. Intracellular daunorubicin (DNR) concentration was measured by flow cytometry. Subcellular DNR distribution was analyzed by confocal laser scanning microscopy. Adriamycin (ADM) and DNR sensitivity was examined by MTT method. Low level expression of mdr1 and mrp mRNAs and no expression of P-Glycoprotein(P-gp) and multidrug resistance-related protein (P(190)) were detected in parental sensitive cells SMMC-7721/S, but over-expression of these two genes was observed in drug-resistant cell SMMC-7721/R. The expression of mdr1 and mrp genes in SMMC-7721/R cells was down-regulated to the level in the SMMC-7721/S cells by AS-ODN. Intracellular DNR concentration in SMMC-7721/S cells was 10 times higher than that in SMMC-7721/R cells. In SMMC7721/S cells intracellular DNR distributed evenly in the nucleus and cytoplasm, while in SMMC-7721/R cells DNR distributed in a punctate pattern in the cytoplasm and was reduced in the nucleus. DNR concentration in SMMC-7721/R cells co-transfected with AS-ODNs targeting to mdr1 and mrp mRNAs recovered to 25 percent of that in SMMC7721/Scells. Intracellular DNR distribution pattern in drug-resistant cells treated by AS-ODN was similar to drug-sensitive cell, and the cells resistance index (RI) to DNR and ADM decreased at most from 88.0 and 116.0 to 4.0 and 2.3, respectively. Co-Transfection of two AS-ODNs showed a stronger synergistic effect than separate transfection. P-gp and P(190) are two members mediating MDR in cell line SMMC7721/R. Intracellular drug concentration increase and subcellular distribution change are two important factors in multidrug resistance (MDR) formation. The second factor, drugs transport by P-gp and P(190) from cell nucleus to organell in cytoplasm, may play a more important role.

Inhibitors of multidrug resistance to antitumor agents (MDR).

Multidrug resistance is one of the main obstacles in the chemotherapy of cancer. Its inhibition by combination of chemosensitizers with antitumor compounds is a very active field of research, since safe and potent reversal agents would be beneficial for clinical use. Most modulators act by binding to membrane transport proteins (specially P-gp and MRP) and inhibiting their drug-effluxing activity, or by indirect mechanisms related to phosphorylation of the transport proteins or expression of the mdr1 and mrp1 genes. The main body of the review focuses on the study of the known MDR modulators, which are classified according to their chemical structures. General structure-activity studies of this therapeutic group are hampered by the very heterogeneous chemical structure of the compounds, although some conclusions have been drawn from the study of homogeneous series of molecules.

Characterization of the efflux transporter(s) responsible for restricting intestinal mucosa permeation of the coumarinic acid-based cyclic prodrug of the opioid peptide DADLE.

To elucidate the efflux transporter(s) responsible for restricting the permeation of a coumarinic acid-based cyclic prodrug of the opioid peptide DADLE (CD) thorough Caco-2 cell monolayers. The cellular permeability characteristics of CD were investigated using Caco-2 cells, Madin-Darby canine kidney-wild type II cells (MDCK-WT). MDCK cells transfected with the human MDR1 gene (MDCK-MDR1), and MDCK cells transfected with human MRP2 gene (MDCK-MRP2). These cells were grown as monolayers onto microporous membranes. The disappearance from the donor side and appearance on the receiver side of CD were monitored by HPLC. The substrate activity of CD for P-gp was determined by using GF120918. a known P-gp specific inhibitor. The substrate activity of CD for MRP2 was determined by using cyclosporin A (CsA), a known MRP2 and P-gp inhibitor. In Caco-2 cells, the ratio of the apparent permeability coefficients (Papp) of CD flux in the basolateral (BL) to apical (AP) direction vs. the flux in the AP-to-BL direction (Papp-BL-to-AP/Papp AP-to-BL) was 71. In the presence of GF120918 (2 microM), the Papp BL-to-AP/Papp AP-to-BL ratio was decreased to 16. In the presence of CsA (25 microM), the ratio was decreased to 5.6. In MDCK-WT. MDCK-MDR1, and MDCK-MRP2 cells, the Papp BL-AP/Papp AP-to-BL ratios of CD were 13, 35, and 22, respectively. CsA (25 microM) greatly decreased the Papp BL-P-AP/Papp AP-to-BL ratios in MDCK-WT and MDCK-MDR1 cells to 1.5 and 3.2, respectively. However, in MDCK-MRP2 cells. CsA (25 microM) decreased the ratio only to 11. A mixture of GF120918 (2 microM) and CsA (25 microM) decreased the Papp BL-to-AP/Papp AP-to-BL ratios of CD in MDCK-WT, MDCK-MDR1, and MDCK-MRP2 cells to 1.4, 2.7, and 5.4. respectively. These data suggest that CD is a good substrate for both P-gp and MRP2 and that the restricted permeation of this cyclic prodrug in Caco-2 cells and in the intestinal mucosa is probably due to its substrate activities for both of these efflux transporters.

A modified coumarinic acid-based cyclic prodrug of an opioid peptide: its enzymatic and chemical stability and cell permeation characteristics.

To evaluate the chemical/enzymatic stability and the cell permeation characteristics of the modified coumarinic acid-based cyclic prodrug 2 of DADLE (H-Tyr-D-Ala-Gly-Phe-D-Leu-OH), which has an aldehyde equivalent (oxymethyl) inserted between the phenolic group of the promoiety and the carboxylic acid group of the peptide. The rates of the chemical/enzymatic conversion of the oxymethyl-modified prodrug 2 to DADLE were measured by HPLC. The cellular permeation characteristics of DADLE and its oxymethyl-modified prodrug 2 were measured by HPLC using Caco-2 cells, wild type Madin-Darby Canine Kidney cells (MDCK-WT), MDCK cells transfected with human MDR1 gene (MDCK-MDR1), and MDCK cells transfected with human MRP2 gene (MDCK-MRP2) grown onto microporous membranes. The oxymethyl-modified coumarinic acid-based cyclic prodrug 2 degraded chemically to DADLE in a pH-dependent manner, i.e., rates of conversion increased with increasing pH. The prodrug 2 degraded rapidly in rat plasma (t1/2 = 39 min) and rat liver homogenate (t1/2 = 59.2 min), but much slower in Caco-2 cell homogenate (t1/2 = 678.7 min) and human plasma (t1/2 = 264.3 min). In all four cell lines used for transport studies, the flux rates of the oxymethyl prodrug 2 in the basolateral (BL)-to-apical (AP) direction (Papp BL-to-AP) were significantly greater than the flux rates in the AP-to-BL direction (Papp AP-to-BL). The Papp BB-to-AP/Papp AP-to-BL ratios were >116, 35.1, 21.2, and 12.6 in Caco-2, MDCK-MDR1, MDCK-MRP2, and MDCK-WT cells, respectively. The efflux of the modified prodrug could be inhibited by GF120918 (an inhibitor for P-gp) and cyclosporin A (an inhibitor for P-gp and MRP2). The oxymethyl-modified coumarinic acid-based cyclic prodrug 2 of DADLE could be converted to DADLE in both chemical and enzymatic media. However, the prodrug was a good substrate for both P-gp and MRP2 suggesting that its permeation across intestinal mucosa and blood-brain barrier would be significantly restricted.

Characterization of the efflux transporter(s) responsible for restricting intestinal mucosa permeation of an acyloxyalkoxy-based cyclic prodrug of the opioid peptide DADLE.

To elucidate the efflux transporter(s) responsible for restricting the permeation of an acyloxyalkoxy-based cyclic prodrug of the opioid peptide DADLE (AD) through Caco-2 cell monolayers. The cellular permeation characteristics of AD were investigated using Caco-2 cells, Madin-Darby canine kidney wild-type II cells (MDCK-WT), MDCK cells transfected with the human MDR1 gene (MDCK-MDR1), and MDCK cells transfected with the human MRP2 gene (MDCK-MRP2). These cells were grown as monolayers onto microporous membranes. The disappearance of AD from the donor side and its appearance on the receiver side were monitored by high-performance liquid chromatography. The substrate activity of AD for P-glycoprotein (P-gp) was determined using GF120918, a known P-gp specific inhibitor. The substrate activity of AD for MRP2 was determined by using cyclosporin A, a known MRP2 and P-gp inhibitor. In Caco-2 cells, the ratio of the apparent permeability coefficients (Papp) of AD flux measured in the basolateral (BL) to apical (AP) direction vs. the flux in the AP-to-BL direction (Papp BL-to-AP/ Papp AP-to-BL) was 99. In the presence of 2 microM GF120918 or 25 microM cyclosporin A. the Papp BL-to-AP/Papp AP-to-BL ratio was decreased to 11. In MDCK-WT, MDCK-MDR1, and MDCK-MRP2 cells, the Papp BL-to-AP/Papp AP-to-BL ratios of AD were 4.7, 10, and 5.8, respectively. A mixture of GF120918 (2 microM) and cyclosporin A (25 microM) decreased the Papp BL-to-AP/Papp AP-to-BL ratios of AD in MDCK-WT, MDCK-MDR1, and MDCK-MRP2 cells to 1.2,1.8, and 2.3, respectively. These data suggest that AD is a much better substrate for P-gp than MRP2 and that the restricted permeation of this cyclic prodrug in Caco-2 cells and in the intestinal mucosa probably is due primarily to its substrate activity for P-gp.

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The MDM2 protein is known to be overexpressed in some sarcomas including rhabdomyosarcoma. However, the extent to which the MDM2 protein influences sensitivity to chemotherapeutic drugs is unclear. We have analysed this further using stable transfection of the mdm2 gene into 4 well-characterised human paediatric rhabdomyosarcoma cell lines. Transfection with the mdm2 gene resulted in increased levels of the MDM2 protein in all the cell lines. In 2 of the lines, SCMC and RD, the mdm2 gene caused between 2-fold and 61-fold increase in resistance to vincristine, etoposide and doxorubicin but not to cisplatin. In these lines there was an increase in expression of the mdr-1 gene which encodes P-glycoprotein, but not the mrp1 gene which encodes the multidrug resistance protein (MRP). The resistance was reversible using the MDR modulator PSC833, confirming the presence of P-glycoprotein. We conclude that MDM2 overexpression may be a mechanism by which multidrug resistance is regulated in some rhabdomyosarcomas. © 2001 Cancer Research Campaign http://www.bjcancer.com