Combination of 5-FU and MDM2/4 peptide inhibitors as a promising strategy to enhance 5-FU induced nucleolar stress.

The inactivation of tumor suppressor p53 is crucial for tumor onset and progression. Half of colorectal cancer cases carry wild-type p53 that is inactivated by the overexpression of MDM2 and MDM4, the main negative regulators of p53 activity [1]. Hence, the reactivation of p53 by inhibiting MDM2/4-p53 interaction represents a useful strategy to enhance the p53-depemdent cancer cell response to chemotherapeutic drugs. Recently, it has been demonstrated that 5-Fluoruracil (5-FU), the standard first-line treatment for colorectal cancer therapy, exerts its cytotoxic effect through the activation of p53-dependent nucleolar stress response [2]. It has been recently discovered that Pep3, a 12-mer peptide, is able to disrupt the MDM2/4 heterodimer producing a more efficient p53 reactivation [3]. In this study, we developed a library of sixteen Pep3 derivatives with sequence lengths ranging from 5- to 8-mer. Intriguingly, the newly truncated peptides displayed lower IC50 values than Pep3; among which the most active peptides were VLP-13 and VLP-24. We incorporated them, alone or in association with 5-FU, in novel biodegradable nanoparticles, and we analyzed their cytotoxic activity against p53 proficient colon cancer cells. We found that the cytotoxic activity of VLP-24 was higher than VLP-13 alone or in association with 5-FU. Notably, the combined treatment with 5-FU and VLP-24 caused a significant unbalance of ribosomal RNA precursor levels associated to a strong increase of p53 and p21 expression levels leading to the activation of apoptosis. In conclusion, our data demonstrate that VLP-24 is a promising strategy to enhance 5-FU mediated activation of p53-dependent nuclear stress response. [1] Liebl MC et al. Cancers (2021); 13, 2125. [2] Pecoraro A et al. Int J Mol Sci. (2021); 22, 5496. [3] Pellegrino M et al. Cancer Res. (2015); 75; 4560-72.