Fig. 5

Ab fragment as an Ab lock for shielding antigen binding ability of specific Ab drugs. a Metz et al. constructed a trivalent bi-specific Ab by linking a disulfide-stabilized variable fragment (dsFv), which is specific against one antigen (e.g., c-Met), to the C-terminus of the heavy chain of a whole Ab (e.g., anti-HER3 Ab) with a one-armed protease substrate peptide (e.g., GPLGMLSQ, GPLGLWAQ and GPLGIAGQ for MMP-2 and MMP-9 or GGGRR for urokinase plasminogen activator (uPA)). In this design, the antigen binding ability of dsFv was sterically interfered with by the Fc portion of the front whole Ab until protease cleavage and reactivation of the dsFv activity. b Onuoha’s and Pai’s groups developed an activatable dual variable domain (aDVD) Ab by linking the dsFv from one Ab (e.g., anti-ICAM-1 Ab or anti-PSCA Ab) to the N-terminus of light and heavy chains of another Ab (e.g., anti-TNF-α Ab or anti-CTLA-4 Ab) with MMP-1- (PLGLWA) or MT-SP1-cleavable sequence (LSGRSDNH). The outer dsFv can significantly shield the antigen binding ability of the inner Ab and lead the aDVD to the disease site (e.g., tumor site), to be reactivated by disease-specific proteases and restore the antigen neutralizing ability of inner Ab drugs. Ab, antibody; HER3, human epidermal growth factor receptor 3; TNF-α, tumor necrosis factor α; MMP, matrix metalloproteinase; MT-SP1, activated membrane type-serine protease 1; ICAM-1, intercellular adhesion molecule 1; CTLA-4, cytotoxic T-lymphocyte-antigen 4