Differentiation and multidrug resistance in response to drug treatment in the K562 human leukaemia cell line

Inhibition of glycosphingolipid biosynthesis reverts multidrug resistance by differentially modulating ABC transporters in chronic myeloid leukemias

Multidrug resistance (MDR) in cancer arises from cross-resistance to structurally- and functionally-divergent chemotherapeutic drugs. In particular, MDR is characterized by increased expression and activity of ATP-binding cassette (ABC) superfamily transporters. Sphingolipids are substrates of ABC proteins in cell signaling, membrane biosynthesis, and inflammation, for example, and their products can favor cancer progression. Glucosylceramide (GlcCer) is a ubiquitous glycosphingolipid (GSL) generated by glucosylceramide synthase, a key regulatory enzyme encoded by the UDP-glucose ceramide glucosyltransferase (UGCG) gene. Stressed cells increase de novo biosynthesis of ceramides, which return to sub-toxic levels after UGCG mediates incorporation into GlcCer. Given that cancer cells seem to mobilize UGCG and have increased GSL content for ceramide clearance, which ultimately contributes to chemotherapy failure, here we investigated how inhibition of GSL biosynthesis affects the MDR phenotype of chronic myeloid leukemias. We found that MDR is associated with higher UGCG expression and with a complex GSL profile. UGCG inhibition with the ceramide analog d-threo-1-(3,4,-ethylenedioxy)phenyl-2-palmitoylamino-3-pyrrolidino-1-propanol (EtDO-P4) greatly reduced GSL and monosialotetrahexosylganglioside levels, and co-treatment with standard chemotherapeutics sensitized cells to mitochondrial membrane potential loss and apoptosis. ABC subfamily B member 1 (ABCB1) expression was reduced, and ABCC-mediated efflux activity was modulated by competition with nonglycosylated ceramides. Consistently, inhibition of ABCC-mediated transport reduced the efflux of exogenous C₆-ceramide. Overall, UGCG inhibition impaired the malignant glycophenotype of MDR leukemias, which typically overcomes drug resistance through distinct mechanisms. This work sheds light on the involvement of GSL in chemotherapy failure, and its findings suggest that targeted GSL modulation could help manage MDR leukemias.

Verapamil Induces Upregulation of P-glycoprotein Expression on Human Monocyte Derived Dendritic Cells

Overexpression of P-glycoprotein, a transmembrane drug efflux pump that mediates efflux of chemotherapeutic agents contributes to drug resistance in many leukaemia and other cancerous cells. Non-malignant cells including leukocytes also express P-glycoprotein, but physiologic functions for P-glycoprotein are poorly defined. Recently, P-glycoprotein expression has been described in human mononuclear phagocytes and Langerhans cells. It has been shown to play a role in phagocytic cell transmigration through endothelial-lined vessels in an ablumenal-lumenal direction, a process that mimics their migration into lymphatic vessels. Using the monoclonal antibody 4E3, and the P-glycoprotein antagonist, verapamil, the expression of P-glycoprotein on human monocyte-derived dendritic cells was evaluated. Dendritic cells used in this study were CD1a+, CD11c+, CD14-, CD80+, CD83+, CD86+ and MHC-II(High). The expression of these markers increased significantly as the cells matured. P-glycoprotein expression was upregulated as the dendritic cells matured as well as in the presence of the "inflammatory stress" of the pathogenic bacteria Strept. pyogenes. Addition of verapamil or Strept. pyogenes to the culture medium during the final 24 hours significantly upregulated P-glycoprotein expression. Immortalized cell lines did not upregulate P-glycoprotein in the presence of verapamil. Evaluation of other normal cells showed that P-glycoprotein upregulation in the presence of verapamil was also a characteristic of macrophages. This novel observation of the upregulation of P-glycoprotein in the presence of verapamil appears to be a characteristic of activated myeloid derived antigen presenting cells and suggest that P-glycoprotein is essential for these cells as when it is blocked, they respond by increasing expression of this protein. In summary, this work describes that human dendritic cells generated from plastic-adherent monocytes rapidly upregulate expression of P-glycoprotein as they mature, and in the presence of inflammatory stress and the pharmacological agent verapamil, which blocks P-glycoprotein activity, suggesting that P-glycoprotein may play a role in activation as well as in migration of dendritic cells.

Differential quantitative zinc-induced expression of human metallothionein isogenes in haematopoietic precursor cell lines

The expression pattern of functional members of the metallothionein (MT) gene family was studied in the haematopoietic precursor cell lines, K562, DAMI, MEG-01, and ELF-153 in order to strengthen the proposed function of MT in differentiation. Cells were cultured in RPMI 1640 with 10% (v/v) foetal calf serum, with or without different zinc supplements. Expression of MT isogenes was analysed by quantitative real-time PCR (RT-PCR) using mRNA extracted from cultured cells. The more mature K562, DAMI, and MEG-01 cell lines exhibited transcription of all MT isogenes, except MT-3 and MT-4. Relative quantitative expression of MT isogenes in the mature cell lines such as K562, DAMI, and MEG-01 was higher than in the immature ELF-153 cell line. Immunohistochemical staining (IHC) reveals an increased MT protein biosynthesis in more mature cell lines such as K562, DAMI and MEG-01 greater than in the immature ELF-153 cell line. Real-time PCR and immunohistochemical staining for investigating the effect of phorbol ester and hemin (haematopoietic differentiation stimuli) on expression of MT isogenes in K562 cells reveals that phorbol ester induces increased MT transcription and biosynthesis. Therefore, to our knowledge, the role of MT in differentiation in human haematopoietic precursor cell lines is here reported for the first time.

Assessment of the downstream portion of the mitochondrial pathway of caspase activation in patients with acute myeloid leukemia

Most chemotherapeutic agents used in the treatment of acute myeloid leukemia (AML) induce apoptosis by triggering the mitochondrial pathway of caspase activation. To investigate the downstream portion of the mitochondrial pathway of caspase activation in patients with AML, cytosolic lysates were stimulated with cytochrome c and dATP and hydrolysis of Ac-DEVD-AFC by effector caspases was measured. Defects in the distal mitochondrial pathway were more common in samples from patients with AML that relapsed rapidly after induction chemotherapy compared to samples from treatment naïve patients. The incidence of blocked pathways did not differ based on response to induction chemotherapy, as even nonresponders generally had an intact pathway. When the distal mitochondrial pathway was blocked, defects were usually at the level of the effector caspases. Thus, functional defects in the distal portion of the mitochondrial pathway of caspase activation may help explain the nature of response and relapse after treatment.

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.

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.

Expression of a Y559F mutant CSF-1 receptor in M1 myeloid cells: a role for Src kinases in CSF-1 receptor-mediated differentiation

We have established two M1 myeloid cell lines, M1/WT cells overexpressing the wild-type CSF-1 receptor and M1/Y559F cells expressing a specific tyrosine mutant. M1/WT cells differentiated in response to CSF-1, with a reduction in their proliferative capacity. CSF-1-mediated differentiation was partially abrogated in the M1/Y559F cells, with a less marked reduction in proliferative capacity. The Src tyrosine kinases c-Src, c-Yes, c-Fyn, and c-Hck were tyrosine phosphorylated in the M1/WT cells in response to CSF-1 and bound to the WT CSF-1R through their SH2 domains. Binding of the Src kinases to the CSF-1 receptor was greatly reduced in the M1/Y559F cells. CSF-1-mediated activation of STAT3 was also abrogated in the M1/Y559F cell line. Treatment of M1/WT cells with the Src family inhibitor PP2 resulted in an inhibition of CSF-1-mediated differentiation, equivalent to that observed in the M1/Y559F cells. These data suggest that the reduced Src binding observed in the M1/Y559F cells may contribute to their reduced ability to differentiate.

Effect of the microtubular inhibitor vinblastine on ferritin clearance and release in the rat

We have previously demonstrated that colchicine inhibits ferritin clearance from the circulation of normal and iron-loaded rats and stimulates endogenous ferritin release into both the serum and bile of iron-loaded rats. The aim of the present study was to determine the effect of vinblastine on ferritin clearance and release in normal and iron-loaded rats. Vinblastine was administered at either 1 or 10 mg/kg to both normal and iron-loaded rats, infused over a 5 h period with either a rat liver ferritin or saline solution. Serum and biliary ferritin levels were determined every 30 min. After 5 h, 90% of the infused ferritin was cleared from the circulation in the absence of vinblastine. Low-dose vinblastine decreased ferritin uptake 10-20% in iron-loaded rats. High-dose vinblastine inhibited ferritin clearance by 25% in normal rats and 20-40% in iron-loaded rats. Vinblastine administration caused a 2-3-fold increase in the serum ferritin concentration and a 3-5-fold peak in biliary ferritin levels. Thus, vinblastine caused the release of endogenous ferritin into both the serum and bile of iron-loaded rats in the presence of a ferritin load. We therefore conclude that disturbed microtubule function accounts for the observed inhibition of ferritin uptake and intracellular transport; however, the mechanism of increased ferritin release remains unclear.

Chemosensitizing interactions of clofazimine and B669 with human K562 erythroleukaemia cells with varying levels of expression of P-glycoprotein

Differential expression of a permeability glycoprotein (P-gp) in human myeloleukaemia K562 cells grown in the presence of the anti-cancer drug, doxorubicin, gave rise to subclones with varying degrees of resistance to other anti-tumour drugs such as vinblastine and daunorubicin. Subclones K562/MMB, MMG and MMF were produced from the parental (K562/P) cell line via limiting dilution and their MDR nature confirmed with flow cytometry using an MRK 16 monoclonal antibody directed at a surface epitope of the P-gp pump. The pattern of increasing P-gp expression in the series K562/P, MMF, MMG and MMB was paralleled by increasing resistance to vinblastine and daunorubicin. When the subclones were pre-incubated with the chemosensitizing drugs clofazimine and B669, a pattern of increasing reversal of resistance to vinblastine and daunorubicin was seen in the series K562/P, MMF, MMG and MMB.

Expression of multidrug resistance in response to differentiation in the K562 human leukaemia cell line

With the increasing use of inducers of cellular differentiation in the treatment of leukaemia, it is essential to understand the relationship between differentiation and the expression of the multidrug resistance. Using the K562 human leukaemia cell line and its multidrug resistant subline K562/E15B, differentiation was examined along two different pathways, megakaryocyte in response to treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA), and erythroid in response to treatment with sodium butyrate, in the same cell line. P-glycoprotein expression was increased in the multidrug resistant K562/E15B subline, but not induced in the parental K562 cell line. However, both treatments conferred a different phenotype on the drug resistant subline. TPA treatment caused an increase in P-glycoprotein, increased drug resistance and decreased rhodamine-123 accumulation which was verapamil sensitive, demonstrating that TPA induced a fully functional P-glycoprotein. However, sodium butyrate treatment caused an increase in P-glycoprotein without increased drug resistance or without decreased rhodamine-123 accumulation suggesting that the P-glycoprotein induced by sodium butyrate was nonfunctional. These results stress the importance of examining not only the expression of P-glycoprotein in cells, but also the function of the P-glycoprotein induced.

Drug resistance mechanisms and MRP expression in response to epirubicin treatment in a human leukaemia cell line

A drug resistant series of sublines were developed by treating the human leukaemia CCRF-CEM cell line with 16-1000 ng/ml of the anthracycline, epirubicin. The sublines developed resistance in two stages, neither involving detectable levels of P-glycoprotein. Treatment with up to 50 ng/ml epirubicin produced sublines with cross resistance limited to the anthracyclines and etoposide. Treatment with 100-1000 ng/ml epirubicin produced sublines with increased expression of the mrp gene, increased resistance to the anthracyclines and etoposide, additional cross resistance to vincristine and colchicine, decreased drug accumulation and reversal of resistance by verapamil and by buthionine sulphoximine (BSO; an inhibitor of glutathione synthesis). Our results indicate an interaction between MRP and glutathione metabolism as a mechanism for multidrug resistance.

Development of extended multidrug resistance in HL60 promyelocytic leukaemia cells

In an attempt to mimic clinical conditions for the treatment of leukaemia, the HL60 promyelocytic cell line was treated for 18 h with low, clinically relevant, levels of the anthracycline epirubicin and the Vinca alkaloid vinblastine. The resulting drug-resistant sublines not only expressed P-glycoprotein and the MDR phenotype but were also cross-resistant to chlorambucil, methotrexate and cisplatinum, and had increased resistance to radiation. Development of resistance was associated with an aberrant differentiation phenotype with decreased expression of myeloid antigens and expression of glycophorin A, an antigen normally associated with erythroid differentiation. The ability of HL60 cells to terminally differentiate in response to all-trans-retinoic acid (vitamin A acid) was lost in the sublines. These results suggest that either a single novel mechanism is responsible for multiple drug resistance or the initial response to drug treatment is the co-induction of multiple mechanisms. These cells and the method by which they were generated therefore provide a clinically relevant model for the study of the initial events in the development of not only multidrug resistance but also the extended multiple drug resistance usually encountered in the treatment of leukaemia.