15th European Molecular Imaging Meeting
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PET/SPECT, Radionuclide, X-Ray, CT II| Probe Chemistry

Session chair: Matteo Zanda (Loughborough, UK); Jane Sosabowski (London, UK)
 
Shortcut: PW26
Date: Friday, 28 August, 2020, 12:00 p.m. - 1:30 p.m.
Session type: Poster

Contents

Abstract/Video opens by clicking at the talk title.

740

Pharmacokinetics evaluation of new drugs with potential application in Duchenne muscular dystrophy

Rossana Passannante1, Unai C. Arrieta1, Vanessa G. Vallejo1, Ainara V. Illarramendi2, 3, Maite Eceiza2, Maialen S. Aizpurua2, Abraham Martín4, Pablo Aguiar5, Jonas Bergare6, Lee Kingston6, Charles S. Elmore6, Miguel A. Morcillo7, Jesus M. Aizpurua2, Jordi Llop1

1 CIC biomaGUNE, Radiochemistry and Nuclear Imaging Group, Donostia, Spain
2 UPV/EHU, Department of Organic Chemistry-I, Donostia, Spain
3 Biodonostia Healt Research Institute, Donostia, Spain
4 Achucarro Basque Center for Neuroscience, Leioa, Spain
5 Universidad de Santiago de Compostela, Molecular Imaging and Medical Physics Group, IDIS, A Coruña, Spain
6 AstraZeneca, Early Chmical Development, Pharmaceutical Sciences R&D, Gothenburg, Sweden
7 CIEMAT, Biomedical Applications and Pharmacokinetics Unit, Madrid, Spain

Introduction

Positron emission tomography (PET) is an ideal technique to investigate the pharmacokinetic properties of new chemical entities, after appropriate radiolabelling. Here, we use a multi-radionuclide/multi-position labelling approach to investigate pharmacokinetics (distribution, metabolism and excretion) of the triazole-based FKBP12-RyR stabilizer AHK21 (Fig. 1A) with potential application in Duchenne muscular dystrophy (DMD), a lethal genetic muscular disease.

Methods

The drug candidate was labelled either with 11C via 11C-methylation (AHK2.1 and AHK2.2) or by reduction of the corresponding bromide using 3H gas (Fig. 1A). Metabolism was first investigated in vitro using liver microsomes. PET imaging studies in rats after intravenous (IV) administration at different doses (1µg/Kg and 5mg/Kg) were combined with determination of arterial blood time-activity curves (TACs) and analysis of plasma samples by high performance liquid chromatography (HPLC) to quantify radioactive metabolites. Arterial TACs were obtained in continuous mode by using an in-house developed system which enables extracorporeal blood circulation and continuous measurement of radioactivity in the blood. Pharmacokinetic parameters were determined by non-compartmental analysis of the TACs.

Results/Discussion

11C- and 3H-labelled compounds could be obtained in overall non-decay corrected radiochemical yields of 14±3% and 0.15±0.05%, respectively. Molar activities were 40-140 and 0.5-1 GBq/μmol, respectively. In vitro results showed that demethylation of the CH3O-Ar residue is the main metabolic pathway, followed by demethylation of –N(CH3)2 and oxidation of the thioether group into sulfoxyde (Fig. 1B). Fast metabolism was observed in vivo. Pharmacokinetic parameters obtained from metabolite-corrected arterial blood TACs (Fig. 1C) showed short half-life and high plasma clearance (Table 1). Dynamic PET imaging (Fig. 1D) showed accumulation in the gastrointestinal track when AHK2.1 was administered. Contrarily, elimination via urine was observed after administration of AHK2.2, probably reflecting the biodistribution of [11C]methanol as the major metabolite.

Conclusions

In vitro and in vivo studies performed with the 3H- and 11C-labelled FKBP12-RyR stabilizer AHK2 confirm a high plasma clearance, linear pharmacokinetics, rapid metabolism and demethylation of the CH3-O-Ar moiety as the main pathway. PET studies suggest that knowledge about metabolic pathways is paramount to interpret images.

Acknowledgment

This project has received funding from the European Union’s H2020-MSCA-ITN Framework Programme, project reference 675417, and from the Spanish Ministry of Economy and Competitiveness, grant number CTQ2017-87637-R. ​

References
[1] Aizpurua, J. M.; Irastorza, A.; Ferrón, P.; Miranda. J. I.; Vallejo, A.; López de Munain, A. J.; Toral, I.; Aldanondo G.; Triazoles for regulating intracellular calcium homeostasis. Patent WO2017203083A1.
Figure 1

A) Structures of triazole-based FKBP12-RyR stabilizer labelled in different positions; B) Chromatograms corresponding to the in vitro metabolism (radioactivity detector). The position of the peaks corresponding to the parent compound and the identified metabolites are shown; C) AHK2.1 Time activity curves in no carried added (NCA) conditions (total dose ca. 1µg/Kg) before (yellow) and after (red) metabolite correction; D) PET images at different time points after intravenous administration of AHK2.1 and AHK2.2.

Table 1
Keywords: FKBP12-RyR stabilizer, Arterial TACs, Pharmacokinetics, PET-CT
741

In vivo 68Ga Radiolabelling of Liposomal Nanomedicines: Exploiting the Fast Complexation Kinetics and Selectivity of Tris(hydroxypyridinone) Ligands Towards Gallium(III)

Aishwarya Mishra1, Jana Kim1, Rafael T. M. de Rosales1

1 King's college London, School of Biomedical Engineering & Imaging Sciences, London, United Kingdom

Introduction

PEGylated liposomal nanomedicines are efficient drug carriers that passively accumulate in tumours1 and inflamed tissues2. However, variable uptake in diseased tissues may result in variable clinical efficacies3. Nuclear imaging can address this by providing pre-therapy biodistribution information, but does not allow longitudinal studies. We hypothesised that liposomes with accessible tris(hydroxypyridinone) ligands4, with known high affinity/selectivity for the PET radionuclide 68Ga (t1/2 = 68 min), may allow in vivo liposome radiolabelling and potential for longitudinal imaging (Fig 1A).

Methods

A tris(hydroxypyridinone)-phospholipid (THP-PL) (Fig 1B) conjugate was synthesised via conjugation of DSPE-PEG(2k)-NH2 (PL) to THP-NCS in DMSO/DIPEA, RT/24 h. THP-PL was purified using dialysis and characterised by NMR and HRMS. THP-PL was inserted into the bilayer of PEGylated liposomes (Lip) by incubation of THP-PL (3 mol%, 100 μL 20% EtOH/H2O) with lip (60 mM,100 μL) to give THP-PL-lip. THP-PL-lip was purified using size exclusion chromatography and characterized by DLS and 68Ga radiolabelling (in PBS and serum). (Fig 1C). In vivo imaging experiments were performed on healthy mice: test group (THP-PL-lip i.v. followed by 68Ga-acetate i.v.), Positive control (67Ga-THP-PL-lip i.v.) and negative control (68Ga-acetate i.v.). The mice were culled post-imaging for biodistribution (Fig 2A).

Results/Discussion

The desired THP-phospholipid conjugate (THP-PL, Fig 1B) was synthesised and purified by dialysis giving a yield of 76%. The NMR of the purified conjugate shows the formation of a thiourea linkage and disappearance of the amine resonance from PL. Unlike PL, THP-PL shows high affinity towards 68Ga with 85 % radiochemical yield at 30 μM concentrations demonstrating successful THP conjugation. The incubation of 3 molar % of THP-PL conjugate with liposomes resulted in its incorporation into the lipid bilayer (THP-PL-lip). THP-PL-lip showed efficient in vitro 68Ga radiolabelling in serum and PBS, maintaining size and zeta potential (Fig 1C-D). 68Ga-THP-PL-lip was stable in human serum and at 37 C (Fig 1E). The in vivo experiment (Fig 2) shows labelling of liposomes with 68Ga in vivo at t = 2h, showing high uptake in the blood pool, heart and spleen. However, at t = 24h, no in vivo labelling is observed and scans show similar uptake to the negative control (free 68Ga- acetate) scan (Fig 2).

Conclusions

THP-PL-lip was successfully synthesised and characterised. The presence of THP chelators on the surface allows for efficient 68/67Ga radiolabelling in the presence of human serum proteins and ions, both in vitro and in vivo. However, in vivo labelling is only effective in blood, as this approach was only able to identify blood-circulating liposomes and not those that had extravasated into organs such as the liver/spleen.

AcknowledgmentFunding: EPSRC, King's College London and Imperial College London
References
[1] Shi, J., Kantoff, P. W., Wooster, R. & Farokhzad, O. C. Cancer nanomedicine: Progress, challenges and opportunities. Nature Reviews Cancer (2017).
[2] Ozbakir, B., Crielaard, B. J., Metselaar, J. M., Storm, G. & Lammers, T. Liposomal corticosteroids for the treatment of inflammatory disorders and cancer. Journal of Controlled Release 190, 624–636 (2014)
[3] Man, F., Lammers, T. & T. M. de Rosales, R. Imaging Nanomedicine-Based Drug Delivery: a Review of Clinical Studies. Mol. Imaging Biol. 1–13 (2018).
[4] Berry, D. J. et al. Efficient bifunctional gallium-68 chelators for positron emission tomography: tris(hydroxypyridinone) ligands. Chem. Commun. (Camb). 47, 7068–70 (2011).
Figure 1:

(A) Schematic representation of the proposed in vivo 68Ga radiolabeling approach; (B) Structure of THP-PL; (C) Comparison of DLS size, zeta potential and 68Ga-radiolabelling yields of liposomes where THP-PL has been incorporated (THP-PL-lip) and unmodified PEGylated liposomes (lip); demonstrating that THP-PL can be incorporated into PEGylated liposomes providing them with radiolabelling properties while maintaining the original physicochemical properties; (D) THP-PL-lip can be radiolabelled with 68Ga in the presence of serum proteins; (E) 68Ga-THP-PL-lip is stable in human serum and 37°C

Figure 2
Figure 2:(A) Schematic representation of the in vivo study, including a negative control group (i.v injection of unchelated 68Ga, a test group (i.v. injection of THP-PL-Lip followed by i.v. injection of unchelated 68Ga) and a positive control group (i.v. injection of ex vivo radiolabelled 67Ga-THP-PL-Lip); (B) PET and SPECT images with corresponding image-based quantification, demonstrating that in vivo THP-PL-Lip 68Ga radiolabelling occurs to liposomes that are circulating in blood (t = 2h) , and not when liposomes have accumulated in other organs (t =24h)
Keywords: THP, PET, liposomes, in vivo, radiochemistry
742

Synthesis and evaluation of 18F-radiolabeled anticancer agents as tracers of nucleic acid metabolism

Gitanjali Sharma1, 2, Alice King2, Dave Turton2, Philip Miller1, Graham Smith2, Gabriela Kramer-Marek2

1 Imperial College London, Department of Chemistry, London, United Kingdom
2 Institute of Cancer Research, Radiotherapy and Imaging, London, United Kingdom

Introduction

PET imaging of proliferation is a valuable tool in the clinical assessment of tumours with utility in both patient management and clinical evaluation of new therapeutics. As a result radiolabelled nucleoside analogues based on a thymidine core such as [18F]FLT have been the subject of considerable interest. We have investigated the anticancer nucleoside [18F]trifluoridine as an alternative to [18F]FLT with superior DNA incorporation potential. Initial results indicate that radiolabelling is possible and tumour uptake in  HCT116 xenograft model showed selective uptake of [18F]trifluoridine.

Methods

Recently we have begun a programme to further optimise the radiochemistry process and investigated uptake in orthotopic U87-MGvIII mouse model. [18F]Trifluoridine was synthesised on a Trasis AllInOne using 18F-trifluoromethylation radiochemistry. [18F]trifluoridine was evaluated to establish phosphorylation potential and metabolic stability; in vivo biodistribution and PET imaging was performed in HCT116 xenograft mice. The orthotopic glioblastoma xenografts were established by intracranial injection of U87-MGvIII cells.

Results/Discussion

We have developed a fully GMP-compatible radiosynthesis of [18F]trifluoridine (Figure 1) using [18F]trifluoromethylation radiochemistry in less than 100 minutes and with 3.5% non-decay corrected radiochemical yield. Biodistribution and PET-imaging using HCT116 xenograft mice showed a 2.5 %ID/g tumour uptake of [18F]trifluridine at 60 minutes post-injection. Ex vivo metabolite analysis of selected tissues revealed the presence of the original radiolabelled nucleoside analogue, together with deglycosylated and phosphorylated [18F]trifluridine as the main metabolites. Investigation of uptake in mouse brain tumours is ongoing.

Conclusions

[18F]Trifluoridine radiosynthesis is now fully-optimised for automated cassette-based radiosynthesis. Selective uptake in mouse tumour HCT116 xenograft was observed and evaluation in orthotopic mouse tumours is ongoing.

References
[1] A. King, A. Doepner, D. Turton, D. M. Ciobota, C. Da Pieve, A. C. Wong Te Fong, G. Kramer-Marek, Y. L. Chung and G. Smith, Radiosynthesis of the anticancer nucleoside analogue Trifluridine using an automated 18F-trifluoromethylation procedure, Org. Biomol. Chem., 2018, 16, 2986–2996.
Figure 1
Radiolabelled trifluoromethylation of [18F]trifluoridine
Keywords: radiosynthesis, trifluoromethylation, anticancer
743

Fully automated copper-mediated fluorine-18 radiolabelling of boronic esters

Anna Pacelli1, Florian Guibbal1, 2, Rebekka Hueting1, Gouverneur Veronique2, Bart Cornelissen1

1 University of Oxford, Department of Oncology, Oxford, United Kingdom
2 University of Oxford, Department of Chemistry, Oxford, United Kingdom

Introduction

Poly (ADP‐ribose) polymerase (PARP) inhibitors are increasingly being studied as cancer drugs, as single agents or as a part of combination therapies. Imaging of PARP using a radiolabelled inhibitor has been proposed for patient selection, outcome prediction, and dose optimization of novel PARP‐targeting agents.
We have previously published the copper-mediated manual synthesis of the fluorine-18 radiolabelled version of olaparib and its biological in vitro and in vivo evaluation. Here, our aim was to develop a fully automated radiosynthesis of isotopologues of two PARP inhibitors.

Methods

The radiosynthesis was performed on an Eckert & Ziegler ModularLab system.
[18F]fluoride was eluted from a QMA carbonate with a solution of Kryptofix®222, K2C2O4 and K2CO3, then dried under N2 flow with dry MeCN.
Air was introduced in the reactor, followed by [Cu(OTf)2(impy)4] and protected BPin precursor dissolved in DMI. The reactor was heated at 120°C to perform the labelling. After 20 min, 500 µL of TFA was added and the temperature was increased to 125°C to perform the deprotection.
After 20 min, the reaction mixture was quenched and cooled down to 30°C. The mixture was transferred through a fritted reservoir to a vial containing 1 mL of buffer and injected onto a semipreparative column. The peak corresponding to tracer was collected and reformulated in 10% EtOH in saline.

Results/Discussion

Starting from the optimised conditions for the manual synthesis, an automated process was designed and programmed, for reproducibility and ease of setup. The total synthesis time is 120 min.
The radiochemical yield of [18F]olaparib was 6% ± 5% (n = 3) n.d.c. Up to 1200 MBq of [18F]olaparib were isolated, with a molar activity of up to 319 GBq/μmol.
The radiochemical yield of [18F]AZD2461 was in 3% ± 1% (n = 4) n.d.c. Up to 980 MBq of [18F]AZD2461 were isolated with a molar activity of up to 237 GBq/μmol.
Quality control was performed using analytical radio-HPLC, confirming radiochemical and chemical purity of the tracers.
No protodeborylated compound, a common byproduct of this reaction, was detected in the final dose.
Co-injection with cold reference confirmed the identity of the tracers.

Conclusions

We have developed a fully automated copper-mediated radiosynthesis of [18F]olaparib and [18F]AZD2461 starting from boronic esters as precursors. Further work will be performed to validate this process to GMP standards.

References
[1] Wilson T et al, J Nucl Med, 2019, 60(4), 504-510
Keywords: PARP, automation, F-18
744

Thallium-201 as a candidate for targeted radionuclide therapy: chemistry and DNA damaging potential

Alex Rigby1, Katarzyna Osytek1, Vincenzo Abbate2, Philip Blower1, Samantha Terry1

1 King's College London, School of Biomedical Engineering & Imaging Sciences, London, United Kingdom
2 King's College London, School of Population Health and Environmental Sciences, London, United Kingdom

Introduction

Auger electron therapy uses low energy electrons emitted during radioactive decay which travel very short distances (typically < 1 mm). Their high linear energy transfer (LET) and therefore reduced unwanted toxicity to non-targeted cells make them attractive for targeted radionuclide therapy (TRT). 201Tl (t1/2 = 73 hours, ~37 Auger electrons/decay) as thallous chloride has previously been routinely used for myocardial perfusion imaging as the gamma emissions can be imaged. Despite this, the chelation chemistry and therapeutic potential of 201Tl is yet to be explored.

Methods

Targeted delivery of 201Tl has been hindered to date due to lack of suitable bifunctional chelator chemistry. 201Tl3+ is more likely than 201Tl+ to be amenable to stable chelation. Use of ozone to generate [201Tl]TlCl3 from commercially available [201Tl]TlCl has been reported previously.(1) Here we report a novel oxidation method using chloramine-T to make [201Tl]TlCl3 and an ITLC method to quantify the conversion, prior to evaluation of 201Tl3+ chelation with commercially available chelators.
DNA damage was investigated in a cell-free system by gel electrophoresis of plasmid (pBR322) incubated with varying activity of  [201Tl]TlCl and [201Tl]TlCl3. After incubation with each, single strand breaks (SSBs) and double strand breaks (DSBs) were observed over to time course of the experiment.

Results/Discussion

[201Tl]TlCl3 was prepared quantitatively from [201Tl]TlCl under mild conditions within 15 minutes at room temperature. The ITLC method developed was able to easily differentiate between 201Tl+ and 201Tl3+, as shown in Fig. 1B. [201Tl]TlCl3 thus generated was been chelated using commercially available chelators such as EDTA, DOTA, DTPA, PCTA and oxo-DOTA in high yields (70 – 100 %) at room temperature in less than one hour. A TLC method based on previous literature reports was able to differentiate between complexed 201Tl3+ and uncomplexed 201Tl3+/201Tl+, as shown in Fig. 1C.(1)
201Tl(I) and 201Tl3+ caused SSBs and DSBs in DNA in isolated DNA plasmids. SSBs are seen after 1 hour for both oxidation states, and DSBs are observed after 72 – 144 hours incubation, as shown in Fig. 1A.

Conclusions

We conclude that 201Tl+ can be quantitatively converted to 201Tl3+ using chloramine-T as a mild oxidising agent compatible with biomolecules. 201Tl induces DNA damage in an isolated DNA plasmid model. 201Tl3+ can be chelated at room temperature in less than 60 minutes by various commercially available chelator. The in vivo stability, biodistribution and therapeutic efficacy of these complexes is yet to be explored.

AcknowledgmentFunding: EPSRC Centre for Doctoral Training in Medical Imaging and Rosetrees Trust 
References
[1] Hijnen, Nicole M., de Vries, Anke, Blange, Roy, Burdinski, Dirk, Grull, Holger, 2011, 'Synthesis and in vivo evaluation 201Tl(III)-DOTA complexes for applications in SPECT imaging', 38, 585-592, Nuclear Medicine and Biology
Figure 1
A) The fraction of DNA damage in PBS control (left), fraction of DNA damage in non-radioactive thallium salts (middle) and fraction of DNA damage in radioactive thallium salt (right). Red = relaxed DNA (SSB), black = linear DNA (DSB), blue = supercoiled DNA (undamaged). B) ITLCs of 201TlCl (left) and 201Tl(III)Cl3 (right) post oxidation reaction with chloramine-T. C) Reverse phase TLCs of TlCl/TlCl3 controls (left) and various Tl-complexes (right)
Keywords: Thallium, Chelation, Radiochemistry
745

Use of microalgae as carrier for 18F-FDG and first tests with mussels towards PET imaging of small aquatic animals

Christian Schmidt1, Denise Bruhn1, 2, Magdalena Rafecas2

1 Universität zu Lübeck, Isotopenlabor der Sektion Naturwissenschaften, Lübeck, Germany
2 Universität zu Lübeck, Institute of Medical Engineering, Lübeck, Germany

Introduction

Zebrafish is being increasingly used as animal model in biomedical research; understanding the physiology, metabolism and mechanisms of disease of aquatic animals is also important in environmental or aquaculture sciences. On the other hand, Positron Emission Tomography (PET) is a well-established molecular imaging method, of interest to study small aquatic animals but tracer administration still remains a challenge. In some works, the animals were immersed in aqueous radioactive solutions. Here we study the use of microalgae labelled with 18F-fluorodeoxyglucose (FDG) and test it with mussels.

Methods

The target animals were Mytilus edulis (mussels). Two procedures for tracer administration were compared: either FDG (direct), or radiolabelled microalgae (indirect) were added into salt-water. For the latter, we compared the radiotracer uptake of Chlorella sorokiniana (SAG 211-31) and Mychonastes homosphaera (SAG 6.95). Algae suspensions were mixed with growth medium containing FDG. Various amounts and incubation times were studied. After washing, the resulting algae pellets were resuspended and added to the tank containing the mussels. Different feeding protocols were tested and the uptake in the mussels was measured. The activity present in water samples as a function of time was also measured. The FDG distribution in the mussels was visualized with a phosphor imager.

Results/Discussion

Direct method: Between 0.1 and 0.34 MBq/ml of FDG were tested (A0=24-48 MBq in 100 to 400 ml). The activity uptake by the mussels increased with time. Considering radioactive decay, the maximum uptake was achieved after ~119-183 min, ranging between 4.0% (for 0.1 MBq/ml, 40 MBq) and 14.7% (0.34 MBq/ml, 34 MBq). Microalgae labelling: As Chlorella showed higher uptake efficiency (42-57% within 45 min and 40-63% within 90 min) and better manageability, it was used for all further studies. Indirect method: 250 μl Chlorella cell suspension were added in 15 to 30 min intervals (final concentration<10.000 cells/ml); 3 to 4 rations within 90 to 100 min were enough to achieve a maximal activity in the mussel: between 2 and 2.8 MBq for previously washed microalgae, and higher uptakes from 4.1 to 11.1 MBq otherwise. For both methods the region of the retraction muscle, byssus trunk and foot showed highest FDG accumulation (Fig.1), possibly due to muscular activity (mussel motion during feeding).

Conclusions

In average, FDG administration using labelled Chlorella led to faster uptakes (83% within 20 min) and higher efficiency over direct administration into the water (10,5% uptake within 29 min). In both cases, large variations among individuals were found. The images were in agreement with the expected glucose metabolism [3]. To reduce variability, labeling and administration procedures will be optimized. Next steps include studies using zebrafish.

Acknowledgment

This project is part of ATTRACT that has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement No. 777222.
The authors would like to thank Jan-Christer Schorch (Isotopenlabor der Sektion Naturwissenschaften, Universität zu Lübeck), Cindy Läken (Institute of Medical Engineering, Universität zu Lübeck) and Dr. Inga Buchmann  (University Hospital Schleswig-Holstein, UKSH) for their valuable contribution.

References
[1] Koba W et al. 2013, 'MicroPET/SPECT/CT imaging of small animal models of disease', Am J Pathol 182, 319.
[2] Browning ZS et al. 2013, 'Using PET/CT imaging to characterize 18F-fluorodeoxyglucose utilization in fish', J Fish Dis 36,  911.
[3] Pajor, AM et al. 1989, 'Sodium d-glucose cotransport in the gill of marine mussels: Studies with intact tissue and brush-border membrane vesicles', J Mem Biol 107 77.
Activity distribution in a mussel visualized with a phosphor imager

Left: Schematic view of the mussel anatomy. Activity distribution for mussels fed with Chlorella sorokiniana previously labelled with 18F-FDG (center) and, for comparison, with 125I-iodine (right). The latter appears mostly located in the region of stomach and intestines. This is expectable as iodine will be primarily attached to insoluble and presumably slowly digestible components of the algae cell wall. In contrast 18F-FDG accumulates in other tissues with an expected high demand for glucose. Thus, FDG seems to be readily released from the algae cells.

Keywords: FDG, microalgae radiolabelling, acquatic animal imaging, PET
746

Optimized imaging protocol for in vivo evaluation of iron-doped nanoparticles using scintigraphy and SPECT/CT

Maritina Rouchota1, 2, Eirini Fragogeorgi3, Irinaios Pilatis1, Sophia Sarpaki1, Alessio Adamiano4, Lorenzo Degli Esposti4, Michele Iafisco4, Maria Georgiou1, Penelope Bouziotis3, Daniele Catalucci5, George Loudos1, 3, George Kagadis2

1 Bioemission Technology Solutions (BIOEMTECH), Lefkippos Attica Technology Park, NCSR “Demokritos”, Ag. Paraskevi-Athens, Greece
2 University of Patras, Department of Physics, Patra, Greece
3 National Center for Scientific Research (NCSR) “Demokritos”, Institute of Nuclear & Radiological Sciences & Technology, Energy &Safety (INRASTES), Ag. Paraskevi-Athens, Greece
4 National Research Council (CNR), Institute of Science and Technology for Ceramics (ISTEC), Faenza, Italy
5 National Research Council (CNR), Institute of Genetic and Biomedical Research (IRGB), Milan, Italy

Introduction

Molecular imaging holds great promises in the non-invasive monitoring of several diseases with nanoparticles (NPs) being considered an efficient imaging tool for cancer, central nervous system and heart or bone-related diseases and for disorders of the mononuclear phagocytic system (MPS)1,2. In the present study, we used an iron-based nanoformulation, already established as an MRI/SPECT probe3, likely to load different biomolecules, to investigate its potential for nuclear planar and tomographic imaging of several target tissues following its delivery via different administration routes.

Methods

Iron-doped hydroxyapatite NPs (FeHA) were radiolabeled with the single photon γ-emitting imaging agent [99mTc]TcMDP3. Administration of the radioactive NPs (with a volume ranging from 50-150 ul and corresponding to 50-100 uCi and ~0.5 mg of NPs per normal female mouse) was performed via the three following delivery methods: (1) standard intravenous (i.v.) tail vein, (2) i.v. retro-orbital injection and (3) intra-tracheal (i.t.) instillation. Real-time, live, fast dynamic screening studies were performed on a dedicated bench top, mouse-sized, planar SPECT system (γ-eye by BIOEMTECH, Athens, Greece) from t=0 to 1 hour post-injection (p.i.) and followingly, tomographic SPECT/CT imaging was performed with y-CUBE and x-CUBE (Molecubes, Belgium).

Results/Discussion

The highest NP concentrations following i.v. injections were found in liver, followed by spleen and bladder, while for i.t. most of the activity is located to lungs, followed by stomach and bladder. The i.v. route through the tail vein is the most popular administration route and many studies have already demonstrated that when high amounts of NPs reach the liver, they can boost hepatic therapy schemes for fibrosis or cancer. The same is applicable for i.v. administrations through the retro-orbital vein, which has been proven to provide the same biodistribution profile, with the added advantage of minimum stress for the animals. Regarding the i.t. installation, there are many lung diseases that could be targeted with this method, such as pulmonary fibrosis or lung cancer. The administration routes that have been studied provide a wide range of possible popular target tissues, for a multitude of diseases.

Conclusions

Studies can be optimized following this workflow, as it is possible to quickly assess more parameters in a small number of animals (injection route, dosage and fasting conditions). Thus, such an imaging protocol combines the strengths of both planar dynamic and tomographic imaging and, by using an iron-based NP of high biocompatibility along with the appropriate administration route, a potential diagnostic or therapeutic effect could be attained.

AcknowledgmentThis project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 720834 and from the program of Industrial Scholarships of Stavros Niarchos Foundation.
References
[1] Sharifi, S., et al., “Superparamagnetic iron oxide nanoparticles for in vivo molecular and cellular imaging” Contrast Media Mol. Imaging 2015, 10 329–355.
[2] Kiessling F., et al., “Nanoparticles for imaging: Top or Flop?” Radiology 2014, 273 (1), 10-28
[3] Adamiano A., et al., “On the use of superparamagnetic hydroxyapatite nanoparticles as an agent for magnetic and nuclear in vivo imaging”Acta Materialia 2018, 73, 458-469.
Indicative SPECT/CT images of all the administration routes at 2 hrs p.i.
Keywords: nanoparticles, scinitgraphic, spect/ct imaging, administration routes