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Hypoxic Signaling and the Cellular Redox Tumor Environment Determine Sensitivity to MTH1 Inhibition
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Number of Authors: 13
2016 (English)In: Cancer Research, ISSN 0008-5472, E-ISSN 1538-7445, Vol. 76, no 8, p. 2366-2375Article in journal (Refereed) Published
Abstract [en]

Cancer cells are commonly in a state of redox imbalance that drives their growth and survival. To compensate for oxidative stress induced by the tumor redox environment, cancer cells upregulate specific nononcogenic addiction enzymes, such as MTH1 (NUDT1), which detoxifies oxidized nucleotides. Here, we show that increasing oxidative stress in nonmalignant cells induced their sensitization to the effects of MTH1 inhibition, whereas decreasing oxidative pressure in cancer cells protected against inhibition. Furthermore, we purified zebrafish MTH1 and solved the crystal structure of MTH1 bound to its inhibitor, highlighting the zebrafish as a relevant tool to study MTH1 biology. Delivery of 8-oxo-dGTP and 2-OH-dATP to zebrafish embryos was highly toxic in the absence of MTH1 activity. Moreover, chemically or genetically mimicking activated hypoxia signaling in zebrafish revealed that pathologic upregulation of the HIF1 alpha response, often observed in cancer and linked to poor prognosis, sensitized embryos to MTH1 inhibition. Using a transgenic zebrafish line, in which the cellular redox status can be monitored in vivo, we detected an increase in oxidative pressure upon activation of hypoxic signaling. Pretreatment with the antioxidant N-acetyl-L-cysteine protected embryos with activated hypoxia signaling against MTH1 inhibition, suggesting that the aberrant redox environment likely causes sensitization. In summary, MTH1 inhibition may offer a general approach to treat cancers characterized by deregulated hypoxia signaling or redox imbalance.

Place, publisher, year, edition, pages
2016. Vol. 76, no 8, p. 2366-2375
National Category
Biological Sciences
Research subject
Biochemistry
Identifiers
URN: urn:nbn:se:su:diva-130645DOI: 10.1158/0008-5472.CAN-15-2380ISI: 000374170700031OAI: oai:DiVA.org:su-130645DiVA: diva2:932698
Available from: 2016-06-02 Created: 2016-05-27 Last updated: 2018-01-08Bibliographically approved
In thesis
1. Structural and functional studies of proteins of medical relevance: Protein-ligand complexes in cancer and novel structural folds in bacteria
Open this publication in new window or tab >>Structural and functional studies of proteins of medical relevance: Protein-ligand complexes in cancer and novel structural folds in bacteria
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

X-ray crystallography is a tool for determining the structures of proteins and protein-ligand complexes. In this thesis the method has been employed to study several proteins of medical relevance.

Cancer is a terrible disease, severely impacting those affected, as well as their family and friends. Current cancer treatments involve a combination of cytostatic drugs, surgery and radiation treatment. Unfortunately many cytostatic drugs also kill healthy cells, which gives rise to serious side-effects. The discovery of treatments which selectively inhibit proteins essential for cancer cell survival but which are non-essential in normal cells, could reduce such side-effects.

MTH1 is a protein that degrades oxidised nucleotides, which when incorporated into DNA cause mutations and subsequent cell death. Cancer cells have higher levels of reactive oxygen species, which create oxidised nucleotides.  In Paper I it was discovered that cancer cells are dependent on MTH1 for their survival. Crystal structures of MTH1 in complex with small molecules guided their development into potent MTH1 inhibitors, capable of killing cancer cells. Cells with increased amounts of oxidised nucleotides, or with induced hypoxia, were more susceptible to MTH1 inhibition, as shown in Paper II. In Paper III several MTH1 orthologues from organisms often used in pre-clinical studies were tested for MTH1 inhibition. Leucine 116 of mouse MTH1 was determined to be important for the lower inhibition of the developed inhibitors towards this enzyme. A virtual fragment screening study using commercial chemicals resulted in several potent MTH1 inhibitors, as shown in Paper IV. The crystal structures with the fragments or optimised inhibitors did in most cases agree with the docking pose determined from the virtual screening. In addition to the known function of MTH1 in the degradation of oxidised nucleotides, Paper V showed that MTH1 also degrades methylated nucleotides.

MTHFD2 is responsible for providing one-carbon units for nucleotide synthesis in cancer cells. As MTHFD2 is present in cancer cells but not in healthy cells, targeting the enzyme would make it possible to selectively kill cancer cells. Paper VI presents the first structure of MTHFD2, along with the first inhibitor of the protein. This information provides a starting point for the development of potent and selective MTHFD2 inhibitors.

The botulinum neurotoxin from the bacterium Clostridium Botulinum is the causative agent of the deadly disease botulism. The action of the botulinum neurotoxin on nerve cells results in paralysis, and is life-threatening if the patient is not helped with breathing support. However, low doses of the neurotoxin are used as a successful treatment for several medical conditions, such as involuntary spasms. In Paper VII the structure of two proteins, P47 and OrfX2, encoded in the gene cluster of a botulinum neurotoxin, were determined. The structures resembled tubular lipid-binding proteins, previously only found in eukaryotes. The proteins were also found to be able to bind lipids. This work gives new insight into the structure and function of this group of proteins, which help the deadly botulinum neurotoxins.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2018. p. 79
Keyword
X-ray crystallography, Cancer, MTH1, oxidised nucleotides, MTHFD2, nucleotide metabolism, one-carbon metabolism, Botulism, Botulinum neurotoxin, OrfX, OrfX gene cluster
National Category
Biochemistry and Molecular Biology Structural Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:su:diva-150688 (URN)978-91-7797-097-2 (ISBN)978-91-7797-098-9 (ISBN)
Public defence
2018-02-16, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 5: Manuscript.

Available from: 2018-01-24 Created: 2018-01-02 Last updated: 2018-01-22Bibliographically approved

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