Inhibition of Intercellular Communication between Prostate Cancer Cells by A Specific Anti-STEAP-1 Single Chain Antibody

Six-Transmembrane epithelial antigen of the prostate-1 (STEAP-1) is present at the intercellular junctions of the secretory epithelium of prostate and is overexpressed in all steps of prostate cancer. STEAP-1 acts as a transporter protein or a putative channel between cancer cells while it has limited expression in normal human tissues. This protein has been suggested as an attractive target for prostate cancer immunotherapy.This study aimed at the development of a specific single chain fragment variable (scFv) antibody against STEAP-1 epitope and testing the inhibitory effect of the selected scFv antibody in blocking gap junctions between tumor cells.In the current study, a phage library was used and a specific scFv antibody was isolated against STEAP-1 epitope using panning process.PCR and DNA fingerprinting of the obtained clones demonstrated a dominant pattern of a specific clone. Binding of the selected scFv to the corresponding target on PC3 and LNCaP cell lines was tested using ELISA and flow cytometry techniques. The inhibitory effect of the selected scFv antibody in blocking gap junctions between the cells was tested using intercellular communication assay. The selected antibody reacted with the corresponding epitope in ELISA and bound to prostate cancer cells with an intensity of 44.6% (PC3 cells) and 73.4% (LNCap cells) as shown by FACS analysis. Intercellular communication assay indicated that dye transfer between the cells in PC3 and LNCaP cell lines treated with 1000 scFv/cell was significantly inhibited (80-90%).Our results suggested that the selected specific anti-STEAP1 scFv highly inhibited intercellular communication between prostate cancer cells and has the potential to be used as a new effective agent in prostate cancer immunotherapy.