Total cellular protein presence of the transcription factor IRF8 does not necessarily correlate with its nuclear presence.

The transcription factor interferon regulatory factor-8 (IRF8) plays an essential role in myeloid differentiation and lineage commitment, based largely on molecular and genetic studies. The detection of IRF8 in specific cell populations by flow cytometry (FCM) has the potential to provide new insights into normal and pathologic myelopoiesis, but critical validation of this protein-based approach, particularly in human samples, is lacking. In this study, the assessment of total cellular IRF8 presence was compared to its specific nuclear presence as assessed by imaging flow cytometry (IFC) analysis.

Nuclear translocation of nuclear factor of activated T cells (NFAT) as a quantitative pharmacodynamic parameter for tacrolimus.

Nuclear factor of activated T cells (NFAT) is a family of transcription factors involved in regulating the immune response. The canonical NFAT pathway is calcium-dependent and upon activation, NFAT is dephosphorylated by the phosphatase, calcineurin. This results in its translocation from the cytoplasm to the nucleus and transcription of downstream target genes that include the cytokines IL-2, IL-10, and IFNγ.

Human ovarian tumor ascites fluids rapidly and reversibly inhibit T cell receptor-induced NF-κB and NFAT signaling in tumor-associated T cells.

Human memory T cells present in ovarian tumor ascites fluids fail to respond normally to stimulation via the T cell receptor (TCR). This immunosuppression is manifested by decreases in NF-κB and NFAT activation, IFN-γ production, and cell proliferation in response to TCR stimulation with immobilized antibodies to CD3 and CD28. The anergy of the tumor-associated T cells (TATs) is mediated by soluble factors present in ovarian tumor ascites fluids.

Tenofovir selectively regulates production of inflammatory cytokines and shifts the IL-12/IL-10 balance in human primary cells.

Objectives: In this study, we aimed to investigate the possible immune modulatory effects of HIV nucleoside reverse transcriptase inhibitors during secondary infections and inflammation, focusing on inflammatory cytokine responses and the interleukin (IL)-12/IL-10 balance.

Methods: We investigated the in vitro effect of tenofovir and zidovudine (AZT) on production of proinflammatory cytokines in monocytes and human peripheral blood mononuclear cells (PBMCs). Stimulation panels included Toll-Like receptor (TLR) ligands; the inflammation mediator tumor necrosis factor-α; and the pathogens cytomegalovirus, Neisseria meningitides, Escherichia coli, and Streptococcus pneumoniae.

Arsenic trioxide affects signal transducer and activator of transcription proteins through alteration of protein tyrosine kinase phosphorylation.

Purpose: Arsenic trioxide decreases proliferation of acute myeloid leukemia (AML) cells, but its precise mechanism of action is unknown.

Experimental Design: We studied the effect of arsenic trioxide on patient samples and the AML cell line HEL, which, like leukemic blasts from 50% of AML cases, has constitutively activated signal transducer and activator of transcription (STAT) proteins.

Results: Arsenic trioxide induced mitotic arrest starting at 24 hours and significant cell death at 48 hours.

Bortezomib activity and in vitro interactions with anthracyclines and cytarabine in acute myeloid leukemia cells are independent of multidrug resistance mechanisms and p53 status.

Purpose: The proteasome inhibitor bortezomib may be effective in combination with cytarabine and anthracyclines in the treatment of acute myeloid leukemia (AML) by virtue of targeting aberrantly activated NF-kappaB in AML stem cells. We tested whether bortezomib cytotoxicity is affected by multidrug resistance (MDR) proteins expressed in AML cells. We also tested whether bortezomib interactions with cytarabine and anthracyclines are affected by p53, because proteasome inhibition stabilizes p53 and may thus cause cell cycle arrest.

The 4'-O-benzylated doxorubicin analog WP744 overcomes resistance mediated by P-glycoprotein, multidrug resistance protein and breast cancer resistance protein in cell lines and acute myeloid leukemia cells.

Background: The synthetic 4'-O-benzylated doxorubicin analog WP744 was designed to abrogate transport by the multidrug resistance (MDR)-associated ATP-binding cassette (ABC) proteins P-glycoprotein (Pgp) and multidrug resistance protein (MRP-1). We compared its uptake and cytotoxicity with those of doxorubicin and daunorubicin in cell lines overexpressing Pgp, MRP-1 or breast cancer resistance protein (BCRP) and in acute myeloid leukemia (AML) cells.

Methods: Cellular uptake was studied by flow cytometry and cytotoxicity in 96-h 96-well cultures in cell lines overexpressing Pgp, MRP-1 or wild type (BCRP(R482)) or mutant (BCRP(R482T), BCRP(R482G)) BCRP and in pre-treatment AML marrow cells.

Differential effects of the immunosuppressive agents cyclosporin A, tacrolimus and sirolimus on drug transport by multidrug resistance proteins.

Purpose: We sought to determine the effects of the immunosuppressants, cyclosporin A (CsA), tacrolimus and sirolimus, on drug transport by the ATP-binding cassette proteins, P-glycoprotein (Pgp; ABCB1), multidrug resistance protein-1 (MRP-1; ABCC1) and breast cancer resistance protein (BCRP; ABCG2), and the major vault protein lung resistance protein (LRP).

Methods: Cellular content of mitoxantrone, a Pgp, MRP-1 and BCRP substrate, was measured by flow cytometry in cells overexpressing these proteins following incubation with and without CsA, tacrolimus or sirolimus. Interaction of BCRP with these compounds was studied by photolabeling and ATPase assays.

Sequential administration of irinotecan and cytarabine in the treatment of relapsed and refractory acute myeloid leukemia.

Purpose: Based on reported synergy of the topoisomerase-I (topo-I) inhibitor irinotecan with antimetabolites, irinotecan and cytarabine (Ara-C) were administered sequentially to patients with acute myeloid leukemia (AML) refractory to or relapsed following high-dose Ara-C and anthracycline therapy. Pharmacokinetic and pharmacodynamic studies were performed with the first irinotecan dose.

Experimental Design: In vitro synergy of irinotecan followed by Ara-C was confirmed in a human AML cell line as a basis for the clinical trial.

In vitro and in vivo irinotecan-induced changes in expression profiles of cell cycle and apoptosis-associated genes in acute myeloid leukemia cells.

Objective: To study irinotecan (CPT-11)-induced changes in expression profiles of genes associated with cell cycle control and apoptosis in myeloid leukemia cells in vitro and in vivo.

Methods: HL60 cells were exposed to clinically achievable concentrations of 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of CPT-11, and blood sampled from patients with acute myeloid leukemia and chronic myeloid leukemia in myeloid blast transformation treated with CPT-11. Gene expression changes were studied by cDNA microarray and correlated with biological responses by studying DNA distributions by flow cytometry.

Cyclosporin A is a broad-spectrum multidrug resistance modulator.

Purpose: Overexpression of the multidrug resistance proteins P-glycoprotein (Pgp), multidrug resistance protein (MRP-1), breast cancer resistance protein (BCRP), and lung resistance protein (LRP) is associated with treatment failure in acute myeloid leukemia (AML) and other malignancies. The Pgp modulator cyclosporin A has shown clinical efficacy in AML, whereas its analogue PSC-833 has not. Cyclosporin A is known to also modulate MRP-1, and we hypothesized that broad-spectrum multidrug resistance modulation might contribute to its clinical efficacy.

Breast cancer resistance protein (BCRP/MXR/ABCG2) in adult acute lymphoblastic leukaemia: frequent expression and possible correlation with shorter disease-free survival.

Drugs used in treatment of adult acute lymphoblastic leukaemia (ALL) are substrates for breast cancer resistance protein (BCRP, MXR, ABCG2), which may thus play a role in resistance in this disease. Pretreatment blasts from 30 adult ALL patients were studied for BCRP mRNA by quantitative reverse transcription polymerase chain reaction analysis, BCRP protein by immunophenotyping with three antibodies and BCRP function by fumitremorgin C modulation of intracellular mitoxantrone retention, measured by flow cytometry. BCRP mRNA in all cases encoded wild type protein (BCRP(R482)), which mediates mitoxantrone and methotrexate resistance, but only low-level anthracycline resistance.

Expression of the neural cell adhesion molecule CD56 is not associated with P-glycoprotein overexpression in core-binding factor acute myeloid leukemia.

Acute myeloid leukemia (AML) with rearrangement of the core-binding factor (CBF) alpha or beta subunit gene has a favorable prognosis, but CD56 expression in CBFalpha-AML is associated with short disease-free survival. A proposed mechanism is overexpression of the multidrug resistance (MDR) protein P-glycoprotein (Pgp). CD56 expression, Pgp expression and function, and expression of the additional MDR proteins multidrug resistance protein-1 (MRP-1), lung resistance protein (LRP) and breast cancer resistance protein (BCRP) were studied in pretreatment blasts from 25 CBF-AML patients.

Broad-spectrum modulation of ATP-binding cassette transport proteins by the taxane derivatives ortataxel (IDN-5109, BAY 59-8862) and tRA96023.

Purpose: The taxanes paclitaxel and docetaxel are substrates for P-glycoprotein (Pgp), an ATP-binding cassette (ABC) transport protein associated with multidrug resistance (MDR). In contrast, the synthetic taxane ortataxel (BAY 59-8862, IDN-5109) is effective against Pgp-expressing cells by virtue of modulation of Pgp-mediated transport. The synthetic taxane tRA96023 also modulates Pgp and is noncytotoxic due to removal of the tubulin-binding side chain at the C-13 position of the taxane backbone.

VX-710 (biricodar) increases drug retention and enhances chemosensitivity in resistant cells overexpressing P-glycoprotein, multidrug resistance protein, and breast cancer resistance protein.

Purpose: The pipecolinate derivative VX-710 (biricodar; Incel) is a clinically applicable modulator of P-glycoprotein (Pgp) and multidrug resistance protein (MRP-1); we studied its activity against the third multidrug resistance (MDR)-associated drug efflux protein, breast cancer resistance protein (BCRP).

Experimental Design: VX-710 modulation of uptake, retention, and cytotoxicity of mitoxantrone, daunorubicin, doxorubicin, topotecan, and SN38 was studied in cell lines overexpressing Pgp, MRP-1 and wild-type (BCRP(R482)) and mutant (BCRP(R482T)) BCRP.

Results: In 8226/Dox6 cells (Pgp), VX-710 increased mitoxantrone and daunorubicin uptake by 55 and 100%, respectively, increased their retention by 100 and 60%, respectively, and increased their cytotoxicity 3.

Taxane-based reversal agents modulate drug resistance mediated by P-glycoprotein, multidrug resistance protein, and breast cancer resistance protein.

Overexpression of ATP-binding cassette transport proteins, including P-glycoprotein (Pgp), multidrug resistance (MDR) protein (MRP-1), and breast cancer resistance protein (BCRP), is a well-characterized mechanism of MDR in tumor cells. Although the cytotoxic taxanes paclitaxel and docetaxel are substrates for Pgp-mediated efflux, the semisynthetic taxane analogue ortataxel inhibits drug efflux mediated by Pgp as well as, as we recently demonstrated, MRP-1 and BCRP. Nevertheless, ortataxel is not optimal for development as a clinical MDR modulator because of its cytotoxicity [corrected].

Phase 3 study of the multidrug resistance modulator PSC-833 in previously untreated patients 60 years of age and older with acute myeloid leukemia: Cancer and Leukemia Group B Study 9720.

The Cancer and Leukemia Group B conducted a phase 3 trial of the P-glycoprotein modulator PSC-833 in untreated acute myeloid leukemia patients aged 60 years and older. Patients were randomized to 1 of 2 regimens, with doses determined in a prior phase 1 study, consisting of cytarabine 100 mg/m(2)/d by 7-day infusion, with daunorubicin 60 mg/m(2) and etoposide 100 mg/m(2) daily for 3 days (ADE), or daunorubicin 40 mg/m(2) and etoposide 60 mg/m(2) for 3 days with PSC-833, 2.8 mg/kg over 2 hours, and then 10 mg/kg/d by 3-day infusion (ADEP).

Flow cytometric analysis of breast cancer resistance protein expression and function.

Background: The breast cancer resistance protein (BCRP) is an ATP-binding cassette (ABC) half-transporter that mediates energy-dependent drug efflux. Assessing the clinical relevance of the BCRP will require sensitive and specific methods for detecting its expression and function that allow high-volume specimen throughput and employ widely available instrumentation.

Methods: The BXP-34 and BXP-21 monoclonal antibodies were evaluated for flow cytometric detection of BCRP expression.

Erythropoietin-dependent transformation of myelodysplastic syndrome to acute monoblastic leukemia.

Acute monoblastic leukemia (acute myeloid leukemia [AML], French-American-British type M5a) with leukemia cutis developed in a patient 6 weeks after the initiation of erythropoietin (EPO) therapy for refractory anemia with ringed sideroblasts. AML disappeared from both marrow and skin after the discontinuation of EPO. Multiparameter flow cytometric analysis of bone marrow cells demonstrated coexpression of the EPO receptor with CD45 and CD13 on the surface of blasts.