Deletion of Atm in Tumor but not Endothelial Cells Improves Radiation Response in a Primary Mouse Model of Lung Adenocarcinoma

Abstract

Stereotactic body radiotherapy is utilized to treat lung cancer. The mechanism of tumor response to high-dose radiotherapy (HDRT) is controversial, with competing hypotheses of increased direct tumor cell killing versus 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 ataxia-telangiectasia mutated gene (Atm; KPA FL/þ or KPA FL/FL), whereas adeno-FlpO-infected mice expressed Cre in endothelial cells to delete one or both copies of Atm (KPVA FL/þ or KPVA FL/FL) to modify tumor cell or endothelial cell radiosensitivity, respectively. Deletion of Atm in either tumor cells or endothelial cells had no impact on tumor growth in the absence of radiation. Despite increased endothelial cell death in KPVA FL/FL mice following irradiation, tumor growth delay was not significantly increased. In contrast, a prolonged tumor growth delay was apparent in KPA FL/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. Significance: These findings establish radiosensitizing tumor cells rather than endothelial cells as the primary mechanism of tumor response to high-dose radiotherapy, supporting efforts to maximize local control by radiosensitizing tumors cells. See related commentary by Hallahan, p. 704

ATM Expression Is Elevated in Established Radiation-Resistant Breast Cancer Cells and Improves DNA Repair Efficiency

“…ATM also functions in the NHEJ pathway through phosphorylating kinase DNA-PKcs and nuclease Artemis [18]. Several studies showed that there was some associations between radiosensitivity and ATM expression levels [19][20][21]. Upregulation of ATM protein and its activation are reported to be correlated with enhanced radioresistance [22][23][24].…”

“…Considering ATM as an important modulator of DDR efficiency and its impact on radiosensitivity [17,[19][20][21], we next studied the role of incresed expression of ATM in radioresistance development.…”

Automated in Vivo Assessment of Vascular Response to Radiation Using a Hybrid Theranostic X-Ray Irradiator/Fluorescence Molecular Imaging System

“…However, other studies have observed that endothelial/stromal cell radiosensitivity had no influence on the amount of radiation needed to induce local tumor control of xenografted human tumors, but affected the regrowth rate of relapsed tumors [43]. Other studies have observed similar findings, but also found that increased tumor cell radiosensitivity resulted in increased tumor control [44], [45]. These studies demonstrate the importance of accurate measurements of vascular perfusion for radiation therapy related studies.…”

ATM Inhibition Sensitizes Tumors to High-Dose Irradiation

“…The clinical success has been due to the accuracy and conformality of newer radiotherapy procedures that limit the dose of radiation to surrounding normal tissues. The study by Torok and colleagues supports an exciting new strategy for the development of molecularly targeted radiation sensitizers when high-dose irradiation is administered (1). Examples of conditions where high-dose radiation is used include oligometastases, defined as few metastatic sites (10).…”

“…Torok and colleagues demonstrated that deletion of ATM in the endothelium resulted in vascular destruction (1). Concerns about destruction of tumor blood vessels are related to tumor blood perfusion including reduced drug and oxygen delivery to the tumor during radiotherapy.…”