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

Population Pharmacokinetics of Inotuzumab Ozogamicin in Pediatric Relapsed/Refractory B-Cell Precursor Acute Lymphoblastic Leukemia: Results of Study ITCC-059

BACKGROUND AND OBJECTIVE

Inotuzumab ozogamicin is an antibody-drug conjugate approved for treating relapsed/refractory B-cell precursor acute lymphoblastic leukemia (BCP-ALL) in adults. Pediatric pharmacokinetic data of inotuzumab ozogamicin are lacking. This study is the first to examine the population pharmacokinetics of inotuzumab ozogamicin in pediatric patients with relapsed/refractory BCP-ALL.

METHODS

From 531 adult patients with B-cell non-Hodgkin's lymphoma, 234 adult patients with BCP-ALL, and 53 pediatric patients with BCP-ALL, 8924 inotuzumab ozogamicin serum concentrations were analyzed using non-linear mixed-effects modeling. A published adult inotuzumab ozogamicin population-pharmacokinetic model, a two-compartment model with linear and time-dependent clearance, was adapted to describe the pediatric data.

RESULTS

Modifications in this analysis, compared to the published adult model, included: (i) re-estimating pharmacokinetic parameters and covariate effects; (ii) modifying covariate representation; and (iii) introducing relevant pediatric covariate effects (age on the decay coefficient of time-dependent clearance and ALL effect (disease type and/or different bioanalytical analysis methods) on initial values of time-dependent clearance). For patients with relapsed/refractory BCP-ALL, increasing age was associated with a decreasing decay coefficient of time-dependent clearance, reflecting that the target-mediated drug clearance declines more rapidly in children. In pediatric BCP-ALL, the median [interquartile range] cumulative area under the concentration-time curve was significantly higher among responders (n = 42) versus non-responders (n = 10) at the end of the first cycle (26.1 [18.9-35.0] vs 10.1 [9.19-16.1], × 103 ng*h/mL, p < 0.001). From simulations performed at the recommended pediatric phase II dose, inotuzumab ozogamicin exposure reached a similar level as observed in responding pediatric trial participants.

CONCLUSIONS

The pharmacokinetic profile of inotuzumab ozogamicin in pediatric patients with relapsed/refractory BCP-ALL was well described in this study. No dose adjustment is required clinically for pediatric patients with BCP-ALL based on the simulated inotuzumab ozogamicin exposure at the recommended pediatric phase II dose, promising efficacy and acceptable tolerability.

Non-coding RNAs in leukemia drug resistance: new perspectives on molecular mechanisms and signaling pathways

Like almost all cancer types, timely diagnosis is needed for leukemias to be effectively cured. Drug efflux, attenuated drug uptake, altered drug metabolism, and epigenetic alterations are just several of the key mechanisms by which drug resistance develops. All of these mechanisms are orchestrated by up- and downregulators, in which non-coding RNAs (ncRNAs) do not encode specific proteins in most cases; albeit, some of them have been found to exhibit the potential for protein-coding. Notwithstanding, ncRNAs are chiefly known for their contribution to the regulation of physiological processes, as well as the pathological ones, such as cell proliferation, apoptosis, and immune responses. Specifically, in the case of leukemia chemo-resistance, ncRNAs have been recognized to be responsible for modulating the initiation and progression of drug resistance. Herein, we comprehensively reviewed the role of ncRNAs, specifically its effect on molecular mechanisms and signaling pathways, in the development of leukemia drug resistance.

Multiplex Single-Cell Analysis of Cancer Cells Enables Unbiased Uncovering Subsets Associated with Cancer Relapse: Heterogeneity of Multidrug Resistance in Precursor B-ALL

Earlier detection of biomarkers responsible for cancer relapse facilitates more rational cancer treatment regimens to be designed. Herein, we develop a mass cytometry-based strategy for unbiased mining of cell subsets that potentially contribute to cancer recurrence through panoramic examination of the immunophenotypic features and multidrug resistance characteristics. The incorporation of metal tags enables multiplexed information of single cells to be interrogated based on metal fingerprint. Using acute lymphoblastic leukemia (B-ALL) as a showcase, we show overexpressed multidrug resistance biomarkers, i. e., BCRP, Bcl-2, MRP1, and P-gp in B-ALL cells compared with healthy control, and a positive correlation among different multidrug resistance biomarkers. Different cell subsets with multidrug resistance are well-defined, featured with CD34⁺ CD38⁺ CD10^- and CD34⁺ CD38^+/int CD10⁺ . Importantly, we uncovered that CD34 expression level is positively correlated to multidrug resistance, indicative of a higher potential of immature cells to induce B-ALL relapse. In addition, the cell subsets positively expressing CD73 and CD304 (CD34⁺ CD10⁺ CD304⁺ ; CD34⁺ CD38^+/int CD10⁺ CD73⁺ ) also overexpress multidrug resistance biomarkers, suggesting that they may serve as additional new biomarkers for B-ALL stratification and prognosis. Our data provide the first evidence that highly expressed multidrug resistance biomarkers in certain cell subpopulations with specific immunophenotypes may potentially induce B-ALL recurrence. The incorporation of multidrug resistance features with cell phenotypes using mass cytometry proposed in this study provides a general strategy for risk assessment and the prediction of recurrence of different types of cancers.

The Relationship of Glutathione-S-Transferase and Multi-Drug Resistance-Related Protein 1 in Nitric Oxide (NO) Transport and Storage

Nitric oxide is a diatomic gas that has traditionally been viewed, particularly in the context of chemical fields, as a toxic, pungent gas that is the product of ammonia oxidation. However, nitric oxide has been associated with many biological roles including cell signaling, macrophage cytotoxicity, and vasodilation. More recently, a model for nitric oxide trafficking has been proposed where nitric oxide is regulated in the form of dinitrosyl-dithiol-iron-complexes, which are much less toxic and have a significantly greater half-life than free nitric oxide. Our laboratory has previously examined this hypothesis in tumor cells and has demonstrated that dinitrosyl-dithiol-iron-complexes are transported and stored by multi-drug resistance-related protein 1 and glutathione-S-transferase P1. A crystal structure of a dinitrosyl-dithiol-iron complex with glutathione-S-transferase P1 has been solved that demonstrates that a tyrosine residue in glutathione-S-transferase P1 is responsible for binding dinitrosyl-dithiol-iron-complexes. Considering the roles of nitric oxide in vasodilation and many other processes, a physiological model of nitric oxide transport and storage would be valuable in understanding nitric oxide physiology and pathophysiology.

N-alkylisatin-based microtubule destabilizers bind to the colchicine site on tubulin and retain efficacy in drug resistant acute lymphoblastic leukemia cell lines with less in vitro neurotoxicity

BACKGROUND

Drug resistance and chemotherapy-induced peripheral neuropathy continue to be significant problems in the successful treatment of acute lymphoblastic leukemia (ALL). 5,7-Dibromo-N-alkylisatins, a class of potent microtubule destabilizers, are a promising alternative to traditionally used antimitotics with previous demonstrated efficacy against solid tumours in vivo and ability to overcome P-glycoprotein (P-gp) mediated drug resistance in lymphoma and sarcoma cell lines in vitro. In this study, three di-brominated N-alkylisatins were assessed for their ability to retain potency in vincristine (VCR) and 2-methoxyestradiol (2ME2) resistant ALL cell lines. For the first time, in vitro neurotoxicity was also investigated in order to establish their suitability as candidate drugs for future use in ALL treatment.

METHODS

Vincristine resistant (CEM-VCR R) and 2-methoxyestradiol resistant (CEM/2ME2-28.8R) ALL cell lines were used to investigate the ability of N-alkylisatins to overcome chemoresistance. Interaction of N-alkylisatins with tubulin at the the colchicine-binding site was studied by competitive assay using the fluorescent colchicine analogue MTC. Human neuroblastoma SH-SY5Y cells differentiated into a morphological and functional dopaminergic-like neurotransmitter phenotype were used for neurotoxicity and neurofunctional assays. Two-way ANOVA followed by a Tukey's post hoc test or a two-tailed paired t test was used to determine statistical significance.

RESULTS

CEM-VCR R and CEM/2ME2-28.8R cells displayed resistance indices of > 100 to VCR and 2-ME2, respectively. CEM-VCR R cells additionally displayed a multi-drug resistant phenotype with significant cross resistance to vinblastine, 2ME2, colchicine and paclitaxel consistent with P-gp overexpression. Despite differences in resistance mechanisms observed between the two cell lines, the N-alkylisatins displayed bioequivalent dose-dependent cytotoxicity to that of the parental control cell line. The N-alkylisatins proved to be significantly less neurotoxic towards differentiated SH-SY5Y cells than VCR and vinblastine, evidenced by increased neurite length and number of neurite branch points. Neuronal cells treated with 5,7-dibromo-N-(p-hydroxymethylbenzyl)isatin showed significantly higher voltage-gated sodium channel function than those treated with Vinca alkaloids, strongly supportive of continued action potential firing.

CONCLUSIONS

The N-alkylisatins are able to retain cytotoxicity towards ALL cell lines with functionally distinct drug resistance mechanisms and show potential for reduced neurotoxicity. As such they pose as promising candidates for future implementation into anticancer regimes for ALL. Further in vivo studies are therefore warranted.

Resistance of t(17;19)-acute lymphoblastic leukemia cell lines to multiagents in induction therapy

t(17;19)(q21‐q22;p13), responsible for TCF3‐HLF fusion, is a rare translocation in childhood B‐cell precursor acute lymphoblastic leukemia(BCP‐ALL). t(1;19)(q23;p13), producing TCF3‐PBX1 fusion, is a common translocation in childhood BCP‐ALL. Prognosis of t(17;19)‐ALL is extremely poor, while that of t(1;19)‐ALL has recently improved dramatically in intensified chemotherapy. In this study, TCF3‐HLF mRNA was detectable at a high level during induction therapy in a newly diagnosed t(17;19)‐ALL case, while TCF3‐PBX1 mRNA was undetectable at the end of induction therapy in most newly diagnosed t(1;19)‐ALL cases. Using 4 t(17;19)‐ALL and 16 t(1;19)‐ALL cell lines, drug response profiling was analyzed. t(17;19)‐ALL cell lines were found to be significantly more resistant to vincristine (VCR), daunorubicin (DNR), and prednisolone (Pred) than t(1;19)‐ALL cell lines. Sensitivities to three (Pred, VCR, and l‐asparaginase [l‐Asp]), four (Pred, VCR, l‐Asp, and DNR) and five (Pred, VCR, l‐Asp, DNR, and cyclophosphamide) agents, widely used in induction therapy, were significantly poorer for t(17;19)‐ALL cell lines than for t(1;19)‐ALL cell lines. Consistent with poor responses to VCR and DNR, gene and protein expression levels of P‐glycoprotein (P‐gp) were higher in t(17;19)‐ALL cell lines than in t(1;19)‐ALL cell lines. Inhibitors for P‐gp sensitized P‐gp‐positive t(17;19)‐ALL cell lines to VCR and DNR. Knockout of P‐gp by CRISPRCas9 overcame resistance to VCR and DNR in the P‐gp‐positive t(17;19)‐ALL cell line. A combination of cyclosporine A with DNR prolonged survival of NSG mice inoculated with P‐gp‐positive t(17;19)‐ALL cell line. These findings indicate involvement of P‐gp in resistance to VCR and DNR in Pgp positive t(17;19)‐ALL cell lines. In all four t(17;19)‐ALL cell lines, RAS pathway mutation was detected. Furthermore, among 16 t(1;19)‐ALL cell lines, multiagent resistance was usually observed in the cell lines with RAS pathway mutation in comparison to those without it, suggesting at least a partial involvement of RAS pathway mutation in multiagent resistance of t(17;19)‐ALL.

Effects of Clostridium difficile toxin A on K562/A02 cell proliferation, apoptosis and multi-drug resistance

The aim of the present study was to investigate the cytotoxic effect and multi-drug resistance (MDR) of Clostridium difficile toxin A (TcdA) on K562/A02 cells, and understand its underlying molecular pathways. K562/A02 cells were treated with TcdA at different concentrations for 24, 48 and 72 h, and the inhibition effect and drug resistance of TcdA on K562/A02 cell proliferation was assessed by methyl thiazolyl tetrazolium colorimetric assay. Furthermore, cell cycle-apoptosis was analyzed by flow cytometry, P-glycoprotein (P-gp) expression was determined by western blot analysis and caspase-3 activity was measured using a caspase-3 activity kit. TcdA inhibited K562/A02 cell proliferation in a time- and dose-dependent manner. The inhibition rate of K562/A02 cells reached 8.76±0.76, 28.55±0.43, 47.89±0.27, 58.08±0.06 and 57.70±0.79% following treatment with 50, 100, 200, 400 and 800 ng/ml TcdA, respectively, for 24 h. K562/A02 cells in the G0/G1 phase increased and cells in the S phase decreased following treatment with TcdA (P<0.05), and the apoptotic rates in the 200 and 400 ng/ml concentration groups were 14.05 and 22.89%, respectively. In addition, TcdA (50 ng/ml) significantly inhibited the proliferation of K562/A02 cells and reduced the half maximal inhibitory concentration of these drugs in combination with chemotherapy drugs. The reversal folds were 3.09, 2.89 and 2.79, respectively. Furthermore, TcdA treatment was associated with the upregulation of P-gp in K562/A02 cells, and caspase-3 activity was observed to increase in K562/A02 cells following TcdA treatment, when compared with untreated controls (P<0.05). These findings suggested that TcdA may be able to inhibit K562/A02 cell growth, induce cell apoptosis by decreasing P-gp levels and caspase-3 activation, and partially reverse MDR. Further studies are required to evaluate the potential of TcdA as a candidate for the chemotherapy of hematologic malignancies.

JNK/AP-1 activation contributes to tetrandrine resistance in T-cell acute lymphoblastic leukaemia

T-cell acute lymphoblastic leukaemia (T-ALL) is a challenging malignancy with a high relapse rate attributed to drug resistance. Tetrandrine (TET), a bisbenzylisoquinoline alkaloid extracted from a Chinese herb, is a potential anti-cancer and anti-leukaemic drug. In this study we investigated the mechanisms of TET resistance in T-ALL cells in vitro. Among the four T-ALL cell lines tested, Jurkat and CEM cells exhibited the lowest and highest resistance to TET with IC₅₀ values at 24 h of 4.31±0.12 and 16.53±3.32 μmol/L, respectively. When treated with TET, the activity of transcription factor activator protein 1 (AP-1) was significantly decreased in Jurkat cells but nearly constant in CEM cells. To avoid cell-specific variation in drug resistance and transcription factor activities, we established a TET-R Jurkat subclone with the estimated IC₅₀ value of 10.90±.92 μmol/L by exposing the cells to increasing concentrations of TET. Interestingly, when treated with TET, TET-R Jurkat cells exhibited enhanced AP-1 and NF-κB activity, along with upregulation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) signaling pathways, whereas the expression of P-gp was not altered. Selective inhibition of JNK but not ERK suppressed AP-1 activity and TET resistance in TET-R Jurkat cells and in CEM cells. These results demonstrate that Jurkat cells acquire TET resistance through activation of the JNK/AP-1 pathway but not through P-gp expression. The JNK/AP-1 pathway may be a potential therapeutic target in relapsed T-ALL.

Aberrant methylation of protocadherin 17 and its prognostic value in pediatric acute lymphoblastic leukemia

BACKGROUND

The outcome of approximately 20% of patients with acute lymphoblastic leukemia (ALL) remains poor because of disease recurrence. We examined whether DNA methylation of cadherin superfamily genes is a useful biomarker for ALL relapse.

PROCEDURE

We used Infinium Methylation 450K Arrays to assess genome-wide DNA methylation status. The methylation status of each individual gene was then determined by a combination of bisulfite restriction analysis and genome bisulfite sequencing. mRNA expression was evaluated by reverse-transcriptase PCR (RT-PCR) and quantitative real-time PCR.

RESULTS

Cadherin superfamily genes including cadherin (CDH) 1, protocadherin (PCDH) 8, and PCDH17 were selected for analysis of methylation status. In 40 patient samples with B-cell precursor (BCP) ALL at diagnosis, the methylation frequencies of CDH1, PCDH8, and PCDH17 were 62.5, 55, and 30%, respectively. CDH1 and PCDH8 methylation was also detected in 80 and 20% of control bone marrow (BM) samples, respectively. On the contrary, PCDH17 was unmethylated in all control BM samples. There was a significant correlation between the methylation status of PCDH17 (but not CDH1 and PCDH8) and event-free survival or overall survival. Univariate and multivariate analyses showed that only PCDH17 methylation was associated with an increased risk for relapse and mortality in patients with BCP ALL.

CONCLUSION

PCDH17 methylation at diagnosis was closely related to poor prognosis and thus could be used as a new biomarker to predict relapse in patients with BCP ALL.

Clinical significance of the ABCB1 and ABCG2 gene expression levels in acute lymphoblastic leukemia

OBJECTIVES

Acute lymphoblastic leukemia (ALL) is a clonal disease that accounts for 20% of acute leukemias in adults. A high percentage of adult patients (ranging from 70 to 80%) reach complete remission; however, the 5-year survival rate is only 20-40%. One of the main obstacles to treatment success is the drug resistance of leukemic cells. Therefore, our research group analyzed the ABCB1 and ABCG2 gene expression levels in 61 patients diagnosed with ALL and assessed whether the levels affected the clinical parameters and 40-month survival rate.

METHODS

The ABCB1 and ABCG2 gene expression levels were analyzed using real-time polymerase chain reaction in 61 patients diagnosed with ALL and 99 healthy donors as controls. The association between ABCB1 and ABCG2 gene expression levels and clinical variables was determined using the Chi-square test and Fisher's exact test. Overall survival (OS) was determined using the Kaplan-Meier method.

RESULTS

The results showed high ABCB1 and ABCG2 gene levels, which were 4.5 and 2.3 times the levels of healthy donors, respectively. A total of 52% of the study patients expressed high ABCB1 levels and were significantly associated with the high-risk patient group and a decreased 40-month survival rate of 78%. Only 49% of the patients expressed high ABCG2 gene levels. No association was found between the clinical parameters and the ABCG2 gene expression levels.

CONCLUSIONS

Early detection of ABCB1 gene expression levels could be important for the diagnosis and monitoring of ALL patients.

Overexpression of SORCIN is a Prognostic Biomarker for Multidrug-Resistant Pediatric Acute Lymphoblastic Leukemia and Correlates with Upregulated MDR1/P-gp

BACKGROUND

Multidrug resistance is one of the major causes of treatment failure in pediatric acute lymphoblastic leukemia (ALL), and SORCIN is an intracellular calcium modulator protein. The current study was designed to investigate the in vitro and in vivo relationships between the expression levels of SORCIN: in tumor cell lines and children with ALL; its possible correlation with MDR1/P-glycoprotein (P-gp), a multidrug resistance-related gene; and response to therapy.

MATERIALS AND METHODS

Childhood T-lymphoblastic leukemia (CCRF-CEM) cell lines resistant to methotrexate (MTX) were developed. Patient studies were performed by including 30 children with ALL at diagnosis, 3 children with bone marrow relapse, and 15 children with no symptoms of cancer. The mRNA expression profiles of SORCIN and MDR1/P-gp was assessed using quantitative polymerase chain reaction (qPCR). Minimal residual disease (MRD) was measured in the patient population, a year following the initial therapy using qPCR.

RESULTS

Cell line data analyses showed a positive correlation between SORCIN mRNA levels and resistance to MTX. The difference between patient and control groups for SORCIN expression levels was not significant. However, patients with a negative response to therapy showed an increase in SORCIN mRNA levels (up to 6.8-fold) compared with those with negative MRD. In addition, the results demonstrated a significant positive correlation between SORCIN and MDR1/P-gp gene expression levels.

CONCLUSION

The current study introduces, for the first time, a possible prognostic value of SORCIN in childhood ALL, which may be correlated with MDR1/P-gp gene expression in these patients.

mRNA overexpression of BAALC: A novel prognostic factor for pediatric acute lymphoblastic leukemia

BAALC is a novel molecular marker in leukemia that is highly expressed in patients with acute leukemia. Increased expression levels of BAALC are known as poor prognostic factors in adult acute myeloid and lymphoid leukemia. The purpose of the present study was to evaluate the prognostic significance of the BAALC gene expression levels in pediatric acute lymphoblastic leukemia (ALL) and its association with MDR1. Using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), the mRNA expression levels of BAALC and MRD1 were measured in bone marrow samples of 28 new diagnosed childhood ALL patients and 13 children without cancer. Minimal residual disease (MRD) was measured one year after the initiation of the chemotherapy using the RT-qPCR method. The high level expression of BAALC had a significant association with the pre-B-ALL subtype, leukocytosis and positive MRD after one year of treatment in leukemic patients. In addition, a positive correlation between BAALC and MDR1 mRNA expression was shown in this group. In conclusion, to the best of our knowledge, the increase of BAALC expression as a poor prognostic factor for childhood ALL is shown for the first time. Additionally, the correlation between BAALC and MDR1 in mRNA expression levels can aid for an improved understanding of the mechanism through which BAALC may function in ALL and multidrug resistance.

Glutathione S-transferase and MRP1 form an integrated system involved in the storage and transport of dinitrosyl-dithiolato iron complexes in cells

Nitrogen monoxide (NO) is vital for many essential biological processes as a messenger and effector molecule. The physiological importance of NO is the result of its high affinity for iron in the active sites of proteins such as guanylate cyclase. Indeed, NO possesses a rich coordination chemistry with iron and the formation of dinitrosyl-dithiolato iron complexes (DNICs) is well documented. In mammals, NO generated by cytotoxic activated macrophages has been reported to play a role as a cytotoxic effector against tumor cells by binding and releasing intracellular iron. Studies from our laboratory have shown that two proteins traditionally involved in drug resistance, namely multidrug-resistance protein 1 and glutathione S-transferase, play critical roles in intracellular NO transport and storage through their interaction with DNICs (R.N. Watts et al., Proc. Natl. Acad. Sci. USA 103:7670-7675, 2006; H. Lok et al., J. Biol. Chem. 287:607-618, 2012). Notably, DNICs are present at high concentrations in cells and are biologically available. These complexes have a markedly longer half-life than free NO, making them an ideal "common currency" for this messenger molecule. Considering the many critical roles NO plays in health and disease, a better understanding of its intracellular trafficking mechanisms will be vital for the development of new therapeutics.

Pharmacogenetics of childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. Although treatment outcome has improved owing to advances in chemotherapy, there is still a group of patients for which therapy fails while some patients experience severe toxicity. In the last few years, several pharmacogenetic studies have been performed to search for markers of outcome and toxicity in pediatric ALL. However, to date, TPMT is the only pharmacogenetic marker in ALL with clinical guidelines for drug dosing. In this article, we will provide an overview of the most important findings carried out in pharmacogenetics for pediatric ALL, such as the interest drawn by methotrexate transporters in the context of methotrexate treatment. Even if most of the studies are centered on coding genes, we will also point to new approaches focusing on noncoding regions and epigenetic variation that could be interesting for consideration in the near future.

Bone marrow neoplastic niche in leukemia

OBJECTIVES

Neoplastic niche is a specific microenvironment for growth and proliferation of malignant cells. Here we review the leukemic niche and its constituent stem cells, signaling pathways and essential chemokines.

METHODS

Relevant literature was identified by a PubMed search (2000-2013) of English-language literature using the terms neoplastic niche, chemokines, and leukemia.

DISCUSSION

Leukemia is caused by malignant hematopoietic stem cells and precursors. Important molecules and signals are involved in interactions between leukemic cells and their microenvironment. MicroRNAs (miRNAs) play an important role in expression regulation of oncogenes, transcription factors, signaling molecules and in eventual fate of the cell. It seems necessary to evaluate the relationship between aberrant miRNA expression and malignant transformation of bone marrow niche.

CONCLUSIONS

Characterizing malignant leukemic cells, activated signaling pathways, and molecules involved in disease progression will result in understanding the causes of drug resistance, relapse factors, and effective treatments.

Increased glutathione and mitogen-activated protein kinase phosphorylation are involved in the induction of doxorubicin resistance in hepatocellular carcinoma cells

AIM

  The human hepatocellular carcinoma (HCC) cell line HepG2 can easily acquire resistance to doxorubicin. However, the mechanism of action is unclear.

METHODS

  In the present study, we used confocal microscopy, flow cytometry and other methods to reveal the mechanisms by which HepG2 cells acquire doxorubicin resistance.

RESULTS

  Our results showed that R-HepG2 cells, a doxorubicin-resistant sub-line of HepG2, exhibited decreased intracellular accumulation of doxorubicin and increased expression of P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 when compared with HepG2 cells. R-HepG2 cells also harbored higher levels of glutathione and increased expression of glutathione peroxidase. Furthermore, we demonstrated that the phosphorylation of mitogen-activated protein kinases (p38 and c-jun-N-terminal kinases), IkBα and CREB were increased in R-HepG2 cells. Specific p38 inhibitor SB203580 decreased P-gp expression. The multi-kinase inhibitor sorafenib tosylate also significantly suppressed the phosphorylation of these proteins and inhibited the expression of P-gp.

CONCLUSION

  These findings reveal that the drug resistance could be acquired through mitogen-activated protein kinase-dependent upregulation of P-gp. This mechanism protects R-HepG2 cells from the anticancer action of doxorubicin.

Importance of detecting multidrug resistance proteins in acute leukemia prognosis and therapy

Multidrug resistance (MDR) is a multifactorial phenomenon and the role of these proteins in generating the MDR phenotype is controversial. With this in mind, this review compiled the current data on the role of ABCB1, ABCC1, and LRP proteins in the prognosis of hematologic neoplasms and their influence on the choice of therapy. Literature showed that the detection of these proteins, mainly ABCB1, is important in the AL prognosis. However, there is controversy regarding the methodology used for their detection. In summary, the expression and activity profiles of ABCB1, ABCC1, and LRP, proteins capable of promoting the efflux of a variety of chemotherapeutic agents from the cell cytoplasm represent one of the greatest causes of failure in AL treatment.

Oleanolic acid derivative methyl 3,11-dioxoolean-12-en-28-olate targets multidrug resistance related to ABCB1

Multidrug resistance (MDR) in leukemia patients is a great incentive to the development of new drugs. In a search for potential multidrug resistance modulators we tested a group of oleanolic acid (OA) analogues modified at C-3, C-11, C-12 and C-28 using an experimental model consisting of three human acute lymphoblastic leukemia cell lines (CCRF-CEM and the multidrug resistant sublines CCRF-VCR1000 and CCRF-ADR5000). The most effective compound, methyl 3,11-dioxoolean-12-en-28-olate (DIOXOL) was more potent in cell viability inhibition than its precursor - OA, and showed similar or even higher activity in the drug resistant than in the wild-type cells. Resistance factor (RF) values obtained for CCRF-VCR1000 and CCRF-ADR-5000 cells using MTT assay were 0.7 and 0.8 (24 h of treatment) and after 72 h of treatment 0.9 and 1.1, respectively. Moreover, 5 μM DIOXOL significantly reduced the expression of the ABCB1 gene in MDR cells by around 30%, and also decreased the level of P-gp protein. Compared to untreated control cells, DIOXOL treatment resulted in a significant P-gp decrease (30% in CCRF-ADR5000 and 50% in CCRF-VCR1000), that was detected by western blot and confirmed by flow cytometry analysis. Moreover, DIOXOL (at 10 μM) significantly inhibited P-gp transport function by more than twofold comparing to control, untreated cells that was demonstrated using rhodamine 123-based functional test. The compound exhibited synergistic activity with ABCB1 substrate - adriamycin in CCRF-VCR1000 cells, indicating partial but significant MDR reversing ability.

A systematic review and meta-analysis of MTHFR polymorphisms in methotrexate toxicity prediction in pediatric acute lymphoblastic leukemia

Methotrexate (MTX) is an important component of therapy used to treat childhood acute lymphoblastic leukemia (ALL). Two single-nucleotide polymorphisms (SNPs) in the methylenetetrahydrofolate reductase (MTHFR) gene, C677T and A1298C, affect MTHFR activity. A large body of studies has investigated the potential role of MTHFR SNPs in MTX toxicity in pediatric ALL. However, the results are controversial. In this review and meta-analysis, we critically evaluate the relationship between the C677T and A1298C polymorphisms of MTHFR and MTX toxicity in pediatric ALL. The majority of published reports do not find associations between MTHFR polymorphisms and toxicity in pediatric ALL. When associations are reported, often the results are contradictory to each other. The meta-analysis confirms a lack of association. In conclusion, MTHFR, C677T and A1298C polymorphisms do not seem to be good markers of MTX-related toxicity in pediatric ALL.

The pharmacogenetic basis of individual variation in thiopurine metabolism

Thiopurines are an important class of immunosuppressive therapy, which have been used in clinical practice for over 50 years. Despite this extensive experience many of the pharmacodynamic and pharmacokinetic properties of these drugs remain unknown. As a consequence there is often no clear explanation for the individual variation in response to treatment, both in terms of efficacy or adverse drug reactions. This review, which emphasizes practice in gastroenterology, summarizes the current understanding of thiopurine drug metabolism and highlights the role of nongenetic and genetic factors other than TPMT, which should be a focus for future research. Correlation of polymorphic variations in these genes with clinical outcomes is expected to clarify the basis for interindividual differences in thiopurine metabolism and enable a more personalized approach to therapy.

Flow cytometry-based assessment of mitoxantrone efflux from leukemic blasts varies with response to induction chemotherapy in acute myeloid leukemia

BACKGROUND

Accurate prediction of chemotherapy drug resistance would aid treatment decisions in acute myeloid leukemia (AML). The aim of this study was to determine if mitoxantrone efflux from AML blasts would correlate with response to induction chemotherapy.

METHODS

Flow cytometry was used to measure the median fluorescence intensity (MFI) for AML blasts incubated with mitoxantrone [an ATP-binding cassette (ABC) transporter substrate] with or without coincubation with cyclosporine A (a broad-spectrum inhibitor of ABC transporters) and a ratio (MFIR) between the inhibited and uninhibited MFI was calculated.

RESULTS

Among 174 AML patient blast samples, the mean MFIR for complete remission (CR) patients was lower than that obtained for induction failure (IF) patients (mean MFIR ± SD 1.62 ± 0.53 for CR after one cycle of chemotherapy vs. 2.22 ± 1.29 for CR after two cycles and 2.59 ± 0.98 for IF, P < 0.001). Logistic regression analysis determined 2.45 as the MFIR threshold above which 29% of patients achieved CR vs. a CR rate of 84% when the MFIR was ≤ 2.45 (P < 0.0001). In AML patients with normal karyotype (n = 80), CR was obtained for 33% of patients with an MFIR > 2.45 vs. 89% of those with MFIR ≤ 2.45 (P < 0.0001). In patients > age 60 (n = 77), 30% vs. 87% of those with MFIR > vs. ≤ 2.45 achieved CR (P < 0.0001).

CONCLUSIONS

This assay of ABC transporter function can potentially predict response to induction chemotherapy in AML.

Apatinib (YN968D1) enhances the efficacy of conventional chemotherapeutical drugs in side population cells and ABCB1-overexpressing leukemia cells

P-glycoprotein (P-gp, ABCB1) overexpression and enrichment of stem-like cells are linked to poor prognosis in tumor patients. In this study, we investigated the effect of apatinib, an oral multi-targeted tyrosine kinase inhibitor (TKI) on enhancing the efficacy of conventional anticancer drugs in side population (SP) cells and ABCB1-overexpressing leukemia cells in vitro, in vivo and ex vivo. Our results showed that apatinib significantly enhanced the cytotoxicity and cell apoptosis induced by doxorubicin in SP cells sorted from K562 cells. Furthermore, apatinib also strongly reversed multidrug resistance (MDR) in K562/ADR cells, and the primary leukemia blasts overexpressing ABCB1 while showed no synergistic interactions with chemotherapeutic agents in MRP1-, MRP4-, MRP7- and LRP-overexpressing cells. Apatinib treatment markedly increased the intracellular accumulation of doxorubicin and rhodamine 123 in K562/ADR cells and the accumulation of rhodamine 123 in the primary leukemia blasts with ABCB1 overexpression. Apatinib stimulated the ATPase activity of P-gp in a dose-dependent manner but did not alter the expression of ABCB1 at both mRNA and protein levels. The phosphorylation level of AKT and ERK1/2 remained unchanged after apatinib treatment in both sensitive and MDR cells. Importantly, apatinib significantly enhanced the antitumor activity of doxorubicin in nude mice bearing K562/ADR xenografts. Taken together, our results suggest that apatinib could target to SP cells and ABCB1-overexpressing leukemia cells to enhance the efficacy of chemotherapeutic drugs. These findings should be useful for the combination of apatinib and chemotherapeutic agents in the clinic.

Polymorphisms of the SLCO1B1 gene predict methotrexate-related toxicity in childhood acute lymphoblastic leukemia

BACKGROUND

Methotrexate (MTX) is an important component of the therapy for childhood acute lymphoblastic leukemia. Treatment with high-dose MTX often causes toxicity, recommending a dose reduction and/or cessation of treatment. Polymorphisms in genes involved in the MTX metabolism have been associated with toxicity with controversial results. The discrepancies could be due to differences in treatment protocols among studies, small, or non-homogeneous populations or the use of different toxicity criteria. The aim of the present study was to analyze the possible correlation of polymorphisms of genes involved in the MTX metabolism with the toxicity during therapy with the well-established LAL/SHOP protocol.

PROCEDURE

We analyzed 10 polymorphisms in seven genes (MTHFR, TS, SHMT1, RFC1, ABCB1, ABCG2, and SLCO1B1) from the MTX metabolism in 115 Spanish pediatric B-ALL patients, using MTX plasma concentration as an objective and quantifiable marker of toxicity.

RESULTS

We confirmed the suitability of MTX plasma levels as a toxicity marker. We found a statistically significant association between MTX plasma concentration and the SLCO1B1 rs11045879 CC genotype (P = 0.030). The rs4149081 AA genotype, in the same gene, could also be an indicator for high-MTX plasma concentrations. We did not find any significant association in the other genetic polymorphisms analyzed.

CONCLUSIONS

Identification of the rs4149081 and rs11045879 SLCO1B1 polymorphisms in children with ALL could be a useful tool for monitoring patients at risk of low-MTX clearance in order to avoid MTX-related toxicity.

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.

Resistance to the translation initiation inhibitor silvestrol is mediated by ABCB1/P-glycoprotein overexpression in acute lymphoblastic leukemia cells

Protein synthesis is a powerful therapeutic target in leukemias and other cancers, but few pharmacologically viable agents are available that affect this process directly. The plant-derived agent silvestrol specifically inhibits translation initiation by interfering with eIF4A/mRNA assembly with eIF4F. Silvestrol has potent in vitro and in vivo activity in multiple cancer models including acute lymphoblastic leukemia (ALL) and is under pre-clinical development by the US National Cancer Institute, but no information is available about potential mechanisms of resistance. In a separate report, we showed that intraperitoneal silvestrol is approximately 100% bioavailable systemically, although oral doses were only 1% bioavailable despite an apparent lack of metabolism. To explore mechanisms of silvestrol resistance and the possible role of efflux transporters in silvestrol disposition, we characterized multi-drug resistance transporter expression and function in a silvestrol-resistant ALL cell line generated via culture of the 697 ALL cell line in gradually increasing silvestrol concentrations. This resistant cell line, 697-R, shows significant upregulation of ABCB1 mRNA and P-glycoprotein (Pgp) as well as cross-resistance to known Pgp substrates vincristine and romidepsin. Furthermore, 697-R cells readily efflux the fluorescent Pgp substrate rhodamine 123. This effect is prevented by Pgp inhibitors verapamil and cyclosporin A, as well as siRNA to ABCB1, with concomitant re-sensitization to silvestrol. Together, these data indicate that silvestrol is a substrate of Pgp, a potential obstacle that must be considered in the development of silvestrol for oral delivery or targeting to tumors protected by Pgp overexpression.

In vitro and in vivo evidence for the importance of breast cancer resistance protein transporters (BCRP/MXR/ABCP/ABCG2)

The breast cancer resistance protein (BCRP/ABCG2) is a member of the G-subfamiliy of the ATP-binding cassette (ABC)-transporter superfamily. This half-transporter is assumed to function as an important mechanism limiting cellular accumulation of various compounds. In context of its tissue distribution with localization in the sinusoidal membrane of hepatocytes, and in the apical membrane of enterocytes ABCG2 is assumed to function as an important mechanism facilitating hepatobiliary excretion and limiting oral bioavailability, respectively. Indeed functional assessment performing mouse studies with genetic deletion or chemical inhibition of the transporter, or performing pharmacogenetic studies in humans support this assumption. Furthermore the efflux function of ABCG2 has been linked to sanctuary blood tissue barriers as described for placenta and the central nervous system. However, in lactating mammary glands ABCG2 increases the transfer of substrates into milk thereby increasing the exposure to potential noxes of a breastfed newborn. With regard to its broad substrate spectrum including various anticancer drugs and environmental carcinogens the function of ABCG2 has been associated with multidrug resistance and tumor development/progression. In terms of cancer biology current research is focusing on the expression and function of ABCG2 in immature stem cells. Recent findings support the notion that the physiological function of ABCG2 is involved in the elimination of uric acid resulting in higher risk for developing gout in male patients harboring genetic variants. Taken together ABCG2 is implicated in various pathophysiological and pharmacological processes.

Acute lymphoblastic leukemia cells that survive combination chemotherapy in vivo remain sensitive to allogeneic immune effects

Allogeneic hematopoietic stem cell transplantation is often performed for patients with acute lymphoblastic leukemia (ALL) whose disease has relapsed after chemotherapy treatment. However, graft versus leukemia (GVL) effects in ALL are generally weak and the mechanisms of this weakness are unknown. These studies tested the hypothesis that ALL cells that have survived conventional chemotherapy in vivo acquire relative resistance to the allogeneic GVL effect. C57BL/6 mice were injected with murine pre-B ALL lines driven by human mutations and then were treated with combination chemotherapy. ALL cells surviving therapy were analysed in vitro and in vivo for acquisition of resistance to chemotherapy, radiation, cytolytic T cells, NK cells, LAK cells and cytokines. In vivo drug treatment did lead to leukemia population with more rapid proliferation and also decreased sensitivity to vincristine, doxorubicin and radiation. However, drug treatment did not produce ALL populations that were less sensitive to GVL effects in vitro or in vivo.

Drug transporter pharmacogenetics in nucleoside-based therapies

This article focuses on the different types of transporter proteins that have been implicated in the influx and efflux of nucleoside-derived drugs currently used in the treatment of cancer, viral infections (i.e., AIDS) and other conditions, including autoimmune and inflammatory diseases. Genetic variations in nucleoside-derived drug transporter proteins encoded by the gene families SLC15, SLC22, SLC28, SLC29, ABCB, ABCC and ABCG will be specifically considered. Variants known to affect biological function are summarized, with a particular emphasis on those for which clinical correlations have already been established. Given that relatively little is known regarding the genetic variability of the players involved in determining nucleoside-derived drug bioavailability, it is anticipated that major challenges will be faced in this area of research.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

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.

mRNA expression profile of multidrug resistance genes in childhood acute lymphoblastic leukemia. Low expression levels associated with a higher risk of toxic death

BACKGROUND

Increased activity of multidrug resistance (MDR) genes has been associated with treatment failure in acute leukemias, although with controversial reports. The objective of the present study was to assess the expression profile of the genes related to MDR: ABCB1, ABCC1, ABCC3, ABCG2, and LRP/MVP in terms of the clinical and biological variable and the survival of children with acute lymphoblastic leukemia (ALL).

PROCEDURE

The levels of mRNA expression of the drug resistance genes ABCB1, ABCC1, ABCC3, ABCG2, and LRP/MVP were analyzed by quantitative real-time PCR using the median values as cut-off points, in consecutive samples from 140 children with ALL at diagnosis.

RESULTS

Expression levels of the ABCG2 gene in the patient group as a whole (P = 0.05) and of the ABCG2 and ABCC1 genes in patients classified as being at high risk were associated with higher rates of 5-year event-free survival (EFS) (P = 0.04 and P = 0.01). Expression levels of the ABCG2 gene below the median were associated with a greater chance of death related to treatment toxicity for the patient group as a whole (P = 0.009) and expression levels below the median of the ABCG2 and ABCC1 genes were associated with a greater chance of death due to treatment toxicity for the high-risk group (P = 0.02 and P = 0.03, respectively).

CONCLUSION

The present data suggest a low participation of the drug efflux genes in treatment failure in patients with childhood ALL. However, the low expression of some of these genes may be associated with a higher death risk related to treatment toxicity.

Advances in individual prediction of methotrexate toxicity: a review

As the cure rates for haematological malignancies have improved, the exploration of the balance between efficacy and side effects has become a major research target. The antifolate methotrexate is widely used in the treatment of acute lymphoblastic leukaemia, non-Hodgkin lymphoma, and osteosarcoma. Even when given identical methotrexate doses, patients vary significantly in their response and pattern of toxicities. This diversity can, to some extent, be linked to sequence variations in genes involved in drug absorption, metabolism, excretion, cellular transport, and effector targets or target pathways. In the coming years pharmacogenomics is expected to change our approaches to individualised therapy with methotrexate. However, genetic polymorphisms affect the pharmacokinetics and dynamics of all the drugs a patient receive as well as the normal tissues tolerance to a given drug exposure. Thus, although high-throughput techniques will allow mapping of tens of thousands of genetic polymorphisms in one run, it will be a major challenge to dissect out which of these have the strongest impact on efficacy and toxicity and hence should be the targets for intervention. This paper discusses the pharmacology of methotrexate and reviews studies on haematological malignancies that have attempted to predict the risk of toxicity by specific clinical or genetic features.

Expression of ABCC-type nucleotide exporters in blasts of adult acute myeloid leukemia: relation to long-term survival

PURPOSE

Successful treatment of acute myeloid leukemia (AML) remains a therapeutic challenge, with a high percentage of patients suffering from persistent or relapsed disease. Resistance to drug therapy can develop from increased drug export and/or altered intracellular signaling. Both mechanisms are mediated by the efflux transporters ABCC4 (MRP4), ABCC5 (MRP5), and ABCC11 (MRP8), which are involved in cellular efflux of endogenous signaling molecules (e.g., cyclic adenosine 3', 5'-monophosphate and cyclic guanosine 3',5'-monophosphate) and nucleoside analogues. The nucleoside analogue cytosine arabinoside (AraC) is administered to all patients with AML.

EXPERIMENTAL DESIGN

Expression of ABCC transporters MRP4, MRP5, and MRP8 in blast samples from 50 AML patients was investigated by real-time reverse transcription-PCR analysis and correlated with clinical outcome measures. Accumulation of radiolabeled AraC, transport of AraC metabolites, and AraC cytotoxicity were analyzed in MRP8-transfected LLC-PK1 cells.

RESULTS

Regression analysis revealed that high expression of MRP8 is associated with a low probability of overall survival assessed over 4 years (P<0.03). MRP8-transfected LLC-PK1 cells accumulated reduced intracellular levels of AraC (63% of the parental vector-transfected LLC-PK1 control cells) as well as AraC metabolites. Furthermore, AraC monophosphate was transported by MRP8-enriched membrane vesicles (116+/-6 versus 65+/-13 pmol/mg/10 minutes by control vesicles), and MRP8-transfected cells were resistant to AraC.

CONCLUSION

These data suggest that MRP8 is differentially expressed in AML blasts, that expression of MRP8 serves as a predictive marker for treatment outcome in AML, and that efflux of AraC metabolites by MRP8 is a mechanism that contributes to resistance of AML blasts.

Chemo-sensitivity in a panel of B-cell precursor acute lymphoblastic leukemia cell lines, YCUB series, derived from children

Sensitivity to 10 anticancer drugs was evaluated in 6 childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) cell lines. Authenticity of newly established cell lines was confirmed by genomic fingerprinting. The line YCUB-5R established at relapse was more resistant to 4-hydroperoxy-cyclophosphamide, cytarabine, L-asparaginase, topotecan, fludarabine, and etoposide than YCUB-5 from the same patient at diagnosis. Of the drugs tested, etoposide and SN-38 (irinotecan) showed highest efficacy in the panel, with 50% growth inhibition at 0.22-1.8 microg/ml and 0.57-3.6 ng/ml, respectively. This cell line panel offers an in vitro model for the development of new therapies for childhood BCP-ALL.

CD34 expression is associated with poor survival in pediatric T-cell acute lymphoblastic leukemia

BACKGROUND

Children with T-lineage acute lymphoblastic leukemia (T-ALL) have an inferior outcome with combination chemotherapy compared to B-lineage ALL, and still about 30% of the patients relapse within the first 2 years following diagnosis. As CD34 has been related with poor outcome in ALL in general, we investigated the prognostic significance of the stem cell marker CD34, as well as the association of CD34 positivity with the expression of several multidrug resistance (MDR) genes.

PROCEDURE

In this retrospective study, we investigated the prognostic significance of the expression of the early T-cell differentiation marker CD34 and the expression of MDR genes in relation to outcome in a cohort of 72 newly diagnosed pediatric T-ALL patients.

RESULTS

CD34 expression was related to a poor 5-year disease-free-survival and a poor 5-year overall survival. Using the Cox proportional hazard model, CD34 expression predicted for increased risk for relapse and death. Expression of CD34 was associated with elevated MDR1 and MRP1 mRNA expression levels. For the entire T-ALL cohort, these expression levels of MDR1 or MRP1 did not independently predict for poor outcome.

CONCLUSIONS

We conclude that CD34-positive T-ALL has a relatively poor survival that is not explained by the mRNA expression levels of MDR1, LRP, or MRP1.

Pharmacogenetics influence treatment efficacy in childhood acute lymphoblastic leukemia

Pharmacogenetics covers the genetic variation affecting pharmacokinetics and pharmacodynamics, and their influence on drug-response phenotypes. The genetic variation includes an estimated 15 million single nucleotide polymorphisms (SNPs) and is a key determinator for the interindividual differences in treatment resistance and toxic side effects. As most childhood acute lymphoblastic leukemia treatment protocols include up to 13 different chemotherapeutic agents, the impact of individual SNPs has been difficult to evaluate. So far focus has mainly been on the widely used glucocorticosteroids, methotrexate, and thiopurines, or on metabolic pathways and transport mechanisms that are common to several drugs, such as the glutathione S-transferases. However, beyond the thiopurine methyltransferase polymorphisms, the candidate-gene approach has not established clear associations between polymorphisms and treatment response. In the future, high-throughput, low-cost, genetic platforms will allow screening of hundreds or thousands of targeted SNPs to give a combined gene-dosage effect (=individual SNP risk profile), which may allow pharmacogenetic-based individualization of treatment.

Chemotoxicity recovery of mitochondria in non-Hodgkin lymphoma resulting in minimal residual disease

BACKGROUND

The mechanisms responsible for resistant disease or recurrence of non-Hodgkin lymphoma (NHL) in children cover a wide spectrum from drug resistance to genetic mutations. A unique mechanism suggesting the role of mitochondria as the key energy source is studied following a clinical observation where pediatric Burkitt lymphoma (BL) specimens from patients on therapy were found to have increased copies of mitochondria DNA (mtDNA) in specimens which were shown to be positive for minimal residual disease and/or persistent disease (MRD/PD). This study hypothesized that the mitochondria play an important role in a cell's recovery from toxicity via a compensatory increase in mtDNA.

PROCEDURE

BL specimens with MRD/PD were assayed for mtDNA. An in vitro model was then designed using Ramos cell lines by exposing the lymphoma cells to varying concentrations of doxorubicin and vincristine for 1 hr; and allowing for recovery in culture over 7 days. DNA was extracted from aliquots over several days to determine mtDNA copy numbers by real-time polymerase chain reaction (PCR).

RESULTS

Increased mtDNA copy numbers were found in clinical specimens with MRD/PD as well as in recovering Ramos cells from chemotoxicity.

CONCLUSIONS

The recovering lymphoma cells from the chemotoxic effects appeared to compensate by increasing mtDNA content, which may contribute to the clinical residual or resistant disease in some cases of childhood BL.

Multi-functional nanocarriers to overcome tumor drug resistance

The development of resistance to variety of chemotherapeutic agents is one of the major challenges in effective cancer treatment. Tumor cells are able to generate a multi-drug resistance (MDR) phenotype due to microenvironmental selection pressures. This review addresses the use of nanotechnology-based delivery systems to overcome MDR in solid tumors. Our own work along with evidence from the literature illustrates the development of various types of engineered nanocarriers specifically designed to enhance tumor-targeted delivery through passive and active targeting strategies. Additionally, multi-functional nanocarriers are developed to enhance drug delivery and overcome MDR by either simultaneous or sequential delivery of resistance modulators (e.g., with P-glycoprotein substrates), agents that regulate intracellular pH, agents that lower the apoptotic threshold (e.g., with ceramide), or in combination with energy delivery (e.g., sound, heat, and light) to enhance the effectiveness of anticancer agents in refractory tumors. In preclinical studies, the use of multi-functional nanocarriers has shown significant promise in enhancing cancer therapy, especially against MDR tumors.

The changing scene of adult acute lymphoblastic leukemia

PURPOSE OF REVIEW

The review focuses on the most recent advances in the diagnostic and prognostic work-up of adult acute lymphoblastic leukemia (ALL) and its implications in the clinical management of the disease.

RECENT FINDINGS

ALL can be identified on the basis of morphologic, cytochemical and immunophenotypic criteria; modern management of ALL is also based on cytogenetic and genetic evaluations. New technologies, such as gene expression profile analysis, may allow us to further unravel the intrinsic biology of the disease, to improve diagnostic and prognostic stratification, and to design innovative therapeutic strategies. In potentially all cases, specific markers of the disease can be found and utilized together with the rearrangement of immunoglobulin and T-cell receptor genes to monitor minimal residual disease during clinical follow-up. These biologically-defined subgroups of patients may have a different clinical course, response to treatment and variable prognosis.

SUMMARY

Recent biologic advancements are progressively realising the possibility of designing targeted and individualized therapeutic strategies according to the more refined, molecularly defined features of leukemic cells and the presence or absence of residual disease in adult ALL.

Natural triterpenoids from Cecropia lyratiloba are cytotoxic to both sensitive and multidrug resistant leukemia cell lines

The cytotoxicity of four triterpenoids, euscaphic acid (1), tormentic acid (2), 2alpha-acetyl tormentic acid (3), and 3beta-acetyl tormentic acid (4), isolated from the roots of Cecropia lyratiloba (Moraceae) by countercurrent chromatography, was evaluated in vitro in sensitive and multidrug resistant leukemia cell lines. A structure/activity relationship analysis of the compounds was performed. Acetylation of compound 2 at C2 increased its activity by a factor of 2 while acetylation at C3 had a smaller effect. Compound 1 induces death by activation of caspase-3, dependent apoptotic pathway. Furthermore, the four triterpenoids were also active toward a multidrug resistant (MDR) leukemia cell line, overexpressing glycoprotein-P (P-gp). These results reveal the potential of the terpenoids as source for the development of new anti-neoplastic and anti-MDR drugs.

A role for altered microtubule polymer levels in vincristine resistance of childhood acute lymphoblastic leukemia xenografts

The microtubule-depolymerizing drug, vincristine, is effective in the treatment of acute lymphoblastic leukemia (ALL). Although vincristine resistance mechanisms have been extensively characterized in cell lines, their clinical relevance is poorly understood. The aim of the current study was to define clinically relevant mechanisms of vincristine resistance in a panel of childhood ALL xenografts established in immune-deficient (nonobese diabetic/severe combined immunodeficient) mice. We also studied two independent xenograft sublines that were selected by in vivo vincristine exposure. In vitro vincristine sensitivity determined by a stromal coculture, murine bone marrow stromal cell line (MS-5), assay, but not methyl-thiazolyl-tetrazolium metabolic activity assay, significantly correlated (P = 0.05) with the length of the patients' first remission. Investigations into mechanisms of resistance revealed no association with steady-state vincristine accumulation or increased activity and/or expression of ATP-binding cassette transporters, although increased intracellular levels of polymerized tubulin significantly correlated with resistance (r = 0.85; P = 0.0019). Two xenograft sublines selected by in vivo vincristine exposure exhibited a 2-fold increase in polymerized tubulin levels compared with the parental subline (P < 0.05), reflecting their in vivo vincristine resistance. In this study, a vincristine-resistant xenograft with high levels of polymerized tubulin was relatively sensitive to the microtubule-polymerizing drug paclitaxel. These results indicate that the balance between polymerized and nonpolymerized tubulin may be an important determinant of response to Vinca alkaloid-based chemotherapy regimens in childhood ALL.

Expression of adenosine triphosphate-binding cassette (ABC) drug transporters in peripheral blood cells: relevance for physiology and pharmacotherapy

Adenosine triphosphate-binding cassette (ABC)-type transport proteins were initially described for their ability to reduce intracellular concentrations of anticancer compounds, thereby conferring drug resistance. In recent years, expression of this type of proteins has also been reported in numerous cell types under physiological conditions; here, these transporters are often reported to alter systemic and local drug disposition (e.g. in the brain or the gastrointestinal tract). In this context, peripheral blood cells have also been found to express several ABC-type transporters. While erythrocytes mainly express multidrug resistance protein (MRP) 1, MRP4 and MRP5, which are discussed with regard to their involvement in glutathione homeostasis (MRP1) and in the efflux of cyclic nucleotides (MRP4 and MRP5), leukocytes also express P-glycoprotein and breast cancer resistance protein. In the latter cell types, the main function of efflux transporters may be protection against toxins, as these cells demonstrate a very high turnover rate. In platelets, only two ABC transporters have been described so far. Besides MRP1, platelets express relatively high amounts of MRP4 not only in the plasma membrane but also in the membrane of dense granules, suggesting relevance for mediator storage. In addition to its physiological function, ABC transporter expression in these structures can be of pharmacological relevance since all systemic drugs reach their targets via circulation, thereby enabling interaction of the therapeutic agent with peripheral blood cells. Moreover, both intended effects and unwanted side effects occur in peripheral blood cells, and intracellular micropharmacokinetics can be affected by these transport proteins. The present review summarises the data available on expression of ABC transport proteins in peripheral blood cells.