Metabolism and Cancer

Bob Harris D-3034 Roudebush VA Medical Center988-4544raharris@iupui.edu

Fall 2010

Metabolism and Cancer

Objectives:1. Define and explain the Pasteur effect.2. Define and explain the Warburg effect.3. Define aerobic glycolysis.4. Give a biochemical explanation for why

cancer cells accumulate greater amounts 18F-fluorodeoxyglucose than normal cells.

5. Explain why the Warburg hypothesis for cancer is not considered correct.

Metabolism and Cancer

Objectives6. Explain what causes cancer.7. Describe how the metabolism of glucose in

cancer cells differs from normal cells.8. Describe how the metabolism of glutamine in

cancer cells differs from normal cells.9. What purpose does altered metabolism serve

in cancer cells? 10. List things that promote ROS production.11. List things that decrease ROS.

Metabolism and Cancer

Objectives12. Illustrate how mitochondria are involved in

ROS production. 13. Explain why uncouplers of oxidative

phosphorylation decrease ROS production.14. Discuss whether the difference in

metabolism is important for growth and survival of cancer cells.

15. Explain whether you think the metabolic difference between normal cells and cancer cells has therapeutic potential.

Normal cell metabolism

• Tight coupling of glucose to pyruvate and pyruvate to CO2 and H2O

Glucose 2 Pyruvate 6 CO2

O2

2 Lactate

Normal cell metabolism

• Tight coupling of glucose to pyruvate and of pyruvate to CO2 and H2O

Glucose 2 Pyruvate 6 CO2

2 Lactate

•Effect of Lack of O2

Normal cell metabolism

• Louis Pasteur: 1822-1895– Rates of fermentation are high

anaerobically but low aerobically

• Pasteur effect: inhibition of fermentation by oxygenGlucose 2 pyruvate

2 lactate

Normal cell metabolism

• Louis Pasteur: 1822-1895– Rates of fermentation are high

anaerobically but low aerobically

• Pasteur effect: inhibition of fermentation by oxygenGlucose 2 pyruvate

2 lactate

O26 CO2

Cancer Cell Metabolism

• Defective coupling of glucose to pyruvate and pyruvate to CO2 and H2O

• Cancer cells produce large amounts of lactate in the presence of oxygen

• Pasteur effect is defective in cancer cells

Metabolism and Cancer

• Otto Warburg: 1883-1970– Warburg effect: “Aerobic glycolysis”:

generation of lactate in the presence of oxygen

Glucose 2 pyruvate 6 CO2

• Effect of lack of O2

• “Dysfunctional mitochondria likely responsible”

2 lactate

O2

Is aerobic glycolysis an in vitro artifact?

18F-fluorodeoxyglucose

Positron emission tomography

Vander Heiden et al. Science

2009; 329: 1029

Metabolism and Cancer

• Otto Warburg:1930.– recognized Pasteur effect is defective in cancer– discovered cancer cells carry out aerobic

glycolysis (Warburg effect) – suggested “deficiencies in mitochondrial

oxidative metabolism is responsible”.– proposed “replacement of respiration by

fermentation is the primary cause of malignant cell transformation” (Warburg hypothesis)

– suggested “altered metabolism of cancer cells might provide a means to treat cancer”

Metabolism and Cancer

• The Warburg hypothesis (replacement of respiration by fermentation is the primary cause of cancer) is not correct

• Cancer is caused by mutations that:– inactivate tumor suppressor genes– activate proto-oncogenes

Why altered metabolism in cancer?

• Warburg was wrong about what causes cancer – but he discovered an intrinsic difference in metabolism between cancer cells and normal cells

• Are there other metabolic differences between normal and cancer cells?

• Is the difference important for growth and survival of cancer cells?

• Does the difference in metabolism between normal and cancer cells have therapeutic potential?

Glutamine metabolism also differs between normal and

cancer cells

Metabolism and Cancer

• The metabolism of glucose and glutamine by normal cells is very efficient. Primary end products are CO2, H2O, and ammonia (or urea). Maximum ATP yield per mole of glucose and glutamine is achieved.

• The metabolism of glucose and glutamine by cancer cells is very wasteful. Primary end products are CO2, H2O, lactate, pyruvate, alanine, and aspartate. Maximum ATP yield per mole of glucose and glutamine is not achieved.

What purpose does altered metabolism serve in cancer

cells?• Assures ATP synthesis when tumor outgrows its

oxygen supply• Assures supply of building blocks for proliferation and

growth• Creates space by starving neighboring cells for

nutrients• Release of acid lowers extracellular which favors tumor

invasion and suppresses immune effectors• Increases resistance to oxidative stress by promoting

NADPH production and reduction of glutathione• Reduces production of reactive oxygen species (ROS)

by mitochondria

Can normal cell metabolism cause cancer?

• Normal metabolism produces reactive oxygen species (ROS)

• ROS can induce cancer

Reactive oxygen species and cancer

• The good things about ROS– Second messenger in signal transduction– Kills bacteria that invade cells– Induces senescence and apoptosis

• The bad thing about ROS– High concentrations react with DNA

What increases ROS production and oxidative damage?

• Smoking• Chemicals (carcinogens)• UV radiation• Over eating

Production of ROS by mitochondria

Brownlee Diabetes 2005; 54: 1615

What decreases ROS?

• Uncoupling of oxidative phosphorylation• Enzymes that destroy superoxide

radicals and hydrogen peroxide• Caloric restriction• Warburg effect

Mechanisms responsible for Warburg effect

• Induction of glycolytic enzymes• Induction of pryuvate dehydrogenase kinases• Down regulation of mitochondrial enzymes

and decrease in the number of mitochondria

Multiple changes in gene expression are responsible for

aerobic glycolysis in cancer cells

• Inactivation of p53

• Activation of HIF-1

How “aerobic” glycolysis is increased in cancer cells

• Hypoxia induces HIF-1 which induces expression of glycolytic enzymes.

• Tumor suppressor p53, which normally maintains low concentration of F2,6P2

(activator of PFK1), is down regulated in cancer cells.

• HIF-1 induces expression of PDK1 which inhibits the pyruvate dehydrogenase complex, which inhibits pyruvate oxidation.

p53 reduces “aerobic” glycolysis

• p53 promotes transcription of TIGAR, a phosphatase, that hydrolyzes F2,6P2, a positive effector of PFK1.

• p53 promotes expression of the thiamine transporter. Greater uptake of thiamine increases cellular [TPP], which increases activities of the pyruvate dehydrogenase and -ketoglutarate dehydrogenase complexes.

P53 reduces “aerobic” glycolysis

• p53 increases activity of the cytochrome oxidase. Greater cytochrome oxidase promotes ATP production. Greater cellular ATP suppresses glycolysis at PFK1.

• p53 down regulates expression of PDK2. This increases pyruvate dehydrogenase complex which decreases the need to generate ATP by glycolysis and therefore decreases aerobic glycolysis.

p53 and Cancer

• Mutations in the p53 gene is the most common cause of cancer.

• Loss of p53 function in cancer cells causes greater glycolytic flux, reduced pyruvate oxidation, and reduced production of ATP by oxidative phosphorylation.

HIF-1 increases “aerobic” glycolysis

• HIF-1 increases glucose uptake by up regulating GLUT1 expression.

• HIF-1 increases glucose phosphorylation by up regulating hexokinase 2 expression.

• HIF-1 increases flux through PFK-1 by up regulating expression of the “hypoxia-inducible 6-PF-2-K/F-2,6-P2ase”, a form of this bifunctional enzyme in which the kinase moiety is activated by AMPK.

HIF-1 increases “aerobic” glycolysis

• HIF-1 up regulates expression of pyruvate kinase M2, aldolase A, enolase 1, and carbonic anhydrase IX.

• HIF-1 up regulates LDHA and the lactate transporter MCT4.

• HIF-1 up regulates expression of PDK1 and PDK3.

HIF-1, p53 and Cancer

• HIF-1 is activated in many cancers. • Increase in HIF-1 induces the same effects as

loss of p53 function, i.e. causes greater glycolytic flux, reduced pyruvate oxidation, and reduced production of ATP by oxidative phosphorylation.

• Therefore, because of increase in HIF-1 and decrease in p53, many tumors use “aerobic” glycolysis as their major energy pathway.

Activation of glycolysis and inhibition of the mitochondria in cancer

Glucose

Pyruvate

PDCAcetyl-CoA

CACCO2

ATPMitochondrion

Lactate― + H+

Tumor

Is the metabolic difference important for growth and survival of

cancer cells?Inhibitors of:• Hexokinase • Pyruvate kinase • LDH-A • Monocarboxylate translocase (MCT)• Pyruvate dehydrogenase kinase • Glutaminase

Does the metabolic difference have therapeutic

potential?Vander Heiden et al. Science 2009;

329: 1029