Supplementary Table S1. Total list of detection antibodies used for reverse phase protein array.

Supplementary Table S3. Limma output from comparison of 4626 with parental SNU-5 cells treated with emibetuzumab.

Suppl. Figure 1 In vivo efficacy of Sym015 treatment at various dose levels in the EBC-1 xenograft model. Suppl. Figure 2 In vivo efficacy of Sym015 and unbalanced mixtures of the two constituent antibodies Hu9006 and Hu9338, applied at 10 mg/kg or 50 mg/kg doses in the EBC-1 xenograft model. Suppl. Figure 3 In vivo efficacy of Sym015 treatment in the H596 CDX model, which harbors a MET exon 14 deletion without MET gene amplification. Suppl. Figure 4 2 Map of clinically relevant mutations, obtained from the Cancer Cell Line Encyclopedia(31), in 64 cell lines. Suppl. Table S1 List of the 64 cell lines used in the study with information on tissue of origin, supplier, and growth medium used for propagation. Suppl. Table S2 Yellow columns: FISH scores for CDX and PDX models, denoting the average number of MET and CEP7 signals per cell, the MET/CEP7 ratio, and the percentage of tumor cells amplified. Suppl. Table S3 Prediction of human pharmacokinetics based on one-species allometric scaling(33).

Supplementary Table S5. Detection of HGF in cell supernatants.

Supplementary Table S4. Sensitivity of emibetuzumab-resistant cell lines to various TKIs compared with SNU-5 cells.

Supplementary Figure S1. Sequence homology to human and mouse reference genomes. Supplementary Figure S2. No SNU-5 tumors establish upon continuous treatment with emibetuzumab Supplementary Figure S3. MET level in 7333 and with or without emibetuzumab treatment. Supplementary Figure S4. Log2 ratios for MYC, PVT1, and ERBB3 copy number gains in the 4626 tumor. Supplementary Figure S5. HER3 level in SNU-5 cell lines. Supplementary Figure S6. Both emibetuzumab-resistant cell lines are resistant to Sym015 in vitro. Supplementary Figure S7. SNU-5 are equally sensitive to Sym015 and Sym015 LALA in vivo.

Supplementary Table S2. Limma output from comparison of 7333 with parental SNU-5 cells treated with emibetuzumab.

Supplementary Materials and Methods and Figure Legends

Abstract Failure of clinical trials due to development of resistance to MET-targeting therapeutic agents is an emerging problem. Mechanisms of acquired resistance to MET tyrosine kinase inhibitors are well described, whereas characterization of mechanisms of resistance toward MET-targeting antibodies is limited. This study investigated mechanisms underlying in vivo resistance to two antibody therapeutics currently in clinical development: an analogue of the MET-targeting antibody emibetuzumab and Sym015, a mixture of two antibodies targeting nonoverlapping epitopes of MET. Upon long-term in vivo treatment of a MET-amplified gastric cancer xenograft model (SNU-5), emibetuzumab-resistant, but not Sym015-resistant, tumors emerged. Resistant tumors were isolated and used to establish resistant cell lines. Characterization of both tumors and cell lines using extensive protein and signaling pathway activation mapping along with next-generation sequencing revealed two distinct resistance profiles, one involving PTEN loss and the other involving activation of the PI3K pathway, likely via MYC and ERBB3 copy number gains. PTEN loss left one model unaffected by PI3K/AKT targeting but sensitive to mTOR targeting, while the PI3K pathway–activated model was partly sensitive to targeting of multiple PI3K pathway proteins. Importantly, both resistant models were sensitive to treatment with Sym015 in vivo due to antibody-dependent cellular cytotoxicity–mediated tumor growth inhibition, MET degradation, and signaling inhibition. Taken together, our data provide key insights into potential mechanisms of resistance to a single MET-targeting antibody, demonstrate superiority of Sym015 in preventing acquired resistance, and confirm Sym015 antitumor activity in tumors resistant to a single MET antibody. Mol Cancer Ther; 17(6); 1259–70. ©2018 AACR.

Abstract Purpose: Activation of the receptor tyrosine kinase MET is associated with poor clinical outcome in certain cancers. To target MET more effectively, we developed an antagonistic antibody mixture, Sym015, consisting of two humanized mAbs directed against nonoverlapping epitopes of MET. Experimental Design/Results: We screened a large panel of well-annotated human cancer cell lines and identified a subset with highly elevated MET expression. In particular, cell lines of lung cancer and gastric cancer origin demonstrated high MET expression and activation, and Sym015 triggered degradation of MET and significantly inhibited growth of these cell lines. Next, we tested Sym015 in patient- and cell line–derived xenograft models with high MET expression and/or MET exon 14 skipping alterations, and in models harboring MET amplification as a mechanism of resistance to EGFR-targeting agents. Sym015 effectively inhibited tumor growth in all these models and was superior to an analogue of emibetuzumab, a monoclonal IgG4 antibody against MET currently in clinical development. Sym015 also induced antibody-dependent cellular cytotoxicity (ADCC) in vitro, suggesting that secondary effector functions contribute to the efficacy of Sym015. Retrospectively, all responsive, high MET-expressing models were scored as highly MET-amplified by in situ hybridization, pointing to MET amplification as a predictive biomarker for efficacy. Preclinical toxicology studies in monkeys showed that Sym015 was well tolerated, with a pharmacokinetic profile supporting administration of Sym015 every second or third week in humans. Conclusions: The preclinical efficacy and safety data provide a clear rationale for the ongoing clinical studies of Sym015 in patients with MET-amplified tumors. Clin Cancer Res; 23(19); 5923–35. ©2017 AACR.

Abstract Aberrant over-activation of MET receptor tyrosine kinase is involved in driving malignancies such as gastric and non-small cell lung cancer (NSCLC), and in the development of resistance to EGFR-targeting therapeutics. This has led to the development of several MET-targeting agents in the form of tyrosine kinase inhibitors (TKIs) and monoclonal antibodies (mAbs), many of which are in clinical development. However, resistance to MET-targeted agents is an emerging problem. This study aims to understand mechanisms underlying resistance development to an analogue of emibetuzumab, a mAb targeting MET. Upon long term in vivo treatment, emibetuzumab-resistant tumors and cell lines were generated, isolated, and characterized to investigate their acquired resistance mechanisms. Extensive reverse phase protein array and network analysis were used to characterize the proteomic profiles of three resistant cell lines, revealing three distinct resistance profiles, one involving activation of the PI3Kinase/AKT/mTOR pathway. We further show, how these resistance mechanisms can be overcome by treatment with other targeting therapeutics both in vitro and in vivo. Two of the models demonstrated in vivo sensitivity to Sym015, a novel mixture of two mAbs targeting non-overlapping epitopes of MET, partly due to ADCC, indicating that Sym015 can overcome acquired resistance to emibetuzumab. The third model demonstrated a marked increase in PI3Kinase/AKT/mTOR pathway activation. This activation translated into induced cancer cell and tumor growth, which could be inhibited by agents targeting PI3Kinase, AKT, or mTOR. This study thus points to treatment of patients with acquired resistance to single targeting MET mAbs with PI3Kinase/AKT/mTOR-targeting agents or a MET-targeting antibody mixture such as Sym015. Citation Format: Sofie Ellebæk Pollmann, Emanuel Frank Petricoin, Valerie Calvert, Shruti Rao, Simina Boca, Subha Madhavan, Ivan David Horak, Andreas Kjær, Michael Kragh, Thomas Tuxen Poulsen. In vivo acquired resistance to an emibetuzumab analogue in MET-amplified gastric xenografts can be overcome by a MET-targeting antibody mixture or PIK3CA/AKT/mTOR inhibition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3158. doi:10.1158/1538-7445.AM2017-3158

The human epidermal growth factor receptor (HER)-family is involved in development of many epithelial cancers. Therefore, HER-family members constitute important targets for anti-cancer therapeutics such as monoclonal antibodies (mAbs). A limitation to the success of single HER-targeting mAbs is development of acquired resistance through mechanisms such as alterted receptor dimerization patterns and dependencies. Pan-HER is a mixture of six mAbs simultaneously targeting epidermal growth factor receptor (EGFR), HER2 and HER3 with two mAbs against each receptor. Pan-HER has previously demonstrated broader efficacy than targeting single or dual receptor combinations also in resistant settings. In light of this broad efficacy, we decided to investigate the effect of Pan-HER compared with single HER-targeting with single and dual mAbs on HER-family cross-talk and dimerization focusing on EGFR. The effect of Pan-HER on cell proliferation and HER-family receptor degradation was superior to treatment with single mAbs targeting either single receptor, and similar to targeting a single receptor with two non-overlapping antibodies. Furthermore, changes in EGFR-dimerization patterns after treatment with Pan-HER were investigated by in situ proximity ligation assay and co-immunoprecipitation, demonstrating that Pan-HER and the EGFR-targeting mAb mixture efficiently down-regulate basal EGFR homo- and heterodimerization in two tested cell lines, whereas single mAbs had limited effects. Pan-HER and the EGFR-targeting mAb mixture also blocked EGF-binding and thereby ligand-induced changes in EGFR-dimerization levels. These results suggest that Pan-HER reduces the cellular capability to switch HER-dependency and dimerization pattern in response to treatment and thus hold promise for future clinical development of Pan-HER in resistant settings.

Abstract Members of the human epidermal growth factor receptor (HER)-family, i.e. EGFR, HER2, and HER3, are key oncogenic drivers in numerous cancer forms. Monoclonal antibody therapeutics targeting EGFR and HER2 have been clinically approved and HER3-targeting antibodies are in clinical development. However, resistance to single HER treatment occurs due to mechanisms such as incomplete target elimination and a switch of receptor dependency in the resistant cancer cell population. Another potential escape mechanism for the cancer cells to become resistant and maintain oncogenic signaling is receptor heterodimerization. It is therefore relevant to investigate how heterodimers can be downregulated when targeted with antibodies against a single or multiple HER targets. It is well established that mixtures of two or more antibodies against a single HER family receptor induce superior and rapid receptor downregulation and elimination compared with monoclonal antibodies. However, the effect of antibody mixtures on HER heterodimer distribution has not been investigated. At Symphogen, we have generated Pan-HER, a combination of two EGFR-, two HER2-, and two HER3-targeting monoclonal antibodies with non-overlapping epitopes in a single drug compound. Detection and quantification of the HER family member distribution in selected cancer cell lines, as well as proliferation assays with combinations of the antibody components comprising Pan-HER have been performed to investigate the effects of 2-, 4- and 6-mixtures of antibodies. Results from studies focusing on characterization of receptor levels, surface expression and heterodimer formation in Pan-HER responsive cancer cell lines will be presented, as well as the effect of Pan-HER on receptor heterodimer distribution, investigated by Co-IP and Duolink Proximity Ligation Assay technology. Our results show that mixtures of antibodies against more than one HER family member potently downregulate the HER family receptor levels and significantly alter the HER family heterodimerization pattern upon short- and long-term exposure to HER-targeting antibodies. Citation Format: Sofie Ellebæk, Thomas Bouquin, Michael V. Grandal, Michael Kragh, Thomas T. Poulsen. Effect of antibody mixtures on HER-family heterodimerization. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 655. doi:10.1158/1538-7445.AM2014-655