Evaluation of plasma nucleosome concentrations in dogs with a variety of common cancers and in healthy dogs.

BACKGROUND: Cell free DNA, in the form of nucleosomes, is released into circulation during apoptosis and necrosis in a variety of diseases. They are small fragments of chromosomes that are composed of DNA wrapped around a histone core made of four duplicate histone proteins forming an octamer. The nucleosome compartment is a relatively uninvestigated area of circulating tumor biomarkers in dogs. The objectives of this study were to quantify and better characterize nucleosome concentrations in 528 dogs with various common malignancies and compare them to 134 healthy dogs. RESULTS: The sensitivity of increased circulating nucleosome concentrations for the detection of cancer in all dogs was 49.8% with a specificity of 97% with an area under the curve of 68.74%. The top 4 malignancies detected by the test included lymphoma, hemangiosarcoma, histiocytic sarcoma and malignant melanoma. The malignancies least likely to be detected were soft tissue sarcomas, osteosarcoma and mast cell tumors. CONCLUSIONS: A variety of tumor types may cause increased nucleosome concentrations in dogs. Tumors of hematopoietic origin are most likely to cause elevations and local tumors such as soft tissue sarcomas are least likely to cause elevations in plasma nucleosome concentrations.

Identification and evaluation of putative tumour-initiating cells in canine malignant melanoma cell lines.

Tumour-initiating cells (TICs) have been identified in many solid human tumours, including malignant melanoma. In this study, an enriched TIC population was identified in two canine malignant melanoma cell lines (CML1 and CML6M) using cell surface markers and functional assays, including the sphere forming assay, aldehyde dehydrogenase (ALDH) assay, reverse transcriptase-polymerase chain reaction and γH2AX staining for double-stranded DNA (dsDNA)break identification and repair. The CD34(-) population of cells in both cell lines expressed stem cell genes, such as Oct4, Nanog and Ptch1, were more efficient at making spheres in adherence-free media conditions and were able to repair dsDNA breaks faster than the CD34(+) population. A subpopulation of cells with high expression of ALDH was identified in both cell lines by flow cytometry. The findings indicate the presence of TICs in two canine malignant melanoma cell lines.