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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.
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.
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.
These results suggest a potential role of Gleevec as adjuvant therapeutic agent for treatment of non-small cell lung cancer.
PMCID: PMC149413  PMID: 12537587
Lung cancer A549 cell; Gleevec (STI571); PDGF receptor
2.  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.
PMCID: PMC2805033  PMID: 20028860
3.  Giant malignant gastrointestinal stromal tumors: Recurrence and effects of treatment with STI-571 
AIM: Malignant gastrointestinal stromal tumors (GISTs) are rare. Tumors larger than 10 cm tend to recur earlier: the larger the volume of the tumor, the worse the prognosis. We hypothesized that treatment with imatinib mesylate (Gleevec; STI-571), a c-kit tyrosine kinase inhibitor, as palliative therapy would prolong the survival of patients with recurrent giant malignant GISTs after resection.
METHODS: We performed a retrospective analysis of the effects of resection on patients with giant GISTs (>10 cm in diameter) to determine the overall survival and recurrence rates. Twenty-three patients diagnosed with giant GISTs were included from June 1996 to December 2003. STI-571 was not available until January 2000. After that time, 9 patients received this drug. The factors of age, sex, tumor location, histological surgical margin, and STI-571, tumor size changes and drug side effects were reviewed. We compared the survival rate to determine the prognostic factors and the effects of STI-571 on patients with recurrent malignant gastrointestinal stromal tumor.
RESULTS: The positive surgical margin group had a significantly higher recurrence rate than the negative margin group (P = 0.012). A negative surgical margin and palliative treatment with STI-571 were significant prognostic variables (Log-rank test, P<0.05). Age, sex and tumor location were not significant prognostic variables. The 5-year survival rate of the surgical margin free patients was 80% and the 2-year survival rate of the surgical margin positive patients was 28%. The 5-year survival rate was 80% for the patients given STI-571 and 30% for the patients not given STI-571. The use of STI-571 gave a significant tumor shrinkage (6/9) rate in patients with giant GIST recurrence after resection.
CONCLUSION: A negative surgical margin and the use of STI-571 after surgical resection were good prognostic indicators. Achieving a tumor-free surgical margin is still the best primary treatment for patients with such tumors. If STI-571 is used immediately when the surgical margin is positive and the tumor recurs after resection, then the prognosis of patients with giant GISTs can be improved.
PMCID: PMC4205413  PMID: 15633227
Giant malignant gastrointestinal stromal tumors; STI-571
4.  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.
PMCID: PMC2594583  PMID: 12934870
5.  Gastrointestinal stromal tumor and its targeted therapeutics 
Chinese Journal of Cancer  2011;30(5):303-314.
Over the past 60 years, investigators of basic science, pathology, and clinical medicine have studied gastrointestinal stromal tumor (GIST) and made minor advances in patient care. Recent discoveries have led to an understanding of the biological role of KIT and platelet-derived growth factor receptor-α in GIST and the development of the tyrosine kinase inhibitor imatinib mesylate (Gleevec, formerly STI-571), one of the most exciting examples of targeted therapy to date. The success of targeted therapy in GIST has lead to new developments in our understanding of the medical and surgical management of the disease. Intense study of GIST may lead to new paradigms in the management of cancer.
PMCID: PMC4013395  PMID: 21527063
Gastrointestinal stromal tumor; KIT; platelet-derived growth factor receptor; imatinib mesylate
6.  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
7.  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.
PMCID: PMC1951756  PMID: 17626163
8.  Rectal GIST Presenting as a Submucosal Calculus 
Digestive Diseases and Sciences  2007;52(4):1047-1049.
This case report presents an incidental finding of a rectal GIST (gastrointestinal stromal tumor) presenting as a submucosal calculus, not previously reported. A 53-year-old man without a significant medical history presented with abdominal pain in the left lower quadrant, and with constipation. Upon rectal examination, a hard submucosal swelling was palpated 4 cm from the anus, at 3 o’clock, in the left rectum wall. X-ray photos, computerized tomography (CT)-scan and a magnetic resonance imaging (MRI) scan clearly showed a calculus. Excision revealed a turnip-like lesion, 3.1×2.3×1.8 cm. Analysis showed it was a rectal GIST, a rare mesenchymal tumor of the gastrointestinal tract, which expressed CD117 (or c-kit, a marker of kit-receptor tyrosine kinase) and CD34. Calcification is not a usual clinicopathological feature of GISTs [1–3], and although a number of rectal GISTs have been reported [4–9], we have found no cases so far of rectal GIST presenting as a submucosal calculus.
In general, GISTs are rare mesenchymal tumors of the gastrointestinal tract (nerve tissue, smooth muscle). Histology and immunohistochemistry discriminate gastrointestinal stromal tumors from leiomyomas and neurinomas. The most important location is the stomach; the rectal location is rare. Usually, the classic signs of malignancy such as cellular invasion and metastasis are missing. A set of histologic criteria stratifies GIST for risk of malignant behavior such as mitotic activity and tumor size, cellular pleomorphism, developmental stage of the cell and quantity of cytoplasma [7,13]. Tumors with a high mitotic activity and size above 5 cm are considered malignant. Recent pharmacological advances such as tyrosine kinase inhibitors have determined c-kit (i.e., CD117) as the most important marker, amongst others. C-kit positive tumors respond extremely well to chemotherapy with Imatinib (Glivec®, Gleevec®) [10–12].
PMCID: PMC1914226  PMID: 17268837
Gastrointestinal stromal tumors; Rectal tumor; Calculus
9.  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
10.  The HSP90 Inhibitor, AT13387, Is Effective against Imatinib-Sensitive and -Resistant Gastrointestinal Stromal Tumor Models 
Molecular cancer therapeutics  2012;11(8):1799-1808.
The majority of gastrointestinal stromal tumors (GIST) are characterized by activating mutations of KIT, an HSP90 client protein. Further secondary resistance mutations within KIT limit clinical responses to tyrosine kinase inhibitors, such as imatinib. The dependence of KIT and its mutated forms on HSP90 suggests that HSP90 inhibition might be a valuable treatment option for GIST, which would be equally effective on imatinib-sensitive and -resistant clones. We investigated the activity of AT13387, a potent HSP90 inhibitor currently being evaluated in clinical trials, in both in vitro and in vivo GIST models. AT13387 inhibited the proliferation of imatinib-sensitive (GIST882, GIST-T1) and -resistant (GIST430, GIST48) cell lines, including those resistant to the geldanamycin analogue HSP90 inhibitor, 17-AAG. Treatment with AT13387 resulted in depletion of HSP90 client proteins, KIT and AKT, along with their phospho-forms in imatinib-sensitive and -resistant cell lines, irrespective of KIT mutation. KIT signaling was ablated, whereas HSP70, a marker of HSP90 inhibition, was induced. In vivo, antitumor activity of AT13387 was showed in both the imatinib-sensitive, GIST-PSW, xenograft model and a newly characterized imatinib-resistant, GIST430, xenograft model. Induction of HSP70, depletion of phospho-KIT and inhibition of KIT signaling were seen in tumors from both models after treatment with AT13387. A combination of imatinib and AT13387 treatment in the imatinib-resistant GIST430 model significantly enhanced tumor growth inhibition over either of the monotherapies. Importantly, the combination of AT13387 and imatinib was well tolerated. These results suggest AT13387 is an excellent candidate for clinical testing in GIST in combination with imatinib.
PMCID: PMC3992119  PMID: 22714264
11.  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.
PMCID: PMC3561297  PMID: 23383209
12.  Small molecule receptor tyrosine kinase inhibitor of platelet-derived growth factor signaling (SU9518) modifies radiation response in fibroblasts and endothelial cells 
BMC Cancer  2006;6:79.
Several small receptor tyrosine kinase inhibitors (RTKI) have entered clinical cancer trials alone and in combination with radiotherapy or chemotherapy. The inhibitory spectrum of these compounds is often not restricted to a single target. For example Imatinib/Gleevec (primarily a bcr/abl kinase inhibitor) or SU11248 (mainly a VEGFR inhibitor) are also potent inhibitors of PDGFR and other kinases. We showed previously that PDGF signaling inhibition attenuates radiation-induced lung fibrosis in a mouse model. Here we investigate effects of SU9518, a PDGFR inhibitor combined with ionizing radiation in human primary fibroblasts and endothelial cells in vitro, with a view on utilizing RTKI for antifibrotic therapy.
Protein levels of PDGFR-α/-β and phosphorylated PDGFR in fibroblasts were analyzed using western and immunocytochemistry assays. Functional proliferation and clonogenic assays were performed (i) to assess PDGFR-mediated survival and proliferation in fibroblasts and endothelial cells after SU9518 (small molecule inhibitor of PDGF receptor tyrosine kinase); (ii) to test the potency und selectivity of the PDGF RTK inhibitor after stimulation with PDGF isoforms (-AB, -AA, -BB) and VEGF+bFGF. In order to simulate in vivo conditions and to understand the role of radiation-induced paracrine PDGF secretion, co-culture models consisting of fibroblasts and endothelial cells were employed.
In fibroblasts, radiation markedly activated PDGF signaling as detected by enhanced PDGFR phosphorylation which was potently inhibited by SU9518. In fibroblast clonogenic assay, SU9518 reduced PDGF stimulated fibroblast survival by 57%. Likewise, SU9518 potently inhibited fibroblast and endothelial cell proliferation. In the co-culture model, radiation of endothelial cells and fibroblast cells substantially stimulated proliferation of non irradiated fibroblasts and vice versa. Importantly, the RTK inhibitor significantly inhibited this paracrine radiation-induced fibroblast and endothelial cell activation.
Radiation-induced autocrine and paracrine PDGF signaling plays an important role in fibroblast and endothelial cell proliferation. SU9518, a PDGFR tyrosine kinase inhibitor, reduces radiation-induced fibroblast and endothelial cell activation. This may explain therapeutic anticancer effects of Imatinib/Gleevec, and at the same time it could open a way of attenuating radiation-induced fibrosis.
PMCID: PMC1458351  PMID: 16556328
13.  Imatinib Mesylate Exerts Anti-Proliferative Effects on Osteosarcoma Cells and Inhibits the Tumour Growth in Immunocompetent Murine Models 
PLoS ONE  2014;9(3):e90795.
Osteosarcoma is the most common primary malignant bone tumour characterized by osteoid production and/or osteolytic lesions of bone. A lack of response to chemotherapeutic treatments shows the importance of exploring new therapeutic methods. Imatinib mesylate (Gleevec, Novartis Pharma), a tyrosine kinase inhibitor, was originally developed for the treatment of chronic myeloid leukemia. Several studies revealed that imatinib mesylate inhibits osteoclast differentiation through the M-CSFR pathway and activates osteoblast differentiation through PDGFR pathway, two key cells involved in the vicious cycle controlling the tumour development. The present study investigated the in vitro effects of imatinib mesylate on the proliferation, apoptosis, cell cycle, and migration ability of five osteosarcoma cell lines (human: MG-63, HOS; rat: OSRGA; mice: MOS-J, POS-1). Imatinib mesylate was also assessed as a curative and preventive treatment in two syngenic osteosarcoma models: MOS-J (mixed osteoblastic/osteolytic osteosarcoma) and POS-1 (undifferentiated osteosarcoma). Imatinib mesylate exhibited a dose-dependent anti-proliferative effect in all cell lines studied. The drug induced a G0/G1 cell cycle arrest in most cell lines, except for POS-1 and HOS cells that were blocked in the S phase. In addition, imatinib mesylate induced cell death and strongly inhibited osteosarcoma cell migration. In the MOS-J osteosarcoma model, oral administration of imatinib mesylate significantly inhibited the tumour development in both preventive and curative approaches. A phospho-receptor tyrosine kinase array kit revealed that PDGFRα, among 7 other receptors (PDFGFRβ, Axl, RYK, EGFR, EphA2 and 10, IGF1R), appears as one of the main molecular targets for imatinib mesylate. In the light of the present study and the literature, it would be particularly interesting to revisit therapeutic evaluation of imatinib mesylate in osteosarcoma according to the tyrosine-kinase receptor status of patients.
PMCID: PMC3944320  PMID: 24599309
14.  Critical Role for Kit-mediated Src Kinase But Not PI 3-Kinase Signaling in Pro T and Pro B Cell Development 
The Kit receptor functions in hematopoiesis, lymphocyte development, gastrointestinal tract motility, melanogenesis, and gametogenesis. To investigate the roles of different Kit signaling pathways in vivo, we have generated knock-in mice in which docking sites for PI 3-kinase (KitY719) or Src kinase (KitY567) have been mutated. Whereas steady-state hematopoiesis is normal in KitY719F/Y719F and KitY567F/Y567F mice, lymphopoiesis is affected differentially. The KitY567F mutation, but not the KitY719F mutation, blocks pro T cell and pro B cell development in an age-dependent manner. Thus, the Src family kinase, but not the PI 3-kinase docking site in Kit, mediates a critical signal for lymphocyte development. In agreement with these results, treatment of normal mice with the Kit tyrosine kinase inhibitor imatinib (Gleevec®) leads to deficits in pro T and pro B cell development, similar to those seen in KitY567F/Y567F and KitW/W mice. The two mutations do not affect embryonic gametogenesis but the KitY719F mutation blocks spermatogenesis at the spermatogonial stages and in contrast the KitY567F mutation does not affect this process. Therefore, Kit-mediated PI 3-kinase signaling and Src kinase family signaling is highly specific for different cellular contexts in vivo.
PMCID: PMC2212729  PMID: 15024050
Kit receptor signaling; Src kinase; PI 3-kinase; pro T and pro B cell development
15.  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.
PMCID: PMC2735063  PMID: 18515258
c-kit expression; imatinib; immune-suppression; metastatic breast cancer
16.  Imatinib Enhances Docetaxel-Induced Apoptosis Through Inhibition of Nuclear Factor-κB Activation in Anaplastic Thyroid Carcinoma Cells 
Thyroid  2012;22(7):717-724.
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.
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.
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.
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.
PMCID: PMC3387763  PMID: 22650230
17.  The Tumor Suppressor Gene, RASSF1A, Is Essential for Protection against Inflammation -Induced Injury 
PLoS ONE  2013;8(10):e75483.
Ras association domain family protein 1A (RASSF1A) is a tumor suppressor gene silenced in cancer. Here we report that RASSF1A is a novel regulator of intestinal inflammation as Rassf1a+/−, Rassf1a−/− and an intestinal epithelial cell specific knockout mouse (Rassf1a IEC-KO) rapidly became sick following dextran sulphate sodium (DSS) administration, a chemical inducer of colitis. Rassf1a knockout mice displayed clinical symptoms of inflammatory bowel disease including: increased intestinal permeability, enhanced cytokine/chemokine production, elevated nuclear factor of kappa light polypeptide gene enhancer in B-cells (NFκB) activity, elevated colonic cell death and epithelial cell injury. Furthermore, epithelial restitution/repair was inhibited in DSS-treated Rassf1a−/− mice with reduction of several makers of proliferation including Yes associated protein (YAP)-driven proliferation. Surprisingly, tyrosine phosphorylation of YAP was detected which coincided with increased nuclear p73 association, Bax-driven epithelial cell death and p53 accumulation resulting in enhanced apoptosis and poor survival of DSS-treated Rassf1a knockout mice. We can inhibit these events and promote the survival of DSS-treated Rassf1a knockout mice with intraperitoneal injection of the c-Abl and c-Abl related protein tyrosine kinase inhibitor, imatinib/gleevec. However, p53 accumulation was not inhibited by imatinib/gleevec in the Rassf1a−/− background which revealed the importance of p53-dependent cell death during intestinal inflammation. These observations suggest that tyrosine phosphorylation of YAP (to drive p73 association and up-regulation of pro-apoptotic genes such as Bax) and accumulation of p53 are consequences of inflammation-induced injury in DSS-treated Rassf1a−/− mice. Mechanistically, we can detect robust associations of RASSF1A with membrane proximal Toll-like receptor (TLR) components to suggest that RASSF1A may function to interfere and restrict TLR-driven activation of NFκB. Failure to restrict NFκB resulted in the inflammation-induced DNA damage driven tyrosine phosphorylation of YAP, subsequent p53 accumulation and loss of intestinal epithelial homeostasis.
PMCID: PMC3797720  PMID: 24146755
18.  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.
PMCID: PMC3810688  PMID: 22846208
CD117 c-kit; ependymomas; glial tumors; oligodendrogliomas
19.  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.
PMCID: PMC3014172  PMID: 20962097
20.  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.
PMCID: PMC2952484  PMID: 20957137
Gleevec; adjuvant; neoadjuvant; metastasis; sunitinib
21.  Molecular Characterization of Pediatric Gastrointestinal Stromal Tumors 
Pediatric gastrointestinal stromal tumors (GIST) are rare and occur preferentially in females as multifocal gastric tumors, typically lacking mutations in KIT and PDGFRA. As KIT oncoprotein is consistently overexpressed in pediatric GIST, we sought to investigate the activation of KIT downstream targets and alterations of KIT/PDGFRA gene copy number, mine novel therapeutic targets by gene expression, and test tyrosine kinase receptor activation by proteomic profiling.
Experimental Design
Seventeen pediatric GISTs were investigated for KIT/PDGFRA genotype and biochemical activation of KIT downstream targets. The transcriptional profile of 13 nodules from 8 pediatric patients was compared with 8 adult wild-type (WT) GISTs, including 3 young adults. The drug sensitivity of second-generation kinase inhibitors was tested in murine Ba/F3 cells expressing human WT KIT, as well as in short-term culture of explants of WT GIST cells.
A KIT/PDGFRA WT genotype was identified in all 12 female patients, whereas two of five males had either a KIT exon 11 or PDGFRA exon 18 mutation. KIT downstream targets were consistently activated. Pediatric GISTs showed a distinct transcriptional signature, with overexpression of BAALC, PLAG1, IGF1R, FGF4, and NELL1. In vitro studies showed that nilotinib, sunitinib, dasatinib, and sorafenib are more effective than imatinib against WT KIT.
Rare cases of pediatric GIST may occur in male patients and harbor activating KIT/PDGFRA mutations. Pediatric GISTs show distinct transcriptional signature, suggesting a different biology than WT GIST in adults. In vitro drug screening showed that second-generation kinase inhibitors may provide greater clinical benefit in pediatric GIST.
PMCID: PMC3805121  PMID: 18483389
22.  Protein Kinase C Theta (PKCθ) Regulates KIT Expression and Proliferation in Gastrointestinal Stromal Tumors 
Oncogene  2008;27(42):5624-5634.
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.
PMCID: PMC2811224  PMID: 18521081
PRKCQ; KIT; shRNA; gastrointestinal neoplasm; sarcoma; imatinib
23.  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.
PMCID: PMC3572958  PMID: 23420128
stem cell factor; gastrointestinal stromal tumor; KIT; imatinib resistance
24.  DOG1 regulates growth and IGFBP-5 in gastrointestinal stromal tumors 
Cancer research  2013;73(12):3661-3670.
Gastrointestinal stromal tumors (GIST) are characterized by activating mutations of KIT or platelet-derived growth factor receptor alpha (PDGFRA) which can be therapeutically targeted by tyrosine kinase inhibitors (TKI) such as imatinib. Despite long lasting responses most patients eventually progress after TKI therapy. The calcium-dependent chloride channel DOG1 (ANO1/TMEM16A), which is strongly and specifically expressed in GIST, is used as a diagnostic marker to differentiate GIST from other sarcomas. Here we report that loss of DOG1 expression occurs together with loss of KIT expression in a subset of GIST resistant to KIT inhibitors, and we illustrate the functional role of DOG1 in tumor growth, KIT expression and imatinib response. While DOG1 is a crucial regulator of chloride balance in GIST cells, we found that RNAi-mediated silencing or pharmacological inhibition of DOG1 did not alter cell growth or KIT signaling in vitro. In contrast, DOG1 silencing delayed the growth of GIST xenografts in vivo. Expression profiling of explanted tumors after DOG1 blockade revealed a strong upregulation in the expression of IGFBP5, a potent antiangiogenic factor implicated in tumor suppression. Similar results were obtained after selection of imatinib-resistant DOG1- and KIT-negative cells derived from parental DOG1 and KIT-positive GIST cells, where a 5000-fold increase in IGFBP5 mRNA transcripts were documented. In summary, our findings establish the oncogenic activity of DOG1 in GIST involving modulation of IGF/IGFR signaling in the tumor microenvironment through the antiangiogenic factor IGFBP5.
PMCID: PMC3694361  PMID: 23576565
25.  Expression of the Platelet-Derived Growth Factor Receptor in Prostate Cancer and Treatment Implications with Tyrosine Kinase Inhibitors1 
Neoplasia (New York, N.Y.)  2004;6(5):503-512.
The platelet-derived growth factor receptor (PDGFR) is a receptor tyrosine kinase overexpressed in a subset of solid tumors and therefore is the target of drugs inhibiting this function such as imatinib mesylate (Gleevec). Thus far, drug therapy has played a limited role in the treatment of localized prostate cancer (PCa). This study characterizes PDGFR-β expression in a wide spectrum of PCa samples to provide empirical data as part of a rational treatment strategy. A survey of five published prostate expression array studies, including 100 clinically localized PCa, did not identify tumors with increased PDGFR-β expression level. Protein expression of PDGFR-β, as determined by immunohistochemistry, revealed 5% of clinically localized PCa and 16% of metastatic PCa cases to show moderate or strong expression. To develop a strategy to detect patients most likely to profit from Gleevec treatment, we analyzed cDNA expression array data from 10,000 transcripts for PDGFR-β expression and divided tumors in groups based on PDGFR-β expression level. Performing a supervised analysis to identify potential comarkers of PDGFR-β in PCa, we identified a set of genes whose expression was associated with PDGFR-β status including early growth response 1 (Egr1), an upstream effector of PDGF (4.2-fold upregulation), α-methylacyl-CoA racemase, as well as v-Maf and neuroblastoma suppressor of tumorigenicity (both with a 2.2-fold downregulation). Taken together, this study suggests that only a small subset of PCas may be amenable to tyrosine kinase inhibitors specific for PDGFR.
PMCID: PMC1531653  PMID: 15548358
Platelet-derived growth factor receptor (PDGFR); prostate cancer; imatinib mesylate; tissue microarray; cDNA expression

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