Small Molecule Contrast Agents Research Articles

Rose Bengal Labeled Bovine Serum Albumin for Protein Transport Imaging in Subcutaneous Tissues Using Computed Tomography and Fluorescence Microscopy.

Subcutaneous (SC) injection of protein-based therapeutics is a convenient and clinically established drug delivery method. However, progress is needed to increase the bioavailability. Transport of low molecular weight (Mw) biotherapeutics such as insulin and small molecule contrast agents such as lipiodol has been studied using X-ray computed tomography (CT). This analysis, however, does not translate to the investigation of higher Mw therapeutics, such as monoclonal antibodies (mAbs), due to differences in molecular and formulation properties. In this study, an iodinated fluorescein analog rose bengal (RB) was used as a radiopaque and fluorescent label to track the distribution of bovine serum albumin (BSA) compared against unconjugated RB and sodium iodide (NaI) via CT and confocal microscopy following injection into ex vivo porcine SC tissue. Importantly, the high concentration BSA-RB exhibited viscosities more like that of viscous biologics than the small molecule contrast agents, suggesting that the labeled protein may serve as a more suitable formulation for the investigation of injection plumes. Three-dimensional (3D) renderings of the injection plumes showed that the BSA-RB distribution was markedly different from unconjugated RB and NaI, indicating the need for direct visualization of large protein therapeutics using conjugated tags rather than using small molecule tracers. Whereas this proof-of-concept study shows the novel use of RB as a label for tracking BSA distribution, our experimental approach may be applied to high Mw biologics, including mAbs. These studies could provide crucial information about diffusion in SC tissue and the influence of injection parameters on distribution, transport, and downstream bioavailability.

Abstract 4165: Influence of halogens in squaraine dye on optoacoustic signal

Abstract Optoacoustic imaging has grown in clinical relevance due to inherent advantages in sensitivity, resolution, and contrast, compared to standard modalities, such as fluorescence. However, guiding principles for development of small molecule contrast agents specific for optoacoustic imaging is lacking. This study assesses the influence of specific structural features of small molecule dyes, specifically squaraine dyes, that result in optoacoustic activity. Through computational models, in vitro testing, and in vivo experimentation this study assesses the effects of halogens on small molecule squaraine dyes to increase optoacoustic signal. By using the aid of our computational model, we decorated the squaraine scaffold with heavy halogenation of squaraines increased optoacoustic activity (2.12 a.u. vs. 0.21 a.u., p<0.001). Density functional theory models suggest the origin of increased optoacoustic signal is due to increases in transition dipole moment which manifested experimentally as increased absorbance in the NIR wavelength range and decreased fluorescence quantum yield, respectively. This study provides an insight into the structure-function relationships that lead to guiding principles for designing optoacoustic-specific contrast agents. Further developments of squaraines and other types of optoacoustic agents will further increase relevance of optoacoustic imaging in a clinical setting. Citation Format: Kavita Belligund, William MacCuaig, Carly Wickizer, Yihan Shao, Lacey R. McNally. Influence of halogens in squaraine dye on optoacoustic signal [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4165.

Cyclodextrin-conjugated low-molecular-weight polyethyleneimine as a macromolecular contrast agent for tumor-targeted magnetic resonance imaging.

Macromolecular contrast agents (CAs) usually possess excellent contrast ability and tumor-targeting ability in comparison with small-molecule CAs, especially for early tumor detection. Herein, cyclodextrin-conjugated low-molecular-weight polyethyleneimine was synthesized as a macromolecular backbone. Afterward, a linear polymer with adamantane terminal and Gd chelates was synthesized, followed by conjugating with the backbone via host-guest interaction. Finally, folic acid was conjugated onto the as-prepared CAs through bioorthogonal chemistry, which endowed the CAs with the capability to accumulate into the tumor region. Compared to Magnevist (r1 = 4.25 mM-1 s-1) used in clinic, the PC/Ad-PEG2000-PLL(DTPA-Gd)-FA exhibited higher longitudinal relaxivity (r1 = 11.62 mM-1 s-1) with excellent biocompatibility. Furthermore, in vivo experiments demonstrated that PC/Ad-PEG2000-PLL(DTPA-Gd)-FA could effectively accumulate in the tumor region and produce a brighter image than that of Magnevist. The H&E staining and metabolic data further illustrated that this CA possessed excellent biocompatibility in vivo. Finally, these results above suggest that this macromolecular CA could be a potential candidate as a MRI CA for tumor-targeted diagnosis.

Cucurbit[8]uril-based water-dispersible assemblies with enhanced optoacoustic performance for multispectral optoacoustic imaging

Organic small-molecule contrast agents have attracted considerable attention in the field of multispectral optoacoustic imaging, but their weak optoacoustic performance resulted from relatively low extinction coefficient and poor water solubility restrains their widespread applications. Herein, we address these limitations by constructing supramolecular assemblies based on cucurbit[8]uril (CB[8]). Two dixanthene-based chromophores (DXP and DXBTZ) are synthesized as the model guest compounds, and then included in CB[8] to prepare host-guest complexes. The obtained DXP-CB[8] and DXBTZ-CB[8] display red-shifted and increased absorption as well as decreased fluorescence, thereby leading to a substantial enhancement in optoacoustic performance. Biological application potential of DXBTZ-CB[8] is investigated after co-assembly with chondroitin sulfate A (CSA). Benefiting from the excellent optoacoustic property of DXBTZ-CB[8] and the CD44-targeting feature of CSA, the formulated DXBTZ-CB[8]/CSA can effectively detect and diagnose subcutaneous tumors, orthotopic bladder tumors, lymphatic metastasis of tumors and ischemia/reperfusion-induced acute kidney injury in mouse models with multispectral optoacoustic imaging.

Tungsten-based nanoparticles as contrast agents for liver tumor detection using dual-energy computed tomography.

Dual-energy computed tomography (DECT) is a commonly used imaging technique for detecting and diagnosing liver cancer. Currently, it is performed using clinically approved iodinated small molecule contrast agents (CAs). However, these iodinated CAs have several drawbacks, including sub-optimal contrast generation and contra-indication in patients with renal insufficiency. Herein, we synthesized tungsten-based CAs (i.e., WO3-x NPs) with excellent biocompatibility and investigated their effectiveness in DECT imaging. WO3-x NPs significantly enhanced the contrast between liver tumors and normal liver tissues as indicated by in vivo DECT imaging. Furthermore, WO3-x NPs exhibited excellent biocompatibility and minimal systemic toxicity. This study introduces a novel class of CAs for DECT and presents a promising method for accurate early diagnosis of liver tumors.

Degradable multifunctional gold-liposomes as an all-in-one theranostic platform for image-guided radiotherapy

To improve tumor destruction and minimize adverse effects to healthy tissues, image-guided radiation therapy (IGRT) has been developed to allow for the accurate delivery of radiation energy to tumor sites facilitated by real-time imaging. Nevertheless, the current IGRT platform still suffers from the limitation of poor tissue contrast, resulting in the incidental irradiation of healthy tissue. Gold nanoparticles (GNPs) have been identified as promising candidates to simultaneously improve both radiotherapy and imaging, thereby improving both the accuracy and safety of IGRT. However, despite much preclinical study, little clinical progress has been made due to uncertainty over GNP toxicity. Herein, we demonstrate the great potential of using GNP-coated liposomes, i.e., Lipogold, which combine the advantages of both large and small nanoparticles into one multifunctional formulation, as an ideal platform for IGRT. When irradiated with low doses (<2 Gy) of therapeutic X-rays, Lipogold induced a significant radiosensitization effect for PC-3 prostate cancer cells, which are moderately radiation-resistant. When imaged with computed tomography (CT), Lipogold was also found to possess consistent X-ray contrast of ∼ 18–23 HU/mg across tube X-ray voltages (70–140 kVp), which could be boosted via the encapsulation of a small-molecule contrast agent containing iodine.

Organic Small Molecule Contrast Agent for Targeted Photoacoustic Imaging of Patient-Derived Brain Tumors.

Traditional glioblastoma (GBM) cell lines do not maintain the heterogeneity of the original tumor, cell interactions, and therapy response, thus limiting their investigation in GBM theranostics. Herein, a kind of GBM tumor-targeting nanoparticles (NPs) TCFNP@iRGD are designed and constructed, which are generated by photoacoustic (PA) contrast agent 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene) malononitrile (TCF)-OH through facile nanoprecipitation and decorated with an active targeting ligand iRGD. Their potential in GBM detection via PA imaging on glioma patient-derived cells intracranial xenograft models is evaluated for the first time. Excellent tumor-specific PA mapping performance of GBM is realized by TCFNP@iRGD, demonstrating its promising potential in the clinical diagnosis of GBM.

Construction of ultrasmall gold nanoparticles based contrast agent via Host-Guest interaction for Tumor-targeted magnetic resonance imaging

In order to overcome the shortcomings of small-molecule contrast agents (CAs) in clinic, gadolinium-based CAs have attracted increasingly interesting in tumor diagnosis. Herein, β-cyclodextrin-modified ultrasmall gold nanoparticle (AuNP@CD) was prepared as a functional core, which provided a large number of binding sites through host–guest interaction. Afterward, AD-PEG2000-PLL(Gd-DTPA) was anchored on the surface of AuNP@CD followed by the conjugation of folic acid through bioorthogonal chemistry, which endowed the AuNP with the capability to targeting tumor cells. Compared to Magnevist (Gd-DTPA, r1 = 4.25 mM−1 s−1) used in clinic, the AuNP nanocomposite exhibited higher longitudinal relaxivity (r1 = 19.47 mM−1 s−1), and presented excellent biocompatibility. Furthermore, in vivo studies indicated that AuNP@CD-AD-PEG2000-PLL (DTPA-Gd) nanocomposite could effectively permeate through tumor and accumulate in the tumor region, thus acquiring MR images with high resolution. These results suggest that this AuNP nanocomposite could be a potential candidate as MRI CA for tumor-targeted diagnosis.

Magnetic Resonance Imaging and Rna Interference of Tumor with Reducible Poly(Urethane-Amine) Nanocomposite System

Gadolinium-based small-molecule contrast agents are commonly utilized in clinics. However, these agents have a short retention time in vivo and possess a certain level of cytotoxicity. The reducible polymer poly(urethane-amine) can increase the relaxation rate and blood circulation time of small-molecule gadolinium chelates. Moreover, the polymer can be used as a gene carrier to bind small interfering RNA (siRNA). We synthesized an active targeting integrated diagnosis and treatment nanocomposite system with reducible poly(urethane-amine) as the carrier. This system incorporated functional units such as MRI contrast agent Gd-diethylenetriamine pentacetate (Gd-DTPA) and siRNA-vascular endothelial growth factor (siRNA-VEGF), and folic acid (FA) modified onto the surface of the polymer directed it to actively target tumor cells, thus improving the imaging effect of MRI. Meanwhlie, siRNA-VEGF carried by the system could reduce the expression of VEGF in tumor cells and inhibited tumor growth. The system showed good biocompatibility and was an integrated system of tumor diagnosis and treatment.

Renoprotective Angiographic Polymersomes

AbstractComputed tomography (CT) angiography is powerful for the diagnosis of vascular diseases. Unfortunately, this method usually requires a high dosage of iodinated contrast agents, which can lead to severe elevation of reactive oxygen species (ROS) levels within kidneys. This causes oxidative stress, apoptosis, and hence contrast‐induced nephropathy (CIN), a leading cause of iatrogenic renal failure, especially for patients with renal insufficiency. Herein, a route is shown to circumvent such problems with the usage of rationally designed renoprotective angiographic polymersomes (RAPs) as blood pool CT contrast agents. RAPs are biodegradable nanoparticles prepared via self‐assembly of poly(ethylene oxide)‐block‐poly(triiodobenzoic chloride‐conjugated polylysine‐stat‐phenylboronic acid pinacol ester‐conjugated polylysine) (PEO45‐b‐P[(Lys‐IBC)45‐stat‐(Lys‐PAPE)15]). The key to the efficiency of such nanoparticles as renoprotective contrast agents arises from the rationally chosen repeat units: Lys‐IBC exhibits a concentration‐dependent X‐ray attenuation capability and Lys‐PAPE introduces an ROS‐scavenging ability to the polymersome. The study shows that RAPs can reduce the risk of CIN in mice with kidney injury. Additionally, a 5‐fold increase in angiographic live time is observed using RAPs, compared to commonly used iodinated small molecule contrast agents. In summary, a new strategy is proposed for the design of a renoprotective angiographic contrast agent that is capable of reducing the risk of CIN.

Preparation and Properties of Tumor-Targeting MRI Contrast Agent Based on Linear Polylysine Derivatives.

We developed a tumor-targeted contrast agent based on linear polylysine (PLL) by conjugating a small molecular imaging agent, fluorescent molecule and targeting agent amino phenylboronic acid onto the amino groups of polylysine, which can specifically target monosaccharide sialic acid residues overexpressing on the surface of tumor cell membranes. Further, 3,4,5,6-Tetrahydrophthalic anhydride (DCA) was attached to the free amino groups of the polylysine to change to a negative charge at physiology pH to lower the cytotoxicity, but it soon regenerated to a positive charge again once reaching the acidic intratumoral environment and therefore increased cell uptake. Laser confocal microscopy images showed that most of the polymeric contrast agents were bound to the cancer cell membrane. Moreover, the tumor targeting contrast agent showed the same magnetic resonance imaging (MRI) contrasting performance in vitro as the small molecule contrast agent used in clinic, which made it a promising tumor-targeting polymeric contrast agent for cancer diagnosis.

A fluorinated aza-BODIPY derivative for NIR fluorescence/PA/19F MR tri-modality in vivo imaging.

A fluorinated aza-BODIPY derivative BDPF was developed as a small molecule contrast agent, which displayed highly efficient near infrared fluorescence/photoacoustic/19F MR tri-modality tumor imaging.

Small Molecule Optoacoustic Contrast Agents: An Unexplored Avenue for Enhancing In Vivo Imaging.

Almost every variety of medical imaging technique relies heavily on exogenous contrast agents to generate high-resolution images of biological structures. Organic small molecule contrast agents, in particular, are well suited for biomedical imaging applications due to their favorable biocompatibility and amenability to structural modification. PET/SPECT, MRI, and fluorescence imaging all have a large host of small molecule contrast agents developed for them, and there exists an academic understanding of how these compounds can be developed. Optoacoustic imaging is a relatively newer imaging technique and, as such, lacks well-established small molecule contrast agents; many of the contrast agents used are the same ones which have found use in fluorescence imaging applications. Many commonly-used fluorescent dyes have found successful application in optoacoustic imaging, but others generate no detectable signal. Moreover, the structural features that either enable a molecule to generate a detectable optoacoustic signal or prevent it from doing so are poorly understood, so design of new contrast agents lacks direction. This review aims to compile the small molecule optoacoustic contrast agents that have been successfully employed in the literature to bridge the information gap between molecular design and optoacoustic signal generation. The information contained within will help to provide direction for the future synthesis of optoacoustic contrast agents.

Gadolinium(III)-based Polymeric Magnetic Resonance Imaging Agents for Tumor Imaging.

Contrast agents (CAs) are widely used to improve the signal-noise ratio in the magnetic resonance imaging (MRI) examinations. The majority of MRI CAs used in clinic are gadolinium( III) (Gd(III)) chelates with low molecular weight. Compared with these small-molecule CAs, Gd(III)-based polymeric magnetic resonance imaging agents (i.e. macromolecular contrast agents, mCAs), prepared by conjugating small-molecule Gd(III) chelates onto macromolecules, possess high relaxivity and relative long blood circulation time, which are favorable for MRI examinations. In last decades, increasing attention was paid to the design of mCAs with various structures, and further evaluation of the MRI performance both in vitro and in vivo. Herein, we focus on the recent progress of mCAs, including structures, properties and applications. Meanwhile, this review also highlights the emerging MRI mCAs with smart response and multi-function: tumor microenvironment- stimulated MRI, multi-mode imaging and MRI-based theranostics.

Recent advances on stimuli-responsive macromolecular magnetic resonance imaging (MRI) contrast agents

Magnetic resonance imaging (MRI) has been extensively used in clinical diagnosis and currently over 30% MRI runs are performed in the presence of contrast agents. However, commercially available contrast agents originated from small molecules typically exhibit relatively low relaxivities and insufficient circulation time. Therefore, there is a long pursuit to develop new contrast agents with high relaxivities to discriminate pathological tissues from normal ones. Compared with small molecule MRI contrast agents, the incorporation of small molecule contrast agents into macromolecular scaffolds allows for constructing macromolecular MRI contrast agents, remarkably elevating the relaxivities due in part to increased rotational correlation time (τR). Moreover, if the macromolecular scaffolds are responsive to external stimuli, the MRI signals could be selectively switched on at the desired sites (e.g., pathological tissues), further intensifying the imaging contrast. In this feature article, we outline the recent achievements in the fabrication of stimuli-responsive macromolecular MRI contrast agents. Specifically, macromolecular contrast agents being responsive to acidic pH, redox potentials, and other stimuli including photoirradiation, pathogens, and salt concentration are discussed. These smart contrast agents could affect either longitudinal (T1) or transverse (T2) relaxation times of water protons or other nuclei (e.g., 19F), exhibiting enhanced signals in pathological tissues yet suppressed signals in normal ones and displaying promising potentials in in vitro and in vivo MRI applications.

An Innovation for Treating Orthotopic Pancreatic Cancer by Preoperative Screening and Imaging-Guided Surgery.

Pancreatic cancer is still associated with a poor outcome and low patient quality of life, which are mainly attributed to the late detection and requirement of distal pancreatectomy with extended resection of pancreatic tumors. Therefore, novel strategies for early screening and precise tumor resection are urgently needed. In this study, we evaluated the feasibility of a low-density lipoprotein receptor (LDLR)-targeted small-molecule contrast agent (peptide-22-Cy7) for early screening with photoacoustic tomography and near-infrared (NIR) imaging as guided surgical navigation to achieve precise resection. Normal pancreatic cells (HPDE6-C7) and cancer cells (PANC-1) were respectively used in the in vitro targeting evaluations. The ability of peptide-22-Cy7 for preoperative in vivo pancreatic tumor detection was investigated in a mouse orthotopic pancreatic cancer model (n = 10) using photoacoustic tomography; 18 tumor-bearing mice were further divided into three groups for different treatments. After intravenous injection of peptide-22-Cy7, surgical navigation was conducted through laparotomy. Histopathological analysis was used to further confirm the tumor area and the state of surgical margins. Flow cytometry demonstrated that peptide-22 is highly specific to pancreatic cancer cells, with a fluorescence intensity of approximately 87.3%. Orthotopic pancreatic tumors with a size of 4mm could be accurately detected by photoacoustic tomography. Surgical navigation effectively achieved R0 resection and minimized the range of resection, which led to increased body weight of the mice following surgery. Overall, our newly developed targeted contrast agent facilitated the accurate positioning and resection of pancreatic tumors. Photoacoustic tomography and optical imaging-guided surgical navigation may be a novel direction for improving the survival, quality of life, and disease management of pancreatic cancer patients.

Electrostatic self-assembled nanoparticles based on spherical polyelectrolyte brushes for magnetic resonance imaging.

Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques for clinical diagnosis. Contrast agents (CAs) are commonly necessarily used to enhance the imaging quality of MRI and differentiate diseased tissues from normal ones. Herein, we introduced a macromolecular carrier, spherical polyelectrolyte brushes (SPBs), which consists of a solid polystyrene (PS) core and polyacrylic acid (PAA) chains as a brush layer to host Gd(iii) complexes. The cationic Gd(iii) complex Gd-DTPA-NO-C4 was synthesized through a 6-step approach and then formed electrostatic self-assemblies with SPBs to afford magnetic assemblies. The regular appearance of the core-shell type structure of the assemblies was confirmed by TEM and SEM. Besides, a remarkable enhancement in relaxivity up to 62 mM-1 s-1 of these assemblies was determined, much higher than that of clinically used small molecule CAs (4-5 mM-1 s-1). It is noteworthy that the assemblies exhibit non-cytotoxicity even at the concentration of Gd(iii) up to 150 μM, showing great potential for clinical MRI applications.

A biomimetic Au@BSA-DTA nanocomposites-based contrast agent for computed tomography imaging

Early detection of cancer is increasingly important for being considered to increase the survival rate in the treatment process. The past decades years have witnessed the great progress in the biological detection application of gold nanoparticles. Herein, we reported a facile one-pot synthesis process to obtain gold nanoparticles (Au@BSA) with bovine serum albumin (BSA) as a biotemplate following with conjugation of diatrizoic acid (DTA) for a potential X-ray computed tomography (CT) imaging contrast agent (Au@BSA-DTA). The as-prepared biomimetic material was characterized systematically by several techniques. It was shown that the prepared biomaterial is colloid stable under the tested range of pH and temperature. The cell cytotoxicity assay, hemolytic assay and cell morphology observation showed that Au@BSA-DTA has good biocompatibility and hemocompatibility at a concentration of Au even up to 80μg/mL. Besides, the biomimetic material Au@BSA-DTA with double radiodense elements of Au and iodine displayed much stronger CT imaging effect compared with the traditional small molecule contrast agents, which paves the potential clinical application in cancer early diagnosis.

Nanopolymersomes with an Ultrahigh Iodine Content for High‐Performance X‐Ray Computed Tomography Imaging In Vivo

Biocompatible and biodegradable nanopolymersomes with an unprecedented iodine content, low viscosity, and iso-osmolality achieve significantly enhanced CT imaging of blood pool and the reticuloendothelial system. Moreover, in subcutaneous and orthotopic tumor models in mice, they show enhanced in vivo imaging when compared to iohexol, a clinically used small-molecule contrast agent.

Functional Hyperbranched Polylysine as Potential Contrast Agent Probes for Magnetic Resonance Imaging.

Researchers have never stopped questing contrast agents with high resolution and safety to overcome the drawbacks of small-molecule contrast agents in clinic. Herein, we reported the synthesis of gadolinium-based hyperbranched polylysine (HBPLL-DTPA-Gd), which was prepared by thermal polymerization of l-lysine via one-step polycondensation. After conjugating with folic acid, its potential application as MRI contrast agent was then evaluated. This contrast agent had no obvious cytotoxicity as verified by WST assay and H&E analysis. Compared to Gd(III)-diethylenetriaminepentaacetic acid (Gd-DTPA) (r1 = 4.3 mM(-1) s(-1)), the FA-HBPLL-DTPA-Gd exhibited much higher longitudinal relaxivity value (r1 = 13.44 mM(-1) s(-1)), up to 3 times higher than Gd-DTPA. The FA-HBPLL-DTPA-Gd showed significant signal intensity enhancement in the tumor region at various time points and provided a long time window for MR examination. The results illustrate that FA-HBPLL-DTPA-Gd will be a potential candidate for tumor-targeted MRI.