Drug resistance and new therapies in colorectal cancer

Figure 1 Potential mechanisms of resistance to chemotherapy agents. In this schematic representation, the grey boxes highlight major contributors to chemotherapy resistance of irinotecan, 5-FU, capecitabine and oxaliplatin. TopoI: TopoisomeraseI; CES: Carboxylesterases; UGT: Uridine diphosphate glucuronosyltransferase; CYP3A: Hepatic cytochrome P450 enzymes; HDAC: Histone deacetylase; ABC protein: ATP-binding cassette transporter protein; TP: Thymidine phosphorylase; NER: Nucleotide excision repair; TGF-β1: Transforming growth factor β1; TS: Thymidylate synthase; UP: Uridine phosphorylase; OPRT: Orotate phosphoribosyl transferase; DPD: Dihydropyrimidine dehydrogenase.