Biogenic Imaging Contrast Agents

Measuring glymphatic function: Assessing the toolkit

Glymphatic flow has been proposed to clear brain waste while we sleep. Cerebrospinal fluid moves from periarterial to perivenous spaces through the parenchyma, with subsequent cerebrospinal fluid drainage to dural lymphatics. Glymphatic disruption is associated with neurological conditions such as Alzheimer's disease and traumatic brain injury. Therefore, investigating its structure and function may improve understanding of pathophysiology. The recent controversy on whether glymphatic flow increases or decreases during sleep demonstrates that the glymphatic hypothesis remains contentious. However, discrepancies between different studies could be due to limitations of the specific techniques used and confounding factors. Here, we review the methods used to study glymphatic function and provide a toolkit from which researchers can choose. We conclude that tracer analysis has been useful, ex vivo techniques are unreliable, and in vivo imaging is still limited. Finally, we explore the potential for future methods and highlight the need for in vitro models, such as microfluidic devices, which may address technique limitations and enable progression of the field.

Novel Mitochondria-Targeted Asymmetric Heptamethine Cyanine Dye for Cancer Targeted NIR Imaging and Potent Necrosis and Senescence Induction with Prolonged Retention

Developing small molecules that inherently integrate highly tumor-targeted near-infrared fluorescence (NIRF) imaging with potent therapeutic effects remains challenging in anticancer theranostics. Here, we synthesized and characterized a series of heptamethine cyanine PSs with symmetric and asymmetric structures. Among them, we first discovered that asymmetric structures significantly enhanced tumor targeting. Also, a novel mitochondria-targeted asymmetric compound 17 exhibited superior NIRF imaging capability, exceptional tumor selectivity (TNR = 8.54), and strong antitumor activity. Compound 17 selectively accumulates in mitochondria, driven by MMP, where it generates ROS, induces DNA damage, and triggers senescence, apoptosis, and necrosis. Its strong therapeutic efficacy was demonstrated across multiple models, including patient-derived xenograft (PDX), where it allowed precise tumor visualization, significantly suppressed tumor growth with a single administration, and showed no detectable toxicity. Notably, the single-dye small molecule 17 was retained in tumors for over 120 h, enabling prolonged imaging, targeted therapy, and drug delivery for integrated antitumor treatment.

PD-L1 blockade peptide-functionalized NaGdF4 nanodots for efficient magnetic resonance imaging-guided immunotherapy for breast cancer

Immune checkpoint blockade (ICB) inhibitors have shown great promise for the treatment of numerous types of cancers, including triple-negative breast cancer (TNBC), by interrupting immunosuppressive checkpoints. Herein, programmed cell death ligand 1 (PD-L1) blockade peptide-functionalized NaGdF4 nanodots (designated as PDL1-NaGdF4 NDs) were prepared for magnetic resonance imaging (MRI)-guided TNBC immunotherapy through covalent conjugation of the PD-L1 blockade peptide (sequence, CALNNCVRARTR) with tryptone-capped NaGdF4 NDs (designated as Try-NaGdF4 NDs). MDA-MB-231 tumor could be easily tracked using in vivo MRI with PDL1-NaGdF4 ND enhancement because the as-prepared PDL1-NaGdF4 NDs have a high longitudinal relaxivity (r 1) value (22.8 mM-1 S-1) and accumulate in the tumor site through binding with programmed cell death ligand-1 (PD-L1)-overexpressed cells. A series of in vitro/in vivo results demonstrated that the PDL1-NaGdF4 NDs could effectively suppress MDA-MB-231 tumor growth in mice (66% volume ratio) by inhibiting migration and proliferation of tumor cells. In addition, the results of pharmacokinetic study showed that the PDL1-NaGdF4 NDs were excreted from the body through the kidneys. These results highlight the potential of PDL1-NaGdF4 NDs as a biocompatible nanomedicine for TNBC diagnosis and immunotherapy.

Magnetic resonance imaging contrast agents based on albumin nanoparticles

Despite the potential safety hazards and side effects, small molecular magnetic resonance imaging (MRI) contrast agents have been generally used in clinical medical imaging. The development of stable, but low-toxicity and high-efficiency magnetic resonance contrast agents has been receiving continuous attention and research interest. With the deepening of studies, the combination of small molecular magnetic resonance contrast agents and albumin-based carriers is an effective strategy to obtain new MRI contrast agents with safety, low toxicity, high relaxation efficiency and targeting capability. In particular, the relaxivity values of some albumin-based nano-magnetic resonance contrast agents are greater than 100 mM-1 s-1, which is much higher than the relaxivity values of some small molecule MRI contrast agents. Therefore, herein, current research on albumin nanoparticle related MRI contrast agents is summarized, which is of great significance for clarifying the development direction of contrast agents.

Kilogram-Scale Synthesis of Extremely Small Gadolinium Oxide Nanoparticles as a T1-Weighted Contrast Agent for Magnetic Resonance Imaging

Magnetic resonance imaging contrast agents are frequently used in clinics to enhance the contrast between diseased and normal tissues. The previously reported poly(acrylic acid) stabilized exceedingly small gadolinium oxide nanoparticles (ES-GdON-PAA) overcame the problems of commercial Gd chelates, but limitations still exist, i.e., high r2/r1 ratio, long blood circulation half-life, and no data for large scale synthesis and formulation optimization. In this study, polymaleic acid (PMA) is found to be an ideal stabilizer to synthesize ES-GdONs. Compared with ES-GdON-PAA, the PMA-stabilized ES-GdON (ES-GdON-PMA) has a lower r2/r1 ratio (2.05, 7.0 T) and a lower blood circulation half-life (37.51 min). The optimized ES-GdON-PMA-9 has an exceedingly small particle size (2.1 nm), excellent water dispersibility, and stability. A facile, efficient, and environmental friendly synthetic method is developed for large-scale synthesis of the ES-GdONs-PMA. The weight of the optimized freeze-dried ES-GdON-PMA-26 synthesized in a 20 L of reactor reaches the kilogram level. The formulation optimization is also finished, and the concentrated ES-GdON-PMA-26 formulation (CGd = 100 mm) after high-pressure steam sterilization possesses eligible physicochemical properties (i.e., pH value, osmolality, viscosity, and density) for investigational new drug application.

Fluorogenic RNA Aptamer-Based Amplification and Transcription Strategy for Label-free Sensing of Methyltransferase Activity in Complex Matrixes

DNA methyltransferase is significant in cellular activities and gene expression, and its aberrant expression is closely linked to various cancers during initiation and progression. Currently, there is a great demand for reliable and label-free techniques for DNA methyltransferase evaluation in tumor diagnosis and cancer therapy. Herein, a low-background fluorescent RNA aptamer-based sensing approach for label-free quantification of cytosine-guanine (CpG) dinucleotides methyltransferase (M.SssI) is reported. The fluorogenic light-up RNA aptamers-based strategy exhibits high selectivity via restriction endonuclease, padlock-based recognition, and RNA transcription. By combining rolling circle amplification (RCA), and RNA transcription with fluorescence response of RNA aptamers of Spinach-dye compound, the proposed platform exhibited efficiently ultrahigh sensitivity toward M.SssI. Eventually, the detection can be achieved in a linear range of 0.02-100 U mL-1 with a detection limit of 1.6 × 10-3 U mL-1. Owing to these superior features, the method is further applied in serum samples spiked M.SssI, which delivers a recovery ranging from 92.0 to 107.0% and a relative standard deviation <7.0%, providing a promising and practical tool for determining M.SssI in complex biological matrices.

Hyperpolarized Xenon-129 Chemical Exchange Saturation Transfer (HyperCEST) Molecular Imaging: Achievements and Future Challenges

Molecular magnetic resonance imaging (MRI) is an emerging field that is set to revolutionize our perspective of disease diagnosis, treatment efficacy monitoring, and precision medicine in full concordance with personalized medicine. A wide range of hyperpolarized (HP) 129Xe biosensors have been recently developed, demonstrating their potential applications in molecular settings, and achieving notable success within in vitro studies. The favorable nuclear magnetic resonance properties of 129Xe, coupled with its non-toxic nature, high solubility in biological tissues, and capacity to dissolve in blood and diffuse across membranes, highlight its superior role for applications in molecular MRI settings. The incorporation of reporters that combine signal enhancement from both hyperpolarized 129Xe and chemical exchange saturation transfer holds the potential to address the primary limitation of low sensitivity observed in conventional MRI. This review provides a summary of the various applications of HP 129Xe biosensors developed over the last decade, specifically highlighting their use in MRI. Moreover, this paper addresses the evolution of in vivo applications of HP 129Xe, discussing its potential transition into clinical settings.