EGFR-mutant lung cancers are highly sensitive to EGFR tyrosine kinase inhibitors (TKIs; erlotinib/gefitinib/afatinib), but tumors develop drug resistance within 9-16 months. Resistance to gefitinib/erlotinib commonly occurs via a second-site EGFR mutation, T790M. Two strategies to overcome T790M+ resistance are mutant-specific EGFR TKIs, such as AZD9291, and dual inhibition of EGFR with afatinib plus the anti-EGFR antibody, cetuximab (A+C). Unfortunately, second-line acquired resistance to A+C and AZD9291, after first-line acquired resistance to erlotinib/gefitinib/afatinib, also occurs. To prevent/delay resistance to AZD9291, the combination of AZD9291 plus selumetinib (MEK1/2 inhibitor; AZD6244/ARRY-142886) is also currently being tested in a Phase I clinical trial (NCT02143466). The effects of sequential and combination treatment with various anti-EGFR agents on tumor evolution and drug resistance are largely unknown. In these studies, we modeled drug resistance pre-clinically to: 1. Assess the heterogeneity of mechanisms of first-line resistance to erlotinib and afatinib 2. Determine the optimum order of treatment with A+C vs. AZD9291 in the setting of T790M+ EGFR-mutant lung tumors 3. Elucidate mechanisms of first- and second-line acquired resistance to AZD9291 and 4. Elucidate mechanisms of resistance to AZD9291 plus selumetinib. Next-generation sequencing of genomic DNA from cell line models of resistance to erlotinib/afatinib revealed multiple potentially functional genomic changes within a given pool of resistant cells (including T790M). We also found that AZD9291 is more potent than A+C at inhibiting cell growth in the setting of T790M+ resistance to erlotinib. A+C-resistant cell lines remain sensitive to AZD9291, but AZD9291-resistant cell lines are cross-resistant to A+C. Resistance to AZD9291 is associated with dysregulation of MAPK signaling and can be overcome by addition of the MEK 1/2 inhibitor, selumetinib. Finally, AZD9291 plus selumetinib-resistant cell lines display increased baseline phospho-MEK/ERK and are sensitive to in vitro treatment with an ERK inhibitor, SCH772984 or alternative MEK inhibitor, trametinib. These studies provide a more comprehensive understanding of how EGFR-mutant tumors undergo rewiring of their signaling circuitry in response to single-agent EGFR- and combined EGFR+MEK-inhibition. This work, emphasizing a mechanistic understanding of the effects of therapies on tumor evolution, provides a framework for future clinical trials testing different treatment sequences.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-07202015-172236 |
| Date | 23 July 2015 |
| Creators | Meador, Catherine Belle |
| Contributors | Christine Lovly, Jennifer Pietenpol, Rebecca Cook, William Pao |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-07202015-172236/ |
| Rights | restricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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