Purpose: The human epidermal growth factor receptors EGFR (erbB1) and HER2 (erbB2/neu) are involved in mediating resistance to chemotherapy and ionising radiation (IR). In vitro studies demonstrate that small molecule tyrosine kinase inhibitors (TKIs) which target these receptors can increase the effectiveness of DNA damaging agents. However, these combinations have failed to produce the clinical results anticipated and one potential explanation is that the inhibition of EGFR and HER2 cell signalling pathways by TKIs is short lived, with cells able to switch to alternative mechanisms of signalling through HER3. The purpose of this study was to examine whether the duration of exposure to TKIs modulates the induction and repair of DNA damage produced by chemotherapy or IR and describes attempts to elucidate the role of HER2 in mediating resistance to chemotherapy. Experimental design: Two HER targeting TKIs, lapatinib and gefitinib were investigated. The effect of lapatinib in combination with cisplatin and doxorubicin on the inhibition of cell proliferation and the role of schedule were examined in drug combination assays. The influence of the duration of exposure to TKIs on the induction and repair of DNA lesions induced by cisplatin, IR, doxorubicin, etoposide and m-AMSA were investigated using the alkaline and neutral Comet assays and measurement of γH2AX and RAD51 foci. DNA expression arrays were used to identify the potential mechanisms through which HER2 produces resistance to cisplatin in cells transfected with HER2. Results: Lapatinib is able to synergistically inhibit cell proliferation in combination with cisplatin or doxorubicin in a schedule dependent manner. Duration of exposure to TKIs has no effect on the induction of DNA lesions by cisplatin or IR, but significantly reduces the production of DNA double strand breaks by doxorubicin, etoposide and m-AMSA in part through the down-regulation of the expression of topoisomerase IIα (Topo IIα), increasing resistance to these drugs. Conclusions: These results indicate the scheduling of small molecule TKIs targeted against EGFR and HER2 is important and continuous exposure to these drugs induces resistance to doxorubicin, etoposide and m-AMSA, through reduced expression of their target, Topo IIα. The importance of schedule should be considered when combining TKIs with chemotherapy in clinical practice.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:565813 |
| Date | January 2012 |
| Creators | Bhosle, J. |
| 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/1344180/ |
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