EGF receptor and COX-1/COX-2 enzyme proteins as related to corresponding mRNAs in human per-operative biopsies of colorectal cancer

Background: Cyclooxygenase (COX) and epidermal growth factor receptor (EGFR) activities promote progression of colorectal cancer. Combined treatment against these targets has not been more effective than single treatments alone. Therefore, our aim was to analyze relationships between COX and EGFR in peroperative colorectal tumor biopsies. Method: Tumor and colon mucosa tissue were collected at primary intended curative operations in patients according to well-recognized statistical distributions of tumor stages in colorectal cancer. COX-1, COX-2 and EGFR content in tumor and colon mucosa tissue were quantified by western blot and Q-PCR. Results: COX-2 protein appeared as two bands, one at 66 kDa in almost all tumor and mucosa samples and one at 74 kDa in 73% of the tumors and in 23% of the mucosa samples. Tumor COX-2 mRNA was not different from the content in mucosa samples, while COX-2 protein was increased in tumor tissue (p < 0.0003). A correlation between 74 kDa COX-2 protein and COX-2 mRNA occurred in tumor tissue, with significantly increasing COX-2 mRNA across tumor stages. EGFR mRNA content was lower in tumor tissue (p < 0.0001), while EGFR protein was similar in tumor and mucosa samples. COX-2 and EGFR proteins showed a positive correlation in mucosa, while a negative correlation occurred in tumor tissue. Tumor tissue with high COX-2 74 kDa protein lacked EGFR protein. Conclusion: Our present results are compatible with the theory that COX-2 and EGFR signalling pathways are inversely related in colorectal cancer tissue. This may explain why combinatorial clinical treatments have been less rewarding.