title: Regulation of 18F-FDG accumulation in colorectal cancer cells with mutated KRAS.
abstract: KRAS gene mutations occur in approximately 40% of colorectal cancers (CRCs) and are associated with resistance to anti-epidermal growth factor receptor antibody therapy. We previously demonstrated that (18)F-FDG accumulation in PET was significantly higher in CRCs with mutated KRAS than in those with wild-type KRAS in a clinical setting. Here, we investigated the mechanisms by which mutated KRAS increased (18)F-FDG accumulation.
  
  
  METHODS
  Using paired isogenic human CRC cell lines that differ only in the mutational status of the KRAS gene, we measured (18)F-FDG accumulation in these cells in vitro and in vivo. We also investigated the roles of proteins that have a function in (18)F-FDG accumulation. Finally, we examined the relationship among mutated KRAS, hypoxia-inducible factor 1α (HIF-1α), and maximum standardized uptake value with 51 clinical CRC samples.
  
  
  RESULTS
  In the in vitro experiments, (18)F-FDG accumulation was significantly higher in KRAS-mutant cells than in wild-type controls under normoxic conditions. The expression levels of glucose transporter 1 (GLUT1) and hexokinase type 2 (HK2) were higher in KRAS-mutant cells, and (18)F-FDG accumulation was decreased by knockdown of GLUT1. Hypoxic induction of HIF-1α was higher in KRAS-mutant cells than in wild-type controls; in turn, elevated HIF-1α resulted in higher GLUT1 expression and (18)F-FDG accumulation. In addition, HIF-1α knockdown decreased (18)F-FDG accumulation under hypoxic conditions only in the KRAS-mutant cells. Small-animal PET scans showed in vivo (18)F-FDG accumulation to be significantly higher in xenografts with mutated KRAS than in those with wild-type KRAS. The immunohistochemistry of these xenograft tumors showed that staining of GLUT1 was consistent with that of HIF-1α and pimonidazole. In a retrospective analysis of clinical samples, KRAS mutation exhibited a significantly positive correlation with expressions of GLUT1 and HIF-1α and with maximum standardized uptake value.
  
  
  CONCLUSIONS
  Mutated KRAS caused higher (18)F-FDG accumulation possibly by upregulation of GLUT1; moreover, HIF-1α additively increased (18)F-FDG accumulation in hypoxic lesions. (18)F-FDG PET might be useful for predicting the KRAS status noninvasively.
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Iwamoto
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan kkawada@kuhp.kyoto-u.ac.jp.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kawada
authors.affiliation: Department of Diagnostic Imaging and Nuclear Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Nakamoto
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Itatani
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Inamoto
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Toda
authors.affiliation: Division of Molecular Imaging, Radioisotope Research Center, Kyoto University, Kyoto, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kimura
authors.affiliation: Institute for Advanced Study, Kyushu University, Fukuoka, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Sasazuki
authors.affiliation: Department of Cell Biology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan; and.
authors.forename: Senji
authors.initials: S
authors.lastname: Shirasawa
authors.affiliation: Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Okuyama
authors.affiliation: Department of Biochemistry, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Inoue
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Suguru
authors.initials: S
authors.lastname: Hasegawa
authors.affiliation: Department of Diagnostic Imaging and Nuclear Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Togashi
authors.affiliation: Department of Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Yoshiharu
authors.initials: Y
authors.lastname: Sakai
mesh_terms: D000818:Animals; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000000981:diagnostic imaging* / Q000235:genetics / Q000378:metabolism*; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D005947:Glucose / Q000378:metabolism; D006801:Humans; D051379:Mice; D009154:Mutation / Q000235:genetics / Q000502:physiology; D009368:Neoplasm Transplantation; D049268:Positron-Emission Tomography; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D018631:ras Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D005947:Glucose
keywords: 18F-FDG PET scans; KRAS; colon cancer; glucose metabolism;; imaging