Introduction A knowledge of the biological phenotype of colorectal liver metastases would be invaluable to inform clinical decision making; however, deriving this information from the metastatic lesions is not feasible until after resection. We aimed to use proteomic analysis to identify biomarkers in the primary tumour which predict response to neoadjuvant chemotherapy in liver metastases.
Method Fresh tissue from both primary colorectal tumour and liver metastases from 17 patients was subjected to proteomic analysis using isobaric tagging for relative quantification, with stratification of patients into those showing low or high response to chemotherapy permitting the identification of potential predictive biomarkers. These markers were subsequently validated by immunohistochemistry on a tissue microarray of 57 patients and further investigated in an in vitro model.
Results We identified 5768 discrete proteins, 5 of which predicted histopathological response to fluorouracil-based chemotherapy regimens. Immunostaining of NQO1 in the metastases was lower in those responding to chemotherapy (p = 0.041), with a significant correlation between primary and metastatic disease sites (r = 0.44, p = 0.001). Knockdown of NQO1 with small interfering RNA followed by treatment with irinotecan and 5FU reduced the IC50 from 100.1µM to 49.8µM and from 200.1µM to 25.0µM respectively. Pre-treating cells with dicoumarol (a known competitive inhibitor) prior to incubation in irinotecan and 5FU reduced the IC50 from 100.0µM to 50.0µM and from 183.7µM to 49.9µM respectively.
Conclusion These results show that proteomic sequencing of matched metastatic colorectal cancer samples is feasible, with high protein coverage. The high degree of similarity between the primary and secondary proteomes suggests that primary tissue is predictive of the metastatic phenotype. NQO1 expression in the primary tumour predicts response to neoadjuvant chemotherapy in the liver metastases, and inhibition of this protein at both genetic and functional levels improves chemosensitivity. Further validation in an in vivo model is planned.
Disclosure of interest P. Sutton Grant/ Research Support from: Cancer Research UK, J. Evans: None Declared, R. Jones: None Declared, C. Goldring: None Declared, D. Palmer: None Declared, N. Kitteringham: None Declared, H. Malik: None Declared, D. Vimalachandran: None Declared.