Antibody-induced growth inhibition is mediated through immunochemically and functionally distinct epitopes on the extracellular domain of the c-erbB-2 (HER-2/neu) gene product p185

Challenges in Detection of Serum Oncoprotein: Relevance to Breast Cancer Diagnostics

Breast cancer is a highly prevalent malignancy that shows improved outcomes with earlier diagnosis. Current screening and monitoring methods have improved survival rates, but the limitations of these approaches have led to the investigation of biomarker evaluation to improve early diagnosis and treatment monitoring. The enzyme-linked immunosorbent assay (ELISA) is a specific and robust technique ideally suited for the quantification of protein biomarkers from blood or its constituents. The continued clinical relevancy of this assay format will require overcoming specific technical challenges, including the ultra-sensitive detection of trace biomarkers and the circumventing of potential assay interference due to the expanding use of monoclonal antibody (mAb) therapeutics. Approaches to increasing the sensitivity of ELISA have been numerous and include employing more sensitive substrates, combining ELISA with the polymerase chain reaction (PCR), and incorporating nanoparticles as shuttles for detection antibodies and enzymes. These modifications have resulted in substantial boosts in the ability to detect extremely low levels of protein biomarkers, with some systems reliably detecting antigen at sub-femtomolar concentrations. Extensive utilization of mAb therapies in oncology has presented an additional contemporary challenge for ELISA, particularly when both therapeutic and assay antibodies target the same protein antigen. Resolution of issues such as epitope overlap and steric hindrance requires a rational approach to the design of diagnostic antibodies that takes advantage of modern antibody generation pipelines, epitope binning techniques and computational methods to strategically target biomarker epitopes. This review discusses technical strategies in ELISA implemented to date and their feasibility to address current constraints on sensitivity and problems with interference in the clinical setting. The impact of these recent advancements will depend upon their transformation from research laboratory protocols into facile, reliable detection systems that can ideally be replicated in point-of-care devices to maximize utilization and transform both the diagnostic and therapeutic monitoring landscape.

Structural insight into a matured humanized monoclonal antibody HuA21 against HER2-overexpressing cancer cells

HER2, a member of the epidermal growth factor receptor (EGFR) family, has been associated with human breast, ovarian and gastric cancers. Anti-HER2 monoclonal antibodies (mAbs) have demonstrated clinical efficacy for HER2-overexpressing breast cancer. A chimeric antibody chA21 that specifically inhibits the growth of HER2-overexpressing cancer cells both in vitro and in vivo has previously been developed. To reduce a potential human anti-mouse immune response, the humanized antibody HuA21 was developed and was further subjected to affinity maturation by phage display on the basis of chA21. Here, the crystal structure of HuA21-scFv in complex with the extracellular domain of HER2 is reported, which demonstrates that HuA21 binds almost the same epitope as chA21 and also provides insight into how substitutions in HuA21 improve the binding affinity compared with chA21, which could facilitate structure-based optimization in the future. Furthermore, the effects of HuA21 variants with constant domains of different lengths were explored and it was noticed that the deletion of constant domain 1 could improve the inhibition efficacy in a cell-proliferation assay, possibly functioning via increased internalization, which might guide the design of other monoclonal antibodies.

A bispecific anti-ErbB2 antibody potently induces ErbB2 internalization and suppresses ErbB2-overexpressing tumor growth

The anti-ErbB2 humanized antibody trastuzumab was approved for ErbB2-positive metastatic gastric and gastro-esophageal junction cancer in 2010. Despite the effectiveness of trastuzumab, its efficacy remains variable and often modest. Thus, there is an urgent need to improve ErbB2-targeting therapy. Down-regulation of surface receptors induced by monoclonal antibody (mAb) contributes to its antitumor efficacy. Previous studies have demonstrated that if two anti-ErbB2 mAbs did not compete with each other for binding to ErbB2, the combination of them can enhance ErbB2 internalization. In the present study, we investigated ErbB2 internalization-inducing ability of non-competitive anti-ErbB2 mAb combinations and surprisingly found that most of the mAb combinations tested did not down-regulate ErbB2. Only 4 of 18 non-competitive mAb pairs efficiently induced ErbB2 internalization. Interestingly, although the non-competitive anti-ErbB2 mAbs trastuzumab and pertuzumab, either alone or in combination, were ineffective at inducing ErbB2 internalization, TPL, a bispecific antibody engineered from trastuzumab and pertuzumab, potently down-regulated the ErbB2 molecule. Importantly, TPL exhibited a far greater antitumor effect on ErbB2-overexpressing gastric cancer cell line than trastuzumab plus pertuzumab, suggesting that it may be a promising agent for the treatment of gastric cancer.

Multi-level model for the investigation of oncoantigen-driven vaccination effect

Background

Cancer stem cell theory suggests that cancers are derived by a population of cells named Cancer Stem Cells (CSCs) that are involved in the growth and in the progression of tumors, and lead to a hierarchical structure characterized by differentiated cell population. This cell heterogeneity affects the choice of cancer therapies, since many current cancer treatments have limited or no impact at all on CSC population, while they reveal a positive effect on the differentiated cell populations.

Results

In this paper we investigated the effect of vaccination on a cancer hierarchical structure through a multi-level model representing both population and molecular aspects. The population level is modeled by a system of Ordinary Differential Equations (ODEs) describing the cancer population's dynamics. The molecular level is modeled using the Petri Net (PN) formalism to detail part of the proliferation pathway. Moreover, we propose a new methodology which exploits the temporal behavior derived from the molecular level to parameterize the ODE system modeling populations. Using this multi-level model we studied the ErbB2-driven vaccination effect in breast cancer.

Conclusions

We propose a multi-level model that describes the inter-dependencies between population and genetic levels, and that can be efficiently used to estimate the efficacy of drug and vaccine therapies in cancer models, given the availability of molecular data on the cancer driving force.

Bispecific designed ankyrin repeat proteins (DARPins) targeting epidermal growth factor receptor inhibit A431 cell proliferation and receptor recycling

The EGF receptor (EGFR) has been implicated in the development and progression of many tumors. Although monoclonal antibodies directed against EGFR have been approved for the treatment of cancer in combination with chemotherapy, there are limitations in their clinical efficacy, necessitating the search for robust targeting molecules that can be equipped with new effector functions or show a new mechanism of action. Designed ankyrin repeat proteins (DARPins) may provide the targeting component for such novel reagents. Previously, four DARPins were selected against EGFR with (sub)nanomolar affinity. As any targeting module should preferably be able to inhibit EGFR-mediated signaling, their effect on A431 cells overexpressing EGFR was examined: three of them were shown to inhibit proliferation by inducing G(1) arrest, as seen for the Food and Drug Administration-approved antibody cetuximab. To understand this inhibitory mechanism, we mapped the epitopes of the DARPins using yeast surface display. The epitopes for the biologically active DARPins overlapped with the EGF-binding site, whereas the fourth DARPin bound to a different domain, explaining the lack of a biological effect. To optimize the biological activity of the DARPins, we combined two DARPins binding to different epitopes with a flexible linker or with a leucine zipper, leading to a homodimer. The latter DARPin was able to reduce surface EGFR by inhibiting receptor recycling, leading to a dramatic decrease in cell viability. These results indicate that multispecific EGFR-specific DARPins are superior to cetuximab and may form the basis of new opportunities in tumor targeting and tumor therapy.

Structural insights into the down-regulation of overexpressed p185(her2/neu) protein of transformed cells by the antibody chA21

p185(her2/neu) belongs to the ErbB receptor tyrosine kinase family, which has been associated with human breast, ovarian, and lung cancers. Targeted therapies employing ectodomain-specific p185(her2/neu) monoclonal antibodies (mAbs) have demonstrated clinical efficacy for breast cancer. Our previous studies have shown that p185(her2/neu) mAbs are able to disable the kinase activity of homomeric and heteromeric kinase complexes and induce the conversion of the malignant to normal phenotype. We previously developed a chimeric antibody chA21 that specifically inhibits the growth of p185(her2/neu)-overexpressing cancer cells in vitro and in vivo. Herein, we report the crystal structure of the single-chain Fv of chA21 in complex with an N-terminal fragment of p185(her2/neu), which reveals that chA21 binds a region opposite to the dimerization interface, indicating that chA21 does not directly disrupt the dimerization. In contrast, the bivalent chA21 leads to internalization and down-regulation of p185(her2/neu). We propose a structure-based model in which chA21 cross-links two p185(her2/neu) molecules on separate homo- or heterodimers to form a large oligomer in the cell membrane. This model reveals a mechanism for mAbs to drive the receptors into the internalization/degradation path from the inactive hypophosphorylated tetramers formed dynamically by active dimers during a "physiologic process."

Molecular-targeted therapy for cancer and nanotechnology

In order to stop malignant tumor growth, >90% of a critical biochemical pathway needs to be blocked. Due to extraordinary advances in molecular biology, there is an increased understanding of rationale and relevant molecular targets in cancer. However, due to the heterogeneity of the molecular abnormalities in multiple tumor types, strategies designed to interfere with multiple molecular abnormalities will be necessary to impact survival. Nanoparticles have the potential to provide therapies not possible with other drug modalities. Researchers and clinicians must take advantage of these opportunities in order for nanotechnology to make an impact in the diagnosis and treatment of malignancy. A discussion of relevant targets either on the cell surface or the cytoplasm and strategies to achieve optimal drug targeting are the focus of this chapter.

Interactions between anti-ErbB2 antibody A21 and the ErbB2 extracellular domain provide a basis for improving A21 affinity

Anti-ErbB2 antibodies are well researched for the therapy of ErbB2-overexpressing tumors. The therapeutic potential and efficacy of these antibodies are closely related to their affinities to ErbB2. Previously we reported that an anti-ErbB2 antibody A21 targeting a conformational epitope comprising several loops in ErbB2 extracellular subdomain I and II could inhibit the proliferation of ErbB2-overexpressing cancer cells in vitro and in vivo. Here we found that another structureless and non-conserved loop in subdomain I of ErbB2 extracellular domain (ECD) was important for binding to A21, and then the antigen-contact sites on A21 were determined by site-directed mutation. The loop was constructed by molecular modeling, and a new model of A21-ErbB2 complex was generated by docking using the crystal structure of the scfv A21 and the model of ErbB2 ECD with the loop built. Based on the complex model, computational design for A21 affinity improvement was performed to enhance its affinity to ErbB2. Two mutants with about 1.7-fold improvement in affinity were obtained. Our study provided a rational molecular basis for affinity improvement and mechanism investigation of A21.

Persistent elimination of ErbB-2/HER2-overexpressing tumors using combinations of monoclonal antibodies: relevance of receptor endocytosis

Monoclonal antibodies (mAbs) to ErbB-2/HER2 or to its sibling, the epidermal growth factor receptor (EGFR), prolong survival of cancer patients, especially when combined with cytotoxic therapies. However, low effectiveness of therapeutic mAbs and the evolution of patient resistance call for improvements. Here we test in animals pairs of anti-ErbB-2 mAbs and report that pairs comprising an antibody reactive with the dimerization site of ErbB-2 and an antibody recognizing another distinct epitope better inhibit ErbB-2-overexpressing tumors than other pairs or the respective individual mAbs. Because the superiority of antibody combinations extends to tumor cell cultures, we assume that nonimmunological mechanisms contribute to mAb synergy. One potential mechanism, namely the ability of mAb combinations to instigate ErbB-2 endocytosis, is demonstrated. Translation of these lessons to clinical applications may enhance patient response and delay acquisition of resistance.

Antibody-based cancer therapy

BACKGROUND

The clinical efficacy of mAbs is generally ascribed to interference with signaling pathways leading to arrest of cell-cycle progression and inhibition of tumor growth. Furthermore, mAbs also have the capacity to activate effector functions of the innate immune system and facilitate the destruction of malignant cells.

OBJECTIVES

The induction of tumor-specific immunity is a desired outcome in cancer immunotherapy. The prevailing situation raises one major question that has to be addressed. This is the clear need for the induction of tumor-specific immunity by combining mAb treatment with other modalities of cancer immunotherapy.

METHODS

Through mAb treatment, recent efforts focus at initiating or enhancing active antitumor immune responses by i) potentiating co-stimulation and blocking co-inhibition; and ii) rendering tumors more immunogenic through increased tumor peptide expression.

RESULTS/CONCLUSIONS

In this review, the functional characteristics of mAbs, together with their mechanisms of action and clinical application, is summarized as is the potential of combination immunotherapies using mAbs for the augmentation of adaptive antitumor immunity. The results from preclinical and clinical studies demonstrate that mAbs can also promote tumor-specific active immunity.

Therapy of human carcinoma xenografts with antibodies to EGFr and HER-2 conjugated to radionuclides emitting low-energy electrons

PURPOSE

Low-energy electrons (10-50 keV) can be effective and specific cytotoxic agents when delivered to the cell surface by antibodies, because their path length in tissue is comparable to a cell diameter. In this study, we have begun to evaluate the therapeutic potential of antibodies (Abs) conjugated to (111)In against carcinoma xenografts in nude mice.

METHODS

Abs to EGFr or HER-2 were labeled with (111)In to a high specific activity of approximately 1.48 GBq/mg (40 mCi/mg). They were injected into nude mice 5-6 days after inoculation of human carcinoma cells, either A431 or SK-OV-3, and tumor growth was monitored. In preliminary in vitro experiments, we calculated the cumulative decays per cell, estimated the centigray dose delivered to the nucleus, and related this to the fraction surviving.

RESULTS

Abs to both antigens provided significant protection in nude mouse xenograft models (p values ranging from <0.05 to <0.001). Some mice appeared to be cured, but most had delayed tumor growth. The specificity of the effect was demonstrated by testing non-reactive Abs labeled in the same way. The radioactivity was required, because unconjugated Abs had no therapeutic effect. The maximum tolerated dose was required in order for therapy to be effective, but most of the treated mice had no significant weight loss or other overt signs of toxicity.

CONCLUSION

Abs labeled with nuclides emitting low-energy electrons, such as (111)In, can be effective therapeutic agents against microscopic s.c. tumors. This strategy should be considered for clinical applications.

Epitope mapping and structural analysis of an anti‐ErbB2 antibody A21: Molecular basis for tumor inhibitory mechanism

Anti-ErbB2 antibodies targeting distinct epitopes can have different biological functions on cancer cells. A21 prepared by surface epitope masking (SEM) method is a tumor-inhibitory anti-ErbB2 monoclonal antibody. Previously we engineered a single chain chimeric antibody chA21 with potential for therapy of ErbB2-overexpressing tumors. Here, we mapped the A21 epitope on ErbB2 extracellular domain (ECD) by screening a combinatorial phage display peptide library, serial subdomain deletion, and mutagenesis scanning. X-ray crystal structure of the A21 scFv fragment at 2.1 A resolution was also determined. A molecular model of Ag-Ab complex was then constructed based on the crystal structures of the A21 scFv and ErbB2 ECD. Some of biological functions of the A21 mAb and its derivative antibodies including their tumor cell growth inhibition and effects on the expression, internalization, and phosphorylation of ErbB2 receptor were also investigated. The results showed that A21 recognized a conformational epitope comprising a large region mostly from ErbB2 extracellular subdomain I with several surface-exposed residues important for the binding affinity. These data provide unique functional properties of A21 that are quite different from two broadly used anti-ErbB2 mAbs, Herceptin and 2C4. It suggested that the A21 epitope may be another valuable target for designing new anti-ErbB2 therapeutics.

Targeting the function of the HER2 oncogene in human cancer therapeutics

The year 2007 marks exactly two decades since human epidermal growth factor receptor-2 (HER2) was functionally implicated in the pathogenesis of human breast cancer (Slamon et al., 1987). This finding established the HER2 oncogene hypothesis for the development of some human cancers. An abundance of experimental evidence compiled over the past two decades now solidly supports the HER2 oncogene hypothesis. A direct consequence of this hypothesis was the promise that inhibitors of oncogenic HER2 would be highly effective treatments for HER2-driven cancers. This treatment hypothesis has led to the development and widespread use of anti-HER2 antibodies (trastuzumab) in clinical management resulting in significantly improved clinical antitumor efficacies that have transformed the clinical practice of oncology. In the shadows of this irrefutable clinical success, scientific studies have not yet been able to mechanistically validate that trastuzumab inhibits oncogenic HER2 function and it remains possible that the current clinical advances are a consequence of the oncogene hypothesis, but not a translation of it. These looming scientific uncertainties suggest that the full promise of the treatment hypothesis may not yet have been realized. The coming decade will see a second generation of HER2-targeting agents brought into clinical testing and a renewed attempt to treat HER2-driven cancers through the inactivation of HER2. Here, I review the development of treatments that target HER2 in the context of the HER2 oncogene hypothesis, and where we stand with regards to the clinical translation of the HER2 oncogene hypothesis.

In vitro cytotoxicity of carcinoma cells with 111In-labeled antibodies to HER-2

Antibodies conjugated to radionuclides emitting low-energy electrons, which include Auger electrons and some conversion electrons, were recently shown to efficiently kill cells bearing a high density of the antigen recognized. The primary purpose of this study was to determine if such killing could be obtained with anti-HER-2 antibodies conjugated to (111)In, using the chelator benzyl-diethylenetriaminepentaacetic acid, or (125)I. Target cells were the breast carcinoma SK-BR-3 and the ovarian carcinoma SK-OV-3.ip1. In preliminary experiments, antibody accumulation and catabolism during a 2- to 3-day incubation with antibody was investigated. The level of antibody uptake, in terms of molecules per cell, was high enough such that killing seemed feasible. With an (125)I label, but not an (111)In label, increasing the antibody concentration past a certain point caused a decrease in total antibody accumulation, which might be attributed to effects of antibody binding. To test for cytotoxicity, cells were incubated for 2 days with the labeled antibody, then assayed for colony-forming units with a limiting dilution assay. SK-BR-3 cells were strongly killed ( approximately 3 logs) by antibody 21.1, and 100% kill was obtained by combining two noncompeting antibodies to HER-2 (21.1 and 4D5). SK-OV-3.ip.1 cells were more resistant to killing, but use of the two-antibody mixture produced a surviving fraction of approximately 0.002. (111)In-labeled antibodies to other high-density antigens, epithelial glycoprotein-1 and epithelial glycoprotein-2, also killed these target cells. In contrast, unlabeled antibodies or a nonreactive-labeled antibody produced much less cytotoxicity. The same experiment with an (131)I label (a beta-particle emitter) resulted in much greater levels of nonspecific cytotoxicity and essentially no specific cytotoxicity. This approach may be effective for therapy of micrometastases.

The adjuvant activity of BAT antibody enables DNA vaccination to inhibit the progression of established autochthonous Her-2/neu carcinomas in BALB/c mice

Over the course of 33 weeks from birth, the mammary glands of virgin female BALB/c mice transgenic for the transforming rat Her-2/neu oncogene progress from atypical hyperplasia to invasive carcinoma. By week 12, all their mammary glands display many foci of in situ carcinoma. DNA vaccination at weeks 12 and 14 through in vivo electroporation of a plasmid encoding for the extracellular and transmembrane domain of the protein product of rat Her-2/neu oncogene kept 33% of mice tumor-free until week 35, when the experiment ended. To improve its efficacy the vaccine was combined with a T cell stimulatory monoclonal antibody (BAT). When each plasmid electroporation was followed by intravenous administration of 10 microg of BAT monoclonal antibody at weeks 13 and 15, 55% of mice remained tumor free (p < 0.0001) and stronger T cell and antibody-mediated immune responses were elicited. These data suggest that costimulation by BAT monoclonal antibody enables DNA vaccination to establish an effective protection against incipient carcinomas.

Synergistic down-regulation of receptor tyrosine kinases by combinations of mAbs: implications for cancer immunotherapy

mAbs to receptor tyrosine kinases such as EGF receptor/ErbB-1 and HER2/ErbB-2 inhibit the tumorigenic growth of certain cancer cells, but although recombinant versions of such Abs are already used in oncology wards, the mechanism underlying immunotherapy remains unknown. We report that anti-EGF receptor Abs promote a slow endocytic process distinct from the rapid EGF-induced receptor internalization. Combining mAbs that engage distinct epitopes significantly accelerates receptor degradation. In addition, mAb combinations are more effective than single Abs in inhibiting HER2 signaling in vitro and tumorigenesis in animals. We present a model attributing efficacy of immunotherapy to the size of Ab-receptor lattices formed at the cell surface, which dictates the rate of endocytic clearance and extent of signaling blockade.

Inhibition of tumor cell growth by antibodies induced after vaccination with peptides derived from the extracellular domain of Her-2/neu

The anti Her-2/neu monoclonal antibody Trastuzumab has strong inhibiting effects on tumor growth in vitro and in vivo and is therefore used for immunotherapy in breast cancer patients. Due to necessity of frequent applications, however, cost intensiveness of Trastuzumab treatment and its limited duration of affectivity, an active immunization inducing a perhaps preventive and long-term immunity to Her-2/neu remains a desirable goal. We attempted to induce anti Her-2/neu antibodies by peptide vaccination and to test their efficacy in inhibiting tumor cell growth in vitro. By computer aided analyses, 7 putative B cell epitopes of Her-2/neu were defined and synthesized. These peptide epitopes were coupled to tetanus toxoid and used for immunization in BALB/c mice. Among these peptides, immunizations with 2 single peptides or a combination of 2 peptides induced anti-peptide antibody levels, primarily of the IgG1 isotype. These antibodies were also directed against the native Her-2/neu antigen, as shown in precipitation assays and ELISA with cell lysates of the Her-2/neu overexpressing breast cancer cell line SK-BR-3. Isolated IgG fractions from immune sera incubated with SK-BR-3 cells led to a moderate inhibition of the tumor cell growth in vitro, as well as to complement dependent cell lyses comparable to that achieved by incubation with Trastuzumab. Moreover, peptide immunization in rabbits generated anti-Her 2-neu IgG that, in contrast to mouse sera, were able to mediate a 31-46% lysis of SK-BR-3 cells in ADCC experiments. We conclude from our data that immunization with Her-2/neu peptides successfully induced humoral immune response with anti-tumor activity in an animal model.

Novel pharmacological approaches in the treatment of breast cancer

Breast cancer is the most common malignancy among women. Novel pharmacological agents, including hormonal, cytotoxic and biological therapies, are currently being developed and tested in clinical trials and may offer patients more treatment options and an improved chance of long-term survival. Signal transduction inhibitors that block endocrine or growth factor pathways have demonstrated exciting antitumour effects in clinical trials. In addition to new chemotherapeutic drugs, numerous biological agents including growth factor receptor-directed monoclonal antibodies and tyrosine kinase inhibitors that target specific molecular lesions are being examined as potential breast cancer treatments.

Growth factor receptors in breast cancer: potential for therapeutic intervention

Increased expression and activation of receptor tyrosine kinases occurs frequently in human breast carcinomas. Several therapies targeting these receptors are currently in clinical trials. Therapeutic strategies include blockade of individual receptors with monoclonal antibodies and inhibition of tyrosine kinase function. Trastuzumab is the first of these biologic therapies to be approved for patients with human epidermal growth factor receptor 2 (HER2)-overexpressing metastatic breast cancer. Novel trastuzumab-based combinations are being investigated in patients with advanced breast cancer. Large clinical trials have also been launched in the adjuvant setting. Small molecules that inhibit specific tyrosine kinases (e.g., epidermal growth factor receptor, HER2) are in phase I and phase II clinical trials. Other growth-factor-targeted drugs that have reached clinical development include STI571 and antibodies directed at the insulin-like growth factor pathway. Biologic therapies directed against these important receptors are promising. In this review we discuss challenges and opportunities for the development of growth-factor-targeted approaches for the treatment of breast cancer.

A chimeric multi-human epidermal growth factor receptor-2 B cell epitope peptide vaccine mediates superior antitumor responses

Immunotherapeutic approaches to cancer should focus on novel undertakings that modulate immune responses by synergistic enhancement of antitumor immunological parameters. Cancer vaccines should preferably be composed of multiple defined tumor Ag-specific B and T cell epitopes. To develop a multiepitope vaccine, 12 high ranking B cell epitopes were identified from the extracellular domain of the human epidermal growth factor receptor-2 (HER-2) oncoprotein by computer-aided analysis. Four novel HER-2 B cell epitopes were synthesized as chimeras with a promiscuous T cell epitope (aa 288-302) from the measles virus fusion protein (MVF). Two chimeric peptide vaccines, MVF HER-2(316-339) and MVF HER-2(485-503) induced high levels of Abs in outbred rabbits, which inhibited tumor cell growth. In addition, Abs induced by a combination of two vaccines, MVF HER-2(316-339) and MVF HER-2(628-647) down-modulated receptor expression and activated IFN-gamma release better than the individual vaccines. Furthermore, this multiepitope vaccine in combination with IL-12 caused a significant reduction (p = 0.004) in the number of pulmonary metastases induced by challenge with syngeneic tumor cells overexpressing HER-2. Peptide Abs targeting specific sites in the extracellular domain may be used for exploring the oncoprotein's functions. The multiepitope vaccine may have potential application in the treatment of HER-2-associated cancers.

Therapeutic efficacy of anti-ErbB2 immunoliposomes targeted by a phage antibody selected for cellular endocytosis

Many targeted cancer therapies require endocytosis of the targeting molecule and delivery of the therapeutic agent to the interior of the tumor cell. To generate single chain Fv (scFv) antibodies capable of triggering receptor-mediated endocytosis, we previously developed a method to directly select phage antibodies for internalization by recovering infectious phage from the cytoplasm of the target cell. Using this methodology, we reported the selection of a panel of scFv that were internalized into breast cancer cells from a nonimmune phage library. For this work, an immunotherapeutic was generated from one of these scFv (F5), which bound to ErbB2 (HER2/neu). The F5 scFv was reengineered with a C-terminal cysteine, expressed at high levels in Escherichia coli, and coupled to sterically stabilized liposomes. F5 anti-ErbB2 immunoliposomes were immunoreactive as determined by surface plasmon resonance (SPR) and were avidly internalized by ErbB2-expressing tumor cell lines in proportion to the levels of ErbB2 expression. F5-scFv targeted liposomes containing doxorubicin had antitumor activity and produced significant reduction in tumor size in xenografted mice compared to nontargeted liposomes containing doxorubicin. This strategy should be applicable to generate immunotherapeutics for other malignancies by selecting phage antibodies for internalization into other tumor types and using the scFv to target liposomes or other nanoparticles.

Immunological prevention of spontaneous tumors: a new prospect?

Recent demonstrations of the specific immune prevention of mammary cancer in female BALB/c mice transgenic for the rat Her-2/neu oncogene (BALB-neuT) have resulted in reconsideration of the immune mechanisms that inhibit tumor growth. All the mammary glands of these mice progress asynchronously, but consistently, from hyperplasia to invasive carcinoma. Overexpression of the oncogene product p185neu is first evident in the rudimentary glands of 3-week-old mice. Carcinogenesis is prevented by vaccination with plasmids coding for the extracellular and transmembrane domains of this p185neu, or with allogeneic cells expressing p185neu on their membrane, plus the systemic administration of IL-12. This inhibition is the outcome of a delayed-type hypersensitivity specific for p185neu and the production of anti-p185neu antibodies that restrain the proliferation of tumor cells by stripping p185neu from their membrane, whereas cytotoxic T lymphocytes seem devoid of a major role.

Identification of epitope regions recognized by tumor inhibitory and stimulatory anti-ErbB-2 monoclonal antibodies: implications for vaccine design

The self-oncoprotein ErbB-2 is overexpressed in a number of malignancies. The presence of endogenous anti-ErbB-2 Ab and T cell immune responses to this protein in cancer patients has made ErbB-2 an attractive target for active immunization. However, the finding that murine anti-ErbB-2 Abs can have stimulatory, inhibitory, or no effects on cancer cell growth suggests that an inappropriately induced immune response may have an adverse effect. To ensure the induction of a beneficial Ab response, it is important to identify the epitopes recognized by these Abs. In this study we have used phage-displayed ErbB-2 gene fragment libraries and synthetic peptides to epitope-map a panel of anti-ErbB-2 mAbs. The epitopes of three mAbs, N12, N28, and L87, were successfully located to C531-A586, T216-C235, and C220-C235 of ErbB-2, respectively. It was found that while N12 inhibited tumor cell proliferation, N28 stimulated the proliferation of a subset of breast cancer cell lines overexpressing ErbB-2. The peptide region recognized by N12, (C531-A586; EP531), was used as an immunogen to selectively induce an inhibitory immune response in mice. Mice immunized with the GST fusion peptide (GST-EP531) recognized the peptide region EP531 as well as native ErbB-2. More importantly, Igs purified from mouse sera were able to inhibit up to 85% of tumor cell proliferation. In conclusion, our study provides direct evidence of the function-epitope relationship of anti-ErbB-2 Abs and also emphasizes the value of inducing a potent tumor inhibitory polyclonal Ab response by rationally selecting regions of ErbB-2 used for immunization.

Insertion of the DNA for the 163-171 peptide of IL1beta enables a DNA vaccine encoding p185(neu) to inhibit mammary carcinogenesis in Her-2/neu transgenic BALB/c mice

An assessment was made of the effectiveness of DNA vaccination in prevention of the mammary adenocarcinomas of BALB/c female mice transgenic for the activated rat Her-2/neu oncogene. Atypical hyperplasia is evident in their mammary glands when they are 6 weeks old and in situ carcinoma by the 13th week. Palpable invasive carcinomas appear around the 17th week and are always evident in all 10 glands by the 33rd week. Intramuscular vaccinations with 100 microg plasmid DNA encoding the extracellular domain of the Her-2/neu p185 (ECD) performed at the 6th, 12th, 18th and 24th week provided no significant protection, whereas those ECD plasmids in which the DNA coding for the immunomodulatory 163-171 (VQGEESNDK) nonapeptide of human IL1beta (ECD-IL1betap) had been inserted both delayed carcinogenesis and reduced tumor multiplicity. This reduction was associated with a marked immune-inflammatory reaction and a conspicuous leukocyte infiltrate located in the stroma surrounding the hyperplastic mammary ductul-alveolar structures. It was also directly correlated with a high anti-p185(neu) antibody production and an immunoglobulin switch to IgG2a and IgA. No anti-p185(neu) cytotoxic response was found. No significant protection was obtained when the DNA coding for the non-active peptide 189-197 of IL1beta was inserted.

Synergistic interaction between an anti-p185HER-2 pseudomonas exotoxin fusion protein [scFv(FRP5)-ETA] and ionizing radiation for inhibiting growth of ovarian cancer cells that overexpress HER-2

OBJECTIVES

The HER-2 proto-oncogene is overexpressed in 15-30% of ovarian cancers, providing a target for therapy in a fraction of patients. We previously described the ability of a recombinant single-chain anti-p185HER-2-Pseudomonas exotoxin A fusion protein, scFv(FRP5)-ETA, to inhibit growth of cancer cells in culture and tumor xenografts in vivo. We have also described synergistic interaction between an anti-p185HER-2-ricin A chain immunotoxin and ionizing radiation for inhibiting growth of ovarian and breast cancer cells that overexpress HER-2. Our objective in this report was to evaluate the in vitro and in vivo effects of scFv(FRP5)-ETA against SKOv3 ovarian cancer cells that have been transfected to express >10(6) p185HER-2 receptors per cell (clone-9002-18).

METHODS

Inhibition of clonogenic growth was measured in vitro by limiting dilution analysis. Inhibition of tumor growth was measured in vivo using heterografts established with the same ovarian cancer cell lines.

RESULTS

Clone-9002-18 cells were substantially more sensitive than parental SKOv3 cells to the cytotoxic effects of scFv(FRP5)-ETA. Exotoxin fusion protein induced apoptosis in clone-9002-18 cells, but did not affect parental SKOv3 cells. Treatment of clone-9002-18 cells with 200- to 2000-cGy external beam irradiation in combination with scFv(FRP5)-ETA produced synergistic elimination of clonogenic tumor cells in culture. In vivo, subcutaneous or intraperitoneal growth of tumor xenografts in nu/nu mice was significantly inhibited (P = 0.004) by treatment for 10 days with scFv(FRP5)-ETA or with 131I-labeled-520C9 anti-p185HER-2 radionuclide conjugate, but additive effects were not observed with combined treatment.

CONCLUSION

ScFv(FRP5)-ETA deserves further evaluation for intraperitoneal therapy of ovarian cancers that overexpress p185HER-2.

DNA vaccination against rat her-2/Neu p185 more effectively inhibits carcinogenesis than transplantable carcinomas in transgenic BALB/c mice

The ability of vaccination with plasmids coding for the extracellular and the transmembrane domain of the product of transforming rat Her-2/neu oncogene (r-p185) to protect against r-p185(+) transplantable carcinoma (TUBO) cells and mammary carcinogenesis was evaluated. In normal BALB/c mice, DNA vaccination elicits anti-r-p185 Ab, but only a marginal CTL reactivity, and protects against a TUBO cell challenge. Massive reactive infiltration is associated with TUBO cell rejection. In BALB/c mice transgenic for the rat Her-2/neu gene (BALB-neuT), DNA vaccination elicits a lower anti-r-p185 Ab response, no CTL activity and only incompletely protects against TUBO cells, but markedly hampers the progression of carcinogenesis. At 33 wk of age, when control BALB-neuT mice display palpable tumors in all mammary glands, about 60% of immunized mice are tumor free, and tumor multiplicity is markedly reduced. Tumor-free mammary glands still display the atypical hyperplasia of the early stages of carcinogenesis, and a marked down-modulation of r-p185, along with a massive reactive infiltrate. However, BALB-neuT mice protected against mammary carcinogenesis fail to efficiently reject a TUBO cell challenge. This suggests that the mechanisms required for the rejection of transplantable tumors may not coincide with those that inhibit the slow progression of carcinogenesis.

Radioiodinated antibody targeting of the HER-2/neu oncoprotein: effects of labeling method on cellular processing and tissue distribution

Monoclonal antibody (MAb) internalization can have a major effect on tumor retention of radiolabel. Two anti-HER-2/neu MAbs (TA1 and 520C9) were radioiodinated using the iodogen, N-succinimidyl 5-iodo-3-pyridinecarboxylate (SIPC), and tyramine-cellobiose (TCB) methods. Paired-label studies compared internalization and cellular processing of the labeled MAbs by SKOv3 9002-18 ovarian cancer cells in vitro. Intracellular radioiodine activity for 520C9 was up to 2.6 and 3.0 times higher for SIPC and TCB labeling, respectively, compared with iodogen. Likewise, intracellular activity for TA1 was up to 2.3 and 2.9 times higher with the SIPC and TCB methods compared with iodogen labeling. Unfortunately, similar advantages in tumor accumulation were not achieved in athymic mice bearing SKOv3 9008-18 ovarian cancer xenografts.

Relative cytotoxic activity of immunotoxins reactive with different epitopes on the extracellular domain of the c-erbB-2 (HER-2/neu) gene product p185

Different epitopes on the extracellular domain of the HER-2 receptor can serve as distinct targets for immunotoxins. To determine the optimal epitope target for immunotoxin therapy, 7 anti-HER-2 ricin A chain murine monoclonal immunotoxins, each reactive with different epitopes of HER-2 receptor, were tested for cytotoxic activity. The immunotoxins produced 1.2-4.6 logs of cytotoxicity in limiting dilution clonogenic assays with 2 breast cancer cell lines that overexpressed HER-2. Cytotoxicity did not correlate with immunoglobulin isotype, binding affinity, relative position of epitopes or internalization of the anti-HER-2 immunotoxins. Interestingly, the most and least effective immunotoxins bound to epitopes in very close proximity. Competitive binding assays with unconjugated antibodies have previously indicated that our antibodies recognized epitopes that are arranged in a linear array. To orient this relative epitope map, deletions were prepared in the HER-2/neu gene and these mutant constructs were expressed in NIH3T3 cells. Epitope expression was determined by antibody binding and radioimmunoassay. Epitopes targeted by the PB3, 454C11 and NB3 antibodies are localized N-terminal to the epitopes recognized by ID5, BD5, 741F8 and 520C9 antibodies. The 2 non-conformational epitopes PB3 and NB3 were localized to regions corresponding to amino acides 78-242 of the p185(HER-2) protein.

Coexpression of the HER-2 gene product, p185HER-2, and epidermal growth factor receptor, p170EGF-R, on epithelial ovarian cancers and normal tissues

Monoclonal antibodies (MAbs) and immunoconjugates reactive with different antigens expressed by neoplastic cells can inhibit tumor growth. Use of these agents in combination with one another or with chemotherapy can exert additive or synergistic cytotoxicity against tumor cells. An augmented therapeutic activity with favorable therapeutic index might be attained when coexpression is observed on tumor cells, but not in normal tissues. In this study frozen sections of 19 ovarian cancers (2 stage I, 10 stage III, 2 stage IV, and 5 recurrent), as well as 29 normal tissues, were evaluated by immunohistochemistry using 11 distinct MAbs against HER-2/p185 and 2 antibodies against EGF-R/p170 to assess coexpression of these receptors. HER-2/p185 expression was detected in 5 to 100% of ovarian cancers and 0 to 50% of normal ovarian epithelia, depending on the antibody used. EGF-R/p170 expression was detected in approximately 70% of cancers and 40% of normal ovaries by both antibodies. Coexpression of p185 and p170 was observed in 47-68% of ovarian cancers and 9-18% of normal ovarian epithelial specimens depending upon the combination of antibodies used. Staining of 273 specimens from 29 normal tissues indicated that coexpression of HER-2 and EGF-R is rare. Normal tissues that coexpressed both receptors in > or =50% of the cases included cervix, endometrium, esophagus, skin, and prostate. These data confirm that HER-2 and EGF-R are more frequently expressed in advanced ovarian cancers than in normal ovarian epithelium and a significant fraction of these tumors coexpress both HER-2 and EGF-R.

Suppression of diacylglycerol levels by antibodies reactive with the c-erbB-2 (HER-2/neu) gene product p185c-erbB-2 in breast and ovarian cancer cell lines

Seven of 10 murine monoclonal antibodies reactive with the extracellular domain of p185c-erbB-2 inhibited the anchorage independent growth of the SKBr3 breast cancer cell line that overexpressed p185c-erbB-2. Significant inhibition (56-72%) of diacylglycerol (DAG) levels (P < 0.0001) was observed with the 10 antibodies that inhibited SKBr3 growth (RC1, NB3, RC6, PB3, 741F8, DB5, ID5), whereas the 3 antibodies (TA1, 520C9, 454C11) that failed to inhibit SKBr3 growth also failed to affect DAG levels. Thus, DAG levels correlated with antibody-mediated growth regulation for each of the 10 monoclonal reagents. Antibody-induced inhibition of anchorage-independent growth of SKBr3 could be reversed by incubation with phorbol myristate acetate. The ID5 antibody inhibited growth of the SKBr3, SKOv3, and OVCA 432 tumor cell lines, but not of OVCA 420, OVCA 429, and OVCA 433. DAG levels were significantly decreased after ID5 treatment of the SKBr3 and SKOv3 cell lines, but not the OVCA 420, OVCA 429, and OVCA 433 lines. In the 432 line, there was a decrease which did not reach significance. Consequently, changes in DAG levels correlated with growth regulation in 5 of 6 breast and ovarian carcinoma cell lines tested with a trend toward correlation in the sixth. Decreases in DAG may be one mediator of the growth regulatory signals produced by anti-p185c-erbB-2 antibodies.

Human tumor growth suppression by apoptosis induced with anti-ErbB-2 chimeric monoclonal antibody

We established an anti-ErbB-2 mouse-human chimeric monoclonal antibody (MoAb), CH401, which was able to kill cancer cells overexpressing the ErbB-2 protein in vitro. The analysis of the killing mechanism indicated that MoAb CH401 might be the first anti-erbB-2 mouse-human chimeric MoAb which can induce the apoptosis of cancer cells, since morphological changes and DNA fragmentation were recognized in MoAb CH401-treated cells. The ErbB-2 receptor appears to have two opposing functions: acting as a receptor both for a growth factor and for an apoptotic factor. Our results indicate that MoAb CH401 treatment may prove to be very useful for cancer therapy.

A linear region of a monoclonal antibody conformational epitope mapped on p185HER2 oncoprotein

Analysis of epitopes recognized by therapeutic monoclonal antibodies (mAb) is critical in clinical applications and in structure/function studies of target antigen. mAb MGr6 recognizes the extracellular domain of the p185HER2 oncoprotein and is a promising candidate for cancer immunodiagnosis and immunotherapy. Thus, epitope location and structure on p185HER2 need to be investigated. The use of MGr6-selected phage-displayed peptides for epitope analysis served to dissect the MGr6 epitope into at least two subregions, mimicked by CHSDC- and (L)P-(L)K(L) phage displayed peptides, respectively. Comparison of amino acid sequences of CHSDC peptides with the p185HER2 protein sequence and analysis of MGr6 reactivity with p185HER2 deletion mutants identified the linear subregion CCHEQCAAG of the MGr6 epitope, corresponding to amino acids 235-243 of the p185HER2 protein. This continuous subregion is part of a larger conformational epitope, and other amino acids, including a proline, a lysine and leucine residues contained in (L)P-(L)K(L) phage-displayed peptides appear to contribute to the formation of the MGr6 epitope surface.

Inducible antisense inhibition of erbB-2 expression reduces anchorage independent growth of ovarian carcinoma cells

We have investigated the effect of c-erbB-2 expression on the growth of ovarian carcinoma cell lines using antisense methodology. A 1.5 kb fragment of c-erbB-2 cDNA was cloned in an antisense and sense orientation into an IPTG inducible vector. These vectors were stably transfected into two ovarian carcinoma cell lines, one of which (NIH:OVCAR-8) grew well in soft agar. Inhibition of expression of endogenous c-erbB-2 protein was detected by immunoprecipitation and Western blot in both of the induced transfectants with the antisense construct. Although growth in monolayer culture was unaffected, NIH:OVCAR-8 cells transfected with the antisense construct and induced with IPTG lost their ability to form colonies in soft agar. Consequently, endogenous expression of c-erbB-2 modulates anchorage-independent growth of NIH:OVCAR-8.

HER-2/neu protein: a target for antigen-specific immunotherapy of human cancer

The HER-2/neu oncogenic protein is a tumor antigen. Some patients with cancer have a preexistent immune response directed against the HER-2/neu protein. Effective cancer vaccines targeting HER-2/neu will be able to boost this immunity to potentially therapeutic levels. In addition, HER-2/neu-directed monoclonal antibody therapy has been effective in eradicating malignancy in animal models and has shown benefit in the treatment of human HER-2/neu-overexpressing cancers. This review outlines studies that define HER-2/neu-specific immunity in patients with cancer and overviews the current vaccine strategies for generating or augmenting neu-specific immunity. The potential problems associated with eliciting HER-2/neu-specific immunity are addressed, including the question of precipitating autoimmune toxicity against this "self" -protein and the mechanisms of immunological escape that may play a role in preventing effective function of the HER-2/neu-specific immune response. Finally, antibody-based HER-2/neu-directed therapies are overviewed. HER-2/neu is a prototype antigen for groups investigating innovative modifications of monoclonal antibody technology, and cutting edge therapies targeting this antigen are being contemplated for clinical use in the treatment of human malignancy. Immune-based treatments designed to target the HER-2/neu oncogenic protein will soon give the clinical oncologist new therapeutic weapons, directed against a biologically relevant tumor-related protein, with which to fight cancer.

Oncogenes in gynecologic oncology

Advances in molecular biology have facilitated the recent investigation of gynecological malignancies. The presence of certain oncogenes within gynecological tumors indicates that transformation may be associated with genetic alteration of normal regulatory processes. This paper reviews several oncogenes that have been implicated in the transformation of gynecological tissues.

Antigenic and immunogenic mimicry of the HER2/neu oncoprotein by phage-displayed peptides

To recover peptides that antigenically and immunogenically mimic the p185HER2 oncoprotein, we selected the phage-peptide libraries pVIII-9aa and pVIII-9aa. Cys using murine monoclonal antibodies (mAb) MGr2 and MGr6, directed against two distinct epitopes of the p185HER2 extracellular domain. Phage-displayed peptides containing consensus amino acid motifs were recovered and shown to compete specifically for mAb binding on tumor cells that overexpress p185HER2. The deduced amino acid sequence of the peptides suggests that both epitopes defined by the mAb on p185HER2 are discontinuous and that hydrophobic interactions are involved in binding with the mAb. A phage clone displaying the GPLDSLFAQ peptide elicited a specific immune response against the p185HER2 in BALB/c mice, demonstrating that this phage-displayed peptide represents an immunological equivalent of the MGr2 epitope on p185HER2 and might be used as a substitute for this oncoprotein in in vitro and in vivo immunological studies.

The tyrosine kinase activity of the C-erbB-2 gene product (p185) is required for growth inhibition by anti-p185 antibodies but not for the cytotoxicity of an anti-p185-ricin-A chain immunotoxin

Our previous studies have demonstrated that 7 of 10 IgG antibodies against distinct epitopes on the extracellular domain of the c-erbB-2 gene product (p185) inhibit the anchorage-independent growth of SKBr3 human breast-cancer cells that overexpress this transmembrane tyrosine kinase growth-factor receptor. Two of 7 growth-inhibitory antibodies also block the binding and function of the gp30 and p75 c-erbB-2 ligands. In this report we have studied phosphorylation of p185 and different intracellular substrates after binding of antibodies that do or do not inhibit tumor-cell growth. A correlation has been found between antibodies that inhibit growth and the intensity of tyrosine phosphorylation of p185. At late intervals, serine phosphorylation of at least 3 intracellular substrates is increased preferentially by growth-inhibitory antibodies. To test the importance of p185 kinase activity more critically, NIH3T3 cells were transfected with an expression vector containing the full-length human c-erbB-2 gene (cell line 17313), c-erbB-2 with deletion of the kinase region from codons 751-979 (cell line 9309) or c-erbB-2 with deletion of most of the intracellular domain from codons 684-1255 (cell line 9310). Unconjugated antibodies inhibited anchorage-independent growth of 17313 cells as well as SKBr3 cells, but did not inhibit growth of either 9309 or 9310 cells. In contrast, the cytotoxic effect of anti-p185-ricin A chain (RTA) conjugates was comparable for 17313, 9309 and 9310. The tyrosine-kinase activity of p185 is required for growth inhibition mediated by unconjugated anti-p185 antibodies, but not for the cytotoxic activity of anti-p185-RTA immunotoxins.

Soluble c-erbB-2 fragment in serum correlates with disease stage and predicts for shortened survival in patients with early-stage and advanced breast cancer

Seventy-nine patients with advanced breast cancer were tested for the presence, in serum, of a 110 kDa soluble, c-erbB-2 fragment. Thirty-nine patients were seropositive. There was no correlation between seropositivity and menopausal status, or with oestrogen status. In addition, no correlation could be found between tissue c-erbB-2 immunostaining for the external domain of the c-erbB-2 receptor and the presence of soluble c-erbB-2 in serum. The presence of serum soluble c-erbB-2, however, had a significant impact on survival of patients with advanced disease, suggesting that this test may become a useful independent prognostic indicator.