Endocrine-specific NIR fluorophores for adrenal gland targeting

Precise and safe pulmonary segmentectomy enabled by visualizing cancer margins with dual-channel near-infrared fluorescence

BACKGROUND

Segmentectomy is a type of limited resection surgery indicated for patients with very early-stage lung cancer or compromised function because it can improve quality of life with minimal removal of normal tissue. For segmentectomy, an accurate detection of the tumor with simultaneous identification of the lung intersegment plane is critical. However, it is not easy to identify both during surgery. Here, the authors report dual-channel image-guided lung cancer surgery using renally clearable and physiochemically stable targeted fluorophores to visualize the tumor and intersegmental plane distinctly with different colors; cRGD-ZW800 (800 nm channel) targets tumors specifically, and ZW700 (700 nm channel) simultaneously helps discriminate segmental planes.

METHODS

The near-infrared (NIR) fluorophores with 700 nm and with 800 nm channels were developed and evaluated the feasibility of dual-channel fluorescence imaging of lung tumors and intersegmental lines simultaneously in mouse, rabbit, and canine animal models. Expression levels of integrin αvβ3, which is targeted by cRGD-ZW800-PEG, were retrospectively studied in the lung tissue of 61 patients who underwent lung cancer surgery.

RESULTS

cRGD-ZW800-PEG has clinically useful optical properties and outperforms the FDA-approved NIR fluorophore indocyanine green and serum unstable cRGD-ZW800-1 in multiple animal models of lung cancer. Combined with the blood-pooling agent ZW700-1C, cRGD-ZW800-PEG permits dual-channel NIR fluorescence imaging for intraoperative identification of lung segment lines and tumor margins with different colors simultaneously and accurately.

CONCLUSION

This dual-channel image-guided surgery enables complete tumor resection with adequate negative margins that can reduce the recurrence rate and increase the survival rate of lung cancer patients.

Microwave-Assisted Synthesis of the Red-Shifted Pentamethine Tetrahydroxanthylium Core with Absorbance within the Near Infrared-II Window

Thirteen red-shifted pentamethine dimethyl and diethylamino tetrahydroxanthylium derivatives have been successfully synthesized via the microwave-assisted approach. The optimized conditions developed in the synthesis provided an excellent yield in expedited reaction time. These newly synthesized dyes show well-defined optical properties resulting from the diverse substitutions at the central meso positions. The majority of the compounds have a maximum wavelength of absorbance within 946-1022 nm with extinction coefficients in the range of 9700-110,680 M-1 cm-1 in various solvents such as MeOH, EtOH, DMSO, DCM, MeCN, and DMF. These fluorophores, to the best of our knowledge, are the first NIR-II small molecules synthesized using microwave chemistry. We also investigated these dyes for their NIR fluorescence imaging capabilities. Diethylamino-substituted compounds and bromination resulted in higher uptake in the adrenal gland compared to dimethylamino fluorophores. In addition, micellar structures of compounds 7 and 15 improved the targetability of the original dyes to the bone marrow, lymph nodes, and nerves. Overall, NIR-II imaging has the potential to visualize biologically targeted tissues in living organisms.

Shortwave Infrared Absorptive and Emissive Pentamethine-Bridged Indolizine Cyanine Dyes

Shortwave infrared (SWIR)-emitting small molecules are desirable for biological imaging applications. In this study, four novel pentamethine indolizine cyanine dyes were synthesized with N,N-dimethylaniline-based substituents on the indolizine periphery at varied substitution sites. The dyes are studied via computational chemistry and optical spectroscopy both in solution and when encapsulated. Dramatic spectral shifts in the absorption and emission spectrum wavelengths with added donor groups are observed. Significant absorption and emission with an emissive quantum yield as high as 3.6% in the SWIR region is possible through the addition of multiple donor groups per indolizine.

Near-Infrared Heptamethine Cyanine Dyes for Nanoparticle-Based Photoacoustic Imaging and Photothermal Therapy

We have synthesized and characterized a library of near-infrared (NIR) heptamethine cyanine dyes for biomedical application as photoacoustic imaging and photothermal agents. These hydrophobic dyes were incorporated into a polymer-based nanoparticle system to provide aqueous solubility and protection of the photophysical properties of each dye scaffold. Among those heptamethine cyanine dyes analyzed, 13 compounds within the nontoxic polymeric nanoparticles have been selected to exemplify structural relationships in terms of photostability, photoacoustic imaging, and photothermal behavior within the NIR (∼650-850 nm) spectral region. The most contributing structural features observed in our dye design include hydrophobicity, rotatable bonds, heavy atom effects, and stability of the central cyclohexene ring within the dye core. The NIR agents developed within this project serve to elicit a structure-function relationship with emphasis on their photoacoustic and photothermal characteristics aiming at producing customizable NIR photoacoustic and photothermal tools for clinical use.

A double-indole structure fluorescent probe for monitoring sulfur dioxide derivatives with distinct ratiometric fluorescence signals in mammalian cells

Based on the addition reaction of the sulfur dioxide derivative to the CC double bond, the probe HDI was designed and synthesized. The two-channel fluorescent probe HDI changed from orange to colorless and the fluorescence changed from red to blue when the bisulfite was detected. And the probe responds rapidly to bisulfite within 2 min, with high sensitivity and specificity. In addition, the probe can be used to detect the concentration of bisulfite with a low detection limit (80 nM). Cytological experiments have also demonstrated that probe HDI has low cytotoxicity and could be used for ratiometric detection of sulfur dioxide derivatives in living cells.

Fluorometric Imaging for Early Diagnosis and Prognosis of Rheumatoid Arthritis

Early diagnosis and monitoring of disease progress are of significant importance in the effective treatment of rheumatoid arthritis (RA), because the continuing inflammation can lead to irreversible joint damage and systemic complications. However, applying imaging modalities for the prognosis of RA remains challenging, because no tissue-specific guidelines are available to monitor the progressive course of RA. In this study, fluorometric imaging of RA is reported using bioengineered targeted agents of the blood vessel, bone, and cartilage in combination with the customized optical fluorescence imaging system. Separate but simultaneous tissue-specific images of synovitis, cartilage destruction, and bone resorption are obtained from a mouse model of RA, which allows quantification of the prognosis of diseases at each stage. Thus, the fluorometric imaging of RA by using tissue-specific contrast agents plays a key role in the systemic treatment of RA by monitoring structural damage and disease progression.

Near-Infrared Contrast Agents for Bone-Targeted Imaging

Background

For the bone-specific imaging, a structure-inherent targeting of bone tissue recently has been reported a new strategy based on incorporation of targeting moieties into the chemical structure of near-infrared (NIR) contrast agents, while conventional methods require covalent conjugation of bone-targeting ligands to NIR contrast agents. This will be a new approach for bone-targeted imaging by using the bifunctional NIR contrast agents.

Methods

The goal of this review is to provide an overview of the recent advances in optical imaging of bone tissue, highlighting the structure-inherent targeting by developing NIR contrast agents without the need for a bone-targeting ligand such as bisphosphonates.

Results

A series of iminodiacetated and phosphonated NIR contrast agents for the structure-inherent targeting of bone tissue showed excellent bone-targeting ability in vivo without non-specific binding. Additionally, the phosphonated NIR contrast agents could be useful in the diagnosis of bone metastasis.

Conclusion

By developing bone-targeted NIR contrast agents, optical imaging of bone tissue makes it very attractive for preclinical studies of bone growth or real-time fluorescence guided surgery resulting in high potential to shift the clinical paradigms.

Real-Time Fluorescence Imaging in Thoracic Surgery

Near-infrared (NIR) fluorescence imaging provides a safe and cost-efficient method for immediate data acquisition and visualization of tissues, with technical advantages including minimal autofluorescence, reduced photon absorption, and low scattering in tissue. In this review, we introduce recent advances in NIR fluorescence imaging systems for thoracic surgery that improve the identification of vital tissues and facilitate the resection of tumorous tissues. When coupled with appropriate NIR fluorophores, NIR fluorescence imaging may transform current intraoperative thoracic surgery methods by enhancing the precision of surgical procedures and augmenting postoperative outcomes through improvements in diagnostic accuracy and reductions in the remission rate.

Counter Anion Effect on the Photophysical Properties of Emissive Indolizine-Cyanine Dyes in Solution and Solid State

Near-infrared emissive materials with tunable Stokes shifts and solid-state emissions are needed for several active research areas and applications. To aid in addressing this need, a series of indolizine-cyanine compounds varying only the anions based on size, dipole, and hydrophilicity were prepared. The effect of the non-covalently bound anions on the absorption and emission properties of identical π-system indolizine-cyanine compounds were measured in solution and as thin films. Interestingly, the anion choice has a significant influence on the Stokes shift and molar absorptivities of the dyes in solution. In the solid-state, the anion choice was found to have an effect on the formation of aggregate states with higher energy absorptions than the parent monomer compound. The dyes were found to be emissive in the NIR region, with emissions peaking at near 900 nm for specific solvent and anion selections.

Introduction of various substitutions to the methine bridge of heptamethine cyanine dyes Via substituted dianil linkers

The unique optical properties of cyanine dyes have prompted their use in numerous applications. Heptamethine cyanines are commonly modified on the methine bridge after synthesis of a meso-chlorine containing cyanine. Herein, a series of heptamethine cyanines containing modified methine bridges were synthesized using substituted dianil linkers. Their optical properties including, molar absorptivity, fluorescence, and quantum yield were measured as well as their hydrophobic effects in polar buffer solution. It was shown that dyes containing cyclopentene in the methine bridge or a phenyl ring in the meso position display increased molar absorptivity while the increased flexibility of the dye containing a cycloheptene in the methine bridge prevented fluorescence.

Synthesis and Optical Properties of Near-Infrared meso-Phenyl-Substituted Symmetric Heptamethine Cyanine Dyes

Heptamethine cyanine dyes are a class of near infrared fluorescence (NIRF) probes of great interest in bioanalytical and imaging applications due to their modifiability, allowing them to be tailored for particular applications. Generally, modifications at the meso-position of these dyes are achieved through Suzuki-Miyaura C-C coupling and S_RN1 nucleophilic substitution of the chlorine atom at the meso-position of the dye. Herein, a series of 15 meso phenyl-substituted heptamethine cyanines was synthesized utilizing a modified dianil linker. Their optical properties, including molar absorptivity, fluorescence, Stokes shift, and quantum yield were measured. The HSA binding affinities of two representative compounds were measured and compared to that of a series of trimethine cyanines previously synthesized by our lab. The results indicate that the binding of these compounds to HSA is not only dependent on hydrophobicity, but may also be dependent on steric interferences in the binding site and structural dynamics of the NIRF compounds.

Fluorescence-Guided Surgery

Surgical resection of cancer remains an important treatment modality. Despite advances in preoperative imaging, surgery itself is primarily guided by the surgeon’s ability to locate pathology with conventional white light imaging. Fluorescence-guided surgery (FGS) can be used to define tumor location and margins during the procedure. Intraoperative visualization of tumors may not only allow more complete resections but also improve safety by avoiding unnecessary damage to normal tissue which can also reduce operative time and decrease the need for second-look surgeries. A number of new FGS imaging probes have recently been developed, complementing a small but useful number of existing probes. In this review, we describe current and new fluorescent probes that may assist FGS.

Structure-Guided Design and Synthesis of a Mitochondria-Targeting Near-Infrared Fluorophore with Multimodal Therapeutic Activities

An urgent challenge for imaging-guided disease-targeted multimodal therapy is to develop the appropriate multifunctional agents to meet the requirements for potential applications. Here, a rigid cyclohexenyl substitution in the middle of a polymethine linker and two asymmetrical amphipathic N-alkyl side chains to indocyanine green (ICG) (the only FDA-approved NIR contrast agent) are introduced, and a new analog, IR-DBI, is developed with simultaneous cancer-cell mitochondrial targeting, NIR imaging, and chemo-/PDT/PTT/multimodal therapeutic activities. The asymmetrical and amphipathic structural modification renders IR-DBI a close binding to albumin protein site II to form a drug-protein complex and primarily facilitates its preferential accumulation at tumor sites via the enhanced permeability and retention (EPR) effect. The released IR-DBI dye is further actively taken up by cancer cells through organic-anion-transporting polypeptide transporters, and the lipophilic cationic property leads to its selective accumulation in the mitochondria of cancer cells. Finally, based on the high albumin-binding affinity, IR-DBI is modified into human serum albumin (HSA) via self-assembly to produce a nanosized complex, which exhibits significant improvement in the cancer targeting and multimodal cancer treatment with better biocompatibility. This finding may present a practicable strategy to develop small-molecule-based cancer theranostic agents for simultaneous cancer diagnostics and therapeutics.

Structure-Inherent Targeting of Near-Infrared Fluorophores for Image-Guided Surgery

Although various clinical imaging modalities have been developed to visualize internal body structures and detect abnormal tissues prior to surgical procedures, most medical imaging modalities do not provide disease-specific images in real-time. Optical imaging can provide the surgeon with real-time visualization of the surgical field for intraoperative image-guided surgery. Imaging in the near-infrared (NIR) window (650-900 nm), also known as the "therapeutic window" has high potential by offering low absorbance and scattering in tissues resulting in minimized background autofluorescence. Clinically, optical fluorescence imaging with the targeted contrast agents provides opportunities for significant advances in intraoperative image-guided surgery. There are only two clinically available NIR fluorophores, indocyanine green (ICG) and methylene blue (MB), that support the image-guided surgery. However, neither of them perform in vivo by providing optimum specificity and stability for targeted image guidance. Therefore, it is of paramount importance to develop targeted NIR fluorophores for unmet clinical needs. Using the right combination of an NIR fluorescence imaging system and a targeted fluorophore, the desired target tissues can be imaged to provide real-time fluorescence guidance without changing the field-of-view during surgery. Thus, in a clinical discipline, the development of NIR fluorophores for 'structure-inherent targeting' is an unmet need for early phase diagnostics with accurate targeting.

Next generation NIR fluorophores for tumor imaging and fluorescence-guided surgery: A review

Cancer is a group of diseases responsible for the major causes of mortality and morbidity among people of all ages. Even though medical sciences have made enormous growth, complete treatment of this deadly disease is still a challenging task. Last few decades witnessed an impressive growth in the design and development of near infrared (NIR) fluorophores with and without recognition moieties for molecular recognitions, imaging and image guided surgeries. The present article reviews recently reported NIR emitting organic/inorganic fluorophores that targets and accumulates in organelle/organs specifically for molecular imaging of cancerous cells. Near infrared (NIR probe) with or without a tumor-targeting warhead have been considered and discussed for their applications in the field of cancer imaging. In addition, challenges persist in this area are also delineated in this review.