Gene expression of indoleamine and tryptophan dioxygenases and three long non-coding RNAs in breast cancer

The kynurenine pathway (KP) has a principal role in the metabolism of tryptophan. This pathway is also involved in the pathogenesis of cancer. We evaluated expression of two rate limiting enzymes from this pathway (IDO1 and TDO2) as well as three long non-coding RNAs (lncRNAs) that have been predicted to alter expression of IDO1 (ITGB2-AS1, HCP5 and MIR155HG) in 82 breast cancer tissues and their adjacent non-cancerous tissues (ANCTs). While IDO1 expression levels were not significantly different between malignant tissues and ANCTs (expression ratio = 0.56, P = .21), TDO2 was significantly down-regulated in malignant tissues compared with ANCTs (Expression ratio = 0.001, P < .001). Among lncRNAs, expression of HCP5 was significantly lower in malignant tissues compared with ANCTs (Expression ratio = 0.17, P < .001). However, expression of ITGB2-AS1 was higher in malignant tissues compared with ANCTs (Expression ratio = 3.38, P = .01). Expressions of genes were not associated with any of clinical or demographic data of patients. However, there were trends towards association between IDO1 expression and tumor size as well as estrogen receptor (ER) status (P values 0.09 and 0.08 respectively). Significant pairwise correlations were found between expression levels of genes especially in ANCTs. Notably, TDO2 expression levels were correlated with expression of all other genes in ANCTs but none of them in tumor tissues. Based on the area under curve (AUC) values, HCP5 and TDO2 had "fair" diagnostic power (AUC values of 0.73 and 0.72). Notably, combination of HCP5, ITGB2-AS1 and TDO2 genes increased the diagnostic power to the level of "good". The current investigation underscores the role of KP in breast cancer and potentiates some genes within this pathway as diagnostic markers in breast cancer.