Primary and Secondary Prevention of Non–Small-Cell Lung Cancer: The SPORE Trials of Lung Cancer Prevention

Protein farnesyltransferase-catalyzed isoprenoid transfer to peptide depends on lipid size and shape, not hydrophobicity

Protein farnesyl transferase (FTase) catalyzes transfer of a 15-carbon farnesyl group from farnesyl diphosphate (FPP) to a conserved cysteine in the C-terminal Ca(1)a(2)X motif of a range of proteins, including the oncoprotein H-Ras ("C" refers to the cysteine, "a" to any aliphatic amino acid, and "X" to any amino acid) and the lipid chain interacts with, and forms part of the Ca(1)a(2)X peptide binding site. Previous studies have shown that H-Ras biological function is ablated when it is modified with lipids that are 3-5 orders of magnitude less hydrophobic than FPP. Here, we employed a library of anilinogeranyl diphosphate (AGPP) and phenoxygeranyl diphosphate (PGPP) derivatives with a range of polarities (log P (lipid alcohol) = 0.7-6.8, log P (farnesol) = 6.1) and shapes to examine whether FTase-catalyzed transfer to peptide is dependent on the hydrophobicity of the lipid. Analysis of steady-state transfer kinetics for analogues to dansyl-GCVLS peptide revealed that the efficiency of lipid transfer was highly dependent on both the shape and size, but was independent of the polarity of the analogue. These observations indicate that hydrophobic features of isoprenoids critical for their association with membranes and/or protein receptors are not required for efficient transfer to Ca(1)a(2)X peptides by FTase. Furthermore, the results of these studies indicate that the role played by the farnesyl lipid in the FTase mechanism is primarily structural. To explain these results we propose a model in which the FTase active site stabilizes a membrane interface-like environment.

Epidermal Growth Factor Receptor and Hedgehog Signaling Pathways Are Active in Esophageal Cancer Cells From Rat Reflux Model

BACKGROUND

Advancements in experimental therapeutics for esophageal cancers have been hampered by the lack of a reliable preclinical model that recapitulates the biology of human cancer, including in vivo growth in an animal model.

METHODS

Bilious reflux was induced by esophago-jejunostomy in Sprague-Dawley rats. Nine of 12 (75%) Sprague-Dawley rats developed squamous or adenosquamous cancers, and three cell lines were created by in vitro propagation of freshly resected tumors, JA and JB lines from one cancer, and the AMY cell line from another. We subsequently tested the ability of these cell lines to propagate long-term in vitro and form xenografts in vivo, both hallmarks of transformed cells. In addition, we determined the effects of small molecule inhibitors of two important oncogenic pathways-the epidermal growth factor receptor (EGFR) and Hedgehog (Hh) signaling pathways, in vitro, as a "proof of principle" of using these unique cell lines for developing targeted therapies for esophageal cancer. Mechanism-based growth inhibition was assessed by down-regulation of activated downstream targets of EGFR in the case of Iressa, and by Hh luciferase reporter activity with cyclopamine.

RESULTS

JA, JB, and AMY cell lines were able to grow continuously in vitro and consistently form xenografts in vivo in athymic mice, both subcutaneously, as well as in the "orthotopic" location at the gastroesophageal serosal junction (n = 2 mice per line, six of six engrafted). By histology, the tumors grow in vivo as well-differentiated keratinizing squamous cell carcinomas. JB cells had the highest expression of EGFR protein and also the most profound response to Iressa (gefitinib), an EGFR inhibitor (IC50 < 1 microm). Growth inhibition by Iressa was mirrored functionally by down-regulation of activated targets of the EGFR pathway, phospho-ERK1/2 and phospho-MEK levels. AMY cells expressed approximately 900-fold elevation of the Hh ligand, Indian Hh (Ihh), compared with normal esophageal epithelium, whereas expression of another Hh ligand, Sonic Hh (Shh), was not detected. On treatment with the specific Hh small molecule inhibitor cyclopamine, AMY cells demonstrated growth inhibition, which was accompanied by significant down-regulation of endogenous Hh luciferase reporter activity at 24 h and increased apoptosis in treated cells.

CONCLUSIONS

We have established a model of esophageal carcinogenesis, capable of long-term in vitro and in vivo passage, and demonstrated therapeutic potential of targeting the EGFR and Hh pathways in the cell lines created from the rodent cancers. These unique cell lines should provide a platform for rapid preclinical validation of novel therapeutics for esophageal cancers.

Small tumor size and limited smoking history predicts activated epidermal growth factor receptor in early-stage non-small cell lung cancer

STUDY OBJECTIVE

Epidermal growth factor receptor (EGFR) signaling has been implicated in the pathogenesis of bronchial dysplasia and overt non-small cell lung cancer (NSCLC). We hypothesized that assaying for EGFR activity using an antibody that recognizes phosphorylated EGFR (pEGFR) may identify a subset of patients whose tumor cells are dependent on EGFR signaling. We also hypothesized that EGFR activity may be prognostic for early-stage NSCLC.

DESIGN

We constructed high-density tissue microarrays using tissues from 193 surgically resected stage I NSCLCs. These arrays were immunostained with a pEGFR antibody, and the intensity of staining was correlated with clinicopathologic variables, as well as disease-free and overall survival (OS). Staining was scored by intensity and the percentage of positively stained tumor cells in triplicate.

MEASUREMENTS AND RESULTS

We found the expression of pEGFR (with > 50% of tumor cells staining positive) in 51% of tumor tissues. We found an inverse correlation between pEGFR, and both tumor size and the degree of tobacco smoking. In addition, we found a trend in which pEGFR expression was inversely correlated with disease stage (IA higher than IB). There was no correlation with sex, histology, or disease-free or OS.

CONCLUSIONS

Our results suggest that pEGFR levels are present in early-stage NSCLC, especially in patients with small tumors and in those with short smoking histories, but there is no prognostic impact on a patient's disease course. Targeting EGFR may therefore have more promise in chemoprevention or in patients with smaller early-stage NSCLCs compared with those with more advanced disease.

Molecularly targeted agents: Their promise as cancer chemopreventive interventions

Molecular medicine has fully entered in to the oncology arena. The development of targeted therapies is one of the major ongoing efforts in cancer treatment. Targeted therapy refers to treatment strategies directed against molecular targets considered to be involved in neoplastic transformation. Such molecularly targeted agents (MTA) are currently under study in all treatment settings including that of chemoprevention, defined as the use of natural or synthetic agents to interrupt the carcinogenic process, to nip tumours in the bud. This review article aims to provide a general overview of the potential use of some of these MTA in the chemoprevention setting.

Chemoprevention Strategies for Patients with Lung Cancer in the Context of Screening

Despite major advances in the treatment and management of lung cancer, most patients with lung cancer eventually die of this disease. Because conventional therapies have failed to make a major impact on survival, newer approaches are necessary in the battle against lung cancer. Better understanding of molecular biology of several tumors has led to novel targeted therapeutic approaches with potential utility in cancer treatment in general and lung cancer in particular. In addition to smoking cessation, targeting individuals at high risk by use of early detection or aiming at reversal of premalignant lesions seem like attractive strategies. In light of the noted improvement in molecular diagnostic tools and targeted therapies, the question of chemoprevention in the context of early detection deserves a closer look. In this article, we review what has been achieved in the area of chemoprevention and discuss possible prospects that may help reduce lung cancer mortality in the context of early detection.

Molecular oncology — perspectives in lung cancer

Despite novel therapies in lung cancer treatment the 5-year survival rate still remains poor. Furthermore, screening concepts for early diagnosis, based on conventional sputum cytology and chest radiography, have so far not demonstrated an impact on decreasing lung-cancer mortality. More specific molecular markers allow new insights in the process of lung carcinogenesis. Furthermore they raise the hope that they provide new tools for early diagnosis and screening of high-risk individuals, determination of prognosis, and identification of innovative treatments. In this review, these perspectives of molecular targets in lung cancer will be discussed and summarised. Angiogenesis-stimulating factors (VEGF, FGF, MMP, etc.), parameters concerning tumour cell proliferation and apoptosis (EGFR, p53, K-ras, rb, bcl-2, etc.) are well known. Several of these genetic factors have already been investigated, but no single parameter has yet gained a sufficient selectivity regarding prognostic significance or therapeutic efficacy. New aspects in the complex tumour-stroma interaction and the interactive, cross-talking signal transduction pathways and recently developed functional genomic approaches, such as DNA microarrays and proteomics might lead to further progress in biological staging models and treatment concepts.

Screening for lung cancer: a review

PURPOSE OF REVIEW

After the disappointing results of lung cancer screening trials conducted in the 1960s to the 1980s, a renewed interest in lung cancer screening emerged in the 1990s with the development of new technologies such as low-dose spiral CT. The literature regarding screening with biomarkers and CT continues to expand rapidly.

RECENT FINDINGS

Although the specificity of CT screening is relatively poor, the sensitivity for the detection of early-stage cancers, particularly adenocarcinoma, is considerably superior to that of chest radiography used in older screening trials. The results of uncontrolled cohort studies of CT screening are promising, but such studies are susceptible to screening biases such as overdiagnosis.

SUMMARY

There is insufficient evidence to support widespread screening in current practice. However, randomized controlled trials are now being conducted to determine whether improved detection by CT will translate into reduced lung cancer mortality. Alternative approaches to secondary prevention such as screening with biomarkers, autofluorescence bronchoscopy, and chemoprevention hold great promise for the future but await further development and evaluation in prospective trials.