The interface between ErbB and non-ErbB receptors in tumor invasion: clinical implications and opportunities for target discovery

Strategies for siRNA navigation to desired cells

Whilst small interfering (si) RNAs have emerged as a promising therapeutic modality for treating a diversity of human diseases, delivery constitutes the most serious obstacle to siRNA drug development. As the most used delivery agents can enter all cell types, specificity must be built into the delivery agents or directly attached to the siRNA molecules. The use of antibodies, peptides, Peptide-Fc fusions, aptamers, and other targeting ligands has now enabled efficient gene silencing in the desired cell populations/tissues in vitro and in vivo. The present review summarizes these current innovations, which are important for the design of safe therapeutic siRNAs.

[Relationship of epidermal growth factor receptor in lung development]

The epidermal growth factor receptor (EGFR), a transmembrane protein receptor, is a member of ErbB family with signal-transducing tyrosine kinase activity. After combined with the ligand, EGFR homologous or heterologous dimers are formed to induce intracellular signal transduction, activate downstream signal transduction pathways, and then produce a series of biological effects. RAF/MEK/RAS/ERK pathway is relevant to cell proliferation, differentiation and apoptosis; while PDK1/AKT /PI3K pathway is involved in cell migration and adhesion. EGFR can promote the maturity of pulmonary type II epithelial cells and the synthesis and secretion of pulmonary surfactant. EGFR shows the effect on mammal lungs in a time-space and dose-dependent manner. The down-regulated expression of it will lead to immature lung development, while the over-expression can promote the cell proliferation, invasion and metastasis of the lung cancer cells. This paper reviewed advances in the study for EGFR and its signal pathway, as well as the relationship among EGFR, atelectasis and lung cancer.

The effects of artesunate on the expression of EGFR and ABCG2 in A549 human lung cancer cells and a xenograft model

Non-small cell lung cancer (NSCLC) is the leading cause of cancer death worldwide. Clinical and laboratory studies have suggested that multi-targeting approaches against neoplastic cells could help to increase patient survival and might reduce the emergence of cells that are resistant to single-target inhibitors. Artesunate (ART) is one of the most potent and rapidly acting antimalarial agents known, and it also exerts a profound cytotoxic activity toward cancer cells and reverses multi-drug resistance. In the present study, we found that artesunate inhibited NSCLC A549 cell growth and proliferation, induced apoptosis and suppressed tumor growth in a dose-dependent manner in A549 cells and a mouse xenograft model. Furthermore, artesunate down-regulated the expression of epidermal growth factor receptor (EGFR), Akt and ATP-binding cassette subfamily G member 2 (ABCG2) at the mRNA and protein levels in vitro and in vivo. In conclusion, artesunate is an effective anti-cancer drug that may enhance the effectiveness of other anticancer drugs and may reverse multi-drug resistance by suppressing the transcription of ABCG2, which inhibits drug efflux.

A new daunomycin-peptide conjugate: synthesis, characterization and the effect on the protein expression profile of HL-60 cells in vitro

Daunomycin (Dau) is a DNA-binding antineoplastic agent in the treatment of various types of cancer, such as osteosarcomas and acute myeloid leukemia. One approach to improve its selectivity and to decrease the side effects is the conjugation of Dau with oligopeptide carriers, which might alter the drug uptake and intracellular fate. Here, we report on the synthesis, characterization, and in vitro biological properties of a novel conjugate in which Dau is attached, via an oxime bond, to one of the cancer specific small peptides (LTVSPWY) selected from a random phage peptide library. The in vitro cytostatic effect and cellular uptake of Dau═Aoa-LTVSPWY-NH(2) conjugate were studied on various human cancer cell lines expressing different levels of ErbB2 receptor which could be targeted by the peptide. We found that the new daunomycin-peptide conjugate is highly cytostatic and could be taken up efficiently by the human cancer cells studied. However, the conjugate was less effective than the free drug itself. RP-HPLC data indicate that the conjugate is stable at least for 24 h in the pH 2.5-7.0 range of buffers, as well as in cell culture medium. The conjugate in the presence of rat liver lysosomal homogenate, as indicated by LC-MS analysis, could be degraded. The smallest, Dau-containing metabolite (Dau═Aoa-Leu-OH) identified and prepared expresses DNA-binding ability. In order to get insight on the potential mechanism of action, we compared the protein expression profile of HL-60 human leukemia cells after treatment with the free and peptide conjugated daunomycin. Proteomic analysis suggests that the expression of several proteins has been altered. This includes three proteins, whose expression was lower (tubulin β chain) or markedly higher (proliferating cell nuclear antigen and protein kinase C inhibitor protein 1) after administration of cells with Dau-conjugate vs free drug.

What are the key targeted delivery technologies of siRNA now?

Whilst significant advances have been made in the delivery of nucleic acids to mammalian cells, most of the used strategies do not distinguish between normal and cancer cells. The same challenge is also facing radioactive- and chemo-therapies which are highly toxic and poorly tolerated due to limited tumor specificity. Regardless of the nature of the drug, there is a need for developing a technology platform which targets drugs only to tumors cells, leaving normal cells undamaged. Among the targeting strategies, receptor-targeted delivery provides an innovative strategy to selectively direct therapeutics to cancer cells. Receptor-binding ligands (e.g., peptides, antibodies, aptamers) can be incorporated into gene delivery vesicles or directly conjugated to siRNA in the hope in promoting their localization in target cell expressing the cognate receptors. The present chapter discusses the current progress made in the specific delivery of siRNAs.

Serum proteomic approach for the identification of serum biomarkers contributed by oral squamous cell carcinoma and host tissue microenvironment

The lack of serum biomarkers for head and neck carcinoma limits early diagnosis, monitoring of advanced disease, and prediction of relapses in patients. We conducted a comprehensive proteomics study on serum from mice bearing orthotopic human oral squamous cell carcinomas (OSCC) with distinct invasive phenotypes. Matched established cell lines were transplanted orthotopically into tongues of RAG-2/gamma(c) mice and mouse serum was analyzed by 2-dimensional-differential gel electrophoresis(2D-DIGE)/liquid chromatography (LC)-MS/MS and by online 2D-LC-MS/MS of iTRAQ labeled samples. We identified several serum proteins as being differentially expressed between control and cancer-bearing mice and between noninvasive and invasive cancer (p<0.05). Differentially expressed proteins of human origin included the epidermal growth factor receptor (EGFR), cytokeratins, G-protein coupled receptor 87, Rab11 GTPase, PDZ-domain containing proteins, and PEST-containing nuclear proteins. Identified proteins of mouse origin included clusterin, titin, vitronectin, vitamin D-binding protein, hemopexin, and kininogen I. The levels of serum and cell secreted EGFR were further validated to match proteomic data regarding the inverse correlation with the invasive phenotype. In summary, we report a comprehensive patient-based proteomics approach for the identification of potential serum biomarkers for OSCC using an orthotopic xenograft mouse model.

Targeted delivery of antisense oligonucleotides and siRNAs into mammalian cells

RNA interference (RNAi) is a natural mechanism for gene silencing that can be harnessed for the development of RNA-based drugs. Although synthetic small interfering RNA (siRNAs) can be delivered in vitro to virtually all cell types using lipid-based transfection agents or electroporation, efficient strategies for achieving either systemic or targeted delivery remains one of the major in vivo challenges. Among the targeting strategies, receptor-targeted delivery provides an innovative strategy to selectively direct therapeutics to cancer cells. Receptor-binding peptides can be incorporated into gene-delivery vesicles or directly conjugated to siRNAs in the hope of promoting their localization in target cells expressing the cognate receptors. This chapter discusses the current status of siRNA-targeting strategies using either peptides identified through iterative screening of random peptide phage libraries or naturally occurring peptides. Also, transcriptional targeting strategies and detailed protocols for the selection of cancer cell-binding peptide from random peptide libraries are described.

Protein tyrosine kinase signaling diversity and susceptibility to targeted kinase inhibitors

Protein kinases, including tyrosine kinases, are one of the largest classes of proteins implicated in cancer development and progression. Recent discovery of selective therapies targeting tyrosine kinase receptor signaling has provided encouraging clinical results. Clinical trials with anti-EGFR, anti-ErbB2/Her2, anti-Bcr-Abl and others have demonstrated the clinical utility of tyrosine kinases as therapeutic targets and as surrogate markers to guide the selection of patients susceptible to respond to treatment. This success has been tempered in part because resistance to targeted therapies is now documented to occur in experimental models and in patients, which hampers therapeutic efficacy. Mechanisms of resistance include cell heterogeneity in target expression, mutations in target's encoding genes, and compensatory signaling mechanisms. This paper provides a brief overview on the diversity of tyrosine kinase signaling and the impact on cancer cell response to targeted tyrosine kinase inhibitors.

Resistance to epidermal growth factor receptor-targeted therapy

The epidermal growth factor receptor (EGFR) has been a major target of molecular anticancer therapy. Two approaches have been developed, involving monoclonal antibodies and receptor tyrosine kinase inhibitors, and both have demonstrated benefit in clinical trials. However, evidence of resistance to these drugs has been described. Cellular levels of EGFR do not always correlate with response to the EGFR tyrosine kinase inhibitors, indicating acquired resistance to these drugs. Since EGFR antagonists interfere with the activation of several intracellular pathways that control cell proliferation, survival, apoptosis, angiogenesis, invasion and metastasis, acquired resistance can occur as a result of several different molecular mechanisms: autocrine/paracrine production of ligand, receptor mutation, constitutive activation of the downstream pathway and activation of alternative pathways. We will describe here potential mechanisms that can cause resistance to EGFR-targeted drugs. Combinations of EGFR antagonists with inhibitors targeting different signaling mechanism(s) - such as insulin-like growth factor receptor and vascular endothelial growth factor receptor - that share the same downstream mediator (e.g., phosphatidylinositol 3-kinase/Akt, mitogen-activated protein kinase), may circumvent or delay the development of resistance to EGFR antagonists resulting in enhanced antitumor activities.

Multifaceted roles of cyclooxygenase-2 in lung cancer

Lung cancer is the leading cause of cancer death in the United States. Although the low 5-year survival rate (under 15%) has changed minimally in the last 25 years, new agents and combinations of agents that target tumor proliferation, invasion, and survival may lead to improvement in patient outcomes. There is evidence that cyclooxygenase-2 (COX-2) is overexpressed in lung cancer and promotes tumor proliferation, invasion, angiogenesis, and resistance to apoptosis. COX-2 inhibitors have been found to inhibit tumor growth in animal models and have demonstrated responses when combined with conventional therapy in phase II clinical trials. Further understanding of the mechanisms involved in COX-2-mediated tumorigenesis and its interaction with other molecules in lung cancer may lead to improved therapeutic strategies for this disease. In addition, delineation of how COX-2-dependent genes modulate the malignant phenotype will provide novel insights in lung cancer pathogenesis.

New cancer therapeutics: target-specific in, cytotoxics out?

The International Conference on Molecular Targets and Therapeutics, jointly sponsored by the American Association for Cancer Research (AACR), National Cancer Institute (NCI) and European Organization for Research and Treatment of Cancer (EORTC), was held in Boston on November 17-21, 2003. It offered updates of the latest developments and emerging trends in anti-cancer research. One of the most exciting areas was the development of molecular target-specific therapeutics that have the potential to maximize therapeutic benefit while minimizing toxicity to normal cells. Signifying the coming of age of tumour-specific targets and agents was the recurring theme, to urgently develop and validate biomarker assays as surrogate endpoints; both for showing that targeted agents act as expected and for providing proof of concept in the scientific rationale of new agents. Given the dominance of protein tyrosine kinase inhibitors in small-molecule drug design, a strong case was made for the implementation of phospho-proteomics or signal transduction signatures and pharmaco-proteomics or chemotherapeutic scans in phase I/II trials--or for the future "Nanolab", eloquently described by Leroy Hood. However, molecular targeted agents-other than imanitib (Gleevec)--have yet to enter broad clinical use and several presentations described efforts for improving classical (cytotoxic) chemotherapeutic agents by targeting them selectively to tumour cells.

Selective targeting of cancer cells using synthetic peptides

To establish efficient and reliable therapeutic delivery into cancer cells, a number of delivery agents and concepts have been investigated in the recent years. Among many improvements in targeted and controlled delivery of therapeutics, cell-targeting peptides have emerged as the most valuable non-immunogenic approach to target cancer cells. Peptides can be incorporated into multicomponent gene-delivery complexes for cell-specific targeting. In contrast to larger molecules such as monoclonal antibodies, peptides have an excellent tumor penetration, which make them ideal carriers of therapeutics to the site of primary tumor and the distant metastatic sites. Here we give an update on the progress made during the last two years on the identification and potential of specific synthetic tumor targeting peptides.