A Novel Toll-Like Receptor 9 Agonist Cooperates with Trastuzumab in Trastuzumab-Resistant Breast Tumors through Multiple Mechanisms of Action

Abstract

Purpose: Resistance to anti-HER2 monoclonal antibody trastuzumab is a relevant issue in breast cancer patients. Among the mechanisms implicated in trastuzumab resistance, increasing evidence supports a role of tumor microenvironment. We previously found that a novel toll-like receptor 9 agonist, referred to as immune modulatory oligonucleotide (IMO) and currently under clinical investigation, acts through epidermal growth factor receptor (EGFR) and shows direct antiangiogenic effects by cooperating with anti-EGFR or anti-VEGF drugs, thus interfering with cancer cells and microenvironment. Experimental Design: In this study, we used KPL-4 and JIMT-1 trastuzumab-resistant breast cancer cells to evaluate the combination IMO plus trastuzumab as a therapeutic option for trastuzumab-resistant breast cancers. Results: IMO inhibits KPL-4 and JIMT-1 xenografts growth and potentiates trastuzumab antitumor effect, with complete suppression of tumor growth, potent enhancement of trastuzumab-mediated antibody-dependent cell-mediated cytotoxicity, and strong inhibition of EGFR/HER2-related signaling. In KPL-4 xenografts, IMO alone interferes with HER signal transduction, whereas trastuzumab is ineffective. IMO induces an HERdependent signal inhibition also in vitro by modulating a functional interaction between toll-like receptor 9 and HER receptors occurring at membrane level. Finally, IMO plus trastuzumab produces a cooperative antiangiogenic effect related to suppression of endothelial HER-related signaling. Conclusions: We showed a cooperative effect of IMO plus trastuzumab in trastuzumabresistant breast cancers due to IMO direct antitumor and antiangiogenic activity and antibody-dependent cell-mediated cytotoxicity enhancement. Moreover, we provided first evidence of a toll-like receptor 9/HER interaction at membrane level as novel mechanism of action. Altogether, we propose IMO plus trastuzumab as an effective strategy in trastuzumab-resistant breast cancers. (Clin Cancer Res 2009;15(22):6921-30) The aberrant activity of HER2 signaling is associated with breast cancer development and progression, and ∼20% to 25% of invasive breast cancers exhibit overexpression of HER2. Because elevated HER2 levels are associated with reduced disease-free and overall survival in metastatic breast cancer, therapeutic strategies are being developed to target this oncoprotein (1). Trastuzumab, a recombinant humanized monoclonal antibody (mAb) directed against an extracellular region of HER2, was the first HER2-targeted therapy approved by the U.S. Food and Drug Administration for the treatment of HER2-overexpressing metastatic breast cancer. In addition, trastuzumab with adjuvant chemotherapy (either in sequence or in combination) significantly improved disease-free and overall survival rates in patients with early stage HER2-overexpressing breast cancer (2). However, despite the great Authors' Affiliations:

Toll-like Receptor 9 Agonist IMO Cooperates with Cetuximab in K-Ras Mutant Colorectal and Pancreatic Cancers

“…We have previously contributed to clarify some of these mechanisms showing that a TLR9 agonist, IMO, potentiates the ADCC activity of anti-EGFR mAb cetuximab (18) and anti-HER2 mAb trastuzumab (19) in in vivo models of colorectal and breast cancers, respectively. In addition to this immunomodulating function, we showed that IMO acts also by impairing EGFR signaling and potently synergizes in vivo both with cetuximab or EGFR TKI gefitinib in EGFR-addicted colorectal cancer models (20).…”

Toll-Like Receptors as Novel Therapeutic Targets for the Treatment of Pancreatic Cancer

“…The novel Toll-like receptor 9 (TLR9) agonist termed IMO, immune modulatory oligonucleotide, potentiates the anti-EGFR/HER2 signaling of monoclonal trastuzumab. It modulates a functional interaction between TLR9 and HER receptors at a membrane level, producing a cooperative antiangiogenic effect (Damiano et al, 2009). …”

“…Nevertheless, Grote et al and others (Chang et al, 2005;Spaner & Masellis, 2007;Damiano et al, 2009) suggest that future modulation of TLR signaling could be the basis for a therapeutic approach to cancer and inhibition or control of abnormal angiogenesis to limit tumor growth. However, this is potentially difficult because not only are there TLR-induced pro-angiogenic signals but also anti-angiogenic signals.…”

Trastuzumab-Resistance and Breast Cancer

“…Attenuation of FoxM1 expression either by small interfering RNA or by an alternate reading frame (ARF)-derived peptide inhibitor increased the sensitivity to trastuzumab (Carr et al, 2010). Damiano et al report that a novel toll-like receptor 9 agonist, which is also referred as the immune modulatory oligonucleotide (IMO), exerts antiangiogenic effects by cooperating with anti-EGFR or anti-VEGF antobodies, (Damiano et al, 2009). It was also shown that IMO and trastuzumab exert a cooperative antiangiogenic effect on trastuzumab-resistant breast cancer xenografts and that combining IMO and trastuzumab may be a potential strategy for the treatment of trastuzumab-resistant breast cancers (Damiano et al, 2009).…”

“…Damiano et al report that a novel toll-like receptor 9 agonist, which is also referred as the immune modulatory oligonucleotide (IMO), exerts antiangiogenic effects by cooperating with anti-EGFR or anti-VEGF antobodies, (Damiano et al, 2009). It was also shown that IMO and trastuzumab exert a cooperative antiangiogenic effect on trastuzumab-resistant breast cancer xenografts and that combining IMO and trastuzumab may be a potential strategy for the treatment of trastuzumab-resistant breast cancers (Damiano et al, 2009). The Y-box binding protein-1 (YB-1) is an oncogenic transcription/translation factor mediating expression of growth promoting genes such as EGFR and HER2.…”