Abstract 765: Overcoming acquired EGFRi resistance in NSCLC with targeted beam irradiation in combination with targeted agents
Authors: McKenzie Andrew , Papadopoulou Nektaria , Page Lucy , Jiang Simon , Wrigley Jane , Yin Yinfei , Shi Qian , Page Martin , Wilson Ian , Kumari Rajendra 
Published: August 2015

BACKGROUND: Non-small cell lung cancer (NSCLC) patients undergo primary, adjuvant or neoadjuvant radiotherapy treatment with image-guided radiotherapy (IGRT) being widely used to provide more accurate treatment plans and reduced side effects.

Patients who have activating mutations in the epidermal growth factor receptor (EGFR) gene are treated with EGFR tyrosine kinase inhibitors (EGFRi). However, resistance to EGFRi occurs in the majority of patients with the main clinical drivers being secondary gatekeeper mutations (T790M) or amplification of genes such as c-MET and Her2.

The small animal radiation research platform (SARRP), which allows the treatment of rodent models of cancer more accurately with planned protocols similar to those utilised in the clinic, was used in combination with EGFRi, to assess the efficacy of combination treatment strategies of irradiation (IR) in EGFRi resistant NSCLC xenografts.

METHODS: Resistance to EGFRi in the NSCLC cell line HCC827, which harbours an activating EGFR mutation, was generated through repeated exposure to Gefitinib or Erlotinib. Resistant models were characterised for further mutations in the EGFR gene by direct sequencing and for c-MET, Axl and Her2 over-expression/genomic amplification by quantitative PCR.

EGFRi resistant or parental HCC827 cells were implanted subcutaneously into nude mice, xenograft growth was monitored by calliper measurements and treatment initiated when the mean tumour volume reached ∼200mm3. An image guided IR dose of 3Gy/mouse/day (30Gy total) was targeted directly to the xenografts whilst sparing the surrounding normal tissue. Mice were treated with IR either alone or in combination with Erlotinib or Crizotinib; response to treatment was evaluated by tumour volume measurement.

RESULTS: EGFR-TKI resistant HCC827 cell lines were generated following successive cycles of treatment. Amplification of c-MET was identified in a number of clones, but no Her2 amplification or gatekeeper mutations; therefore Crizotinib, a c-MET inhibitor, was selected for evaluation in these models.

When assessed in vivo, treatment of parental HCC827 xenografts with targeted IR or Erlotinib treatment resulted in tumour regression. However, in the c-MET driven resistant model, both the IR and Erlotinib response was significantly attenuated, resulting in tumour re-growth. Combination testing with Crizotinib restored the efficacy of both IR and Erlotinib to naïve treatment levels confirming the role of c-MET in resistance.

CONCLUSIONS: Resistance to EGFRi and IR in a HCC827 model is driven by c-MET amplification. Treatment with Crizotinib restored sensitivity to both EGFRi and IR demonstrating that pre-clinical models of resistance are invaluable in assessing novel agents targeting the EGFR pathway and the development of new combination strategies which seek to prevent/overcome resistance to EGFRi.

Citation Format: Andrew McKenzie, Nektaria Papadopoulou, Lucy Page, Simon Jiang, Jane Wrigley, Yinfei Yin, Qian Shi, Martin Page, Ian Wilson, Rajendra Kumari. Overcoming acquired EGFRi resistance in NSCLC with targeted beam irradiation in combination with targeted agents. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 765. doi:10.1158/1538-7445.AM2015-765