Purpose: Integrin alpha(v)beta(3) and vascular endothelial growth factor receptor 2 (Flk-1) have been shown to be involved in tumor-induced angiogenesis. Selective targeting of upregulated alpha(v)beta(3) and Flk-1 on the neovasculature of tumors is a novel antiangiogenesis strategy for treating a wide variety of solid tumors. In the studies described here, we investigated the potential therapeutic efficacy of two three-component treatment regimens using two murine tumor models. Methods and Materials: The treatment regimens used nanoparticle (NP) based targeting agents radiolabeled with Y-90. The small molecule integrin antagonist (IA) 4-[2-(3,4,5,6-tetrahydropyrimidin-2-ylamino)ethoxy]benzoyl-2-(5)-aminoethylsulfonylamino-beta-alanine, which binds to the integrin a,,03, and a monoclonal antibody against murine Flk-1 (anti-Flk-1 MAb) were used to target the NPs. Murine tumor models K1735-M2 (melanoma) and CT-26 (colon adenocarcinoma) were used to evaluate the treatment efficacy. Results: In K1735-M2- and CT-26 tumors, a single treatment with IA-NP-Y-90 (14.2 mug/g IA, 5 or 6 muCi/g Y-90) caused a significant tumor growth delay compared to untreated control tumors, as well as tumors treated with IA, IA-NP, and NP-Y-90, respectively (p < 0.025, Wilcoxon test). In K1735-M2 tumors, a single treatment with anti-Flk-1 MAb-NP-Y-90 (0.36 mu g/g anti-Flk-1 MAb, 5 mu Ci/g Y-90) also caused a significant tumor growth delay (p < 0.05, Wilcoxon test) compared to untreated tumors, as well as tumors treated with anti-Flk-1 MAb, anti-Flk-1 MAb-NP, and conventional radioimmunotherapy with Y-90-labeled anti-Flk mAb. Anti-CD31 staining showed a marked decrease in vessel density in tumors treated with anti-Flk-1 MAb-NP-Y-90, which was associated with a high level of apoptotic death in these tumors, as shown by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. Conclusions: The present studies provide proof of principle that targeted radiotherapy works using different targeting agents on a nanoparticle, to target both the integrin alpha(v)beta(3) and the vascular endothelial growth factor receptor. These encouraging results demonstrate the potential therapeutic efficacy of the IA-NP-Y-90 and anti-Flk-1 MAb-(NPY)-Y-90-complexes as novel therapeutic agents for the treatment of a variety of tumor types. (C) 2004 Elsevier Inc.
