Lesson 11 Genomic Instability, deregulated energetics

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• The material in this communication may be subject to copyright under the Act
• Brown text is examinable, grey text is just for your interest: not examinable
• Hanahan D, Weinberg RA: 'Hallmarks of cancer: the next generation'

  
• Hallmark 5: Genome instability and mutation

  • Mutagenic effect of DNA repair defects
  • Driver versus passenger mutations
  • BRCA1/2 and PARP in DNA repair
  • PARP inhibitors as anti-cancer drugs

  
• DNA damage and (mis)repair

  1. Many stimuli can damage DNA

  2. If the DNA is too damaged to be repaired, → apoptosis or cell cycle arrest

  3. Others perturb crucial pathways, leading to apoptosis

  4. Rarely, a gene involved in a cancer hallmark is mutated. Some of these mutations can give the cell cancerous properties. These are called "driver" mutations

  5. Selection leads to these predominating in cancers

  6. Our cells have multiple mechanisms that repair DNA damage. Some are accurate. Others are inaccurate – these can create mutations than are transmitted to daughter cells during mitosis

  7. Defects in accurate DNA repair pathways lead to cells acquiring numerous mutations

  8. Most mutations have no impact on cellular function, but some of these can provide neo-epitopes for immune attack

  
• Driver mutations

  • Due to selection, driver mutations would be expected to appear more frequently in tumours than other specific mutations
  • By surveying mutations in numerous tumours, researchers estimated the minimum number of mutations required to form cancers of various types
  • Across all cancers, several genes known to be involved in cancer hallmarks (some of which were mentioned in previous lectures) were frequently identified: eg p53, Ras, BRaf, Smad4
  • About half of the frequently mutated genes were not previously linked to cancer

  
• Ratio coding to non-coding changes
• Germline or somatic DNA repair defects


  Lead to mutations
• BRCA1/2 defects can lead to inaccurate DNA repair → cancer


  1. Single strand breaks can be accurately repaired by a complex involving PARP

  2. Double strand breaks, which can result from unrepaired single strand breaks, can be accurately repaired by a complex involving BRCA1 & 2

  3. Excessive double-strand breaks trigger apoptosis

  
• Inherited BRCA1/2 defects predispose to breast and ovarian cancer
• Of familial cases, about a quarter are due to inherited mutations in BRCA1 or 2
• These mutations increase the risk of breast (or ovarian) cancer a lot, especially when young
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• These cancers typically arise when the remaining wild type allele is mutated

  
• MED3ATA Cancer Module

  
• Some women who inherit these alleles have preventative surgery to remove breasts, ovaries
• Christine Hawkins
• Most breast (and ovarian) cancer is "sporadic"
• Lecture 11.2: Deregulating Cellular Energetics Hallmark
• PARP inhibitors preferentially target BRCA1/2 mutant cancer cells


  1. Some chemotherapy drugs can create single strand breaks

  2. If PARP inhibitors plus these drugs are given to a cancer patient, the single strand breaks cannot be repaired, and progress to form double strand breaks

  3. The patient's normal cells can repair these double strand breaks using BRCA-dependent processes, so toxicity is minimised

  4. Their cancer cells lack BRCA activity, so most die
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• Phase III trial data: PARP inhibitor for BRCA1/2 mutant breast cancer

  • PARP inhibitor
  • Placebo

  
• Warning: This material has been reproduced and communicated to you by or on behalf of La Trobe University under Section 113P of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further copying or communication of this material by you may be the subject of copyright protection under the Act. Do not remove this notice.
• Throughout these cancer lectures: Brown text is examinable, Grey text is just for your interest: not examinable
• Hanahan D, Weinberg RA. Hallmarks of cancer: the next generation. Cell. 2011;144:646-74.

  
• ATP production pathways

  • Aerobic glycolysis
  • Targeting aerobic glycolysis for cancer (ketogenic diets and 2DG)

  
• Normal cells

  • Glucose
  • Aerobic (high [oxygen])
  • 38 ATP
  • Lactate
  • Acetyl-CoA + CO2
  • CO2 + H2O
  • Pyruvate
  • Glycolysis
  • Citric acid cycle, OXPHOS
  • Anaerobic (low [oxygen])
  • 2 ATP

  
• Cancer cells

  • Glucose
  • Aerobic (high [oxygen])
  • 38 ATP
  • Lactate
  • Acetyl-CoA + CO2
  • CO2 + H2O
  • Pyruvate
  • Glycolysis
  • Citric acid cycle, OXPHOS
  • Anaerobic (low [oxygen])
  • 2 ATP
• How do cancer cells get enough energy? LOTS of ATP
• GLUT-1 (Glucose transporter) is upregulated in cancer cells

  
• PET (Positron Emission Tomography)


  Images tissue function, Radioactive tracer (usually 18FDG) is introduced into the body, Cells take up variable amounts of sugar, depending on metabolism. Tumour > normal, PET scanner detects radiation given off by the sugar
• Immunohistochemistry


  Slices of tissue on slide, Probe with antibody recognising GLUT-1, secondary antibody conjugated to fluorophore or enzyme that can produce coloured product or light
• Cancer detection exploiting aerobic glycolysis

  
• Hypotheses for why aerobic glycolysis benefits cancer cells

  • Adaptation to deal with defective mitochondria
  • Reduce oxidative stress
  • Increased lactate secretion lowers pH in tissue, promoting metastasis
  • Glycolysis yields raw materials for making new nucleotides, amino acids

  
• Hyperglycaemia is associated with increased risk for many cancers and poor outcomes
• Knockdown of GLUT1


  Reduces tumour growth in mice
• Inhibition of hexokinase by 2DG

  Reduces tumour growth in mice
• 2DG is tolerated by cancer patients, may reduce tumour growth
• Further work will be needed to exploit this hallmark for cancer therapy