Salivary Exosomal miRNA-1307-5p Predicts Disease Aggressiveness and Poor Prognosis in Oral Squamous Cell Carcinoma Patients

<b>Background:</b> Salivary exosomal miRNAs as biomarkers facilitate repeated sampling, real-time disease monitoring and assessment of therapeutic response. This study identifies a single salivary exosomal miRNA prognosticator that will aid in improved patient outcome using a liquid biopsy approach. <b>Method:</b> Small RNA and transcriptome sequencing profiles of tumour tissues (<i>n</i> = 12) and salivary exosomes (<i>n</i> = 8) from oral cancer patients were compared to their non-cancerous counterparts. We validated these results using The Cancer Genome Atlas database and performing Real-time PCR on a large patient cohort (<i>n</i> = 19 tissue samples; <i>n</i> = 12 salivary exosomes). Potential target genes and the miRNA-mRNA networks and enriched biological pathways regulated by this microRNA were identified using computational tools. <b>Results:</b> Salivary exosomes (size: 30-50 nm) demonstrated a strong expression of CD47 and detectable expression of tetraspanins CD63, CD81 and CD9 by flow cytometry. miR-1307-5p was exclusively overexpressed in tissues and salivary exosomes of oral cancer patients compared to their non-cancerous counterparts. Enhanced expression of miR-1307-5p clinically correlated with poor patient survival, disease progression, aggressiveness and chemo-resistance. Transcriptome analysis suggested that miRNA-1307-5p could promote oral cancer progression by suppressing <i>THOP1</i>, <i>EHF</i>, <i>RNF4</i>, <i>GET4</i> and <i>RNF114</i>. <b>Conclusions:</b> Salivary exosomal miRNA-1307-5p is a potential prognosticator for predicting poor survival and poor patient outcome in oral cancers.