P53 is always present in cells but needs to be activated. Basically it's on standby to quickly kill cells in case there's DNA damage(very bad=cancer usually), so FOX helps keep it from killing healthy cells.
On a side note peptides tend to get a lot of scrutiny from drug companies/designers. Our bodies readily metabolize peptides, so drug stability/delivery issues are usually the kiss of death for peptide drugs.
Also, senescence is a good thing. Senescent cells don't actively divide, the alternative is mitotic cells that do divide. More divisions you have, more likely it is cancer forms. So as always, cancer and aging are inseparable and we're all doomed :)