Molecular Targeting with Peptides or Peptide-Polymer Conjugates: Just a Question of Size?

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   FIGURE 1.

   Factors influencing uptake of RGD-peptide-polymer conjugates: expression of αvβ3 integrins on tumor cells and vasculature (1), formation of clusters of activated αvβ3 integrins (2), enhanced permeability (3), impaired lymphatic drainage result in EPR (4), nonspecific tumor accumulation of peptide-polymer conjugates by EPR (5), nonspecific uptake in nontumor tissue (6), blood clearance (kinetics) (7), catabolism (8), and whole-body-retention and excretion kinetics (9).
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   FIGURE 2.

   Subsequent steps of integrin activation and multimeric RGD binding. FAK = focal adhesion kinase.
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   FIGURE 3.

   Selected characteristics of monovalent and polyvalent ligands and consequences for molecular targeting.