Monoclonal antibody-mediated drug targeting to choroidal neovascularization in the rat

PURPOSE. Active drug targeting mediated by monoclonal antibodies (mAbs) of vascular endothelial cells in tumors is a new concept in cancer therapy. In tegrin alphav beta3 has been reported to be strongly expressed in vascular endothelial cells of surgically excised choroidal neovascular membranes and is thought to be a potential antigen for mAb-mediated drug targeting of ch oroidal neovascularization (CNV). The objective of this study was to evalua te the efficacy of drug targeting mediated by antiintegrin alphav beta3 mAb s in a laser-induced CN-V rat model. METHODS. The mitomycin C (MMC)-dextran (MMCD) conjugate was synthesized wit h a carbodiimide-catalyzed reaction. The mAb was conjugated with MMCD (MMCD -mAb). To evaluate the feasibility of mAb-mediated drug targeting in vitro, we investigated the effect of the immunoconjugates involving dextran-bindi ng MMC on the proliferation of human umbilical vein endothelial cells (HUVE Cs). CNV was induced by laser photocoagulation in male Brown Norway rats. I mmunolocalization of integrin alphav beta3 in CNV lesions was assessed immu nohistochemically with the anti-von Willebrand factor antibody as an endoth elial cell marker. Intravenous administration of saline (n = 7), 1 mg/day m Ab (n = 7), 100 mug/kg per day free MMC (n = 7), MMCD with irrelevant Ab (n = 7), unconjugated MMCD with unconjugated mAb (MMCD+mAb; n = 7), or MMCD w ith mAb (MMCD-mAb; n = 8) containing an equal amount of free MMC, was perfo rmed daily for 3 days from day 14 after CNV induction. CNV was assessed by fluorescein angiography 2 weeks after treatment. Fluorescein leakage was sc ored on a four-grade scale. The animals were killed 2 weeks after treatment , and the lesions were evaluated histologically. RESULTS. The inhibition of immunoconjugates on the proliferation of HUVECs was enhanced specifically by the mediatory effect of the mAb. Endothelial c ells demonstrated strong immunoreactivity of integrin alphav beta3 in the C NV. In the vehicle-treated group, fluorescein leakage equal to that before treatment was observed 2 weeks after treatment, with an average score of 2. 00 +/- 0.17 (mean +/- SEM). MMCD-mAb significantly inhibited the developmen t of CNV in rats (P < 0.01). Moreover, the thickness of the lesions was sig nificantly reduced in the MMCD-mAb-treated group (P < 0.01). CONCLUSIONS. Immunoconjugates effectively inhibited progression of CNV in t his model. The results suggest that mAb-mediated drug targeting may be bene ficial in the treatment of CNV.