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.
Subject(s)
Breast Neoplasms/metabolism , Cell Cycle Checkpoints , Cell Proliferation , Pyrimidines/biosynthesis , Ribosomes/metabolism , Tumor Suppressor Protein p53/deficiency , Animals , Antineoplastic Combined Chemotherapy Protocols/pharmacology , Breast Neoplasms/drug therapy , Breast Neoplasms/genetics , Breast Neoplasms/pathology , Cell Cycle Checkpoints/drug effects , Cell Proliferation/drug effects , Checkpoint Kinase 1/antagonists & inhibitors , Checkpoint Kinase 1/genetics , Checkpoint Kinase 1/metabolism , Dihydroorotate Dehydrogenase , Female , Gene Expression Regulation, Neoplastic , Genes, erbB-2 , HCT116 Cells , Humans , Leflunomide/pharmacology , MCF-7 Cells , Mice, Inbred BALB C , Mice, Inbred NOD , Mice, SCID , Mice, Transgenic , Oxidoreductases Acting on CH-CH Group Donors/antagonists & inhibitors , Oxidoreductases Acting on CH-CH Group Donors/genetics , Oxidoreductases Acting on CH-CH Group Donors/metabolism , Phenylurea Compounds/pharmacology , Protein Kinase Inhibitors/pharmacology , Pyrazines/pharmacology , Ribosomes/genetics , Signal Transduction , Tumor Suppressor Protein p53/geneticsABSTRACT
Cellular senescence is a form of cell cycle arrest that limits the proliferative potential of cells, including tumour cells. However, inability of immune cells to subsequently eliminate senescent cells from the organism may lead to tissue damage, inflammation, enhanced carcinogenesis and development of age-related diseases. We found that the anticancer agent mitochondria-targeted tamoxifen (MitoTam), unlike conventional anticancer agents, kills cancer cells without inducing senescence in vitro and in vivo. Surprisingly, it also selectively eliminates both malignant and non-cancerous senescent cells. In naturally aged mice treated with MitoTam for 4 weeks, we observed a significant decrease of senescence markers in all tested organs compared to non-treated animals. Mechanistically, we found that the susceptibility of senescent cells to MitoTam is linked to a very low expression level of adenine nucleotide translocase-2 (ANT2), inherent to the senescent phenotype. Restoration of ANT2 in senescent cells resulted in resistance to MitoTam, while its downregulation in non-senescent cells promoted their MitoTam-triggered elimination. Our study documents a novel, translationally intriguing role for an anticancer agent targeting mitochondria, that may result in a new strategy for the treatment of age-related diseases and senescence-associated pathologies.
Subject(s)
Adenine Nucleotide Translocator 2/metabolism , Antineoplastic Agents, Hormonal/pharmacology , Cellular Senescence/drug effects , Mitochondria/drug effects , Tamoxifen/pharmacology , Adenine Nucleotide Translocator 2/genetics , Animals , Apoptosis/drug effects , Apoptosis/genetics , Cell Proliferation/drug effects , Cell Survival/drug effects , Cell Survival/genetics , Gene Knockdown Techniques , Humans , MCF-7 Cells , Mice , Mice, Inbred NOD , Mice, SCID , Mice, Transgenic , Mitochondria/metabolism , Transfection , Xenograft Model Antitumor AssaysABSTRACT
Mitochondria and oxidative phosphorylation (OXPHOS) are emerging as intriguing targets for the efficient elimination of cancer cells. The specificity of this approach is aided by the capacity of non-proliferating non-cancerous cells to withstand oxidative insult induced by OXPHOS inhibition. Recently we discovered that mitochondrial targeting can also be employed to eliminate senescent cells, where it breaks the interplay between OXPHOS and ATP transporters that appear important for the maintenance of mitochondrial morphology and viability in the senescent setting. Hence, mitochondria/OXPHOS directed pharmacological interventions show promise in several clinically-relevant scenarios that call for selective removal of cancer and senescent cells.
Subject(s)
Cellular Senescence , Mitochondria/metabolism , Neoplasms/pathology , Adenosine Diphosphate/metabolism , Adenosine Triphosphate/metabolism , Biological Transport , Cell Death , Cell Proliferation , Humans , Neoplasms/metabolism , Oxidative Phosphorylation , Reactive Oxygen Species/metabolismABSTRACT
Cancer cells without mitochondrial DNA (mtDNA) do not form tumors unless they reconstitute oxidative phosphorylation (OXPHOS) by mitochondria acquired from host stroma. To understand why functional respiration is crucial for tumorigenesis, we used time-resolved analysis of tumor formation by mtDNA-depleted cells and genetic manipulations of OXPHOS. We show that pyrimidine biosynthesis dependent on respiration-linked dihydroorotate dehydrogenase (DHODH) is required to overcome cell-cycle arrest, while mitochondrial ATP generation is dispensable for tumorigenesis. Latent DHODH in mtDNA-deficient cells is fully activated with restoration of complex III/IV activity and coenzyme Q redox-cycling after mitochondrial transfer, or by introduction of an alternative oxidase. Further, deletion of DHODH interferes with tumor formation in cells with fully functional OXPHOS, while disruption of mitochondrial ATP synthase has little effect. Our results show that DHODH-driven pyrimidine biosynthesis is an essential pathway linking respiration to tumorigenesis, pointing to inhibitors of DHODH as potential anti-cancer agents.