To exam the lipid profile following radiotherapy in prostate cancer cells and tumors by using proton (1H) nuclear magnetic resonance (NMR).In this study we investigated the changes of lipid metabolites in murine TRAMP-C prostate cancer following radiotherapy. The optimal treatment dose of radiation therapy was determined to be 3 Gy with about 25% of the adhering cells in the treated group (n=5) comparing the control group (n=5) at 24 hours. Cells were scraped and collected by standard dual phase extraction method (methaol:water:chloroform 1:1:1). To investigate the in vivo condition, we inoculated TRAMP-C prostate cancer cells on the flanks of male C57B L/6 mice. Once the tumor reached the size of 1 cm, we irradiated the tumor with single fraction radiation (15 Gy) and collected the tumor 3 days after treatment (n=10). Mice in control group (n=10) also bear tumor on flanks (1 cm) but without irradiation, and their tumors were collected at the same time as the treated group. After dual-phase extraction of the samples, the lipid layer was dried and reconstituted in deuterochloroform, with tetramethylsilane (TMS) added for chemical shift calibration. High-resolution 1H NMR spectroscopy was performed on the lipid cell extracts using a 600MHz Bruker NMR system. Ratios of lipid integrals relative to TMS were calculated and standardized to cell number or wet tumor weight (~90 mg), respectively. Student t-test was used to compare levels of lipid metabolites in control and treatment groups.In the TRAMP-C cells, significant metabolic alterations were shown on 1H NMR spectra following radiotherpay, including a 2- to 4-fold increase in the fatty acid signals at 1.20 ppm and 2.30 ppm, and unsaturated fatty acids at 2.04 ppm, 2.80 ppm, and 5.34 ppm (P < .05, Figure 1). Signals from phosphatidylcholine (3.33 ppm) and glycerol backbone at 4.27 ppm were also signficantly increased. In TRAMP-C tumors following radiotherpay, there was no significant change in tumor size as compared to their controls (P = .58). However, 1.5- to 3-fold increases were still found in fatty acid signals (0.88 ppm, 2.30 ppm) and unsaturated fatty acids (2.04 ppm, 2.80 ppm, and 5.34 ppm, P = .08).In this study, we found a consistent increase of lipid metabolites in murine TRAMP-C prostate cancer following radiolotherapy, in both cell and tumor experiments. The intracellular storage and utilization of lipids can play an essential role in maintaining energy homeostasis in starvation or under stress ¹. There is increased interest in studying lipid profile as a response biomarker to cancer therapeutics, and 1H NMR analysis of lipid metabolites has been used as a tool to assess apoptosis both in vitro ² and in vivo ³. Indeed the lipid profiles following radiotherapy in this study shared some common features in apoptosis, such as increased levels of fatty acids and triacylglycerols, even before change of tumor size.Radiotherapy alone has led tumor cells to accumulate more lipid, indicating a metabolic switch after radiation exposure. The increase of lipids signals can potentially translated in clinical magnetic resonance spectroscopy to assess response in prostate cancer patients following radiotherapy.