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Emerging results from clinical trials with epidermal growth factor receptor (EGFR) inhibitors indicate good tolerability and, at best, modest to no clinical activity in a variety of epithelial tumors, including breast carcinomas. Although the EGFR is widely expressed in epithelial cancers, there is no evidence of frequent EGFR alterations at the DNA level in human tumors. This lack of molecular evidence to suggest a pathogenic role for the EGFR in breast cancer questions the notion that use of single-agent EGFR inhibitors in this disease is a viable therapeutic approach. The lack of selection of EGFR-dependent breast tumors into trials with EGFR inhibitors suggests the possibility that these were not true-negative studies. A point of view regarding challenges in the development of anti-EGFR therapies for patients with breast cancer and possible approaches to overcome them is presented in this article.
PURPOSE - Gefitinib, an inhibitor of the epidermal growth factor receptor tyrosine kinase, induces radiographic regressions and symptomatic improvement in patients with non-small-cell lung cancer (NSCLC). Phase II trials suggested female sex and adenocarcinoma were associated with response. We undertook this analysis to identify additional clinical and pathologic features associated with sensitivity to gefitinib.
PATIENTS AND METHODS - We reviewed medical records, pathologic material, and imaging studies of all 139 NSCLC patients treated on one of three consecutive studies of gefitinib monotherapy performed at our institution. We identified patients experiencing a major objective response and compared their clinical and pathologic features with the others. Univariate and multivariable analyses were performed on potential predictive features associated with sensitivity to gefitinib.
RESULTS - Of 139 patients, 21 (15%; 95% CI, 9% to 21%), experienced a partial radiographic response. Variables identified as significant in univariate analysis included adenocarcinoma versus other NSCLC (19% v 0%; P=.004), adenocarcinoma with bronchioloalveolar features versus other adenocarcinomas (38% v 14%; P<.001), never smoker status versus former/current (36% v 8%; P<.001), and Karnofsky performance status > or =80% versus < or =70% (22% v 8%; P=.03). Multivariable analysis revealed the presence of adenocarcinoma with any bronchioloalveolar features (P=.004) and being a never smoker (P=.006) were independent predictors of response.
CONCLUSION - Our data suggest that individuals in whom gefitinib is efficacious are more likely to have adenocarcinomas of the bronchioloalveolar subtype and to be never smokers. These observations may provide clues to mechanisms determining sensitivity to this agent and suggest that NSCLC has a different biology in patients who never smoked and those with bronchioloalveolar carcinoma.
Gefitinib (ZD1839, Iressa), a selective drug inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase (TK), was recently approved for the treatment of patients with advanced non-small cell lung cancer (NSCLC). This article reviews the identification of EGFR as a therapeutic target and the steps in the development of gefitinib as "targeted" monotherapy for patients with NSCLC. Whether EGFR is required for the maintenance of lung tumor survival is also discussed. Finally, strategies to identify predictors of response to gefitinib are explored.
OBJECTIVES/HYPOTHESIS - Both the epidermal growth factor receptor (EGFR) and the p53 homologue p63 are overexpressed in a significant number of cases of head and neck squamous cell carcinoma (HNSCC). Epidermal growth factor receptor and p63 both possess oncogenic properties, including the potential to increase cell proliferation and antagonize apoptosis. ZD1839 ("Iressa") is an adenosine triphosphate-competitive inhibitor specific to the EGFR tyrosine kinase currently under evaluation as a chemotherapeutic agent in HNSCC. The objective was to investigate whether p63 expression is decreased after treatment of HNSCC cells with ZD1839. Downregulation of p63 by ZD1839 would identify a potential molecular relationship between EGFR signaling and p63 and could provide insight into the mechanism of action of ZD1839.
STUDY DESIGN - In vitro examination of p63 expression after ZD1839 treatment.
METHODS - A human HNSCC cell line, SCC-012, was treated with varying doses of ZD1839. p63 protein and messenger RNA levels were analyzed by Western and Northern blot analyses. The effect of ZD1839 on SCC-012 cell cycle was analyzed by flow cytometric analysis.
RESULTS - In SCC-012 cells there was a dose-dependent decrease in p63 protein and messenger RNA levels over the course of ZD1839 treatment. Levels of phosphorylated MAPK decreased and p27KIP-1 levels increased after ZD1839 treatment. ZD1839 treatment induced a twofold increase in G1-phase cells and a 3.5-fold decrease in S-phase cells consistent with growth arrest.
CONCLUSION - ZD1839 downregulates p63 expression at the messenger RNA level, suggesting that p63 is a downstream target of EGFR signaling.
The overexpression and aberrant function of the epidermal growth factor receptor (EGFR) and its ligands in several human carcinomas have provided a rationale for targeting this signaling network with novel treatment approaches. The epidermal growth factor receptor-tyrosine kinase (EGFR-TK) is a selective target for inhibiting cancer because it is activated in many tumor cells, yet is strictly controlled in normal cells. The EGFR-TK initiates diverse signal transduction pathways in tumor cells that have a profound effect on their biology. Activation of the EGFR-TK provides signals that drive dysregulated proliferation, invasion and metastasis, angiogenesis, and enhanced cell survival. Therefore, the EGFR-TK is a promising drug target for many types of solid tumors, and its inhibition has potential in both the treatment and prevention of these neoplasias. Based on the structure and function of the EGFR, two antireceptor therapeutic strategies have been developed. The first strategy uses humanized monoclonal antibodies generated against the receptor's ligand-binding, extracellular domain. These antibodies block binding of receptor-activating ligands and, in some cases, can induce receptor endocytosis and downregulation. The second approach uses small molecules that compete with adenosine triphosphate for binding to the receptor's kinase pocket, thus blocking receptor activation and the transduction of postreceptor signals. Early clinical studies suggest that both of these approaches, either alone or in combination with standard anticancer therapies, are well tolerated and can induce clinical responses and tumor stabilization in a variety of common carcinomas. ZD1839 (Iressa; AstraZeneca Pharmaceuticals LP, Wilmington, DE) is the EGFR-TK inhibitor furthest along in clinical development, and it is currently being investigated in a variety of solid tumors, including non-small-cell lung cancer.
Copyright 2003, Elsevier Science (USA)
The epidermal growth factor receptor (EGFR) is a rational target for antitumor strategies. EGFR signaling causes increased proliferation, decreased apoptosis, and enhanced tumor cell motility and neo-angiogenesis. The EGFR is expressed or highly expressed in a variety of human tumors of epithelial origin. ZD1839 (Iressa) is an orally active, selective EGFR tyrosine kinase inhibitor, which blocks signal transduction pathways implicated in proliferation and survival of cancer cells. The lack of a consistent method of evaluating levels of EGFR has caused a disparity in reports of the EGFR as a prognostic factor; however, for some tumors, EGFR is a strong prognostic indicator associated with more aggressive disease and reduced survival. So far, no clear association between EGFR levels and response to EGFR-targeted agents has been found. Preclinical studies with ZD1839 have noted a relationship between the two in some cases, but not others. EGFR signaling may be increased by a number of mechanisms in addition to high expression levels of EGFR, including receptor mutations, heterodimerization with other members of this receptor family such as HER2 (erbB2), increased expression of (autocrine/ paracrine) ligands, and alterations in molecules that control receptor signaling output. Each of these components could be assessed to give an indication of the magnitude of EGFR signal amplification. Evaluation of signaling components downstream from EGFR should provide information on the activation of the EGFR pathway. Until EGFR-based assays predictive of a response to receptor-targeted therapies are available, there is no clear justification for stratifying patients by EGFR status or excluding patients with low EGFR levels from trials with ZD1839 or other EGFR inhibitors.
Protein tyrosine kinases are tightly regulated enzymes that play an important role in the control of most fundamental cellular processes, including cell proliferation, differentiation, metabolism, migration, and survival. These signaling proteins are the frequent target of oncogenic mutations or other genetic alterations leading to dysregulated tyrosine kinase activity, cellular transformation, and subsequent tumor progression. Many of the known dominant oncogenes encode aberrant protein tyrosine kinases and are causally associated with a significant fraction of human neoplasms, including breast carcinoma. The epidermal growth factor receptor and HER2/neu are two transmembrane tyrosine kinases that are members of the HER (erbB) signaling network. Aberrant signaling by this network is present in a cohort of breast carcinomas. Structure/function studies of these kinases have led to the identification of molecular approaches aimed at disabling signaling by this transforming network. Trastuzumab, a monoclonal antibody that binds the ectodomain of HER2, was recently shown to induce regression of HER2-overexpressing breast cancers, confirming the role of HER2 in tumor maintenance and progression. A rational therapeutic approach that builds on these results with trastuzumab and expands the targeting of the HER network will be presented.
Copyright 2002, Elsevier Science (USA). All rights reserved.
Rutaecarpine, evodiamine, and dehydroevodiamine are quinazolinocarboline alkaloids isolated from a traditional Chinese medicine, Evodia rutaecarpa. The in vitro effects of these alkaloids on cytochrome P450 (P450)-catalyzed oxidations were studied using mouse and human liver microsomes. Among these alkaloids, rutaecarpine showed the most potent and selective inhibitory effect on CYP1A-catalyzed 7-methoxyresorufin O-demethylation (MROD) and 7-ethoxyresorufin O-deethylation (EROD) activities in untreated mouse liver microsomes. The IC(50) ratio of EROD to MROD was 6. For MROD activity, rutaecarpine was a noncompetitive inhibitor with a K(i) value of 39 +/- 2 nM. In contrast, rutaecarpine had no effects on benzo[a]pyrene hydroxylation (AHH), aniline hydroxylation, and nifedipine oxidation (NFO) activities. In human liver microsomes, 1 microM rutaecarpine caused 98, 91, and 77% decreases of EROD, MROD, and phenacetin O-deethylation activities, respectively. In contrast, less than 15% inhibition of AHH, tolbutamide hydroxylation, chlorzoxazone hydroxylation, and NFO activities were observed in the presence of 1 microM rutaecarpine. To understand the selectivity of inhibition of CYP1A1 and CYP1A2, inhibitory effects of rutaecarpine were studied using liver microsomes of 3-methylcholanthrene (3-MC)-treated mice and Escherichia coli membrane expressing bicistronic human CYP1A1 and CYP1A2. Similar to the CYP1A2 inhibitor furafylline, rutaecarpine preferentially inhibited MROD more than EROD and had no effect on AHH in 3-MC-treated mouse liver microsomes. For bicistronic human P450s, the IC(50) value of rutaecarpine for EROD activity of CYP1A1 was 15 times higher than the value of CYP1A2. These results indicated that rutaecarpine was a potent inhibitor of CYP1A2 in both mouse and human liver microsomes.
Signaling by the HER2 proto-oncogene product results in the activation of several biochemical pathways that in turn modulate the expression and function of molecules involved in cell proliferation and survival. It is well established that forced overexpression of HER2 results in transformation of nontumor cells, and that high levels of HER2 in tumors are associated with a more aggressive biological behavior. It is also clear that a subset of HER2-overexpressing tumors is dependent on HER2 function for proliferation and/or survival. Over the last few years, several elegant studies have dissected the biochemical mechanisms of HER2 signaling. This research has provided information about critical functional domains in HER2 that can be targeted with rational molecular approaches, some of which are already being implemented at the bedside. This report will focus on one of these anti-HER2 signaling strategies.
Copyright 2001 by W.B. Saunders Company.
Aberrrant signaling by the epidermal growth factor receptor [EGFR (HER1, erbB1)] and/or HER2/neu tyrosine kinases is present in a cohort of breast carcinomas. Because HER2 is constitutively phosphorylated in some breast tumors, we speculated that, in these cancers, transmodulation of HER2 may occur via EGFR signaling. To test this possibility, we examined the effect of EGFR-specific kinase inhibitors against the HER2-overexpressing human breast tumor lines BT-474, SKBR-3, MDA-361, and MDA-453. ZD1839 (Iressa) is an ATP-mimetic that inhibits the purified EGFR and HER2 kinases in vitro with an IC(50) of 0.033 and >3.7 microM, respectively. The specificity of ZD1839 against EGFR was confirmed in Rat1 fibroblasts transfected with EGFR or HER2 chimeric receptors activated by synthetic ligands without the interference of endogenous receptors. Treatment of all breast cancer cell lines (except MDA-453) with 1 microM ZD1839 almost completely eliminated HER2 phosphorylation. In contrast, the incorporation of [gamma-(32)P]ATP in vitro onto HER2 receptors isolated from BT-474 cells was unaffected by 1 microM ZD1839. EGFR is expressed by BT-474, SKBR-3, and MDA-361 but not by MDA-453 cells, suggesting that ZD1839-mediated inhibition of the EGFR kinase explained the inhibition of HER2 phosphorylation in vivo. In SKBR-3 cells, ZD1839 exhibited a greater growth-inhibitory effect than Herceptin, a monoclonal antibody against the HER2 ectodomain. In both SKBR-3 and BT-474 cells, treatment with ZD1839 plus Herceptin induced a greater apoptotic effect than either inhibitor alone. Finally, ZD1839 completely prevented growth of BT-474 xenografts established in nude mice and enhanced the antitumor effect of Herceptin. These data imply that EGFR tyrosine kinase inhibitors will be effective against HER2-overexpressing breast tumor cells that also express EGFR and support their use in combination with HER2 antibodies, such as Herceptin, against mammary carcinomas with high levels of the HER2 proto-oncogene.