Effect of cyclosporin and verapamil on the cellular kinetics of daunorubicin

A simple and fast microfluidic approach of same-single-cell analysis (SASCA) for the study of multidrug resistance modulation in cancer cells

Due to the cellular heterogeneity in multidrug resistance (MDR) cell populations, positive drug effects on the modulation of MDR can be obscured in conventional methods, especially when only a small number of cells are available. To address cellular variations among different MDR cells, we report a new microfluidic approach to study drug effect on MDR modulation, by investigating drug accumulation of daunorubicin in MDR leukemia cells. We have demonstrated that the new approach of same-single-cell analysis by accumulation (denoted as SASCA-A) is not only superior to different-single-cell analysis, but also has key advantages over our previous approach of same-single-cell analysis. First, SASCA-A is much simpler as it does not require multiple cycles of drug uptake and drug efflux. Second, it is faster, only taking about one fourth of the time used in the previous approach. Third, it provides a more 'identical' and reliable control because it compares the time points just before MDR modulator tests. To help understand the dynamics of drug accumulation in MDR cells, we also developed a mathematical model to describe the kinetics of drug accumulation conducted in individual cells. The SASCA-A method will benefit drug resistance research in minor cell subpopulations (e.g., cancer "stem" cells) because this method requires only a small number of cells in identifying the MDR reversal effect.

Pumping of drugs by P-glycoprotein: a two-step process?

The apparent inhibition constant, Kapp, for the blockade of P-glycoprotein (P-gp) by four drugs, verapamil, cyclosporin A, XR9576 (tariquidar), and vinblastine, was measured by studying their ability to inhibit daunorubicin and calcein-AM efflux from four strains of Ehrlich cells with different levels of drug resistance and P-gp content. For daunorubicin as a transport substrate, Kapp was independent of [P-gp] for verapamil but increased strictly linearly with [P-gp] for vinblastine, cyclosporin A, and XR9576. A theoretical analysis of the kinetics of drug pumping and its reversal shows that Kapp for inhibition should increase linearly with the amount of pumps present in the membrane for a reverser that inhibits pumping from the cytoplasmic face. In contrast, if the reverser acts by blocking transport from the outer face, i.e., preemptively, Kapp should be independent of the number of pumps present. The experimental data suggest that verapamil blocks pumping at the extracellular face of the membrane, whereas the other three blockers act on pumping from the cytoplasmic phase. The maximum degree of inhibition was the same for all four blockers; thus, they do not act in parallel but rather, in serial, i.e., a drug that is pumped from the cytoplasmic phase has to pass the preemptive route upon leaving the cell. Our results are consistent with the Sauna-Ambudkar two-step model for pumping by P-gp. We suggest that the vinblastine/cyclosporin A/XR9576-binding site accepts daunorubicin at the cytoplasmic face and transfers it to the verapamil-binding site, from where daunorubicin is emptied at the extracellular surface.

Induction of MDR1 gene expression by anthracycline analogues in a human drug resistant leukaemia cell line

The effects of 4-demethoxydaunorubicin (idarubicin, IDA) and MX2, a new morpholino-anthracycline, on up-regulation of the MDR1 gene in the low-level multidrug resistant (MDR) cell line CEM/A7R were compared at similar concentrations (IC₁₀, IC₅₀and IC₉₀) over a short time exposure (4 and 24 h). The chemosensitivity of each drug was determined by a 3-day cell growth inhibition assay. Compared with epirubicin (EPI), IDA and MX2 were 17- and eightfold more effective in the CEM/A7R line respectively. No cross-resistance to 5-FU was seen in the CEM/A7R line. Verapamil (5 μM) and PSC 833 (1 μM), which dramatically reversed resistance to EPI in the CEM/A7R line, had no sensitizing effect on the resistance of this line to MX2, but slightly decreased resistance to IDA. The sensitivity to 5-FU was unchanged by these modulators. The induction of MDR1 mRNA expression by IDA, MX2 and 5-FU was analysed by Northern blotting and semiquantitatively assessed by scanning Northern blots on a phosphorimager. The relative level of MDR1 expression was expressed as a ratio of MDR1 mRNA to the internal RNA control glyceraldehyde-3-phosphate dehydrogenase (GAPDH). IDA, MX2 and 5-FU differentially up-regulated MDR1 mRNA in the CEM/A7R line in a dose-dependent manner. Both IDA and MX2 induced MDR1 expression within 4 h. 5-FU up-regulated MDR1 expression only when drug exposure was prolonged to 24 h. Based on MRK 16 binding, flow cytometric analysis of P-glycoprotein (Pgp) expression paralleled the increase in MDR1 mRNA levels. For the three anthracyclines, the increase in MDR1 expression was stable in cells grown in the absence of drug for more than 3 weeks after drug treatment. The induction of MDR1 expression by 5-FU was transient, associated with a rapid decrease in the increased Pgp levels which returned to baseline 72 h after the removal of 5-FU. This study demonstrates that MDR1 expression can be induced by analogues of anthracyclies not pumped by Pgp, and that this induction appears to be stable despite a 3-week drug-free period. © 1999 Cancer Research Campaign

A novel method for direct and fluorescence independent determination of drug efflux out of leukemic blast cells

Multi drug resistance (MDR) is often due to an increased efflux of anti cancer drugs out of leukemic blast cells. Efflux assays are used to get an impression of functional resistance in those cells. Dyes like rhodamine 123 or 3'3'-diethyloxocarbocyanine iodide are commonly used for this purpose. A major known disadvantage is that dyes do not behave like cytotoxic drugs in efflux experiments. Assays using the self fluorescence of drugs like anthracyclines can not reveal a real impression of intracellular or effluxed drug due to quenching of the drug fluorescence in the nuclei of the cells. We have developed a reproducible and sensitive assay for direct and quantitative determination of drug efflux out of blast cells. This was done by a novel double radioactive labelling using a 3H-labelled drug and 14C-labelled sucrose as extracellular marker. So this assay can be applied to every drug of interest. Quenching of fluorescence is also by-passed with this technique as well as protracting washing or silicon oil procedures. As a model system we used the T-lymphoblastoid cell line CCRF CEM and its resistant sublines vincristine 100 and adriamycin 5000. The results were also transferable to clinical specimens of leukemic patients. In conclusion our assay may be used for precise and direct efflux measurement of a broad range of anti-cancer drugs in clinical MDR evaluation.

Competitive, non-competitive and cooperative interactions between substrates of P-glycoprotein as measured by its ATPase activity

We have studied the interaction between verapamil and other modulators of the P-glycoprotein ATPase from membranes of CR1R12 Chinese hamster ovary cells. Four major categories of interaction were identified. (i) Non-competitive inhibition of verapamil's stimulation of enzyme activity was found with vanadate. (ii) Competitive inhibition of the ATPase was found for the pair verapamil and cyclosporin A. (iii) Allosteric inhibition with an increase in the Hill number for verapamil was found in the cases of daunorubicin, epirubicin, gramicidin S and D, vinblastine, amiodarone, and colchicine. (iv) Cooperative stimulation of verapamil-induced ATPase activity was found with progesterone, diltiazem, amitriptyline, and propranolol. At high levels, progesterone and verapamil mutually enhanced each other's inhibitory action on the ATPase. Our data show that the substrate binding behavior of P-glycoprotein is complex with more than one binding site being present. This information could form the basis for the development of improved modulators of P-glycoprotein.

Modulation of the function of human MDR1 P-glycoprotein by the antimalarial drug mefloquine

MDR1 P-glycoprotein in membranes of human tumor cells of the CEM/VBL100 line was selectively labelled using photoreactive analogs of verapamil, N-(p-azido-3-[125I]salicyl)amino-verapamil ([125I]ASA-V) and prazosin, 2-[4-(4-azido-3-[125I]iodobenzoyl)piperazin-1-yl]4 -amino-6,7-dimethoxyyquinazoline ([125I]ASA-P). Mefloquine, a quinolinemethanol antimalarial drug, was shown to inhibit the labelling of P-glycoprotein with an efficiency similar to that for verapamil, a known chemosensitizer. By contrast, chloroquine competed poorly for the binding site on P-glycoprotein. Mefloquine also inhibited the functional activity of P-glycoprotein. It decreased the rates of extrusion of [3H]vinblastine and the fluorescent dyes, fluo-3 acetomethoxy ester and rhodamine 123, from drug-resistant cells and decreased the level of resistance of these cells to vinblastine. The ability of mefloquine to inhibit P-glycoprotein function may be involved in the neurotoxic side-effects occasionally associated with the use of mefloquine as an antimalarial drug.

Inhibitors of P-glycoprotein-mediated daunomycin transport in rat liver canalicular membrane vesicles

P-glycoprotein (P-gp), the multidrug resistance (MDR) gene product, is exclusively located on the canalicular membrane of hepatocytes. Recent studies using isolated rat canalicular liver plasma membrane (cLPM) vesicles indicate that daunomycin (DNM) is a substrate for the ATP-dependent P-gp efflux system in the rat liver. The isoforms of P-gp present in cLPM and in cancer cell lines differ in that the major form present in the liver represents the gene product of mdr2 in mice (MDR3 in humans; class III) while the isoform of P-gp in cancer cells is the gene product of mdr1 in mice (MDR1 in humans, class I). The objective of this study was to examine the inhibitory effects of various organic compounds, most of which have been studied previously in MDR cancer cells, on P-gp-mediated [3H]DNM uptake into cLPM. Also, the stereospecificity of P-gp for its substrates was investigated by comparing the inhibitory effects of the enantiomers and the racemic mixtures of verapamil and propranolol. DNM exhibited ATP-dependent active transport into rat liver cLPM with a Km of 26.8 +/- 13.4 microM and a Vmax of 4.9 +/- 0.8 nmol/45 s/mg of protein (n = 4). ADP, AMP, and a nonhydrolyzable ATP analogue did not increase DNM transport over the control value. Thirty-one potential inhibitors were examined; only acridine orange, doxorubicin, verapamil, propranolol, phosphatidylcholine, beta-estradiol glucuronide, and DNM itself showed statistically significant inhibition of [3H]DNM uptake into cLPM. These results suggest that only a limited number of substrates bind to or are transported across the hepatic canalicular membrane via P-gp. Phosphatidylcholine, a substrate for the gene product of the class III P-gp gene, produced significant inhibition of [3H]DNM transport (30.6% at a 10-fold-higher substrate concentration), suggesting that transport may be mediated, at least in part, by this P-gp gene product. There were no statistically significant differences in the inhibitory effects of the enantiomers and racemate of verapamil on [3H]DNM transport into cLPM, but the enantiomers of propranolol exhibited stereospecific inhibition of DNM transport. (R)-(+)-Propranolol produced a statistically significant inhibition of [3H]DNM transport similar to that observed with the racemic mixture, while (S)(-)-propranolol showed no inhibition. These findings suggest that bile canalicular P-gp may exhibit stereospecificity of binding or transport for its substrates.

A marine natural product, patellamide D, reverses multidrug resistance in a human leukemic cell line

A cyclic octapeptide (patellamide D) isolated from the marine tunicate, Lissaclinum patella, acts as a resistance-modifying agent in the multidrug resistant CEM/VLB100 human leukemic cell line. A three-day microculture tetrazolium proliferation assay was used to determine the 50% inhibitory concentration (IC50) for vinblastine, colchicine and adriamycin and calculate the degree of resistance modulation. Patellamide D at 3.3 microM was compared with 5.1 microM verapamil in modulating drug resistance in vitro. The IC50 for vinblastine was reduced from 100 ng/ml to 1.5 ng/ml in the presence of patellamide D or to 2.1 ng/ml when exposed to verapamil. Colchicine cytotoxicity was enhanced only 1.4-fold by verapamil, as compared with 2.8-fold using patellamide D (IC50 was reduced from 140 ng/ml to 100 ng/ml or 50 ng/ml). Adriamycin toxicity was reduced from IC50 > 1000 ng/ml to 110 ng/ml and 160 ng/ml when coexposed to patellamide D and verapamil, respectively. Our results indicate that patellamide D acts as a selective antagonist in multidrug resistance and stresses the importance of investigating marine-derived compounds as a potential new source for modulators of the drug-resistance phenotype.

Comparative effects of racemic verapamil vs R-verapamil on normal and leukemic progenitors

R-Verapamil (R-VPM), an enantiomer of racemic verapamil (VPM), has been recently reported to possess an activity equivalent to VPM in reverting drug resistance in vitro, without showing remarkable cardiovascular toxicity in animal models, even in doses three times higher than VPM. In this study, we assessed the effects of R-VPM in vitro, on clonogenic leukemia cells (CFU-L) from 15 patients with acute nonlymphoid leukemia (ANLL) at diagnosis, and on bone marrow erythroid (BFU-E) and myeloid (CFU-GM) progenitors from 15 healthy volunteers. On CFU-L, continuous exposure to VPM or R-VPM alone showed a slight inhibitory activity; in combination with daunorubicin (DNR), R-VPM proved more effective (mean IC50 of DNR: alone = 24.53 ng/ml +/- 6.2 SE, + VPM = 18.8 ng/ml +/- 4.6 SE, +R-VPM = 17.9 ng/ml +/- 4.8 SE). On CFU-GM, both VPM and R-VPM were minimally toxic at the lowest concentration used, but 30 microM VPM were significantly more toxic than R-VPM at the same dose (residual growth = 39.2% +/- 6.5% vs. 71.8% +/- 9.3% with R-VPM, p = 0.005). On BFU-E, both VPM and R-VPM caused more consistent growth inhibition; at high doses, VPM was again more toxic than R-VPM (33.4% +/- 12.8% vs 53.4% +/- 10.4% residual growth at 30 microM, p = 0.03). DNR toxicity on bone marrow was more greatly enhanced by VPM than R-VPM, and this difference was statistically significant on erythroid progenitor colony growth (p = 0.04). In conclusion, in comparison to VPM, R-VPM appeared to be at least equally effective on leukemic clonogenic cells and less toxic on normal bone marrow precursors, thus suggesting a possible safe use in vivo, even in concentrations that cannot be achieved with VPM, owing to its toxic effects.

Differential effects of estrogen, tamoxifen and the pure antiestrogen ICI 182,780 in human drug-resistant leukemia cell lines

ICI 182,780, a potent, new steroidal antiestrogen without apparent agonist activity, appears to be a potent modulator of the classic multidrug resistance (MDR) phenotype in the CEM/A7, CEM/VLB100 and K562/VIN100 MDR cell lines. This reagent had no effect on the respective parental CCRF-CEM and K562 cell lines. The use of 1.25 microM ICI 182,780 resulted in a 6- to 7-fold decrease in doxorubicin resistance in the CEM/A7 and CEM/VLB100 cell lines. A dose-response effect was observed at ICI 182,780 concentrations of up to 5 microM. As compared with tamoxifen (TAM), ICI 182,780 was 2 and 4 times more effective in the K562/VIN100 and CEM/A7 cell lines, respectively. ICI 182,780 at 0.625 microM increased [3H]-daunomycin uptake (P < 0.0001) as effectively as 5 microM TAM in the resistant CEM/A7 line. Drug-efflux studies showed that 5 microM ICI 182,780 significantly decreased drug efflux as compared with 5 microM TAM (P < 0.0001). Estradiol (EST) at 10 microM increased doxorubicin resistance by 1.2-1.3 times in the CEM/A7 and CEM/VLB100 cell lines and significantly decreased drug accumulation (P = 0.002) and retention (P < 0.001) in the CEM/A7 cell line. However, the addition of 10 microM EST to 1-2 microM ICI 182,780 did not inhibit the ability of ICI 182,780 to modulate doxorubicin resistance in the two resistant cell lines. Using reverse-phase high-performance liquid chromatography (HPLC) to measure lipophilicity, we found no apparent association between the ability of ICI 182,780, TAM or EST to modulate resistance and their relative hydrophobicity.

Cyclosporins as drug resistance modifiers

Cyclosporin A (CsA), a cyclic peptide of 11 amino acids isolated from the fungus Tolypoclodium inflatum Gams, is the principle drug used for immunosuppression in organ transplant patients. It is known to have a very specific effect on T-cell proliferation although the precise mechanism remains unclear. Following internalization, CsA binds to a cytosolic protein, cyclophilin, which has been shown to possess peptidyl-prolyl cis-trans isomerase activity. CsA is an effective modifier of multidrug resistance in human and rodent cells at doses in the range of 1 to 5 micrograms/mL. Although it reverses the drug accumulation deficit associated with multidrug resistance in some cell types, this is not always the case. CsA has P-glycoprotein binding activity but less specific membrane effects and inhibition of protein kinase C may also be involved in its resistance modifier action. A number of non-immunosuppressive analogues of CsA have been shown to have resistance modifier activity and some are more potent than the parent compound. One analogue from Sandoz, PSC-833, has been shown to be approximately 10-fold more potent than CsA and is expected to enter clinical trial in the near future. The use of such agents may allow a full test of the hypothesis that reversal of multidrug resistance will prove a useful clinical strategy.

Circumvention of doxorubicin resistance in multi-drug resistant human leukaemia and lung cancer cells by the pure antioestrogen ICI 164384

ICI 164384, a new steroidal antioestrogen, entirely devoid of oestrogenic activity, modulates doxorubicin resistance in vitro. At non-cytotoxic concentrations, ICI 164384 potentiated the cytotoxicity of doxorubicin in a dose-dependent manner in both the classical multi-drug resistant (MDR) human leukaemia cell lines CEM/VLB 100 and CEM/VLB 1000 and the human small cell lung cancer cell line H69 LX4. ICI 164384 had no effect on the two respective parental cell lines, CEM/CCRF and H69 P. None of these cell lines expressed the oestrogen receptor. In comparative studies at concentrations ranging from 1.25 to 10 mumols/l, ICI 164384 was significantly more effective (1.2-6-fold) than tamoxifen in reducing the IC50 of doxorubicin in the CEM/VLB 100 line. In resistant cells, ICI 164384 increased 3H-daunomycin accumulation in a dose-dependent manner and was significantly more effective than tamoxifen at concentrations ranging from 2.5 to 10 mumol/l. ICI 164384 reduced the efflux of daunomycin from resistant cells more effectively than tamoxifen. These studies suggest that ICI 164384 is an effective modulator of MDR.

Chemosensitisation of a drug-sensitive parental cell line by low-dose cyclosporin A

We investigated the chemosensitisation of the parental EMT6 mouse mammary tumour cell line by low doses of cyclosporin A (CsA). This cell line has not previously been exposed to cytotoxic drugs but expresses low levels of P-glycoprotein. We produced greater than 2-fold sensitisation to doxorubicin, colchicine and vincristine using 0.084 microM (0.1 micrograms/ml) CsA. Cellular accumulation of doxorubicin and daunorubicin was also increased by this dose. In the MDR subline EMT6/AR1.0, much higher doses of CsA were required to effect optimal restoration of doxorubicin or daunorubicin accumulation. The effects of CsA on the parent line could not be increased by extended preincubation of cells with the sensitiser. These effects of CsA in the EMT6 parent cell line occur at a dose that is 1 order of magnitude lower than those previously reported to produce significant chemosensitisation.