Cetuximab is a monoclonal antibody targeting the epidermal growth factor receptor (EGFR) and is used for the treatment of metastatic colorectal cancer (mCRC) as monotherapy or in combination with chemotherapy. Recent clinical trials have shown little benefit in combining cetuximab with oxaliplatin in contrast to the positive interactions observed with irinotecan. This thesis aims to understand why a subset of colorectal cancers do not benefit from cetuximab and oxaliplatin combined treatment. In vitro drug combination assays showed that the addition of cetuximab to oxaliplatin resulted in antagonistic effects on cell proliferation as opposed to the synergism observed with 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan. Although both oxaliplatin and SN-38 increased the levels of reactive oxygen species (ROS), only oxaliplatin was able to induce ROS-mediated apoptosis via the activation of p38 Mitogen-Activated Protein Kinase (MAPK). RT-PCR oxidative stress array analysis revealed that oxaliplatin can produce ROS through the upregulation of the NADPH oxidase ROS generating enzyme Dual Oxidase 2 (DUOX2) and that cetuximab, by preventing DUOX2 induction, can inhibit ROS generation by oxaliplatin. Chromatin Immunoprecipitation (ChIP) of Signal Transducer and Activator of Transcription 1 (STAT1) following oxaliplatin treatment, indicated a role for this protein in the transcriptional upregulation of DUOX2 by direct promoter-binding. Cetuximab, by impairing STAT1 activation and DUOX2 upregulation, can antagonise ROS-mediated apoptosis by oxaliplatin through the activation of the p38 pathway. Microarray analysis was employed to identify deregulated genes in the p38 pathway following cetuximab and oxaliplatin treatment in order to better clarify the role that p38-regulated genes play in the negative interactions of these drugs. The results presented in this thesis highlight the importance of ROS generation for the cytotoxic effects of oxaliplatin and indicate that combination with ROS-reducing agents such as cetuximab can result in negative cellular effects. Understanding how these drug interactions lead to antagonistic effects will be useful for the optimisation of future therapeutic combinations in the clinical setting.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:634613 |
| Date | January 2014 |
| Creators | Santoro, V. |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1454999/ |
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