Salivary Biomarkers for Gastric Cancer Detection: The Saliva RNA Interactome

Objective: Gastric cancer is one of the most prevalent cancers in Asian countries. In collaboration with Korean SamSung Medical Center, we have discovered a panel of discriminatory salivary mRNA and miRNA biomarkers in gastric cancer. The objective of this study was to verify these salivary biomarkers and test the hypothesis that there are mRNA-miRNA interactions in saliva. This is highly impactful for developing salivary biomarkers for a prevalent cancer and exploring the biological relevance of the salivary RNA interactome.

Method: Unstimulated saliva supernatant samples were collected from 63 gastric cancer patients and 31 normal healthy subjects. Salivary mRNA biomarkers were discovered using Affymetrix U133 Plus 2.0 Array. Highest ranked salivary mRNA biomarkers were verified using qRT-PCR. Salivary miRNA biomarkers were discovered using Taqman MicroRNA Array cards. The highest ranked salivary miRNA biomarkers were verified using Taqman MicroRNA arrays. Group differences of expression levels were tested by t-test or Mann-Whitney test. Logistic regression models and receiver operating characteristic (ROC) curves were constructed to determine the diagnostic capabilities of these respective salivary biomarkers. Spearman’s correlation analysis was performed with direct miRNA targets and expression levels of mRNA from microarray. R software and TargetScan were used to analyze mRNA-miRNA interactions.

Result: From 25 salivary transcriptomic candidate biomarkers tested, 12 were verified in the discovery sample set (11 mRNAs significantly down-regulated and 1 mRNA significantly up-regulated). Of the 15 salivary candidate miRNAs tested, 6 miRNAs were verified and all significantly down-regulated. There are 9091 mRNA-miRNA pair correlations (6321 positive and 2770 negative), indicating significant mRNA/miRNA interplay with biological and functional implications in saliva of gastric cancer patients.

Conclusion: Twelve salivary mRNA biomarkers and 6 salivary miRNA biomarkers were discovered to discriminate gastric cancer in a Korean population. We have definitive evidence of interplay between mRNA-miRNA in saliva with important biological relevance to gastric cancer.