Preclinical pharmacokinetics of MEHD7945A, a novel EGFR/HER3 dual-action antibody, and prediction of its human pharmacokinetics and efficacious clinical dose

Mechanism-based pharmacokinetic and pharmacodynamic modeling for bispecific antibodies: challenges and opportunities

INTRODUCTION

Unlike conventional antibodies, bispecific antibodies (bsAbs) are engineered antibody- or antibody fragment-based molecules that can simultaneously recognize two different epitopes or antigens. Over the past decade, there has been an explosion of bsAbs being developed across therapeutic areas. Development of bsAbs presents unique challenges and mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) modeling has served as a powerful tool to optimize their development and realize their clinical utility.

AREAS COVERED

In this review, the guiding principles and case examples of how fit-for-purpose, mechanism-based PK/PD models have been applied to answer questions commonly encountered in bsAb development are presented. Such models characterize the key pharmacological elements of bsAbs, and they can be utilized for model-informed drug development. We also include the discussion of challenges, knowledge gaps and future direction for such models.

EXPERT OPINION

Mechanistic PK/PD modeling is a powerful tool to support the development of bsAbs. These models can be extrapolated to predict treatment outcomes based on mechanisms of action (MoA) and clinical observations to form positive learn-and-confirm cycles during drug development, due to their abilities to differentiate system- and drug-specific parameters. Meanwhile, the models should keep being adapted according to novel drug design and MoA, providing continuous opportunities for model-informed drug development.

Non-human primates in the PKPD evaluation of biologics: Needs and options to reduce, refine, and replace. A BioSafe White Paper

Monoclonal antibodies (mAbs) deliver great benefits to patients with chronic and/or severe diseases thanks to their strong specificity to the therapeutic target. As a result of this specificity, non-human primates (NHP) are often the only preclinical species in which therapeutic antibodies cross-react with the target. Here, we highlight the value and limitations that NHP studies bring to the design of safe and efficient early clinical trials. Indeed, data generated in NHPs are integrated with in vitro information to predict the concentration/effect relationship in human, and therefore the doses to be tested in first-in-human trials. The similarities and differences in the systems defining the pharmacokinetics and pharmacodynamics (PKPD) of mAbs in NHP and human define the nature and the potential of the preclinical investigations performed in NHPs. Examples have been collated where the use of NHP was either pivotal to the design of the first-in-human trial or, inversely, led to the termination of a project prior to clinical development. The potential impact of immunogenicity on the results generated in NHPs is discussed. Strategies to optimize the use of NHPs for PKPD purposes include the addition of PD endpoints in safety assessment studies and the potential re-use of NHPs after non-terminal studies or cassette dosing several therapeutic agents of interest. Efforts are also made to reduce the use of NHPs in the industry through the use of in vitro systems, alternative in vivo models, and in silico approaches. In the case of prediction of ocular PK, the body of evidence gathered over the last two decades renders the use of NHPs obsolete. Expert perspectives, advantages, and pitfalls with these alternative approaches are shared in this review.

Differences in genomic profile of high-grade urothelial carcinoma according to tumor location

OBJECTIVES

To establish targeted therapies based on the molecular landscape in upper urinary tract urothelial carcinoma (UTUC), we tried to investigate the molecular characteristics of UTUC compared with those of bladder urothelial carcinoma (BLUC) by next-generation sequencing (NGS).

MATERIALS AND METHODS

We selected 71 high-grade infiltrating urothelial carcinoma tissue specimens from 33 UTUC and 38 BLUC patients. NGS analysis was performed with the Illumina TruShigt Oncology-500 panel.

RESULTS

Both UTUC and BLUC showed similar clinicopathologic characteristics, as well as morphologic similarities. The median tumor mutation burden (TMB) of all cases was 7.8 mutations/Mb. The majority of alterations were missense mutations. TP53 (40/71, 56.3%), KDM6A (30/71, 42.3%), and TERT promoter mutations (23/71, 32.4%) were observed regardless of tumor location. Compared with UTUC, BLUC showed frequent mutations in several genes: ARID1A (P = 0.001), ASXL1 (P = 0.017), ERBB3 (P = 0.005), PRKDC (P = 0.004) and RB1 (P = 0.041). On the contrary, copy number loss of FGFR3 was observed more in UTUC than BLUC (P = 0.018). Also, 6 cases showed oncogenic fusions: 3 cases with FGFR2 fusion in UTUC and 3 cases with FGFR3-TACC3 fusion in BLUC.

CONCLUSION

Despite the small cohort size, we identified genetic differences between UTUC and BLUC in Korean patients by NGS. An understanding of the comprehensive molecular characteristics of UTUC and BLUC may be helpful in detecting candidates for targeted therapy.

B-cell epitope peptide cancer vaccines: a new paradigm for combination immunotherapies with novel checkpoint peptide vaccine

In light of the numerous US FDA-approved humanized monoclonal antibodies (mAbs) for cancer immunotherapy, it is surprising that the advancement of B-cell epitope vaccines designed to elicit a natural humoral polyclonal antibody response has not gained traction in the immune-oncology landscape. Passive immunotherapy with humanized mAbs (Trastuzumab [Herceptin®]; Pertuzumab [Perjeta®]) has provided clinical benefit to breast cancer patients, albeit with significant shortcomings including toxicity problems and resistance, high costs, sophisticated therapeutic regimen and long half-life. The role of B-cell humoral immunity in cancer is under appreciated and underdeveloped. We have advanced the idea of active immunotherapy with chimeric B-cell epitope peptides incorporating a 'promiscuous' T-cell epitope that elicits a polyclonal antibody response, which provides safe, cost-effective therapeutic advantage over mAbs. We have created a portfolio of validated B-cell peptide epitopes against multiple receptor tyrosine kinases (HER-1, HER-3, IGF-1R and VEGF). We have successfully translated two HER-2 combination B-cell peptide vaccines in Phase I and II clinical trials. We have recently developed an effective novel PD-1 vaccine. In this article, I will review our approaches and strategies that focus on B-cell epitope cancer vaccines.

Prediction of Human Pharmacokinetics and Clinical Effective Dose of SI-B001, an EGFR/HER3 Bi-specific Monoclonal Antibody

SI-B001 is a new EGFR/HER3 bi-specific antibody showing encouraging anti-tumor efficacy in the preclinical studies and was ready for further clinical research. To help with the dose design, human pharmacokinetics (PK) and clinical effective doses of SI-B001 were predicted by PK and PK/PD modeling and simulation. A Michaels-Menten (M-M) PK model was first used to describe the PK of SI-B001 in cynomolgus monkeys, whose parameters were allometrically scaled to humans for the simulation of human PK profiles. Besides, the anti-tumor efficacy of SI-B001 on different xenografts in tumor-bearing mice was quantitatively described by PK/PD models. The clinical effective doses were predicted by comparing the effective exposure (AUCs) in mice with simulated human AUCs. The clinical effective doses of SI-B001 were predicted to be over 16 mg/kg, 5-7 mg/kg or 5-6 mg/kg per week for colon cancer, head and neck cancer or esophageal cancer, respectively, which may help with the optimization of dose escalation schemes and the selection of indications for SI-B001.

Single cell-produced and in vitro-assembled anti-FcRH5/CD3 T-cell dependent bispecific antibodies have similar in vitro and in vivo properties

Bispecific antibody production using single host cells has been a new advancement in the antibody engineering field. We previously showed comparable in vitro biological activity and in vivo mouse pharmacokinetics (PK) for two novel single cell variants (v10 and v11) and one traditional dual cell in vitro-assembled anti-human epidermal growth factor receptor 2/CD3 T-cell dependent bispecific (TDB) antibodies. Here, we extended our previous work to assess single cell-produced bispecific variants of a novel TDB against FcRH5, a B-cell lineage marker expressed on multiple myeloma (MM) tumor cells. An in vitro-assembled anti- FcRH5/CD3 TDB antibody was previously developed as a potential treatment option for MM. Two bispecific antibody variants (designs v10 and v11) for manufacturing anti-FcRH5/CD3 TDB in single cells were compared to in vitro-assembled TDB in a dual-cell process to understand whether differences in antibody design and production led to any major differences in their in vitro biological activity, in vivo mouse PK, and PK/pharmacodynamics (PD) or immunogenicity in cynomolgus monkeys (cynos). The binding, in vitro potencies, in vitro pharmacological activities and in vivo PK in mice and cynos of these single cell TDBs were comparable to those of the in vitro-assembled TDB. In addition, the single cell and in vitro-assembled TDBs exhibited robust PD activity and comparable immunogenicity in cynos. Overall, these studies demonstrate that single cell-produced and in vitro-assembled anti-FcRH5/CD3 T-cell dependent bispecific antibodies have similar in vitro and in vivo properties, and support further development of single-cell production method for anti-FcRH5/CD3 TDBs and other single-cell bispecifics.

Tutorial on Monoclonal Antibody Pharmacokinetics and Its Considerations in Early Development

The tutorial introduces the readers to the fundamentals of antibody pharmacokinetics (PK) in the context of drug development. Topics covered include an overview of antibody development, PK characteristics, and the application of antibody PK/pharmacodynamics (PD) in research and development decision-making. We also discuss the general considerations for planning a nonclinical PK program and describe the types of PK studies that should be performed during early development of monoclonal antibodies.

HER3 signaling and targeted therapy in cancer

ERBB family members including epidermal growth factor receptor (EGFR) also known as HER1, ERBB2/HER2/Neu, ERBB3/HER3 and ERBB4/HER4 are aberrantly activated in multiple cancers and hence serve as drug targets and biomarkers in modern precision therapy. The therapeutic potential of HER3 has long been underappreciated, due to impaired kinase activity and relatively low expression in tumors. However, HER3 has received attention in recent years as it is a crucial heterodimeric partner for other EGFR family members and has the potential to regulate EGFR/HER2-mediated resistance. Upregulation of HER3 is associated with several malignancies where it fosters tumor progression via interaction with different receptor tyrosine kinases (RTKs). Studies also implicate HER3 contributing significantly to treatment failure, mostly through the activation of PI3K/AKT, MAPK/ERK and JAK/STAT pathways. Moreover, activating mutations in HER3 have highlighted the role of HER3 as a direct therapeutic target. Therapeutic targeting of HER3 includes abrogating its dimerization partners’ kinase activity using small molecule inhibitors (lapatinib, erlotinib, gefitinib, afatinib, neratinib) or direct targeting of its extracellular domain. In this review, we focus on HER3-mediated signaling, its role in drug resistance and discuss the latest advances to overcome resistance by targeting HER3 using mono- and bispecific antibodies and small molecule inhibitors.

Translational pharmacokinetics and pharmacodynamics of monoclonal antibodies

Monoclonal antibodies (mAbs) are an important therapeutic class with complex pharmacology and interdependent pharmacokinetic (PK) and pharmacodynamics (PD) properties. Understanding the PK and PD of mAbs and their biological and mechanistic underpinnings are crucial in enabling their design and selection, designing appropriate efficacy and toxicity studies, translating PK/PD parameters to humans, and optimizing dose and regimen to maximize success in the clinic. Significant progress has been made in this field however many critical questions still remain. This article gives a brief overview of the PK and PD of mAbs, factors that influence them, and areas of ongoing inquiry. Current tools and translational approaches to predict the PK/PD of mAbs in humans are also discussed.

Targeting pathways mediating resistance to anti-EGFR therapy in squamous cell carcinoma of the head and neck

INTRODUCTION

As epidermal growth factor receptor (EGFR) is overexpressed in approximately 90% of squamous cell carcinomas of the head and neck (SCCHN), several therapeutic agents that target EGFR have been evaluated for the treatment of SCCHN. Although patients with SCCHN derive clinical benefit from anti-EGFR agents, most notably the EGFR monoclonal antibody cetuximab, these patients eventually become resistant to EGFR-based therapies; preclinical studies have shown activation of secondary signaling pathways that lead to resistance to EGFR inhibition and, as such, serve as potential therapeutic targets to overcome resistance to EGFR inhibitors.

AREAS COVERED

This review summarizes the results of recently completed trials of anti-EGFR agents in SCCHN, highlights the various mechanisms that drive resistance to EGFR inhibitors in SCCHN, and focuses on several novel targeted agents that could potentially help overcome resistance to EGFR-based therapies in SCCHN. Expert commentary: Due to the development of resistance to EGFR-targeted therapies, novel treatment approaches to overcome resistance are a key unmet need for SCCHN.

Molecularly targeted therapy for the treatment of head and neck cancer: a review of the ErbB family inhibitors

The majority of patients with head and neck squamous cell carcinoma (HNSCC) present with locally advanced disease, which requires site-specific combinations of surgery, radiation, and chemotherapy. Despite aggressive therapy, survival outcomes remain poor, and treatment-related morbidity is not negligible. For patients with recurrent or metastatic disease, therapeutic options are further limited and prognosis is dismal. With this in mind, molecularly targeted therapy provides a promising approach to optimizing treatment efficacy while minimizing associated toxicity. The ErbB family of receptors (ie, epidermal growth factor receptor [EGFR], ErbB2/human epidermal growth factor receptor [HER]-2, ErbB3/HER3, and ErbB4/HER4) is known to contribute to oncogenic processes, such as cellular proliferation and survival. EGFR, specifically, is upregulated in more than 90% of HNSCC, has been implicated in radiation resistance, and correlates with poorer clinical outcomes. The central role of EGFR in the pathogenesis of HNSCC suggests that inhibition of this pathway represents an attractive treatment strategy. As a result, EGFR inhibition has been extensively studied, with the emergence of two classes of drug therapy: monoclonal antibodies and tyrosine kinase inhibitors. While the monoclonal antibody cetuximab is currently the only US Food and Drug Administration-approved EGFR inhibitor for the treatment of HNSCC, numerous investigational drugs are being evaluated in clinical trials. This paper will review the role of the ErbB family in the pathogenesis of HNSCC, as well as the evidence-based data for the use of ErbB family inhibition in clinical practice.

A paradigm shift: Cancer therapy with peptide-based B-cell epitopes and peptide immunotherapeutics targeting multiple solid tumor types: Emerging concepts and validation of combination immunotherapy

There is a recognizable and urgent need to speed the development and application of novel, more efficacious anti-cancer vaccine therapies that inhibit tumor progression and prevent acquisition of tumor resistance. We have created and established a portfolio of validated peptide epitopes against multiple receptor tyrosine kinases and we have identified the most biologically effective combinations of EGFR (HER-1), HER-2, HER-3, VEGF and IGF-1R peptide vaccines/mimics to selectively inhibit multiple receptors and signaling pathways. The strategy is based on the use of chimeric conformational B-cell epitope peptides incorporating "promiscuous" T-cell epitopes that afford the possibility of generating an enduring immune response, eliciting protein-reactive high-affinity anti-peptide antibodies as potential vaccines and peptide mimics that act as antagonists to receptor signaling that drive cancer metastasis. In this review we will summarize our ongoing studies based on the development of combinatorial immunotherapeutic strategies that act synergistically to enhance immune-mediated tumor killing aimed at addressing mechanisms of tumor resistance for several tumor types.

Dual targeting of HER3 and EGFR in colorectal tumors might overcome anti-EGFR resistance

Multiple genetic alterations have been associated with resistance to anti-EGFR therapy in metastatic colorectal cancer (CRC) patients. Research has been mainly focused on driver mutations in KRAS, NRAS, BRAF and PI3K. However, recent evidence suggests a crucial role for non-genetic mechanisms in conferring resistance to anti-EGFR therapy. Specifically, the HER3 receptor is capable of heterodimerizing with multiple EGFR family members resulting in downstream activation of the PI3K and MAPK pathways. Monoclonal antibodies targeted against the HER3 receptor are being investigated in clinical trials; however, preliminary data has shown limited clinical activity. Thus, given the relevance of the HER3 receptor in activating downstream effector pathways and in conferring resistance to anti-EGFR therapy, the therapeutic targeting of HER3 in combination with primary drivers of the tumor is also being investigated. Here, we review the role of HER3 as a promoter of clinical resistance to EGFR therapy and discuss therapeutic approaches that could potentially overcome this resistance.

Cross-arm binding efficiency of an EGFR x c-Met bispecific antibody

Multispecific proteins, such as bispecific antibodies (BsAbs), that bind to two different ligands are becoming increasingly important therapeutic agents. Such BsAbs can exhibit markedly increased target binding and target residence time when both pharmacophores bind simultaneously to their targets. The cross-arm binding efficiency (χ) describes an increase in apparent affinity when a BsAb binds to the second target or receptor (R2) following its binding to the first target or receptor (R1) on the same cell. χ is an intrinsic characteristic of a BsAb mostly related to the binding epitopes on R1 and R2. χ can have significant impacts on the binding to R2 for BsAbs targeting two receptors on the same cell. JNJ-61186372, a BsAb that targets epidermal growth factor receptor (EGFR) and c-Met, was used as the model compound for establishing a method to characterize χ. The χ for JNJ-61186372 was successfully determined via fitting of in vitro cell binding data to a ligand binding model that incorporated χ. The model-derived χ value was used to predict the binding of JNJ-61186372 to individual EGFR and c-Met receptors on tumor cell lines, and the results agreed well with the observed IC50 for EGFR and c-Met phosphorylation inhibition by JNJ-61186372. Consistent with the model, JNJ-61186372 was shown to be more effective than the combination therapy of anti-EGFR and anti-c-Met monovalent antibodies at the same dose level in a mouse xenograft model. Our results showed that χ is an important characteristic of BsAbs, and should be considered for rationale design of BsAbs targeting two membrane bound targets on the same cell.

Molecular Targeting of Growth Factor Receptor Signaling in Radiation Oncology

Ionizing radiation has been shown to activate and interact with multiple growth factor receptor pathways that can influence tumor response to therapy. Among these receptor interactions, the epidermal growth factor receptor (EGFR) has been the most extensively studied with mature clinical applications during the last decade. The combination of radiation and EGFR-targeting agents using either monoclonal antibody (mAb) or small-molecule tyrosine kinase inhibitor (TKI) offers a promising approach to improve tumor control compared to radiation alone. Several underlying mechanisms have been identified that contribute to improved anti-tumor capacity after combined treatment. These include effects on cell cycle distribution, apoptosis, tumor cell repopulation, DNA damage/repair, and impact on tumor vasculature. However, as with virtually all cancer drugs, patients who initially respond to EGFR-targeted agents may eventually develop resistance and manifest cancer progression. Several potential mechanisms of resistance have been identified including mutations in EGFR and downstream signaling molecules, and activation of alternative member-bound tyrosine kinase receptors that bypass the inhibition of EGFR signaling. Several strategies to overcome the resistance are currently being explored in preclinical and clinical models, including agents that target the EGFR T790 M resistance mutation or target multiple EGFR family members, as well as agents that target other receptor tyrosine kinase and downstream signaling sites. In this chapter, we focus primarily on the interaction of radiation with anti-EGFR therapies to summarize this promising approach and highlight newly developing opportunities.

HER3/ErbB3, an emerging cancer therapeutic target

HER3 is a member of the HER (EGFR/ErbB) receptor family consisting of four closely related type 1 transmembrane receptors (EGFR, HER2, HER3, and HER4). HER receptors are part of a complex signaling network intertwined with the Ras/Raf/MAPK, PI3K/AKT, JAK/STAT, and PKC signaling pathways. Aberrant activation of the HER receptors and downstream signaling molecules tips the balance on cellular events, leading to various types of cancers. Monoclonal antibodies (mAbs) and small molecule inhibitors targeting EGFR and HER2 tyrosine kinase activities exhibit clinical benefits in the treatment of several types of cancers, but their clinical efficacy is limited by the occurrence of drug resistance. HER3 is the preferred dimerization partner of HER2 and it is well established that HER3 plays an important role in drug resistance to EGFR- and HER2-targeting therapies. Since HER3 has limited kinase activity, mAbs are being explored to target HER3 for cancer therapy. Currently, approximately a dozen of anti-HER3 mAbs are at different stages of clinical development. However, the lack of established biomarkers has made it more challenging to stratify cancer patients to whom HER3-targeting therapies can be more effective. In this review, we focus on the validation of HER3 as a cancer drug target, the recent development in biomarker discovery for anti-HER3 therapies, and the progress made in the clinical development of HER3-targeting mAbs.

Other targeted drugs in melanoma

Targeted therapy drugs are developed against specific molecular alterations on cancer cells. Because they are "targeted" to the tumor, these therapies are more effective and better tolerated than conventional therapies such as chemotherapy. In the last decade, great advances have been made in understanding of melanoma biology and identification of molecular mechanisms involved in malignant transformation of cells. The identification of oncogenic mutated kinases involved in this process provides an opportunity for development of new target therapies. The dependence of melanoma on BRAF-mutant kinase has provided an opportunity for development of mutation-specific inhibitors with high activity and excellent tolerance that are now being used in clinical practice. This marked a new era in the treatment of metastatic melanoma and much research is now ongoing to identify other "druggable" kinases and transduction signaling networking. It is expected that in the near future the spectrum of target drugs for melanoma treatment will increase. Herein, we review the most relevant potential novel drugs for melanoma treatment based on preclinical data and the results of early clinical trials.

Emerging drugs for head and neck cancer

INTRODUCTION

Despite improvements in treatment, survival rates of head and neck squamous cell carcinoma (HNSCC) are stagnant. The existing chemotherapeutic agents are non-selective and associated with toxicities. Combinations of the only the US FDA-approved epidermal growth factor receptor (EGFR)-targeted agent, cetuximab, with chemotherapy or radiation improves overall survival. However, the response rates to cetuximab are modest. Thus, there is an urgent need for new agents that can be safely integrated into current treatment regimens to improve outcome.

AREAS COVERED

Current EGFR-targeted drugs under clinical development include mAbs and tyrosine kinase inhibitors. The modest efficacy of these drugs implicates intrinsic or acquired resistance. Novel molecular agents inhibiting alternative targets to overcome anti-EGFR resistance in HNSCC are under investigation. Gene therapy and immunotherapy are also promising strategies to improve efficacy and reduce toxicity.

EXPERT OPINION

To date, only six drugs have been FDA-approved for the treatment of head and neck cancer. Cetuximab is the only approved molecular targeting agent for HNSCC and despite ubiquitous expression of EGFR in HNSCC tumors, clinical responses are limited. Genetic and epigenetic characterization of HNSCC tumors, coupled with improved preclinical models, should facilitate the development of more effective drugs.

Mechanisms of and therapeutic approaches for overcoming resistance to epidermal growth factor receptor (EGFR)-targeted therapy in squamous cell carcinoma of the head and neck (SCCHN)

The majority of squamous cell carcinoma of the head and neck (SCCHN) overexpress epidermal growth factor receptor (EGFR), which has been associated with poor treatment response and survival. However, only modest success has been achieved with the use of single agents that target EGFR, possibly due to primary and acquired resistance. This review will discuss key mechanisms of and therapeutic approaches to overcoming resistance to EGFR-targeted therapy in SCCHN. Recent preclinical and clinical investigations have demonstrated that other ErbB family receptors (eg, HER2 and HER3) and other horizontal resistance mechanisms, as well as activation of downstream signaling pathways, epigenetic events, and nuclear EGFR, are possible mediators of resistance to anti-EGFR therapeutics. Key downstream pathways that may be implicated in EGFR resistance include phosphatidylinositol-3-kinase/protein kinase B, vascular endothelial growth factor (VEGF), and mammalian target of rapamycin (mTOR). Multiple agents that target EGFR and other ErbB family members (ie, lapatinib, afatinib, and dacomitinib), as well as combination therapies that target EGFR and selected other pathways (eg, VEGF, mTOR, and c-Met) are being investigated clinically. In addition, several phase II and III trials continue to investigate strategies to enhance the efficacy of EGFR-targeted therapy in SCCHN.

Preclinical pharmacokinetics, pharmacodynamics, and efficacy of RG7116: a novel humanized, glycoengineered anti-HER3 antibody

Purpose

RG7116 is a novel anti-HER3 therapeutic antibody that inhibits HER3 signalling and induces antibody-dependent cellular cytotoxicity of tumor cells due to a glycoengineered antibody Fc moiety. We investigated the efficacy and pharmacokinetic/pharmacodynamic properties of HER3 signal inhibition by RG7116 in a murine xenograft model of human head and neck cancer.

Methods

SCID-beige mice bearing FaDu cells were treated with RG7116 at a weekly dose of 0.3–10 mg/kg, and tumor growth control and modulation of selected proteins (HER3 and AKT) were examined.

Results

Complete tumor stasis up to Day 46 was observed at a dose >3 mg/kg, and this dose down-modulated membrane HER3 expression and inhibited HER3 and AKT phosphorylation. Systemic RG7116 exposure was greater than dose-proportional and total clearance declined with increasing dose, indicating that RG7116 elimination is target-mediated. This is consistent with the better efficacy, and the HER3 and pAKT inhibition, that was observed at doses >1 mg/kg. Tumor regrowth occurred from Day 46 onwards and was associated with HER1 and HER2 upregulation, indicating the activation of alternative HER escape pathways. Modulation of HER3 and phospho-HER3 was also demonstrated in the skin and mucosa of an RG7116-treated cynomolgus monkey, suggesting that these may be useful surrogate tissues for monitoring RG7116 activity.

Conclusions

These data confirm the promising efficacy of RG7116 and highlight the value of assessing the PK behavior of the antibody and measuring target protein modulation as a marker of biological activity. Clinical development of RG7116 has now begun, and phase I trials are ongoing.

HER-3 peptide vaccines/mimics: Combined therapy with IGF-1R, HER-2, and HER-1 peptides induces synergistic antitumor effects against breast and pancreatic cancer cells

The human epidermal growth factor receptor 3 (HER-3/ErbB3) is a unique member of the human epidermal growth factor family of receptors, because it lacks intrinsic kinase activity and ability to heterodimerize with other members. HER-3 is frequently upregulated in cancers with epidermal growth factor receptor (EGFR/HER-1/ErbB1) or human epidermal growth factor receptor 2 (HER-2/ErBB2) overexpression, and targeting HER-3 may provide a route for overcoming resistance to agents that target EGFR or HER-2. We have previously developed vaccines and peptide mimics for HER-1, HER-2 and vascular endothelial growth factor (VEGF). In this study, we extend our studies by identifying and evaluating novel HER-3 peptide epitopes encompassing residues 99-122, 140-162, 237-269 and 461-479 of the HER-3 extracellular domain as putative B-cell epitopes for active immunotherapy against HER-3 positive cancers. We show that the HER-3 vaccine antibodies and HER-3 peptide mimics induced antitumor responses: inhibition of cancer cell proliferation, inhibition of receptor phosphorylation, induction of apoptosis and antibody dependent cellular cytotoxicity (ADCC). Two of the HER-3 epitopes 237-269 (domain II) and 461-479 (domain III) significantly inhibited growth of xenografts originating from both pancreatic (BxPC3) and breast (JIMT-1) cancers. Combined therapy of HER-3 (461-471) epitope with HER-2 (266-296), HER-2 (597-626), HER-1 (418-435) and insulin-like growth factor receptor type I (IGF-1R) (56-81) vaccine antibodies and peptide mimics show enhanced antitumor effects in breast and pancreatic cancer cells. This study establishes the hypothesis that combination immunotherapy targeting different signal transduction pathways can provide effective antitumor immunity and long-term control of HER-1 and HER-2 overexpressing cancers.

Incorporating target-mediated drug disposition in a minimal physiologically-based pharmacokinetic model for monoclonal antibodies

Target-mediated drug disposition (TMDD) usually accounts for nonlinear pharmacokinetics (PK) of drugs whose distribution and/or clearance are affected by their targets owing to high affinity and limited capacity. TMDD is frequently reported for monoclonal antibodies (mAb) for such reason. Minimal physiologically-based pharmacokinetic models (mPBPK), which accommodate the unique PK behaviors of mAb, provide a general approach for analyzing mAbs PK and predicting mAb interstitial concentrations in two groups of tissues. This study assessed the feasibility of incorporating TMDD into mPBPK models to consider target-binding in either plasma (cTMDD) or interstitial fluid (ISF) (pTMDD). The dose-related signature profiles of the pTMDD model reveal a parallel early decay phase, in contrast with the cTMDD model that exhibits a faster initial decline for low doses. The parallel early phase in the pTMDD model is associated with the slow perivascular extravasation of mAb, which restricts the initial decline regardless of interstitial target-mediated elimination. The cTMDD and pTMDD models both preserve the long terminal phase that is typically perceived in conventional two-compartment (2CM) and TMDD models. Having TMDD in ISF impacts the typical relationships between plasma concentrations and receptor occupancy, and between saturation of apparent nonlinear clearance and saturation of receptors. The vascular reflection coefficient (σ v ) was found to affect receptor occupancy in ISF. In the cTMDD model, saturation of nonlinear clearance is equivalent to saturation of receptors. However, in the pTMDD model, they are no longer equal and all parameters pertaining to receptors or receptor binding (R total , K D , K ss , k int ) shifts such relationships. Different TMDD models were utilized in analyzing PK for seven mAbs from digitized literature data. When the target is in plasma, the cTMDD model performed similarly to the 2CM and TMDD models, but with one less system parameter. When the target exists in ISF, the pTMDD functioned well in analyzing only plasma data to reflect interstitial target binding properties. Assigning TMDD consistent with target-expressing tissues is important to obtain reliable characterizations of receptors and receptor binding. The mPBPK model exhibits excellent feasibility in integrating TMDD not only in plasma but also in ISF.

EGF receptor family: twisting targets for improved cancer therapies

The epidermal growth factor receptor (EGFR) undergoes a conformational change in response to ligand binding. The ligand-induced changes in cell surface aggregation and mobility have a profound effect on the function of all the family members. Ligand also activates the EGFR intracellular kinase, stimulating proliferation and cell survival. The EGFR family are often activated, overexpressed or mutated in cancer cells and therapeutic drugs (including antibodies) can slow the progress of some cancers. This article provides a brief, annotated summary of the presentations and discussion which occurred at the Epidermal Growth Factor Receptor - Future Directions Conference held in Jerusalem in November 2013.

Current challenges and clinical investigations of epidermal growth factor receptor (EGFR)- and ErbB family-targeted agents in the treatment of head and neck squamous cell carcinoma (HNSCC)

Overexpression of the epidermal growth factor receptor (EGFR) is a common characteristic of head and neck squamous cell carcinomas (HNSCC). Cetuximab is a chimeric anti-EGFR monoclonal antibody (mAb) with multiple approved indications in HNSCC, including with radiation therapy (RT) for locoregionally advanced disease, as monotherapy after platinum progression, and with platinum/5-fluorouracil for recurrent or metastatic disease. There remain, however, numerous unanswered questions regarding the optimal use of cetuximab in HNSCC, including patient selection, its mechanisms of action and resistance, the effect of human papillomavirus status on outcomes, its role when combined with induction chemotherapy or adjuvant radiation, and optimal management of skin toxicity and hypersensitivity reactions. In addition, a variety of other anti-EGFR agents (the multitargeted small molecule tyrosine kinase inhibitors [TKIs] lapatinib, dacomitinib, and afatinib and the anti-EGFR mAbs zalutumumab, nimotuzumab, and panitumumab) are currently under investigation in phase II and III clinical trials in different HNSCC therapeutic settings. The anti-EGFR TKI erlotinib is currently in phase III development for oral cancer prevention. Numerous other drugs are in earlier stages of development for HNSCC treatment, including novel anti-EGFR mAbs (MEHD7945A, necitumumab, and RO5083945), small-molecule TKIs (vandetanib, icotinib, and CUDC-101), EGFR antisense, various add-on therapies to radiation and chemotherapy (bevacizumab, interleukin-12, lenalidomide, alisertib, and VTX-2337), and drugs (temsirolimus, everolimus, OSI-906, dasatinib, and PX-866) intended to overcome resistance to anti-EGFR agents. Overall, a wealth of clinical trial data is expected in the coming years, with the potential to modify significantly the approach to anti-EGFR therapy for HNSCC.

Death receptor 5 agonistic antibody PRO95780: preclinical pharmacokinetics and concentration-effect relationship support clinical dose and regimen selection

PURPOSE

PRO95780, a human monoclonal antibody (mAb) against death receptor 5 (DR5/TRAIL-R2/TNFRSF10B), was developed for the treatment for cancer. Our objective was to characterize pharmacokinetics (PK) in mice, rats, and cynomolgus monkeys and concentration-effect relationships of PRO95780 in xenograft mouse models of human cancers; this would guide the selection of dose and regimen for clinical trials.

METHODS

The PK profiles were determined in mice, rats, and cynomolgus monkeys. Three xenograft models with a wide range of in vitro sensitivities to PRO95780 were selected for efficacy studies. Tumoristatic serum concentrations (TSCs) were determined using PK/pharmacodynamic (PD) modeling with tumor growth as a PD endpoint. A species-invariant time PK scaling method was employed to estimate disposition in humans using PK data in cynomolgus monkeys. Furthermore, the predicted human PK parameters were used to estimate dose and regimen to achieve TSC observed in mice at the steady-state trough concentrations (C trough ss) in the clinic.

RESULTS

Linear PK was observed across species. A serum concentration of 22 μg/mL was identified to be the target TSC in mice. A dose of 10 mg/kg administered once every 2 weeks (Q2W) was predicted to achieve a TSC at C trough ss in 95 % of patients.

CONCLUSIONS

PRO95780 has linear PK in mice, rats, and monkeys. Estimated TSCs varied among different xenograft models. A projected target dose in humans is achievable for Q2W administration within the dose range used for other commercial mAbs.

Profiling epidermal growth factor receptor and heregulin receptor 3 heteromerization using receptor tyrosine kinase heteromer investigation technology

Heteromerization can play an important role in regulating the activation and/or signal transduction of most forms of receptors, including receptor tyrosine kinases (RTKs). The study of receptor heteromerization has evolved extensively with the emergence of resonance energy transfer based approaches such as bioluminescence resonance energy transfer (BRET). Here, we report an adaptation of our Receptor-Heteromer Investigation Technology (Receptor-HIT) that has recently been published as the G protein-coupled receptor (GPCR) Heteromer Identification Technology (GPCR-HIT). We now demonstrate the utility of this approach for investigating RTK heteromerization by examining the functional interaction between the epidermal growth factor (EGF) receptor (EGFR; also known as erbB1/HER1) and heregulin (HRG) receptor 3 (HER3; also known as erbB3) in live HEK293FT cells using recruitment of growth factor receptor-bound protein 2 (Grb2) to the activated receptors. We found that EGFR and HER3 heteromerize specifically as demonstrated by HRG inducing a BRET signal between EGFR/Rluc8 and Grb2/Venus only when HER3 was co-expressed. Similarly, EGF stimulation promoted a specific BRET signal between HER3/Rluc8 and Grb2/Venus only when EGFR was co-expressed. Both EGF and HRG effects on Grb2 interaction are dose-dependent, and specifically blocked by EGFR inhibitor AG-1478. Furthermore, truncation of HER3 to remove the putative Grb2 binding sites appears to abolish EGF-induced Grb2 recruitment to the EGFR-HER3 heteromer. Our results support the concept that EGFR interacts with Grb2 in both constitutive and EGF-dependent manners and this interaction is independent of HER3 co-expression. In contrast, HER3-Grb2 interaction requires the heteromerization between EGFR and HER3. These findings clearly indicate the importance of EGFR-HER3 heteromerization in HER3-mediated Grb2-dependent signaling pathways and supports the central role of HER3 in the diversity and regulation of HER family functioning.

The promise of anti-ErbB3 monoclonals as new cancer therapeutics

In the last 3-5 years strong evidence has been gathered demonstrating ErbB3 as a key node for the progression of several cancer types. From the mechanistic standpoint the intracellular region of this receptor is rich of tyrosine residues that, upon phosphorylation, become high affinity binding sites for PI3K and other proteins involved in signal transduction. The involvement of ErbB3 occurs at different levels, most likely as a consequence of its promiscuity in the interaction with other RTKs of the same or other families. Several efforts are therefore being put in the development of antibodies that target this receptor either singly or in combination with other synergizing receptors. Some of these compounds have already entered clinical development. Although clinical proof-of-concept has not yet been achieved, this is likely to occur soon and will further accelerate the inclusion of anti-ErbB3 monoclonals in the repertoire of anticancer agents for more effective combination therapy. In this paper we review the wealth of anti-ErbB3 antibodies under development and compare their properties and potential to become marketed drugs.

Investigational therapies targeting the ErbB (EGFR, HER2, HER3, HER4) family in GI cancers

INTRODUCTION

Gastrointestinal (GI) malignancies account for nearly one-fourth of all cancer-related deaths in the United States and approximately 30% of all cancer-related deaths worldwide. Use of combination cytotoxic therapy offers a modest improvement in survival, but the prognosis and long-term survival of most patients with GI cancer remains poor. In certain GI malignancies, therapies that target members of the HER family of receptors have positively impacted patient care.

AREAS COVERED

In this review, we discuss the significance of the HER family of receptors in esophagogastric, hepatobiliary, pancreatic, and colorectal cancers and explain the rationale supporting the use of monoclonal antibodies (mAbs) and small molecule tyrosine kinase inhibitors (TKIs) to inhibit HER activation and downstream events that contribute to tumor proliferation, migration, and survival.

EXPERT OPINION

Despite recent advances, the treatment of GI cancers remains challenging. Therapies targeting the HER family of receptors have been extensively studied in these malignancies with inconsistent results. The rationale behind varied tumor responses with these agents remains uncertain. We believe that additional studies are needed to identify biomarkers that could help identify a population of patients who would be more responsive to a given therapy.

Trifunctional antibody ertumaxomab: Non-immunological effects on Her2 receptor activity and downstream signaling

BACKGROUND

The trifunctional antibody ertumaxomab bivalently targets the human epidermal growth factor receptor 2 (Her2) on epithelial (tumor) cells and the T cell specific CD3 antigen, and its Fc region is selectively recognized by Fcγ type I/III receptor-positive immune cells. As a trifunctional immunoglobulin, ertumaxomab therefore not only targets Her2 on cancer cells, but also triggers immunological effector mechanisms mediated by T and accessory cells (e.g., macrophages, dendritic cells, natural killer cells). Whether molecular effects, however, might contribute to the cellular antitumor efficiency of ertumaxomab are largely unknown.

METHODS

Potential molecular effects of ertumaxomab on Her2-overexpressing BT474 and SK-BR-3 breast cancer cells were evaluated. The dissociation constant Kd of ertumaxomab was calculated from titration curves that were recorded by flow cytometry. Treatment-induced changes in Her2 homodimerization were determined by flow cytometric fluorescence resonance energy transfer measurements on a cell-by-cell basis. Potential activation / deactivation of Her2, ERK1/2, AKT and STAT3 were analyzed by western blotting, Immunochemistry and immunofluorescent cell staining.

RESULTS

The Kd of ertumaxomab for Her2-binding was determined at 265 nM and the ertumaxomab binding epitope was found to not overlap with that of the therapeutic anti-Her2 monoclonal antibodies trastuzumab and pertuzumab. Ertumaxomab caused an increase in Her2 phosphorylation at higher antibody concentrations, but changed neither the rate of Her2-homodimerization /-phosphorylation nor the activation state of key downstream signaling proteins analyzed.

CONCLUSIONS

The unique mode of action of ertumaxomab, which relies more on activation of immune-mediated mechanisms against tumor cells compared with currently available therapeutic antibodies for breast cancer treatment, suggests that modular or sequential treatment with the trifunctional bivalent antibody might complement the therapeutic activity of other anti-Her2/anti-ErbB receptor reagents.