Synthesis, in vitro, and in vivo characterization of an integrin α_vβ₃-targeted molecular probe for optical imaging of tumor

Integrin α_vβ₃ is a widely-recognized target for the development of targeted molecular probes for imaging pathological conditions. α_vβ₃ is a cell-surface receptor protein that is upregulated in various pathological conditions including osteoporosis, rheumatoid arthritis, macular degeneration, and cancer. The synthesis of an α_vβ₃-targeted optical probe 7 from compound 1, and its in vitro and in vivo characterization is described. A series of aliphatic carbamate derivatives of the potent non-peptide integrin antagonist 1 was synthesized and the binding affinity to α _vβ₃ was determined in both enzyme linked immunosorbent assay (ELISA) and cell adhesion inhibition assays. The hydrophobic carbamate-linked appendages improved the binding affinity of the parent compound for α_vβ₃ by 2-20 times. A Boc-protected neopentyl derivative in the series is shown to have the best binding affinity to α_vβ₃ (IC₅₀ = 0.72 nM) when compared to compound 1 as well as to c-RGDfV. Optical probe 7 utilizes the neopentyl linker and demonstrates increased binding affinity and significant tumor cell uptake in vitro as well as specific tumor accumulation and retention in vivo. These results illustrate the potential of employing integrin-targeted molecular probes based on 1 to image a multitude of diseases associated with α_vβ₃ overexpression.