Distinct signalling pathways for mutated KIT(V560G) and KIT(D816V) in mastocytosis

Pharmaco-phosphoproteomic analysis of cancer-associated KIT mutations D816V and V560G

The CD117 mast/stem cell growth factor receptor tyrosine kinase (KIT) is critical for haematopoiesis, melanogenesis and stem cell maintenance. KIT is commonly activated by mutation in cancers including acute myeloid leukaemia, melanoma and gastrointestinal stromal tumours (GISTs). The kinase and the juxtamembrane domains of KIT are mutation hotspots; with the kinase domain mutation D816V common in leukaemia and the juxtamembrane domain mutation V560G common in GISTs. Given the importance of mutant KIT signalling in cancer, we have conducted a proteomic and phosphoproteomic analysis of myeloid progenitor cells expressing D816V- and V560G-KIT mutants, using an FDCP1 isogenic cell line model. Proteomic analysis revealed increased abundance of proteases and growth signalling proteins in KIT-mutant cells compared to empty vector (EV) controls. Pathway analysis identified increased oxidative phosphorylation in D816V- and V560G-mutant KIT cells, which was targetable using the inhibitor IACS010759. Dysregulation of RNA metabolism and cytoskeleton/adhesion pathways was identified in both the proteome and phosphoproteome of KIT-mutant cells. Phosphoproteome analysis further revealed active kinases such as EGFR, ERK and PKC, which were targetable using pharmacological inhibitors. This study provides a pharmaco-phosphoproteomic profile of D816V- and V560G-mutant KIT cells, which reveals novel therapeutic strategies that may be applicable to a range of cancers.

Synergistic Targeting of DNA-PK and KIT Signaling Pathways in KIT Mutant Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is the most common and aggressive form of acute leukemia, with a 5-year survival rate of just 24%. Over a third of all AML patients harbor activating mutations in kinases, such as the receptor tyrosine kinases FLT3 (receptor-type tyrosine-protein kinase FLT3) and KIT (mast/stem cell growth factor receptor kit). FLT3 and KIT mutations are associated with poor clinical outcomes and lower remission rates in response to standard-of-care chemotherapy. We have recently identified that the core kinase of the non-homologous end joining DNA repair pathway, DNA-PK (DNA-dependent protein kinase), is activated downstream of FLT3; and targeting DNA-PK sensitized FLT3-mutant AML cells to standard-of-care therapies. Herein, we investigated DNA-PK as a possible therapeutic vulnerability in KIT mutant AML, using isogenic FDC-P1 mouse myeloid progenitor cell lines transduced with oncogenic mutant KIT (V560G and D816V) or vector control. Targeted quantitative phosphoproteomic profiling identified phosphorylation of DNA-PK in the T2599/T2605/S2608/S2610 cluster in KIT mutant cells, indicative of DNA-PK activation. Accordingly, proliferation assays revealed that KIT mutant FDC-P1 cells were more sensitive to the DNA-PK inhibitors M3814 or NU7441, compared with empty vector controls. DNA-PK inhibition combined with inhibition of KIT signaling using the kinase inhibitors dasatinib or ibrutinib, or the protein phosphatase 2A activators FTY720 or AAL(S), led to synergistic cell death. Global phosphoproteomic analysis of KIT-D816V cells revealed that dasatinib and M3814 single-agent treatments inhibited extracellular signal-regulated kinase and AKT (RAC-alpha serine/threonine-protein kinase)/MTOR (serine/threonine-protein kinase mTOR) activity, with greater inhibition of both pathways when used in combination. Combined dasatinib and M3814 treatment also synergistically inhibited phosphorylation of the transcriptional regulators MYC and MYB. This study provides insight into the oncogenic pathways regulated by DNA-PK beyond its canonical role in DNA repair and demonstrates that DNA-PK is a promising therapeutic target for KIT mutant cancers.

Targeting KIT by frameshifting mRNA transcripts as a therapeutic strategy for aggressive mast cell neoplasms

Activating mutations in c-KIT are associated with the mast cell (MC) clonal disorders cutaneous mastocytosis and systemic mastocytosis and its variants, including aggressive systemic mastocytosis, MC leukemia, and MC sarcoma. Currently, therapies inhibiting KIT signaling are a leading strategy to treat MC proliferative disorders. However, these approaches may have off-target effects, and in some patients, complete remission or improved survival time cannot be achieved. These limitations led us to develop an approach using chemically stable exon skipping oligonucleotides (ESOs) that induce exon skipping of precursor (pre-)mRNA to alter gene splicing and introduce a frameshift into mature KIT mRNA transcripts. The result of this alternate approach results in marked downregulation of KIT expression, diminished KIT signaling, inhibition of MC proliferation, and rapid induction of apoptosis in neoplastic HMC-1.2 MCs. We demonstrate that in vivo administration of KIT targeting ESOs significantly inhibits tumor growth and systemic organ infiltration using both an allograft mastocytosis model and a humanized xenograft MC tumor model. We propose that our innovative approach, which employs well-tolerated, chemically stable oligonucleotides to target KIT expression through unconventional pathways, has potential as a KIT-targeted therapeutic alone, or in combination with agents that target KIT signaling, in the treatment of KIT-associated malignancies.

An evaluation of masitinib for treating systemic mastocytosis

Introduction: Systemic Mastocytosis (SM) is a complex family of rare diseases, against which pharmacological therapies are still very few. It is a c-kit driven disease, whose disregulation leads to uncontrolled activation and proliferation of mast cells (MCs) with consequent release of effector molecules which are responsible for its clinical manifestations. Areas covered: Masitinib is a relatively new potential drug against SM and its chemical structure strictly derives from imatinib, the first tyrosine kinase inhibitor which entered the pharmaceutical market about 15 years ago. In this review, the authors present masitinib in all its properties, from chemistry to pharmacology and toxicity to its potential clinical application in SM, focusing the discussion on the few clinical trials in which it has been involved, with a particular attention on the still open challenge to determine how to measure the response to therapy. Expert opinion: In spite of their similarity in chemistry and biological activity against submolecular targets, masitinib is much more selective towards c-kit receptors than other tyrosine kinases, such as Bcl-Abl. Furthermore, its ability to inhibit degranulation, cytokine production and MCs migration from bone marrow gives it a great chance to become an important therapeutic option for selected SM patients.

The upregulation of Pim kinases is essential in coordinating the survival, proliferation, and migration of KIT D816V-mutated neoplastic mast cells

About ˜80% of mast cell neoplasm patients harbor the c-Kit activating mutation D816 V, which is associated with c-Kit inhibitor resistance and poor prognosis. However, the molecular basis for these effects is not fully known. To address this issue, in this study we screened molecules whose expression is altered by KIT D816 V mutation and found that Pim kinases were overexpressed in D816V-mutant neoplastic mast cells. This was accompanied by upregulation of signal transducer and activator of transcription (STAT) and mammalian target of rapamycin (mTOR) and downregulation of Akt and extracellular signal-regulated kinase (ERK1/2). Activated Pim kinases promoted the survival of D816 V cells by maintaining mTOR and p70S6K activation even under nutrient starvation. Conversely, cell proliferation was suppressed by inhibiting Pim kinases. The mRNA level of C-X-C chemokine receptor type 4 (CXCR4) was about 2-fold higher in D816 V cells; this was associated with a 2-fold increase in migratory capacity, which was modulated by Pim kinases. We also confirmed that upregulation of Pim kinases is a feature specific to cells with the D816 V mutation and is not observed in cells with the c-Kit activating N822 K mutation. These data suggest Pim kinases as a promising therapeutic target for the treatment of mast cell neoplasms with KIT D816 V mutation.

Comparison of lesional skin c-KIT mutations with clinical phenotype in patients with mastocytosis

BACKGROUND

Activating c-KIT mutations cause abnormal mast cell growth and appear to play a role in mastocytosis. However, the correlation of c-KIT mutations with disease phenotypes is poorly characterized.

AIM

To evaluate the correlation of c-KIT mutations with clinical presentations and laboratory findings.

METHODS

Total cellular RNA was isolated from the skin lesions of 43 adults and 7 children with mastocytosis, and PCR amplicons of cDNA were sequenced for c-KIT mutations.

RESULTS

The most common activating mutation, KIT-D816V, was identified in 72% of adults and 57% of children. Additional activating mutations, namely, V560G and the internal tandem duplications (ITDs) 502-503dupAY, were detected in 12% of adults and 8% of children. V560G occurred more commonly in our patients than previously reported, and it appeared to be associated with more advanced disease. Otherwise, the presence or absence of activating mutations did not correlate with skin lesion morphology, disease extent or total serum tryptase levels. Four adults had expression only of wild-type KIT, while two others had expression of a truncated KIT lacking tyrosine kinase activity; yet these patients were clinically indistinguishable from those patients with activating c-KIT mutations.

CONCLUSIONS

Activating c-KIT mutations exist in a significant portion of patients with mastocytosis, but not all patients showed expression of these mutations. Except for V560G, the presence or absence of activating c-KIT mutations did not predict the extent of disease. These observations suggest that although activating c-KIT mutations are associated with mast cell growth, other genes probably play a role in the cause of mastocytosis.

Systemic mastocytosis with KIT V560G mutation presenting as recurrent episodes of vascular collapse: response to disodium cromoglycate and disease outcome

Background

Mastocytosis are rare diseases characterized by an accumulation of clonal mast cells (MCs) in one or multiple organs or tissues. Patients with systemic mastocytosis (SM), whose MCs frequently arbor the activating D816V KIT mutation, may have indolent to aggressive diseases, and they may experience MC mediator related symptoms. Indolent SM with recurrent anaphylaxis or vascular collapse in the absence of skin lesions, ISMs(−), is a specific subtype indolent SM (ISM), and this clonal MC activation disorder represents a significant fraction of all MC activation syndromes. The V560G KIT mutation is extremely rare in patients with SM and its biological and prognostic impact remains unknown.

Case presentation

A 15-year old boy was referred to our hospital because of repeated episodes of flushing, hypotension and syncope since the age of 3-years, preceded by skin lesions compatible with mastocytosis on histopathology that had disappeared in the late-early childhood. Diagnosis of ISM, more precisely the ISMs(−) variant, was confirmed based on the clinical manifestations together with increased baseline serum tryptase levels and the presence of morphologically atypical, mature appearing (CD117+high, FcεRI+) phenotypically aberrant (CD2+, CD25+) MCs, expressing activation-associated markers (CD63, CD69), in the bone marrow. Molecular genetic studies revealed the presence of the KIT V560G mutation in bone marrow MCs, but not in other bone marrow cells, whereas the screening for mutations in codon 816 of KIT was negative. The patient was treated with oral disodium cromoglycate and the disease had a favorable outcome after an eleven-year follow-up period, during which progressively lower serum tryptase levels together with the fully disappearance of all clinical manifestations was observed.

Conclusions

To the best of our knowledge this first report of a patient with ISM, whose bone marrow MCs carry the KIT V560G activating mutation, manifesting as recurrent spontaneous episodes of flushing and vascular collapse in the absence of skin lesions at the time of diagnosis, in whom disodium cromoglycate had led to long term clinical remission.

Mast cell activation disease and the modern epidemic of chronic inflammatory disease

A large and growing portion of the human population, especially in developed countries, suffers 1 or more chronic, often quite burdensome ailments which either are overtly inflammatory in nature or are suspected to be of inflammatory origin, but for which investigations to date have failed to identify specific causes, let alone unifying mechanisms underlying the multiple such ailments that often afflict such patients. Relatively recently described as a non-neoplastic cousin of the rare hematologic disease mastocytosis, mast cell (MC) activation syndrome-suspected to be of greatly heterogeneous, complex acquired clonality in many cases-is a potential underlying/unifying explanation for a diverse assortment of inflammatory ailments. A brief review of MC biology and how aberrant primary MC activation might lead to such a vast range of illness is presented.

Receptor tyrosine kinase (c-Kit) inhibitors: a potential therapeutic target in cancer cells

c-Kit, a receptor tyrosine kinase, is involved in intracellular signaling, and the mutated form of c-Kit plays a crucial role in occurrence of some cancers. The function of c-Kit has led to the concept that inhibiting c-Kit kinase activity can be a target for cancer therapy. The promising results of inhibition of c-Kit for treatment of cancers have been observed in some cancers such as gastrointestinal stromal tumor, acute myeloid leukemia, melanoma, and other tumors, and these results have encouraged attempts toward improvement of using c-Kit as a capable target for cancer therapy. This paper presents the findings of previous studies regarding c-Kit as a receptor tyrosine kinase and an oncogene, as well as its gene targets and signaling pathways in normal and cancer cells. The c-Kit gene location, protein structure, and the role of c-Kit in normal cell have been discussed. Comprehending the molecular mechanism underlying c-Kit-mediated tumorogenesis is consequently essential and may lead to the identification of future novel drug targets. The potential mechanisms by which c-Kit induces cellular transformation have been described. This study aims to elucidate the function of c-Kit for future cancer therapy. In addition, it has c-Kit inhibitor drug properties and their functions have been listed in tables and demonstrated in schematic pictures. This review also has collected previous studies that targeted c-Kit as a novel strategy for cancer therapy. This paper further emphasizes the advantages of this approach, as well as the limitations that must be addressed in the future. Finally, although c-Kit is an attractive target for cancer therapy, based on the outcomes of treatment of patients with c-Kit inhibitors, it is unlikely that Kit inhibitors alone can lead to cure. It seems that c-Kit mutations alone are not sufficient for tumorogenesis, but do play a crucial role in cancer occurrence.

Pharmacological treatment options for mast cell activation disease

Mast cell activation disease (MCAD) is a term referring to a heterogeneous group of disorders characterized by aberrant release of variable subsets of mast cell (MC) mediators together with accumulation of either morphologically altered and immunohistochemically identifiable mutated MCs due to MC proliferation (systemic mastocytosis [SM] and MC leukemia [MCL]) or morphologically ordinary MCs due to decreased apoptosis (MC activation syndrome [MCAS] and well-differentiated SM). Clinical signs and symptoms in MCAD vary depending on disease subtype and result from excessive mediator release by MCs and, in aggressive forms, from organ failure related to MC infiltration. In most cases, treatment of MCAD is directed primarily at controlling the symptoms associated with MC mediator release. In advanced forms, such as aggressive SM and MCL, agents targeting MC proliferation such as kinase inhibitors may be provided. Targeted therapies aimed at blocking mutant protein variants and/or downstream signaling pathways are currently being developed. Other targets, such as specific surface antigens expressed on neoplastic MCs, might be considered for the development of future therapies. Since clinicians are often underprepared to evaluate, diagnose, and effectively treat this clinically heterogeneous disease, we seek to familiarize clinicians with MCAD and review current and future treatment approaches.