Cholesterol biosynthesis induced by radiotherapy inhibits cGAS-STING activation and contributes to colorectal cancer treatment resistance.

Radiotherapy-induced DNA damage can lead to apoptotic cell death and trigger an anti-tumor immune response via the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, which senses cytoplasmic double-stranded DNA. However, radiotherapy resistance poses a significant challenge in treating cancers, including colorectal cancer (CRC). Understanding the mechanisms underlying this resistance is crucial for developing effective therapies. Here we report that radiotherapy enhances cholesterol synthesis, which subsequently inhibits the cGAS-STING pathway, leading to radiotherapy resistance. Mechanistically, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) levels increase rapidly in response to radiation, resulting in increased cholesterol synthesis. This increased cholesterol sequesters STING in the endoplasmic reticulum, hindering its activation and downstream interferon signaling. Elevated HMGCR and cholesterol levels correlate with poor prognosis and reduced response to radiation therapy in patients with CRC. Importantly, pharmacological inactivation of HMGCR significantly enhanced radiotherapy responsiveness in animal models, dependent on cGAS-STING signaling-mediated anti-tumor responses. Our findings reveal that radiotherapy-induced cholesterol inhibits cGAS-STING signaling, facilitating tumor immune escape. Therefore, combining statins with radiotherapy represents a promising therapeutic strategy for treating CRC.