Abstract 615: Novel Toll-like Receptor 9 (TLR9) agonist IMO inhibits tumor growth and cooperates with cetuximab in K-Ras mutant colon and pancreatic cancers

Abstract

Abstract Background. Somatic mutations in the K-Ras gene, leading to constitutive activation of the Ras/MAPK signalling cascade, represent a strong predictive biomarker for resistance to Epidermal Growth Factor Receptor (EGFR) inhibitors in colorectal and pancreatic cancer patients. We previously demonstrated that a novel Toll-like Receptor 9 (TLR9) agonist currently under clinical development, IMO, has a strong in vivo activity in colorectal cancer models interfering with EGFR-related signalling, synergizing with the anti-EGFR monoclonal antibody cetuximab and boosting its ADCC activity. Methods. In this study, we investigated IMO antitumor effect in colon and pancreatic cancer models with resistance to EGFR inhibitors due to K-Ras mutations. We evaluated the in vitro activity of IMO, alone or in combination with cetuximab, on growth, survival and EGFR-dependent signal transduction of cetuximab-sensitive and cetuximab-resistant colon and pancreatic cancer cells. We also investigated the antitumor effect of the combination IMO plus cetuximab on in vivo growth of orthotopically injected pancreatic cancer models. Results. We verified that K-Ras mutant colon and pancreatic cancer cell lines exhibit lower sensitivity to the anti-EGFR drugs cetuximab and erlotinib compared to K-Ras wild-type cell lines. IMO moderately inhibits in vitro growth of colon and pancreatic cancer cells, regardless of both TLR9 expression levels and K-Ras status. Surprisingly, IMO is able to partially restore cetuximab sensitivity of K-Ras mutant cancer cells. In fact, a strong inhibition of cell survival and a total suppression of MAPK phosphorylation/activation was observed with the combination IMO plus cetuximab in resistant cancer cells. IMO capability to interfere with EGFR-dependent signalling in K-Ras mutant, cetuximab-resistant cells seems to be related to modulation of a functional interaction between TLR9 and EGFR occurring at membrane level. The antitumor effect of the combination IMO plus cetuximab was confirmed also in vivo. In the luciferase- tagged AsPC1 (K-Rasmut) pancreatic cancer orthotopic model, IMO plus cetuximab causes a strong reduction of tumor burden and a significant increase in mice survival as compared to single agent treatments. Conclusion. We demonstrated for the first time that the TLR9 agonist IMO is effective in K-Ras mutant colon and pancreatic cancers, strongly inhibiting tumor growth and cooperating with cetuximab. This effect is due to multiple mechanisms of action, including interference with EGFR signalling by modulation of a TLR9/EGFR interaction and enhancement of cetuximab ADCC. Therefore, we suggest that IMO plus cetuximab may be a potentially effective therapeutic strategy for K-Ras mutant, cetuximab-resistant colorectal and pancreatic cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 615.