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1.  Gleevec (STI-571) inhibits lung cancer cell growth (A549) and potentiates the cisplatin effect in vitro 
Molecular Cancer  2003;2:1.
Background
Gleevec (aka STI571, Imatinib) is a recently FDA approved anti-tumor drug for chronic myelogenous leukemia. Gleevec binds specifically to BCR-ABL tyrosine kinase and inhibit the tyrosine kinase activity. It cross-reacts with another two important membrane tyrosine kinase receptors, c-kit and PDGF receptors. We sought to investigate if Gleevec has a potential role in treatment of non-small cell lung cancer.
Results
We have shown that Gleevec alone can inhibit the A549 lung cancer cell growth in dose-dependent manner, and the optimal concentration of Gleevec inhibition of A549 cell growth is at the range of 2–3 μM (IC50). We have also shown that A549 cells are resistant to cisplatin treatment (IC50 64 μM). Addition of Gleevec to the A549 cells treated with cisplatin resulted in a synergistic cell killing effect, suggesting that Gleevec can potentiate the effect of cisplatin on A549 cells. We also showed that the A549 lung cancer cells expresses the platelet derived growth factor receptor α, and the inhibitory effects of Gleevec on A549 cells is likely mediated through inhibition of PDGFR α phosphorylation. We further tested 33 lung cancer patients' tumor specimens to see the frequency of PDGFR-α expression by tissue micro-arrays and immunohistochemistry. We found that 16 of the 18 squamous carcinomas (89%), 11 of the 11 adenocarcinomas (100%), and 4 of the 4 small cell lung cancers (100%) expressed PDGFR-α.
Conclusion
These results suggest a potential role of Gleevec as adjuvant therapeutic agent for treatment of non-small cell lung cancer.
doi:10.1186/1476-4598-2-1
PMCID: PMC149413  PMID: 12537587
Lung cancer A549 cell; Gleevec (STI571); PDGF receptor
2.  Hypopigmentation in an African patient treated with imatinib mesylate: a case report. 
Imatinib mesylate (STI 571, Gleevec) is a potent bcr-abl tyrosine kinase inhibitor. It also inhibits c-kit tyrosine kinase. Imatinib mesylate is active in the treatment of cronic myeloid leukemia (CML) and gastrointestinal stromal tumors (GIST). It is considered by some authorities to be the standard of care in newly diagnosed CML as well as patients in chronic phase who do not have a related match. C-kit and its ligand stem-cell factor regulate melanocyte development and survival. Hypopigmentation in patients receiving imatinib mesylate for CML has been reported recently. In this article, we report a black Nigerian male with GIST, who developed hypopigmentation of distal parts of digits, as well as generalized lightening of skin on the body three months after receiving imatinib mesylate. We believe that this is the first case of hypopigmentation reported in a black patient with GIST.
Images
PMCID: PMC2594583  PMID: 12934870
3.  Pro-apoptotic activity of bortezomib in gastrointestinal stromal tumor (GIST) cells 
Cancer research  2009;70(1):150-159.
Gastrointestinal stromal tumors (GISTs) are caused by activating mutations in the KIT or PDGFRA receptor tyrosine kinase genes. Although more than 85% of GIST patients treated with the small molecule inhibitor imatinib mesylate (Gleevec®) achieve disease stabilization, complete remissions are rare and a substantial proportion of patients develop resistance to imatinib over time. We previously reported that upregulation of soluble, non chromatin-bound histone H2AX has an important role in imatinib-induced GIST cell apoptosis and that H2AX levels, in untreated GIST, are maintained at low levels by a pathway that involves KIT, PI3K, and the ubiquitin-proteasome system. Here, we asked whether bortezomib-mediated inhibition of the ubiquitin-proteasome machinery could lead to upregulation of histone H2AX and GIST cell death. We show that bortezomib rapidly triggers apoptosis in GIST cells through a combination of mechanisms involving H2AX upregulation and loss of KIT protein expression. We demonstrate downregulation of KIT transcription as an underlying mechanism for bortezomib-mediated inhibition of KIT expression. Modulation of the nuclear factor-kappa-B (NF-κB) signaling pathway did not appear to play a major role in bortezomib-induced GIST cell death. Importantly, bortezomib induced apoptosis in two imatinib-resistant GIST cell lines as well as a short-term culture established from an imatinib-resistant GIST. Collectively, our results show that inhibition of the proteasome using bortezomib can effectively kill imatinib-sensitive and imatinib-resistant GIST cells in vitro and provide a rationale to test the efficacy of bortezomib in GIST patients.
doi:10.1158/0008-5472.CAN-09-1449
PMCID: PMC2805033  PMID: 20028860
4.  Advanced gastrointestinal stromal tumors successfully treated with imatinib mesylate: a report of two cases. 
Activation of kit-receptor tyrosine kinase occurs in all cases of gastrointestinal stromal tumors, regardless of the mutation status of kit. Imatinib mesylate (STI 571,Gleevec) is a selective inhibitor of certain protein tyrosine kinases. It has been shown in preclinical models and clinical studies to have activity against such tumors. The aim of the present study was to report the efficacy of imatinib mesylate in the treatment of advanced gastrointestinal stromal tumors. Two adults with histologically confirmed, unresectable, and metastatic gastrointestinal stromal tumors that expressed CD117 (a marker of kit-receptor tyrosine kinase) were identified at our institution during 2000-2002. As the diseases were advanced and not amenable to surgery, chemotherapy, or radiation therapy, imatinib mesylate was used, because this targeted inhibitor has been shown to be active against advanced gastrointestinal stromal tumors and has a mild toxicity profile. Imatinib mesylate induced a sustained response in both patients with advanced unresectable or metastatic gastrointestinal stromal tumors. Inhibition of the KIT signal-transduction pathway is a promising treatment for advanced gastrointestinal stromal tumors, which resist conventional chemotherapy.
PMCID: PMC2594846  PMID: 14717479
5.  Imatinib mesylate inhibits CD4+CD25+ regulatory T cell activity and enhances active immunotherapy against BCR-ABLnegative tumors 
Imatinib mesylate (Gleevec, STI571), a selective inhibitor of a restricted number of tyrosine kinases, has been effectively used for the treatment of Philadelphia chromosome positive leukemias and gastrointestinal stromal tumors. Imatinib may also directly influence immune cells. Suppressive as well as stimulating effects of this drug on CD4+ and CD8+ T lymphocytes or dendritic cells have been reported. In the current study, we have investigated the influence of imatinib mesylate on CD4+CD25+FoxP3+ regulatory T cells (Treg), a critical population of lymphocytes that contributes to peripheral tolerance. Used at concentrations achieved clinically, imatinib impaired Treg immunosuppressive function and FoxP3 expression but not production of IL-10 and TGF-β in vitro. Imatinib significantly reduced the activation of the transcription factors STAT3 and STAT5 in Treg. Analysis of Treg TCR-induced signaling cascade indicated that imatinib inhibited phosphorylation of ZAP70 and LAT. Substantiating these observations, imatinib treatment of mice decreased Treg frequency and impaired their immunosuppressive function in vivo. Furthermore, imatinib mesylate significantly enhanced anti-tumor immune responses to dendritic cell-based immunization against an imatinib-resistant BCR-ABL negative lymphoma. The clinical applications of imatinib mesylate might thus be expanded with its use as a potent immunomodulatory agent targeting Treg in cancer immunotherapy.
PMCID: PMC2579962  PMID: 18981115
Tumor Immunity; T cells; Tolerance/Suppresssion/Anergy; Vaccination; Imatinib Mesylate
6.  Gleevec Increases Levels of the Amyloid Precursor Protein Intracellular Domain and of the Amyloid-β–degrading Enzyme Neprilysin 
Molecular Biology of the Cell  2007;18(9):3591-3600.
Amyloid-β (Aβ) deposition is a major pathological hallmark of Alzheimer's disease. Gleevec, a known tyrosine kinase inhibitor, has been shown to lower Aβ secretion, and it is considered a potential basis for novel therapies for Alzheimer's disease. Here, we show that Gleevec decreases Aβ levels without the inhibition of Notch cleavage by a mechanism distinct from γ-secretase inhibition. Gleevec does not influence γ-secretase activity in vitro; however, treatment of cell lines leads to a dose-dependent increase in the amyloid precursor protein intracellular domain (AICD), whereas secreted Aβ is decreased. This effect is observed even in presence of a potent γ-secretase inhibitor, suggesting that Gleevec does not activate AICD generation but instead may slow down AICD turnover. Concomitant with the increase in AICD, Gleevec leads to elevated mRNA and protein levels of the Aβ-degrading enzyme neprilysin, a potential target gene of AICD-regulated transcription. Thus, the Gleevec mediated-increase in neprilysin expression may involve enhanced AICD signaling. The finding that Gleevec elevates neprilysin levels suggests that its Aβ-lowering effect may be caused by increased Aβ-degradation.
doi:10.1091/mbc.E07-01-0035
PMCID: PMC1951756  PMID: 17626163
7.  Gastrointestinal stromal tumor (GIST) recurrence following surgery: review of the clinical utility of imatinib treatment 
Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the gastrointestinal tract. Surgery with complete removal of the tumor is the primary treatment for resectable GIST and the only chance of cure. However, recurrence after surgery is common. The 2 main prognostic factors are the mitotic activity and the size of the tumor. Tumor rupture is also a risk factor for postoperative recurrence, and extra care should be taken while manipulating this soft and friable tumor. Imatinib mesylate (IM, Gleevec®, Novartis, Basel, Switzerland) is a tyrosine kinase inhibitor and was first studied in the palliative setting for metastatic GIST patients in the year 2000. It is now the cornerstone of metastatic GIST treatment. IM also plays an important role as an adjuvant treatment for resectable GIST and has been shown to increase the recurrence-free survival in phase III studies. However, some points remain to be clarified. Notably, the ideal duration of adjuvant IM after surgery is still unclear. It is also difficult to determine the exact place of surgery in metastatic or recurrent GIST patients in the IM era. A multidisciplinary approach is, therefore, mandatory to offer GIST patients the best treatment available.
doi:10.2147/TCRM.S5634
PMCID: PMC2952484  PMID: 20957137
Gleevec; adjuvant; neoadjuvant; metastasis; sunitinib
8.  An update on molecular genetics of gastrointestinal stromal tumours 
Journal of Clinical Pathology  2006;59(6):557-563.
Gastrointestinal stromal tumours (GISTs) are the most common primary mesenchymal tumours of the gastrointestinal tract. Most of them show activating mutations of the genes coding for KIT or platelet‐derived growth factor receptor α (PDGFRα), two receptor tyrosine kinases (RTKs). The RTK inhibitor Imatinib (Gleevec®, Novartis, Switzerland), induces regression of the tumour. The level of response to treatment, together with other clinicopathological parameters is related to the type and site of the activating mutation, thus suggesting that these tumours should be classified according to the molecular context. This is confirmed also by the phenomenon of the resistance to treatment, which arises because of different mechanisms (second mutation, amplification, activation of other RTKs) and can be fought only by specific RTK inhibitors, that are at present under development. RTK activation involves an homogeneous transduction pathway whose components (MAPK, AKT, PI3K, mTOR and RAS) are possible targets of new molecular treatment. A new paradigm of classification integrating the classic pathological criteria with the molecular changes will permit personalised prognosis and treatment.
doi:10.1136/jcp.2005.031112
PMCID: PMC1860404  PMID: 16731599
9.  Evaluation of the Expression of C-kit (CD117) in Ependymomas and Oligodendrogliomas 
Disease markers  2012;33(2):61-68.
C-kit is a proto-oncogene located on the long arm of chromosome 4. Its product, CD117, is a specific immunohistochemical (IHQ) marker that is associated with response to a potent tyrosine kinase inhibitor therapy with STI-571 (Gleevec®) in chronic myelogenous leukemia and GISTs. In our study, we aimed to evaluate the expression of CD117 in glial tumors as this finding may guide therapeutic approaches for these brain tumors. Ependymomas and oligodendrogliomas, in formalin fixed and paraffin embedded blocks were assayed for CD117 immunoreactivity using anti-c-kit (CD117, DAKO). GISTs were used as positive control. We observed immunoreactivity of CD117 protein in 25.5% of tumors in both histological types. In oligodendrogliomas, there was an association between older age at diagnosis and positivity for CD117 (P = 0.039). In addition, we observed an association between higher tumor grade (grade III) and positivity for CD117 (P = 0.007). No clinical association was observed in ependymomas (P > 0.05). This study encourages further investigations, considering that CD117 may be a possible oncogenic factor in some glial tumors. In this case, tumors that express this marker may eventually benefit from a therapy with selective inhibitors of receptor kinases.
doi:10.3233/DMA-2012-0905
PMCID: PMC3810688  PMID: 22846208
CD117 c-kit; ependymomas; glial tumors; oligodendrogliomas
10.  Pityriasis rosea-like Drug Eruption Induced by Imatinib Mesylate (Gleevec™) 
Annals of Dermatology  2011;23(Suppl 3):S360-S363.
Imatinib mesylate (Gleevec™, STI571), a selective inhibitor of BCR-ABL, c-Kit, and platelet-derived factor receptor, has been used to treat chronic myelogenous leukemia (CML) and gastrointestinal stromal tumors. Although its use has been associated with various adverse cutaneous reactions, pityriasis rosea-like drug eruptions are rare. Here, we report a case of pityriasis rosea-like drug eruption that developed following the administration of imatinib mesylate to treat CML.
doi:10.5021/ad.2011.23.S3.S360
PMCID: PMC3276797  PMID: 22346278
Imatinib mesylate; Pityriasis rosea
11.  Is exon mutation analysis needed for adjuvant treatment of gastrointestinal stromal tumor? 
Gastrointestinal stromal tumors (GISTs) are the most common soft tissue sarcoma of the gastrointestinal tract, resulting from an activating mutation of stem cell factor receptor (KIT), and an activating mutation of the homologous platelet-derived growth factor receptor alpha (PDGFRA) kinase. Most GISTs (90%-95%) are KIT-positive. About 5% of GISTs are truly negative for KIT expression. GISTs have been documented to resistant conventional chemotherapeutics. Due to the KIT activation that occurs in the majority of the cases, KIT inhibition is the primary treatment approach in the adjuvant treatment of metastatic GISTs. Imatinib mesylate is an oral agent that is a selective protein tyrosine kinase inhibitor of the KIT protein tyrosine kinase, and it has demonstrated clinical benefit and objective tumor responses in most GIST patients in phase II and III trials. The presence and the type of KIT or PDGFRA mutation are predictive of response to imatinib therapy in patients with advanced and metastatic disease. Molecular analysis in phase I-II trials revealed significant differences in objective response, progression-free survival, and overall survival between GISTs with different kinase mutations. The aim of this letter is to touch on the need for exon mutation analysis for adjuvant treatment with imatinib in GIST patients.
doi:10.3748/wjg.v19.i1.144
PMCID: PMC3542749  PMID: 23326179
Imatinib; Gastrointestinal stromal tumor; Activating mutation; Stem cell factor receptor; Platelet-derived growth factor receptor alpha; Mutation analysis
12.  Study of the role of “gatekeeper” mutations V654A and T670I of c-kit kinase in the interaction with inhibitors by means mixed molecular dynamics/docking approach 
Bioinformation  2011;7(6):296-298.
The over-expression of c-kit proto-oncogene has been reported in hematopoietic cells, small cell lung cancer, and gastrointestinal stromal tumors. The clinical importance of c-kit expression in tumors focused the research towards inhibitors of this tyrosine kinase. Imatinib (Gleevec®) was the first compound used in therapy, but mutations on c-kit led to reduced effectiveness or ineffectiveness of this treatment. Other compounds are likely to be effective against mutants, such as Sunitinib (Sutent®), but the need for new and most effective inhibitors against mutants is still critical. We report mixed Molecular Dynamics/Docking study with the aim to unveil the molecular mechanism involved in the resistance of Imatinib, Sunitinib, and other known compounds against the “gatekeeper” mutants V654A e T670I. We tried to evidence strong and weak features of actual inhibitors in order to identify the guidelines to design new and most potent inhibitors against c-kit mutants.
PMCID: PMC3280498  PMID: 22355224
13.  Synthesis and positron emission tomography studies of carbon-11-labeled imatinib (Gleevec) 
Nuclear medicine and biology  2007;34(2):153-163.
Introduction
Imatinib mesylate (Gleevec) is a well known drug for treating chronic myeloid leukemia and gastrointestinal stromal tumors. Its active ingredient, imatinib ([4-[(4-methyl-1-piperazinyl)methyl]-N-[4-methyl-3-[[4-(3-pyridyl)-2-pyrimidinyl]amino]phenyl]benzamide), blocks the activity of several tyrosine kinases. Here we labeled imatinib with carbon-11 as a tool for determining the drug distribution and pharmacokinetics of imatinib, and we carried out positron emission tomography (PET) studies in baboons.
Methods
[N-11C-methyl]imatinib was synthesized from [11C]methyl iodide and norimatinib was synthesized by the demethylation of imatinib (isolated from Gleevec tablets) according to a patent procedure [Collins JM, Klecker RW Jr, Anderson LW. Imaging of drug accumulation as a guide to antitumor therapy. US Patent 20030198594A1, 2003]. Norimatinib was also synthesized from the corresponding amine and acid. PET studies were carried out in three baboons to measure pharmacokinetics in the brain and peripheral organs and to determine the effect of a therapeutic dose of imatinib. Log D and plasma protein binding were also measured.
Results
[N-11C-methyl]imatinib uptake in the brain is negligible (consistent with P-glycoprotein-mediated efflux); it peaks and clears rapidly from the heart, lungs and spleen. Peak uptake and clearance occur more slowly in the liver and kidneys, followed by accumulation in the gallbladder and urinary bladder. Pretreatment with imatinib did not change uptake in the heart, lungs, kidneys and spleen, and increased uptake in the liver and gallbladder.
Conclusions
[N-11C-methyl]imatinib has potential for assessing the regional distribution and kinetics of imatinib in the human body to determine whether the drug targets tumors and to identify other organs to which the drug or its labeled metabolites distribute. Paired with tracers such as 2-deoxy-2-[18F]fluoro-D-glucose (18FDG) and 3′-deoxy-3′-[18F]fluorothymidine (18FLT), [N-11C-methyl]imatinib may be a useful radiotracer for planning chemotherapy, for monitoring response to treatment and for assessing the role of drug pharmacokinetics in drug resistance.
doi:10.1016/j.nucmedbio.2006.11.004
PMCID: PMC2866181  PMID: 17307123
Imatinib (Gleevec); PET; Carbon-11; Drug pharmacokinetics
14.  FoxO Tumor Suppressors and BCR-ABL-Induced Leukemia: A Matter of Evasion of Apoptosis 
Biochimica et biophysica acta  2007;1785(1):63-84.
Numerous studies have revealed that the BCR-ABL oncoprotein abnormally engages a multitude of signaling pathways, some of which may be important for its leukemogenic properties. Central to this has been the determination that the tyrosine kinase function of BCR-ABL is mainly responsible for its transforming potential, and can be targeted with small molecule inhibitors, such as imatinib mesylate (Gleevec, STI-571). Despite this apparent success, the development of clinical resistance to imatinib therapy, and the inability of imatinib to eradicate BCR-ABL-positive malignant hematopoietic progenitors demand detailed investigations of additional effector pathways that can be targeted for CML treatment. The promotion of cellular survival via the suppression of apoptotic pathways is a fundamental characteristic of tumor cells that enables resistance to anti-cancer therapies. As substrates of survival kinases such as Akt, the FoxO family of transcription factors, particularly FoxO3a, has emerged as playing an important role in the cell cycle arrest and apoptosis of hematopoietic cells. This review will discuss our current understanding of BCR-ABL signaling with a focus on apoptotic suppressive mechanisms and alternative approaches to CML therapy, as well as the potential for FoxO transcription factors as novel therapeutic targets.
doi:10.1016/j.bbcan.2007.10.003
PMCID: PMC2180393  PMID: 17980712
Apoptosis; BCR-ABL; CML; FoxO; Imatinib Resistance; Proteasomal Degradation
15.  Imatinib Reverses Doxorubicin Resistance by Affecting Activation of STAT3-Dependent NF-κB and HSP27/p38/AKT Pathways and by Inhibiting ABCB1 
PLoS ONE  2013;8(1):e55509.
Despite advances in cancer detection and prevention, a diagnosis of metastatic disease remains a death sentence due to the fact that many cancers are either resistant to chemotherapy (conventional or targeted) or develop resistance during treatment, and residual chemoresistant cells are highly metastatic. Metastatic cancer cells resist the effects of chemotherapeutic agents by upregulating drug transporters, which efflux the drugs, and by activating proliferation and survival signaling pathways. Previously, we found that c-Abl and Arg non-receptor tyrosine kinases are activated in breast cancer, melanoma, and glioblastoma cells, and promote cancer progression. In this report, we demonstrate that the c-Abl/Arg inhibitor, imatinib (imatinib mesylate, STI571, Gleevec), reverses intrinsic and acquired resistance to the anthracycline, doxorubicin, by inducing G2/M arrest and promoting apoptosis in cancer cells expressing highly active c-Abl and Arg. Significantly, imatinib prevents intrinsic resistance by promoting doxorubicin-mediated NF-κB/p65 nuclear localization and repression of NF-κB targets in a STAT3-dependent manner, and by preventing activation of a novel STAT3/HSP27/p38/Akt survival pathway. In contrast, imatinib prevents acquired resistance by inhibiting upregulation of the ABC drug transporter, ABCB1, directly inhibiting ABCB1 function, and abrogating survival signaling. Thus, imatinib inhibits multiple novel chemoresistance pathways, which indicates that it may be effective in reversing intrinsic and acquired resistance in cancers containing highly active c-Abl and Arg, a critical step in effectively treating metastatic disease. Furthermore, since imatinib converts a master survival regulator, NF-κB, from a pro-survival into a pro-apoptotic factor, our data suggest that NF-κB inhibitors may be ineffective in sensitizing tumors containing activated c-Abl/Arg to anthracyclines, and instead might antagonize anthracycline-induced apoptosis.
doi:10.1371/journal.pone.0055509
PMCID: PMC3561297  PMID: 23383209
16.  Imatinib mesylate (Gleevec®) in advanced breast cancer-expressing C-Kit or PDGFR-β: clinical activity and biological correlations 
Annals of Oncology  2008;19(10):1713-1719.
Background: Novel molecular therapies for metastatic breast cancer (MBC) are necessary to improve the dismal prognosis of this condition. Imatinib mesylate (Gleevec®) inhibits several protein tyrosine kinases, including platelet-derived growth factor receptor (PDGFR) and c-kit, which are preferentially expressed in tumor cells. We tested the activity of imatinib mesylate in MBC with overexpression of PDGFR or c-kit. Additionally, we sought to determine the biological correlates and immunomodulatory effects.
Patients and methods: Thirteen patients were treated with Imatinib administered orally at 400 mg p.o. b.i.d. (800 mg/day), until disease progression. All patients demonstrated PDGFR-β overexpression and none showed c-kit expression.
Results: No objective responses were observed among the 13 patients treated in an intention-to-treat analysis. All patients experienced disease progression, with a median time to progression of 1.2 months. Twelve patients have died, and the median overall survival was 7.7 months. No patient had a serious adverse event. Imatinib therapy had no effect on the plasma levels of the angiogenesis-related cytokines, vascular endothelial growth factor, PDGF, b-fibroblast growth factor, and E-selectin. Immune studies showed imatinib inhibits interferon-γ production by TCR-activated CD4+ T cells.
Conclusion: Imatinib as a single agent has no clinical activity in PDGFR-overexpressing MBC and has potential immunosuppressive effects.
doi:10.1093/annonc/mdn352
PMCID: PMC2735063  PMID: 18515258
c-kit expression; imatinib; immune-suppression; metastatic breast cancer
17.  Expression of stem cell factor in gastrointestinal stromal tumors: Implications for proliferation and imatinib resistance 
Oncology Letters  2012;5(2):552-558.
KIT autophosphorylation caused by mutation of KIT is considered to be a critical mechanism for the oncogenesis of gastrointestinal stromal tumors (GISTs). However, little is known regarding whether stem cell factor (SCF), the KIT ligand, is able to induce the proliferation of GIST cells by activating the wild-type KIT receptor in GISTs. Imatinib, a tyrosine kinase inhibitor, has been demonstrated to be effective as treatment for the majority of GISTs. However, primary resistance to imatinib in GISTs with wild-type KIT and acquired resistance in GISTs with mutant KIT are becoming increasingly significant problems. The aims of this study were to detect the expression and function of SCF in 68 GIST samples, and to explore the relationship between SCF activity and imatinib resistance using immunohistochemical staining and western blot analysis. Results showed abundant expression of SCF in GISTs and demonstrated that SCF is capable of enhancing GIST cell proliferation. Similar to its ineffectiveness in wild-type GISTs, imatinib also failed to inhibit SCF-induced KIT activation in GISTs with mutant KIT. We also found increased SCF expression in GIST cells treated with imatinib. Overall, our results indicated that SCF-induced KIT activation is a novel essential pathway for the proliferation of GISTs. Imatinib was not able to inhibit the activity of SCF, while it promoted the expression of SCF, which may have contributed to acquired imatinib resistance.
doi:10.3892/ol.2012.1019
PMCID: PMC3572958  PMID: 23420128
stem cell factor; gastrointestinal stromal tumor; KIT; imatinib resistance
18.  RelB-dependent Differential Radiosensitization Effect of STI571 on Prostate Cancer Cells 
Molecular cancer therapeutics  2010;9(4):803-812.
Radiation therapy is an effective treatment for localized prostate cancer (PCa). However, when high-risk factors are present, such as increased PSA, elevated Gleason scores and advanced T-stage, undetected spreading of the cancer and development of radiation resistant cancer cells are concerns. Thus, additional therapeutic agents that can selectively sensitize advanced prostate cancer to radiation therapy are needed. Imatinib mesylate (Gleevec, STI571), a tyrosine kinase inhibitor, was evaluated for its potential to enhance the efficacy of ionizing radiation (IR) against aggressive PCa cells. STI571 significantly enhances IR-induced cytotoxicity of androgen-independent PCa cells but not of androgen-responsive PCa cells. The differential cytotoxic effects due to STI571 are associated with the nuclear level of RelB in PCa cells. STI571 inhibits IR-induced RelB nuclear translocation, leading to increased radiosensitivity in aggressive androgen-independent PC-3 and DU-145 cells. In contrast, STI571 enhances RelB nuclear translocation in androgen-responsive LNCaP cells. The different effects of STI571 on RelB nuclear translocation are consistent with RelB DNA binding activity and related target gene expression. STI571 inhibits the PI3K-ATK-IKKα pathway in PC-3 cells by decreasing the phosphorylation levels of PI3K (Tyr458) and AKT (Ser473), while STI571 increases NIK (Thr559) phosphorylation, leading to activation of IKKα in LNCaP cells. These results reveal that STI571 exhibits differential effects on the upstream kinases leading to different downstream effects on the NF-κB alternative pathway in PCa cells and suggest that STI571 is effective for the treatment of androgen-independent PCa in the context of high constitutive levels of RelB.
doi:10.1158/1535-7163.MCT-09-1001
PMCID: PMC2852498  PMID: 20371728
STI571; RelB; NF-κB signaling; Radiosensitization; Prostate cancer
19.  Protein Kinase C Theta (PKCθ) Regulates KIT Expression and Proliferation in Gastrointestinal Stromal Tumors 
Oncogene  2008;27(42):5624-5634.
Summary
Oncogenic KIT or PDGFRA receptor tyrosine kinase mutations are compelling therapeutic targets in gastrointestinal stromal tumors (GISTs), and the KIT/PDGFRA kinase inhibitor, imatinib, is standard of care for patients with metastatic GIST. However, most of these patients eventually develop clinical resistance to imatinib and other KIT/PDGFRA kinase inhibitors and there is an urgent need to identify novel therapeutic strategies. We reported previously that protein kinase C theta (PKCθ) is activated in GIST, irrespective of KIT or PDGFRA mutational status, and is expressed at levels unprecedented in other mesenchymal tumors, therefore serving as a diagnostic marker of GIST. Herein, we characterize PKCθ biological functions in imatinib-sensitive and imatinib-resistant GISTs, showing that lentivirus-mediated PKCθ knockdown is accompanied by inhibition of KIT expression in three KIT+/ PKCθ+ GIST cell lines, but not in a comparator KIT+/PKCθ- Ewing sarcoma cell line. PKCθ knockdown in the KIT+ GISTs was associated with inhibition of the PI3-K/AKT signaling pathway, upregulation of the cyclin-dependent kinase inhibitors p21 and p27, anti-proliferative effects due to G1 arrest, and induction of apoptosis, comparable to the effects seen after direct knockdown of KIT expression by KIT shRNA. These novel findings highlight that PKCθ warrants clinical evaluation as a potential therapeutic target in GISTs, including those cases containing mutations which confer resistance to KIT/PDGFRA kinase inhibitors.
doi:10.1038/onc.2008.177
PMCID: PMC2811224  PMID: 18521081
PRKCQ; KIT; shRNA; gastrointestinal neoplasm; sarcoma; imatinib
20.  Imatinib Enhances Docetaxel-Induced Apoptosis Through Inhibition of Nuclear Factor-κB Activation in Anaplastic Thyroid Carcinoma Cells 
Thyroid  2012;22(7):717-724.
Background
We previously reported the partial effectiveness of imatinib (also known as STI571, Glivec, or Gleevec) on anaplastic thyroid cancer (ATC) cells. Imatinib is a selective tyrosine kinase inhibitor that has been used for various types of cancer treatments. Recently, several reports have demonstrated that imatinib enhanced the sensitivity of cancer cells to other anticancer drugs. In this study, therefore, we investigated whether imatinib enhances the antitumor activity of docetaxel in ATC cells.
Methods
Two ATC cell lines, FRO and KTC-2, were treated with imatinib and/or docetaxel. Cell survival assay and flow cytometry for annexin V were used to assess the induction of apoptosis. Changes of pro- and antiapoptotic factors were determined by Western blot. Nuclear factor-κB (NF-κB) activity was measured by DNA-binding assay. Tumor growth was also investigated in vivo.
Results
The combined treatment significantly enhanced apoptosis compared with single treatment. ATC cells themselves expressed high levels of antiapoptotic factors, X-linked inhibitor of apoptosis (XIAP), and survivin. The treatment with docetaxel alone further increased their expressions; however, the combined treatment blocked the inductions. Although imatinib alone had no effect on NF-κB background levels, combined treatment significantly suppressed the docetaxel-induced NF-κB activation. Further, the combined administration of the drugs also showed significantly greater inhibitory effect on tumor growth in mice xenograft model.
Conclusions
Imatinib enhanced antitumor activity of docetaxel in ATC cells. Docetaxel seemed to induce both pro- and antiapoptotic signaling pathways in ATC cells, and imatinib blocked the antiapoptotic signal. Thus, docetaxel combined with imatinib emerges as an attractive strategy for the treatment of ATC.
doi:10.1089/thy.2011.0380
PMCID: PMC3387763  PMID: 22650230
21.  Pathology of Gastrointestinal Stromal Tumors 
Gastrointestinal stromal tumor (GIST) is a well recognized and relatively well understood soft tissue tumor. Early events in GIST development are activating mutations in KIT or PDGFRA, which occur in most GISTs and encode for mutated tyrosine receptor kinases that are therapeutic targets for tyrosine kinase inhibitors, including imatinib and sunitinib. A small minority of GISTs possessing neither KIT nor PDGFRA mutations may have germline mutations in SDH, suggesting a potential role of SDH in the pathogenesis. Immunohistochemical detection of KIT, and more recently DOG1, has proven to be reliable and useful in the diagnosis of GISTs. Because current and future therapies depend on pathologists, it is important that they recognize KIT-negative GISTs, GISTs in specific clinical contexts, GISTs with unusual morphology, and GISTs after treatment. This review focuses on recent developments in the understanding of the biology, immunohistochemical diagnosis, the role of molecular analysis, and risk assessment of GISTs.
doi:10.4137/CPath.S9689
PMCID: PMC3408870  PMID: 22855636
GIST; sarcoma; soft tissue; gastrointestinal; molecular analysis; immunohistochemistry
22.  Variola and Monkeypox Viruses Utilize Conserved Mechanisms of Virion Motility and Release That Depend on Abl and Src Family Tyrosine Kinases▿ † 
Journal of Virology  2010;85(1):21-31.
Vaccinia virus (VacV) enters mammalian cells, replicates extranuclearly, and produces virions that move to the cell surface along microtubules, fuse with the plasma membrane, and move from infected cells toward apposing cells on actin-filled membranous protrusions or actin tails. To form actin tails, cell-associated enveloped virions (CEV) require Abl and Src family tyrosine kinases. Furthermore, release of CEV from the cell requires Abl but not Src family tyrosine kinases and is blocked by imatinib mesylate (STI-571; Gleevec), an Abl family kinase inhibitor used to treat chronic myelogenous leukemia in humans. Here we demonstrate that the Poxviridae family members monkeypox virus (MPX) and variola virus (VarV) use conserved mechanisms for actin motility and extracellular enveloped virion (EEV) release. Furthermore, we show that imatinib mesylate is effective in a mouse model of infection with VacV, whether delivered prophylactically or postinfection, and restricts spread of virions from the site of inoculation. While inhibitors of both Src and Abl family kinases, such as dasatinib (BMS-354825; Sprycel), are effective in limiting dissemination of VacV, VarV, and MPX in vitro, members of this class of drugs appear to have immunosuppressive effects in vivo that preclude their use as anti-infectives. Together, these data suggest a possible utility for imatinib mesylate in treating smallpox or MPX infections or complications associated with vaccination.
doi:10.1128/JVI.01814-10
PMCID: PMC3014172  PMID: 20962097
23.  Imatinib blocks migration and invasion of medulloblastoma cells by concurrently inhibiting activation of PDGFR and transactivation of EGFR 
Molecular cancer therapeutics  2009;8(5):1137-1147.
Platelet-derived growth factor receptor (PDGFR) expression correlates with metastatic medulloblastoma. PDGF stimulation of medulloblastoma cells phosphorylates Erk and promotes migration. We sought to determine whether blocking PDGFR activity effectively inhibits signaling required for medulloblastoma cell migration and invasion. DAOY and D556 human medulloblastoma cells were treated with imatinib mesylate (Gleevec®), a PDGFR tyrosine kinase inhibitor, or transfected with siRNA to PDGFRB to test the effects of blocking PDGFR phosphorylation and expression, respectively. PDGFR cell signaling, migration, invasion, survival and proliferation following PDGF-BB stimulation, with and without PDGFR inhibition, were measured. PDGF-BB treatment of cells increased PDGFRB, Akt and Erk phosphorylation, and transactivated EGFR, which correlated with enhanced migration, survival and proliferation. Imatinib (1 uM) treatment of DAOY and D556 cells inhibited PDGF-BB- and serum-mediated migration and invasion at 24 h and 48 h, respectively, and concomitantly inhibited PDGF-BB activation of PDGFRB, Akt and Erk, but induced increased PTEN expression and activity. Imatinib treatment also induced DAOY cell apoptosis at 72 h and inhibited DAOY and D556 cell proliferation at 48 h. siRNA silencing of PDGFRB similarly inhibited signaling, migration and survival and both siRNA and imatinib treatment inhibited PDGF-BB-mediated EGFR transactivation, indicating that the effects of imatinib treatment are specific to PDGFRB target inhibition. These results indicate that PDGFRB tyrosine kinase activity is critical for migration and invasion of medulloblastoma cells, possibly by transactivating EGFR, and thus imatinib may represent an important novel therapeutic agent for the treatment of medulloblastoma.
doi:10.1158/1535-7163.MCT-08-0889
PMCID: PMC2891380  PMID: 19417143
Medulloblasotma; Imatinib mesylate; PDGFR; EGFR; PTEN
24.  Selecting Tyrosine Kinase Inhibitors for Gastrointestinal Stromal Tumor with Secondary KIT Activation-Loop Domain Mutations 
PLoS ONE  2013;8(6):e65762.
Advanced gastrointestinal stromal tumors (GIST), a KIT oncogene-driven tumor, on imatinib mesylate (IM) treatment may develop secondary KIT mutations to confer IM-resistant phenotype. Second-line sunitinib malate (SU) therapy is largely ineffective for IM-resistant GISTs with secondary exon 17 (activation-loop domain) mutations. We established an in vitro cell-based platform consisting of a series of COS-1 cells expressing KIT cDNA constructs encoding common primary±secondary mutations observed in GISTs, to compare the activity of several commercially available tyrosine kinase inhibitors on inhibiting the phosphorylation of mutant KIT proteins at their clinically achievable plasma steady-state concentration (Css). The inhibitory efficacies on KIT exon 11/17 mutants were further validated by growth inhibition assay on GIST48 cells, and underlying molecular-structure mechanisms were investigated by molecular modeling. Our results showed that SU more effectively inhibited mutant KIT with secondary exon 13 or 14 mutations than those with secondary exon 17 mutations, as clinically indicated. On contrary, at individual Css, nilotinib and sorafenib more profoundly inhibited the phosphorylation of KIT with secondary exon 17 mutations and the growth of GIST48 cells than IM, SU, and dasatinib. Molecular modeling analysis showed fragment deletion of exon 11 and point mutation on exon 17 would lead to a shift of KIT conformational equilibrium toward active form, for which nilotinib and sorafenib bound more stably than IM and SU. In current preclinical study, nilotinib and sorafenib are more active in IM-resistant GISTs with secondary exon 17 mutation than SU that deserve further clinical investigation.
doi:10.1371/journal.pone.0065762
PMCID: PMC3688691  PMID: 23840364
25.  Emerging functions of c-kit and its ligand stem cell factor in dendritic cells 
Cell cycle (Georgetown, Tex.)  2008;7(18):2826-2832.
The receptor tyrosine kinase, c-kit, and its ligand, stem cell factor (SCF), function in a diverse range of biological functions. The role of c-kit in the maintenance and survival of hematopoietic stem cells and of mast cells is well recognized. c-kit also plays an important role in melanogenesis, erythropoiesis and spermatogenesis. Recent work from our laboratory highlights an important role of c-kit in the regulation of expression of two molecules in dendritic cells (DCs), interleukin-6 (IL-6) and Jagged-2 (a ligand of Notch), which are known to regulate T helper cell differentiation. Our study shows that induction of c-kit expression and its signaling in DCs promotes Th2 and Th17 responses but not Th1 response. c-kit inhibition by imatinib mesylate (Gleevec) in DCs was previously shown to promote natural killer cell activation which may be due to dampening of IL-6 production by the DCs. Since dysregulation of c-kit function has been associated with various disease states including cancer, in this perspective we have focused on known and novel functions of c-kit to include molecules such as IL-6 and Notch that were not previously recognized to be within the purview of c-kit biology. We have also reviewed the differential expression pattern of SCF and c-kit on various cell types and its variation during development or pathology. The recognition of previously unappreciated roles for c-kit will provide better insights into its function within and beyond the immune system and pave the way for developing better therapeutic strategies.
PMCID: PMC3694436  PMID: 18787413
c-kit; SCF; interleukin-6; jagged-2; dendritic cells; T cells; differentiation

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