Expression, function and activation of the proto-oncogene c-kit product in human leukemia cells

Nobiletin Down-Regulates c-KIT Gene Expression and Exerts Antileukemic Effects on Human Acute Myeloid Leukemia Cells

Nobiletin, a dietary citrus flavonoid, has been reported to possess several biological activities such as antioxidant, anti-inflammatory, and anticancer properties. The aim of this study was to investigate the antileukemic effects of nobiletin and its underlying mechanisms on human acute myeloid leukemia (AML) cells. We demonstrated that nobiletin (0-100 μM) significantly reduced cell viability from 100.0 ± 9.6% to 31.1 ± 2.8% in human AML THP-1 cell line. Nobiletin arrested cell cycle progression in G1 phase and induced myeloid cell differentiation in human AML cells. Microarray analysis showed that mRNA expression of the c- KIT gene, a critical proto-oncogene associated with leukemia progression, was dramatically reduced in nobiletin-treated AML cells. Furthermore, we verified that AML cells treated with nobiletin (40 and 80 μM) for 48 h markedly suppressed c-KIT mRNA expression (from 1.00 ± 0.07-fold to 0.62 ± 0.08- and 0.30 ± 0.05-fold) and reduced the level of c-KIT protein expression (from 1.00 ± 0.11-fold to 0.60 ± 0.15- and 0.34 ± 0.05-fold) by inhibition of KIT promoter activity. The knockdown of c-KIT expression by shRNA attenuated cancer cell growth and induced cell differentiation. Moreover, we found that the overexpression of c-KIT abolished nobiletin-mediated cell growth inhibition in leukemia cells. These results indicate that nobiletin exerts antileukemic effects through the down-regulation of c-KIT gene expression in AML cells. Finally, we demonstrated that the combination of a conventional AML chemotherapeutic agent, cytarabine, with nobiletin resulted in more reduction of cell viability in AML cells. Our current findings suggest that nobiletin is a novel c-KIT inhibitor and may serve as a chemo-preventive or -therapeutic agent against human AML.

TAK1 and IKK2, novel mediators of SCF-induced signaling and potential targets for c-Kit-driven diseases

NF-κB activation depends on the IKK complex consisting of the catalytically active IKK1 and 2 subunits and the scaffold protein NEMO. Hitherto, IKK2 activation has always been associated with IκBα degradation, NF-κB activation, and cytokine production. In contrast, we found that in SCF-stimulated primary bone marrow-derived mast cells (BMMCs), IKK2 is alternatively activated. Mechanistically, activated TAK1 mediates the association between c-Kit and IKK2 and therefore facilitates the Lyn-dependent IKK2 activation which suffices to mediate mitogenic signaling but, surprisingly, does not result in NF-κB activation. Moreover, the c-Kit-mediated and Lyn-dependent IKK2 activation is targeted by MyD88-dependent pathways leading to enhanced IKK2 activation and therefore to potentiated effector functions. In neoplastic cells, expressing constitutively active c-Kit mutants, activated TAK1 and IKKs do also not induce NF-κB activation but mediate uncontrolled proliferation, resistance to apoptosis and enables IL-33 to mediate c-Kit-dependent signaling. Together, we identified the formation of the c-Kit-Lyn-TAK1 signalosome which mediates IKK2 activation. Unexpectedly, this IKK activation is uncoupled from the NF-κB-machinery but is critical to modulate functional cell responses in primary-, and mediates uncontrolled proliferation and survival of tumor-mast cells. Therefore, targeting TAK1 and IKKs might be a novel approach to treat c-Kit-driven diseases.

Phase I study of quizartinib administered daily to patients with relapsed or refractory acute myeloid leukemia irrespective of FMS-like tyrosine kinase 3-internal tandem duplication status

PURPOSE

FMS-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutations in acute myeloid leukemia (AML) are associated with early relapse and poor survival. Quizartinib potently and selectively inhibits FLT3 kinase activity in preclinical AML models.

PATIENTS AND METHODS

Quizartinib was administered orally at escalating doses of 12 to 450 mg/day to 76 patients (median age, 60 years; range, 23 to 86 years; with a median of three prior therapies [range, 0 to 12 therapies]), enrolled irrespective of FLT3-ITD mutation status in a phase I, first-in-human study in relapsed or refractory AML.

RESULTS

Responses occurred in 23 (30%) of 76 patients, including 10 (13%) complete remissions (CR) of any type (two CRs, three CRs with incomplete platelet recovery [CRp], five CRs with incomplete hematologic recovery [CRi]) and 13 (17%) with partial remissions (PRs). Of 17 FLT3-ITD-positive patients, nine responded (53%; one CR, one CRp, two CRis, five PRs); of 37 FLT3-ITD-negative patients, five responded (14%; two CRps, three PRs); of 22 with FLT3-ITD-indeterminate/not tested status, nine responded (41%; one CR, three CRis, five PRs). Median duration of response was 13.3 weeks; median survival was 14.0 weeks. The most common drug-related adverse events (> 10% incidence) were nausea (16%), prolonged QT interval (12%), vomiting (11%), and dysgeusia (11%); most were ≤ grade 2. The maximum-tolerated dose was 200 mg/day, and the dose-limiting toxicity was grade 3 QT prolongation. FLT3-ITD phosphorylation was completely inhibited in an in vitro plasma inhibitory assay.

CONCLUSION

Quizartinib has clinical activity in patients with relapsed/refractory AML, particularly those with FLT3-ITD, and is associated with an acceptable toxicity profile.

Stem Cell Factor Receptor/c-Kit: From Basic Science to Clinical Implications

Stem cell factor (SCF) is a dimeric molecule that exerts its biological functions by binding to and activating the receptor tyrosine kinase c-Kit. Activation of c-Kit leads to its autophosphorylation and initiation of signal transduction. Signaling proteins are recruited to activated c-Kit by certain interaction domains (e.g., SH2 and PTB) that specifically bind to phosphorylated tyrosine residues in the intracellular region of c-Kit. Activation of c-Kit signaling has been found to mediate cell survival, migration, and proliferation depending on the cell type. Signaling from c-Kit is crucial for normal hematopoiesis, pigmentation, fertility, gut movement, and some aspects of the nervous system. Deregulated c-Kit kinase activity has been found in a number of pathological conditions, including cancer and allergy. The observation that gain-of-function mutations in c-Kit can promote tumor formation and progression has stimulated the development of therapeutics agents targeting this receptor, e.g., the clinically used inhibitor imatinib mesylate. Also other clinically used multiselective kinase inhibitors, for instance, sorafenib and sunitinib, have c-Kit included in their range of targets. Furthermore, loss-of-function mutations in c-Kit have been observed and shown to give rise to a condition called piebaldism. This review provides a summary of our current knowledge regarding structural and functional aspects of c-Kit signaling both under normal and pathological conditions, as well as advances in the development of low-molecular-weight molecules inhibiting c-Kit function.

Kit inhibitor APcK110 extends survival in an AML xenograft mouse model

BACKGROUND

Constitutive activation of kit contributes to pathogenesis of acute myeloid leukemia (AML) and targeting Kit may be of therapeutic benefit. APcK110, a novel inhibitor of Kit, has potent proapoptotic and antiproliferative activity in AML cell lines and primary AML samples. Here we extend our studies to the activity of APcK110 in a xenograft mouse model.

METHODS

After sub-lethal whole body radiation, OCI/AML3 cells were injected intravenously in NOD-SCID mice. Ten days later, either APcK110 or phosphate buffered saline (PBS) was injected intraperitoneally every other day. Kaplan-Meier estimates were used to calculate survival.

RESULTS

We show that 1) all mice injected with OCI/AML3 cells developed a clinical and histological picture consistent with myelomonocytic AML; and 2) survival of APcK110-treated mice was significantly longer compared with mice injected with PBS (p = .02).

CONCLUSIONS

APcK110 is a novel kit kinase inhibitor with anti-AML activity in vitro and in vivo. Further evaluation in toxicology and clinical studies is warranted.

Management of resectable gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is a rare neoplasm that recently has become an intense focus of scientific investigation, as it serves as a model for the molecular therapy for cancer. Although surgery remains the principle treatment of primary localized GIST, imatinib mesylate, a selective inhibitor of KIT protein, achieves dramatic responses in metastatic GIST. Multimodality therapy integrating surgery and molecular therapy has shown promise. This article summarizes the epidemiology, clinicopathologic features, natural history, and clinical management of GIST.

Gastrointestinal stromal tumors and leiomyosarcomas

Only recently has gastrointestinal stromal tumor (GIST) been recognized as the most frequent GI mesenchymal neoplasm. Prior to the use of KIT staining, most GI stromal tumors were identified as leiomyosarcoma (LMS). For primary GIST, surgery remains the principal treatment and adjuvant imatinib may improve outcomes. Multimodality therapy may also be effective in patients with metastatic GIST. In this review, we summarize the epidemiology, clinicopathologic features, natural history, and clinical management of LMS and GIST.

Targeting receptor tyrosine kinase signaling in acute myeloid leukemia

Acute myeloid leukemia (AML) is a quickly progressing, heterogeneous clonal disorder of hematopoietic progenitor cells. Significant progress in understanding the pathogenesis of AML has been achieved in the past few years. Two major types of genetic events are thought to give rise to leukemic transformation: alterations in the activity of transcription factors controlling hematopoietic differentiation and activation of components of receptor tyrosine kinase (RTK) signaling pathways. This has led to the development of promising new therapeutic strategies for the disease. In this article, we will discuss recent developments in the field of molecularly targeted therapies for AML, which involve RTKs such as FMS-like tyrosine kinase 3 (Flt3), c-Kit and signal transduction via the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways. Initial results imply that targeting RTKs is a very promising approach for AML and that other receptors, such as the insulin-like growth factor receptor (IGF-IR), could also represent new targets in the future.

Expression of c-kit proto-oncogene in canine mastocytoma: a kinetic study using real-time polymerase chain reaction

KIT receptor, the c-kit gene product, is thought to play a major role in canine mastocytoma, one of the most common neoplastic diseases in dogs. In the present study, the expression of c-kit proto-oncogene in blood and in tumor biopsies from 41 dogs with histologically confirmed mastocytoma at different grades of cellular differentiation and 5 negative control dogs was investigated using real-time (quantitative) reverse transcription-polymerase chain reaction (RRT-PCR). The animals were followed up for over 1 year after surgery in order to characterize the kinetics of c-kit expression in blood. Transcript mRNAs extracted from blood at different time points after surgery and from tumor tissue surgically removed from each dog were used in a quantitative RRT-PCR assay targeting the extracellular coding region of the c-kit gene. Tissues constitutively expressing c-kit (brain and spleen) were used as positive controls. Levels of expression of c-kit were higher in tumor biopsies than in blood; the blood level decreased in the patients between 1 and 3 months after surgery. No KIT expression was detected in blood from the 5 dogs not affected by mastocytoma (negative controls). The RRT-PCR appears to be a suitable method for sensitive and quantitative detection of c-kit gene expression in canine blood and neoplastic tissues. Although c-kit expression levels measured by RRT-PCR do not correlate with prognosis, they confirm that surgery remains the main treatment to reduce circulating mastocytes and that circulating mast cells can be detected even in benign highly differentiated forms of mastocytoma such as grade I.

KIT (CD117): a review on expression in normal and neoplastic tissues, and mutations and their clinicopathologic correlation

CD117 (KIT) is a type III receptor tyrosine kinase operating in cell signal transduction in several cell types. Normally KIT is activated (phosphorylated) by binding of its ligand, the stem cell factor. This leads to a phosphorylation cascade ultimately activating various transcription factors in different cell types. Such activation regulates apoptosis, cell differentiation, proliferation, chemotaxis, and cell adhesion. KIT-dependent cell types include mast cells, some hematopoietic stem cells, germ cells, melanocytes, and Cajal cells of the gastrointestinal tract, and neoplasms of these cells are examples of KIT-positive tumors. Other KIT-positive normal cells include epithelial cells in skin adnexa, breast, and subsets of cerebellar neurons. KIT positivity has been variably reported in sarcomas such as angiosarcoma, Ewing sarcoma, synovial sarcoma, leiomyosarcoma, and MFH; results of the last three are controversial. The variations in published data may result from incomplete specificity of some polyclonal antibodies, possibly contributed by too high dilutions. Also, KIT is expressed in pulmonary and other small cell carcinomas, adenoid cystic carcinoma, renal chromophobe carcinoma, thymic, and some ovarian and few breast carcinomas. A good KIT antibody reacts with known KIT positive cells, and smooth muscle cells and fibroblasts are negative. KIT deficiency due to hereditary nonsense/missense mutations leads to disruption of KIT-dependent functions such as erythropoiesis, skin pigmentation, fertility, and gastrointestinal motility. Conversely, pathologic activation of KIT through gain-of-function mutations leads to neoplasia of KIT-dependent and KIT-positive cell types at least in three different systems: mast cells/myeloid cells--mastocytosis/acute myeloid leukemia, germ cells--seminoma, and Cajal cells--gastrointestinal stromal tumors (GISTs). KIT tyrosine kinase inhibitors such as imatinib mesylate are the generally accepted treatment of metastatic GISTs, and their availability has prompted an active search for other treatment targets among KIT-positive tumors such as myeloid leukemias and small cell carcinoma of the lung, with variable and often nonconvincing results.

Mutations in the receptor tyrosine kinase pathway are associated with clinical outcome in patients with acute myeloblastic leukemia harboring t(8;21)(q22;q22)

AML1-MTG8 generated by t(8;21) contributes to leukemic transformation, but additional events are required for full leukemogenesis. We examined whether mutations in the receptor tyrosine kinase (RTK) pathway could be the genetic events that cause acute myeloblastic leukemia (AML) harboring t(8;21). Mutations in the second tyrosine kinase domain, juxtamembrane (JM) domain and exon 8 of the C-KIT gene were observed in 10, one and three of 37 AML patients with t(8;21), respectively. Three patients showed an internal tandem duplication in the JM domain of the FLT3 gene. One patient had a mutation in the K-Ras gene at codon 12. As the occurrence of these mutations was mutually exclusive, a total of 18 (49%) patients showed mutations in the RTK pathway. These results suggest that activating mutations in the RTK pathway play a role in part as an additional event leading to the development of t(8;21) AML. The 6-year cumulative incidence of relapse in patients with RTK pathway mutations was 79.8%, compared with 13.5% in patients lacking such mutations (P=0.0029). Furthermore, the 6-year relapse-free survival in patients with mutations was 18% compared to 60% in those without mutations (P=0.0340), indicating that RTK mutations are associated with the clinical outcome in t(8;21) AML.

Normal and Oncogenic Forms of the Receptor Tyrosine Kinase Kit

Kit is a receptor tyrosine kinase (RTK) that binds stem cell factor. This receptor ligand combination is important for normal hematopoiesis, as well as pigmentation, gut function, and reproduction. Structurally, Kit has both an extracellular and intracellular region. Theintra-cellular region is comprised of a juxtamembrane domain (JMD), a kinase domain, a kinase insert, and a carboxyl tail. Inappropriate expression or activation of Kit is associated with a variety of diseases in humans. Activating mutations in Kit have been identified primarily in the JMD and the second part of the kinase domain and have been associated with gastrointestinal stromal cell tumors and mastocytosis, respectively. There are also reports of activating mutations in some forms of germ cell tumors and core binding factor leukemias. Since the cloning of the Kit ligand in the early 1990s, there has been an explosion of information relating to the mechanism of action of normal forms of Kit as well as activated mutants. This is important because understanding this RTK at the biochemical level could assist in the development of therapeutics to treat primary and secondary defects in the tissues that require Kit. Furthermore, understanding the mechanisms mediating transformation of cells by activated Kit mutants will help in the design of interventions for human disease associated with these mutations. The objective of this review is to summarize what is known about normal and oncogenic forms of Kit. We will place particular emphasis on recent developments in understanding the mechanisms of action of normal and activated forms of this RTK and its association with human disease, particularly in hematopoietic cells.

Efficacy and safety of imatinib in adult patients with c-kit–positive acute myeloid leukemia

This phase 2 pilot study was conducted to determine the efficacy and safety of imatinib mesylate in patients with c-kit–positive acute myeloid leukemia (AML) refractory to or not eligible for chemotherapy. Twenty-one patients were enrolled and received imatinib 600 mg orally once daily. Five responses were seen primarily in patients, starting with relatively low blast counts in bone marrow (BM) and peripheral blood (PB): 2 patients who were considered refractory on chemotherapy on the basis of persistence of blasts in PB and BM met the criteria for complete hematologic remission, 1 patient had no evidence of leukemia, and 2 patients achieved a minor response. Treatment with imatinib demonstrated a good safety profile and was well tolerated. Western blot analysis and immunohistochemistry demonstrated c-Kit activation in primary AML cells. Further, imatinib treatment of primary AML cells inhibited c-Kit tyrosine-phosphorylation. Genomic DNA-sequencing of c-KIT showed no mutations in exons 2, 8, 10, 11, 12, and 17. Although some of the responses derived from relatively small reductions in leukemic blasts and may be attributable, in part, to prior chemotherapy, these cases suggest that imatinib has interesting clinical activity in a subset of patients with c-kit–positive AML. Further clinical trials are warranted to explore the clinical potential of imatinib in AML and to identify the underlying molecular mechanism.

C-kit receptor expression in acute leukemias—association with patient and disease characteristics and with outcome

We hypothesize that c-kit expression may be associated with disease-specific features and have prognostic value in acute leukemias. In acute lymphocytic leukemia (ALL), higher levels of c-kit expression predicted lower complete response (CR) rates, suggesting that these patients may benefit from acute myelogenous leukemia (AML) therapy. Despite a negative association with the Philadelphia-chromosome, there was no correlation with disease-free survival (DFS) in CR. In AML, c-kit was associated with older age and cytogenetic abnormality t(-5, -7). Consequently higher levels of c-kit predicted lower CR rates. However, after accounting for these covariates, multivariate analysis indicates that higher c-kit expression predicts higher CR rates, although there was no effect on DFS in CR.

Sustained complete hematologic remission after administration of the tyrosine kinase inhibitor imatinib mesylate in a patient with refractory, secondary AML

Imatinib mesylate, a tyrosine kinase inhibitor targeting bcr-abl, platelet-derived growth factor receptor (PDGF-R), and c-Kit, effectively induces hematologic and cytogenetic remissions in bcr-abl(+) chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL) with only mild to moderate side effects. Here, we describe the successful treatment of a 64-year-old man with c-Kit(+) secondary acute myeloid leukemia (AML) refractory to standard chemotherapy. Upon 2 weeks of imatinib mesylate administration, the patient achieved a complete hematologic remission in peripheral blood. In addition, complete clearance of leukemic blasts in bone marrow and a significant cytogenetic response lasting for more than 5 months was observed. Sequence analysis of exons 2, 8, 10, 11, and 17 of the c-Kit receptor did not reveal structural alterations as previously described in a subset of AML cases. This is the first report of complete remission achieved upon administration of imatinib mesylate in a patient with highly refractory, secondary AML.

Evaluation of an intron deletion in the c-kit gene of canine mast cell tumors

OBJECTIVE

To evaluate molecular abnormalities in the c-kit gene of canine mast cell tumors (MCT) with different grades of cellular differentiation.

SAMPLE POPULATION

31 normal tissue specimens from dogs and 45 canine MCT classified according to grade of cell differentiation.

PROCEDURES

Genomic DNA extractions were made from canine MCT and normal tissues. Parts of exon 11, intron 11, and exon 12 of the c-kit gene were amplified by use of polymerase chain reaction. These regions were cloned, sequenced, and compared with GenBank sequences of the National Center for Biotechnology International. A statistical analysis was used to compare sequences from canine MCT and normal tissues.

RESULTS

A significantly higher percentage of homozygous intron 11 deletion was found in canine MCT (49%) than in normal tissues (13%). This percentage was also higher in moderately and poorly differentiated MCT, compared with well-differentiated MCT Although no mutations were detected in any of the specimens, a polymorphism at amino acid position 606 of the canine c-kit sequence was found in all the studied sequences.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated a relationship between intron 11 deletion and MCT and the grade of MCT differentiation. We suggest that intron 11 deletion may be implicated in the pathogenesis of MCT and could be used as a marker for diagnosis and prognosis of canine MCT.

Smart drugs: tyrosine kinase inhibitors in cancer therapy

Cancer therapy directed at specific, frequently occurring molecular alterations in signaling pathways of cancer cells has been validated through the clinical development and regulatory approval of agents such as Herceptin for the treatment of advanced breast cancer and Gleevec for chronic myelogenous leukemia and gastrointestinal stromal tumors. While most novel, target-directed cancer drugs have pregenomic origins, one can anticipate a postgenomic wave of sophisticated "smart drugs" to fundamentally change the treatment of all cancers. With these prospects, interest in this new class of therapeutics extends from basic research scientists to practicing oncologists and their patients. An extension of the initial successes in molecular oncology will occur more quickly and successfully through an appreciation of lessons learned with the first group of agents in their progress through clinical development.

Classes of c-KIT activating mutations: proposed mechanisms of action and implications for disease classification and therapy

Mutations causing constitutive activation of KIT have been shown to be causative in some forms of mastocytosis, and several types of mutations have been associated with myeloproliferative disorders (MPDs), acute myelogenous leukemia (AML), sinonasal lymphomas, and gastrointestinal stromal tumors (GIST). We divide these activating mutation into two types - 'regulatory type' mutations, which affect regulation of the kinase molecule, and 'enzymatic pocket type' mutations, which alter the amino acid sequence directly forming the enzymatic site. KIT inhibitors have been suggested as therapeutic drugs for these conditions, but different types of activating mutations respond differentially to KIT inhibitors, so classification of individuals on the basis of specific mutations is necessary to guide therapy.

Expression of high amounts of the CD117 molecule in a case of B-cell non-Hodgkin's lymphoma carrying the t(14:18) translocation

The c-kit proto-oncogen (CD117) has been described to be present in normal and neoplastic hemopoietic cells including both myeloid and lymphoid lineages. Among the normal lymphoid cells CD117 expression would be restricted to a small subset of NK-cells, and to early T-cell precursors and it is not expressed by normal B-cells. Regarding chronic lymphoproliferative disorders the only data provided up to now suggests that CD117 expression is restricted to cases of Hodgkin's disease and anaplastic large-cell lymphoma. In the present paper we describe a case of a B-cell chronic lymphoproliferative disorder carrying the t(14:18) translocation as demonstrated by molecular studies, in which the flow cytometric immunophenotypic analysis of both peripheral blood and bone marrow samples revealed the expression of high amounts of the CD117 antigen in the surface of the clonal B-cell population. Further studies are necessary to explore both the functional role of c-kit expression in the neoplastic B-cells from this patient and its potential utility for the diagnosis and follow-up of patients with B-cell non-Hodgkin's lymphoma.

Canine mast cell tumors express stem cell factor receptor

c-kit protooncogene encodes a type III transmembrane receptor kinase, the stem cell factor receptor, or KIT. The ligand of the KIT. stem cell factor, is a cytokine that stimulates mast cell growth and differentiation. We have studied immunohistochemically KIT expression in 23 canine mast cell tumors (MCTs), 10 histiocytomas, 5 malignant melanomas, and in 2 cell lines derived from mast cells (HMC-1, human and C2, canine). As expected, KIT was detected both in the human mast cell leukemia cell line (HMC- ) and in the canine mastocytoma cell line C2. In normal canine skin, KIT expression was confined to mast cells. All canine MCTs expressed KIT, although the intensity of the staining reaction varied considerably among the 23 neoplasms. Grade III tumors showed the highest expression of KIT, whereas grade I tumors showed the lowest expression of KIT. Two patterns of KIT expression were detected in mast cells. In normal canine mast cells and in some neoplastic mast cells, KIT appeared mainly on the cell membrane. However, in many canine MCTs, KIT is accumulated in the cytoplasm, usually near the cell nucleus. The meaning of these two patterns is not clear. Expression of KIT could not be detected immunohistochemically in any of the other neoplasias investigated. According to our results, it can be concluded that most, if not all, canine MCT express KIT. Furthermore, there is an inverse correlation between the degree of differentiation and the expression of KIT. Moreover, according to our results, KIT can be used as a reliable immunohistochemical marker for canine mast cells and undifferentiated mast cell tumors.

Immunocytoma: a retrospective analysis from St Bartholomew's Hospital-1972 to 1996

PURPOSE

To analyze the presentation features and outcome for patients with immunocytoma (IMC) managed at St Bartholomew's Hospital (SBH), London, United Kingdom, between 1972 and 1996. Outcome was compared with that of patients with small lymphocytic lymphoma (SLL)/B-cell chronic lymphocytic leukemia (B-CLL) treated at SBH during the same period.

PATIENTS AND METHODS

One hundred twenty-six patients with newly diagnosed IMC were identified. Patients were subclassified (using the Kiel classification) as having lymphoplasmacytoid (n =92), lymphoplasmacytic (n = 24), polymorphous (n = 9), or undetermined (n = 1) IMC. Six patients (5%) had stage I to IIE disease; the rest had advanced disease. Treatment was given according to disease stage. Seven patients were managed expectantly.

RESULTS

Eighty-two (69%) of 119 patients responded to treatment, but complete remission was seen in only 15 (13%) of 119. Treatment failed in 29 (24%) of 119 patients. There were three treatment-related deaths; five patients were not assessable for response. When survival of patients with IMC was compared with that of patients with B-CLL/SLL, a significant difference was found (P <. 01); this difference was maintained when only patients in whom the diagnosis was based on lymph node biopsy were considered (P =.01). A comparison of the three IMC subgroups showed that there was a trend (P =.06) toward a difference between B-CLL/SLL and the lymphoplasmacytoid subtype.

CONCLUSION

Patients diagnosed with IMC are generally older and present with advanced disease. Conventional therapies usually result in incomplete responses of short duration. Overall, these results support the proposed World Health Organization reclassification of IMC to include lymphoplasmacytoid lymphoma (Kiel classification) as a variant of B-CLL/SLL.

c-kit proto-oncogene exon 8 in-frame deletion plus insertion mutations in acute myeloid leukaemia

Genomic DNA from 60 cases of acute myeloid leukaemia (AML) was screened for mutations in the c-kit gene. DNA from all 21 exons was subjected to polymerase chain reaction (PCR) amplification and analysis by conformation sensitive gel electrophoresis (CSGE); exons showing altered CSGE patterns were then sequenced. Mutations were identified only in those patients with inv(16) (3/7 cases) or t(8;21) (1/2 cases) and comprised three in-frame deletion plus insertion mutations (exon 8) and one point mutation (exon 10, GTA --> ATA, Val530Ile). Exons 8 and 10 were then analysed in 31 further cases of inv(16) (n = 14) and t(8;21) (n = 17), revealing four additional exon 8 in-frame deletion plus insertion mutations, all of which were in cases of inv(16). All exon 8 in-frame deletion plus insertion mutations (n = 7) involved the loss or replacement of the codon for Asp419 which is highly conserved cross species and is located in the receptor's extracellular domain. The high frequency of the c-kit proto-oncogene exon 8 deletion plus insertion mutations in AML suggests an essential role for this region of the receptor's extracellular domain. The association with inv(16) invites speculation as to the link between these two changes in the pathogenesis of AML.

Hemopoietic growth factor receptor abnormalities in leukemia

Growth factor and cytokine control of hemopoiesis, the process of blood cell development, is mediated by specific interactions with cell-surface receptors. Hemopoietic growth factor receptors belong to two major families, the transmembrane protein tyrosine kinases and the hemopoietin receptors. Ligand binding stimulates receptor aggregation and activation resulting in transduction of signals that induce diverse cellular responses including proliferation, maturation, prevention of apoptosis and/or functional activation. Deregulation of hemopoiesis can result in leukemia, the malignant transformation of blood cells, or the development of other hemoproliferative disorders. As hemopoietic growth factor receptors are integral to blood cell regulation, it is feasible that receptor abnormalities may contribute to leukemia by circumventing normal growth factor control or altering the balance of proliferation and differentiation. Although considerable experimental evidence has clearly established the leukemogenic potential of mutated growth factor receptors, studies to date suggest that such abnormalities contribute only rarely to human disease.

Mediastinal mature teratoma with coexistence of angiosarcoma, granulocytic sarcoma and a hematopoietic region in the tumor: a rare case of association between hematological malignancy and mediastinal germ cell tumor

An association between mediastinal germ cell tumors (MGCT) and hematological malignancies (e.g. acute leukemia, malignant histiocytosis) has been recognized since 1984. A rare case of mediastinal mature teratoma with angiosarcoma, a hematopoietic region and granulocytic sarcoma is reported in a 29-year-old male. The resected tumor was 9.0 x 6.5 cm, weighed 65 g and showed extensive necrosis, forming a cyst. The histological features of the tumor showed a mature teratoma, which contained a large gland lined by ciliated epithelium, hyalinous cartilage, a paraganglion-like structure, well-differentiated angiosarcoma with atypical hematopoiesis composed of CD34-positive cells, and malignant round cells. The malignant round cells did not stain for CD34 but were positive for leukocyte common antigen (LCA) and c-kit product. From these findings, the round cells were diagnosed as granulocytic sarcoma. The patient died of metastasis of the granulocytic sarcoma in the tonsils and cervical lymph nodes 8 months after surgery. A leukemic condition was not present throughout the clinical course. The association between MGCT and hematological malignancy is a distinctive syndrome. However, its pathogenesis is still obscure and the origin of the hematopoietic malignancy has not been fully elucidated. In this particular case, it is suggested that the granulocytic sarcoma might have arisen from the abnormal hematopoietic area in the mediastinal teratoma.

C-kit receptors in childhood malignant lymphoblastic cells

The product of the protooncogene c-kit is the receptor for the hematopoietic cytokine stem cell factor (SCF). C-kit is expressed on leukemic cells of the erythroid, myeloid, and mast-cell lineage and SCF has a proliferative effect on some of these cells. The role of SCF and c-kit in lymphoid malignancies is much less clear. Here we review the role of c-kit in normal lymphopoiesis and summarize its role in lymphoid malignancies. C-kit is expressed in normal lymphopoiesis and its ligand SCF synergizes with IL-7 to enhance the proliferation of B- and T-cell progenitors. In malignant lymphopoiesis, c-kit can also be expressed in B and T-lymphoblastic cells from children with non Hodgkin's lymphoma (NHL) or acute lymphoblastic leukemia (ALL) when analyzed by the highly sensitive reverse transcriptase polymerase chain reaction (RT-PCR). While c-kit receptors were detected by flow cytometric (FCM) analysis on about 40% of fresh T-lymphoblastic biopsy tumor cell preparations or T-lymphoblastic cell lines, no receptors were detected on B-lymphoblastic fresh cells or cell lines from children with B-ALL or Burkitt's lymphoma (BL). Almost all of the lymphoblastic cells expressing c-kit protein responded to recombinant human (rh)SCF with a downregulation of c-kit receptors. A proliferative response was detected only in a minority of these cells. B-ALL or BL cell lines showed no response to rhSCF. Upregulation of c-kit in T-lymphoblastic cells could be demonstrated by the addition of IL-1 beta, TNF-alpha, TGF-beta or A23187, and downregulation by rhSCF or phorbol myristate acetate (PMA). Despite upregulation of c-kit mRNA, protein remained undetectable on B-ALL or BL cells in the presence of A23187. The metabolic state of the cells seemed to influence c-kit expression, since c-kit was upregulated in T-lymphoblastic cells by the addition of new medium. C-kit appears to play a role in the growth of some malignant T-lymphoblastic but not B-lymphoblastic cells.

Expression of c-kit receptor (CD117) and CD34 in leukemic cells

The expression of c-kit receptor (c-kit R; CD117) and CD34 was examined in acute myeloid leukemia (AML), acute lymphoid leukemia (ALL), chronic myeloid leukemia (CML) in blastic transformation (BT), and myelofibrosis (MF) in myeloid BT. In myeloid leukemia including AML, CML-myeloid BT and MF-myeloid BT, both c-kit R and CD34 were expressed synchronously, while in lymphoid leukemia including ALL and CML-lymphoid BT, only CD34 was highly expressed. A close correlation between c-kit R and CD33 expression and an inverse correlation between c-kit R and CD19 expression were observed when all of the myeloid plus lymphoid leukemia cells were analysed. There was a close correlation between c-kit R and CD34 expression in the myeloid leukemia cells. c-kit R expression may be associated with myeloid phenotypes of leukemic cells and may be useful for the diagnosis of myeloid leukemia. The literature of c-kit R expression in leukemic cells is reviewed here and the comparison of c-kit R and CD34 expression in normal hematopoietic progenitor cells with those on the leukemic counterparts was discussed.