The Second Generation of BCR-ABL Tyrosine Kinase Inhibitors

Imatinib was developed as the first molecularly targeted therapy to specifically inhibit the BCR-ABL kinase in Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML). Because of the excellent hematologic and cytogenetic responses, imatinib has moved toward first-line treatment for newly diagnosed CML. However, the emergence of resistance to imatinib remains a major problem in the treatment of Ph-positive leukemia. Several mechanisms of imatinib resistance have been identified, including BCR-ABL gene amplification that leads to overexpression of the BCR-ABL protein, point mutations in the BCR-ABL kinase domain that interfere with imatinib binding, and point mutations outside of the kinase domain that allosterically inhibit imatinib binding to BCR-ABL. The need for alternative or additional treatment for imatinib-resistant BCR-ABL-positive leukemia has guided the way to the design of a second generation of targeted therapies, which has resulted mainly in the development of novel small-molecule inhibitors such as AMN107, dasatinib, NS-187, and ON012380. The major goal of these efforts is to create new compounds that are more potent than imatinib and/or more effective against imatinib-resistant BCR-ABL clones. In this review, we discuss the next generation of BCR-ABL kinase inhibitors for overcoming imatinib resistance.

FLT3 inhibitor KRN383 on xenografted human leukemic cells harboring FLT3-activating mutations FLT3 in AML: much more to learn about biology and optimal targeting

Aberrant FLT3 function in leukemia blasts is associated with a poor prognosis. A number of FLT3 modulators are in development. FLT3 mutations may synergistize with other molecular abnormalities in myeloid transformation. Further insights into FLT3 biology are needed to optimally study the therapeutic role of FLT3 inhibitors.

Coexistence of multiple mechanisms of PT523 resistance in human leukemia cells harboring 3 reduced folate carrier alleles: transcriptional silencing, inactivating mutations, and allele loss

The reduced folate carrier (RFC) is the dominant route for the uptake of various antifolates including PT523, a potent dihydrofolate reductase inhibitor (Ki = 0.35 pM) and an excellent transport substrate of the RFC (Kt = 0.7 μM). Here, we describe the multiple mechanisms of RFC inactivation in human leukemia PT523-resistant cells originally harboring 3 RFC alleles. Cellular exposure to gradually increasing PT523 concentrations resulted in sublines displaying up to 3500-fold resistance to various hydrophilic antifolates that rely on RFC for their cellular uptake. Antifolate-resistant cells lost RFC gene expression (65%-99% loss) due to impaired promoter binding of various transcription factors that regulate RFC gene expression. Additionally, DNA sequencing revealed that PT523-resistant cells contained a cluster of 4 nearly consecutive mutations residing on a single RFC allele including L143P, A147V, R148G, and Q150Stop. Southern blot analysis established the loss of an RFC allele in PT523-resistant cells. These alterations resulted in markedly decreased RFC protein levels (∼80%-99% loss) and consequently impaired [3H]methotrexate transport (87%-99% loss). This study provides the first evidence that acquisition of PT523 resistance in human leukemia cells harboring 3 RFC alleles is due to multiple coexisting alterations including transcriptional silencing, inactivating mutations, and RFC allele loss.

Analysis of telomerase activity and RNA expression in a patient with acute promyelocytic leukemia treated with all-trans retinoic acid

In this study, we show that all-trans retinoic acid (ATRA) treatment leads to a rapid decrease in telomerase activity, which was associated with the reduction in myeloblasts and occurs before the appearance of myelocytes, in a patient with acute promyelocytic leukemia (APL). Microarray analysis by ATRA treatment for 48 hr in peripheral blood mononuclear cells (in vivo) and in cultured bone marrow mononuclear cells (in vitro) from a patient with APL revealed upregulation of CD11b, CD11c, CCAAT enhancer binding protein epsilon, Rb1, Mad, and tumor necrosis factor-related genes; and downregulation of hTERT, c-Myc, WT1, bcl-2, and eukaryotic translation elongation factor 1alpha2. The results might offer the potential to define the molecular mechanism underlying ATRA-induced granulocytic differentiation in patients with APL, and provide clues to identify novel molecular therapeutic targets.

Antitumor effects of celecoxib on K562 leukemia cells are mediated by cell-cycle arrest, caspase-3 activation, and downregulation of Cox-2 expression and are synergistic with hydroxyurea or imatinib

Celecoxib, a specific cyclooxygenase-2 (Cox-2) inhibitor, has been shown to possess antitumor activity in a variety of cancer cells. However, the antitumor activity of celecoxib in hematopoietic tumors, especially in chronic myeloid leukemia (CML), has not been well established. This study was designed to investigate the effect of celecoxib on growth and apoptosis in a human CML cell line (K562 cells) or in primary CML cells, and to examine the synergistic actions of celecoxib and hydroxyurea or imatinib on K562 cell proliferation and apoptosis. Celecoxib significantly inhibited the growth of both K562 and primary CML cells and induced apoptosis in a dose-dependent fashion. The IC50 of celecoxib was 46 microM for inhibition of K562 cell proliferation. The effect of celecoxib on growth inhibition was accompanied by the downregulation of cyclin D1 and cyclin E and p-Rb expression, the upregulation of P16(INK4a) and P27KIP expression, and a G1-S phase arrest of the cell cycle. The pro-apoptotic effect of celecoxib was determined to be mediated by caspase-3 activation. When K562 cells were pretreated with DEVD-fmk, a specific inhibitor of caspases, the apoptotic activity of celecoxib was, in part, abrogated. Importantly, we demonstrated for the first time that K562 cells were Cox-2-positive both at the mRNA and protein levels. We noted the following observations: (i) we detected Cox-2 mRNA in K562 cells by reverse transcription-PCR (RT-PCR) and protein expression by western blot analysis; (ii) Cox-2 expression in K562 cells was stimulated by IL-1beta, a specific inducing agent of Cox-2 expression; (iii) primary CML cells from CML patient bone marrow also exhibited Cox-2 protein expression. Furthermore, Cox-2 expression was downregulated at higher doses of celecoxib (80-160 microM), suggesting a Cox-2-dependent mechanism was involved in the drug's effects of growth inhibition and induction of apoptosis. In addition, a synergistic effect was observed when cells were exposed to low-dose celecoxib (40 microM) and hydroxyurea (10 mM) or a combination of celecoxib (40 microM) and imatinib (0.2 microM). These findings provide the basis for uncovering the mechanism of celecoxib's antitumor effects and developing a new therapeutic strategy for treating CML.

[Effect of glucocorticoid on the expression of Puma in acute lymphoblastic leukemia]

OBJECTIVE

Glucocorticoid can induce apoptosis by regulating some genes' expression, but its effect on the pro-apoptotic protein Puma in leukemia remains unclear. This study was designed to investigate the effect of glucocorticoid on the expression of Puma in glucocorticoid-induced apoptosis of acute lymphoblastic leukemia cells in vitro.

METHODS

Leukemia cells from acute lymphoblastic leukemia patients were transplanted into the immunodeficient mice. The transplanted leukemia cells were collected and then were treated with dexamethasone at the final concentration of 1 microM. The expression of Puma protein and mRNA in leukemia cells after dexamethasone treatment was detected by Western Blot and real-time quantitative PCR. A drug sensitive test was performed by MTT assay.

RESULTS

The leukemia cells which came from the patients who had good clinical outcomes were sensitive to dexamethasone, while the ones from the patients who had poor clinical outcomes were resistant to dexamethasone in vitro. The sensitivity to dexamethasone in vitro between the resistant and sensitive leukemia cells was significantly different (P < 0.05). No upregulation of Puma protein and mRNA was detected in resistant and sensitive leukemia cells after dexamethasone treatment.

CONCLUSIONS

Glucocorticoid can not upregulate the expression of Puma in glucocorticoid-induced apoptosis of acute lymphoblastic leukemia cells in vitro.

Epigenetic heterochromatin markers distinguish terminally differentiated leukocytes from incompletely differentiated leukemia cells in human blood

OBJECTIVE

During terminal cell differentiation, nuclear chromatin becomes condensed and the repertoire of epigentic heterochromatin proteins responsible for chromatin condensation is dramatically changed. In order to identify the chromatin regulatory factors associated with incomplete cell differentiation and impaired chromatin condensation in hematological malignancies, we examined expression levels of major heterochromatin proteins in normal blood cells and cells derived from a number of chronic and acute myeloid leukemia patients exhibiting different degrees of differentiation.

METHODS

We used immunoblotting and immunofluorescence to examine the levels and localization of epigenetic heterochromatin factors in isolated cell nuclei and fractionated peripheral blood cells.

RESULTS

While the major epigenetic heterochromatin factor, histone H3 methylated at lysine 9, is present in all cell types, its main counterparts, nonhistone proteins, heterochromatin proteins 1 (HP1) alpha, beta, and gamma, are dramatically reduced in peripheral blood leukocytes of normal donors and chronic myeloid leukemia patients, but are substantially increased in the blood of accelerated phase and blast crisis patients. In the terminally differentiated cells, nuclear chromatin accumulates a nucleocytoplasmic serpin, monocyte and neutrophil elastase inhibitor (MNEI). HP1 and MNEI levels inversely correlate in a number of normal and leukemia myeloid cells and show strikingly opposite coordinated changes during differentiation of U937 cell line induced by retinoic acid.

CONCLUSIONS

Our results suggest that repression of HP1 and accumulation of MNEI are linked to terminal cell differentiation and that their levels may be monitored in blood cell populations to detect transitions in cell differentiation associated with leukemia progression and treatment.

Advances in the treatment of hematologic malignancies. Part 1 of a 3-part series: Aggressive lymphomas

The treatment of patients with aggressive lymphomas has improved significantly in recent years, primarily due to the introduction of targeted therapy with the anti-CD20 monoclonal antibody rituximab in combination with chemotherapy. Rituximab has significantly improved overall survival and progression-free survival in patients with aggressive lymphomas, even those with high-risk disease. Ongoing research aims to determine the optimal uses of rituximab for inducing and maintaining remission in a variety of settings. Another important area of focus has been the investigation into prognostic and predictive factors. Assessing each patient according to different prognostic factors allows clinicians to best determine a patient's risk and develop a suitable therapy. Microarray analysis is being used in this area to determine gene expression patterns associated with responses to therapy and, ultimately, to identify specific genes associated with various outcomes. The identification of relevant genes could indicate specific patients that might benefit from targeted therapy, and may reveal additional therapeutic targets. These investigations have already identified several candidate genes that may be appropriate targets for therapy, such as Bcl-2, protein kinase C-beta, and nuclear factor-kappa B. The future of therapy for aggressive lymphomas will likely involve identifying the molecular profile for each patient and designing an appropriate targeted therapy based on their specific situation. Recent and ongoing studies are moving us closer towards that goal.

Abnormal expression of the programmed cell death 5 gene in acute and chronic myeloid leukemia

To clarify whether expression of the programmed cell death 5 (PDCD5) gene in leukemic cells is abnormal, real-time quantitative reverse transcription polymerase chain reaction (RQ-RT-PCR) was used to examine its expression in marrow cells from leukemia patients. We found lower PDCD5 in both AML and CML marrow cells than in normal donor marrow cells. A negative correlation was found between relative levels of PDCD5 and BCR/ABL expression in all CML patients and in CML patients in the advanced phase. Treatment with the ABL tyrosine kinase inhibitor Imatinib mesylate increased PDCD5 expression in K562 and MEG-01 cells. These findings suggest that abnormal expression of PDCD5 in leukemia may be involved in the pathomechanism of AML and CML.

Eradication of leukemia stem cells as a new goal of therapy in leukemia

Leukemias have traditionally been classified and treated on the basis of phenotypic characteristics, such as morphology and cell-surface markers, and, more recently, cytogenetic aberrations. These classification systems are flawed because they do not take into account cellular function. The leukemia cell population is functionally heterogeneous: it consists of leukemia stem cells (LSC) and mature leukemia cells that differentiate abnormally to varying extents. Like normal hematopoietic stem cells, LSCs are quiescent and have self-renewal and clonogenic capacity. Because they are quiescent, LSCs do not respond to cell cycle-specific cytotoxic agents used to treat leukemia and so contribute to treatment failure. These cells may undergo mutations and epigenetic changes, further leading to drug resistance and relapse. Recent data suggest that mature leukemia cells may acquire LSC characteristics, thereby evading chemotherapeutic treatment and sustaining the disease. Ongoing research is likely to reveal the molecular mechanisms responsible for LSC characteristics and lead to novel strategies for eradicating leukemia.

Telomerase targeting by retinoids in cells from patients with myeloid leukemias of various subtypes, not only APL

Numerous strategies have been proposed to specifically inhibit telomerase (human telomerase reverse transcriptase (hTERT)) but to date only a few are clinically relevant in anticancer therapy. Recently, we have shown that long-term treatment with all-trans retinoic acid (ATRA), a compound clinically approved for differentiation therapy of acute promyelocytic leukemia (APL), represses hTERT in differentiation-resistant APL cell lines leading to telomere shortening and death. This signaling requires the co-activation of the retinoic acid receptor alpha (RARalpha) and the retinoic X receptor (RXR). In contrast to differentiation-therapy, which is only successful in this subtype of leukemia, the telomerase-targeted pathway could also be of use in non-APL. Here, we demonstrate that repression of hTERT occurs in fresh blasts cells from patients with myeloid leukemias of various subtypes exposed ex vivo to ATRA or synthetic retinoids. These results support the idea that, by hTERT targeting, retinoids can induce telomere shortening and cell death and their integration in therapy protocols for myeloid leukemias refractory to maturation should be considered.

Histone deacetylase inhibitors reduce VEGF production and induce growth suppression and apoptosis in human mantle cell lymphoma

OBJECTIVES

Mantle cell lymphoma (MCL) is an incurable disease with an aggressive course and novel treatment strategies are urgently needed. The purpose of this study was to evaluate the effects of histone deacetylase (HDAC) inhibitors, a new group of antiproliferative agents, on human MCL cells.

METHODS

Three MCL cell lines (JeKo-1, Hbl-2 and Granta-519) were exposed to different concentrations of the HDAC inhibitors sodium butyrate (NaB) and suberoylanilide hydroxamic acid (SAHA) for 8-72 h. Their effects on cell viability, apoptosis induction and cell cycle proliferation were studied. Moreover, the influence of SAHA on the expression of cyclin D1, the cell cycle regulators p21 and p27 and the production of vascular endothelial growth factor (VEGF) were analyzed.

RESULTS

The HDAC inhibitors induced accumulation of acetylated histones in MCL cells. MTT assays and Annexin-V staining showed that they potently inhibited viability in a dose-dependent manner and induced apoptosis in all cell lines tested. Cell cycle analysis indicated that their exposure to SAHA or NaB decreased the proportion of cells in S phase and increased the proportion of cells in the G0/G1 and/or G2/M phases. Incubation with the two HDAC inhibitors resulted in downregulation of cyclin D1. SAHA lead to an upregulation of p21 in all cell lines and an upregulation of p27 in JeKo-1 and Granta-519 cells, while expression of p27 in Hbl-2 was not altered. In addition, SAHA inhibited the production of the angiogenic cytokine VEGF. Treatment with NaB increased the expression of p21 in JeKo-1 and Hbl-2 cells, while in Granta 519 cells no effect was noted. The expression of p27 remained constant in all three cell lines after exposure to NaB.

CONCLUSION

Based on these findings, we provide evidence that HDAC inhibitors have antiproliferative effects in MCL and may represent a promising therapeutic approach.

PKC pathway and ERK/MAPK pathway are required for induction of cyclin D1 and p21Waf1 during 12-o-tetradecanoylphorbol 13-acetate-induced differentiation of myeloleukemia cells

Treatment of human promyelocytic leukemia cell HL60 with 12-o-tetradecanoylphorbol 13-acetate (TPA) induces growth arrest, differentiation towards the monocyte/macrophage lineage, and expression of cell cycle-regulating genes cyclin D1 and p21Waf1. First, we demonstrated that p21Waf1 expression was increased by TPA in other leukemia cell lines also, including THP-1, U937, and KG-1, which differentiate into monocytes/macrophages by TPA. Secondly, we demonstrated the signal transduction pathways of cyclin D1 and p21Waf1 expressions in TPA-treated HL60 cells. Induction of cyclin D1 expression in TPA-treated HL60 cells was inhibited with protein kinase C (PKC) inhibitor bisindolylmaleimide I and mitogen activated protein kinase kinase (MEK) inhibitor PD98059. Induction of p21Waf1 expression in TPA-treated HL60 cells was inhibited with PKC inhibitor bisindolylmaleimide I and Gö6976, MEK inhibitor PD98059, and p38 mitogen-actibated protein kinase (MAPK) inhibitor SB202190. Thus, cyclin D1 and p21Waf1 expressions are considered to be induced via PKC and extracellular signal-regulated kinase/mitogen-activated protein kinase (MAPK/ERK) pathways in TPA-treated HL60 cells. The upregulation of p21Waf1 seems to play a critical role in TPA-induced cell differentiation by suppressing cyclin dependent kinase activity , while the upregulation of cyclin D1 seems to be compensated by p21Waf1.

NF-kappaB is essential for the progression of KSHV- and EBV-infected lymphomas in vivo

Activated NF-kappaB is a critical mechanism by which lymphoma cells infected by Epstein-Barr virus (EBV/HHV-4) and Kaposi sarcoma herpesvirus (KSHV/HHV-8) are protected from apoptotic stress. Selective pharmacologic inhibition of constitutive NF-kappaB activity induces apoptosis in KSHV- and EBV-infected lymphoma cells. In both tumor types, pharmacologic inhibition of NF-kappaB in vitro induced identical mitochondrially mediated apoptosis cascades. Assessment of gene regulation by microarray analysis revealed that the inhibition of NF-kappaB in tumor cells results in the down-regulation of a distinct group of prosurvival genes, including cIAP-1, cIAP-2, cFLIP, and IL-6. Using EBV- and KSHV-associated lymphomas in a murine system, we demonstrated that Bay 11-7082, a selective pharmacologic inhibitor of NF-kappaB, prevents or delays tumor growth and prolongs disease-free survival. Inhibition of NF-kappaB activity and tumor growth responses were further documented using a traceable reporter KSHV-positive cell line and in vivo imaging. These findings indicate that specific NF-kappaB-regulated survival factors work cooperatively to protect KSHV- and EBV-infected lymphoma cells from apoptosis such that they promote the establishment and progression of KSHV- and EBV-associated lymphomas in mice. They also support the use of selective NF-kappaB inhibitors in the treatment of herpesvirus-associated lymphomas.

ATRA resolves the differentiation block in t(15;17) acute myeloid leukemia by restoring PU.1 expression

Tightly regulated expression of the transcription factor PU.1 is crucial for normal hematopoiesis. PU.1 knockdown mice develop acute myeloid leukemia (AML), and PU.1 mutations have been observed in some populations of patients with AML. Here we found that conditional expression of promyelocytic leukemia-retinoic acid receptor alpha (PML-RARA), the protein encoded by the t(15;17) translocation found in acute promyelocytic leukemia (APL), suppressed PU.1 expression, while treatment of APL cell lines and primary cells with all-trans retinoic acid (ATRA) restored PU.1 expression and induced neutrophil differentiation. ATRA-induced activation was mediated by a region in the PU.1 promoter to which CEBPB and OCT-1 binding were induced. Finally, conditional expression of PU.1 in human APL cells was sufficient to trigger neutrophil differentiation, whereas reduction of PU.1 by small interfering RNA (siRNA) blocked ATRA-induced neutrophil differentiation. This is the first report to show that PU.1 is suppressed in acute promyelocytic leukemia, and that ATRA restores PU.1 expression in cells harboring t(15;17).

Hypoxia-simulating agents and selective stimulation of arsenic trioxide-induced growth arrest and cell differentiation in acute promyelocytic leukemic cells

BACKGROUND AND OBJECTIVES

We recently reported that hypoxia-mimetic agents cobalt chloride (CoCl2 CoCl2 ) and desferrioxamine (DFO) could induce differentiation of acute myeloid leukemic (AML) cells. Here, we investigate whether these two agents influence the in vitro differentiation-inducing effect of arsenic trioxide (As2O3) on AML cells, an effective drug for the treatment of acute promyelocytic leukemia (APL) that is a unique subtype of AML with a specific fusion protein, PML-RARalpha.

DESIGN AND METHODS

The APL cell line NB4 and non-APL promonocytic leukemic cell line U937 were treated with As2O3 (0.5 microM) combined with CoCl2 (50 microM) or DFO (10 microM). The U937/PR9 subclone, whose expression of PML-RARalpha protein can be induced by Zn2+, was also investigated. Cellular differentiation was evaluated by morphological criteria and myeloid differentiation-related antigens and marker gene expression. The hypoxia-inducible factor-1alpha (HIF-1alpha) mRNA and protein were detected, respectively, by semi-quantitative/real-time quantitative reverse transcription polymerase chain reaction and immunoblots. PML-RARalpha protein was also analyzed.

RESULTS

CoCl2 and DFO potentiated the growth-inhibiting and differentiation-inducing effects of low-dose As2O3, the latter enhancing CoCl2 and DFO-induced accumulation of HIF-1alpha protein in NB4 cells but not in U937 cells. These two hypoxia-mimetic agents also accelerated As2O3-induced modulation and degradation of PML-RARalpha protein in NB4 cells. Furthermore, inducible expression of the fusion gene restored the co-operative effects of As2O3 and CoCl2/DFO on U937/PR9 cells in terms of growth arrest, differentiation induction and HIF-1alpha protein accumulation.

INTERPRETATION AND CONCLUSIONS

Mimicked hypoxia enhanced As2O3-induced differentiation, in which HIF-1alpha and PML/RARalpha proteins played an important role. These data provide new insights into the understanding of the mechanisms of the action of As2O3 in the treatment of patients with APL.

Identification of glucocorticoid-response genes in children with acute lymphoblastic leukemia

The ability of glucocorticoids (GCs) to kill lymphoid cells led to their inclusion in essentially all chemotherapy protocols for lymphoid malignancies, particularly childhood acute lymphoblastic leukemia (ALL). GCs mediate apoptosis via their cognate receptor and subsequent alterations in gene expression. Previous investigations, including expression profiling studies with subgenome microarrays in model systems, have led to a number of attractive, but conflicting, hypotheses that have never been tested in a clinical setting. Here, we present a comparative whole-genome expression profiling approach using lymphoblasts (purified at 3 time points) from 13 GC-sensitive children undergoing therapy for ALL. For comparisons, expression profiles were generated from an adult patient with ALL, peripheral blood lymphocytes from GC-exposed healthy donors, GC-sensitive and -resistant ALL cell lines, and mouse thymocytes treated with GCs in vivo and in vitro. This generated an essentially complete list of GC-regulated candidate genes in clinical settings and experimental systems, allowing immediate analysis of any gene for its potential significance to GC-induced apoptosis. Our analysis argued against most of the model-based hypotheses and instead identified a small number of novel candidate genes, including PFKFB2, a key regulator of glucose metabolism; ZBTB16, a putative transcription factor; and SNF1LK, a protein kinase implicated in cell-cycle regulation.

AML bearing the translocation t(11;17)(q23;q21): involvement of MLL and a region close to RARA, with no differentiation response to retinoic acid

We describe a case of acute myeloid leukemia (AML) bearing the translocation t(11;17)(q23;q21). The morphological phenotype represented a monoblastic leukemia, AML French-American-British (FAB) M5a. Further analysis of the translocation revealed an involvement of the mixed-lineage leukemia (MLL) gene and a region closely proximal to the retinoic acid (RA) receptor alpha (RARA) gene. AMLs involving both a rearranged MLL and the 17q21 region, in which the RARA gene is located, have only been described in some individual cases. The functional role of this translocation is still unknown. Rearrangements of the MLL (11q23) gene in AML are usually related to the morphological phenotype FAB M5. In general, they are associated with an adverse prognosis. In acute promyelocytic leukemia, the translocation (15;17)(q22;q11-21) involving the RARA leads to a maturation arrest that can be overcome by RA, often inducing remission. In other forms of AML, however, the effects of RA are limited and diverse. To study whether RA might have a therapeutical potential in our case, we performed an in vitro analysis of RA effects on AML cells. We found that RA leads to enhanced cell death and up-regulation of CD38 and CD117. However, no hints of RA-induced in vitro differentiation were visible. Our data indicate that in AML cells bearing the t(11;17)(q23;q21), a differentiation arrest that is overcome by RA is not present. On the contrary, RA induces alterations in cellular regulation that are similar to the RA-induced changes observed in early hematogenic progenitors; thus, a possible therapeutical benefit of RA in such cases remains open.

Enhanced sensitivity to inhibition of SHP2, STAT5, and Gab2 expression in chronic myeloid leukemia (CML)

Although targeting the BCR-ABL tyrosine kinase activity by imatinib mesylate has rapidly become first-line therapy in chronic myeloid leukemia (CML), drug resistance suggests that combination therapy directed to a complementing target may significantly improve treatment results. To identify such potential targets, we used lentivirus-mediated RNA interference (RNAi) as a tool for functional genomics in cell lines as well as primary normal and CML CD34+ cells. In a conditional cell culture model, we demonstrate that RNAi-mediated reduction of SHP2, STAT5, and Gab2 protein expression inhibits BCR-ABL-dependent but not cytokine-dependent proliferation in a dose-dependent manner. Similarly, colony formation of purified primary CML but not of normal CD34+ colony-forming cells is specifically reduced by inhibition of SHP2, STAT5, and Gab2 expression, respectively. In addition, coexpression of both anti-BCR-ABL and anti-SHP2 shRNAs from a single lentiviral vector induces stronger inhibition of colony formation as compared to either shRNA alone. The data indicate that BCR-ABL expression may affect the function of normal signaling molecules. Targeting these molecules may harbor significant therapeutic potential for the treatment of patients with CML.

Human leukemias with mutated FLT3 kinase are synergistically sensitive to FLT3 and Hsp90 inhibitors: the key role of the STAT5 signal transduction pathway

17-allylamino-17-demethoxygeldanamycin (17-AAG), an inhibitor of the molecular chaperone heat shock protein 90, results in cell type-specific inhibition of proliferation of leukemic cells. GTP14564 is a tyrosine kinase inhibitor actively against FLT3. The current study evaluated the single and combined effects of 17-AAG and GTP14564, and the role of FLT3 in their inhibitory effects. The importance of FLT3 mutations was demonstrated using small interfering RNA (siRNA) targeted to FLT3. Similar to FLT3 siRNA, GTP14564 inhibited FLT3 internal tandem duplication (ITD) cells (MV4;11) and FLT3 amplified wild-type cells (SEMK2-M1), but not wild-type FLT3 cells (RS4;11). However, when RS4;11 cells were stimulated with FLT3-ligand, phosphorylation of STAT5 and GTP14564 inhibition were observed. Responses to GTP14564 in all cell types were directly related to the level of STAT5 phosphorylation in the cells. We observed synergistic effects of combined 17-AAG and GTP14564 in cell lines with FLT3-ITD and amplified wild-type FLT3. Combined treatment with 17-AAG and GTP14564 reduced the levels of p-FLT3 and p-STAT5, enhanced G0/G1 arrest and apoptosis in FLT3-ITD and amplified wild-type FLT3. The combination of 17-AAG with FLT3 kinase inhibitors can enhance targeted therapy in leukemias with FLT3 mutations, such as MLL fusion gene leukemias.

Skin homing of Sézary cells involves SDF-1-CXCR4 signaling and down-regulation of CD26/dipeptidylpeptidase IV

Sézary syndrome (SS) is a rare form of cutaneous T-cell lymphoma (CTCL) characterized by a distinct metastatic pattern mainly involving blood and skin. Chemokines and their receptors play a critical role in cellular recruitment and homing to tissues and in the metastatic process of several tumors including non-Hodgkin T-cell lymphomas (NHLs). Here we report that SS cells express a functionally active CXCR4 and that its ligand SDF-1 is abundantly produced in the skin, which represents the main destination of SS cell spreading. SDF-1 is normally inactivated by proteolytic cleavage by the CD26/dipeptidylpeptidase IV (DPPIV). The lack of CD26 from the cell surface is a hallmark of circulating SS cells. We also show that the CD26(-) phenotype is maintained also in skin-infiltrating neoplastic T lymphocytes and that SS-affected individuals exhibit a reduced activity of plasma soluble CD26. Finally, we observe that the addition of soluble CD26 reduces the migratory response of SS cells to SDF-1 whereas the inhibition of the CD26 peptidase activity in Hut78, a CD26(+) CTCL cell line, enhances the SDF-1-induced migration of these cells. Our findings suggest that the SDF-1-CXCR4 axis could play an important role in skin homing of SS through the regulatory activity of CD26.

Heat shock proteins and acute leukemias

Heat shock proteins (HSPs) acts as molecular chaperones by helping in the refolding of misfolded proteins and assisting in their elimination if they become irreversibly damaged. HSPs induced by stress treatment have a role in the modulation of apoptosis. The reduction in protein expression levels was correlated with an increased susceptibility to drug-induced apoptosis. HSPs have also been implicated in the resistance of leukemia cells to potential therapeutic agents. The mechanisms of cellular protection used by HSPs have yet to be fully defined. HSPs were shown highly expressed by acute myeloid leukemia (AML) cells as well as by acute lymphoblastic leukemia (ALL) cells. HSP expressions were correlated with that of differentiation antigens and that of drug-resistance and apoptosis proteins. Complete remission (CR) rates were higher in patients with lower expression of HSPs. Overall survival (OS) was significantly longer in patients with lower expression of HSPs. Therapeutically, inhibition of inducible HSP expression or activity should not cause any undesired side effects. HSPs emerge as novel therapeutic targets in anticancer protocols. Early results of phase I studies indicate that 17-allylamino-17-demethoxygeldamycin (17-AAG), capable of binding and disrupting the function of HSP90, results in an acceptable toxicity profile while achieving in vivo disruption of multiple oncogenic client proteins.

Multi-gene epigenetic silencing of tumor suppressor genes in T-cell lymphoma cells; delayed expression of the p16 protein upon reversal of the silencing

To understand better T-cell lymphomagenesis, we examined promoter CpG methylation and mRNA expression of closely related genes encoding p16, p15, and p14 tumor suppressor genes in cultured malignant T-cells that were derived from cutaneous, adult type, and anaplastic lymphoma kinase (ALK)-expressing T-cell lymphomas. p16 gene was epigenetically silenced in all but one of the 10 malignant T-cell lines examined, p15 gene silenced in roughly half of the lines, and p14 was the least frequently affected. Extensive methylation of the p16 promoter was seen in six out of 10 cutaneous T-cell lymphoma patient samples and corresponded with lack of p16 protein expression in the cases examined. Treatment of cultured T-cells with the DNA methyltransferase inhibitor, 5-aza-2-deoxy-cytidine, resulted in reversal of the p16 gene silencing. However, expression of p16 protein was delayed in relationship to p16 promoter demethylation and required up to 3 weeks to occur, seemingly reflecting late activation of the p16 gene. These findings indicate that epigenetic silencing affects in T-cell malignancies, often simultaneously, several tumor suppressor genes that impact on key cell functions. The observed differential silencing of p16 and p14, and to a lesser degree p15 gene, indicates that the silencing is governed by precise, promoter region-specific mechanisms. The study provides also further rationale for treatment of at least some types of T-cell lymphomas with DNA methyltransferase inhibitors to target the epigenetically silenced tumor suppressor genes.

Phase I to II multicenter study of oblimersen sodium, a Bcl-2 antisense oligonucleotide, in patients with advanced chronic lymphocytic leukemia

PURPOSE

To determine the maximum-tolerated dose (MTD), efficacy, safety, and pharmacokinetics of oblimersen sodium in patients with advanced chronic lymphocytic leukemia (CLL).

PATIENTS AND METHODS

Eligible patients had relapsed or refractory CLL after treatment with fludarabine. Oblimersen was administered at doses ranging from 3 to 7 mg/kg/d as a 5-day continuous intravenous infusion in cycle 1 and as a 7-day continuous intravenous infusion in subsequent cycles every 3 weeks in stable or responding patients.

RESULTS

Forty patients were enrolled and treated (14 patients in phase I and 26 patients in phase II). Dose-limiting reactions in phase I included hypotension and fever, and the MTD for phase II dosing was established at 3 mg/kg/d. Two (8%) of 26 assessable patients achieved a partial response. Other evidence of antitumor activity included > or = 50% reduction in splenomegaly (seven of 17 patients; 41%), complete disappearance of hepatomegaly (two of seven patients; 29%), > or = 50% reduction of lymphadenopathy (seven of 22 patients; 32%), and > or = 50% reduction in circulating lymphocyte counts (11 of 22 patients; 50%). Adverse events included transient hypotension, fever, fatigue, night sweats, diarrhea, nausea, vomiting, hypokalemia, and cough. Plasma concentrations of oblimersen (parent drug) and its major metabolites were variable. Renal clearance represented only a small portion of total parent drug clearance.

CONCLUSION

Dosing with oblimersen sodium in patients with CLL is limited by development of a cytokine release syndrome that is characterized by fever, hypotension, and back pain. Oblimersen sodium has modest single-agent activity in heavily pretreated patients with advanced CLL, and further evaluation of its activity in combination with cytotoxic drugs is warranted.