Epidermal growth factor receptor signaling is required for microadenoma formation in the mouse azoxymethane model of colonic carcinogenesis.
Colonic carcinogenesis involves the progressive dysregulation of homeostatic mechanisms that control growth. The epidermal growth factor (EGF) receptor (EGFR) regulates colonocyte growth and differentiation and is overexpressed in many human colon cancers. A requirement for EGFR in colonic premalignancy, however, has not been shown. In the current study, we used a specific EGFR antagonist, gefitinib, to investigate this role of the receptor in azoxymethane colonic premalignancy. The azoxymethane model shares many clinical, histologic, and molecular features of human colon cancer. Mice received azoxymethane i.p. (5 mg/kg/wk) or saline for 6 weeks. Animals were also gavaged with gefitinib (10 mg/kg body weight) or vehicle (DMSO) thrice weekly for 18 weeks, a dose schedule that inhibited normal receptor activation by exogenous EGF. Compared with control colonocytes [bromodeoxyuridine (BrdUrd), 2.2+/-1.2%], azoxymethane significantly increased proliferation (BrdUrd, 12.6+/-2.8%), whereas gefitinib inhibited this hyperproliferation (BrdUrd, 6.2+/-4.0%; <0.005). Azoxymethane significantly induced pro-transforming growth factor-alpha (6.4+/-1.3-fold) and increased phospho-(active) EGFR (5.9+/-1.1-fold), phospho-(active) ErbB2 (2.3+/-0.2-fold), and phospho-(active) extracellular signal-regulated kinase (3.3+/-0.4-fold) in premalignant colonocytes. Gefitinib inhibited activations of these kinases by >75% (P<0.05). Gefitinib also significantly reduced the number of large aberrant crypt foci and decreased the incidence of colonic microadenomas from 75% to 33% (P<0.05). Gefitinib concomitantly decreased cell cycle-regulating cyclin D1 and prostanoid biosynthetic enzyme cyclooxygenase-2 in microadenomas, suggesting that these regulators are key targets of EGFR in colonic carcinogenesis. These results show for the first time that EGFR signaling is required for early stages of colonic carcinogenesis. Our findings suggest, moreover, that inhibitors of EGFR might be useful in chemopreventive strategies in individuals at increased risk for colonic malignancies.
Fichera
Alessandro
A
Department of Medicine, University of Chicago, Chicago, Illinois 60637, USA.
Little
Nathaniel
N
Jagadeeswaran
Sujatha
S
Dougherty
Urszula
U
Sehdev
Amikar
A
Mustafi
Reba
R
Cerda
Sonia
S
Yuan
Weihua
W
Khare
Sharad
S
Tretiakova
Maria
M
Gong
Can
C
Tallerico
Michael
M
Cohen
Greg
G
Joseph
Loren
L
Hart
John
J
Turner
Jerrold R
JR
Bissonnette
Marc
M
D000236:Adenoma / Q000139:chemically induced / Q000201:enzymology* / Q000235:genetics / Q000517:prevention & control; D000818:Animals; D001397:Azoxymethane / Q000037:antagonists & inhibitors; D002273:Carcinogens; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000139:chemically induced / Q000201:enzymology* / Q000235:genetics / Q000517:prevention & control; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D051546:Cyclooxygenase 2 / Q000096:biosynthesis; D052246:Cyclooxygenase 2 Inhibitors / Q000494:pharmacology; D004195:Disease Models, Animal; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000077156:Gefitinib; D011905:Genes, ras / Q000187:drug effects; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D009154:Mutation / Q000187:drug effects; D011799:Quinazolines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D051176:beta Catenin / Q000096:biosynthesis / Q000235:genetics
D002273:Carcinogens; D052246:Cyclooxygenase 2 Inhibitors; D011799:Quinazolines; D051176:beta Catenin; D019938:Cyclin D1; D051546:Cyclooxygenase 2; D066246:ErbB Receptors; D001397:Azoxymethane; D000077156:Gefitinib