Philipp Steiner

A Potent HER3 Monoclonal Antibody That Blocks Both Ligand-Dependent and -Independent Activities: Differential Impacts of PTEN Status on Tumor Response

HER3/ERBB3 is a kinase-deficient member of the EGFR family receptor tyrosine kinases (RTK) that is broadly expressed and activated in human cancers. HER3 is a compelling cancer target due to its important role in activation of the oncogenic PI3K/AKT pathway. It has also been demonstrated to confer tumor resistance to a variety of cancer therapies, especially targeted drugs against EGFR and HER2. HER3 can be activated by its ligand (heregulin/HRG), which induces HER3 heterodimerization with EGFR, HER2, or other RTKs. Alternatively, HER3 can be activated in a ligand-independent manner through heterodimerization with HER2 in HER2-amplified cells. We developed a fully human mAb against HER3 (KTN3379) that efficiently suppressed HER3 activity in both ligand-dependent and independent settings. Correspondingly, KTN3379 inhibited tumor growth in divergent tumor models driven by either ligand-dependent or independent mechanisms in vitro and in vivo. Most intriguingly, while investigating the mechanistic underpinnings of tumor response to KTN3379, we discovered an interesting dichotomy in that PTEN loss, a frequently occurring oncogenic lesion in a broad range of cancer types, substantially blunted the tumor response in HER2-amplified cancer, but not in the ligand-driven cancer. To our knowledge, this represents the first study ascertaining the impact of PTEN loss on the antitumor efficacy of a HER3 mAb. KTN3379 is currently undergoing a phase Ib clinical trial in patients with advanced solid tumors. Our current study may help us optimize patient selection schemes for KTN3379 to maximize its clinical benefits. Mol Cancer Ther; 15(4); 689–701. ©2016 AACR.

Abstract 5462: MEDI3185, a potent anti-CXCR4 antibody, inhibits tumor cell migration, signaling and tumor growth in preclinical models.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The chemokine receptor CXCR4 is a seven-transmembrane G-protein coupled receptor that mediates chemotaxis and cell migration upon stimulation via its ligand, stromal-derived factor 1 (SDF-1), also called CXCL12. CXCR4 is normally expressed on bone marrow stem and progenitor cells, various circulating lymphocytes, endothelial precursor cells, tissue macrophages and fibroblasts but the aberrant overexpression of CXCR4 is linked to various hematological malignancies, solid tumors and metastatic neoplasms. Moreover, CXCR4 overexpression is correlated with poor prognosis in many types of cancer, including breast, ovarian, colon, pancreatic, AML and glioblastomas. CXCR4 inhibition using siRNA, small-molecule and peptide inhibitors has demonstrated that it can inhibit tumor growth by blocking tumor cell survival/proliferation, metastasis, angiogenesis and tumor immune infiltrates. Here we describe a novel, fully human, antagonistic antibody to CXCR4, MEDI3185, which blocks SDF-1 binding to CXCR4. MEDI3185 has picomolar binding affinity to human CXCR4 and exhibits no significant binding to other chemokine receptors such as CCR4 or CXCR3. In vitro studies demonstrated that MEDI3185 inhibited tumor cell migration, blocked SDF-1 induced tumor cell signaling and induced apoptosis of tumor cells. In preclinical human tumor xenograft models in mouse, MEDI3185 showed single-agent tumor growth inhibition in multiple myeloma and B-cell Burkitts lymphoma models and had combination activity in ovarian models. In addition, MEDI3185 extended survival as combination therapy in mouse models of CLL and also blocked lung tumor burden in a disseminated ovarian model. Combined, these data suggest that MEDI3185 is a potent CXCR4 antibody for the treatment of both hematological and solid tumors because it has pleiotropic effects on tumor biology that may enhance the efficacy of the current standard of care. Citation Format: Adeela Kamal, Youzhen Wang, Philipp Steiner, Anne-Marie Mazzola, Leslie Wetzel, Melissa Passino, Brenda McDermott, Keven Huang, Vahe Bedian, Norman Greenberg. MEDI3185, a potent anti-CXCR4 antibody, inhibits tumor cell migration, signaling and tumor growth in preclinical models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5462. doi:10.1158/1538-7445.AM2013-5462

Abstract A112: Combined targeting of HER2 and HER3 inhibits tumor growth in both trastuzumab-sensitive and trastuzumab-resistant breast cancer models.

HER3 (ERBB3) is a tumor driver in divergent cancer types with high HRG levels or heightened EGFR or HER2 kinase activity via growth signal coupling to the PI3K-AKT pathway. HER3 lacks intrinsic tyrosine kinase activity but is capable of signaling after heterodimerizing with tyrosine kinase ERBB family members EGFR or HER2. Heterodimer formation is driven either by the binding of heregulin (NRG1/HRG) to HER3 (ligand dependent - LD), or alternatively, by overexpression of EGFR or HER2 (ligand-independent - LI). Preclinical evaluation of MEDI3379, a human IgG1 modified monoclonal anti-HER3 antibody that antagonizes both LD and LI signaling, demonstrated tumor growth inhibition in the HER2-expressing MDA-MB-361 breast cancer xenograft model. Anti-tumor activity of MEDI3379 in this model was increased in combination with the HER2-targeting drug trastuzumab to a greater extent than MEDI3379 when combined with either lapatinib or pertuzumab. Combined inhibition of HER2 and HER3 led to strong reduction in pHER3. Unexpectedly, co-administration of MEDI3379 together with trastuzumab in MDA-MB-361 tumor-bearing mice but not in naive mice resulted in reduced serum levels of trastuzumab. A control antibody combined with trastuzumab in MDA-MB-361 tumor bearing mice did not have this effect. Furthermore, in the trastuzumab-resistant JIMT-1 breast cancer xenograft model which has high HRG and pHER3 levels MEDI3379 but not pertuzumab resensitized JIMT-1 tumors to trastuzumab resulting in synergistic anti-tumor activity and a reduction of pHER3. In vivo resistance to this regimen appeared with prolonged treatment of JIMT-1 tumors and was accompanied by a decrease in homogenous expression of HER2. In conclusion, the use of MEDI3379 in combination with trastuzumab in HER2-amplifed breast cancer cell lines has demonstrated additional tumor growth inhibition over single agent trastuzumab and overcoming trastuzumab-resistance mechanisms. This combination warrants further evaluation in preclinical and clinical studies. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A112. Citation Format: Philipp Steiner, Leslie Wetzel, Kevin Schifferli, Raymond Rothstein, Ravinder Tammali, Marlon Rebelatto, Zhan Xiao, Andrew Pierce, Robert Hollingsworth. Combined targeting of HER2 and HER3 inhibits tumor growth in both trastuzumab-sensitive and trastuzumab-resistant breast cancer models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A112.

Abstract 558: MEDI3379, a human monoclonal antibody against HER3, suppresses HER3 activity and cell proliferation in both ligand-dependent and independent cancers.

HER3 (ErbB3) is a member of the EGFR/HER family of receptor tyrosine kinases (RTK), consisting of EGFR, HER2, HER3 and HER4. Due to its unique kinase-deficient nature, HER3 needs to form heterodimers with EGFR, HER2 or other RTKs to be functionally active. Dimerization is induced by either HER3 ligand (Heregulin, HRG) binding, or overexpression of partner RTKs in a ligand-independent (LI) manner. In both settings, HER3 acts as a critical scaffold coupling the upstream RTKs to efficient PI3K/AKT pathway induction to drive tumor growth and survival. We have developed a potent antagonistic human monoclonal antibody against HER3, termed MEDI3379, and tested it in multiple cancer models with either ligand-dependent or ligand-independent HER3 activities. For ligand-dependent models, we have chosen MDA-MB-175VII, a breast cancer cell-line with known γ-HRG expression, and HMCB, a melanoma cell-line with β-HRG expression. Efficient suppression of cell proliferation by MEDI3379 or 2C2, a precursor of MEDI3379, was observed in both models. This anti-tumor effect is directly due to the abrogation of HER3 activation (as determined by pHER3 formation) and its downstream effector pAKT. Her2-amplified breast cancer models such as BT474 are known to display high ligand-independent HER3 activity that is due to constitutive dimerization of HER2 and HER3. Treatment of BT474 with MEDI3379 led to effective suppression of pHER3, pAKT, and cell-proliferation in vitro. We extended this observation in vivo by exploring the antitumor activity of MEDI3379 in several orthotopic HER2-amplified breast cancer xenografts in nude mice. Consistent with in vitro observations, the BT474 xenograft model responded to MEDI3379 treatment with 65% tumor growth inhibition. In contrast, two published HER3 mAbs (Ab #6 and U1-15) failed to display activity in this ligand-independent model. In conclusion, our findings demonstrated that MEDI3379 is a HER3 antagonist that is effective in models of human cancers driven by both ligand-dependent as well as ligand-independent HER3 activities. Citation Format: Carrasco A. Rosa, Leslie Wetzel, Krista Kinner, Hong Chen, Raymond Rothstein, David Tice, Robert Hollingsworth, Philipp Steiner, Zhan Xiao. MEDI3379, a human monoclonal antibody against HER3, suppresses HER3 activity and cell proliferation in both ligand-dependent and independent cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 558. doi:10.1158/1538-7445.AM2013-558

Abstract P4-07-05: MEDI3379, an antibody against HER3, is active in HER2-driven human breast tumor models

HER3 (ERBB3) is a member of the EGFR/HER family of receptor tyrosine kinases (RTK), consisting of EGFR, HER2, HER3 and HER4. Unlike the other HER family members, HER3 lacks intrinsic tyrosine kinase activity and therefore needs to form heterodimers with EGFR, HER2 or other kinase-proficient RTKs to be functionally active. Dimerization is induced by overexpression of EGFR or HER2 in a ligand-independent (LI) manner. In this process HER3 acts as a driver in divergent cancer types including HER2-positive breast cancer (BC) via induction of the PI3K-AKT pathway. Alternatively, heregulin (NRG1/HRG), the major HER3 ligand, induces a conformational shift in HER3 which leads to dimer formation with a partner RTK in a ligand-dependent (LD) manner. We have developed an antagonistic human monoclonal antibody against HER3, termed MEDI3379, and tested it in multiple breast cancer cell lines. We observed effective suppression of constitutive pHER3 and pAKT with MEDI3379, leading to anti-proliferation effects in cell culture models. Preclinical evaluation of MEDI3379 demonstrated antitumor activity in several orthotopic BC xenografts in nude mice which did not express HRG. For example, the BC xenograft model BT474 with amplified HER2 responded to MEDI3379 (65% dTGI). In conclusion, our findings with targeting of HER3 in mouse models support continued development of MEDI3379 for cancer. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-07-05.