The EGF receptor (EGFR) HER3 is emerging as an attractive cancer therapeutic target due to its central position in the HER receptor signaling network. HER3 amplifies phosphoinositide 3-kinase (PI3K)-driven tumorigenesis and its upregulation in response to other anti-HER therapies has been implicated in resistance to them. Here, we report the development and characterization of RG7116, a novel anti-HER3 monoclonal antibody (mAb) designed to block HER3 activation, downregulate HER3, and mediate enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) via glycoengineering of the Fc moiety. Biochemical studies and X-ray crystallography revealed that RG7116 bound potently and selectively to domain 1 of human HER3. Heregulin binding was prevented by RG7116 at concentrations more than 1 nmol/L as was nearly complete inhibition of HER3 heterodimerization and phosphorylation, thereby preventing downstream AKT phosphorylation. In vivo RG7116 treatment inhibited xenograft tumor growth up to 90% relative to controls in a manner accompanied by downregulation of cell surface HER3. RG7116 efficacy was further enhanced in combination with anti-EGFR (RG7160) or anti-HER2 (pertuzumab) mAbs. Furthermore, the ADCC potency of RG7116 was enhanced compared with the nonglycoengineered parental antibody, both in vitro and in orthotopic tumor xenograft models, where an increased median survival was documented. ADCC degree achieved in vitro correlated with HER3 expression levels on tumor cells. In summary, the combination of strong signaling inhibition and enhanced ADCC capability rendered RG7116 a highly potent HER3-targeting agent suitable for clinical development. Cancer Res; 73(16); 5183-94. Ó2013 AACR.

PurposeRG7116 is a novel anti-HER3 therapeutic antibody that inhibits HER3 signalling and induces antibody-dependent cellular cytotoxicity of tumor cells due to a glycoengineered antibody Fc moiety. We investigated the efficacy and pharmacokinetic/pharmacodynamic properties of HER3 signal inhibition by RG7116 in a murine xenograft model of human head and neck cancer.MethodsSCID-beige mice bearing FaDu cells were treated with RG7116 at a weekly dose of 0.3–10 mg/kg, and tumor growth control and modulation of selected proteins (HER3 and AKT) were examined.ResultsComplete tumor stasis up to Day 46 was observed at a dose >3 mg/kg, and this dose down-modulated membrane HER3 expression and inhibited HER3 and AKT phosphorylation. Systemic RG7116 exposure was greater than dose-proportional and total clearance declined with increasing dose, indicating that RG7116 elimination is target-mediated. This is consistent with the better efficacy, and the HER3 and pAKT inhibition, that was observed at doses >1 mg/kg. Tumor regrowth occurred from Day 46 onwards and was associated with HER1 and HER2 upregulation, indicating the activation of alternative HER escape pathways. Modulation of HER3 and phospho-HER3 was also demonstrated in the skin and mucosa of an RG7116-treated cynomolgus monkey, suggesting that these may be useful surrogate tissues for monitoring RG7116 activity.ConclusionsThese data confirm the promising efficacy of RG7116 and highlight the value of assessing the PK behavior of the antibody and measuring target protein modulation as a marker of biological activity. Clinical development of RG7116 has now begun, and phase I trials are ongoing.

HER3 is a member of the Human Epidermal Growth Factor Receptor (HER) family. HER3 is a kinase dead receptor, but by forming heterodimers with other HER family receptors, HER3 works as amplifier for PI3 kinase driven tumorigenesis. It has been reported that tumors treated with EGFR-, HER2- or cMET-targeted therapies can escape via HER3 activation or upregulation. HER3 is expressed in a large variety of tumors for example in non-small cell lung cancer (NSCLC), head and neck, colorectal, gastric, pancreatic, breast, ovarian and prostate cancer. Anti-HER3 antibodies can work via various mechanisms including: (1) blocking ligand (HRGs) binding to the receptor, (2) blocking heterodimerization with other HER family members (HER1, 2 and 4), (3) downregulation of the receptor from the cell surface, and (4) engaging immune effector functions such as antibody-dependent cellular cytotoxicity (ADCC). The first three mechanisms lead to inhibition of HER3 phosphorylation and downstream signaling thereby resulting in tumor cell growth inhibition, while ADCC is a mechanism of direct target cell killing triggered by cross-linking of Fc receptors on immune effector cells (e.g. NK cells, macrophages). GE-huMab-HER3 is a novel humanized and glycoengineered IgG1 antibody that binds to HER3 with high affinity. This antibody prevents ligand binding and receptor heterodimerization thereby blocking receptor phosphorylation. In various tumor xenograft models treatment with this antibody leads to substantial tumor growth inhibition. E.g. GE-huMab-HER3 treatment achieved >50% tumor growth inhibition in 10 out of 17 NSCLC models and in some cases even resulted in complete tumor remission. However, these xenograft experiments only reveal part of this antibody's therapeutic potential. A unique feature of GE-huMab-HER3 that differentiates it from other anti-HER3 antibodies, including AMG 888 and MM-121, is its ability to bind to human FcgRIIIa on immune effector cells with a 50-fold higher affinity than standard IgG1 antibodies, a property conferred by the engineered glycosylation of the antibody Fc region. Consequently, GE-huMab-HER3 exhibits superior potency and efficacy in ADCC, as shown in vitro using recombinant A549 cells and in vivo by its Fc mediated greater anti-tumor effect in A549 orthotopic mouse models compared to a non-glyco-engineered variant of the antibody, WT-huMab-HER3. The combination of strong signaling inhibition and enhanced ADCC capability renders GE-huMabHER3 a highly potent HER3-targeting agent. Phase I clinical testing of this promising novel compound is ongoing. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2508. doi:1538-7445.AM2012-2508

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<div>Abstract<p>The EGF receptor (EGFR) HER3 is emerging as an attractive cancer therapeutic target due to its central position in the HER receptor signaling network. HER3 amplifies phosphoinositide 3-kinase (PI3K)–driven tumorigenesis and its upregulation in response to other anti-HER therapies has been implicated in resistance to them. Here, we report the development and characterization of RG7116, a novel anti-HER3 monoclonal antibody (mAb) designed to block HER3 activation, downregulate HER3, and mediate enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) via glycoengineering of the Fc moiety. Biochemical studies and X-ray crystallography revealed that RG7116 bound potently and selectively to domain 1 of human HER3. Heregulin binding was prevented by RG7116 at concentrations more than 1 nmol/L as was nearly complete inhibition of HER3 heterodimerization and phosphorylation, thereby preventing downstream AKT phosphorylation. <i>In vivo</i> RG7116 treatment inhibited xenograft tumor growth up to 90% relative to controls in a manner accompanied by downregulation of cell surface HER3. RG7116 efficacy was further enhanced in combination with anti-EGFR (RG7160) or anti-HER2 (pertuzumab) mAbs. Furthermore, the ADCC potency of RG7116 was enhanced compared with the nonglycoengineered parental antibody, both <i>in vitro</i> and in orthotopic tumor xenograft models, where an increased median survival was documented. ADCC degree achieved <i>in vitro</i> correlated with HER3 expression levels on tumor cells. In summary, the combination of strong signaling inhibition and enhanced ADCC capability rendered RG7116 a highly potent HER3-targeting agent suitable for clinical development. <i>Cancer Res; 73(16); 5183–94. ©2013 AACR</i>.</p></div>