# Versatile enhancement of the killing potential of anti-cancer agents achieved by peptide mimetics of the PCNA interface towards specialized DNA polymerases

## TL;DR

A peptide that blocks specialized DNA polymerases improves cancer cell death from various treatments.

## Contribution

A novel peptide mimetic disrupts DNA polymerase activity to enhance chemotherapy effectiveness.

## Key findings

- PIR peptide displaces specialized DNA polymerases from replication sites.
- PIR peptide enhances cancer cell killing by DNA-damaging agents like cisplatin.
- Peptide also boosts cytotoxicity of non-DNA-damaging agents like Chk1 inhibitors.

## Abstract

Cancer cells that survive chemotherapy achieve full DNA duplication despite the accumulation of damaged DNA triggered by chemotherapy. This happens because the synthesis of DNA at damaged sites is granted by tolerance events including translesion DNA synthesis (TLS), a process that promotes the use of specialized DNA polymerases (S-Pols) for DNA synthesis. Such a crucial role of S-Pols in the promotion of damaged DNA replication prompted analyses of the cell killing effects of individual S-Pols inhibitors. Because S-Pols can compensate for each other, a global inhibition of S-Pols needs to be designed and tested. Given that S-Pols are recruited to the replisome through their PCNA binding motif, we reasoned that global displacement of S-Pols will occur when delivering a peptide with a strong PCNA binding motif. The cyclin kinase inhibitor p21 contains the strongest PCNA binding motif. Therefore, we designed a peptide representing this C-terminal, PCNA interacting region (PIR) of p21. As hypothesized by us, the PIR peptide achieved global S-Pol displacement from PCNA-associated replication factories and enhanced the cancer cell killing potential of DNA damaging agents including cisplatin, hydroxyurea, olaparib and UV irradiation. Demonstrating strong versatility, the peptide also enhanced the cytotoxicity caused by agents that do not directly provoke DNA damage such as Chk1, ATR and Wee1 inhibitors. In all cases, disrupting the PCNA binding site within the PIR peptide was sufficient to dismantle its cell killing potential. Strengthening the concept, a less potent PIR, namely derived from S-Pol eta, efficiently displaced S-Pols from replication factories exacerbating cell killing by all agents tested. These results collectively indicate that simultaneous displacement of S-Pols from PCNA can be enforced by excess levels of PIR peptides. This strategy is demonstrably valid to enhance the cancer cell killing by different DNA-damaging agents.