Diminished Oligomerization in the Synthesis of New Anti-Angiogenic Cyclic Peptide Using Solution Instead of Solid-Phase Cyclization

The design and synthesis of novel peptides that inhibit angiogenesis is an important area for anti-angiogenic drug development. Cyclic and small peptides present several advantages for therapeutic application, including stability, solubility, increased bio-availability and lack of immune response in the host cell. We describe here the synthesis and biological evaluations of a new cyclic peptide analog of CBO-P11: cyclo(RIKPHE), designated herein as CBO-P23M, a hexamer peptide encompassing residues 82 to 86 of VEGF which are involved in the interaction with VEGF receptor-2. CBO-P23M was prepared using in solution cyclization, therefore reducing the peptide cyclodimerization occurred during solid-phase cyclization. The cyclic dimer of CBO-P23M, which was obtained as the main side product during synthesis of the corresponding monomer, was also isolated and investigated. Both peptides markedly reduce VEGF-A-induced phosphorylation of VEGFR-2 and Erk1/2. Moreover, they exhibit anti-angiogenic activity in an in vitro morphogenesis study. Therefore CBO-P23M and CBO-P23Mdimer appear as attractive candidates for the development of novel angiogenesis inhibitors for the treatment of cancer and other angiogenesis-related diseases.