Absolute levels of MDR-1, MRP, and BCL-2 MRNA and tumor remission in acute leukemia

The Proteasome Inhibitor Bortezomib Sensitizes AML with Myelomonocytic Differentiation to TRAIL Mediated Apoptosis

Acute myeloid leukemia (AML) is an aggressive stem cell malignancy that is difficult to treat. There are limitations to the current treatment regimes especially after disease relapse, and therefore new therapeutic agents are urgently required which can overcome drug resistance whilst avoiding unnecessary toxicity. Among newer targeted agents, both tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) and proteasome inhibitors show particular promise. In this report we show that a combination of the proteasome inhibitor bortezomib and TRAIL is effective against AML cell lines, in particular, AML cell lines displaying myelomonocytic/monocytic phenotype (M4/M5 AML based on FAB classification), which account for 20-30% of AML cases. We show that the underlying mechanism of sensitization is at least in part due to bortezomib mediated downregulation of c-FLIP and XIAP, which is likely to be regulated by NF-κB. Blockage of NF-κB activation with BMS-345541 equally sensitized myelomonocytic AML cell lines and primary AML blasts to TRAIL.

Changes in the MDR1 gene expression after short-term ex vivo therapy with prednisolone have prognostic impact in childhood acute lymphoblastic leukemia

Multidrug resistance 1 (MDR1) gene expression determined by real-time polymerase chain reaction and results of rhodamine assay were analyzed at diagnosis and after 3 days of ex vivo therapy with prednisolone in 36 pediatric patients with acute lymphoblastic leukemia (ALL). Only 62% patients with de novo ALL had significant decrease of MDR1 expression. These patients had over twofold lower rhodamine retention in the presence of cyclosporine A on day 3 than others and had better probability of disease-free survival. In this study, we have shown that changes in the expression of MDR1 gene after short-term incubation of lymphoblasts with prednisolone may have prognostic value in pediatric de novo ALL patients.

Transmembrane transport of endo- and xenobiotics by mammalian ATP-binding cassette multidrug resistance proteins

Multidrug Resistance Proteins (MRPs), together with the cystic fibrosis conductance regulator (CFTR/ABCC7) and the sulfonylurea receptors (SUR1/ABCC8 and SUR2/ABCC9) comprise the 13 members of the human "C" branch of the ATP binding cassette (ABC) superfamily. All C branch proteins share conserved structural features in their nucleotide binding domains (NBDs) that distinguish them from other ABC proteins. The MRPs can be further divided into two subfamilies "long" (MRP1, -2, -3, -6, and -7) and "short" (MRP4, -5, -8, -9, and -10). The short MRPs have a typical ABC transporter structure with two polytropic membrane spanning domains (MSDs) and two NBDs, while the long MRPs have an additional NH2-terminal MSD. In vitro, the MRPs can collectively confer resistance to natural product drugs and their conjugated metabolites, platinum compounds, folate antimetabolites, nucleoside and nucleotide analogs, arsenical and antimonial oxyanions, peptide-based agents, and, under certain circumstances, alkylating agents. The MRPs are also primary active transporters of other structurally diverse compounds, including glutathione, glucuronide, and sulfate conjugates of a large number of xeno- and endobiotics. In vivo, several MRPs are major contributors to the distribution and elimination of a wide range of both anticancer and non-anticancer drugs and metabolites. In this review, we describe what is known of the structure of the MRPs and the mechanisms by which they recognize and transport their diverse substrates. We also summarize knowledge of their possible physiological functions and evidence that they may be involved in the clinical drug resistance of various forms of cancer.

Chromosome microdissection identifies genomic amplifications associated with drug resistance in a leukemia cell line: an approach to understanding drug resistance in cancer

A significant problem encountered in the treatment of cancer patients is that cancer cells often evolve resistance to chemotherapeutic agents. One of the mechanisms responsible for drug resistance is gene amplification. The study of the behavior of genes conferring drug resistance is very important to determine future treatments for cancer patients that will minimize the effect of gene amplification. One of the best methods to investigate this phenomenon is to use chromosome microdissection to directly access the amplified gene or genes. In the present study, chromosome microdissection and fluorescent in-situ hybridization (FISH) were applied for the identification of genes residing in a homogeneously staining region (HSR) in drug-resistant cell sublines developed by treatment of the T-cell leukemia cell line CCRF-CEM with increasing levels of the anthracycline, epirubicin. We have demonstrated that the selection by epirubicin actually elevated the level of the multidrug resistance-associated protein (MRP1) gene. We argue that the breakage fusion bridge (B-F-B) cycle offers a plausible explanation for this amplification. The DNA prepared from the amplified regions by chromosome microdissection provides a resource for future investigations looking for the possible presence of novel genes contributing to drug resistance.

Comparative analysis of the effects of sample source and test methodology on the assessment of protein expression in acute myelogenous leukemia

Numerous studies have analyzed the expression and prognostic importance of various proteins in acute myelogenous leukemia (AML). We sought to determine whether the sample source and methodology used to measure protein expression affect the results obtained. To determine the importance of sample source, we used Western blotting to compare the expression of eight proteins and phosphoproteins in the leukemia blast-enriched fraction of 118 blood- and 108 marrow-derived samples, including 37 paired samples. To determine the importance of methodology, the expression of five proteins was measured in 20 paired samples by Western blotting, laser scanning cytometry (LSC), and flow cytometry. The mean expression and range of expression in blood- and marrow-derived samples were statistically identical for all eight proteins. Expression measurements for the 37 paired blood and marrow samples also had very high statistical correlation. The LSC and flow cytometry data had the highest concordance when compared using Kolmogorov-Smirnoff D-stats (range of R values, 0.8-1.0). High concordance was also observed between the LSC and flow cytometry results when the percentage of cells positive for expression was dichotomized into positive or negative expression. However, there was less correlation between LSC and flow cytometry when the actual percentages of positive cells were compared. The majority of discordant situations involved samples that were positive by flow cytometry but negative by LSC. The correlation between Western blotting signal intensity and the percentage of expression-positive cells measured by LSC or flow cytometry varied by protein but was limited when there was little heterogeneity in expression by either method. In conclusion, provided that leukemia blast-enriched fractions were analyzed, the blood- and marrow-derived samples had identical protein expression. There was good concordance of results between flow cytometry and LSC, which share similar technology, but more limited correlation between these methods and Western blotting.

Functional cloning of SPIN-2, a nuclear anti-apoptotic protein with roles in cell cycle progression

The balance between hematopoietic cell viability and apoptosis is regulated by exogenous growth factors, however, the molecular mechanisms by which these trophic factors exert their effects remain obscure. A functional retroviral cDNA library-based screen was employed to identify genes that prevent growth factor withdrawal-mediated apoptosis in the myeloid progenitor cell 32Dcl3. This approach identified three classes of genes: those with known roles in apoptosis (bcl-X(L) and ornithine decarboxylase); genes previously identified but not linked directly to apoptotic signaling (O-linked N-acetylglucosamine transferase); and a previously uncharacterized gene we termed SPIN-2. In 32Dcl3 cells, expression of exogenous SPIN-2 provides 25% protection from apoptosis following growth factor withdrawal compared to controls which show approximately 1-2% survival. SPIN-2 overexpression slows cell growth rates and increases the percentage of cells in G(2)/M (32% vs control cells at 12%). Immunolocalization studies indicate that myc-epitope tagged SPIN-2 proteins, which retain their anti-apoptotic function, reside in the nucleus, whereas a C-terminal deletion mutant that loses its anti-apoptotic activity is located in the cytoplasm. These studies suggest that SPIN-2 is a novel nuclear protein that functions to regulate cell cycle progression and this activity is related to the inhibition of apoptosis following the removal of essential growth factors.

In vitro drug resistance profiles of adult acute lymphoblastic leukemia: possible explanation for difference in outcome to similar therapeutic regimens

Age has important prognostic impact in acute lymphoblastic leukemia (ALL). Adults with ALL have a worse prognosis compared to children. This may be due to different, unfavorable biology, poor treatment tolerance, drug resistance, higher expression of drug resistance related proteins. The lymphoblasts from adult ALL show an increased in vitro resistance to cytotoxic drugs, including prednisolone, dexamethasone, cytosine arabinoside, daunorubicin, L-asparaginase and methotrexate. Glucocorticoid resistance may be a fundamental difference between children, adolescents and adults with ALL, which may underlie different biological aspects and also explain the difference in prognosis. It seems that in vitro resistance to prednisolone with respect to the age might be a continuous variable in ALL patients, except infants. The greater the age, the higher the in vitro resistance to prednisolone. This may be due to induction of various defense mechanisms, such as an activation of P-glycoprotein, which develops throughout the life and protect the human against xenobiotics. Among a number of various drug resistance mechanisms, only several weak differences between adults and children with ALL have been reported including higher P-glycoprotein expression, lower methotrexate polyglutamate accumulation and possibly more often p53 gene mutations in adults. Intrinsic resistance, induction of drug resistance proteins expression during chemotherapy and co-existence of various mechanisms are common phenomena in adult ALL. It seems that age itself, more than drug resistance profile, reflects factors which have direct effect on chemotherapy response in adult ALL.