Identification of autoantibodies to tumor-derived antigens as candidate biomarkers for the early detection of lung cancer

Proc Amer Assoc Cancer Res, Volume 46, 2005 4363 Identification of tumor-associated antigens that induce auto-antibodies may have utility as serum biomarkers for the early detection of lung cancer. We have used a proteomic approach to identify proteins that commonly induce a humoral response in lung cancer. In this study, aliquots of solubilized proteins from the lung adenocarcinoma cell line NCI-H522 were subjected to 2-D PAGE, followed by Western blot analysis in which sera of individual subjects were tested for primary antibodies. Sera from 21 newly diagnosed patients with lung cancer, 14 patients with chronic obstructive pulmonary disease (COPD), and 21 healthy subjects were analyzed. Replicate analysis of the same sera yielded similar patterns of reactivity with individual protein spots. The integrated intensity measurements of reactive protein spots were computed following gel normalization using a set of reference protein spots. We applied a non-parametric test statistic that counts the number of cancer patients with values larger than the second largest value in the control group for statistical analysis of the data. Auto-antibodies against three proteins, identified by tandem mass spectrometry as 60S acidic ribosomal protein P0 (RPLP0), proteosome subunit beta 7 (PSMB7), and protein gene product 9.5 (PGP 9.5) met our criteria and were each detected in sera from 8/21 (38.1%) patients with lung cancer (p=0.01). Fourteen of 21 (66.7%) lung cancer sera reacted with at least one of these three proteins. In-gel global phosphoprotein and glycoprotein staining patterns revealed that the antigenic form of RPLP0 was phosphorylated, but not glycosylated. The antigenic isoforms of PSMB7 and PGP9.5 were not phosphorylated or glycosylated. Analysis of mRNA expression in human lung adenocarcinoma revealed no expression differences of RPLP0 and PSMB7 in comparison of stage 1 and stage 3 tumors, as compared to normal lung. PGP9.5, on the other hand, was found to be 5-fold over-expressed in stage 1, and 10-fold over-expressed in stage 3 lung adenocarcinoma, as compared to normal lung. PGP9.5 was previously found to exhibit similar reactivity using A549 lung carcinoma lysates, whereas RPLP0 and PSMB7 represent novel antigens in lung adenocarcinoma. Our study identified novel proteins that induce auto-antibodies in lung cancer. The development of a panel of such antigens may have utility for the early diagnosis of lung cancer and may have utility for immunotherapy.