GRP78 is a known cyto-protective gene which is induced in microenvironments typical of tumours with low glucose and hypoxia. Furthermore up-regulation of GRP78 has been linked to chemo- and radioresistance as well as poor survival outcome. This study is the first to confirm that GRP78 is up-regulated in tumours of the oropharynx, larynx and hypopharynx compared with matched histologically normal tissue (p(Χ2)<0.001). Up-regulation of GRP78 may be important for tumour development and therefore we have investigated the consequences of inhibition of GRP78 in cells derived from laryngeal squamous cell carcinomas (LSCC). EGF-SubA is a novel drug consisting of EGF covalently attached to the A subunit of an E.coli derived AB5 toxin which can cleave GRP78. EGF-SubA was able to induce EGFR-dependent cytotoxicity in a panel of seven laryngeal SCC cells with an IC50 range of between 4-100pM. EGF-SubA treatment induced G1 cell cycle arrest as well as apoptosis. Therefore apoptosis may be the mechanism by which EGF-SubA causes cell death. In vitro studies demonstrated that EGF-SubA enhances the effects of clinically relevant genotoxic agents. Two Gy survival fractions (SF2) were significantly reduced with EGF-SubA pre-treatment (p<0.03). In addition EGF-SubA in combination with the primary head and neck cancer chemo-therapeutic agent cisplatin, resulted in IC50 drug combination indexes (CI) as low as 0.542, which is suggestive of a synergistic effect. The potency of EGF-SubA appears to be substantially dependent on EGFR membrane expression since cells expressing higher EGFR levels were associated with increased sensitivity to EGF-SubA where Spearman’s rank correlation coefficient = 0.919 (p=0.003). Furthermore pre-incubation of LSCC cells with sub-toxic doses of cetuximab, a therapeutic monoclonal antibody to EGFR, completely rescued cells from the cytotoxic effects of EGF-SubA (p(t test)≤0.005). This is an important proof of principal for a proposed combined toxin-protectant therapeutic strategy that would permit topical use of EGF-SubA peri- or post-operatively after tumour resection in order to kill any remaining tumour cells, or as an oral rinse in patients who present with pre-malignant lesions of the oral cavity, with any potential systemic toxicity being abrogated by cetuximab. In summary this study has found that GRP78 is up-regulated in head and neck cancers suggesting that this protein may be important for tumour development and survival. Thus inhibition of GRP78 through EGF-SubA may offer a novel approach to cancer therapy. In addition to suppressing the growth of LSCC cell, EGF-SubA was found to enhance the effects of relevant genotoxic agents in vitro of cisplatin and radiation. Further work is now warranted in order to assess the efficacy and toxicity of EGF-SubA, in vivo, before phase I clinical trials can commence.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:559391 |
| Date | January 2011 |
| Creators | Aslam, Mohammed Afeef |
| Contributors | Boyd, Mark. ; Jones, Terry |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/3813/ |
Page generated in 0.0019 seconds