86
3 In-Tether Chiral Center Induced Helical Peptide Modulators …
a period of 20 days after injection, the voluntary running cycles increased steadily
and no significant differences were found between these two groups, which indicates no obvious harmful effect to the motor learning ability of mice treated with
PhR peptide (Fig. 3.23). Histological analysis was performed to further evaluate the
toxicity of PhR in vivo. Major organs including the tumor, heart, liver, spleen, lung,
kidney, and brain tissue sections were harvested for hematoxylin and eosin (H&E)
staining to observe histological changes at 21 days after injection. The PhR group
had a more apparently tumor inhibition effect compared to other groups (Fig. 3.24).
Compared with the PBS-treated mice, no signs of organ lesions were observed in
the mice treated with PhR. Therefore, these in vivo toxicity assessments strongly
indicate PhR as a low-toxic and biocompatible modulator for cancer therapy.
3.3 Discussion and Conclusion
During the past decade, multiple strategies have been conceived with the specific
aim of destroying CSCs and their niche [47]. These include targeting specific surface
markers [48, 49], modulating signaling pathways [50], adjusting microenvironment
signals [51], inhibiting drug-efflux pumps [52], manipulating miRNA expression
[53], and inducing CSCs apoptosis and differentiation [54]. While these alternative
therapies are promising, some of them may not be specific and affect healthy tissue,
since the CSC niche is similar and located close to the normal stem cell niche, which
can also be affected by the compounds [55, 56]. There are also many ways by which
CSCs could evade treatment. The challenges to tackling CSCs include the improving
specificity and efficiency in targeting CSCs, avoiding toxicity to normal tissue stem
cells, and ensuring drug delivery and retention [48, 49].
Recently, we reported a CIH strategy that displays specific tunable characteristics
in the chiral center and thus allows us to switch the biophysical properties of the
peptides. We hypothesized that reactivating the p53 pathway in PA-1 cells, a wellaccepted model for studying cancer cell stemness, with peptides designed based on
the CIH concept would decrease their stemness and kill the cells. As a proof of
concept, we showed that inhibiting the interaction between p53 and MDM2/X can
inhibit the growth of stem-like cancer cells both in vitro and in vivo.
In summary, a potent dual peptide inhibitor based on the CIH concept was designed
to specifically target MDM2/X and could further induce p53-dependent apoptosis
and inhibit cell proliferation. Notably, the CIH strategy provides an ideal way to
obtain peptides with identical chemical compositions as controls instead of mutated
or scrambled control peptides used in all previous studies. The S PDI diastereomers
were used as controls for target binding affinity, cellular uptake, cell viability, cellcycle arrest, apoptosis induction, and protein/mRNA regulation. The results clearly
emphasize the decisive correlation between the peptides’ secondary structure and
their functions.
Although PhR showed comparatively weaker cellular activity than nutlin-3a in
cell assays, it exhibited superior in vivo efficacy within the pluripotency cancer
3 In-Tether Chiral Center Induced Helical Peptide Modulators …
a period of 20 days after injection, the voluntary running cycles increased steadily
and no significant differences were found between these two groups, which indicates no obvious harmful effect to the motor learning ability of mice treated with
PhR peptide (Fig. 3.23). Histological analysis was performed to further evaluate the
toxicity of PhR in vivo. Major organs including the tumor, heart, liver, spleen, lung,
kidney, and brain tissue sections were harvested for hematoxylin and eosin (H&E)
staining to observe histological changes at 21 days after injection. The PhR group
had a more apparently tumor inhibition effect compared to other groups (Fig. 3.24).
Compared with the PBS-treated mice, no signs of organ lesions were observed in
the mice treated with PhR. Therefore, these in vivo toxicity assessments strongly
indicate PhR as a low-toxic and biocompatible modulator for cancer therapy.
3.3 Discussion and Conclusion
During the past decade, multiple strategies have been conceived with the specific
aim of destroying CSCs and their niche [47]. These include targeting specific surface
markers [48, 49], modulating signaling pathways [50], adjusting microenvironment
signals [51], inhibiting drug-efflux pumps [52], manipulating miRNA expression
[53], and inducing CSCs apoptosis and differentiation [54]. While these alternative
therapies are promising, some of them may not be specific and affect healthy tissue,
since the CSC niche is similar and located close to the normal stem cell niche, which
can also be affected by the compounds [55, 56]. There are also many ways by which
CSCs could evade treatment. The challenges to tackling CSCs include the improving
specificity and efficiency in targeting CSCs, avoiding toxicity to normal tissue stem
cells, and ensuring drug delivery and retention [48, 49].
Recently, we reported a CIH strategy that displays specific tunable characteristics
in the chiral center and thus allows us to switch the biophysical properties of the
peptides. We hypothesized that reactivating the p53 pathway in PA-1 cells, a wellaccepted model for studying cancer cell stemness, with peptides designed based on
the CIH concept would decrease their stemness and kill the cells. As a proof of
concept, we showed that inhibiting the interaction between p53 and MDM2/X can
inhibit the growth of stem-like cancer cells both in vitro and in vivo.
In summary, a potent dual peptide inhibitor based on the CIH concept was designed
to specifically target MDM2/X and could further induce p53-dependent apoptosis
and inhibit cell proliferation. Notably, the CIH strategy provides an ideal way to
obtain peptides with identical chemical compositions as controls instead of mutated
or scrambled control peptides used in all previous studies. The S PDI diastereomers
were used as controls for target binding affinity, cellular uptake, cell viability, cellcycle arrest, apoptosis induction, and protein/mRNA regulation. The results clearly
emphasize the decisive correlation between the peptides’ secondary structure and
their functions.
Although PhR showed comparatively weaker cellular activity than nutlin-3a in
cell assays, it exhibited superior in vivo efficacy within the pluripotency cancer