A novel antibody–drug conjugate (ADC) was synthesized incorporating ferritin-based nanoparticles. An average of three molecules of monoclonal antibody (mAb) Ep1 to the human melanoma-specific antigen CSPG4 were conjugated to a single ferritin cage encapsulating about 50 cisplatin molecules (HFt–Pt–Ep1). The HFt–Pt–Ep1 nanoparticle had an estimated molecular size of about 900 kD and 33 nm, and flow cytometry demonstrated specific binding to a CSPG4⁺ melanoma cell line, but not to a CSPG4⁻ breast carcinoma cell line. As compared to the cisplatin-containing ferritin nanoparticle alone (HFt–Pt), which inhibited thymidine incorporation more efficiently in breast carcinoma than melanoma cells, the mAb-derivatized HFt–Pt–Ep1 nanoparticle had a 25-fold preference for the latter. A similar preference for melanoma was observed upon systemic intravenous administration of HFt–Pt–Ep1 to nude mice xenotransplanted with pre-established, palpable melanoma and breast carcinoma tumors. Thus, we have been able to determine precise combinations and stoichiometric relationships between mAbs and nanoparticle protein cages, whereby the latter lose their tropism for ubiquitously distributed cellular receptors, and acquire instead remarkably lineage-selective binding. HFt–Pt–Ep1 is therefore an interesting model to improve the therapeutic index of antiblastic therapy in a tumor such as melanoma, which at its advanced stages is totally refractory to mono- and combination-chemotherapy.

Vascular endothelial growth factor receptor-1 (VEGFR-1) is a tyrosine kinase receptor for several growth factors of the VEGF family. Endothelial cells express a membrane-spanning form of VEGFR-1 and secrete a soluble variant of the receptor comprising only the extracellular region. The role of this variant has not yet been completely defined. In this study, we report that the secreted VEGFR-1 is present within the extracellular matrix deposited by endothelial cells in culture, suggesting a possible involvement in endothelial cell adhesion and migration. In adhesion assays, VEGFR-1 extracellular region specifically promoted endothelial cell attachment. VEGFR-1-mediated cell adhesion was divalent cation-dependent, and inhibited by antibodies directed against the α5β1 integrin. Moreover, VEGFR-1 promoted endothelial cell migration, and this effect was inhibited by anti-α5β1 antibodies. Direct binding of VEGFR-1 to theα5β1 integrin was also detected. Finally, binding to VEGFR-1 initiated endothelial cell spreading. Altogether these results indicate that the soluble VEGFR-1 secreted by endothelial cells becomes a matrix-associated protein that is able to interact with the α5β1 integrin, suggesting a new role of VEGFR-1 in angiogenesis, in addition to growth factor binding.