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

Mastocytosis

Mastocytosis is a spectrum of clonal myeloid disorders defined by abnormal growth and accumulation of mast cells in various organ systems. The disease is divided into cutaneous mastocytosis, systemic mastocytosis (SM) and mast cell sarcoma. SM is further categorized into several non-advanced and advanced forms. The prognosis of cutaneous mastocytosis and non-advanced SM is mostly favourable, whereas prognosis and survival in advanced SM and mast cell sarcoma are poor. During the past 15 years, major advances have been made in the diagnosis, prognosis and management of patients with mast cell neoplasms. Management of mastocytosis consists of symptomatic therapy, including anti-mast cell mediator drugs, and cytoreductive agents for patients with advanced disease and selected individuals with non-advanced disease, as well as recognition and prevention of comorbidities such as osteoporosis and anaphylaxis. The preclinical and clinical development of KIT-D816V-targeting drugs, such as midostaurin or avapritinib, mark a milestone in improving management, the quality of life and survival in patients with SM. These agents induce major responses or even remission in people with advanced SM and lead to rapid improvement of mediator-related symptoms and quality of life in symptomatic patients.

Investigation of the Theragnostic Role of KIT Expression for the Treatment of Canine Mast Cell Tumors with Tyrosine Kinase Inhibitors

Several reports have indicated that canine MCTs express a mutated form of a tyrosine kinase receptor, namely KIT, that is involved in abnormal mast cell growth and differentiation. Currently, the post-surgical prognosis for MCTs is related to three different KIT immunohistochemical expression patterns. However, to our knowledge, there are few studies specifically exploring the efficacy of treatment with tyrosine kinase inhibitors related to KIT staining pattern. The purpose of this study was to investigate the potential theragnostic role of KIT expression patterns by studying their correlation to the overall survival and progression-free survival in dogs treated with only tyrosine kinase inhibitors immediately after surgery. We selected 66 cases of canine cutaneous MCTs with complete clinical background. A statistical analysis was performed to assess the overall survival status. Our data suggest an important role of KIT in the etiopathogenesis of canine MCTs and indicate that the anomalous cytoplasmatic distribution of KIT is potentially related to a lower efficacy of tyrosine kinase inhibitors, thus providing a significant prognostic information about the treatment outcome.

Clinical Use of Molecular Biomarkers in Canine and Feline Oncology: Current and Future

Molecular biomarkers are central to personalised medicine for human cancer patients. It is gaining traction as part of standard veterinary clinical practice for dogs and cats with cancer. Molecular biomarkers can be somatic or germline genomic alterations and can be ascertained from tissues or body fluids using various techniques. This review discusses how these genomic alterations can be determined and the findings used in clinical settings as diagnostic, prognostic, predictive, and screening biomarkers. We showcase the somatic and germline genomic alterations currently available to date for testing dogs and cats in a clinical setting, discussing their utility in each biomarker class. We also look at some emerging molecular biomarkers that are promising for clinical use. Finally, we discuss the hurdles that need to be overcome in going 'bench to bedside', i.e., the translation from discovery of genomic alterations to adoption by veterinary clinicians. As we understand more of the genomics underlying canine and feline tumours, molecular biomarkers will undoubtedly become a mainstay in delivering precision veterinary care to dogs and cats with cancer.

PRL2 Phosphatase Promotes Oncogenic KIT Signaling in Leukemia Cells through Modulating CBL Phosphorylation

Receptor tyrosine kinase KIT is frequently activated in acute myeloid leukemia (AML). While high PRL2 (PTP4A2) expression is correlated with activation of SCF/KIT signaling in AML, the underlying mechanisms are not fully understood. We discovered that inhibition of PRL2 significantly reduces the burden of oncogenic KIT-driven leukemia and extends leukemic mice survival. PRL2 enhances oncogenic KIT signaling in leukemia cells, promoting their proliferation and survival. We found that PRL2 dephosphorylates CBL at tyrosine 371 and inhibits its activity toward KIT, leading to decreased KIT ubiquitination and enhanced AKT and ERK signaling in leukemia cells.

IMPLICATIONS

Our studies uncover a novel mechanism that fine-tunes oncogenic KIT signaling in leukemia cells and will likely identify PRL2 as a novel therapeutic target in AML with KIT mutations.

The Role of Cancer Stem Cell Markers in Ovarian Cancer

Ovarian cancer is the most lethal gynaecological cancer and the eighth most common female cancer. The early diagnosis of ovarian cancer remains a clinical problem despite the significant development of technology. Nearly 70% of patients with ovarian cancer are diagnosed with stages III-IV metastatic disease. Reliable diagnostic and prognostic biomarkers are currently lacking. Ovarian cancer recurrence and resistance to chemotherapy pose vital problems and translate into poor outcomes. Cancer stem cells appear to be responsible for tumour recurrence resulting from chemotherapeutic resistance. These cells are also crucial for tumour initiation due to the ability to self-renew, differentiate, avoid immune destruction, and promote inflammation and angiogenesis. Studies have confirmed an association between CSC occurrence and resistance to chemotherapy, subsequent metastases, and cancer relapses. Therefore, the elimination of CSCs appears important for overcoming drug resistance and improving prognoses. This review focuses on the expression of selected ovarian CSC markers, including CD133, CD44, CD24, CD117, and aldehyde dehydrogenase 1, which show potential prognostic significance. Some markers expressed on the surface of CSCs correlate with clinical features and can be used for the diagnosis and prognosis of ovarian cancer. However, due to the heterogeneity and plasticity of CSCs, the determination of specific CSC phenotypes is difficult.

Sodium butyrate supresses malignant human mast cell proliferation, downregulates expression of KIT and promotes differentiation

Sodium butyrate (NaBu) is a class I histone deacetylase inhibitor (HDACi) that can impede the proliferation of transformed cells. Although some HDACi downregulate the expression of the stem cell factor receptor (KIT/CD117), the effect of NaBu on KIT expression and human mast cell proliferation requires further elucidation. In this study, we examined the effects of NaBu on three transformed human mast cell lines, HMC-1.1, HMC-1.2 and LAD2. NaBu (100 µM) inhibited the proliferation and metabolic activity of all three cell lines without significantly affecting their viability, suggesting that although the cells had ceased to divide, they were not yet undergoing apoptosis. Cell cycle analysis using the cell-permeant dye, propidium iodide, indicated that NaBu significantly blocked the cell cycle progression of HMC-1.1 and HMC-1.2 from G1 to G2/M phases. Furthermore, NaBu downregulated the expression of C-KIT mRNA and KIT protein expression in all three cell lines, but this effect was most significant in the HMC-1.1 and HMC-1.2, both of which harbour activating mutations in KIT, which proliferate more rapidly than LAD2. These data support earlier observations showing that human mast cell lines are sensitive to histone deacetylase inhibition. However, our data presents the novel observation that inhibition of cell proliferation by NaBu was not associated with a loss in cell viability but rather an arrest of the cell cycle. Higher concentrations of NaBu led to modest increases in histamine content, tryptase expression, and granularity. In conclusion, NaBu treatment of human mast cell lines led to a modest enhancement of the hallmarks of mature mast cells.

New C3H KitN824K/WT cancer mouse model develops late-onset malignant mammary tumors with high penetrance

Gastro-intestinal stromal tumors and acute myeloid leukemia induced by activating stem cell factor receptor tyrosine kinase (KIT) mutations are highly malignant. Less clear is the role of KIT mutations in the context of breast cancer. Treatment success of KIT-induced cancers is still unsatisfactory because of primary or secondary resistance to therapy. Mouse models offer essential platforms for studies on molecular disease mechanisms in basic cancer research. In the course of the Munich N-ethyl-N-nitrosourea (ENU) mutagenesis program a mouse line with inherited polycythemia was established. It carries a base-pair exchange in the Kit gene leading to an amino acid exchange at position 824 in the activation loop of KIT. This KIT variant corresponds to the N822K mutation found in human cancers, which is associated with imatinib-resistance. C3H Kit^N824K/WT mice develop hyperplasia of interstitial cells of Cajal and retention of ingesta in the cecum. In contrast to previous Kit-mutant models, we observe a benign course of gastrointestinal pathology associated with prolonged survival. Female mutants develop mammary carcinomas at late onset and subsequent lung metastasis. The disease model complements existing oncology research platforms. It allows for addressing the role of KIT mutations in breast cancer and identifying genetic and environmental modifiers of disease progression.

Does Generic Cyclic Kinase Insert Domain of Receptor Tyrosine Kinase KIT Clone Its Native Homologue?

Receptor tyrosine kinases (RTKs) are modular membrane proteins possessing both well-folded and disordered domains acting together in ligand-induced activation and regulation of post-transduction processes that tightly couple extracellular and cytoplasmic events. They ensure the fine-turning control of signal transmission by signal transduction. Deregulation of RTK KIT, including overexpression and gain of function mutations, has been detected in several human cancers. In this paper, we analysed by in silico techniques the Kinase Insert Domain (KID), a key platform of KIT transduction processes, as a generic macrocycle (KID^GC), a cleaved isolated polypeptide (KID^C), and a natively fused TKD domain (KID^D). We assumed that these KID species have similar structural and dynamic characteristics indicating the intrinsically disordered nature of this domain. This finding means that both polypeptides, cyclic KID^GC and linear KID^C, are valid models of KID integrated into the RTK KIT and will be helpful for further computational and empirical studies of post-transduction KIT events.

Histopathology and Molecular Genetics in Systemic Mastocytosis: Implications for Clinical Management

The diagnosis of systemic mastocytosis (SM) is based on various clinical, dermatological, serological, and hematological findings but essentially relies on histological evidence of an abnormal increase in tissue-localized mast cells (MCs). The extra-cutaneous organ most frequently affected is the bone marrow (BM), and therefore, histological examination of trephine biopsy specimens of the iliac crest is mandatory on suspicion of SM. At microscopic examination, neoplastic MCs show aberrant morphology, usually with prominent spindling. Immunohistochemistry is a useful tool in the diagnosis of SM because mast cell (MC) infiltrates may be slight and scarce, in a mixed background of lymphohistiocytic cells, eosinophils, and plasma cells. Moreover, neoplastic MCs exhibit an aberrant phenotype. Recent evidence, largely derived from molecular genetics, has enhanced the diagnostic capability of SM, also providing the basis for adequate prognostic and therapeutic evaluation. The cases herein reported illustrate the variable clinical manifestations and disease course of SM, focusing on diagnostic and therapeutic challenges. In accordance with the World Health Organization (WHO) classification and the International Consensus Classification (ICC) systems, our findings emphasize the importance of an integrated diagnostic approach for SM, with proper application of diverse assessment methodologies in order to improve SM classification and treatment effectiveness.

Diagnosis, Prognosis and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors

Mast cell tumors (MCTs) are hematopoietic neoplasms composed of mast cells. It is highly common in dogs and is extremely important in the veterinary oncology field. It represents the third most common tumor subtype, and is the most common malignant skin tumor in dogs, corresponding to 11% of skin cancer cases. The objective of this critical review was to present the report of the 2nd Consensus meeting on the Diagnosis, Prognosis, and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors, which was organized by the Brazilian Association of Veterinary Oncology (ABROVET) in August 2021. The most recent information on cutaneous and subcutaneous mast cell tumors in dogs is presented and discussed.

Refined diagnostic criteria for bone marrow mastocytosis: a proposal of the European competence network on mastocytosis

In the current classification of the World Health Organization (WHO), bone marrow mastocytosis (BMM) is a provisional variant of indolent systemic mastocytosis (ISM) defined by bone marrow involvement and absence of skin lesions. However, no additional diagnostic criteria for BMM have been proposed. Within the registry dataset of the European Competence Network on Mastocytosis, we compared characteristics and outcomes of 390 patients with BMM and 1175 patients with typical ISM. BMM patients were significantly older, predominantly male, had lower tryptase and lower burden of neoplastic mast cells, and displayed a higher frequency of allergic reactions, mainly triggered by Hymenoptera, than patients with typical ISM. The estimated 10-year progression-free survival of BMM and typical ISM was 95.9% and 92.6%, respectively. In BMM patients defined by WHO-based criteria, the presence of one B-Finding and tryptase level ≥125 ng/mL were identified as risk factors for progression in multivariate analyses. BMM patients without any of these risk factors were found to have better progression-free survival (p < 0.05) and better overall survival (p < 0.05) than other ISM patients. These data support the proposal to define BMM as a separate SM variant characterized by SM criteria, absence of skin lesions, absence of B-Findings, and tryptase levels <125 ng/mL.

The Role of Avapritinib for the Treatment of Systemic Mastocytosis

Systemic mastocytosis is a rare hematologic disorder characterized by the clonal proliferation of mast cells in extra-cutaneous organs. This disease can be further subdivided into five different phenotypes: indolent systemic mastocytosis (ISM), smoldering systemic mastocytosis (SSM), aggressive systemic mastocytosis (ASM), systemic mastocytosis with an associated hematological neoplasm (SM-AHN) and mast cell leukemia (MCL). The tyrosine kinase inhibitor (and also potent KIT D816V inhibitor) avapritinib, initially approved for the treatment of gastrointestinal stromal tumors (GISTs) bearing a PDGFRA exon 18 mutation, also showed great promise in patients with systemic mastocytosis, a disease known to be driven by a mutation in KIT (D816V). We present an overview of this rare disorder, including a review of the current understanding of the genetic mechanisms which lead to the disease state, the action of the tyrosine kinase inhibitors, as well as the latest clinical trial data which led to the current recommendations for the use of avapritinib.

The novel KIT exon 11 germline mutation K558N is associated with gastrointestinal stromal tumor, mastocytosis, and seminoma development

Familial gastrointestinal stromal tumors (GIST) are dominant genetic disorders that are caused by germline mutations of the type III receptor tyrosine kinase KIT. While sporadic mutations are frequently found in mastocytosis and GISTs, germline mutations of KIT have only been described in 39 families until now. We detected a novel germline mutation of KIT in exon 11 (p.Lys-558-Asn; K558N) in a patient from a kindred with several GISTs harboring different secondary somatic KIT mutations. Structural analysis suggests that the primary germline mutation alone is not sufficient to release the autoinhibitory region of KIT located in the transmembrane domain. Instead, the KIT kinase module becomes constitutively activated when K558N combines with different secondary somatic mutations. The identical germline mutation in combination with an additional somatic KIT mutation was detected in a second patient of the kindred with seminoma while a third patient within the family had a cutaneous mastocytosis. These findings suggest that the K558N mutation interferes with the juxtamembranous part of KIT, since seminoma and mastocystosis are usually not associated with exon 11 mutations.

PATHOGENIC AND DIAGNOSTIC RELEVANCE OF KIT IN PRIMARY MAST CELL ACTIVATION DISORDERS

OBJECTIVE

Mast cell (MC) activation (MCA) defines the mechanism by which certain patients suffer from symptoms due to the effect of a wide range of mediators released from MC upon their activation triggered by different stimuli. When these symptoms are severe and recurrent, the diagnosis of MCA syndrome (MCAS) might be considered. Here we review the relevant aspects related to the pathogenesis of MCAS, with special emphasis on the prevalence and diagnostic relevance of KIT mutations.

DATA SOURCES

PubMed was searched between 1980 and 2021 using the following terms: Mast cell activation syndromes, mast cell activation, anaphylaxis, KIT mutations, KIT D816V, indolent systemic mastocytosis, bone marrow mastocytosis, cutaneous mastocytosis, IgE anaphylaxis and idiopathic anaphylaxis.

STUDY SELECTIONS

Only articles published in English were selected based on their relevance to MCAS and/or severe and recurrent anaphylaxis.

RESULTS

MCAS can be classified in clonal MCAS and non-clonal MCAS depending on the presence vs. absence of an underlying KIT mutation (mostly KIT D816V), respectively. In contrast to clonal MCAS in which MCA is associated with a primary MC disorder (i.e. primary MCAS) such as mastocytosis or monoclonal MCAS, non-clonal MCAS can be secondary to known or unidentified triggers (i.e. secondary and idiopathic MCAS, respectively).

CONCLUSION

The clinical heterogeneity and complexity of the molecular assays needed for the study of MCAS patients might lead to misdiagnosis, particularly when patients are evaluated at non-specialized centers. Thus, referral of patients suffering from clinical manifestations suggestive of MCAS to Reference Centers on mastocytosis and MC diseases is strongly recommended.

Systemic Mastocytosis: Molecular Landscape and Implications for Treatment

Over the past decade, we have witnessed significant advances in the molecular characterization of systemic mastocytosis (SM). This has provided important information for a better understanding of the pathogenesis of the disease but has also practically impacted the way we diagnose and manage it. Advances in molecular testing have run in parallel with advances in therapeutic targeting of constitutive active KIT, the major driver of the disease. Therefore, assessing the molecular landscape in each SM patient is essential for diagnosis, prognosis, treatment, and therapeutic efficacy monitoring. This is facilitated by the routine availability of novel technologies like digital PCR and NGS. This review aims to summarize the pathogenesis of the disease, discuss the value of molecular diagnostic testing and how it should be performed, and provide an overview of present and future therapeutic concepts based on fine molecular characterization of SM patients.

Real-World Efficacy of Midostaurin in Aggressive Systemic Mastocytosis

In April 2017 midostaurin was approved by the US Food and Drug Administration for the treatment of patients with aggressive systemic mastocytosis (ASM). So far, very limited real world data on its efficacy is available. Thirteen patients aged from 48 to 79 years, who received midostaurin in the early access program, were included in the study. Midostaurin was used both in first (n = 5) and subsequent lines of treatment (n = 8). The median duration of exposure was 9 months. Most patients (77%, n = 10) had a clinical improvement already as soon as the second month of therapy. Objective response was noted in 4 (50%) of eight evaluated patients. Among responders, we observed a decrease in serum tryptase level (median 74.14%) and bone marrow infiltration by mast cells (median 50%) in the sixth month of treatment. In one case, in the 10th month of treatment, allogenic stem cell transplantation was performed, achieving complete remission. Five patients died, three due to progression of disease, one in the course of secondary acute myeloid leukemia and one due to reasons not related to mastocytosis. Treatment is ongoing in seven patients. We found that midostaurin therapy is beneficial to patients with ASM.

CD117/c-kit defines a prostate CSC-like subpopulation driving progression and TKI resistance

Cancer stem-like cells (CSCs) are associated with cancer progression, metastasis, and recurrence, and may also represent a subset of circulating tumor cells (CTCs). In our prior study, CTCs in advanced prostate cancer patients were found to express CD117/c-kit in a liquid biopsy. Whether CD117 expression played an active or passive role in the aggressiveness and migration of these CTCs remained an open question. In this study, we show that CD117 expression in prostate cancer patients is associated with decreased overall and progression-free survival and that activation and phosphorylation of CD117 increases in prostate cancer patients with higher Gleason grades. To determine how CD117 expression and activation by its ligand stem cell factor (SCF, kit ligand, steel factor) alter prostate cancer aggressiveness, we used C4-2 and PC3-mm human prostate cancer cells, which contain a CD117+ subpopulation. We demonstrate that CD117+ cells display increased proliferation and migration. In prostaspheres, CD117 expression enhances sphere formation. In both 2D and 3D cultures, stemness marker gene expression is higher in CD117+ cells. Using xenograft limiting dilution assays and serial tumor initiation assays, we show that CD117+ cells represent a CSC population. Combined, these data indicate that CD117 expression potentially promotes tumor initiation and metastasis. Further, in cell lines, CD117 activation by SCF promotes faster proliferation and invasiveness, while blocking CD117 activation with tyrosine kinase inhibitors (TKIs) decreased progression in a context-dependent manner. We demonstrate that CD117 expression and activation drives prostate cancer aggressiveness through the CSC phenotype and TKI resistance.

In Vitro Anticancer Effects of All-trans Retinoic Acid in Combination with Dacarbazine against CD117+ Melanoma Cells

BACKGROUND

Malignant melanoma is a common form of skin cancer that contains different cell types recognized by various cell surface markers. Dacarbazine-based combination chemotherapy is frequently used for the treatment of melanoma. Despite its potent anticancer properties, resistance to dacarbazine develops in malignant melanoma. Here, we aim to improve response to dacarbazine therapy by pretreatment with all-trans retinoic acid (ATRA) in CD117+ melanoma cells.

METHODS

The CD117+ melanoma cells were sorted from A375 malignant melanoma cell line using magnetic-activated cell sorting (MACS). The cell viability was examined by cell proliferation assay (MTT). Apoptosis was determined by acridine orange/ ethidium bromide staining. Indeed, we performed flow cytometry to evaluate the cell cycle arrest.

RESULTS

Here, the CD117+ melanoma cells were incubated with various concentrations of ATRA, dacarbazine, and their combination to determine IC50 values. We found that 20 µM ATRA treatment followed by dacarbazine was found to be more effective than dacarbazine alone. There was an indication that the combination of ATRA with dacarbazine (ATRA/dacarbazine) caused more apoptosis and necrosis in the melanoma cells (P<0.05). Furthermore, ATRA/dacarbazine treatment inhibited the cell at the G0/G1 phase, while dacarbazine alone inhibited the cells at S phase.

CONCLUSION

Collectively, combined treatment with ATRA and dacarbazine induced more apoptosis and enhanced the cell cycle arrest of CD117+ melanoma cells. These results suggested that ATRA increased the sensitivity of melanoma cells to the effect of dacarbazine.

Synthetic Makaluvamine Analogs Decrease c-Kit Expression and Are Cytotoxic to Neuroendocrine Tumor Cells

In an effort to discover viable systemic chemotherapeutic agents for neuroendocrine tumors (NETs), we screened a small library of 18 drug-like compounds obtained from the Velu lab against pulmonary (H727) and thyroid (MZ-CRC-1 and TT) neuroendocrine tumor-derived cell lines. Two potent lead compounds (DHN-II-84 and DHN-III-14) identified from this screening were found to be analogs of the natural product makaluvamine. We further characterized the antitumor activities of these two compounds using pulmonary (H727), thyroid (MZ-CRC-1) and pancreatic (BON) neuroendocrine tumor cell lines. Flow cytometry showed a dose-dependent increase in apoptosis in all cell lines. Induction of apoptosis with these compounds was also supported by the decrease in myeloid cell leukemia-1 (MCL-1) and X-chromosome linked inhibitor of apoptosis (XIAP) detected by Western blot. Compound treatment decreased NET markers chromogranin A (CgA) and achaete-scute homolog 1 (ASCL1) in a dose-dependent manner. Moreover, the gene expression analysis showed that the compound treatment reduced c-Kit proto-oncogene expression in the NET cell lines. Induction of apoptosis could also have been caused by the inhibition of c-Kit expression, in addition to the known mechanisms such as damage of DNA by topoisomerase II inhibition for this class of compounds. In summary, makaluvamine analogs DHN-II-84 and DHN-III-14 induced apoptosis, decreased neuroendocrine tumor markers, and showed promising antitumor activity in pulmonary, thyroid, and pancreatic NET cell lines, and hold potential to be developed as an effective treatment to combat neuroendocrine tumors.

Conjunctival Melanoma: Update on Genetics, Epigenetics and Targeted Molecular and Immune-Based Therapies

Purpose

To present the molecular mechanisms involved in the pathogenesis of conjunctival melanoma (CM) and review the existing literature on targeted molecular inhibitors as well as immune checkpoint inhibitors for the management of locally advanced and metastatic disease.

Methods

A comprehensive review of the literature was performed using the keywords "conjunctival melanoma", "immune checkpoint inhibitors", "BRAF inhibitors", "MEK inhibitors", "CTLA4 inhibitors", "PD1 inhibitors", "c-KIT mutations", "BRAF mutations", "NRAS mutations", "dabrafenib", "trametinib", "vemurafenib", "ipilimumab", "pembrolizumab", and "nivolumab". A total of 250 articles were reviewed and 120 were included in this report.

Results

Mutations of mediators in the MAP kinase pathway, such as RAS, BRAF, MEK and ERK, and mutations of the PI3K/AKT/mTOR pathway play a major role in the pathogenesis of conjunctival melanoma. In addition, alterations of c-KIT, NF1, TERT, chemokine receptors as well as chromosomal copy number alterations and micro RNAs are thought to have a causative association with CM development. Targeted molecular inhibitors, such as BRAF and MEK inhibitors, are currently being implemented in the therapy of BRAF-mutated CM. Furthermore, immune checkpoint PD-1 and CTLA4 inhibitors with favorable clinical outcomes in the treatment of cutaneous melanoma have increased recurrence-free survival and reduced metastatic spread in CM cases.

Conclusion

The complex molecular mechanisms that contribute to the development of CM can be targeted both by molecular inhibitors of oncogenic pathways as well as immune checkpoint inhibitors in order to halt progression of the disease and increase survival.

Clinical features and survival of patients with indolent systemic mastocytosis defined by the updated WHO classification

BACKGROUND

In indolent systemic mastocytosis (ISM), several risk factors of disease progression have been identified. Previous studies, performed with limited patient numbers, have also shown that the clinical course in ISM is stable and comparable to that of cutaneous mastocytosis (CM). The aim of this project was to compare the prognosis of patients with ISM with that of patients with CM.

METHODS

We employed a dataset of 1993 patients from the registry of the European Competence Network on Mastocytosis (ECNM) to compare outcomes of ISM and CM.

RESULTS

We found that overall survival (OS) is worse in ISM compared to CM. Moreover, in patients with typical ISM, bone marrow mastocytosis (BMM), and smoldering SM (SSM), 4.1% of disease progressions have been observed (4.9% of progressions in typical ISM group, 1.7% in BMM, and 9.4% in SSM). Progressions to advanced SM were observed in 2.9% of these patients. In contrast, six patients with CM (1.7%) converted to ISM and no definitive progression to advanced SM was found. No significant differences in OS and event-free survival (EFS) were found when comparing ISM, BMM, and SSM. Higher risk of both progression and death was significantly associated with male gender, worse performance status, and organomegaly.

CONCLUSION

Our data confirm the clinical impact of the WHO classification that separates ISM from CM and from other SM variants.

Recent Advances in the Molecular Biology of Systemic Mastocytosis: Implications for Diagnosis, Prognosis, and Therapy

In recent years, molecular characterization and management of patients with systemic mastocytosis (SM) have greatly benefited from the application of advanced technologies. Highly sensitive and accurate assays for KIT D816V mutation detection and quantification have allowed the switch to non-invasive peripheral blood testing for patient screening; allele burden has prognostic implications and may be used to monitor therapeutic efficacy. Progress in genetic profiling of KIT, together with the use of next-generation sequencing panels for the characterization of associated gene mutations, have allowed the stratification of patients into three subgroups differing in terms of pathogenesis and prognosis: i) patients with mast cell-restricted KIT D816V; ii) patients with multilineage KIT D816V-involvement; iii) patients with "multi-mutated disease". Thanks to these findings, new prognostic scoring systems combining clinical and molecular data have been developed. Finally, non-genetic SETD2 histone methyltransferase loss of function has recently been identified in advanced SM. Assessment of SETD2 protein levels and activity might provide prognostic information and has opened new research avenues exploring alternative targeted therapeutic strategies. This review discusses how progress in recent years has rapidly complemented previous knowledge improving the molecular characterization of SM, and how this has the potential to impact on patient diagnosis and management.

Development and characterization of a fully human antibody targeting SCF/c-kit signaling

CD117/c-kit, a tyrosine kinase receptor, plays a critical role in hematopoiesis, pigmentation, and fertility. The overexpression and activation of c-kit are thought to promote tumor growth and have been reported in various cancers, including leukemia, glioblastoma and mastocytosis. To disrupt the SCF/c-kit signaling axis in cancer, we generated a c-kit antagonist human antibody (NN2101) that binds to domain 2/3 of c-kit. This completely blocked the SCF-mediated phosphorylation of c-kit and inhibited TF-1 cell proliferation, erythroleukemia. In addition, the examination of binding affinity using surface plasmon resonance (SPR) assay showed that NN2101 can bind to c-kit of monkeys (K_D = 2.92 × 10^-10 M), rats (K_D = 1.68 × 10^-6 M), mice (K_D = 11.5 × 10^-9 M), and humans (K_D = 2.83 × 10^-12 M). We showed that NN2101 does not cause antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity. The immunogenicity of NN2101 was similar to that of bevacizumab. Furthermore, the crystal structure of NN2101 Fab was determined and the structure of NN2101 Fab:c-kit complex was modeled. Structural information, as well as mutagenesis results, revealed that NN2101 can bind to the SCF-binding regions of c-kit. Collectively, we generated a c-kit neutralizing human antibody (NN2101) for the treatment of erythroleukemia and characterized its biophysical properties. NN2101 can potentially be used as a therapeutic antibody to treat different cancers.

Pharmacotherapy in Mast Cell Leukemia

INTRODUCTION

Mast cell leukemia (MCL) is one of the most aggressive forms of Systemic Mastocytosis (SM), a complex family of rare diseases, for which standard therapies are very few. MCL represents only <1% cases of SM and this is the reason why there are no specific clinical trials to better explore this disease. As a consequence, MCL is treated and grouped within other forms of SM, being all KIT-driven diseases; however, its KIT dysregulation leads to uncontrolled activation of mast cells (MCs), which correlates with forms of myeloid acute leukemia (AML).

AREAS COVERED

Different therapeutic approaches can be followed in the treatment of MCL. The authors look at both symptomatic therapies along with other approaches including targeted therapy. Further, the authors provide their expert opinion.

EXPERT OPINION

In the scenario of mast cell leukemia treatment, the key approach to achieve clinical results is, more than other similar pathologies, personalizing the therapy. It could be interesting or desirable to introduce for instance KIT mutant forms as minor criteria for the diagnosis of advanced SM, considering the small patient population with MCL and the relatively large panel of activating mutations for KIT and other important proteins involved in MCs' regulation.

Immunohistochemistry as a Genetic Surrogate in Dermatopathology: Pearls and Pitfalls

Immunohistochemistry (IHC) is routinely performed in most laboratories, and other than purchase of commercially available antibodies, requires no additional equipment or reagents. As such, IHC is an accessible and relatively inexpensive test and one that can be performed quite quickly. This is in sharp contrast to genomic or mutational testing methodologies that are routinely "send out" tests as they require specialized equipment and reagents as well as individuals with expertise in the performance of the tests and analysis of the results, resulting in a prolonged turn-round-time and enhanced associated costs. However, many open questions remain in a rapidly changing therapeutic and scientific landscape with most obvious one being what exactly is the utility of "good old fashioned" IHC in the age of targeted therapy? For molecular applications, is a negative immunohistochemical result enough as a stand-alone diagnostic or predictive product? Is a positive immunohistochemical result perhaps more suitable for a role in screening for molecular alterations rather than a definitive testing modality? This review is an attempt to answer those very questions. We elucidate the broad range of entities in which IHC is currently used as a molecular surrogate and underscore pearls and pitfalls associated with each. Special attention is given to entities for which targeted therapies are currently available and to entities in which molecular data is of clinical utility as a prognosticator.

Comparative aspects of mast cell neoplasia in animals and the role of KIT in prognosis and treatment

Mast cell neoplasia clinical presentation and biological behaviour vary considerably across mammalian species, ranging from a solitary benign mass to an aggressive systemic malignancy. Mutations in the KIT Proto‐Oncogene Receptor Tyrosine Kinase (KIT) gene are common molecular abnormalities involved in mast cell tumorigenesis. KIT mutations often occur in dog, cat and human neoplastic mast cells and result in altered Kit protein structure and function. In dogs, certain KIT mutations are associated with more malignant and lethal disease. In contrast, KIT mutations in feline and human mast cell neoplasms are not correlated with prognosis, but are of value in diagnosis and treatment planning in humans. KIT genetic abnormalities have not been well investigated in other species, although aberrant cytoplasmic Kit protein staining detected in neoplasms of the ferret, horse and cow resembles aberrant Kit staining patterns detected in neoplastic mast cells of dogs, cats and humans. Mutations within KIT are classified as either regulatory‐type or enzymatic pocket‐type mutations according to their location within the KIT Proto‐Oncogene. Mutations within the enzymatic pocket domain confer tumour resistance to tyrosine kinase inhibitors (TKIs). Hence, knowledge of tumour KIT mutation status adds valuable information for optimizing patient treatment strategies. The use of TKIs in combination with conventional chemotherapeutics has opened a new treatment avenue for patients unresponsive to existing drugs. This review highlights the similarities and differences of mast cell neoplasia in mammals with a special focus on the involvement of KIT in the canine and feline forms in comparison to human mast cell neoplasia.

Towards Enhancing Therapeutic Glycoprotein Bioproduction: Interventions in the PI3K/AKT/mTOR Pathway

Recombinant glycoproteins produced in mammalian cells are clinically indispensable drugs used to treat a broad spectrum of diseases. Their bio-manufacturing process is laborious, time consuming, and expensive. Investment in expediting the process and reducing its cost is the subject of continued research. The PI3K/Akt/mTOR signaling pathway is a key regulator of diverse physiological functions such as proliferation, global protein, and lipid synthesis as well as many metabolic pathways interacting to increase secretory capabilities. In this review we detail various strategies previously employed to increase glycoprotein production yields via either genetic or pharmacological over-activation of the PI3K/Akt/mTOR pathway, and we discuss their potential and limitations.Key words: mTORC1, CRISPR, specific productivity, translation.

Role of Novel Marker Discovered on Gastrointestinal Stromal Tumor 1 in Evaluation of Gastrointestinal Stromal Tumors

Background: Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors arising from myenteric ganglion cells, termed interstitial cells of Cajal. GISTs occur predominantly between 40 and 60 years of age. CD34 was the initially used for diagnosing GIST. Due to its low specificity for GISTs, CD34 was replaced by C-KIT, which is a reliable marker. However, 5% GISTs lack C-KIT expression. Recent studies have shown GIST1 (DOG1) to be a more sensitive and specific marker compared to C-KIT and CD34. Aims and Objectives: The aim was to study histomorphology characteristics and risk stratification of all cases previously diagnosed as GISTs, to evaluate these cases for CD117 and DOG1 expression by immunohistochemistry (IHC) and to see whether there was any advantage in using novel markers (i.e. DOG1) as compared to conventional (C-KIT) in GIST at our center. Materials and Methods: Fifty patients with histomorphologic or imaging impression of GIST were subjected to IHC using C-KIT and DOG1. Results and Conclusion: Of 50 cases 47 (94%) were positive for C-KIT, and all 50 (100%) cases were positive for DOG1. Hence, DOG1 was positive even in C-KIT-negative cases. Therefore, our study suggests that DOG1 should be added to workup of suspected cases of GIST along with C-KIT.

A familial germline mutation in KIT associated with achalasia, mastocytosis and gastrointestinal stromal tumors shows response to kinase inhibitors

BACKGROUND

Activating mutations of the tyrosine kinase receptor KIT have been described in both mastocytosis and gastrointestinal stromal tumors (GIST), but are usually found in separate domains and often respond differently to signal transduction inhibitors. We describe here a large family with both GIST, mastocytosis, and achalasia. Affected family members have a unique activating mutation in exon 9 of KIT which show promise to a novel signal transduction inhibitor.

METHODS

Clinical data was collected from 15 family members, 7 of whom were variably affected with GIST, achalasia and mastocytosis. DNA was prepared from WBC of 12 subjects (6 affected and 6 unaffected) and exons 9, 11, 13 and 17 of KIT were amplified by PCR and directly sequenced.

RESULTS

A unique activating single base pair mutation in the extracellular domain of KIT was found in all 6 affected subjects resulting in a K>I amino acid change at codon 509.

CONCLUSIONS

In the family reported here, a unique mutation in the extracellular domain leads to receptor activation resulting in GIST and mastocytosis as well as achalasia. Initial data suggests that this activation can be suppressed by signal transduction inhibitors and these patients may benefit from such therapy.

Role of c-Kit in Myocardial Regeneration and Aging

c-Kit, a type III receptor tyrosine kinase (RTK), is involved in multiple intracellular signaling whereby it is mainly considered a stem cell factor receptor, which participates in vital functions of the mammalian body, including the human. Furthermore, c-kit is a necessary yet not sufficient marker to detect and isolate several types of tissue-specific adult stem cells. Accordingly, c-kit was initially used as a marker to identify and enrich for adult cardiac stem/progenitor cells (CSCs) that were proven to be clonogenic, self-renewing and multipotent, being able to differentiate into cardiomyocytes, endothelial cells and smooth muscle cells in vitro as well as in vivo after myocardial injury. Afterwards it was demonstrated that c-kit expression labels a heterogenous cardiac cell population, which is mainly composed by endothelial cells while only a very small fraction represents CSCs. Furthermore, c-kit as a signaling molecule is expressed at different levels in this heterogenous c-kit labeled cardiac cell pool, whereby c-kit low expressers are enriched for CSCs while c-kit high expressers are endothelial and mast cells. This heterogeneity in cell composition and expression levels has been neglected in recent genetic fate map studies focusing on c-kit, which have claimed that c-kit identifies cells with robust endothelial differentiation potential but with minimal if not negligible myogenic commitment potential. However, modification of c-kit gene for Cre Recombinase expression in these Cre/Lox genetic fate map mouse models produced a detrimental c-kit haploinsufficiency that prevents efficient labeling of true CSCs on one hand while affecting the regenerative potential of these cells on the other. Interestingly, c-kit haploinsufficiency in c-kit-deficient mice causes a worsening myocardial repair after injury and accelerates cardiac aging. Therefore, these studies have further demonstrated that adult c-kit-labeled CSCs are robustly myogenic and that the adult myocardium relies on c-kit expression to regenerate after injury and to counteract aging effects on cardiac structure and function.

CD117/c-kit in Cancer Stem Cell-Mediated Progression and Therapeutic Resistance

Metastasis is the primary cause of cancer patient morbidity and mortality, but due to persisting gaps in our knowledge, it remains untreatable. Metastases often occur as patient tumors progress or recur after initial therapy. Tumor recurrence at the primary site may be driven by a cancer stem-like cell or tumor progenitor cell, while recurrence at a secondary site is driven by metastatic cancer stem cells or metastasis-initiating cells. Ongoing efforts are aimed at identifying and characterizing these stem-like cells driving recurrence and metastasis. One potential marker for the cancer stem-like cell subpopulation is CD117/c-kit, a tyrosine kinase receptor associated with cancer progression and normal stem cell maintenance. Further, activation of CD117 by its ligand stem cell factor (SCF; kit ligand) in the progenitor cell niche stimulates several signaling pathways driving proliferation, survival, and migration. This review examines evidence that the SCF/CD117 signaling axis may contribute to the control of cancer progression through the regulation of stemness and resistance to tyrosine kinase inhibitors.

Gastrointestinal Stromal Tumors (GISTs): From Science to Targeted Therapy

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. GISTs represent a distinct category of tumors characterized by oncogenic mutations of the KIT receptor tyrosine kinase in a majority of patients. KIT is useful not only for the diagnosis but also for targeted therapy of this disease. Imatinib, a tyrosine kinase inhibitor, is widely used in advanced and metastatic GISTs. This agent revolutionized the treatment strategy of advanced disease and is being tested in the neoadjuvant and adjuvant settings with encouraging results. New therapeutic agents like sunitinib have now been approved, enriching the treatment scenario for imatinib-resistant GISTs. The present review reports on the peculiar characteristics of this disease through its biology and molecular patterns, focusing on the predictive value of KIT mutations and their correlation with clinical outcome as well as on the activity of and resistance to approved targeted drugs.

Targeted Treatment Options in Mastocytosis

Mastocytosis refers to a heterogeneous group of disorders resulting from the clonal proliferation of abnormal mast cells and their accumulation in the skin (cutaneous mastocytosis when only in the skin, CM) or in various organs (systemic mastocytosis, SM). This leads to a wide variety of clinical manifestations resulting from excessive mediator release in CM and benign forms of SM (indolent SM, ISM) and from tissue mast cell infiltration causing multiorgan dysfunction and failure in more aggressive subtypes (aggressive SM, ASM, or mast cell leukemia). In addition, SM may be associated with hematological neoplasms (AHN). While treatment of ISM primarily aims at symptom management with anti-mediator therapies, cytoreductive and targeted therapies are needed to control the expansion of neoplastic mast cells in advanced forms of SM, in order to improve overall survival. Mast cell accumulation results from a gain-of-function mutation (mostly the D816V mutation) within the KIT tyrosine kinase domain expressed by mast cells and additional genetic and epigenetic mutations may further determine the features of the disease (ASM and AHN). Consequently, tyrosine kinase inhibitors and targeted therapies directed against the oncogenic signaling machinery downstream of KIT are attractive therapeutic approaches. A better understanding of the relative contribution of these genetic and epigenetic events to the molecular pathogenesis of mastocytosis is of particular interest for the development of targeted therapies and therefore to better choose patient subgroups that would best benefit from a given therapeutic strategy.

Clinical features of mastocytosis at pediatric patients

Mastocytosis is relevant to heterogeneous disease group characterized with redundant accumulation and proliferation of mast cells in tissues. The skin form of mastocytosis is mainly occurs in children. The article contains the current data on etiology, pathogenesis, classification, clinical forms, diagnosis, prophylactics and mastocytosis treatment at children.

Familial Progressive Hyperpigmentation, Cutaneous Mastocytosis, and Gastrointestinal Stromal Tumor as Clinical Manifestations of Mutations in the c-KIT Receptor Gene

BACKGROUND

Familial progressive hyperpigmentation (FPH) is an autosomal dominant disorder characterized by the appearance of hyperpigmented patches on the skin from early infancy that increase in size and number with age.

METHODS

We report the clinical and molecular studies of an 11-year-old boy who had areas of hyperpigmentation since birth that had spread across his body as irregular hyperpigmented macules and papules, and include relevant history in family members.

RESULTS

Affected members of his family shared a mutation in the c-KIT gene. All had progressive hyperpigmentation, in some cases accompanied by gastrointestinal stromal tumors and mastocytoma. There have been few reports of familial progressive hyperpigmentation together with systemic manifestations.

CONCLUSIONS

Molecular analysis of c-KIT should be considered in the presence of FPH with systemic involvement.

Activated c-Kit receptor in the heart promotes cardiac repair and regeneration after injury

The role of endogenous c-Kit receptor activation on cardiac cell homeostasis and repair remains largely unexplored. Transgenic mice carrying an activating point mutation (TgD814Y) in the kinase domain of the c-Kit gene were generated. c-Kit^TgD814Y receptor was expressed in the heart during embryonic development and postnatal life, in a similar timing and expression pattern to that of the endogenous gene, but not in the hematopoietic compartment allowing the study of a cardiac-specific phenotype. c-Kit^TgD814Y mutation produced a constitutive active c-Kit receptor in cardiac tissue and cells from transgenic mice as demonstrated by the increased phosphorylation of ERK1/2 and AKT, which are the main downstream molecular effectors of c-Kit receptor signaling. In adult transgenic hearts, cardiac morphology, size and total c-Kit⁺ cardiac cell number was not different compared with wt mice. However, when c-Kit^TgD814Y mice were subjected to transmural necrotic heart damage by cryoinjury (CI), all transgenic survived, compared with half of wt mice. In the sub-acute phase after CI, transgenic and wt mice showed similar heart damage. However, 9 days after CI, transgenic mice exhibited an increased number of c-Kit⁺CD31⁺ endothelial progenitor cells surrounding the necrotic area. At later follow-up, a consistent reduction of fibrotic area, increased capillary density and increased cardiomyocyte replenishment rate (as established by BrdU incorporation) were observed in transgenic compared with wt mice. Consistently, CD45⁻c-Kit⁺ cardiac stem cells isolated from transgenic c-Kit^TgD814Y mice showed an enhanced endothelial and cardiomyocyte differentiation potential compared with cells isolated from the wt. Constitutive activation of c-Kit receptor in mice is associated with an increased cardiac myogenic and vasculogenic reparative potential after injury, with a significant improvement of survival.

Imatinib in systemic mastocytosis: a phase IV clinical trial in patients lacking exon 17 KIT mutations and review of the literature

Resistance to imatinib has been recurrently reported in systemic mastocytosis (SM) carrying exon 17 KIT mutations. We evaluated the efficacy and safety of imatinib therapy in 10 adult SM patients lacking exon 17 KIT mutations, 9 of which fulfilled criteria for well-differentiated SM (WDSM). The World Health Organization 2008 disease categories among WDSM patients were mast cell (MC) leukemia (n = 3), indolent SM (n = 3) and cutaneous mastocytosis (n = 3); the remainder case had SM associated with a clonal haematological non-MC disease. Patients were given imatinib for 12 months -400 or 300 mg daily depending on the presence vs. absence of > 30% bone marrow (BM) MCs and/or signs of advanced disease-. Absence of exon 17 KIT mutations was confirmed in highly-purified BM MCs by peptide nucleic acid-mediated PCR, while mutations involving other exons were investigated by direct sequencing of purified BM MC DNA. Complete response (CR) was defined as resolution of BM MC infiltration, skin lesions, organomegalies and MC-mediator release-associated symptoms, plus normalization of serum tryptase. Criteria for partial response (PR) included ≥ 50% reduction in BM MC infiltration and improvement of skin lesions and/or organomegalies. Treatment was well-tolerated with an overall response rate of 50%, including early and sustained CR in four patients, three of whom had extracellular mutations of KIT, and PR in one case. This later patient and all non-responders (n = 5) showed wild-type KIT. These results together with previous data from the literature support the relevance of the KIT mutational status in selecting SM patients who are candidates for imatinib therapy.

An optimized approach in the synthesis of imatinib intermediates and analogues

We revisited the classical synthetic procedure for imatinib synthesis providing an improved and optimized approach in the preparation of a series of new imatinib analogues.

C-Kit Promotes Growth and Migration of Human Cardiac Progenitor Cells via the PI3K-AKT and MEK-ERK Pathways

A recent phase I clinical trial (SCIPIO) has shown that autologous c-kit+ cardiac progenitor cells (CPCs) improve cardiac function and quality of life when transplanted into patients with ischemic heart disease. Although c-kit is widely used as a marker of resident CPCs, its role in the regulation of the cellular characteristics of CPCs remains unknown. We hypothesized that c-kit plays a role in the survival, growth, and migration of CPCs. To test this hypothesis, human CPCs were grown under stress conditions in the presence or absence of SCF, and the effects of SCF-mediated activation of c-kit on CPC survival/growth and migration were measured. SCF treatment led to a significant increase in cell survival and a reduction in cell death under serum depletion conditions. In addition, SCF significantly promoted CPC migration in vitro. Furthermore, the pro-survival and pro-migratory effects of SCF were augmented by c-kit overexpression and abrogated by c-kit inhibition with imatinib. Mechanistically, c-kit activation in CPCs led to activation of the PI3K and the MAPK pathways. With the use of specific inhibitors, we confirmed that the SCF/c-kit-dependent survival and chemotaxis of CPCs are dependent on both pathways. Taken together, our findings suggest that c-kit promotes the survival/growth and migration of human CPCs cultured ex vivo via the activation of PI3K and MAPK pathways. These results imply that the efficiency of CPC homing to the injury site as well as their survival after transplantation may be improved by modulating the activity of c-kit.

Hymenoptera Anaphylaxis and C-kit Mutations: An Unexpected Association

Clinical manifestations of mastocytosis in adults comprise signs and symptoms linked to mast cell (MC) activation, including anaphylaxis. Depending on MC burden, adults can be diagnosed with systemic mastocytosis, when the WHO criteria are fulfilled, or with other clonal MC disorders, characterized by MC mediator symptoms and demonstration of activating KIT mutations and/or expression of CD25 on MCs. There is a specific link between mastocytosis and hymenoptera venom allergy (HVA): the reported frequency of HVA in mastocytosis is 20-50 % and raises to 60-80 % in patients affected by indolent systemic mastocytosis without skin lesions. The presentation of HVA characterized by severe hypotension in the absence of urticarial or angioedema is typical in patient with an underlying MC disorder, even in the presence of normal baseline serum tryptase levels.

Phosphatase of regenerating liver in hematopoietic stem cells and hematological malignancies

The phosphatases of regenerating liver (PRLs), consisting PRL1, PRL2 and PRL3, are dual-specificity protein phosphatases that have been implicated as biomarkers and therapeutic targets in several solid tumors. However, their roles in hematological malignancies are largely unknown. Recent findings demonstrate that PRL2 is important for hematopoietic stem cell self-renewal and proliferation. In addition, both PRL2 and PRL3 are highly expressed in some hematological malignancies, including acute myeloid leukemia (AML), chronic myeloid leukemia (CML), multiple myeloma (MM) and acute lymphoblastic leukemia (ALL). Moreover, PRL deficiency impairs the proliferation and survival of leukemia cells through regulating oncogenic signaling pathways. While PRLs are potential novel therapeutic targets in hematological malignancies, their exact biological function and cellular substrates remain unclear. This review will discuss how PRLs regulate hematopoietic stem cell behavior, what signaling pathways are regulated by PRLs, and how to target PRLs in hematological malignancies. An improved understanding of how PRLs function and how they are regulated may facilitate the development of PRL inhibitors that are effective in cancer treatment.

Antileukemic Activity of 2-Deoxy-d-Glucose through Inhibition of N-Linked Glycosylation in Acute Myeloid Leukemia with FLT3-ITD or c-KIT Mutations

We assessed the antileukemic activity of 2-deoxy-d-glucose (2-DG) through the modulation of expression of receptor tyrosine kinases (RTK) commonly mutated in acute myeloid leukemia (AML). We used human leukemic cell lines cells, both in vitro and in vivo, as well as leukemic samples from AML patients to demonstrate the role of 2-DG in tumor cell growth inhibition. 2-DG, through N-linked glycosylation inhibition, affected the cell-surface expression and cellular signaling of both FTL3-ITD and mutated c-KIT and induced apoptotic cell death. Leukemic cells harboring these mutated RTKs (MV4-11, MOLM-14, Kasumi-1, and TF-1 c-KIT D816V) were the most sensitive to 2-DG treatment in vitro as compared with nonmutated cells. 2-DG activity was also demonstrated in leukemic cells harboring FLT3-TKD mutations resistant to the tyrosine kinase inhibitor (TKI) quizartinib. Moreover, the antileukemic activity of 2-DG was particularly marked in c-KIT-mutated cell lines and cell samples from core binding factor-AML patients. In these cells, 2-DG inhibited the cell-surface expression of c-KIT, abrogated STAT3 and MAPK-ERK pathways, and strongly downregulated the expression of the receptor resulting in a strong in vivo effect in NOD/SCID mice xenografted with Kasumi-1 cells. Finally, we showed that 2-DG decreases Mcl-1 protein expression in AML cells and induces sensitization to both the BH3 mimetic inhibitor of Bcl-xL, Bcl-2 and Bcl-w, ABT-737, and cytarabine. In conclusion, 2-DG displays a significant antileukemic activity in AML with FLT3-ITD or KIT mutations, opening a new therapeutic window in a subset of AML with mutated RTKs.

Molecular characterization of piebaldism in a Tunisian family

OBJECTIVE

The present study is aimed at performing the molecular characterization of a Tunisian family with piebaldism.

METHODS

As the proband and her mother showed a severe phenotype, we first chose to screen exons 10, 11, 12, 13, 16, 17 and 18 of the KIT proto-oncogene by direct sequencing.

RESULTS

Direct sequencing analysis showed a C to T substitution at 1939 in exon 13 (c.1939C>T) in heterozygous state in the patient and her mother. The mutation was not found in their unaffected family members or normal controls.

CONCLUSION

Our results provide additional support that mutations in the tyrosine kinase domain of the KIT gene are responsible for the severe form of piebaldism.

PRL2/PTP4A2 phosphatase is important for hematopoietic stem cell self-renewal

Hematopoietic stem cell (HSC) self-renewal is tightly controlled by cytokines and other signals in the microenvironment. While stem cell factor (SCF) is an early acting cytokine that activates the receptor tyrosine kinase KIT and promotes HSC maintenance, how SCF/KIT signaling is regulated in HSCs is poorly understood. The protein tyrosine phosphatase 4A (PTP4A) family (aka PRL [phosphatase of regenerating liver] phosphatases), consisting of PTP4A1/PRL1, PTP4A2/PRL2, and PTP4A3/PRL3, represents an intriguing group of phosphatases implicated in cell proliferation and tumorigenesis. However, the role of PTP4A in hematopoiesis remains elusive. To define the role of PTP4A in hematopoiesis, we analyzed HSC behavior in Ptp4a2 (Prl2) deficient mice. We found that Ptp4a2 deficiency impairs HSC self-renewal as revealed by serial bone marrow transplantation assays. Moreover, we observed that Ptp4a2 null hematopoietic stem and progenitor cells (HSPCs) are more quiescent and show reduced activation of the AKT and ERK signaling. Importantly, we discovered that the ability of PTP4A2 to enhance HSPC proliferation and activation of AKT and ERK signaling depends on its phosphatase activity. Furthermore, we found that PTP4A2 is important for SCF-mediated HSPC proliferation and loss of Ptp4a2 decreased the ability of oncogenic KIT/D814V mutant in promoting hematopoietic progenitor cell proliferation. Thus, PTP4A2 plays critical roles in regulating HSC self-renewal and mediating SCF/KIT signaling.

Different role of cAMP pathway on the human mast cells HMC-1(560) and HMC-1(560,816) activation

HMC-1 are inflammatory cells that release vasoactive substances such as histamine. These cells have the c-kit receptor permanently activated in the membrane due to mutations in the proto-oncogene c-kit: Val-560 → Gly and Asp-816 → Val. Thus, there are two known cellular lines: HMC-1(560) and HMC-1(560,816) . These mutations are involved in a disease called mastocitosys. In the present paper both lines were used to study the influence of cAMP/PKA/PDEs pathway on the histamine release and Ca(2+) signaling since this pathway is often involved in these process. For this, the cells were preincubated with cAMP/PKA/PDEs modulators such as dibutyryl cAMP (dbcAMP), forskolin, H89, rolipram, IBMX, or imidazole and then stimulated with ionomycin. When cells were stimulated with agents that increase cAMP levels, the histamine release was not modified in HMC-1(560) but decreased in HMC-1(560,816) cells. The same happened when PKA was blocked. Furthermore, PDEs role on histamine release was independent of cAMP in HMC-1(560) cells and possibly also in HMC-1(560,816) cells. By contrast, the modulation of PKA and PDEs together changed the response in both cellular lines, therefore a relationship between them was suggested. All these modulatory effects on histamine release are Ca(2+) -independent. On the other hand, the effect of c-kit modulation on the cAMP/PKA/PDEs pathway was also checked. This receptor was blocked with STI571 (imatinib) and BMS-354825 (dasatinib), but only the last one caused a decrease in the cellular response to ionomycin. This article demonstrates for the first time than the cAMP/PKA/PDEs pathway is involved in the activation of HMC-1(560) and HMC-1(560,816) cells.