Method To Diversify Cyanine Chromophore Functionality Enables Improved Biomolecule Tracking and Intracellular Imaging

Minimized background tumor imaging through self-assembled disulfide dicyanine nanoparticles

Fluorescence imaging holds great potential as a powerful diagnostic tool for tumor cell visualization. However, a significant challenge in fluorescence imaging is the high background signal, which obscures the tumor-specific signal and reduced the signal-to-noise ratio (SNR) of imaging, thereby reducing the accuracy of tumor detection and delineation. In this research, we designed and synthesized an amphiphilic disulfide dicyanine ss-diCy7, which can self-assemble into nanoparticles with uniform dispersion in aqueous environments. The fluorescence intensity of these nanoparticles is significantly reduced by 96% due to aggregation-induced quenching arising from π-π stacking. The nanoparticles exhibit a highly specific response to glutathione (GSH) in vitro, resulting in a substantial enhancement of fluorescence intensity by a 24-fold. The enhancement was also achieved in cell and mouse imaging experiments. In addition, in the mouse tumor model, ss-diCy7 nanoparticles demonstrated superior performance compared to traditional mono-cyanine dyes, offering a reduced background signal and prolonged fluorescence duration. This work is anticipated to contribute to the high-resolution tumor imaging.

Differential Optical Imaging of Antigen Presentation Machinery Using Molecular Optical Reporters

Detection of antigen presentation is central to understanding immunological processes and developing therapeutics for cancer, infectious diseases, and allergies. However, methods with the ability to dynamically and noninvasively distinguish between major histocompatibility complex class I (MHC-I) and MHC-II antigen presentations remain lacking. Herein, we develop activatable molecular optical reporters (MORs) for real-time differential imaging of antigen presentations in lymph nodes (LNs). These MORs are engineered to passively target LNs and activated through proteolytic cleavage by key enzymes in the MHC-I and MHC-II pathways, the immunoproteasome (iP) and cathepsin S (CTSS), respectively, triggering their chemiluminescent or fluorescent signals. Coupled with minimized signal crosstalk and high sensitivity, MORs delineate the subtle differences in the antigen presentation machinery across various disease models, including cancer and bacterial or viral infection, a feat unattainable for existing imaging methods. After systemic administration, MORs also allow real-time visualization of antigen presentation in the tumor microenvironment. Besides, MORs are validated to have potential for preclinical application in immunotherapeutics screening and clinical application in tissue biopsy. Thus, our study not only presents the first example of real-time, in vivo differential imaging of antigen presentation pathways but also opens new avenues for optical probes in immune contexture analysis.

Mapping Dynamic Protein Clustering with AIEgen-Active Chemigenetic Probe

Protein clustering/disassembling is a fundamental process in biomolecular condensates, playing a crucial role in cell fate decision and cellular homeostasis. However, the inherent features of protein clustering, especially for its reversible behavior and subtle microenvironment variation, present significant hurdles in probe chemistry for tracking protein clustering dynamics. Herein, we report a bilateral-tailored chemigenetic probe, in which an "amphiphilic" aggregate-induced emission luminogen (AIEgen) QMSO3Cl is covalently conjugated to a protein tag that is genetically fused to protein-of-interest (POI). Prior to target POI, the "amphiphilic" AIE-active QMSO3Cl achieves a completely dark state in both aqueous biological environment and lipophilic organelles, thereby ensuring an ultra-low intrinsic background interference. Upon reaching POI, the combination of synthetic molecule and genetically encoded protein allows for protein clustering-dependent ultra-sensitive response, with a substantial lighting-up fluorescence (67.5-fold) as protein transitions from disassembling to clustering state. Such ultra-high signal-to-noise ratio enables to monitor the dynamic and fate of inositol requiring enzyme 1 (IRE1) clustering/disassembling under both acute and chronic endoplasmic reticulum (ER) stress in living cells. For the first time, we have demonstrated the use of chemigenetic probe to reveal therapy-induced ER stress and screen drugs in a three-dimensional scenario: microviscosity change, clustering dynamic, and cluster morphology. This chemigenetic probe design strategy would greatly facilitate the advancement of mapping protein dynamics in cell homeostasis and medicine research.

Tracking the Fate of Therapeutic Proteins Using Ratiometric Imaging of Responsive Shortwave Infrared Probes

Monoclonal antibodies (mAbs) are essential agents for cancer treatment and diagnosis. Advanced optical imaging strategies have the potential to address specific questions regarding their complex in vivo life cycle. This study presents responsive shortwave infrared (SWIR) probes and an associated imaging scheme to assess mAb biodistribution, cellular uptake, and proteolysis. Specifically, we identify a Pegylated benzo-fused norcyanine derivative (Benz-NorCy7) that is activated in acidic environments and can be appended to mAbs without significant changes in optical properties. As a mAb conjugate, this agent shows high tumor specificity in a longitudinal imaging study in a murine model. To enable independent tracking of mAb uptake and lysosomal uptake and retention, a two-color ratiometric imaging strategy was employed using an "always-ON" heptamethine cyanine dye (λex = 785 nm) and the pH-responsive Benz-NorCy7 (λex = 890 nm). To assess proteolytic catabolism, we append a cleavable carbamate to Benz-NorCy7 to create turn-ON probes. These agents facilitate the comparison of two common peptide linkers and provide insights into their in vivo properties. Overall, these studies provide a strategy to assess the fate of protein-based therapeutics using optical imaging.

Harnessing Cyanine-like Properties to Develop Bright Fluorogenic Probes Based on Viscosity-Sensitive Molecular Rotors

Dipolar fluorescent molecular rotors (FMRs) are environmentally-sensitive fluorophores that can be used in bioimaging applications to sense local viscosity and polarity. Their sensitivity to viscosity can also be used for the fluorogenic labeling of biomolecules such as DNA or proteins. In particular, we have previously used FMRs to develop a series of tunable fluorogens targeting the self-labeling protein tag Halotag for wash-free protein imaging in live cells. Despite these very useful properties, FMRs typically display moderate molar absorption coefficients that limits their overall fluorescence brightness. Herein, we synthesized a series of three model hemicyanines based on a styrylindolenium scaffold and performed a detailed study of their photophysical properties in solvents with various polarity and viscosity. We show that with a strong julolidine electron-donating group it is possible to combine intense cyanine-like absorption with the high sensitivity to viscosity of FMRs. We use this property to develop a lysosomal pH sensor and two bright cell-impermeant fluorogens targeting HaloTag for imaging membrane proteins. We believe that this bright fluorogenic scaffold based on a simple chemical structure can be used in the future to build up a variety of probes and sensors with efficient photophysical properties.

Benzyl Ammonium Carbamates Undergo Two-Step Linker Cleavage and Improve the Properties of Antibody Conjugates

Targeted payload delivery strategies, such as antibody-drug conjugates (ADCs), have emerged as important therapeutics. Although considerable efforts have been made in the areas of antibody engineering and labeling methodology, improving the overall physicochemical properties of the linker/payload combination remains an important challenge. Here we report an approach to create an intrinsically hydrophilic linker domain. We find that benzyl α-ammonium carbamates (BACs) undergo tandem 1,6-1,2-elimination to release secondary amines. Using a fluorogenic hemicyanine as a model payload component, we show that a zwitterionic BAC linker improves labeling efficiency and reduces antibody aggregation when compared to a commonly used para-amino benzyl (PAB) linker as well as a cationic BAC. Cellular and in vivo fluorescence imaging studies demonstrate that the model payload is specifically released in antigen-expressing cells and tumors. The therapeutic potential of the BAC linker strategy was assessed using an MMAE payload, a potent microtubule-disrupting agent frequently used for ADC applications. The BAC-MMAE combination enhances labeling efficiency and cellular toxicity when compared to the routinely used PAB-Val-Cit ADC analogue. Broadly, this strategy provides a general approach to mask payload hydrophobicity and improve the properties of targeted agents.

High-Performance Chemigenetic Potassium Ion Indicator

Potassium ion (K+) is the most abundant metal ion in cells and plays an indispensable role in practically all biological systems. Although there have been reports of both synthetic and genetically encoded fluorescent K+ indicators, there remains a need for an indicator that is genetically targetable, has high specificity for K+ versus Na+, and has a high fluorescent response in the red to far-red wavelength range. Here, we introduce a series of chemigenetic K+ indicators, designated as the HaloKbp1 series, based on the bacterial K+-binding protein (Kbp) inserted into HaloTag7 self-labeled with environmentally sensitive rhodamine derivatives. This series of high-performance indicators features high brightness in the red to far-red region, large intensiometric fluorescence changes, and a range of Kd values. We demonstrate that they are suitable for the detection of physiologically relevant K+ concentration changes such as those that result from the Ca2+-dependent activation of the BK potassium channel.

Research Progress of Cyanine-Based Near-Infrared Fluorescent Probes for Biological Application

Cyanine-based near-infrared (NIR) fluorescent probes have played vital roles in biological application due to their low interference from background fluorescence, deep tissue penetration, high sensitivity, and minimal photodamage to biological samples. They are widely utilized in molecular recognition, medical diagnosis, biomolecular detection, and biological imaging. Herein, we provide a review of recent advancements in cyanine-based NIR fluorescent probes for the detection of pH, cells, tumor as well as their application in photothermal therapy (PTT) and photodynamic therapy (PDT).

Extending the emission peak tail of indole cyanine for deep-near-infrared bioimaging

We propose a novel strategy for tailoring the structure of fluorescent molecules to achieve emission at the tail end of the NIR-II window. The favorable spectroscopic properties and low cytotoxicity of YNs make them powerful tools for bioimaging. Notably, YN-4 exhibits a brightness 2.5 times greater than YN-3, 6 times that of IR-783, and 5 times that of ICG. This enhanced brightness enabled high-resolution imaging of mouse thoracic and abdominal cavities, tumor vasculature, and real-time monitoring of gastrointestinal motility using YN-4. Furthermore, covalent grafting of glucose onto the YN-Glu scaffold significantly improved tumor-targeting capability and facilitated tracking of glucose metabolism. This work aims to extend the application of fluorescent molecule imaging beyond the NIR-IIa window.

Divergent Syntheses of Near-Infrared Light-Activated Molecular Jackhammers for Cancer Cell Eradication

Aminocyanines incorporating Cy7 and Cy7.5 moieties function as molecular jackhammers (MJH) through vibronic-driven action (VDA). This mechanism, which couples molecular vibrational and electronic modes, results in picosecond-scale concerted stretching of the entire molecule. When cell-associated and activated by near-infrared light, MJH mechanically disrupts cell membranes, causing rapid necrotic cell death. Unlike photodynamic and photothermal therapies, the ultrafast vibrational action of MJH is unhindered by high concentrations of reactive oxygen species scavengers and induces only a minimal temperature increase. Here, the efficient synthesis of a library of MJH is described using a practical approach to access a key intermediate and facilitating the preparation of various Cy7 and Cy7.5 MJH with diverse side chains in moderate to high yields. Photophysical characterization reveals that structural modifications significantly affect molar extinction coefficients and quantum yields while maintaining desirable absorption and emission wavelengths. The most promising compounds, featuring dimethylaminoethyl and dimethylcarbamoyl substitutions, demonstrate up to sevenfold improvement in phototherapeutic index compared to Cy7.5 amine across multiple cancer cell lines. This synthetic strategy provides a valuable platform for developing potent, light-activated therapeutic agents for cancer treatment, with potentially broad applicability across various cancer types.

Expedient Synthesis and Characterization of π-Extended Luciferins

Bioluminescence imaging enables the sensitive tracking of cell populations and the visualization of biological processes in living systems. Bioluminescent luciferase/luciferin pairs with far-red and near-infrared emission benefit from the reduced competitive absorption by blood and tissue while also facilitating multiplexing strategies. Luciferins with extended π-systems, such as AkaLumine and recently reported CouLuc-1 and -3, can be used for bioluminescence imaging in this long wavelength regime. Existing synthetic routes to AkaLumine and similar π-extended compounds require a multistep sequence to install the thiazoline heterocycle. Here we detail the development of a two-step strategy for accessing these molecules via a Horner-Wadsworth-Emmons reaction and cysteine condensation sequence from readily available aldehyde starting materials. We detail an improved synthesis of AkaLumine, as well as the corresponding two-carbon homologues, Tri- and Tetra-AkaLumine. We then extended this approach to prepare coumarin- and naphthalene-derived luciferins. These putative luciferins were tested against a panel of luciferases to identify capable emitters. Of these, an easily prepared naphthalene derivative exhibits photon emission on par with that of the broadly used Akaluc/AkaLumine pair with similar emission maxima. Overall, this chemistry provides efficient access to several bioluminescent probes for a variety of imaging applications.

Design of an Acidic pH-Activated NIR Fluorescent Convertible Rhodamine-Hemicyanine Probe-Peptide Conjugate for Living Cancer Cell Active Targeted Selective Tracking of Lysosomes

We have synthesized an acidic pH-activatable dual targeting ratiometric fluorescent probe-peptide conjugate using the SPPS protocol on Rink amide AM resin. Living carcinoma cell specific active targeting, successive cell penetration, and selective staining of lysosomes are accomplished. Real-time monitoring of lysosomes, 3D, and multicolor cancer cell imaging are also attained. The de novo design consists of the integration of multifunctionality into a single molecular scaffold, e. g., RGDS peptide residue to target cancer cell surface overexpressed receptor αVβ3 integrin, live-cell penetrating organic unsymmetrical rhodamine-hemicyanine chromophore comprising a lysosome targeting morpholine group, and an acidic pH openable spiro-lactam ring for a visible-to-NIR switchable ratiometric response. Water-soluble fluorescent probe-peptide conjugate exhibits intramolecular spirolactamization at basic pH through Arg amide N. The visible spirolactam state predominantly exists at physiological and basic pH and can be switched to the highly conjugated NIR open amide state (λem=735 nm) through spiro-lactam ring opening triggered by acidic pH with a huge bathochromic shift (Δλabs=336 nm, ΔλFL=265 nm). Moreover, pH-sensitive ratiometric optical switching is achieved. This in situ acidic cancer cell lysosome activatable multifunctional fluorophore-peptide conjugate shows augmented molar absorptivity, enhanced quantum yield, and improved fluorescence lifetime at acidic lysosomal pH; negligible cytotoxicity; and dual targeted ratiometric imaging capability of living cancer cell selective lysosomes with a pKa value of 5.1.

Engineering Central Substitutions in Heptamethine Dyes for Improved Fluorophore Performance

As a major family of red-shifted fluorophores that operate beyond visible light, polymethine dyes are pivotal in light-based biological techniques. However, methods for tuning this kind of fluorophores by structural modification remain restricted to bottom-up synthesis and modification using coupling or nucleophilic substitutions. In this study, we introduce a two-step, late-stage functionalization process for heptamethine dyes. This process enables the substitution of the central chlorine atom in the commonly used 4'-chloro heptamethine scaffold with various aryl groups using aryllithium reagents. This method borrows the building block and designs from the xanthene dye community and offers a mild and convenient way for the diversification of heptamethine fluorophores. Notably, this efficient conversion allows for the synthesis of heptamethine-X, the heptamethine scaffold with two ortho-substituents on the 4'-aryl modification, which brings enhanced stability and reduced aggregation to the fluorophore. We showcase the utility of this method by a facile synthesis of a fluorogenic, membrane-localizing fluorophore that outperforms its commercial counterparts with a significantly higher brightness and contrast. Overall, this method establishes the synthetic similarities between polymethine and xanthene fluorophores and provides a versatile and feasible toolbox for future optimizing heptamethine fluorophores for their biological applications.

Mechanistic Insight into the Thermal "Blueing" of Cyanine Dyes

In recent work to develop cyanine dyes with especially large Stokes shifts, we encountered a "blueing" reaction, in which the heptamethine cyanine dye Cy7 (IUPAC: 1,3,3-trimethyl-2-((1E,3E,5E)-7-((E)-1,3,3-trimethylindolin-2-ylidene)hepta-1,3,5-trien-1-yl)-3H-indol-1-ium) undergoes shortening in two-carbon steps to form the pentamethine (Cy5) and trimethine (Cy3) analogs. Each step blue-shifts the resulting absorbance wavelength by ca. 100 nm. Though photochemical and oxidative chain-shortening reactions had been noted previously, it is simple heating alone or with amine bases that effects this unexpected net C2H2 excision. Explicit acetylene loss would be too endothermic to merit consideration. Our mechanistic studies using 2H labeling, mass spectrometric and NMR spectroscopic analyses, and quantum chemical modeling point instead to electrocyclic closure and aromatization of the heptamethine chain in Cy7 forming Fischer's base FB (1,3,3-trimethyl-2-methyleneindoline), a reactive carbon nucleophile that initiates chain shortening of the cyanine dyes by attack on their polymethine backbones. The byproduct is the cationic indolium species TMP (IUPAC: 1,3,3 trimethyl-2-phenyl indolium).

Pyridine-based strategies towards nitrogen isotope exchange and multiple isotope incorporation

Isotopic labeling is at the core of health and life science applications such as nuclear imaging, metabolomics and plays a central role in drug development. The rapid access to isotopically labeled organic molecules is a sine qua non condition to support these societally vital areas of research. Based on a rationally driven approach, this study presents an innovative solution to access labeled pyridines by a nitrogen isotope exchange reaction based on a Zincke activation strategy. The technology conceptualizes an opportunity in the field of isotope labeling. 15N-labeling of pyridines and other relevant heterocycles such as pyrimidines and isoquinolines showcases on a large set of derivatives, including pharmaceuticals. Finally, we explore a nitrogen-to-carbon exchange strategy in order to access 13C-labeled phenyl derivatives and deuterium labeling of mono-substituted benzene from pyridine-2H5. These results open alternative avenues for multiple isotope labeling on aromatic cores.

Enhancing precision in colorectal cancer surgery: development of an LGR5-targeting RSPO1 peptide mimetic as a contrast agent for intraoperative fluorescence molecular imaging

Colorectal cancer (CRC) is the third most common cancer worldwide. In the United States alone, CRC was responsible for approximately 52,550 deaths in 2023, with an estimated 153,020 new cases. CRC presents with synchronous peritoneal spread in 5-10% of patients, and up to 20-50% of patients with recurrent disease will develop metachronous colorectal cancer peritoneal metastatic (CRC-PM) disease. Eradication of the tumor, tumor margins and microscopic residual disease is paramount, as microscopic residual disease is associated with local recurrences, with 5-year survival rates of less than 35%. The success of resection and reduction of residual disease depends on the accuracy with which cancer cells and normal tissue can be intra-operatively distinguished. Fluorescence Molecular Imaging (IFMI) and tumor-targeted contrast agents represent a promising approach for intraoperative detection and surgical intervention. Proper target selection, the development of scalable imaging agents and enhanced real-time tumor and tumor microenvironment imaging are critical to enabling enhanced surgical resection. LGR5 (leucine-rich repeat-containing G-protein-coupled receptor 5), a colonic crypt stem cell marker and the receptor for the R-spondins (RSPO) in the Wnt signaling pathway, is also expressed on colorectal cancer stem cells (CSC) and on CRC tumors and metastases, suggesting it could be a useful target for imaging of CRC. However, there are numerous diverging reports on the role of LGR5 in CRC therapy and outcomes. Herein, we report on the synthesis and validation of a 37 amino acid RSPO1-mimetic peptide, termed RC18, that was specifically designed to access the R-spondin binding site of LGR5 to potentially be used for interoperative imaging of CRC-PM. The receptor-binding capabilities of the RC18 indicate that direct interactions with LGR5 neither significantly increased LGR5 signaling nor blocked RSPO1 binding and signal transduction, suggesting that the RSPO1-mimetic is functionally inert, making it an attractive contrast agent for intraoperative CRC-PM imaging.

Near-infrared photocatalysis with cyanines: synthesis, applications and perspectives

Cyanines are organic dyes bearing two aza-heterocycles linked by a polymethine chain. Excited states, fluorescence, redox activity, and energy transfer are interesting properties of cyanines which have been used by chemists. Moreover, they are easily accessible and highly tunable. For all these reasons, cyanines are often selected for applications like fluorescent probes, phototherapy and photovoltaics. However, considering cyanines as photocatalysts is a new field of investigation and has been sparsely reported in the literature. This field of research has been launched on the basis of near-infrared light photocatalysis. With a deeper NIR light penetration, the irradiation is compatible with biological tissues. Due to the longer wavelengths that are involved, the safety of the operator can be guaranteed. In this perspective review, the photophysical/redox properties of cyanines are reported as well as their preparations and applications in modern synthetic approaches. Finally, recent examples of cyanine-based NIR-photocatalysis are discussed including photopolymerization and organic synthesis.

Design of Bright Chemogenetic Reporters Based on the Combined Engineering of Fluorogenic Molecular Rotors and of the HaloTag Protein

The combination of fluorogenic probes (fluorogens) and self-labeling protein tags represent a promising tool for imaging biological processes with high specificity but it requires the adequation between the fluorogen and its target to ensure a good activation of its fluorescence. In this work, we report a strategy to develop molecular rotors that specifically target HaloTag with a strong enhancement of their fluorescence. The divergent design facilitates the diversification of the structures to tune the photophysical and cellular properties. Four bright fluorogens with emissions ranging from green to red were identified and applied in wash-free live cell imaging experiments with good contrast and selectivity. A HaloTag mutant adapted from previous literature reports was also tested and shown to further improve the brightness and reaction rate of the most promising fluorogen of the series both in vitro and in cells. This work opens new possibilities to develop bright chemogenetic reporters with diverse photophysical and biological properties by exploring a potentially large chemical space of simple dipolar fluorophores in combination with protein engineering.

Fluorogenic polymethine dyes by intramolecular cyclization

Fluorescence imaging plays a pivotal role in the study of biological processes, and cell-permeable fluorogenic dyes are crucial to visualize intracellular structures with high specificity. Polymethine dyes are vitally important fluorophores in single-molecule localization microscopy and in vivo imaging, but their use in live cells has been limited by high background fluorescence and low membrane permeability. In this review, we summarize recent advances in the development of fluorogenic polymethine dyes via intramolecular cyclization. Finally, we offer an outlook on the prospects of fluorogenic polymethine dyes for bioimaging.

An open and shut case? Chemistry to control xanthene dyes

Fluorescent dyes are an indispensable part of the scientific enterprise. Xanthene-based fluorophores, like fluorescein and rhodamine, have been in continual use across numerous fields since their invention in the late 19th century. Modern methods to synthesize and expand the scope of xanthene dye chemistry have enabled new colors, enhanced stability, and improved brightness. Modifications to the 3-position of xanthene dyes have been, until recently, less well-explored. Here, we discuss how small changes to the identity of the substituent at the 3-position of fluoresceins and rhodamines can profoundly alter the properties of xanthene dyes, with the potential to unlock new applications at the interface of chemistry and biology.

A Modular Approach for the Synthesis of Diverse Heterobifunctional Cyanine Dyes

Herein, we present a straightforward synthetic route for the design and synthesis of diverse heterobifunctional cyanine 5 dyes. We optimized the workup by harnessing the pH- and functional group-dependent solubility of the asymmetric cyanine 5 dyes. Therefore, purification through chromatography is deferred until the last synthesis step. Demonstrating successful large-scale synthesis, our modular approach prevents functional group degradation by introducing them in the last synthesis step. These modifiable heterobifunctional dyes offer significant utility in advancing biological studies.

Engineered fluorogenic HaloTag ligands for turn-on labelling in live cells

Recent years have seen dramatic improvements in the design of organic fluorophores based on limiting non-radiative decay pathways. We sought to extend this understanding to benzothiadiazoles that have been used as turn-on fluorescent substrates for the self-labeling protein HaloTag. When conjugated to HaloTag, the benzothiadiazoles reside in a narrow tunnel that precludes twisted internal charge transfer, which allowed us to explore steric and electronic effects on other non-radiative decay pathways. By minimizing both non-radiative decay and nonspecific interactions with cellular components, we produced improved turn-on dyes with 136-fold increase in fluorescence over background in cells.

Phospha-cyanines in Their Ideal Polymethine State: Synthesis and Structure-Property Relationships

We report the synthesis and full characterization of a family of phosphorus-containing polymethine cyanines (phospha-cyanines). The compounds are easily prepared in two steps, starting from readily available phosphanes. The impact of the P-substituents and the counterions on the structural and optical properties is investigated through a joint experimental/theoretical approach. Based on the study of the single-crystal X-ray diffraction structures, all phospha-cyanines present a bond length alternation close to zero, independently of the substituents and counterions, which indicates an ideal polymethine state. All these compounds display the typical cyanine-like UV-vis absorption with an intense and sharp transition with a vibronic shoulder despite possessing a reverse electronic configuration compared to "classical" cyanines. Time-dependent density-functional theory calculations allowed us to fully rationalize the optical properties (absorption/emission wavelengths, luminescence quantum yields). Interestingly, due to the tetrahedral shape of the P atom, the optical properties are independent of the counterion, which is in marked contrast with N-analogues, which enables predictive engineering of the phospha-cyanines regardless of the medium in which they are used.

Development of Iodinated Indocyanine Green Analogs as a Strategy for Targeted Therapy of Liver Cancer

Liver cancer is one of the leading causes of cancer-related deaths, with a significant increase in incidence worldwide. Novel therapies are needed to address this unmet clinical need. Indocyanine green (ICG) is a broadly used fluorescence-guided surgery (FGS) agent for liver tumor resection and has significant potential for conversion to a targeted therapy. Here, we report the design, synthesis, and investigation of a series of iodinated ICG analogs (I-ICG), which can be used to develop ICG-based targeted radiopharmaceutical therapy. We applied a CRISPR-based screen to identify the solute carrier transporter, OATP1B3, as a likely mechanism for ICG uptake. Our lead I-ICG compound specifically localizes to tumors in mice bearing liver cancer xenografts. This study introduces the chemistry needed to incorporate iodine onto the ICG scaffold and defines the impact of these modifications on key properties, including targeting liver cancer in vitro and in vivo.