Stabilization of Angiotensin-(1–7) by key substitution with a cyclic non-natural amino acid

Angiotensin-(1–7) [Ang-(1–7)], a heptapeptide hormone of the renin–angiotensin–aldosterone system, is a promising candidate as a treatment for cancer that reflects its anti-proliferative and anti-angiogenic properties. However, the peptide’s therapeutic potential is limited by the short half-life and low bioavailability resulting from rapid enzymatic metabolism by peptidases including angiotensin-converting enzyme (ACE) and dipeptidyl peptidase 3 (DPP 3). We report the facile assembly of three novel Ang-(1–7) analogues by solid-phase peptide synthesis which incorporates the cyclic non-natural δ-amino acid ACCA. The analogues containing the ACCA substitution at the site of ACE cleavage exhibit complete resistance to human ACE, while substitution at the DDP 3 cleavage site provided stability against DPP 3 hydrolysis. Furthermore, the analogues retain the anti-proliferative properties of Ang-(1–7) against the 4T1 and HT-1080 cancer cell lines. These results suggest that ACCA-substituted Ang-(1–7) analogues which show resistance against proteolytic degradation by peptidases known to hydrolyze the native heptapeptide may be novel therapeutics in the treatment of cancer.