Assessing the Radiation Response of Lung Cancer with Different Gene Mutations Using Genetically Engineered Mice

Purpose: Non-small cell lung cancers (NSCLC) are a heterogeneous group of carcinomas harboring a variety of different gene mutations. We have utilized two distinct genetically engineered mouse models of human NSCLC (adenocarcinoma) to investigate how genetic factors within tumor parenchymal cells influence the in vivo tumor growth delay after one or two fractions of radiation therapy (RT). Methods and Materials: Primary lung adenocarcinomas were generated in vivo in mice by intra-nasal delivery of an adenovirus expressing Cre-recombinase. Lung cancers expressed oncogenic K-rasG12D and were also deficient in one of two tumor suppressor genes: p53 or Ink4a/ARF. Mice received no radiation treatment or whole lung irradiation in a single fraction (11.6 Gy) or in two 7.3 Gy fractions (14.6 Gy total) separated by 24 hours. In each case, the biologically effective dose (BED) equaled 25 Gy10. Response to RT was assessed by micro-CT two weeks after treatment. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemical staining were performed to assess the integrity of the p53 pathway, the G1 cell-cycle checkpoint, and apoptosis. Results: Tumor growth rates prior to RT were similar for the two genetic variants of lung adenocarcinoma. Lung cancers with wild-type p53 (LSL-Kras; Ink4a/ARFFL/FL mice) responded better to two daily fractions of 7.3 Gy compared to a single fraction of 11.6 Gy (P=0.002). There was no statistically significant difference in the response of lung cancers deficient in p53 (LSL-Kras; p53FL/FL mice) to a single fraction (11.6 Gy) compared to 7.3 Gy x 2 (P=0.23). Expression of the p53 target genes p21 and PUMA were higher and BrdU uptake was lower after RT in tumors with wild-type p53. Conclusions: Using an in vivo model of malignant lung cancer in mice, we demonstrate that the response of primary lung cancers to one or two fractions of RT can be influenced by specific gene mutations.