Viral Nanoparticles for In vivo Tumor Imaging

Summary

Plant viral nanoparticles (VNPs) are promising platforms for applications in biomedicine. Here, we describe the procedures for plant VNP propagation, purification, characterization, and bioconjugation. Finally, we show the application of VNPs for tumor homing and imaging using a mouse xenograft model and fluorescence imaging.

Abstract

The use of nanomaterials has the potential to revolutionize materials science and medicine. Currently, a number of different nanoparticles are being investigated for applications in imaging and therapy. Viral nanoparticles (VNPs) derived from plants can be regarded as self-assembled bionanomaterials with defined sizes and shapes. Plant viruses under investigation in the Steinmetz lab include icosahedral particles formed by Cowpea mosaic virus (CPMV) and Brome mosaic virus (BMV), both of which are 30 nm in diameter. We are also developing rod-shaped and filamentous structures derived from the following plant viruses: Tobacco mosaic virus (TMV), which forms rigid rods with dimensions of 300 nm by 18 nm, and Potato virus X (PVX), which form filamentous particles 515 nm in length and 13 nm in width (the reader is referred to refs. ¹ and ² for further information on VNPs).

From a materials scientist's point of view, VNPs are attractive building blocks for several reasons: the particles are monodisperse, can be produced with ease on large scale in planta, are exceptionally stable, and biocompatible. Also, VNPs are "programmable" units, which can be specifically engineered using genetic modification or chemical bioconjugation methods ³. The structure of VNPs is known to atomic resolution, and modifications can be carried out with spatial precision at the atomic level⁴, a level of control that cannot be achieved using synthetic nanomaterials with current state-of-the-art technologies.

In this paper, we describe the propagation of CPMV, PVX, TMV, and BMV in Vigna ungiuculata and Nicotiana benthamiana plants. Extraction and purification protocols for each VNP are given. Methods for characterization of purified and chemically-labeled VNPs are described. In this study, we focus on chemical labeling of VNPs with fluorophores (e.g. Alexa Fluor 647) and polyethylene glycol (PEG). The dyes facilitate tracking and detection of the VNPs ^5-10, and PEG reduces immunogenicity of the proteinaceous nanoparticles while enhancing their pharmacokinetics ^8,11. We demonstrate tumor homing of PEGylated VNPs using a mouse xenograft tumor model. A combination of fluorescence imaging of tissues ex vivo using Maestro Imaging System, fluorescence quantification in homogenized tissues, and confocal microscopy is used to study biodistribution. VNPs are cleared via the reticuloendothelial system (RES); tumor homing is achieved passively via the enhanced permeability and retention (EPR) effect¹². The VNP nanotechnology is a powerful plug-and-play technology to image and treat sites of disease in vivo. We are further developing VNPs to carry drug cargos and clinically-relevant imaging moieties, as well as tissue-specific ligands to target molecular receptors overexpressed in cancer and cardiovascular disease.

Protocol

1. VNP (CPMV, BMV, PVX, and TMV) Propagation

1. Set the indoor plant chamber controls to 15 hr of day (100% light, 25 °C, 65% humidity) and 9 hr of night (0% light, 22 °C, 60% humidity).
2. Inoculate plants according to the timeline in Table 1.

CPMV	PVX, TMV, and BMV
Day 0: Plant 3 cowpea seeds/pot.	Day 0: Plant ~30 N. benthamiana seeds/pot. Fertilize once a week with 1 tablespoon fertilizer/5 L water.

Results

Figure 1. Plant virus-infected plants. Vigna unguiculata plants infected with CPMV (A). Nicotiana benthamiana plants infected with PVX (B), TMV (C), and BMV (D). The pictures were taken about 10 days post infection by mechanical inoculation.

Discussion

This protocol provides an approach for the chemical modification of VNPs and their applications for in vivo tumor imaging. The animal fluorescence imaging, fluorescence quantification, and immunohistochemistry techniques presented here are useful for studying biodistribution and evaluating tumor homing. These techniques provide valuable information regarding access of the nanoparticles to the tumor via the EPR effect. By combining the results from the various analytical methods, we get a powerful approach for ev.......

Materials

Name	Company	Catalog Number	Comments
Material Name	Company	Catalogue number	Comments (optional)
			VNP production
Indoor plant chamber	Percival Scientific	E-41L2
V. unguiculata seeds (California black-eye no. 5)	Burpee	51771A
N. benthamiana seeds			N. benthamiana seeds were a gift from Salk Institute. Seeds are produced through plant propagation.
Carborundum	Fisher	C192-500
Pro-mix BX potting soil	Premier Horticulture	713400
Jack's Professional 20-10-20 Peat-Lite Fertilizer	JR Peters	77860
			Equipment
50.2 Ti rotor	Beckman	337901
SW 32 Ti rotor	Beckman	369694
Optima L-90K ultracentrifuge	Beckman	365672
SLA-3000 rotor	Thermo Scientific	07149
SS-34 rotor	Thermo Scientific	28020
Sorvall RC-6 Plus centrifuge	Thermo Scientific	46910
Polypropylene bottle	Beckman	355607	For SLA-3000 rotor
Polycarbonate bottle	Beckman	357002	For SS-34 rotor
Ultra-Clear tube	Beckman	344058	For sucrose gradient and SW 32 Ti rotor
Polycarbonate bottle	Beckman	355618	For pelleting and 50.2 Ti rotor
NanoDrop spectrophotometer	Thermo Scientific	NanoDrop2000c
PowerEase 500 pre-cast gel system	Invitrogen	EI8675EU
Superose 6 10/300 GL (24 ml) size-exclusion column	GE Healthcare	17-5172-01
ÄKTA Explorer 100 Chromatograph	GE Healthcare	28-4062-66
Allegra X-12R	Beckman	392302	Benchtop centrifuge
Cryostat	Leica	CM1850
Maestro 2	Caliper Life Sciences		In vivo imaging system
Tissue-Tearor	Biospec Products	985370-395
Microplate reader	Tecan	Infinite-200
Transmission electron microscope	ZEISS	Libra 200FE
FluoView laser scanning confocal microscope	Olympus	FV1000
			Chemicals and Reagents
3-ethynylaniline	Sigma Aldrich	498289-5G
384 well black plate	BD Biosciences	353285
4-12% Bis-Tris NuPAGE SDS gel	Invitrogen	NP0321BOX
4X LDS sample buffer	Invitrogen	NP0008
Acetic Acid	Fisher	A385-500
Acetonitrile	Sigma Aldrich	271004-1L
Alexa Fluor 647 azide	Invitrogen	A10277
Alexa Fluor 647 carboxylic acid, succinimidyl ester	Invitrogen	A20006
Amicon Ultra-0.5 ml Centrifugal Filters	Millipore	UFC501096	10 kDa cut-off
Aminoguanidine hydrochloride	Acros Organics	36891-0250
Boric acid	Fisher	A74-500
Coomassie Brilliant Blue R-250	Fisher	BP101-25
CsCl	Acros Organics	42285-1000
DAPI	MP Biomedicals	157574
Dimethyl sulfoxide	Fisher	BP231-100
Filter paper	Fisher	09-801K	P5 grade
FITC anti-mouse CD31	BioLegend	102406
Goat serum	Invitrogen	16210-064
KCl	Fisher	BP366-500
L-ascorbic acid sodium salt	Acros Organics	35268-0050
Methanol	Fisher	A412P-4
MgCl2	Fisher	BP214-500
Microscope slides	Fisher	12-544-3
Microscope cover glass	VWR	48366-277
MOPS buffer	Invitrogen	NP0001
mPEG-mal	Nanocs	PG1-ML-2k	MW 2000
mPEG-N3	Nanocs	PG1-AZ-5k	MW 5000
mPEG-NHS	Nanocs	PG1-SC-5k	MW 5000
NaCl	Fisher	BP358-212
Oregon Green 488 succinimidyl ester *6-isomer*	Invitrogen	O-6149
p-toluenesulfonic acid monohydrate	Acros Organics	13902-0050
Permount	Fisher	SP15-100
Potassium phosphate dibasic	Fisher	BP363-1
Potassium phosphate monobasic	Fisher	BP362-1
Sodium acetate	Fisher	BP333-500
Sodium nitrite	Acros Organics	42435-0050
Sodium sulfite	Amresco	0628-500G
Sucrose	Fisher	S6-500
TEM grid	Ted Pella	FCF-400Cu
Tris base	Fisher	BP152-500
Triton X-100	EMD Chemicals	TX1568-1
β-mercaptoethanol	Fisher	O3446I-100
			Tissue Culture
Fetal bovine serum	Invitrogen	12483-020
Hemocytometer	Fisher	0267110
HT-29 cells	ATCC	HTB-38
L-glutamine	Invitrogen	25030-080
PBS	Cellgro	21-040-CV
Penicillin-streptomycin	Invitrogen	10378-016
RPMI-1640	Invitrogen	31800-089
Tissue culture flasks	Corning	431080	175 cm2
Trypan Blue	Thermo Scientific	SV30084.01
Trypsin, 0.05% (1X) with EDTA 4Na, liquid	Invitrogen	25300-054
			Animal Studies
18% Protein Rodent Diet	Harlan Teklad	Teklad Global 2018S	Alfalfa free diet
Insulin syringe	BD Biosciences	329410	28 gauge
Isoflurane	Baxter	AHN3637
Matrigel Matrix basement membrane	BD Biosciences	356234
NCR nu/nu mice			CWRU School of Medicine Athymic Animal and Xenograft Core Facility
Sterile syringe	BD Biosciences	305196	18 1/2 gauge
Tissue-Tek CRYO-OCT Compound	Andwin Scientific	4583