Abnormality of c-kit oncoprotein in certain patients with chronic myelogenous leukemia--potential clinical significance

KIT Mutations Correlate with Higher Galectin Levels and Brain Metastasis in Breast and Non-Small Cell Lung Cancer

To investigate a potential role for galectins as biomarkers that enable diagnosis or prognostication of breast or non-small cell lung cancer, the serum levels of galectins -1, -3, -7, -8, and -9 of cancer patients determined by ELISA assays were compared to the mutation status of 50 known cancer-critical genes, which were determined using multiplex PCR in tumors of the same patients. Mutations in the KIT proto-oncogene, which codes for the c-Kit protein, a receptor tyrosine kinase, correlated with higher levels of galectins -1, -3, -8, and -9 in breast cancer patients and galectin-1 in non-small cell lung cancer patients. Mutations in the KIT gene were more likely found in brain metastases from both of these primary cancers. The most common KIT mutation in our panel was p.M541L, a missense mutation in the transmembrane domain of the c-Kit protein. These results demonstrate an association between KIT oncogenic signaling and elevated serum galectins in patients with metastatic disease. Changes in protein trafficking and the glycocalyx composition of cancer cells may explain the observed alterations in galectin expression. This study can be useful for the targeted selection of receptor tyrosine kinase and galectin inhibitor anti-cancer treatments.

Prevalence and significance of M541L single nucleotide polymorphism in the central European cohort of gastrointestinal stromal tumor patients

BACKGROUND

Single nucleotide polymorphisms can create a genetic microenvironment in some tumors that affects the course of treatment, resistance, etc. Whether single nucleotide polymorphisms have an impact on gastrointestinal stromal tumor (GIST) development and disease progression is not yet accurately verified. KIT SNP^M541L in exon 10 correlates with a worse prognosis of many cancers. The impact of KIT SNP^M541L in GISTs is relatively unknown and, therefore, its analyses could have potential in patient therapy and could provide more detailed information on tumor character, clinical presentation, or tumor behavior in treatment.

AIM

The aim of the study was the analysis of the biological and clinical significance of the KIT SNP^M541L polymorphism in exon 10.

MATERIALS AND METHODS

Paraffin sample tissues were obtained from the National GIST Register in Martin. Retrospective samples from 177 GIST patients were divided into several groups. Detection of SNP^M541L was performed by Sanger sequencing. Statisitical analyses were performed to determine the prevalence of KIT SNP^M541L in the Slovak GIST cohort, to search for correlation between c-KIT status and clinicopathological, molecular and biological data.

RESULTS

Overall, 29 samples out of 177 showed KIT SNP^M541L polymorphism.

CONCLUSION

Our results do not support the association between KIT SNP^M541L and increased risk of relapse in localized primary GISTs. Additionally, we found a positive correlation between KIT SNP^M541L occurrence and earlier onset of relapse in PDGFRa and WT subgroup of GISTs.

Expression differences of miR-142-5p between treatment-naïve chronic myeloid leukemia patients responding and non-responding to imatinib therapy suggest a link to oncogenic ABL2, SRI, cKIT and MCL1 signaling pathways critical for development of therapy resistance

Background

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by constitutive activity of the tyrosine kinase BCR-ABL1. Although the introduction of tyrosine kinase inhibitors (TKIs) has substantially improved patients’ prognosis, drug resistance remains one of the major challenges in CML therapy. MicroRNAs (miRNAs), a class of short non-coding RNAs acting as post-transcriptional regulators, are implicated in CML progression and drug resistance. The aim of the present study was to analyze the miRNA expression profiles of 45 treatment-naïve CML patients in chronic phase (28 peripheral blood and 17 bone marrow samples) with respect to future response to imatinib therapy.

Methods

TaqMan low density arrays were used to analyze the miRNA expression pattern of the patient samples. For selected microRNAs, reporter gene assays were performed to study their ability to regulate CML associated target genes.

Results

Significant lower expression levels of miR-142-5p were identified in both, peripheral blood and bone marrow samples of future non-responders suggesting a potential tumor suppressor role of this miRNA. This was supported by reporter gene assays that identified the survival, proliferation and invasion promoting CML related genes ABL2, cKIT, MCL1 and SRI as targets of miR-142-5p and miR-365a-3p, the latter identified as potential biomarker in peripheral blood samples.

Conclusion

MiR-142-5p and to a certain extend also miR-365a-3p were able to discriminate treatment-naïve CML patients not responding to imatinib in the course of their treatment from patients, who responded to therapy. However, further large-scale studies should clarify if the identified miRNAs have the potential as predictive biomarkers for TKI resistance.

Mutational spectrum of tobacco associated oral squamous carcinoma and its therapeutic significance

Oral squamous cell cancer (OSCC) is a common malignancy attributed to use of chewing smokeless tobacco and smoking. Most of the targeted strategies are based on EGFR expression and mutation; however, none of them has shown significant improvement in survival and response rates. We carried out this study to evaluate mutational profile of tobacco associated oral carcinoma with special emphasis on EGFR and its downstream events.

PATIENTS AND METHODS

A total of 46 histologically proven cases were recruited between January 2017 and January 2019. Apart from detailed clinical and histological studies, the paraffin-embedded tissue was submitted for expression of 50 genes using Next Generation Sequencing using Ion Ampliseq Cancer Hotspot Panel v2.

RESULTS

The mean age of patients was 47.8 ± 10.9 years. Majority had tumors on buccal mucosa (24) and tongue (13). Nineteen of these tumors were larger than 4 cm, and 5 had adjacent site involvement. Thirty one were node positive. TP53 mutations were commonest seen in 19 followed by CDKN2A in 11, HRAS in 8, PIK3CA in 3, SMARCB1 in 2, and KIT, EGFR, BRAF, STK11, ABL1, RB1 in one case each. Concomitant TP53 mutation was identified with other mutations like CDKN2A, HRAS, KIT, PIK3CA, STK11, SMARCB1, ABL1, and RB1 making tobacco-associated OSCC as a heterogeneous mutational tumor with multiple events. A patient with TP53 mutations has poor disease free survival (47.4 vs 63% p = 0.17); however, this was not statistically significant.

CONCLUSION

The study shows a heterogeneous mutational spectrum with multiple mutational events in OSCC. The low EGFR mutation rates and higher mutations in EGFR downstream pathways including that in TP53 and HRAS suggest that anti EGFR strategies may not succeed in these tumors and newer agents and therapeutic combinations need to be tried.

Expression and significance of c-kit and epithelial-mesenchymal transition (EMT) molecules in thymic epithelial tumors (TETs)

Background

To investigate the expression and significance of c-kit and epithelial-mesenchymal transition (EMT) molecules (E-cadherin, N-cadherin, Twist, Snail) in thymic epithelial tumors (TETs).

Methods

The tissue microarray technology and immunohistochemistry MaxVisionTM-use kit were used to detect the expression of c-kit and EMT molecular markers in 150 cases of paraffin sections of TET tissue and analysis the correlation between c-kit and EMT molecules and explore the malignancy and the relationship of clinicopathological parameters between c-kit, EMT molecules and TETs.

Results

The expression difference of c-kit and EMT molecular markers (E-cadherin, N-cadherin, Snail, Twist) in TETs subtypes was statistically significant (P<0.01) and their positive expression rate of thymic carcinoma was significantly higher than that in thymoma, and the difference was statistically significant, respectively (P<0.01). There is a negative correlation between the expression of c-kit and E-cadherin as well as a positive correlation between the expression level of c-kit, N-cadherin, Twist, and Snail. Furthermore, E-cadherin was negatively correlated with N-cadherin, Twist, and Snail while N-cadherin expression was positively correlated with Twist, Snail.

Conclusions

Five indicators (c-kit, E-cadherin, N-cadherin, Twist, and Snail) may determine the malignancy of TETs, especially for distinguishing thymoma and thymic carcinoma.

Pharmacogenetics and Pharmacogenomics of Targeted Therapeutics in Chronic Myeloid Leukemia

The advent of targeted therapeutics has greatly improved outcomes of chronic myeloid leukemia (CML) patients. Despite increased efficacy and better clinical responses over cytotoxic chemotherapies, many patients receiving targeted drugs exhibit a poor initial response, develop drug resistance, or undergo relapse after initial success. This inter-individual variation in response has heightened the interest in studying pharmacogenetics and pharmacogenomics (PGx) of cancer drugs. In this review, we discuss the influence of various germline and somatic factors on targeted drug response in CML. Specifically, we examine the role of genetic variants in drug metabolism genes, i.e. CYP3A family genes, and drug transporters, i.e. ABC and SLC family genes. Additionally, we focus on acquired somatic variations in BCR-ABL1, and the potential role played by additional downstream signaling pathways, in conferring resistance to targeted drugs in CML. This review highlights the importance of PGx of targeted therapeutics and its potential application to improving treatment decisions and patient outcomes.

An unusual type of myeloid sarcoma localization following myelofibrosis: A case report and literature review

Myeloid Sarcoma (MS) is a rare malignancy that can present as an isolated disease or more frequently in association with or following acute myeloid leukemia or other myeloid neoplasms and rarely following myelofibrosis.

Since molecular pathogenesis and prognostic factors of MS are not well understood, its prognosis remains poor even in the era of novel agents and target therapies.

We report the case of a patient with MS following myelofibrosis with multiple subcutaneous, cutaneous and muscle localizations; the latter has been reported in the literature as anecdotal. In this way we aimed to enhance the understanding of this disease.

Towards standardization of next-generation sequencing of FFPE samples for clinical oncology: intrinsic obstacles and possible solutions

BACKGROUND

Next generation sequencing has a potential to revolutionize the management of cancer patients within the framework of precision oncology. Nevertheless, lack of standardization decelerated entering of the technology into the clinical testing space. Here we dissected a number of common problems of NGS diagnostics in oncology and introduced ways they can be resolved.

METHODS

DNA was extracted from 26 formalin fixed paraffin embedded (FFPE) specimens and processed with the TrueSeq Amplicon Cancer Panel (Illumina Inc, San Diego, California) targeting 48 cancer-related genes and sequenced in single run. Sequencing data were comparatively analyzed by several bioinformatics pipelines.

RESULTS

Libraries yielded sufficient coverage to detect even low prevalent mutations. We found that the number of FFPE sequence artifacts significantly correlates with pre-normalization concentration of libraries (rank correlation -0.81; p < 1e-10), thus, contributing to sample-specific variant detection cut-offs. Surprisingly, extensive validation of EGFR mutation calls by a combination of aligners and variant callers resulted in identification of two false negatives and one false positive that were due to complexity of underlying genomic change, confirmed by Sanger sequencing. Additionally, the study of the non-EGFR amplicons revealed 33 confirmed unique mutations in 17 genes, with TP53 being the most frequently mutated. Clinical relevance of these finding is discussed.

CONCLUSIONS

Reporting of entire mutational spectrum revealed by targeted sequencing is questionable, at least until the clinically-driven guidelines on reporting of somatic mutations are established. The standardization of sequencing protocols, especially their data analysis components, requires assay-, disease-, and, in many cases, even sample-specific customization that could be performed only in cooperation with clinicians.

Next-generation sequencing of tyrosine kinase inhibitor-resistant non-small-cell lung cancers in patients harboring epidermal growth factor-activating mutations

Background

The aim of this study was to detect the epidermal growth factor receptor (EGFR)-activating mutations and other oncogene alterations in patients with non-small-cell lung cancers (NSCLC) who experienced a treatment failure in response to EGFR-tyrosine kinase inhibitors (TKIs) with a next generation sequencer.

Methods

Fifteen patients with advanced NSCLC previously treated with EGFR-TKIs were examined between August 2005 and October 2014. For each case, new biopsies were performed, followed by DNA sequencing on an Ion Torrent Personal Genome Machine (PGM) system using the Ion AmpliSeq Cancer Hotspot Panel version 2.

Results

All 15 patients were diagnosed with NSCLC harboring EGFR-activating mutations (seven cases of exon 19 deletion, seven cases of L858R in exon 21, and one case of L861Q in exon 21). Of the 15 cases, acquired T790M resistance mutations were detected in 9 (60.0 %) patients. In addition, other mutations were identified outside of EGFR, including 13 cases (86.7 %) exhibiting TP53 P72R mutations, 5 cases (33.3 %) of KDR Q472H, and 2 cases (13.3 %) of KIT M541L.

Conclusions

Here, we showed that next-generation sequencing (NGS) is able to detect EGFR T790M mutations in cases not readily diagnosed by other conventional methods. Significant differences in the degree of EGFR T790M and other EGFR-activating mutations may be indicative of the heterogeneity of disease phenotype evident within these patients. The co-existence of known oncogenic mutations within each of these patients may play a role in acquired EGFR-TKIs resistance, suggesting the need for alternative treatment strategies, with PCR-based NGS playing an important role in disease diagnosis.

KIT exon 10 variant (c.1621 A > C) single nucleotide polymorphism as predictor of GIST patient outcome

Background

Tumor genotype plays a crucial role in clinical management of GIST. Whether genetic polymorphism of KIT may influence GIST patient outcome is unclear.

Methods

We investigated the biological and clinical significance of the presence of KIT exon 10 variant (c.1621 A > C), KIT^L541, in a transfected cell line (3 T3 L541) and in two retrospectively collected series of 109 GIST patients in total. The control group consisted of 60 healthy donors collected at the French department of blood transfusion.

Results

In the 3 T3 L541 cell line, KIT^L541 protein exhibited a spontaneous phosphorylation status comparable to that of wild-type KIT but displayed a phosphorylation pattern of AKT and ERK1/2 that was found similar to that of the classical mutated forms of the KIT receptor. Of 109 patients enrolled in this retrospective translational research study, 24 (22 %) harboured KIT^L541, similarly to the control group of healthy donors (n = 10 of 60, 17 %). A higher prevalence of the variant KIT^L541 was observed in patients with metastatic status at diagnosis (KIT^L541 correlated nine of 22 versus 15 of 87, p = 0.02). In addition, patients with KIT^L541 and localized GIST had a higher rate of relapse at 5 years and lower relapse free survival at 5 years in univariate, as well as in multivariate analysis. Response rate and duration of response to imatinib was similar in KIT^L541 and KIT^M541 patients.

Conclusion

KIT^L541 genotype is associated with a higher risk of metastasis at diagnosis and a higher risk of relapse in GIST patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1817-5) contains supplementary material, which is available to authorized users.

Multiple oncogenic mutations related to targeted therapy in nasopharyngeal carcinoma

INTRODUCTION

An increasing number of targeted drugs have been tested for the treatment of nasopharyngeal carcinoma (NPC). However, targeted therapy-related oncogenic mutations have not been fully evaluated. This study aimed to detect targeted therapy-related oncogenic mutations in NPC and to determine which targeted therapy might be potentially effective in treating NPC.

METHODS

By using the SNaPshot assay, a rapid detection method, 19 mutation hotspots in 6 targeted therapy-related oncogenes were examined in 70 NPC patients. The associations between oncogenic mutations and clinicopathologic factors were analyzed.

RESULTS

Among 70 patients, 12 (17.1%) had mutations in 5 oncogenes: 7 (10.0%) had v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) mutation, 2 (2.8%) had epidermal growth factor receptor (EGFR) mutation, 1 (1.4%) had phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit alpha (PIK3CA) mutation, 1 (1.4%) had Kirsten rat sarcoma viral oncogene homolog (KRAS) mutation, and 1 (1.4%) had simultaneous EGFR and v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) mutations. No significant differences were observed between oncogenic mutations and clinicopathologic characteristics. Additionally, these oncogenic mutations were not associated with tumor recurrence and metastasis.

CONCLUSIONS

Oncogenic mutations are present in NPC patients. The efficacy of targeted drugs on patients with the related oncogenic mutations requires further validation.

Impact of KIT exon 10 M541L allelic variant on the response to imatinib in aggressive fibromatosis: analysis of the desminib series by competitive allele specific Taqman PCR technology

BACKGROUND

Aggressive fibromatosis (AF) is a rare fibroblastic proliferative disease with a locally aggressive behavior and no distant metastasis, characterized by driver mutations in CTNNB1 or the APC gene. When progressive and/or symptomatic AF is not amenable to local management, a variety of medical treatments may be efficient, including imatinib mesylate. The phase II "Desminib trial" included 40 patients with AF to evaluate the toxicity and efficacy of imatinib resulting in a 65% tumor control rate at 1 year. We investigated a potential predictive value of KIT exon 10 M541L variant (KITL541) on this prospective series.

METHODS

DNA was extracted in sufficient quantity from 33 patients included in the Desminib trial. The detection of KITL541 was performed by Competitive Allele-Specific Taqman® PCR technology. Chi-2 analyses were performed to search for a correlation between KIT status and tumor response. Progression free (PFS) and overall survival (OS) were compared by log-rank test after Kaplan-Meier analysis.

RESULTS

In 6 out of 33 cases (18%), the technique failed to determine the mutational status; 5 patients (19%) harboured KITL541 and 22 patients (81%) were classified as KIT wild type. Compared with total cohort, KITL541 frequency did not distinguish between different clinical characteristics. In the KITL541 and the KITWT subgroups, the tumor control rate at 1 year was 100% and 68%, respectively (p = 0.316). The median PFS of patients harboring KITL541 or not is 29.9 and 24.5 months, respectively (p = 0.616), and the median OS is not reached, in any of the groups.

CONCLUSION

Our results do not support a predictive effect of KITL541 on the efficacy of imatinib for patients with AF.

The Hepatocyte Growth Factor (HGF)/Met Axis: A Neglected Target in the Treatment of Chronic Myeloproliferative Neoplasms?

Met is the receptor of hepatocyte growth factor (HGF), a cytoprotective cytokine. Disturbing the equilibrium between Met and its ligand may lead to inappropriate cell survival, accumulation of genetic abnormalities and eventually, malignancy. Abnormal activation of the HGF/Met axis is established in solid tumours and in chronic haematological malignancies, including myeloma, acute myeloid leukaemia, chronic myelogenous leukaemia (CML), and myeloproliferative neoplasms (MPNs). The molecular mechanisms potentially responsible for the abnormal activation of HGF/Met pathways are described and discussed. Importantly, inCML and in MPNs, the production of HGF is independent of Bcr-Abl and JAK2V617F, the main molecular markers of these diseases. In vitro studies showed that blocking HGF/Met function with neutralizing antibodies or Met inhibitors significantly impairs the growth of JAK2V617F-mutated cells. With personalised medicine and curative treatment in view, blocking activation of HGF/Met could be a useful addition in the treatment of CML and MPNs for those patients with high HGF/MET expression not controlled by current treatments (Bcr-Abl inhibitors in CML; phlebotomy, hydroxurea, JAK inhibitors in MPNs).

Next-generation sequencing-based multi-gene mutation profiling of solid tumors using fine needle aspiration samples: promises and challenges for routine clinical diagnostics

Increasing use of fine needle aspiration for oncological diagnosis, while minimally invasive, poses a challenge for molecular testing by traditional sequencing platforms due to high sample requirements. The advent of affordable benchtop next-generation sequencing platforms such as the semiconductor-based Ion Personal Genome Machine (PGM) Sequencer has facilitated multi-gene mutational profiling using only nanograms of DNA. We describe successful next-generation sequencing-based testing of fine needle aspiration cytological specimens in a clinical laboratory setting. We selected 61 tumor specimens, obtained by fine needle aspiration, with known mutational status for clinically relevant genes; of these, 31 specimens yielded sufficient DNA for next-generation sequencing testing. Ten nanograms of DNA from each sample was tested for mutations in the hotspot regions of 46 cancer-related genes using a 318-chip on Ion PGM Sequencer. All tested samples underwent successful targeted sequencing of 46 genes. We showed 100% concordance of results between next-generation sequencing and conventional test platforms for all previously known point mutations that included BRAF, EGFR, KRAS, MET, NRAS, PIK3CA, RET and TP53, deletions of EGFR and wild-type calls. Furthermore, next-generation sequencing detected variants in 19 of the 31 (61%) patient samples that were not detected by traditional platforms, thus increasing the utility of mutation analysis; these variants involved the APC, ATM, CDKN2A, CTNNB1, FGFR2, FLT3, KDR, KIT, KRAS, MLH1, NRAS, PIK3CA, SMAD4, STK11 and TP53 genes. The results of this study show that next-generation sequencing-based mutational profiling can be performed on fine needle aspiration cytological smears and cell blocks. Next-generation sequencing can be performed with only nanograms of DNA and has better sensitivity than traditional sequencing platforms. Use of next-generation sequencing also enhances the power of fine needle aspiration by providing gene mutation results that can direct personalized cancer therapy.

Mutation in the first Ig-like domain of Kit leads to JAK2 activation and myeloproliferation in mice

Myeloproliferative neoplasms constitute a group of hematopoietic neoplasms at the myeloid stem cell level. Although mutations in the receptor tyrosine kinase KIT have been identified in patients with myeloproliferative neoplasm, the functional causality is unknown because of a lack of animal models. Here, we describe a mouse strain harboring a point mutation in the first Ig-like domain of Kit. Intriguingly, the mutant mice develop a myeloproliferative disorder with typical loss-of-function phenotypes in other tissues. The mutant Kit is incompletely N-glycosylated, shows compromised receptor dimerization, and down-regulates Akt and extracellular signal-regulating kinase 1/2 signaling. However, the mutation increases the association of Kit to Janus kinase (JAK)2 and hence the activation of JAK2. The β common receptor of the gp140 family interacts and synergizes with Kit to promote JAK2 phosphorylation, which is further enhanced by the Kit mutation. Inhibition of JAK2 suppresses the proliferation of hematopoietic progenitors in vitro and partially rescues myeloproliferation in mice. Our data suggest that overactivation of JAK2 leads to myeloproliferation in Kit mutant mice and provide mechanistic insights for the diagnosis and treatment of myeloproliferative neoplasms in humans.

KIT mutation detection in Tunisian patients with newly diagnosed myelogenous leukemia: prevalence and prognostic significance

The KIT gene encodes a class III tyrosine kinase receptor in which specific somatic mutations have been found to be associated with many diseases. In this work, we investigated the prevalence of KIT mutations in patients with chronic and acute myelogenous leukemia (CML and AML) and their prognostic significance. A total of 157 subjects were included in the present study (84 patients with CML, 33 with AML, and 40 healthy controls). Patients were analyzed at the first diagnosis, and the KIT mutations were screened by polymerase chain reaction (PCR) and direct sequencing technologies. The results demonstrated the presence of a G/A transition at codon 796, which is associated with the R796K protein variation. This mutation was detected at 21.42% in the CML subgroup and was absent in both AML patients and healthy controls; however, no correlation was found between this mutation and clinical parameters such as the molecular response to Gleevec. In conclusion, we retain that the KIT gene is highly mutated in the CML subgroup, but its role as a prognostic factor needs to be further elucidated.

Expression and mutational status of c-kit in thymic epithelial tumors

BACKGROUND

Overexpression of c-kit, a tyrosine kinase receptor protein encoded by the protooncogene kit, has been previously reported in thymic epithelial tumors and in other neoplasms such as gastrointestinal stromal tumors, myeloproliferative disorders, melanoma, and seminoma. Mutations in the kit gene have been related to response to imatinib in gastrointestinal stromal tumor and one case report of thymic carcinoma. We studied expression of c-kit in a large retrospective series of thymic epithelial malignancies and sequenced the whole gene in a subset of patients.

METHODS

Thymic epithelial tumors from 120 patients (13 thymic carcinomas and 107 thymomas) were examined. Immunohistochemical staining with an antic-kit polyclonal antibody was performed on a tissue microarray. Mutation analyses of exons 1 to 20 were conducted by direct DNA sequencing of polymerase chain reaction products in eight thymic carcinomas, five thymomas, and one thymic carcinoma cell line.

RESULTS

The percentage of c-kit positive cells was significantly higher in thymic carcinoma (46%) than in thymoma (4%). Decreased disease-related survival and progression-free survival were observed in c-kit positive tumors. No mutations were detected.

CONCLUSION

c-kit expression is strongly but not exclusively related to thymic carcinoma histotype, and it is of prognostic value. Mutations are very rare.

Comparative analysis of mutation of tyrosine kinase kit in mast cells from patients with systemic mast cell activation syndrome and healthy subjects

Systemic mast cell activation syndrome is a mast cell disorder characterized by an unregulated increased activation of mast cells leading to a pathologically enhanced release of mediators. Mutations in tyrosine kinase kit which crucially determines mast cell activity have been suggested as a necessary condition for the development of a clinically symptomatic mast cell disease. At the level of mRNA in mast cell progenitor cells of 20 patients with systemic mast cell activation syndrome and of 20 gender- and age-matched healthy volunteers, the tyrosine kinase kit was investigated for genetic alterations by means of RT-PCR and direct sequencing of the amplificates. In mast cells of 13 out of these 20 patients, multiple predominantly novel potential functionally activating point mutations or complex alterations of the mRNA sequence encoding the tyrosine kinase kit were detected. In contrast, in 19 of the 20 healthy subjects, no functionally relevant alterations of c-kit transcripts were detected. The present findings support the idea that the systemic mast cell activation syndrome is a clonal disease most commonly associated with variable activating mutations in the tyrosine kinase kit.

Tel/PDGFRbeta induces stem cell differentiation via the Ras/ERK and STAT5 signaling pathways

OBJECTIVE

Fusion genes involving the platelet-derived growth factor receptor-beta (PDGFRbeta) are found in a subgroup of myeloproliferative neoplasms, with one such fusion, Tel/PDGFRbeta found in a subset of chronic myelomonocytic leukemia patients. Tel/PDGFRbeta results in constitutive activation of several signaling pathways and induces a myeloproliferative disease in mice, with signals via tyrosines 579/581 identified as being important for this phenotype. In this study, we have used a tetracycline-regulated system to express wild-type and the mutated F2 Tel/PDGFRbeta to identify the key signaling pathways, which drive Tel/PDGFRbeta-induced differentiation of embryonic stem (ES) cells.

MATERIALS AND METHODS

The leukemic oncogene Tel/PDGFRbeta and Tel/PDGFRbeta-F2 were inducibly expressed in ES cells and their effects on self-renewal, signal transduction, and gene expression patterns analyzed.

RESULTS

Tel/PDGFRbeta activated several major signal transduction pathways (signal transducers and activators of transcription [STAT] 3, STAT5, mitogen-activated protein kinases, phosphatidylinositol-3 kinase) in ES cells, but only specific inhibition of the mitogen-activated protein kinase kinase/extracellular regulated kinase (MEK/ERK) or STAT5 pathways was able to significantly prevent Tel/PDGFRbeta-induced differentiation and restore ES-cell self-renewal. Inhibiting the tyrosine kinase activity of the oncogene using Gleevec or PDGFRbeta inhibitor III also substantially prevented Tel/PDGFRbeta-induced differentiation and its ability to upregulate key genes involved in myelopoiesis. Tyrosines 579/581 played a critical role in mediating signals via the Ras/ERK and STAT5 pathways, with dual targeting of the tyrosine kinase activity of Tel/PDGFRbeta and the MEK/ERK pathway completely preventing Tel/PDGFRbeta-induced differentiation.

CONCLUSION

These findings suggest that targeted disruption of key signaling pathways in combination with the tyrosine kinase activity of leukemic oncogenes, such as Tel/PDGFRbeta, may result in more efficacious therapies for suppressing leukemic progression in the clinical setting.

Association of paediatric mastocytosis with a polymorphism resulting in an amino acid substitution (M541L) in the transmembrane domain of c-KIT

BACKGROUND

The receptor tyrosine kinase c-KIT plays a key role in normal mast cell development. Point mutations in c-KIT have been associated with sporadic or familial mastocytosis.

OBJECTIVES

Two unrelated pairs of apparently identical twins affected by cutaneous mastocytosis attending the Mastocytosis Clinic at the Royal Children's Hospital, Melbourne, provided an opportunity to assess the possible contribution of c-KIT germline mutations or polymorphisms in this disease.

METHODS

Tissue biopsy, blood and/or buccal swab specimens were collected from 10 children with mastocytosis. To detect germline mutations/polymorphisms in c-KIT, we studied all coding exons by denaturing high pressure liquid chromatography. Exons showing mismatches were examined by direct sequencing. The influence of the substitution identified was further examined by expressing the variant form of c-KIT in factor-dependent FDC-P1 cells.

RESULTS

In both pairs of twins, a heterozygous ATG to CTG transition in codon 541 was observed, resulting in the substitution of a methionine residue in the transmembrane domain by leucine (M541L). In each case, one parent was also heterozygous for this allele. Expression of M541L KIT in FDC-P1 cells enabled them to grow in human KIT ligand (stem cell factor, SCF) but did not confer factor independence. Compared with cells expressing wild-type KIT at a similar level, M541L KIT-expressing cells displayed enhanced growth at low levels of SCF, and heightened sensitivity to the KIT inhibitor, imatinib mesylate.

CONCLUSIONS

The data suggest that the single nucleotide polymorphism resulting in the substitution M541L may predispose to paediatric mastocytosis.

Mutational analysis of the KIT gene in myelodysplastic syndrome (MDS) and MDS-derived leukemia

The progenitor cells of myelodysplastic syndrome (MDS) are thought to undergo a multistep process during their transformation into overt acute leukemia. In this study, the role of mutation of the KIT gene in the extracellular membrane, juxtamembrane and tyrosine kinase domains was investigated in 75 patients with MDS or MDS-derived leukemia (MDS-AML). Mutation was detected in 2 of 15 (13.3%) patients with refractory anemia with excess blasts transformation (RAEB-T), in 1 of 15 (6.6%) patients with chronic myelomonocytic leukemia (CMML), and in 5 of 26 (19.2%) patients with MDS-AML. However, no mutation was found in any of the nine patients with refractory anemia (RA) or the 10 patients with refractory anemia with excess blasts (RAEB). Of the mutations, five patients had changes at the same codon in tyrosine kinase domain, Asp816, while the remainder had unique mutations. These observations suggest that KIT gene mutations identified in the advanced stage of MDS, and genetic abnormality in the KIT gene, particularly at codon 816, might be additional events that contribute to the progression of MDS to AML.

BCR/ABL kinase induces self-mutagenesis via reactive oxygen species to encode imatinib resistance

Mutations in the BCR/ABL kinase domain play a major role in resistance to imatinib mesylate (IM). We report here that BCR/ABL kinase stimulates reactive oxygen species (ROS), which causes oxidative DNA damage, resulting in mutations in the kinase domain. The majority of mutations involved A/T-->G/C and G/C-->A/T transitions, a phenotype detected previously in patients, which encoded clinically relevant amino acid substitutions, causing IM resistance. This effect was reduced in cells expressing BCR/ABL(Y177F) mutant, which does not elevate ROS. Inhibition of ROS in leukemia cells by the antioxidants pyrrolidine dithiocarbamate (PDTC), N-acetylcysteine (NAC), and vitamin E (VE) decreased the mutagenesis rate and frequency of IM resistance. Simultaneous administration of IM and an antioxidant exerted better antimutagenic effect than an antioxidant alone. Therefore, inhibition of ROS should diminish mutagenesis and enhance the effectiveness of IM.

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.

Detection of overexpressed and phosphorylated wild-type kit receptor in surgical specimens of small cell lung cancer

PURPOSE

The combinations of various chemotherapeutic drugs currently used to treat advanced small cell lung cancer (SCLC) led to similarly poor survival outcomes, which is why new molecular biology approaches are needed to design and select targeted therapies.

EXPERIMENTAL DESIGN

Thirteen stage I SCLC surgical specimens were screened for c-Kit gene mutations by sequencing whole cDNA and for KIT receptor expression/activation by immunoprecipitation and Western blotting. Both the paraffin-embedded and frozen materials were analyzed by immunocytochemistry, and the stem cell factor cognate ligand was assessed by retrotranscription PCR.

RESULTS

In all cases, we showed the presence of wild-type KIT receptors by analyzing the entire coding sequence, which together with the detection of the cognate ligand stem cell factor, supports the establishment of an autocrine loop. In addition, the KIT receptor was activated/phosphorylated. The immunoprecipitation/Western blotting data fit the observed immunophenotype. Interestingly, comparison of the level of KIT expression was at least 10 times higher in the tumoral specimens than the normal reference lungs.

CONCLUSIONS

The KIT molecular profile derived from the analysis of SCLC surgical specimens shows that wild-type KIT is overexpressed and phosphorylated in the presence of stem cell factor. This finding, which is consistent with pathological KIT activation driven by an autocrine loop, is particularly interesting in the light of the recent development of new tyrosine kinase inhibitory drugs, which are highly effective in blocking wild-type KIT receptors.

9p21 locus analysis in high-risk gastrointestinal stromal tumors characterized for c-kit and platelet-derived growth factor receptor alpha gene alterations

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are noncomplex sarcomas that often are due to c-kit-activating and platelet-derived growth factor receptor alpha gene (PDGFRalpha)-activating mutations and perturbations of their related signaling pathways. Molecular and cytogenetic findings have indicated correlations between tumor progression and high-risk GISTs with c-kit mutations, the overexpression of genes such as ezrin, and losses at 9p. In particular, it was reported recently that malignant GISTs showed alterations in the p16INK4a gene located at the 9p21 locus.

METHODS

To assess the involvement of p14ARF and p15INK4b in addition to p16INK4a in GISTs, the authors undertook a molecular and cytogenetic study of the 9p21 locus. A series of 22 pre-Gleevec era, cryopreserved, high-risk GISTs that were characterized well in terms of KIT and PDGFRalpha receptors were investigated for mRNA expression, homozygous deletions, mutations, and promoter methylation of locus 9p21, in some instances complemented by fluorescent in situ hybridization studies.

RESULTS

The results indicated the loss of p16INK4a mRNA expression in 41% of the GISTs, mainly due to the homozygous deletion of both the p16INK4a gene and the p14ARF gene (24%). No mutations were found, and promoter methylation (detected by means of methylation-specific polymerase chain reaction analysis in 27% of tumors) was restricted mainly to the p15INK4b gene (20%). It is noteworthy that, in all of the methylated GISTs, the epigenetic promoter alteration was coupled with mRNA expression.

CONCLUSIONS

Alterations in the 9p21 locus were found cumulatively in 54% of the tumors in the current series and were represented mainly by the loss of tumor suppressor gene expression. The p16INK4a deletion, which always was coupled with p14ARF gene loss, seemed to be the most common 9p21 inactivation mechanism.

Sole BCR-ABL inhibition is insufficient to eliminate all myeloproliferative disorder cell populations

Protein kinase inhibitors can be effective in treating selected cancers, but most suppress several kinases. Imatinib mesylate has been useful in the treatment of Philadelphia chromosome-positive chronic myelogenous leukemia and B cell acute lymphoblastic leukemia through the inhibition of BCR-ABL tyrosine kinase activity. Imatinib mesylate has also been shown to inhibit KIT, ARG, and platelet-derived growth factor receptors alpha and beta, and potentially other tyrosine kinases. We have produced a mutant allele of BCR-ABL (T315A) that is uniquely inhibitable by the small molecule 4-amino-1-tert-butyl-3-(1-naphthyl)pyrazolo[3,4-d]pyrimidine and used it to demonstrate that sole suppression of BCR-ABL activity was insufficient to eliminate BCR-ABL(+) KIT(+)-expressing immature murine myeloid leukemic cells. In contrast, imatinib mesylate effectively eliminated BCR-ABL(+) KIT(+)-expressing leukemic cells. In the cellular context of mature myeloid cells and Pro/Pre B cells that do not express KIT, monospecific BCR-ABL inhibition was quantitatively as effective as imatinib mesylate in suppressing cell growth and inducing apoptosis. These results suggest that the therapeutic effectiveness of small molecule drugs such as imatinib mesylate could be due to the inhibitor's ability to suppress protein kinases in addition to the dominant target.

Constitutively activated phosphatidylinositol 3-kinase primes platelets from patients with chronic myelogenous leukemia for thrombopoietin-induced aggregation

In this study, we examined the effect of thrombopoietin (TPO) on the aggregation of platelets from 40 patients with myeloproliferative disorders (MPDs), including 17 patients with chronic myelogenous leukemia in the chronic phase (CML-CP), 10 with polycythemia vera, 10 with essential thrombocythemia, and three with myelofibrosis. TPO by itself dose-dependently induced the aggregation of platelets from patients with CML-CP but not from those with other MPDs or with CML-CP in cytogenetical complete remission. The expression of CD63 in CML-CP platelets was induced by TPO treatment. Phosphatidylinositol 3-kinase (PI3-kinase) was constitutively activated in CML-CP platelets. Pretreatment with PI3-kinase inhibitors (wortmannin and LY294002) dose-dependently inhibited TPO-induced aggregation of CML-CP platelets. The Abl kinase inhibitor imatinib mesylate and the Jak inhibitor AG490 suppressed TPO-induced aggregation of CML-CP platelets. Pretreatment with imatinib mesylate, but not with AG490, inhibited the activity of PI3-kinase in CML-CP platelets. In addition, tyrosine phosphorylation of Jak2 was undetected in CML-CP platelets before TPO treatment. These findings indicate that the constitutive activation of PI3-kinase primes CML-CP platelets for the aggregation induced by TPO, and that Bcr-Abl, but not Jak family protein tyrosine kinases, are involved in the constitutive activation of PI3-kinase in CML-CP platelets.

Stem cell factor attenuates liver damage in a murine model of acetaminophen-induced hepatic injury

Acute liver injury is a common cause of intensive care unit visits. In these studies, we used a murine model of acetaminophen poisoning to examine the role of stem cell factor (SCF) on liver damage. In the initial studies, we identified that the liver produces relatively high constitutive levels of SCF. Upon administration of acetaminophen, the levels of SCF fell dramatically, correlating to damage within the liver. When the liver was allowed to regenerate, the levels of SCF again correlated with the liver regeneration. We next treated mice with anti-SCF before sublethal doses of acetaminophen and significantly increased lethality in anti-SCF-treated animals. When exogenous SCF was given to mice, the lethality was significantly reduced compared with the control acetaminophen-treated animals and the damage within the liver tissue was attenuated. The administration of rSCF reduced the level of steady-state mRNA for cytochrome P450 cyp2E1 enzyme both in vitro and in vivo. These data suggest that SCF functions as an important factor that protects livers from acute damage.