TLR9 agonist acts by different mechanisms synergizing with bevacizumab in sensitive and cetuximab-resistant colon cancer xenografts.
Synthetic agonists of Toll-like receptor 9 (TLR9), a class of agents that induce specific immune response, exhibit antitumor activity and are currently being investigated in cancer patients. Intriguingly, their mechanisms of action on tumor growth and angiogenesis are still incompletely understood. We recently discovered that a synthetic agonist of TLR9, immune modulatory oligonucleotide (IMO), acts by impairing epidermal growth factor receptor (EGFR) signaling and potently synergizes with anti-EGFR antibody cetuximab in GEO human colon cancer xenografts, whereas it is ineffective in VEGF-overexpressing cetuximab-resistant GEO cetuximab-resistant (GEO-CR) tumors. VEGF is activated by EGFR, and its overexpression causes resistance to EGFR inhibitors. Therefore, we used IMO and the anti-VEGF antibody bevacizumab as tools to study IMO's role on EGFR and angiogenesis and to explore its therapeutic potential in GEO, LS174T, and GEO-CR cancer xenografts. We found that IMO enhances the antibody-dependent cell-mediated cytotoxicity (ADCC) activity of cetuximab, that bevacizumab has no ADCC, and IMO is unable to enhance it. Nevertheless, the IMO-plus-bevacizumab combination synergistically inhibits the growth of GEO and LS174T as well as of GEO-CR tumors, preceded by inhibition of signaling protein expression, microvessel formation, and human, but not murine, VEGF secretion. Moreover, IMO inhibited the growth, adhesion, migration, and capillary formation of VEGF-stimulated endothelial cells. The antitumor activity was irrespective of the TLR9 expression on tumor cells. These studies demonstrate that synthetic agonists of TLR9 interfere with growth and angiogenesis also by EGFR- and ADCC-independent mechanisms affecting endothelial cell functions and provide a strong rationale to combine IMO with bevacizumab and EGFR inhibitory drugs in colon cancer patients.
Damiano
Vincenzo
V
Departments of Endocrinologia e Oncologia Molecolare e Clinica, Università di Napoli Federico II, 80131 Napoli, Italy.
Caputo
Rosa
R
Garofalo
Sonia
S
Bianco
Roberto
R
Rosa
Roberta
R
Merola
Gerardina
G
Gelardi
Teresa
T
Racioppi
Luigi
L
Fontanini
Gabriella
G
De Placido
Sabino
S
Kandimalla
Ekambar R
ER
Agrawal
Sudhir
S
Ciardiello
Fortunato
F
Tortora
Giampaolo
G
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000627:therapeutic use* / Q000633:toxicity; D061067:Antibodies, Monoclonal, Humanized; D000068258:Bevacizumab; D002448:Cell Adhesion; D002465:Cell Movement; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D000068818:Cetuximab; D003110:Colonic Neoplasms / Q000188:drug therapy* / Q000276:immunology / Q000378:metabolism / Q000473:pathology*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D042783:Endothelial Cells / Q000166:cytology / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007167:Immunotherapy; D051379:Mice; D008807:Mice, Inbred BALB C; D009841:Oligonucleotides / Q000494:pharmacology; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D051217:Toll-Like Receptor 9 / Q000819:agonists* / Q000235:genetics / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D007166:Immunosuppressive Agents; D009841:Oligonucleotides; D051217:Toll-Like Receptor 9; D042461:Vascular Endothelial Growth Factor A; D000068258:Bevacizumab; D000068818:Cetuximab