Long non-coding RNA and transfer RNA-derived small fragments in exosomes are potential biomarkers for canine oral melanoma.

Novel small non-coding RNAs (sRNAs) represent an emerging line of research in both human and canine oncology, due to their diverse regulatory and functional roles. Novel sRNAs are regarded as distinct from microRNAs, although both are part of the exosomal cargo. Recently, we reported on exosomal miRNAs as biomarkers for canine melanoma; however, it is unknown if novel sRNAs hold similar potential. Accordingly, we aimed to identify and validate novel sRNAs as potential biomarkers of canine oral melanoma, as part of our larger project on sequencing small exosomal RNA for this disease. Next generation sequencing revealed several differentially expressed novel sRNAs in exosomes from two melanoma cell lines (KMeC and LMeC) when compared with reference exosomes (from tumour-free dogs). Among these novel sRNAs, long noncoding RNA fragments, tRNA-derived fragments, snoRNAs and snRNAs were abundantly expressed. We selected four novel sRNAs upregulated in each cell line, and validated their aberrant expression with qPCR. In analysis using plasma-derived exosomes from melanoma patients, six out of the eight selected novel sRNAs showed significantly elevated expression. Receiver operating curve (ROC) analysis showed that one long non-coding RNA-derived small fragment (ENSCAFT00000069599.1) and one transfer RNA-derived small fragment (tRNA-Ala-TGC-5-1) have more than 85% sensitivity and specificity for differentiating melanoma patients from tumour-free dogs. Therefore, we consider that novel sRNAs may serve as candidate biomarkers to facilitate more accurate diagnosis of canine oral melanoma in clinical settings.