Monoclonal antibodies to native mouse angiotensin-converting enzyme (CD143): ACE expression quantification, lung endothelial cell targeting and gene delivery.

We demonstrated previously that the monoclonal antibody 9B9 to angiotensin-converting enzyme (ACE), which accumulates very selectively into the rat lung after systemic injection, is a powerful tool for immunotargeting of therapeutic agents or genes to the rat lung vascular bed. Bearing in mind a high research and therapeutic potential of lung targeting via ACE, we obtained a new set of rat monoclonal antibodies to different epitopes of mouse ACE in order to expand this approach to mice. Nine new monoclonal antibodies, recognizing epitopes on the N- and C-domains of catalytically active mouse ACE, were obtained and examined for their efficacy to bind ACE both in vitro and in vivo. This set of monoclonal antibodies was proved to be useful for ACE quantification (by flow cytometry and cell enzyme-linked immunosorbent assay) on the surface of different mouse ACE-expressing cells: endothelial cells, monocytes, macrophages, dendritic cells and spermatozoa. Moreover, gene delivery into mouse ACE-expressing cells using adenoviruses increased 40-fold after redirecting of these viruses to ACE (by coating these viruses with anti-ACE monoclonal antibodies). Radiolabelled (I(125)) monoclonal antibodies specifically accumulated in the mouse lung after systemic injection. Monoclonal antibodies 3G8.17, 4B10.5 and 4B10.17 demonstrated the highest level of lung uptake, 40-50% of injected dose, and high selectivity of lung uptake. Influence of monoclonal antibodies on ACE shedding was negligible, except monoclonal antibody 1D10.11. None of the tested monoclonal antibodies inhibited ACE activity in vitro. In conclusion, a new set of rat monoclonal antibodies to mouse ACE was obtained suitable to study ACE biology in mice and for ACE expression quantification on mouse cells in particular. These monoclonal antibodies also demonstrated highly efficient and selective lung accumulation and thus has the potential for targeting drugs/genes to the pulmonary vasculature in different mouse models of human lung diseases, including numerous knockout models.