Comparative oncology: The paradigmatic example of canine and human mast cell neoplasms

[Comparative pathology in oncology-Best practice]

Comparative experimental pathology is a research field at the interface of human and veterinary medicine. It is focused on the comparative study of similarities and differences between spontaneous and experimentally induced diseases in animals (animal models) compared to human diseases. The use of animal models for studying human diseases is an essential component of biomedical research. Interdisciplinary teams with species-specific expertise should collaborate wherever possible and maintain close communication. Mutual openness, cooperation, and willingness to learn form the basis for a fruitful collaboration. Research projects jointly led by or involving both animal and human pathologists make a significant contribution to high-quality biomedical research. Such approaches are promising not only in oncological research, as outlined in this article, but also in other research areas where animal models are regularly used, such as infectiology, neurology, and developmental biology.

Immunoreactivity of p21, MMP-1 and CB2 receptor proteins in cutaneous canine mast cell tumours: an association with the three-tier grading system

Introduction

Mast cell tumours (MCTs) arise in the dermis and subcutaneous tissues in animals and humans and are one of the most common neoplasms of the skin in dogs. Cannabinoid type 2 receptor (CB2R), cyclin-dependent kinase inhibitor (p21) and matrix metalloproteinase 1 (MMP-1) are potential targets for novel anti-tumour therapeutic strategies. This study evaluated by immunohistochemical means the reactivity of p21, MMP-1 and CB2R proteins in association with a three-tier grading system in cutaneous canine MCTs.

Material and Methods

Formalin-fixed, paraffin-embedded canine MCTs were processed for histochemical analysis and immunohistochemical staining using antibodies against p21, MMP-1 and CB2R. The results were analysed statistically.

Results

The strongest p21 immunolabelling was detected in grade 3 MCTs, while grade 1 tumours showed mild or no detectable p21 immunoreactivity (P-value < 0.001). Strong immunolabelling of MMP-1 was the most common in grade 1 tumours (P-value < 0.001) and CB2R was significantly less frequent in grade 3 tumours than in grade 1 (P-value < 0.001) and grade 2 (P-value < 0.001).

Conclusion

High immunoreactivity of MMP-1 can be a marker of grade 1 MCTs in dogs, whereas p21 protein overexpression can be a marker of grade 3 canine MCTs. Strong CB2R immunoreactivity with simultaneous underexpression of p21 and high immunoreactivity of MMP-1 proteins may indicate that the use of cannabinoids in grade 1 MCTs in dogs is practicable.

A bitesize introduction to canine hematologic malignancies

Hematologic malignancies are frequently diagnosed in dogs and result in a spectrum of clinical signs associated with specific disease types. The most frequently encountered hematologic tumors in dogs include lymphoma, lymphoid and myeloid leukemias, and mast cell, plasma cell, and histiocytic neoplasias. Coupled with the heterogeneous presentations of the different categories and subtypes of canine hematologic malignancies, outcomes for these tumors are also variable. Considering this, appropriate treatment options range from active surveillance to curative intent approaches harnessing surgical, chemotherapeutic, and radiation-based modalities. The underlying pathology of many of these diseases bears remarkable resemblance to that of the corresponding diagnosis made in human patients. We introduce some of the pathogenic drivers of canine hematologic cancers alongside their clinical presentations. An overview of standard-of-care therapies for each of these diseases is also provided. As comparative oncology gains recognition as a valuable setting in which to investigate the pathogenesis of neoplasia and provide powerful, clinically relevant, immunocompetent models for the evaluation of novel therapies, the number of clinicians and scientists participating in cancer research involving dogs is expected to increase. This review aims at providing an introductory overview of canine hematologic malignancies.

Imatinib Mesylate for the Treatment of Canine Mast Cell Tumors: Assessment of the Response and Adverse Events in Comparison with the Conventional Therapy with Vinblastine and Prednisone

Mast cell tumors (MCTs) are common neoplasms in dogs, and treatments for these diseases include surgery, polychemotherapy and targeted therapy with tyrosine kinase inhibitors. This study aimed to evaluate the response and the adverse events of treatment with imatinib mesylate (IM) compared to conventional therapy using vinblastine and prednisolone (VP) in canine cutaneous MCTs. Twenty-four dogs were included in the study; 13 animals were treated with IM and 11 with VP. Tumor tissue samples were submitted for histological diagnosis, grading and KIT immunostaining. The response to treatment was assessed by tomographic measurements according to VCOG criteria. Adverse events were classified according to VCOG-CTCAE criteria. The IM and VP groups had dogs with similar breeds, gender, ages, MCT localization, WHO stages and lymph node metastasis profiles. Most MCTs were grade 2/low and had KIT- patterns 2 and 3. The objective response rate (ORR) was significantly higher (30.79%) in the IM group then in VP group (9.09%). Adverse events (AE) in IM group were all grade 1, significantly different from VP. In conclusion, IM presented better ORR and less severe adverse events when compared to VP, representing a suitable option for the treatment of low-grade canine MCTs.

Proposed Diagnostic Criteria and Classification of Canine Mast Cell Neoplasms: A Consensus Proposal

Mast cell neoplasms are one of the most frequently diagnosed malignancies in dogs. The clinical picture, course, and prognosis vary substantially among patients, depending on the anatomic site, grade and stage of the disease. The most frequently involved organ is the skin, followed by hematopoietic organs (lymph nodes, spleen, liver, and bone marrow) and mucosal sites of the oral cavity and the gastrointestinal tract. In cutaneous mast cell tumors, several grading and staging systems have been introduced. However, no comprehensive classification and no widely accepted diagnostic criteria have been proposed to date. To address these open issues and points we organized a Working Conference on canine mast cell neoplasms in Vienna in 2019. The outcomes of this meeting are summarized in this article. The proposed classification includes cutaneous mast cell tumors and their sub-variants defined by grading- and staging results, mucosal mast cell tumors, extracutaneous/extramucosal mast cell tumors without skin involvement, and mast cell leukemia (MCL). For each of these entities, diagnostic criteria are proposed. Moreover, we have refined grading and staging criteria for mast cell neoplasms in dogs based on consensus discussion. The criteria and classification proposed in this article should greatly facilitate diagnostic evaluation and prognostication in dogs with mast cell neoplasms and should thereby support management of these patients in daily practice and the conduct of clinical trials.

Canine insulinoma as a model for human malignant insulinoma research: Novel perspectives for translational clinical studies

Insulinomas are considered rare indolent neuroendocrine neoplasms in human medicine, however when metastases occur no curative treatment is available thus, novel therapies are needed. Recently advances have been made in unraveling the pathophysiology of malignant insulinoma still major challenges hinder the development of a functional model to study them. Canine malignant insulinoma have similar recurrence and a poor prognosis as human malignant insulinoma. Additionally, both human and canine patients share extensively the same environment, tend to develop insulinoma seemingly spontaneously with an etiological role for hormones, at a similar incidence and stage of lifespan, with metastasis commonly to liver and regional lymph nodes, which are unresponsive to current therapies. However, the occurrence of metastases in dogs is as high as 95% compared with only 5-16% in human studies. From a comparative oncology perspective, the shared features with human insulinoma but higher incidence of metastasis in canine insulinoma suggests the latter as a model for human malignant insulinomas. With the common purpose of increasing survival rates of human and veterinary patients, in this review we are going to compare and analyze clinical, pathological and molecular aspects of canine and human insulinomas to evaluate the suitability of the canine model for future translational clinical studies.

Immunohistochemical and molecular profiling of CD 117, Oct-4, and Sox-2 in canine cutaneous mast cell tumor of the crossbred dogs in Faculty of Veterinary Science, Chulalongkorn University, Bangkok, Thailand

BACKGROUND AND AIM

CD 117 (c-KIT) internal tandem duplication (ITD), octamer-binding transcription factor 4 (Oct-4), and sex-determining region Y-box 2 (Sox-2) may govern the oncogenicity and aggressiveness of canine cutaneous mast cell tumor (MCT) in the crossbred dogs. Thus, a comprehension of this matter may help us establishing a novel platform to treat the disease in those dogs. However, evidence has lacked so far. Thus, this study aimed to survey CD 117 ITD, Oct-4, and Sox-2 expressions and their relations to the 2-tier grading in a group of Thai crossbreed dogs. The study was done using polymerase chain reaction (PCR), Reverse transcription PCR (RT-PCR), and immunohistochemistry.

MATERIALS AND METHODS

Thirty-three MCT specimens graded by the 2-tier histopathology grading were collected from the crossbred and purebred dogs. CD 117 ITD was detected by conventional PCR and immunohistochemistry. While, Oct-4 and Sox-2 expression levels were determined at the protein and mRNA levels by immunohistochemistry and RT-PCR, respectively. The expression magnitude of each parameter was then related to the grades and breeds.

RESULTS

About 60.61% of specimens were low grade, while 39.39% were high grade. CD 117 ITD was not detected in all specimens. A significant increase of Oct-4 expression was found in the high-grade, crossbred dogs. Meanwhile, Sox-2 expressions were increased both in the purebred and crossbred dogs with high-grade MCT.

CONCLUSION

The study finding has indicated that the level of Sox-2 expression may be a useful tumorigenic and prognostic biomarker because it correlates to the 2-tier grades but not dog breeds.

Translational oncotargets for immunotherapy: From pet dogs to humans

Preclinical studies in rodent models have been a pivotal role in human clinical research, but many of them fail in the translational process. Spontaneous tumors in pet dogs have the potential to bridge the gap between preclinical models and human clinical trials. Their natural occurrence in an immunocompetent system overcome the limitations of preclinical rodent models. Due to its reasonable cellular, molecular, and genetic homology to humans, the pet dog represents a valuable model to accelerate the translation of preclinical studies to clinical trials in humans, actually with benefits for both species. Moreover, their unique genetic features of breeding and breed-related mutations have contributed to assess and optimize therapeutics in individuals with different genetic backgrounds. This review aims to outline four main immunotherapy approaches - cancer vaccines, adaptive T-cell transfer, antibodies, and cytokines -, under research in veterinary medicine and how they can serve the clinical application crosstalk with humans.

Canine mast cell tumour cells regulate tryptophan catabolism via the expression of indoleamine 2,3-dioxygenase

Indoleamine 2,3-deoxygenase (IDO) produced by cancer cells catabolizes tryptophan (TRP) to kynurenine (KYN) in the environment, resulting induction of cancer immune escape through induction of T cell anergy and enhancement of regulatory T cells. Recently, inhibition of IDO has been recognized as one of therapeutic strategies for human neoplastic diseases. However, there have been few reports about IDO-expressing cancers in dogs. In this study, we attempted to examine whether canine mast cell tumour (MCT) cells express IDO and modulate the concentration of TRP and KYN in the environment. BR, MPT-1.2, and MPT-3 cells were used as canine MCT cells. Expression of IDO was examined with RT-PCR and western blotting. Concentrations of TRP and KYN in the culture medium after incubation with canine MCT cells were detected with liquid chromatography-tandem mass spectrometry. The expression of mRNA and protein of IDO were confirmed in all samples extracted from canine MCT cells. TRP concentration in the culture medium was decreased and that of KYN was increased on incubation with canine MCT cells. The ratio of KYN/TRP, widely considered to represent IDO activity, was also significantly elevated. Moreover, treatment with an IDO inhibitor L-1-methyl-tryptophan (L-1MT) clearly diminished the elevation of KYN/TRP ratio induced by the incubation with canine MCT cells. Our results indicate that canine MCT cells could directly regulate the concentrations of TRP and KYN through expressing IDO, suggesting that canine MCT have an immune escape ability. Therefore, inhibition of IDO might be a novel strategy for the treatment of dogs with MCT.

In vitro effects of histamine receptor 1 antagonists on proliferation and histamine release in canine neoplastic mast cells

Canine mastocytomas (MCTs) are characterized by rapid proliferation of neoplastic mast cells (MCs) and clinical signs caused by MC-derived mediators. In dogs suffering from MCT, histamine receptor 1 (HR1) antagonists are frequently used to control mediator-related clinical symptoms. Previous studies have shown that the HR1 antagonists loratadine and terfenadine exert some growth-inhibitory effects on neoplastic MCs. We examined whether other HR1 antagonists used in clinical practice (desloratadine, rupatadine, cyproheptadine, dimetindene, diphenhydramine) affect proliferation and survival of neoplastic MCs. Furthermore, we analysed whether these HR1 antagonists counteract IgE-dependent histamine release from a MC line harbouring a functional IgE-receptor. HR1 antagonists were applied on two canine MC lines, C2 and NI-1, and on primary MCs obtained from three MCT samples. The HR1 antagonists desloratadine, rupatadine and cyproheptadine were found to be more potent in decreasing proliferation of C2 and NI-1 cells when compared with dimetindene and diphenhydramine. Similar effects were seen in primary neoplastic MCs, except for diphenhydramine, which exerted more potent growth-inhibitory effects than the other HR1 antagonists. Drug-induced growth-inhibition in C2 and NI-1 cells was accompanied by apoptosis. Loratadine, desloratadine and rupatadine also suppressed IgE-dependent histamine release in NI-1 cells. However, drug concentrations required to elicit substantial effects on growth or histamine release were relatively high (>10 µM). Therefore, it remains unknown whether these drugs or similar, more potent, HR1-targeting drugs can suppress growth or activation of canine neoplastic MCs in vivo.

Companion Animals as Models for Inhibition of STAT3 and STAT5

The use of transgenic mouse models has revolutionized the study of many human diseases. However, murine models are limited in their representation of spontaneously arising tumors and often lack key clinical signs and pathological changes. Thus, a closer representation of complex human diseases is of high therapeutic relevance. Given the high failure rate of drugs at the clinical trial phase (i.e., around 90%), there is a critical need for additional clinically relevant animal models. Companion animals like cats and dogs display chronic inflammatory or neoplastic diseases that closely resemble the human counterpart. Cat and dog patients can also be treated with clinically approved inhibitors or, if ethics and drug safety studies allow, pilot studies can be conducted using, e.g., inhibitors of the evolutionary conserved JAK-STAT pathway. The incidence by which different types of cancers occur in companion animals as well as mechanisms of disease are unique between humans and companion animals, where one can learn from each other. Taking advantage of this situation, existing inhibitors of known oncogenic STAT3/5 or JAK kinase signaling pathways can be studied in the context of rare human diseases, benefitting both, the development of drugs for human use and their application in veterinary medicine.

Effects of ibrutinib on proliferation and histamine release in canine neoplastic mast cells

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib is effective in the treatment of human chronic lymphocytic leukaemia and mantle cell lymphoma. Recent data have shown that ibrutinib also blocks IgE-dependent activation and histamine release in human basophils (BAs) and mast cells (MCs). The aim of this study was to investigate whether BTK serves as a novel therapeutic target in canine mast cell tumours (MCTs). We evaluated the effects of ibrutinib on two canine MC lines, C2 and NI-1 and on primary MCs obtained from canine MCTs (n = 3). Using flow cytometry, we found that ibrutinib suppresses phosphorylation of BTK and of downstream STAT5 in both MC lines. In addition, ibrutinib decreased proliferation of neoplastic MCs, with IC₅₀ values ranging between 0.1 and 1 μM in primary MCT cells and between 1 and 3 μM in C2 and NI-1 cells. In C2 cells, the combination "ibrutinib + midostaurin" produced synergistic growth-inhibitory effects. At higher concentrations, ibrutinib also induced apoptosis in both MC lines. Finally, ibrutinib was found to suppress IgE-dependent histamine release in primary MCT cells, with IC₅₀ values ranging from 0.05 to 0.1 μM in NI-1 cells, and from 0.05 to 1 μM in primary MCT cells. In summary, ibrutinib exerts anti-proliferative effects in canine neoplastic MCs and counteracts IgE-dependent histamine release in these cells. Based on our data, ibrutinib may be considered as a novel therapeutic agent for the treatment of canine MCT. The value of BTK inhibition in canine MCT patients remains to be elucidated in clinical trials.

Comparative oncology: The paradigmatic example of canine and human mast cell neoplasms

In humans, advanced mast cell (MC) neoplasms are rare malignancies with a poor prognosis. Only a few preclinical models are available, and current treatment options are limited. In dogs, MC neoplasms are the most frequent malignant skin tumours. Unlike low‐grade MC neoplasms, high‐grade MC disorders usually have a poor prognosis with short survival. In both species, neoplastic MCs display activating KIT mutations, which are considered to contribute to disease evolution. Therefore, tyrosine kinase inhibitors against KIT have been developed. Unfortunately, clinical responses are unpredictable and often transient, which remains a clinical challenge in both species. Therefore, current efforts focus on the development of new improved treatment strategies. The field of comparative oncology may assist in these efforts and accelerate human and canine research regarding diagnosis, prognostication, and novel therapies. In this article, we review the current status of comparative oncology approaches and perspectives in the field of MC neoplasms.