CRISPR Screen of Druggable Targets in Small Cell Lung Cancer Identified ATM Inhibitor (AZD1390) as a Radiosensitizer.

Purpose: Small cell lung cancer (SCLC) is an aggressive and lethal form of lung cancer and the overall 5-year survival (OS) for patients is a dismal 7%. Radiation therapy (RT) provides some benefit for selected patients with SCLC but could be improved with radiosensitizing agents. In this study, we identified novel radiosensitizers for SCLC by a CRISPR-Cas9 screen and evaluated the efficacy of ATM inhibitor AZD1390 as a radiosensitizer of SCLC.

Methods And Materials: We transduced the SCLC cell line SBC5 with a custom CRISPR sgRNA library focused on druggable gene targets and treated cells with RT. Cells collected at multiple timepoints were subjected to next-generation sequencing. We determined radiosensitization both in vitro with cell lines assessed by short-term viability and clonogenic assays, and in vivo mouse models by tumor growth delay. Pharmacodynamic effects of AZD1390 were quantified by ATM-Ser1981 phosphorylation, and RT-induced DNA damage by comet assay.

Results: Using a CRISPR dropout screen, we identified multiple radiosensitizing genes for SCLC at various timepoints with ATM as a top determinant gene for radiosensitivity. Validation by ATM knockout (KO) demonstrated increased radiosensitivity by short-term viability assay (dose modification factor [DMF] = 3.25-3.73 in SBC5 ATM-KO) and clonogenic assays (DMF 1.25-1.65 in SBC5 ATM-KO). ATM inhibition by AZD1390 effectively abrogated ATM Ser1981 phosphorylation in SCLC cell lines and increased RT-induced DNA damage. AZD1390 synergistically increased the radiosensitivity of SCLC cell lines (cell viability assay: SBC5 DMF = 2.19, SHP77 DMF = 1.56, H446 DMF = 3.27, KP1 DMF = 1.65 at 100nM; clonogenic assay: SBC5 DMF = 4.23, H1048 DMF = 1.91), and in vivo murine syngeneic, KP1, and patient-derived xenograft (PDX) models, JHU-LX108 and JHU-LX33.

Conclusions: In this study, we demonstrated that genetically and pharmacologically (AZD1390) inhibiting ATM markedly enhanced RT against SCLC, providing a novel pharmacologically tractable radiosensitizing strategy for patients with SCLC.