First-in-human trial exploring safety, antitumor activity, and pharmacokinetics of Sym013, a recombinant pan-HER antibody mixture, in advanced epithelial malignancies.

PURPOSE: Sym013 contains six humanized monoclonal antibodies that bind to non-overlapping epitopes on three human epidermal growth factor receptors (HER1-3). Preclinical studies suggested Sym013 strongly suppresses growth of multiple epithelial tumors. This is a first-in-human study exploring safety and efficacy of Sym013 in patients with advanced epithelial malignancies. METHODS: Dose escalation used single-patient cohorts until the stopping rule was met, followed by 3 + 3 design. Dose levels planned were: 1, 2, 4, 6, 9, 12, 15, and 18 mg/kg. Treatment cycles were 28 days with imaging every eight weeks. Serum samples were collected at multiple time points for assessment of pharmacokinetics and development of anti-drug antibodies. RESULTS: Thirty-two patients were enrolled with multiple solid tumors, most common being colorectal cancer (CRC; 10/32, 31%). Due to mucositis, rash, and diarrhea at 4 mg/kg once-weekly, dosing was changed to biweekly (Q2W). Mandatory prophylaxis was added due to Grade 3 infusion-related reaction and oral mucositis at 9 mg/kg Q2W. The 15 mg/kg Q2W cohort was enrolling when the study was terminated for business reasons. Most common adverse events were skin (81%) and gastrointestinal (75%) disorders, including dermatitis/rash, stomatitis, and diarrhea. One patient with CRC achieved a partial response; 12 patients with varied malignancies had stable disease. CONCLUSION: During the conduct of the study, management of frequent infusion-related reactions, skin toxicities, and mucosal disorders, which are indicative of HER inhibition, necessitated multiple protocol amendments. The investigators, in concert with the Sponsor, agreed that achieving a tolerated regimen with acceptable target saturation was unlikely. TRIAL REGISTRY: www. CLINICALTRIALS: gov ; NCT02906670 (September 20, 2016).

The genomic landscape of response to EGFR blockade in colorectal cancer.

Colorectal cancer is the third most common cancer worldwide, with 1.2 million patients diagnosed annually. In late-stage colorectal cancer, the most commonly used targeted therapies are the monoclonal antibodies cetuximab and panitumumab, which prevent epidermal growth factor receptor (EGFR) activation. Recent studies have identified alterations in KRAS and other genes as likely mechanisms of primary and secondary resistance to anti-EGFR antibody therapy. Despite these efforts, additional mechanisms of resistance to EGFR blockade are thought to be present in colorectal cancer and little is known about determinants of sensitivity to this therapy. To examine the effect of somatic genetic changes in colorectal cancer on response to anti-EGFR antibody therapy, here we perform complete exome sequence and copy number analyses of 129 patient-derived tumour grafts and targeted genomic analyses of 55 patient tumours, all of which were KRAS wild-type. We analysed the response of tumours to anti-EGFR antibody blockade in tumour graft models and in clinical settings and functionally linked therapeutic responses to mutational data. In addition to previously identified genes, we detected mutations in ERBB2, EGFR, FGFR1, PDGFRA, and MAP2K1 as potential mechanisms of primary resistance to this therapy. Novel alterations in the ectodomain of EGFR were identified in patients with acquired resistance to EGFR blockade. Amplifications and sequence changes in the tyrosine kinase receptor adaptor gene IRS2 were identified in tumours with increased sensitivity to anti-EGFR therapy. Therapeutic resistance to EGFR blockade could be overcome in tumour graft models through combinatorial therapies targeting actionable genes. These analyses provide a systematic approach to evaluating response to targeted therapies in human cancer, highlight new mechanisms of responsiveness to anti-EGFR therapies, and delineate new avenues for intervention in managing colorectal cancer.

Simultaneous targeting of HER family pro-survival signaling with Pan-HER antibody mixture is highly effective in TNBC: a preclinical trial with PDXs.

BACKGROUND: The human epidermal growth factor receptor (HER) family, notably EGFR, is overexpressed in most triple-negative breast cancer (TNBC) cases and provides cancer cells with compensatory signals that greatly contribute to the survival and development of resistance in response to therapy. This study investigated the effects of Pan-HER (Symphogen, Ballerup, Denmark), a novel mixture of six monoclonal antibodies directed against members of the HER family EGFR, HER2, and HER3, in a preclinical trial of TNBC patient-derived xenografts (PDXs). METHODS: Fifteen low passage TNBC PDX tumor samples were transferred into the right mammary fat pad of mice for engraftment. When tumors reached an average size of 100-200 mm3, mice were randomized (n ≥ 6 per group) and treated following three 1-week cycles consisting of three times/week intraperitoneal (IP) injection of either formulation buffer (vehicle control) or Pan-HER (50 mg/kg). At the end of treatment, tumors were collected for Western blot, RNA, and immunohistochemistry analyses. RESULTS: All 15 TNBC PDXs were responsive to Pan-HER treatment, showing significant reductions in tumor growth consistent with Pan-HER-mediated tumor downmodulation of EGFR and HER3 protein levels and significantly decreased activation of associated HER family signaling pathways AKT and ERK. Tumor regression was observed in five of the models, which corresponded to those PDX tumor models with the highest level of HER family activation. CONCLUSIONS: The marked effect of Pan-HER in numerous HER family-dependent TNBC PDX models justifies further studies of Pan-HER in TNBC clinical trials as a potential therapeutic option.

Pan-HER-An antibody mixture targeting EGFR, HER2 and HER3 abrogates preformed and ligand-induced EGFR homo- and heterodimers.

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.

Passive immunotherapies protect WRvFire and IHD-J-Luc vaccinia virus-infected mice from lethality by reducing viral loads in the upper respiratory tract and internal organs.

Whole-body bioimaging was employed to study the effects of passive immunotherapies on lethality and viral dissemination in BALB/c mice challenged with recombinant vaccinia viruses expressing luciferase. WRvFire and IHD-J-Luc vaccinia viruses induced lethality with similar times to death following intranasal infection, but WRvFire replicated at higher levels than IHD-J-Luc in the upper and lower respiratory tracts. Three types of therapies were tested: licensed human anti-vaccinia virus immunoglobulin intravenous (VIGIV); recombinant anti-vaccinia virus immunoglobulin (rVIG; Symphogen, Denmark), an investigational product containing a mixture of 26 human monoclonal antibodies (HuMAbs) against mature virion (MV) and enveloped virion (EV); and HuMAb compositions targeting subsets of MV or EV proteins. Bioluminescence recorded daily showed that pretreatment with VIGIV (30 mg) or with rVIG (100 µg) on day -2 protected mice from death but did not prevent viral replication at the site of inoculation and dissemination to internal organs. Compositions containing HuMAbs against MV or EV proteins were protective in both infection models at 100 µg per animal, but at 30 µg, only anti-EV antibodies conferred protection. Importantly, the t statistic of the mean total fluxes revealed that viral loads in surviving mice were significantly reduced in at least 3 sites for 3 consecutive days (days 3 to 5) postchallenge, while significant reduction for 1 or 2 days in any individual site did not confer protection. Our data suggest that reduction of viral replication at multiple sites, including respiratory tract, spleen, and liver, as monitored by whole-body bioluminescence can be used to predict the effectiveness of passive immunotherapies in mouse models.

Capturing the natural diversity of the human antibody response against vaccinia virus.

The eradication of smallpox (variola) and the subsequent cessation of routine vaccination have left modern society vulnerable to bioterrorism employing this devastating contagious disease. The existing, licensed vaccines based on live vaccinia virus (VACV) are contraindicated for a substantial number of people, and prophylactic vaccination of large populations is not reasonable when there is little risk of exposure. Consequently, there is an emerging need to develop efficient and safe therapeutics to be used shortly before or after exposure, either alone or in combination with vaccination. We have characterized the human antibody response to smallpox vaccine (VACV Lister) in immunized volunteers and isolated a large number of VACV-specific antibodies that recognize a variety of different VACV antigens. Using this broad antibody panel, we have generated a fully human, recombinant analogue to plasma-derived vaccinia immunoglobulin (VIG), which mirrors the diversity and specificity of the human antibody immune response and offers the advantage of unlimited supply and reproducible specificity and activity. The recombinant VIG was found to display a high specific binding activity toward VACV antigens, potent in vitro VACV neutralizing activity, and a highly protective efficacy against VACV challenge in the mouse tail lesion model when given either prophylactically or therapeutically. Altogether, the results suggest that this compound has the potential to be used as an effective postexposure prophylaxis or treatment of disease caused by orthopoxviruses.

A human recombinant analogue to plasma-derived vaccinia immunoglobulin prophylactically and therapeutically protects against lethal orthopoxvirus challenge.

Orthopoxviruses such as variola and monkeypox viruses continue to threaten the human population. Monkeypox virus is endemic in central and western Africa and outbreaks have reached as far as the U.S. Although variola virus, the etiologic agent of smallpox, has been eradicated by a successful vaccination program, official and likely clandestine stocks of the virus exist. Moreover, studies with ectromelia virus (the etiological agent of mousepox) have revealed that IL-4 recombinant viruses are significantly more virulent than wild-type viruses even in mice treated with vaccines and/or antivirals. For these reasons, it is critical that antiviral modalities are developed to treat these viruses should outbreaks, or deliberate dissemination, occur. Currently, 2 antivirals (brincidofovir and tecovirimat) are in the U.S. stockpile allowing for emergency use of the drugs to treat smallpox. Both antivirals have advantages and disadvantages in a clinical and emergency setting. Here we report on the efficacy of a recombinant immunoglobulin (rVIG) that demonstrated efficacy against several orthopoxviruses in vitro and in vivo in both a prophylactic and therapeutic fashion. A single intraperitoneal injection of rVIG significantly protected mice when given up to 14 days before or as late as 6 days post challenge. Moreover, rVIG reduced morbidity, as measured by weight-change, as well as several previously established biomarkers of disease. In rVIG treated mice, we found that vDNA levels in blood were significantly reduced, as was ALT (a marker of liver damage) and infectious virus levels in the liver. No apparent adverse events were observed in rVIG treated mice, suggesting the immunoglobulin is well tolerated. These findings suggest that recombinant immunoglobulins could be candidates for further evaluation and possible licensure under the FDA Animal Rule.

Human antibody repertoires.

Symplex is an antibody discovery technology that identifies fully human antigen-specific antibody repertoires directly from plasma cells. The technology utilizes reverse transcription and overlap extension polymerase chain reaction performed on single-cell-sorted plasma cells, whereby the heavy- and light-chain cognate pairing of the antibodies is maintained. The isolated antibodies from a plasma cell donor reflect the diversity, affinity, and selectivity of the donor antibody repertoire, making the technology an ideal tool for identifying drug leads and studying the development of human antibody repertoires.

CD4+ and CD8a+ PET imaging predicts response to novel PD-1 checkpoint inhibitor: studies of Sym021 in syngeneic mouse cancer models.

Predicting the outcome of immunotherapy is essential for efficient treatment. The recent clinical success of immunotherapy is increasingly changing the paradigm of cancer treatment. Accordingly, the development of immune-based agents is accelerating and the number of agents in the global immuno-oncology pipeline has grown 60-70% over the past year. However, despite remarkable clinical efficacy in some patients, only few achieve a lasting clinical response. Treatment failure can be attributed to poorly immunogenic tumors that do not attract tumor infiltrating lymphocytes (TILs). Therefore, we developed positron emission tomography (PET) radiotracers for non-invasive detection of CD4+ and CD8a+ TILs in syngeneic mouse tumor models for preclinical studies. Methods: Seven syngeneic mouse tumor models (B16F10, P815, CT26, MC38, Renca, 4T1, Sa1N) were quantified for CD4+ and CD8a+ TILs using flow cytometry and immunohistochemistry (IHC), as well as for tumor growth response to Sym021, a humanized PD-1 antibody cross-reactive with mouse PD-1. Radiotracers were generated from F(ab)'2 fragments of rat-anti-mouse CD4 and CD8a antibodies conjugated to the p-SCN-Bn-Desferrioxamine (SCN-Bn-DFO) chelator and radiolabeled with Zirconium-89 (89Zr-DFO-CD4/89Zr-DFO-CD8a). Tracers were optimized for in vivo PET/CT imaging in CT26 tumor-bearing mice and specificity was evaluated by depletion studies and isotype control imaging. 89Zr-DFO-CD4 and 89Zr-DFO-CD8a PET/CT imaging was conducted in the panel of syngeneic mouse models prior to immunotherapy with Sym021. Results: Syngeneic tumor models were characterized as "hot" or "cold" according to number of TILs determined by flow cytometry and IHC. 89Zr-DFO-CD4 and 89Zr-DFO-CD8a were successfully generated with a radiochemical purity >99% and immunoreactivity >85%. The optimal imaging time-point was 24 hours post-injection of ~1 MBq tracer with 30 µg non-labeled co-dose. Reduced tumor and spleen uptake of 89Zr-DFO-CD8a was observed in CD8a+ depleted mice and the uptake was comparable with that of isotype control (89Zr-DFO-IgG2b) confirming specificity. PET imaging in syngeneic tumor models revealed a varying maximum tumor-to-heart ratio of 89Zr-DFO-CD4 and 89Zr-DFO-CD8a across tumor types and in-between subjects that correlated with individual response to Sym021 at day 10 relative to start of therapy (p=0.0002 and p=0.0354, respectively). The maximum 89Zr-DFO-CD4 tumor-to-heart ratio could be used to stratify mice according to Sym021 therapy response and overall survival was improved in mice with a 89Zr-DFO-CD4 ratio >9 (p=0.0018). Conclusion: We developed 89Zr-DFO-CD4 and 89Zr-DFO-CD8a PET radiotracers for specific detection and whole-body assessment of CD4+ and CD8a+ status. These radiotracers can be used to phenotype preclinical syngeneic mouse tumor models and to predict response to an immune checkpoint inhibitor. We foresee development of such non-invasive in vivo biomarkers for prediction and evaluation of clinical efficacy of immunotherapeutic agents, such as Sym021.

Sym021, a promising anti-PD1 clinical candidate antibody derived from a new chicken antibody discovery platform.

Discovery of therapeutic antibodies is a field of intense development, where immunization of rodents remains a major source of antibody candidates. However, high orthologue protein sequence homology between human and rodent species disfavors generation of antibodies against functionally conserved binding epitopes. Chickens are phylogenetically distant from mammals. Since chickens generate antibodies from a restricted set of germline genes, the possibility of adapting the Symplex antibody discovery platform to chicken immunoglobulin genes and combining it with high-throughput humanization of antibody frameworks by "mass complementarity-determining region grafting" was explored. Hence, wild type chickens were immunized with an immune checkpoint inhibitor programmed cell death 1 (PD1) antigen, and a repertoire of 144 antibodies was generated. The PD1 antibody repertoire was successfully humanized, and we found that most humanized antibodies retained affinity largely similar to that of the parental chicken antibodies. The lead antibody Sym021 blocked PD-L1 and PD-L2 ligand binding, resulting in elevated T-cell cytokine production in vitro. Detailed epitope mapping showed that the epitope recognized by Sym021 was unique compared to the clinically approved PD1 antibodies pembrolizumab and nivolumab. Moreover, Sym021 bound human PD1 with a stronger affinity (30 pM) compared to nivolumab and pembrolizumab, while also cross-reacting with cynomolgus and mouse PD1. This enabled direct testing of Sym021 in the syngeneic mouse in vivo cancer models and evaluation of preclinical toxicology in cynomolgus monkeys. Preclinical in vivo evaluation in various murine and human tumor models demonstrated a pronounced anti-tumor effect of Sym021, supporting its current evaluation in a Phase 1 clinical trial. Abbreviations: ADCC, antibody-dependent cellular cytotoxicity; CD, cluster of differentiation; CDC, complement-dependent cytotoxicity; CDR, complementarity determining region; DC, dendritic cell; ELISA, enzyme-linked immunosorbent assay; FACS, fluorescence activated cell sorting; FR, framework region; GM-CSF, granulocyte-macrophage colony-stimulating factor; HRP, horseradish peroxidase; IgG, immunoglobulin G; IL, interleukin; IFN, interferon; mAb, monoclonal antibody; MLR, mixed lymphocyte reaction; NK, natural killer; PBMC, peripheral blood mono-nuclear cell; PD1, programmed cell death 1; PDL1, programmed cell death ligand 1; RT-PCR, reverse transcription polymerase chain reaction; SEB, Staphylococcus Enterotoxin B; SPR, surface Plasmon Resonance; VL, variable part of light chain; VH, variable part of heavy chain.

Clonal repertoire diversification of a neutralizing cytomegalovirus glycoprotein B-specific antibody results in variants with diverse anti-viral properties.

Cytomegalovirus induces a chronic infection that in normal individuals is controlled by the immune system. In the case of humoral immunity, epitopes, in particular antigenic domain-1, in glycoprotein B have proven to be important for the induction of virus-neutralizing activity. Such antibodies can exert potent virus-neutralizing activity but can also block neutralizing antibodies from binding. Furthermore, these antibodies differ in their fine recognition of antigenic domain-1 as determined by epitope mapping. By using combinatorial library and phage display technologies we have now isolated a large array of clonally related antibody fragments to understand the origin of this diversity. This procedure allowed us to demonstrate that much of the diversity in functional activity (virus neutralization) and epitope recognition can arise from a single parental molecule through somatic mutation processes. We have thus demonstrated that the clonal diversification of a single antigen-specific clone can account for much of the diversity in antibody anti-viral activity. These findings have implications on the development of a gB-based subunit vaccine, as an effective vaccine preparation need not only to recruit appropriate clones into the immune response but also to evolve them properly so as to maintain an appropriate biological function.

A focused antibody library for improved hapten recognition.

The topography of the antigen-binding site as well as the number and the positioning of the antigen contact residues are strongly correlated with the size of the antigen with which the antibody interacts. On the basis of these considerations, we have designed a focused scFv repertoire biased for haptens, designated the cavity library. The hapten-specific scFv, FITC8, was used as a scaffold for library construction. FITC8, like other hapten binders, displays a characteristic cavity in its paratope into which the hapten binds. In five of the six complementarity-determining regions, diversity-carrying residues were selected rationally on the basis of a model structure of FITC8 and on known antibody structure-function relationships, resulting in variation of 11 centrally located, cavity-lining residues. L3 was allowed to carry a more complex type of diversity. In addition, length variation was introduced into H2, as longer versions of this loop have been shown to correlate with increased hapten binding. The library was screened, using phage display, against a panel of five different haptens, yielding diverse and highly specific binders to four of the antigens. Parallel selections were performed with a library having diversity spread onto a greater area, including more peripherally located residues. This resulted in the isolation of binders, which, in contrast to the clones selected from the cavity library, were not able to bind to the soluble hapten in the absence of the carrier protein. Thus, we have shown that by focusing diversity to the hotspots of interaction a library with improved hapten-binding ability can be created. The study supports the notion that it is possible to create antibody libraries that are biased for the recognition of antigens of pre-defined size.

Isolation of human antibody repertoires with preservation of the natural heavy and light chain pairing.

The humoral immune system in higher vertebrates is unique in its ability to generate highly diverse antibody responses against most pathogens as well as against certain malignancies. Several technologies have been developed to exploit this vast source of potentially therapeutic antibodies, including hybridoma technology, phage display and yeast display. Here, we present a novel, high-throughput technology (the Symplex Technology) for rapid direct cloning and identification of human antigen-specific high-affinity antibodies from single antibody-producing cells of immune individuals. The utility of the technology was demonstrated by isolation of diverse sets of unique high-affinity antibodies against tetanus toxoid and influenza virus from immunized volunteers. Hence, the Symplex Technology is a new method for the rapid isolation of high-affinity antibodies directly from humans.

Simultaneous Targeting of Two Distinct Epitopes on MET Effectively Inhibits MET- and HGF-Driven Tumor Growth by Multiple Mechanisms.

Increased MET activity is linked with poor prognosis and outcome in several human cancers currently lacking targeted therapies. Here, we report on the characterization of Sym015, an antibody mixture composed of two humanized IgG1 antibodies against nonoverlapping epitopes of MET. Sym015 was selected by high-throughput screening searching for antibody mixtures with superior growth-inhibitory activity against MET-dependent cell lines. Synergistic inhibitory activity of the antibodies comprising Sym015 was observed in several cancer cell lines harboring amplified MET locus and was confirmed in vivo Sym015 was found to exert its activity via multiple mechanisms. It disrupted interaction of MET with the HGF ligand and prompted activity-independent internalization and degradation of the receptor. In addition, Sym015 induced high levels of CDC and ADCC in vitro The importance of these effector functions was confirmed in vivo using an Fc-effector function-attenuated version of Sym015. The enhanced effect of the two antibodies in Sym015 on both MET degradation and CDC and ADCC is predicted to render Sym015 superior to single antibodies targeting MET. Our results demonstrate strong potential for use of Sym015 as a therapeutic antibody mixture for treatment of MET-driven tumors. Sym015 is currently being tested in a phase I dose escalation clinical trial (NCT02648724). Mol Cancer Ther; 16(12); 2780-91. ©2017 AACR.

An ERBB1-3 Neutralizing Antibody Mixture With High Activity Against Drug-Resistant HER2+ Breast Cancers With ERBB Ligand Overexpression.

Background: Plasticity of the ERBB receptor network has been suggested to cause acquired resistance to anti-human epidermal growth factor receptor 2 (HER2) therapies. Thus, we studied whether a novel approach using an ERBB1-3-neutralizing antibody mixture can block these compensatory mechanisms of resistance. Methods: HER2+ cell lines and xenografts (n ≥ 6 mice per group) were treated with the ERBB1-3 antibody mixture Pan-HER, trastuzumab/lapatinib (TL), trastuzumab/pertuzumab (TP), or T-DM1. Downregulation of ERBB receptors was assessed by immunoblot analysis and immunohistochemistry. Paired pre- and post-T-DM1 tumor biopsies from patients (n = 11) with HER2-amplified breast cancer were evaluated for HER2 and P-HER3 expression by immunohistochemistry and/or fluorescence in situ hybridization. ERBB ligands were measured by quantitative reverse transcription polymerase chain reaction. Drug-resistant cells were generated by chronic treatment with T-DM1. All statistical tests were two-sided. Results: Treatment with Pan-HER inhibited growth and promoted degradation of ERBB1-3 receptors in a panel of HER2+ breast cancer cells. Compared with TL, TP, and T-DM1, Pan-HER induced a similar antitumor effect against established BT474 and HCC1954 tumors, but was superior to TL against MDA-361 xenografts (TL mean = 2026 mm 3 , SD = 924 mm 3 , vs Pan-HER mean = 565 mm 3 , SD = 499 mm 3 , P = .04). Pan-HER-treated BT474 xenografts did not recur after treatment discontinuation, whereas tumors treated with TL, TP, and T-DM1 did. Post-TP and post-T-DM1 recurrent tumors expressed higher levels of neuregulin-1 (NRG1), HER3 and P-HER3 (all P < .05). Higher levels of P-HER3 protein and NRG1 mRNA were also observed in HER2+ breast cancers progressing after T-DM1 and trastuzumab (NRG1 transcript fold change ± SD; pretreatment = 2, SD = 1.9, vs post-treatment = 11.4, SD = 10.3, P = .04). The HER3-neutralizing antibody LJM716 resensitized the drug-resistant cells to T-DM1, suggesting a causal association between the NRG1-HER3 axis and drug resistance. Finally, Pan-HER treatment inhibited growth of HR6 trastuzumab- and T-DM1-resistant xenografts. Conclusions: These data suggest that upregulation of a NRG1-HER3 axis can mediate escape from anti-HER2 therapies. Further, multitargeted antibody mixtures, such as Pan-HER, can simultaneously remove and/or block targeted ERBB receptor and ligands, thus representing an effective approach against drug-sensitive and -resistant HER2+ cancers.

Sym015: A Highly Efficacious Antibody Mixture against MET-Amplified Tumors.

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.

Recombinant human polyclonal antibodies: A new class of therapeutic antibodies against viral infections.

The mammalian immune system eliminates pathogens by generating a specific antibody response. Polyclonality is a key feature of this immune response: the immune system produces antibodies which bind to different structures on a given pathogen thereby increasing the likelihood of its elimination. The vast majority of current recombinant antibody drugs rely on monospecific monoclonal antibodies. Inherently, such antibodies do not represent the benefits of polyclonality utilized by a natural immune system and this has impeded the identification of efficacious antibody drugs against infectious agents, including viruses. The development of novel technologies has allowed the identification and manufacturing of antigen-specific recombinant polyclonal human antibodies, so-called symphobodies. This review describes the rationale for designing drugs based on symphobodies against pathogenic viruses, including HIV, vaccinia and smallpox virus, and respiratory syncytial virus.

Subtle sequence differences in a tumour-associated peptide epitope translate into major changes in antigenicity.

Antigenicity, the ability to bind to members of repertoire of diverse immune receptors, is a concept that is poorly characterised with respect to its defining parameters. To learn more about its makeup, we have investigated the ability of two peptides with highly related sequences, derived from the tumour-associated antigen mucin-1, to recruit in vitro members from a large naïve repertoire of synthetic human antibody fragments. One of the peptides represents the epitope that is immunodominant in mice. We now demonstrate that the other peptide, which differs from the first only by a very conservative aspartate-threonine to glutamate-serine change, is much less antigenic than the first peptide. This is so despite the fact that there is no observable difference in the tendency of the two peptides to adopt a structure in solution. Furthermore, the peptides differ in their immunodominant parts and the less antigenic peptide selects for antibody fragments targeting residues outside of the epitope considered to be immunodominant in mice. We conclude that subtle sequence changes greatly, affect antigenicity and immunodominance of epitopes in this important tumour-associated antigen.

Pan-HER Inhibitor Augments Radiation Response in Human Lung and Head and Neck Cancer Models.

PURPOSE: Aberrant regulation of the EGF receptor family (EGFR, HER2, HER3, HER4) contributes to tumorigenesis and metastasis in epithelial cancers. Pan-HER represents a novel molecular targeted therapeutic composed of a mixture of six monoclonal antibodies against EGFR, HER2, and HER3. EXPERIMENTAL DESIGN: In the current study, we examine the capacity of Pan-HER to augment radiation response across a series of human lung and head and neck cancers, including EGFR inhibitor-resistant cell lines and xenografts. RESULTS: Pan-HER demonstrates superior antiproliferative and radiosensitizing impact when compared with cetuximab. The mechanisms underlying these effects appear to involve attenuation of DNA damage repair, enhancement of programmed cell death, cell-cycle redistribution, and induction of cellular senescence. Combined treatment of Pan-HER with single or fractionated radiation in human tumor xenografts reveals a potent antitumor and regrowth delay impact compared with Pan-HER or radiation treatment alone. CONCLUSIONS: These data highlight the capacity of Pan-HER to augment radiation response in lung and head and neck cancer models and support investigation of Pan-HER combined with radiation as a promising clinical therapeutic strategy.

Targeting the HER Family with Pan-HER Effectively Overcomes Resistance to Cetuximab.

Cetuximab, an antibody against the EGFR, has shown efficacy in treating head and neck squamous cell carcinoma (HNSCC), metastatic colorectal cancer, and non-small cell lung cancer (NSCLC). Despite the clinical success of cetuximab, many patients do not respond to cetuximab. Furthermore, virtually all patients who do initially respond become refractory, highlighting both intrinsic and acquired resistance to cetuximab as significant clinical problems. To understand mechanistically how cancerous cells acquire resistance, we previously developed models of acquired resistance using the H226 NSCLC and UM-SCC1 HNSCC cell lines. Cetuximab-resistant clones showed a robust upregulation and dependency on the HER family receptors EGFR, HER2, and HER3. Here, we examined pan-HER, a mixture of six antibodies targeting these receptors on cetuximab-resistant clones. In cells exhibiting acquired or intrinsic resistance to cetuximab, pan-HER treatment decreased all three receptors' protein levels and downstream activation of AKT and MAPK. This correlated with decreased cell proliferation in cetuximab-resistant clones. To determine whether pan-HER had a therapeutic benefit in vivo, we established de novo cetuximab-resistant mouse xenografts and treated resistant tumors with pan-HER. This regimen resulted in a superior growth delay of cetuximab-resistant xenografts compared with mice continued on cetuximab. Furthermore, intrinsically cetuximab-resistant HNSCC patient-derived xenograft tumors treated with pan-HER exhibited significant growth delay compared with vehicle/cetuximab controls. These results suggest that targeting multiple HER family receptors simultaneously with pan-HER is a promising treatment strategy for tumors displaying intrinsic or acquired resistance to cetuximab. Mol Cancer Ther; 15(9); 2175-86. ©2016 AACR.