The Role Of Radiation Dose-Dependent Enhancement Of Fatty Acid Oxidation On Radiation Surviving/Resistant Lung Cancer Cells

Abstract

Radiotherapy plays a critical role in the integrated management of lung cancer. However, radioresistance limits the long-term control. Exploring the dynamic changes of metabolic reprogramming in radiation surviving/resistant (S/R) lung cancer cells is helpful to clarify the metabolic mechanism of radiation resistance and to develop new targets for intervention and early detection. Cell lines were irradiated with different doses (2Gy × 20F, 2Gy × 30F, 2Gy × 40F) in conventional dose fractionation. The cellular radiosensitivity was verified by colony formation assay and neutral comet assay. Cell proliferation ability was determined by EdU assay. Metabonomic analysis was used to identify the differentially expressed metabolites between high-dose radiation-resistant cells and their parent cells. Lipid droplet content was detected by Oil Red O (ORO)staining. Cell oxygen consumption rate (OCR) was measured by Seahorse XF24e analyzer. Western blot was used to detect the expression of metabolic enzymes. The growth of xenograft tumors from these cell lines in BALB/c nude mice were measured after the treatment of radiation (2Gy×5F), Etomoxir, or radiation combined with Etomoxir. Compared with parent cells, the radioresistance of S/R lung cancer cells after different doses of radiation was significantly increased with the increase of radiation exposure. ORO staining showed that fatty deposition of radiation S/R cells was obviously higher than their parent cells, and more fatty deposition in cells received higher dose of radiation. The ketone body metabolism-related substances, including acetoacetic acid, a metabolite of FAO, were significantly enriched in high-dose radiation-resistant cells. The expression of carnitine palmitoyltransferase1 (CPT1) and the OCR in radiation S/R cells were also radiation-dose dependently increased. Etomoxir, an inhibitor of fatty acid oxidation, significantly enhanced the radiosensitivity and decreased the OCR and DNA repair ability of various S/R cells exposed to radiation. We further confirmed that Etomoxir could significantly inhibit proliferation of radiation S/R cells in vivo, which also presented with radiation-dose dependent model. The enhancement of radiation dose-dependent FAO promotes radiation surviving/resistance of lung cancer cells. CPT1A, a key metabolic enzyme mediating FAO, may be a potential target for treatment of radiation resistant lung cancer. Funding: 81972853, 81572279, 2016J004, LC2019ZD009, 2018CR033.