Inhibition of ErbB3 by a monoclonal antibody that locks the extracellular domain in an inactive configuration

A novel fully human anti-NT-ANGPTL3 antibody from phage display library exhibits potent ApoB, TG, and LDL-C lowering activities in hyperlipidemia mice

Dyslipidemia is characterized by elevated plasma levels of low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), and TG-rich lipoprotein (TGRLs) in circulation, and is closely associated with the incidence and development of cardiovascular disease. Angiopoietin-like protein 3 (ANGPTL3) deficiency has been identified as a cause of familial combined hypolipidemia in humans, which allows it to be an important therapeutic target for reducing plasma lipids. Here, we report the discovery and characterization of a novel fully human antibody F1519-D95aA against N-terminal ANGPTL3 (NT-ANGPTL3), which potently inhibits NT-ANGPTL3 with a KD as low as 9.21 nM. In hyperlipidemic mice, F1519-D95aA shows higher apolipoprotein B (ApoB) and TG-lowering, and similar LDL-C reducing activity as compared to positive control Evinacumab (56.50% vs 26.01% decrease in serum ApoB levels, 30.84% vs 25.28% decrease in serum TG levels, 23.32% vs 22.52% decrease in serum LDLC levels, relative to vehicle group). Molecular docking and binding energy calculations reveal that the F1519-D95aA-ANGPTL3 complex (10 hydrogen bonds, -65.51 kcal/mol) is more stable than the Evinacumab-ANGPTL3 complex (4 hydrogen bonds, -63.76 kcal/mol). Importantly, F1519-D95aA binds to ANGPTL3 with different residues in ANGPTL3 from Evinacumab, suggesting that F1519-D95aA may be useful for the treatment of patients resistant to Evinacumab. In conclusion, F1519-D95aA is a novel fully human anti-NT-ANGPTL3 antibody with potent plasma ApoB, TG, and LDL-C lowering activities, which can potentially serve as a therapeutic agent for hyperlipidemia and relevant cardiovascular diseases.

Coordinate transcriptional regulation of ErbB2/3 by C-terminal binding protein 2 signals sensitivity to ErbB2 inhibition in pancreatic adenocarcinoma

There is a critical need to identify new therapeutic vulnerabilities in pancreatic ductal adenocarcinoma (PDAC). Transcriptional co-regulators C-terminal binding proteins (CtBP) 1 and 2 are highly overexpressed in human PDAC, and CRISPR-based homozygous deletion of Ctbp2 in a mouse PDAC cell line (CKP) dramatically decreased tumor growth, reduced metastasis, and prolonged survival in orthotopic mouse allografts. Transcriptomic profiling of tumors derived from CKP vs. Ctbp2-deleted CKP cells (CKP/KO) revealed significant downregulation of the EGFR-superfamily receptor Erbb3, the heterodimeric signaling partner for both EGFR and ErbB2. Compared with CKP cells, CKP/KO cells also demonstrated reduced Erbb2 expression and did not activate downstream Akt signaling after stimulation of Erbb3 by its ligand neuregulin-1. ErbB3 expression in human PDAC cell lines was similarly dependent on CtBP2 and depletion of ErbB3 in a human PDAC cell line severely attenuated growth, demonstrating the critical role of ErbB3 signaling in maintaining PDAC cell growth. Sensitivity to the ErbB2-targeted tyrosine kinase inhibitor lapatinib, but not the EGFR-targeted agent erlotinib, varied in proportion to the level of ErbB3 expression in mouse and human PDAC cells, suggesting that an ErBb2 inhibitor can effectively leverage CtBP2-driven transcriptional activation of physiologic ErbB2/3 expression and signaling in PDAC cells for therapeutic benefit.

Transcriptome sequencing reveals novel molecular features of SLE severity

Introduction: Systemic lupus erythematosus (SLE) is an autoimmune disorder characterized by the production of autoantibodies, immune complex deposition, and tissue/organ damage. In this study, we aimed to identify molecular features and signaling pathways associated with SLE severity using RNA sequencing (RNA-seq), single-cell RNA sequencing (scRNA-seq), and clinical parameters. Methods: We analyzed transcriptome profiles of 45 SLE patients, grouped into mild (mSLE, SLEDAI ≤ 9) and severe (sSLE, SLEDAI > 9) based on SLE Disease Activity Index (SLEDAI) scores. We also collected clinical data on anti-dsDNA, ANA, ESR, CRP, snRNP, AHA, and anti-Smith antibody status for each patient. Results: By comparing gene expression across groups, we identified 12 differentially expressed genes (DEGs), including 7 upregulated (CEACAM6, UCHL1, ARFGEF3, AMPH, SERPINB10, TACSTD2, and OTX1) and 5 downregulated (SORBS2, TRIM64B, SORCS3, DRAXIN, and PCDHGA10) DEGs in sSLE compared to mSLE. Furthermore, using the CIBERSORT algorithm, we found that Treg cells were significantly decreased in sSLE and negatively correlated with AMPH expression, which was mainly expressed in Treg cells from SLE patients according to public scRNA-seq data (GSE135779). Discussion: Overall, our findings shed light on the molecular mechanisms underlying SLE severity and provide insight into potential therapeutic targets.

Pathogenic HER3 dimerization domain mutations create a structural bias towards un-conventional EGFR-HER3 signalling axis in breast cancer

Among the EGFR family of receptors, HER3 is considered as a pseudo-kinase which primarily interacts with HER2 in presence of heregulin-1β. We identified two hotspot mutations i.e. G284R and D297Y and one double mutant HER2-S310F/HER3-G284R in breast cancer patients. Long term MDS (7.5 μs) revealed that HER3-D297Y and HER2-S310F:HER3-G284R do not allow the interaction with HER2 as these mutations cause dramatic conformational changes in its flanking regions. This results in formation of an unstable HER2-WT:HER3-D297Y heterodimer, thereby abrogating the downstream signalling by AKT. We found that His228 and Ser300 of HER3-D297Y form stable interactions with Glu245 and Tyr270 of EGFR-WT, in the presence of either EGF or heregulin-1β. Applying TRIM-ing mediated direct knockdown of endogenous EGFR protein, specificity of the unconventional EGFR:HER3-D297Y interaction was validated. Due to this unusual ligand mediated interaction, cancer cells were found susceptible to EGFR targeted therapeutics i.e. Gefitinib and Erlotinib. Further, in TCGA analysis, BC patients harbouring HER3-D297Y mutation showed increased p-EGFR levels as compared to the patients harbouring HER3-WT and HER3-G284R mutations. For the first time, this comprehensive study showed the importance of specific hotspot mutations in HER3 dimerization domain can defy the Trastuzumab therapy, rather cells become susceptible to the EGFR inhibitors.

HER3 in cancer: from the bench to the bedside

The HER3 protein, that belongs to the ErbB/HER receptor tyrosine kinase (RTK) family, is expressed in several types of tumors. That fact, together with the role of HER3 in promoting cell proliferation, implicate that targeting HER3 may have therapeutic relevance. Furthermore, expression and activation of HER3 has been linked to resistance to drugs that target other HER receptors such as agents that act on EGFR or HER2. In addition, HER3 has been associated to resistance to some chemotherapeutic drugs. Because of those circumstances, efforts to develop and test agents targeting HER3 have been carried out. Two types of agents targeting HER3 have been developed. The most abundant are antibodies or engineered antibody derivatives that specifically recognize the extracellular region of HER3. In addition, the use of aptamers specifically interacting with HER3, vaccines or HER3-targeting siRNAs have also been developed. Here we discuss the state of the art of the preclinical and clinical development of drugs aimed at targeting HER3 with therapeutic purposes.

AXL regulates neuregulin1 expression leading to cetuximab resistance in head and neck cancer

BACKGROUND

The receptor tyrosine kinase (RTK) epidermal growth factor receptor (EGFR) is overexpressed and an important therapeutic target in Head and Neck cancer (HNC). Cetuximab is currently the only EGFR-targeting agent approved by the FDA for treatment of HNC; however, intrinsic and acquired resistance to cetuximab is a major problem in the clinic. Our lab previously reported that AXL leads to cetuximab resistance via activation of HER3. In this study, we investigate the connection between AXL, HER3, and neuregulin1 (NRG1) gene expression with a focus on understanding how their interdependent signaling promotes resistance to cetuximab in HNC.

METHODS

Plasmid or siRNA transfections and cell-based assays were conducted to test cetuximab sensitivity. Quantitative PCR and immunoblot analysis were used to analyze gene and protein expression levels. Seven HNC patient-derived xenografts (PDXs) were evaluated for protein expression levels.

RESULTS

We found that HER3 expression was necessary but not sufficient for cetuximab resistance without AXL expression. Our results demonstrated that addition of the HER3 ligand NRG1 to cetuximab-sensitive HNC cells leads to cetuximab resistance. Further, AXL-overexpressing cells regulate NRG1 at the level of transcription, thereby promoting cetuximab resistance. Immunoblot analysis revealed that NRG1 expression was relatively high in cetuximab-resistant HNC PDXs compared to cetuximab-sensitive HNC PDXs. Finally, genetic inhibition of NRG1 resensitized AXL-overexpressing cells to cetuximab.

CONCLUSIONS

The results of this study indicate that AXL may signal through HER3 via NRG1 to promote cetuximab resistance and that targeting of NRG1 could have significant clinical implications for HNC therapeutic approaches.

Synthesis of Multiple Bispecific Antibody Formats with Only One Single Enzyme Based on Enhanced Trypsiligase

Bispecific antibodies (bsAbs) were first developed in the 1960s and are now emerging as a leading class of immunotherapies for cancer treatment with the potential to further improve clinical efficacy and safety. Many different formats of bsAbs have been established in the last few years, mainly generated genetically. Here we report on a novel, flexible, and fast chemo–enzymatic, as well as purely enzymatic strategies, for generating bispecific antibody fragments by covalent fusion of two functional antibody Fab fragments (Fabs). For the chemo–enzymatic approach, we first modified the single Fabs site-specifically with click anchors using an enhanced Trypsiligase variant (eTl) and afterward converted the modified Fabs into the final heterodimers via click chemistry. Regarding the latter, we used the strain-promoted alkyne-azide cycloaddition (SPAAC) and inverse electron-demand Diels–Alder reaction (IEDDA) click approaches well known for their fast reaction kinetics and fewer side reactions. For applications where the non-natural linkages or hydrophobic click chemistry products might interfere, we developed two purely enzymatic alternatives enabling C- to C- and C- to N-terminal coupling of the two Fabs via a native peptide bond. This simple system could be expanded into a modular system, eliminating the need for extensive genetic engineering. The bispecific Fab fragments (bsFabs) produced here to bind the growth factors ErbB2 and ErbB3 with similar K_D values, such as the sole Fabs. Tested in breast cancer cell lines, we obtained biologically active bsFabs with improved properties compared to its single Fab counterparts.

Enhancing Radioiodine Incorporation in BRAF-Mutant, Radioiodine-Refractory Thyroid Cancers with Vemurafenib and the Anti-ErbB3 Monoclonal Antibody CDX-3379: Results of a Pilot Clinical Trial

Background: Oncogenic activation of mitogen-activated protein kinase (MAPK) signaling is associated with radioiodine refractory (RAIR) thyroid cancer. Preclinical models suggest that activation of the receptor tyrosine kinase erbB-3 (HER3) mitigates the MAPK pathway inhibition achieved by BRAF inhibitors in BRAF^V600E mutant thyroid cancers. We hypothesized that combined inhibition of BRAF and HER3 using vemurafenib and the human monoclonal antibody CDX-3379, respectively, would potently inhibit MAPK activation and restore radioactive iodine (RAI) avidity in patients with BRAF-mutant RAIR thyroid cancer. Methods: Patients with BRAF^V600E RAIR thyroid cancer were evaluated by thyrogen-stimulated iodine-124 (¹²⁴I) positron emission tomography-computed tomography (PET/CT) at baseline and after 5 weeks of treatment with oral vemurafenib 960 mg twice daily alone for 1 week, followed by vemurafenib in combination with 1000 mg of intravenous CDX-3379 every 2 weeks. Patients with adequate ¹²⁴I uptake on the second PET/CT then received therapeutic radioactive iodine (¹³¹I) with vemurafenb+CDX-3379. All therapy was discontinued two days later. Treatment response was monitored by serum thyroglobulin measurements and imaging. The primary endpoints were safety and tolerability of vemurafenib+CDX-3379, as well as the proportion of patients after vemurafenb+CDX-3379 therapy with enhanced RAI incorporation warranting therapeutic ¹³¹I. Results: Seven patients were enrolled; six were evaluable for the primary endpoints. No grade 3 or 4 toxicities related to CDX-3379 were observed. Five patients had increased RAI uptake after treatment; in 4 patients this increased uptake warranted therapeutic ¹³¹I. At 6 months, 2 patients achieved partial response after ¹³¹I and 2 progression of disease. Next-generation sequencing of 5 patients showed that all had co-occurring telomerase reverse transcriptase promoter alterations. A deleterious mutation in the SWItch/Sucrose Non-Fermentable (SWI/SNF) gene ARID2 was discovered in the patient without enhanced RAI avidity after therapy and an RAI-resistant tumor from another patient that was sampled off-study. Conclusions: The endpoints for success were met, providing preliminary evidence of vemurafenib+CDX-3379 safety and efficacy for enhancing RAI uptake. Preclinical data and genomic profiling in this small cohort suggest SWI/SNF gene mutations should be investigated as potential markers of resistance to redifferentiation strategies. Further evaluation of vemurafenib+CDX-3379 as a redifferentiation therapy in a larger trial is warranted (ClinicalTrials.gov: NCT02456701).

A protein network map of head and neck cancer reveals PIK3CA mutant drug sensitivity

[Figure: see text].

Targeting ErbB3 Receptor in Cancer with Inhibitory Antibodies from Llama

The human ErbB3 receptor confers resistance to the pharmacological inhibition of EGFR and HER2 receptor tyrosine kinases in cancer, which makes it an important therapeutic target. Several anti-ErbB3 monoclonal antibodies that are currently being developed are all classical immunoglobulins. We took a different approach and discovered a group of novel heavy-chain antibodies targeting the extracellular domain of ErbB3 via a phage display of an antibody library from immunized llamas. We first produced three selected single-domain antibodies, named BCD090-P1, BCD090-M2, and BCD090-M456, in E. coli, as SUMO fusions that yielded up to 180 mg of recombinant protein per liter of culture. Then, we studied folding, aggregation, and disulfide bond formation, and showed their ultimate stability with half-denaturation of the strongest candidate, BCD090-P1, occurring in 8 M of urea. In surface plasmon resonance experiments, two most potent antibodies, BCD090-P1 and BCD090-M2, bound the extracellular domain of ErbB3 with 1.6 nM and 15 nM affinities for the monovalent interaction, respectively. The receptor binding was demonstrated by immunofluorescent confocal microscopy on four different ErbB3⁺ cancer cell lines. We observed that BCD090-P1 and BCD090-M2 bind noncompetitively to two distinct epitopes on the receptor. Both antibodies inhibited the ErbB3-driven proliferation of MCF-7 breast adenocarcinoma cells and HER2-overexpressing SK-BR-3 cells, with the EC₅₀ in the range of 0.1–25 μg/mL. BCD090-M2 directly blocks ligand binding, whereas BCD090-P1 does not compete with the ligand and presumably acts through a distinct allosteric mechanism. We anticipate that these llama antibodies can be used to engineer new biparatopic anti-ErbB3 or bispecific anti-ErbB2/3 antibodies.

Crystal structures of HER3 extracellular domain 4 in complex with the designed ankyrin-repeat protein D5

The members of the human epidermal growth factor receptor (HER) family are among the most intensely studied oncological targets. HER3 (ErbB3), which had long been neglected, has emerged as a key oncogene, regulating the activity of other receptors and being involved in progression and tumor escape in multiple types of cancer. Designed ankyrin-repeat proteins (DARPins) serve as antibody mimetics that have proven to be useful in the clinic, in diagnostics and in research. DARPins have previously been selected against EGFR (HER1), HER2 and HER4. In particular, their combination into bivalent binders that separate or lock receptors in their inactive conformation has proved to be a promising strategy for the design of potent anticancer therapeutics. Here, the selection of DARPins targeting extracellular domain 4 of HER3 (HER3d4) is described. One of the selected DARPins, D5, in complex with HER3d4 crystallized in two closely related crystal forms that diffracted to 2.3 and 2.0 Å resolution, respectively. The DARPin D5 epitope comprises HER3d4 residues 568-577. These residues also contribute to interactions within the tethered (inactive) and extended (active) conformations of the extracellular domain of HER3.

Disruption of the HER3-PI3K-mTOR oncogenic signaling axis and PD-1 blockade as a multimodal precision immunotherapy in head and neck cancer

Immune checkpoint blockade (ICB) therapy has revolutionized head and neck squamous cell carcinoma (HNSCC) treatment, but <20% of patients achieve durable responses. Persistent activation of the PI3K/AKT/mTOR signaling circuitry represents a key oncogenic driver in HNSCC; however, the potential immunosuppressive effects of PI3K/AKT/mTOR inhibitors may limit the benefit of their combination with ICB. Here we employ an unbiased kinome-wide siRNA screen to reveal that HER3, is essential for the proliferation of most HNSCC cells that do not harbor PIK3CA mutations. Indeed, we find that persistent tyrosine phosphorylation of HER3 and PI3K recruitment underlies aberrant PI3K/AKT/mTOR signaling in PIK3CA wild type HNSCCs. Remarkably, antibody-mediated HER3 blockade exerts a potent anti-tumor effect by suppressing HER3-PI3K-AKT-mTOR oncogenic signaling and concomitantly reversing the immune suppressive tumor microenvironment. Ultimately, we show that HER3 inhibition and PD-1 blockade may provide a multimodal precision immunotherapeutic approach for PIK3CA wild type HNSCC, aimed at achieving durable cancer remission.

A Novel Therapeutic Anti-ErbB3, ISU104 Exhibits Potent Antitumorigenic Activity by Inhibiting Ligand Binding and ErbB3 Heterodimerization

ErbB3, a member of the ErbB receptor family, is a potent mediator in the development and progression of cancer, and its activation plays pivotal roles in acquired resistance against anti-EGFR therapies and other standard-of-care therapies. Upon ligand (NRG1) binding, ErbB3 forms heterodimers with other ErbB proteins (i.e., EGFR and ErbB2), which allows activation of downstream PI3K/Akt signaling. In this study, we developed a fully human anti-ErbB3 antibody, named ISU104, as an anticancer agent. ISU104 binds potently and specifically to the domain 3 of ErbB3. The complex structure of ErbB3-domain 3::ISU104-Fab revealed that ISU104 binds to the NRG1 binding region of domain 3. The elucidated structure suggested that the binding of ISU104 to ErbB3 would hinder not only ligand binding but also the structural changes required for heterodimerization. Biochemical studies confirmed these predictions. ISU104 inhibited ligand binding, ligand-dependent heterodimerization and phosphorylation, and induced the internalization of ErbB3. As a result, downstream Akt phosphorylation and cell proliferation were inhibited. The anticancer efficacy of ISU104 was demonstrated in xenograft models of various cancers. In summary, a highly potent ErbB3 targeting antibody, ISU104, is suitable for clinical development.

Development of a novel, fully human, anti-PCSK9 antibody with potent hypolipidemic activity by utilizing phage display-based strategy

Background

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates serum LDL cholesterol (LDL-C) levels by facilitating the degradation of the LDL receptor (LDLR) and is an attractive therapeutic target for hypercholesterolemia intervention. Herein, we generated a novel fully human antibody with favourable druggability by utilizing phage display-based strategy.

Methods

A potent single-chain variable fragment (scFv) named AP2M21 was obtained by screening a fully human scFv phage display library with hPCSK9, and performing two in vitro affinity maturation processes including CDR-targeted tailored mutagenesis and cross-cloning. Thereafter, it was transformed to a full-length Fc-silenced anti-PCSK9 antibody FAP2M21 by fusing to a modified human IgG1 Fc fragment with L234A/L235A/N297G mutations and C-terminal lysine deletion, thus eliminating its immune effector functions and mitigating mAb heterogeneity.

Findings

Our data showed that the generated full-length anti-PCSK9 antibody FAP2M21 binds to hPCSK9 with a K_D as low as 1.42 nM, and a dramatically slow dissociation rate (k_off, 4.68 × 10⁻⁶ s⁻¹), which could be attributed to its lower binding energy (-47.51 kcal/mol) than its parent counterpart FAP2 (-30.39 kcal/mol). We verified that FAP2M21 potently inhibited PCSK9-induced reduction of LDL-C uptake in HepG2 cells, with an EC₅₀ of 43.56 nM. Further, in hPCSK9 overexpressed C57BL/6 mice, a single tail i.v. injection of FAP2M21 at 1, 3 and 10 mg/kg, dose-dependently up-regulated hepatic LDLR levels, and concomitantly reduced serum LDL-C by 3.3% (P = 0.658, unpaired Student's t-test), 30.2% (P = 0.002, Mann-Whitney U-test) and 37.2% (P = 0.002, Mann-Whitney U-test), respectively.

Interpretation

FAP2M21 with potent inhibitory effect on PCSK9 may serve as a promising therapeutic agent for treating hypercholesterolemia and associated cardiovascular diseases.

Thirty Years of HER3: From Basic Biology to Therapeutic Interventions

HER3 is a pseudokinase member of the EGFR family having a role in both tumor progression and drug resistance. Although HER3 was discovered more than 30 years ago, no therapeutic interventions have reached clinical approval to date. Because the evidence of the importance of HER3 is accumulating, increased amounts of preclinical and clinical trials with HER3-targeting agents are emerging. In this review article, we discuss the most recent HER3 biology in tumorigenic events and drug resistance and provide an overview of the current and emerging strategies to target HER3.

Alternative Splicing of a Receptor Intracellular Domain Yields Different Ectodomain Conformations, Enabling Isoform-Selective Functional Ligands

Events at a receptor ectodomain affect the intracellular domain conformation, activating signal transduction (out-to-in conformational effects). We investigated the reverse direction (in-to-out) where the intracellular domain may impact on ectodomain conformation. The primary sequences of naturally occurring TrkC receptor isoforms (TrkC-FL and TrkC.T1) only differ at the intracellular domain. However, owing to their differential association with Protein Disulfide Isomerase the isoforms have different disulfide bonding and conformations at the ectodomain. Conformations were exploited to develop artificial ligands, mAbs, and small molecules, with isoform-specific binding and biased activation. Consistent, the physiological ligands NT-3 and PTP-sigma bind both isoforms, but NT-3 activates all signaling pathways, whereas PTP-sigma activates biased signals. Our data support an "in-to-out" model controlling receptor ectodomain conformation, a strategy that enables heterogeneity in receptors, ligands, and bioactivity. These concepts may be extended to the many wild-type or oncogenic receptors with known isoforms.

A small molecule inhibitor of HER3: a proof-of-concept study

Despite being catalytically defective, pseudokinases are typically essential players of cellular signalling, acting as allosteric regulators of their active counterparts. Deregulation of a growing number of pseudokinases has been linked to human diseases, making pseudokinases therapeutic targets of interest. Pseudokinases can be dynamic, adopting specific conformations critical for their allosteric function. Interfering with their allosteric role, with small molecules that would lock pseudokinases in a conformation preventing their productive partner interactions, is an attractive therapeutic strategy to explore. As a well-known allosteric activator of epidermal growth factor receptor family members, and playing a major part in cancer progression, the pseudokinase HER3 is a relevant context in which to address the potential of pseudokinases as drug targets for the development of allosteric inhibitors. In this proof-of-concept study, we developed a multiplex, medium-throughput thermal shift assay screening strategy to assess over 100 000 compounds and identify selective small molecule inhibitors that would trap HER3 in a conformation which is unfavourable for the formation of an active HER2-HER3 heterodimer. As a proof-of-concept compound, AC3573 bound with some specificity to HER3 and abrogated HER2-HER3 complex formation and downstream signalling in cells. Our study highlights the opportunity to identify new molecular mechanisms of action interfering with the biological function of pseudokinases.

Neuregulin Signaling Is a Mechanism of Therapeutic Resistance in Head and Neck Squamous Cell Carcinoma

EGFR signaling confers resistance to radiotherapy and is a validated target in head and neck squamous cell carcinoma (HNSCC). The inhibition of EGFR in combination with radiotherapy improves local control and overall survival in these patients; however, therapeutic resistance limits the efficacy of this approach. We therefore sought to identify cellular mechanisms that cause resistance to EGFR inhibition and radiotherapy in HNSCC. Though clonal isolation of carcinoma cells exposed to increasing concentrations of cetuximab, we found that resistant cells upregulate prosurvival ErbB3 and AKT signaling. Using EFM-19 cells and confirmatory analysis of protein levels, we demonstrate that cetuximab resistance is characterized by enhanced neuregulin expression identifying a novel adaptive mechanism of therapeutic resistance. Inhibition of this autocrine loop with CDX-3379 (an ErbB3 specific antibody) was sufficient to block ErbB3/AKT signaling in cetuximab resistant cells. The combination of CDX-3379 and cetuximab reduced proliferation and survival after radiotherapy in several HNSCC cell lines. These in vitro findings were confirmed in xenograft tumor growth experiments including an approach using growth factor-supplemented Matrigel. In vivo, the delivery of EGFR and ErbB3 antibodies significantly reduced tumor growth in cetuximab-resistant FaDu and CAL27 xenografts. In summary, this work demonstrates that autocrine NRG ligand secretion is a mechanism for therapeutic resistance to cetuximab and radiotherapy. This cross-resistance to both therapeutic modalities identifies NRG as an actionable therapeutic target for improving treatment regimens in HNSCC.

Afatinib vs Placebo as Adjuvant Therapy After Chemoradiotherapy in Squamous Cell Carcinoma of the Head and Neck: A Randomized Clinical Trial

Importance

Locoregionally advanced head and neck squamous cell cancer (HNSCC) is treated curatively; however, risk of recurrence remains high among some patients. The ERBB family blocker afatinib has shown efficacy in recurrent or metastatic HNSCC.

Objective

To assess whether afatinib therapy after definitive chemoradiotherapy (CRT) improves disease-free survival (DFS) in patients with HNSCC.

Design, Setting, and Participants

This multicenter, phase 3, double-blind randomized clinical trial (LUX-Head & Neck 2) studied 617 patients from November 2, 2011, to July 4, 2016. Patients who had complete response after CRT, comprising radiotherapy with cisplatin or carboplatin, with or without resection of residual disease, for locoregionally advanced high- or intermediate-risk HNSCC of the oral cavity, hypopharynx, larynx, or oropharynx were included in the study. Data analysis was of the intention-to-treat population.

Interventions

Patients were randomized (2:1) to treatment with afatinib (40 mg/d) or placebo, stratified by nodal status (N0-2a or N2b-3) and Eastern Cooperative Oncology Group performance status (0 or 1). Treatment continued for 18 months or until disease recurrence, unacceptable adverse events, or patient withdrawal.

Main Outcomes and Measures

The primary end point was DFS, defined as time from the date of randomization to the date of tumor recurrence or secondary primary tumor or death from any cause. Secondary end points were DFS at 2 years, overall survival (defined as time from the date of randomization to death), and health-related quality of life.

Results

A total of 617 patients were studied (mean [SD] age, 58 [8.4] years; 528 male [85.6%]). Recruitment was stopped after a preplanned interim futility analysis on July 4, 2016, on recommendation from an independent data monitoring committee. Treatment was discontinued. Median DFS was 43.4 months (95% CI, 37.4 months to not estimable) in the afatinib group and not estimable (95% CI, 40.1 months to not estimable) in the placebo group (hazard ratio, 1.13; 95% CI, 0.81-1.57; stratified log-rank test P = .48). The most common grade 3 and 4 drug-related adverse effects were acneiform rash (61 [14.8%] of 411 patients in the afatinib group vs 1 [0.5%] of 206 patients in the placebo group), stomatitis (55 [13.4%] in the afatinib group vs 1 [0.5%] in the placebo group), and diarrhea (32 [7.8%] in the afatinib group vs 1 [0.5%] in the placebo group).

Conclusions and Relevance

This study's findings indicate that treatment with afatinib after CRT did not improve DFS and was associated with more adverse events than placebo in patients with primary, unresected, clinically high- to intermediate-risk HNSCC. The use of adjuvant afatinib after CRT is not recommended.

Trial Registration

ClinicalTrials.gov identifier: NCT01345669.

HER3 targeting potentiates growth suppressive effects of the PI3K inhibitor BYL719 in pre-clinical models of head and neck squamous cell carcinoma

BYL719 is a PI3K inhibitor that has demonstrated efficacy in the treatment of head and neck squamous cell carcinoma. BYL719 exerts its therapeutic effect by suppressing AKT and other proliferative signaling mechanisms. Despite PI3K inhibition and AKT suppression, residual activity of protein S6, a core marker of proliferative activation, has been observed. HER3, either via dimerization or activation by its ligand neurgeulin (NRG), is known to activate PI3K. Thus, we hypothesized that co-targeting HER3 and PI3K would lead to greater suppression of the PI3K-AKT signaling pathway and greater tumor suppression than with BYL719 alone. We investigated biochemical expression and activation of the HER3-PI3K-AKT-S6 pathway in HNSCC cell lines and patient-derived xenografts (PDXs). Antitumor effects of HER3 and PI3K inhibitors alone and in combination were evaluated in cell culture and murine models. Treatment of HNSCC cell lines with BYL719 significantly reduced AKT activation and suppressed tumor growth. However, S6 was persistently activated despite suppression of AKT. Combination treatment with KTN3379, a monoclonal antibody targeted against HER3, and BYL719 led to enhanced suppression of in vitro and in vivo cancer growth and durable suppression of AKT and S6. Therefore, inhibition of HER3 with KTN3379 enhanced the effects of PI3K inhibition in pre-clinical HNSCC models. These data support co-targeting HER3 and PI3K for the treatment of HSNCC.

Functional genomic characterization of a synthetic anti-HER3 antibody reveals a role for ubiquitination by RNF41 in the anti-proliferative response

Dysregulation of the ErbB family of receptor tyrosine kinases is involved in the progression of many cancers. Antibodies targeting the dimerization domains of family members EGFR and HER2 are approved cancer therapeutics, but efficacy is restricted to a subset of tumors and resistance often develops in response to treatment. A third family member, HER3, heterodimerizes with both EGFR and HER2 and has also been implicated in cancer. Consequently, there is strong interest in developing antibodies that target HER3, but to date, no therapeutics have been approved. To aid the development of anti-HER3 antibodies as cancer therapeutics, we combined antibody engineering and functional genomics screens to identify putative mechanisms of resistance or synthetic lethality with antibody-mediated anti-proliferative effects. We developed a synthetic antibody called IgG 95, which binds to HER3 and promotes ubiquitination, internalization, and receptor down-regulation. Using an shRNA library targeting enzymes in the ubiquitin proteasome system, we screened for genes that effect response to IgG 95 and uncovered the E3 ubiquitin ligase RNF41 as a driver of IgG 95 anti-proliferative activity. RNF41 has been shown previously to regulate HER3 levels under normal conditions and we now show that it is also responsible for down-regulation of HER3 upon treatment with IgG 95. Moreover, our findings suggest that down-regulation of RNF41 itself may be a mechanism for acquired resistance to treatment with IgG 95 and perhaps other anti-HER3 antibodies. Our work deepens our understanding of HER3 signaling by uncovering the mechanistic basis for the anti-proliferative effects of potential anti-HER3 antibody therapeutics.

Structure-Guided Combinatorial Engineering Facilitates Affinity and Specificity Optimization of Anti-CD81 Antibodies

Hepatitis C viral infection is the major cause of chronic hepatitis that affects as many as 71 million people worldwide. Rather than target the rapidly shifting viruses and their numerous serotypes, four independent antibodies were made to target the host antigen CD81 and were shown to block hepatitis C viral entry. The single-chain variable fragment of each antibody was crystallized in complex with the CD81 large extracellular loop in order to guide affinity maturation of two distinct antibodies by phage display. Affinity maturation of antibodies using phage display has proven to be critical to therapeutic antibody development and typically involves modification of the paratope for increased affinity, improved specificity, enhanced stability or a combination of these traits. One antibody was engineered for increased affinity for human CD81 large extracellular loop that equated to increased efficacy, while the second antibody was engineered for cross-reactivity with cynomolgus CD81 to facilitate animal model testing. The use of structures to guide affinity maturation library design demonstrates the utility of combining structural analysis with phage display technologies.

Unbiased Combinatorial Screening Identifies a Bispecific IgG1 that Potently Inhibits HER3 Signaling via HER2-Guided Ligand Blockade

HER2-driven cancers require phosphatidylinositide-3 kinase (PI3K)/Akt signaling through HER3 to promote tumor growth and survival. The therapeutic benefit of HER2-targeting agents, which depend on PI3K/Akt inhibition, can be overcome by hyperactivation of the heregulin (HRG)/HER3 pathway. Here we describe an unbiased phenotypic combinatorial screening approach to identify a bispecific immunoglobulin G1 (IgG1) antibody against HER2 and HER3. In tumor models resistant to HER2-targeting agents, the bispecific IgG1 potently inhibits the HRG/HER3 pathway and downstream PI3K/Akt signaling via a "dock & block" mechanism. This bispecific IgG1 is a potentially effective therapy for breast cancer and other tumors with hyperactivated HRG/HER3 signaling.

Crystal structures of a llama VHH antibody BCD090-M2 targeting human ErbB3 receptor

Background: The ability of ErbB3 receptor to functionally complement ErbB1-2 and induce tumor resistance to their inhibitors makes it a unique target in cancer therapy by monoclonal antibodies. Here we report the expression, purification and structural analysis of a new anti-ErbB3 single-chain antibody. Methods: The VHH fragment of the antibody was expressed in E. coli SHuffle cells as a SUMO fusion, cleaved by TEV protease and purified to homogeneity. Binding to the extracellular domain of ErbB3 was studied by surface plasmon resonance. For structural studies, the antibody was crystallized by hanging-drop vapor diffusion in two different forms. Results: We developed a robust and efficient system for recombinant expression of single-domain antibodies. The purified antibody was functional and bound ErbB3 with K D =15±1 nM. The crystal structures of the VHH antibody in space groups C2 and P1 were solved by molecular replacement at 1.6 and 1.9 Å resolution. The high-quality electron density maps allowed us to build precise atomic models of the antibody and the putative paratope. Surprisingly, the CDR H2 existed in multiple distant conformations in different crystal forms, while the more complex CDR H3 had a low structural variability. The structures were deposited under PDB entry codes 6EZW and 6F0D. Conclusions: Our results may facilitate further mechanistic studies of ErbB3 inhibition by single-chain antibodies. Besides, the solved structures will contribute to datasets required to develop new computational methods for antibody modeling and design.

Crystal structures of a llama VHH antibody BCD090-M2 targeting human ErbB3 receptor

Background: The ability of ErbB3 receptor to functionally complement ErbB1-2 and induce tumor resistance to their inhibitors makes it a unique target in cancer therapy by monoclonal antibodies. Here we report the expression, purification and structural analysis of a new anti-ErbB3 single-chain antibody. Methods: The VHH fragment of the antibody was expressed in E. coli SHuffle cells as a SUMO fusion, cleaved by TEV protease and purified to homogeneity. Binding to the extracellular domain of ErbB3 was studied by surface plasmon resonance. For structural studies, the antibody was crystallized by hanging-drop vapor diffusion in two different forms. Results: We developed a robust and efficient system for recombinant expression of single-domain antibodies. The purified antibody was functional and bound ErbB3 with K D = 1 μM. The crystal structures of the VHH antibody in space groups C2 and P1 were solved by molecular replacement at 1.6 and 1.9 Å resolution. The high-quality electron density maps allowed us to build precise atomic models of the antibody and the putative paratope. Surprisingly, the CDR H2 existed in multiple distant conformations in different crystal forms, while the more complex CDR H3 had a low structural variability. The structures were deposited under PDB entry codes  6EZW and 6F0D. Conclusions: Our results may facilitate further mechanistic studies of ErbB3 inhibition by single-chain antibodies. Besides, the solved structures will contribute to datasets required to develop new computational methods for antibody modeling and design.

A comprehensive review of heregulins, HER3, and HER4 as potential therapeutic targets in cancer

Heregulins (HRGs) bind to the receptors HER3 or HER4, induce receptor dimerization, and trigger downstream signaling that leads to tumor progression and resistance to targeted therapies. Increased expression of HRGs has been associated with worse clinical prognosis; therefore, attempts to block HRG-dependent tumor growth have been pursued. This manuscript summarizes the function and signaling of HRGs and review the preclinical evidence of its involvement in carcinogenesis, prognosis, and treatment resistance in several malignancies such as colorectal cancer, non-small cell lung cancer, ovarian cancer, and breast cancer. Agents in preclinical development and clinical trials of novel therapeutics targeting HRG-dependent signaling are also discussed, including anti-HER3 and -HER4 antibodies, anti-metalloproteinase agents, and HRG fusion proteins. Although several trials have indicated an acceptable safety profile, translating preclinical findings into clinical practice remains a challenge in this field, possibly due to the complexity of downstream signaling and patterns of HRG, HER3 and HER4 expression in different cancer subtypes. Improving patient selection through biomarkers and understanding the resistance mechanisms may translate into significant clinical benefits in the near future.

ErbB activation signatures as potential biomarkers for anti-ErbB3 treatment in HNSCC

Head and neck squamous cell carcinoma (HNSCC) accounts for 3–5% of all tumor types and remains an unmet medical need with only two targeted therapies approved to date. ErbB3 (HER3), the kinase-impaired member of the EGFR/ErbB family, has been implicated as a disease driver in a number of solid tumors, including a subset of HNSCC. Here we show that the molecular components required for ErbB3 activation, including its ligand neuregulin-1 (NRG1), are highly prevalent in HNSCC and that HER2, but not EGFR, is the major activating ErbB3 kinase partner. We demonstrate that cetuximab treatment primarily inhibits the ERK signaling pathway and KTN3379, an anti-ErbB3 monoclonal antibody, inhibits the AKT signaling pathway, and that dual ErbB receptor inhibition results in enhanced anti-tumor activity in HNSCC models. Surprisingly, we found that while NRG1 is required for ErbB3 activation, it was not sufficient to fully predict for KTN3379 activity. An evaluation of HNSCC patient samples demonstrated that NRG1 expression was significantly associated with expression of the EGFR ligands amphiregulin (AREG) and transforming growth factor α (TGFα). Furthermore, NRG1-positive HNSCC cell lines that secreted high levels of AREG and TGFα or contained high levels of EGFR homodimers (H11D) demonstrated a better response to KTN3379. Although ErbB3 and EGFR activation are uncoupled at the receptor level, their respective signaling pathways are linked through co-expression of their respective ligands. We propose that NRG1 expression and EGFR activation signatures may enrich for improved efficacy of anti-ErbB3 therapeutic mAb approaches when combined with EGFR-targeting therapies in HNSCC.

ERBB3: A potential serum biomarker for early detection and therapeutic target for devil facial tumour 1 (DFT1)

Devil Facial Tumour 1 (DFT1) is one of two transmissible neoplasms of Tasmanian devils (Sarcophilus harrisii) predominantly affecting their facial regions. DFT1's cellular origin is that of Schwann cell lineage where lesions are evident macroscopically late in the disease. Conversely, the pre-clinical timeframe from cellular transmission to appearance of DFT1 remains uncertain demonstrating the importance of an effective pre-clinical biomarker. We show that ERBB3, a marker expressed normally by the developing neural crest and Schwann cells, is immunohistohemically expressed by DFT1, therefore the potential of ERBB3 as a biomarker was explored. Under the hypothesis that serum ERBB3 levels may increase as DFT1 invades local and distant tissues our pilot study determined serum ERBB3 levels in normal Tasmanian devils and Tasmanian devils with DFT1. Compared to the baseline serum ERBB3 levels in unaffected Tasmanian devils, Tasmanian devils with DFT1 showed significant elevation of serum ERBB3 levels. Interestingly Tasmanian devils with cutaneous lymphoma (CL) also showed elevation of serum ERBB3 levels when compared to the baseline serum levels of Tasmanian devils without DFT1. Thus, elevated serum ERBB3 levels in otherwise healthy looking devils could predict possible DFT1 or CL in captive or wild devil populations and would have implications on the management, welfare and survival of Tasmanian devils. ERBB3 is also a therapeutic target and therefore the potential exists to consider modes of administration that may eradicate DFT1 from the wild.

Neuregulin 1 Allosterically Enhances the Antitumor Effects of the Noncompeting Anti-HER3 Antibody 9F7-F11 by Increasing Its Binding to HER3

Exploratory clinical trials using therapeutic anti-HER3 antibodies strongly suggest that neuregulin (NRG1; HER3 ligand) expression at tumor sites is a predictive biomarker of anti-HER3 antibody efficacy in cancer. We hypothesized that in NRG1-expressing tumors, where the ligand is present before antibody treatment, anti-HER3 antibodies that do not compete with NRG1 for receptor binding have a higher receptor-neutralizing action than antibodies competing with the ligand for binding to HER3. Using time-resolved-fluorescence energy transfer (TR-FRET), we demonstrated that in the presence of recombinant NRG1, binding of 9F7-F11 (a nonligand-competing anti-HER3 antibody) to HER3 is increased, whereas that of ligand-competing anti-HER3 antibodies (H4B-121, U3-1287, Ab#6, Mab205.10.2, and MOR09825) is decreased. Moreover, 9F7-F11 showed higher efficacy than antibodies that compete with the ligand for binding to HER3. Specifically, 9F7-F11 inhibition of cell proliferation and of HER3/AKT/ERK1/2 phosphorylation as well as 9F7-F11-dependent cell-mediated cytotoxicity were higher in cancer cells preincubated with recombinant NRG1 compared with cells directly exposed to the anti-HER3 antibody. This translated in vivo into enhanced growth inhibition of NRG1-expressing BxPC3 pancreatic, A549 lung, and HCC-1806 breast cell tumor xenografts in mice treated with 9F7-F11 compared with H4B-121. Conversely, both antibodies had similar antitumor effect in NRG1-negative HPAC pancreatic carcinoma cells. In conclusion, the allosteric modulator 9F7-F11 shows increased anticancer effectiveness in the presence of NRG1 and thus represents a novel treatment strategy for NRG1-addicted tumors. Mol Cancer Ther; 16(7); 1312-23. ©2017 AACR.

Inhibition of HER3 activation and tumor growth with a human antibody binding to a conserved epitope formed by domain III and IV

Human epidermal growth factor receptor 3 (HER3, also known as ErbB3) has emerged as relevant target for antibody-mediated tumor therapy. Here, we describe a novel human antibody, IgG 3-43, recognizing a unique epitope formed by domain III and parts of domain IV of the extracellular region of HER3, conserved between HER3 and mouse ErbB3. An affinity of 11 nM was determined for the monovalent interaction. In the IgG format, the antibody bound recombinant bivalent HER3 with subnanomolar affinity (K_D = 220 pM) and HER3-expressing tumor cells with EC₅₀ values in the low picomolar range (27 - 83 pM). The antibody competed with binding of heregulin to HER3-expressing cells, efficiently inhibited phosphorylation of HER3 as well as downstream signaling, and induced receptor internalization and degradation. Furthermore, IgG 3-43 inhibited heregulin-dependent proliferation of several HER3-positive cancer cell lines and heregulin-independent colony formation of HER2-overexpressing tumor cell lines. Importantly, inhibition of tumor growth and prolonged survival was demonstrated in a FaDu xenograft tumor model in SCID mice. These findings demonstrate that by binding to the membrane-proximal domains III and IV involved in ligand binding and receptor dimerization, IgG 3-43 efficiently inhibits activation of HER3, thereby blocking tumor cell growth both in vitro and in vivo.

The ERK/MAPK pathway is overexpressed and activated in gallbladder cancer

Gallbladder cancer (GBC) is a highly fatal disease with poor prognosis and few therapeutic alternatives. Molecular profiling has revealed that the deregulation in the ERK/MAPK signaling pathway plays a crucial role in many disease and malignancies, including GBC. The aim of this study was to measure the expression of ERK1/2 and p-ERK1/2 in a population with high GBC-related mortality, such as the Chilean population, and characterize the protein expression of this ERK/MAPK pathway in seven GBC cell lines. Immunohistochemistry (IHC) for ERK1/2 and p-ERK1/2 was performed in 123 GBC tissues and 37 chronic cholecystitis (CC) tissues. In addition, protein expression analysis by western blot for ERK1/2, p-ERK1/2, EGFR, ERBB2 and ERBB3 were performed in seven GBC cell lines (GB-d1, G415, NOZ, OCUG-1, TGBC-1, TGBC-2 and TGBC-24). A higher ERK1/2 and p-ERK1/2 expression was found in GBC tissues compared to chronic cholecystitis (CC) tissues (P<0.001). However, neither significant differences in overall survival nor significant associations with any of the clinicopathological features were found by comparing low and high expression of both ERK1/2 and p-ERK1/2. Western blot analysis of seven GBC cell lines showed that, in general, GB-d1, G415 and NOZ cells evidenced a strong expression of ERK1/2, p-ERK1/2, EGFR, ERBB2 and ERBB3. Therefore, ERK1/2 and p-ERK1/2 seem to be important in the development of GBC and GB-d1, G415 and NOZ cell lines may be used as experimental models for further in vitro and in vivo studies that help to decipher the role of MAPK/ERK pathway in gallbladder carcinogenesis.

Targeting HER3 using mono- and bispecific antibodies or alternative scaffolds

The human epidermal growth factor receptor 3 (HER3) has in recent years been recognized as a key node in the complex signaling network of many different cancers. It is implicated in de novo and acquired resistance against therapies targeting other growth factor receptors, e.g., EGFR, HER2, and it is a major activator of the PI3K/Akt signaling pathway. Consequently, HER3 has attracted substantial attention, and is today a key target for drugs in clinical development. Sophisticated protein engineering approaches have enabled the generation of a range of different affinity proteins targeting this receptor, including antibodies and alternative scaffolds that are either mono- or bispecific. Here, we describe HER3 and its role as a key tumor target, and give a comprehensive review of HER3-targeted proteins currently in development, including discussions on the opportunities and challenges of targeting this receptor.

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.