Inflammation and Cancer The Significance of COX2

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Inflammation and CancerThe Significance of COX-2

• Dan Dixon

Dept. of Biological Sciences South Carolina
Cancer Center ddixon_at_biol.sc.edu
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Inflammation and Cancer
Inflammation is a critical component of tumor
progression

• Cancers can arise from sites of infection,
  chronic irritation and inflammation.
• A vital component of the tumor microenvironment
  are the inflammatory cells.
• Inflammation promotes the neoplastic processes
  involving proliferation, survival, and
  migration.
• Tumor cells have co-opted inflammatory signaling
  molecules and receptors.

Tumors act as wounds that fail to heal
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Historical Perspective

• In 1863, German physician Rudolf Virchow
  hypothesized that certain classes of irritants,
  together with the tissue injury and inflammation,
  promote enhanced cell proliferation.
• In 1918, Yamagiwa and Ichikawa, who showed that
  repeated painting of coal tar onto rabbits' ears
  causes carcinomas.

the worlds first man-made cancer on the ears of
a rabbit
Rudolf Virchow
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Time, Feb. 23, 2004
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Inflammation Overview

• In response to tissue injury, signals start and
  maintain a host response to heal the damage.
• This involves getting activated leukocytes
  (WBCs) to the proper damaged location.
• Adhesion molecules and integrins with their
  respective receptors/ligands modulate WBC rapid
  adhesion, activation of gene expression, and
  transmigration into the tissue.
• Expression of chemokines attract specific WBC
  populations and promote the natural progression
  of the inflammatory response.
• The normal inflammatory response associated
  with wound healing is self-limiting.
  Dysregulation of key steps leads to
  abnormalities pathogenesis neoplasia.

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Some of the Players

• Neutrophils (and eosinophils) The first cells
  recruited to damaged tissues and invading
  bactera.
• Monocytes Chemotactic factors guide monocytes
  to the injury migrate into the site of injury.
• Macrophages Primarily stem from differentiated
  monocytes they are the main source of growth
  factors and cytokines. Their presence profoundly
  effects the surrounding microenvironment cells.
• Mast cells Release histamine, cytokines, and
  proteases let the body know something is wrong.
• Lymphocytes Provide firepower for the immune
  response.
• Platelets They aggregate to form a fibrin clot
  to close the wound.

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The Roles of Tumor-Associated Macrophages in
Tumor Progression

• Invasion Macrophages secrete a variety of
  proteases to breakdown the basement membrane
  around areas of proliferating tumor cells thereby
  prompting their escape into the surrounding
  stromal tissue.
• Angiogenesis In areas of tumor hypoxia,
  macrophages cooperate with tumor cells to induce
  a vascular supply for the area by up-regulating a
  number of angiogenic growth factors. These
  proangiogenic factors stimulate vascular
  endothelial cells in neighboring areas to migrate
  into new vessels for the tumor.
• Immunosuppression Macrophages secrete factors
  that suppress the anti-tumor functions of innate
  immune system.
• Metastasis Macrophages associated with tumor
  vessels secretes factors that guide tumor cells
  toward blood vessels where they then escape into
  the circulation. In the stromal compartment,
  macrophages secrete growth factors to stimulate
  tumor cell growth and motility.

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Chronic Inflammation is a Risk Factor for Cancer
Chronic Inflammation
Dysplasia
Ulcerative colitis (UC)
Adenocarcinoma

• Patients with UC have a 5 to 7-fold greater risk
  of getting colon cancer.
• UC persisting for 35-40 years increases the risk
  20-35.
• Colon cancer associated with IBD has the worst
  prognosis.
• Management with anti-inflammatory agents reduce
  incidence of cancer.

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Normal Colon
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Inflammatory Syndromes and Their Associated
Cancers
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Chronic Inflammation Promotes Tumor Development
Insulted stromal cells recruit activated
inflammatory cells
Activated monocyte/macrophages
Chronic activation promotes continued
inflammation, angiogenesis, and ECM remodeling
Inflammatory cells express factors that stimulate
cell growth and progression
Malignant conversion
Promotion
mutation
initiated epithelium
epithelial cells
benign
carcinoma
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Anti-Inflammatory Drugs as Chemotherapeutic Agents

• Aspirin and NSAIDs Aspirin and NSAIDs inhibit
  prostaglandin synthesis. Aspirin inhibits
  platelet aggregation. Flurbiprofin has
  anti-metastatic effects. NSAIDs promote
  apoptosis, interfere with cell-cycle progression,
  and stimulate immune surveillance.
• Anti-TNFa Antibodies Effective in controlling
  IBD. Regulates TNFa activity which promotes
  cytokine, chemokine, adhesions, MMPs, and
  pro-angiogenic activities.
• Adhesion Molecule Receptor Antagonists Cancer
  cells and tumors contain mucins and ligands for
  cell adhesion molecules. Blocking adhesion may
  alter metastasis.
• MMP Inhibitors MMPs can promote tumor growth
  and also attenuate growth.

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Cyclooxygenase and Arachidonic Acid Metabolism

• Arachidonic acid (AA) is a 20-carbon
  polyunsaturated fatty acid.
• AA is liberated from the membrane
  glycerophospholipids by phospholipases.
• 3 Major pathways convert AA into biologically
  active eicosanoids.
• Cyclooxygenase (COX) catalyses a key step in the
  formation of prostaglandins.

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Cellular Arachidonic Acid Metabolism
Prostaglandins
Leukotrienes
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Cyclooxygenase Activity is a Key Step in
Prostaglandin Synthesis
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Prostaglandin Regulate Physiological Functions
Prostaglandins are biologically active
phospholipid molecules that regulate many
physiological functions
Proper balance of prostaglandins are critical for
normal homeostasis
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Prostaglandin Signaling Mechanisms
Prostaglandins control cellular function through
G-coupled membrane receptors and nuclear
receptors
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Prostaglandin Signaling Promotes Cell Growth
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Prostaglandins Trigger Signal Transduction
Pathways Associated with Cancer Growth
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Increased PGE2 Promotes Many Facets of
Tumorigenesis
Metastasis Invasion
Vascular Angiogenesis
Reduced Apoptosis
MMP-2 ? MMP-9 ?
VEGF ?
BCL-2 ?
PGE2
PI3-K Activation
IL-10 ? IL-12 ?
Immune Suppression
Proliferation Motility
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Multiple COX Enzymes Exist in Cells
COX-1 Constitutively present COX-2 Inducible
isoform COX-3 Splice variant of COX-1
Feature COX-1 COX-2 Expression Constitutive
Inducible Protein Size 72 kDa 72/74 kDa Gene
Size 22 kb 8.3 kb mRNA size 2.7 kb 4.5
kb contains multiple AU-rich elements in
3UTR Localization ER, nuclear envelope ER,
nuclear envelope Cell Tissue Expression Platelet
s, stomach, kidney, Expressed in most cells or
tissues after stimulation with colon, most
tissues cytokines, growth factors, or tumor
promoters Gene Regulation Constitutive low-level
expression Immediate-early response gene, rapidly
transcribed, mRNA is rapidly degraded,
translation is controlled
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Differing Functions of COX-1 COX-2
Arachidonic Acid
COX-2 (inducible)
COX-1 (constitutive)

• Pathophysiology
• Inflammation, Pain
• Fever
• Cancer
• Morbus Alzheimer
• Ischemia (CNS)

• Homeostasis
• Stomach/GI protection
• Platelet aggregation
• Renal blood flow

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Evidence of a COX-2 Dependent Role in Neoplasia
Epidemiological Studies w Decreased risk of
CRC-associated deaths in aspirin users. w The
NSAID sulindac decreases the size and number of
polyps (FAP). w Prostaglandin levels are
increased in CR tumors. w Overexpression of
COX-2 detected in adenomas and adenocarcinomas. A
nimal Studies w Min mice and AOM-treated rats
have elevated COX-2 levels. w Sulindac and other
NSAIDs attenuate intestinal tumor and xenografted
cancer cell growth in mice. Cellular
Studies w Overexpression of COX-2 in epithelial
cells results in Decreased
apoptosis Angiogenesis (increased VEFG,
FGF, PDGF expression) Metastatic
potential (increased adhesion and MMP
expression) Genetic Model w Mice defective in
COX-2 have a dramatic reduction (86) in
colorectal polyp formation.
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COX-2 is Overexpressed in Colon Cancer
COX-2 protein staining in colon tumor
Normal colon epithelium
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COX-2 is Overexpressed in Multiple Components of
Cancer
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Increased COX-2 Increased Prostaglandins
COX-2-derived PGs promote cell growth,
proliferation, and angiogenic gene expression in
cells composing a tumor
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Genetic Removal of COX-2 Suppresses
Tumorigenesis
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Involvement of COX-2 in the Progression of Colon
Cancer
- COX-2
/- COX-2
COX-2
COX-2
Loss of COX-2 gene regulation
COX-2 overexpression
Increased PG levels
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NSAIDs A History of COX Inhibition

• BC Ancient Greeks and Romans used salicylate
  extracts derived from willow leaves as
  analgesics and antipyretics.
• Middle Ages Medicinal herb gardens featured
  salicylate containing wintergreen and
  meadowsweet plants.
• 1763 Edward Stone reported on use of willow
  bark powder as an anti-inflammatory.
• 1853 Von Gerhardt synthesizes a crude form of
  aspirin (acetylsalicyclic acid).
• 1860 Felix Hoffman working for Bayer
  synthesizes pure aspirin.
• 1949 The NSAID Phenylbutazone introduced.
• 1963 Indomethacin introduced.
• 1971 Vane and Piper demonstrated NSAIDs inhibit
  prostaglandin production.
• 1974 Ibuprofen introduced.
• 1976 Miyamoto et al purified the COX-1 enzyme.
• 1989 Simmons et al (and others) identified the
  COX-2 enzyme.
• 1999 The COXIBs Celebrex (celecoxib) and Vioxx
  (rofecoxib) introduced.

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Aspirin and NSAIDs

• NSAIDs have pain-relieving (analgesic) effects
  as well as effects of reducing inflammation and
  fever.
• NSAIDs are non-selective COX-1 and COX-2
  enzymatic inhibitors.
• Aspirin is an irreversible inhibitor of COX
  Other NSAIDs are reversible.
• Aspirin protects against CV disease NSAIDs are
  chemopreventive.
• Chronic NSAID use can lead to GI ulcers and
  renal problems.

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Long-Term Aspirin and NSAID Use Reduces The Risk
of Developing Colorectal Cancer
adapted from Thun et al, JNCI, 2002
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NSAIDs

• Non Steroidal Anti-Inflammatory Drugs (NSAIDs)
  are the oldest and most widely used drugs in
  human history.
• NSAIDs have pain-relieving (analgesic) effects
  as well as effects of reducing inflammation and
  fever.
• NSAIDs are non-selective COX-1 and COX-2
  enzymatic inhibitors.
• Chronic NSAID use reduces CRC risk 50 and
  reduce polyp size and number.
• Extended NSAID use can lead to GI ulcers and
  renal problems.

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COXIBs

• COX-2 inhibitors (COXIBs) are a special category
  of NSAIDs that target only COX-2 enzyme.
• Because they do not block the actions of the
  COX-1 enzyme, COXIBs generally have the
  side-effects of traditional NSAIDs.
• COXIBs reduce CRC polyp burden by 31 in colon
  cancer patients.
• COX-2 inhibitors also dont offer the same kind
  of protection against heart disease.

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 Purpose-designed selective inhibitors of COX-2
the COXIBs.
Although rofecoxib (Vioxx) has been withdrawn,
celecoxib (Celebrex) and valdecoxib (Bextra)
remain on the US market. Lumiracoxib and
etoricoxib remain under consideration by the FDA.
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Schematic depiction of the structural differences
between the substrate-binding channels of COX-1
and COX-2 that allowed the design of selective
inhibitors
Grosser, T. et al. J. Clin. Invest. 20061164-15
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COXIBs are Chemopreventive Agents
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NSAIDs and COXIBs Inhibit Tumorigenesis
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COXIBs are not without their problems
Summary of relevant trials examining CV events
associated with extended COXIB use
Study
Drug
Results
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Confirmed Cardiovascular Events with Extended
Vioxx Use
The APPROVe study compared Vioxx vs. placebo in
the prevention of colon cancer
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Where do we go from here?