Biomedical subjects

Mei Huang

Publications and source records attributed to Mei Huang.

At least 37 records · Page 2Linked to original sources

PubMed2004

Hyperactivation of STAT3 is involved in abnormal differentiation of dendritic cells in cancer.

Abnormal differentiation of myeloid cells is one of the hallmarks of cancer. However, the molecular mechanisms of this process remain elusive. In this study, we investigated the effect of tumor-derived factors on Janus kinase (Jak)/STAT signaling in myeloid cells during their differentiation into dendritic cells. Tumor cell conditioned medium induced activation of Jak2 and STAT3, which was associated with an accumulation of immature myeloid cells. Jak2/STAT3 activity was localized primarily in these myeloid cells, which prevented the differentiation of immature myeloid cells into mature dendritic cells. This differentiation was restored after removal of tumor-derived factors. Inhibition of STAT3 abrogated the negative effects of these factors on myeloid cell differentiation, and overexpression of STAT3 reproduced the effects of tumor-derived factors. Thus, this is a first demonstration that tumor-derived factors may affect myeloid cell differentiation in cancer via constitutive activation of Jak2/STAT3.

Animals↗

PubMed2004

Effect of ligustrazine on the expression of LFA-1, ICAM-1 following bone marrow transplantation in mice.

The effects of ligustrazine on the expression of LFA-1, ICAM-1 in bone marrow tissue and the mechanism promoting hematopoietic reconstitution following bone marrow transplantation (BMT) were investigated. The 150 mice were randomly divided into 3 groups: normal group, saline group and ligustrazine group. The normal group received no treatment, while in the saline group and ligustrazine group, the mice were subjected to normal saline (0.2 ml, twice a day) and ligustrazine (0.2 ml, twice a day) respectively through a gastric tube. At the 7th, 14th, 21st and 28th day after BMT, survival rate, colony forming unit of spleen (CFU-S), peripheral blood cells and bone marrow mononuclear cells (BMMNC) were measured, histological changes in bone marrow tissue were observed and the expression level of LFA-1, ICAM-1 was detected. In ligustrazine group CFU-S counts on the 10th day and the peripheral blood WBC, PLT, BMMNC counts, hematopoietic tissue volume as well as the expression level of LFA-1 on the 7th, 14th, 21st, 28th day after BMT were higher than in saline group (P<0.01 or P<0.05). Mature RBC volume and the expression level of ICAM-1 were significantly lower in the ligustrazine group than in the saline group (P<0.01 or P<0.05). In the ligustrazine group, fat tissue volume was higher on the 7th, 14th day after BMT (P<0.01) and was lower on the 21st, 28th day (P<0.01) after BMT than in the saline group. It was concluded that Ligustrazine could improve bone marrow microenvironment and promote hematopoietic reconstitution.

Animals↗

PubMed2004

The effect of sodium butyrate in combination with ATRA on the proliferation/differentiation of SKM-1.

To explore the molecular mechanisms of sodium butyrate working on SKM-1 cell proliferation/differentiation and to study its synergistic effect with all-trans retinoic acid (ATRA), SKM-1 cells were grown in the absence or presence of sodium butyrate and/or ATRA. The percentage of viable cells was determined by trypan blue exclusion. Differentiation was determined by nitroblue tetrazolium (NBT) reduction and cell surface adhesion molecules was analyzed by FACS. Cell cycle distribution was examined after DNA staining by propidium iodide. D-type cyclins, cdks and P21 mRNA were studied by reverse transcription-polymerase chain reaction. Our results showed that sodiun butyrate and/or ATRA blocked cells mainly in the G0/G1 phase of the cell cycle. ATRA inhibited the mRNA expression of CDK6, CDK4, cyclinD3 and cyclinD1. Sodium butyrate inhibited the mRNA expression of CDK2, cyclinD2 and cyclinD1. ATRA and sodium butyrate inhibited the mRNA expression of CDK6, CDK4, CDK2, cyclinD1, cyclinD2 and cyclinD3. Both ATRA and/or sodium butyrate stimulated p21 expression at the mRNA levels. Our results suggest that the effect of sodium butyrate on cell proliferation/differentiation might be linked to its ability to induce expression of p21 mRNA and inhibit the cyclin-cdk complexes. Our observations support the notion that the sodium butyrate works synergistically with ATRA.

Antineoplastic Agents↗

PubMed2004

Clinical observation of patients with hematologic malignancies treated with hematopoietic stem cell transplantation.

To evaluate the therapeutic effect of hematopoietic stem cell transplantation (HSCT), we performed HSCT in 30 patients with hematologic maligancies. Of the 30 patients, 10 underwent autologous peripheral blood stem cell transplantation (auto-PBSCT), 13 underwent myeloablative allogeneic HSCT while 7 underwent nonmyeloablative allogeneic HSCT, which were designated as autologous group, myeloablative group and nonmyeloablative group, respectively. All patients except the one who underwent cord blood transplantation, were successfully engrafted. Median time for the granulocytes > or = 0.5 x 10(9)/L and platelets > or = 20 x 10(9)/L were 12 days and 13 days respectively in autologous group, 16 days and 19 days in myeloablative group, 15 days and 12 days in nonmyeloablative group. In myeloablative group, acute graft-versus-host diseases (aGVHD) was observed in 3 patients, all of which were I-II grade. Oral mucous cGVHD was observed in 1 patient. In nonmyeloablative group, 1 patient developed intestinal aGVHD grade IV and cutaneous cGVHD was induced by donor lymphocyte infusions (DLI) in 3 patients. 1 patient had hematological relapse in autologous group. 1 patient had cytogenetic relapse in myeloablative group. In nonmyeloablative group 3 patients had cytogenetic relapse and were cured by DLI, 1 patient had hematological relapse. 4 of the 30 patients died of infection (2 patients), grade IV aGVHD (1) and relapse (1) respectively. 26 patients are still alive. 3 years overall survival (OS) and 3 years disease free survival (DFS) were 100% and 64.81% respectively in autologous group, 78.75% and 63% respectively in myeloablative group while both 66.67% in nonmyeloablative group. In conclusion, autologous group had less transplant-related complications and mortality. Active prophylaxis of relapse could significantly promote DFS. The transplant-related mortality limited DFS in myeloablative group. More relapses occurred in nonmyeloablative group, but could be cured by DLI.

Adolescent↗

PubMed2004

CHIP mediates degradation of Smad proteins and potentially regulates Smad-induced transcription.

Transforming growth factor beta (TGF-beta)/bone morphogenetic protein (BMP) family ligands interact with specific membrane receptor complexes that have serine/threonine kinase activities. The receptor phosphorylation and activation induced by the ligands leads to phosphorylation of the Smad proteins, which translocate to the nucleus, controlling gene expression. Thus, regulation of Smad proteins is a key step in TGF-beta/BMP-induced signal transduction. Here we report a novel mechanism of the regulation of SMAD-mediated signaling, by which the Smad1 protein level is controlled through expression of the CHIP protein. CHIP is a U-box-dependent E3 ubiquitin ligase, previously identified as a cochaperon protein. However, we have isolated CHIP as a Smad-interacting protein in a yeast two-hybrid screen using Smad1 as bait. Furthermore we have shown CHIP-Smad interaction using the (35)S-labeled CHIP protein, which can interact with glutathione S-transferase (GST)-Smad1 and GST-Smad4 in an in vitro protein-binding assay. The CHIP-Smad interaction has been confirmed in vivo in mammalian cells through coimmunoprecipitation. Interestingly, we demonstrate that the coexpression of Smad1 and Smad4 with the CHIP protein results in the degradation of the Smad proteins through a ubiquitin-mediated process. Consistent with the observation that CHIP induces Smad1 degradation, we further show that the expression of CHIP can inhibit the transcriptional activities of the Smad1/Smad4 complex induced by BMP signals. Intriguingly, pBS/U6/CHIPi, which diminishes CHIP expression, significantly enhanced Smad1/Smad4- or BMPRIB(QD)-induced gene transcription. These results suggest that CHIP can interact with the Smad1/Smad4 proteins and block BMP signal transduction through the ubiquitin-mediated degradation of Smad proteins.

Binding Sites↗

PubMed2004

p42/p44 Mitogen-activated protein kinase signal transduction pathway regulates interleukin-6 expression in PC3 cells, a line of hormone-refractory prostate cancer cells.

The mechanisms that regulate prostate cancer growth and proliferation are not fully understood. IL-6, a multifunctional cytokine, has been shown to play an important role in prostate cancer biology. Functional role of MAP-kinase signal transduction pathways in prostate biology has not been evaluated in detail. In the present study we evaluated the effects of modulation of p42/44 MAP kinase signal transduction pathway on IL-6 expression and secretion by PC3 cells, a line of hormone refractory prostate cancer cells. Results presented, herein, demonstrate that modulation of p42/44 MAP kinase activity results in partial inhibition of synthesis and secretion of IL-6. These data suggest that modulation of p42/p44 may result in regulation of other survival pathways as well.

Base Sequence↗

PubMed2004

Novel peptidomimetic inhibitors of signal transducer and activator of transcription 3 dimerization and biological activity.

The critical role of signal transducer and activator of transcription 3 (Stat3) in the growth and survival of human tumor cells identifies it as a promising target for cancer drug discovery. We previously identified a Stat3 SH2 domain-binding phosphopeptide, PY*LKTK, and its tripeptide derivatives, PY*L and AY*L (where Y* represents phosphotyrosine), which inhibit Stat3 biochemical activity and biological function. Here, we report novel peptidomimetic compounds based on PY*L (or AY*L) with substitution of the Y-1 residue by benzyl, pyridyl, or pyrazinyl derivatives that are selective and greater than 5-fold more potent in disrupting Stat3 activity in vitro than lead tripeptides. The biological activities of these derivatives mirror that originally observed for peptides. In this context, the representative peptidomimetic ISS 610 with 4-cyanobenzoate substitution inhibits constitutive Stat3 activity in Src-transformed mouse fibroblasts and human breast and lung carcinoma cells. This effect is not evident with the non-phosphorylated counterpart, ISS 610NP, consistent with interaction of peptidomimetics with the SH2 domain of Stat3. Moreover, ISS 610 induces cell growth inhibition and apoptosis of Src-transformed fibroblasts that contain persistently active Stat3. We present the first report of a peptidomimetic approach to design of small-molecule inhibitors of Stat3 that are also among the first examples of disruptors of transcription factor dimerization with the potential for novel cancer therapy.

Agar↗

PubMed2004

[Establishment of high-throughput drug screening cell models based on JAK-STAT signal pathway].

AIM: To discover new drugs which may be applied to diseases of the immune system, hemogenesis system diseases and tumors, several high-throughput drug screening cell models based on JAK-STAT signal pathway have been established. METHODS: Four repeats of STAT DNA binding conserved sequences were synthesized, subcloned into pGL-Luc reporter vector and stably transfected into cell lines in vitro. Cell clones with high copy numbers of STAT binding sites and reporter genes were chosen as high-throughput drug screening cell models. The cell models were tested with known anti-allergic drugs and anti-tumor drugs by determining luciferase activity. The reaction was performed in 96 well micro-plates with a final volume of 50 microL. RESULTS: The cell models by performing rapid fluorescence assay were shown to be highly sensitive and stable after testing with cytokine and drugs. The modification of the expression plasmid simplified this method and made it more practical. It also provided good linear correlation, wide range of assay, highly sensitive and good reproducibility. CONCLUSION: The method can be performed by high-throughput drug screening for effective extraction of Chinese traditional herbs.

Anti-Allergic Agents↗

PubMed2004

[Effect of sodium butyrate in combination with ATRA on the proliferation/differentiation of MDS cell line SKM-1].

The study was purposed to explore the molecular mechanisms of sodium butyrate (NaB) action on SKM-1 cell proliferation/differentiation and to study its synergistic effect with all-trans retinoic acid (ATRA). SKM-1 cells were grown in the absence or presence of NaB and/or ATRA; the percentage of viable cells was determined by trypan blue exclusion; differentiation was investigated by nitro-blue tetrazolium (NBT) reduction; adhesion molecules of cell surface were analysed by FACS; cell cycle distribution was studied after DNA staining by propidium iodide; D-type cyclins, CDK and P21 mRNA were detected by reverse transcription-polymerase chain reaction (RT-PCR). The results showed that NaB and/or ATRA blocked cells mainly in the G0/G1 phase of the cell cycle; ATRA inhibited the mRNA expression of CDK6, CDK4, cyclin D3 and cyclin D1; NaB inhibited the mRNA expression of CDK2, cyclin D2 and cyclin D1; ATRA and NaB inhibited the mRNA expression of CDK6, CDK4, CDK2, cyclin D1, cyclin D2 and cyclin D3; ATRA and/or NaB both stimulated p21 expression at the mRNA levels. It is concluded that the NaB effect on cell proliferation/differentiation may be linked to its ability to induce expression of p21 mRNA and inhibit the cyclin D-CDK complexes. These observations support the claim that NaB has the synergistic effect with ATRA.

Aged↗

PubMed2003

Ascorbic acid antagonizes the inhibitory effect of acute ethanol on nitrite levels in the striatum of freely moving mice.

The effect of exogenous ascorbic acid (AA) on acute ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice was investigated by using microdialysis coupled to high performance liquid chromatography with electrochemical detection. The results showed that exogenous AA had no effect on basal extracellular levels of nitrites, but significantly increased striatal extracellular contents of AA in a dose-depended manner. Co-administration of AA with ethanol significantly antagonized the ethanol-induced decrease in extracellular nitrites contents, but did not affect ethanol-induced release of AA. These data provided the first evidence of an antagonistic action of AA on ethanol-induced decrease in extracellular nitrites contents in striatum of freely moving mice.

Animals↗

PubMed2003

Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice.

In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) and electrochemical detection were used to evaluate the effects of either L-arginine (L-Arg), the substrate of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a non-selective NOS inhibitor, or sodium nitroprusside (SNP), a donor of NO, on the ethanol-induced release of ascorbic acid (AA) in the striatum of freely moving mice. Drugs were administered intrastriatally via the microdialysis probe and ethanol (2-4 g/kg) was administered intraperitoneally. The results showed that L-arginine (1-10 mg/ml) had no effect on either the basal AA contents in striatal extracellular fluid or the ethanol-induced release of AA. L-NAME (10(-4) to 10(-3) mg/ml) and SNP (10(-4) to 10(-3) mg/ml) both reduced the basal AA concentrations in striatal extracellular fluid. L-NAME significantly inhibited ethanol-induced release of AA, while SNP only had a transient inhibitory effect on the ethanol-induced release of AA. SNP significantly increased dehydroascorbic acid (DHAA) contents and DHAA/AA ratio but had no effect on the total AA contents (AA and DHAA contents) in striatal extracellular fluid, while L-NAME had no effect on DHAA contents but decreased the total AA contents in striatal extracellular fluid. Only high concentration L-NAME induced a transient increase in DHAA/AA ratio. Our results suggest that nitric oxide (NO) might not directly be involved in the mechanism of ethanol-induced release of AA in mouse striatum.

Animals↗

PubMed2003

Regulation of the cyclin D3 promoter by E2F1.

We have previously demonstrated that ectopic expression of E2F1 is sufficient to drive quiescent cells into S phase and that E2F1 expression can contribute to oncogenic transformation. Key target genes in this process include master regulators of the cell cycle, such as cyclin E, which regulates G(1) progression, and cyclin A, which is required for the initiation of DNA synthesis. In the present work, we present novel evidence that a second G(1) cyclin, cyclin D3, is also potently activated by E2F1. First, an estrogen receptor-E2F1 fusion protein (ER-E2F1) potently activates the endogenous cyclin D3 mRNA upon treatment with 4-hydroxytamoxifen, which induces nuclear accumulation of the otherwise cytosolic fusion protein. Furthermore, trans-activation of cyclin D3 by ER-E2F1 occurs even in the presence of the protein synthesis inhibitor cycloheximide and thus appears direct. Second, all of the growth-stimulatory members of the E2F family (E2F1, -2, and -3A) potently activate a cyclin D3 promoter reporter, whereas growth-restraining members of the family (E2F4, -5, and -6) have little effect. Third, recombinant E2F1 binds with high affinity to the cyclin D3 promoter in vitro. Fourth, chromatin immunoprecipitation assays demonstrate that endogenous E2F1 is associated with the cyclin D3 promoter in vivo. Finally, mapping experiments localize the essential E2F regulatory element of the cyclin D3 promoter to a noncanonical E2F site in the promoter between nucleotides -143 and -135 relative to the initiating methionine codon. We conclude that in addition to cyclins E and A, E2F family members can also activate one member of the D-type cyclins, further contributing to the ability of the stimulatory E2F family members to drive cellular proliferation.

Cell Cycle Proteins↗

PubMed2003

Flavopiridol down-regulates antiapoptotic proteins and sensitizes human breast cancer cells to epothilone B-induced apoptosis.

The molecular mechanisms underlying the cell cycle growth-inhibitory and apoptotic effects of flavopiridol (FP) were determined in human breast cancer cells. Treatment with FP caused accumulation in the G(1) phase of the cell cycle and induced apoptosis of SKBR-3 and MB-468 cells. This was associated with down-regulation of the levels of cyclins D1 and B1, as well as with inhibition of cyclin-dependent kinase (cdk) 1, cdk2, and cdk4. FP-induced apoptosis was accompanied by a conformational change and mitochondrial localization of Bax. This resulted in the accumulations of cytochrome c, Smac, and Omi/HtrA2 in the cytosol and induced the poly(ADP-ribose) polymerase cleavage activity of caspase-3. Treatment with FP also attenuated the mRNA and protein levels of XIAP, cIAP-2, Mcl-1, Bcl-x(L), and survivin. In MB-468 cells with overexpression of Bcl-2 (468/Bcl-2), FP-induced Bax conformational change and apoptosis were inhibited, whereas the FP-mediated decline in the levels of IAP proteins, Mcl-11 and Bcl-x(L) remained unaltered. The effects of cotreatment with FP and the nontaxane tubulin-polymerizing agent epothilone (Epo) B were also determined in MB-468 cells. Sequential treatment with Epo B followed by FP induced significantly more apoptosis of MB-468 cells than treatment with the reverse sequence of FP followed by Epo B or treatment with either agent alone (P < 0.05). Treatment with Epo B followed by FP induced more Bax conformational change and was associated with a greater decline in the levels of XIAP, cIAP-2, Mcl-1, and Bcl-x(L). However, MB-468/Bcl-2 cells remained relatively resistant to Epo B followed by FP. Taken together, these findings suggest that the superior sequence-dependent anti-breast cancer activity of Epo B followed by FP may be due to FP-induced Bax conformational change and down-regulation of the antiapoptotic IAP, Bcl-x(L), and Mcl-1 proteins, but this treatment may not overcome the resistance to apoptosis of breast cancer cells conferred by overexpression of Bcl-2.

Antineoplastic Agents↗

PubMed2003

A critical role for Stat3 signaling in immune tolerance.

Antigen-presenting cells (APCs) can induce T cell activation as well as T cell tolerance. The molecular mechanisms by which APCs regulate this critical decision of the immune system are not well understood. Here we show that Stat3 signaling plays a critical role in the induction of antigen-specific T cell tolerance. Targeted disruption of Stat3 signaling in APCs resulted in priming of antigen-specific CD4(+) T cells in response to an otherwise tolerogenic stimulus in vivo. Furthermore, APCs devoid of Stat3 effectively break antigen-specific T cell anergy in vitro. Conversely, increased Stat3 activity in APCs led to impaired antigen-specific T cell responses. Stat3 signaling provides, therefore, a novel molecular target for manipulation of immune activation/tolerance, a central decision with profound implications in autoimmunity, transplantation, and cancer immunotherapy.

Animals↗

PubMed2003

Synthesis and characterization of nano-HA/PA66 composites.

Based on the bioactivity and biocompatibility of hydroxyapatite (HA) and the excellent mechanical performance of polyamide 66 (PA66), a composite of nanograde HA with PA66 was designed and fabricated to mimic the structure of biological bone which exhibits a composite of nanograde apatite crystals and natural polymer. The HA/PA66 composite combines the bioactivity of HA and the mechanical property of PA66. This study focused on the preparation method of HA/PA66 composite and the influence of HA crystals on the characterization of the composite. HA slurry was used directly to prepare HA/PA66 composite by a solution method, in which HA is able to form hydrogen bond, i.e. chemical bonding with PA66. The nano-HA needle-like crystals treated by hydrothermal method are better in the particle size distribution and the particle dispersion. The morphology, crystal structure and crystallinity as well as crystal size of these needle-like crystals are similar to bone apatite. The nano-HA needle-like crystals dispersed uniformly in PA66 matrix with reinforcement effect and can prevent the micro-crackle spreading into cleft and fracture during the deformation process. The mechanical testing shows that the nano-HA/PA66 composite has a good mechanical property, and may be a promising bone replacement material.

Journal Article↗

PubMed2003

Effects of sintering temperature on structure of hydroxyapatite studied with Rietveld method.

It is obvious that the sintering temperature of hydroxyapatite (HA) ceramics significantly affects their biological responses in vitro or in vivo. The HA ceramics sintered at different temperatures exhibit a wide variation of biological response, but the correlation of this variation with the parameters of HA crystalline structure is not fully investigated. In present study, the crystalline structure of HA powders sintered at different temperatures at 600, 800, 1000, 1200 degrees C, was characterized using X-ray diffraction (XRD), and then refined with Rietveld method. A series of structure parameters, such as, cell lattice parameters (a and c) and bond length, distances of special atoms on surface to nearest atom, a numerical index of distortion for PO(4) tetrahedron, as well as internal energy and density of HA cell, were calculated to characterize the crystalline structure of HA at atom level. The broadening effect of XRD reflections was also separated to calculate the micro-strain/crystalline size, respectively. These parameters of HA crystalline structure and cell demonstrated that with rising of the sintered temperature, the internal energy and micro-strain of HA cell decreased, but the crystalline size increased. The regularity of PO(4) tetrahedron and distance between Ca(1) and O(3) in HA cell showed the same tendency as the internal energy and micro-strain with sintering temperature. All of these parameters indicated that HA became more stable with the rising of sintering temperature.

Journal Article↗

PubMed2002

Inhibition of Bcr-Abl kinase activity by PD180970 blocks constitutive activation of Stat5 and growth of CML cells.

Chronic myelogenous leukemia (CML) is a myeloproliferative disease characterized by the BCR-ABL genetic translocation and constitutive activation of the Abl tyrosine kinase. Among members of the Signal Transducers and Activators of Transcription (STAT) family of transcription factors, Stat5 is activated by the Bcr-Abl kinase and is implicated in the pathogenesis of CML. We recently identified PD180970 as a new and highly potent inhibitor of Bcr-Abl kinase. In this study, we show that blocking Bcr-Abl kinase activity using PD180970 in the human K562 CML cell line resulted in inhibition of Stat5 DNA-binding activity with an IC(50) of 5 nM. Furthermore, abrogation of Abl kinase-mediated Stat5 activation suppressed cell proliferation and induced apoptosis in K562 cells, but not in the Bcr-Abl-negative myeloid cell lines, HEL 92.1.7 and HL-60. Dominant-negative Stat5 protein expressed from a vaccinia virus vector also induced apoptosis of K562 cells, consistent with earlier studies that demonstrated an essential role of Stat5 signaling in growth and survival of CML cells. RNA and protein analyses revealed several candidate target genes of Stat5, including Bcl-x, Mcl-1, c-Myc and cyclin D2, which were down-regulated after treatment with PD180970. In addition, PD180970 inhibited Stat5 DNA-binding activity in cultured primary leukemic cells derived from CML patients. To detect activated Stat5 in CML patient specimens, we developed an immunocytochemical assay that can be used as a molecular end-point assay to monitor inhibition of Bcr-Abl signaling. Moreover, PD180970 blocked Stat5 signaling and induced apoptosis of STI-571 (Gleevec, Imatinib)-resistant Bcr-Abl-positive cells. Together, these results suggest that the mechanism of action of PD180970 involves inhibition of Bcr-Abl-mediated Stat5 signaling and provide further evidence that compounds in this structural class may represent potential therapeutic agents for CML.

Apoptosis↗

PubMed2002

Molecular characterization and sensitivity of STI-571 (imatinib mesylate, Gleevec)-resistant, Bcr-Abl-positive, human acute leukemia cells to SRC kinase inhibitor PD180970 and 17-allylamino-17-demethoxygeldanamycin.

Using human acute leukemia HL-60/Bcr-Abl (with ectopic expression of p185 Bcr-Abl) and K562 cells (with endogenous expression of p210 Bcr-Abl) subjected to a continuous selection pressure of up to 1.0 micro M Gleevec (imatinib mesylate, STI-571), we have isolated Gleevec-resistant K562 R (+Bcr-Abl), K562 R (-Bcr-Abl), and HL-60/Bcr-Abl R cells, which display disparate level and activity of Bcr-Abl tyrosine kinase (TK). As compared with their sensitive counterparts, Gleevec-resistant cell types were >/=5-fold resistant to Gleevec-induced apoptosis. Bcr-Abl protein levels were significantly increased in HL-60/Bcr-Abl R and K562 R (+Bcr-Abl) cells, but K562 R (-Bcr-Abl) cells showed a marked decline in the mRNA and protein levels and activity of Bcr-Abl. Bcr-Abl TK level and activity corresponded to the signal transducers and activators of transcription-5 DNA binding activity and up-regulation of heat shock protein 70 levels. The decline in Bcr-Abl expression and TK activity in K562 R (-Bcr-Abl) cells was associated with reduced AKT kinase and signal transducers and activators of transcription-5 DNA binding activities and increased sensitivity to the death ligand Apo-2 ligand/tumor necrosis factor-related apoptosis-inducing ligand and 1-beta-D-arabinofuranosylcytosine-induced apoptosis. All Gleevec-resistant cell types were sensitive to 17-allylamino-17-demethoxygeldanamycin (17-AAG)- and PD180970 (a SRC and Bcr-Abl TK inhibitor)-induced apoptosis. Treatment with 17-AAG or PD180970 also induced apoptosis of CD34+ leukemic cells from three patients with chronic myeloid leukemia in blast crisis who had progressive leukemia while receiving Gleevec therapy. Taken together, these findings indicate that in addition to overexpression or mutations in Bcr-Abl, resistance to Gleevec may also develop due to a loss of Bcr-Abl expression. These findings also support the rationale to test the in vivo efficacy of 17-AAG and PD180970 against STI-571-resistant Bcr-Abl-positive acute leukemias.

Benzamides↗