A potent protein-tyrosine kinase inhibitor which selectively blocks proliferation of epidermal growth factor receptor-expressing tumor cells in vitro and in vivo

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.

Lack of EGF receptor contributes to drug sensitivity of human germline cells

Germline mutations have been associated with generation of various types of tumour. In this study, we investigated genetic alteration of germline tumours that affect the drug sensitivity of cells. Although all germline tumour cells we tested were hypersensitive to DNA-damaging drugs, no significant alteration was observed in their DNA repair activity or the expression of DNA repair proteins. In contrast, germline tumours expressed very low level of epidermal growth factor receptor (EGFR) compared to drug-resistant ovarian cancer cells. An immunohistochemical analysis indicated that most of the primary germline tumours we tested expressed very low level of EGFR. In accordance with this, overexpression of EGFR in germline tumour cells showed an increase in drug resistance, suggesting that a lack of EGFR, at least in part, contributes to the drug sensitivity of germline tumours.

Sequence-specific peptide aptamers, interacting with the intracellular domain of the epidermal growth factor receptor, interfere with Stat3 activation and inhibit the growth of tumor cells

Receptor tyrosine kinases of the epidermal growth factor (EGF) receptor family regulate essential cellular functions such as proliferation, survival, migration, and differentiation but also play central roles in the etiology and progression of tumors. We have identified short peptide sequences from a random peptide library integrated into the thioredoxin scaffold protein, which specifically bind to the intracellular domain of the EGF receptor (EGFR). These molecules have the potential to selectively inhibit specific aspects of EGF receptor signaling and might become valuable as anticancer agents. Intracellular expression of the aptamer encoding gene construct KDI1 or introduction of bacterially expressed KDI1 via a protein transduction domain into EGFR-expressing cells results in KDI1.EGF receptor complex formation, a slower proliferation, and reduced soft agar colony formation. Aptamer KDI1 did not summarily block the EGF receptor tyrosine kinase activity but selectively interfered with the EGF-induced phosphorylation of the tyrosine residues 845, 1068, and 1148 as well as the phosphorylation of tyrosine 317 of p46 Shc. EGF-induced phosphorylation of Stat3 at tyrosine 705 and Stat3-dependent transactivation were also impaired. Transduction of a short synthetic peptide aptamer sequence not embedded into the scaffold protein resulted in the same impairment of EGF-induced Stat3 activation.

Developing inhibitors of the epidermal growth factor receptor for cancer treatment

Progress in identifying and understanding the molecular and cellular causes of cancer has led to the discovery of anomalies that characterize cancer cells and that represent targets for the development of cancer therapeutics. One such target is the epidermal growth factor receptor (EGFR), a transmembrane protein that is frequently dysregulated in cancer cells. Preclinical studies have demonstrated that pharmacologic interventions that abrogate EGFR dysfunction result in antitumor effects. On the basis of these findings, therapeutic strategies to inhibit EGFR and EGFR-related pathways, including the use of monoclonal antibodies against the extracellular ligand-binding domain of EGFR and small-molecule inhibitors of the tyrosine kinase activity of EGFR, have entered clinical testing where they have demonstrated favorable safety profiles and adequate clinical pharmacology. Further development of these agents has been fueled by evidence of their antitumor activities, both as single agents and in combination with chemotherapy and radiation therapy. Areas that require investigation are the definition of patient populations most likely to derive benefits from these drugs, the implementation of biologic correlative studies to aid the selection of pharmacodynamically relevant doses and schedules, the characterization of population pharmacokinetic parameters and pharmacogenomic variables, and the most appropriate clinical scenario for proceeding with the clinical development of these agents.

Monoclonal antibodies to target epidermal growth factor receptor-positive tumors: a new paradigm for cancer therapy

BACKGROUND

Traditional cytotoxic approaches to tumor management are associated with efficacy and toxicity limitations. Blockade of the epidermal growth factor receptor (EGFR) and its ligands is a novel approach to the treatment of human tumors that offers a noncytotoxic alternative to cancer treatment.

METHODS

An English-language literature search was conducted to identify studies assessing the in vitro and in vivo effects of EGFR blockade with an emphasis on approaches that use monoclonal antibody therapy.

RESULTS

The EGF pathway regulates normal cellular processes and appears to be correlated with the development of malignancy. Approximately 30% of human tumors express EGFR, which has been reported to be correlated with poor prognosis and diminished disease-free and overall survival in selected tumor types. A number of anti-EGFR monoclonal antibodies have been developed, which currently are undergoing clinical trials in humans. Effective anti-EGFR monoclonal antibodies compete with endogenous ligands, primarily EGF and transforming growth factor-alpha, for receptor ligand-binding sites. Binding to EGFR blocks critical signaling pathways and interferes with the growth of tumors expressing EGFR. Anti-EGFR monoclonal antibodies that currently are under study include IMC-C225, EMD 55900, ICR 62, and ABX-EGF.

CONCLUSIONS

These antibodies have demonstrated promising results and appear to have been well tolerated. EGFR-targeted therapy addresses important, unmet needs in the treatment of human tumors, particularly EGFR-positive epithelial tumors including common malignancies of the head and neck, lung, and colon.

Overview of rationale and clinical trials with signal transduction inhibitors in lung cancer

Most cellular proto-oncogenes encode proteins that participate in signaling pathways by which cells receive and execute instructions that lead to mitogenesis, differentiation, lineage determination, cell migration, extracellular matrix production, and apoptosis, among others. These proto-oncogene protein products include transmembrane receptor tyrosine kinases and receptor substrates, serine/threonine kinases, receptor adaptor molecules, low-molecular-weight GTPases, and transcription factors that, when overexpressed or mutationally activated, can lead to cell transformation and tumor progression. The large number of oncogenic protein tyrosine kinases plus the rare presence of phosphotyrosine in nontransformed cells argue persuasively that tyrosine phosphorylation and activation of signaling molecules downstream from receptor tyrosine kinases are critical events in growth control and transformation and are, therefore, rational targets for anticancer molecular therapies. We will review some of the more recent treatment strategies in non-small cell and small cell lung cancer targeted to dysregulated signaling pathways that are causally associated with tumor maintenance and progression.

The EGF receptor family as targets for cancer therapy

Human carcinomas frequently express high levels of receptors in the EGF receptor family, and overexpression of at least two of these receptors, the EGF receptor (EGFr) and closely related ErbB2, has been associated with a more aggressive clinical behavior. Further, transfection or activation of high levels of these two receptors in nonmalignant cell lines can lead to a transformed phenotype. For these reasons therapies directed at preventing the function of these receptors have the potential to be useful anti-cancer treatments. In the last two decades monoclonal antibodies (MAbs) which block activation of the EGFr and ErbB2 have been developed. 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. Clinical activity with these antibodies has been documented: trastuzumab, a humanized anti-ErbB2 MAb, is active and was recently approved in combination with paclitaxel for the therapy of patients with metastatic ErbB2-overexpressing breast cancer; IMC-C225, a chimeric anti-EGFr MAb, has shown impressive activity when combined with radiation therapy and reverses resistance to chemotherapy. In addition to antibodies, compounds that directly inhibit receptor tyrosine kinases have shown preclinical activity and early clinical activity has been reported. A series of phase III studies with these antibodies and direct tyrosine kinase inhibitors are ongoing or planned, and will further address the role of these active anti-receptor agents in the treatment of patients with cancer.

The Raf signal transduction cascade as a target for chemotherapeutic intervention in growth factor-responsive tumors

This review focuses on the Ras-Raf-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK) signal transduction pathway and the consequences of its unregulation in the development of cancer. The roles of some of the cell membrane receptors involved in the activation of this pathway, the G-protein Ras, the Raf, MEK and ERK kinases, the phosphatases that regulate these kinases, as well as the downstream transcription factors that become activated, are discussed. The roles of the Ras-Raf-MEK-ERK pathway in the regulation of apoptosis and cell cycle progression are also analyzed. In addition, potential targets for pharmacological intervention in growth factor-responsive cells are evaluated.

Development of inhibitors for protein tyrosine kinases

In the last 5 years, through combinatorial chemistry, high-throughput screening, computational chemistry, and traditional medicinal chemistry, numerous inhibitors for various protein tyrosine kinases (PTKs) have been developed. The majority of these compounds are small molecules that compete at the ATP binding site of the catalytic domain of the enzymes. Some compounds such as pseudosubstrate-based peptide inhibitor binds to the peptide/protein substrate site of the catalytic domain. Some inhibitors, primarily monoclonal antibodies, bind to the extracellular domain of receptor tyrosine kinases. Some of these inhibitors are highly potent and selective. Several are currently undergoing clinical trials for a number of diseases such as cancer.

Tyrosine kinase inhibitors in preclinical development

Due to the limited efficacy of cytotoxic chemotherapy in the treatment of advanced malignancy and its excessive toxicity precluding its use in chemoprevention, new therapeutic and preventive strategies have been sought. One of the most interesting of these new approaches is the manipulation of signal transduction pathways. Among the approaches being considered to eventuate such a strategy is the inhibition of autophosphorylation, a critical first step in the signal transduction pathways of many cell surface receptor tyrosine kinases, as well as of non-receptor tyrosine kinases. This article is intended to review those tyrosine kinase inhibitors that are currently in preclinical development, for which there are data to support consideration for their use in chemoprevention or cancer treatment. We will focus upon those agents that have received attention in the past several years.

Expression and function of EGF-related peptides and their receptors in gynecological cancer--from basic science to therapy

EGF-related peptides and their receptors play an important, but not fully understood role, both, in epithelial physiology and pathophysiology but also in human tumor carcinogenesis and tumor behavior, respectively. Overexpression of EGF-related growth factors from normal epithelium to carcinomas has been demonstrated for several human tissues such as breast, endometrium, cervix and ovary. Additionally, the differential overexpression of EGFR or erb B-2 in various malignancies has already proven to be efficacious in stratifying patients with respect to a poor prognosis. These data suggest that EGF-related growth factors, erb B receptors or signaling proteins that function either upstream or downstream from these receptors may represent novel targets for selective tumor therapy. In the future, conventional chemotherapy regimes will ultimately be wedded to more biologically-oriented therapies. One important target for these novel therapeutic approaches in solid tumors will be the EGF-related growth factors and their receptors.

Tyrosine kinase inhibitors. 16. 6,5,6-tricyclic benzothieno[3, 2-d]pyrimidines and pyrimido[5,4-b-] and -[4,5-b]ĭndoles as potent inhibitors of the epidermal growth factor receptor tyrosine kinase

Several elaborations of the fundamental anilinopyrimidine pharmacophore have been reported as potent and selective inhibitors of the epidermal growth factor receptor (EGFr) tyrosine kinase. This paper reports on a series of inhibitors whereby some 6,5-bicyclic heteroaromatic systems were fused through their C-2 and C-3 positions to this anilinopyrimidine pharmacophore. Although the resulting tricycles did not produce the enormous potency of some of the (5/6),6,6-bicyclic systems, the best of them had IC(50)s for the EGFr TK around 1 nM. Investigation of 4-position side chains in the indolopyrimidines confirmed that m-bromoaniline was an optimal substituent for potency. Investigation of substitution within the C-(benzo)ring of benzothienopyrimidines confirmed that introduction of an extra ring can change sharply the effects of substituents when compared to similar bicyclic nuclei, and only two substituents were found which even moderately enhanced inhibitory activity over the parent compound for this series.

The epidermal growth factor receptor and its inhibition in cancer therapy

Much effort has been expended in the search for inhibitors of signalling molecules that may prove to be important therapeutically in cancer. The epidermal growth factor receptor (EGFR) family and their associated ligands has been one such area extensively investigated. The complex nature of EGFR biology allows for potential opportunities for EGFR inhibitors in a number of areas of cancer therapy, including proliferative, angiogenic, invasive, and metastatic aspects. Much positive evidence of likely benefit has already been gathered from a multiplicity of laboratory experiments. Clinical trials are now urgently required to further evaluate the advantages of such agents.

Irreversible inhibition of epidermal growth factor receptor tyrosine kinase with in vivo activity by N-[4-[(3-bromophenyl)amino]-6-quinazolinyl]-2-butynamide (CL-387,785)

It has been shown previously that 4-anilino quinazolines compete with the ability of ATP to bind the epidermal growth factor receptor (EGF-R), inhibit EGF-stimulated autophosphorylation of tyrosine residues in EGF-R, and block EGF-mediated growth. Since millimolar concentrations of ATP in cells could reduce the efficacy of 4-anilino quinazolines in cells and the activity of these compounds would not be sustained once they were removed from the body, we reasoned that irreversible inhibitors of EGF-R might improve the activity of this series of compounds in animals. Molecular modeling of the EGF-R kinase domain was used to design irreversible inhibitors. We herein describe one such inhibitor: N-[4-[(3-bromophenyl)amino]-6-quinazolinyl]2-butynamide, known as CL-387,785. This compound covalently bound to EGF-R. It also specifically inhibited kinase activity of the protein (IC50 = 370+/-120 pM), blocked EGF-stimulated autophosphorylation of the receptor in cells (ic50 approximately 5 nM), inhibited cell proliferation (IC50 = 31-125 nM) primarily in a cytostatic manner in cell lines that overexpress EGF-R or c-erbB-2, and profoundly blocked the growth of a tumor that overexpresses EGF-R in nude mice (when given orally at 80 mg/kg/day for 10 days, daily). We conclude that CL-387,785 is useful for studying the interaction of small molecules with EGF-R and may have clinical utility.