Increased Levels of Oxidative Damage in Liver Metastases Compared with Corresponding Primary Colorectal Tumors: Association with Molecular Subtype and Prior Treatment

High levels of oxidative stress in disseminated colorectal cancer tumor cells may form a therapeutically exploitable vulnerability. However, it is unclear whether oxidative stress and damage persist in metastases. Therefore, we analyzed markers of oxidative damage in primary colorectal tumors and their corresponding liver metastases. Markers of generic and oxidative DNA damage [phosphorylated histone H2AX (γH2AX) and 8-hydroxy-2'-deoxyguanosine (8-OHdG)] were significantly higher in liver metastases compared with their corresponding primary tumors. Chemotherapy and/or radiotherapy before tumor resection was associated with increased persistent oxidative DNA damage, and this effect was more pronounced in metastases. Immunohistochemistry-based molecular classification into epithelial- and mesenchymal-like molecular subtypes revealed that untreated mesenchymal-like tumors contained lower levels of oxidative DNA damage compared with epithelial-like tumors. Treated mesenchymal-like tumors, but not epithelial-like tumors, showed significantly higher levels of γH2AX and 8-OHdG. Mesenchymal-like tumors expressed significantly lower levels of phosphorylated nuclear factor erythroid 2-related factor 2, a master regulator of the antioxidant response, and nuclear factor erythroid 2-related factor 2-controlled genes. Of interest, a positive 8-OHdG status identified a subgroup of mesenchymal-like metastases with a poor overall survival. An increased capacity to tolerate therapy-induced oxidative damage in mesenchymal-like colorectal cancer may explain, at least in part, the poor responsiveness of these tumors to chemotherapy, which could contribute to the poor survival of this patient subgroup.