Sensitivity to the abl inhibitor STI571 in fresh leukaemic cells obtained from chronic myelogenous leukaemia patients in different stages of disease

The role of heterogeneous nuclear ribonucleoprotein K in the progression of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a neoplastic disease of the hematopoietic stem cell. Heterogeneous nuclear ribonucleoprotein K (hnRNPK) may up-regulate the transcriptional activity of some oncogenes in cancerous cells. The aim of this study was to verify the expression pattern of hnRNPK in patients with CML, to explore its association with BCR-ABL and some abnormal signaling pathways, and to discover how hnRNPK contributes to the progression of CML. In this study, 15 patients with CML (9 in chronic phase and 6 in blast crisis) were enrolled in this study. The expression of hnRNPK in mononuclear cells (MNCs) from these patients was detected by Western blotting and fluorimeter-based quantitative real-time reverse transcriptase polymerase chain reaction. hnRNPK expression levels in K562 cell line and imatinib-resistant leukemic cell line K562R, following the treatments with the inhibitors of Ras-MAPK (PD98059), PI3K/AKT (LY294002), JAK/STAT (AG490) signaling pathways, and BCR-ABL [imatinib mesylate (IM)], were also determined. As the results, the overexpression of hnRNPK in protein and gene patterns was detected in MNCs from patients with CML comparing with normal donors. Especially, its level in MNCs from patients with CML-blast crisis was significantly higher than in CML-chronic phase cells (P < 0.01). After the treatment with PD98059 (at 4, 8, 24, and 48 h) and IM (at 48 h), the expression levels of hnRNPK in leukemic cell lines were decreased, comparing with DMSO control group (P < 0.05). In conclusion, the results suggest that the overexpression of hnRNPK, which is regulated by BCR-ABL and Ras-MAPK signaling pathways, may promote the progression of CML. hnRNPK would be a potential marker and therapeutic target of CML evolution.

The development of imatinib as a therapeutic agent for chronic myeloid leukemia

Imatinib has revolutionized drug therapy of chronic myeloid leukemia (CML). Preclinical studies were promising but the results of clinical trials by far exceeded expectations. Responses in chronic phase are unprecedented, with rates of complete cytogenetic response (CCR) of more than 40% in patients after failure of interferon-α (IFN) and more than 80% in newly diagnosed patients, a level of efficacy that led to regulatory approval in record time. While most of these responses are stable, resistance to treatment after an initial response is common in more advanced phases of the disease. Mutations in the kinase domain (KD) of BCR-ABL that impair imatinib binding have been identified as the leading cause of resistance. Patients with CCR who achieve a profound reduction of BCR-ABL mRNA have a very low risk of disease progression. However, residual disease usually remains detectable with reverse transcription–polymerase chain reaction (RT-PCR), indicating that disease eradication may pose a significant challenge. The mechanisms underlying the persistence of minimal residual disease are unknown. In this manuscript, we review the preclinical and clinical development of imatinib for the therapy of CML, resistance and strategies that may help to eliminate resistant or residual leukemia.

Tumoral drug metabolism: overview and its implications for cancer therapy

Drug-metabolizing enzymes (DME) in tumors are capable of biotransforming a variety of xenobiotics, including antineoplastics, resulting in either their activation or detoxification. Many studies have reported the presence of DME in tumors; however, heterogeneous detection methodology and patient cohorts have not generated consistent, firm data. Nevertheless, various gene therapy approaches and oral prodrugs have been devised, taking advantage of tumoral DME. With the need to target and individualize anticancer therapies, tumoral processes such as drug metabolism must be considered as both a potential mechanism of resistance to therapy and a potential means of achieving optimal therapy. This review discusses cytotoxic drug metabolism by tumors, through addressing the classes of the individual DME, their relevant substrates, and their distribution in specific malignancies. The limitations of preclinical models relative to the clinical setting and lack of data on the changes of DME with disease progression and host response will be discussed. The therapeutic implications of tumoral drug metabolism will be addressed-in particular, the role of DME in predicting therapeutic response, the activation of prodrugs, and the potential for modulation of their activity for gain are considered, with relevant clinical examples. The contribution of tumoral drug metabolism to cancer therapy can only be truly ascertained through large-scale prospective studies and supported by new technologies for tumor sampling and genetic analysis such as microarrays. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to improve drug efficacy and individualize therapy.

Relationship between elevated levels of the alpha 1 acid glycoprotein in chronic myelogenous leukemia in blast crisis and pharmacological resistance to imatinib (Gleevec®) in vitro and in vivo

The Abl tyrosine kinase inhibitor imatinb is becoming a standard for the treatment of chronic myelogenous leukemia (CML). However, Bcr-Abl gene mutations have been reported mainly in relapsing or resistant patients. In primary resistant patients, only few mutations have been documented so far, suggesting alternative mechanisms. We aimed to investigate if alpha 1 acid glycoprotein (AGP), an acute phase drug binding protein, could be a biological marker for pharmacological resistance to imatinib in nine patients in acute phase CML. All patients (3/3) with high AGP dosages (2.31+/-0.17 mg/mL; normal values, 0.5-1.3mg/mL) were primary resistant to imatinib whereas an early clinical response was observed for the six patients with normal AGP levels (1.13+/-0.2mg/mL). No mutation in the adenosine triphosphate domain of Abl were detected before the initiation of imatinib therapy. By using in vitro tests combining various imatinib concentrations (1-10 microM) with purified human AGP (1 and 3 mg/mL), we demonstrate that imatinib-induced apoptosis of K562 or fresh leukemic CML cells is abrogated or reduced. The same effect was observed using sera from donors with high AGP levels (1.9-3.28 mg/mL). In patients with CML in blastic phase, AGP levels could reflect pharmacological resistance to imatinib, suggesting that increased dosage of imatinib or the use of a competitor to drug binding should be recommended to optimize the therapeutic effect of the drug.

Chronic myelogenous leukemia as a paradigm of early cancer and possible curative strategies

The chronological history of the important discoveries leading to our present understanding of the essential clinical, biological, biochemical, and molecular features of chronic myelogenous leukemia (CML) are first reviewed, focusing in particular on abnormalities that are responsible for the massive myeloid expansion. CML is an excellent target for the development of selective treatment because of its highly consistent genetic abnormality and qualitatively different fusion gene product, p210(bcr-abl). It is likely that the multiple signaling pathways dysregulated by p210(bcr-abl) are sufficient to explain all the initial manifestations of the chronic phase of the disease, although understanding of the circuitry is still very incomplete. Evidence is presented that the signaling pathways that are constitutively activated in CML stem cells and primitive progenitors cooperate with cytokines to increase the proportion of stem cells that are activated and thereby increase recruitment into the committed progenitor cell pool, and that this increased activation is probably the primary cause of the massive myeloid expansion in CML. The cooperative interactions between Bcr-Abl and cytokine-activated pathways interfere with the synergistic interactions between multiple cytokines that are normally required for the activation of stem cells, while at the same time causing numerous subtle biochemical and functional abnormalities in the later progenitors and precursor cells. The committed CML progenitors have discordant maturation and reduced proliferative capacity compared to normal committed progenitors, and like them, are destined to die after a limited number of divisions. Thus, the primary goal of any curative strategy must be to eliminate all Philadelphia positive (Ph+) primitive cells that are capable of symmetric division and thereby able to expand the Ph+ stem cell pool and recreate the disease. Several highly potent and moderately selective inhibitors of Bcr-Abl kinase have recently been discovered that are capable of killing the majority of actively proliferating early CML progenitors with minimal effects on normal progenitors. However, like their normal counterparts, most of the CML primitive stem cells are quiescent at any given time and are relatively invulnerable to the Bcr-Abl kinase inhibitors as well as other drugs. We propose that survival of dormant Ph+ stem cells may be the most important reason for the inability to cure the disease during initial treatment, while resistance to the inhibitors and other drugs becomes increasingly important later. An outline of a possible curative strategy is presented that attempts to take advantage of the subtle differences in the proliferative behavior of normal and Ph+ stem cells and the newly discovered selective inhibitors of Bcr-Abl. Leukemia (2003) 17, 1211-1262. doi:10.1038/sj.leu.2402912

Ex vivo purging with NK-92 prior to autografting for chronic myelogenous leukemia

Although controversial, purging of the autograft may be necessary to optimize transplant outcome, especially if better treatments become available to eliminate or control residual disease that may be left after the conditioning regimen. The intent of this study was to show that immunological purging with the cytotoxic cell line NK-92 effectively reduces the number of clonogenic cells and that the method can be performed in compliance with GMP. Owing to the easy quantification of bcr-abl transcripts, chronic myelogenous leukemia (CML) was used as a model disease for proof of principle. A detection level of 10(-7) bcr-abl+ cells and purging efficiency of four logs were achievable for the bcr-abl+ cell line, K562. Leukapheresis products collected from CML patients after stem cell mobilization were then tested. For all patients tested, residual CML cells were highly sensitive to purging by NK-92 with a purging efficacy of several logs. No adverse effect on hematopoietic progenitor cell function was noted. These results demonstrate the efficacy of NK-92 as a purging agent to decrease or eliminate malignant contamination of autologous stem cell grafts and establish proof of principle for ex vivo purging of CML autografts using cytotoxic effector cells.

Chronic myelogenous leukemia: mechanisms underlying disease progression

Chronic myelogenous leukemia (CML), characterized by the BCR-ABL gene rearrangement, has been extensively studied. Significant progress has been made in the area of BCR-ABL-mediated intracellular signaling, which has led to a better understanding of BCR-ABL-mediated clinical features in chronic phase CML. Disease progression and blast crisis CML is associated with characteristic non-random cytogenetic and molecular events. These can be viewed as increased oncogenic activity or loss of tumor suppressor activity. However, what causes transformation and disease progression to blast crisis is only poorly understood. This is in part due to the lack of a good in vivo model of chronic phase CML even though animal models developed over the last few years have started to provide insights into blast crisis development. Thus, additional in vitro and in vivo studies will be needed to provide a complete understanding of the contribution of BCR-ABL and other genes to disease progression and to improve therapeutic approaches for blast crisis CML.

Down-regulation of the phosphatidylinositol 3-kinase/Akt pathway is involved in retinoic acid-induced phosphorylation, degradation, and transcriptional activity of retinoic acid receptor gamma 2

Nuclear retinoic acid (RA) receptors (RARs) are phosphorylated at conserved serine residues located in their N-terminal domain. Phosphorylation of RARgamma2 at these residues is increased in response to RA subsequently to the activation of p38MAPK. We show here that this RA-induced phosphorylation of RARgamma2 resulted from the down-regulation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. By overexpressing Akt and by using agents that activated or inhibited the PI3K/Akt pathway, we also demonstrated that the RA-induced down-regulation of the PI3K/Akt pathway targeted not only the phosphorylation of RARgamma2 but also the turnover and transcriptional activity of the receptor. Altogether these data indicate that the PI3K/Akt pathway plays an important role in retinoic acid signaling.

STI-571 must select for drug-resistant cells but 'no cell breathes fire out of its nostrils like a dragon'

Seemingly disappointing, the Bcr-Abl kinase inhibitor STI-571 shares an 'unfortunate' characteristic with conventional cancer drugs: the development of drug resistance. I argue that the resistance must develop even faster to STI-571 than to conventional drugs, because STI-571 is so effective. This is predictable, but is it inevitable? And how do mechanisms of resistance in relapse depend on a degree of remission. In addition to mutation rate and number of tumor cells, one additional factor determines relapse vs. 'extinction' of the leukemia cell population.

hnRNP A1 nucleocytoplasmic shuttling activity is required for normal myelopoiesis and BCR/ABL leukemogenesis

hnRNP A1 is a nucleocytoplasmic shuttling heterogeneous nuclear ribonucleoprotein that accompanies eukaryotic mRNAs from the active site of transcription to that of translation. Although the importance of hnRNP A1 as a regulator of nuclear pre-mRNA and mRNA processing and export is well established, it is unknown whether this is relevant for the control of proliferation, survival, and differentiation of normal and transformed cells. We show here that hnRNP A1 levels are increased in myeloid progenitor cells expressing the p210(BCR/ABL) oncoprotein, in mononuclear cells from chronic myelogenous leukemia (CML) blast crisis patients, and during disease progression. In addition, in myeloid progenitor 32Dcl3 cells, BCR/ABL stabilizes hnRNP A1 by preventing its ubiquitin/proteasome-dependent degradation. To assess the potential role of hnRNP A1 nucleocytoplasmic shuttling activity in normal and leukemic myelopoiesis, a mutant defective in nuclear export was ectopically expressed in parental and BCR/ABL-transformed myeloid precursor 32Dcl3 cells, in normal murine marrow cells, and in mononuclear cells from a CML patient in accelerated phase. In normal cells, expression of this mutant enhanced the susceptibility to apoptosis induced by interleukin-3 deprivation, suppressed granulocytic differentiation, and induced massive cell death of granulocyte colony-stimulating factor-treated cultures. In BCR/ABL-transformed cells, its expression was associated with suppression of colony formation and reduced tumorigenic potential in vivo. Moreover, interference with hnRNP A1 shuttling activity resulted in downmodulation of C/EBPalpha, the major regulator of granulocytic differentiation, and Bcl-X(L), an important survival factor for hematopoietic cells. Together, these results suggest that the shuttling activity of hnRNP A1 is important for the nucleocytoplasmic trafficking of mRNAs that encode proteins influencing the phenotype of normal and BCR/ABL-transformed myeloid progenitors.

FLT3 internal tandem duplication mutations associated with human acute myeloid leukemias induce myeloproliferative disease in a murine bone marrow transplant model

FLT3 receptor tyrosine kinase is expressed on lymphoid and myeloid progenitors in the hematopoietic system. Activating mutations in FLT3 have been identified in approximately 30% of patients with acute myelogenous leukemia, making it one of the most common mutations observed in this disease. Frequently, the mutation is an in-frame internal tandem duplication (ITD) in the juxtamembrane region that results in constitutive activation of FLT3, and confers interleukin-3 (IL-3)-independent growth to Ba/F3 and 32D cells. FLT3-ITD mutants were cloned from primary human leukemia samples and assayed for transformation of primary hematopoietic cells using a murine bone marrow transplantation assay. FLT3-ITDs induced an oligoclonal myeloproliferative disorder in mice, characterized by splenomegaly and leukocytosis. The myeloproliferative phenotype, which was associated with extramedullary hematopoiesis in the spleen and liver, was confirmed by histopathologic and flow cytometric analysis. The disease latency of 40 to 60 days with FLT3-ITDs contrasted with wild-type FLT3 and enhanced green fluorescent protein (EGFP) controls, which did not develop hematologic disease (> 200 days). These results demonstrate that FLT3-ITD mutant proteins are sufficient to induce a myeloproliferative disorder, but are insufficient to recapitulate the AML phenotype observed in humans. Additional mutations that impair hematopoietic differentiation may be required for the development of FLT3-ITD-associated acute myeloid leukemias. This model system should be useful to assess the contribution of additional cooperating mutations and to evaluate specific FLT3 inhibitors in vivo.