Development of a human antibody fragment directed against the alpha folate receptor as a promising molecule for targeted application

Abstract

Alpha folate receptor (FRa) is currently under investigation as a target for the treatment of patients with non-small-cell lung cancer (NSCLC), since it is highly expressed in tumor cells but is largely absent in normal tissue. In this study, a novel human variable domain of a heavy-chain (VH) antibody fragment specific to FRa was enriched and selected by phage bio-planning. The positive phage clone (3A102 VH) specifically bound to FRa and also cross-reacted with FRb, as tested by ELISA. Clone 3A102 VH was then successfully expressed as a soluble protein in an E. coli shuffle strain. The obtained soluble 3A102 VH demonstrated a high affinity for FRa with affinity constants (K aff ) values around 7.77 ± 0.25 Â 10 7 M À1 , with specific binding against both FRa expressing NSCLC cells and NSCLC patient-derived primary cancer cells, as tested by cell ELISA. In addition, soluble 3A102 VH showed the potential desired property of a targeting molecule by being internalized into FRa-expressing cells, as observed by confocal microscopy. This study inspires the use of phage display to develop human VH antibody (Ab) fragments that might be well suited for drug targeted therapy of NSCLC and other FRapositive cancer cells.