Canine Oral Melanoma

Melan-A immunolabeling in canine extramedullary plasmacytomas

Histologic diagnosis of less well-differentiated cases of canine extramedullary plasmacytomas (CEMPs) may require immunohistochemical confirmation to discriminate these tumors from other round cells tumors including lymphoma, cutaneous histiocytoma, and amelanotic melanomas. CEMPs are characterized by widespread immunoreactivity for multiple myeloma 1 (MUM1) antigen and λ light chains, while the melanocytic marker melan-A has been reported to yield negative results. Here, 33 randomly selected CEMPs, 20 melanocytomas, and 20 malignant melanomas were immunohistochemically tested for MUM1, melan-A, and PNL2. In addition, CEMPs were examined for PAX5, E-cadherin, CD3, CD18, CD20, S100, as well as λ and κ light chain immunoreactivity. All CEMPs were characterized by labeling for MUM1 and λ light chain, as well as variable immunopositivity for the remaining antibodies. Notably, 13 cases of CEMPs (39.4%) exhibited immunolabeling for melan-A. Melanocytic tumors immunolabeled for melan-A (40/40; 100%) and PNL2 (34/40; 85%). An unexpected cytoplasmic immunoreactivity for MUM1 was observed in 2 melanocytic tumors. Summarized, MUM1 or melan-A immunomarkers alone are not sufficient to differentiate between CEMPs and amelanotic melanomas and should be part of a larger immunopanel including λ light chain, CD20, and PNL2.

Preclinical evaluation and first-in-dog clinical trials of PBMC-expanded natural killer cells for adoptive immunotherapy in dogs with cancer

BACKGROUND

Natural killer (NK) cells are cytotoxic cells capable of recognizing heterogeneous cancer targets without prior sensitization, making them promising prospects for use in cellular immunotherapy. Companion dogs develop spontaneous cancers in the context of an intact immune system, representing a valid cancer immunotherapy model. Previously, CD5 depletion of peripheral blood mononuclear cells (PBMCs) was used in dogs to isolate a CD5dim-expressing NK subset prior to co-culture with an irradiated feeder line, but this can limit the yield of the final NK product. This study aimed to assess NK activation, expansion, and preliminary clinical activity in first-in-dog clinical trials using a novel system with unmanipulated PBMCs to generate our NK cell product.

METHODS

Starting populations of CD5-depleted cells and PBMCs from healthy beagle donors were co-cultured for 14 days, phenotype, cytotoxicity, and cytokine secretion were measured, and samples were sequenced using the 3'-Tag-RNA-Seq protocol. Co-cultured human PBMCs and NK-isolated cells were also sequenced for comparative analysis. In addition, two first-in-dog clinical trials were performed in dogs with melanoma and osteosarcoma using autologous and allogeneic NK cells, respectively, to establish safety and proof-of-concept of this manufacturing approach.

RESULTS

Calculated cell counts, viability, killing, and cytokine secretion were equivalent or higher in expanded NK cells from canine PBMCs versus CD5-depleted cells, and immune phenotyping confirmed a CD3-NKp46+ product from PBMC-expanded cells at day 14. Transcriptomic analysis of expanded cell populations confirmed upregulation of NK activation genes and related pathways, and human NK cells using well-characterized NK markers closely mirrored canine gene expression patterns. Autologous and allogeneic PBMC-derived NK cells were successfully expanded for use in first-in-dog clinical trials, resulting in no serious adverse events and preliminary efficacy data. RNA sequencing of PBMCs from dogs receiving allogeneic NK transfer showed patient-unique gene signatures with NK gene expression trends in response to treatment.

CONCLUSIONS

Overall, the use of unmanipulated PBMCs appears safe and potentially effective for canine NK immunotherapy with equivalent to superior results to CD5 depletion in NK expansion, activation, and cytotoxicity. Our preclinical and clinical data support further evaluation of this technique as a novel platform for optimizing NK immunotherapy in dogs.

Hypoxia-associated markers in the prognosis of oral canine melanoma

Canine oral malignant melanoma (COMM) is the most common neoplasm in the oral cavity characterized by local invasiveness and high metastatic potential. Hypoxia represents a crucial feature of the solid tumor microenvironment promoting cancer progression and drug resistance. Hypoxia-inducible factor-1α (HIF-1α) and its downstream effectors, vascular endothelial growth factor A (VEGF-A), glucose transporter isoform 1 (GLUT1), C-X-C chemokine receptor type 4 (CXCR4), and carbonic anhydrase IX (CAIX), are the main regulators of the adaptive response to low oxygen availability. The prognostic value of these markers was evaluated in 36 COMMs using immunohistochemistry. In addition, the effects of cobalt chloride-mediated hypoxia were evaluated in 1 primary COMM cell line. HIF-1α expression was observed in the nucleus, and this localization correlated with the presence or enhanced expression of HIF-1α-regulated genes at the protein level. Multivariate analysis revealed that in dogs given chondroitin sulfate proteoglycan-4 (CSPG4) DNA vaccine, COMMs expressing HIF-1α, VEGF-A, and CXCR4 were associated with shorter disease-free intervals (DFI) compared with tumors that were negative for these markers (P = .03), suggesting hypoxia can influence immunotherapy response. Western blotting showed that, under chemically induced hypoxia, COMM cells accumulate HIF-1α and smaller amounts of CAIX. HIF-1α induction and stabilization triggered by hypoxia was corroborated by immunofluorescence, showing its nuclear translocation. These findings reinforce the role of an hypoxic microenvironment in tumor progression and patient outcome in COMM, as previously established in several human and canine cancers. In addition, hypoxic markers may represent promising prognostic markers, highlighting opportunities for their use in therapeutic strategies for COMMs.

Elevated expression of miR-301a and its functional roles in canine oral melanoma

miR-301a is one of numerous dysregulated microRNAs (miRNAs) in canine oral melanoma (COM), one of which is miR-301a (upregulated). Its biological role has been described in various human cancer types, including malignant melanoma, but not in COM. Accordingly, in this study, we investigated miR-301a expression in COM in greater detail to ascertain whether it could serve as a diagnostic biomarker, elucidate its functional roles in this cancer, and predict the possible pathways by which it exerts its effects. Relative expression of miR-301a was investigated in clinical oral tissue and plasma samples and COM cell (KMeC and LMeC) lines using qRT-PCR. Knockdown of miR-301a was also validated for KMeC and LMeC cells using qRT-PCR. We performed CCK-8 assays to assess cell proliferation, monolayer wound-healing, and transwell migration assays to assess cell migration, a colony-formation assay to assess clonogenicity, a TUNEL assay and flow cytometry to assess apoptosis-related effects, and gene enrichment analyses to predict possible related pathways. miR-301a was markedly upregulated in COM oral tissue and plasma clinically, suggesting its potential as a diagnostic biomarker for COM diagnosis. In vitro assays demonstrated that miR-301 significantly inhibited apoptosis in COM cells while promoting cell migration, proliferation, and clonogenicity. We also predicted that miR-301 exerts cancer-promoting effects through the Wnt signalling pathway for COM. Our findings suggest that miR-301a is a COM oncomiR that regulates several oncogenic phenotypes with the potential to be a diagnostic biomarker.

Tumor-localized interleukin-2 and interleukin-12 combine with radiation therapy to safely potentiate regression of advanced malignant melanoma in pet dogs

The clinical use of interleukin-2 and -12 cytokines against cancer is limited by their narrow therapeutic windows due to on-target, off-tumor activation of immune cells when delivered systemically. Engineering IL-2 and IL-12 to bind to extracellular matrix collagen allows these cytokines to be retained within tumors after intralesional injection, overcoming these clinical safety challenges. While this approach has potentiated responses in syngeneic mouse tumors without toxicity, the complex tumor-immune interactions in human cancers are difficult to recapitulate in mouse models of cancer. This has driven an increased role for comparative oncology clinical trials in companion (pet) dogs with spontaneous cancers that feature analogous tumor and immune biology to human cancers. Here, we report the results from a dose-escalation clinical trial of intratumoral collagen-binding IL-2 and IL-12 cytokines in pet dogs with malignant melanoma, observing encouraging local and regional responses to therapy that may suggest human clinical benefit with this approach.

Single institution study of the immune landscape for canine oral melanoma based on transcriptome analysis of the primary tumor

Introduction

Understanding a tumor's immune context is paramount in the fight against cancer. Oral melanoma in dogs serves as an excellent translational model for human immunotherapy. However, additional study is necessary to comprehend the immune landscape of dog oral melanomas, including their similarity to human melanomas in this context.

Methods

This retrospective study utilizes formalin-fixed paraffin-embedded (FFPE) tissue samples to analyze RNA sequences associated with oral melanoma in dogs. Nanostring Technologies was used for conducting RNA sequencing. The focus is on understanding the differences between melanoma tumors restricted to the oral cavity (OL) and the same primary oral tumors with a history of metastasis to the lymph nodes or other organs (OM). Normal buccal mucosa samples are also included as a normal tissue reference.

Results

In the OM patient group, gene signatures exhibit significant changes relative to the OL patient group, including significantly decreased expression of S100, BRAF, CEACAM1, BCL2, ANXA1, and tumor suppressor genes (TP63). Relative to the OL tumors, the OM tumors had significantly increased expression of hypoxia-related genes (VEGFA expression), cell mobility genes (MCAM), and PTGS2 (COX2). The analysis of the immune landscape in the OM group indicates a shift from a possible "hot" tumor suppressed by immune checkpoints (PDL1) to significantly heightened expression not only of those checkpoints but also the inclusion of other immune blockades such as PD1 and IDO2. In addition, the OM group had significantly reduced expression of Toll-like receptors (TLR4) and IL-18 relative to the OL group, contributing to the tumor's immune escape. Additionally, signs of immune cell exhaustion are evident in both the OM and OL groups through significantly increased expression of TIGIT relative to normal tissue. Both the OM and OL groups had significantly increased expression of the immune cell marker CD4 expression relative to normal tissue. Further, CD4 expression significantly decreased in OM relative to OL; however, this study cannot determine the specific cell types expressing CD4 in OM and OL tumors.

Discussion

This preliminary study reports significant changes in gene expression for oral melanoma between canine patients with localized disease relative to those with metastatic disease. In the future, a more in-depth investigation involving immunohistochemistry analysis and single-cell RNA expression is necessary to confirm our findings.

Tissue transcriptome profiling and pathway analyses revealed novel potential biomarkers in the tumor progression of canine oral melanoma

Canine oral melanoma (COM) is an aggressive oral malignancy in dogs, mostly with metastasis. However, the understanding of total gene expression of oral melanoma (OM) at different clinical stages has been limited. The objective of this study was to identify novel mRNA biomarkers of early-stage OM (EOM) and late-stage OM (LOM). Transcriptome sequencing of 3 EOM, 5 LOM and 4 normal gingival tissues (controls) was performed. Selected transcriptome results were validated by quantitative reverse transcription-PCR (qRT-PCR) using 12 LOM and 10 controls. We found 534 differentially expressed in EOM compared with controls, whereas 696 genes in LOM were differentially expressed compared with controls (P < 0.05). Moreover, 27 genes were differentially expressed in LOM compared with EOM (P < 0.05). The genes expressed in COM were involved in the molecular mechanism of cancer and melanocyte development pathways, promoting melanoma progression. qRT-PCR confirmed an increased expression of genes encoding an important protein in chemotherapy resistance (dopachrome tautomerase, DCT) and tumor progression (forkhead box M1, FOXM1), and decreased expression of a tumor suppression gene (N-myc downstream-regulated gene 2, NDRG2) in LOM, concordant with transcriptome results. In conclusion, this study revealed the comprehensive transcriptome from COM tissues, and increased DCT and FOXM1 and decreased NDRG2 gene expression indicated the potential candidate biomarkers in COM progression.

Quality of Life After Partial Mandibulectomy or Maxillectomy in 45 Dogs With Oral Tumors

Treatment for oral tumors in dogs may involve aggressive surgery, radiation therapy, and/or chemotherapy. It is of utmost importance that veterinarians can document the good quality of life (QoL) for patients during and after cancer treatment. In this retrospective study, medical records from 2 private practices during a 10-year period (2011-2020) were searched to identify dogs with confirmed histopathological diagnosis of an oral tumor. Owners of dogs who underwent surgery received a questionnaire to assess their perception of QoL before and after surgery, clinical signs from the oral tumor, pain before and after surgery, physical appearance, and drinking and eating ability after surgery. Forty-two of 45 (93%) owners answered the questionnaire. Thirty-eight owners (90%) perceived that their dog had not changed its appearance after surgery after the hair had regrown. Thirty owners (71%) reported that their dog prehended food and water normally within 4 weeks after surgery. Forty owners (95%) perceived that their dog had more "good'' than ''bad'' days after surgery. Thirty-eight owners (90%) would choose the same treatment again. Our results strongly support that dog owners perceived that their dogs had good QoL after partial mandibulectomy or maxillectomy.

Canine oral melanoma with suspected pulmonary metastasis: Combination of immunotherapy and tyrosine kinase inhibitor treatment

This case report follows a 10-year-old castrated male Miniature Schnauzer dog presented with a history of incomplete surgical resection of an oral malignant melanoma (amelanotic type) on the right mandible. Melanoma vaccine therapy was administered due to incomplete surgical resection, however, new masses were detected on the contralateral mandible and suspected pulmonary metastasis occurred at 2 weeks and 7 months, respectively, following the first melanoma vaccination. At the time of detecting the pulmonary metastasis, targeted chemotherapy was initiated with the owner's consent using imatinib (10 mg/kg/day, p.o.), a tyrosine kinase inhibitor (TKI). The patient did not show any significant adverse events related to both anticancer treatments. Three months following the first dose of imatinib, the absence of the suspected pulmonary metastatic nodules on radiography indicated complete remission. In conclusion, this report describes the achievement of clinical remission of suspected pulmonary metastatic oral malignant melanoma and an extension of survival time in a dog given a combination treatment of immunotherapy and tyrosine kinase inhibitor.

Beyond Canine Adipose Tissue-Derived Mesenchymal Stem/Stromal Cells Transplantation: An Update on Their Secretome Characterization and Applications

A dog is a valuable animal model and concomitantly a pet for which advanced therapies are increasingly in demand. The characteristics of mesenchymal stem/stromal cells (MSCs) have made cell therapy more clinically attractive. During the last decade, research on the MSC therapeutic effectiveness has demonstrated that tissue regeneration is primarily mediated by paracrine factors, which are included under the name of secretome. Secretome is a mixture of soluble factors and a variety of extracellular vesicles. The use of secretome for therapeutic purposes could have some advantages compared to cell-based therapies, such as lower immunogenicity and easy manufacturing, manipulation, and storage. The conditioned medium and extracellular vesicles derived from MSCs have the potential to be employed as new treatments in veterinary medicine. This review provides an update on the state-of-the-art characterization and applications of canine adipose tissue-derived MSC secretome.

Therapeutic applications of local injection of hsa-miR-634 into canine spontaneous malignant melanoma tumors

Malignant melanoma (MM) is one of the most common tumors in both dogs and humans. As canine MM (CMM) and human MM (HMM) have similar clinical characteristics, CMM appears to be a good clinical model for HMM. We previously demonstrated that the introduction of a synthetic double-strand-microRNA-634 (miR-634) mimic triggered apoptotic cell death by directly targeting the genes associated with cytoprotective processes in various human cancer cell lines, including those of HMM. This study aimed to investigate the antitumor effects of the local administration of miR-634 on spontaneous CMMs to provide a basis for future applications of miR-634 formulations in HMM treatment. We found that miR-634 administration induced apoptosis in CMM cell lines in vitro via downregulation of Asct2, Nrf2, and survivin expression, similar to the mechanisms in HMM cell lines. Furthermore, intratumoral miR-634 administration induced antitumor effects in four of seven spontaneous CMM cases, with no adverse effects. Local administration of miR-634 to lung metastasis under ultrasound guidance induced tumor shrinkage. These results confirm the antitumor effect of the local administration of miR-634 in spontaneous CMM, a model for spontaneous HMM, thereby providing a novel treatment strategy for HMM.

Safety and clinical efficacy of an anti-PD-L1 antibody (c4G12) in dogs with advanced malignant tumours

Immune checkpoint inhibitors (ICIs) have been developed for canine tumour treatment, and pilot clinical studies have demonstrated their antitumour efficacy in dogs with oral malignant melanoma (OMM). Although ICIs have been approved for various human malignancies, their clinical benefits in other tumour types remain to be elucidated in dogs. Here, we conducted a clinical study of c4G12, a canine chimeric anti-PD-L1 antibody, to assess its safety and efficacy in dogs with various advanced malignant tumours (n = 12) at the Veterinary Teaching Hospital of Hokkaido University from 2018 to 2023. Dogs with digit or foot pad malignant melanoma (n = 4), osteosarcoma (n = 2), hemangiosarcoma (n = 1), transitional cell carcinoma (n = 1), nasal adenocarcinoma (n = 1), B-cell lymphoma (n = 1), or undifferentiated sarcoma (n = 2) were treated with 2 or 5 mg/kg c4G12 every 2 weeks. Treatment-related adverse events of any grade were observed in eight dogs (66.7%), including elevated aspartate aminotransferase (grade 3) in one dog (8.3%) and thrombocytopenia (grade 4) in another dog (8.3%). Among dogs with target disease at baseline (n = 8), as defined by the response evaluation criteria for solid tumours in dogs (cRECIST), one dog with nasal adenocarcinoma and another with osteosarcoma experienced a partial response (PR), with an objective response rate of 25.0% (2 PR out of 8 dogs; 95% confidence interval: 3.2-65.1%). These results suggest that c4G12 is safe and tolerable and shows antitumor effects in dogs with malignant tumours other than OMM. Further clinical studies are warranted to identify the tumour types that are most likely to benefit from c4G12 treatment.

Antineoplastic effects of sodium dichloroacetate and omeprazole, alone or in combination, on canine oral mucosal melanoma cells

Oral mucosal melanoma (OMM) is a common neoplasm in canines, although it is rare in humans. Cancer cells present alterations in energetic metabolism, and the Warburg effect states that most cancer cells undergo aerobic glycolysis. This can be reversed by certain drugs, resulting in decreased cell viability and cell death. We sought to evaluate the effects of sodium dichloroacetate (DCA) and omeprazole (OMP) alone or in combination on canine OMM and human melanoma cells. CMGD5 and SK-MEL-28 cell lines were treated with DCA and OMP alone or in combination, and cell viability was assessed using the crystal violet assay. Cell death (apoptosis and necrosis) was assessed by Annexin V and propidium iodide (PI) staining assays using flow cytometry. In addition, the oxygen consumption rate (OCR) was evaluated using a SeaHorse XF assay. Treatment with DCA or OMP alone resulted in a significant, but not dose-dependent, reduction in cell viability in both cell lines; however, the combination of DCA and OMP resulted in a significant and dose-dependent decrease in viability in both cell lines. DCA and OMP, alone or in combination, did not alter OCR at the concentrations tested in either cell line. Since the combination of DCA and OMP potentialized the inhibition of viability and increased cell death in a synergistic manner in melanoma cells, this approach may represent a new repurposing strategy to treat cancer.

Clinical utility of liquid biopsy in canine oral malignant melanoma using cell-free DNA

Introduction

Cell-free DNA (cfDNA), an extracellular free DNA released into the bloodstream by cells, is a potentially useful noninvasive marker to detect human malignancies and monitor response to treatment. In the present study, we evaluated the utility of circulating cfDNA in canine patients with oral malignant melanoma (OMM) in assessing therapeutic response and clinical outcomes.

Methods

Plasma samples were collected from 12 dogs with OMM and 9 healthy controls. cfDNA concentration was quantified by real-time PCR resulting in short (99bp) and long (218bp) fragments of long interspersed nuclear element-1 (LINE-1), and the DNA integrity index (DII) was then calculated (218/99). A follow-up study was conducted on 6 dogs with OMM, and the plasma cfDNA and DII were quantified throughout disease progression.

Results

Although cfDNA levels obtained from dogs with OMM were not significantly different compared to those obtained from healthy controls, the DII was significantly lower in dogs with OMM than in healthy controls. The DII tended to decrease as the disease stage progressed. Moreover, changes in cfDNA concentration and DII along the clinical course were observed when major changes, such as metastasis or apparent tumor progression, were observed.

Discussion

The results of our study suggest that measurements of serum cfDNA and DII using LINE-1 might be valuable new biomarkers for monitoring OMM progression in dogs. This preliminary study demonstrated the potential clinical utility of monitoring plasma cfDNA in canine patients with OMM.

Electrochemotherapy Plus IL-2+IL-12 Gene Electrotransfer in Spontaneous Inoperable Stage III-IV Canine Oral Malignant Melanoma

Electrochemotherapy (ECT) is a standard of care in veterinary and human oncology. The treatment induces a well-characterized local immune response which is not able to induce a systemic response. In this retrospective cohort study, we evaluated the addition of gene electrotransfer (GET) of canine IL-2 peritumorally and IL-12 intramuscularly to enhance the immune response. Thirty canine patients with inoperable oral malignant melanoma were included. Ten patients received ECT+GET as the treatment group, while twenty patients received ECT as the control group. Intravenous bleomycin for the ECT was used in both groups. All patients had compromised lymph nodes which were surgically removed. Plasma levels of interleukins, local response rate, overall survival, and progression-free survival were evaluated. The results show that IL-2 and IL-12 expression peaked around days 7-14 after transfection. Both groups showed similar local response rates and overall survival times. However, progression-free survival resulted significantly better in the ECT+GET group, which is a better indicator than overall survival, as it is not influenced by the criterion used for performing euthanasia. We can conclude that the combination of ECT+GET using IL-2 and IL-12 improves treatment outcomes by slowing down tumoral progression in stage III-IV inoperable canine oral malignant melanoma.

The human and animals' malignant melanoma: comparative tumor models and the role of microbiome in dogs and humans

Currently, the most progressively occurring incident cancer is melanoma. The mouse is the most popular model in human melanoma research given its various benefits as a laboratory animal. Nevertheless, unlike humans, mice do not develop melanoma spontaneously, so they need to be genetically manipulated. In opposition, there are several reports of other animals, ranging from wild to domesticated animals, that spontaneously develop melanoma and that have cancer pathways that are similar to those of humans. The influence of the gut microbiome on health and disease is being the aim of many recent studies. It has been proven that the microbiome is a determinant of the host's immune status and disease prevention. In human medicine, there is increasing evidence that changes in the microbiome influences malignant melanoma progression and response to therapy. There are several similarities between some animals and human melanoma, especially between canine and human oral malignant melanoma as well as between the gut microbiome of both species. However, microbiome studies are scarce in veterinary medicine, especially in the oncology field. Future studies need to address the relevance of gut and tissue microbiome for canine malignant melanoma development, which results will certainly benefit both species in the context of translational medicine.

Expression and Prognostic Evaluation of the Receptor Tyrosine Kinase MET in Canine Malignant Melanoma

The overexpression and activation of the MET receptor tyrosine kinase has been identified in many human malignancies, but its role in canine cancer has only been minimally investigated. In this study we evaluated the expression of MET in two canine malignant melanoma (CMM) cell lines as well as in 30 CMM tissue samples that were collected from the clinical service at our institution. We were able to confirm the expression of the MET protein in both melanoma cell lines, and we demonstrated MET activation by its ligand, HGF, through phosphorylation, in Western blot analysis. We were also able to demonstrate, by immunohistochemistry, the expression of MET in 63% of the tumor tissue samples analyzed, with the majority demonstrating a relatively low expression profile. We then evaluated the association of MET expression scores with histologic parameters, metastasis, and survival. While statistically significant associations were not found across these parameters, an inverse relationship between MET expression levels and time to lymph node versus distant metastasis was suggested in our cohort. These findings may require assessment in a larger group of specimens to further evaluate the role of MET expression in the homing of metastasis in lymph nodes versus that in distant organs.

Prognostic Factors for the Efficiency of Radiation Therapy in Dogs with Oral Melanoma: A Pilot Study of Hypoxia in Intraosseous Lesions

Unresectable oral melanoma is often treated with radiation therapy (RT) and may show a temporary response to therapy. The clinical stage is one of the well-known prognostic factors for canine oral melanoma. However, the factors that directly affect the response to RT have remained unclear. This study aimed to validate the risk factors for recurrence after RT. Sixty-eight dogs with oral melanomas were included in this study. All dogs were treated with palliative RT using a linear accelerator without adjuvant therapies. After RT, the time to local recurrence (TTR) and overall survival (OS) were evaluated using the log-rank test. As a result, clinical stage and response to therapy were the significant independent prognostic factors in the multivariate analysis. The presence of local bone lysis and non-combination with cytoreductive surgery were associated with a worse response to RT. Immunohistochemical analysis for hypoxia-inducible factor-1α indicated that tumor cells invading the bone are under hypoxic conditions, which may explain a poorer efficiency of RT in dogs with bone lysis. In conclusion, clinical stage and combination with debulking surgery were needed to improve the efficiency of RT.

Utilizing MALDI-TOF MS and LC-MS/MS to access serum peptidome-based biomarkers in canine oral tumors

Tumors frequently found in dogs include canine oral tumors, either cancerous or noncancerous. The bloodstream is an important route for tumor metastasis, particularly for late-stage oral melanoma (LOM) and late-stage oral squamous cell carcinoma (LOSCC). The present study aimed to investigate serum peptidome-based biomarkers of dogs with early-stage oral melanoma, LOM, LOSCC, benign oral tumors, chronic periodontitis and healthy controls, using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and liquid chromatography tandem mass spectrometry. A principal component analysis plot showed distinct clusters among all groups. Four peptides were identified, including peptidyl-prolyl cis-trans isomerase FKBP4 isoform X2 (FKBP4), steroid hormone receptor ERR1 (ESRRA or ERRA), immunoglobulin superfamily member 10 (IGSF10) and ATP-binding cassette subfamily B member 5 (ABCB5). FKBP4, ESRRA and ABCB5 were found to be overexpressed in both LOM and LOSCC, whereas IGSF10 expression was markedly increased in LOSCC only. These four proteins also played a crucial role in numerous pathways of cancer metastasis and showed a strong relationship with chemotherapy drugs. In conclusion, this study showed rapid screening of canine oral tumors using serum and MALDI-TOF MS. In addition, potential serum peptidome-based biomarker candidates for LOM and LOSCC were identified.

Interleukin-1β triggers matrix metalloprotease-3 expression through p65/RelA activation in melanoma cells

Melanoma shows highly aggressive behavior (i.e., local invasion and metastasis). Matrix metalloprotease-3 (MMP-3), a zinc-dependent endopeptidase, degrades several extracellular substrates and contributes to local invasion by creating a microenvironment suitable for tumor development. Here, we report that interleukin-1β (IL-1β) triggers the MMP-3 expression in canine melanoma cells. The activity of MMP-3 in the culture supernatant was increased in IL-1β-treated melanoma cells. IL-1β time- and dose-dependently provoked the mRNA expression of MMP-3. IL-1β induced the migration of melanoma cells; however, this migration was attenuated by UK356618, an MMP-3 inhibitor. When the cells were treated with the nuclear factor-κB (NF-κB) inhibitor TPCA-1, the inhibition of MMP-3 expression was observed. In IL-1β-treated cells, the phosphorylation both of p65/RelA and p105 was detected, indicating NF-κB pathway activation. In p65/RelA-depleted melanoma cells, IL-1β-mediated mRNA expression of MMP-3 was inhibited, whereas this reduction was not observed in p105-depleted cells. These findings suggest that MMP-3 expression in melanoma cells is regulated through IL-1β-mediated p65/RelA activation, which is involved in melanoma cell migration.

Immunology of Canine Melanoma

Malignant melanoma is one of the most important tumors in dogs and is highly metastatic and aggressive disease. In recent years, molecular knowledge regarding canine melanoma has increased, and some chromosomal imbalances and tyrosine kinase pathways have been identified to be dysregulated. Mxoreover, canine melanoma is an immunogenic tumor that provides opportunities to administer immunotherapy to the patient. Podoplanin and chondroitin sulfate proteoglycan-4 (CSPG4) are markers against which monoclonal antibodies have been developed and tested in dogs in vivo with promising results. Owing to the importance of canine melanoma in the veterinary oncology field, this chapter reviews the most important aspects related to immunological involvement in the prognosis and treatment of canine melanoma.

The Use of Oncept Melanoma Vaccine in Veterinary Patients: A Review of the Literature

The Oncept melanoma vaccine is xenogeneic DNA vaccine targeting tyrosinase. It is USDA approved for treatment of stage II to III canine oral melanoma and is also used off-label for melanomas arising in other locations and in other species. While the vaccine appears safe, the published data is mixed as to whether it provides a survival benefit, and the use of the vaccine is somewhat controversial in the veterinary oncology community. In this paper, the published literature describing the use of Oncept is reviewed and evaluated.

Pilot Study: Assessing the Expression of Serum Lactate Dehydrogenase and Peripheral Leukocyte Ratios in Canine Oral Malignant Melanoma

Measurement of blood biomarkers such as lactate dehydrogenase (LDH) and peripheral leukocyte ratios have been shown to be of prognostic value in human melanoma patients. Previous veterinary studies have demonstrated that changes in these values are detectable in multiple canine cancer patients. However, to the authors’ knowledge, no studies have yet demonstrated an increase in LDH in canine oral malignant melanoma patients, nor has the effect of metastasis on LDH levels been explored. This retrospective pilot study included 18 dogs, of which 10 were healthy controls, 5 OMM patients with metastasis and 3 without metastasis. Serum LDH was measured and pre-treatment peripheral leucocyte ratios were calculated. LDH was measurable within all patient groups and a statistically significant difference in LDH levels was detected between patients with OMM and healthy controls (p < 0.05); however, no significant difference was detected between patients with or without metastatic disease. This study suggests that serum LDH levels are significantly increased in dogs with OMM compared to healthy controls, paving the way for further research to investigate the prognostic value of this biomarker.

Quantification of Canine Apocrine Gland Anal Sac Adenocarcinoma (AGASACA) Tumor Specimen Shrinkage after Formalin Fixation

Simple Summary

As the evidence in apocrine gland anal sac adenocarcinoma tumors grows, it is becoming more evident that stage-specific treatment strategies will become the mainstay. Thus, having confidence in the measurements of primary tumors is paramount. We aimed to quantify the degree of tumor tissue shrinkage after 24 and 48 h of formalin fixation to guide clinicians in their use of post-fixation measurements. We prospectively enrolled 23 client-owned dogs with naturally occurring apocrine gland anal sac adenocarcinoma that underwent surgical resection of at least the primary tumor. Measurements were recorded immediately before being placed in 10% buffered formalin and then again after 24 and 48 h of fixation, respectively. Overall, we found that tumors shrank by a mean of 4.8% and 7.2% after 24 and 48 h, respectively. This in real terms was a median of 1 mm. Other factors associated with the tumor, like the predominant microscopic pattern, the amount of necrosis, or the amount of fibrovascular stroma, did not have an impact on the degree of shrinkage. This study shows that the degree of shrinkage following formalin fixation should not impact the use of post-fixation measurements and can be used in clinical staging schema.

Abstract

The aim was to prospectively measure the shrinkage of primary apocrine gland anal sac adenocarcinoma (AGASACA) tumors after 24 and 48 h of formalin fixation. Dogs that were diagnosed with AGASACA pre-operatively by aspiration cytology were prospectively enrolled in the study. Tumor extirpation was performed in a closed technique. The tumor and associated tissues were examined on the back table away from the patient and the widest dimension of the tumor was measured using a sterile ruler (Medline^®; Northfield, IL, USA). This measurement was recorded in mm (t₀). The tissue was placed in 10% buffered formalin and stored at room temperature. Two further measurements were taken after 24 (t₂₄) and 48 (t₄₈) hours of formalin fixation. Once the 48 h measurement was taken, the tissue was submitted for histopathology. The percentage of shrinkage between time points was calculated by using the following equation: (1 − [time b/time a]) × 100. Overall, 23 dogs with 23 tumors were enrolled. The mean percentage of shrinkage after 24 and 48 h of formalin fixation was 4.8% and 7.2%, respectively. The median diameter of the tumors reduced by 1 mm over 48 h and was not significantly different at any time point. These data will aid clinicians in interpreting measurements of AGASACA tumors following formalin fixation and shows that minimal change in tumor size is expected following 48 h.

Unraveling the Risk Factors and Etiology of the Canine Oral Mucosal Melanoma: Results of an Epidemiological Questionnaire, Oral Microbiome Analysis and Investigation of Papillomavirus Infection

Simple Summary

Oral mucosal melanoma (OMM) is one of the most common oral cancers in dogs; however, the risk factors for its development remain obscure and the etiology is unknown. This study aimed to investigate the risk factors and etiology of OMM in dogs. An epidemiological questionnaire was applied to the owners of 15 dogs with OMM and their paired controls, and the oral microbiome was comparatively determined in the two groups. Additionally, the presence of papillomavirus was investigated in the same OMM samples. Most OMM and control dogs had grade 3 periodontal disease. No risk factors were identified through the epidemiological questionnaire, and papillomaviruses were not identified in the samples. The bacteria Tannerella forsythia and Porphyromonas gingivalis were significantly overrepresented in dogs with OMM, and their presence could be considered a risk factor for the development of canine OMM.

Abstract

Oral mucosal melanoma (OMM) is the most common oral cancer in dogs and is very aggressive in this species; its risk factors and etiology are yet to be determined. This study aimed to unravel the risk factors for the development of OMM in dogs and to investigate the possible presence of papillomaviruses as an etiological factor. A case-control study was conducted in 15 dogs with OMM and 15 paired controls whose owners answered an epidemiological questionnaire. Oral swabs from the same dogs were subjected to 16S rRNA sequencing for microbiome analyses. In addition, DNA fragments of OMM had their DNA extracted and amplified by polymerase chain reaction in an attempt to detect canine papillomaviruses. The gingiva was the most frequent anatomical site (47%) of OMM, and most tumors were stage III when diagnosed. Most dogs bearing OMM and the controls had grade 3 periodontal disease, and this factor, along with tartar treatment and tooth brushing, did not differ between cases and controls. Most dogs with OMM and most controls had contact with smokers; there was no statistically significant difference. Canine papillomaviruses were not detected among OMM cases. Tannerella forsythia and Porphyromonas gingivalis were significantly increased in case dogs compared to the controls. As these bacteria are reportedly involved in the pathogenesis of periodontal disease and esophageal cancer in humans, we suggest that they might be risk factors for the development of canine OMM. The limitations of this study include the low number of dogs, and therefore, further studies on canine OMM with larger numbers of animals are encouraged.

Prevalence and Clinicopathologic Features of Canine Metastatic Melanoma Involving the Central Nervous System: A Retrospective Analysis and Comparative Review

Background

Central nervous system (CNS) involvement is the leading cause of death in malignant melanoma. Rodent models, while vital to mechanistic investigation, have had limited success identifying effective therapies for melanoma brain metastases. The companion dog with de novo melanoma is a promising complementary model for developmental therapeutic investigation, as these tumors occur in an immunologically outbred host that has shared environmental exposures with humans. However, relatively little is known regarding the prevalence and clinicopathological features of canine melanoma metastasis to the CNS. To further validate the dog as an appropriate model for human metastatic melanoma, the aims of this study were to determine the rate of CNS metastasis and associated clinicopathologic features in canine malignant melanoma.

Methods

Medical records of dogs diagnosed with malignant melanoma from 1985-2019 at the University of California Davis Veterinary Medical Teaching Hospital were assessed retrospectively. Clinicopathologic features were compared between dogs with CNS metastasis (CNS+) and dogs without CNS metastasis (CNS-). Site of CNS involvement and associated neurological signs were analyzed via Wilcoxon-Mann-Whitney rank sum and Fisher’s exact tests. Survival data were analyzed via Kaplan-Meier estimates.

Results

CNS metastasis was identified in 38% of dogs in this study (20/53). The oral cavity was the most common site of primary melanoma in both groups [CNS+: n=12 (60%) vs. CNS-: n=22 (67%); p>0.99]. The total burden of metastatic disease was higher in the CNS+ group (CNS+: 4, 95% CI 3-5 vs. CNS-: 3, 95% CI 1-3; p<0.001). The cerebrum was the most common site of CNS metastasis (n=15, 75%) and seizures were the most observed neurological sign (n=9, 64%). There was no difference in overall survival between CNS+ and CNS- groups. However, the median survival time following onset of neurological signs was 9.5 days (95% CI 1-43), with 5 dogs euthanized within 24 hours of the onset of neurological signs.

Conclusions

Canine and human MM patients share similar rates of CNS metastasis and clinical presentation. This study will guide clinical management of canines with malignant melanoma and inform future studies using dogs with spontaneously occurring melanoma as a preclinical model for human melanoma brain metastases.

Treatment of Canine Oral Melanomas: A Critical Review of the Literature

Critical appraisal of the available literature for the treatment of canine oral malignant melanoma (OMM) is lacking. This critical review aimed to evaluate the current literature and provide treatment recommendations and possible suggestions for future canine OMM research. PubMed, Web of Science and Google Scholar were searched in June 2021, for terms relevant to treatment of OMM. Inclusion and exclusion criteria were applied and information on clinical response and outcome extracted. Eighty-one studies were included. The overall level of evidence supporting the various canine OMM treatment options was low. The majority of studies included confounding treatment modalities and lacked randomization, control groups and consistency in reporting clinical response and outcomes. Within these limitations, surgery remains the mainstay of therapy. Adjunctive radiotherapy provided good local control and improved median survival times (MST), chemotherapy did not offer survival benefit beyond that of surgery, while electrochemotherapy may offer a potential alternative to radiotherapy. Immunotherapy holds the most promise in extending MST in the surgical adjunctive setting, in particular the combination of gene therapy and autologous vaccination. Prospective, randomized, double-blinded clinical trials, with a lack of confounding factors and reporting based on established guidelines would allow comparison and recommendations for the treatment of canine OMM.

Diagnosis and Prognosis of Canine Melanocytic Neoplasms

Canine melanocytic neoplasms have a highly variable biological behavior ranging from benign cutaneous melanocytomas to malignant oral melanomas that readily metastasize to lymph nodes and internal organs. This review focuses on the diagnosis and prognosis of canine melanocytic neoplasms. While pigmented melanocytic neoplasms can be diagnosed with fine-needle aspirates, an accurate prognosis requires surgical biopsy. However, differentiating amelanotic spindloid melanomas from soft tissue sarcomas is challenging and often requires immunohistochemical labeling with a diagnostic cocktail that contains antibodies against Melan-A, PNL-2, TRP-1, and TRP-2 as the current gold standard. For questionable cases, RNA expression analysis for TYR, CD34, and CALD can further differentiate these two entities. The diagnosis of amelanotic melanomas will be aided by submitting overlying and/or lateral flanking epithelium to identify junctional activity. Wide excision of lateral flanking epithelium is essential, as lentiginous spread is common for malignant mucosal melanomas. Combining histologic features (nuclear atypia, mitotic count, degree of pigmentation, level of infiltration, vascular invasion; tumor thickness and ulceration) with the Ki67 index provides the most detailed prognostic assessment. Sentinel lymph nodes should be evaluated in cases of suspected malignant melanomas using serial sectioning of the node combined with immunohistochemical labeling for Melan-A and PNL-2.

Canine oral melanoma: a retrospective study of 101 dogs treated with a 6 Gy x 6 radiotherapy protocol

One radiotherapy (RT) protocol used for canine oral melanoma (OM) gives 36 Gy total, in six weekly or biweekly fractions (6 Gy × 6). This retrospective study characterizes oncologic outcomes for a relatively large group of dogs treated with this protocol and determines whether radiation dose intensity (weekly vs. biweekly) affected either progression‐free or overall survival (PFS and OS). Dogs were included if 6 Gy × 6 was used to treat grossly evident OM, or if RT was used postoperatively in the subclinical disease setting. Kaplan–Meier statistics and Cox regression modelling were used to determine the predictive or prognostic value of mitotic count, bony lysis, World Health Organization (WHO) stage (I, II, III, or IV), using systemic anti‐cancer therapies, tumour burden at the time of RT (macroscopic vs. subclinical), radiation dose intensity (weekly vs. biweekly), and treatment planning type (manual vs. computerized). The median PFS and OS times for all dogs (n = 101) were 171 and 232 days, respectively. On univariate analysis PFS and OS were significantly longer (p = <.05) with subclinical tumour burden, WHO stages I or II, and weekly irradiation. On multivariable analysis, only tumour stage remained significant; therefore, cases were grouped by WHO stage (I/II vs. III/IV). With low WHO stage (I/II), PFS and OS were longer when irradiating subclinical disease (PFS: risk ratio = 0.449, p = .032; OS: risk ratio = 0.422, p = .022); this was not true for high WHO stage (III/IV). When accounting for other factors, radiation dose intensity had no measurable impact on survival in either staging group.

Prognostic impact of bone invasion in canine oral malignant melanoma treated by surgery and anti-CSPG4 vaccination: A retrospective study on 68 cases (2010-2020)

Prognosis of canine oral malignant melanoma encompasses clinical, histological and immunohistochemical parameters. The aim of this study was to evaluate the prognostic impact of bone invasion in oral canine melanoma. Sixty-eight dogs bearing oral melanoma staged II and III that underwent surgery and anti-CSPG4 electrovaccination, with available histological data and a minimum follow up of minimum 1 year, were retrospectively selected. Bone invasion was detected on imaging and/or histology. Median survival time of dogs with evidence of bone invasion (group 1) was 397 days and significantly shorter compared with dogs with oral melanomas not invading the bone (group 2, 1063 days). Dogs with tumours localised at the level of the cheek, lip, tongue and soft palate (soft tissue - group 3) lived significantly longer compared with dogs having tumours within the gingiva of the maxilla or mandible (hard tissue - group 4) with a median survival time of 1063 and 470 days, respectively. Within group 4, the subgroup of dogs with tumours not invading the bone (group 5) showed a significant prolonged survival time (972 days) in comparison with dogs of group 1 (bone invasion group). Similar results were obtained for the disease-free intervals amongst the different groups. Statistical analysis showed that Ki67 and mitotic count were correlated with shorter survival in patients of group 1 (with bone invasion). Bone invasion should always be assessed since it appears to be a negative prognostic factor.

Curative Intent Surgery of Oral Malignant Melanoma and Regional Lymph Node Biopsy Assessment in 25 Dogs: 2006-2017

Medical records were searched for dogs that had received curative intent surgery for oral malignant melanoma and ipsilateral excisional regional lymph node biopsy. Twenty-seven dogs were operated on and 25 dogs of these dogs met the inclusion criteria of signalment, post-excision margin status, presence of metastasis for each biopsied lymphocentrum, survival time post-excision, presence of recurrence or metastasis at follow-up or at death/euthanasia, location of the primary tumor, and any postoperative adjuvant treatment. These 25 dogs had complete tumor excision with tumor-free margins and 19 (76%) had postoperative adjuvant therapy. Median survival time after excision for the dogs in this study was 335.5 days. Results of this study support previous work that documents prolonged survival time following complete excision of oral malignant melanoma with tumor-free surgical margins in dogs. Additionally, 4 dogs (16%) had histologically confirmed regional lymph node metastasis at the time of definitive surgery.

Prognostic Value of Intratumoral Collagen Quantification in Canine Oral Melanomas

The majority of the melanocytic neoplasms are considered malignant and highly metastatic. However, a subset of the melanocytic tumors has a more favorable prognosis and the identification of precise prognostic markers for this neoplasm may be useful to guide treatment. The collagen architecture and density have been shown to correlate with tumor progression in human breast cancer and canine mast cell tumors. The purpose of the present study was to investigate the prognostic value of the intratumoral collagen index (ICI) as an indicator of postsurgical survival and its relation with other prognostic markers for canine oral melanomas (OMs). Twenty-two cases were tested for intratumoral collagen density using Masson's trichrome stain and morphometry. No differences were found between dogs regarding survival. The ICI was not correlated with proliferative activity or nuclear atypia. The results presented herein indicate that the quantity of intratumoral collagen in canine OMs is not an efficient indicator of postsurgical survival. Complementary studies about the expression and activity of enzymes that are capable of degrading extracellular matrix (ECM) components are necessary.

Employing deep convolutional neural networks for segmenting the medial retropharyngeal lymph nodes in CT studies of dogs

While still in its infancy, the application of deep convolutional neural networks in veterinary diagnostic imaging is a rapidly growing field. The preferred deep learning architecture to be employed is convolutional neural networks, as these provide the structure preferably used for the analysis of medical images. With this retrospective exploratory study, the applicability of such networks for the task of delineating certain organs with respect to their surrounding tissues was tested. More precisely, a deep convolutional neural network was trained to segment medial retropharyngeal lymph nodes in a study dataset consisting of CT scans of canine heads. With a limited dataset of 40 patients, the network in conjunction with image augmentation techniques achieved an intersection-overunion of overall fair performance (median 39%, 25 percentiles at 22%, 75 percentiles at 51%). The results indicate that these architectures can indeed be trained to segment anatomic structures in anatomically complicated and breed-related variating areas such as the head, possibly even using just small training sets. As these conditions are quite common in veterinary medical imaging, all routines were published as an open-source Python package with the hope of simplifying future research projects in the community.

Molecular and Immunohistochemical Expression of LTA4H and FXR1 in Canine Oral Melanoma

Oral melanoma is a common canine tumor whose prognosis is considered ominous, but poorly predicted by histology alone. In the present study the gene and protein expression of Leukotriene A4 hydrolase (LTA4H) and Fragile-X-mental retardation-related protein1 (FXR1), both reported as related to metastatic potential in different tumors, were investigated in canine oral melanoma. The main aim of the study was to confirm and quantify the presence of LTA4H and FXR1 genes and protein in oral melanomas. A secondary aim was to investigate their association with histologic prognostic criteria (mitotic count, Ki-67 index). Formalin-fixed-paraffin-embedded canine oral melanomas (36) were collected and histopathological evaluation carried out. Immunolabelling for LTA4H and FXR1 and Ki-67 were performed. RT-PCR evaluated LTA4H and FXR1 gene expressions. Histologically, most tumors were epithelioid cell melanomas (19/36) and were amelanotic, mildly or moderately pigmented (5, 12 and 13/36 respectively), only 6 were highly pigmented. Mitotic count ranged 1-106, Ki-67 index ranged 4.5–52.3. Thirty-two (32/32) melanomas immunolabelled for LTA4H and 33/34 for FXR1. RT-PCR values ranged 0.76–5.11 ΔCt for LTA4H and 0.22–6.24 ΔCt for FXR1. Molecular and immunohistochemical expression of both LTA4H and FXR1 did not statically correlate with mitotic count or Ki-67 index. The present study demonstrates LTA4H and FXR1 gene and protein in canine oral melanoma, however their expression is apparently unrelated to histopathologic prognostic criteria. Although LTA4H and FXR1 seem unrelated to tumor behavior, their extensive expression in the present cohort of cases suggest that they may play a role in canine oral melanoma oncogenesis.

Cancer-Immunity Cycle and Therapeutic Interventions- Opportunities for Including Pet Dogs With Cancer

The tumor-immune interplay represents a dynamic series of events executed by cellular and soluble participants that either promote or inhibit successful tumor formation and growth. Throughout a tumor’s development and progression, the host organism’s immune system reacts by generating anti-cancer defenses through various incremental and combinatorial mechanisms, and this reactive orchestration is termed the cancer-immunity cycle. Success or failure of the cancer-immunity cycle dictates the fate of both host and tumor as winner or loser. Insights into how the tumor and host immune system continuously adapt to each other throughout the lifecycle of the tumor is necessary to rationally develop new effective immunotherapies. Additionally, the evolving nature of the cancer-immunity cycle necessitates therapeutic agility, requiring real-time serial assessment of immunobiologic markers that permits tailoring of therapies to the everchanging tumor immune microenvironment. In order to accelerate advances in the field of immuno-oncology, this review summarizes the steps comprising the cancer-immunity cycle, and underscores key breakpoints in the cycle that either favor cancer regression or progression, as well as shaping of the tumor microenvironment and associated immune phenotypes. Furthermore, specific large animal models of spontaneous cancers that are deemed immunogenic will be reviewed and proposed as unique resources for validating investigational immunotherapeutic protocols that are informed by the cancer-immunity cycle. Collectively, this review will provide a progressive look into the dynamic interplay between tumor and host immune responses and raise awareness for how large animal models can be included for developing combinatorial and sequenced immunotherapies to maximizing favorable treatment outcomes.

A Comparative View on Molecular Alterations and Potential Therapeutic Strategies for Canine Oral Melanoma

Canine oral melanoma (COM) is a highly aggressive tumour associated with poor prognosis due to metastasis and resistance to conventional anti-cancer therapies. As with human mucosal melanoma, the mutational landscape is predominated by copy number aberrations and chromosomal structural variants, but differences in study cohorts and/or tumour heterogeneity can lead to discordant results regarding the nature of specific genes affected. This review discusses somatic molecular alterations in COM that result from single nucleotide variations, copy number changes, chromosomal rearrangements, and/or dysregulation of small non-coding RNAs. A cross-species comparison highlights notable recurrent aberrations, and functionally grouping dysregulated proteins reveals unifying biological pathways that may be critical for oncogenesis and metastasis. Finally, potential therapeutic strategies are considered to target these pathways in canine patients, and the benefits of collaboration between science, medical, and veterinary communities are emphasised.

Comparative Review of Malignant Melanoma and Histologically Well-Differentiated Melanocytic Neoplasm in the Oral Cavity of Dogs

Oral malignant melanoma (OMM) is the most common neoplasm of the canine oral cavity. It is characterized by its aggressive local disease as well as its high rate of lymphatic invasion and distant metastasis. OMM carries a poor prognosis, with most patients succumbing to the disease due to progression of the neoplasm. Histopathologically, OMM is characterized by significant nuclear atypia, a mitotic index of greater than 4/10 hpf, and evidence of vascular invasion or metastasis. Clinically, these lesions can become locally invasive, causing lysis of bones and severe inflammation of the surrounding soft tissue. With time, these lesions can spread to the regional lymph node and to the lungs and other organs. Prognosis can vary depending on the size of the primary tumor, regional node involvement, and distant metastatic disease; however, multiple studies report a relatively short median survival time ranging from less than 4 months to 8 months. Histologically well- differentiated melanocytic neoplasms (HWDMN) are a variant of OMM and sometimes referred to as canine oral melanocytic neoplasms of low malignant potential. Unlike OMM, patients with HWDMN have longer survival times. Histopathologically, HWDMNs have well-differentiated melanocytes with a low mitotic index of 3 or less per 10 hpf and minimal nuclear atypia. HWDMNs have better prognosis with a mean survival time of up to 34 months. This article is a comparative review of OMM and its less aggressive counterpart.

Quantification of Global DNA Methylation in Canine Melanotic and Amelanotic Oral Mucosal Melanomas and Peripheral Blood Leukocytes From the Same Patients With OMM: First Study

Oral mucosal melanomas (OMMs) are aggressive and resistant cancers of high importance in veterinary oncology. Amelanotic OMM produces comparatively less melanin and is considered to be more aggressive than melanotic OMM. Global DNA methylation profiles with hypomethylated or hypermethylated patterns have both been associated with aggressive neoplasms; however, global DNA hypomethylation seems to correlate to higher aggressiveness. Accordingly, global DNA methylation in peripheral blood leukocytes has been investigated to understand the role of systemic or environmental factors in cancer development. This study aimed to quantify global DNA methylation in canine melanotic and amelanotic OMM samples and in the peripheral blood leukocytes of the same dogs. Tumor tissue samples were collected from 38 dogs, of which 19 were melanotic and 19 were amelanotic OMM. These were submitted to immunohistochemistry (IHC) with anti-5-methylcytosine (5mC) and anti-Ki67 primary antibodies. Ki67- and 5mC-positive nuclei were manually scored with the help of an image analysis system. Peripheral blood samples were collected from 18 among the 38 OMM-bearing dogs and from 7 additional healthy control dogs. Peripheral blood leukocytes were isolated from the 25 dogs, and DNA was extracted and analyzed by high-performance liquid chromatography (HPLC) for global DNA methylation. The pattern of global DNA methylation in both canine melanotic and amelanotic OMM indicated higher percentages of weakly or negatively stained nuclei in most of the OMM cells, presuming predominant global DNA hypomethylation. In addition, Ki67 counts in amelanotic OMM were significantly higher than those in melanotic OMM (p < 0.001). Global DNA methylation different immunostaining patterns (strong, weak or negative) correlated with Ki67 scores. Global DNA methylation in circulating leukocytes did not differ between the 9 melanotic and 9 amelanotic OMM or between the 18 OMM-bearing dogs and the 7 healthy dogs. This study provides new information on canine melanotic and amelanotic OMM based on global DNA methylation and cell proliferation.

Adenoviral CD40 Ligand Immunotherapy in 32 Canine Malignant Melanomas-Long-Term Follow Up

Malignant melanoma is a serious disease in both humans and dogs, and the high metastatic potential results in poor prognosis for many patients. Its similarities with human melanoma make spontaneous canine melanoma an excellent model for comparative studies of novel therapies and tumor biology. Gene therapy using adenoviruses encoding the immunostimulatory gene CD40L (AdCD40L) has shown promise in initial clinical trials enrolling human patients with various malignancies including melanoma. We report a study of local AdCD40L treatment in 32 cases of canine melanoma (23 oral, 5 cutaneous, 3 ungual and 1 conjunctival). Eight patients were World Health Organization (WHO) stage I, 9 were stage II, 12 stage III, and 3 stage IV. One to six intratumoral injections of AdCD40L were given every seven days, combined with cytoreductive surgery in 20 cases and only immunotherapy in 12 cases. Tumor tissue was infiltrated with T and B lymphocytes after treatment, suggesting immune stimulation. The best overall response based on result of immunotherapy included 7 complete responses, 5 partial responses, 5 stable and 2 progressive disease statuses according to the World Health Organization response criteria. Median survival was 285 days (range 20–3435 d). Our results suggest that local AdCD40L therapy is safe and could have beneficial effects in dogs, supporting further treatment development. Clinical translation to human patients is ongoing.

Identification of melanoma-specific exosomal miRNAs as the potential biomarker for canine oral melanoma

Considering the importance of the canine cancer model of human disease, as well as the need for strategies for canine cancer management, the properties of exosomes are an emerging topic in canine oncology. In our study, exosomal RNA was isolated and investigated by next-generation sequencing. We identified several differentially expressed microRNAs (miRNAs/miRs) in the exosomes of two melanoma cell lines compared with non-tumor reference exosomes. We explored these potential melanoma-specific exosomal miRNAs further and found that miR-143 and let-7b increased in primary, whereas miR-210, 708, 221, and 222 increased in metastatic site originated melanoma cells. Further analysis showed miR-143 and 221 significantly increased in plasma exosomes of metastatic melanoma patients. Moreover, the sensitivity and specificity are >85% for differentiating the non-metastatic and metastatic patients. Therefore, these miRNAs can be an incredible biomarker candidate to identify metastatic melanoma and facilitate a better prognosis.

CT features of malignant and benign oral tumors in 28 dogs

An improved understanding of the computed tomographic (CT) features for malignant versus benign oral tumors would be helpful for guiding prognosis and treatment planning decisions in dogs. This retrospective, multi-center, observational study compared the CT features of malignant and benign tumors in 28 dogs with 31 oral masses. Malignant tumors were present in 20 dogs, including malignant melanoma (n = 14), squamous cell carcinoma (SCC, n = 4), adenocarcinoma (n = 1), and fibrosarcoma (n = 1). Eight dogs had benign tumors, including giant cell granuloma (n = 2), peripheral odontogenic fibroma (n = 2), acanthomatous ameloblastoma (n = 2), plasmacytoma (n = 1), and oncocytoma (n = 1). Common CT features of malignant tumors included heterogeneous enhancement, tumor invasion into the adjacent bone, tooth loss, and ipsilateral mandibular lymphadenopathy. Malignant tumors were significantly larger than benign tumors. Bone lysis was found in benign tumors (n = 4) such as acanthomatous ameloblastoma, giant cell granuloma, and plasmacytoma. The bone lysis was a well-defined geographic area regardless of malignancy and tumor type. In periosteal reactions, amorphous patterns were seen in both malignant (n = 2) and benign tumors (n = 2); the latter subgroup also showed solid patterns. Bone expansion (n = 2) was identified in malignant melanoma and acanthomatous ameloblastoma. Findings supported a diagnosis of possible malignancy for dogs with oral tumors having the following CT characteristics: large size, heterogeneous contrast enhancement pattern, bone lysis, tooth loss, and ipsilateral lymphadenopathy. However, there was a considerable overlap of CT findings among the different types of oral tumors and between benign and malignant tumors. Histological evaluation therefore remains necessary for definitive diagnosis.

Effects of Alpha-Connexin Carboxyl-Terminal Peptide (aCT1) and Bowman-Birk Protease Inhibitor (BBI) on Canine Oral Mucosal Melanoma (OMM) Cells

Oral mucosal melanomas (OMM) are aggressive cancers in dogs, and are good models for human OMM. Gap junctions are composed of connexin units, which may have altered expression patterns and/or subcellular localization in cancer cells. Cell-to-cell communication by gap junctions is often impaired in cancer cells, including in melanomas. Meanwhile, the upregulated expression of the gap junction protein connexin 43 (Cx43) inhibits melanoma progression. The α-connexin carboxyl-terminal (aCT1) peptide reportedly maintains Cx43 expression and cell-cell communication in human mammary cells and increases the communication activity through gap junctions in functional assays, therefore causing decreased cell proliferation. The Bowman-Birk protease inhibitor (BBI), a component of soybeans, induces Cx43 expression in several tumor cells as a trypsin–chymotrypsin inhibition function, with antineoplastic effects. This study investigated the effect of aCT1 peptide and BBI treatment, alone or in combination, on TLM1 canine melanoma cell viability. Cell viability after treatment with aCT1, the reverse sequence peptide (R-pep), and/or BBI for 5 days was analyzed by PrestoBlue assay. Immunofluorescence was used to observe Cx43 localization and expression. aCT1 (200 μM) alone did not significantly decrease cell viability in TLM1 cells, whereas BBI (400 μg/ml) alone significantly decreased the TLM1 viability. Combined treatment with both aCT1 (200 μM) and BBI (400 μg/ml) significantly decreased cell viability in TLM1 cells. Cx43 expression, as identified by immunostainings in TLM1 cells, was increased in the cell membrane after the combination treatment with BBI and aCT1. This dual treatment can be combined to achieve the anticancer activity, possibly by increasing Cx 43 expression and affecting Cx43 migration to the cell membrane. In conclusion, a treatment strategy targeting Cx43 with BBI and aCT1 may possibly lead to new effective therapies for canine OMM.

Evaluation of prognostic impact of pre-treatment neutrophil to lymphocyte and lymphocyte to monocyte ratios in dogs with oral malignant melanoma treated with surgery and adjuvant CSPG4-antigen electrovaccination: an explorative study

The role of systemic inflammation in cancer's progression has been widely investigated, especially in melanoma in humans. Pre-treatment leukocyte counts and ratios play a recognized prognostic role in several types of malignancies, but no information is available regarding canine oral malignant melanoma (COMM). The purpose of this explorative retrospective study was to investigate the prognostic impact of pre-treatment neutrophil to lymphocyte (NLR) and lymphocyte to monocyte (LMR) ratios in dogs with oral malignant melanoma that underwent surgical resection and immunotherapy with adjuvant CSPG4-antigen electrovaccination. Thirty-nine dogs with histologically confirmed oral melanoma and with available pre-treatment haematological analyses, performed at maximum 60 days before the first treatment, were retrospectively enrolled. Statistical analysis was performed to explore possible correlations among NLR and LMR with age, clinical stage, tumour pigmentation, tumour size, nuclear atypia, mitotic index, Ki67, CSPG4 expression, ulceration, bone invasion and excision margins status. The impact of NLR and LMR on overall survival time (OST) was explored among various ratio cut off and across different time points with Kaplan-Meier method. No significant relationship was identified between leukocytes ratios and histological parameters, CSPG4 expression, excision margin status, age, tumour size and clinical stage. NLR and LMR did not display a prognostic impact on the survival time of the entire population. Pre-treatment leukocyte ratios may not represent a useful prognostic factor in dogs with oral melanoma, especially in absence of distant metastatic disease.

Frequent genetic defects in the p16/INK4A tumor suppressor in canine cell models of breast cancer and melanoma

The cyclin-dependent kinase inhibitors (CKIs) belong to a group of key cell cycle proteins that regulate important cancer drug targets such as the cyclin/CDK complexes. Gene defects in the INK4A/B CKI tumor suppressor locus are frequently associated with human cancers and we have previously identified similar defects in canine models. Many of the cancer-associated genetic alterations, known to play roles in mammary tumor development and progression, appear similar in humans and dogs. The objectives of this study were to characterize expression defects in the INK4 genes, and the encoded p16 family proteins, in spontaneous canine primary mammary tumors (CMT) as well as in canine malignant melanoma (CML) cell lines to further develop these models of spontaneous cancers. Gene expression profiles and characterization of p16 protein were performed by rtPCR assay and immunoblotting followed by an analysis of relevant sequences with bioinformatics. The INK4 gene family were expressed differentially and the genes encoding the tumor suppressor p16, p14, and p15 proteins were often identified as defective in CMT and CML cell lines. The altered expression profiles for INK4 locus encoded tumor suppressor genes was also confirmed by the identification of similar gene defects in primary canine mammary tumor biopsy specimens which were also comparable to defects found in human breast cancer. These data strongly suggest that defects identified in the INK4 locus in canine cell lines are lesions originating in spontaneous canine cancers and are not the product of selection in culture. These findings further validate canine tumor models for use in developing a clear understanding of the gene defects present and may help identify new therapeutic cancer treatments that restore these tumor suppressor pathways based on precision medicine in canine cancers.

Targeting neovascularization and respiration of tumor grafts grown on chick embryo chorioallantoic membranes

Since growing tumors stimulate angiogenesis, via vascular endothelial growth factor (VEGF), angiogenesis inhibitors (AIs, blockers of the VEGF signaling pathway) have been introduced to cancer therapy. However, AIs often yielded only modest and short-lived gains in cancer patients and more invasive tumor phenotypes in animal models. Combining anti-VEGF strategies with lactate uptake blockers may boost both efficacy and safety of AIs. We assessed this hypothesis by using the ex ovo chorioallantoic membrane (CAM) assay. We show that AI-based monotherapy (Avastin®, AVA) increases tumor hypoxia in human CAM cancer cell xenografts and cell spread in human as well as canine CAM cancer cell xenografts. In contrast, combining AVA treatment with lactate importer MCT1 inhibitors (α-cyano-4-hydroxycinnamic acid (CHC) or AZD3965 (AZD)) reduced both tumor growth and cell dissemination of human and canine explants. Moreover, combining AVA+AZD diminished blood perfusion and tumor hypoxia in human explants. Thus, the ex ovo CAM assay as an easy, fast and cheap experimental setup is useful for pre-clinical cancer research. Moreover, as an animal-free experimental setup the CAM assay can reduce the high number of laboratory animals used in pre-clinical cancer research.

Immunohistochemical expression and prognostic significance of MAGE-A in canine oral malignant melanoma

Canine oral malignant melanoma (COMM) is considered a chemo-resistant cancer with a poor long-term prognosis. The melanoma-associated antigen A (MAGE-A) genes, which belong to the cancer-testis antigen family, are expressed in several different canine cancers but not in normal somatic tissue. This study evaluates the expression of MAGE-A proteins and their prognostic role in COMM. The study was conducted in 2 parts. During the first part, biopsies from oral malignant melanomas from 43 dogs were examined and immunohistochemically assessed for expression of MAGE-A proteins. For the second part, the association between MAGE-A expression and outcome was assessed using follow-up data which was available for 20 dogs whose primary tumour had been controlled with surgery +/- radiation therapy. MAGE-A proteins were expressed in 88.4% (38/43) of oral malignant melanomas and had a predominantly cytoplasmic expression pattern. Immunopositivity was observed in more than 50% of the cells in 21 dogs (48.8%). Immunostaining intensity was classified as weak, moderate and intense in 16 (37%), 16 (37%) and 6 (14%) cases, respectively. No staining for MAGE-A was seen in 5 dogs (11%). Dogs whose COMM had weak MAGE-A staining intensity had a median survival time (MST) of 320 days while this was 129 days for dogs with moderate and intense immunostaining (p = 0.161). Dogs whose COMM had >50% of positive staining neoplastic cells had an MST of 141 days and dogs with a staining <50% had an MST of 320 days (p = 0.164). MAGE-A expression did not influence survival in our cohort.

Metastatic perioral melanoma in a wild mountain gorilla (Gorilla beringei beringei)

A 30-year-old free-ranging female mountain gorilla (Gorilla beringei beringei) developed a perioral mass that was surgically debulked and diagnosed as malignant melanoma. After tumor recurrence, a canine melanoma vaccine was administered. However, the gorilla died shortly thereafter, and metastases to lymph nodes, lung, liver, and kidney were found post-mortem.

Intratumoral T-Lymphocyte Subsets in Canine Oral Melanoma and Their Association With Clinical and Histopathological Parameters

Canine oral melanoma is a common, aggressive tumor with limited treatment options. Tumor-infiltrating lymphocytes (TILs) are important in antitumor immunity. This study used histopathology and immunophenotyping by flow cytometry to evaluate the presence and distribution of TILs in canine oral melanoma, including the frequency of CD8⁺ T cells, CD4⁺ T cells, and regulatory T cells. Fifty samples of oral melanoma from 45 dogs that did not receive treatment prior to surgery were included in the study. The distribution of TILs in the tissue (brisk, nonbrisk, and absent) was evaluated in 48 samples. Twenty-eight (58%) samples had a brisk distribution pattern, 10 (21%) samples had a nonbrisk pattern, and 10 (21%) samples had an absent TIL pattern. Comparing the histological evaluation and the immunophenotyping data, it was observed that samples with a brisk TIL pattern had a higher frequency of CD8⁺ T lymphocytes (P = .05) and a lower frequency of CD4⁺/CD25⁺/FoxP3⁺ Tregs (P = .03), compared to the samples with nonbrisk and absent infiltrate patterns. Patients with a higher survival rate had higher TIL scores (P = .002), a brisk or nonbrisk TIL pattern (P = .001), and an increased frequency of CD8⁺ T lymphocytes infiltrating the tumor (P = .003). Our analysis suggests that the evaluation of TILs in canine oral melanoma is relevant to predict tumor aggressiveness and patient prognosis.

Involvement of GLUT1 and GLUT3 in the growth of canine melanoma cells

The rate of glucose uptake dramatically increases in cancer cells even in the presence of oxygen and fully functioning mitochondria. Cancer cells produce ATP by glycolysis rather than oxidative phosphorylation under aerobic conditions, a process termed as the “Warburg effect.” In the present study, we treated canine melanoma cells with the glucose analog 2-deoxy-D-glucose (2-DG) and investigated its effect on cell growth. 2-DG attenuated cell growth in a time- and dose-dependent manner. Cell growth was also inhibited following treatment with the glucose transporter (GLUT) inhibitor WZB-117. The treatment of 2-DG and WZB-117 attenuated the glucose consumption, lactate secretion and glucose uptake of the cells. The mRNA expression of the subtypes of GLUT was examined and GLUT1 and GLUT3 were found to be expressed in melanoma cells. The growth, glucose consumption and lactate secretion of melanoma cells transfected with siRNAs of specific for GLUT1 and GLUT3 was suppressed. These findings suggest that glucose uptake via GLUT1 and GLUT3 plays a crucial role for the growth of canine melanoma cells.