Overcoming the Lack of Oral Availability of Cyclic Hexapeptides: Design of a Selective and Orally Available Ligand for the Integrin αvβ3

We describe a systematic approach for the development of both orally bioavailable and bioactive cyclic N methylated hexapeptides as high affinity ligands for the integrin αvβ3. The work is based on two concepts: (a) screening of systematically designed libraries with spatial diversity and (b) masking of the peptide charge with lipophilic pro-moiety. The key steps of the method are i) initial design of combinatorial library of N-methylated analogs of the stem peptide cyclo(D Ala Ala5); ii) selection of cyclic peptides with highest intestinal permeability; iii) design of sub-libraries with the bioactive RGD sequence in all possible positions; iv) selection of the best ligands for RGD-recognizing integrin subtypes; v) fine tuning of affinity and selectivity by additional Ala to Xaa substitutions; vi) protection of the charged functional groups according to the pro drug concept to regain intestinal and oral permeability; vii) proof of biological effects in mice after oral administration