IMMUNOTARGETING OF STREPTAVIDIN TO THE PULMONARY ENDOTHELIUM

We have observed previously that monoclonal antibody to angiotensin-co nverting enzyme (Mab 9B9) accumulates selectively in the lung after in travenous injection. The objective of the present work is the developm ent of a universal system for targeting of drug or radiolabel to the l ung, using biotinylated Mab 9B9 and streptavidin. Methods: Mab 9B9 was biotinylated with biotin succinimide ester (b-Mab 9B9), while strepta vidin (SA) was radiolabeled with I-125. Interaction between b-Mab 9B9 and SA has been estimated in solid-phase radioassay. Radiolabeled SA w as conjugated with b-Mab 9B9 or with b-IgG and injected intravenously in rats or perfused in isolated rat lungs. Results: Radiolabeled b-Mab 9B9 biotinylated at biotin-to-antibody molar ratio 10 (b-Mab 9B9) ret ains its ability to accumulate in rat lungs after intravenous injectio n. Radiolabeled SA conjugated with b-Mab 9B9 accumulates in the lung t issue in perfused isolated rat lungs. About 20% of injected SA accumul ates in the rat lung 1 hr after intravenous injection (localization ra tio is 20, immunospecificity of the conjugate pulmonary uptake is 70). As compared with conjugate injection, stepwise intravenous injection of b-Mab 9B9 and radiolabeled SA leads to a marked reduction of SA pul monary uptake. Maximal pulmonary uptake of Mab 9B9 has been observed 2 -3 hr after intravenous injection, while 24 hr rater, radioactivity in the lung was markedly reduced. In contrast to radiolabeled Mab 9B9 al one, radiolabeled SA conjugated with b-Mab 9B9 was retained in the lun g for at least 48 hr. In concert with effective blood clearance of the conjugate, its prolonged lung retention leads to a marked increase in its lung-to-blood ratio: 80 for SA-b-Mab 9B9 versus 15-20 for Mab 9B9 . Conclusion: Conjugation of Mab 9B9 with streptavidin enhances select ive pulmonary uptake of the preparation, providing a background for in trapulmonary immunotargeting of various biotinylated agents.