Purpose: Inflammatory breast cancer (IBC) is a highly aggressive form of breast cancer, and patients with IBC remain at high risk of locoregional recurrence after radiotherapy. We previously demonstrated that depleting intracellular cholesterol induces radiosensitivity in IBC cells in vitro, and that IBC patients with high levels of high-density lipoprotein (HDL) and those taking a statin, which inhibits de novo cholesterol biosynthesis, have improved locoregional control after radiotherapy. These results suggest that targeting cholesterol metabolism may improve the radiotherapeutic management of IBC. Here, we aimed to understand the molecular mechanism(s) linking cholesterol metabolism and radiation-induced DNA damage and DNA repair and to evaluate statin pharmacotherapy as a DNA repair inhibitor and radiotherapeutic adjunct in an in vivo pre-clinical model of IBC.

Methods: KPL4, SUM149, SUM190, and IBC3 IBC cell lines were used to examine the effect(s) of simvastatin and human serum lipoproteins on radiation-induced DNA damage induction, DNA damage signaling, DNA damage-associated G1, intra-S, and G2/M cell cycle checkpoint activation, and DNA double strand break (DSB) repair by homologous recombination (HR) and non-homologous end joining (NHEJ).

Results: We have generated multiple IBC cells lines with an integrated Traffic Light Reporter (TLR) that is capable of measuring HR and NHEJ, and demonstrate that depletion of intracellular cholesterol abrogates HR-mediated repair of DNA DSBs. We also show that intracellular cholesterol has pleiotropic effects on cell cycle distribution and DNA damage-associated cell cycle checkpoints. We also report a novel polycistronic dual bioluminescence reporter system that can robustly visualize and quantitate DNA DSB induction and repair in vitro and in vivo.

Conclusions: Cholesterol is an important determinant of intrinsic radiosensitivity in IBC, and appears to regulate repair of radiation-induced DNA DSBs. Targeting cholesterol metabolism is a potential strategy to overcome IBC radioresistance and improve the prognosis for this aggressive disease.

Citation Format: Shane R. Stecklein, Adam R. Wolfe, Bisrat G. Debeb, Richard A. Larson, Wendy A. Woodward. Intracellular cholesterol regulates the DNA damage response in inflammatory breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2397.