Comparison of drug accumulation in P-glycoprotein-expressing and MRP-expressing human leukaemia cells

P-glycoprotein (ABCB1) activity decreases raltegravir disposition in primary CD4+P-gphigh cells and correlates with HIV-1 viral load

Objectives

To evaluate the role of P-glycoprotein (P-gp) and multidrug-resistant-protein 1 (MRP1) on raltegravir intracellular drug disposition in CD4+ T cells, investigate the effect of HIV-1 infection on P-gp expression and correlate HIV-1 viraemia with P-gp activity in primary CD4+ T cell subsets.

Methods

The cellular accumulation ratio of [³H]raltegravir was quantified in CD4+ T cell lines overexpressing either P-gp (CEM-P-gp) or MRP1 (CEM-MRP1) and in primary CD3+CD4+ T cells with high (P-gp^high) and low P-gp activity (P-gp^low); inhibition of efflux transporters was confirmed by the intracellular retention of calcein-AM. The correlation of P-gp activity with HIV-1 viraemia was assessed in naive and memory T cell subsets from 21 HIV-1-infected treatment-naive subjects.

Results

[³H]Raltegravir cellular accumulation ratio decreased in CEM-P-gp cells (P < 0.0001). XR9051 (a P-gp inhibitor) and HIV-1 PIs reversed this phenomenon. Primary CD4+P-gp^high cells accumulated less raltegravir (38.4% ± 9.6%) than P-gp^low cells, whereas XR9051 also reversed this effect. In vitro HIV-1 infection of PBMCs and stimulation of CD4+ T cells increased P-gp mRNA and P-gp activity, respectively, while primary CD4+P-gp^high T cells sustained a higher HIV-1 replication than P-gp^low cells. A significant correlation between HIV-1 viraemia and P-gp activity was found in different CD4+ T cell subsets, particularly memory CD4+ T cells (r = 0.792, P < 0.0001).

Conclusions

Raltegravir is a substrate of P-gp in CD4+ T cells. Primary CD4+P-gp^high T cells eliminate intracellular raltegravir more readily than P-gp^low cells and HIV-1 viraemia correlates with P-gp overall activity. Specific CD4+P-gp^high T cell subsets could facilitate the persistence of viral replication in vivo and ultimately promote the appearance of drug resistance.

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.

Intracellular 'boosting' of darunavir using known transport inhibitors in primary PBMC

AIMS

ABCB1, some ABCCs and SLCOs have been reported to affect the intracellular accumulation of various protease inhibitors in vitro and ex vivo. Darunavir is the most recently licensed protease inhibitor and we sought to investigate the ability of transport inhibitors to influence its intracellular accumulation in lymphocytes from healthy volunteers.

METHODS

The intracellular accumulation of radiolabelled darunavir was assessed using CEM cells and ABCB1-overexpressing CEM(VBL) cells. Apical and basolateral transport of radiolabelled darunavir through MDCKII monolayers was also studied. Finally the ability of known inhibitors to influence intracellular accumulation of darunavir in peripheral blood mononuclear cells (PBMC) was investigated.

RESULTS

CEM(VBL) cells (1.4 +/- 0.6, P < 0.001, 95% CI for the difference = 0.46, 0.80, n= 7) had significantly lower accumulation of darunavir compared with CEM cells (5.6 +/- 0.7, n= 7) and this was reversed by addition of tariquidar (30 nm, 4.6 +/- 0.8, P < 0.001, 95% CI =-0.64, -0.41, n= 4). In MDCKII-ABCBI cells, transport from the basal to the apical compartment was observed and this was also reversible with the addition of tariquidar. In PBMCs, dipyridamole (6.9 +/- 1.3, P < 0.01, 95% CI for the difference =-1.16, -0.30, (n= 8) significantly increased whilst montelukast (5.7 +/- 1.0, P < 0.01, 95% CI for the difference = 0.16, 0.79, n= 8) significantly decreased the intracellular accumulation of darunavir when compared with control (6.2 +/- 1.1, n= 8).

CONCLUSIONS

Darunavir is a substrate for efflux and influx transporters in PBMC and intracellular concentrations can be manipulated using known inhibitors.

Membrane microparticles mediate transfer of P-glycoprotein to drug sensitive cancer cells

Multidrug resistance (MDR), a significant impediment to the successful treatment of cancer clinically, has been attributed to the overexpression of P-glycoprotein (P-gp), a plasma membrane multidrug efflux transporter. P-gp maintains sublethal intracellular drug concentrations by virtue of its drug efflux capacity. The cellular regulation of P-gp expression is currently known to occur at either pre- or post-transcriptional levels. In this study, we identify a 'non-genetic' mechanism whereby microparticles (MPs) serve as vectors in the acquisition and spread of MDR. MPs isolated from drug-resistant cancer cells (VLB(100)) were co-cultured with drug sensitive cells (CCRF-CEM) over a 4 h period to allow for MP binding and P-gp transfer. Presence of P-gp on MPs was established using flow cytometry (FCM) and western blotting. Whole-cell drug accumulation assays using rhodamine 123 and daunorubicin (DNR) were carried out to validate the transfer of functional P-gp after co-culture. We establish that MPs shed in vitro from drug-resistant cancer cells incorporate cell surface P-gp from their donor cells, effectively bind to drug-sensitive recipient cells and transfer functional P-gp to the latter. These findings serve to substantially advance our understanding of the molecular basis for the emergence of MDR in cancer clinically and lead to new treatment strategies which target and inhibit MP mediated transfer of P-gp during the course of treatment.

Cultured CD4T cells and primary human lymphocytes express hOATPs: intracellular accumulation of saquinavir and lopinavir

BACKGROUND AND PURPOSE

Drug efflux tranporters (P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP)) limit the cellular uptake of human immunodeficiency virus protease inhibitors but the contribution of influx transporters in cells that (over)express P-gp or MRP is less clear. Here, we studied the expression of one influx transporter system, human organic anion-transporting polypeptide (hOATP), in some T-cell lines (CEM, CEM(VBL), CEM(E1000)) and in peripheral blood mononuclear cells (PBMCs) and examined the effects of manipulation of influx/efflux transporters on the uptake of saquinavir and lopinavir.

EXPERIMENTAL APPROACH

The expression of hOATPs was studied by PCR. We used hOATP substrate or inhibitor (estrone-3-sulphate (E-3-S) or montelukast, respectively) and inhibitors of P-gp (XR9576) and MRP (MK571 and frusemide) to study functional interactions between influx and efflux transporters in the uptake of saquinavir and lopinavir. Lipophilicity of the drugs was measured by octanol/saline partition coefficient.

KEY RESULTS

CEM cells, their variants and PBMCs express various hOATP isoforms, with OATP3A1 detected in all of the cells. MK571, XR9576 and frusemide increased the uptake of saquinavir and lopinavir. E-3-S and montelukast reduced the uptake of saquinavir and lopinavir in some, but not all, of the cells. Pretreatment of the cells with MK571, XR9576 or frusemide, followed by E-3-S co-incubation reduced the cellular accumulation of saquinavir and lopinavir. Lopinavir is much more lipophilic than saquinavir.

CONCLUSIONS AND IMPLICATIONS

Human OATPs, MRP, P-gp and lipophilicity determine the cellular uptake and retention of saquinavir and lopinavir. These data may have important implications for drug-drug interactions, drug safety and efficacy.

Inhibition of placental P-glycoprotein: impact on indinavir transfer to the foetus

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

We have shown previously using the dually perfused isolated human placenta model that the maternal to foetal transfer of the antiviral protease inhibitor drug indinavir is substantially lower than the transfer in the opposite direction. This finding is not consistent with passive diffusion and indicates that a carrier-mediated mechanism is involved in retarding the movement in the maternal to foetal direction. The efflux transporter P-gp located in the apical membrane domain of the placental trophoblast cells has been implicated as the likely cause of the differential bi-directional transport.

WHAT THIS STUDY ADDS

The present study also utilizes the human perfused human isolated placenta to investigate the possible inhibitory effects of the P-gp inhibitor PSC833 and the P-gp substrate/inhibitor ritonavir on the maternal to foetal transfer clearance of indinavir. The studies, which were conducted such that each placenta served as its own control, demonstrated a statistically significant increase in the maternal to foetal transfer of indinavir in the presence of PSC833 but not in the presence of ritonavir, a protease inhibitor that is often used in combination with other protease inhibitors in dual therapy. The lack of effect of ritonavir is most likely related to the relatively low inhibitory activity at the clinically relevant concentration used in this study.

AIMS

To investigate the effect of P-gp inhibition on the maternal to foetal transfer of indinavir.

METHODS

Term human placentae (n = 12) were from non-HIV infected women. Maternal to foetal transfer of indinavir was examined in the absence and presence of P-gp inhibitors PSC833 (n = 7) or ritonavir (n = 5), in the perfused human placenta. Antipyrine and [(3)H]-vinblastine were included as markers of passive diffusion and P-gp transport, respectively. These markers and indinavir were added to maternal perfusate at 0 min; PSC833 or ritonavir was added at 25 min. Steady-state maternal to foetal transfer clearance was calculated during control and inhibitor phases. Indinavir and vinblastine clearances were normalized to antipyrine clearance (clearance index).

RESULTS

Indinavir clearance index increased between the control (0.25 +/- 0.03) and PSC833 phases (0.37 +/- 0.14) (95% CI of the difference -0.23, -0.002). Vinblastine clearance index increased from (0.25 +/- 0.08) to (0.34 +/- 0.06) in the control and PSC833 phases, respectively (95% CI of difference -0.14, -0.05). Indinavir clearance index was unchanged between control (0.34 +/- 0.14) and ritonavir phases (0.39 +/- 0.13) (95% CI of the difference -0.19, 0.08). Vinblastine clearance index increased from (0.24 +/- 0.12) to (0.32 +/- 0.12) in the control and ritonavir phases, respectively (95% CI of the difference -0.15, -0.009).

CONCLUSIONS

Maternal to foetal transfer clearance of indinavir and vinblastine increased following P-gp inhibition. The potential role for co-administration of P-gp inhibitors with PIs to reduce perinatal HIV transmission warrants further investigation.

Active efflux of ciprofloxacin from J774 macrophages through an MRP-like transporter

The accumulation and efflux kinetics of ciprofloxacin have been examined by using murine J774 macrophages. Accumulation (at equilibrium) was increased (three- to fourfold) (i) when cells were incubated with high extracellular drug concentrations (typically 200 mg/liter) as opposed to clinically meaningful concentrations (10 mg/liter or lower), (ii) during ATP- depletion and at acid pH, and (iii) during coincubation with probenecid, gemfibrozil and the preferential multidrug resistance-related protein (MRP) inhibitor MK571. All these conditions were also associated with a marked decrease in ciprofloxacin efflux (half-lives increased from <2 min in controls to up to 10 min). Monensin (a proton ionophore), verapamil, and the preferential P-glycoprotein (P-gp) inhibitor GF120918 had no or only minimal effect, while cyclosporin A, which is not specific for P-gp but also acts on MRP, had an intermediate effect. Short-term uptake studies showed that the influence of the modulators on the apparent drug influx was almost immediate (delay of < or =1 min). Cells made resistant to probenecid and showing a marked overexpression of MRP1 (by Western blot analysis and confocal microscopy) accumulated ciprofloxacin to almost the same extent as did control cells, but efflux was inhibited less by probenecid, gemfibrozil, and MK571. We conclude that ciprofloxacin is subject to constitutive efflux in J774 macrophages through the activity of an MRP-related transporter which is probably distinct from MRP1. We also suggest that the cellular accumulation of ciprofloxacin in wild-type cells is constitutively impaired at therapeutically meaningful concentrations.

Doxorubicin-resistant, MRP1-expressing U-1285 cells are sensitive to idarubicin

A doxorubicin-resistant subline (U-1285dox(900)) was derived from the human small cell lung carcinoma cell line U-1285. U-1285dox(900) was exposed to a wide range of anticancer agents to determine its resistance profile. In contrast to U-1285 cells, the resistant subline U-1285dox(900) expressed elevated MRP1 mRNA detected by reversed transcriptase-polymerase chain reaction (RT-PCR) and MRP1 protein analyzed with Western blot. Neither MDR1 mRNA nor P-glycoprotein could be detected in the parental cell line or resistant subline. U-1285dox(900) exhibited high resistance to doxorubicin, epirubicin, daunorubicin, and vincristine, an intermediate resistance to mitoxantrone, and a low resistance to etoposide. A collateral sensitivity to cytosine arabinoside, chlorodeoxyadenosine, and melphalan was observed. The resistance could be reversed by buthionine-sulphoximine and verapamil for all tested drugs. Compared with daunorubicin, resistance to idarubicin was very low, 14-fold and 2.6-fold, respectively. This was associated with a higher accumulation due to a slower transport of idarubicin out of U-1285dox(900) cells.

The use of Tris-lipidation to modify drug cytotoxicity in multidrug resistant cells expressing P-glycoprotein or MRP1

1. Increasing the lipophilicity is a strategy often used to improve a compound's cellular uptake and retention but this may also convert it into a substrate for an ATP-dependent transporter such as P-glycoprotein or the multidrug resistance-associated protein (MRP1), which are involved in cellular efflux of drugs. Tris-Lipidation of compounds is a convenient way of modifying drug lipophilicity and generating an array of derivatives with diverse properties. 2. To determine the effect of Tris-Lipidation on a drug's cytoxicity in multidrug resistant cells, various glycyl-Tris-mono- (GTP1), di- (GTP2) and tri-palmitate (GTP3) derivatives were prepared of the cancer chemotherapeutic drugs chlorambucil and methotrexate, and of the anti-HIV drug AZT. The cytotoxicity of these derivatives and their parent compounds was determined in the CEM/VLB(100) cells with increased P-glycoprotein expression, the CEM/E1000 cells that overexpress MRP1 and the parent, drug-sensitive CCRF-CEM cells. 3. Increasing the lipophilicity of AZT increased its cytotoxicity in the sensitive CCRF-CEM parental cell line while decreased cytotoxicity was observed for the methotrexate derivatives. For the chlorambucil derivatives, both increased (GTP1) and decreased (GTP2) cytotoxicity occurred in the CCRF-CEM cells. With the exception of AZT-GTP1, all GTP1 and GTP2 derivatives of chlorambucil, methotrexate and AZT had decreased cytotoxicity in the P-glycoprotein-expressing CEM/VLB(100) cells while chlorambucil-GTP1, methotrexate-GTP2 and methotrexate-GTP3 were the only compounds with decreased cytotoxicity in the MRP1-overexpressing CEM/E1000 cells. 4. The number of palmitate residues, the position of derivatisation and the type of linkage all may affect the P-glycoprotein and MRP1 substrate properties. 5. Tris-Lipidation may therefore provide a useful way of manipulating the pharmacokinetic properties of drugs.

Using flow cytometry to follow the apoptotic cascade

Flow cytometry has been extensively used to follow the apoptotic cascade and to enumerate apoptotic cells, both in cell cultures and, to a lesser extent, in tissue biopsies. An overview of the apoptotic cascade and how flow cytometric measurements can be used to observe the different elements of this process is presented.

Activity of drugs from traditional Chinese medicine toward sensitive and MDR1- or MRP1-overexpressing multidrug-resistant human CCRF-CEM leukemia cells

There is considerable interest among basic and clinical researchers in novel drugs with activity against leukemia. The vast history of experience of traditional Chinese medicine (TCM) with medicinal plants may facilitate the identification of novel antileukemic compounds. In the present investigation, we tested 22 drugs for their activity toward CCRF-CEM cell lines: artesunate, artemisinin, baicalein, baicalin, berberine, bufalin, cantharidin, cephalotaxine, curcumin, daidzein, daidzin, diallyl disulfide, ginsenoside Rh2, glycyrrhizic acid, isonardosinon, homoharringtonine, nardosinon, nardofuran, puerarin, quercetin, tannic acid, and tetrahydronardosinon. As compounds from folk medicinal remedies are sometimes looked upon as alternative medicine with some hesitation or criticism, we investigated only chemically pure compounds and tested the drugs independently in two different laboratories in Germany and Australia. We used CCRF-CEM parental cells and doxorubicin-selected P-glycoprotein (P-gp)/MDR1-expressing CEM/ADR5000, vinblastine-selected P-gp/MDR1-expressing CEM/VLB(100), and epirubicin-selected multidrug resistance-related protein 1 (MRP1)-expressing CEM/E1000 sublines thereof. While CEM/ADR5000, CEM/VLB(100), and CEM/E1000 cells were highly resistant to the corresponding selecting agents, no or only minimal degrees of cross-resistance were observed to TCM drugs in both growth inhibition assay and MTT assay (range from 0.4- to 8-fold). Homoharringtonine, artesunate, and bufalin were most active among this panel of compounds. As shown by flow cytometry, artesunate significantly increased daunorubicin accumulation in CEM/E1000 cells, but not in CEM/VLB(100) or CCRF-CEM parental cells. Bufalin caused a small, but significant increase in daunorubicin accumulation in CEM/VLB(100) and CEM/E1000 cells. As artesunate and bufalin showed both antileukemic activity if applied alone and modulation activity in combination with daunorubicin in multidrug-resistant (MDR) cells, these two drugs may be suitable for novel combination treatment regimens to improve leukemia cell killing.

Verapamil-stimulated glutathione transport by the multidrug resistance-associated protein (MRP1) in leukaemia cells

Multidrug resistance mediated by the multidrug resistance-associated protein MRP1 is associated with decreased drug accumulation, which is in turn dependent on cellular glutathione. We have reported that verapamil, an inhibitor of drug transport, caused a decrease in cellular glutathione in CCRF-CEM/E1000 MRP1-overexpressing leukaemia cells (Biochem Pharmacol 55;1283--9, 1998). We now demonstrate that other inhibitors of MRP1-mediated drug transport (e.g. MK571, indomethacin, genistein, and nifedipine) deplete cellular glutathione in these leukaemia cells (>30% decrease; P < 0.01) while having no effect on the parental CCRF-CEM cells. However, treatment with etoposide or vincristine (at similar molar concentrations) caused a 20% decrease in glutathione. Verapamil-stimulated glutathione transport correlated with MRP1 expression in a series of drug-resistant cells, and glutathione was quantitatively recovered in the extracellular media. Further, verapamil-stimulated glutathione transport was rapid (50% decrease in 10 min), dose-dependent, and inhibited by vanadate, an inhibitor of ATPase activity, but not by sulphobromophthalein (BSP) or methionine, inhibitors of hepatic glutathione transporters. Incubation of CCRF-CEM/E1000 cells in 25 mM glutathione not only showed that verapamil-mediated efflux occurred against the concentration gradient, but also demonstrated the MRP1-mediated uptake of glutathione (P < 0.01 compared to the parental CCRF-CEM cells), which was not inhibited by vanadate. These results demonstrate that while MRP1 transports glutathione in the presence of inhibitors of drug transport, there is no convincing evidence for co-transport of glutathione with drug. They further demonstrate that MRP1 mediates the facilitated transport of glutathione into the MRP1-overexpressing CEM/E1000 cells, suggesting that MRP1 may play a major role in cellular glutathione homeostasis.

P-Glycoprotein and transporter MRP1 reduce HIV protease inhibitor uptake in CD4 cells: potential for accelerated viral drug resistance?

BACKGROUND

The multidrug transporters P-glycoprotein (P-gp) and MRP1 are functionally expressed in several subclasses of lymphocytes. HIV-1 protease inhibitors interact with both; consequently the transporters could reduce the local concentration of HIV-1 protease inhibitors and, thus, influence the selection of viral mutants.

OBJECTIVES

To study the effect of the expression of P-gp and MRP1 on the transport and accumulation of HIV-1 protease inhibitors in human lymphocytes and to study the effects of specific P-gp and MRP1 inhibitors.

METHODS

The initial rate and the steady-state intracellular accumulation of radiolabelled ritonavir, indinavir, saquinavir and nelfinavir was measured in three human lymphocyte cell lines: control CEM cells, CEM-MDR cells, which express 30-fold more P-gp than CEM cells, and CEM-MRP cells, which express fivefold more MRP1 protein than CEM cells. The effect of specific inhibitors of P-gp (GF 120918) and MRP1 (MK 571) was also examined.

RESULTS

Compared with CEM cells, the initial rates of uptake and the steady-state intracellular concentrations of all protease inhibitors are significantly reduced in CEM-MDR cells. The intracellular concentrations of the protease inhibitors are increased upon co-administration with GF 120918, in some cases to levels approaching those in CEM cells. The intracellular concentrations of the protease inhibitors are also significantly reduced in CEM-MRP cells. Co-administration with MK -571 can partially overcome these effects.

CONCLUSIONS

The overexpression of multidrug transporters significantly reduces the accumulation of protease inhibitors at this major site of virus replication, which, potentially, could accelerate the acquisition of viral resistance. Targeted inhibition of P-gp may represent an important strategy by which this problem can be overcome.

Evidence that natural killer cells express mini P-glycoproteins but not classic 170 kDa P-glycoprotein

Several lines of evidence including reverse transcription polymerase chain reaction, immunoreactivity and their ability to efflux rhodamine 123 have implied the existence of P-glycoprotein in natural killer (NK) cells. It has been a natural tendency to assume that NK-cell P-glycoprotein is identical to the P-glycoprotein of multidrug resistant (MDR) cell lines, however, the present study uncovered major differences. Functionally, NK cells demonstrated a restricted substrate profile, being unable to transport daunorubicin and calcein acetoxymethylester while efficiently transporting other P-glycoprotein substrates. Furthermore, physical differences in NK-cell P-glycoprotein were established by differential reactivity with P-glycoprotein antibodies. NK cells demonstrated strong reactivity with C494 and JSB-1, but did not react appreciably with C219. In addition, NK cells were unable to bind to the antibody MM4.17 unless they had been fixed and permeabilized, yet this antibody normally recognizes an extracellular epitope of P-glycoprotein. These differences culminated in the demonstration using Western analysis that NK cells did not express detectable levels of 170 kDa P-glycoprotein. Instead, NK cells expressed small-molecular-weight 'mini P-glycoprotein' products, of approximately 70 and 80 kDa. Collectively, these data indicate that the predominant P-glycoprotein species of NK cells are novel mini P-glycoproteins and not the classic P-glycoprotein of MDR models.

Carbamazepine is not a substrate for P-glycoprotein

AIMS

To determine whether the anticonvulsant carbamazepine (CBZ), a known CYP3A4 substrate, is also a substrate for the multidrug efflux transporter P-glycoprotein (Pgp).

METHODS

The role of Pgp in the transport of CBZ was assessed in three systems: (a) in mdr1a/1b(-/-) and wild-type mice after administration of 2 mg kg-1 and 20 mg kg-1, which served as a model for brain penetration; (b) in Caco-2 cells, an in vitro model of the intestinal epithelium that is known to express high Pgp levels; and (c) by flow cytometry in lymphocytes using rhodamine 123, a fluorescent substrate for PgP.

RESULTS

Brain penetration of both doses of CBZ at 1 h and 4 h was comparable in wild-type and mdr1a/1b(-/-) mice. Transport across the Caco-2 cell monolayer was Pgp-independent, and was not affected by the Pgp inhibitor PSC-833. CBZ had no effect on rhodamine 123 efflux from lymphocytes, in contrast to verapamil, which increased fluorescence intensity fivefold.

CONCLUSION

CBZ is not a substrate for Pgp. Its efficacy is unlikely to be affected by Pgp over-expression in the brain. Furthermore, the interaction of CBZ with drugs that modulate both CYP3A4 and Pgp function such as verapamil is probably due to inhibition of CYP3A4 and not Pgp.

The drug resistance proteins, multidrug resistance-associated protein and P-glycoprotein, do not confer resistance to Fas-induced cell death

BACKGROUND

Multidrug resistance (MDR) is mediated by the drug resistance proteins, the multidrug resistance-associated protein (MRP) and P-glycoprotein, both of which confer resistance by the active efflux of chemotherapeutic drugs from the cell. Reduced Fas (CD95/APO-1) expression and resistance to Fas-mediated apoptosis have also been correlated with P-glycoprotein-mediated MDR.

METHODS

We investigated cell surface Fas expression (using anti-Fas monoclonal antibody DX2.1) in a series of MRP-expressing drug-resistant leukemia sublines, and P-glycoprotein-expressing leukemia sublines, and their susceptibility to apoptosis induced by anti-Fas treatment (CH-11 monoclonal antibody). Caspase-3 activation was detected by Western blot and apoptosis was determined by flow cytometry with 7-aminoactinomycin D (7-AAD) staining of cells.

RESULTS

Fas expression was not reduced in either the MRP- or P-glycoprotein-expressing drug-resistant cell lines, although expression was reduced by 15% in one low-level drug-resistant subline. Expression of MRP or P-glycoprotein did not confer resistance to caspase-3 activation or to anti-Fas-induced cell death.

CONCLUSIONS

MDR mediated by the drug transport proteins MRP and P-glycoprotein does not correlate with resistance to Fas-mediated cell death or resistance to caspase-3 activation.

Drug resistance does not correlate with resistance to Fas-mediated apoptosis

Recent reports have correlated multidrug resistance (MDR) and P-glycoprotein expression with decreased Fas expression and resistance to Fas-mediated apoptosis. We report the MRP-overexpressing MDR subline CEM/E1000 has the same Fas expression (MFI 74.3 +/- 0.7) as the parental CCRF-CEM T-cell leukaemia cells (MFI 70.0 +/- 3.6; P>0.05), and that the level of apoptosis induced by anti-Fas antibody or drug was similar in both cell lines. Further the P-glycoprotein-expressing CEM/VLB(100) subline of the CCRF-CEM cells showed increased Fas expression (MFI 114.8 +/- 3.6; P<0.001) and no resistance to Fas-mediated apoptosis. This questions the hypothesis that selection of drug resistance results in resistance to Fas-mediated apoptosis, with important implications for the rational use of immunotherapy in the treatment of drug resistant cancer.

Cyclosporin increases cellular idarubicin and idarubicinol concentrations in relapsed or refractory AML mainly due to reduced systemic clearance

The feasibility of adding both the multidrug resistance modulator cyclosporin (CsA) and granulocyte colony-stimulating factor (G-CSF) to a standard salvage regimen of idarubicin (IDA) and cytarabine was evaluated in patients with resistant or relapsed acute myeloid leukemia and myelodysplastic syndrome. Three patients received IDA 12 mg/m2/day, the next four patients 9 mg/m2/day. The dose of CsA was 16 mg/kg/day. Six patients showed Pgp expression and none MRP1 expression. Grade III or IV toxicity (CTC-NCIC criteria) was registered in six patients for gastrointestinal, two patients for cardiovascular and one patient for neurological complications. Three patients died in hypoplasia and three patients showed leukemic regrowth. Three control patients were treated with IDA 12 mg/m2/day and cytarabine, but no CsA and G-CSF. The plasma IDA and idarubicinol (ida-ol) area under the curve's of patients treated with IDA 12 mg/m2 plus CsA were higher (P< 0.05) than in controls. Cellular IDA concentrations were almost similar, but cellular ida-ol concentrations were significantly higher (P < 0.05) in the presence of CsA than in controls. We conclude that the toxicity either with IDA 12 or 9 mg/m2/day was too high. The modulating effect of CsA was mainly based on changes in plasma kinetics of IDA and ida-ol, although ida-ol cellular clearance was delayed in the presence of CsA.

Molecular identification and functional characterization of Mdr1a in rat cholangiocytes

BACKGROUND & AIMS

The multidrug resistance P-glycoprotein 170 gene products (mdr1a and 1b) are glycosylated plasma membrane proteins that function as adenosine triphosphate-dependent transmembrane export pumps for lipophilic xenobiotics of widely different structure. We assessed whether these P-glycoproteins are functionally expressed in cholangiocytes.

METHODS

A reverse-transcription polymerase chain reaction was performed on RNA from a normal rat cholangiocyte cell line using mdr1-specific primers. Northern and Western blot analyses were performed on cholangiocytes immunoisolated from 2-week bile duct-ligated rats and cholangiocytes and isolated cholangiocyte membrane subfractions, respectively. Functional assays were performed in isolated bile duct units from bile duct-ligated rats and incubated with rhodamine 123, a P-glycoprotein substrate, with or without the P-glycoprotein inhibitors verapamil or GF120918.

RESULTS

A 400-base pair fragment with 99% homology to the cytosolic domain of rat intestinal mdr1a (5' 1953-2350 3') was identified that hybridized to a 5.2-kilobase RNA transcript in a normal rat cholangiocyte cell line, isolated rat cholangiocytes, and ileum. Western analysis localized mdr1 to the apical membrane of cholangiocytes. Confocal microscopy showed active secretion of rhodamine 123 into the lumen of isolated bile duct units that was abolished by vanadate and P-glycoprotein competitive antagonists, verapamil and GF120918, in a dose-dependent manner.

CONCLUSIONS

These findings provide the first molecular and functional evidence for the expression of mdr1a on the luminal membrane of cholangiocytes, where it may have a protective role.

Regulation of cellular glutathione modulates nuclear accumulation of daunorubicin in human MCF7 cells overexpressing multidrug resistance associated protein

Multidrug resistance (MDR) is frequently associated with the overexpression of P-glycoprotein (Pgp) and/or multidrug resistance associated protein (MRP1), both members of the ABC superfamily of transporters. Pgp and MRP1 function as ATP-dependent efflux pumps that extrude cytotoxic drugs from tumour cells. Glutathione (GSH) has been considered to play an important role in the MRP1-mediated MDR. In our study, we examined the effects of buthionine sulphoximine (BSO), an inhibitor of GSH biosynthesis, on the nuclear accumulation of daunorubicin (DNR), in etoposide (VP16) and doxorubicin (ADR) resistant MCF7 cell lines, overexpressing respectively MRP1 (MCF7/VP) and Pgp (MCF7/ADR). The study of DNR transport was carried out using scanning confocal microspectrofluorometry. This technique allows the determination of the nuclear accumulation of anthracyclines in single living tumour cells. Treatment of MCF7/VP cells with BSO increased the sensitivity of these cells to DNR whilst the cytotoxicity of the drug in MCF7/ADR cells remained unchanged. In MCF7 resistant cells treated with BSO, their GSH level decreased as observed by confocal microscopy. DNR nuclear accumulation in MCF7/VP cells was increased by BSO whereas in MCF7/ADR cells BSO was unable to significantly increase the DNR nuclear accumulation. These data suggest a requirement for GSH in MRP1-mediated resistance whilst the nuclear efflux of GSH conjugates is probably not the primary mechanism of Pgp-mediated MDR. Finally, BSO might be a useful agent in clinical assays for facilitating detection of MRP1 expression.

Altered drug sensitivity in response to idarubicin treatment in K562 human leukaemia cells

Relative to the commonly used anthracyclines, little is known about idarubicin and the development of multidrug resistance. We have previously shown the K562/IDA subline resulting from intermittent treatment of the K562 human leukaemia cell line with 20 ng/ml idarubicin did not develop multidrug resistance but became more sensitive to etoposide. Additional similar treatments of this subline produced the K562/IDA20 subline which partially retained its etoposide sensitivity although these cells expressed P-glycoprotein and were resistant to paclitaxel. Sensitization to etoposide was associated with increased decatenation activity of topoisomerase II, although there were no changes in topoisomerase IIalpha expression or formation of etoposide-dependent cleavable complexes. In comparison, the K562/IDA10 subline produced by intermittent treatment of the K562 cells, firstly with 5 ng/ml then 10 ng/ml idarubicin, showed no detectable expression of P-glycoprotein, decreased topoisomerase IIalpha expression and increased resistance to etoposide and amsacrine, but not to idarubicin or genistein. Even though intermittent treatment with idarubicin caused increased drug resistance in both sublines, they remained sensitive to idarubicin. Therefore the potential of idarubicin as a substitute for other anthracyclines in the treatment of cancer warrants further investigation.

Multidrug resistance in aggressive lymphoproliferative disorders of T and natural-killer origin

The measurement of rhodamine 123 (Rho123) efflux in hematological malignancies, using flow-cytometry, provides an accurate assessment of multidrug resistance (MDR) of both P-glycoprotein and MRP. While their normal counterparts display high levels of PgP and Rho123 efflux, we investigated the MDR status of marked T/NK proliferations. When diagnosed according to natural killer (NK) markers (CD16, CD56, CD57) 8 of nine NK lymphoproliferative disorders (LPD) were markedly positive (3 NK non Hodgkin's lymphomas (NHL), 1 NK lymphoproliferative disease of large granular lymphocytes (LGL), and 5 T/NK LGL). These results are in accordance with the observed response to chemotherapy in the treated cases. Mature T LPD (prolymphocytic leukemia (PLL), and NHL) cells gave varying results, as did cells from Sezary syndromes. Marked Rho123 efflux was detected in the two cases of T-PLL suggesting the expression of MRP as previously described. Immature T-lymphomas or leukemias (6 cases) were all negative. These data should be considered in relation to NK proliferations which clearly display an MDR phenotype and therefore raise the question, of the relevance of this phenotype in normal cells, and secondly of the negativity of immature T-LPD. The latter could indicate that MDR inhibitors may be superfluous in the initial treatment of acute lymphoblastic leukemia (ALL). Finally the resistance to treatment of T-ALL or mature T cells LPD invokes the importance of exploring other mechanisms of drug resistance such as the lung resistance related protein (LRP).

Induction of broad drug resistance in small cell lung cancer cells and its reversal by paclitaxel

The H82 "variant" and the H69 "classic" small cell lung cancer (SCLC) cell lines were treated with low levels of epirubicin (69 and 14 nM) which caused little cell death but produced the H82/E8 and H69/E8 extended-multidrug resistant sublines. Both were resistant to drugs associated with multidrug resistance (MDR), and to chlorambucil (9.5- and 5.6-fold, respectively) and cisplatin (2.3- and 8.5-fold, respectively). There was increased expression of the multidrug resistance-associated protein (MRP1) in the H82/E8 subline while P-glycoprotein expression was not detected in any cells or sublines. Treatment of the H82 cells for 1 hr with 69 nM epirubicin increased MRP1-mRNA expression within 4 hr and this was associated with an increase in the resistance to epirubicin, chlorambucil, cisplatin and paclitaxel. Further, a 1 hr treatment with non-cytotoxic doses of chlorambucil (2.5 microM), cisplatin (1.3 microM) or paclitaxel (13 nM), drugs not normally associated with MRP1-mediated MDR, also increased MRP1-mRNA expression in the H82 cells with paclitaxel causing the highest increase (4.5-fold). For chlorambucil treatment, this increased MRPI-mRNA expression was accompanied by increased drug resistance while paclitaxel treatment had no effect on drug resistance in the H82 cells. For the drug resistant H82/E8 subline, these drug treatments had no effect on the MRP1-mRNA expression and little effect on increasing the subline drug resistance. However, pretreatment with paclitaxel sensitised the H82/E8 subline to chlorambucil and cisplatin returning the subline to the sensitivity of the H82 cell line. We conclude that treatment with low levels of MDR and non-MDR drugs can induce extended-multidrug resistance in SCLC cells, a process that probably involves the co-ordinate upregulation of MRP1 and other resistance mechanisms. The results also suggest paclitaxel may have a role as a response modifier in the treatment of refractory SCLC.

The relationship between modulation of MDR and glutathione in MRP-overexpressing human leukemia cells

Multidrug resistance-associated protein (MRP) causes multidrug resistance (MDR) involving the anthracyclines and epipodophyllotoxins. Many studies show modulation of anthracycline levels and cytotoxicity in MRP-overexpressing cells, but there is limited data on the modulation of etoposide levels and cytotoxicity in MRP-overexpressing or in P-glycoprotein-expressing cells. Etoposide accumulation was 50% reduced in both the CEM/E1000 MRP-overexpressing subline and the CEM/VLB100 P-glycoprotein-expressing subline compared to the parental CEM cells, correlating with similar resistance to etoposide (200-fold) of the two sublines. For the CEM/VLB100 subline, the P-glycoprotein inhibitor SDZ PSC 833, but not verapamil, was able to increase etoposide accumulation and cytotoxicity. For the CEM/E1000 subline, neither SDZ PSC 833 nor verapamil had any effect on etoposide accumulation. However, verapamil caused a 4-fold sensitization to etoposide in this subline, along with an 80% decrease in cellular glutathione (P < 0.05). Buthionine sulfoximine (BSO), which depletes glutathione, also caused a 2.5-fold sensitization to etoposide with no effect on accumulation in the CEM/E1000 subline. In contrast, SDZ PSC 833 was able to increase daunorubicin accumulation in the CEM/E1000 subline (P < 0.05), but had no effect on daunorubicin cytotoxicity, or cellular glutathione. These results show that modulation of etoposide cytotoxicity in MRP-overexpressing cells may be through changes in glutathione metabolism rather than changes in accumulation and confirm that changes in drug accumulation are not related to drug resistance in MRP-overexpressing cells.

Anthracyclines in haematology: preclinical studies, toxicity and delivery systems

The anthracyclines are widely used in the treatment of haematological and non-haematological malignancy and there is now more than 30 years' clinical experience with these agents but despite this, their mechanism of action is incompletely understood. The anthracyclines have been shown to intercalate with DNA and indirectly inhibit the activity of the enzyme topoisomerase II, resulting in DNA strand breaks. More recently, workers have focused on induction of apoptosis and have shown that daunorubicin stimulates production of the apoptotic mediator, ceramide and that the activity of doxorubicin can be blocked by inhibitors of CD95 (fas). One of the major problems with anthracycline therapy is the development of resistance which may be mediated by p-glycoprotein or by other mechanisms. Much recent research has concentrated on methods to modulate the drug-resistant phenotype and these include development of new analogues and use of specific reversal agents. The toxicity profile of the anthracyclines includes bone marrow suppression, severe local reaction following extravasation, radiation recall, alopecia, gastrointestinal and hepatic effects, development of secondary malignancies and significant cardiac toxicity. The risk factors for the development of anthracycline-related cardiac toxicity are well documented and several methods have been exploited in attempts at prevention. Finally, a number of drug delivery systems have been developed in order to improve therapeutic response and reduce toxicity to normal tissues, including the use of liposomal preparations.

Increased MRP expression is associated with resistance to radiation, anthracyclines and etoposide in cells treated with fractionated gamma-radiation

The failure of chemotherapy is often associated with the failure of radiotherapy in the treatment of cancer. To investigate this relationship, the CCRF-CEM (CEM) human T-cell leukaemia cell line was treated with fractionated gamma-radiation totalling 75 Gy (10 cycles of 1.5 Gy daily for 5 days). This produced the CEMRR subline which was 1.5-fold resistant to radiation compared with the parental CEM cells. The CEMRR subline was also resistant to daunorbicin, idarubicin and etoposide but not to paclitaxel, cis-platinum or chlorambucil. Treatment with 50 microM buthionine sulphoximine, an inhibitor of glutathione synthesis, reversed the daunorubicin resistance in the CEMRR subline. Multidrug resistance-associated protein (MRP) mRNA was 6-fold higher in the CEMRR subline than in the CEM cells, and there was no detectable expression of P-glycoprotein in either the CEM cells or the CEMRR subline. Treatment of the CEM cells with 2 Gy of gamma-radiation caused an increase in MRP-mRNA within 4 hr which, by 24 hr, was greater than 5-fold that of the untreated CEM cells. No change in MRP mRNA was observed in the CEMRR subline with similar treatment. We conclude that MRP is involved in the immediate response to radiation and it may account for the drug resistance that often develops following radiation treatment.