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MRI Assessment of Prostate-Specific Membrane Antigen (PSMA) Targeting by a PSMA-Targeted Magnetic Nanoparticle: Potential for Image-Guided Therapy Ethel J Ngen, Babak Behnam Azad, Srikanth Boinapally, Ala Lisok, Mary Brummet, Desmond Jacob, Martin G Pomper, and Sangeeta R. Banerjee Mol. Pharmaceutics, Just Accepted Manuscript • Publication Date (Web): 26 Mar 2019 Downloaded from http://pubs.acs.org on April 1, 2019
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MRI Assessment of Prostate-Specific Membrane Antigen (PSMA)
2
Targeting by a PSMA-Targeted Magnetic Nanoparticle: Potential for
3
Image-Guided Therapy
4 5
Ethel J. Ngen1, Babak Benham Azad1, Srikanth Boinapally1, Ala Lisok1, Mary Brummet1,
6
Desmond Jacob1, Martin G. Pomper1,2, Sangeeta R. Banerjee1,2,3*
7 8 9
1
The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins
10
University School of Medicine, Baltimore, MD 21287, USA.
11
2
12
Medicine, Baltimore, MD 21231, USA.
13
3
14
Institute, Baltimore, Maryland 21205, USA.
The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of
The F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research
15 16 17
*Correspondence
should be addressed to: Sangeeta R. Banerjee, Ph.D. (
[email protected])
18 19 20 21 MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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Table of Content (TOC) Graphic
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MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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Abstract
2
Magnetic nanoparticle (MNP)-induced hyperthermia is currently being evaluated for
3
localized prostate cancer. We evaluated the feasibility of tumor-selective delivery of prostate-
4
specific membrane antigen (PSMA)-targeted MNPs in a murine model with high-resolution
5
magnetic resonance imaging (MRI) after intravenous administration of MNPs at a concentration
6
necessary for hyperthermia. A PSMA-targeted MNP was synthesized and evaluated using T2-
7
weighted MRI after intravenous administration of 50 mg/kg of the MNP. Significant contrast
8
enhancement (P < 0.0002, n = 5) was observed in PSMA(+) tumors compared to PSMA(-) tumors
9
24 h and 48 h after contrast agent administration. Mice were also imaged with near-infrared
10
fluorescence imaging, to validate the MRI results. Two-photon microscopy revealed higher
11
vascular density at the tumor periphery in keeping with peripheral accumulation of PSMA-targeted
12
MNPs. These results suggest that the delivery of PSMA-targeted MNPs to PSMA(+) tumors is
13
both actively targeted and passively mediated.
14 15 16
Keywords: prostate cancer, MNP, magnetic resonance imaging, optical imaging, magnetic
17
hyperthermia therapy
18 19 20
MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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1. Introduction
2
Prostate cancer (PC) is the most common non-cutaneous cancer among men in the United
3
States.1 Although PC screening via the measurement of prostate specific antigen (PSA) levels in
4
serum has improved PC detection, it has also resulted in over-treatment, especially in patients with
5
a low risk of developing aggressive and metastatic disease.2, 3 Generally, PC confined within the
6
prostate capsule is treated by radical prostatectomy and radiation therapy.4 However, despite the
7
development of nerve-sparing radical prostatectomy and stereotactic radiotherapy, therapeutic
8
interventions still result in substantial morbidity.5
9
Although active surveillance has been effective in monitoring and deferring treatment for
10
patients with low-risk disease, those with intermediate-risk disease enrolled in active surveillance
11
programs may have compromised survival outcomes compared to intermediate-risk patients who
12
receive treatment.6, 7 Accordingly, minimally invasive and less morbid focal therapies are being
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developed for treatment of patients with intermediate-risk PC. Focal therapies are also being
14
developed for patients with recurrent, aggressive, castration-resistant PC localized within the
15
prostate capsule.8, 9
16
A hallmark of focal therapy is targeted destruction of tumors and preservation of
17
surrounding healthy tissues.8,
9
18
therapy that is being evaluated to address localized, aggressive PC.10,
19
hyperthermia, MNPs provide a means to deliver high concentrations of encapsulated/conjugated
20
chemotherapeutic agents and genetic material specifically to the tumor microenvironment, while
21
minimizing systemic toxicity.12, 13 MNPs also provide a means of image guidance by magnetic
22
resonance imaging (MRI) during therapy.14, 15 To ensure localized therapy, targeted MNPs with
23
appropriate pharmacokinetics are necessary.16, 17
Magnetic nanoparticle (MNP)-induced hyperthermia is a focal 11
In addition to
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Prostate-specific membrane antigen (PSMA) is a type II integral membrane glycoprotein
2
that is overexpressed in PC, especially aggressive, castration-resistant disease.18, 19 Several groups
3
have exploited different strategies to target PSMA expression in aggressive PC for imaging and
4
therapy. Those strategies include: PSMA-targeted monoclonal antibodies
5
fragments such as single-chain antibody fragments 22, 23 and nanobodies 24 as well as aptamers.25,
6
26
7
been effective20, 27, antibody-drug conjugates have disadvantages compared to low-molecular-
8
weight PSMA-targeting ligands.27 Those disadvantages include: potential immunogenicity and
9
slow clearance rates, which could lead to systemic toxicity.28, 29 Previously, we and others have
10
demonstrated both preclinically and clinically the feasibility of using low-molecular-weight
11
targeting ligands such as Glu-Lys-ureas to access PSMA expression in PC.30-33 Here, we
12
hypothesize that PSMA targeting using a low-molecular-weight ligand, previously tested Glu-Lys-
13
urea-suberate ((((S)-1-carboxy-5-(7-carboxyheptanamido)pentyl)carbamoyl)-L-glutamic acid),
14
could also be used to enhance the delivery and retention of MNPs to PC at MNP concentrations
15
necessary for MRI detection and hyperthermia.
20, 21
and antibody
Although PSMA targeting using high-molecular-weight targeting entities such as antibodies has
16
Recently, direct correlations have been made between the iron content and the thermal and
17
magnetic properties of MNPs.34, 35 MNPs ranging between 100 - 200 nm in diameter, with high
18
iron content, and capable of specifically targeting tumors are highly desirable for MRI-guided
19
hyperthermia.36
20
We previously developed a PSMA-targeted MNP and demonstrated the feasibility of
21
preferentially targeting PSMA(+) tumors compared to PSMA(-) tumors at low MNP
22
concentrations.37 Here, we used the high spatial resolution of MRI to evaluate the feasibility of
23
this MNP construct (Figure 1) to serve as a PSMA-targeted MRI contrast agent and preferentially MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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accumulate in PSMA(+) tumors compared to PSMA(-) tumors, after the systemic administration
2
of a high MNP dose (50-fold higher than we previously reported), needed for effective MRI
3
detection and hyperthermia.11 We also used the high spatial resolution of MRI to determine the
4
intra-tumoral biodistribution pattern of the delivered PSMA-targeted MNPs. Finally, we used
5
high-resolution multi-photon microscopy to elucidate the effects of intra-tumoral vascular patterns
6
on the intra-tumoral delivery and biodistribution of PSMA-targeted MNP.
7
8 9 10
Figure 1. Structure of a PSMA-targeted MNP. A low-molecular-weight PSMA-targeting ligand (T), Glu-Lys-urea-suberate, was used to target PSMA.
11
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2. Experimental Section
2 3
2.1 Materials and Reagents
4
Starch-coated, amine-surface-modified bionized nanoferrite (BNF) particles (80 nm in
5
diameter) were obtained from Micromod Partikeltechnologie GmbH (Rostock, Germany) and
6
were used as the magnetic nanoparticle (MNP) core. LI-COR IR Dye® 800CW, obtained from LI-
7
COR Biosciences (Lincoln, NE), was used as an optical imaging moiety. All magnetic separations
8
were carried out using a DynaMag™-Spin magnet, obtained from Thermo Fisher Scientific,
9
(Waltham, MA).
10 11
2.2 Instrumentation
12
Size and ζ-potential measurements were performed using a Malvern ζ-sizer Nano ZS-90,
13
obtained from Malvern Instruments Ltd (Worcestershire, UK). MRI scans were performed on a
14
Bruker Biospec 11.7T, horizontal bore scanner, equipped with a quadrature proton resonator
15
radiofrequency coil (RF RES 500 1H 075/040 QSN TR), for 500 MHz MR systems (Billerica,
16
MA). Paravision 6.1.0 software was used for image acquisition. Phantom and small animal optical
17
images were acquired using a LI-COR Pearl® Trilogy imaging system (Lincoln, NE). Optical
18
microscopy images were acquired using a Nikon Eclipse 80i microscope, equipped with either a
19
Nikon DS-Fi1 bright field camera or a Nikon DS-Qi1Mc dark field camera. NIS-Elements BR 3.2
20
software and National Institute of Health (NIH) ImageJ software were used for image processing.
21
Multi-photon microscopy experiments were performed on an Olympus Laser Scanning FV1000
22
microscope equipped with a 25xw/1.05XLPLN MP lens and obtained from Olympus Corporation
23
(Center Valley, PA). MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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2.3 PSMA-Targeted Magnetic Nanoparticle (MNP) Functionalization PSMA-targeted MNPs were functionalized by conjugating amine-surface-modified bionized
3
nanoferrite
particles
to
((((S)-1-carboxy-5-(8-((2,5-dioxopyrrolidin-1-yl)oxy)-8-
4
oxooctanamido)pentyl)carbamoyl)-L-glutamic acid via NHS-ester/amine chemistry in an aqueous
5
buffer (Supplementary Scheme S1), as previously described.37 Briefly, starch-coated and amine-
6
surface-modified MNPs, (amine density = 11 - 12 nmol/mg of Fe) were added to 0.01 M phosphate
7
buffered saline (PBS) at pH 7.0 to a final concentration of 6.0 mg of Fe/mL. A 50-fold molar
8
excess
9
oxooctanamido)pentyl)carbamoyl)-L-glutamic acid was then added to the MNP suspension and
10
swirled on a rotary shaker for 2 h at room temperature. The urea-conjugated MNPs were then
11
purified by magnetic separation using a DynaMag™-spin magnet and rinsed thrice with 0.01 M
12
PBS. The MNPs were next reformulated in 0.01 M PBS at a concentration of 6.0 mg of Fe/mL.
13
Next the urea-conjugated MNPs were PEGylated via conjugation to an N-hydroxylsuccinimide
14
(NHS) bifunctionalized polyethylene glycol linker (NHS-PEG1000-NHS) obtained from Creative
15
PEG Works (Durham, NC). Briefly, a 50-fold molar excess of the NHS-PEG1000-NHS
16
crosslinker was added to the MNP-urea conjugates in 0.01 M PBS and the suspension was swirled
17
on a rotary shaker for 2 h at room temperature. The PEGylated-urea-conjugated MNPs were then
18
purified by magnetic separation as described above. A LI-COR IR Dye® 800CW was next
19
conjugated to the MNP-urea-PEGylated construct via NHS/amine chemistry, under the same
20
conditions stated above. The MNPs were then purified by magnetic separation and reformulated
21
in 0.01 M PBS at a final concentration of 2.5 mg of Fe/mL. Non-targeted MNPs were also
22
functionalized with PEG as control MNPs (Supplementary Methods S1 and Supplementary
23
Scheme S2), as previously described.37
of
(((S)-1-carboxy-5-(8-((2,5-dioxopyrrolidin-1-yl)oxy)-8-
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2.4 Nanoparticle Characterization
2
The hydrodynamic diameter (Z-average), polydispersity index (PDI) and the ζ-potential of
3
the functionalized nanoparticles were measured using a Malvern ζ-sizer Nano ZS-90. For size
4
measurements, the nanoparticles were suspended in water at 10 µg/mL and both the hydrodynamic
5
diameter and the PDI were measured at 25 °C, using disposable square polystyrene cuvettes. The
6
hydrodynamic diameter and PDI results were represented as the average value of three
7
measurements, with each measurement consisting of 30 runs. The ζ-potentials of the respectively
8
functionalized nanoparticles suspended in water (10 µg/mL) were next measured using disposable
9
capillary cells. The results were represented as the average value of three measurements, with 20
10
- 25 runs within each measurement.
11 12
2.5 Phantom Magnetic Resonance Imaging (MRI) and Optical Imaging
13
MRI phantoms of the PSMA-targeted MNPs were prepared by mixing nanoparticles in 0.01
14
M PBS (100 µL) at different concentrations in 200 µL eppendorf tubes. The PSMA-targeted MNP
15
suspensions were then imaged with both T2-weighted (T2-W) MRI and optical imaging. Phantom
16
MRI experiments were performed on a Bruker Biospec 11.7T horizontal bore scanner, equipped
17
with a quadrature proton resonator radiofrequency coil. T2-W images were acquired using a spin
18
echo pulse sequence: rapid acquisition with refocused echoes (RARE); echo time (TE) = 10 ms;
19
effective echo time (TEEff) = 30 ms; RARE factor = 8; repetition time (TR) = 2000 ms; number of
20
averages (NA) = 2; field of view (FOV) = 25 × 25 mm; matrix size (MS) = 128 × 128 pixels; and
21
slice thickness = 0.5 mm. Final image analyses were performed using the NIH ImageJ software.
22
The amount of T2-W contrast enhancement from the MNPs in each phantom was calculated
23
relative to that of a 0.01 M PBS phantom without MNPs. Phantom optical imaging experiments MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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were performed using a LI-COR Pearl® Trilogy imaging system. Briefly, LI-COR IR Dye®
2
800CW on the PSMA-targeted MNPs was detected, using a fixed excitation wavelength of 785
3
nm and emission wavelength of 800 nm. The images were acquired at a resolution of 170 μm. The
4
fluorescence signal from each region of interest on the original image, was then quantified using
5
the LI-COR Pearl® Trilogy Imaging Software Version 2.0. The amount of optical contrast
6
enhancement from the MNPs in each optical phantom was calculated relative to that of a 0.01 M
7
PBS phantom without MNPs.
8 9
2.6 Cell Lines
10
Cell sublines derived from an androgen-independent PC3 human prostate tumor xenograft
11
were used. Those sublines were genetically engineered either to express high levels of PSMA (PC3
12
PIP cells) or not to express PSMA (PC3 flu cells), and were generously provided by Dr. Warren
13
Heston (Cleveland Clinic).38, 39 Both PSMA(+) PC3 PIP and PSMA(-) PC3 flu prostate cancer cell
14
lines were cultured in RPMI 1640 medium (Corning Cellgro, Manassas, VA) containing 10% fetal
15
bovine serum (FBS) (Invitrogen) and 1% penicillin-streptomycin (Corning Cellgro, Manassas,
16
VA) as previously described.32, 38, 40 All cell cultures were maintained in 5% carbon dioxide (CO2),
17
at 37 °C in a humidified incubator.
18 19
2.7 Mouse Model
20
Animal experiments were conducted in accordance with guidelines of the Johns Hopkins
21
University Animal Care and Use Committee. Six-to-eight week-old, male non-obese diabetic
22
severe-combined immune-deficient (NOD-SCID) mice (Charles River Laboratories, Wilmington,
23
MA), were used. Mice were subcutaneously inoculated with 1 × 106 PSMA(+) PC3 PIP and MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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PSMA(−) PC3 flu cells at the right and left upper flanks, respectively. Tumor growth was closely
2
monitored until the xenografts reached 8 to 10 mm in diameter, in at least one direction at which
3
time the mice were imaged.
4 5
2.8 In vivo MRI and Optical Imaging
6
To determine the best time point for MRI acquisition, a small cohort of mice (n = 3), were
7
catheterized and imaged before administration of the PSMA-targeted MNP. The PSMA-targeted
8
MNP was then administered and the mice were imaged sequentially over 4 h, then at 24 h, 48 h
9
and 72 h after contrast administration. Based on results of the preliminary study, the optimum
10
imaging time points were obtained (0 h, 24 h and 48 h). A larger cohort of mice (n = 10), each
11
bearing both a PSMA(+) PC3 PIP and a PSMA(−) PC3 flu tumor in the upper flanks, was then
12
imaged before (0 h), and 24 h after the administration of the PSMA-targeted MNPs with MRI and
13
optical imaging. Following in vivo imaging at 24 h, five of the mice were sacrificed and imaged
14
ex vivo with optical imaging. The remaining five mice were imaged in vivo with both MRI and
15
optical imaging, 48 h after the administration of the PSMA-targeted MNPs. Following in vivo
16
imaging at the 48 h time point, the mice were sacrificed and imaged ex vivo with optical imaging
17
at the 48 h time point.
18
Animal MRI procedures were carried out under anesthesia using 2% isoflurane in an
19
oxygen and air mixture. Contrast enhanced T2-weighted (T2-W) MRIs were acquired following
20
the bolus intravenous administration of the nanoparticles formulated in 0.01 M PBS and
21
administered at a dose of 50 mg/kg. T2-W MRIs were acquired using a spin echo pulse sequence.
22
T2-W MRI sequence: rapid acquisition with refocused echoes (RARE); echo time (TE) = 10 ms;
23
effective echo time (TEEff) = 30 ms; RARE factor = 8; repetition time (TR) = 4000 ms; number of MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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averages (NA) = 2; field of view (FOV) = 25 × 25 mm; matrix size (MS) = 128 × 128 pixels; and
2
slice thickness = 0.5 mm. Final image analyses were performed using NIH ImageJ software.
3
To evaluate the ability of PSMA-targeted MNPs to accumulate in PSMA(+) tumors
4
compared to PSMA(-) tumors (which served as internal negative controls for active PSMA
5
targeting), we compared the ratio of contrast enhancement in PSMA(+) tumors to PSMA(-) tumors
6
for each mouse, before the administration of the contrast agent (0 h), to that after the administration
7
of the contrast agent (at the 24 h and 48 h time points, respectively).The amount of contrast
8
enhancement in the respective tumors of each mouse, at each time-point, was analyzed using a
9
modified black pixel analyses, as previously reported 41 and described in Supporting Methods S2
10
and Supporting Figures S1.
11
In vivo MRI findings were validated with optical imaging at each time point after MRI.
12
Mice were imaged using a LI-COR Pearl® Trilogy Small Animal Imaging system. Briefly, LI-
13
COR IR Dye® 800CW on the PSMA-targeted MNPs was detected, using a fixed excitation
14
wavelength of 785 nm and emission wavelength of 800 nm. The images were acquired at a
15
resolution of 170 μm. The fluorescence signal from each region of interest on the original image,
16
was then quantified using the LI-COR Pearl® Trilogy Imaging software version 2.0.
17 18
2.9 Immunohistochemistry
19
Tumors were harvested from the mice after in vivo imaging. Tumors were fixed in 10%
20
neutral buffered formalin, paraffin-embedded and sectioned into 30 µm slices. Adjacent tumor
21
sections were then stained with hematoxylin and eosin (H & E) and for PSMA expression. A
22
standard immunohistochemistry procedure was used for PSMA staining. Slides were
23
deparaffinized using a xylene rinse and an alcohol gradient rinse. The slides were then treated with MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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antigen retrieval buffer in a steam chamber. Next, the slides were blocked with 10% fetal bovine
2
serum for 30 min, then incubated overnight in a humidified chamber at 4°C, with an anti-PSMA
3
primary antibody (1:50 dilution, Clone 3E6, Dako, Carpinteria, CA). The slides were then rinsed
4
with PBS and incubated with an Alexa Fluor 569 goat anti-mouse secondary antibody (1:1000,
5
Invitrogen) for 60 min at room temperature. Next, the slides were rinsed with PBS and counter
6
stained with 4, 6-diamidino-2-phenylindole (DAPI).
7 8
2.10 Multi-photon Microscopy
9
Mice bearing both PSMA(+) PC3 PIP and PSMA(−) PC3 flu tumors subcutaneously were
10
intravenously administered 50 µL of a 2,000 kDa Texas Red conjugated dextran polymer (Sigma
11
Aldrich), prepared at a concentration of 1 µg/µL. The mice were then euthanized and the tumors
12
excised immediately, sectioned into 1 mm slices and mounted on an in-house built mounting slide.
13
The sections were then imaged using an Olympus Laser Scanning FV1000 MPE microscope using
14
an excitation wavelength of 820 nm and an emission of 615 nm.42 Each tumor slice was divided
15
into two main regions (Supplementary Figure S2): 1) The tumor periphery (< 2 mm from the tumor
16
margin) and 2) the tumor center (˃ 2 mm from the tumor margin). At least three fields of views
17
(FOVs) were acquired from each of the two regions per tumor slice. A 25× objective was used to
18
acquire confocal z-stacks with FOV 508 × 508 μm2, and z-intervals of 5 μm.
19 20
2.11 Statistical Analyses
21
Data were presented as the mean ± standard deviation of at least three independent
22
experiments (technical replicates). Statistical comparisons were made using appropriate statistical
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tests. The results were considered statistically significant at P < 0.05, except when otherwise
2
stated.
3 4 5
3. Results
6 7
3.1 Characterization of the Functionalized Nanoparticles
8
PSMA-targeted MNPs were successfully functionalized, as previously reported.37 PSMA-
9
targeted MNPs possessed a hydrodynamic diameter of 147 ± 8 nm and a ζ-potential of -10.9 ± 0.3
10
mV (Table 1). These values were different from those obtained from the unmodified MNPs, with
11
a hydrodynamic diameter of 133 ± 1 nm and a ζ-potential of +24.0 ± 2.0 mV (Table 1). Diameter (nm)
Poly Dispersity Index
ζ-Potential (mV)
PSMA-Targeted MNP
147 ± 8
0.08 ± 0.03
-10.9 ± 0.3
Unmodified MNP
133 ± 1
0.15 ± 0.07
+24.0 ± 2.0
12 13
Table 1. Hydrodynamic diameters, polydispersity indices and ζ-potentials of PSMA-targeted
14
MNPs and unmodified MNPs, measured using a Malvern ζ-sizer.
15 16
3.2 Phantom MRI and Optical Imaging
17
MRI contrast enhancement was detected in the phantoms, at MNP concentrations as low as
18
0.07 µg/µL (0.039 μg of Fe/µL), using T2-W MRI (Figure 2). An exponential correlation was
19
observed between the T2-W MRI contrast enhancement and the MNP concentration, at high MNP
20
concentrations. Optical contrast enhancement was also detected in the phantoms, at MNP MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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concentrations as low as 0.07 μg/µL (Figure 2). Similarly, an exponential correlation was observed
2
between the optical contrast enhancement and the MNP concentration, at high MNP
3
concentrations. This similarity in the T2-W MRI contrast enhancement trend and the optical
4
imaging contrast enhancement trend suggested that the T2-W MRI signal obtained from the
5
PSMA-targeted MNP could be validated with its optical signal.
6
7 8
Figure 2. a) T2-W MRIs (axial view) and optical images of phantoms containing PSMA-targeted
9
MNPs at different nanoparticle concentrations, respectively. b) Graph of normalized contrast
10
enhancement generated by the PSMA-targeted MNPs present in the phantoms. The graph
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represents the normalized amount of contrast enhancement in each phantom relative, to that from
2
a phantom without nanoparticles (blank phantom).
3 4
3.2 In vivo MRI
5
Significant T2-W MRI contrast enhancement was detected in PSMA(+) tumors compared
6
to PSMA(-) tumors, 24 h (P < 0.0001; n = 10) and 48 h (P < 0.0002; n = 5) after the administration
7
of the PSMA-targeted MNPs (Figure 3a). This contrast enhancement was quantified by comparing
8
the ratio of contrast enhancement in PSMA(+) tumors to PSMA(-) tumors for each mouse, before
9
the administration of the contrast agent (at the 0 h time point), to that after the administration of
10
the contrast agent at the 24 h and 48 h time points, respectively (Figure 3, Supplementary Methods
11
S2, and Supplementary Figure S1). A 287% contrast enhancement was calculated for the PSMA(+)
12
tumors compared to the PSMA(-) tumors at the 24 h time point, relative to that at the 0 h time
13
point (before contrast administration). That enhancement in the PSMA(+) tumors compared to
14
PSMA(-) tumors, increased to ~ 330% at the 48 h time point, relative to that at the 0 h time point
15
(before contrast administration).
16
Non-targeted MNPs on the other hand displayed no statistically significant T2-W MRI
17
contrast enhancement in either PSMA(+) or PSMA(-) tumors, at any given time point (n = 3,
18
Supplementary Figures S4 and S5). Nevertheless, moderate contrast enhancement was detected in
19
both PSMA(+) and PSMA(-) tumors, from the non-targeted MNPs.
20
Using the high spatial resolution of MRI, we assessed the intra-tumoral contrast
21
enhancement patterns from the delivered PSMA-targeted MNPs in both PSMA(+) and PSMA(-)
22
tumors. The MRIs revealed preferential contrast enhancement at the tumor peripheries of both
23
PSMA(+) and PSMA(-) tumors, as opposed to homogenous contrast enhancement throughout the MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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tumors (Figure 4). This suggested preferential delivery of the PSMA-targeted MNPs to the tumor
2
peripheries.
3 4
Figure 3. Active Targeting Component. a) T2-W MRIs (gray scale and color coded) of a
5
representative male NOD/SCID mouse bearing both human PSMA(+) PC3 PIP and human
6
PSMA(-) PC3 flu prostate tumor xenografts. The MRIs were acquired before contrast
7
administration; 24 h and 48 h after administration of the PSMA-targeted MNP. Pixel intensity
8
histograms of PSMA(+) PC3 PIP and PSMA(-) PC3 flu prostate tumor xenografts; b) before
9
contrast administration; c) 24 h after administration of the PSMA-targeted MNP; and d) 48 h after
10
administration of the PSMA-targeted MNP. e) The ratio of contrast enhancement in PSMA(+) PC3
11
PIP tumors versus PSMA(-) tumors 0 h, 24 h, and 48 h after administration of the PSMA-targeted MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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MNP. A significant difference of contrast enhancement was observed in PSMA(+) tumors 24 h (P
2
< 0.0001; n = 10) and 48 h (P < 0.0002; n = 5) after administration of the PSMA-targeted MNP
3
compared to 0 h using a one-sample paired two-tailed t-test analysis.
4 5
Figure 4. Passive Targeting Component. T2-W MRI assessment of the intra-tumoral contrast
6
enhancement pattern generated from the delivered PSMA-targeted MNP in human PSMA(+) PC3
7
PIP and human PSMA(-) PC3 flu prostate tumor xenografts. T2-W MRI (gray scale and color
8
coded) before the administration of the PSMA-targeted MNP and 24 h after the administrations of
9
the PSMA-targeted MNP revealed greater contrast enhancement in the tumor periphery, in both
10
PSMA(+) PC3 PIP and PSMA(-) PC3 flu tumor xenografts, as opposed to homogeneous contrast
11
enhancement throughout the tumors. This suggested peripheral intra-tumoral distribution of the
12
PSMA-targeted MNP.
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3.3 In vivo Optical Imaging
2
In vivo optical imaging of mice 24 h and 48 h post-contrast administration revealed a
3
significant difference in the uptake of the PSMA-targeted MNPs in PSMA(+) tumors compared to
4
PSMA(-) tumors, at both the 24 h time point and the 48 h time point, compared to the 0 h time
5
point (Figure 5 and Supplementary Figure S6). Ex vivo optical imaging also showed that there is a
6
statistically significant difference in the uptake of the PSMA-targeted MNPs in PSMA(+) tumors
7
versus PSMA(-) tumors, after the administration of the PSMA-targeted MNPs (Supplementary
8
Figure S7).
9
The PSMA-targeted MNPs were also detected in organs of the reticuloendothelial system,
10
such as the liver, spleen and kidney (Figure 5). Weight measurements of the excised tumors
11
confirmed that both PSMA(+) and PSMA(-) tumors were of comparable sizes (Supplementary
12
Figure S8).
13
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1 2
Figure 5. a) In vivo near-infrared fluorescence images of a representative male NOD/SCID mouse
3
bearing both human PSMA(+) PC3 PIP and human PSMA(-) PC3 flu prostate tumor xenografts,
4
0 h, 24 h and 48 h after administration of PSMA-targeted MNPs. Ex vivo fluorescence images of
5
the organs of a representative male NOD/SCID mouse bearing both human PSMA(+) PC3 PIP
6
and human PSMA(-) PC3 flu prostate tumor xenografts 24 h and 48 h after the administration of
7
PSMA-targeted MNPs. b) Quantification of the in vivo fluorescence signal ratio from the
8
PSMA(+) tumors to the PSMA(-) tumors in each mouse, 0 h, 24 h and 48 h after the administration
9
of PSMA-targeted MNPs. A statistically significant difference in the uptake of the PSMA-targeted
10
MNPs in PSMA(+) tumors compared to PSMA(-) tumors, at both the 24 h time point (P = 0.002; MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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n = 10) and the 48 h time point (P = 0.024; n = 5), compared to the 0 h time point, were calculated
2
using a one-sample paired two-tailed t-test statistical analysis. c) Immunohistochemistry of PSMA
3
expression in PSMA(+) PC3 PIP and PSMA(−) PC3 flu tumors. The fluorescence images indicate
4
high levels of cell surface PSMA expression in PSMA(+) PC3 PIP tumors and no PSMA-
5
expression in PSMA(−) PC3 flu tumors. The scale bar represents 20 µm.
6 7
3.4 Immunohistochemistry
8
Immunohistochemistry of the excised tumors confirmed high PSMA expression levels in the
9
PSMA(+) PC3 PIP tumor cell surfaces and no PSMA expression on the PSMA(-) PC3 flu tumor
10
cell surfaces (Figure 5c), as was expected. H&E staining revealed that both PSMA(+) and PSMA(-
11
) tumors were more cellular at the tumor periphery and less so at the tumor center. That suggested
12
necrotic tumor cores (Figure 6 and Supplementary Figure S9).
13
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1 2
Figure 6. a) Hematoxylin and eosin (H&E) staining of human PSMA(+) PC3 PIP and human
3
PSMA(-) PC3 flu prostate tumors, excised from mice after in vivo imaging. The scale bar
4
represents 20 µm. b) Quantification of the ratio of loss of cellularity at the tumor center compared
5
to the tumor periphery. The images revealed that both tumor types were more cellular at the tumor
6
peripheries compared to the tumor centers.
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3.5 Two-photon Microscopy
2
High resolution two-photon microscopy revealed a higher density of blood vessels at the
3
tumor peripheries compared to the tumor centers, in both PSMA(+) tumors and PSMA(-) tumors
4
(Figure 7). Additionally, blood vessels of larger diameters were found at the tumor peripheries,
5
while blood vessels of smaller diameters were found at the tumor centers, in both PSMA(+) tumors
6
and PSMA(-) tumors (Figure 7).
7 8
Figure 7. a) Two-photon microscopy images of both human PSMA(+) PC3 PIP and human
9
PSMA(-) PC3 flu prostate tumors, excised from mice after the intravenous administration of a
10
2,000 kDa Texas Red conjugated dextran polymer, revealed higher tumor vascular densities at the MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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tumor peripheries compared to the tumor centers, of both PSMA(+) PC3 PIP and PSMA(-) PC3
2
flu prostate tumors. The scale bar represents 50 µm. b) Quantification of tumor blood vessel
3
diameters, at the tumor peripheries and the tumor centers of both PSMA(+) PC3 PIP and PSMA(-)
4
PC3 flu prostate tumors. Blood vessels of larger diameters were found at the tumor peripheries,
5
while blood vessels of smaller diameters were found at the tumor centers (P = 0.008; n = 3 for
6
PSMA(-) PC3 flu tumors and P = 0.021; n = 3 for PSMA(+) PC3 PIP tumors). c) Quantification
7
of the ratio of the surface area occupied by blood vessels at the tumor periphery to the surface area
8
occupied at the tumor center, in PSMA(+) PC3 PIP and PSMA(-) PC3 flu prostate tumors, revealed
9
no statistically significant difference between both tumor types.
10 11
4. Discussion
12
Current clinical practices for the delivery of MNPs to PC for MNP-induced hyperthermia
13
involve directly injecting the MNPs into the tumors.11 However, that is an invasive procedure,
14
which might also miss remote or even nearby lesions. We have chosen to develop targeted MNPs
15
capable of accumulating in tumors at concentrations necessary for MRI-guided hyperthermia after
16
systemic administration. Our previous report described the synthesis, optimization of surface
17
functionalization and the full characterization of the MNP formulation used here.37 We empirically
18
determined and demonstrated that PSMA targeting by the synthesized MNP could be optimized
19
by controlling the stoichiometry of the PSMA-targeting urea relative to the free amines on the
20
nanoparticle surface. In this report we examined the high spatial resolution of MRI and optical
21
imaging to evaluate the feasibility of PSMA-specific delivery of MNPs to PC in vivo at
22
concentrations necessary for MRI-guided hyperthermia.
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The PSMA-targeted MNP was administered intravenously to mice at a dose of 50 mg/kg (30
2
mg of Fe/kg) to enable T2-W MRI detection. That dose is approximately three times higher than
3
that reported for the iron oxide nanoparticle (ferumoxytol) used clinically for the treatment of iron
4
deficiency anemia.43,
5
nanoparticles currently in clinical trials.45, 46 Importantly, that dose is 50-fold higher that what we
6
previously reported for PSMA-targeting.37 We previously showed that mice treated with these
7
PSMA-targeted MNPs at doses up to 200 mg/kg, were healthy and showed no signs of distress.37
8
We detected significant T2-W MRI contrast enhancement in PSMA(+) tumors compared to
9
PSMA(-) tumors, 24 h after contrast agent administration indicating target specificity. That
10
enhancement persisted up to 48 h. Using the high spatial resolution of T2-W MRI, we assessed the
11
intra-tumoral distribution of the delivered PSMA-targeted MNP and observed that the
12
nanoparticles preferentially accumulated at the tumor periphery compared to the tumor centers, in
13
both PSMA(+) and PSMA(-) tumors. Two-photon microscopic images revealed greater tumor
14
vascular density at the periphery compared to centrally for both PSMA(+) and PSMA(-) tumors.
15
By comparing the intra-tumoral distribution pattern of the PSMA-targeted MNP to the intra-
16
tumoral vascular distribution patterns, we inferred that the delivery and retention of PSMA-
17
targeted MNP to PSMA(+) tumors was mediated by two main factors: (1): Presence of high tumor
18
vascular density, with resulting high tumor perfusion; and, (2) PSMA expression in the tumor
19
epithelium. In PSMA(+) tumors, where PSMA expression levels were high on the cell surface, the
20
delivery and retention of the PSMA-targeted MNPs was greater at the periphery, which was more
21
vascularized and more cellular than at the tumor center. That suggested that the delivery and
22
retention of the PSMA-targeted MNP to PSMA(+) tumors, was mediated by a combination of both
44
It is also ~ 2.5 times higher than the dose reported for several other
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passive tumor targeting through the enhanced permeability and retention (EPR) effect and through
2
active PSMA targeting.
3
We also noticed that the extravasation and accumulation of the PSMA-targeted MNPs was
4
affected by both the location of tumor implantation and the size of the tumors (Supplementary
5
Figure S10). In small tumors (~ 50 mm3), irrespective of their location, minimal accumulation of
6
the MNPs was detected. However, in larger tumors (8 to 10 mm in diameter in at least one
7
direction, ~250 mm3), accumulation of nanoparticles could be detected. The tumor sizes used in
8
our current study were larger than what we have typically used in our studies with low-molecular-
9
weight PSMA-targeted agents.32,
38
These findings related to tumor size suggest that the
10
accumulation of the PSMA-targeted MNPs is greatly affected by both the blood supply and the
11
EPR effect. Because in small tumors the EPR effect is less pronounced, MNP extravasation is
12
reduced. In larger tumors where the EPR effect is more pronounced, MNP extravasation is also
13
greater and more PSMA-targeting by the PSMA-targeted MNP can be achieved. However, in these
14
larger tumors with improved EPR, there is also a greater possibility of necrosis at the tumor core
15
(Figure 6 and Supplementary Figure S9). These data underscore the important contribution of the
16
EPR effect to active PSMA-targeting.
17
Based on the organ distribution ratio obtained from the ex vivo fluorescence images, we
18
estimated that ~ 6.2% ID/g of the administered PSMA-targeted MNPs is present in the PSMA(+)
19
tumors vs ~ 5.2% ID/g in the PSMA(-) tumors; and 76.4% ID/g in the liver; 8.2% ID/g in the
20
spleen; and 4.0% ID/g in the kidney at the 48 h time point (Supplementary Table S5 and S6).
21
Those biodistribution ratios are similar to our previous reports.37, 40 These findings also suggest
22
that although increasing the administered dose of the PSMA-targeted MNPs increases their
23
presence in the PSMA(+) tumors, it also increases non-specific uptake in the PSMA(-) tumors via MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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the EPR effect. Alternative strategies are needed to increase the accumulation of targeted MNPs
2
specifically for enhanced therapy. We and others are currently developing targeted tumor priming
3
strategies to achieve such enhancement.47
4
Our current findings have several implications, especially since targeted nanoparticle
5
delivery to tumors remains a challenge.48 Since the delivery and intra-tumoral biodistribution of
6
the PSMA-targeted MNPs can be detected with MRI, MRI could be used to monitor tumor
7
response patterns noninvasively during and after therapy, while taking into account the MNP
8
pattern of intra-tumoral distribution.49 That will be particularly significant given the higher spatial
9
resolution of MRI compared to optical imaging and radionuclide imaging. Finally, current clinical
10
practice for the delivery of MNPs involve direct injection of the MNPs into the tumor site.11
11
However, that is invasive and precludes targeting of remote or even nearby lesions. Accordingly,
12
understanding the roles of vascular supply EPR in the delivery and intra-tumoral biodistribution
13
patterns of these PSMA-targeted MNPs could aid in better design strategies to optimize intra-
14
tumoral MNP delivery and biodistribution.47, 50
15 16
5. Conclusion
17
Here, we evaluated the feasibility of selectively delivering PSMA-targeted MNPs to
18
PSMA-expressing human prostate tumor xenografts in a preclinical murine model, with optical
19
imaging and high resolution T2-W MRI, in concentrations necessary for MNP-induced
20
hyperthermia therapy to be accomplished. Through a number of complementary techniques,
21
including the high spatial resolution of T2-W MRI and optical imaging, we demonstrated that the
22
delivery of the targeted MNPs is due not only to active PSMA targeting – as is the dominant mode
23
of delivery of the low-molecular-weight agents we have developed for imaging – but also includes MRI Assessment of PSMA Targeting by a PSMA-Targeted Magnetic Nanoparticle
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a passive, EPR-mediated effect that resulted in inhomogeneous distribution of MNPs within the
2
tumors. This inhomogeneous MNP distribution seemed to be influenced by the intra-tumoral blood
3
vessel density as demonstrated with multi-photon microscopy. Accordingly, we anticipate that this
4
strategy could be used to deliver PSMA-targeted drug-loaded magnetic nanoparticles to localized,
5
aggressive, PSMA-expressing, castration-resistant prostate tumors, for enhanced MRI-guided
6
hyperthermia and sustained drug release.
7 8
Supporting Information.
9
Synthetic schemes; MRI analyses; Two-photon microscopy; MRIs; In vivo fluorescence images;
10
ex vivo fluorescence images; histology.
11 12
Acknowledgements
13
We would like to thank Dr. Jiadi Xu and Ms. Kazi Akhter for assistance with the MRI
14
acquisitions. This research was sponsored by the National Institutes of Health (grant numbers:
15
R01CA134675, U01CA183031, P50CA058236, P41EB024495 and K25CA148901).
16 17 18 19 20 21
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