Deletion of ATM in tumor but not endothelial cells improves radiation response in a primary mouse model of lung adenocarcinoma.

Stereotactic body radiation therapy is utilized to treat lung cancer. The mechanism of tumor response to high dose RT (HDRT) is controversial, with competing hypotheses of increased direct tumor cell killing vs indirect effects on stroma including endothelial cells. Here we used dual recombinase technology in a primary murine lung cancer model to test whether tumor cells or endothelial cells are critical HDRT targets. Lenti-Cre deleted one or two copies of Atm (KPAFL/+ or KPAFL/FL), whereas adeno-FlpO infected mice expressed Cre in endothelial cells to delete one or both copies of Atm (KPVAFL/+ or KPVAFL/FL) to modify tumor cell or endothelial cell radiosensitivity, respectively. Deletion of Atm in either tumor cells or endothelial cells had noimpact on tumor growth in the absence of radiation. Despite increased endothelial cell death in KPVAFL/FL mice following irradiation, tumor growth delay was not significantly increased. In contrast, a prolonged tumor growth delay was apparent in KPAFL/FL mice. Primary tumor cell lines lacking Atm expression also demonstrated enhanced radiosensitivity as determined via a clonogenic survival assay. These findings indicate that tumor cells, rather than endothelial cells, are critical targets of HDRT in primary murine lung cancer.