Poster Presentation 7th Modern Solid Phase Peptide Synthesis & Its Applications Symposium 2019

Peptidomimetic PCNA inhibitors with defined 310-helical structure (#111)

Aimee J Horsfall 1 2 , Wioleta Kowalczyk 3 , Jordan Pederick 4 , Denis B Scanlon 1 , Andrew D Abell 1 2 , John B Bruning 4
  1. School of Physical Sciences, Institute of Photonics & Advanced Sensing, The University of Adelaide, Adelaide, South Australia, Australia
  2. The ARC Centre of Excellence for Nanoscale BioPhotonics (CNBP), Adelaide, South Australia, Australia
  3. CSIRO Manufacturing, Clayton South, Victoria, Australia
  4. The School of Biological Sciences, Institute of Photonics & Advanced Sensing, The University of Adelaide, Adelaide, South Australia, Australia

Proliferating Cell Nuclear Antigen (PCNA) mediates access of DNA-replication and -repair machinery to the replication fork. It is thus a prime target for the development of broad-spectrum cancer therapeutics. PCNA interacts with these proteins through a conserved motif referred to as the PCNA-Interacting Protein (PIP) box, defined as Qxxhxxaa [where Q is glutamine; ‘h’ is hydrophobic, ‘a’ is aromatic and ‘x’ is any amino-acid].1 p21 has the highest known affinity for PCNA and as such provides an optimum template for design of peptides with improved affinity and pharmacological profile.

Here we present three series of p21 peptide analogues synthesised by solid-phase peptide synthesis. The first series probes all p21 PIP-box positions through individual point mutations. This series details the tolerance of each position and highlights cooperative relationships within the PIP-box, such as hydrogen bonding pairs that enhance binding affinity.

The second series of peptides incorporates the PIP-box from twenty native partners into a standardised sequence. This study is the first to show direct impact of PIP-box sequence on PCNA affinity, without influence from the native flanking regions. We also show PIP-box sequences that naturally stabilise the 310-helix binding conformationhave enhanced PCNA binding affinity, despite consensus sequence divergence. This is supported by an analysis of literature co-crystal structures.2

We recently published the first constrained-peptide PCNA inhibitor with a six-atom lactam linker.3 This constrained p21 peptide has a stabilised 310-helix,as shown by NMR structural calculations, and affinity comparable to the native peptide; improved analogues are presented here. The third peptide series comprises of p21 peptide bis-thioether macrocycles, each with a stabilised 310-helix. All three series of p21 analogues demonstrate that stabilising the 310-helix can lead to enhanced PCNA binding affinity and allow accelerated development of new peptide-based broad-spectrum cancer therapeutics.

  1. 1. J. B. Bruning, Y. Shamoo, Structure 2004, 12, 2209-2219.
  2. 2. A. J. Horsfall, A. D. Abell, J. B. Bruning, ChemBioChem 2019, Submitted
  3. 3. K. L. Wegener, A. E. McGrath, N. E. Dixon, A. J. Oakley, D. B. Scanlon, A. D. Abell, J. Bruning, Chemistry - A European Journal 2018, 24, 11325-11331.