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Title: Modulation of mucin expression in respiratory epithelial cells : effect of ErbB receptor tyrosine kinase inhibitors
Author: Nuseibeh, Samir
ISNI:       0000 0004 2670 8584
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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Secretion of mucins (e.g. MUC5AC) by the airway epithelium into the respiratory tract mucus layer is an important homeostatic mechanism which safeguards the lung from invasive pathogens and harmful particles. Airway mucus hypersecretion features in the pathophysiology of inflammatory-based airway diseases such as chronic obstructive pulmonary disease (COPD) and asthma. Signalling of the ErbB receptor tyrosine kinase subfamily, particularly the ErbB1 and ErbB2 receptor subtypes, has been implicated in the process of airway mucus hypersecretion, and upregulation of ErbB1 receptor occurs in the lungs of asthmatics, COPD sufferers, and cigarette smokers. Thus, ErbB receptor tyrosine kinase inhibitors (RTKIs) offer a potential treatment for airway mucus hypersecretion. This thesis studied the effects of five such inhibitors; an ErbB1, an ErbB2, and three dual ErbB1+B2 inhibitors, in an in vitro system of mucin synthesis using NCI-H292 cells - a carcinoma-based lung epithelial cell line. After pharmacological characterisation of the NCI-H292 cell in vitro system, Taqman RT-qPCR was used to measure the effect of the five inhibitors on EGF-induced MUC5AC mRNA expression (as a marker of mucin synthesis). The effect of the five ErbB RTKIs on cell proliferation was also measured (as a positive control) by analysing DNA synthesis. All five inhibitors attenuated DNA synthesis with similar potencies suggesting all drugs were pharmacologically active, but only the single ErbB1 RTK inhibitor attenuated EGF-induced MUC5AC mRNA expression. To address the discrepancy in pharmacological activity between the five ErbB RTKIs, activity of the ERK1/2-dependent signal pathway involved in ErbB receptor-mediated MUC5AC synthesis was analysed by measuring ErbB receptor autophosphorylation (measuring phosphorylation of four specific tyrosine residues involved in ERK1/2 induction) and ERK1/2 phosphorylation by Western blot or ELISA. Although all five ErbB RTKI compounds inhibited ErbB1 and ErbB2 receptor autophosphorylation to some extent (particularly at 10 μM), only the single ErbB1 RTK inhibitor convincingly inhibited autophosphorylation of all four tyrosine residues implicated in ERK1/2 signalling. Most importantly, the single ErbB1 RTK inhibitor was the only inhibitor to block downstream phosphorylation of ERK1/2. The reason for the varying potencies exhibited by the five ErbB1 RTK inhibitors was unclear but most likely reflects a difference in the pharmacological properties (for example, the receptor dissociation rate) of each compound. These data indicate that selective ErbB1 RTK inhibitors would be of therapeutic benefit for the airway mucus hypersecretion of asthma and COPD.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available