Variability of Proliferation and Diffusion in Different Lung Cancer Models as Measured by 3'-Deoxy-3'-¹⁸F-Fluorothymidine PET and Diffusion-Weighted MR Imaging.
Molecular imaging allows the noninvasive assessment of cancer progression and response to therapy. The aim of this study was to investigate molecular and cellular determinants of 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) PET and diffusion-weighted (DW) MR imaging in lung carcinoma xenografts.


METHODS
Four lung cancer cell lines (A549, HTB56, EBC1, and H1975) were subcutaneously implanted in nude mice, and growth was followed by caliper measurements. Glucose uptake and tumor proliferation were determined by (18)F-FDG and (18)F-FLT PET, respectively. T2-weighted MR imaging was performed, and the apparent diffusion coefficient (ADC) was determined by DW MR imaging as an indicator of cell death. Imaging findings were correlated to histology with markers for tumor proliferation (Ki67, 5-bromo-2'-deoxyuridine [BrdU]) and cell death (caspase-3, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling). The expression of human equilibrative nucleoside transporter 1 (hENT1), thymidine kinase 1 (TK1), thymidylate synthase, and thymidine phosphorylase (TP) were analyzed by Western blot and immunohistochemistry. Thymidine levels were determined by liquid chromatography-mass spectrometry.


RESULTS
Xenografts varied with respect to in vivo growth rates. MR imaging and PET revealed intratumoral heterogeneities, which were confirmed by histology. (18)F-FLT uptake differed significantly between tumor lines, with A549 and H1975 demonstrating the highest radiotracer accumulation (A549, 8.5 ± 3.2; HTB56, 4.4 ± 0.7; EBC1, 4.4 ± 1.2; and H1975, 12.1 ± 3.5 maximal percentage injected dose per milliliter). In contrast, differences in (18)F-FDG uptake were only marginal. No clear relationship between (18)F-FLT accumulation and immunohistochemical markers for tumor proliferation (Ki67, BrdU) as well as hENT1, TK1, or TS expression was detected. However, TP was highly expressed in A549 and H1975 xenografts, which was accompanied by low tumor thymidine concentrations, suggesting that tumor thymidine levels influence (18)F-FLT uptake in the tumor models investigated. MR imaging revealed higher ADC values within proliferative regions of H1975 and A549 tumors than in HTB56 and EBC1. These ADC values were negatively correlated with cell density but not directly related to cell death.


CONCLUSIONS
A direct relationship of (18)F-FLT with proliferation or ADC with cell death might be complicated by the interplay of multiple processes at the cellular and physiologic levels in untreated tumors. This issue must be considered when using these imaging modalities in preclinical or clinical settings.
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
Sonja
S
Schelhaas
Department of Clinical Radiology, University Hospital of Münster, Münster, Germany.
Lydia
L
Wachsmuth
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
Thomas
T
Viel
Cancer Research United Kingdom Cambridge Institute, Cambridge, United Kingdom.
Davina J
DJ
Honess
Cancer Research United Kingdom Cambridge Institute, Cambridge, United Kingdom.
Kathrin
K
Heinzmann
Cancer Research United Kingdom Cambridge Institute, Cambridge, United Kingdom.
Donna-Michelle
DM
Smith
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
Sven
S
Hermann
Department of Nuclear Medicine, University Hospital of Münster, Münster, Germany.
Stefan
S
Wagner
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany.
Michael T
MT
Kuhlmann
Department of Hematology and Oncology, University Hospital of Münster, Münster, Germany.
Carsten
C
Müller-Tidow
Department of Nuclear Medicine, University Hospital of Münster, Münster, Germany.
Klaus
K
Kopka
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany Department of Nuclear Medicine, University Hospital of Münster, Münster, Germany.
Otmar
O
Schober
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany Department of Nuclear Medicine, University Hospital of Münster, Münster, Germany.
Michael
M
Schäfers
Merck Serono, Darmstadt, Germany.
Richard
R
Schneider
Comprehensive Cancer Imaging Centre, Imperial College London, London, United Kingdom; and.
Eric O
EO
Aboagye
Cancer Research United Kingdom Cambridge Institute, Cambridge, United Kingdom.
John
J
Griffiths
Department of Clinical Radiology, University Hospital of Münster, Münster, Germany.
Cornelius
C
Faber
European Institute for Molecular Imaging (EIMI), Westfälische Wilhelms-Universität (WWU) Münster, Münster, Germany Department of Geriatric Medicine, Johanniter Hospital, Bonn, Germany ahjacobs@uni-muenster.de.
Andreas H
AH
Jacobs
D000818:Animals; D001692:Biological Transport; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D015224:Dideoxynucleosides / Q000378:metabolism; D004058:Diffusion; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D049268:Positron-Emission Tomography
D015224:Dideoxynucleosides; D019788:Fluorodeoxyglucose F18; C002854:alovudine
18F-FLT PET; DW MRI; lung cancer; molecular imaging