To date, a number of potential
biomarkers for lung
squamous cell cancer (SCC) have been identified; however, sensitive
biomarkers are currently lacking to detect early stage SCC due to low sensitivity and specificity. In the present study, we compared the 7 serum proteomic profiles of 11 SCC patients, 7
chronic obstructive pulmonary disease (
COPD) patients and 7 healthy smokers as controls to identify potential serum
biomarkers associated with SCC and
COPD. Two-dimensional difference gel electrophoresis (2D-DIGE) and mass-spectrometric analysis (MS) using an affinity column revealed two candidate
proteins,
haptoglobin (HP) and
apolipoprotein 4, as
biomarkers of SCC, and α-1-antichymotrypsin as a marker of
COPD. The iTRAQ technique was also used to identify SCC-specific
peptides. HP
protein expression was significantly higher in SCC patients than in
COPD patients. Furthermore, two HP
protein peptides showed significantly higher serum levels in SCC patients than in
COPD patients. We established novel polyclonal
antibodies for the two HP
peptides and subsequently a sandwich
enzyme-linked
immunosorbent assay (ELISA) for the quantification of these specific
peptides in patient and control sera. The sensitivity of detection by ELISA of one HP
peptide (HP216) was 70% of SCC patients, 40% of COPDs patients and 13% of healthy controls. We also measured CYFRA, a
cytokeratin fragment clinically used as an SCC
tumor marker, in all the 28 cases and found CYFRA was detected in only seven SCC cases. However, when the measurement of HP216 was combined with that of CYFRA, 100% (10 of 10 patients) of SCC cases were detected. Our proteomic profiling demonstrates that the SCC-specific HP
peptide HP216 may potentially be used as a diagnostic
biomarker for SCC.