Modulating Protein-Protein Interactions of the Mitotic Polo-like Kinases to Target Mutant KRAS

Ana J Narvaez,Suzan Ber,Alex Crooks,Amy Emery,Bryn Hardwick,Estrella Guarino Almeida,David J Huggins,David Perera,Meredith Roberts-Thomson,Roberta Azzarelli,Fiona E Hood,Ian A Prior,David W Walker,Richard Boyce,Robert G Boyle,Samuel P Barker,Christopher J Torrance,Grahame J Mckenzie,Ashok R Venkitaraman

doi:10.1016/j.chembiol.2017.07.009

Abstract

SummaryMutations activating KRAS underlie many forms of cancer, but are refractory to therapeutic targeting. Here, we develop Poloppin, an inhibitor of protein-protein interactions via the Polo-box domain (PBD) of the mitotic Polo-like kinases (PLKs), in monotherapeutic and combination strategies to target mutant KRAS. Poloppin engages its targets in biochemical and cellular assays, triggering mitotic arrest with defective chromosome congression. Poloppin kills cells expressing mutant KRAS, selectively enhancing death in mitosis. PLK1 or PLK4 depletion recapitulates these cellular effects, as does PBD overexpression, corroborating Poloppin's mechanism of action. An optimized analog with favorable pharmacokinetics, Poloppin-II, is effective against KRAS-expressing cancer xenografts. Poloppin resistance develops less readily than to an ATP-competitive PLK1 inhibitor; moreover, cross-sensitivity persists. Poloppin sensitizes mutant KRAS-expressing cells to clinical inhibitors of c-MET, opening opportunities for combination therapy. Our findings exemplify the utility of small molecules modulating the protein-protein interactions of PLKs to therapeutically target mutant KRAS-expressing cancers.

Highlights

Human Polo-like kinase 1 (PLK1) regulates multiple events that lead to accurate chromosome segregation during cell division
Genetic modulation of the pathway linking PLK1 to APC/C activation curtailed the proliferation of mutant KRAS G12D-expressing cancer cells, while ATP-competitive PLK1 inhibitors suppressed their growth as xenografts
Poloppin Sensitizes Mutant KRAS-Expressing Cells to Death in Mitosis Using live-cell imaging to track the fate of single wild-type HeLa cells exposed to Poloppin (Figure 4), we find that Poloppin exposure prolongs mitosis from an average of 60 to 100 min, and increases the frequency of aneuploid divisions to 38%, compared with 4% after DMSO treatment

Summary

Introduction

Human Polo-like kinase 1 (PLK1) regulates multiple events that lead to accurate chromosome segregation during cell division (reviewed in Bruinsma et al, 2012). It comprises an N-terminal kinase catalytic domain, and a C-terminal segment with tandem motifs that form the Polo-box domain (PBD). Homologous PBDs, in which key residues implicated in phosphopeptide substrate recognition are conserved, occur in the related human Polo-like kinases PLK2, PLK3, and PLK4 (reviewed in Archambault and Glover, 2009). PLK1’s essential role in mitosis, and its dysregulation in several different forms of human cancer, has prompted efforts to create small-molecule inhibitors (reviewed in Liu, 2015). Compounds that inhibit PBD binding to phosphopeptide substrates are reported to induce mitotic arrest and apoptosis in cancer cell lines at micromolar concentrations (Reindl et al, 2008; Scharow et al, 2015; Watanabe et al, 2009; Yuan et al, 2011); but several have recently been identified as non-specific protein alkylators (Archambault and Normandin, 2017)

Results

Discussion

Conclusion