Non-Invasive PET/MR Imaging in an Orthotopic Mouse Model of Hepatocellular Carcinoma

Summary

Here, we present a protocol to create orthotopic hepatocellular carcinoma xenografts with and without hepatic artery ligation and perform non-invasive positron emission tomography (PET) imaging of tumor hypoxia using [¹⁸F]Fluoromisonidazole ([¹⁸F]FMISO) and [¹⁸F]Fluorodeoxyglucose ([¹⁸F]FDG).

Abstract

Preclinical experimental models of hepatocellular carcinoma (HCC) that recapitulate human disease represent an important tool to study tumorigenesis and evaluate novel therapeutic approaches. Non-invasive whole-body imaging using positron emission tomography (PET) provides critical insights into the in vivo characteristics of tissues at the molecular level in real-time. We present here a protocol for orthotopic HCC xenograft creation with and without hepatic artery ligation (HAL) to induce tumor hypoxia and the assessment of their tumor metabolism in vivo using [¹⁸F]Fluoromisonidazole ([¹⁸F]FMISO) and [¹⁸F]Fluorodeoxyglucose ([¹⁸F]FDG) PET/magnetic resonance (MR) imaging. Tumor hypoxia could be readily visualized using the hypoxia marker [¹⁸F]FMISO, and it was found that the [¹⁸F]FMISO uptake was higher in HCC mice that underwent HAL than in the non-HAL group, whereas [¹⁸F]FDG could not distinguish tumor hypoxia between the two groups. HAL tumors also displayed a higher level of hypoxia-inducible factor (HIF)-1α expression in response to hypoxia. Quantification of HAL tumors showed a 2.3-fold increase in [¹⁸F]FMISO uptake based on the standardized value uptake (SUV) approach.

Introduction

Hepatocellular carcinoma (HCC) is the sixth most diagnosed cancer and the third most common cause of death from cancer worldwide, with more than 900,000 new cases and 800,000 deaths in 2020¹. The major risk factor is cirrhosis, which occurs as a result of viral infections (hepatitis B and C viruses), alcohol abuse, diabetes, and non-alcoholic steatohepatitis². The management of HCC is rather complex, and several treatment options are available, including surgical resection, thermal or chemical ablation, transplantation, transarterial chemoembolization, radiation, and chemotherapy, depending on the disease staging

Protocol

All animal studies were carried out in accordance with the Committee on the Use of Live Animals in Teaching and Research (CULATR) in the Centre for Comparative Medicine Research (CCMR) at the University of Hong Kong, a program accredited by the Association for the Assessment and Accreditation of Laboratory Animal Care International (AAALAC). The animals used in the study were female BALB/cAnN-nu (Nude) mice at the age of 6-8 weeks, weighted at 20 g ± 2 g. Food and water were provided ad libitum.

Discussion

In this study, we described the procedures to perform HAL on liver orthotopic HCC xenografts using subcutaneous tumors, along with methods for the non-invasive monitoring of tumor hypoxia in orthotopic xenografts using [¹⁸F]FMISO and [¹⁸F]FDG PET/MR. Our interest lies in the metabolic imaging of various cancer and disease models for early diagnosis and treatment response evaluation^11,13,14,

Materials

Name	Company	Catalog Number	Comments
0.9% sterile saline	BBraun	N/A	0.9% sodium chloride intravenous infusion, 500 mL
10# Scalpel blade	RWD Life Science Co.,ltd	S31010-01	Animal surgery tool
10% povidone-iodine solution	Banitore	6.425.678	For disinfection
25G needle with a 1 mL syringe	BD PrecisionGlide	N/A	1 mL syringe with 25G needle for cell suspensions injections
5 mL syringe	Terumo	SS05L	5 mL syringe Luer Lock
70% Ethanol	Merck	1.07017	For disinfection
Automated Cell Counter	Invitrogen	AMQAF2000	For automated cell counting
Buprenorphine	HealthDirect	N/A	Subcutaneous injection (0.05-0.2 mg/kg/12 hours) for analgesic after surgery
Cell Culture Dish (60 mm diameter)	Thermo Scientific	150462	For tumor tissue processing
Centrifuge	Sigma	3-16KL, fixed-angle rotor 12311	For cell suspensions collection
Centrifuge Conical Tube	Eppendorf	EP0030122151	For cell suspensions collection
Culture media (Dulbecco’s modified Eagle’s medium)	Gibco	10566024	high glucose, GlutaMAX™ Supplement
Digital Caliper	RS PRO	841-2518	For subcutaneous tumor size measurement
Direct heat CO2 incubator	Techcomp Limited	NU5841	For cell culture
Dose calibrator	Biodex	N/A	Atomlab 500
DPBS (Dulbecco’s phosphate-buffered saline)	Gibco	14287072	For cell wash and injection
Eye lubricant	Alcon Duratears	N/A	Sterile ocular lubricant ointment, 3.5 g
Fetal bovine serum (FBS)	Gibco	A4766801	Used for a broad range of cell types, especially sensitive cell lines
Forceps (curved fine and straight blunt)	RWD Life Science Co.,ltd	F12012-10 & F12011-13	Animal surgery tool
Heating pad	ALA Scientific Instruments	N/A	Heat pad for mice during surgery
Insulin syringe	Terumo	10ME2913	1 mL insulin syringe with needle for radiotracer injections
InterView fusion software	Mediso	Version 3.03	Post-processing and image analysis software
Inverted microscope	Yu Lung Scientific Co., Ltd	BM-209G	For cells morphology visualization
Isoflurane	Chanelle Pharma	N/A	Iso-Vet, inhalation anesthetic, 250 mL
Ketamine	Alfasan International B.V.	HK-37715	Ketamine 10% injection solution, 10 mL
Medical oxygen	Linde HKO	101-HR	compressed gas, 99.5% purity
nanoScan PET/MR Scanner	Mediso	N/A	3 Tesla MR
Needle holder	RWD Life Science Co.,ltd	F31026-12	Animal surgery tool
Nucline nanoScan software	Mediso	Version 3.0	Scanner operating software
Nylon Suture (6/0 and 5/0)	Healthy Medical Company Ltd	000524 & 000526	Animal surgery tool
Penicillin- Streptomycin	Gibco	15140122	Culture media for a final concentration of 50 to 100 I.U./mL penicillin and 50 to 100 µg/mL streptomycin.
Pentabarbital	AlfaMedic	13003	Intraperitoneal injection (330 mg/kg) to induce cessation of breathing of mice
Sharp scissors	RWD Life Science Co.,ltd	S14014-10	Animal surgery tool
Spring Scissors	RWD Life Science Co.,ltd	S11005-09	Animal surgery tool
Trypan Blue Solution, 0,4%	Gibco	15250061	For cell counting
Trypsin-ethylenediaminetetraacetic acid (EDTA, 0.25%), phenol red.	Gibco	25200072	For cell digestion
Xylazine	Alfasan International B.V.	HK-56179	Xylazine 2% injection solution, 30 mL