Enhanced 5-FU-mediated activation of p53-dependent nucleolar stress by MDM2/4 peptide inhibitors in colon cancer cells

Recent evidence suggest that the p53-dependent nucleolar stress induced by some anticancer drugs, such as 5-Fluorouracil (5-FU), might not be sufficient to produce cell cycle arrest and/or apoptosis, given the hyperactivation of MDM2 and MDM4, main inhibitors of the p53 activity. Besides, it has been recently discovered that the disruption of the MDM2/4 heterodimer produce a more efficient reactivation of p53. Pep3 is a 12-mer peptide able to reduce p53 ubiquitination, representing the only peptide inhibitor of the MDM2/4 complex known to date. In this study, we developed a library of Pep3 derivatives with sequence lengths ranging from 5- to 8-mer. Of note, the newly truncated peptides showed lower IC50 values than Pep3. We incorporated the most active peptides (VLP-13 and VLP-24), alone or in association with 5-FU, in biodegradable nanoparticles, and we analyzed their cytotoxicity against p53 proficient colon cancer cells. We found that the cytotoxic activity of VLP-24 was higher than VLP-13 both alone and in association with 5-FU. The combined treatment 5-FU/VLP-24 caused a significant unbalance of ribosomal RNA precursor levels associated to a strong increase of p53 expression levels triggering apoptosis. In conclusion, our data reveal VLP-24 as a promising molecule able to enhance 5-FU mediated activation of p53-dependent nucleolar stress.