Treatment of poor prognosis AML patients using PSC833 (valspodar) plus mitoxantrone, etoposide, and cytarabine (PSC-MEC)

A New ABCB1 Inhibitor Enhances the Anticancer Effect of Doxorubicin in Both In Vitro and In Vivo Models of NSCLC

In tumors, the multi drug resistance phenomenon may occur through the efflux of chemotherapeutic drugs out of cancer cells, impeding their accumulation, and eventually reducing their toxicity. This process is mediated by transporters overexpressed in the plasma membranes of tumor cells, among which is the P-glycoprotein/multidrug resistance 1/ATP-binding cassette B1 (P-gp/MDR1/ABCB1). The aim of this study was to explore the effect of a new molecule, called AIF-1, on ABCB1 activity. In a cellular model of non-small cell lung cancer (NSCLC), AIF-1 significantly inhibited ABCB1 activity, which was evaluated by the fluorimetric measurement of the intracellular accumulation of calcein. AIF-1 also significantly increased the intracellular content of doxorubicin, which was evaluated by confocal microscopy and LC-MS/MS analysis. This effect translated to higher cytotoxicity of doxorubicin and reduced cellular proliferation. Finally, in a murine xenograft model, the tumor volume increased by 267% and 148% on average in mice treated with vehicle and doxorubicin alone, respectively. After the co-administration of doxorubicin with AIF-1, tumor volume increased by only 13.4%. In conclusion, these results suggest enhancement of the efficacy of the chemotherapeutic drug doxorubicin by AIF-1, laying the basis for the future development of new ABCB1 inhibitors for tumor treatment.

Clinical Perspective of FDA Approved Drugs With P-Glycoprotein Inhibition Activities for Potential Cancer Therapeutics

P-glycoprotein (also known as multidrug resistance protein 1 (MDR1) or ATP-binding cassette sub-family B member 1 (ABCB1) plays a crucial role in determining response against medications, including cancer therapeutics. It is now well established that p-glycoprotein acts as an ATP dependent pump that pumps out small molecules from cells. Ample evidence exist that show p-glycoprotein expression levels correlate with drug efficacy, which suggests the rationale for developing p-glycoprotein inhibitors for treatment against cancer. Preclinical and clinical studies have investigated this possibility, but mostly were limited by substantial toxicities. Repurposing FDA-approved drugs that have p-glycoprotein inhibition activities is therefore a potential alternative approach. In this review, we searched the Drugbank Database (https://www.drugbank.ca/drugs) and identified 98 FDA-approved small molecules that possess p-glycoprotein inhibition properties. Focusing on the small molecules approved with indications against non-cancer diseases, we query the scientific literature for studies that specifically investigate these therapeutics as cancer treatment. In light of this analysis, potential development opportunities will then be thoroughly investigated for future efforts in repositioning of non-cancer p-glycoprotein inhibitors in single use or in combination therapy for clinical oncology treatment.

Prevalence of p-glycoprotein (PGP) expression, function and its effect on efficacy of rifampicin in patients with lymph node tuberculosis

OBJECTIVE

P-glycoprotein (PGP) overexpression may be one of the operating mechanisms of suboptimal responses to antitubercular treatment (ATT) in patients with lymph node tuberculosis. This might become responsible for the development of drug resistance later due to exposure of subtherapeutic concentrations to the mycobacteria. In this study we aim to study the prevalence of PGP expression and function and its relationship with serum concentrations of Rifampicin in consecutive patients with lymph node tuberculosis.

METHODS

All newly diagnosed treatment naïve subjects with a confirmed diagnosis of tubercular lymphadenopathy were included in the study and the expression and function of PGP in blood was determined by flowcytometry at baseline and after two months of treatment. Serum levels of Rifampicin was measured at 2 months by high performance liquid chromatography (HPLC). The mean net PGP expression expressed as percent and relative fluorescence indices (RFI) of PGP expression and function respectively was compared at baseline at 2 months and was also correlated with serum rifampicin levels.

RESULTS

The mean net PGP expression, RFI of PGP expression and RFI of PGP function were significantly higher in patients with lymph node tuberculosis as compared to healthy controls and the mean net PGP expression and RFI of PGP expression were significantly higher at 2 months as compared to baseline (25.64 ± 5.18% vs. 27.68 ± 4.89%, 4.34 ± 1.09% vs. 4.95 ± 1.55). There was no significant difference in RFI of PGP expression and RFI of PGP function between the poor-responders and responders at baseline and 2 months however there was a trend towards significantly higher net PGP expression amongst poor responders at baseline. The mean serum rifampicin levels were 10.74 ± 2.36 μg/ml in the responder group and 7.86 ± 1.21 μg/ml in the non-responder group and the difference between the two was statistically significant (p = 0.004).

CONCLUSIONS

Overexpression of PGP is common in patients with lymph node tuberculosis and leads to lower concentrations of Rifampicin in blood which subsequently may give rise to development of drug resistance. This is also responsible for poor therapeutic responses in these patients. Nonspecific inhibitors of PGP may be used in conjunction with ATT to augment therapeutic response in such cases.

Role of P-glycoprotein on CD69+CD4+ cells in the pathogenesis of proliferative lupus nephritis and non-responsiveness to immunosuppressive therapy

Introduction

P-glycoprotein (P-gp) expression on activated lymphocytes in systemic lupus erythematosus (SLE) plays a role in active efflux of intracellular drugs, resulting in drug resistance. The role of P-gp-expressing lymphocytes in the pathogenesis of SLE remains unclear. The aim of this study was to determine the importance of P-gp⁺CD4⁺ cells in organ manifestations in refractory SLE.

Methods

The proportion of P-gp⁺CD4⁺ cells was determined by flow cytometry in peripheral blood of patients with SLE (n=116) and healthy adults (n=10). Renal biopsy specimens were examined by immunohistochemistry for P-gp expression.

Results

CD69 is a marker of CD4 cell activation. The proportion of both P-gp-expressing CD4⁺ cells and CD69-expressing CD4⁺ cells in peripheral blood was higher in SLE than control. The proportion of P-gp⁺CD69⁺CD4⁺ cells correlated with Systemic Lupus Erythematosus Disease Activity Index and was higher in poor responders to corticosteroids. Furthermore, the proportion of P-gp⁺CD69⁺CD4⁺ cells was significantly higher in proliferative lupus nephritis (LN) with poor response to corticosteroids. The efficacy of immunosuppressive therapy depended on the regulation of the proportion of P-gp⁺CD69⁺CD4⁺ cells. Marked accumulation of P-gp⁺CD4⁺ cells in renal interstitial tissue and high proportion of peripheral P-gp⁺CD69⁺CD4⁺ cells were noted in patients with proliferative LN.

Conclusions

The results showed high proportion of P-gp⁺CD69⁺CD4⁺ cells in peripheral blood and their accumulation in renal tissue in patients with proliferative LN refractory to CS therapy, suggesting that P-gp expression on activated CD4⁺ T cells is a potentially useful marker for refractoriness to treatment and a novel target for treatment.

Relevance of P-glycoprotein on CXCR4+ B cells to organ manifestation in highly active rheumatoid arthritis

INTRODUCTION

In rheumatoid arthritis (RA), P-glycoprotein (P-gp) expression on activated B cells is associated with active efflux of intracellular drugs, resulting in drug resistance. CXCR4 is associated with migration of B cells. This study was designed to elucidate the relevance of P-gp expression on CXCR4⁺ B cells to clinical manifestations in refractory RA.

METHODS

CD19⁺ B cells were analyzed using flow cytometry and immunohistochemistry.

RESULTS

P-gp was highly expressed especially on CXCR4⁺CD19⁺ B cells in RA. The proportion of P-gp-expressing CXCR4⁺ B cells correlated with disease activity, estimated by Simplified Disease Activity Index (SDAI), and showed marked expansion in RA patients with high SDAI and extra-articular involvement. In highly active RA, massive infiltration of P-gp⁺CXCR4⁺CD19⁺ B cells was noted in CXCL12-expressing inflammatory lesions of RA synovitis and RA-associated interstitial pneumonitis. In RA patient with active extra-articular involvement, intracellular dexamethasone level (IDL) in lymphocytes diminished with expansion of P-gp⁺CXCR4⁺ CD19⁺ B cells. Adalimumab reduced P-gp⁺CXCR4⁺ CD19⁺ B cells, increased IDL in lymphocytes, and improved the clinical manifestation and allowed tapering of concomitant medications.

CONCLUSIONS

Expansion of P-gp⁺CXCR4⁺ B cells seems to be associated with drug resistance, disease activity and progressive destructive arthritis with extra-articular involvement in RA.

Persistent expression and function of P-glycoprotein on peripheral blood lymphocytes identifies corticosteroid resistance in patients with systemic lupus erythematosus

Corticosteroids (CS) are the mainstay of treatment in systemic lupus erythematosus (SLE) patients. However, some patients have poor response to CS treatment. Among the multiple mechanisms of CS resistance, overexpression of P-glycoprotein (P-gp) on peripheral blood lymphocytes (PBL) may be one of them as this result in efflux of CS from lymphocytes. Thus, we evaluated the role of P-gp protein on PBLs in patients with SLE in its response to CS therapy. SLE patients (n = 42) (fulfilling ACR revised criteria) who were naïve to CS and immunosuppressive drugs were enrolled. Disease activity was assessed using SLE disease activity index (SLEDAI) and expression, and function of P-gp was evaluated by flow cytometry at baseline and after 3 months of therapy with CS. At 3 months, patients with SLEDAI >4 and SLEDAI ≤4 were grouped as nonresponders and responders, respectively. P-gp expression was significantly increased on PBLs of SLE patients as compared to healthy controls (p < 0.001). P-gp expression and function correlated with SLEDAI (r = 0.49, p = 0.005; and r = 0.49, p = 0.001, respectively). P-gp expression and function were not different in responders and nonresponders at baseline. However, at 3 months of CS therapy, P-gp expression and function decreased in responders (p < 0.001 and p < 0.005, respectively), whereas in nonresponders, it remained unchanged. Persistent overexpression and activity of P-gp are associated with poor response to CS in CS naïve patients of SLE.

Treatment strategy based on targeting P-glycoprotein on peripheral lymphocytes in patients with systemic autoimmune disease

Although corticosteroids, immunosuppressants and disease-modifying antirheumatic drugs (DMARDs) are widely used in the treatment of various systemic autoimmune diseases such as systemic lupus erythematosus (SLE), we often experience patients with systemic autoimmune diseases who are resistant to these treatments. P-glycoprotein (P-gp) of membrane transporters, a product of the multiple drug resistance (MDR)-1 gene, is known to play a pivotal role in the acquisition of drug resistance to chemotherapy in malignancy. However, the relevance of MDR-1 and P-gp to resting and activated lymphocytes, which are the major target in the treatment of systemic autoimmune diseases, remains unclear. Studies from our laboratories found surface expression of P-gp on peripheral lymphocytes in patients with SLE and a significant correlation between the expression level and disease activity. Such expression is induced not only by genotoxic stresses but also by various stimuli including cytokines, resulting in active efflux of drugs from the cytoplasm of lymphocytes, resulting in drug-resistance and high disease activity. However, the use of both P-gp antagonists (e.g., cyclosporine) and inhibition of P-gp synthesis with intensive immunosuppressive therapy successfully reduces the efflux of corticosteroids from lymphocytes in vitro, suggesting that P-gp antagonists and P-gp synthesis inhibitors could be used to overcome drug-resistance in vivo and improve outcome. In conclusion, lymphocytes activated by various stimuli in patients with highly active disease apparently acquire MDR-1-mediated multidrug resistance against corticosteroids and probably some DMARDs, which are substrates of P-gp. Inhibition/reduction of P-gp could overcome such drug resistance. The expression of P-gp on lymphocytes is a promising marker of drug resistance and a suitable target to combat drug resistance in patients with active systemic autoimmune diseases.

Tacrolimus, a calcineurin inhibitor, overcomes treatment unresponsiveness mediated by P-glycoprotein on lymphocytes in refractory rheumatoid arthritis

OBJECTIVE

Tacrolimus, a calcineurin inhibitor, is used for treatment of rheumatoid arthritis (RA). It also inhibits functions of P-glycoprotein, which is involved in drug resistance. We examined the mechanisms of early response to 2-week tacrolimus treatment in patients with RA.

METHODS

One hundred thirteen patients with refractory RA despite at least 3 antirheumatic agents, including methotrexate, were treated with tacrolimus (1.5-3 mg/day) and the response was assessed at 2 weeks. Expression of the multidrug resistance (MDR-1) gene and P-glycoprotein was assessed in peripheral blood mononuclear cells (PBMC) collected from 113 patients and 40 healthy subjects. The drug exclusion function by the P-glycoprotein was measured by the residual amount of intracellular tritium-labeled dexamethasone cell/medium ratio (C/M ratio).

RESULTS

The disease activity of enrolled patients was 5.8 +/- 1.2 (mean +/- SD) by DAS28 erythrocyte sedimentation rate. A good response to tacrolimus was noted at 2 weeks in 22 of 113 patients. At baseline, PBMC of patients with RA showed upregulated expression of MDR-1 gene and P-glycoprotein and low C/M ratio. The response to tacrolimus correlated with P-glycoprotein expression and C/M ratio. A significant improvement in C/M ratio was noted after 2 weeks of treatment. The C/M ratio correlated significantly with P-glycoprotein expression on CD4+ lymphocytes.

CONCLUSION

Early efficacy of tacrolimus treatment depended on its inhibitory effect on the drug exclusion function of P-glycoprotein, leading to restoration of intracellular therapeutic levels of corticosteroids and clinical improvement. Evaluation of P-glycoprotein expression on lymphocytes is potentially useful for predicting the response to RA treatment.

Sequential phase II Southwest Oncology Group studies (S0112 and S0301) of daunorubicin and cytarabine by continuous infusion, without and with ciclosporin, in older patients with previously untreated acute myeloid leukaemia

Attempts to overcome multi-drug resistance in acute myeloid leukaemia (AML) have been limited by toxicities. To investigate the effect of reducing peak drug levels, we performed sequential phase II studies using continuous infusion daunorubicin and cytarabine without (AD) and then with ciclosporin (ADC) in older patients with AML. Untreated patients (age 56+ years) received daunorubicin (45 mg/m2 per day for 3 d) and cytarabine (200 mg/m2 per day for 7 d), both by continuous infusion, without (S0112, 60 patients) and then with (S0301, 50 patients) the addition of ciclosporin. Complete response (CR) rates were 38% on S0112 and 44% on S0301. Fatal induction toxicities occurred in 17% and 12% respectively, arising primarily from infection and haemorrhage. Median overall and relapse-free survival was 7 and 8 months for AD respectively, and 6 and 14 months for ADC. Patients with phenotypic or functional P-glycoprotein had somewhat higher CR rates with ADC than AD, although confidence intervals overlapped. In these sequential trials, continuous infusion AD produced CR rates comparable to those with bolus daunorubicin. The addition of ciclosporin did not cause undue toxicities, produced a similar CR rate, and possibly improved relapse-free survival. Further correlate analyses did not identify a subpopulation specifically benefitting from the addition of ciclosporin.

Leukemic blast and natural killer cell P-glycoprotein function and inhibition in a clinical trial of zosuquidar infusion in acute myeloid leukemia

A bioassay was developed to assess P-glycoprotein (P-gp) function of peripheral blood natural killer (NK) cells and AML blasts during zosuquidar infusion. Cells were incubated with the fluorescent dye DiOC(2)(3) in the presence and absence of zosuquidar, and dye accumulation measured by flow cytometry. The assay performance was assessed using NK cells and the P-gp-positive K562/R7 cell line, and then utilized to determine the function of P-gp and its inhibition by zosuquidar in AML blasts and NK cells from patients enrolled in a Phase I trial. The assay of zosuquidar-inhibitable accumulation of DiOC(2) is robust and reproducible.

P-glycoprotein functions as a differentiation switch in antigen presenting cell maturation

P-glycoprotein (P-gp) expressed on human antigen presenting cells (APC) regulates alloantigen-dependent T-cell activation, but the associated mechanisms are not well understood. Here we demonstrate that P-gp functions in IL-12-dependent monocyte differentiation into dendritic cell (DC) lineages during APC maturation, thereby regulating the capacity of myeloid-derived APCs to elicit alloimmune Th1 responses. Human CD14+ monocytes cultured in vitro in the presence of IL-4/GM-CSF differentiated into CD14(-) CD1A+ APCs of the immature DC phenotype. In contrast, P-gp blockade during differentiation inhibited CD1a induction, down-regulated CD80 expression, enhanced CD86 expression and induced CD68 expression. APCs differentiated in the presence of P-gp blockade stimulated alloimmune T-cell proliferation significantly less than controls and this effect was associated with 97% inhibition of Th1 IFN-gamma production, but preserved Th2 IL-5 secretion. MAb-mediated blockade of the P-gp transport substrate IL-12 in the course of APC differentiation also inhibited IFN-gamma production, while addition of rIL-12 to P-gp-blocked APC differentiation cultures significantly reversed this effect, demonstrating that P-gp functions in APC differentiation in part via IL-12 regulation. Our findings define a novel role for P-gp as a differentiation switch in APC maturation and resultant alloimmune Th1 responses, thereby identifying P-gp as a potential novel therapeutic target in allotransplantation.

Fragmented hyaluronan induces transcriptional up-regulation of the multidrug resistance-1 gene in CD4+ T cells

P-glycoprotein, encoded by the multidrug resistance (MDR)-1 gene, expels various drugs from cells resulting in multidrug resistance. We found previously that interleukin-2, a lymphocyte-activation cytokine, induces P-glycoprotein expression on lymphocytes. Lymphocyte activation involves adhesion with the extracellular matrix, such as hyaluronan, through adhesion molecules on lymphocytes. We investigated the transcriptional regulation of MDR-1 in lymphocytes by fragmented hyaluronan. Fragmented hyaluronan (especially the 6.9-kDa form), not native high molecular hyaluronan, induced translocation of YB-1, a specific transcriptional factor for MDR-1, from the cytoplasm into the nucleus and resulted in the transcription of MDR-1 and the expression of P-glycoprotein on lymphocytes in a dose-dependent manner. Transfection of YB-1 antisense oligonucleotides inhibited P-glycoprotein expression induced by fragmented hyaluronan. The fragmented hyaluronan induced significant P-glycoprotein expression on only activated CD4+ T cells, which highly expressed CD69, and resulted in excretion of intracellular dexamethasone added in vitro. Cyclosporin A, a competitive P-glycoprotein inhibitor, restored intracellular dexamethasone levels in CD4+ T cells. Anti-CD44 monoclonal antibody (Hermes-1) inhibited fragmented hyaluronan-induced YB-1 activation and P-glycoprotein expression in CD4+ T cells. We provide the first evidence that binding of fragmented hyaluronan to CD44 induces YB-1 activation followed by P-glycoprotein expression in accordance with activation of CD4+ T cells. Our findings imply that CD4+ T cell activation by fragmented hyaluronan, induced by characteristic extracellular matrix changes in inflammation, tumors, and other conditions, results in P-glycoprotein-mediated multidrug resistance.

Clinical relevance of the expression of P-glycoprotein on peripheral blood lymphocytes to steroid resistance in patients with systemic lupus erythematosus

OBJECTIVE

P-glycoprotein (P-gp) of membrane transporters leads to drug resistance by the exclusion of intracellular drugs, including corticosteroids. Some patients with highly active systemic lupus erythematosus (SLE) show poor response to corticosteroids; however, the mechanisms of steroid resistance remain unclear. The aim of this study was to elucidate the clinical relevance of P-gp expression on lymphocytes to steroid resistance in patients with active SLE.

METHODS

Flow cytometric analyses of the expression of P-gp on peripheral blood lymphocytes from 20 normal volunteers and 80 SLE patients were performed. Steroid-exclusion analysis of peripheral blood mononuclear cells (PBMCs) was conducted by using radioisotope-labeled dexamethasone.

RESULTS

P-gp was expressed at significantly high levels on most of the peripheral blood lymphocytes from SLE patients, whereas normal lymphocytes had only marginal expression. The quantity of P-gp on SLE lymphocytes correlated with the disease activity in each patient, as estimated by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). Furthermore, in SLE patients whose SLEDAI scores were >12 despite taking >0.5 mg/kg/day of prednisolone, P-gp expression on lymphocytes was markedly increased, and intracellular dexamethasone in their PBMCs was significantly decreased. However, intensive immunosuppressive treatment in these SLE patients resulted in successful control of disease activity, which occurred in parallel with a marked reduction of P-gp on lymphocytes.

CONCLUSION

The overexpression of P-gp on lymphocytes might lead to exclusion of corticosteroids from lymphocytes, resulting in steroid resistance in patients with highly active SLE. Reduction of P-gp expression achieved by intensive immunosuppressive treatment overcame the steroid resistance. We therefore propose that measurement of P-gp expression on lymphocytes is useful in the assessment of steroid resistance and is a good marker for indicating the need for intensive immunosuppressive treatment in patients with highly active SLE.

Transcriptional regulation of multidrug resistance-1 gene by interleukin-2 in lymphocytes

P-glycoprotein, encoded by the multidrug resistance (MDR)-1 gene, expels various drugs from cells resulting in drug resistance. However, its functional relevance to lymphocytes and the regulatory mechanism remain unclear. Although MDR-1 is known to be induced by various cytotoxic stimuli, it is poorly understood whether the activation stimuli such as cytokines induce MDR-1 transcription. We investigated the transcriptional regulation of MDR-1 in lymphocytes by activation stimuli, particularly by interleukin (IL)-2. IL-2 induced translocation of YB-1, a specific transcriptional factor for MDR-1, from the cytoplasm into nucleus of lymphocytes in a dose-dependent manner and resulted in the sequential events; transcription of MDR-1, expression of P-glycoprotein on the cell surface, and excretion of the intracellular dexamethasone added in vitro. Transfection of YB-1 anti-sense oligonucleotides inhibited P-glycoprotein expression induced by IL-2. Cyclosporin A, a competitive inhibitor of P-glycoprotein, recovered intracellular dexamethasone levels in lymphocytes. We provide the first evidence that IL-2, a representative lymphocyte-activation stimulus, induces YB-1 activation followed by P-glycoprotein expression in lymphocytes. Our findings imply that lymphocytes activation by IL-2 in vivo, in the context of the pathogenesis of autoimmune diseases, results in P-glycoprotein-mediated multidrug resistance, and that P-glycoprotein could be an important target for the treatment of refractory autoimmune diseases.

New agents in acute myeloid leukemia and other myeloid disorders

Over the past several decades, improvements in chemotherapeutic agents and supportive care have resulted in significant progress in treating patients with acute myeloid leukemia (AML). More recently, advances in understanding the biology of AML have resulted in the identification of new therapeutic targets. The success of all-trans-retinoic acid in acute promyelocytic leukemia and of imatinib mesylate in chronic myeloid leukemia have demonstrated that targeted therapy may be more effective and less toxic when well defined targets are available. At the same time, understanding mechanisms of drug resistance and means to overcome them has led to modification of some of the existing cytotoxic agents. Rational design and conduct of clinical trials is necessary to ensure that the full potential of these new agents is realized.

Where do we stand with hepatoblastoma? A review

Hepatoblastoma (HB) is the most common pediatric liver malignancy, comprising approximately 1% of all pediatric cancers. The disparate clinical staging systems and histologic classifications that were developed during the last decades, nevertheless, reflect the remaining difficulties and uncertainties in characterizing HB. Furthermore, the combination of surgery and (neo)adjuvant chemotherapy has improved patient outcomes dramatically. A poor prognosis is associated with large tumor size, multifocality, extrahepatic disease, and metastatic spread. The exact etiology of HB remains unknown, but the cytogenetic alterations, phenotypic features, and biologic aspects that accompany this neoplasm yield more and more insight into its pathogenesis. New cell-biologic and molecular-biologic insights may lead to the development of new treatment modalities, especially for patients with a bad prognosis. This review summarizes the different aspects of this intriguing tumor and discusses the current status of research and treatment for patients with HB.

Mdr1 gene expression and mutations in Ras proto-oncogenes in acute myeloid leukemia

Resistance to cytotoxic therapy and development of refractory disease in acute myeloid leukemia (AML) is frequently associated with the expression of mdr1/P-gp. In the last years many potential signaling pathways leading to modulation of mdr1 expression have been described. Thus, it has been assumed that activated Ras may influence mdr1 expression. This activation can be realized by mutations in the Ras oncogene leading to constitutive signaling. Ras mutations are observed in many human cancers, including AML. Recently, we could show a negative correlation between Ras mutations and mdr1 expression in blast samples of AML patients. Taking this up the potential possibilities of Ras influence on mdr1 activity and their implications on treatment outcome in AML are discussed.

Molecular, cytogenetic and genetic abnormalities in MDS and secondary AML

Myelodysplasia (MDS) is a clonal disease, which increases with age, suggesting that multiple steps are required for the evolution of the condition. Approximately 30% of MDS evolve into acute myelogenous leukemia (AML). In this review, we intend to delineate the genetic events, which may drive this sequence and therefore we will focus primarily on cytogenetic abnormalities where the genes have been identified and oncogenes and suppressor genes that have been implicated. In terms of the biological mechanisms, which characterise this process, it is generally thought that the MDS cell has impaired differentiation, and has increased apoptosis. As the disease progresses in addition, the cells have increased proliferation. As the disease evolves, the population of cells, which predominate remain immature, have decreased apoptosis and in many cases, upregulate anti-apoptotic genes and have deregulated proliferation as the number of blast cells increase. Etiological factors, which contribute to the development of leukemia, include therapeutic agents administered for a primary malignancy. The cytogenetic abnormalities, predisposition factors and genes involved in secondary leukemia will also be reviewed.

Acute myeloid leukemia: treatment of adults under 60 years

Current chemotherapy with advanced supportive care will enable 75-80% of acute myeloid leukemia patients aged 60 years or under to enter complete remission. Several regimens achieve broadly similar results. For patients who enter complete remission, the overall relapse risk is now 45-50%, but this is highly variable and is primarily determined by the biology of the disease. Cytogenetics are strongly influential in response to induction and consolidation with t(15:17), t(8:21) and inv(16) either occurring alone or with additional abnormalities having a relapse risk of about 30% and complex changes, abnormal 3q or abnormalities of chromosomes 5 and 7 resulting in a lower remission rate and a rapid relapse cumulating to 80%. FLT3 mutations occur in 25% of patients and are an independent predictor of relapse and, when combined with cytogenetics, adversely influence the prognosis in each cytogenetic risk group. Recent prospective collaborative group trials have endeavored to evaluate allogeneic and autologous bone marrow transplant against or in addition to consolidation chemotherapy. Suboptimal treatment delivery emerged as a problem. When the results were reported on an intention-to-treat basis, no overall survival advantage was consistently seen for either type of transplant. However, a significant reduction in risk of relapse was usually seen overall and within risk groups. Analysis within risk groups suggests that transplant is not indicated in good risk disease and continues to require evaluation in standard or poor risk patients. It is probable that traditional dose intensification has now reached its limits of tolerability, so new approaches will be required for further progress to be made. Modulation of chemoresistance mechanisms or immunologically directed chemotherapy represent immediate prospects for clinical study.

Activity and expression of the multidrug resistance proteins P-glycoprotein, MRP1, MRP2, MRP3 and MRP5 in de novo and relapsed acute myeloid leukemia

The multidrug resistance proteins (MRPs) MRP1, MRP2, MRP3, MRP5 and P-glycoprotein (P-gp) act in concert with each other to give a net resultant pump function in acute myeloid leukemia (AML). The aim of the present study was to analyze the activity of these proteins, which might be upregulated at relapse as compared with de novo AML due to clonal selection. The mRNA expression and activity of P-gp and the MRPs were determined with RT-PCR and flow cytometry, in conjunction with phenotype, as measured with the monoclonal antibodies CD34, CD38 and CD33, in 30 paired samples of de novo and relapsed AML. P-gp and MRP activity varied strongly between the cases (rhodamine 123 efflux-blocking by PSC833: 5.4+/-7.7, and carboxyfluorescein efflux-blocking by MK-571: 4.3+/-6.7, n = 60). P-gp and MRP activity were increased in 23% and 40% of the relapse samples, and decreased in 30% and 20% of the relapse samples, respectively (as defined by a difference of >2 x standard deviation of the assays). Up- or downregulation of mRNA expression was observed for MDR1 (40%), MRP1 (20%), MRP2 (15%), MRP3 (30%), and MRP5 (5%). Phenotyping demonstrated a more mature phenotype in 23% of the relapsed AML cases, and a more immature phenotype in 23% of the relapses, which was independent of the karyotypic changes that were observed in 50% of the studied cases. P-gp and MRP activity correlated with the phenotypic changes, with higher P-gp and MRP activities in less mature cells (r = -0.66, P < 0.001 and r = -0.31, P = 0.02, n = 58). In conclusion, this study shows that P-gp and MRP activity are not consistently upregulated in relapsed AML. However, P-gp and MRP activities were correlated with the maturation stage as defined by immune phenotype, which was observed to be different in 46% of the relapses.

Combined action of PSC 833 (Valspodar), a novel MDR reversing agent, with mitoxantrone, etoposide and cytarabine in poor-prognosis acute myeloid leukemia

PSC 833 (Valspodar) can reverse multidrug resistance (MDR) in patients with hematologic malignancies, but alters the pharmacokinetics of concomitant anticancer agents. A phase I, dose-finding study was initiated to define a safe and effective regimen of mitoxantrone, etoposide, and cytarabine (MEC) when administered with PSC 833 to patients with early relapsed or refractory acute myeloid leukemia (AML). Poor-prognosis AML patients refractory to first-line induction therapy or relapsing within 9 months of attaining complete remission (CR) were treated with cytarabine (1.0 g/m2/day), etoposide (30 mg/m2/day), and mitoxantrone at a dose of either 3.0 mg/m2/day (cohort 1) or 4.5 mg/m2/day (cohorts 2 and 3) for 6 days plus continuous-infusion PSC 833 (10 mg/kg/24 h with a 2.0 mg/kg loading dose) for 6 or 7 days each 21-day cycle. Patients achieving CR were given a 4-day MEC plus PSC 833 consolidation cycle. Twenty-three patients were enrolled (eight with primary refractory AML and 15 in relapse). Dose-limiting toxicity occurred in one of six patients in cohort 2 (grade 4 mucositis) and one of seven patients in cohort 3 (grade 4 hyperbilirubinemia). The maximum tolerated dose of mitoxantrone was defined as 4.5 mg/m2/day. Clinically significant grade 4 hyperbilirubinemia, possibly related to PSC 833, occurred in four patients. Hematologic toxicities were as expected in this patient population, but were not dose limiting. Mild to moderate cerebellar ataxia and paresthesia occurred in six (26%) and five (22%) patients, respectively, but were not dose limiting. Overall, six of 23 (26%) patients achieved CR, including five patients with demonstrated P-glycoprotein expression and/or function. The median overall survival was 4 months. All six patients with a CR were alive and four (17%) patients were disease free at 12 months. Blood levels of PSC 833 were well above the target level of 1000 ng/ml, a concentration that is known to reverse MDR in vitro. PSC 833 reduced the clearance of etoposide by approximately two-fold. No correlation was observed between the mitoxantrone or etoposide area under the curve and response. In conclusion, the MEC plus PSC 833 tested regimen was well tolerated and the 26% CR rate warrants further testing of this regimen in a randomized, phase III trial.

Chemotherapy resistance in acute myeloid leukaemia

The development of refractory disease in acute myeloid leukaemia (AML) is frequently associated with the expression of one or several multidrug resistance (MDR) genes. MDR1, MRP1 and LRP have been identified as important adverse prognostic factors in AML. Recently it has become possible to reverse clinical multidrug resistance by blocking P-glycoprotein-mediated drug efflux. The potential relevance of MDR and new approaches to treat refractory disease, are discussed.

Calcein assay for multidrug resistance reliably predicts therapy response and survival rate in acute myeloid leukaemia

In this study, we evaluated the suitability of the calcein assay as a routine clinical laboratory method for the identification of multidrug-resistant phenotype in acute leukaemia. This study presents the results of the calcein tests obtained in two large haematological centres in Hungary. Assays were performed with blast cells of 93 de novo acute leukaemia patients, including 65 patients with acute myeloid leukaemia (AML). Results were expressed as multidrug resistance activity factor (MAF) values. AML patients were divided into responders and non-responders and MAF values were calculated for each group. In both centres, responder patients displayed significantly lower MAF values than non-responders (P = 0.0045 and P = 0.0454). Cut-off values were established between the MAFR + SEM and MAFNR - SEM values. On the basis of these cut-off levels, multidrug resistance (MDR) negativity showed a 72% predictive value for the response to chemotherapy, whereas MDR positivity was found to have an average predictive value of 69% for therapy failure. MDR activity was a prognostic factor for survival rate and the test was suitable for detecting patients at relapse. The calcein assay can be used as a quantitative, standardized, inexpensive screening test in a routine clinical laboratory setting. The assay detects both P-glycoprotein and multidrug resistance-associated protein activities, and identifies AML patients with unfavourable therapy responses.