Relationship between the intracellular daunorubicin concentration, expression of major vault protein/lung resistance protein and resistance to anthracyclines in childhood acute lymphoblastic leukemia

The novel calicheamicin-conjugated CD22 antibody inotuzumab ozogamicin (CMC-544) effectively kills primary pediatric acute lymphoblastic leukemia cells

We investigated whether the newly developed antibody (Ab) -targeted therapy inotuzumab ozogamicin (CMC-544), consisting of a humanized CD22 Ab linked to calicheamicin, is effective in pediatric primary B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cells in vitro, and analyzed which parameters determine its efficacy. CMC-544 induced dose-dependent cell kill in the majority of BCP-ALL cells, although IC(50) values varied substantially (median 4.8 ng/ml, range 0.1-1000 ng/ml at 48 h). The efficacy of CMC-544 was highly dependent on calicheamicin sensitivity and CD22/CMC-544 internalization capacity of BCP-ALL cells, but hardly on basal and renewed CD22 expression. Although CD22 expression was essential for uptake of CMC-544, a repetitive loop of CD22 saturation, CD22/CMC-544 internalization and renewed CD22 expression was not required to achieve intracellular threshold levels of calicheamicin sufficient for efficient CMC-544-induced apoptosis in BCP-ALL cells. This is in contrast to studies with the comparable CD33 immunotoxin gemtuzumab ozogamicin (Mylotarg) in acute myeloid leukemia (AML) patients, in which complete and prolonged CD33 saturation was required for apoptosis induction. These data suggest that CMC-544 treatment may result in higher response rates in ALL compared with response rates obtained in AML with Mylotarg, and that therefore clinical studies in ALL, preferably with multiple low CMC-544 dosages, are warranted.

Expression of lung resistance protein and multidrug resistance-related protein (MRP1) in pediatric acute lymphoblastic leukemia

Multidrug resistance (MDR) is a phenomenon by which cells become resistant to unrelated chemotherapeutic agents. The prognostic value that lung resistance protein (LRP) and multidrug resistance-related protein 1 (MRP1) have in the setting of pediatric acute lymphoblastic leukemia (ALL) is controversial. The aim of this study was to investigate the expression of LRP and MRP1 and effect on clinical outcome and prognosis. The mRNA expression of LRP and MRP1 were analyzed in leukemic blasts of 34 pediatric ALL patients. LRP and MRP1 mRNA expression were detected in 41.2% and 35.3%, respectively. Eleven (91.7%) of 12 patients without LRP achieved CR compared with 9 (50.0%) of 18 with LRP expression. Similarly, 11 (100%) of 11 patients without MRP1 expression achieved CR compared with 9 (47.4%) of 19 with MRP1 expression and higher LRP expression rate or MRP1 expression rate was present in patients with relapse than MDR genes negative patients. The expression of either of two genes was associated with poorer 2-year survival. Also, patients expressing both genes had poorer outcomes and had worse 2-year survival. We suggest that MDR expression affects complete remission and survival rates in ALL patients. Thus, diagnosis appears to provide prognostic information for pediatric ALL.

Enhanced invasiveness of drug-resistant acute myeloid leukemia cells through increased expression of matrix metalloproteinase-2

The acquired drug resistance as well as extramedullary tissue infiltration of leukemic cells is a major obstacle in leukemia treatment. Excessive egress of leukemia cell blasts results in invasion into various organs or tissues, which is facilitated by the catalytic activities of matrix metalloproteinases (MMPs). However, the migration of chemoresistant leukemia cells remains unclear. Here, we generated drug-resistant variants of the human acute myeloid leukemia cell line (AML-2/WT) by stepwise exposure to anticancer drugs and evaluated the level of MMP-2 in the drug-resistant variants, along with their invasiveness. Each of the drug-resistant cell variants demonstrated predominant increases in the expression and gelatinolytic activity of MMP-2 as well as in invasiveness, which were significantly suppressed by both a MMP-2 inhibitor and a blocking antibody. Knockdown experiments using MMP-2 short hairpin RNA also indicated that its upregulation was strongly associated with the cells' increased invasive properties. Importantly, elevated levels of MMP-2 activity and invasiveness were observed in ex vivo mononuclear cell of bone marrow from patients with poor responses to chemotherapy. These findings suggest that advanced malignancy due to acquired drug resistance is responsible for the progressive invasiveness of leukemia cells via MMP-2.

Predictive value of multidrug resistance proteins and cellular drug resistance in childhood relapsed acute lymphoblastic leukemia

PURPOSE

Cellular resistance in childhood acute leukemias might be related to profile and function of multidrug resistance proteins and apoptosis regulating proteins. The aims of the study were: (1) analysis of expression of MRP1, PGP1, LRP, BCL-2 and p53 proteins; (2) correlation with ex vivo drug resistance, and (3) analysis of their prognostic impact on clinical outcome in childhood acute lymphoblastic (ALL) and acute myeloid (AML) leukemia.

METHODS

Total number of 787 children diagnosed for initial ALL (n = 527), relapsed ALL (n = 104), initial AML (n = 133) and relapsed AML (n = 23) were included into the study. Mean follow-up period was 3.5 years. Drug resistance for up to 30 anticancer agents was performed by the MTT assay. Expression of all proteins was tested by flow cytometry.

RESULTS

Both initial AML and relapsed ALL samples showed higher drug resistance than initial ALL samples. No significant differences were found in drug resistance between initial and relapsed AML samples. The presence of multidrug resistance and apoptosis proteins had no impact on pDFS in iALL and iAML, however strong trend towards adverse prognostic impact of MRP1, PGP and LRP on pDFS in rALL was observed. The same trend was observed for each of analyzed co-expressions of tested multidrug resistance proteins.

CONCLUSIONS

The phenomenon of cellular drug resistance in childhood acute leukemias is multifactorial and plays an important role in response to therapy. Expression of MRP1, PGP and LRP proteins, as well as their co-expression play possible role in childhood relapsed ALL.

Expression profiling of ATP-binding cassette transporters in childhood T-cell acute lymphoblastic leukemia

A major issue in the treatment of T-cell acute lymphoblastic leukemia (T-ALL) is resistance to chemotherapeutic drugs. Multidrug resistance can be caused by ATP-binding cassette (ABC) transporters. The majority of these proteins have not yet been examined in T-ALL. Using a newly developed microarray for the simultaneous quantification of 38 ABC transporter genes, we observed a consistent overexpression of ABCA2/ABCA3 in clinical samples of ALL. Therefore, we analyzed the association of these two genes with drug resistance. Treatment of CCRF-CEM and Jurkat cells with methotrexate, vinblastine, or doxorubicin led to an induction of ABCA3 expression, whereas a significant increase of ABCA2 expression was only observed in Jurkat cells. To study the causal relationship of ABCA2/A3 overexpression with drug resistance, we applied RNA interference (RNAi) technology. RNAi specific for ABCA2 or ABCA3 led to a partial decrease of expression in these two ABC transporters. Upon cotreatment of RNAi for ABCA2 with methotrexate and vinblastine, a partial decrease of ABCA2 expression as well as a simultaneous increase of ABCA3 expression was observed. Vice versa, ABCA3 RNAi plus drugs decreased ABCA3 and increased ABCA2 expression. This indicates that down-regulation of one ABC transporter was compensated by the up-regulation of the other. Application of RNAi for both ABCA2 and ABCA3 resulted in a more efficient reduction of the expression of both transporters. As a consequence, a significant sensitization of cells to cytostatic drugs was achieved. In conclusion, ABCA2 and ABCA3 are expressed in many T-ALL and contribute to drug resistance.

Differences in absorption, distribution, metabolism and excretion of xenobiotics between the paediatric and adult populations

In children, the therapeutic benefits and potential risks associated with drug treatment may be different from those in adults and will depend on the exposure, receptor sensitivity and relationship between effect and exposure. In this paper, key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the paediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, secretion and activity of bile and pancreatic fluid, bacterial colonisation and transporters, such as P-glycoprotein (P-gp), are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the paediatric population and adults are organ size, membrane permeability, plasma protein concentration and characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and transporters such as P-gp, which is present not only in the gut, but also in liver, kidney, brain and other tissues. As far as drug metabolism is concerned, important differences have been found in the paediatric population compared with adults both for phase I enzymes (oxidative [e.g., cytochrome P450 (CYP)1A2, and CYP3A7 versus -3A4], reductive and hydrolytic enzymes) and phase II enzymes (e.g., N-methyltransferases and glucuronosyltransferases). Generally, the major enzyme differences observed in comparison with the adult age are in newborn infants, although for some enzymes (e.g., glucuronosyltransferases and other phase II enzymes) important differences still exist between infants and toddlers and adults. Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the paediatric population compared with adults are glomerular filtration and tubular secretion. The ranking of the key factors varies according to the chemical structure and physicochemical properties of the drug examined, as well as to the characteristics of its formulation. It would be important to generate additional information on the developmental aspects of renal P-gp and of other renal transporters, as has been done and is still being done with the different -isozymes involved in drug metabolism.

Prognostic significance of multidrug resistance-related proteins in childhood acute lymphoblastic leukaemia

An important problem in the treatment of children with acute lymphoblastic leukaemia (ALL) is pre-existent or acquired resistance to structurally and functionally unrelated chemotherapeutic compounds. Various cellular mechanisms can give rise to multidrug resistance (MDR). Best studied is the transmembrane protein-mediated efflux of cytotoxic compounds that leads to decreased cellular drug accumulation and toxicity. Several MDR-related efflux pumps have been characterised, including P-glycoprotein (P-gp), multidrug resistance-associated protein 1 (MRP1), breast cancer resistance protein (BCRP) and lung resistance protein (LRP). P-gp expression and/or activity has been associated with unfavourable outcome in paediatric ALL patients, whereas MRP1 and BCRP do not seem to play a major role. LRP might contribute to drug resistance in B-lineage ALL, but larger studies are needed to confirm these results. The present review summarises the current knowledge concerning multidrug resistance-related proteins and focuses on the clinical relevance and prognostic value of these efflux pumps in childhood ALL.

The prognostic significance of P-glycoprotein, multidrug resistance-related protein 1 and lung resistance protein in pediatric acute lymphoblastic leukemia: a retrospective study of 295 newly diagnosed patients by the Children's Oncology Group

Multidrug resistance (MDR) is a phenomenon by which cells become resistant to an array of structurally unrelated chemotherapeutic agents. The prognostic value that P-glycoprotein (Pgp), multidrug resistance-related protein 1 (MRP1), and lung resistance protein (LRP) have in the setting of pediatric acute lymphoblastic leukemia (ALL) is controversial. In a retrospective study, we analyzed samples obtained from 295 similarly treated pediatric ALL patients to assess whether the overexpression and/or function of these proteins at diagnosis affects outcome. Most patients (70%, 207/295) did not overexpress an MDR protein. A small number of patients expressed functional Pgp (1%, 3/295) and some overexpressed functional MRP1 (10%, 19/295), with a statistically significant number of the latter being of T-lineage as opposed to pre-B (P < 0.001). A small number of patients (2%, 6/295) also overexpressed both Pgp and MRP1. Additional patients expressed increased levels of LRP. Elevated levels of these proteins at diagnosis did not correlate with risk factors and did not predict an adverse prognosis. Life-table estimates and Kaplan-Meier plots did not show any significant differences between patients who overexpressed an MDR protein compared with those who did not, nor was any difference noted when the different MDR + groups were compared with one another. These data strongly support the conclusion that the overexpression of these functional drug efflux pumps at diagnosis does not contribute to treatment failure in pediatric ALL.

Reversal of P-glycoprotein-mediated multidrug resistance with small interference RNA (siRNA) in leukemia cells

The multidrug resistance (MDR) mediated by P-glycoprotein (P-gp), the MDR1 gene product, is one of the major obstacles in leukemia treatment. The present study was designed to explore a MDR1-targeted small interfering RNA (si-MDR1) approach for reversal of P-gp-mediated MDR in the MDR human leukemia cell line k562/A02. It was found that si-MDR1 significantly inhibited MDR1 expression at both mRNA and protein levels. Depletion of MDR1 by si-MDR1 correlated with the increased sensitivity of the cells to cytotoxic agents and with the enhanced intracellular retention of daunorubicin (DNR). One base-pair mutated control (si-MDR1-Mut) lost the effect of si-MDR1 on both the degradation of mdr1 mRNA and the reduction of P-gp expression. These findings indicate that siRNA specifically and efficiently interferes with the expression of mdr1 and could be used as a molecularly defined therapeutic approach for MDR in the treatment of leukemia.

New invMED1 element cis-activates human multidrug-related MDR1 and MVP genes, involving the LRP130 protein

The MDR1 gene is a key component of the cytotoxic defense network and its overexpression results in the multidrug resistance (MDR) phenotype. However, the molecular mechanisms that regulate the MDR1 gene and coordinate multiple MDR-related genes expression are poorly understood. In a previous study, we identified a new 12 bp cis-activating region in the 5'-flanking region of the human MDR1 gene, which we called inverted MED1. In the present study, we characterized the precise binding element, which we named invMED1, and revealed the presence of the LRP130 protein as the nuclear factor. Its binding intensity increases with the endogenous MDR1 geneexpression and with the MDR level of CEM leukemia cells. Interestingly, the LRP130 level did not vary with the chemoresistance level. We observed the involvement of LRP130 in the transcriptional activity of the MDR1 gene promoter, and moreover, in that of the MDR-related, invMED1-containing, MVP gene promoter. We used siRNAs and transcriptional decoys in two unrelated human cancer cell lines to show the role of the invMED1/LRP130 couple in both MDR1 and MVP endogenous genes activities. We showed that invMED1 was localized in the -105/-100 and -148/-143 regions of the MDR1 and MVP gene promoters, respectively. In addition, since the invMED1 sequence is primarily located in the -160/-100 bp region of mammalian MDR-related genes, our results present the invMED1/LRP130 couple as a potential central regulator of the transcription of these genes.

Vaults: a ribonucleoprotein particle involved in drug resistance?

Vaults are ribonucleoprotein particles found in the cytoplasm of eucaryotic cells. The 13 MDa particles are composed of multiple copies of three proteins: an M(r) 100 000 major vault protein (MVP) and two minor vault proteins of M(r) 193 000 (vault poly-(ADP-ribose) polymerase) and M(r) 240 000 (telomerase-associated protein 1), as well as small untranslated RNA molecules of approximately 100 bases. Although the existence of vaults was first reported in the mid-1980s no function has yet been attributed to this organelle. The notion that vaults might play a role in drug resistance was suggested by the molecular identification of the lung resistance-related (LRP) protein as the human MVP. MVP/LRP was found to be overexpressed in many chemoresistant cancer cell lines and primary tumor samples of different histogenetic origin. Several, but not all, clinico-pathological studies showed that MVP expression at diagnosis was an independent adverse prognostic factor for response to chemotherapy. The hollow barrel-shaped structure of the vault complex and its subcellular localization indicate a function in intracellular transport. It was therefore postulated that vaults contributed to drug resistance by transporting drugs away from their intracellular targets and/or the sequestration of drugs. Here, we review the current knowledge on the vault complex and critically discuss the evidence that links vaults to drug resistance.

Drug metabolism and disposition in children

Key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the pediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, bacterial colonization and probably P-glycoprotein are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein concentration and plasma protein characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and probably P-glycoprotein, mainly that present in the gut, liver and brain. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I enzymes [oxidative (e.g. cytochrome CYP3A7 vs. CYP3A4 and CYP1A2), reductive and hydrolytic enzymes] and phase II enzymes (e.g. N-methyltransferases and glucuronosyltransferases). Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the pediatric population compared with adults are glomerular filtration and tubular secretion. It would be important to generate information on the developmental aspects of renal P-glycoprotein and of other renal transporters as done and still being done with the different isozymes involved in drug metabolism.

Major vault protein/lung resistance-related protein (MVP/LRP) expression in nervous system tumors

Lung resistance-related protein (LRP) was identified as the major vault protein (MVP), the main component of multimeric vault particles. It functions as a transport-associated protein that can be associated with multidrug resistance. In previous studies, expression of MVP/LRP has been documented in tumors of various types. In general, good correlations have been reported for expression of MVP/LRP and decreased sensitivity to chemotherapy and poor prognosis. MVP/LRP expression has been documented in glioblastomas, but its expression in nervous system tumors in general has not been well characterized. Immunohistochemistry using anti-human MVP/LRP antibody (LRP-56) was performed on formalin-fixed, paraffin-embedded archival tissue from 69 primary central nervous system tumors. Expression of MVP/LRP was observed in 81.2% (56/69) of primary nervous system tumors, including astrocytomas (11/13), oligodendrogliomas (1/2), oligoastrocytomas (5/5), ependymoma (1/1), meningiomas (35/45), schwannomas (2/2), and neurofibroma (1/1). Various degrees and distributions of immunoreactivity to MVP/ LRP were observed. Neither the presence nor the degree of immunoreactivity to MVP/LRP showed any correlation with either tumor grade or the presence of brain invasion.

Messenger RNA analysis of the multidrug resistance related protein (MRP1) and the lung resistance protein (LRP) in de novo and relapsed childhood acute lymphoblastic leukemia

In this study, 86 children (58 initial ALL and 28 children with relapsed disease) were investigated for lung resistance protein (LRP) and multidrug resistance related protein (MRPI)-mRNA expression by semiquantitative RT-PCR. The majority of investigated cases demonstrated variable LRP and MRP1 mRNA expression, when normalized for beta-microglobulin expression. LRP and MRPI mRNA expression may be coordinately regulated, as expression of both transcripts was found to be significantly correlated (p = 0.0001). No differences of LRP and MRP expression were observed between initial and relapsed stage patients (LRP: p = 0.89 and for MRP: p = 0.09). The prognostic value of both resistance mechanisms was subjected to Kaplan-Meier analysis for event-free survival. For this analysis the patients were divided into groups with high or low LRP or MRPI mRNA expression by utilizing the median value as the cut-off point. Overexpression of both resistance mechanisms had no prognostic significance in our retrospective study (log-rank test for LRP: p = 0.12 and for MRPI: p = 0.95), however, patients who showed high LRP expression exhibited a lower tendency of remaining in continuous first remission.

Noninvasive detection of multidrug resistance in patients with hematological malignancies: are we there yet?

The success of chemotherapy in the treatment of malignancies may be limited by cellular mechanisms leading to drug resistance. In hematological malignancies, mechanisms leading to the development of multidrug resistance (MDR) include overexpression of the membrane-based export pump P-glycoprotein (Pgp) and the MDR-associated protein (MRP). Recently, the overexpression of the lung-resistance protein (LRP) has also been associated with reduced intracellular drug accumulation. A major problem in assessing the significance of the expression of these resistance proteins in clinical MDR has been the variability of detection techniques either at the mRNA or protein level. Currently, the detection of resistance proteins relies heavily on antibody and cDNA probes, and these methods may not be informative about the in vivo function of Pgp, MRP, or LRP. Nuclear medicine imaging techniques such as single-photon emission tomography (SPECT) and positron emission tomography (PET) have been evaluated for noninvasive determination of the presence and the function of Pgp- and MRP-mediated transport systems. Technetium 99m ((99m)Tc)-sestamibi, an agent in clinical use for myocardial perfusion and tumor imaging, is recognized as a substrate for Pgp and MRP, and has been used to visualize Pgp expression. (99m)Tc-tetrofosmin is also a substrate for the Pgp efflux pump mechanism and is used to evaluate Pgp function in in vitro and in vivo studies. Recently, radiopharmaceuticals including carbon 11-labeled colchicine, verapamil, and daunorubicin have been used in cell line and animal studies for the evaluation of Pgp-mediated transport functions using PET technology. Preliminary results suggest that the potential to detect MDR in tumors prior to or after exposure to chemotherapeutic agents exists in imaging using either (99m)Tc-labeled compounds and SPECT or positron emitting compounds and PET.

Drug resistance in hematologic malignancies

Drug resistance eventually occurs in most hematologic malignancies treated with chemotherapy. The mechanisms responsible for drug resistance include expression of transporters of xenobiotics of the adenosine triphosphate-binding cassette protein superfamily (P-glycoprotein, multidrug resistance associated proteins, breast cancer resistance protein), modifications of enzymes like deoxycytidine kinase, and defects in chemotherapy-induced apoptosis. The efforts to overcome this drug resistance have been focused, thus far, on modulation of P-glycoprotein. Several compounds were manufactured for this purpose, and phase III trials of PSC833, one of the most potent P-glycoprotein inhibitors, are completed. The emergence of modulators with several adenosine triphosphate-binding cassette protein targets, like GG120918 (inhibiting P-glycoprotein and breast cancer resistance protein) and VX710 (inhibiting P-glycoprotein and multidrug resistance associated protein 1), are of clinical interest in malignancies often expressing several efflux pumps simultaneously. Another approach is the use of "furtive" drugs like liposomal or nanoparticular anthracyclines.

Significance of MDR1, MRP1, GSTpi and GSTmu mRNA expression in acute lymphoblastic leukemia in Indian patients

Using, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in 167 patients of acute lymphoblastic leukemia (ALL) from India at different stages of the disease (presentation 125, remission 33, first relapse nine), MRP1 and GSTpi expression were significantly higher at relapse than presentation (P=0.03 and P=0.01, respectively) and remission (P=0.007 and P=0.003, respectively). MRP1, GSTpi and GSTmu were expressed simultaneously in several samples with significant association of expression levels (P=0.0001). Association with clinicopathological features included higher MDR1 expression with age >15 years (P=0.04) and higher MRP1, GSTpi, GSTmu expression with WBC counts >100x10(9)/l. In 71 patients (age <25 years), inability to achieve CR was associated with a significantly higher MDR1 mRNA expression (P=0.03) indicating a prognostic significance. However, relapse or shorter Event Free Survival was independent of mRNA expression levels of the four genes. In view of the increased mRNA expression of MRP1/GST at the time of relapse and an association with risk factors such as a high WBC count, further studies directed towards investigating the functional aspects of GSH/GST/MRP1 mediated drug transport are warranted.

Lung resistance-related protein/major vault protein and vaults in multidrug-resistant cancer

Tumor cells that are insensitive to anticancer drugs frequently have a multidrug-resistant (MDR) phenotype. Proteins that can be involved in this phenomenon are transport-associated proteins such as P-glycoprotein, multidrug-resistance protein 1, breast cancer resistance protein, and lung resistance-related protein (LRP). LRP was identified as the major vault protein (MVP), the main component of multimeric vault particles. With the recent identification of the two minor vault proteins as telomerase-associated protein (TEP1) and vault-poly (ADP-ribose) polymerase (VPARP), and with high-resolution three-dimensional imaging, the composition of vaults is almost unraveled. Although the first direct evidence for a causal relationship between LRP/MVP expression and drug resistance has been obtained, many functional aspects of vaults in normal physiology and in MDR still need to be clarified. The current clinical data on LRP/MVP detection indicate that LRP/MVP expression can be of high clinical value to predict the response to chemotherapy of several tumor types.