J Gastric Cancer.  2020 Mar;20(1):60-71. 10.5230/jgc.2020.20.e7.

Establishment of a [¹⁸F]-FDG-PET/MRI Imaging Protocol for Gastric Cancer PDX as a Preclinical Research Tool

• Bae SW
• Berlth F
• Jeong KY
• Suh YS
• Kong SH
• Lee HJ
• Kim WH
• Chung JK
• Yang HK

• KMID: 2471926
• DOI: http://doi.org/10.5230/jgc.2020.20.e7

Abstract

PURPOSE
The utility of 18-fluordesoxyglucose positron emission tomography ([¹â¸F]-FDG-PET) combined with computer tomography or magnetic resonance imaging (MRI) in gastric cancer remains controversial and a rationale for patient selection is desired. This study aims to establish a preclinical patient-derived xenograft (PDX) based [¹â¸F]-FDG-PET/MRI protocol for gastric cancer and compare different PDX models regarding tumor growth and FDG uptake.
MATERIALS AND METHODS
Female BALB/c nu/nu mice were implanted orthotopically and subcutaneously with gastric cancer PDX. [¹â¸F]-FDG-PET/MRI scanning protocol evaluation included different tumor sizes, FDG doses, scanning intervals, and organ-specific uptake. FDG avidity of similar PDX cases were compared between ortho- and heterotopic tumor implantation methods. Microscopic and immunohistochemical investigations were performed to confirm tumor growth and correlate the glycolysis markers glucose transporter 1 (GLUT1) and hexokinase 2 (HK2) with FDG uptake.
RESULTS
Organ-specific uptake analysis showed specific FDG avidity of the tumor tissue. Standard scanning protocol was determined to include 150 μCi FDG injection dose and scanning after one hour. Comparison of heterotopic and orthotopic implanted mice revealed a long growth interval for orthotopic models with a high uptake in similar PDX tissues. The H-score of GLUT1 and HK2 expression in tumor cells correlated with the measured maximal standardized uptake value values (GLUT1: Pearson r=0.743, P=0.009; HK2: Pearson r=0.605, P=0.049).
CONCLUSIONS
This preclinical gastric cancer PDX based [¹â¸F]-FDG-PET/MRI protocol reveals tumor specific FDG uptake and shows correlation to glucose metabolic proteins. Our findings provide a PET/MRI PDX model that can be applicable for translational gastric cancer research.

Keyword

Xenograft; PET scan; Glycolysis; Gastric cancer

MeSH Terms

Animals
Female
Glucose
Glucose Transport Proteins, Facilitative
Glycolysis
Heterografts
Hexokinase
Humans
Magnetic Resonance Imaging
Mice
Patient Selection
Positron-Emission Tomography
Stomach Neoplasms*
Glucose
Glucose Transport Proteins, Facilitative
Hexokinase

Figure

• 

  Fig. 1 Orthotopic xenograft model of gastric cancer PDX. Schematic illustration of modeling with photographs. (A) A small gastrotomy pouch to expose mucosa. (B) Preparation of PDX tissue. (C) Position in the gastrotomy pouch. (D) Suturing over the tissue.PDX = patient-derived xenograft.

• 

  Fig. 2 Selection of optimal tumor size and dose for [18F]-FDG-PET imaging protocol. (A) Serial PET/MRI images in a heterotopic model at 54 (1st imaging), 61 (2nd imaging), and 72 (3rd imaging) days after modeling. The green ellipsoid indicates a tumor. (B) Evaluation of [18F]-FDG uptake in different sized tumors. (C) Consecutive PET/MRI images of mice bearing heterotopic PDX tumor 1, 3, and 5 hours following [18F]-FDG injection (n=4). The yellow arrow indicates a tumor. (D) [18F]-FDG uptake in tumors and normal background tissues. Box plots with error bars indicate the mean uptake and standard deviation across the mice. (E) Injection dose selection for PET imaging protocol from the theoretical decay curve of F-18.[18F]-FDG-PET = 18-fluordesoxyglucose positron emission tomography; PET = positron emission tomography; MRI = magnetic resonance imaging; PDX = patient-derived xenograft; SUVmax = maximal standardized uptake value; ns = not significant.*P-value ≤0.05.

• 

  Fig. 3 Inflammatory PET signal aspect for orthotopic model. (A) [18F]-FDG-PET/MRI images of normal (n=2) and sham mouse models. The green ellipsoid indicates the stomach. (B) Quantitative analysis of FDG uptake using SUVmax in stomach.[18F]-FDG-PET = 18-fluordesoxyglucose positron emission tomography; PET = positron emission tomography; MRI = magnetic resonance imaging; FDG = fluordesoxyglucose; SUVmax = maximal standardized uptake value.

• 

  Fig. 4 Comparison of corresponding PDX tissue in heterotopic and orthotopic models. (A) Representative H&E staining images of tumor growth in established models (H&E stain, ×200). (B) [18F]-FDG-PET/MRI images of heterotopic and orthotopic mouse models. (C) Quantitative analysis of [18F]-FDG uptake using SUVmax in heterotopic and orthotopic models bearing PDX tumor.PDX = patient-derived xenograft; H&E = hematoxylin and eosin; [18F]-FDG-PET = 18-fluordesoxyglucose positron emission tomography; PET = positron emission tomography; MRI = magnetic resonance imaging; FDG = fluordesoxyglucose; SUVmax = maximal standardized uptake value; ns = not significant.

• 

  Fig. 5 Correlation between FDG uptake and glycolysis-related protein levels. (A) Representative immunohistochemical results of GLUT1 and HK2 in PET-scanned tumors (IHC stain, ×200). (B) Comparative analysis between [18F]-FDG uptake and immunohistochemical staining score.FDG = fluordesoxyglucose; GLUT1 = glucose transporter 1; HK2 = hexokinase 2; PET = positron emission tomography; IHC = immunohistochemistry; [18F]-FDG = 18-fluordesoxyglucose; MRI = magnetic resonance imaging; SUVmax = maximal standardized uptake value.Pearson r=0.743, P-value <0.01 and Pearson r=0.605, P-value <0.05 for GLUT1 and HK2, respectively.

• 

  Fig. 6 Schematic flow chart of PET imaging protocol for gastric cancer PDX models. All procedures were performed under the anesthesia with 2% isoflurane and warming condition using a heating pad.PET = positron emission tomography; PDX = patient-derived xenograft; [18F]-FDG = 18-fluordesoxyglucose.

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