Overexpression of P-glycoprotein in adult T-cell leukaemia

Synergy between parthenolide and arsenic trioxide in adult T-cell leukemia/lymphoma cells in vitro

OBJECTIVES

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive lymphoid malignancy with low survival rate and distinct geographical distribution. In search for novel chemotherapeutics against ATLL, we investigated the combinatorial effects of parthenolide, a sesquiterpene lactone with valuable pharmaceutical activities, and arsenic trioxide (ATO) in vitro.

MATERIALS AND METHODS

MT2 cells, an ATLL cell line, were treated with increasing concentrations of parthenolide (1.25, 2.5, and 5 μg/ml) and ATO (2, 4, 8, and 16 µM) to determine their IC50. Then, cells were treated with a combination of sub-IC50 concentrations of parthenolide (1 μg/ml) and ATO (2 µM) for 72 hr. Cell viability and cell cycle changes were assessed by Alamar blue and PI staining, respectively. To understand the mechanisms responsible for observed effects, expression of CD44, NF-κB (REL-A), BMI-1, and C-MYC were investigated by real-time PCR.

RESULTS

Assessment of cell viability indicated that parthenolide significantly increased the toxicity of ATO, as confirmed by accumulation of MT2 cells in the sub G1 phase of the cell cycle. Moreover, molecular analysis revealed significant down-regulation of CD44, NF-κB (REL-A), BMI-1, and C-MYC upon combinatorial administration of parthenolide and ATO in comparison with relevant controls.

CONCLUSION

Taken together, present results showed that parthenolide significantly enhanced the toxicity of ATO in MT2 cells. Therefore, the future possible clinical impact of our study could be combinatorial use of parthenolide and ATO as a novel and more effective approach for ATLL.

Improved outcome of adult T cell leukemia/lymphoma with allogeneic hematopoietic stem cell transplantation

Adult T cell leukemia/lymphoma (ATL) is a poor prognosis T cell malignancy. In order to improve the outcome, we employed allogeneic stem cell transplantation (allo-SCT) for ATL in 10 patients, nine of whom were from HLA-identical siblings and one from an unrelated donor. Conditioning regimens varied among the patients except that all received total body irradiation. The patients tolerated the regimens well with mild, if any toxicity, and engraftment occurred in all cases. Median leukemia-free survival after allo-SCT was 17.5+ months (range 3.7-34.4+). Six of the 10 patients developed acute GVHD (one case each with grade I, III or IV, and three cases with grade II) and three patients developed extensive chronic GVHD. Four patients died after allo-SCT during the study period from either acute GVHD (grade IV), pneumonitis, gastrointestinal bleeding or renal insufficiency. Two of the 10 cases with no symptoms of GVHD relapsed with clinical ATL. These results strongly suggest that allo-SCT may improve the survival in ATL if a controlled degree of GVHD develops.

Adult T-cell leukemia cells over-express the multidrug-resistance-protein (MRP) and lung-resistance-protein (LRP) genes

Adult T-cell leukemia (ATL) is a T-cell malignancy caused by human T-cell-leukemia-virus-I (HTLV-I) infection. ATL comprises 4 clinical forms: acute, chronic, smoldering and lymphoma types. ATL is usually resistant to conventional chemotherapy and has a relatively poor prognosis; however, the resistance mechanisms remain undetermined. To explore the multidrug-resistance (MDR) mechanisms of ATL, we examined the expression and functional activity of MDR-related genes in peripheral-blood mononuclear cells (PBMC) from ATL patients by semi-quantitative RT-PCR and FACScan with calcein-AM. PBMC from ATL patients expressed similar or higher levels of MRP, LRP and cMOAT mRNAs, as compared with normal PBMC. In normal controls and ATL patients, MDR1 mRNA expression was undetectable in this study. PBMC from acute and chronic ATL patients expressed significantly higher levels of MRP and LRP mRNA than did normal PBMC (p < 0.01 and p < 0.05 respectively). In chronic ATL, positive correlations were apparent between levels of MRP and LRP mRNA expression (r = 0.759, p = 0.018), and between each mRNA level and the absolute number of abnormal lymphocytes in peripheral blood. Probenecid, an inhibitor of the MRP pump, significantly increased the accumulation of calcein in PBMC from 3 chronic ATL patients. Our findings suggest that the MRP and LRP genes in ATL are often activated by HTLV-I infection and may confer MDR of ATL cells in vivo. Combined chemotherapy with inhibitors of these MDR genes may be promising in the treatment of ATL.

The mechanism of trans-activation of the MDR1 gene by human T-cell leukemia virus

Overexpression of P-glycoprotein (P-gp), the protein product of the multidrug resistance gene (MDR1), confers a drug resistant phenotype on cells. We have recently demonstrated that the MDR1 promoter is transcriptionally activated by the HTLV-I tax protein, providing an explanation for the development of drug resistance in HTLV-I infections. Here we report that HTLV-I mediated MDR1 activation is dependent on the presence of an NF-IL6-binding site located between base pairs -148 and -141 relative to the transcription start site. This finding opens up the possibility of moderating P-gp expression through interference with NF-IL6 binding to its trans recognition element and subsequent repression of MDR1 transcription.

Enhanced MDR1 Gene Expression in Human T-Cell Leukemia Virus-I–Infected Patients Offers New Prospects for Therapy

Overexpression of P-glycoprotein (P-gp), the protein product of the multidrug resistance gene (MDR1), confers a drug resistant phenotype on cells. This phenotype is reminiscent of human T-cell leukemia virus (HTLV)-transformed leukemic cells, for which no consistently effective chemotherapeutic regime has been found. The presence of an active multiple drug resistance (MDR) phenotype in freshly isolated peripheral blood mononuclear cells (PBMC) from HTLV-I–infected subjects was investigated. Significant P-gp–mediated efflux activity and enhanced MDR1 mRNA expression was observed in nine of 10 HTLV-infected subjects. The development of MDR phenotypes was found to be independent of disease type or status with significant MDR activities being observed in adult T-cell leukemia (ATL), HTLV-associated myelopathy (HAM)/tropical spastic paraparesis (TSP), and asymptomatic HTLV-infected individuals. P-gp–mediated drug efflux was also found to be restricted to CD3+ T-cell populations. Furthermore, we show the novel finding that theMDR1 gene promoter is transcriptionally activated by the HTLV-I tax protein, suggesting a molecular basis for the development of drug resistance in HTLV-I infections. These observations open up the possibility of new chemotherapeutic approaches to HTLV-associated diseases through the use of P-gp inhibitors.

Enhanced MDR1 Gene Expression in Human T-Cell Leukemia Virus-I–Infected Patients Offers New Prospects for Therapy

Overexpression of P-glycoprotein (P-gp), the protein product of the multidrug resistance gene (MDR1), confers a drug resistant phenotype on cells. This phenotype is reminiscent of human T-cell leukemia virus (HTLV)-transformed leukemic cells, for which no consistently effective chemotherapeutic regime has been found. The presence of an active multiple drug resistance (MDR) phenotype in freshly isolated peripheral blood mononuclear cells (PBMC) from HTLV-I–infected subjects was investigated. Significant P-gp–mediated efflux activity and enhanced MDR1 mRNA expression was observed in nine of 10 HTLV-infected subjects. The development of MDR phenotypes was found to be independent of disease type or status with significant MDR activities being observed in adult T-cell leukemia (ATL), HTLV-associated myelopathy (HAM)/tropical spastic paraparesis (TSP), and asymptomatic HTLV-infected individuals. P-gp–mediated drug efflux was also found to be restricted to CD3+ T-cell populations. Furthermore, we show the novel finding that theMDR1 gene promoter is transcriptionally activated by the HTLV-I tax protein, suggesting a molecular basis for the development of drug resistance in HTLV-I infections. These observations open up the possibility of new chemotherapeutic approaches to HTLV-associated diseases through the use of P-gp inhibitors.

Absence of correlation between cytotoxicity and drug transport by P-glycoprotein in clinical leukemic cells

Development of resistance to cytotoxic agents is a common problem in the treatment of acute leukemia. In cell lines having multidrug resistance (MDR) phenotype, a decrease in the intracellular accumulation of drugs has been closely related to the overexpression of P-glycoprotein/mdr1 genes. We analyzed the relationship between the cytotoxicity of adriamycin (ADR) in vitro, intracellular accumulation of ADR, and the expression of P-glycoprotein on fresh leukemic cells from 19 patients at their initial presentation and from 9 relapsed patients. Pretreatment patients showed significantly higher ratio of complete remission than relapsed patients, and mean value of IC50 for adriamycin in initial presentation was higher than at relapse. But we found no significant relationship between in vitro cytotoxicity and drug transport. In addition, only 2 of the 5 relapsed patients examined by monoclonal antibody C219 expressed the P-glycoprotein. These results suggest that the acquisition of clinical drug resistance may involve various mechanisms other than the reduction of drug accumulation with P-glycoprotein expression.

Drug resistance mechanisms in leukaemia

Although considerable advances have been made over the past 20 years in the treatment of leukaemia, many patients still die either of their disease, or of the attempts made to cure it. A major contribution to this unacceptable level of mortality is the presence of drug resistance in the residual leukaemic cells. Although many laboratory studies have been performed which have indicated possible cellular mechanisms for the development of resistance, comparatively little is known of the relevance of these processes to resistance as it occurs in patients. Information from such studies should provide a basis for the rational design of agents capable of reversing resistance, and thereby improving the chances of achieving sustainable remission in the majority of patients presenting with leukaemia.

Multidrug resistance

Resistance of malignant cells to cytotoxic agents is often a limiting factor to successful chemotherapy. The classical multidrug resistance is characterised by overexpression of a membrane protein, P-glycoprotein, which acts like a drug extruding pump reducing accumulation of cytotoxic agents inside malignant cells, thereby preventing their function. Resistance is expressed simultaneously towards several structurally unrelated drugs. P-glycoprotein is also expressed in many normal human tissues, e.g., in the gastrointestinal tract, and this may be the reason for intrinsic resistance observed clinically in cancers derived from certain tissues. More often multidrug resistance is acquired during chemotherapy. The physiological function of P-glycoprotein is still unknown but it may have a role in cellular detoxification and secreting mechanisms. Interest in the phenomenon of multidrug resistance centres on the correlation of P-glycoprotein expression to clinical drug resistance. Another goal is to find mechanisms by which the function of P-glycoprotein as a multidrug transporter is prevented and drug resistance reversed.