Preparation and In Vitro Evaluation of a MRI Contrast Agent Based on Aptamer-Modified Gadolinium-Loaded Liposomes for Tumor Targeting

Tenascin-C targeting strategies in cancer

Tenascin-C (TNC) is a matricellular and multimodular glycoprotein highly expressed under pathological conditions, especially in cancer and chronic inflammatory diseases. Since a long time TNC is considered as a promising target for diagnostic and therapeutic approaches in anti-cancer treatments and was already extensively targeted in clinical trials on cancer patients. This review provides an overview of the current most advanced strategies used for TNC detection and anti-TNC theranostic approaches including some advanced clinical strategies. We also discuss novel treatment protocols, where targeting immune modulating functions of TNC could be center stage.

Recent Advances in Biomedical Applications of Mannans and Xylans

Plant-based phytochemicals, including flavonoids, alkaloids, tannins, saponins, and other metabolites, have attracted considerable attention due to their central role in synthesizing nanomaterials with various biomedical applications. Hemicelluloses are the second most abundant among naturally occurring heteropolymers, accounting for one-third of all plant constituents. In particular, xylans, mannans, and arabinoxylans are structured polysaccharides derived from hemicellulose. Mannans and xylans are characterized by their linear configuration of β-1,4-linked mannose and xylose units, respectively. At the same time, arabinoxylan is a copolymer of arabinose and xylose found predominantly in secondary cell walls of seeds, dicotyledons, grasses, and cereal tissues. Their widespread use in tissue engineering, drug delivery, and gene delivery is based on their properties, such as cell adhesiveness, cost-effectiveness, high biocompatibility, biodegradability, and low immunogenicity. Moreover, it can be easily functionalized, which expands their potential applications and provides them with structural diversity. This review comprehensively addresses recent advances in the field of biomedical applications. It explores the potential prospects for exploiting the capabilities of mannans and xylans in drug delivery, gene delivery, and tissue engineering.

Clinical advances in TNC delivery vectors and their conjugate agents

Tenascin C (TNC), a glycoprotein that is abundant in the tumor extracellular matrix (ECM), is strongly overexpressed in tumor tissues but virtually undetectable in most normal tissues. Many TNC antibodies, peptides, aptamers, and nanobodies have been investigated as delivery vectors, including 20A1, α-A2, α-A3, α-IIIB, α-D, BC-2, BC-4 BC-8, 81C6, ch81C6, F16, FHK, Ft, Ft-NP, G11, G11-iRGD, GBI-10, 19H12, J1/TN1, J1/TN2, J1/TN3, J1/TN4, J1/TN5, NJT3, NJT4, NJT6, P12, PL1, PL3, R6N, SMART, ST2146, ST2485, TN11, TN12, TNFnA1A2-Fc, TNfnA1D-Fc, TNfnBD-Fc, TNFnCD-Fc, TNfnD6-Fc, TNfn78-Fc, TTA1, TTA1.1, and TTA1.2. In particular, BC-2, BC-4, 81C6, ch81C6, F16, FHK, G11, PL1, PL3, R6N, ST2146, TN11, and TN12 have been tested in human tissues. G11-iRGD and simultaneous multiple aptamers and arginine-glycine-aspartic acid (RGD) targeting (SMART) may be assessed in clinical trials because G11, iRGD and AS1411 (SMART components) are already in clinical trials. Many TNC-conjugate agents, including antibody-drug conjugates (ADCs), antibody fragment-drug conjugates (FDCs), immune-stimulating antibody conjugates (ISACs), and radionuclide-drug conjugates (RDCs), have been investigated in preclinical and clinical trials. RDCs investigated in clinical trials include 111In-DTPA-BC-2, 131I-BC-2, 131I-BC-4, 90Y-BC4, 131I81C6, 131I-ch81C6, 211At-ch81C6, F16124I, 131I-tenatumomab, ST2146biot, FDC 131I-F16S1PF(ab')2, and ISAC F16IL2. ADCs (including FHK-SSL-Nav, FHK-NB-DOX, Ft-NP-PTX, and F16*-MMAE) and ISACs (IL12-R6N and 125I-G11-IL2) may enter clinical trials because they contain components of marketed treatments or agents that were investigated in previous clinical studies. This comprehensive review presents historical perspectives on clinical advances in TNC-conjugate agents to provide timely information to facilitate tumor-targeting drug development using TNC.

Exploring the Unique Contrast Properties of Aptamer-Gadolinium Conjugates in Magnetic Resonance Imaging for Targeted Imaging of Thrombi

Objective: An important clinical question in the determination of the extent of thrombosis-related vascular conditions is the identification of blood clot location. Fibrin is a major molecular constituent of blood clots and can, therefore, be utilized in molecular imaging. In this proof-of-concept study, we sought to prepare a fibrin-targeting magnetic resonance imaging contrast agent, using a Gd(III)-loaded fibrinogen aptamer (FA) chelate conjugate (Gd(III)-NOTA-FA) (NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid), to endow the ability to specifically accumulate at the location of blood clots, thereby enhancing contrast capabilities. Methods: The binding affinity of FA for fibrin was confirmed by fluorescence microscopy and microscale thermophoresis. The preparation and effective loading of the chelate-aptamer conjugates were confirmed by mass spectrometry and a xylenol orange colorimetric test. Longitudinal and transverse relaxivities and the effects of target binding were assessed using T1- and T2-map sequences at 7 T. T1- and T2-weighted images were acquired after blood clots were treated with Gd(III)-NOTA-FA. Collagen was used as the protein control, while an unrelated aptamer sequence, FB139, was used as the aptamer control. Results: FA demonstrated a high affinity and selectivity toward the polymeric protein, with a K_d of 16.6 nM, confirming an avidity over fibrinogen. The longitudinal (r1) and transverse (r2) relaxivities of Gd(III)-NOTA-FA demonstrated that conjugation to the long aptamer strand shortened T1 relaxation times and increased T2 relaxation times (3.04 and 38.7 mM^-1 s^-1, respectively). These effects were amplified by binding to the fibrin target (1.73 and 46.5 mM^-1 s^-1, respectively). In vitro studies with thrombin-polymerized human blood (clots) in whole blood showed an unexpected enhancement of signal intensity (hyperintense) produced exclusively at the location of the clot during the T2-weighted scan, while the presence of fibrinogen within a whole blood pool resulted in T1 signal intensity enhancement throughout the pool. This is advantageous, as simply reversing the type of a scan from a typical T1-weighted to a T2-weighted would allow to selectively highlight the location of blood clots. Conclusions: Gd(III)-NOTA-FA can be used for molecular imaging of thrombi, through fibrin-targeted delivery of contrast to the location of blood clots in T2-weighted scans.

Advances in Medical Imaging: Aptamer- and Peptide-Targeted MRI and CT Contrast Agents

Computed tomography (CT) and magnetic resonance imaging (MRI) are among the most well-established modalities in the field of noninvasive medical imaging. Despite being powerful tools, both suffer from a number of limitations and often fall short when it comes to full delineation of pathological tissues. Since its conception, molecular imaging has been commonly utilized to further the understanding of disease progression, as well as monitor treatment efficacy. This has naturally led to the advancement of the field of targeted imaging. Targeted imaging research is currently dominated by ligand-modified contrast media for applications in MRI and CT imaging. Although a plethora of targeting ligands exist, a fine balance between their size and target binding efficiency must be considered. This review will focus on aptamer- and peptide-modified contrast agents, outlining selected formulations developed in recent years while highlighting the advantages offered by these targeting ligands.

Aptamer-Based Targeted Drug Delivery Systems: Current Potential and Challenges

Aptamers are single-stranded DNA or RNA with 20-100 nucleotides in length that can specifically bind to target molecules via formed three-dimensional structures. These innovative targeting molecules have attracted an increasing interest in the biomedical field. Compared to traditional protein antibodies, aptamers have several advantages, such as small size, high binding affinity, specificity, good biocompatibility, high stability and low immunogenicity, which all contribute to their wide application in the biomedical field. Aptamers can bind to the receptors on the cell membrane and mediate themselves or conjugated nanoparticles to enter into cells. Therefore, aptamers can be served as ideal targeting ligands for drug delivery. Since their excellent properties, different aptamer-mediated drug delivery systems had been developed for cancer therapy. This review provides a brief overview of recent advances in drug delivery systems based on aptamers. The advantages, challenges and future prospectives are also discussed.

Gadolinium-containing carbon nanomaterials for magnetic resonance imaging: Trends and challenges

Gadolinium-containing carbon nanomaterials are a new class of contrast agent for magnetic resonance imaging. They are characterized by a superior proton relaxivity to any current commercial gadolinium contrast agent and offer the possibility to design multifunctional contrasts. Intense efforts have been made to develop these nanomaterials because of their potential for better results than the available gadolinium contrast agents. The aim of the present work is to provide a review of the advances in research on gadolinium-containing carbon nanomaterials and their advantages over conventional gadolinium contrast agents. Due to their enhanced proton relaxivity, they can provide a reliable imaging contrast for cells, tissues or organs with much smaller doses than currently used in clinical practice, thus leading to reduced toxicity (as shown by cytotoxicity and biodistribution studies). Their active targeting capability allows for improved MRI of molecular or cellular targets, overcoming the limited labelling capability of available contrast agents (restricted to physiological irregularities during pathological conditions). Their potential of multifunctionality encompasses multimodal imaging and the combination of imaging and therapy.

Using Omniscan-Loaded Nanoparticles as a Tumor-Targeted MRI Contrast Agent in Oral Squamous Cell Carcinoma by Gelatinase-Stimuli Strategy

In this study, the tumor-targeted MRI contrast agent was prepared with gelatinase-stimuli nanoparticles (NPs) and Omniscan (Omn) by double emulsion method. The size, distribution, morphology, stability, drug loading, and encapsulation efficiency of Omn-NPs were characterized. The macroscopic and microscopic morphological changes of NPs in response to gelatinases (collagenases IV) were observed. The MR imaging using Omn-NPs as a contrast agent was evaluated in the oral squamous cell carcinoma models with Omn as a control. We found clear evidence that the Omn-NPs were transformed by gelatinases and the signal of T1-weighted MRI sequence showed that the tumor-to-background ratio was significantly higher in Omn-NPs than in Omn. The peak point of time after injection was much later for Omn-NPs than Omn. This study demonstrates that Omn-NPs hold great promise as MRI contrast agent with improved specificity and prolonged circulation time based on a relatively simple and universal strategy.

Aptamer-integrated α-Gal liposomes as bispecific agents to trigger immune response for killing tumor cells

A novel bispecific α-Gal liposome was constructed by self-assembling AS1411 aptamers into the α-Gal containing liposomes. The α-Gal liposomes were prepared using cell membranes of red blood cells from rabbit, which are composed of cholesterol, phospholipids, and α-Gal glycolipids. AS1411 is a DNA aptamer with high specificity and affinity for nucleolin and could integrate into liposomes by the modification of cholesterol. The bispecific α-Gal liposomes surface-functionalized by α-Gal and AS1411 aptamer could recognize anti-Gal antibodies and nucleolin overexpressed by tumor cells simultaneously, followed by activating the immune system to attack the tumor cells, resulting in the lysis of the tumor cells by antibody dependent cell-mediated cytotoxicity. Under simulated tumor environment, the lysis rate of MCF-7 cells treated by the AS1411 modified α-Gal liposomes drastically increased compared to the liposomes without AS1411 aptamer. This study suggests that the AS1411 modified α-Gal liposomes can recognize nucleolin-overexpressing tumor cells selectively, subsequently improve the effect of the immunotherapy with high specificity. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1176-1183, 2019.

Contrast Agents Delivery: An Up-to-Date Review of Nanodiagnostics in Neuroimaging

Neuroimaging is a highly important field of neuroscience, with direct implications for the early diagnosis and progression monitoring of brain-associated diseases. Neuroimaging techniques are categorized into structural, functional and molecular neuroimaging, each possessing advantages and disadvantages in terms of resolution, invasiveness, toxicity of contrast agents and costs. Nanotechnology-based approaches for neuroimaging mostly involve the development of nanocarriers for incorporating contrast agents or the use of nanomaterials as imaging agents. Inorganic and organic nanoparticles, liposomes, micelles, nanobodies and quantum dots are some of the most studied candidates for the delivery of contrast agents for neuroimaging. This paper focuses on describing the conventional modalities used for imaging and the applications of nanotechnology for developing novel strategies for neuroimaging. The aim is to highlight the roles of nanocarriers for enhancing and/or overcome the limitations associated with the most commonly utilized neuroimaging modalities. For future directions, several techniques that could benefit from the increased contrast induced by using imaging probes are presented.

The Bioactivity of D-/L-Isonucleoside- and 2'-Deoxyinosine-Incorporated Aptamer AS1411s Including DNA Replication/MicroRNA Expression

In this study, chemical modification of 2'-deoxyinosine (2'-dI) and D-/L-isothymidine (D-/L-isoT) was performed on AS1411. They could promote the nucleotide-protein interaction by changing the local conformation. Twenty modified sequences were obtained, FCL-I and FCL-II showed the most noticeable activity improvement. They stabilized the G-quadruplex, remained highly resistant to serum degradation and specificity for nucleolin, further inhibited tumor cell growth, exhibited a stronger ability to influence the different phases of the tumor cell cycle, induced S-phase arrest, promoted the inhibition of DNA replication, and suppressed the unwound function of a large T antigen as powerful as AS1411. The microarray analysis and TaqMan PCR results showed that FCL-II can upregulate the expression of four breast-cancer-related, lowly expressed miRNAs and downregulate the expression of three breast-cancer-related, highly expressed miRNAs (>2.5-fold). FCL-II resulted in enhanced treatment effects greater than AS1411 in animal experiments (p < 0.01). The computational results further proved that FCL-II exhibits more structural advantages than AS1411 for binding to the target protein nucleolin, indicating its great potential in antitumor therapy.