Structure‐Activity Relationships of Conformationally Constrained Peptide Analogues of Loop 2 of Brain‐Derived Neurotrophic Factor

Abstract

Brain-derived neurotrophic factor (BDNF) promotes the survival of various neuronal populations and thus shows potential in the treatment of neurodegenerative disease. However, BDNF is not pharmacokinetically optimal for use as a therapeutic agent. As a step toward the development of low-molecular-weight BDNF-like drugs, we have designed a series of small, conformationally constrained peptides of various sizes using the threedimensional structure of BDNF derived by homology modeling as a template. When tested in cultures of embryonic chick sensory neurons the peptides produced concentration-dependent inhibition of BDNF-mediated neuronal survival and caused both a rightward shift and depression of the maximum of the BDNF concentrationresponse curve. The compounds had no effect on the survival response to nerve growth factor and were without intrinsic trophic or toxic effects when added to cultures alone. With the aid of pharmacodynamic simulations we demonstrated that the inhibitory activity of the active peptides is consistent with them acting as competitive antagonists of BDNF for its high-affinity receptor, trkB. An alanine scan of the largest peptide identified several residues important in mediating the inhibitory action of the peptides. We intend to use the data from these studies to develop small peptidic BDNF-like agonists.

Design of a Conformationally Defined and Proteolytically Stable Circular Mimetic of Brain-derived Neurotrophic Factor

“…For example, replacement of the residues of loop 2 from NGF with the corresponding residues from loop 2 of BDNF gives a molecule able to bind to and activate TrkB (16). In support of this, we have shown that monomeric monocyclic peptides designed to mimic a single loop 2 of BDNF act as antagonists of BDNF-mediated neuronal survival in culture (17). The x-ray crystal structure of the complex of NGF with one of the Ig domains of TrkA shows that residues from loop 1 of NGF make direct contact with the receptor (18).…”

“…The three sequential p75 NTR -binding residues in loop 4 of BDNF (Lys 94 -Lys 95 -Arg 96 ) were isolated from a model of the three-dimensional structure of BDNF derived via homology modeling techniques (17,23). Using visual examination, a wide range of means of constraining this tripeptide were explored, from which a selection were built by adding appropriate amino acid(s) to the tripeptide and forming a single bond between the N and C termini.…”

“…These well characterized cultures are known to contain a subpopulation of neurons that require exogenously added BDNF for their survival (17,33). Of the compounds examined, the circular pentapeptide 2 produced a robust concentration-dependent survival effect in these cultures ( Fig.…”

TDP6, a brain-derived neurotrophic factor-based trkB peptide mimetic, promotes oligodendrocyte myelination

“…TDP6 is a highly conformationally constrained tricyclic dimeric mimetic of the loop 2 region of BDNF that acts as a putative TrkB agonist (O'Leary and Hughes, 1998). We have previously shown that TDP6 is very potent in promoting sensory neuronal survival and that this is potentially mediated via TrkB signalling (O'Leary and Hughes, 2003).…”

Modified low molecular weight cyclic peptides as mimetics of BDNF with improved potency, proteolytic stability and transmembrane passage in vitro

“…The ability of synthetic peptides to promote neuronal survival was assessed in primary cultures of dorsal root ganglion (DRG) sensory neurons obtained from embryonic chicks using the method previously described by our laboratory, 7,9 which is based on the protocol first described by Barde and co-workers. 35 Peptides were examined in log 10 increments over the following ranges: Peptide 1: 1 Â 10 À10 to 1 Â 10 À5 M); peptides 2-6: 1 Â 10 À8 to 1 Â 10 À5 M; peptide 7: 1 Â 10 À8 to 1 Â 10 À5 M as well as from 1 Â 10 À10 to 1 Â 10 À5 M. Experiments were performed in triplicate, a total of three or four times.…”