Evaluation of the kinase domain of c-KIT in canine cutaneous mast cell tumors

Genetic Changes in Mastocytes and Their Significance in Mast Cell Tumor Prognosis and Treatment

Mast cell tumors are a large group of diseases occurring in dogs, cats, mice, as well as in humans. Systemic mastocytosis (SM) is a disease involving the accumulation of mast cells in organs. KIT gene mutations are very often seen in abnormal mast cells. In SM, high KIT/CD117 expression is observed; however, there are usually no KIT gene mutations present. Mastocytoma (MCT)-a form of cutaneous neoplasm-is common in animals but quite rare in humans. KIT/CD117 receptor mutations were studied as the typical changes for human mastocytosis. In 80% of human cases, the KIT gene substitution p.D816H was present. In about 25% of MCTs, metastasis was observed. Changes in the gene expression of certain genes, such as overexpression of the DNAJ3A3 gene, promote metastasis. In contrast, the SNORD93 gene blocks the expression of metastasis genes. The panel of miR-21-5p, miR-379, and miR-885 has a good efficiency in discriminating healthy and MCT-affected dogs, as well as MCT-affected dogs with and without nodal metastasis. Further studies on the pathobiology of mast cells can lead to clinical improvements, such as better MCT diagnosis and treatment. Our paper reviews studies on the topic of mast cells, which have been carried out over the past few years.

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.

Internal Tandem Duplication of Exon 8 of c-kit Is Associated With Longer Total Survival in Canine Cutaneous Mast Cell Tumors

Canine cutaneous mast cell tumors (ccMCTs) have a highly variable biological behavior and accurate prognostication is essential for therapeutic intervention. Internal tandem duplications (ITD) of exon 11 are the most commonly detected c-kit mutation in ccMCTs and are associated with poor prognosis and increased cellular proliferation. The prognostic value of detecting mutations in other exons of c-kit has not been systematically examined. In this study, we analyzed the prognostic value of ITD mutations of exon 8 in c-kit of ccMCTs in comparison to ccMCTs with ITD mutations of exon 11 and ccMCTs without mutations of exon 8 or 11. The mutational status, histological grade, KIT expression pattern, Ki67 index, AgNOR (argyrophilic nucleolar organizing region) score, and Ag67 score were determined in 221 ccMCTs, and outcome was available for 101 dogs. ITD mutations of exon 8 were found in 73/221 (33%), of exon 11 in 100/221 (45%), and none of these mutations in 50/221 (22%) of ccMCTs. None of the dogs with mutations of exon 8 died due to suspected ccMCT-related cause, but 23% dogs with ccMCTs with mutations of exon 11 died due to suspected ccMCT-related cause. Prognostic parameters in ccMCTs with exon 11 mutations were commonly associated with a high proliferative activity and poor prognosis, while prognostic markers in ccMCTs with mutations of exon 8 had lower values similar to those observed in ccMCTs without mutations in exons 8 or 11 of c-kit. This study indicates that screening for ITD mutations in exon 8 in ccMCTs may be helpful to identify less aggressive ccMCTs and may be recommended as a supplementary prognostic test.

Significant advances in veterinary oncology - 60 years on

The first edition of the Journal of Small Animal Practice published in February 1960, contained a paper entitled "Recent Treatments of Malignant Neoplasia" by Dr Larry Owen. Now we have reached the 60th anniversary of JSAP, that article provides a baseline from which to review subsequent advances in veterinary oncology, which now includes worldwide networks that have resulted in veterinary oncology becoming the multidisciplinary speciality that it is today. There certainly have been many advances in understanding of the pathology and epidemiology of animal cancers and in methods of diagnosis and treatment. However, the subject has become so large and diverse that not all aspects can be covered in detail here. It should also be acknowledged that there are still many gaps in knowledge in this field and that, because of a lack of randomised clinical trials, the evidence base for what is often regarded as "standard of care" is weak.

Prognostic and predictive significance of KIT protein expression and c-kit gene mutation in canine cutaneous mast cell tumours: A consensus of the Oncology-Pathology Working Group

One of the primary objectives of the Oncology-Pathology Working Group (OPWG), a joint initiative of the Veterinary Cancer Society and the American College of Veterinary Pathologists, is for oncologists and pathologists to collaboratively generate consensus documents to standardize aspects of and provide guidelines for oncologic pathology. Consensus is established through critical review of peer-reviewed literature relevant to a subgroup's particular focus. Subsequent acceptance and approval of the document by the OPWG membership at large establishes consensus. The intent of this publication is to help educate practitioners and pathologists on the value of diagnostics related to the KIT receptor tyrosine kinase for canine cutaneous mast cell tumours and to provide a guide for the use of these tests in veterinary medicine. This document represents the opinions of the OPWG and the authors and does not constitute a formal endorsement by the American College of Veterinary Pathologists or the Veterinary Cancer Society.

Oncolytic Sendai Virus Therapy of Canine Mast Cell Tumors (A Pilot Study)

Background: Canine mastocytomas (mast cell tumors) represent a common malignancy among many dog breeds. A typical treatment strategy for canine mastocytomas includes surgery, chemo- and radio-therapy, although in many cases the therapy fails and the disease progression resumes. New treatment approaches are needed. Aims: The goal of this pilot study was to examine safety and efficacy of oncolytic Sendai virus therapy administered to canine patients with cutaneous or subcutaneous mastocytomas. Materials and Methods: Six canine patients, with variable grades and stages of the disease, received virus therapy, either as a monotherapy, or in combination with surgery. The therapy included two or more virus applications administered weekly or biweekly. Each application of Sendai virus (107-108.6 EID50) consisted of multiple individual 0.01-0.1 ml injections delivered intratumorally, intradermally around a tumor, and under a tumor bed. Results: The treatment was well tolerated, with minor transitory side effects. Of the six dogs, two did not receive surgery or any other treatment besides the virus injections. The other four animals underwent radical or debulking surgeries, and in three of them the subsequent administration of Sendai virus completely cleared locally recurrent or/and remaining tumor masses. Five dogs demonstrated a complete response to the treatment, the animals remained disease free during the time of observation (2-3 years). One dog responded only partially to the virotherapy; its after-surgical recurrent tumor and some, but not all, metastases were cleared. This dog had the most advanced stage of the disease with multiple enlarged lymph nodes and cutaneous metastases. Conclusion: The results of the pilot study suggest that Sendai virus injections could be safe and efficient for the treatment of dogs affected by mastocytomas.They also suggest the need of further studies for finding optimal schemes and schedules for this kind of therapy.

Confocal Laser Scanning Analysis of an Equine Oral Mast Cell Tumor with Atypical Expression of Tyrosine Kinase Receptor C-KIT

A 20-year-old female horse showed a nodular, firm, focal ulcerated mast cell tumor at the right dorsobuccal face of the tongue. Histologically, the nonencapsulated tumor consisted of dense, infiltrating aggregates of well-differentiated, Cresyl violet-positive mast cells accompanied by numerous eosinophils. Furthermore, they exhibited a strong, diffuse, intracytoplasmatic immunohistochemical signal for tryptase and a faint membrane-associated and perinuclear signal for tyrosine kinase receptor KIT. Confocal laser scanning microscopy confirmed an aberrant spatial colocalization of KIT in the Golgi apparatus, which may be the result of a defective protein processing within the tumor cells. The tumor was not associated with a poor prognosis.

Mast cell stabilization alleviates acute lung injury after orthotopic autologous liver transplantation in rats by downregulating inflammation

Background

Acute lung injury (ALI) is one of the most severe complications after orthotopic liver transplantation. Amplified inflammatory response after transplantation contributes to the process of ALI, but the mechanism underlying inflammation activation is not completely understood. We have demonstrated that mast cell stabilization attenuated inflammation and ALI in a rodent intestine ischemia/reperfusion model. We hypothesized that upregulation of inflammation triggered by mast cell activation may be involve in ALI after liver transplantation.

Methods

Adult male Sprague–Dawley rats received orthotopic autologous liver transplantation (OALT) and were executed 4, 8, 16, and 24 h after OALT. The rats were pretreated with the mast cell stabilizers cromolyn sodium or ketotifen 15 min before OALT and executed 8 h after OALT. Lung tissues and arterial blood were collected to evaluate lung injury_. β-hexosaminidase and mast cell tryptase levels were assessed to determine the activation of mast cells. Tumor necrosis factor α (TNF-α), interleukin (IL)-1β and IL-6 in serum and lung tissue were analyzed by enzyme-linked immunosorbent assay. Nuclear factor-kappa B (NF-κB) p65 translocation was assessed by Western blot.

Results

The rats that underwent OALT exhibited severe pulmonary damage with a high wet-to-dry ratio, low partial pressure of oxygen, and low precursor surfactant protein C levels, which corresponded to the significant elevation of pro-inflammatory cytokines, β-hexosaminidase, and tryptase levels in serum and lung tissues. The severity of ALI progressed and maximized 8 h after OALT. Mast cell stabilization significantly inhibited the activation of mast cells, downregulated pro-inflammatory cytokine levels and translocation of NF-κB, and attenuated OALT-induced ALI.

Conclusions

Mast cell activation amplified inflammation and played an important role in the process of post-OALT related ALI.

Histologic Characteristics and KIT Staining Patterns of Equine Cutaneous Mast Cell Tumors

Mast cell tumors are uncommon in horses and typically have a benign clinical course, but there are occasional reports of more aggressive behavior. The objective of this study was to review histologic features and KIT expression patterns of 72 previously diagnosed equine cutaneous mast cell tumors to determine if either is associated with clinical outcomes. Biopsy specimens were reviewed using histologic criteria derived from grading schemes, and KIT antibody expression patterns used in canine tumors and surveys were sent to referring veterinarians for follow-up clinical data. Arabians were overrepresented relative to the reference population. Most tumors were well differentiated with low mitotic rates (96%), and aberrant KIT staining patterns, as described in dogs, were uncommonly identified (12%). Associated clinical disease was uncommon and no tumors exhibited malignant behavior. Overall, KIT staining pattern and histologic features were not associated with poor clinical outcome or abnormal tumor behavior.

The use of COLD-PCR, DHPLC and GeneScanning for the highly sensitive detection of c-KIT somatic mutations in canine mast cell tumours

The conventional polymerase chain reaction (PCR)/sequencing methods may be poorly suited for the detection of somatic mutations in canine mast cell tumour (MCT) samples owing to limited sensitivity. This study was aimed at establishing novel and more sensitive methods, assessing their limit of detection and comparing their sensitivity with conventional methods.Two different 'driver' somatic mutations of c-KIT, together with the wild-type counterparts, were cloned in plasmids to prepare standard samples with known concentrations of mutated alleles in a background of wild-type alleles; the plasmids standards were assayed using either conventional or novel, highly sensitive technique. Conventional PCR/sequencing showed a sensitivity of 50-20%. Conversely, all the novel methods obtained higher sensitivities allowed reaching as low as 2.5-1.2% of the mutated DNA.The study demonstrates that early conventional methods could likely have underestimated the prevalence of KIT mutations of MCTs, therefore affecting the assessment of their relevance in prognosis and tyrosine kinase inhibitor (TKI) treatment effectiveness.

A model of study for human cancer: Spontaneous occurring tumors in dogs. Biological features and translation for new anticancer therapies

Murine cancer models have been extremely useful for analyzing the biology of pathways involved in cancer initiation, promotion, and progression. Interestingly, several murine cancer models also exhibit heterogeneity, genomic instability and an intact immune system. However, they do not adequately represent several features that define cancer in humans, including long periods of latency, the complex biology of cancer recurrence and metastasis and outcomes to novel therapies. Therefore, additional models that better investigate the human disease are needed. In the pet population, with special references to the dog, cancer is a spontaneous disease and dogs naturally develop cancers that share many characteristics with human malignancies. More than 40 years ago, optimization of bone marrow transplantation protocols was undertaken in dogs and recently novel targeted therapies such as liposomal muramyl tripeptide phosphatidylethanolamine and several tyrosine kinase inhibitors, namely masitinib (AB1010) and toceranib phosphate (SU11654), have been developed to treat dog tumors which have then been translated to human clinical trials. In this review article, we will analyze biological data from dog tumors and comparative features with human tumors, and new therapeutic approaches translated from dog to human cancer.

Advances in personalized targeted treatment of metastatic melanoma and non-invasive tumor monitoring

Despite extensive scientific progress in the melanoma field, treatment of advanced stage melanoma with chemotherapeutics and biotherapeutics has rarely provided response rates higher than 20%. In the past decade, targeted inhibitors have been developed for metastatic melanoma, leading to the advent of more personalized therapies of genetically characterized tumors. Here we review current melanoma treatments and emerging targeted molecular therapies. In particular we discuss the mutant BRAF inhibitors Vemurafenib and Dabrafenib, which markedly inhibit tumor growth and advance patients' overall survival. However this response is almost inevitably followed by complete tumor relapse due to drug resistance hampering the encouraging initial responses. Several mechanisms of resistance within and outside the MAPK pathway have now been uncovered and have paved the way for clinical trials of combination therapies to try and overcome tumor relapse. It is apparent that personalized treatment management will be required in this new era of targeted treatment. Circulating tumor cells (CTCs) provide an easily accessible means of monitoring patient relapse and several new approaches are available for the molecular characterization of CTCs. Thus CTCs provide a monitoring tool to evaluate treatment efficacy and early detection of drug resistance in real time. We detail here how advances in the molecular analysis of CTCs may provide insight into new avenues of approaching therapeutic options that would benefit personalized melanoma management.

Classification of canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas based on microscopic, immunohistochemical, and molecular characteristics

Canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas have been previously diagnosed as gastrointestinal stromal tumors (GIST), leiomyosarcomas, or nonspecified spindle cell sarcomas, but diagnostic criteria for each entity are poorly defined. We propose a classification for canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas based on microscopic, immunohistochemical, and molecular characteristics. Applying the classification to 40 canine nonangiogenic, nonlymphogenic, gastrointestinal sarcomas documented its diagnostic and prognostic value. Eighteen (45%) sarcomas were classified as GIST based on positive KIT immunoreactivity. All GISTs were positive for vimentin, 14 (78%) were positive for S-100, and 6 (33%) were positive for smooth muscle actin (SMA). In contrast to their human counterparts, canine GISTs occurred mainly in the small intestine (67%) but commonly metastasized (5/18) to liver, lymph nodes, and omentum. Six GISTs had an activated KIT mutation in exon 11 of c-Kit, but no mutations were detected in exons 8, 9, 13, and 17. Twelve (30%) sarcomas were classified as leiomyosarcomas based on positive labeling for SMA and negative labeling for KIT. Four of these neoplasms were well differentiated leiomyosarcomas characterized by weak to no labeling for vimentin, and 8 were poorly differentiated leiomyosarcomas characterized by strong labeling for vimentin. None of the leiomyosarcomas metastasized, but poorly differentiated leiomyosarcomas had a higher risk of local invasion. Ten (25%) sarcomas were classified as non-GIST/nonleiomyosarcomas that were negative for KIT and SMA but positive for vimentin and either S-100 and/or PGP 9.5. These neoplasms most likely represent sarcomas of neurogenic differentiation resembling Schwann cells or perineurial or endoneurial fibroblasts, respectively.

Breed-predispositions to cancer in pedigree dogs

Cancer is a common problem in dogs and although all breeds of dog and crossbred dogs may be affected, it is notable that some breeds of pedigree dogs appear to be at increased risk of certain types of cancer suggesting underlying genetic predisposition to cancer susceptibility. Although the aetiology of most cancers is likely to be multifactorial, the limited genetic diversity seen in purebred dogs facilitates genetic linkage or association studies on relatively small populations as compared to humans, and by using newly developed resources, genome-wide association studies in dog breeds are proving to be a powerful tool for unravelling complex disorders. This paper will review the literature on canine breed susceptibility to histiocytic sarcoma, osteosarcoma, haemangiosarcoma, mast cell tumours, lymphoma, melanoma, and mammary tumours including the recent advances in knowledge through molecular genetic, cytogenetic, and genome wide association studies.

The value of molecular expression of KIT and KIT ligand analysed using real-time polymerase chain reaction and immunohistochemistry as a prognostic indicator for canine cutaneous mast cell tumours

This study investigated the correlation between KIT gene expression determined by immunohistochemistry and real-time polymerase chain reaction (RT-PCR) and the rate of tumour recurrence and tumour-related deaths in dogs affected with mast cell tumour (MCT). Kaplan-Meier curves were constructed to compare tumour recurrence and tumour-related death between patients. The log-rank test was used to check for significant differences between curves. KIT-I, KIT-II and KIT-III staining patterns were observed in 9 (11.11%), 50 (61.73%) and 22 (27.16%) tumours, respectively. Tumour recurrence rates and tumour-related deaths were not associated with KIT staining patterns (P = 0278, P > 0.05), KIT (P = 0.289, P > 0.05) or KIT ligand (P = 0.106, P > 0.05) gene expression. Despite the lack of association between KIT staining pattern and patient survival time, the results suggest a correlation between aberrant KIT localization and increased proliferative activity of MCTs. RT-PCR seems to be a sensible method for quantitative detection of KIT gene expression in canine MCT, although expressions levels are not correlated with prognosis.

Histomorphological and immunohistochemical characterization of 172 cutaneous round cell tumours in dogs

This paper describes the use of a panel of antibodies (CD117, CD3, CD79a, CD45, cytokeratin, vimentin and E-cadherin) on formalin-fixed, paraffin-embedded sections of canine cutaneous round cell tumours. Neoplastic tumours were diagnosed by histology and histochemical stains and included 107 mast cell tumours, 31 cutaneous histiocytomas, two localized histiocytic sarcomas, 21 cutaneous lymphomas, three plasma cell tumours, one transmissible venereal tumour and seven unclassified round cell tumours. The histologic diagnosis was modified in 39.5% of the total 172 neoplasms. The staining for CD45 and Ecadherin were variable, and therefore, the final diagnoses of cutaneous histiocytoma and localized histiocytic sarcoma were made based on histology in association with negative results for CD3, CD79a, CD117 and cytokeratin. The cellular origin of unclassified round cell tumours was defined in all cases. Cutaneous B-cell lymphoma and plasma cell tumours were CD79a-positive and could be distinguished from each other by the morphological characteristics. Mast cell tumours and T cell lymphoma were CD117 and CD3 positive, respectively. The positive staining for vimentin and the negative staining for CD3, CD79a, CD117 and cytokeratin favoured the diagnosis of transmissible venereal tumours. Thus, the final diagnosis of cutaneous round cell tumours should be based on the interpretation of immunohistochemical results together with the cellular morphology observed by histology. Therefore, more studies to optimize the specific markers in formalin-fixed, paraffinembedded tissues (especially for histiocytes) are required for definitive diagnosis of round cell tumours in dogs.

NI-1: a novel canine mastocytoma model for studying drug resistance and IgER-dependent mast cell activation

BACKGROUND

Advanced mast cell (MC) disorders are characterized by uncontrolled growth of neoplastic MC in various organs, mediator-related symptoms, and a poor prognosis. Kit mutations supposedly contribute to abnormal growth and drug resistance in these patients.

METHODS

We established a novel canine mastocytoma cell line, NI-1, from a patient suffering from MC leukemia.

RESULTS

NI-1 cells were found to form mastocytoma lesions in NOD/SCID IL-2Rgamma(null) mice and to harbor several homozygous Kit mutations, including missense mutations at nucleotides 107(C→T) and 1187(A→G), a 12-bp duplication (nucleotide 1263), and a 12-bp deletion (nucleotide 1550). NI-1 cells expressed several MC differentiation antigens, including tryptase, Kit, and a functional IgE receptor. Compared to the C2 mastocytoma cell line harboring a Kit exon 11 mutation, NI-1 cells were found to be less responsive against the Kit tyrosine kinase inhibitors (TKI) masitinib and imatinib, but were even more sensitive against proliferation-inhibitory effects of the mammalian target of rapamycin (mTOR) blocker RAD001 and PI3-kinase/mTOR blocker NVP-BEZ235. The Kit-targeting multikinase inhibitors PKC412 and dasatinib were also found to override TKI resistance in NI-1 cells, and produced growth inhibition with reasonable IC(50) values (<0.1 μM).

CONCLUSION

NI-1 may serve as a useful tool to investigate IgE-dependent reactions and mechanisms of abnormal growth and drug resistance in neoplastic MC in advanced mastocytosis.

From genes to drugs: targeted strategies for melanoma

The past decade has revealed that melanoma is comprised of multiple subclasses that can be categorized on the basis of key features, including the clinical stage of disease, the oncogenic molecular 'drivers', the anatomical location or the behaviour of the primary lesion and the expression of specific biomarkers. Although exercises in subclassification are not new in oncology, progress in this area has produced both conceptual and clinical breakthroughs, which, for melanoma, are unprecedented in the modern history of the disease. This Review focuses on these recent striking advances in the strategy of molecularly targeted approaches to the therapy of melanoma in humans.

Immunohistochemical evaluation of AKT protein activation in canine mast cell tumours

The pathogenesis of canine mast cell tumour (MCT) remains unknown. Moreover, therapeutic options are limited and resistance to targeted drugs and recurrences are common, necessitating the identification of additional cellular targets for therapy. In this study we investigated the expression of phosphorylated AKT protein in 25 archival canine MCT samples by immunohistochemistry and examined the correlation between the immunohistochemical scores and histopathological tumour grades. AKT protein was detected in all of the samples and 24 of the 25 samples expressed the phosphorylated form of the protein, albeit with variable intensity. However, when the immunohistochemical scores of weak, intermediate and strong labelling were compared with the histopathological grades I to III, there was no strong correlation. This study suggests that canine MCT cells have activated AKT and indicates the need for further research on the role of the AKT protein and the possibility of targeting the AKT signalling pathway in MCTs.

c-KIT messenger RNA and protein expression and mutations in canine cutaneous mast cell tumors

Cutaneous mast cell tumors (MCTs) are among the most common neoplasms in dogs and show a highly variable biologic behavior. Histological grading, cell proliferation markers, and KIT immunohistochemistry are typically used to predict post-surgical prognosis. In the present study, c-KIT messenger RNA (mRNA) expression was measured in canine MCTs and its relationship with tumor grade, immunohistochemical staining pattern, post-surgical prognosis, and mutations was investigated. A significant increase of c-KIT mRNA was observed in MCTs versus healthy skin and surgical margins. Mutations were observed in 8.3% of cases. The KIT staining pattern was investigated for both grading systems. In particular, staining pattern III was associated with grade II (G2) and G3 MCTs, while staining patterns I and II were associated with G1 and G2 MCTs. Considering the 2-tier histological grading, the high grade was mainly associated with pattern III (71%) while the low grade was associated with patterns II (70%) and I (28%). A weak association between the KIT staining pattern and outcome was also observed. The results obtained suggest that c-KIT mRNA is overexpressed in canine MCT, although the fold variations were not associated with the protein localization or complementary DNA mutations. These observations suggested that the 3 events were independent. The histological grading and the KIT staining pattern have prognostic value as previously published. Staining pattern I could be especially helpful in predicting a good prognosis of G2 MCTs. Sequence mutations were not necessarily suggestive of a worse prognosis, but might be useful in choosing a chemotherapy protocol.

Targeted knockdown of canine KIT (stem cell factor receptor) using RNA interference

Canine mast cell tumours often express KIT mutations that result in constitutive activation of the c-kit receptor and which are associated with more aggressive disease. The aim of the current study was to determine whether small inhibitory RNA (SiRNA) molecules could specifically target canine KIT mRNA for knock-down. Canine beta-2 microglobulin (B2M), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and KIT sequences were cloned into the psiCHECK™-2 vector. SiRNA molecules, designed to target gene-specific sequences, were co-transfected with plasmid DNA into Chinese hamster ovary (CHO) cells. Renilla and firefly luciferase activity was measured using the Dual-GLO(®) Luciferase Assay (Promega). Using this reporter system, canine housekeeping gene-specific SiRNA molecules demonstrated knockdown of their targets (72.0% knockdown for B2M and 94.5% knockdown for GAPDH). An SiRNA molecule targeting exon 2 of canine KIT successfully knocked-down reporter gene expression of a KIT(26-407) construct (90.8% knockdown). An SiRNA molecule targeting a 48 base-pair in-tandem duplication mutation in KIT exon 11 selectively knocked down expression of the KIT(1569-1966mutant) construct (93.1% knockdown) but had no effect on the KIT(1569-1918wild-type) construct. The results show that RNA interference can be used to inhibit canine KIT mRNA expression and has the potential to selectively target the mutant version of KIT that is expressed by some malignant mast cells.

A new era: melanoma genetics and therapeutics

We have recently witnessed an explosion in our understanding of melanoma. Knowledge of the molecular basis of melanoma and the successes of targeted therapies have pushed melanoma care to the precipice of a new era. Identification of significant pathways and oncogenes has translated to the development of targeted therapies, some of which have produced major clinical responses. In this review, we provide an overview of selected key pathways and melanoma oncogenes as well as the targeted agents and therapeutic approaches whose successes suggest the promise of a new era in melanoma and cancer therapy. Despite these advances, the conversion of transient remissions to stable cures remains a vital challenge. Continued progress towards a better understanding about the complexity and redundancy responsible for melanoma progression may provide direction for anti-cancer drug development.

Canine and human gastrointestinal stromal tumors display similar mutations in c-KIT exon 11

Background

Gastrointestinal stromal tumors (GISTs) are common mesenchymal neoplasms in the gastrointestinal tract of humans and dogs. Little is known about the pathogenesis of these tumors. This study evaluated the role of c-KIT in canine GISTs; specifically, we investigated activating mutations in exons 8, 9, 11, 13, and 17 of c-KIT and exons 12, 14, and 18 of platelet-derived growth factor receptor, alpha polypeptide (PDGFRA), all of which have been implicated in human GISTs.

Methods

Seventeen canine GISTs all confirmed to be positive for KIT immunostaining were studied. Exons 8, 9, 11, 13 and 17 of c-KIT and exons 12, 14, and 18 of PDGFRA, were amplified from DNA isolated from formalin-fixed paraffin-embedded samples.

Results

Of these seventeen cases, six amplicons of exon 11 of c-KIT showed aberrant bands on gel electrophoresis. Sequencing of these amplicons revealed heterozygous in-frame deletions in six cases. The mutations include two different but overlapping six base pair deletions. Exons 8, 9, 13, and 17 of c-KIT and exons 12, 14, and 18 of PDGFRA had no abnormalities detected by electrophoresis and sequencing did not reveal any mutations, other than synonymous single nucleotide polymorphisms (SNPs) found in exon 11 of c-KIT and exons 12 and 14 of PDGFRA.

Conclusions

The deletion mutations detected in canine GISTs are similar to those previously found in the juxtamembrane domain of c-KIT in canine cutaneous mast cell tumors in our laboratory as well as to those reported in human GISTs. Interestingly, none of the other c-KIT or PDGFRA exons showed any abnormalities in our cases. This finding underlines the critical importance of c-KIT in the pathophysiology of canine GISTs. The expression of KIT and the identification of these activating mutations in c-KIT implicate KIT in the pathogenesis of these tumors. Our results indicate that mutations in c-KIT may be of prognostic significance and that targeting KIT may be a rational approach to treatment of these malignant tumors. This study further demonstrates that spontaneously occurring canine GISTs share molecular features with human GISTs and are an appropriate model for human GISTs.

TSLC1 tumour-suppressor gene expression in canine mast cell tumours

Tumour suppressor in lung cancer-1 (TSLC1) is a tumour-suppressor gene coding for an adhesion molecule that is expressed by mast cells. Reduced TSLC1 expression is associated with a poor prognosis in several human tumours, and this study sought to investigate if TSLC1 expression could be used to predict outcome in dogs with mast cell tumours (MCTs). Sections of MCTs of different tumour grades from 45 dogs (Group 1) were immunohistochemically assessed for TSLC1 and Ki67 expression. In addition, 35 intermediate-grade MCTs (Group 2) from dogs with known clinical follow-up were immunohistochemically stained for TSLC1 and Ki67. The TSLC1 staining intensity was found to strongly inversely correlate with tumour grade for Group 1 (P = 0.002857). For Group 2 there was a trend towards dogs with lower TSLC1 scores being more likely to die from MCT-related disease (P = 0.058). The intensity of TSLC1 staining inversely correlated with Ki67 expression for both groups.

Mutation-driven drug development in melanoma

PURPOSE OF REVIEW

The identification of mutations in signal transduction pathways that are central in melanoma pathophysiology has provided new therapeutic targets for drug development. The purpose of this review is to define those oncogenes for which there are preclinical data supporting clinical trials and to summarize results from clinical investigations.

RECENT FINDINGS

CKIT mutations were first reported in 2005 but are present in only a small subpopulation of melanoma patients. The validation of inhibitors developed in gastrointestinal stromal tumors has taken several years, but recent evidence suggests that responses can be seen in CKIT mutant melanoma. First reported in 2002, BRAF is mutated in 50% of all melanomas and subsets of other cancers. The melanoma field is leading the clinical trials evaluating the value of targeting BRAF and MEK in BRAF mutant tumors. Results from the first clinical trial with a potent and selective BRAF inhibitor clearly show the therapeutic promise of this approach.

SUMMARY

Larger clinical trials are needed to fully define the efficacy of BRAF and CKIT-directed therapy in melanoma, but early results suggest that this strategy will transform treatment options. Additional potential targets have been identified, and clinical trials evaluating novel drugs against them are underway.

KIT polymorphisms and mutations determine responses of neoplastic mast cells to bafetinib (INNO-406)

OBJECTIVE

Advanced systemic mastocytosis (SM) is characterized by uncontrolled growth of neoplastic mast cells (MC) and drug resistance. The tyrosine kinase receptor KIT is often mutated and activated and thus contributes to malignant growth of MC. Therefore, KIT-targeting drugs are currently tested for their ability to block growth of malignant MC.

MATERIALS AND METHODS

We determined the effects of the multikinase inhibitor INNO-406 (bafetinib) on primary neoplastic MC, the canine mastocytoma cell line C2, the human MC leukemia cell line HMC-1.1 bearing the KIT mutant V560G, and HMC-1.2 cells harboring KIT V560G and KIT D816V.

RESULTS

INNO-406 was found to inhibit proliferation in HMC-1.1 cells (IC(50): 30-40 nM), but not in HMC-1.2 cells or primary neoplastic cells in patients with KIT D816V-positive SM. In canines, growth-inhibitory effects of INNO-406 were seen in C2 cells (IC(50): 50-100 nM) exhibiting a KIT exon 11 internal tandem-duplication and in primary neoplastic MC harboring wild-type exon 11, whereas no effects were seen in MC exhibiting a polymorphism at amino acid 581 in exon 11. INNO-406 was found to block KIT phosphorylation and expression in HMC-1.1 cells and C2 cells, but not in HMC-1.2 cells, whereas Lyn-phosphorylation was blocked by INNO-406 in all types of MC.

CONCLUSIONS

In neoplastic MC, the major target of INNO-406 appears to be KIT. Drug responses may depend on the presence and type of KIT mutation. In human MC, the KIT D816V mutant introduces resistance, and in canine mastocytomas, an exon 11 polymorphism may be indicative of resistance against INNO-406.

Multicentric mast cell tumors in a horse

A 6-year-old female Rocky Mountain horse was presented for evaluation of draining tracts and distal limb subcutaneous edema on the left front and left hind limbs that had been present for 2 weeks. Direct smears of fluid collected by fine-needle aspiration of subcutaneous fluid from both limbs were highly cellular with a predominance of eosinophils accompanied by numerous, moderately atypical, variably granulated mast cells. The cytologic diagnosis was mast cell tumor (MCT) with prominent eosinophilic infiltration with a differential diagnosis of eosinophilic granuloma. Histologic evaluation of surgical biopsies of lesions from both limbs was performed on sections stained with H&E, toluidine blue, and Luna stains. The histologic diagnosis was MCT, and staining with toluidine blue and Luna stains confirmed the presence of mast cells and eosinophils, respectively. In addition, the mast cells strongly expressed CD117. This is the first reported case of cutaneous mast cell neoplasia in a horse in which primary presenting complaints were draining tracts and distal limb subcutaneous edema involving multiple limbs. This case illustrates the utility of staining for CD117 expression in combination with traditional stains, such as toluidine blue and Luna, in differentiating MCTs from other eosinophilic lesions in horses.

Expression of KIT Receptor in Feline Cutaneous Mast Cell Tumors

Twenty-seven feline cutaneous mast cell tumors (MCTs) were selected for this retrospective study. Samples were routinely processed and stained with hematoxylin and eosin (HE) and toluidine blue, and tumors were classified as well-differentiated (19/27), atypical or poorly granulate (7/27), and pleomorphic (1/27). Immunohistochemistry to detect KIT protein was performed on all samples. The immunoreactivity was recorded by distribution within the tumor, cellular location, and intensity. Well-differentiated MCTs were predominantly characterized by diffuse cytoplasmic (8/19) and membranous stain (7/19); a diffuse distribution of KIT positive cells was displayed in most of these tumors as well (15/19). Atypical MCTs showed diffuse distribution of labeled cells (4/7), and diffuse cytoplasm immunostaining was seen most (5/7). The pleomorphic MCT showed diffuse cytoplasmic KIT stain, with moderate labeling intensity, typically displaying focal distribution in deeper areas of the neoplasm. According to the results, there was no correlation between the type of MCTs and KIT expression, although the use of feline KIT immunohistochemistry could be useful to assess the mast cell origin.

Canine mast cell tumours: a review of the pathogenesis, clinical features, pathology and treatment

Mast cells (MCs) are well known for their neoplastic transformation in solitary and multiple cutaneous mast cell tumours (MCTs), as well as visceral and systemic mastocytosis. Dogs have a unique risk of developing cutaneous MCTs, and they account for 7% to 21% of all canine skin tumours. The aetiology of canine MCTs is unknown but is probably multifactorial. This article reviews up-to-date knowledge on the pathogenesis, the clinical presentation, the clinical prognostic factors, the diagnostic workup including clinical staging, cytological findings, histological findings and the various grading systems which have been evaluated based on morphology, the assessment of proliferation markers and other factors such as vessel density. Furthermore, detailed information about current treatment protocols for canine cutaneous MCTs is provided.

Susceptibility of the C2 canine mastocytoma cell line to the effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family, which preferentially induces apoptosis in cells that have undergone malignant transformation. In humans, non-neoplastic cells are normally protected from the effects of TRAIL by expressing decoy receptors, lacking death domains. In contrast, neoplastic cells tend to downregulate their decoy receptor expression, increasing their susceptibility to the pro-apoptotic effects of TRAIL, via the functional TRAIL receptors. The aim of the current study was to investigate the effect of TRAIL on the canine C2 mastocytoma cell line to determine whether this agent might be a suitable treatment for mast cell tumors in dogs. C2 and MDCK cells were cultured with recombinant human TRAIL. Apoptosis was assessed using a Caspase 3 and 7 chemiluminescence assay and flow cytometry following Annexin V:FITC labelling. Cell metabolism was assessed using a colorimetric MTT-based assay. C2 cells demonstrated greater sensitivity to TRAIL-induced apoptosis compared to MDCK cells by all assessment methods. The dog genome assembly was searched for orthologs of TRAIL and its receptors using published sequences from other species for reference. Although a canine ortholog for TRAIL was identified, only one TRAIL receptor ortholog (TNFRSF11B) could be found. C2, but not MDCK, cells expressed mRNA for TNFRSF11B, detected by RT-PCR. In other species, TNFRSF11B is a decoy receptor, as even though it has a death domain it is secreted due to its lack of a transmembrane domain. The effect of TRAIL on the C2 cell line suggests that this cytokine might be suitable for treatment of mast cell tumors in dogs.

Computer simulations reveal a novel nucleotide-type binding orientation for ellipticine-based anticancer c-kit kinase inhibitors

Receptor tyrosine kinase (RTK) enzymes regulate cell signaling pathways and so are an important target for cancer chemotherapy. Current inhibitors of c-kit, a key RTK stem cell factor receptor, are inactive against the most common mutated variant Asp816Val, associated with highly malignant cancers. Recent combined experimental/simulation work has highlighted the utility of the ellipticine pharmacore in inhibiting mutant c-kit, and the present simulation study applies a combination of high-level simulation tools to probe further the binding of ellipticine-based derivatives to c-kit. We find a large preference for protonation of bound ellipticine, which stabilizes the negative protein residues that coordinated ADP.Mg (2+) in the native complex. The resulting ellipticine inhibitor binding mode resembles the native nucleotide complex and serves to explain some existing experimental data on binding specificities, indicating that functionalization at the C4/C5 sites of ellipticine derivatives may be important for the design of novel nucleotide analogues that inhibit mutant c-kit.

Targeting of heat-shock protein 32/heme oxygenase-1 in canine mastocytoma cells is associated with reduced growth and induction of apoptosis

OBJECTIVE

Advanced mast cell (MC) neoplasms are usually resistant to conventional therapy. Therefore, current research focuses on new targets in neoplastic MC and development of respective targeted drugs. Mastocytomas in dogs often behave as aggressive tumors. We report that heat-shock protein 32 (Hsp32), also known as heme oxygenase-1, is a survival-enhancing molecule and new target in canine mastocytoma cells.

MATERIALS AND METHODS

As assessed by reverse transcriptase polymerase chain reaction, Northern blotting, immunocytochemistry, and Western blotting, primary neoplastic dog MC, and the canine mastocytoma-derived cell line C2 expressed Hsp32 mRNA and the Hsp32 protein in a constitutive manner.

RESULTS

The KIT-targeting drug midostaurin inhibited expression of Hsp32, as well as survival in C2 cells. Confirming the functional role of Hsp32, the inhibitory effect of midostaurin on C2 cells was markedly reduced by the Hsp32-inductor hemin. Two pharmacologic Hsp32-inhibitors, styrene maleic-acid micelle-encapsulated ZnPP (SMA-ZnPP) and pegylated zinc-protoporphyrin (PEG-ZnPP) were applied. Both drugs were found to inhibit proliferation of C2 cells as well as growth of primary neoplastic canine MC. The growth-inhibitory effects of SMA-ZnPP and PEG-ZnPP were dose- and time-dependent (IC(50): 1-10 muM) and found to be associated with induction of apoptosis.

CONCLUSIONS

Hsp32 is an important survival factor and interesting new target in neoplastic canine MC. Trials with Hsp32-targeted drugs are now warranted to define the clinical efficacy of these drugs.

Advances in the diagnosis and management of cutaneous mast cell tumours in dogs

Mast cell tumours are one of the most common tumours of the canine skin and have a reputation for being difficult to manage because of their variable clinical presentation, behaviour and response to treatment. This review of recent literature on canine mast cell tumours suggests that the majority of such tumours may not be as bad as their reputation suggests. Most grade I and grade II tumours can be managed successfully by good surgery. Recent literature also calls into question the utility of clinical staging systems and the value of assessing surgical margins for prognosis and highlights the paucity of well-conducted, case-controlled clinical trials in assessing the efficacy of medical management of high-risk tumours. In terms of more basic research, recent studies have implicated the stem cell factor receptor KIT as having a role in the aetiology of canine mast cell tumours and there appears to be an association between c-kit mutation and higher grade of tumour. This may offer a possible target for new therapeutic approaches.