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The Importance of Acetyl Coenzyme A Synthetase for ¹¹C-Acetate Uptake and Cell Survival in Hepatocellular Carcinoma

¹ Division of Nuclear Medicine, Department of Radiology, Yonsei University College of Medicine; and ² Biochemistry and Molecular Biology, Yonsei University College of Medicine, Seoul, Republic of Korea

Correspondence: For correspondence or reprints contact: Jong Doo Lee, Division of Nuclear Medicine, Department of Radiology, Yonsei University, College of Medicine, 134 Shinchon-dong, Seodaemoon-ku, Seoul, Korea, 120-752. E-mail: jdlee{at}yuhs.ac

We analyzed the pattern of ¹¹C-acetate and ¹⁸F-FDG uptake on PET/CT in patients with hepatocellular carcinoma (HCC). We also assessed the expression of important regulatory enzymes related to glycolysis and lipid synthesis in relation to ¹⁸F-FDG and ¹¹C-acetate uptake in human HCC cell lines. The significance of ¹¹C-acetate uptake regulation was further evaluated with regard to cell viability. Methods: ¹⁸F-FDG and ¹¹C-acetate uptake patterns in HCC in 11 patients and in 5 HCC cell lines were assessed. We evaluated the gene expression of metabolic enzymes related to glycolysis and lipid synthesis in a cell line with the highest ¹⁸F-FDG uptake and another cell line with the highest ¹¹C-acetate uptake. They included hexokinase II, adenosine triphosphate citrate lyase, acetyl coenzyme A (CoA) synthetase 1 (ACSS1), acetyl CoA synthetase 2 (ACSS2), acetyl CoA carboxylase, and fatty acid synthase. In a cell line with high ¹¹C-acetate uptake, the enzymatic activities of ACSS1 and ACSS2 were blocked using respective small, interfering RNAs (siRNAs), and the impact on ¹¹C-acetate uptake and cell viability was assessed. Results: In all 11 patients and 4 of the 5 cell lines, the uptake patterns of the 2 radiotracers were complementary. ACSS1 and ACSS2 were highly expressed in a cell line with low ¹⁸F-FDG uptake and high ¹¹C-acetate uptake, whereas only ACSS2 was expressed in a cell line with high ¹⁸F-FDG uptake and low ¹¹C-acetate uptake. Fatty acid synthase expression was seen in cells with high ¹⁸F-FDG or ¹¹C-acetate uptake. These findings indicate the possibility that both glucose and acetate can be a compensatory carbon source for lipid synthesis in cancer. Transient transfection with ACSS1 or ACSS2 siRNA in cells with high ¹¹C-acetate uptake decreased ¹¹C-acetate uptake and cell viability. Conclusion: The patterns of ¹⁸F-FDG and ¹¹C-acetate uptake seemed to complement each other in both human HCC and HCC cell lines. Fatty acid synthase expression was seen in cells with high ¹⁸F-FDG or ¹¹C-acetate uptake, suggesting glucose- or acetate-dependent lipid synthesis. Acetyl CoA synthetase appears to be important in ¹¹C-acetate uptake and acetate-dependent lipid synthesis for the growth of cancer cells with a low-glycolysis phenotype. Inhibition of acetyl CoA synthetase in these cells may be promising for anticancer treatment.

Key Words: ¹⁸F-FDG • ¹¹C-acetate • fatty acid synthesis • hepatocellular carcinoma • acetyl CoA synthetase

COPYRIGHT © 2009 by the Society of Nuclear Medicine, Inc.

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JNM 2009 50: 11A-12A. [Full Text]