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

Abstract

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).Materials and Methods: Primary lung adenocarcinomas were generated in vivo in mice by intranasal delivery of an adenovirus expressing Cre-recombinase. Lung cancers expressed oncogenic KrasG12D 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 h. In each case, the biologically effective dose (BED) equaled 25 Gy10. Response to RT was assessed by micro-CT 2 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 (WT) 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 × 2 (P = 0.23). Expression of the p53 target genes p21 and PUMA were higher and bromodeoxyuridine uptake was lower after RT in tumors with WT p53.Conclusion: 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.

Functional p53 is required for rapid restoration of daunorubicin-induced lesions of the spleen

“…We therefore analysed spleens from DNR-treated Trp53- wt and -null mice for p21 induction. Immunoblotting showed elevated expression of p21 in spleens from wt-mice at 24 and 48 hours after DNR treatment (Figure 3, left panel) similar to what is seen with other DNA-damaging agents [22,23]. The Trp53 null mice had only modest increase in p21 levels (Figure 3, right panel).…”

Synergy of radiotherapy and PD-1 blockade in Kras-mutant lung cancer

“…In this study, we utilized our previously tested RT regimen, which consists of 17 Gy in 2 fractions of 8.5 Gy, given on 2 consecutive days approximately 24 hours apart (8.5 Gy × 2). While the translation of radiation doses and fractionation schemes used in humans to mice is difficult and not very well studied (8,18), prior work has shown that multi-fraction RT is more effective than single-fraction RT when combined with CTLA-4 checkpoint blockade in syngeneic tumor models (19). Additionally, we used a previously described timing approach of the immunomodulatory agent and initiated αPD-1 treatment 6 hours after the second fraction of 8.5 Gy ( Figure 1A) (20).…”

“…The translation of treatment doses and fractionation schemes used in humans to mice is difficult and not very well studied (8,18). Whereas in the majority of in vivo RT studies a single dose is prescribed, Dewan and colleagues specifically analyzed the efficacy of different dose-fractionation regimens with CTLA-4 blockade in two syngeneic mouse models (breast and colorectal cancer) and showed superiority of the multi-fraction versus single-fraction approach (19).…”

Treatment with the nitric oxide synthase inhibitor L-NAME provides a survival advantage in a mouse model of Kras mutation-positive, non-small cell lung cancer

“…Mice were then humanly euthanized at either a fixed time point (four months post AdCre) or upon reaching a moribundity endpoint. A subset of the latter mice were also radiologically imaged monthly using micro-computed tomography (CT) [43]. CT scans were reviewed in a blinded fashion using Image-J.…”