Acute myeloid leukemia cells with low P-glycoprotein expression and high rhodamine 123 efflux capacity display high clonogenicity

The intestinal nematode inhibits T-cell reactivity by targeting P-GP activity

Host immunosuppression occurs during chronic nematode infection, partly due to effector T-cell hyporesponsiveness. The role of P-glycoprotein (P-gp), a member of the ABC transporter family, has been assessed in T-cell activity. This study assesses the possible role of P-gp in T-cell activity during nematode infection. Our findings indicate that blockade of P-gp in vivo increased protection against Heligmosomoides polygyrus nematode infection and was associated with the enhanced T-cell activity. Three P-gp-inhibitors, verapamil (VRP), cyclosporine (CsA) and tariquidar (XR9576), were used to determine the influence of nematode infection on the P-gp function of T cells. The influence of the nematode on the uptake, efflux and kinetics of extrusion in T-cell subsets CD4⁺ and CD8⁺ was assessed by the accumulation of Rho123 dye. The results indicate that H. polygyrus infection contributes to the inhibition of T-cell function by elevating P-gp activity. The blockade of P-gp in the T cells of infected mice led to an impressive increase in T-cell proliferation and IL-4 cytokine release through the upregulation of NF-κB activation. These results provide the first evidence that the P-gp function of T cells is altered during nematode infection to open the way for further studies aiming to explore the role of P-gp in host-parasite interactions.

P-glycoprotein inhibition using valspodar (PSC-833) does not improve outcomes for patients younger than age 60 years with newly diagnosed acute myeloid leukemia: Cancer and Leukemia Group B study 19808

Cancer and Leukemia Group B 19808 (CALGB 19808) is the only randomized trial of a second-generation P-glycoprotein (Pgp) modulator in untreated patients with acute myeloid leukemia (AML) younger than age 60 years. We randomly assigned 302 patients to receive induction chemotherapy regimens consisting of cytosine arabinoside (Ara-C; A), daunorubicin (D), and etoposide (E), without (ADE) or with (ADEP) PSC-833 (P). The incidence of complete remission was 75% with both regimens. Reversible grade 3 and 4 liver and mucosal toxicities were significantly more common with ADEP. Therapy-related mortality was 7% and did not differ by induction arm. Excess cardiotoxicity was not seen with high doses of D in ADE. The median disease-free survival was 1.34 years in the ADE arm and 1.09 years in the ADEP arm (P = .74, log-rank test); the median overall survival was 1.86 years in the ADE arm and 1.69 years in the ADEP arm (P = .82). There was no evidence of a treatment difference within any identifiable patient subgroup. Inhibition of Pgp-mediated drug efflux by PSC-833 did not improve clinical outcomes in younger patients with untreated AML. This trial was registered at www.clinicaltrials.gov as #NCT00006363.

Expression of beta-catenin by acute myeloid leukemia cells predicts enhanced clonogenic capacities and poor prognosis

Activation of the Wnt/beta-catenin pathway has recently been shown to be crucial to the establishment of leukemic stem cells in chronic myeloid leukemia. We sought to determine whether beta-catenin was correlated to clonogenic capacity also in the acute myeloid leukemia (AML) setting. Eighty-two patients were retrospectively evaluated for beta-catenin expression by Western blot. beta-Catenin was expressed (although at various protein levels) in 61% of patients, and was undetectable in the remaining cases. In our cohort, beta-catenin expression was correlated with the clonogenic proliferation of AML-colony forming cells (AML-CFC or CFU-L) in methylcellulose in the presence of 5637-conditioned medium, and more strikingly with self-renewing of leukemic cells, as assessed in vitro by a re-plating assay. In survival analyses, beta-catenin appeared as a new independent prognostic factor predicting poor event-free survival and shortened overall survival (both with P<0.05). Furthermore, variations in beta-catenin protein levels were dependent on post-transcriptional mechanisms involving the Wnt/beta-catenin pathway only in leukemic cells. Indeed, beta-catenin negative leukemic cells were found to increase beta-catenin in response to Wnt3a agonist in contrast to normal counterparts. Altogether, our data pave the way to the evaluation of Wnt pathway inhibition as a new rationale for eradicating the clonogenic pool of AML cells.

Influence of ceramide metabolism on P-glycoprotein function in immature acute myeloid leukemia KG1a cells

Previous studies have emphasized the role of glucosylceramide (Glu-Cer) synthase in multidrug resistance (MDR) regulation. However, the mechanism by which the inhibition of this enzyme results in increased drug retention and cytotoxicity remains unclear. In this study, we investigated the respective role of ceramide (Cer) accumulation and Glu-Cer derivatives depletion in MDR reversal effect of 1-phenyl-2-decanoylamino-3-morpholino-1-propanolol (PDMP), a Glu-Cer synthase inhibitor. We show here that treatment with PDMP resulted in increased rhodamine 123 (Rh123) retention and potent chemosensitization of P-glycoprotein (P-gp)-expressing cells, including KG1a cells, KG1a/200 cells, K562/138 cells, and K562/mdr-1 cells. Metabolic studies revealed that PDMP induced not only time-dependent Cer accumulation but also reduction of all glycosylated forms of Cer, including Glu-Cer, lactosylceramide (Lac-Cer), monosialo ganglioside (GM3) and disialo ganglioside (GD3). The influence of these metabolites on P-gp function was investigated by measuring Rh123 retention in PDMP-treated cells. P-gp function was found to be stimulated only by the addition of gangliosides in all resistant cell lines, whereas Glu-Cer, Lac-Cer, and Cer had no effect. Moreover, in KG1a/200 cells, GD3 and, to a lesser extent, GM3 were found to phosphorylate P-gp on serine residues. Altogether, these results suggest that, at least in leukemic cells, gangliosides depletion accounts for PDMP-mediated MDR reversal effect, and that gangliosides are important P-gp regulators perhaps through their capacity to modulate P-gp phosphorylation.

Effect of calcineurin inhibitor therapy on P-gp expression and function in lymphocytes of renal transplant patients: a preliminary evaluation

Cyclosporine and tacrolimus are substrates and potent inhibitors of the multidrug transporter, P-glycoprotein, in vitro. The authors have investigated the effect of chronic therapy with these and other immunosuppressive drugs on the expression and function of P-glycoprotein in T lymphocytes. Using a P-gp antibody, the authors studied the level of expression of P-gp in CD4 and CD8 T cells over a period of time in renal transplant patients. For comparison, a group of healthy volunteers and patients who did not receive any calcineurin inhibitors but were maintained on mycophenolate mofetil was included. The P-gp expression on lymphocytes from these two groups remained constant (over several months' time). However, patients who were started on tacrolimus or cyclosporine had an initial decline in expression of P-gp on CD4 T cells. Patients who were initiated on calcineurin therapy on day 1 posttransplant also had a decrease in expression of P-gp on CD4 T lymphocytes. This preliminary analysis suggests that the calcineurin inhibitors might be modulating the expression and function of transporters in lymphocytes, thus changing not only the drug concentration but also the apparent efficacy of these drugs. Further understanding and elucidation of such effects would be important in understanding the relationship between pharmacokinetics and pharmacodynamics of these and other drugs, especially for immunosuppressive and anti-AIDS therapy.

Significance of lung resistance-related protein in the clinical outcome of acute leukaemic patients with reference to P-glycoprotein

Lung resistance-related protein (LRP) overexpression in leukaemic blast cells from acute leukaemia patients and the effect of LRP or P-glycoprotein (P-gp) on the clinical outcome of acute leukaemia were investigated individually by dividing patients into four groups. The complete remission rate of group I (LRP and P-gp both negative) was 81.7%, group II (only LRP positive) 87.5%, group III (only P-gp positive) 87.1% and group IV (LRP and P-gp both positive) 40.0%. There were no statistical differences between group I and groups II or III, but a significant difference was observed between groups I, II or III and group IV. Median overall survival in group IV was significantly shorter (4.6 months) than in groups I, II or III, although no significant differences were observed between group I and groups II or III (18.9, 20.5 and 31.8 months). There was a tendency for disease-free survival in group III to be longer than that in groups I, II or IV. The reasons for these findings are discussed. Our present results indicate that the co-existence of LRP and P-gp strongly influenced the effectiveness of induction chemotherapy and long-term prognosis, whereas the isolated presence of LRP or P-gp did not.