Despite extensive research effort there are no accepted clinical biomarkers that predict for response to systemic combination chemotherapy in advanced colorectal cancer. Current assessment is based on computed tomography (CT), approximately 6-8 weeks after treatment. Earlier molecular predictors of response would be highly beneficial for both patients and clinicians. We have investigated whether useful protein biomarkers could be found in patient plasma, through the use of advanced mass spectrometry techniques. We have developed targeted and highly specific assays for multiplexed quantitation of over 30 high-to-medium abundance plasma proteins using a technique known as selected reaction monitoring (SRM).
First, we examined whether the type of blood collection tube would dramatically impact on SRM measurement of plasma proteins. By studying a panel of 18 plasma proteins our resulted showed that EDTA-blood collection tubes were appropriate for SRM based analyses. We next quantitated the degree of temporal variation in the levels of 31 plasma proteins in healthy individuals over a 19 week time course and showed the plasma proteome to be remarkably stable. We then applied SRM to monitor 31 plasma proteins in a trial cohort of advanced CRC patients receiving FOLFOX chemotherapy. Our results indicated that the baseline levels of the extracellular matrix related protein vitronectin was associated with chemotherapy response as determined by CT. We developed specific SRM assays for vitronectin peptides using synthetic peptide standards then validated our findings in a cohort of 29 patients. These findings pave the way for more extensive testing in larger cohorts and could lead to more cost-effective and rational uses of systemic chemotherapy.