Red Light-Initiated Cross-Linking of NIR Probes to Cytoplasmic RNA: An Innovative Strategy for Prolonged Imaging and Unexpected Tumor Suppression

Spatiotemporally Controllable Covalent Bonding of RNA for Multi-Protein Interference

Many diseases are associated with genetic mutation and expression of mutated proteins, such as cancers. Therapeutic approaches that selectively target the synthesis process of multiple proteins show greater potential compared to single-protein approaches in oncological diseases. However, conventional agents to regulate the synthesis of multiple protein still suffer from poor spatiotemporal selectivity and stability. Here, a new method using a dye-peptide conjugate, PRFK, for multi-protein interference with spatiotemporal selectivity and reliable stability, is reported. By using the peptide sequence that targets tumor cells, PRFK can be efficiently taken up, followed by specific binding to the KDELR (KDEL receptor) protein located in the endoplasmic reticulum (ER). The dye generates 1O2 under light irradiation, enabling photodynamic therapy. This process converts the furan group into a cytidine-reactive intermediate, which covalently binds to mRNA, thereby blocking protein synthesis. Upon treating 4T1 cells, the proteomics data show alterations in apoptosis, ferroptosis, proliferation, migration, invasion, and immune infiltration, suggesting that multi-protein interference leads to the disruption of cellular physiological activities, ultimately achieving tumor treatment. This study presents a multi-protein interference probe with the potential for protein interference within various subcellular organelles in the future.

A Golgi Apparatus-Targeted Photothermal Agent with Protein Anchoring for Enhanced Cancer Photothermal Therapy

The Golgi apparatus (GA) is central in shuttling proteins from the endoplasmic reticulum to different cellular areas. Therefore, targeting the GA to precisely destroy its proteins through local heat could induce apoptosis, offering a potential avenue for effective cancer therapy. Herein, a GA-targeted photothermal agent based on protein anchoring is introduced for enhanced photothermal therapy of tumor through the modification of near-infrared molecular dye with maleimide derivative and benzene sulfonamide. The photothermal agent can actively target the GA and covalently anchor to its sulfhydryl proteins, thereby increasing its retention within the GA. Under laser irradiation, the heat generated by the photothermal agent efficiently disrupts sulfhydryl proteins in situ, leading to GA dysfunction and ultimately inducing cell apoptosis. In vivo experiments demonstrate that the photothermal agent can precisely treat tumors and significantly reduce side effects.

Dihydroxanthene-based monoamine oxidase A-activated photosensitizers for photodynamic/photothermal therapy of tumors

Small molecule photosensitizers for combined in vivo tailored cancer diagnostics and photodynamic/photothermal therapy are desperately needed. Monoamine oxidase A (MAO-A)-activated therapeutic and diagnostic compounds provide great selectivity because MAO-A can be employed as a biomarker for associated Tumors. In order to screen photosensitizers with photodynamic therapeutic potential, we have created a range of near-infrared fluorescent molecules in this work by combining dihydroxanthene parent with various heterocyclic fluorescent dyes. The NIR fluorescent diagnostic probe, DHMQ, was created by combining the screened fluorescent dye matrices with the propylamino group, which is the recognition moiety of MAO-A, based on the oxidative deamination mechanism of the enzyme. This probe has a low toxicity level and can identify MAO-A precisely. It has the ability to use fluorescence imaging on mice and cells to track MAO-A activity in real-time. It has strong phototoxicity and can produce singlet oxygen when exposed to laser light. The temperature used in photothermal imaging can get up to 50 °C, which can harm tumor cells permanently and have a positive phototherapeutic impact on tumors grown from SH-SY5Y xenograft mice. The concept of using MAO-A effectively in diseases is expanded by the MAO-A-activated diagnostic-integrated photosensitizers, which offer a new platform for in vivo cancer diagnostics and targeted anticancer treatment.

Recent Advances in RNA-Targeted Cancer Therapy

Ribonucleic acid (RNA) plays a pivotal role in gene regulation and protein biosynthesis. Interfering the physiological function of key RNAs to induce cell apoptosis holds great promise for cancer treatment. Many RNA-targeted anti-cancer strategies have emerged continuously. Among them, RNA interference (RNAi) has been recognized as a promising therapeutic modality for various disease treatments. Nevertheless, the primary obstacle in siRNA delivery-escaping the endosome and crossing the plasma membrane severely impedes its therapeutic potential. Thus far, a variety of nanosystems as well as carrier-free bioconjugation for siRNA delivery have been developed and employed to enhance the drug delivery and anti-tumor efficiency. Besides, the use of small molecules to target specific RNA structures and disrupt their function, along with the covalent modification of RNA, has also drawn tremendous attention recently owing to high therapeutic efficacy. In this review, we will provide an overview of recent progress in RNA-targeted cancer therapy including various siRNA delivery strategies, RNA-targeting small molecules, and newly emerged covalent RNA modification. Finally, challenges and future perspectives faced in this research field will be discussed.

Ultrabright NIR-II Nanoprobe for Image-Guided Accurate Resection of Tiny Metastatic Lesions

Fluorescence imaging is a vital way to delineate the tumor boundaries. Here, we achieve a NIR-II aggregation-induced emission luminogen (AIEgen) with a fluorescence quantum yield (QY) of 12.6% in water through straightforward alkyl side chain modification. After loading of NIR-II AIEgen into polystyrene (PS) nanospheres, the thermal deactivation pathway is extremely limited, thereby concentrating absorption excitation on fluorescence emission. The fluorescence intensity is further enhanced by 5.4 times, the QY increases to 21.1%, and the NIR-II imaging signal is accordingly enhanced by 8.7 times, surpassing conventional DSPE-PEG carriers. The NIR-II@PS nanoprobe showcases superior resolution and tissue penetration depth compared to indocyanine green (ICG) and short-range near-infrared AIEgens. In vivo investigations underscore its tumor-to-normal tissue ratio (3.9) at 24 h post intravenous injection, enabling complete resection of ≤1 mm metastases under NIR-II bioimaging guidance. Additionally, the PS carrier-nanoparticles exhibit low toxicity in vivo, laying a promising foundation for the future design of medical nanomaterials.

β-Galactosidase-Activated and Red Light-Induced RNA Modification Strategy for Prolonged NIR Fluorescence/PET Bimodality Imaging

Improving the retention of small-molecule-based therapeutic agents in tumors is crucial to achieve precise diagnosis and effective therapy of cancer. Herein, we propose a β-galactosidase (β-Gal)-activated and red light-induced RNA modification (GALIRM) strategy for prolonged tumor imaging. A β-Gal-activatable near-infrared (NIR) fluorescence (FL) and positron emission tomography (PET) bimodal probe 68Ga-NOTA-FCG consists of a triaaza triacetic acid chelator NOTA for 68Ga-labeling, a β-Gal-activated photosensitizer CyGal, and a singlet oxygen (1O2)-susceptible furan group for RNA modification. Studies have demonstrated that the probe emits an activated NIR FL signal upon cleavage by endogenous β-Gal overexpressed in the lysosomes, which is combined with the PET imaging signal of 68Ga allowing for highly sensitive imaging of ovarian cancer. Moreover, the capability of 68Ga-NOTA-FCG generating 1O2 under 690 nm illumination could be simultaneously unlocked, which can trigger the covalent cross-linking between furan and nucleotides of cytoplasmic RNAs. The formation of the probe-RNA conjugate can effectively prevent exocytosis and prolong retention of the probe in tumors. We thus believe that this GALIRM strategy may provide entirely new insights into long-term tumor imaging and efficient tumor treatment.

NIR Light-Activated Mitochondrial RNA Cross-Linking Strategy for H2S Monitoring and Prolonged Colorectal Tumor Imaging

Molecular diffusion and leakage impede the long-term retention of probes/drugs and may cause potential adverse effects in theranostic fields. Spatiotemporally manipulating the organelle-immobilization behavior of probes/drugs for prolonged tumor retention is indispensable to achieving effective cancer diagnosis and therapy. Herein, we propose a rational strategy that could realize near-infrared light-activated ribonucleic acids (RNAs) cross-linking for prolonged tumor retention and simultaneously endogenous hydrogen sulfide (H2S) monitoring in colorectal tumors. Profiting from efficient singlet oxygen (1O2) generation from Cy796 under 808 nm light irradiation, the 1O2-animated furan moiety in Cy796 could covalently cross-link with cytoplasmic RNAs via a cycloaddition reaction and realize organelle immobilization. Subsequently, specific thiolysis of Cy796 assisted with H2S resulted in homologous product Cy644 with reduced 1O2 generation yields and enhanced absolute fluorescence quantum yields (from 7.42 to 27.70%) with blue-shifted absorption and emission, which avoided the molecular oxidation fluorescence quenching effect mediated by 1O2 and validated fluorescence imaging. Furthermore, studies have demonstrated that our proposed strategy possessed adequate capacity for fluorescence imaging and endogenous H2S detection in HCT116 cells, particularly accumulated at the tumor sites, and retained long-term imaging with excellent biocompatibility. The turn-on fluorescence mode and turn-off 1O2 generation efficiency in our strategy successfully realized a diminished fluorescence cross-talk and oxidation quenching effect. It is adequately envisioned that our proposed strategy for monitoring biomarkers and prolonged tumor retention will contribute tremendous dedication in the clinical, diagnostic, and therapeutic fields.

Small molecules and conjugates as theranostic agents

Theranostics, the integration of therapy and diagnostics into a single entity for the purpose of monitoring disease progression and treatment response. Diagnostics involves identifying specific characteristics of a disease, while therapeutics refers to the treatment of the disease based on this identification. Advancements in medicinal chemistry and technology have led to the development of drug modalities that provide targeted therapeutic effects while also providing real-time updates on disease progression and treatment. The inclusion of imaging in therapy has significantly improved the prognosis of devastating diseases such as cancer and neurodegeneration. Currently, theranostic treatment approaches are based on nuclear medicine, while nanomedicine and a wide diversity of macromolecular systems such as gels, polymers, aptamers, and dendrimer-based agents are being developed for the purpose. Theranostic agents have significant roles to play in both early-stage drug development and clinical-stage therapeutic-containing drug candidates. This review will briefly outline the pros and cons of existing and evolving theranostic approaches before comprehensively discussing the role of small molecules and their conjugates.

Furan-based (photo)oxidation reactions and their application in nucleic acid and protein targeting

Oligonucleotides (ODNs) find applications as diagnostic and therapeutic tools due to their unique ability to interact, thanks to Watson-Crick base pairing, with a specific DNA or RNA target strand. Although most of the tools available today rely on mere hydrogen bond formation, chemical modifications to enable covalent interstrand-crosslinking (ICL) have been reported, and are gaining a place under the spotlight as they potentially offer a series of advantages over the state of the art, including a higher potency and selectivity. This methodological paper focuses on the use of a pro-reactive furan moiety and its subsequent oxidation for applications in ODN targeting. The design of effective capture and targeting probes to ensure high ICL yields is discussed and the mechanisms underlying the (photo)chemical oxidation of furan are explained. Furthermore, examples of furan-containing DNAs designed for different applications, including DNA-DNA or DNA-RNA ICL and DNA-peptide/protein targeting, are provided. The paper highlights the advantages of using different oxidative chemical triggers, such as N-bromosuccinimide or singlet oxygen, to offer additional selectivity control over the ICL reaction.

A tumor-targetable NIR probe with photoaffinity crosslinking characteristics for enhanced imaging-guided cancer phototherapy

Spatiotemporally manipulating the in situ immobilization of theranostic agents within cancer cells to improve their bioavailability is highly significant yet challenging in tumor diagnosis and treatment. Herein, as a proof-of concept, we for the first time report a tumor-targetable near-infrared (NIR) probe DACF with photoaffinity crosslinking characteristics for enhanced tumor imaging and therapeutic applications. This probe possesses great tumor-targeting capability, intensive NIR/photoacoustic (PA) signals, and a predominant photothermal effect, allowing for sensitive imaging and effective photothermal therapy (PTT) of tumors. Most notably, upon 405 nm laser illumination, DACF could be covalently immobilized within tumor cells through a photocrosslinking reaction between photolabile diazirine groups and surrounding biomolecules resulting in enhanced tumor accumulation and prolonged retention simultaneously, which significantly facilitates the imaging and PTT efficacy of tumor in vivo. We therefore believe that our current approach would provide a new insight for achieving precise cancer theranostics.

Afterglow/Fluorescence Dual-Emissive Ratiometric Oxygen Probe for Tumor Hypoxia Imaging

Hypoxia is a common feature of many diseases such as solid tumors. The measurement and imaging of oxygen (O₂) are extremely important for disease diagnosis and therapy evaluation. In this work, the afterglow/fluorescence dual-emissive ratiometric O₂ probe based on a photochemical reaction-based afterglow system is reported. The afterglow is highly sensitive to O₂ because the O₂ content is directly related to the ¹O₂ yield and eventually affects the afterglow intensity. The O₂-insensitive fluorescence of an emitter can serve as an internal reference. As the O₂ concentration changes from 0.08 to 18.5 mg L^-1, the ratio value shows a remarkable 53-fold increase. Compared with the intensity of a single peak, the ratiometric signal can eliminate the interference of the probe concentration to achieve higher accuracy. This afterglow/fluorescence dual-emissive ratiometric O₂ probe is successfully applied to hypoxia imaging in tumor-bearing mice, which may further promote the development of O₂ sensing in the biomedical field.

Development of a Novel 18F-Labeled Probe for PET Imaging of Estrogen Receptor β

Estrogen receptor beta (ERβ) is an important ER subtype that plays crucial roles in many physiological and pathological disorders. Herein, we developed the probe [¹⁸F]PVBO for in vivo ERβ targeted PET imaging and obtained promising results. The nonradioactive PVBO showed a 12.5-fold stronger binding affinity to ERβ than to ERα in vitro. In vitro assays revealed the specific uptake of [¹⁸F]PVBO by DU145 cells. The uptake of [¹⁸F]PVBO by DU145 xenografts increased during the 120 min dynamic scanning, with a maximum uptake of 2.80 ± 0.30% ID/g. Based on time activity curves (TACs), the injection of [¹⁸F]PVBO with unlabeled PVBO or ERB-041 resulted in a significant signal reduction with the tumor/muscle (T/M) ratio <1 at 30, 60, 75, and 120 min post-injection (p < 0.05). [¹⁸F]PVBO demonstrates the feasibility of noninvasively imaging ERβ-positive tumors by small-animal PET and provides a new strategy for visualizing ERβ in vivo.

In Vivo Quantitative Assessment of a Radiation Dose Based on Ratiometric Photoacoustic Imaging of Tumor Apoptosis

Accurately assessing the radiation level of tumors and surrounding tissues is of great significance for the optimization of clinical therapeutic interventions as well as minimizing the radiation-induced side effects. Therefore, the development of noninvasive and sensitive biological dosimeters is vital to achieve quantitative detection of a radiation dose in a living system. Herein, as a proof of concept, we report a tumor-targeted and caspase-3-activatable NIR fluorogenic probe AcDEVD-Cy-RGD consisting of a hemicyanine fluorophore as a signal reporter, a caspase-3 specific Asp-Glu-Val-Asp (DEVD) peptide, and a cyclic Arg-Gly-Asp peptide (cRGD) for tumor targeting. Upon cleavage with activated caspase-3, this probe not only displays the lighted-up NIR fluorescence, but also ratiometric photoacoustic (PA₇₁₀/PA₆₈₀) signals concurrently in a caspase-3 concentration-dependent manner, allowing for sensitive and quantitative detection of caspase-3 activity through both fluorescence and PA imaging, which provides the possibility for real-time monitoring of tumor cell apoptosis in a living system. More notably, we utilized this probe to successfully realize the direct visualization of tumor response to chemo- or radiotherapy and, for the first time, achieve the accurate estimation of radiation doses imparted to the tumors. We thus believe that our current strategy would offer an attractive and valuable means for the precise assessment of locally delivered radiation doses in various clinical settings.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (¹O₂) is the excited state of ground, triplet state, molecular oxygen (O₂). Photosensitized ¹O₂ has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of ¹O_2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of ¹O₂, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring ¹O₂ generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor ¹O₂ generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

Molecular engineering of organic-based agents for in situ bioimaging and phototherapeutics

In situ monitoring of the location and transportation of bioactive molecules is essential for deciphering diverse biological events in the field of biomedicine. In addition, obtaining the in situ information of lesions will provide a clear perspective for surgeons to perform precise resection in clinical surgery. Notably, delivering drugs or operating photodynamic therapy/photothermal therapy in situ by labeling the lesion regions of interest can improve treatment and reduce side effects in vivo. In various advanced imaging and therapy modalities, optical theranostic agents based on organic small molecules can be conveniently modified as needed and can be easily internalized into cells/lesions in a non-invasive manner, which are prerequisites for in situ bioimaging and precision treatment. In this tutorial review, we first summarize the in situ molecular immobilization strategies to retain small-molecule agents inside cells/lesions to prevent their diffusion in living organisms. Emphasis will be focused on introducing the application of these strategies for in situ imaging of biomolecules and precision treatment, particularly pertaining to why targeting therapy in situ is required.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

Chemically modified biomacromolecules-i.e., proteins, nucleic acids, glycans, and lipids-have become crucial tools in chemical biology. They are extensively used not only to elucidate cellular processes but also in industrial applications, particularly in the context of biopharmaceuticals. In order to enable maximum scope for optimization, it is pivotal to have a diverse array of biomacromolecule modification methods at one's disposal. Chemistry has driven many significant advances in this area, and especially recently, numerous novel visible-light-induced photochemical approaches have emerged. In these reactions, light serves as an external source of energy, enabling access to highly reactive intermediates under exceedingly mild conditions and with exquisite spatiotemporal control. While UV-induced transformations on biomacromolecules date back decades, visible light has the unmistakable advantage of being considerably more biocompatible, and a spectrum of visible-light-driven methods is now available, chiefly for proteins and nucleic acids. This review will discuss modifications of native functional groups (FGs), including functionalization, labeling, and cross-linking techniques as well as the utility of oxidative degradation mediated by photochemically generated reactive oxygen species. Furthermore, transformations at non-native, bioorthogonal FGs on biomacromolecules will be addressed, including photoclick chemistry and DNA-encoded library synthesis as well as methods that allow manipulation of the activity of a biomacromolecule.

Real-Time Visualization of Embryonic Apoptosis Using a Near-Infrared Fluorogenic Probe for Embryo Development Evaluation

Developing an accurate and reliable detection technique for early embryonic apoptosis is of great significance for real-time monitoring and evaluation of embryonic development in living systems. Herein, we have rationally designed and synthesized a novel near-infrared (NIR) fluorogenic probe CGK(QSY21)DEVD-Cy5.5 for real-time imaging of embryonic apoptosis. This probe is constructed with a NIR dye Cy5.5, a fluorescence quencher QSY21, and a peptide substrate Asp-Glu-Val-Asp (DEVD) of the caspase-3 enzyme that is a key executor of cell apoptosis. The probe was initially nonfluorescent in aqueous solution but emitted strong NIR fluorescence upon specific cleavage by activated caspase-3 in a concentration-dependent manner. Taking advantage of this unique feature, this fluorogenic probe was for the first time used for real-time imaging of caspase-3 activity in apoptotic embryos. More notably, significant fluorescence enhancement was solely determined from the apoptotic embryos with the treatment of the probe both in vitro and in vivo, highly suggesting that this probe has great potential to monitor the apoptosis of embryos. We thus envision that this probe would provide a very useful means for real-time visualization and accurate evaluation of embryonic development in the future.

Enabling In Vivo Photocatalytic Activation of Rapid Bioorthogonal Chemistry by Repurposing Silicon-Rhodamine Fluorophores as Cytocompatible Far-Red Photocatalysts

Chromophores that absorb in the tissue-penetrant far-red/near-infrared window have long served as photocatalysts to generate singlet oxygen for photodynamic therapy. However, the cytotoxicity and side reactions associated with singlet oxygen sensitization have posed a problem for using long-wavelength photocatalysis to initiate other types of chemical reactions in biological environments. Herein, silicon-Rhodamine compounds (SiRs) are described as photocatalysts for inducing rapid bioorthogonal chemistry using 660 nm light through the oxidation of a dihydrotetrazine to a tetrazine in the presence of trans-cyclooctene dienophiles. SiRs have been commonly used as fluorophores for bioimaging but have not been applied to catalyze chemical reactions. A series of SiR derivatives were evaluated, and the Janelia Fluor-SiR dyes were found to be especially effective in catalyzing photooxidation (typically 3%). A dihydrotetrazine/tetrazine pair is described that displays high stability in both oxidation states. A protein that was site-selectively modified by trans-cyclooctene was quantitatively conjugated upon exposure to 660 nm light and a dihydrotetrazine. By contrast, a previously described methylene blue catalyst was found to rapidly degrade the protein. SiR-red light photocatalysis was used to cross-link hyaluronic acid derivatives functionalized by dihydrotetrazine and trans-cyclooctenes, enabling 3D culture of human prostate cancer cells. Photoinducible hydrogel formation could also be carried out in live mice through subcutaneous injection of a Cy7-labeled hydrogel precursor solution, followed by brief irradiation to produce a stable hydrogel. This cytocompatible method for using red light photocatalysis to activate bioorthogonal chemistry is anticipated to find broad applications where spatiotemporal control is needed in biological environments.

Interrogating biological systems using visible-light-powered catalysis

Light-powered catalysis has found broad utility as a chemical transformation strategy, with widespread impact on energy, environment, drug discovery and human health. A noteworthy application impacting human health is light-induced sensitization of cofactors for photodynamic therapy in cancer treatment. The clinical adoption of this photosensitization approach has inspired the search for other photochemical methods, such as photoredox catalysis, to influence biological discovery. Over the past decade, light-mediated catalysis has enabled the discovery of valuable synthetic transformations, propelling it to become a highly utilized chemical synthesis strategy. The reaction components required to achieve a photoredox reaction are identical to photosensitization (catalyst, light source and substrate), making it ideally suited for probing biological environments. In this Review, we discuss the therapeutic application of photosensitization and advancements made in developing next-generation catalysts. We then highlight emerging uses of photoredox catalytic methods for protein bioconjugation and probing complex cellular environments in living cells.