Replication and ribosomal stress induced by targeting pyrimidine synthesis and cellular checkpoints suppress p53-deficient tumors

Sona Hubackova,Jaromira Kovarova,Ana Coelho,Jiri Neuzil,Henrik J Ditzel,Jakub Rohlena,Stepana Boukalova,Martina Bajzikova,Mikkel G Terp,Eliska Davidova

doi:10.1038/s41419-020-2224-7

Abstract

p53-mutated tumors often exhibit increased resistance to standard chemotherapy and enhanced metastatic potential. Here we demonstrate that inhibition of dihydroorotate dehydrogenase (DHODH), a key enzyme of the de novo pyrimidine synthesis pathway, effectively decreases proliferation of cancer cells via induction of replication and ribosomal stress in a p53- and checkpoint kinase 1 (Chk1)-dependent manner. Mechanistically, a block in replication and ribosomal biogenesis result in p53 activation paralleled by accumulation of replication forks that activate the ataxia telangiectasia and Rad3-related kinase/Chk1 pathway, both of which lead to cell cycle arrest. Since in the absence of functional p53 the cell cycle arrest fully depends on Chk1, combined DHODH/Chk1 inhibition in p53-dysfunctional cancer cells induces aberrant cell cycle re-entry and erroneous mitosis, resulting in massive cell death. Combined DHODH/Chk1 inhibition effectively suppresses p53-mutated tumors and their metastasis, and therefore presents a promising therapeutic strategy for p53-mutated cancers.

Highlights

Mitochondria are essential organelles with fundamental role in cellular metabolism and energy homeostasis
Pyrimidine synthesis inhibition induces replication stress and cell cycle arrest Recently we showed that reactivation of dihydroorotate dehydrogenase (DHODH)
Transcriptome analysis of cell cycle regulators revealed that D0–D10 cells, which are auxotrophic for uridine due to the lack of DHODH-dependent pyrimidine biosynthesis, clustered separately from D15 to D25 cells featuring fully restored DHODH-dependent de novo pyrimidine synthesis[20] (Fig. 1a)

Summary

Introduction

Mitochondria are essential organelles with fundamental role in cellular metabolism and energy homeostasis. DHODH converts dihydroorotate (DHO) to orotate within the de novo pyrimidine synthesis pathway, generating electrons. Since constant replenishment of the pyrimidine pool from glutamine via UMP is required for replication of nuclear DNA and cell growth, dysfunction of DHODH may result in genomic instability[5], replication stress[6], and cell cycle arrest[7]. This is relevant for rapidly proliferating cancer cells that are not able to efficiently replenish their pyrimidine pool by salvage pathways and are ‘addicted’ to DHODH-dependent synthesis of pyrimidines. Several DHODH inhibitors have been shown to suppress proliferation and to induce cell death in various types of tumors[6,8,9]

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Results

Conclusion