Vascular immunotargeting is a mean for a site-selective delivery of drugs and genes to endothelium. In this study, we compared recognition of pulmonary and systemic vessels in rats by candidate carrier monoclonal antibodies (MAbs) to endothelial antigens platelet endothelial cell adhesion molecule (PECAM)-1 (CD31), intercellular adhesion molecule (ICAM)-1 (CD54), Thy-1.1 (CD90.1), angiotensin-converting enzyme (ACE; CD143), and OX-43. Tissue immunostaining showed that endothelial cells were Thy-1.1 positive in capillaries but negative in large vessels. In the lung, anti-ACE MAb provided a positive staining in 100% capillaries vs. 5-20% capillaries in other organs. Other MAbs did not discriminate between pulmonary and systemic vessels. We determined tissue uptake after infusion of 1 microg of (125)I-labeled MAbs in isolated perfused lungs (IPL) or intravenously in intact rats. Uptake in IPL attained 46% of the injected dose (ID) of anti-Thy-1.1 and 20-25% ID of anti-ACE, anti-ICAM-1, and anti-OX-43 (vs. 0.5% ID of control IgG). However, after systemic injection at this dose, only anti-ACE MAb 9B9 displayed selective pulmonary uptake (16 vs. 1% ID/g in other organs). Anti-OX-43 displayed low pulmonary (0.5% ID/g) but significant splenic and cardiac uptake (7 and 2% ID/g). Anti-Thy-1.1 and anti-ICAM-1 displayed moderate pulmonary (4 and 6% ID/g, respectively) and high splenic and hepatic uptake (e.g., 18% ID/g of anti-Thy-1.1 in spleen). The lung-to-blood ratio was 5, 10, and 15 for anti-Thy-1.1, anti-ACE, and anti-ICAM-1, respectively. PECAM antibodies displayed low pulmonary uptake in perfusion (2% ID) and in vivo (3-4% ID/g). However, conjugation with streptavidin (SA) markedly augmented pulmonary uptake of anti-PECAM in perfusion (10-54% ID, depending on an antibody clone) and in vivo (up to 15% ID/g). Therefore, ACE-, Thy-1.1-, ICAM-1-, and SA-conjugated PECAM MAbs are candidate carriers for pulmonary targeting. ACE MAb offers a high selectivity of pulmonary targeting in vivo, likely because of a high content of ACE-positive capillaries in the lungs.

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Adenoviral (Ad) vectors are promising gene therapy vehicles due to their in vivo stability and efficiency, but their potential utility is compromised by their restricted tropism. Targeting strategies have been devised to improve the efficacy of these agents, but specific targeting following in vivo systemic administration of vector has not previously been demonstrated. The distinct aim of the current study was to determine whether an Ad-targeting strategy could maintain fidelity upon systemic vascular administration. We used a bispecific antibody to target Ad infection specifically to angiotensin-converting enzyme (ACE), which is preferentially expressed on pulmonary capillary endothelium and which may thus enable gene therapy for pulmonary vascular disease. Cell-specific gene delivery to ACE-expressing cells was first confirmed in vitro. Administration of retargeted vector complex via tail vein injection into rats resulted in at least a 20-fold increase in both Ad DNA localization and luciferase transgene expression in the lungs, compared to the untargeted vector. Furthermore, targeting led to reduced transgene expression in nontarget organs, especially the liver, where the reduction was over 80%. Immunohistochemical and immunoelectron microscopy analysis confirmed that the pulmonary transgene expression was specifically localized to endothelial cells. Enhancement of transgene expression in the lungs as a result of the ACE-targeting strategy was also confirmed using a new noninvasive imaging technique. This study shows that a retargeting approach can indeed specifically modify the gene delivery properties of an Ad vector given systemically and thus has encouraging implications for the further development of targetable, injectable Ad vectors.

We investigated the effects of the angiotensin-converting enzyme inhibitor captopril on neurologic outcome in a rat model of incomplete cerebral ischemia. Twenty male SpragueDawley rats were anesthetized with 70% nitrous oxide in oxygen and fentanyl (10/igxkg" 1 i.v. bolus, 25 /*gxkg~'xhr~1 i.v. continuous infusion). Animals in group 1 (n=10) received no angiotensin-converting enzyme inhibitor while animals in group 2 (n=10) were given 10 mgxkg" 1 i.v. captopril 30 minutes prior to the ischemic period. Ischemia was produced by unilateral carotid artery ligation and hemorrhagic hypotension to 35 mm Hg for 30 minutes. Body temperature, arterial blood gases, and arterial pH were maintained constant Neurologic outcome was evaluated every 24 hours for 3 days using a graded deficit score (0, normal; 18, stroke-related death). On the third day after ischemia, captopril significantly improved neurologic outcome (median deficit score=4) compared with controls (median deficit score=18) (p<0.05). These results suggest that reduced angjotensin II levels or increased tissue kinin concentrations may decrease ischemic brain injury. (Stroke 1991;22:910-914) C ontroversy exists on the influence of the brain renin-angiotensin system 12 in the modulation of cerebral ischemia. Studies in strokeprone spontaneously hypertensive rats and gerbils suggest that the administration of angiotensin-converting enzyme inhibitors reduce stroke-related mortality and neurologic symptoms. 34 In contrast, experiments on unilateral brain ischemia in gerbils demonstrate a reduction of stroke-related mortality in the presence of angiotensin II. 5 The protective effect of angiotensin II could be reversed using angiotensin-converting enzyme inhibitors or angiotensin II antagonists. 6 These results may be due in part to the cardiovascular effects of the drugs. The hypotensive effect of angiotensin-converting enzyme inhibitors may improve outcome from hypertensive stroke while angiotensin II may increase blood pressure and enhance cerebral perfusion during focal ischemia. We investigated the effect of the angiotensin-converting enzyme inhibitor captopril on neurologic outcome in a model of incomplete cerebral ischemia in rats.

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