Trypanothione reductase inhibition and anti-leishmanial activity of all-hydrocarbon stapled α-helical peptides with improved proteolytic stability

Trypanothione reductase (TryR) is a well-established target in the search for novel antitrypanosomal and antileishmanial agents. We have previously identified linear and lactam-bridged 13-residue peptides derived from an α-helical region making up part of the dimeric interface of Leishmania infantum TryR (Li-TryR) which prevent trypanothione reduction by disrupting enzyme dimerization. We now show that i,i + 4 side-chain cross-linking with an all-hydrocarbon staple stabilizes the helical structure of these peptides and significantly improves their resistance to protease cleavage relative to previous linear and cyclic lactam analogues. Interestingly, replacement of the amide bridge by the hydrocarbon staple at the same cyclization positions generates derivatives (2 and 3) that similarly inhibit oxidoreductase activity of the enzyme but unexpectedly stabilize the TryR homodimer. The most proteolytically stable peptide 2 covalently linked to oligoarginines displayed potent in vitro leishmanicidal activity against L. infantum parasites. [Display omitted] •All-hydrocarbon stapled peptides were derived from the monomer-monomer interface of Li-TryR.•Li-TryR oxidoreductase activity was potently inhibited by these peptides.•Unexpected stabilization of the TryR homodimer was observed.•α-helicity and proteolytic stability were significantly increased relative to their linear counterparts.•Conjugation with cell-penetrating peptides resulted in leishmanicidal activity.