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Inflammation and Cancer
The Significance of COX-2
Dan Dixon
Dept. of Biological Sciences
South Carolina Cancer Center
[email protected]
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
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.
Rudolf Virchow
the world’s first man-made cancer on the ears of a rabbit
Time, Feb. 23, 2004
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.
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.
eosinophil
 Macrophages: Primarily stem from differentiated monocytes;
they are the main source of growth factors and cytokines.
Their presence profoundly effects the surrounding
microenvironment cells.
platelets
neutrophil
 Mast cells: Release histamine, cytokines, and proteases; let
the body know something is wrong.
 Lymphocytes: Provide firepower for the immune response.
lymphocyte
Monocyte
 Platelets: They aggregate to form a fibrin clot to close the
wound.
Wound Healing: Normal tissues have a highly organized and segregated architecture. Epithelial
cells sit atop a basement membrane separated from the vascularized stromal (dermis)
compartment. Upon wounding or tissue assault, platelets are activated and form a haemostatic plug
where they release vasoactive mediators that regulate vascular permeability, influx of serum
fibrinogen, and formation of the fibrin clot. Chemotactic factors such as transforming growth factorand platelet-derived growth factor, derived from activated platelets, initiate granulation tissue
formation, activation of fibroblasts, and induction and activation of proteolytic enzymes necessary
for remodelling of the extracellular matrix (for example, matrix metalloproteinases and urokinasetype plasminogen activator). In combination, granulocytes, monocytes and fibroblasts are recruited,
the venous network restored, and re-epithelialization across the wound occurs. Epithelial and
stromal cell types engage in a reciprocal signalling dialogue to facilitate healing. Once the wound is
healed, the reciprocal signalling subsides.
Invasive Tumor Growth: Invasive carcinomas are less organized. Neoplasia-associated
angiogenesis and lymphangiogenesis produces a chaotic vascular organization of blood vessels
and lymphatics where neoplastic cells interact with other cell types (mesenchymal, haematopoietic
and lymphoid) and a remodelled extracellular matrix. Although the vascular network is not disrupted
in the same way during neoplastic progression as it is during wounding, many reciprocal
interactions occur in parallel. Neoplastic cells produce an array of cytokines and chemokines that
are mitogenic and/or chemoattractants for granulocytes, mast cells, monocytes/macrophages,
fibroblasts and endothelial cells. In addition, activated fibroblasts and infiltrating inflammatory cells
secrete proteolytic enzymes, cytokines and chemokines, which are mitogenic for neoplastic cells,
as well as endothelial cells involved in neoangiogenesis and lymphangiogenesis. These factors
potentiate tumour growth, stimulate angiogenesis, induce fibroblast migration and maturation, and
enable metastatic spread via engagement with either the venous or lymphatic networks.
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 upregulating 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.
Chronic Inflammation is a Risk Factor for Cancer
Ulcerative colitis (UC)
Chronic
Inflammation
Dysplasia
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.
Normal Colon
Ulcerative colitis
Colon
Adenocarcinoma
Inflammatory Syndromes and Their
Associated Cancers
Inflammatory bowel disease
Colorectal cancer
Gastric intestinal metaplasia
Gastric cancer
Barrett’s esophagus
Esophageal cancer
Chronic hepatitis
Hepatocellular carcinoma
Chronic pancreatitis
Pancreatic cancer
Oral leukoplasia
Head/neck cancer
Atypical adenomatous hyperplasia Non-small cell lung cancer
Ductal carcinoma in situ
Breast cancer
Prostatic intraepithelial neoplasia
Prostate cancer
Bladder dysplasia
Bladder cancer
Cervical dysplasia
Cervical cancer
Actinic keratoses
Skin cancer
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
epithelial cells
initiated epithelium
benign
carcinoma
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.
Cyclooxygenase and Arachidonic
Acid Metabolism
COOH
Arachidonic Acid
Cycloxygenase
Prostaglandins (PGs)
Thromboxanes (TXs)
Lipoxygenase
Leukotrienes (LTs)
Lipoxins (LXs)
Epoxygenase
Epoxy Acids (EETs)
Dihydroxy Acids
• 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.
Cellular Arachidonic Acid Metabolism
Leukotrienes
Prostaglandins
Cyclooxygenase
Activity is a Key
Step in
Prostaglandin
Synthesis
or
COX
Prostaglandin Regulate Physiological Functions
TxA2 PROMOTES
PLATELET AGGREGATION;
PGI2 INHIBITS IT
PGE2, PGFa, and PGI2
RELAX VASCULAR
SMOOTH MUSCLE
PGE2 and PGI2
INCREASE
RENAL BLOOD FLOW
PGE2 and PGI2
PROTECT
GASTRIC MUCOSA
PGE2 and PGI2
RELAX BRONCHIAL
SMOOTH MUSCLE;
PGFa CONTRACTS IT
PGE2 and PGFa
CONTRACT UTERINE
SMOOTH MUSCLE;
PGI2 RELAXES IT
Prostaglandins are
biologically active
phospholipid
molecules that
regulate many
physiological
functions
Proper balance of
prostaglandins are
critical for normal
homeostasis
Prostaglandin Signaling Mechanisms
Prostaglandins control
cellular function through
G-coupled membrane
receptors and nuclear
receptors
Prostaglandin Signaling
Promotes Cell Growth
Prostaglandins
Trigger Signal
Transduction
Pathways
Associated with
Cancer Growth
Increased PGE2 Promotes Many
Facets of Tumorigenesis
Vascular
Angiogenesis
VEGF 
IL-10 
IL-12 
Immune
Suppression
Metastasis
Invasion
MMP-2 
MMP-9 
PGE2
Reduced
Apoptosis
BCL-2 
PI3-K
Activation
Proliferation
Motility
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 3’UTR
Localization
ER, nuclear envelope
ER, nuclear envelope
Cell & Tissue Expression
Platelets, stomach, kidney,
colon, most tissues
Expressed in most cells or tissues after stimulation with
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
Differing Functions of COX-1 & COX-2
Arachidonic Acid
COX-1
(constitutive)
Homeostasis
• Stomach/GI protection
• Platelet aggregation
• Renal blood flow
COX-2
(inducible)
Pathophysiology
• Inflammation, Pain
• Fever
• Cancer
• Morbus Alzheimer
• Ischemia (CNS)
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.
Animal 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.
COX-2 is Overexpressed in Colon Cancer
COX-2 protein staining in colon tumor
Normal colon epithelium
COX-2 is
Overexpressed
in Multiple
Components of
Cancer
Increased COX-2 = Increased Prostaglandins
COX-2-derived PGs promote cell growth, proliferation, and
angiogenic gene expression in cells composing a tumor
COX-2 gene dosage effect on polyp number
(100%)
Total Polyp Number/Mouse
Genetic
“Removal” of
COX-2
Suppresses
Tumorigenesis
COX-2
COX-2
COX-2
(34%)
(14%)
COX-2
Genotype
Involvement of COX-2 in the Progression
of Colon Cancer
APC TGFß IIR
mutation hMSH
K-ras
mutation
p53
mutation
Normal
Epithelium
Carcinoma
Early Adenoma
- COX-2
+/- COX-2
Loss of COX-2
gene regulation
Late Adenoma
++ COX-2
COX-2
overexpression
+++ COX-2
Increased PG
levels
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.
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.
Long-Term Aspirin and NSAID Use Reduces
The Risk of Developing Colorectal Cancer
Kune 1988
Rosenberg 1991
Suh 1993, men
Suh 1993, women
Peleg 1994
Muscat 1994, men
Muscat 1994, women
Muller 1994
Reeves 1996
Bansal 1996
LaVecchia 1997
Rosenberg 1998
Friedman 1998
Coogen 2000A
Coogen 2000B
0
0.5
1
1.5
2
Relative Risk of Colorectal Cancer
adapted from Thun et al, JNCI, 2002
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.
Generic Name
Brand Names
Aspirin
Made by several companies
Ibuprofen
Motrin®, Advil®, Motrin IB®
Naproxen
Naprosyn®, Aleve®
Nabumetone
Relafen®
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 don’t offer the same kind of protection
against heart disease.
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.
Generic Name
Brand Names
Celecoxib
Celebrex®
Rofecoxib
Vioxx®
Valdecoxib
Bextra
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. 2006;116:4-15
COXIBs are Chemopreventive Agents
NSAIDs and COXIBs
Inhibit Tumorigenesis
COXIBs are not without their problems…
Summary of relevant trials examining CV events associated with extended COXIB use
Study
Drug
Results
Arthritis Studies
VIGOR
Vioxx
Vioxx associated w/higher risk of CV events
CLASS
Celebrex
No difference in CV events
APPROVe
Vioxx
2-fold increase risk of CV-events.
Vioxx removed from market.
APC
Celebrex
2.5-fold increase risk of CV-events.
FDA recommends limited use of Celebrex and Bextra.
PreSAP
Celebrex
No difference in CV events
Colon Cancer Studies
Confirmed Cardiovascular Events with
Extended Vioxx Use
The APPROVe study compared Vioxx vs. placebo in the prevention of colon cancer
After 18 months increases CV events were detected
and led to removal of Vioxx from the market.
Where do we go from here?
You can call your lawyer…
Or dust off the bottle of aspirin…