A series of anti-CEA/anti-DOTA bispecific antibody formats evaluated for pre-targeting: comparison of tumor uptake and blood clearance

Abstract

A series of anti-tumor/anti-chelate bispecific antibody formats were developed for pre-targeted radioimmunotherapy. Based on the anti-carcinoembryonic antigen humanized hT84.66-M5A monoclonal antibody and the anti-DOTA C8.2.5 scFv antibody fragment, this cognate series of bispecific antibodies were radioiodinated to determine their tumor targeting, biodistribution and pharmacokinetic properties in a mouse xenograft tumor model. The in vivo biodistribution studies showed that all the bispecific antibodies exhibited specific high tumor uptake but the tumor targeting was approximately one-half of the parental anti-CEA mAb due to faster blood clearance. Serum stability and FcRn studies showed no apparent reason for the faster blood clearance. A dual radiolabel biodistribution study revealed that the (111)In-DOTA bispecific antibody had increased liver and spleen uptake, not seen for the (125)I-version due to metabolism and release of the radioiodine from the cells. These data suggest increased clearance of the antibody fusion formats by the mononuclear phagocyte system. Importantly, a pre-targeted study showed specific tumor uptake of (177)Lu-DOTA and a tumor : blood ratio of 199 : 1. This pre-targeted radiotherapeutic and substantial reduction in the radioactive exposure to the bone marrow should enhance the therapeutic potential of RIT.

Aberrant bispecific antibody pharmacokinetics linked to liver sinusoidal endothelium clearance mechanism in cynomolgus monkeys

“…[7][8][9][10][11] However, there are more examples of aberrant pharmacokinetic observations for bispecific mAbs that are unexplainable, and not readily attributable to these 'other' mechanisms that can influence mAb disposition. [11][12][13][14][15][16][17][18] Since these inferior in vivo properties can limit the potential advantages offered pharmacologically, further study of factors influencing their disposition is critical to their successful development for therapeutic application. In addition, despite the increased emphasis on developing these more complex structures, there remains a substantial gap in understanding the factors in vivo that result in the aberrant peripheral clearance of some bispecific antibodies.…”

A systematic approach for analysis and characterization of mispairing in bispecific antibodies with asymmetric architecture

“…The third class of molecules are appended IgGs with symmetric architecture in which the second binding site is fused to either the IgG heavy or light chain in a symmetrical fashion. 12-15 …”

Characterization and analysis of scFv-IgG bispecific antibody size variants

“…24 Since then, the secondary binding site, often in an scFv format, has been fused to the C terminus/N terminus of the heavy chain, the hinge region, the C terminus/N terminus of the light chain, the CH3 domain of the heavy chain, or other regions. 25–27 …”