Specific Targeting of Human Integrin αvβ3 with 111In-Labeled Abegrin™ in Nude Mouse Models

The cell adhesion molecule integrin alpha(v)beta(3) is an important player in the process of tumor angiogenesis and metastasis. Abegrin (TM), a fully humanized anti-integrin alpha(v)beta(3) monoclonal antibody, was currently in clinical trials for cancer therapy. Herein, we labeled Abegrin (TM) with In-111, evaluated the in vitro and in vivo characteristics, and investigated whether the expression of integrin alpha(v)beta(3) in tumors could be imaged with In-111-labeled Abegrin (TM). The binding affinity and specificity of Abegrin (TM) was analyzed using U87MG glioblastoma cells. Abegrin (TM) was coupled with 1,4,7,10-tetraazadodecane-N,N',NaEuro(3),N'aEuro(3)-tetraacetic acid (DOTA) for In-111 radiolabeling. gamma Imaging of In-111-DOTA-Abegrin (TM) was carried out in nude mice bearing both integrin alpha(v)beta(3)-positive U87MG and integrin alpha(v)beta(3)-negative HT-29 tumors. Biodistribution and blocking studies of In-111-DOTA-Abegrin (TM) were investigated in U87MG tumor-bearing nude mice. Abegrin (TM) exhibited high-binding affinity to human integrin alpha(v)beta(3) expressed on U87MG cells (K (d) of 0.35 +/- 0.06 nM). The antibody retained antigen-binding affinity/specificity after DOTA conjugation. gamma Imaging showed that the tumor uptake of In-111-DOTA-Abegrin (TM) in integrin alpha(v)beta(3)-positive U87MG tumors was much higher than that in integrin alpha(v)beta(3)-negative HT-29 tumors. In the HT-29 tumors, Abegrin (TM) was mainly nonspecifically accumulated around the blood vessels, while in the U87MG tumors, besides the nonspecific tumor retention, Abegrin (TM) also specifically bound the human integrin alpha(v)beta(3) expressed on the tumor cells. Biodistribution and blocking studies exhibited that the U87MG tumor uptake of In-111-DOTA-Abegrin (TM) decreased from 14.12 +/- 0.44 to 6.93 +/- 0.94 percentage of injected dose per gram of tissue after coinjection of excess dose of cold Abegrin (TM), which confirmed the in vivo integrin alpha(v)beta(3) binding specificity of In-111-DOTA-Abegrin (TM). Abegrin (TM) showed specific binding to human integrin alpha(v)beta(3) expressed on the tumor cells. In-111-DOTA-Abegrin (TM) can specifically target the human integrin alpha(v)beta(3) expression in the nude mouse model. In-111-DOTA-Abegrin (TM) has a potential for clinical translation as an agent for integrin alpha(v)beta(3)-positive tumor imaging, evaluating tumor angiogenic status and monitoring the therapeutic efficacy of Abegrin (TM)-based cancer therapy.