Date Published: July 27, 2017
Publisher: Public Library of Science
Author(s): Precious Takondwa Makondi, Chi-Ming Chu, Po-Li Wei, Yu-Jia Chang, Irina V Lebedeva.
Acquired drug resistance to the chemotherapeutic drug irinotecan (the active metabolite of which is SN-38) is one of the significant obstacles in the treatment of advanced colorectal cancer (CRC). The molecular mechanism or targets mediating irinotecan resistance are still unclear. It is urgent to find the irinotecan response biomarkers to improve CRC patients’ therapy.
Genetic Omnibus Database GSE42387 which contained the gene expression profiles of parental and irinotecan-resistant HCT-116 cell lines was used. Differentially expressed genes (DEGs) between parental and irinotecan-resistant cells, protein-protein interactions (PPIs), gene ontologies (GOs) and pathway analysis were performed to identify the overall biological changes. The most common DEGs in the PPIs, GOs and pathways were identified and were validated clinically by their ability to predict overall survival and disease free survival. The gene-gene expression correlation and gene-resistance correlation was also evaluated in CRC patients using The Cancer Genomic Atlas data (TCGA).
The 135 DEGs were identified of which 36 were upregulated and 99 were down regulated. After mapping the PPI networks, the GOs and the pathways, nine genes (GNAS, PRKACB, MECOM, PLA2G4C, BMP6, BDNF, DLG4, FGF2 and FGF9) were found to be commonly enriched. Signal transduction was the most significant GO and MAPK pathway was the most significant pathway. The five genes (FGF2, FGF9, PRKACB, MECOM and PLA2G4C) in the MAPK pathway were all contained in the signal transduction and the levels of those genes were upregulated. The FGF2, FGF9 and MECOM expression were highly associated with CRC patients’ survival rate but not PRKACB and PLA2G4C. In addition, FGF9 was also associated with irinotecan resistance and poor disease free survival. FGF2, FGF9 and PRKACB were positively correlated with each other while MECOM correlated positively with FGF9 and PLA2G4C, and correlated negatively with FGF2 and PRKACB after doing gene-gene expression correlation.
Targeting the MAPK signal transduction pathway through the targeting of the FGF2, FGF9, MECOM, PLA2G4C and PRKACB might increase tumor responsiveness to irinotecan treatment.
Colorectal cancer (CRC) is the third most frequently diagnosed cancer and the third leading cause of cancer deaths worldwide representing 10% of the world-wide cancer incidence and mortality. Surgical removal of the tumor is the first choice treatment for non-metastatic CRC though approximately one-quarter of CRC patients have metastases at diagnosis and half developing metastases even after complete resection[2,3]. The addition of cytotoxic drugs oxaliplatin and irinotecan and the monoclonal anti-bodies cetuximab, bevacizumab or panitunumab to the backbone of the antimetabolite 5-fluorouracil has improved the median survival of metastatic CRC(mCRC) from 8 to 24 months[4–6]. Drug resistance still hampers the efficient treatment of mCRC as half of the patients have intrinsic or acquired resistance contributing to a 5-year survival rate of 60% to 65%[7–10] and with the chemotherapy side effects being many, there is an unmet need for therapy response predictive biomarkers.
CRC remains a significant cause of morbidity and mortality worldwide with high disease incidence and significant numbers of patients presenting with advanced, metastatic disease. Despite advances in medical and surgical therapy, the 5-year overall survival rate is still is low at 60% to 65% . The development of resistance to irinotecan treatment is still the major challenge in managing CRC . The mechanisms leading to development of irinotecan-resistance are poorly characterized. The understanding of the etiological factors and mechanisms of irinotecan-resistance will help to improve the therapeutic efficacy of CRC patients.
In conclusion, targeting the MAPK signal transduction pathway through the targeting of FGF9, FGF2, MECOM, PRKACB and PLA2G4C might increase tumor responsiveness to irinotecan and improve patient survival thus being therapeutically and prognostic significant in CRC patients.