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

Abstract

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.

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

“…The clinical, pathological, and prognostic features of canine melanoma have recently been reviewed [ 15 , 16 ]. OMM can be classified as melanotic or amelanotic, and its amelanotic counterpart is considered more aggressive than its melanotic counterpart [ 17 , 18 ]. Spontaneous melanomas in dogs, including OMM, are considered good models of human melanomas [ 19 , 20 , 21 ].…”

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

“…While the former are usually methylated, CGIs are frequently unmethylated, and within promoters, methylation can lead to gene silencing, either through a steric interference with transcription machinery, or by recruiting chromatin remodelling factors [65]. A recent canine study has taken an IHC approach with a monoclonal antibody to 5-methylcytosine, revealing predominantly weak staining or negative nuclei in COMs, but staining intensity in normal melanocytes was not determined, and gene-specific methylation was not determined [67]. Alternative next generation sequencing methods illustrate that, as with various human cancers, the genome-wide methylation signature in COM shows a reversal of the normal pattern, with tumours showing widespread hyper-methylation in CGIs and relative hypo-methylation at non-CGI sites [68].…”