In Vivo Imaging of [60]Fullerene-Based Molecular Spherical Nucleic Acids by Positron Emission Tomography

Abstract

fullerene-based molecular spherical nucleic acids (MSNAs), consisting of a human epidermal growth factor receptor 2 (HER2) mRNA antisense oligonucleotide sequence with a native phosphodiester and phosphorothioate backbone, were synthesized, site-specifically labeled with a positron emitting fluorine-18 and intravenously administrated via tail vein to HER2 expressing HCC1954 tumor-bearing mice. The biodistribution of the MSNAs was monitored in vivo by positron emission tomography/computed tomography (PET/CT) imaging. MSNA with a native phosphodiester backbone (MSNA-PO) was prone to rapid nuclease-mediated degradation, whereas the corresponding phosphorothioate analogue (MSNA-PS) with improved enzymatic stability showed an interesting biodistribution profile in vivo. One hour after the injection, majority of the radioactivity was observed in spleen and liver but also in blood with an average tumor-tomuscle ratio of 2. The prolonged radioactivity in blood circulation may open possibilities to the targeted delivery of the MSNAs.

Tetrazine Glycoconjugate for Pretargeted Positron Emission Tomography Imaging of trans-Cyclooctene-Functionalized Molecular Spherical Nucleic Acids

“…NH 2 -MSNA used as precursor for [ 18 F]TCO-MSNA and pretargeted experiments was synthesized using a previously reported two-step protocol for controlled assembly of MSNAs. 59 The degree of TCOsubstitution was assessed using a fluorescent label prior to radiolabeling, and two different TCO conjugation degrees were investigated: 400 and 140% TCO-loaded MSNAs.…”

“…TCO-functionalized MSNAs were prepared following a previously published protocol with minor modifications. 59 Bicyclononyne (BCN)modified HER2 mRNA targeting antisense phosphorothioate oligonucleotide (ON) sequence ON1 (Figure S9) was synthesized by an automated synthesizer using commercially available phosphoramidite building blocks and 3-phenyl 1,2,4dithiazoline-5-one (POS) as a sulfurization reagent. The biological activity of the sequence in SNA formulation has previously been demonstrated.…”

“…Female Rj:Athymic-Foxn1 nu/nu mice (8−10 weeks old) bearing subcutaneous HER2-expressing HCC1954 tumors were used for pretargeted and control preclicked experiments with [ 18 F]TCO-MSNA, detailed information for the mice preparation was described earlier. 59 Animals were housed in individually ventilated cages under a 12 h light/dark cycle with ad libitum access to water and food unless otherwise stated. Animals were anesthetized with isoflurane (induction 4−5%, maintenance 1.5−2.5%, 0.4 L/ min O 2 ) and sacrificed by cervical dislocation after applying cardiac puncture for blood collection.…”

Imaging-Assisted Antisense Oligonucleotide Delivery for Tumor-Targeted Gene Therapy

“…Tye665-labeled ASO was covalently loaded onto silica-based iron oxide-containing nanoparticles (NPs), which were applied for FLI and MRI-assisted liver cancer-targeted ASO delivery . Fluorine-18 ( 18 F) was introduced onto the outer shell of [60]fullerene-based SNAs via tetrazine-cyclooctene ligation, which was used for PET imaging of breast cancer-targeted ASO delivery . USI-guided nanocomplex delivery systems are usually facilitated by the utilization of microbubbles.…”

“…This study has achieved iodine-123, iodine-125, iodine-131, and bromine-76, in addition to fluorine-18 labeling and PET imaging. An alternative approach for constructing the modality involves click chemistry employing a trans -cycloctene (TCO)-labeled ASO and a tetrazine (Tz)-labeled small-molecule radiotracer. , …”