Y. Hu et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1469–1471
1471
of p53 to MDM2. Potent oligomeric peptidomimetics have been re-
ported, including scaffolds based on peptoids,29,30 b-peptides,5,31,32
N-acylpolyamine,33 b-sheet cyclic peptides,34 etc. These oligomers
were able to project functional groups to occupy the positions of
those three critial residues of p53. Here AApeptides were designed
to bear either all or some of the three functional groups (Phe, Trp
and Leu), which were assumed to compete with Phe19, Trp23
and Leu26 of p53 and disrupt p53/MDM2 interaction. The other
functional groups were randomly chosen and introduced from car-
boxylic acids into AApeptides through the formation of tertiary
amide bonds. Indeed, the ELISA results show that AApeptide AA4
out systematic studies to probe structural requirements for AApep-
tides to adopt predicted conformations using 2D-NMR, Circular
Dichroism (CD) and X-ray crystallography. Optimization of
AApeptide sequences through rational design to achieve more
potent bioactivity towards p53/MDM2 and other proteins/nucleic
acids/carbohydrates interactions are also under investigation.
Acknowledgments
This work is supported by the start-up fund from University of
South Florida.
has an IC50 of 38 lM, which is only fourfold less active than the
wild-type p53-derived peptides,26 and comparable to several pre-
viously reported peptoids and b-peptides.29,35,36 As shown in Fig-
ure S1, the side chains of Phe, Trp and Leu of AA4 overlap very
well with those residues (Phe19, Trp23 and Leu26) in p53, which
are responsible for recognizing MDM2 in its binding cleft. Such
inhibition, on the other hand, may indicate that the AApeptides
are likely to adopt extended conformations when binding to
MDM2 as shown in the computer modeling results (Fig. S1). The
information will be very valuable for rational design of bioactive
and functional AApeptides in the future. Based on the ELISA results,
more potent AApeptide inhibitors should be obtained by introduc-
ing halogen atoms,26,29,32 restraining backbone to stabilize second-
ary structure, and carrying out further computer-aided design.
The AApeptides also exhibit excellent selectivity. AApeptide AA1
is a poor inhibitor of p53/MDM2 interaction, while AA2 and AA3 are
weaker inhibitors compared to AA4. Structure–activity relationship
(SAR) is consistent to previous reported studies.26 Phe, Typ and Leu
functionalities are necessary for strong binding, which are absent in
AA1 but present in all other sequences. Comparing AA2 to the same
length AApeptide AA1, the change of Leu into Val decreases the
activity at least 10-fold. Second, it seems longer sequences have
better activities, as seen for AA4 and AA2, possibly due to the higher
stability of the backbone conformations. Side chains that are not in-
volved in the recognition of MDM2 hydrophobic binding cleft also
play a very important role for the overall interactions, since AA3
and AA4 differ for only one residue. In AA3, the Phe0 side chain
may clash with the residues of MDM2 near the edge of the binding
domain, which probably increases its binding energy to MDM2. De-
tailed SAR study for sequences with a variety of lengths and distri-
bution of functional groups along the AApeptide backbone is
currently ongoing, which could further shed light on the rational
design of AApeptide library for drug discovery.
Supplementary data
Supplementary data (experimental details include AApeptide
building block and sequence synthesis, purification, characteriza-
tion, ELISA, CD, and assay for enzymatic hydrolysis) associated
with this article can be found, in the online version, at
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the enzymes.
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In conclusion, we have designed a new family of peptide mim-
ics-AApeptides and described a simple approach for their efficient
synthesis based on N-acylated-N-Fmoc-amino ethyl amino acid
building blocks. The potential of AApeptide diversification by
introducing a wide variety of side groups is substantial. The
preliminary results demonstrated their superior stability against
proteolysis, significant bioactivity and excellent selectivity toward
p53/MDM2 protein–protein interaction. The development of such
sequence-specific AApeptides may expand the applications of pep-
tidomimetics in the areas of biomedical and material sciences, such
as modulation of protein–protein interactions, and generation of
focused library for drug discovery, etc. We are currently carrying