Monoclonal antibody 425 inhibits growth stimulation of carcinoma cells by exogenous EGF and tumor-derived EGF/TGF-alpha

Cetuximab Resistance in Squamous Carcinomas of the Upper Aerodigestive Tract Is Driven by Receptor Tyrosine Kinase Plasticity: Potential for mAb Mixtures

Squamous cell carcinomas (SCC) arising in upper parts of the aerodigestive tract are among the leading causes of death worldwide. EGFR has been found to play an essential role in driving the malignancy of SCC of the upper aerodigestive tract (SCCUAT), but, despite this, clinical results using a range of different EGFR-targeted agents have been disappointing. Cetuximab is currently the only EGFR-targeted agent approved by the FDA for treatment of SCCUAT. However, intrinsic and acquired cetuximab resistance is a major problem for effective therapy. Thus, a better understanding of the mechanisms responsible for cetuximab resistance is valuable for development of the next generation of antibody therapeutics. In order to better understand the underlying mechanisms of cetuximab resistance in SCCUAT, we established from cetuximab-sensitive models cell lines with acquired resistance to cetuximab by continuous selective pressure in vitro and in vivo Our results show that resistant clones maintain partial dependency on EGFR and that receptor tyrosine kinase plasticity mediated by HER3 and IGF1R plays an essential role. A multitarget mAb mixture against EGFR, HER3, and IGF1R was able to overcome cetuximab resistance in vitro To our surprise, these findings could be extended to include SCCUAT cell lines with intrinsic resistance to cetuximab, suggesting that the triad consisting of EGFR, HER3, and IGF1R plays a key role in SCCUAT. Our results thus provide a rationale for simultaneous targeting of EGFR, HER3, and IGF1R in SCCUAT. Mol Cancer Ther; 15(7); 1614-26. ©2016 AACR.

Recombinant IgE antibody engineering to target EGFR

Monoclonal antibodies have become a mainstay for the targeted treatment of cancer today. Some of the most successful targets of monoclonal antibodies are constituted by the epidermal growth factor receptor family spearheaded by the epidermal growth factor receptor (EGFR). Prompted by studies indicating that IgE compared to IgG may harness alternate effector functions to eradicate malignant cells, we addressed the establishment, engineering, and the potential tumoricidal effects of recombinant anti-EGFR IgE. Therefore, two different therapeutic EGFR-specific antibodies, 225 and 425, were chosen for re-cloning into different chimeric IgE and IgG formats and produced in human cells. Simultaneous antibody binding to the sEGFR demonstrated accessibility of both epitopes for recombinant IgE. Proliferation and cytotoxicity assays demonstrated signal blocking and effector mediating capability of IgE isotypes. Pronounced degranulation in the presence of sEGFR upon activation exclusively with two IgE antibodies verified the epitope proximity and provides evidence that tumor-targeting by anti-EGFR IgE is safe with regard to soluble target structures. Degranulation mediated by tumor cells expressing EGFR could be demonstrated for singular and combined IgE antibodies; however, use of two IgE specificities was not superior to use of one IgE alone. The data suggest that the surface distribution of EGFR is optimally suited to mount a robust effector cell trigger and corroborate the potential and specificity of the IgE/IgE receptor network to react to xenobiotic or pathogenic patterns for targeting malignancies.

EGFR Intron Recombination in Human Gliomas: Inappropriate Diversion of V(D)J Recombination?

The epidermal growth factor receptor (EGFR) is a membrane-bound, 170 kDa, protein tyrosine kinase that plays an important role in tumorigenesis. The EGFR gene, which is composed of over 168 kb of sequence, including a 123-kb first intron, is frequently amplified and rearranged in malignant gliomas leading to the expression of oncogenic deletion (DM) and tandem duplication (TDM) mutants. The most common DM in gliomas is EGFRvIII, which arises from recombination between introns 1 and 7 with deletion of exons 2 through 7 and intervening introns. In addition, some human gliomas express 180- to 190-kDa TDM, which are constitutively active and highly oncogenic. Both DM and TDM arise by recombination of introns that contain sequences with homology to the recombination signal sequence (RSS) heptamers and nonamers present in the V(D)J region of the immunoglobin and T lymphocyte antigen receptor genes. V(D)J RSS have also been identified in certain proto-oncogenes like bcl-2 that are involved in translocations associated with the development of human lymphomas and in other genes such as hypoxanthine-guainine phosphoribosyl transferase (HPRT) in which deletion mutations and intron rearrangements are a common phenomenon. Together with the expression of recombination associated gene (RAG) and nonhomologous end-joining (NHEJ) proteins in gliomas, these observation suggest that aberrant activity of the V(D)J recombinase may be involved in the activation of proto-oncogenes in both liquid and solid tumors.

Refinement of the population pharmacokinetic model for the monoclonal antibody matuzumab: external model evaluation and simulations

OBJECTIVES

A developed population pharmacokinetic model of the humanized monoclonal antibody (mAb) matuzumab was evaluated by external evaluation. Based on the estimates of the final model, simulations of different dosing regimens and the covariate effect were performed.

METHODS

The development dataset included 90 patients, and the evaluation dataset included 81 patients; the two sets of patients were from three different studies. In all studies, the patients had different types of advanced carcinoma - mainly colon, rectal and pancreatic cancer. They received matuzumab as multiple 1-hour intravenous infusions in a wide range of dosing regimens (development dataset: from 400 mg every 3 weeks to 2000 mg in the first week followed by 1600 mg weekly; evaluation dataset: from 100 mg weekly to 800 mg weekly). In addition to 1256 serum mAb concentrations for model development, there were 1124 concentrations available for model evaluation. Serum concentration-time data were simultaneously fitted using NONMEM software. The developed two-compartment model - with the parameters central volume of distribution (V(1)) and peripheral volume of distribution (V(2)), intercompartmental clearance and linear clearance (CLL), an additional nonlinear elimination pathway (Michaelis-Menten constant: the concentration with the half-maximal elimination rate and V(max): the maximum elimination rate) and covariate relations - was evaluated by an external dataset. Different simulation scenarios were performed to demonstrate the impact of the incorporated covariate effect and the influence of different dosing regimens and dosing strategies on the concentration-time profiles.

RESULTS

The developed model included the covariate fat-free mass (FFM) on V(1) and on CLL. The evaluation did not support the covariate FFM on V(1) and, after deletion of this covariate, the model parameters of the refined model were estimated. The model showed good precision for all parameters: the relative standard errors (RSEs) were <42% for the development dataset and < or = 51% for the evaluation dataset (excluding the higher RSEs for the correlation between V(2) and V(max) and the interindividual variability on V(2) for the evaluation dataset). The model showed good robustness for the ability to estimate highly precise parameters for the combined dataset of 171 patients (RSE <29%). Simulations revealed that variability in concentration-time profiles for minimum and maximum steady-state concentrations was reduced to a marginal extent by a proposed dose adaptation.

CONCLUSION

The population pharmacokinetic model for matuzumab was improved by evaluation with an external dataset. The new model obtained precise parameter estimates and demonstrated robustness. After correlation with efficacy data simulation results in particular could serve as a tool to guide dose selection for this 'targeted' cancer therapy.

Interaction of antibodies with ErbB receptor extracellular regions

Antibodies to the extracellular region of the ErbB receptors have played key roles in the development of a mechanistic understanding of this family of receptor tyrosine kinases. An extensively studied class of such antibodies inhibits activation of ErbB receptors, and these antibodies have been the focus of intense development as anti-cancer agents. In this review we consider the properties of ErbB receptors antibodies in light of the current structure-based model for ErbB receptor homo- and hetero-dimerization and activation. Crystal structures of the Fab fragments from five different inhibitory antibodies in complex with the extracellular regions of EGFR and ErbB2 have been determined. These structures highlight several different modes of binding and mechanisms of receptor inhibition. Information about antibody interactions with the structurally well-characterized soluble extracellular regions of ErbB receptors can be combined with the rich knowledge of the effects of these antibodies in cultured cells, and in vivo, to provide insights into the conformation and activation of ErbB receptors at the cell surface.

Matuzumab binding to EGFR prevents the conformational rearrangement required for dimerization

An increasing number of therapeutic antibodies targeting tumors that express the epidermal growth factor receptor (EGFR) are in clinical use or late stages of clinical development. Here we investigate the molecular basis for inhibition of EGFR activation by the therapeutic antibody matuzumab (EMD72000). We describe the X-ray crystal structure of the Fab fragment of matuzumab (Fab72000) in complex with isolated domain III from the extracellular region of EGFR. Fab72000 interacts with an epitope on EGFR that is distinct from the ligand-binding region on domain III and from the cetuximab/Erbitux epitope. Matuzumab blocks ligand-induced receptor activation indirectly by sterically preventing the domain rearrangement and local conformational changes that must occur for high-affinity ligand binding and receptor dimerization.

Recent new approaches to the treatment of head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer in the world and affects 50,000 Americans annually. During the past 20 years, treatments for HNSCC have changed dramatically due largely to the advent of novel approaches such as combined modality therapy, as well as improvements in surgical and radiotherapeutic techniques. Ongoing advances in the multidisciplinary management of this complex and multivariate disease process are resulting in improved function, quality of life and survival. Here, we review state-of-the-art therapy and presents selected advances in the treatment of head and neck cancer.

Epidermal growth factor receptor inhibitors in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death in both men and women. Despite the introduction of the newer cytotoxic agents in NSCLC treatment during the last decade the survival rates of patients have reached a plateau. New strategies are clearly needed to improve treatment outcomes. Epidermal growth factor receptor (EGFR) has a key role in cancer development and progression and has been recognised as a target of increasing importance in NSCLC. Gefitinib, erlotinib and cetuximab are EGFR-targeting agents that are being extensively evaluated in NSCLC. EGFR inhibitors demonstrate significant clinical activity in approximately 10-20% of pretreated NSCLC patients. Somatic mutations in the kinase domain of the receptor have been shown to be associated with enhanced sensitivity to EGFR inhibitors. However, four large Phase III randomised, placebo-controlled trials of gefitinib and erlotinib in combination with standard platinum-based first-line chemotherapy failed to show any survival benefit in patients receiving the study drugs. Possible reasons include patient selection, drug scheduling, trial design or other factors. Active research is ongoing to improve the efficacy of EGFR inhibitors as monotherapy or in combination with other treatment modalities.

Molecular therapy of head and neck cancer

Aberrant expression of growth factor receptor systems and dysregulation of the downstream cell signalling molecules have been reported in a wide range of epithelial tumours including head and neck cancer. In some cases, such alterations have been associated with a poor prognosis. In the past 25 years, several antigen specific monoclonal antibodies (mAbs, mouse, chimeric, humanized and human versions), and small molecule kinase inhibitors have been developed that are at different stages of preclinical and clinical developments. Some of these agents (e.g. Herceptin, Iressa, cetuximab, avastin) have already been approved for the treatment of epithelial tumours and may also have potential in the treatment of head and neck cancer patients. This review discusses, the development and potential of these antigen specific agents, in particular the human epidermal growth factor receptor (EGFR) inhibitors, either as a single agent or in combination with other EGFR inhibitors, biological agents (e.g. inhibitors of cycloogenase-2, angiogenesis, insulin like growth factor-I receptor and others), and conventional forms of therapy in the prevention and treatment of head and neck cancer. From preclinical and clinical studies with some of these compounds, it is evident that further detailed studies of biopsies from cancer patients are needed in order to identify markers that can be used not only in the selection of the specific population of cancer patients who would benefit from such antigen specific therapeutic strategies, but also those factors which are responsible for the poor response and the development of a phenotype resistance to such inhibitors. The results of such studies could in turn facilitate the widespread use of such agents in the treatment of a wide range of human cancers including head and neck cancer.

Anti-epidermal growth factor receptor-antibody therapy for treatment of breast cancer

Recent studies demonstrated that tumors overexpressing the epidermal growth factor receptor (EGF-R, erbB-1) are associated with poor clinical outcome. This led to the development of a variety of monoclonal antibodies targeting the extracellular domain of this receptor tyrosine kinase. The aim of our study was the evaluation of anti-EGF-R antibody EMD 55900 therapy for treatment of breast cancer. On the basis of 299 tumor specimens derived from breast cancer patients, we investigated EGF-R expression and generated a collective of primary xenotransplants in athymic nude mice. The animals received therapy in 2 treatment schedules to investigate the therapeutic response in early stages of tumor formation as well as on well established tumors. Using 6 different tumors with EGF-R expression levels between 10-300 fmol/mg total protein, we found a therapeutic effect when the EGF-R expression of the tumors was at least 40 fMol/mg. On the basis of these experimental data and our EGF-R expression analysis of breast cancer specimens, we conclude that up to 15% of breast cancer patients could benefit from this monotherapy with EMD 55900.

Antitumor effect of MAb EMD 55900 depends on EGF-R expression and histopathology

The proliferative stimulus of the epidermal growth factor (EGF) in human epithelial cells is mediated by its binding to the external domain of the EGF receptor (EGF-R). The purpose of this study was to investigate whether growth arrest of tumors treated with anti-EGF-R MAb (EMD 55900) was dependent on EGF-R expression and distinct histopathologic criteria of those neoplasms. Nine different adenocarcinomas, squamous cell carcinomas and two neoplastic epithelial cell lines (A431 and Detroit 562), which were characterized by high EGF-R expression, were xenotransplanted onto NMRI-nu/nu mice and treated with an anti-EGF-R antibody (EMD 55900). Results revealed that EGF-R expression and distinct histopathologic growth patterns play an important role for the therapeutic effect of the EGF-R antibody treatment. Tumors with high epithelial cellularity and little connective tissue responded to EMD 55900 treatment to a greater degree of growth reduction than tumors with lower cellularity. These results will be helpful for evaluation of patients who would benefit from tumor therapy with anti-EGF-R antibody.

Keratinocyte apoptosis induced by ultraviolet B radiation and CD95 ligation -- differential protection through epidermal growth factor receptor activation and Bcl-x(L) expression

Previous work has shown that activation of the epidermal growth factor receptor by endogenous or exogenous signals markedly enhances survival of cultured keratinocytes upon cellular stress such as passaging. This is due, in part, to epidermal-growth-factor-receptor-dependent expression of Bcl-x(L), an antiapoptotic Bcl-2 homolog. In this study we tested whether epidermal-growth-factor-receptor-dependent signal transduction and attendant Bcl-x(L) expression affected survival of human keratinocytes upon exposure to a frequently encountered apoptotic stimulus, radiation with ultraviolet B. We describe that blocking epidermal-growth-factor-receptor-dependent signal transduction sensitized normal keratinocytes to undergo apoptosis upon ultraviolet B radiation with solar light characteristics. Forced expression of Bcl-x(L) partially but significantly inhibited ultraviolet-B-induced apoptosis of immortalized keratinocytes (HaCaT). Bcl-x(L) overexpression afforded no protection to HaCaT cells against apoptosis induced by binding of an agonist antibody to the death receptor CD95, however. CD95 activation has previously been shown to functionally contribute to apoptosis in ultraviolet-irradiated keratinocytes. These results indicate that epidermal growth factor receptor activation and attendant Bcl-x(L) expression provided a physiologically relevant protective pathway of keratinocytes against ultraviolet-induced but not CD95-dependent apoptosis.

Epidermal growth factor receptor-dependent control of keratinocyte survival and Bcl-xL expression through a MEK-dependent pathway

Previous work has shown that the epidermal growth factor receptor (EGFR) tyrosine kinase moiety provides protection to normal human keratinocytes against apoptosis. This protection is, at least in part, due to EGFR-dependent expression of the antiapoptotic Bcl-2 family member, Bcl-x(L). Here we focused on intracellular signaling pathways relevant to keratinocyte survival and/or Bcl-x(L) expression. By using pharmacological inhibitors and dominant negative expression constructs, we observed that phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha activation were required for keratinocyte survival independently of EGFR activation or Bcl-x(L) expression. By contrast, MEK activity required EGFR activation and, as shown by use of the MEK inhibitor PD98059 and a dominant negative MEK construct, was necessary for Bcl-x(L) expression and survival. Consistent with an earlier study, blocking SRC kinase activities similarly led to down-regulation of Bcl-x(L) protein expression and impaired keratinocyte survival. In conclusion, our results demonstrate that EGFR-dependent MEK activity contributes to both Bcl-x(L) expression and survival of normal keratinocytes. Other signaling pathways (i.e. phosphatidylinositol 3-kinase/AKT and phospholipase C gamma/protein kinase C alpha) are obligatory to keratinocyte survival but not to Bcl-x(L) expression, and control of these pathways by EGFR activation is not rate-limiting to normal keratinocyte survival.

A central role of Bcl-X(L) in the regulation of keratinocyte survival by autocrine EGFR ligands

The epidermal growth factor receptor has multiple roles in epidermal biology relating to growth, migration, and, as shown recently, survival of keratinocytes. In cultured keratinocytes activation of the epidermal growth factor receptor upregulates expression of Bcl-x(L), an anti-apoptotic Bcl-2 homolog. The functional contribution of epidermal growth factor receptor-dependent Bcl-x(L) expression to keratinocyte survival is poorly understood. Here we demonstrate that inhibition of the epidermal growth factor receptor tyrosine kinase activity with either an epidermal growth factor receptor antagonistic monoclonal antibody (MoAb 425) or an epidermal growth factor receptor-selective tyrosine kinase inhibitor (AG 1478) downregulated Bcl-x(L) expression in normal human keratinocytes but had no effect on expression of the pro-apoptotic Bcl-2 homologs Bad, Bak, and Bax. Bovine pituitary extract and insulin partially alleviated both, downregulation of Bcl-x(L) expression and cell death upon epidermal growth factor receptor inhibition. Forced expression of Bcl-x(L) attenuated cell death of immortalized keratinocytes (HaCaT) induced by either forced suspension (anoikis) or by epidermal growth factor receptor blockade. These results demonstrate that epidermal growth factor receptor-dependent signaling pathways control the balance of pro-apoptotic and anti-apoptotic Bcl-2 family members expressed in normal keratinocytes. Inappropriate survival supported by aberrant signaling through the epidermal growth factor receptor may contribute to the pathogenesis of psoriasis and of squamous cell carcinomas.

Bacterial expression and characterization of recombinant biologically active anti-tyrosine kinase receptor antibody forms

Homomeric and heteromeric interactions among cell-surface tyrosine kinase receptors belonging to the ErbB family lead to intracellular signaling cascades which are involved in cell activation, cytoskeletal interactions, and cellular transformation leading to neoplasia. Monoclonal antibodies which specifically bind to p185neu or epidermal growth factor receptor (EGFR), such as 7.16.4 and 225, respectively, can elicit tumor growth-inhibitory effects on transformed cells which overexpress either or both of these receptors. In order to better understand these receptor-receptor and receptor-antibody interactions and to gain insights that may be useful in the production and design of an antibody-based anticancer therapeutic, novel small recombinant 7.16.4 and 225 single-chain Fv fragments (scFv) were constructed, expressed, and characterized. We showed that these recombinant antibody fragments, which retain binding affinity, can be produced and purified from bacterial cell lysates. Our analyses further demonstrate that fusion of a 61 amino-acid dimerization domain with 7.16.4 and 225 scFv (7.16.4hth and 225hth) is sufficient to restore biological activity to these recombinant proteins.

Expression of TGFalpha autocrine activity in human colon carcinoma CBS cells is autoregulated and independent of exogenous epidermal growth factor

Autocrine transforming growth factor alpha (TGFalpha) activity and control mechanisms for its expression were examined in a representative clonal isolate (CBS4) of a well-differentiated human colon carcinoma cell line designated CBS. CBS4 cells expressed TGFalpha and its receptor, epidermal growth factor receptor (EGFr). Blockade of EGFr and TGFalpha by neutralizing antibodies inhibited clonal growth and the initiation of DNA synthesis from quiescence in CBS4 cells. Therefore, TGFalpha is an autocrine growth factor for CBS4 cells. Several studies have indicated that activation of the EGFr by exogenous EGF stimulates TGFalpha expression. However, in CBS4 cells EGF did not induce TGFalpha mRNA expression, indicating that EGF does not affect TGFalpha transcription in these cells. Exogenous treatment of exponentially growing cells with either EGF or EGFr blocking antibody enhanced release of TGFalpha protein into the conditioned medium. This indicated that the release of TGFalpha into the conditioned medium by exogenous EGF was at least partially due to the displacement of TGFalpha from the TGFalpha/EGFr complexes. Similarly to exponentially growing cells, the EGFr blocking antibody and EGF also enhanced TGFalpha release into the medium of CBS4 cells after release from quiescence. These results indicated that exogenous EGF had little if any effect on TGFalpha expression in these cells and suggested that TGFalpha expression might be under endogenous TGFalpha control. Blockade of the autocrine TGFalpha loop by TGFalpha neutralizing antibody suppressed TGFalpha mRNA both in exponentially growing and quiescent cells, demonstrating that autocrine TGFalpha is autoregulatory in this system.

Induction of a T- and B-cell response against a unique amino acid sequence of the mouse IgG2A hinge region in a MAb-treated patient

A patient with malignant glioblastoma was treated with intratumoral infusions of the murine MAb425 (IgG2A) directed against the epidermal growth factor receptor. At the 10th infusion, the patient developed somnolence, fever and headache. The symptoms increased during the subsequent 48 hr but then gradually disappeared within a week. The cerebrospinal fluid (CSF) contained increased concentrations of interleukin-2. The main CSF cell subset was CD4 T-cells. A marked blood lymphocyte proliferative response against mouse IgG2A was noted. The reactive T-cell epitope(s) could be localized to a 14 amino acid (RGPTIKPCPPCKCP) long peptide of the hinge region. A B-cell response (IgG antibodies) against this peptide was also induced.

Regulation of Bcl-xL expression in human keratinocytes by cell-substratum adhesion and the epidermal growth factor receptor

Cell-substratum adhesion is an essential requirement for survival of human neonatal keratinocytes in vitro. Similarly, activation of the epidermal growth factor receptor (EGF-R) has recently been implicated not only in cell cycle progression but also in survival of normal keratinocytes. The mechanisms by which either cell-substratum adhesion or EGF-R activation protect keratinocytes from programmed cell death are poorly understood. Here we describe that blockade of the EGF-R and inhibition of substratum adhesion share a common downstream event, the down-regulation of the cell death protector Bcl-xL. Expression of Bcl-xL protein was down-regulated during forced suspension culture of keratinocytes, concurrent with large-scale apoptosis. Similarly, EGF-R blockade was accompanied by down-regulation of Bcl-xL steady-state mRNA and protein levels to an extent comparable to that observed in forced suspension culture. However, down-regulation of Bcl-xL expression by EGF-R blockade was not accompanied by apoptosis; in this case, a second signal, generated by passaging, was required to induce rapid and large-scale apoptosis. These findings are consistent with the conclusions that (i) Bcl-xL represents a shared molecular target for signaling through cell-substrate adhesion receptors and the EGF-R, and (ii) reduced levels of Bcl-xL expression through EGF-R blockade lower the tolerance of keratinocytes for cell death signals generated by cellular stress.

Type I receptor tyrosine kinases as targets for therapy in breast cancer

Breast carcinomas express high levels of type I tyrosine kinase receptors and their ligands. For these reason therapies directed at these receptors have the potential to be useful anticancer agents. A series of monoclonal antibodies (MAbs)3 directed against the EGF receptor and the closely related erbB2/HER2/neu receptor are currently under evaluation. These MAbs have shown promising preclinical activity and "chimeric" and "humanized" MAbs have been produced in order to obviate the problem of host immune reactions. These antibodies are currently being tested in clinical trials either alone or in combination with chemotherapeutic agents. Clinical activity with anti-HER2/neu MAbs has been documented in patients with advanced breast cancer. In addition, compounds that inhibit receptor tyrosine kinases have shown significant preclinical activity and are potential candidates for clinical testing.

Immunocytochemical expression of growth factors by odontogenic jaw cysts

AIM

To determine the immunocytochemical pattern of expression of transforming growth factor (TGF) alpha, epidermal growth factor (EGF), and TGF beta in the three most common types of odontogenic jaw cyst.

METHODS

Growth factor expression was detected in paraffin wax sections of odontogenic cysts (27 odontogenic keratocysts, 10 dentigerous cysts, and 10 radicular cysts) using a streptavidin-biotin peroxidase technique with monoclonal antibodies directed against TGF alpha (clone 213-4.4) and TGF beta (clone TB21) and a polyclonal antibody directed against EGF (Z-12).

RESULTS

The epithelial linings of all cysts showed reactivity for TGF alpha which was mainly localised to basal and suprabasal layers. Odontogenic keratocyst linings expressed higher levels of TGF alpha than those of dentigerous and radicular cysts, with 89% (24/27) of odontogenic keratocysts exhibiting a strong positive reaction compared with 50% (five of 10) of dentigerous and radicular cysts, respectively. EGF reactivity was similar in all cyst groups, weaker than that for TGF alpha and predominantly suprabasal. TGF alpha and EGF were also detected in endothelial cells, fibroblasts and inflammatory cells within the cyst walls. The most intense TGF beta staining in odontogenic cysts was extracellular within the fibrous tissue capsules, irrespective of cyst type.

CONCLUSIONS

These results, together with previous studies of EGF receptor, indicate differential expression of TGF alpha, EGF and their common receptor between the different types of odontogenic cyst, suggesting that these growth factors (via autocrine or paracrine, or both, pathways) may be involved in their pathogenesis.

EGF-R dependent regulation of keratinocyte survival

Tissue organization and maintenance within multicellular organisms is in part dependent on the ability of cells to undergo programmed cell death or apoptosis. Conversely, disruption of cell death pathways often is associated with tumor development. At present, the molecular control of apoptosis in epithelial cells is poorly understood. Here we describe evidence linking epidermal growth factor-receptor (EGF-R) activation to survival of normal human keratinocytes in culture. Inhibition of EGF-R activation by an anti-EGF-R antagonistic monoclonal antibody (mAb 425), followed by detachment of keratinocytes from the substratum, induced extensive death with several features of apoptosis in keratinocyte cultures. Other, non-epithelial normal human cells including melanocytes and fibroblasts, did not show this effect. Similar to EGF-R blockade by mAb 425, inhibition of the EGF-R tyrosine kinase activity using tyrphostin AG1478 resulted in lack of attachment and extensive cell death upon passaging. Attachment to keratinocyte-derived ECM partially resuced mAb 425-treated keratinocytes from cell death, indicating that adhesion-dependent and EGF-R-dependent signal transduction pathways serve partially overlapping but not redundant roles in supporting keratinocyte survival.

Alterations in transforming growth factor-alpha and epidermal growth factor receptor expression during rat esophageal tumorigenesis

Transforming growth factor-alpha (TGF-alpha) stimulates cell proliferation through interaction with its receptor, the epidermal growth factor receptor (EGFR), by activating its tyrosine kinase activities. The simultaneous overexpression of TGF-alpha and EGFR by tumor cells is thought to trigger the autocrine growth pathway, leading to uncontrolled proliferation. To examine their roles in rat esophageal tumorigenesis induced by the chemical carcinogen N-nitrosomethylbenzylamine (NMBA), TGF-alpha, and EGFR expression was evaluated in normal rat esophageal epithelium, in NMBA-induced preneoplastic lesions, and in papillomas by quantitative reverse transcription-polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemical analyses. Compared with the levels in normal epithelium, the TGF-alpha and EGFR mRNA levels in esophageal papillomas were 3.6 and 1.9 times higher, respectively. In the preneoplastic epithelium, although a trend of increased TGF-alpha and EGFR mRNA levels was observed, collectively there were no significant differences between preneoplastic and normal samples by RT-PCR analysis. In situ hybridization and immunohistochemical staining showed increased levels of TGF-alpha and EGFR mRNA and protein products in papillomas and in pronounced hyperplastic and dysplastic lesions. TGF-alpha and EGFR expression correlated with each other and with the expression of proliferating cell nuclear antigen, a marker for cell proliferation. These results suggest that disregulation of TGF-alpha and EGFR expression may contribute to autonomous cell growth and may play an important role in rat esophageal tumorigenesis induced by NMBA.

Cytokine modulation of epidermal growth factor receptor expression on bladder cancer cells is not a major contributor to the antitumour activity of cytokines

Epidermal growth factor is a potential mitogen for many different human tumours. Its effect is mediated via a bispecific receptor (EGFR), the expression of which correlates well with invasive disease. We investigated the modulation of EGFR by cytokines produced following bacillus Calmette Guerin (BCG)-immunotherapy. Our data demonstrate the IFN gamma, TNF alpha and IL-1 alpha can decrease the expression of EGFR on some bladder tumour cell lines. IFN gamma reduced EGFR expression on two of eight cell lines (RT4, SD). However, IL-1 and TNF did not share this activity. When cells were treated with a combination of all three cytokines, EGFR was decreased on three cell lines (RT4, RT112, SD) and furthermore, the change in the receptor expression was even more marked. Treatment with phorbol ester (thereby activating protein kinase C) resulted in rapid disappearance of the receptor from the cell surface. Interestingly, the decrease of EGFR expression did not require protein synthesis. Although the cytokines studied could down modulate EGFR, this only occurred on three out of eight cell lines; therefore, it is unlikely that the suppression of proliferative activity caused by cytokine-induced decrease of EGFR expression is central to the antitumour action of BCG therapy, but in a proportion of tumours this mechanism may be involved.

Identification and evaluation of the role of endogenous tyrosine kinases in azoxymethane induction of proliferative processes in the colonic mucosa of rats

Although tyrosine kinases (Tyr-k) are known to play a role in regulating proliferation of normal, preneoplastic and neoplastic cells, little is known about the identity of different species of Tyr-k involved in this process. Utilizing a non-denaturing polyacrylamide gel electrophoresis system, in which the separated proteins from tissue extracts are assayed directly for Tyr-k, we attempted to identify the species of Tyr-k that may be involved in azoxymethane (AOM) induction of colonic mucosal ornithine decarboxylase (ODC) activity, an enzyme whose activity is known to rise in rapidly proliferating cells. We have observed that 5 days after a single injection of the colonic carcinogen AOM (20 mg/kg body wt) to 3-4-month old rats, a significant 230% rise in colonic mucosal proliferative activity (as evidenced by 5-bromo-2'-deoxyuridine (BrdU) immunoreactivity) was also accompanied by a 550% increase in ODC activity. This was also associated with a marked rise (140-240%) in the relative activity of Tyr-k of three mucosal proteins with MI of 165, 145 and 125 kDa. Since the molecular mass of one of the Tyr-k (165 kDa) corresponded to that of EGF-receptor (EGF-R), this led us to examine the role of EGF-R Tyr-k in AOM induction of colonic mucosal ODC. We observed that a 320% increase in mucosal ODC activity, 5 days after AOM injection, was accompanied by over 200% rise in Tyr-k activity of EGF-R. Daily injection of tyrphostin (300 micrograms/kg body wt.), a Tyr-k inhibitor with a higher specificity for EGF-R Tyr-k, significantly attenuated AOM-induced stimulation of both ODC and Tyr-k activity of EGF-R. Administration of AOM also stimulated the rate of synthesis and secretion of TGF-alpha in isolated colonocytes. In addition, the levels of TGF-alpha and its mRNA in the colonic mucosa were also found to be 100% and 250% higher, respectively, in AOM-treated rats when compared with the controls. We suggest that (a) activation of intrinsic Tyr-k of EGF-R is an important event in AOM induction of colonic mucosal proliferative processes, and (b) this activation is thought to be mediated by TGF-alpha through an autocrine mechanism.

Induction of autocrine epidermal growth factor receptor ligands in human keratinocytes by insulin/insulin-like growth factor-1

Autocrine activation of the epidermal growth factor (EGF) receptor on keratinocytes has been recognized as an important growth regulatory mechanism involved in epithelial homeostasis, and, possibly, hyperproliferative diseases. Insulin-like growth factor (IGF)-1 and insulin have been shown to be paracrine keratinocyte mitogens that bind to the type I IGF receptor which is expressed on actively proliferating keratinocytes in situ. In this report, we demonstrate that IGF-1/insulin induced production of keratinocyte-derived autocrine growth factors that bind to the EGF receptor. Increased steady-state mRNA levels for transforming growth factor alpha (TGF-alpha) and for amphiregulin (AR) were observed upon incubation of keratinocytes with mitogenic concentrations of IGF-1. IGF-1 also induced production and secretion of TGF-alpha and AR proteins as detected by immunoassays. An EGF receptor antagonistic monoclonal antibody abolished the mitogenic effect of IGF-1 on cultured keratinocytes. These results suggest that stimulation of keratinocyte growth of IGF-1 requires activation of an EGF receptor-mediated autocrine loop.

Molecular/cell engineering approach to autocrine ligand control of cell function

Tissue engineering, along with other modern cell- and tissue-based health care technologies, depends on successful regulation of cell function by molecular means, including pharmacological agents, materials, and genetics. This regulation is generally mediated by cell receptor/ligand interactions providing primary targets for molecular intervention. While regulatory ligands may often be exogenous in nature, in the categories of endocrine and paracrine hormone systems, they are being increasingly appreciated as crucial in local control of cell and tissue function. Improvements in design of health care technologies involving autocrine ligand interactions with cell receptors should benefit from increased qualitative and quantitative understanding of the kinetic and transport processes governing these interactions. In this symposium paper we offer a concise overview of our recent efforts combining molecular cell biology and engineering approaches to increase the understanding of how molecular and cellular parameters may be manipulated for improved control of cell and tissue function regulated by autocrine ligands.

Receptor blockade with monoclonal antibodies as anti-cancer therapy

Human tumors express high levels of growth factors and their receptors, and many types of malignant cells appear to exhibit autocrine- or paracrine-stimulated growth. Therefore, antireceptor directed therapies have the potential of being useful anti-cancer agents. A series of murine monoclonal antibodies (MAbs) directed against human growth factor receptors and their corresponding growth factors have been produced. MAbs against the receptors for epidermal growth factor, Her2/Neu, transferrin, insulin-like growth factor, interleukin, (IL)-2 and IL-1 are currently being evaluated. MAbs directed against epidermal growth factor, transforming growth factor-alpha, bombesin, IL-2, and IL-6 also are under study. These MAbs have shown promising preclinical activity, and some of them are being tested in clinical trials. So far, anti-tumor responses have been observed with anti-IL-2 receptor, anti-bombesin and anti-IL-6 MAbs. Further research is focusing in the production of "chimeric" and "humanized" MAbs, in order to obviate the problem of host immune reactions.

Growth inhibition of xenotransplanted human carcinomas by a monoclonal antibody directed against the epidermal growth factor receptor

In the athymic nude mice model with xenotransplanted human carcinomas, the effect of a monoclonal antibody (MAb 425), directed against the human epidermal growth factor (EGFR), on tumour growth was studied. Five different solid human breast carcinomas and one vulvar epidermoid cancer cell line (A431) were transplanted in nude mice, and treated with MAb 425 2.2 mg intraperitoneally (i.p.) on day 7 post-transplantation. Tumours with EGFR concentrations of > or = 16 fmol/mg soluble cytosolic protein showed growth inhibition, whereas the growth pattern of EGFR-negative tumours was unaffected. Variation of MAb 425 dosage (1.1 versus 2.2 mg) revealed no difference in the growth inhibiting effect. Different application schedules (application on day 0, 12 or 26) showed different onsets and durations of tumour growth inhibition. Repeated application (1.1 mg, day 0 and 12) was followed by a prolonged inhibitory effect. Our results suggest that growth inhibition of EGFR-positive tumours by MAb 425 may lead to an additional treatment option for patients with EGFR-positive cancer.

The epidermal growth factor receptor as a target for therapy in breast carcinoma

The epidermal growth factor (EGF) receptor and its ligands have an important regulatory role in breast carcinoma. We have produced a series of monoclonal antibodies (MAbs) directed against the external portion of the EGF receptor. These MAbs prevent the binding of the ligands to the receptor, block ligand-induced activation of the receptor, and can inhibit the growth of breast cancer cells both in tissue culture and in human tumor xenografts in nude mice. We have also shown that anti-EGF receptor antibodies greatly enhance the antitumor effects of chemotherapeutic agents active in breast cancer. Phase I clinical trials with single doses of MAb conducted in patients with tumors over-expressing EGF receptors demonstrated favorable pharmacokinetics, good tumor imaging, and a lack of toxicity. A human:murine chimeric antibody has been produced with comparable affinity and antitumor activity that will enable us to administer repeated doses of MAb either alone or in combination with chemotherapy. Our pre-clinical data support the concept that the EGF receptor may be an optimal target for treatment with receptor blocking antibodies, either alone or in combination with chemotherapy.

Activation of protein kinase C inhibits human keratinocyte migration

The involvement of protein kinase C (PKC) in epidermal growth factor (EGF)-induced human keratinocyte migration was studied with the phagokinetic assay. It was concluded that PKC activation does not mediate, but rather inhibits, EGF-induced keratinocyte migration. The following experimental observations support these conclusions: 1) The PKC inhibitor H-7 did not inhibit EGF-induced migration but instead led to a modest enhancement. 2) PKC activators such as phorbol-12-myristate-13-acetate (PMA), phorbol-12,13-dibutyrate (PDBu), and 1,2-dioctanoly-sn-glycerol inhibited migration, but biologically inactive 4 alpha-PMA had no effect. 3) PMA did not inhibit keratinocyte attachment and spreading but blocked migration almost immediately after addition. 4) Migration of PKC-depleted cells, which were produced by prolonged treatment with PDBu, was enhanced similarly to normal cells by EGF. 5) PKC-depleted cells were not susceptible to the inhibitory effects of phorbol esters on migration. Additional experiments, in which cells were preactivated with EGF, suggested that PKC inhibits the EGF effect at a post-receptor level. The inhibitory effect of PKC on keratinocyte migration was not restricted to EGF-induced migration; PKC activation also inhibited keratinocyte migration induced by bovine pituitary extract, insulin, insulin-like growth factor-1, and keratinocyte growth factor.

Autocrine/paracrine regulation of keratinocyte urokinase plasminogen activator through the TGF-alpha/EGF receptor

Transforming growth factor-alpha (TGF-alpha) appears to be an important autocrine/paracrine regulator of keratinocyte function. Not only does TGF-alpha induce keratinocyte proliferation and migration in vitro, but it also has been detected in normal human epidermis and at elevated levels in hyperproliferative epidermis. In the present study we report that exogenous TGF-alpha increases urokinase-type plasminogen activator (uPA) in cultured human keratinocytes. Furthermore, in the absence of exogenous growth factors, the "basal" levels of uPA are decreased by an antagonist monoclonal antibody to the receptor shared by TGF-alpha and epidermal growth factor (EGF). These results suggest that an endogenous factor serves as an autocrine/paracrine regulator of keratinocyte uPA. We hypothesize that activation of the TGF-alpha/EGF receptor may coordinately regulate the keratinocyte response to cutaneous wounding, which includes enhanced uPA expression, migration, and proliferation.

Interrupting autocrine ligand-receptor binding: comparison between receptor blockers and ligand decoys

Stimulation of cell behavioral functions by ligand/receptor binding can be accomplished in autocrine fashion, where cells secrete ligand capable of binding to receptors on their own surfaces. This proximal secretion of autocrine ligands near the surface receptors on the secreting cell suggests that control of these systems by inhibitors of receptor/ligand binding may be more difficult than for systems involving exogenous ligands. Hence, it is of interest to predict the conditions under which successful inhibition of cell receptor binding by the autocrine ligand can be expected. Previous theoretical work using a compartmentalized model for autocrine cells has elucidated the conditions under which addition of solution decoys for the autocrine ligand can interrupt cell receptor/ligand binding via competitive binding of the secreted molecules (Forsten, K. E., and D. A. Lauffenburger. 1992. Biophys. J. 61:1-12.) We now apply a similar modeling approach to examine the addition of solution blockers targeted against the cell receptor. Comparison of the two alternative inhibition strategies reveals that a significantly lower concentration of receptor blockers, compared to ligand decoys, will obtain a high degree of inhibition. The more direct interruption scheme characteristic of the receptor blockers may make them a preferred strategy when feasible.

Autonomous proliferation of colon cancer cells that coexpress transforming growth factor alpha and its receptor. Variable effects of receptor-blocking antibody

Four human colon adenocarcinoma cell lines, SNU-C1, SNU-C4, SNU-C5, and NCI-H716, that are capable of proliferating autonomously in serum-free medium containing no added peptide growth factors were identified. All four cell lines show epidermal growth factor (EGF) receptors (EGFRs), express transforming growth factor alpha (TGF-alpha) messenger RNA, and release anti-TGF-alpha-immunoreactive molecules. The blocking anti-EGFR monoclonal antibody (mAb) 225 blocks autonomous proliferation of SNU-C1 and SNU-C4 cells. In both of these cell lines, the inhibitory effect of mAb 225 is reversible by the addition of EGF, TGF-alpha, or conditioned medium from any of the four cell lines. In contrast, autonomous proliferation of SNU-C5 and NCI-H716 cells is not inhibited by mAb 225 and is not affected by exogenous EGF, TGF-alpha, or conditioned medium. Together, these data confirm the previous finding that anti-EGFR antibodies can inhibit the proliferation of some carcinoma cell lines that coexpress TGF-alpha and EGFR. However, here it is shown that the mechanisms of autonomous proliferation of colon carcinoma cell lines are heterogeneous and not always sensitive to antibody disruption of TGF-alpha/EGFR autocrine interactions.

Growth-factor-independence and invasive properties of colorectal carcinoma cells

During serial passage of the colorectal carcinoma cell line SW1116 in athymic nude mice, we selected 2 variants that metastasized to the lungs and liver. The metastatic capacity of these in vivo variant cell lines was associated with their ability to (1) grow under growth-factor-deprived conditions, (2) invade and transgress a reconstructed basement membrane with high effectiveness, and (3) produce higher activities of the substrate-degrading enzymes collagenase and plasminogen activator as compared to parental cells. To assess the relative contribution of growth-factor-independence and high levels of invasiveness/motility to the metastatic phenotype, variants of 6 colorectal carcinomas were selected in vitro by adaptation to a growth-factor-free culture medium followed by selection of highly invasive cells in chemoinvasion assays. Four out of 6 cell lines selected for growth-factor-independence showed significantly higher levels of invasiveness through reconstructed membranes, suggesting co-segregation of growth-factor-independence and high levels of invasiveness in vitro. Using an in vitro chemoinvasion assay, 2 poorly and 1 highly invasive cell line were further selected for invasiveness. After 6 selection passages, all cell lines were highly invasive and showed high motility rates. However, when injected s.c. into athymic nude mice to test their metastatic capacity in vivo, double-selected variant cell lines did not form spontaneous metastases. Our results indicate that growth-factor-independence and high levels of invasiveness, although associated with the metastatic phenotype, are not sufficient for experimental metastasis formation of colorectal carcinoma cells in vivo.

Constitutive expression of multiple growth factor genes by melanoma cells but not normal melanocytes

In a panel of metastatic melanoma cell lines we found steady-state mRNA transcripts for multiple growth factors including basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF)-A, PDGF-B, transforming growth factor (TGF)- beta 1, TGF- alpha, melanoma growth-stimulating activity (MGSA), interleukin (IL)-1 alpha, and IL-1 beta but not insulin-like growth factor (IGF)-1 or IGF-2. Expression of growth factor genes was constitutive because prior to RNA extraction melanoma cells were maintained in a chemically defined culture medium free of exogenous growth factors. Each of four cell lines had an individual pattern of expression of either two, four, five, or seven growth factors; however, all cell lines shared expression of the bFGF gene. Two strains of normal melanocytes expressed TGF- beta 1 but not bFGF, PDGF, TGF- alpha , or MGSA mRNA at detectable levels. We tested growth-modulatory effects of the growth factors most frequently expressed by melanoma cells (bFGF, TGF- alpha, TGF- beta, PDGF). None of these stimulated melanoma cell growth consistently, whereas exogenous, acid-activated TGF- beta inhibited melanoma growth at concentrations greater than 10 ng/ml, suggesting that bioactive TGF- beta may represent a physiologic growth inhibitor. Neither neutralizing antisera to PDGF or TGF- alpha nor a monoclonal antibody to the epidermal growth factor (EGF)-receptor inhibited melanoma cell growth. Our results indicate that multiple growth factors are expressed simultaneously and constitutively by melanoma cells but not normal melanocytes in culture. Expression of bFGF is a common feature underscoring the significance of bFGF as an autocrine factor for melanoma cells as described earlier. Secreted PDGF and TGF- alpha are apparently not involved in or not essential for autocrine growth stimulation of melanoma cells.

Growth factors in melanoma

Human melanoma cells in culture are the source of a wide variety of polypeptide growth factors. Melanoma-derived basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF)-A and PDGF-B chains, transforming growth factor (TGF)-alpha and TGF-beta, interleukin (IL)-1 alpha and IL-1 beta, and melanoma growth stimulatory activity (MGSA) have similar biochemical and functional properties when compared to their counterparts produced by untransformed cells. In contrast to melanoma cells, normal melanocytes, even under optimal growth conditions, express only TGF-beta 1 and MGSA at detectable levels suggesting that production of the other growth factors is a tumor-associated phenomenon. Recent evidence suggests that at least two of the growth factors, bFGF and MGSA, contribute to autocrine growth stimulation of melanoma cells. Whether PDGF, TGF-alpha, IL-1, and TGF-beta act in an autocrine mode is unclear at present. However, these four growth factors are among those secreted by melanoma cells and, therefore, can be expected to interact with normal cells of the tumor stroma in vivo. Such paracrine effects include not only growth modulation in the context of angiogenesis and stroma formation, but also tissue degradation by proteolytic enzymes, the modification of extracellular matrix composition, and expression of adhesion receptors.