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

Chondroitin Sulfate-Coated Heteroduplex-Molecular Spherical Nucleic Acids

Molecular Spherical Nucleic Acids (MSNAs) are atomically uniform dendritic nanostructures and potential delivery vehicles for oligonucleotides. The radial formulation combined with covalent conjugation may hide the oligonucleotide content and simultaneously enhance the role of appropriate conjugate groups on the outer sphere. The conjugate halo may be modulated to affect the delivery properties of the MSNAs. In the present study, [60]fullerene-based molecular spherical nucleic acids, consisting of a 2'-deoxyribonucleotide and a ribonucleotide sequence, were used as hybridization-mediated carriers ("DNA and RNA-carriers") for an antisense oligonucleotide, suppressing Tau protein, (i. e. Tau-ASO) and its conjugates with chondroitin sulfate tetrasaccharides (CS) with different sulfation patterns. The impact of the MSNA carriers, CS-moieties on the conjugates and the CS-decorations on the MSNAs on cellular uptake and - activity (Tau-suppression) of the Tau-ASO was studied with hippocampal neurons in vitro. The formation and stability of these heteroduplex ASO-MSNAs were evaluated by UV melting profile analysis, polyacrylamide gel electrophoresis (PAGE), dynamic light scattering (DLS) and size exclusion chromatography equipped with a multi angle light scattering detector (SEC-MALS). The cellular uptake and - activity were studied by confocal microscopy and Western blot analysis, respectively.

Biological Evaluation of Molecular Spherical Nucleic Acids: Targeting Tumors via a Hybridization-Based Folate Decoration

Folate receptors (FRs), membrane-bound proteins that bind specifically to folate with high affinity, are overexpressed by various cancer types and are therefore used as targets for delivery of therapeutic agents. Molecular spherical nucleic acids (MSNAs) are dendritic formulations of oligonucleotides (ONs) that may have advantages over linear parent ONs with respect to delivery properties. Here, we assembled folate-decorated MSNAs, site-specifically radiolabeled them, and then biologically evaluated their effects in mice bearing HCC1954 breast cancer xenograft tumors. The biodistribution of intravenously administered 18F-radiolabeled MSNAs was monitored using positron emission tomography/computed tomography imaging. The results revealed higher accumulation of folate-decorated MSNAs in FR-expressing organs such as the liver, kidney, and spleen, as well as a higher tumor-to-muscle ratio than that observed for MSNAs without the folate decoration. However, the observed increase was statistically significant only for MSNA structures with a PO backbone. The observed selective uptake of folate-decorated MSNAs highlights their potential as targeted delivery vehicles for therapeutic and diagnostic agents in FR-overexpressing cancers.

Cathepsin B-Activated PET Tracer for In Vivo Tumor Imaging

Cathepsin B, a lysosomal protease, is considered as a crucial biomarker for tumor diagnosis and treatment as it is overexpressed in numerous cancers. A stimulus-responsive SF scaffold has been reported to detect the activity of a variety of tumor-associated enzymes. In this work, a small-molecule PET tracer ([68Ga]NOTA-SF-CV) was developed by combining an SF scaffold with a cathepsin B-specific recognition substrate Cit-Val. Upon activation by cathepsin B, [68Ga]NOTA-SF-CV could form the cyclization product in a reduction environment, resulting in reduced hydrophilicity. This unique property could effectively prevent exocytosis of the tracer in cathepsin B-overexpressing tumor cells, leading to prolonged retention and amplified PET imaging signal. Moreover, [68Ga]NOTA-SF-CV had great targeting specificity to cathepsin B. In vivo microPET imaging results showed that [68Ga]NOTA-SF-CV was able to effectively visualize the expression level of cathepsin B in various tumors. Hence, [68Ga]NOTA-SF-CV may be served as a potential tracer for diagnosing cathepsin B-related diseases.