calcein-am and fluorexon

Co-treatment with calcineurin inhibitors, such as tacrolimus and cyclosporin A, can sensitize chemotherapy-resistant cancer cells with P-glycoprotein (P-gp)-over-expression. Pimecrolimus (PIME) is a clinically available calcineurin inhibitor with a structure similar to that of tacrolimus. Whether PIME can sensitize P-gp-over-expressing resistant cancer cells remains unclear.. Cell viability assay, annexin V analyses, cellular morphology and density observation with a microscope, western-blotting, fluorescence-activated cell sorting (FACS), and analysis for P-gp inhibitory activity were performed to investigate the mechanism of action.. PIME, currently used in clinics, can be repositioned for treating patients with P-gp-over-expressing resistant cancer (stem) cells.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Calcineurin Inhibitors; Cyclosporine; Humans; Neoplasms; Rhodamine 123; Tacrolimus

The quality of the endothelial graft is critical to the success of DMEK and to the survival time of the graft. The peeling technique, preservation method, and skill level of graft preparers need to be evaluated and validated. The most reliable method of evaluation is the viability test based on a triple staining of Hoechst- Ethidium-Calcein AM (H-E-C) which allows the determination of the total number of viable cells on the graft. However, this test has some shortcomings for DMEK grafts: 1) The undesirable fluorescence of the Calcein AM stain prevents accurate viability analysis, especially in cases where the graft is attached to the cornea for preservation; 2) Incompatibility with immunofluorescence (IF) that could provide additional information. The objective of this study is to develop technical tricks to overcome these drawbacks.. Two strategies were employed to improve Calcein AM staining: 1. Increase the specific fluorescence intensity by changing the diluent and the concentration of Calcein AM; 2. Decrease undesired fluorescence from keratocytes by adding Trypan Blue (BT). In order to combine the IF after the HEC test, an extension wash in PBS was performed.. Calcein AM at 4µM diluted in OptiMEM increased fluorescence intensity 3-fold (p=0.0017, n=5) compared with conventional staining at 2µM in PBS. BT decreased the undesired fluorescence of Calcein and thus optimized count variability between different operators by 42% (p=0.0027, n=10) and saved 40% (p=0.0002, n=10) of count time. To perform IF after HEC, prolonged washing in PBS is an effective method to remove residual Calcein fluorescence and allows release of the FITC/Alexa 488 filter.. This study provides effective technical tips for optimizing the endothelial viability assay using Calcein AM and for performing IF after the viability assay.

Topics: Biological Assay; Ethidium; Fluoresceins; Fluorescent Dyes; Staining and Labeling; Transplants

P-glycoprotein (P-gp), a membrane transport protein overexpressed in certain drug-resistant cancer cells, has been the target of numerous drug discovery projects aimed at overcoming drug resistance in cancer. Most characterized P-gp inhibitors bind at the large hydrophobic drug binding domain (DBD), but none have yet attained regulatory approval. In this study, we explored the potential of designing inhibitors that target the nucleotide binding domains (NBDs), by computationally screening a large library of 2.6 billion synthesizable molecules, using a combination of machine learning-guided molecular docking and molecular dynamics (MD). 14 of the computationally best-scoring molecules were subsequently tested for their ability to inhibit P-gp mediated calcein-AM efflux. In total, five diverse compounds exhibited inhibitory effects in the calcein-AM assay without displaying toxicity. The activity of these compounds was confirmed by their ability to decrease the verapamil-stimulated ATPase activity of P-gp in a subsequent assay. The discovery of these five novel P-gp inhibitors demonstrates the potential of in-silico screening in drug discovery and provides a new stepping point towards future potent P-gp inhibitors.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Drug Resistance, Neoplasm; Molecular Docking Simulation; Nucleotides

To evaluate the effect of graft preparation and organ-culture storage on endothelial cell density (ECD) and viability of Descemet membrane endothelial keratoplasty (DMEK) grafts.. DMEK grafts (n=27) were prepared at Amnitrans EyeBank Rotterdam from 27 corneas (15 donors) that were eligible for transplantation but could not be allocated due to the COVID-19-related cancellation of elective surgeries. Cell viability (by Calcein-AM staining) and ECD of 5 grafts originally scheduled for transplantation, were evaluated on the originally planned surgery day, whereas 22 grafts from paired donor corneas were evaluated either directly post-preparation or after 3-7 days of storage. ECD was analyzed by light microscopy (LM ECD) and Calcein-AM staining (Calcein-ECD) RESULTS: Light microscopy (LM) evaluation of all grafts showed an unremarkable endothelial cell monolayer directly after preparation. However, median Calcein-ECD for the 5 grafts initially allocated for transplantation was 18% (range 9-73%) lower than median LM ECD. For the paired DMEK grafts, Calcein-ECD determined by Calcein-AM staining on the day of graft preparation and after 3-7 days of graft storage showed a median decrease of 1% and 2%, respectively. Median percentage of central graft area populated by viable cells after preparation and after 3-7 days of graft storage was 88% and 92%, respectively.. Cell viability of most of the grafts will not be affected by preparation and storage. Endothelial cell damage may be observed for some grafts within hours after preparation with insignificant additional ECD changes during 3-7 days of graft storage. Implementing an additional post-preparation step in the eye bank to evaluate cell density before graft release for transplantation may help to reduce postoperative DMEK complications.

Topics: Cell Survival; COVID-19; Descemet Stripping Endothelial Keratoplasty; Endothelium, Corneal; Humans

Cyclophilin D is a peptidyl-prolyl cis-trans isomerase localized in the mitochondrial matrix. Although its effects on mitochondrial characteristics have been well studied, its relation to the uptake of molecules by mitochondria remains unknown. Here, we demonstrated the effects of cyclophilin D on the intracellular translocation of calcein AM. Following addition of calcein AM to control cells or cells overexpressing wild-type cyclophilin D, calcein fluorescence was observed in mitochondria. However, long-term inhibition of cyclophilin D in these cells altered the localization of calcein fluorescence from mitochondria to lysosomes without changing mitochondrial esterase activity. In addition, depletion of glucose from the medium recovered calcein localization from lysosomes to mitochondria. This is the first demonstration of the effects of cyclophilin D on the intracellular translocation of molecules other than proteins and suggests that cyclophilin D may modify mitochondrial features by inducing the translocation of molecules to the mitochondria through the mechanism associated with cellular energy metabolism.

Topics: Animals; Cell Line; cis-trans-Isomerases; Cyclophilins; Fluoresceins; Glucose; HeLa Cells; Humans; Lysosomes; Microscopy, Fluorescence; Mitochondria; Mitochondrial Membrane Transport Proteins; Peptidyl-Prolyl Isomerase F; Protein Transport; Rats

Low levels of graphene and graphene oxide (GO) are considered to be environmentally safe. In this study, we analyzed the potential effects of graphene and GO at relatively low concentrations on cellular xenobiotic defense system mediated by efflux transporters. The results showed that graphene (<0.5 μg/mL) and GO (<20 μg/mL) did not decrease cell viability, generate reactive oxygen species, or disrupt mitochondrial function. However, graphene and GO at the nontoxic concentrations could increase calcein-AM (CAM, an indicator of membrane ATP-binding cassette (ABC) transporter) activity) accumulation, indicating inhibition of ABC transporters' efflux capabilities. This inhibition was observed even at 0.005 μg/mL graphene and 0.05 μg/mL GO, which are 100 times and 400 times lower than their lowest toxic concentration from cytotoxicity experiments, respectively. The inhibition of ABC transporters significantly increased the toxicity of paraquat and arsenic, known substrates of ABC transporters. The inhibition of ABC transporters was found to be based on graphene and GO damaging the plasma membrane structure and fluidity, thus altering functions of transmembrane ABC transporters. This study demonstrates that low levels of graphene and GO are not environmentally safe since they can significantly make cell more susceptible to other xenobiotics, and this chemosensitizing activity should be considered in the risk assessment of graphene and GO.

Topics: ATP-Binding Cassette Transporters; Blotting, Western; Cell Membrane; Cell Survival; Dose-Response Relationship, Drug; Fluoresceins; Graphite; Hep G2 Cells; Humans; Microscopy, Electron, Transmission; Nanoparticles; Oxides; Reactive Oxygen Species; Real-Time Polymerase Chain Reaction; Xenobiotics

The blood-brain barrier prevents the passage of toxic compounds from blood circulation into brain tissue. Unfortunately, drugs for the treatment of neurodegenerative diseases, brain tumors, and other diseases also do not cross the blood-brain barrier. In the present investigation, we used isolated porcine brain capillary endothelial cells and a flow cytometric calcein-AM assay to analyze inhibition of P-glycoprotein, a major constituent of the blood-brain barrier. We tested 8 alkamides isolated from Echinacea angustifolia and found that four of them inhibited P-glycoprotein-mediated calcein transport in porcine brain capillary endothelial cells.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B; Biological Transport; Blood-Brain Barrier; Brain; Cells, Cultured; Dose-Response Relationship, Drug; Echinacea; Endothelial Cells; Flow Cytometry; Fluoresceins; Molecular Structure; Polyunsaturated Alkamides; Swine

ATP-binding cassette (ABC) proteins play key role in tissue defence by transporting metabolic waste and toxic chemicals out of the cells. Consequently, intact cell systems are required to study xenobiotic interactions with ATP-dependent transporters. The aim of the present study was to set up an intestinal precision-cut slice technique to study the interactions of ABC transporters with xenobiotics. Rat intestinal slices were incubated with verapamil, indomethacin and glibenclamide, and the ability of the above-mentioned drugs to inhibit the multidrug resistance glycoprotein (MDR) and/or multidrug-resistance-associated protein (MRP) was assessed by measuring the intracellular conversion of calcein-AM to fluorescent calcein. The ABC transporters' inhibitors caused a time-dependent florescence increase which reached the maximum value at 30 min. Verapamil and glibenclamide promoted a concentration-dependent intracellular accumulation of calcein (IC(50) 8.1×10(-6) M, 1.9×10(-4) M, respectively). The effect of glibenclamide was fully reversed by washing the slices, suggesting the reversible nature of calcein accumulation. These data suggest that the precision-cut intestinal slices are a reliable, simple and fast system to evaluate xenobiotic interactions with ABC transporters in rat and, hopefully, in human intestine.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B; ATP-Binding Cassette Transporters; Fluoresceins; Fluorescent Dyes; Glyburide; Indomethacin; Intestine, Small; Male; Microtomy; Multidrug Resistance-Associated Proteins; Rats; Rats, Wistar; Verapamil; Xenobiotics

About 70% of the patients suffering from temporal lobe epilepsy (TLE) are resistant to currently available antiepileptic drugs (AEDs). For them one therapeutic option to achieve seizure control is to undergo epilepsy surgery. Expression of multidrug transporters is upregulated in resected tissue specimens from TLE patients, as well as in animal models of chronic epilepsy, which might lead to altered tissue availability of AEDs and therefore contribute to drug refractoriness. Here we describe a functional test of multidrug transporter activity in brain slices from TLE patients based on intracellular accumulation of the fluorescent multidrug transporter substrate calcein and compare functional data to the expression pattern of multidrug transporters. The rate of cytosolic calcein fluorescence increase was altered by inhibitors of multidrug transport such as probenecid (400 μM) and verapamil (40 μM) in a subset of slices, indicating the presence of functional multidrug transport proteins in human epileptic tissue. Interestingly, there were differences between the expression pattern of multidrug transporters and their ability to remove calcein-AM. Consequently, in vitro studies on multidrug transporters should always include functional tests of their activity as expression alone is not necessarily conclusive.

Topics: Adjuvants, Pharmaceutic; Anticonvulsants; ATP Binding Cassette Transporter, Subfamily B, Member 1; Epilepsy; Fluoresceins; Gene Expression Regulation; Hippocampus; Humans; In Vitro Techniques; Multidrug Resistance-Associated Proteins; Neocortex; Nerve Tissue Proteins; Neurons; Probenecid; Verapamil

Putative cancer stem cell (CSC) populations efflux dyes such as Hoechst 33342 giving rise to side populations (SP) that can be analyzed or isolated by flow cytometry. However, Hoechst 33342 is highly toxic, more so to non-SP cells, and thus presents difficulties in interpreting in vivo studies where non-SP cells appear less tumorigenic than SP cells in immunodeficient mice. We searched for non-toxic dyes to circumvent this problem as well as to image these putative CSCs. We found that the fluorescent dye calcein, a product of intracellular Calcein AM cleavage, is effluxed by a small subpopulation, calcein low population (C(lo)P). This population overlaps with SP and demonstrated long term cell viability, lack of cell stress and proliferation in several cancer cell lines when stained whereas Hoechst 33342 staining caused substantial apoptosis and ablated proliferation. We also found that the effluxed dye D-luciferin exhibits strong UV-fluorescence that can be imaged at cellular resolution and spatially overlaps with Calcein AM. In order to evaluate the hypothesis that p53 loss promotes enrichment of putative CSC populations we used Calcein AM, D-luciferin and Mitotracker Red FM as a counterstain to visualize dye-effluxing cells. Using fluorescence microscopy and flow cytometry we observed increased dye-effluxing populations in DLD-1 colon tumor cells with mutant p53 versus wild-type (WT) p53-expressing HCT116 cells. Deletion of the wild-type p53 or pro-apoptotic Bax genes induced the putative CSC populations in the HCT116 background to significant levels. Restoration of WT p53 in HCT116 p53(-/-) cells by an adenovirus vector eliminated the putative CSC populations whereas a control adenovirus vector, Ad-LacZ, maintained the putative CSC population. Our results suggest it is possible to image and quantitatively analyze putative CSC populations within the tumor microenvironment and that loss of pro-apoptotic and tumor suppressing genes such as Bax or p53 enrich such tumor-prone populations.

Topics: Adenocarcinoma; Aldehyde Dehydrogenase; Aldehyde Dehydrogenase 1 Family; Apoptosis; ATP-Binding Cassette Transporters; bcl-2-Associated X Protein; Benzimidazoles; Benzothiazoles; Biological Transport, Active; Calcium Channel Blockers; Cell Line, Tumor; Colonic Neoplasms; DNA Damage; Flow Cytometry; Fluoresceins; Fluorescent Dyes; Genes, p53; Humans; Isoenzymes; Microscopy, Fluorescence; Neoplasm Proteins; Neoplastic Stem Cells; Prodrugs; Retinal Dehydrogenase; Staining and Labeling; Tumor Suppressor Protein p53

Topics: Adenocarcinoma; ATP-Binding Cassette Transporters; Benzimidazoles; Biological Transport, Active; Cell Line, Tumor; Cell Separation; Colonic Neoplasms; Flow Cytometry; Fluoresceins; Fluorescent Dyes; Humans; Neoplasm Proteins; Neoplastic Stem Cells; Phenotype; Prodrugs; Staining and Labeling

Acetylcholine sensitive TE 671 cells were cultured on nanoporous membranes and chemically stimulated by localized application of i), calcein-AM and ii), acetylcholine, respectively, onto the bottom face of the membrane employing an ink jet print head. Stimulus correlated response of cells was recorded by fluorescence microscopy with temporal and spatial resolution. Calcein fluorescence develops as a result of intracellular enzymatic conversion of calcein-AM, whereas Ca(2+) imaging using fluo-4 dye was employed to visualize cellular response to acetylcholine stimulation. Using 25 pl droplets and substance concentration ranging from 10 microM to 1 mM on Nucleopore membranes with pore diameters between 50 nm and 1 microm, a resolution on the order of 50 microm was achieved.

Topics: Acetylcholine; Benzimidazoles; Calcium; Cell Adhesion; Cell Culture Techniques; Eosine Yellowish-(YS); Fluoresceins; Fluorescent Dyes; Humans; Kinetics; Membranes, Artificial; Microscopy, Fluorescence; Models, Chemical; Tumor Cells, Cultured

Leukemia is the most common malignancy in children. Combined chemotherapy is currently the primary treatment modality. During the past decade, very high cure rates of childhood acute lymphoblastic leukemia (ALL) have been reported both at home and abroad. However, the cure rates of children with acute myeloid leukemia (AML) remain low due to the multiple-drug resistance (MDR). P-glycoprotein (P-gp) is one of the most important mechanisms of MDR for leukemia cells. However, the function of the protein, the clinical application of its reversal agents and the efficacy of the combination of the reversal agents remain to be elucidated. The present study aimed to evaluate the P-gp pump function on leukemia cell membrane and the effects of the combined administration of the reversal agents cyclosporin A (CSA) and verapamil (VER) through the observation of Calcein-AM (C-AM) metabolism in the cell line K562 and its multi-drug resistant subline K562/VCR.. The mean fluorescence intensity (MFI) of C-AM inside the cytoplasm was analyzed with flow cytometry (FCM). The events of K562 and K562/VCR cells treated and untreated with CSA, VER and CSA + VER were acquired at time points 0, 30, 60, 90 and 120 minutes, respectively, and the data obtained were analyzed with CellQuest software.. The C-AM in the K562 and K562/VCR varied more apparently in the fist 24 hours. In addition, the MFI of the C-AM in K562 was significantly higher than that in K562/VCR cells indicating that the P-gp pump molecules were functioning. The MFIs of the CSA, VER and CSA + VER groups co-cultured with K562/VCR cells were 4014 +/- 219, 3879 +/- 116 and 4158 +/- 302, respectively after 120 min of incubation, significantly higher as compared to that of control group (3251 +/- 107, P < 0.05). On the other hand, significant inhibition of the efflux from the K562/VCR cell line was also noticed after the same time period of incubation with the MFIs of 2237 +/- 155, 1932 +/- 233 and 2231 +/- 147, respectively in the three groups, which was significantly higher than that of control group (1622 +/- 191, P < 0.05). CSA, VER and CSA + VER could increase the uptake and inhibit the efflux of C-AM by K562/VCR cells, while no evident influence on those functions inside the parental cell line K562 cells was noticed.. CSA, VER and CSA + VER could increase the uptake and reduce the efflux of C-AM by K562/VCR cells while no significant difference between the CSA + VER and CSA or VER was noticed. P-gp pump function and the effects of its reversal agents on leukemic cells can be rapidly and easily evaluated by using the C-AM and FCM.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Child; Drug Resistance, Multiple; Flow Cytometry; Fluoresceins; Humans; K562 Cells; Tumor Cells, Cultured; Verapamil; Vincristine

We compared growth rate, cell glucose turnover and expression of ATP-binding-cassette (ABC) transporters in Leishmania amazonensis (LTB0016; LTB) versus LTB(160) selected for resistance against the ABC transporter blocker glibenclamide. Additionally, we evaluated the influence of drug-resistance on Leishmania sensitivity against 2-mercaptoacetate and 2-deoxyglucose. Our data demonstrate that (1) LTB(160) and LTB constitutively express ABC transporters for neutral substrates, (2) glibenclamide resistance induces the expression of organic anion ABC transporters, members of the drug resistance associated transporters subfamily, (3) LTB(160) parasites use less glucose as energy substrate and exhibit a slower glucose uptake than LTB cells, and (4) LTB(160) parasites are less sensitive to 2-mercaptoacetate and 2-deoxyglucose than the glibenclamide-sensitive Leishmania LTB. Together these and previous results indicate that the metabolic adaptations expressed in drug-resistant LTB(160) differ from those described for mammalian drug resistant cells and constitute general mechanisms that underlie drug resistance in Leishmania and may be helpful for identifying alternative strategies to circumvent drug resistance in leishmaniasis.

Topics: Adaptation, Physiological; Animals; ATP-Binding Cassette Transporters; Deoxyglucose; Drug Resistance; Fluoresceins; Fluorescent Dyes; Glucose; Glyburide; Leishmania mexicana; Multidrug Resistance-Associated Proteins; Thioglycolates

Multidrug resistance-associated protein 1 and P-glycoprotein are major ATP-binding cassette transporters that function as efflux pumps and confer resistance to a variety of structurally unrelated anticancer agents. To evaluate the comparative importance of these transporters with respect to anticancer agents, we established and characterized SV40-immortalized [mrp1(-/-)] (KO), [mdr1a/1b(-/-)] (DKO), and combined [mrp1 (-/-), mdr1a/1b(-/-)] (TKO) deficient fibroblast lines derived from primary embryonic fibroblasts of knockout mice. Western blot analyses demonstrated that KO and DKO fibroblasts exhibited similar levels of P-glycoprotein and mrp1, respectively, to that of wild-type (WT) fibroblasts. In addition, semiquantitative reverse transcription-PCR measurements of other multidrug resistance-associated protein (mrp) family members demonstrated that TKO fibroblasts displayed expression profiles of mrps 2-7 comparable to that of WT fibroblasts. These results indicate that loss of mrp1, P-glycoprotein, or both transporters does not cause overt compensatory changes in the expression of the other determined transporters. Using cell viability and calcein accumulation assays, we demonstrated that KO and DKO fibroblasts exhibited a low to moderate increase in sensitivity to vincristine and etoposide and in calcein accumulation compared to WT fibroblasts, whereas TKO fibroblasts displayed a markedly enhanced sensitivity to these agents and further elevated calcein accumulation. Furthermore, verapamil, an inhibitor of both mrp1 and P-glycoprotein, significantly sensitized WT fibroblasts to both vincristine and etoposide while having no effect on the sensitivity of TKO cells to these agents. Collectively, these findings indicate that mrp1 and P-glycoprotein are major determinants of drug sensitivity in immortalized mouse embryonic fibroblasts. They also suggest the existence of a compensatory mechanism by which the loss of one transporter can be functionally offset by the other in the transport of common drug substrates.

Topics: Animals; Anticarcinogenic Agents; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; ATP Binding Cassette Transporter, Subfamily B, Member 1; Biological Transport; Blotting, Western; Cell Survival; Cells, Cultured; Chemokines, CC; Dose-Response Relationship, Drug; Etoposide; Fibroblasts; Fluoresceins; Inhibitory Concentration 50; Mice; Mice, Knockout; Precipitin Tests; Reverse Transcriptase Polymerase Chain Reaction; RNA; Time Factors; Transfection; Tumor Cells, Cultured; Vincristine

We demonstrated the existence of three transport activities in promastigotes of Leishmania braziliensis, Leishmania guyanensis, and Leishmania mexicana. The first activity, an energy-dependent efflux of pirarubicin, was observed in all Leishmania species and inhibited by verapamil, by 2-[4-(diphenylmethyl)-1-piperazinyl]ethyl-5-(trans-4,6-dimethyl-1, 3,2-dioxaphosphorinan-2-yl)-2,6-dimethyl-4-(3-nitrophenyl)-3-py ridinecarboxylate P oxide (PAK104P) and by the phenothiazine derivatives: thioridazine, prochlorperazine, trifluoperazine, chlorpromazine and trifluoropromazine. The second activity, an energy-dependent efflux of calcein acetoxymethylester, was observed in all Leishmania species and inhibited by PAK104P and the same phenothiazine derivatives, but not by verapamil. The third activity, an energy-dependent efflux of calcein, was clearly detected in L. braziliensis and guyanensis and inhibited only by prochlorperazine and trifluoperazine. The fact that prochlorperazine and trifluoperazine inhibited the energy-dependent efflux of the three substrates suggests that these activities are mediated by the same transport system. It is noteworthy that the transport system identified in this study shares several properties with the mammalian multidrug resistance pump, MRP1. Pirarubicin, calcein acetoxymethylester and calcein are well known substrates of the MRP. Furthermore, the three types of inhibitors are also inhibitors of the MRP function.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B; Biological Transport; Cyclic P-Oxides; Doxorubicin; Drug Resistance, Multiple; Energy Metabolism; Fluoresceins; Fluorescent Dyes; Leishmania; Nicotinic Acids; Phenothiazines; Tumor Cells, Cultured; Verapamil

Thirteen cell lines with different levels of Pgp and MRP1 expression were used to assess the ability of calcein-AM uptake and calcein efflux to measure Pgp and MRP1 functions, respectively. There was a good correlation between MRP1 expression and the modulatory effect of probenecid (a specific modulator of MRP1) on the calcein efflux (r = 0.91, p = 0.0003) and between Pgp expression and the modulatory effect of CsA on calcein-AM uptake (r = 0.96, p < 0.0001). On light of the high correlations for both proteins, we tested calcein-AM uptake and efflux in fresh myeloid leukemic cells. In 53 AML patients, there was also a good correlation between MRP1 expression (measured by RT/PCR and by MRPm6 expression by flow cytometry) and the modulatory effect of probenecid on the calcein fluorescence (r = 0.92, p < 0.0001) and between Pgp expression as measured by UIC2 antibody binding on flow cytometry and the modulatory effect of CsA on calcein-AM uptake (r = 0.83, p < 0.0001). Pgp activity was higher in CD34+ leukemia than in CD34- leukemia (2.26 +/- 1.50 vs 1.46 +/- 1.21 respectively, p = 0.003) and MRP1 activity was higher in CD34- leukemia than in CD34+ leukemia (1.77 +/- 0.40 vs 1.4 +/- 0.29 respectively, p = 0.004). Pgp expression and activity (p = 0.004 and p = 0.01, respectively), MRP1 activity (p = 0.03) but not MRP1 expression were prognostic factors for achievement of CR. The effect of probenecid and CsA together were higher than the effect of either probenecid or CsA alone on calcein-AM uptake. These results suggest that functional testing (with calcein-AM +/- modulators) for the presence of both MRP1 and Pgp activities is of prognostic value and that MRP1 contributes to drug resistance in AML.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B, Member 1; Base Pair Mismatch; Biological Transport; Calcium; Cyclosporine; DNA-Binding Proteins; Drug Resistance, Multiple; Female; Flow Cytometry; Fluoresceins; Fluorescent Dyes; Genes, MDR; Humans; K562 Cells; Leukemia, Myeloid, Acute; Male; Multidrug Resistance-Associated Proteins; MutS Homolog 3 Protein; RNA, Messenger; Transcription, Genetic; Tumor Cells, Cultured

Multidrug resistance protein (MRP) and P-glycoprotein (Pgp) are both members of the superfamily of ATP binding cassette plasma membrane drug transport proteins, which may be partly responsible for multidrug resistance of tumor cells. Although MRP has been identified as an organic anion transporter and Pgp as a transporter of certain positively charged compounds, there is considerable overlap in resistance spectrum, suggesting that both proteins transport important anticancer agents such as doxorubicin, etoposide, and vincristine. To obtain more insight in the handling of drugs by both proteins, we performed a detailed kinetic analysis of the efflux of calcein-acetoxymethyl ester (CAL-AM), a common neutral substrate for both proteins and compared it with the kinetics of efflux of calcein (CAL) which is only effluxed by MRP. CAL, the hydrolysis product of the nonfluorescent CAL-AM, is negatively charged and highly fluorescent. For this purpose Pgp+ K562/ADR and MRP+ GLC4/ADR tumor cells were incubated with CAL-AM in ATP-rich or ATP-depleted buffer, and the calcein formation was followed in time by fluorescence development. The intracellular CAL could be distinguished from effluxed (extracellular) CAL by addition to the medium of Co2+, which completely quenched the extracellular CAL fluorescence. The results showed that the Vmax for efflux of CAL-AM and CAL by MRP were very similar (1.0-1.2 x 10(5) molecules/cell/s) but that the Km for CAL-AM was much lower (0.05 microM) than for CAL (268 microM). The latter therefore is much less efficiently transported by MRP than CAL-AM. The Km for CAL-AM transport by Pgp (0.12 microM) was similar to that for MRP. Compared to previously published data for anthracyclines, the kinetic data for MRP-mediated CAL-AM pumping are most similar to those for the neutral hydroxydaunorubicin. These data give a quantitative account of transport properties of MRP for two related but differently charged compounds.

Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Biological Transport, Active; Cell Line; Drug Resistance, Multiple; Fluoresceins; Fluorescent Dyes; Humans; Kinetics; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; Spectrometry, Fluorescence; Tumor Cells, Cultured

In this study we report that the multidrug resistance protein (MRP) transports calcein from the cytoplasmic compartment of tumor cells, in contrast to P-glycoprotein which transports calcein acetoxymethyl ester from the plasmamembrane. The transport of calcein by MRP is ATP-dependent and is inhibited by probenecid and vincristine. Intracellular glutathione (GSH) depletion which occurred when cells were exposed to buthionine sulfoximine had no effect on the efflux of calcein, whereas it reversed the daunorubicin accumulation deficit in MRP overexpressing tumor cells. In conclusion, ATP-dependent transport of calcein and possibly other organic anions by MRP is not inhibited by a large decrease of the intracellular GSH concentration, that inhibits daunorubicin efflux by MRP.

Topics: Adenosine Triphosphate; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP-Binding Cassette Transporters; Biological Transport, Active; Buthionine Sulfoximine; Cytoplasm; Daunorubicin; Fluoresceins; Glutathione; Humans; Indicators and Reagents; Methionine Sulfoximine; Multidrug Resistance-Associated Proteins; Neoplasm Proteins; Probenecid; Tumor Cells, Cultured

We have developed a novel method for monitoring the mitochondrial permeability transition in single intact hepatocytes during injury with t-butylhydroperoxide (t-BuOOH). Cultured hepatocytes were loaded with the fluorescence probes, calcein and tetramethylrhodamine methyl ester (TMRM). Depending on loading conditions, calcein labelled the cytosolic space exclusively and did not enter mitochondria or it stained both cytosol and mitochondria. TMRM labelled mitochondria as an indicator of mitochondrial polarization. Fluorescence of two probes was imaged simultaneously using laser-scanning confocal microscopy. During normal incubations, TMRM labelled mitochondria indefinitely (longer than 63 min), and calcein did not redistribute between cytosol and mitochondria. These findings indicate that the mitochondrial permeability transition pore ('megachannel') remained closed continuously. After addition of 100 microM t-BuOOH, mitochondria filled quickly with calcein, indicating the onset of mitochondrial permeability transition. This event was accompanied by mitochondrial depolarization, as shown by loss of TMRM. Subsequently, the concentration of ATP declined and cells lost viability. Trifluoperazine, a phospholipase inhibitor that inhibits the permeability transition in isolated mitochondria, prevented calcein redistribution into mitochondria, mitochondrial depolarization, ATP depletion and cell death. Carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, also rapidly depolarized mitochondria of intact hepatocytes but did not alone induce a permeability transition. Trifluoperazine did not prevent ATP depletion and cell death after the addition of CCCP. In conclusion, the permeability transition pore does not 'flicker' open during normal incubation of hepatocytes but remains continuously closed. Moreover, mitochondrial depolarization per se does not cause the permeability transition in intact cells. During oxidative stress, however, a permeability transition occurs quickly which leads to mitochondrial depolarization and cell death.

Topics: Adenosine Triphosphate; Animals; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Compartmentation; Cell Death; Cytosol; Fluoresceins; Fluorescent Dyes; Male; Membrane Potentials; Mitochondria, Liver; Permeability; Peroxides; Phospholipases; Rats; Rats, Sprague-Dawley; Rhodamines; tert-Butylhydroperoxide; Trifluoperazine