Background: Non-small cell lung cancer (NSCLC) patients that have activating mutations in the epidermal growth factor receptor (EGFR) gene are treated with EGFR tyrosine kinase inhibitors (TKIs) e.g. Erlotinib (Tarceva®) and Gefitinib (Iressa®). Most NSCLC patients with activating EGFR mutations will respond to EGFR-TKIs; however, in about 50% of these cases a secondary mutation in EGFR (T790M) subsequently occurs which results in resistance to treatment. Other mechanisms of clinical resistance can also occur such as amplification of c-MET kinase, Her-2 and EMT conversion; however, additional routes of resistance are poorly defined. Using a novel NSCLC patient-derived xenograft (PDX) model, driven by the L858R EGFR mutation, we set out to recapitulate the reported clinical routes of resistance to EGFR inhibitors and to evaluate if additional mechanism could also be identified.

Methods: LU6422 is a Caucasian NSCLC adenocarcinoma PDX model with an activating EGFR mutation (L858R) which is maintained subcutaneously in vivo admixed with a human stromal cell component. HCC827 is NSCLC adenocarcinoma cell line with an activating EGFR mutation (exon 19 del E746-A750).

Resistant models of LU6422 and HCC827 were generated in vivo and in vitro (respectively) through repeated dosing or exposure to EGFR-TKIs. Resistant tumour material was characterised for further mutations in the EGFR gene by direct sequencing and for c-MET, Axl and Her2 over-expression and genomic amplification by quantitative PCR. Combination efficacy treatment (in vitro and in vivo) was carried out to verify documented resistance mechanisms.

Results: Naïve LU6422 and HCC827 tissue exhibited exquisite sensitivity to EGFR-TKIs (100% reduction in pre-treatment tumour volume, p<0.0001). Following successive cycles of EGFR-TKI treatment several resistant subtypes were generated, cloned and characterized. Combination treatment of resistant HCC827 variants restored efficacy to naïve treatment levels.

Conclusions: EGFR-TKI resistant subtypes were generated in vivo and in vitro from a proprietary patient-derived xenograft model (LU6422) and the HCC827 cell line and were characterised for their resistance mechanisms.

Pre-clinical modes of acquired resistance will be invaluable in assessing novel agents targeting the EGFR pathway and the development of new combination strategies which seek to prevent or overcome resistance to EGFR-TKIs.

Citation Format: Andrew McKenzie, Nektaria Papadopoulou, Simon Jiang, Martin Page, Henry Li, Rajendra Kumari, Jane Wrigley. In vivo and in vitro generation and characterisation of EGFR-TKI resistance in patient-derived xenograft (PDX) and cell line-derived xenograft (CDX) models of NSCLC with activating EGFR mutations. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4875. doi:10.1158/1538-7445.AM2014-4875