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Biomedical subjects

M Heijn

Publications and source records attributed to M Heijn.

15 recordsLinked to original sources
PubMed2000

Anti-Vascular endothelial growth factor treatment augments tumor radiation response under normoxic or hypoxic conditions.

Recent studies in experimental animals have shown that combining antiangiogenic therapy with radiation can enhance tumor response. Whether this enhancement is mainly attributable to angiogenesis inhibition, endothelial cell radiosensitivity, tumor cell apoptosis, or a decrease in the number of hypoxic cells (improved oxygenation) is not known. We designed this study to discern the role of tumor oxygenation. We chose an anti-vascular endothelial growth factor (anti-VEGF) monoclonal antibody (mAb) which has a known target, human VEGF. We also measured interstitial fluid pressure (IFP) to test the hypothesis that the decreased vascular permeability induced by the anti-VEGF mAb can lower IFP. The effect of anti-VEGF mAb on vascular density, partial oxygen tension (pO2), and apoptosis was also measured. Athymic NCr/Sed nu/nu mice bearing 6-mm xenograft of the human glioblastoma multiforme (U87), or colon adenocarcinoma (LS174T) were treated with anti-VEGF mAb injected i.p. on alternate days for a total of six injections at a dosage of 100 microg/injection/mouse. For combined anti-VEGF and radiation, single radiation doses were given under normal blood flow (20 and 30 Gy) or clamped hypoxic conditions (30 and 40 Gy) 24 h after the sixth injection of mAb. The inhibition of the growth of U87 and LS174T tumors by the anti-VEGF mAb was associated with a significant reduction in tumor vascular density and a relatively small increase in the number of apoptotic cells. Compared with size-matched controls, IFP decreased by 74% in LS174T, and 73% in U87 in mice treated with anti-VEGF mAb. After antibody treatment PO2 increased significantly in U87, but did not change in LS174T tumors. Combined treatment induced in U87 tumors a tumor-growth delay (TGD) which was greater than additive; in LS174T except for the 40-Gy hypoxic group, the effect was only additive. In both U87 and LS174T the TGD induced by the antibody was independent of oxygen levels in the tumor at the time of radiation. The fact that the increase in TGD occurred under both normoxic and hypoxic conditions suggests that anti-VEGF mAb treatment can compensate for the resistance to radiation induced by hypoxia.

Adenocarcinoma↗
PubMed2000

Specific detection of multidrug resistance proteins MRP1, MRP2, MRP3, MRP5, and MDR3 P-glycoprotein with a panel of monoclonal antibodies.

Tumor cells may display a multidrug resistance phenotype by overexpression of ATP binding cassette transporter genes such as multidrug resistance (MDR) 1 P-glycoprotein (P-gp) or the multidrug resistance protein 1 (MRP1). MDR3 P-gp is a close homologue of MDR1 P-gp, but its role in MDR is probably minor and remains to be established. The MRP1 protein belongs to a family of at least six members. Three of these, i.e., MRP1, MRP2, and MRP3, can transport MDR drugs and could be involved in MDR. The substrate specificity of the other family members remains to be defined. Specific monoclonal antibodies are required for wide-scale studies on the putative contribution of these closely related transporter proteins to MDR. In this report, we describe the extensive characterization of a panel of monoclonal antibodies (Mabs) detecting several MDR-related transporter proteins in both human and animal tissues. The panel consists of P3II-1 and P3II-26 for MDR3 P-gp; MRPr1, MRPm6, MRPm5, and MIB6 for MRP1; M2I-4, M2II-12, M2III-5 and M2III-6 for MRP2; M3II-9 and M3II-21 for MRP3; and M5I-1 and M5II-54 for MRP5. All Mabs in the panel appeared to be fully specific for their cognate antigens, both in Western blots and cytospin preparations, as revealed by lack of cross-reactivity with any of the other family members. Indeed, all Mabs were very effective in detecting their respective antigens in cytospins of transfected cell lines, whereas in flow cytometric and immunohistochemical analyses, distinct differences in reactivity and suitability were noted. These Mabs should become valuable tools in studying the physiological functions of these transporter proteins, in screening procedures for the absence of these proteins in hereditary metabolic (liver) diseases, and in studying the possible contributions of these molecules to MDR in cancer patients.

ATP-Binding Cassette Transporters↗
PubMed1999

Cellular membrane permeability of anthracyclines does not correlate with their delivery in a tissue-isolated tumor.

The clearance of anthracyclines from the vasculature was studied in perfused tissue-isolated tumors. Human tumor lines MCF-7, U87, and LS174T were implanted in the ovarian fat pad of immune-deficient mice and grown isolated from the surrounding tissue. The initial and continuous tissue uptakes of doxorubicin, daunorubicin, and idarubicin were measured. The clearance of these anthracyclines from the perfused vasculature of the tissue-isolated tumor was calculated using BSA as an intravascular marker. The measured clearances ranged from 50-200 microl/min/g tumor tissue, and the fractional clearances were between 0.30 and 0.70. On the basis of the in vitro cellular uptake rates of the anthracyclines, we expected a higher clearance of idarubicin than of doxorubicin. No significant differences were found among the clearances of the anthracyclines or among the tumor lines. The observed similarities in clearance of the anthracyclines was largely explained by differences in their protein binding and tissue diffusion gradients.

Animals↗
PubMed1999

Canalicular multispecific organic anion transporter/multidrug resistance protein 2 mediates low-affinity transport of reduced glutathione.

The canalicular multispecific organic anion transporter (cMOAT), a member of the ATP-binding cassette transporter family, mediates the transport of a broad range of non-bile salt organic anions from liver into bile. cMOAT-deficient Wistar rats (TR-) are mutated in the gene encoding cMOAT, leading to defective hepatobiliary transport of a whole range of substrates, including bilirubin glucuronide. These mutants also have impaired hepatobiliary excretion of GSH and, as a result, the bile flow in these animals is reduced. In the present work we demonstrate a role for cMOAT in the excretion of GSH both in vivo and in vitro. Biliary GSH excretion in rats heterozygous for the cMOAT mutation (TR/tr) was decreased to 63% of controls (TR/TR) (114+/-24 versus 181+/-20 nmol/min per kg body weight). Madin-Darby canine kidney (MDCK) II cells stably expressing the human cMOAT protein displayed >10-fold increase in apical GSH excretion compared with wild-type MDCKII cells (141+/-6.1 pmol/min per mg of protein versus 13.2+/-1.3 pmol/min per mg of protein in wild-type MDCKII cells). Similarly, MDCKII cells expressing the human multidrug resistance protein 1 showed a 4-fold increase in GSH excretion across the basolateral membrane. In several independent cMOAT-transfectants, the level of GSH excretion correlated with the expression level of the protein. Furthermore, we have shown, in cMOAT-transfected cells, that GSH is a low-affinity substrate for the transporter and that its excretion is reduced upon ATP depletion. In membrane vesicles isolated from cMOAT-expressing MDCKII cells, ATP-dependent S-(2,4-dinitrophenyl)glutathione uptake is competitively inhibited by high concentrations of GSH (Ki approximately 20 mM). We concluded that cMOAT mediates low-affinity transport of GSH. However, since hepatocellular GSH concentrations are high (5-10 mM), cMOAT might serve an important physiological function in maintenance of bile flow in addition to hepatic GSH turnover.

Animals↗
PubMed1999

Potent interaction of flavopiridol with MRP1.

The multidrug resistance protein 1 (MRP1) is an ATP-dependent transport protein for organic anions, as well as neutral or positively charged anticancer agents. In this study we show that flavopiridol, a synthetic flavonoid currently studied in phase 1 trials for its antiproliferative characteristics, interacts with MRP1 in a potent way. Flavopiridol, as well as other (iso)flavonoids stimulate the ATPase activity of MRP1 in a dose-dependent way at low micromolar concentrations. A new specific monoclonal antibody against MRP1 (MIB6) inhibits the (iso)flavonoid-induced ATPase activity of plasma membrane vesicles prepared from the MRP1 overexpressing cell line GLC4/ADR. The accumulation of daunorubicin in GLC4/ADR cells is increased by flavopiridol and by other non-glycosylated (iso)flavonoids that interact with MRP1 ATPase activity. However, flavopiridol is the only tested compound that affects the daunorubicin accumulation when present at concentrations below 1 microM. Glycosylated (iso)flavonoids do not affect MRP1-mediated transport or ATPase activity. Finally, MRP1 overexpressing and transfected cells are resistant to flavopiridol, but not to other (iso)flavonoids tested. These findings may be of relevance for the development of anticancer therapies with flavopiridol.

Adenosine Triphosphatases↗
PubMed1998

A method for studying plasma membrane transport with intact cells using computerized fluorometry.

A new method is presented for measuring rapid efflux of fluorescent compounds from monolayer cells. Cells grown on a glass coverslip were loaded with a fluorescent substrate. Thereafter, the coverslip was installed outside the light path in a stirred and thermostated cuvette of a fluorometer. The efflux was recorded by measuring the changes of fluorescence in the extracellular medium. The method was used to study the kinetics of active and passive plasma membrane transport of the P-glycoprotein substrates rhodamine 123 and daunorubicin. The method has advantages over other methods: (1) no radioactively labeled substrate is needed, (2) fluorescence of the transported substrate is not compromised by the cells, (3) changes in the extracellular concentration of the substrate can be monitored continuously and therefore a substantial improvement of the kinetic resolution is obtained, and (4) the measurement setup is relatively simple and a standard fluorometer can be used. From the efflux data, cellular transport parameters could be calculated, such as passive permeation coefficients and active transport rates.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

P-glycoprotein-independent decrease in drug accumulation by phorbol ester treatment of tumor cells.

The effect of a change in the phosphorylation state of the drug transporter P-glycoprotein (P-gp) on its drug transport activity was studied for the substrates daunorubicin (DNR), etoposide (VP-16), and calcein acetoxymethyl ester (Cal-AM). Phorbol ester (PMA), added to stimulate phosphorylation of P-gp by protein kinase C (PKC), caused a decrease in the cellular accumulation of DNR and VP-16, both in multidrug-resistant (MDR) P-gp-overexpressing cells and in wild-type cells. Since treatment of cells with kinase inhibitor staurosporine (ST) reversed this effect of PMA and the non-PKC-stimulating phorbol ester 4alpha-phorbol, 12,13-didecanoate (4alphaPDD) did not result in a decreased DNR accumulation, we conclude that this effect is the result of kinase activity. The concentration dependence of the inhibition of P-gp by verapamil (Vp) was not influenced by PMA. Accumulation of the P-gp substrate Cal-AM was not influenced by PMA in wild-type cells. Therefore, Cal-AM was used to study the effect of PMA-induced phosphorylation of P-gp on its transport activity. Activation of PKC with PMA or inhibition of protein phosphatase 1/2A (PP1/PP2A) with okadaic acid (OA) did not affect the accumulation of Cal-AM in the MDR cells or wild-type cells. The kinase inhibitor ST increased the Cal-AM accumulation only in the MDR cells. Neither stimulating PKC with PMA nor inhibiting PP1/PP2A with OA led to a decreased inhibition of P-gp by ST, indicating that ST inhibits P-gp directly. From these experiments, we conclude that PKC and PP1/PP2A activity do not regulate the drug transport activity of P-gp. However, these studies provide evidence that PMA-induced PKC activity decreases cellular drug accumulation in a P-gp-independent manner.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Modulation by (iso)flavonoids of the ATPase activity of the multidrug resistance protein.

The multidrug resistance protein (MRP) is an ATP-dependent transport protein for organic anions, as well as neutral or positively charged anticancer agents. In this study we report that dinitrophenyl-S-glutathione increases ATPase activity in plasma membrane vesicles prepared from the MRP-overexpressing cell line GLC4/ADR. This ATPase stimulation parallels the uptake of DNP-SG in these vesicles. We also show that the (iso)flavonoids genistein, kaempferol and flavopiridol stimulate the ATPase activity of GLC4/ADR membranes, whereas genistin has no effect. The present data are consistent with the hypothesis that certain (iso)flavonoids affect MRP-mediated transport of anticancer drugs by a direct interaction with MRP.

ATP-Binding Cassette Transporters↗
PubMed1997

Anthracyclines modulate multidrug resistance protein (MRP) mediated organic anion transport.

We studied the ATP-dependent uptake of dinitrophenyl-glutathione (GS-DNP) into plasma membrane vesicles derived from parental GLC4 cells and from multidrug resistant GLC4/ADR cells. The latter have a high expression of the multidrug resistance protein (MRP). Uptake of GS-DNP into membrane vesicles from GLC4/ADR cells was highly stimulated by the addition of ATP, compared to the uptake into membrane vesicles from GLC4 cells. This ATP-dependent uptake into membrane vesicles from GLC4/ADR cells was saturable with a Km of 1.2 +/- 0.2 microM and a Vmax of 560 +/- 80 pmol/mg prot./min. ATP stimulated GS-DNP uptake with a Km of 187 +/- 4 microM. This uptake was specifically inhibited by a polyclonal serum raised against a fusion protein containing a segment of MRP. The ATP-dependent uptake of GS-DNP was not only inhibited by organic anions, such as oxidized glutathione (GSSG), methotrexate (MTX) and some bile acids, but also by non-anionic natural product drugs, such as anthracyclines, vinca alkaloids and etoposide (VP-16). Uptake of GSSG and MTX into membrane vesicles from GLC4/ADR cells could be stimulated by ATP. The ATP-dependent uptake of GSSG had a Km of 43 +/- 3 microM and a Vmax of 900 +/- 200 nmol/mg protein/min. The ATP-dependent uptake of GS-DNP seemed to be non-competitively inhibited by the anthracycline daunorubicin (DNR), whereas the ATP-dependent GSSG uptake seemed to be competitively inhibited by DNR. A substrate binding site on MRP is proposed that comprises a pocket in which both DNR and GS-DNP or GSSG bind in random order to different, only partly overlapping sites. In this pocket binding of a second compound is influenced by the compound which was bound first.

ATP-Binding Cassette Transporters↗
PubMed1995

Redistribution of canalicular organic anion transport activity in isolated and cultured rat hepatocytes.

The hepatocanalicular transport of a large number of organic anions, such as bilirubin glucuronides and glutathione conjugates in the rat, is mediated by an adenosine triphosphate (ATP)-dependent transport system, which is termed canalicular multispecific organic anion transporter (cMOAT). This system is mainly defined by its deficiency in mutant TR rats. We have previously reported that in cultured hepatocytes the fluorescent organic anion glutathione-bimane (GS-B) accumulates in intracellular vesicles and that this transport is mediated by cMOAT. We now show that this intracellular accumulation of fluorescent organic anion is largely absent in freshly isolated hepatocytes but appears when cells are incubated in suspension at 37 degrees C or cultured for periods of 1 to 24 hours. The appearance of intracellular cMOAT activity coincides with the disappearance of 70% of cMOAT activity from the plasma membrane as measured by the transport activity of the cells for the organic anion dinitrophenyl-glutathione (GS-DNP). Both the appearance of intracellular cMOAT and the disappearance of transport activity from the plasma membrane were completely inhibited at temperatures below 20 degrees C. Residual cMOAT activity in 24-hour cultured hepatocytes could be further diminished by incubation of the cells with 1 mumol/L monensin or 10 mmol/L methylamine. We conclude that after disruption of the cell polarity by collagenase isolation of the hepatocytes, remnants of apical membrane containing cMOAT are rapidly endocytosed when the cells are kept at 37 degrees C. Evidence suggests that at least part of the transporters may recycle back to the plasma membrane after endocytosis. These observations may be relevant for the understanding of regulation of canalicular transport.

Alkaloids↗
PubMed1993

Accumulation of organic anion in intracellular vesicles of cultured rat hepatocytes is mediated by the canalicular multispecific organic anion transporter.

Transport of organic anions within hepatocytes and the possible involvement of intracellular vesicles were studied with fluorescence microscopy. For this purpose monochlorobimane, a nonfluorescent hydrophobic compound that readily permeates into cells and is conjugated with glutathione to form the fluorescent glutathione bimane, was used. In the isolated perfused livers of normal rats, glutathione bimane is rapidly secreted into bile. In contrast, in our study of livers from mutant TR- rats, a 100-fold reduction in glutathione bimane secretion into bile occurred. Mutant TR- rats have an inherited defect in the canalicular multispecific organic anion transporter, which mediates the ATP-dependent secretion of a wide range of organic anions over the canalicular membrane into bile. When cultured Wistar and TR- hepatocytes were loaded with glutathione bimane, both cell types displayed a strong cytosolic fluorescence. Wistar cells completely lost this cytosolic fluorescence at incubation on monochlorobimane-free medium because of secretion of glutathione bimane. A clear punctate fluorescence remained, however, which was scattered through the cell with some perinuclear concentration. In some cells vesicular fluorescence was also concentrated around a canaliculus. In contrast, TR- cells lost their cytosolic fluorescence more slowly and completely lacked the vesicular fluorescence. Making cells selectively permeable with digitonin directly after loading them with glutathione bimane to remove cytosolic fluorescence again revealed the presence of fluorescent vesicles in Wistar cells and their absence in TR- cells. In Wistar cells vesicular fluorescence could be increased by preincubation with monensin or methylamine, compounds that have been shown to interfere with plasma membrane recycling. In conclusion, these results suggest that apart from secretion over the plasma membrane, the canalicular multispecific organic anion transporter may be involved in accumulation of organic anion in intracellular vesicles. It is hypothesized that this intracellular localization of the canalicular multispecific organic anion transporter is caused by recycling of the transporter between the plasma membrane and intracellular membranes.

Adenosine Triphosphate↗
PubMed1992

ATP-dependent multispecific organic anion transport system in rat erythrocyte membrane vesicles.

The uptake of oxidized glutathione (GSSG) into inside-out membrane vesicles of Wistar rat erythrocytes was studied. Uptake was ATP dependent, into an osmotically active space, and saturable. Analysis of saturable ATP-dependent GSSG uptake showed two affinities for GSSG [concentration for half-maximal velocity (K1/2 1), 26 microM; K 1/2 2, 4 mM; maximum transport rate (Vmax 1), 100 pmol.mg-1.min-1; Vmax 2, 360 pmol.mg-1.min-1]. Interactions of the high-affinity system with different organic compounds were studied. Leukotriene C4, bromosulfophthalein-S-glutathione, and 2,4-dinitrophenyl-S-glutathione were effective inhibitors. In addition, anionic nonglutathione conjugates, like indocyanine green, rose bengal, dibromosulfophthalein, and sulfated or glucuronidated (divalent) bile acids inhibited GSSG transport. Monovalent bile acids had no influence on GSSG transport. Inhibition by 2,4-dinitrophenyl-S-glutathione [inhibition constant (Ki) = 2.6 microM] and sulfated glycolithocholic acid (Ki = 2.9 microM) was purely competitive. The use of adenosinetriphosphatase (ATPase) inhibitors suggested a resemblance with E1E2-type ATPase. Vesicles of erythrocytes isolated from the TR- rat, a mutant rat strain with a defective biliary secretion of organic anions, have an impaired uptake of GSSG (Vmax was decreased 2-fold). In conclusion, erythrocytes have an ATP-dependent organic anion transport system that can be inhibited by a broad range of organic anions. This system is very similar if not identical to the hepatocanalicular ATP-dependent organic anion transporter.

Adenosine Triphosphatases↗
PubMed1991

Effect of substituted benzoates on p-aminohippurate transport in dog renal membrane vesicles.

The effect of substituted benzoates on the transport of p-aminohippurate (PAH) was studied in basolateral (BLMV) and brush border membrane vesicles (BBMV) isolated from dog kidney cortex. For both membranes, kinetic analysis of [3H]PAH transport in the presence of a fixed concentration of two different benzoates, respectively, revealed an increase in the apparent Km for PAH, while the transport capacity (Vmax) was unaffected. This is compatible with competitive inhibition of a common transport pathway. A range of 19 monosubstituted benzoates were then tested as potential inhibitors by measuring the probenecid-sensitive fraction of 100 mumol/l PAH uptake into BLMV and BBMV in the presence of 5 mmol/l benzoate, and apparent inhibition constants (Ki) were calculated. For all benzoates the inhibitory potency in BBMV was lower than in BLMV, but the pattern of inhibition was similar; the most pronounced inhibition was found for 3-Cl- and 4-Cl-benzoate, while the least pronounced inhibition was found for the 3-NH2 and 4-NH2 substitutes. The inhibitory potency, expressed as logKi, correlated significantly with the relative hydrophobicity of the benzoates determined by reversed phase HPLC, whereas a poor correlation was found between pKa and logKi. This indicates that hydrophobic and electronic parameters are the main determinants of affinity for the PAH transport system. It is suggested that the PAH transport system present in the proximal tubules is responsible for the active secretion of benzoates by the mammalian kidney.

Animals↗
PubMed1988

Na+ and H+ gradient-dependent transport of p-aminohippurate in membrane vesicles from dog kidney cortex.

The transport of p-aminohippurate (PAH) was studied in basolateral (BLMV) and brush border membrane vesicles (BBMV) isolated from dog kidney cortex. Imposition of an inwardly directed 100 mN Na+ gradient stimulated the uptake of 50 microM [3H]PAH into BLMV, whereas a pH gradient (pHout = 6.0, pHin = 7.4) only slightly enhanced uptake. The Na+ gradient-dependent uptake of PAH was electroneutral, saturable and sensitive to inhibition by probenecid and several anionic drugs, with (apparent) Km = 0.79 +/- 0.16 mM, Vmax = 0.80 +/- 0.05 nmol/mg protein, 15 sec and Ki for probenecid = 0.08 +/- 0.01 mM. Simultaneous imposition of the pH gradient (outward OH- gradient) and inward Na+ gradient stimulated PAH uptake significantly over that with an Na+ gradient alone. These results are consistent with an Na+ gradient-stimulated PAH/OH- exchange mechanism in the basolateral membrane. In BBMV, PAH uptake could be stimulated by an outwardly directed OH- gradient as well as an inward Na+ gradient. Both gradients could drive PAH transport via a mediated probenecid-sensitive pathway. Na+ gradient-stimulated uptake was electrogenic with a (apparent) Km = 4.93 +/- 0.57 mM, Vmax = 6.71 +/- 0.36 nmol/mg protein, 15 sec and Ki,prob = 0.13 +/- 0.01 mM. The kinetic parameters for PAH/OH- exchange were virtually the same, (apparent) Km = 5.72 +/- 0.49 mM, Vmax = 7.87 +/- 0.33 nmol/mg protein, 15 sec and Ki,prob = 0.16 +/- 0.02 mM. When both the Na+ and pH (outward OH-) gradient were simultaneously imposed an almost twofold stimulation in uptake was observed over that with either an Na+ or pH gradient alone. These results suggested that both gradients stimulate PAH transport in BBMV via the same pathway. However, inhibition experiments with various organic anions showed that the specificities of Na+ and pH gradient-stimulated PAH uptake do not entirely overlap. Thus, our results support a simple transport in BBMV, but it cannot be excluded that two separate pathways are involved.

Aminohippuric Acids↗