This work was supported by NIH/NIBIB grants R00 EB009105 (to NFS) and P30 EB011317 (to NFS), a NIH/NIBIB training grant T32 EB007509 (to AMW), a Case Western Reserve University Interdisciplinary Alliance Investment Grant (to NFS), and a Case Comprehensive Cancer Center grant P30 CA043703 (to NFS). We thank the Steinmetz Lab undergraduate student researchers for their hands-on support: Nadia Ayat, Kevin Chen, Sourav (Sid) Dey, Alice Yang, Sam Alexander, Craig D'Cruz, Stephen Hern, Lauren Randolph, Brian So, and Paul Chariou.

1. VNP (CPMV, BMV, PVX, and TMV) Propagation
<ol>
	<li>Set the indoor plant chamber controls to 15 hr of day (100% light, 25 &deg;C, 65% humidity) and 9 hr of night (0% light, 22 &deg;C, 60% humidity).</li>
	<li>Inoculate plants according to the timeline in Table 1.</li>
</ol>
<table border="1">
	<tbody>
		<tr>
			<td>CPMV</td>
			<td>PVX, TMV, and BMV</td>
		</tr>
		<tr>
			<td rowspan="2">Day 0: Plant 3 cowpea seeds/pot.</td>
			<td>Day 0: Plant ~30 N. benthamiana seeds/pot. Fertilize once a week with 1 tablespoon fertilizer/5 L water.</td>
		</tr>
		<tr>
			<td>Day 14: Re-pot N. benthamiana at 1 plant/pot.</td>
		</tr>
		<tr>
			<td>Day 10: Infect leaves primary leaves with CPMV (5 &mu;g/50 &mu;l/leaf) by mechanical inoculation using a light dusting of carborundum.</td>
			<td>Day 28: Infect three to five leaves with PVX, TMV, or BMV (5 &mu;g/50 &mu;l/leaf) by mechanical inoculation using a light dusting of carborundum.</td>
		</tr>
		<tr>
			<td>Day 20: Harvest leaves and store in -80 &deg;C.</td>
			<td>Day 42: Harvest leaves and store in -80 &deg;C.</td>
		</tr>
	</tbody>
</table>
Table 1. Timeline for growing, infecting, and harvesting leaves.
Note: only CPMV propagation is demonstrated as an example.
2. VNP (CPMV, BMV, PVX, and TMV) Purification
Note: All steps are carried out on ice or at 4 &deg;C.
<ol>
	<li>Homogenize 100 g of frozen leaves in a standard blender using 2 volumes of cold buffer (see Table 2). Filter through 2-3 layers of cheesecloth.</li>
	<li>For PVX, adjust pH to 6.5 using 1 M HCl. Add 0.2% (w/v) ascorbic acid and 0.2% (w/v) sodium sulfite.</li>
	<li>Centrifuge crude plant homogenate at 5,500 x g for 20 min. Collect supernatant.</li>
	<li>For BMV, layer 25 ml of supernatant over 5 ml of 10% (w/v) sucrose solution. Centrifuge at 9,000 x g for 3 hr and resuspend pellets in 38.5% CsCl solution (w/v). Mix by shaking for 5 hr, then continue with step 2.12.</li>
	<li>Extract plant material by adding 0.7 volumes of 1:1 (v/v) chloroform:1-butanol. Stir mixture for 30-60 min.</li>
	<li>Centrifuge solution at 5,500 x g for 20 min. Collect the upper aqueous phase.</li>
	<li>Add NaCl to 0.2 M and 8% (w/v) PEG (MW 8,000). For TMV, also add 1% (v/v) Triton X-100. Stir for at least 1 hr, then let sit for at least 1 hr.</li>
	<li>Centrifuge solution at 15,000 x g for 15 min. Resuspend pellet in 10 ml of buffer. For PVX, add 0.1% &beta;-mercaptoethanol and urea to 0.5 M.</li>
	<li>Centrifuge at 8,000 x g for 30 min and collect supernatant.</li>
	<li>Ultracentrifuge supernatant at 160,000 x g for 3 hr. Resuspend pellet in 5 ml buffer overnight.</li>
	<li>Prepare a 10-40% sucrose gradient using equal volumes of 10%, 20%, 30%, and 40% sucrose in buffer (heaviest first). Allow the gradient to equilibrate overnight at room temperature.</li>
	<li>Ultracentrifuge resuspended pellet over sucrose gradient at 100,000 x g for 2 hr (24 hr for BMV).</li>
	<li>Collect light scattering band and dialyze against buffer.</li>
	<li>Characterize the VNPs (below) and store at 4 &deg;C. For long-term storage, store at -80 &deg;C.</li>
</ol>
<table border="1">
	<tbody>
		<tr>
			<td>CPMV and TMV</td>
			<td>0.1 M potassium phosphate buffer (pH 7.0) 
			38.5 mM KH2PO4 
			61.5 mM K2HPO4</td>
		</tr>
		<tr>
			<td>PVX</td>
			<td>0.5 M borate buffer (pH 7.8) 
			0.5 M boric acid 
			Adjust pH with NaOH</td>
		</tr>
		<tr>
			<td>BMV</td>
			<td>SAMA buffer (pH 4.5) 
			250 mM sodium acetate 
			10 mM MgCl2 
			2 mM &beta;-mercaptoethanol (add fresh)</td>
		</tr>
	</tbody>
</table>
Table 2. Buffers and their recipes for each VNP.
Note: only CPMV propagation is demonstrated as an example.
3. VNP (CPMV, BMV, PVX, and TMV) Characterization
<ol>
	<li>Perform UV/visible spectroscopy to determine the concentration of VNPs.
	<ol>
		<li>Measure the absorbance of 2 &mu;l of sample using a NanoDrop spectrophotometer.</li>
		<li>Determine the concentration of particles and dyes using the Beer-Lambert law (A=&epsilon;cl, where A is the absorbance, &epsilon; is the extinction coefficient, c is the concentration, and l is the path length). The path length is 0.1 cm for the NanoDrop. 
		The VNP-specific extinction coefficients are: 
		CPMV: 8.1 cm-1mg-1ml (at 260 nm) 
		PVX: 2.97 cm-1mg-1ml (at 260 nm) 
		TMV: 3.0 cm-1mg-1ml (at 260 nm) 
		BMV: 5.15 cm-1mg-1ml (at 260 nm)</li>
	</ol>
	</li>
	<li>Analyze particles by size-exclusion fast protein liquid chromatography (FPLC).
	<ol>
		<li>Using a Superose 6 size-exclusion column and the &Auml;KTA Explorer, load 50-100 &mu;g of VNPs in 200 &mu;l of 0.1 M potassium phosphate buffer (pH 7.0).</li>
		<li>Set detectors to 260 nm (nucleic acid), 280 nm (protein), and the excitation wavelength of any dyes attached.</li>
		<li>Run at a flow rate of 0.5 ml/min for 72 min.</li>
		<li>The elution profile and A260:A280 nm indicates whether the VNP preparation is pure and whether particles are intact and assembled. 
		The following A260:280 ratios indicate a pure VNP preparation: 
		CPMV: 1.8&plusmn;0.1 
		PVX: 1.2&plusmn;0.1 
		TMV: 1.1&plusmn;0.1 
		BMV: 1.7&plusmn;0.1</li>
	</ol>
	</li>
	<li>Perform denaturing (pre-cast NuPAGE) Bis-Tris polyacrylamide 4-12% gradient gel electrophoresis to analyze purity of preparation and conjugation to individual coat proteins.
	<ol>
		<li>Add 3 ml of 4x LDS sample buffer to 10 &mu;g of the particles in 9 &mu;l of potassium phosphate buffer. Add an additional 1 &mu;l of 4x LDS sample buffer and 3 &mu;l of &beta;-mercaptoethanol to BMV to reduce the high number of disulfide bonds.</li>
		<li>Incubate in heat block for 5 min at 100 &deg;C.</li>
		<li>Load samples onto an SDS gel.</li>
		<li>Run samples at 200 V for 1 hr in 1x MOPS running buffer.</li>
		<li>Document the gel under UV light to visualize fluorescent coat proteins.</li>
		<li>For non-fluorescent protein, stain with Coomassie blue (0.25% (w/v) Coomassie Brilliant Blue R-250, 30% (v/v) methanol, 10% (v/v) acetic acid) for 1 hr.</li>
		<li>Destain with 30% methanol, 10% acetic acid overnight. Change the solution if required.</li>
		<li>Document the gel under white light.</li>
	</ol>
	</li>
	<li>Analyze integrity of particles by transmission electron microscopy (TEM).
	<ol>
		<li>Dilute samples to 0.1-1 mg/ml in 20 &mu;l of DI water.</li>
		<li>Place 20 &mu;l drops of the samples on Parafilm.</li>
		<li>Cover drops with a TEM grid and let sit for 2 min. Wick off the excess solution on the grid with filter paper.</li>
		<li>Wash grid by placing on a drop of DI water then wicking dry.</li>
		<li>Stain grid by placing on a 20 &mu;l drop of 2% (w/v) uranyl acetate for 2 min. Wick off the excess stain with filter paper.</li>
		<li>Wash grid once more in water.</li>
		<li>Observe grid under a transmission electron microscope.</li>
	</ol>
	</li>
</ol>
4. Chemical Conjugation of VNPs with PEG and Fluorophores, Purification, and Characterization
<ol>
	<li>For calculations for the reactions below, the molar mass of the VNPs are: 
	CPMV: 5.6 x 106 g/mol 
	PVX: 35 x 106 g/mol 
	TMV: 41 x 106 g/mol 
	BMV: 4.6 x 106 g/mol</li>
	<li>Conjugate dyes and PEG to surface lysines of CPMV and PVX using a one-step N-hydroxy succinimide coupling reaction: Add 2,500 molar equivalents (all molar excesses refer to molar excess per VNP) of Alexa Fluor 647 succinimidyl ester and 4,500 equivalents of NHS-PEG (M.W. 5,000) dissolved in DMSO to CPMV in 0.1 M potassium phosphate buffer. When working with PVX, add a 10,000 molar excess of NHS-dye and NHS-PEG. Adjust the buffer and DMSO volumes such that the final concentration of CPMV and PVX is 2 mg/ml and DMSO content is 10% of the total reaction volume. Incubate the reaction mixture overnight at room temperature protected from light. CPMV and PVX have 300 and 1,270 addressable lysines, respectively. (The reader is referred to the following references for further reading on chemical modification of CPMV and PVX: 13-15).</li>
	<li>Conjugate dyes and PEG to tyrosines of TMV by diazonium coupling followed by copper(I)-catalyzed azide-alkyne cycloaddition.
	<ol>
		<li>Prepare diazonium salt (alkyne) by mixing 400 &mu;l of 0.3 M p-toluenesulfonic acid monohydrate, 25 &mu;l of 3.0 M sodium nitrite, and 75 &mu;l of 0.68 M distilled 3-ethynylaniline dissolved in acetonitrile at 4 &deg;C for 1 hr.</li>
		<li>Add 3.3 ml of borate buffer, pH 8.8, containing 100 mM NaCl to 1.25 ml of TMV (20 mg/ml stock solution).</li>
		<li>React the TMV with 450 &mu;l of the diazonium salt (alkyne) solution in an ice bath for 3 hr to add an alkyne ligation handle to TMV by diazonium coupling. The solution will turn into a light brown color. TMV has 2,140 available tyrosines for conjugation.</li>
		<li>Purify the final product using a sucrose cushion as described in step 4.4.</li>
		<li>Attach azide-functional Alexa Fluor 647 and PEG-azide (M.W. 5,000) using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Add 2 equivalents of dye- and PEG-azide per coat protein and incubate with 1 mM CuSO4, 2 mM AMG, and 2 mM sodium ascorbate at room temperature for 15 min. Adjust the buffer volume such that the final reaction concentration of TMV is 2 mg/ml. (The reader is referred to the following references for further reading on chemical modification of TMV: 16,17).</li>
	</ol>
	</li>
	<li>Conjugate dyes to lysines and PEG to cysteines of BMV cysteine mutant (cBMV):
	<ol>
		<li>Add 2,000 molar equivalents of Oregon Green 488 succinimidyl ester dissolved in DMSO to cBMV in 0.1 M TNKM buffer (50 mM Tris base, 50 mM NaCl, 10 mM KCl, 5 mM MgCl2, pH 7.4). Adjust the buffer and DMSO volumes such that the final concentration of BMV is 1 mg/ml and DMSO content is 10% of the total reaction volume. Incubate the reaction mixture overnight at 4 &deg;C protected from light.</li>
		<li>Purify particles using centrifugal filters as described in step 4.4.</li>
		<li>Add 2,000 molar excess of PEG-maleimide (M.W. 2,000) using the same reaction conditions as before and incubate the reaction mixture for 2 hr at 4 &deg;C. cBMV has 180 reactive lysines and cysteines. (The reader is referred to the following references for further reading on chemical modification of BMV:18).</li>
	</ol>
	</li>
	<li>Purification: Pass the solution through a 40% (w/v) sucrose cushion at 160,000 x g for 2.5 hr. Re-dissolve the pellet in buffer. Alternatively, dialyze against appropriate buffer using 10 kDa cut-off spin filters.</li>
	<li>Characterization: PEGylated and fluorescently-labeled VNPs are analyzed using the above-described methods: UV/visible spectroscopy, SDS gel electrophoresis, FPLC, and TEM (not shown, however, refer to Figures 6 and 7) .</li>
</ol>
5. Tumor Targeting and Imaging using a Mouse Xenograft Model
<ol>
	<li>Culture HT-29 human colon cancer cells in RPMI medium supplemented with 5% FBS, 1% penicillin-streptomycin, and 1% L-glutamine at 37 &deg;C in 5% CO2 using 175 cm2 cell culture flasks.</li>
	<li>Wash cells twice with sterile PBS and harvest by incubating with 5 ml of trypsin-EDTA at 37 &deg;C for 5 min. Inactivate the trypsin with 5 ml of RPMI medium. Collect cells by centrifuging at 500 x g for 5 min. at 4 &deg;C and resuspend in fresh RPMI at 5x106 cells/50 &mu;l medium (determine total cell count using trypan blue and a hemocytometer). Mix with an equal volume of matrigel prior to injection (keep all solutions and reagents sterile).</li>
	<li>Procure six-week old NCR nu/nu mice and maintain them on an alfalfa free diet for 2 weeks. [Note: all animal procedures must be IACUC approved.] Induce tumor xenografts by subcutaneous injection of 5x106 cells/100 &mu;l/tumor in the flanks (2 tumors/mouse) using an 18 1/2 gauge sterile needle. Monitor the animals regularly. Measure the tumor size using calipers and allow the tumors to grow to an average volume of 20 mm3 (within the next 12 days). Assign mice to two different groups randomly: PBS and VNP (n = 3 animals/group/time point). Using a 1 ml 28 gauge insulin syringe, administer by intravenous tail vein injection 100 &mu;l of sterile PBS or 10 mg/kg VNP formulation.</li>
</ol>
Note: Tissue culture experiments and studies with live animals will not be demonstrated. Hands-on demonstration will be limited to tissue processing and data acquisition. For a reference on the HT-29 tumor xenograft model, the reader is referred to ref. 19
Three techniques are used to evaluate tumor homing of VNPs:
<ol start="4">
	<li>Fluorescence imaging using Maestro Imaging System: Sacrifice mice at different time points (2, 24, and 72 hr) using CO2 gas. Dissect the animals and excise all major organs (brain, heart, lungs, spleen, kidneys and liver) along with the tumors on the flanks, place the tissues on parafilm, and analyze with fluorescence imaging instrument using yellow excitation and emission filters (800 ms exposure) to detect the presence of fluorescent signals in the tissues (derived from A647 label conjugated to the VNPs). Save the images and analyze fluorescent intensities using ImageJ 1.44o software (<a href="http://imagej.nih.gov/ij" target="_blank">http://imagej.nih.gov/ij</a>). Compare the pattern of uptake of the VNPs in tumors with other major tissues with time.</li>
	<li>After imaging, cut each tissue in half and embed one half in OCT compound for cryo-sectioning and confocal analysis. Collect the other half in pre-weighed cryo-vials and immediately freeze them using liquid N2. Store at -80 &deg;C until ready for further processing.</li>
	<li>Fluorescence quantification: Record tissues weights. Thaw frozen tissues at room temperature and place them in separate 50 ml Falcon tubes containing 1 ml of PBS. Using a handheld tissue homogenizer, homogenize the tissues for 2-3 min in PBS then transfer the homogenate to microfuge tubes. Centrifuge the homogenates for 10 min at 13,000 x g to remove non-homogenized tissue.</li>
	<li>Pipet 100 &mu;l of the supernatant from the tissues from each group (PBS and VNP formulations/time points) into a 384 well black UV plate. Evaluate fluorescence intensity (Ex/Em wavelengths 600/665) using a plate reader. Normalize the obtained fluorescent values by the tissue weights.</li>
	<li>Immunohistochemistry: Prepare cryo-microtome sections (10 &mu;m) and store at -20 &deg;C. Stain tissue sections for cell nuclei (DAPI) and endothelial cell marker (FITC-labeled anti-mouse CD31 antibody). Carry out confocal microscopy analysis to map the vascular and intra-tumoral localization of fluorescently-labeled VNPs.</li>
</ol>
Note: This procedure will not be demonstrated, representative data are shown in Figure 8. For a reference on immunohistochemistry and the described staining methods, the reader is referred to ref. 19

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No conflicts of interest declared.

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...

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

viral nanoparticles for in vivo tumor imaging

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.

<img alt="Figure 1" src="/files/ftp_upload/4352/4352fig1.jpg" /> 
 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.
<img alt="Figure 2" fo:content-width="3in" fo:src="/files/ftp_upload/4352...

Watch this Scientific Journal Video about Viral Nanoparticles for In vivo Tumor Imaging at JoVE.com

Viral Nanoparticles for In vivo Tumor Imaging

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.

Viral Nanoparticles for In vivo Tumor Imaging

The use of nanomaterials has the potential to revolutionize materials science and medicine. Currently, a number of different nanoparticles are being ...

viral-nanoparticles-for-in-vivo-tumor-imaging

Research

JoVE Journal

Bioengineering

17.1K Views.  Case Western Reserve University. 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.