Sandwich immunoassay for evaluation of serum Kita-Kyushu Lung Cancer Antigen-1 as a potential diagnostic biomarker for gastric cancer.

BACKGROUND: Kita-Kyushu Lung Cancer Antigen-1 (KK-LC-1) has been proved to be highly expressed in gastric cancer. Nevertheless, no studies have yet investigated the expression levels of KK-LC-1 in the serum of patients with gastric cancer, its diagnostic potential, or its association with immune infiltration. METHODS: Designed Ankyrin Repeat Proteins (DARPins) that specifically target KK-LC-1 were identified through phage display screening. A method for quantifying KK-LC-1 concentration utilizing these DARPins was developed based on the sandwich immunoassay technique, and this method was employed to assess the expression levels of KK-LC-1 in serum samples from both gastric cancer patients and healthy donors. RESULTS: We found that compared to healthy donors, serum levels of KK-LC-1 were significantly elevated in gastric cancer patients and demonstrated a positive correlation with TNM stage, distant metastasis, conventional biomarkers, and tissue expression levels of KK-LC-1. Additionally, the expression levels of KK-LC-1 exhibited a negative correlation with the infiltration of various immune cell types. Furthermore, we have successfully developed a method for quantifying the concentration of KK-LC-1 protein and established a linear standard curve. CONCLUSIONS: KK-LC-1 has the potential to serve as a valuable diagnostic biomarker for gastric cancer and is correlated with immune cell infiltration.