MYC as a candidate upstream controller involved in TYMS gene expression and 5-FU/folate treatment efficacy in colorectal cancer.

Abstract

e15512 Background: One of the target enzymes of 5-fluorouracil (5-FU)-based therapies is thymidylate synthase (TS) encoded by the TYMS gene. To enhance the effect of 5-FU, a folate analogue is often provided as part of the treatment. In this context, it has previously been shown in the ISO-CC-005 clinical study that TYMS gene expression can be predictive of response to 5-FU + folate analogue Arfolitixorin. Methods: To better understand the role of TYMS expression as a predictor of response to 5-FU + folate-based therapies and identify potential mechanisms and biomarkers of sensitivity/resistance, we leveraged data from the publicly available cancer genome atlas database (TCGA). We combined this information with a knowledgebase of causal biological relationships extracted from peer reviewed publications, to identify other relevant genes and candidate upstream controllers directly or indirectly related to TYMS expression and 5-FU + folate efficacy. Results: In TCGA subjects suffering from colorectal cancer (CRC) (stage IV tumors, treated with FOLFOX/FOLFIRI (n = 38)), lower TYMS expression was associated with a better overall survival (OS). This is consistent with what has been observed in the ISO-CC-005 study. Applying our causal biology knowledgebase to both genes identified as correlated to TYMS expression in TCGA CRC tumors and other published sets of genes associated with FOLFOX or FOLFIRI efficacy, we identified overlap with a MYCN signature. Notably MYC has been shown to directly activate TYMS expression. Thus, the MYC family is a compelling candidate upstream controller of these genes. We scored TCGA CRC tumors for inferred MYC activity, using this MYCN gene signature, and evaluated the inferred activity with respect to OS. In stage IV tumors, higher inferred MYC activity appears to be associated with worse OS. To further characterize this inferred MYC activity, we employed a transcriptomics-based cell deconvolution estimation of immune cell population proportions in the TCGA CRC cohort. We found inferred MYC activity inversely correlated with immune cell proportions overall, specifically strongest with those of pDCs and classical monocytes. Conclusions: MYC activation, a known transcriptional regulator of TYMS, has been identified as a potentially relevant common upstream controller of a group of genes involved in 5-FU + folate analogue efficacy. Here we have also observed a similar relationship to OS between TYMS and inferred MYC activity in Stage IV CRC. MYC family activity (and activated protein forms), genes of the MYCN signature, or the identified immune cell proportions are all potential biomarker candidates to explore as factors in 5-FU + folate analogue efficacy.