CBIO 7: Cancer Metabolism Flashcards
1
Q
Observe the learning outcomes of this session
A
2
Q
Recap the hallmarks of cancer
A
3
Q
What building blocks do cancer cells need to divide?
What are they used for?
A
4
Q
What is cancer metabolism and why is it an emerging hallmark of cancer?
A
- Cancer cells must be able to adapt their metabolism to allow them to cope with their growth needs.
- Therefore, cancer cells have unique metabolic requirements.
- These metabolic changes can be regarded as being generic across multiple cancer types – therefore the alteration of metabolism in cancer could also be regarded as being an additional hallmark of cancer, or as an emerging hallmark of cancer.
5
Q
Why are cancer cells genetically reprogrammed to allow for improved cellular fitness?
A
- To provide a selective advantage during tumorigenesis.
- To support cell survival under stressful conditions.
- To allow cells to grow and proliferate at pathologically elevated levels.
6
Q
What are the three main types of alteration that occur in cancer cell metabolism?
When in cancer do these alterations occur?
A
- increased bioenergetics
- increased biosynthesis
- alteration in redox balance
These 3 pathways are closely interlinked.
Some activities become essential very early on in tumorigenesis as the primary tumour begins to experience nutrient limitations. Other changes occur later, as cells undergo metastasis.
7
Q
Give a recap on glycolysis
A
8
Q
Recap the TCA/Krebs Cycle
A
9
Q
Observe the overview of glycolysis and the TCA cycle
What happens after?
A
- The 2 carbon intermediate (acetyl-CoA) generated at the end of glycolysis is then fed into the TCA cycle to generate ATP and reducing equivalents (chemical species that transfer the equivalent of one electron in redox reactions, e.g. NADH).
- This happens in the mitochondria.
- The NADH are then used by the electron transport chain to generate ATP.
- This process requires oxygen (O2 - aerobic).
10
Q
Describe the oxygen requirement in normal and cancer cells
A
- normal:
- have good blood supply, which carries oxygen and nutrients
- tumours:
- grow very quickly and rapidly outgrow the blood supply that feeds them
- tumour cells can exist in a low nutrient and low oxygen environment
- ranging from 0-2% oxygen in the centre of solid tumours
- this is called hypoxia
11
Q
Describe tumour hypoxia
A
- Hypoxia occurs when cells are deprived of oxygen.
- Often in tumours when cells grow so rapidly they can outgrow the local blood supply - leaving regions of the tumour with oxygen concentrations significantly lower than in healthy tissues.
12
Q
What is HIF-1a?
How does it function?
A
- it is a transcription factor in mammalian cells that is part of the cell’s mechanism to detect and monitor levels of ambient oxygen
- The transcription factor HIF-1a responds to systemic oxygen levels.
- HIF-1a stability, localisation, and activity are affected by oxygen levels.
- Under normal oxygen (normoxic) conditions, the HIF-1a protein is targeted for degradation (left side panel).
- However, under low oxygen (hypoxia), HIF-1a protein degradation is prevented and levels accumulate.
- The HIF-1a transcription factor then binds DNA and activates hypoxia response genes (right side panel).
13
Q
Describe the metabolic adaptation of tumour cells that use the activation of hypoxia-inducible factor (HIF-1a)
A
- One metabolic adaptation that tumour cells use is the activation of hypoxia inducible factor (or HIF-1a).
- HIF-1a is a transcription factor that is activated at low oxygen levels and is known to increase the levels of more than 60 genes, including those encoding VEGF and erythropoietin (EPO) that are involved in processes such as angiogenesis (new blood vessel growth) and erythropoiesis (red blood cell production), which assist in promoting and increasing oxygen delivery to hypoxic regions.
- HIF-1a also induces transcription of genes involved in cell survival, as well as glucose and iron metabolism.
- The activation of HIF-1a increases the use of glucose via glycolysis.
- The advantage of this is that oxygen is not required for glycolysis, and the cell can produce energy very quickly.
- It can metabolise glucose to lactate producing rapid amounts of ATP and NADH.
- The lactate is released from the cell, again helped by HIF-1a-regulated genes, into the local environment.
14
Q
Describe what happens when low oxygen levels activate HIF-1a transcription factor
A
- Low oxygen levels in cells can activate the HIF-1a transcription factor, which activates several genes, including those involved in glycolysis.
- This can result in increased glucose flux and increased amounts of waste products in the form of lactate, which is actively excreted from the cell.
15
Q
Why do tumour cells have a lower extracellular pH?
How does this have a survival advantage?
A
- Tumour cells often have a lower extracellular pH as a result of lactic acid export.
- This lowered pH may confer a survival advantage for cancer cells
i) it can inhibit cytotoxic T lymphocytes which helps tumour cells evade the immune system
ii) it helps activate enzymes required to digest local tissue for invasion, and
iii) it makes the local environment generally less favourable for normal cells.
16
Q
Give examples of how oncogene activation can cause cancer cells to drive forward glycolysis
A
- the activation of the oncogene MYC can upregulate genes involved in glucose uptake from the surroundings.
- The PI3kinase/Akt signalling axis can also stimulate glycolysis
17
Q
What is the overall tumour cell response to hypoxia?
A
- Therefore, as a response to hypoxia, tumour cells switch on adaptive mechanisms to increase energy production from glucose without the need for oxygen.
18
Q
What is the Warburg effect?
A
- also called aerobic glycolysis
- tumours take up large amount of glucose, compared to surrounding tissue
- additionally, glucose was fermented to produce lactate
- and importantly, tumours did this even in the presence of normal levels of oxygen
19
Q
What are the major advantages of aerobic glycolysis
A
- Cancer cells can live in conditions of varying oxygen levels (due to irregular functions of blood vessels) that would be harmful or lethal to normal cells that rely on oxidative phosphorylation to generate ATP.
- Glycolysis generates rapid amounts of NADH and ATP – this is not as efficient as the TCA cycle - but is faster and better suits their rapid growth.
20
Q
Why would tumour cells break down so much glucose?
A
- They need to obtain energy in the form of ATP & NADH.
- They need to obtain building blocks for biosynthesis.
21
Q
Summarise the Warburg effect
A
- It is an adaptation to a low-oxygen environment.
- It may be a consequence of genetic changes in cancer cells.
- It is a rapid mechanism for energy production.
- It may involve downregulation of mitochondrial activity in general (as they are involved in apoptosis – which cancer cells switch off).
- It may involve the generation of glycolytic intermediates for biosynthesis
22
Q
Why does the Warburg effect remain controversial?
A
- The Warburg effect remains controversial and partly unresolved - as it describes cancer cells wasting a lot of potential carbon-based intermediates via lactate production and secretion.
- Initially the Warburg effect was believed to be the cause of cancer, but recent evidence suggests it is a by-product of cancer.
23
Q
How does production of lactate from the Warburg Effect give cancer cells an advantage?
A
24
Q
What is anabolism and what do these reactions require?
A
- Anabolism is the set of metabolic pathways that construct molecules from smaller units.
- These reactions require energy.
- Anabolic reactions, such as lipid and nucleic acid biosynthesis, require NADPH as a reducing agent.
- The demands on the rapidly replicating cells are high as they need to synthesise large quantities of DNA, proteins and lipids.
25
Q
What are some biosynthetic pathways modified in cancer cells?
A
- pentose phosphate pathway:
- Glucose (6C) is taken and metabolised to a 5C sugar called ribose 5 phosphate.
- This pathway is extremely important for cancer cells as, firstly, it generates NADPH for further use in biosynthesis, and, secondly, it produces ribose, the sugar required for the backbone of DNA and RNA.
- hexosamine biosynthesis:
- Glucose is diverted from glycolysis and is converted to glucosamine and other modified carbohydrates.
- These are used as covalently bound structural groups attached to proteins to modify their properties.
- glycerol 3 phosphate pathway:
- The 3 carbon intermediates are used for the manufacture of glycerol which is an important step in the production of lipids.
- Fatty acids are esterified with glycerol to make lipids.
- serine/glycine biosynthesis:
- Simple amino acids can be manufactured from 3 carbon glycolysis intermediates e.g. serine and glycine.
26
Q
Describe how the pentose phosphate pathway is modified in cancer cells
A
- Glucose (6C) is taken and metabolised to a 5C sugar called ribose 5 phosphate.
- This pathway is extremely important for cancer cells as, firstly, it generates NADPH for further use in biosynthesis, and, secondly, it produces ribose, the sugar required for the backbone of DNA and RNA.
- Glucose is diverted along biosynthetic pathways to generate ribose for DNA and RNA.
27
Q
Describe how the hexosamine biosynthesis pathway is modified in cancer cells
A
- Glucose is diverted from glycolysis and is converted to glucosamine and other modified carbohydrates.
- These are used as covalently bound structural groups attached to proteins to modify their properties.
- Glycosylation of specific proteins is common in all cells.
- Many important cell surface receptors and cell-to-cell interacting proteins are glycosylated.
28
Q
Describe how the glycerol 3 phosphate pathway is modified in cancer cells
A
- The 3 carbon intermediates are used for the manufacture of glycerol which is an important step in the production of lipids.
- Fatty acids are esterified with glycerol to make lipids
- Three carbon glycolytic intermediates are taken for the production of glycerol 3-phosphate which is an essential component of lipid biosynthesis.
- Additionally, the fatty acids themselves are produced by pulling intermediates out of the TCA cycle for lipid biosynthesis.
29
Q
Describe how the serine/glycine biosynthesis pathway is modified in cancer cells
A
- Simple amino acids can be manufactured from 3 carbon glycolysis intermediates e.g. serine and glycine.
- Glucose and glutamine are used by cells to synthesise other amino acids e.g. serine and glycine, which are themselves used later for more complex amino acids.
30
Q
What is glutamine?
What is its function?
Why is it needed?
A
- glutamine is the major way in which nitrogen is transported between cells
- it is a major donor of nitrogen for several biosynthetic pathways, including
- amino acid synthesis
- glucosamine synthesis
- production of purine and pyrimidine bases for DNA
32
Q
Observe this diagram to summarise how cancer cells modify biosynthetic pathways
A
- In summary, cancer cells take intermediates from the glycolytic pathways and the TCA cycle intermediates to act as precursors for biosynthesis of many, if not all, cellular constituents.
- Intermediates of glycolysis (& from the TCA cycle) are taken and used for biosynthesis pathways.
- These pathways are frequently upregulated in cancer cells.
33
Q
Compare the differences in the metabolism and biosynthesis pathways between normal and cancer cells
A
35
Q
How do ROS arise?
A
- Reactive oxygen species (ROS) arise as a natural by-product of mitochondrial oxidative phosphorylation, oxygen metabolism and NADPH oxidase functions.
- Rapid cell growth can produce enough ROS to inflict serious damage on DNA, lipids and other cellular materials.
- Rapidly proliferating cells can have electron flux through the mitochondria that exceeds the capacity of the ATP synthase = resulting in ROS.
37
Q
What does glutathione do?
A
- Glutathione is used in the scavenging of free radicals and peroxides.
- Glutathione peroxidase uses glutathione to reduce the peroxide to water.
39
Q
How is NADPH important for dealing with ROS?
Where does the NADPH come from?
A
- NADPH is again very important in the recycling of enzymes and cofactors required to deal with ROS.
- The NADPH comes from pathways mentioned earlier e.g. the pentose phosphate pathway.
- Glutathione peroxidase uses glutathione to reduce (& detoxify) the peroxide to water.
- The enzyme also uses selenium in its active site.
- This is why selenium is considered to be an essential micronutrient and antioxidant.
- The cell must expend energy in the form of NADPH to reduce back the glutathione - for it to be used again to remove Reactive Oxygen Species (ROS).
40
Q
Describe the oncogene regulation of metabolic pathways
A
- Normal cells, upon stimulation to grow by growth factors, will activate downstream signalling pathways
– which will promote anabolic programmes e.g. increased glycolytic flux and fatty acid synthesis.
- Such pathways often involve proteins such as PI3kinase/AKT signalling, Ras, Myc and Src.
- For example, c-Myc increases the expression of the glucose transporters as well as glycolytic enzymes.
- It also upregulates splice variants of enzymes with increased glycolytic activities.
- C-Myc also interacts and inhibits the breakdown of HIF1a - see the previous section
42
Q
Describe how p53 is activated by ROS in cancer cells
A
- Normal Cellular Metabolism Produces Manageable Levels of ROS
- Efficient oxidative metabolism in normal cells produces low levels of ROS, which is dealt with via normal anti-oxidant pathways. - Altered Metabolism in Cancer Cells Cause Increased ROS and p53 Activation
- Fluctuating oxygen levels and increased metabolism causes increased ROS in cancer cells.
- The production of free radicals can damage cellular components e.g. DNA, and can rapidly activate the transcription factor p53.
- Along with halting the cell cycle and triggering apoptosis, p53 can inhibit glycolysis.
Summary: P53 is activated following damage caused by oxygen free radicals. P53 activates genes which downregulate glycolysis.
44
Q
Summarise the roles of oncogenes and tumour suppressors in cancer metabolism
A
- Oncogenes drive cell proliferation forward and stimulate glycolytic gene expression
- while tumour suppressors can reduce the expression of glycolytic genes
- however their protective functions are often lost in cancer
- The rapid proliferation and growth of cancer cells alters the cellular pools of metabolites and molecules that are required for various processes, including epigenetic control of gene expression.
- These processes directly impact or drive forward the tumorigenic process.
46
Q
What is the Reverse-Warburg Effect model?
A
- when the Warburg effect is not a=occurring in the cancer cell itself, but in surrounding cells
- cancer cells induce stress in neighbouring stromal cells
- stromal cells produce lactate
- and cancer cells use stromal cell lactate
- it’s a model, not yet accepted
47
Q
How do FDG-PET scans detect cancer?
A
- FDG-PET (fluorodeoxyglucose positron emission tomography) scans highlight metabolically-active tumours
- tumours that exhibit the Warbug effect
48
Q
What can you do with FDG-PET scans?
A
- monitor cancer location
- disease progression
- response
50
Q
How do we study metabolomics?
A
- using NMR metabolomics
55
Q
Describe this metabolism-related technique for cancer detection: Breath and sweat test
- Principle behind it
- Methods used for analysis
- Metabolites measured
- How useful is it in clinic?
A
- Volatile organic compounds emitted from the human body have been of interest to researchers e.g. butyric acid, hexanoic acid, butanal, decanal.
- Association with lung, bladder, and breast cancers
- Breath is analysed by ion flow tube mass spectrometry
56
Q
Describe this metabolism-related technique for cancer detection: sweat test for lung cancer
- Principle behind it
- Methods used for analysis
- Metabolites measured
- How useful is it in clinic?
A
- Sweat is analysed by ion flow tube mass spectrometry
-
60
Q
Describe how lonidamine targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
- Inhibits mitochondrial-bound hexokinase type II (HKII), reducing glucose phosphorylation and amounts of glucose intermediates.
- Also inhibits monocarboxylate transporters to reduce lactate. Can also inhibit downstream mitochondrial activity.
- Synergises with chemotherapy agents e.g. cisplatin, melphalan.
- Causes cell death by apoptosis.
- LND a derivative of indazole-3-carboxylic acid that inhibits aerobic glycolysis and energy metabolism in tumour cells.
- Can also inhibit the succinate-ubiquinone reductase activity of respiratory complex II, leading to enhanced formation of reactive oxygen species (ROS).
- Phase II and Phase III trials targeting lung cancer showed limited efficacy.
- Now they are targeting it to mitochondria (Mito-LND).
- MPC inhibition is the most sensitive anti-tumour target for LND, with additional inhibitory effects on MCT-mediated l-lactic acid efflux, Complex II and glutamine/glutamate oxidation.
- Mitochondrial pyruvate carrier (MPC) has highest affinity for lonidamine (LND).
- Followed by monocarboxylate transporters (MCTs)
- Inhibition of the MPC and MCTs is essential for lowering intracellular pH
- Inhibition of the MPC may suffice to produce tumour de-energization.
- De-energization also involves inhibition of the ETC (Electron Transport Chain).
61
Q
Describe how 3-bromopyruvate targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
- Is an inhibitor of several enzymes – hexokinase, GAPDH and pyruvate kinase.
- The molecule is a mimic of pyruvic acid and binds itself to the enzymatic active site thus inhibiting the enzyme.
- The effect is an inhibition and stoppage of the glycolytic pathway.
- This stops the production of ATP and energy for the cell.
- 3-BrPA enters tumour cells via MCTs, followed by the inhibition of glycolysis (e.g., HK-II, GAPDH, and 3-PGK), mitochondrial OXPHOS (e.g., PDH, SDH, IDH, and αKD), PPP (e.g., G6PDH), glutaminolysis (e.g., IDH and αKD), the MG pathway (e.g., glyoxylase I and II), HDACs, and H+-vacuolar ATPase, downregulation of G6PDH and direct conjugation with GSH, leading to the decrease of intracellular ATP, an increase in oxidative stress (e.g., ROS), inhibition of anabolic process (e.g., PPP), carbonyl stress (e.g., MG), and destabilization of liposome.
- Consequentially, 3-BrPA selectively induces cell death by apoptosis or necrosis, while normal cell remains unaffected.
62
Q
Describe how cariporide targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
- Cancer cells have a completely different acid-base balance compared to normal cells.
- Cancer cells may have a slightly increased alkaline conditions within the cells, whilst having an acidic extracellular environment.
- Cariporide is a selective Na+/H+ exchange inhibitor.
- Aerobic glycolysis implies excessive production of protons, which if inside cells results in fatal intracellular acidosis (maintaining a strict acid–base balance is essential for the survival of eukaryotic cells).
- Malignant cells solve this problem by increasing mechanisms of proton transport to expel the excess acidity.
- The proton excess expelled accumulates in the ECM, where chronic hypoxia and relative lack of blood vessels impedes proton clearance, creating an acidic microenvironment.
- Driven by membrane bound proton transporters, Na+/H+ exchangers, H+ ATPases, H+/Cl- symporter, and the monocarboxylate transporter (MCT).
- The Na+/H+ exchanger (NHE1) expressed in tumour cells contributes to metastasis, motility and resistance to chemotherapy.
- Inhibiting NHE1 with cariporide leads to cell growth arrest, acidification of the cellular cytoplasm and induced apoptosis.
- Despite the cardioprotective value of cariporide, use of the drug was associated with a significant increase in mortality (cerebrovascular events).
63
Q
Describe how enasidenib targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
- Inhibitor of mutated isocitrate dehydrogenase 2 (IDH2).
- The IDH enzymes normally metabolize isocitrate into α-ketoglutarate.
- When they are mutated in cancers, they also convert α-ketoglutarate into 2-hydroxyglutarate, an oncometabolite that causes cell differentiation defects by impairing histone demethylation.
- The neomorphic mutation in IDH generates an oncometabolite product, 2-hydroxyglutarate (2HG), which has been linked to the disruption of metabolic and epigenetic mechanisms responsible for cellular differentiation and is likely an early and critical contributor to oncogenesis.
64
Q
Describe how CB-839 targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
65
Q
Describe how TVB-2640 targets cancer metabolism
What is it?
What type of agent/molecule?
What does it target/site of action?
Explain its mechanism of action and effects on cancer cells
Has it been used clinically?
A
- Fatty acid synthase (FASN) is a multifunctional, homo-dimeric protein overexpressed by many solid and hematopoietic tumours, including non-small cell lung, breast, ovarian, prostate, colon, pancreatic cancers, and lymphoma.
- FASN tumour expression increases in a stage-dependent manner that is associated with diminished survival.
- TVB-2640 is a small molecule human FASN inhibitor that is the first highly selective FASN inhibitor to enter clinical studies.
- It has therapeutic potential in patients with NAFLD and no-nalcoholic steatohepatitis.
