Preface
Regulation of aberrant intracellular Protein-Protein Interactions (PPIs) is a promising
strategy for disease management. Constrained peptides that are fixed into a helical
conformation by chemical means are a representative molecular modality to modulate
PPIs. Many peptide stabilizing strategies have been established and been widely used
in the past decade. However, the correlation between peptides’ secondary structure
and their biophysical and biochemical properties remains elusive. The core question is how the secondary structure influences a peptide’s cell permeability, binding
affinity, and serum stability. To answer this question, the probable biggest obstacle
is a lack of a method to obtain peptide epimers that possess the same chemical
composition but distinct secondary structures.
To overcome this limitation, I designed a novel peptide stapling strategy, named
as “chiral center induced peptide helicity (CIH)”, for which the major feature is
the introduction of a precise chiral center in the peptide crosslinker. I found that
this precisely positioned carbon chiral center determines the secondary structure of
a peptide, and the R-configured chiral center induces a helical conformation while
the S-configured chiral center results in a random coil. Moreover, I proved that the
peptides with R-configuration chiral centers display enhanced cell permeabilities and
target binding affinities than the S-configuration chiral center counterpart peptides.
These results unambiguously demonstrate that helical conformation is good for the
pharmacological properties of stapled peptides. This CIH method also provides a
robust platform to investigate the relationship between peptide secondary structure
and bioactivities.
Harnessing the CIH method, I then developed peptide inhibitors targeting the p53
and MDM2/MDMX interactions, which is a typical PPI and has been demonstrated
a potential target for cancer intervention. I first designed a series of CIH peptides
with different in-tether substitution groups or peptide sequences, among which two
peptides, namely MeR and PhR, effectively restored the function of p53. The restoration of p53 function leads to cell proliferation inhibition and apoptosis induction in
multiple p53-wild type cancer cells, for instance, breast cancer cell line MCF-7 and
ovarian teratocarcinoma (PA-1) cancer cell line. Moreover, these peptides showed
little toxicity towards normal cells or cancer cell lines with mutated p53. The in vivo
vii
Regulation of aberrant intracellular Protein-Protein Interactions (PPIs) is a promising
strategy for disease management. Constrained peptides that are fixed into a helical
conformation by chemical means are a representative molecular modality to modulate
PPIs. Many peptide stabilizing strategies have been established and been widely used
in the past decade. However, the correlation between peptides’ secondary structure
and their biophysical and biochemical properties remains elusive. The core question is how the secondary structure influences a peptide’s cell permeability, binding
affinity, and serum stability. To answer this question, the probable biggest obstacle
is a lack of a method to obtain peptide epimers that possess the same chemical
composition but distinct secondary structures.
To overcome this limitation, I designed a novel peptide stapling strategy, named
as “chiral center induced peptide helicity (CIH)”, for which the major feature is
the introduction of a precise chiral center in the peptide crosslinker. I found that
this precisely positioned carbon chiral center determines the secondary structure of
a peptide, and the R-configured chiral center induces a helical conformation while
the S-configured chiral center results in a random coil. Moreover, I proved that the
peptides with R-configuration chiral centers display enhanced cell permeabilities and
target binding affinities than the S-configuration chiral center counterpart peptides.
These results unambiguously demonstrate that helical conformation is good for the
pharmacological properties of stapled peptides. This CIH method also provides a
robust platform to investigate the relationship between peptide secondary structure
and bioactivities.
Harnessing the CIH method, I then developed peptide inhibitors targeting the p53
and MDM2/MDMX interactions, which is a typical PPI and has been demonstrated
a potential target for cancer intervention. I first designed a series of CIH peptides
with different in-tether substitution groups or peptide sequences, among which two
peptides, namely MeR and PhR, effectively restored the function of p53. The restoration of p53 function leads to cell proliferation inhibition and apoptosis induction in
multiple p53-wild type cancer cells, for instance, breast cancer cell line MCF-7 and
ovarian teratocarcinoma (PA-1) cancer cell line. Moreover, these peptides showed
little toxicity towards normal cells or cancer cell lines with mutated p53. The in vivo
vii