Serum phosphopeptide profiling for colorectal cancer diagnosis using liquid chromatography-mass spectrometry

The identification and evaluation of novel biomarkers are essential to clinical diagnosis and prognosis of colorectal cancer (CRC). Serum phosphopeptides have been recognized as a potential signature pool for cancers; therefore, we aim to profile the expression of serum phosphopeptides and to evaluate their feasibility in CRC diagnosis.

We conducted the characterization and absolute quantification of endogenous phosphopeptides in sera using liquid chromatography-mass spectrometry analysis in combination with enrichment of phosphopeptides by ZrAs-Fe₃ O₄ @SiO₂ nanoparticles and use of deuterium-labeled standards. Differentially expressed analysis of four phosphopeptides was performed, generating a two-phosphopeptide-based biomarker, L_F3-4 , by logistic regression analysis, where L_F3-4 is equal to (5.85 - 5.13 × [F3] - 3.57 × [F4]), and [F3] and [F4] are the concentration of phosphopeptides DpSGEGDFLAEGGGVR and ADpSGEGDFLAEGGGVR in sera, respectively.

The L_F3-4 values showed significant difference in CRC cases compared with controls, and yielded a specificity of 100%, leading to correct classification of 56 (93%) out of 60 CRC patients, including 12 (92.3%) of 13 CRC cases in stage I. Double-blind validation showed that 97.5% of CRC cases were discriminated accurately.

The L_F3-4 value was firstly verified to be a potential biomarker for CRC diagnosis, and may expand our view in underlying mechanisms for CRC.