Aggregate Formation of Oligonucleotides that Assist Molecular Imaging for Tracking of the Oxygen Status in Tumor Tissue

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Functionalized Ultrasmall Iron Oxide Nanoparticles for T1-Weighted Magnetic Resonance Imaging of Tumor Hypoxia

Hypoxia is a common biological condition in many malignant solid tumors that plays an imperative role in regulating tumor growth and impacting the treatment’s therapeutic effect. Therefore, the hypoxia assessment is of great significance in predicting tumor development and evaluating its prognosis. Among the plenty of existing tumor diagnosis techniques, magnetic resonance imaging (MRI) offers certain distinctive features, such as being free of ionizing radiation and providing images with a high spatial resolution. In this study, we develop a fluorescent traceable and hypoxia-sensitive T₁-weighted MRI probe (Fe₃O₄-Met-Cy5.5) via conjugating notable hypoxia-sensitive metronidazole moiety and Cy5.5 dye with ultrasmall iron oxide (Fe₃O₄) nanoparticles. The results of in vitro and in vivo experiments show that Fe₃O₄-Met-Cy5.5 has excellent performance in relaxivity, biocompatibility, and hypoxia specificity. More importantly, the obvious signal enhancement in hypoxic areas indicates that the probe has great feasibility for sensing tumor hypoxia via T₁-weighted MRI. These promising results may unlock the potential of Fe₃O₄ nanoparticles as T₁-weighted contrast agents for the development of clinical hypoxia probes.

Nanotech Probes: A Revolution in Cancer Diagnosis

Recent advances in nanotechnologies for cancer diagnosis and treatment have received considerable attention worldwide. Nanoparticles are being used to create nanodrugs and probes to diagnose and treat a variety of diseases, including cancer. Nanomedicines have unique advantages, such as increased surface-to-volume ratios, which enable them to interact with, absorb, and deliver small biomolecules to a very specific target, thereby improving the effectiveness of both probes and drugs. Nanoprobe biotechnology also plays an important role in the discovery of novel cancer biomarkers, and nanoprobes have become an important part of early clinical diagnosis of cancer. Various organic and inorganic nanomaterials have been developed as biomolecular carriers for the detection of disease biomarkers. Thus, we designed this review to evaluate the advances in nanoprobe technology in tumor diagnosis.

Modulation of cell membrane functionalization with aggregates of oligodeoxynucleotides containing alkyl chain-modified uridines

In this study, we prepared oligodeoxynucleotides (ODNs) containing the uridine base modified by an alkyl chain at the 5-position (AU) and characterized their aggregate formation, localization, and functions in cells. These experiments revealed that aggregates of these ODNs were readily transported into cells, but their localization was dependent upon the number of hydrophobic units. ODNs with one modified AU were transported in the cytosol, while ODNs with multiple AU modifications resulted in their accumulation at the cell membrane. We also examined the ability of the AU-modified ODNs to capture small molecules at the cell membrane and their cellular uptake. We positioned a thioflavin-T (ThT)-binding aptamer on the cell membrane by means of hybridization with ODNs with three AUs at the strand end. Treatment with ThT resulted in its efficient uptake into cells, due to the capture of the ThT by the aptamers on the cell membrane. Thus, we demonstrated the functionalization of cell membranes with modified ODNs and the efficient delivery of small molecules into the cells.

Nano versus Molecular: Optical Imaging Approaches to Detect and Monitor Tumor Hypoxia

Hypoxia is a ubiquitous feature of solid tumors, which plays a key role in tumor angiogenesis and resistance development. Conventional hypoxia detection methods lack continuous functional detection and are generally less suitable for dynamic hypoxia measurement. Optical sensors hereby provide a unique opportunity to noninvasively image hypoxia with high spatiotemporal resolution and enable real-time detection. Therefore, these approaches can provide a valuable tool for personalized treatment planning against this hallmark of aggressive cancers. Many small optical molecular probes can enable analyte triggered response and their photophysical properties can also be fine-tuned through structural modification. On the other hand, optical nanoprobes can acquire unique intrinsic optical properties through nanoconfinement as well as enable simultaneous multimodal imaging and drug delivery. Furthermore, nanoprobes provide biological advantages such as improving bioavailability and systemic delivery of the sensor to enhance bioavailability. This review provides a comprehensive overview of the physical, chemical, and biological analytes for cancer hypoxia detection and focuses on discussing the latest nano- and molecular developments in various optical imaging approaches (fluorescence, phosphorescence, and photoacoustic) in vivo. Finally, this review concludes with a perspective toward the potentials of these optical imaging approaches in hypoxia detection and the challenges with molecular and nanotechnology design strategies.

Hybridizing Oligonucleotides with Hydrophobic Peptide Nucleic Acids Assists Their Cellular Uptake through Aggregate Formation

We applied hybridization between hydrophobic peptide nucleic acids (PNAs) and oligodeoxynucleotides (ODNs) to achieve their cellular uptake without any need for transfection reagents. We employed a pyrenyl unit as a hydrophobic functional group and introduced it at the terminus of the PNA strand. The pyrene-tethered PNA (PyPNA) strongly bound with its complementary ODNs to generate amphiphiles; the resulting hybrids formed aggregates that showed efficient cellular uptake and high biological stability. Aggregates containing a functional DNA aptamer that bound to the PyPNA penetrated the cell membrane smoothly, with the aptamer exerting its original function in living cells. Thus, PyPNA efficiently assisted the additive-free cellular uptake of ODNs.

Biological reduction of nitroimidazole-functionalized gold nanorods for photoacoustic imaging of tumor hypoxia

Tumor-selective accumulation of gold nanorods (GNR) has been demonstrated for visualization of tumor hypoxia by photoacoustic imaging. We prepared GNRs with hypoxia-targeting nitroimidazole units (G-NI) on their surface. Biological experiments revealed that G-NI produced a strong photoacoustic signal in hypoxic tumor cells and tissues.

Tumor-selective accumulation of gold nanorods (GNR) has been demonstrated for visualization of tumor hypoxia by photoacoustic imaging.

Recent Advances in the Development of Optical Imaging Probes for γ-Glutamyltranspeptidase

γ-Glutamyltranspeptidase (GGT) is a cell-membrane-bound protease that participates in cellular glutathione and cysteine homeostasis, which are closely related to many physiological and pathological processes. The accurate measurement of GGT activity is useful for the early diagnosis of diseases. In the past few years, many efforts have been made to build optical imaging probes for the detection of GGT activity both in vitro and in vivo. In this Minireview, recent advances in the development of various optical imaging probes for GGT, including activatable fluorescence probes, ratiometric fluorescence probes, and activatable bioluminescence probes, are summarized. This review starts from the instruction of the GGT enzyme and its biological functions, followed by a discussion of activatable fluorescence probes that show off-on fluorescence in response to GGT. GGT-activatable two-photon fluorescence imaging probes with improved imaging depth and spatial resolution are also discussed. Ratiometric fluorescence probes capable of accurately reporting on GGT levels through a self-calibration mechanism are discussed, followed by describing GGT-activatable bioluminescence probes that can offer a high signal-to-background ratio to detect GGT in living mice. Finally, current challenges and further perspectives for the development of molecular imaging probes for GGT are addressed.

Phosphorescent ruthenium complexes with bromopyrene unit that enhance oxygen sensitivity

Ruthenium complexes are very useful phosphorescent probes for the visualization of hypoxia. We designed and synthesized three ruthenium complexes possessing bromopyrene, naphthalene, or anthracene units to improve the oxygen response. These ruthenium complexes provided strong phosphorescence under hypoxic conditions, while an increase in oxygen concentration led to a decrease in phosphorescence intensity. Among the ruthenium complexes, that with a bromopyrene unit (Ru-BrPy) had the best properties. This showed good cellular uptake and bright emission in cells, and had the highest sensitivity for molecular oxygen. Thus, Ru-BrPy is a promising candidate as a molecular probe for detecting cellular hypoxia.

Construction of a hypoxia responsive upconversion nanosensor for tumor imaging by fluorescence resonance energy transfer from carbon dots to ruthenium complex

Hypoxia responsive upconversion nano-aggregates are synthesized which can be excited by NIR light to give oxygen dependent phosphorescence emission via the FRET process.

Recent Advances in Nucleic Acid Targeting Probes and Supramolecular Constructs Based on Pyrene-Modified Oligonucleotides

In this review, we summarize the recent advances in the use of pyrene-modified oligonucleotides as a platform for functional nucleic acid-based constructs. Pyrene is of special interest for the development of nucleic acid-based tools due to its unique fluorescent properties (sensitivity of fluorescence to the microenvironment, ability to form excimers and exciplexes, long fluorescence lifetime, high quantum yield), ability to intercalate into the nucleic acid duplex, to act as a π-π-stacking (including anchoring) moiety, and others. These properties of pyrene have been used to construct novel sensitive fluorescent probes for the sequence-specific detection of nucleic acids and the discrimination of single nucleotide polymorphisms (SNPs), aptamer-based biosensors, agents for binding of double-stranded DNAs, and building blocks for supramolecular complexes. Special attention is paid to the influence of the design of pyrene-modified oligonucleotides on their properties, i.e., the structure-function relationships. The perspectives for the applications of pyrene-modified oligonucleotides in biomolecular studies, diagnostics, and nanotechnology are discussed.